Comparative Assessment of Arsenic Contamination in Raw Milk, Infant Formulas and Breast Milk-Juniper Publishers

Journal of Dairy & Veterinary sciences

 

Abstract

Rapidly growing urbanization and increased industrialization has led to introduction of numerous detrimental toxicants into the environment. Such toxicants which are hazardous to human health, ultimately become a part of our food chain and accumulate in human body, in levels exceeding permissible limits. One of the most common food toxicants is heavy metals out of which Arsenic ranks 1st in the list of top 20 hazardous substances. Arsenic intake has been found to induce skin, liver, bladder and lung cancers, disturb GIT, cause fatigue, arrhythmia, bruising, nerve impairment, hyperkeratosis, hyperpigmentation of skin, gangrene, cyanosis and black foot disease. Milk and milk-based products from different milch animals that make up one of the most nutritious categories of food are reported for being contaminated with Arsenic, worldwide. Arsenic is introduced in milk from human and other milk producing animals by the intake of arsenic contaminated water or through their feed. On the other hand, breast feeding is reducing day by day due to a false verdict that it is unsafe for infants whereas infant formula milk is safer, as heavy metals like arsenic become a part of human milk in areas with high arsenic content in drinking waters. Therefore, this review highlights various studies determining arsenic contamination in raw milk, infant milk formulas as well as breast milk, in an attempt to create awareness regarding which mode of infant nutrition is safest to choose

Keywords: Arsenic; Heavy Metals; Milk Contamination; Infant formulas; Breast feeding

Introduction

From farm to fork, food is subjected to numerous potential hazards of physical, chemical and microbiological nature, making it quite a challenge to ensure that the food is not at all toxic for human consumption [1,2].Toxicity is a condition when a micronutrient or additive or any toxic compound exceeds its safety limit and causes adverse health effects. The trace elements in different foods are of significant interest because of their essential (as micronutrients) or toxic nature. Although there are many potential toxins related to foodstuff but heavy metals are quite common and abundant. Heavy metals are the metals which have high density (more than 5 g/cm3) and are dangerous for human consumption if exceeding their safety limits. According to the list of “Top 20 Hazardous Substances” compiled by the U.S. Environmental Protection Agency and the Agency for Toxic Substances and Disease Registry (ATSDR), heavy metals including Arsenic (As), Lead (Pb), Mercury (Hg), and Cadmium (Cd) stand on 1st, 2nd, 3rd and 4th position, respectively. Arsenic is of prime importance as it is a common yet potent water contaminant and from there it transfers to different food by coming in contact directly or indirectly. This heavy metal has been reported to pose multiple adverse effects on human health as well.

Milk and milk-based products make up one of the most nutritious category of foods rich in protein and minerals, a great source of calcium and magnesium, as well as trace amounts of essential elements such as iron, copper and zinc. Since, the primary form of feed at infant level to almost all ages is milk, therefore milk and milk-based products have always been valued for their significant role in body growth and development. Unfortunately, the rapidly increasing urbanization and growing industrialization have immensely polluted the environment and consequently milk and milk-based products have been highly contaminated with several toxic substances particularly heavy metals that may pose detrimental effects to human health [3]. Milk is also being contaminated with arsenic. Arsenic is introduced in milk from human and other milk producing animals by the intake of arsenic contaminated water or through their feed. This is known to exceed the safety limits i.e. 0.1 mg/ml. Breast feeding is reducing day by day due to false consideration that it is not safe for infants whereas infant formula milk is safer, as heavy metals like arsenic becomes a part of human milk in areas with high arsenic content in drinking waters. This review paper is written to shed some light on this issue and highlight the studies that indicate the arsenic contamination in milk.

Heavy Metals

Heavy metals are the metals whose specific gravity exceeds 5g/cm3 in their standard state. The most toxic heavy metals are namely Arsenic, Lead, Mercury, and Cadmium ranked 1st, 2nd, 3rd, and 4th in the list, respectively. Presence of these heavy metals is to be measured in parts per million (ppm), and the obtained values are to be compared to the Provisional Tolerable Weekly Intake (PTWI) for toxic metals as set by the FAO. Heavy metals that contaminate milk might originate from the milking utensils, milking personnel, milk processing, contaminated water used for agricultural purposes and animal fodder, as well as the immediate surroundings of milch animal [2].

Heavy Metals Toxicity

The toxicity of heavy metals results due to the longterm exposure to low contamination sources in our environment, including in the air we breathe, water and food we consume. Lead, chromium, nickel, cadmium and cobalt are the common heavy metals that might contaminate cows and other environments, disrupt milk at different levels and cause numerous problems. The contamination of milk products with heavy metals might be a consequence of the contamination of the basic cow milk that has been exposed to contaminated atmosphere including feed or poor water source. Moreover, contamination of raw milk might occur during its production. Cadmium, mercury and lead are quite hazardous to human health therefore they are referred to as a major menace to humans when consumed along with food [2]. Another study named as “Lead and Mercury in Breast Milk”, has reported the presence of Mercury in breast milk as well as bovine milk in substantially higher amounts as compared to those observed in common infant formulas. Whereas the Levels of lead in breast milk are relatively lesser than that found in milk-based infant formulas [4].

Health Risks Associated with Heavy Metals

Heavy metals belong to a class of pervasive toxicants that prevail everywhere in land, air and water. Among all the toxicants, arsenic (As) and mercury (Hg) were considered to be unusual, since they exist in a series of different chemical species with diverse toxicities to human beings [5]. Heavy metals when accumulate in the body might cause various diseases including nervous system disorders, renal failure, genetic mutations, types of cancers, neurological disorders, respiratory disorders, cardiovascular diseases, immune system weakening and infertility. Lead causes onset and development of various cancers, central nervous system disorders, anemia, renal, hepatic and cardiac damage, compromised immune system as well as weakened GIT tract. Lead can also cause encephalitis and hepatitis. Whereas Cadmium deposits in body tissues just like the liver and kidneys, causing anemia, as well as elevated blood pressure. Cadmium is also a potent carcinogen that can readily induce tumor development particularly in the prostrate and lungs.

Health Risks Linked with Arsenic

Arsenic toxicity has emerged as a worldwide health issue that has affected masses of people because of its high prevalence in land, air and water resources, as well as absorption in food crops. The maximum permissible limit for arsenic in milk established by European Union Commission is about 0.1 mg/ ml (European Union 2006). The organic forms of arsenic such as monomethylarsenic (MMA), dimethylarsenic (DMA), arsenobetaine and arsenocholinehave been observed to be relatively nontoxic in comparison to its inorganic formsarsenite (AsIII) and arsenate (AsV) that have been categorized as Type 1 carcinogens by the International Agency for Research on Cancer (IARC) [6]. Comprehensive data is present to validate the oraltoxicity of inorganic arsenic along with its various carcinogenic and non-carcinogenic effects. Its intake has been reported to cause generalized body fatigue, disturbed GIT, arrhythmia, bruising and nerve impairment. The most distinctive effects that are observed as a result of prolonged oral exposure of arsenic are hyperpigmentation of the skin and hyperkeratosis. Other noncarcinogenic effects might include peripheral vascular effects such as gangrene, cyanosis, blackfoot disease and various other cardiovascular effects including circulatory problems as well as increased blood pressure. Oral exposure to inorganic arsenic has also been observed to increase the risk of cancer in the skin, liver, bladder and lungs [7]. Previous century witnessed a massive, endemic disease just due to contamination of drinking water with arsenic, called Hydroarsenism Chronic Regional Endemic that is associated with a specific type of skin cancer.

A number of factors are responsible for severity of toxicity of arsenic in humans. These factors include age, sex, nutritional status, concentration, dose and duration of exposure to arsenic. Arsenic exposure during gestation period has been observed to pose detrimental effects on development of fetus through irreversible faltering of thioredoxinreductase, methyltransferases and DNA repair enzymes. Human arsenic toxicity has also been associated with epigenetic changes like DNA methylation, histone modification and RNA interference whereas chronic arsenic exposure might result in an increased risk of diabetes mellitus. Arsenic is the first metalloid which is directly associated with adverse pregnancy outcomes (APO) and even induces lungs, skin and urinary bladder cancers [8,9]. Long-term exposure to As might result in arsenicosis-a term that refers to arsenic related health effects including internal cancers (lung, kidney, bladder), skin problems, skin cancers, diseases of the blood vessels of the legs and feet, hyperkeratosis, hyperpigmentation, hair hypomelanosis and mee’s lines [10]. The actual mechanism behind how arsenic induces cancers is yet not completely understood. While certain studies declare arsenic toxicity to be affective on child intelligence (e.g., perceptual reasoning, verbal comprehension and working memory) as well [11].

Arsenic in Breast Milk

Mothers’ milk is the basic source of nutrition of the offspring; therefore, it is indispensable to ensure that the composition of human milk is safe enough for the infant. Lately, the presence of lead, cadmium and mercury in human milk, has been reported as well. Due to prevalence of arsenic rich bedrock in widespread areas of the world, ground water is often detected with high concentration of arsenic and travels through the entire food chain to ultimately become a part of mother’s milk as well. Native Andeans living in a village at the northwest of Argentina have been reported with high concentrations of arsenic (200μg/l) in the drinking water. Whereas, low concentrations of arsenic were detected in the breast milk and urine of the nursing babies in relation to the high level of maternal exposure. This shows that inorganic arsenic is not found in breast milk to a significant extent. Therefore, there is a quite valid reason for long breast-feeding periods for newborns [12].

A study revealed that in Izmir, breast milk was observed to be considered toxic for suckling infants, but still less than the cow’s milk. Therefore, the point to ponder is that arsenic contamination through breast or cow’s milk is relatively higher in babies living in areas with higher thermal activity or in regions where ground water has higher arsenic concentration (Ulman, C. et al.,1998). In another study atomic absorption spectrometry was used to measure level of arsenic in 64 samples of breast milk collected from Ankara, Turkey and the arsenic level appeared to be below the limit of quantification (LOQ, 7.6μg/l) in all samples [13]. The probable effects of arsenic contamination for nursing new-borns and infants, were also analyzed by Sternowsky & Moser [14] with a Perkin-Elmer Type 403 hydride-generation atomic absorption spectrometer, equipped with an arsenic EDL-lamp using 36 breast milk samples obtained from three different regions of Germany. Arsenic was not detectable, i.e. below 0.3μg/l, in majority of samples whereas the greatest concentration of 2.8μg/l was obtained in a sample from the rural area. It was revealed that Arsenic concentrations did not vary in samples obtained before and after nursing nor with the age of the infant.

Khan & Ismail [15] also determined arsenic concentration in breast milk samples collected from all over Pakistan. The results of the study indicated the presence of arsenic in the mother milk samples within the range of 0.092-1.240mg/L, while the mean as level was 0.504 ppb. The concentration of arsenic in the mother milk was found to be within the safe limits. Although, Breastfeeding is the primary preventive measure that can be given to the child at birth, the ratio of exclusively breast milk fed babies for their first six months has dropped from about 20% in 1998 to 16% in 2003 [12].

Arsenic in Milk and Milk Products

Arsenic is considered as one of the inevitable contaminants for human beings and is well known as a toxic element since ancient times. Humans are exposed to many chemical forms of both inorganic and organic arsenic but the highly stable organic forms are apparently nontoxic. Arsenic content of foods is generally less than 1 mg/kg, with the exception of seafood in which arsenic is predominantly in the organic form [16]. Prolonged, chronic exposure to inorganic arsenic through breathing, drinking or ingestion has been linked to, skin, lungs and urinary bladder cancer [17]. In past decade, almost 13,000 Japanese infants have been afflicted with contaminated milk powder, majorly in the western part of the country where industrialization was considerable. Affected infants reported diarrhea, fever, skin pigmentation, whereas more than 100 died from acute poisoning [4].

Carrera et al, 2004 also determined the concentration of arsenic in cow milk samples collected from Cordoba. The arsenic was found to be in the range of 0.3-10.5 ng/g. Dakeisi et al, 2006 analyzed the concentration of arsenic in milk powder as well. The level of arsenic contamination in milk powder was found to be in the range of 4-7mg/l. In 2005, ANTUNOVIĆ et al, used a hybrid technique on an atomic absorption spectrophotometerto determine the arsenic content of milk and the results revealed that arsenic concentrations in ewe milk varied depending on the lactation stage. Concentration of arsenic was lower in colostrum at 2nd lactation day (As0.011mg/kg) as compared with milk on the 10th (As: 0.025 mg/kg), 30th (As: 0.028 mg/kg) and 60th (As: 0.029mg/kg) lactation day. Licata & Trombetta [18] assessed the milk from 40 cows bred on various farms in Calabria to determine the load of heavy metal contamination in them. Quantitative analyses performed using an atomic absorption spectrophotometer with graphite furnace; followed by hot vapor generation technique showed the mean concentration of as in samples was about (37.90μg/kg). In 1999 arsenic levels were determined in cow milk samples collected at the most important dairy farms of the Comarca Lagunera in Coahuila and Durango, Mexico, a region naturally rich in Arsenic. Arsenic concentrations found in milk ranged from <0.9 to 27.4 ng g-1. Using a pharmacokinetic approach, it was found that the cow’s milk biotransfer factor for arsenic was up to 6 × 10-4 [19].

The concentration of Arsenic in Philippine’s infant formula milk for 6-12 months old was also analyzed by Cruz, Din [20] using Atomic Absorption Spectrophotometry and results were compared with an existing standard for permissible quantities of arsenic in food products as set by the World Health Organization. All the infant formulas tested showed up to be negative for Arsenic. Another study was conducted to determine arsenic concentration in 32 raw cow milk samples collected from traditional and industrial sites of Arak City, Markazi Province, Iran using an atomic absorption spectrometer. The residual amounts of as were found out to be lower than permissible limits established by Codex Alimentarius [2].

Therefore, considering the stated previous studies, we cannot conclude that all the infant formula milk available in markets worldwide, contains toxic heavy metals or not. However, this study can be further utilized as a reference or a foundation for future in-depth analysis of heavy metal contamination in various foods. This review can also help create awareness among consumers, manufacturers, and the professionals in the health care system because of its cumulative display of important statistics regarding heavy metal contamination in foodstuff.

Conclusion

Milk is no doubt affected by the heavy metal contaminated water sources, yet the above discussed studies showed that human milk is still the safest of all, as arsenic levels do not vary significantly even if one is taking arsenic contaminated water in daily routine, however it may be a potent risk on a long term basis. Furthermore, safety of milk obtained from different animals with respect to arsenic contamination showed that if it is taken from a sheep, it is least susceptible to Arsenic toxicity even from a place with higher Arsenic content in water, but the cow milk is most susceptible. In a nutshell the misconception of breast milk being unsafe and infant formulas being safer is under question and the studies show that breast milk is the safest among all other milk sources. 

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Evidence-Based Instructional Strategies in Learning Review-Juniper Publishers

Trend in Technical & Scientific Research

Introduction

Active learning instructional strategies include a wide range of activities that normally share some common elements that entail involving students in doing things and thinking about the things they are doing [1]. Essentially, active learning must engage the learners actively as failure to do so may lead to low rates of comprehension. At the high school level, learners have already developed different learning methodologies, but the teacher should not assume they will involve themselves in active learning without being guided effectively [1]. A robotics and computer programming teacher need to guide learners closely and actively so that they can grab applicable knowledge and skills in robotics as well as computer systems and programming.

As a teacher of the said subject, learners cannot completely comprehend without being involved in real work such as programming and coding. Robotics and computer programming must involve some practical work so as to improve the rates of comprehension. More so, the teacher needs to make them think about what they are doing before they can evaluate the outcomes such as running a program through a text editor. Doing so enables the learners to understand the theory behind the practical sessions [1]. It is worth point out that active learning not only involves active engagement of the learner but also other processes and strategies such as exploring personal attitudes, thinking critically, and giving feedbacks among others as will be looked into in the following sections.

Discussion

Active learning instructional strategies encompass numerous methodologies that may be applied by a teacher or an instructor. The methodologies applied may vary from one subject to another, but the teacher should be able to choose the most effective for the learners [2]. For instance, for a robotics and computer programming teacher, he or she must be able to choose strategies that will boost the comprehension rates. Learners have negative attitudes towards robotics and computer programming and hence the teacher should be able to motivate them effectively. In order to do so, one needs to introduce topics and allow learners’ time to reflect and analyze while also allowing them time to ask questions they may have [2]. More so, it is imperative to allow learners to shortly discuss among themselves the topics and concepts as a means of making them feel motivated and involved.

It is imperative to point out that active learning instructional strategies can be created and used to engage students in various processes as follows. First, they must be involved in thinking critically and creatively [2]. Robotics and computer programming is a field that calls for creative and critical thinking so that one can understand and apply the theory and basic skills learnt. For instance, computer programming starts with designing algorithms which are then translated to a computer program. In order to do so, the learners must be made to think critically and creatively. A teacher will need to motivate learners through a number of approaches such as guiding them through examples while allowing them to ask any questions, allowing group and peer discussions, and providing them with extra materials that will boost their creativity such as reference books [2]. Additionally, it is important for a teacher to ensure that the learners get rid of their negative attitudes that may hinder their creative and critical thinking.

Second, active learning can also be attained through giving and receiving feedback. This process should take place as early as learning begins so as to ensure that any issues are sorted out before they transition to bigger issues [2]. For instance, learners may want to suggest new reference materials or approaches that may seem better during class work. In this regard, the teacher should pay attention to the learners’ feedbacks and suggestions which may be helpful in the whole learning process. In doing so, the teacher is able to learn about students’ concerns and issues and hence adopt strategies and mechanisms which will effectively address their needs. Further, when an instructor or a teacher attends to suggestions and feedbacks of the learners, the latter feel motivated and inspired to learn and hence will develop a very positive attitude about the course. It is worth pointing out that receiving feedbacks from learners is one of the major ways through which the teacher and the students should communicate. Through communication, the teacher learns much about the students which is highly important [2]. However, a teacher should implement other methodologies that will improve the communication such as encouraging learners to ask more questions in class as well as making any new suggestions.

Third, active learning instructional strategies also involves involving learners in reflecting upon the learning process [3]. Learning about robotics and computer programming must involve reflection so that students will not quickly forget about concepts learnt in class. Notably, reflection should not only be done in class but also out of class. While in class, the teacher should engage learners in quick tests and note taking as a means of reflection. However, it is imperative to point out that learners should be allowed to interact among themselves so as to share concepts and ideas. While out of class, the teacher should allow interactions with the learners through emailing and should be there to answer questions that may be asked while also guiding them through personal tests and exercises as a means of reflection.

Fourth, active learning instructional strategies also involve spending greater proportion of time helping students develop their understanding and skills [3]. In robotics and computer programming learners must be made to effectively understand and gain skills. In order to attain such a goal, the teacher needs to support surface learning while also providing opportunities for learners to apply and demonstrate their understanding. Without making them demonstrate their understanding, it may be challenging for the teacher to evaluate learners’ strengths and weaknesses which need to be known before going forward. Essentially, the teacher needs to be ensure that the learners completely understand the basics which are very important in the robotics and computer programming field.

For a robotics and computer programming teacher, he or she must be able to transform a traditional classroom into an interactive classroom so as to promote active learning instructional strategies. The course is about gaining skills and in-depth understanding and hence a teacher must be able to promote interactions in classrooms. In order to do so, the following approaches will need to be employed.

First, the teacher can adopt the pause procedure which normally entails promoting greater student engagement through pausing procedure where the instructor pauses for a few minutes to allow students to work in pairs to discuss concepts and rework their notes [3]. For instance, in Robotics, there are concepts such as software-hardware integration that may seem challenging to the learners. However, if learners could be allowed to discuss among themselves, it may seem easier for them to comprehend. When using the pause procedure, it imperative to point out that the instructor or the teacher should pause in intervals that will bring about the best outcomes [3]. For instance, pauses should be made after introducing new concepts and topics so as to allow learners enough time for reflecting. More so, pauses should be made to allow discussions before learners can undertake individual short tests. The pause procedure is highly effective in promoting class interactions which are highly needed in a classroom setting.

Second, the teacher can adopt the think-pair-share methodology which also promotes active interactions in learning. It often begins when information is shared through reading an assignment and then a teacher poses a single questions and students are instructed to reflect and note it through note taking [3]. They are then instructed to pair with peers so as to share their responses. The pairs can then join creating groups which then reflects and discusses their responses. The approach is very effective in making learners to get used to group work and helpful interactions that tend to promote their understanding. More so, the approach is also applicable when dealing with large classes where attending to the needs of each and every learner may not be possible during class work [3]. Further, the approach enables learners to improve their interpersonal and communication skills.

Third, the teacher can also use concept tests as an approach towards attaining active learning. In robotics and computer programming, learners should be encouraged to understand the concept as opposed to memorizing them. Concept testing enables conceptual understanding and it is done at predetermined intervals where a challenging conceptual question is posed in a multiple-choice format [4]. Learners are encouraged to work together so as to come up with the final answer collaboratively. They can share their answers and responses with other groups as a means of interaction. In order to fully promote conceptual understanding, the teacher should make a follow up and explain to learners why a certain answer is the most suitable. In case of robotics and computer programming, the teacher can offer some practical tests that aim at testing conceptual understanding.

Additionally, the teacher can implement a personal response system, which is an exciting new way of engaging learners closely. For instance, clickers can be used as avenues for facilitating personal responses. Currently, the teacher can apply other approaches that can attain better personal responses in a timely manner so that the teacher can learn about the plight of every student. It is important to note that personal response systems cannot work effectively while in class as they are prone to more time consuming which may not be available [4]. Hence, the teacher can make a follow up to learn more about students especially those with negative attitudes about class projects and assignments.

Further, classroom demonstrations have become subtle in teaching robotics and computer programming. A teacher needs to explicitly demonstrate about computer systems and robotics in class so that learners can harmonize theory with practicals. During introduction, demonstration may not be necessary as such, but the teacher must be able to make the learners understand what specifically the course will entail [4]. As learners gain an in-depth knowledge about computer programming and robotics, it is imperative for the teacher to demonstrate meticulously. For instance, in computer programming, the teacher must be able to demonstrate how a program is compiled and debugged. Doing so enables the learners to quickly grab what the whole procedure entails. On-screen demonstrations to the students will be most applicable. Every step and process should be explained and learners encouraged to ask questions regarding what is being demonstrated [4]. During demonstrations, the instructor or the teacher should ensure that all learners are keenly paying attention and focusing on what is being demonstrated. Doing so will allow uniformity in the learning process.

On the other hand, it is always good practice when a teacher employs illustrative excerpts in stimulating critical and creative thinking. In today’s classrooms, learners are looking for new ways of doing things and hence any creativity will be welcomed warmly [4]. For instance, an illustrative excerpts may be used to explain how a certain program is compiled and debugged. More so, they can be used to explain how software and hardware relate in a robotic system. Illustrative excerpts help make the classroom lively while also making learners feel motivated and excited. In most cases, popular film excerpts and video-vignettes may be used before a concept can be explained so as to promote conceptual understanding.

In addition, use of illustrative excerpts in classroom should also involve making learners connect course content to current events. Doing so enables learners to develop a clearer sense of personal relevance and significance of the course [4]. It has been established that learners’ are likely to develop a negative attitude towards a course if they feel it has no practical relevance in their daily lives. It is the duty of the teacher to make the learners connect the course content to the outside world so that they can feel the urge and need to understand the concepts introduced through the course [4]. Learners with a positive attitude are more eager and motivated to learn and hence will effectively cooperate.

Research findings have pointed out that students’ concentration and focus tend to decline after 10-15 minutes of the session [4]. In this regard, it is the duty of the teacher to effectively exploit the time when learners are most attentive. This is the time when learners are most likely to understand the concepts introduced. After this time, the teacher needs to introduce demonstrations and practicals which will basically entail connecting the concepts to real work [4]. For instance, in robotics and computer programming, there are numerous concepts that need to be understood by the learners. However, the teacher needs to come up with strategies that will ensure learners are able to effectively comprehend a concept and apply through the following active learning instructional strategies.

In a classroom setting, it is important for the teacher to ensure that there are sufficient resources such as computer desktops needed for the coding. If resource-sharing is to apply, the teacher should ensure the resources have been shared optimally. More so, it is imperative for the teacher to ensure that all learners are keen and ready for the class session. A quick and random check is enough to enough to ensure that learning can begin. A teacher should not enter a classroom and immediately start introducing new concepts. Normally, he or she should first involve the teachers in some form of interaction as a means of drawing their attention to the class session.

Use of video-vignettes among other illustrative excerpts can also apply in drawing the learners’ attention in a manner which does not make them feel challenged or demotivated [4]. A teacher should be able to choose materials that relate to the learners’ experiences and expectations. Essentially, the teacher must hook up learners before new concepts and practices can be introduced. Doing so prepares the learners for a class session. As earlier highlighted, active learning does not only encompass methodologies applied in classroom but also approaches that aim at closely engaging the learners and making them feel motivated.

Teaching robotics and computer programming should also entail application of technological tools that will boost the learners’ conceptual understanding. Currently, most high schools are already deploying technological tools in learning but have not keenly examined the applicability of those tools. In this regard, it is highly important for the teacher to choose technological tools that will help learners develop a new interest and creativity while learning. For instance, the teacher can guide the learners through internet resources that have additional information, questions, answers and links that will complement the content learnt in class [4]. However, it is imperative to point out that the teacher must discern legitimate and illegitimate sources and should guide the learners in distinguishing between the two sources. More so, the teacher can ask the learners to confirm with him or her when seeking additional resources from the internet.

It is important to note that the internet cannot be overlooked when it comes to active learning instructional strategies especially in courses such as robotics and computer programming [5]. The internet is a powerful tool that has diverse resources that will be applied in complementing what has been learnt in class. In order for the teacher to avoid unlikely outcomes such as learners spending time on the internet on materials that may not help them complement classroom content, he or she should guide the leaners in exploiting the internet resources [5]. More so, the teacher ought to do so in line with school’s policies. Essentially, so that a teacher can effectively promote conceptual understanding, he or she must involve learners in doing things while also making them think about what they are doing.

Active learning instructional strategies are helpful in learning but lead to a number of challenges as follows. First, one cannot cover as much content within the time available [6]. This means that a teacher needs to strike a balance between using the tools and covering as much course content as possible. This can best be done through planning and scheduling which will enable effective time allocation. Second, it has been established that using the tools requires extensive pre-class preparation. A teacher should have enough time for the preparations to avoid shortcomings that may hamper effective learning. In order to prepare sufficiently, the teacher should also plan and schedule for activities [6]. Third, large class sizes have also been established as challenges to active learning instructional strategies. Employing tools such as personal response systems cannot be effective when the class size is larger than normal. In such a case, the teacher must create groups whose collective concerns and needs will be addressed during classwork [6]. Additionally, insufficient materials and equipment to support active learning instructional strategies negatively impacts the learning process. A teacher should be able to share resource available optimally among learners. Other additional challenges are students’ resistance to new approaches and some teachers lacking enough time to prepare for class sessions [6]. It can be seen that most of the challenges can be addressed through school’s administration collaborating with teachers to formulate working strategies.

Conclusion

Active learning instructional strategies encompass tools that aim at engaging students actively while also making them think critically about what they are doing. The strategies cannot be attained without the teacher transforming a traditional classroom into an interactive one where learners are able to interact not only with their peers but also teachers. A teacher needs to choose tools that will be applied in demonstrations and collecting feedbacks from learners as well as motivating them. Students must be motivated so as to get rid of negative attitudes that may hamper their conceptual understanding. In courses such as robotics and computer programming, the teacher must demonstrate and must involve learners in sessions that help them acquire skills as opposed to memorizing concepts. The teacher should design strategies and methodologies that will help engage learners both in classroom and outside classroom. He or she must also guide them in exploiting resources such as internet in complementing the course content. On the other hand, implementing active learning instructional strategies faces some challenges such as large class sizes, limited time, and insufficient resources and materials which must be dealt with through a teacher’s collaboration with the school’s administration.

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Biogas Energy Production Potential of Grass under Anaerobic Digestion: Review-Juniper Publishers

 Agricultural Research & Technology: Open Access Journal  

Abstract

Because of the recent increase demand of energy, interest in environmental issues and depletion of fossil fuel, the demand of renewable energy sources as substitute of fossil fuel is rapidly increasing. Production of biogas under anaerobic digestion as methane can be used to replace nonrenewable energy resources in both heat and power generation and as a vehicle. For biogas production various organic feedstocks are used. Most often used are animal manure, food waste, agricultural wastes and crop residues, aquatic waste, forest residues, municipal solid wastes and grass. The review is based on secondary data obtained through various sources such as textbooks, journals, documents and conference papers with the objective of providing an overview of biogas energy production from biomass, thus providing information toward anaerobic digestion contributing to methane rich biogas production. The review shows that biogas production from biomass as a good fuel alternative because the source biomass can be grown renewably and decrease environmental stress.

Keywords: Anaerobic digestion; Biogas; Methane; Feedstocks

Introduction

Energy is an essential factor in development since it stimulates and supports a country’s economic growth and development [1]. The global energy demand is growing rapidly, and about 88 % of this demand is met at current time by fossil fuels. The depletion of fossil fuel and the impact of greenhouse gases on the environment initiated the concern in searching and exploring alternative sources of energy [2]. These sources are described as renewable energies such as solar energy, wind energy, different thermal and hydro sources of energy, and biomass [3]. Biomass residues available from agricultural and forest processing constitute a potential source for biofuel production. Currently there exist five forms of biofuels such as bioethanol, biodiesel, biomethanol, biohydrogen and biogas [4].

The production of methane rich biogas (biomethane) involves a complex biochemical reaction that takes place under anaerobic conditions in the absence of oxygen and the presence of highly pH sensitive microbiological catalysts that are mainly bacteria [5]. The anaerobic digestion process is a fermentation process where organic raw materials such as manure, food waste, and sewage sludge, organic industrial waste and energy crops used as substrates for biogas production. From energy crops the grass has the greatest potential for biogas production (587.5m3 methane production/tone of dry organic matter) [6]. The production of biogas through anaerobic digestion offers several environmental advantages compared to fossil fuels, because available and cheap resources to feedstock, relatively easy and cheap technology for production, extra values of digestate as a fertilizer [7], avoiding health problems, reduce greenhouse gas (GHG) emissions , reduce deforestation , reduce workload from women and children [8]. The objective of this review is to provide an overview of biogas energy production from biomass, thus providing information toward anaerobic digestion contributing to methane rich biogas production.

Biogas Energy Production Under Anaerobic Digestion

Anaerobic digestion is a natural decomposition processes in which microorganisms break down biodegradable material in the absence of oxygen [3]. Anaerobic digestion is widely used as a renewable energy source because the process produces a methane and carbon dioxide rich biogas suitable for energy production, helping to replace fossil fuels. The nutrient-rich digestate which is also produced can be used as fertilizer. Fig .1 shows that the digestion process begins with bacterial hydrolysis of the input materials in order to break down insoluble organic polymers such as carbohydrates and make them available for other bacteria. Acidogenic bacteria then convert the sugars and amino acids into carbondioxide, hydrogen, ammonia, and organic acids. Acetogenic bacteria then convert these resulting organic acids into acetic acid, along with additional ammonia, hydrogen, and carbon dioxide. Finally, methanogens convert these products to methane and carbon dioxide [9] (Figure 1).

Substrates for Biogas Energy Production

Biogas can be produced from biodegradable substrates such as animal manure, food waste, agricultural wastes and crop residues, aquatic waste, forest residues and municipal solid wastes [10]. According to [11] a brief description of the various feedstocks is provided in this section.

Animal manure

Animal manure is considered a promising way for biogas production and fertilizers through the anaerobic digestion process [12]. There are significant populations of livestock in many countries. Livestock produce large amounts of manure which are suitable substrates for AD. Manure is a mixture of faeces and urine, and its chemical composition varies markedly depending on the chemical characteristics of the feed consumed by the animal. Animal manure comprises huge amounts of lignocelluloses, polysaccharides, proteins, and other biomaterials.

Municipal solid waste (MSW) and food waste

The food industry and municipal authorities produce a wide range of lignocellulosic waste types. These include food waste and municipal waste which can be used as substrates for biogas [2].

Crops and their residues

A number of crops and activities produce residues that can be used as a feedstock for biogas production [10]. Many forage and sugar beets, due to their high organic dry matter yield per hectare which produce high biogas yield [13]. Biogas also produced from non- food crops like Justicia schimperiana (Hochst. ex A. Nees) T. Ander (JS) [14].

Sewage sludge

Production of biogas from sewage sludge provides dual benefits such as biogas energy and waste management [11].

Biogas Energy Production from Grass

Compared with other feedstocks, grass has suitable and promising characteristics as energy. Crop for biogas production due to their fastest growing rates even in infertile land, low cultivation costs, higher accessibility, and consumption of whole plants. In addition, the usage of grassland as a renewable source of energy during biogas production will provide considerable quantity of environment protection, owing to the capability of grass to sequester carbon into the soil [15].

Biogas production potential of napier grass

Napier grass is a complex material that is composed of cellulose, hemicellulose and lignin. Commonly, cellulose and hemicellulose primarily contain glucose and xylose, respectively. They can be fermented to produce renewable energy using several microbial processes [16]. As shown in Table 1, the maximum methane content and methane yield of 5% and 122.4ml CH4/g- TVS remove was obtained using napier grass as the substrate [17].

Biogas production potential of vetiver grass

Vetiver (Vetiveria zizanioides) is a perennial tufted grass belonging to the Poaceae family and the common domesticated cultivars used around the world are non-invasive. It has become known as a miracle grass with diverse environmental applications, including: a source of scented oil from its roots, fodder for livestock, soil and water conservation, rehabilitation, remediation, waste water treatment and a raw material for biogas production [18].

Experiment conducted in China on vetiver grass as raw material for biogas production and the result point out that the production potential of biogas were 310mL.Ts and 332Ml/g. vs of the grinding process group and 322 and 349 of the shearing process group [19] (Table 2).

Biogas production potential of elephant grass (Pennisetum Purpureum)

Elephant grass is a species native to African grasslands and is low in water and nutrient requirements, allowing it to make use of otherwise uncultivated lands [1]. Elephant grass possesses several advantages that make it suitable as bioenergy crop; elephant grass is perennial, it can be vegetative propagated and it can withstand repeated cutting/harvesting and regenerates [20] other features that made elephant grass suitable for bioenergy purposes include the possibility of multiple harvest per year.

Conclusion

Demand and dependency on fossil fuels have namely been increasing since the industrial revolution. It has become clear that fossil energy sources of the earth are finite, moreover, their use causes more and more damages to the environment (climate change, air pollution, greenhouse effect, etc.). In this context, biogas from biomass will play a vital role in future. Biogas is a versatile renewable energy source, which can be used for replacement of fossil fuels in power and heat production, and it can be used also as gaseous vehicle fuel. Grass biomass growing is importance as it offers extensive environment protection, owing to the capability of grass to sequester carbon into the soil matrix as a result CO2 emissions reduced. Furthermore, various socioeconomic profits are possible to achieve without compete with food production. Due to their fastest growing rates even in infertile land, low cultivation costs, higher accessibility, consumption of whole plants.

On the other hand, farmers can use grass for biogas production feedstocks and its digestate as fertilizer because it is readily available, it doesn’t require any pretreatment, thus helping farmers to reduce their energy cost. Even environmental concerns such as deforestation and ecological damage will not be an issue as the grass which will be cut will grow in a short span of time.

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From Corn to Rice: Cultural Conception of Food among the Madurese Community Indonesia-Juniper Publishers

Global Journal of Archaeology & Anthropology

Abstract

Food is closely linked to culture. The choice of food is not solely based on nutritional considerations, but also involves far more complex considerations such as group identity and symbolical function. This paper discusses the meaning of food for Madurese ethnic group, Indonesia. More specifically it will be studied the adoption of corn as a staple food and shifting staple food from corn to rice in the Madurese ethnic group. It is argued that for Madurese community the shifting of staple food is a reasonable historical process and takes place for various reasons.

Keywords: Corn; Rice; Cultural conception; Food shift; Madurese Community

Mini Review

The Madurese people have been familiar with a variety of foods. There are three foods that are most often mentioned in colonial reports, namely corn, rice, and cassava [1]. Among the three foodstuffs, corn once occupied an important position before later being replaced by rice. Corn has been seen as an integral part of the Maduerese ethnic identity. The significance of corn is evident from the stereotype that developed and is often attached to the Madurese as corn eaters [2]. The important position of corn for the Madurese ethnic group is reflected in various Madurese folklore. In a collection of folklore from Madura, for example, corn is part of it [3]. In other traditional Madurese story, Lesap, corn is also mentioned. When facing Prince Tjakraningrat and giving an explanation of the king’s questions, Patih Ardja Mantjanegara, among others, replied, “The people prospered, the conditions of the countryside were safe, the corn trees had begun to flower ...”. In another part, when asked by the king about his work, Lesap replied, “The servant does not have a job, except planting corn [4]....” In both Madurese literature, rice does not appear at all.

In Madurese society, corn has various functions. In addition to consumption item, corn is also used as a means to strengthen kinship and social relations. Even until 1980s when people die, mourners, especially mothers, always bring corn to be handed over to the bereaved family [5]. Corn also has an important position as a means of ritual activities. Corn is one of the ingredients in the offering when establishing a house [6]. Despite its importance, corn which was once the identity of Madura is not native to the island of Madura. Corn is believed to originate from the American continent and is generally known as a staple food of Indian tribes [7]. From the Americas, corn spread throughout the world during the post-Columbian food exchange process along with the colonization of Westerners. In new places, a number of new plants were even expanding widely. Even on Madura island, corn was the most important food crop [8]. It is estimated that corn has been widespread in Madura since 1550 and at the beginning of the 19th century Thomas Stamford Raffles intended to make corn as a measure to set taxes on dry land [9].

There are several basic reasons that made corn a popular crop among the Madurese ethnic group. First, corn offers higher productivity per unit of land and labor. Compared to rice, corn provides a higher yield ratio, guaranteeing greater crop success, with relatively low labor requirements. Second, corn has several advantages. The needs of the growing environment of this plant are more flexible, including less fertile areas. To grow corn requires irrigation in a much less volume than rice. In terms of cultivation techniques, corn planting can be done intercropping with other plants, so as to reduce the risks and losses due to crop failure [10]. Similar reasons also underlie why corn is popularly accepted in African regions [11]. Because the expansion of agricultural land was mostly in the dry land areas and investment in irrigation networks requiring large costs, one of the most appropriate adaptation patterns was through the choice of plants suitable for limited irrigation environments. In such an ecological context, the choices of commodities available were corn and cassava. The advantages of corn compared to cassava were among others in terms of prices that were much higher and easier to store for a long period of time. Unlike corn, cassava must be consumed immediately a few days after harvesting. For long-term consumption, the cassava preservation process was more complicated and without adequate handling the quality decreases quickly. Another reason was more important, corn plants provide feed for livestock, especially cattle, domestic animals that are very important among Madurese. The importance of cattle for them leads to a stereotype that the Madurese love cows more than their wives [12].

Madurese preferences for corn began to shift in the New Order era. With the food crisis backround in the 1960s, the New Order government targeted increasing rice production through a green revolution policy. Besides providing various components of production, including seed technology, fertilizers and pesticides, irrigation sector development was one of the pillars. In Madura, the expansion of rice plants or what Kuntowijoyo termed a “process of ricefication “ was inseparable from the introduction of water pumps for agriculture and the discovery of various short-lived rice varieties [13]. The reduced area of corn cultivation reflected the shift in staple food preference among the Madurese. The position of corn as staple food began to be replaced by rice. This shift can be recognized by comparing the two phenomena that contradict the tendency. On the one hand, the Madurese population continues to grow and food needs are increasing. On the other hand, corn cultivation has actually decreased in area and corn production has also declined. It can be ascertained that the food needs of the Madurese are fulfilled by the consumption of non-corn food, and in this case rice. A historian who is an expert on Madura describes, “food stalls in Madura now also no longer provide corn food but rice [14]...”

In addition to ecological changes, the shift in consumption of staple foods from corn to rice among Madurese is related to a number of factors. Economically the government policy of providing subsidies for production facilities and fixing the price of rice on the market, which is also supported by the rice import policy, succeeded in suppressing seasonal fluctuations in rice prices. Rice becomes relatively stable in price and, no less important, can be affordable by people’s purchasing power. The combination of various policies is an important incentive that drives the transition of eating patterns with rice as the main component. Another advantage of rice is the ease in the preparation process compared to corn which requires more time and is complex. The shift to rice is also related to the flow of Madurese migrants to Java who play an important role in introducing rice culture to its original place when going home [15].

From a sociological perspective, rice consumption is considered to have a higher prestige than corn. Rice has a special position. In the 1990s for the purposes of ceremonies and weddings, the standard is rice [16]. Symbolically corn consumption as well as cassava as a basic component of the diet is often considered in Indonesian society in the past as a sign of poverty [17]. The same thing was expressed in a statement that appeared around 70 years ago that the replacement of rice with other foods was seen as a setback [18]. In several other places in the world including France and Italy, only the poor people used to adopt corn as a staple food [19]. Changes in the pattern of consumption of staple food from corn to rice are regarded as a sign of success in vertical social mobility from the lower strata to the higher social strata. This is parallel with Lury’s view that the practice of consumption is also closely linked with cultural and symbolic nuances. Consumption practices are part of the struggle of individuals to reach social class positions, not merely a means of meeting biological or economic needs. In other words, through food people also intend to define their social status in society [20]. The Madurese also don’t seem to be different. For them a shift from corn to rice is part of an effort to prove success in improving class position. 

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Rank Estimators Versus Least Square Estimators for Estimating the Parameters of Semiparametric Accelerated Failure Time Model-Juniper Publishers

Biostatistics and Biometrics Open Access Journal

Abstract

Rank-based method and least square approach are the most common techniques for estimating the regression parameters of accelerated failure time model. In this paper, both inference procedures are considered, their advantages and disadvantages are explained, and their similarities and differences are discussed.

Keywords: Accelerated failure time model; Rank-based inference; Least square method; Semiparametric method; Censored data; Linear regression; Biostatistics

Introduction

Accelerated failure time model is an appealing regression model to biostatistics researchers due to its simple interpretation [1]. Estimating the regression parameters of the model through parametric methods is quite challenging in the presence of censored observations [2]. In such cases, semiparametric approaches are very common. Two main semiparametric methods for estimating the unknown parameters of the model are rank-based method [3], and least square method [4]. In this paper, both inference procedures are briefly explained and their main theoretical and computational aspects are considered. Both approaches are also compared and their advantages and disadvantages are discussed. The main focus of this study is on investigating the similarities and differences of two methods in theory as well as their performance in applications.

Inference procedures

Accelerated failure time model: For the i^th subject of a random sample of n subjects let T_i denote the failure time, iC denote the censoring time, and Z_i denote the 1p× vector of corresponding covariates. Assume that conditional on covariates ,Z_i failure times T_i and censoring times C_i are independent. The accelerated failure time model takes the form

Where β is a p-vector of unknown model parameters, and i∈ are the error terms of the model for 1,,in= with a common distribution function F which is unspecified [5]. The data consists of and otherwise. The introduced model is a semiparametric linear regression model which relates the log-transformed failure times to the covariates.

Rank estimators

Define is the indicator function, and The weighted log-rank estimating function for the unknown parameter β is given by

Where is a weight function. The estimating function correspond to Gehan Let ˆRβ denote the rank estimator for the unknown parameter of the model which is the solution of (){}0.Ubφ= For estimating the unknown parameters of the model Jin et al. [3] proposed an iterative algorithm on the basis of the general weighted estimating function. The algorithm at its kth iteration is given by

According to Jin et al. [3] the rank estimator is asymptotically normal for any .k

Least square estimators

When there is no censored observations the least square estimator of the unknown model parameters is obtained by solving the following estimating equation:

This estimating equation cannot be used when data contains censored observations since the actual value of iT is unknown for subject i when 0.iδ= For obtaining the least square estimators in the presence of censored data Jin et al. [4] proposed an iterative algorithm which at its kth iteration is given by

In this equation,which is proposed by Buckley & James [8] and can be approximated by

Where ˆF is the Kaplan–Meier estimator of .F According to Jin et al. [4] the least square estimator ()ˆkSβ is asymptotically normal if the initial value ()0ˆSβ is asymptotically normal.

Discussion

Both the rank-based method and the least square approach are semiparametric inference procedures since the probability distribution of error terms of the model is completely unknown. One advantage of rank-based inference over the least square method is that it does not involve estimating the distribution of the error terms, while obtaining least square estimators requires the Kaplan–Meier estimator of the distribution of the error terms. This makes the least square method and its corresponding algorithm more complicated than the rank-based method, both theoretically and computationally. Note that, both algorithms need a consistent estimator of the model parameter such as Gehan estimator for their initial values. Thus, the least square approach requires to obtain a rank estimator prior to the computational stage of its associated algorithm. In addition, it has been established that rank estimators are always asymptotically normal [9,10] while the asymptotic normality of least square estimators strongly depend on the asymptotic normality of the initial value of their corresponding algorithm. However, the results of the simulation studies by Jin et al. [4] illustrated that there was no significant difference between the efficiency of rank estimators and least square estimators. More precisely, the rank estimators were slightly more efficient under extreme-value error, and the least square estimators were slightly more efficient under logistic and normal errors.

Conclusion

For estimating the regression parameters of semiparametric accelerated failure time model both rank estimators and least square estimators are common. From a theoretical point of view, rank-based inference procedure involves less technical difficulties since it does not require estimating the probability distribution of the error terms while least square approach involves Kaplan–Meier estimator of the distribution of the error terms. Moreover, the asymptotic normality of rank estimators does not depend on the distribution of the initial value of its associated algorithm. In application, the results of simulation studies show that there is no significant difference between the efficiency of rank estimators and least square estimators. Therefore, in studies that researcher is free to choose between these two methods rank estimators are definitely more recommended than least square estimators.

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Stem Cells to Improve the Wound Healing-Juniper Publishers

Journal of Head Neck & Spine Surgery

Abstract

The cellular therapy using Mesenchymal Stem Cells, specially its two subtypes - Bone-marrow Mesenchymal Stem Cells and Adipose Derived Stem Cells - can benefit by virtue of the possibility of differentiating in specialized cells that secrete and suppress growing factors and cytokines necessary in the lesion niche. When attracted by the pro-inflammatory sinalization of the lesion, they act using the paracrine signaling, decreasing the inflammation, increasing the angiogenesis and the cell migration and proliferation. The development in the researches regarding the association of the application of MSCs, with reconstructive surgery practices, leads to effective future results that can bring more benefits to the clinic practice of this field. This paper has the objective of briefly reviewing the literature about the usage of MSCs and its subtypes, the ADSCs, to improve the skin cicatrization.

Keywords: Mesenchymal stem cells; Adipose derived stem cells; Bone-Marrow Mesenchymal Stem cells; Skin flaps; Skin grafts; Wound contraction; Paracrine signaling; Pro-inflammatory Interleukins; Anti-inflammatory Interleukins.

Abbreviations: MSC: Mesenchymal Stem Cells; HLA-DR: Human Leukocyte Antigen; ADSC - Adipose derived stem cells; BM-MSC: Bone-Marrow Mesenchymal Stem Cells; SDF1: Stromal Cell-Derived Factor; PDGF: Platelet-Derived Growth Factor; IL: interleukin; TNFα: Tumor Necrosis Factor-α; IFNγ: Interferon-γ; VEGF: Vascular Endothelial Growth Factor; BFGF: Basic Fibroblast Growth Factor; EGF: Epidermal Growth Factor; KGF: Keratinocyte Growth Factor; HGF: Hepatocyte Growth Factor; PDGF: Platelet-Derived Growth Factor; TGF-β: Transforming Growth Factor-β; FGF: Fibroblast Growth Factor; α-SMA: Alpha-smooth muscle actin's; IRI: Ischemia-Reperfusion Injury

Introduction

Mesenchymal stem cells (MSCs) were first described by Friedenstein et al. [1,2]. MSCs are heterogeneous cell populations, called multipotent adult cells or somatic stem cells [3,4], capable of differentiation in most cell types in order to maintain and repair the organism. They are resident in different organs and tissues such as adipose tissue [4,5], bone marrow, umbilical cord, amniotic membrane [2,4], kidneys, liver, spleen, lungs, pancreas, tendons, synovial membranes, placenta, amniotic fluid and dental pulp [4]. The International Society for Cellular Therapy proposed three minimal criteria for defining MSCs:

a) Plastic adherence;
b) Positive expression (greater than 95% of the cell population) for CD105, CD73 and CD90 markers and negative, (maximum 2% of the population) for CD45, CD34, CD14, CD11b, CD79a, CD19 and Human leukocyte antigen (HLA-DR) surface molecules, and
c) Ability to differentiate into osteoblasts, adipocytes and chondroblasts under standard in vitro differentiating conditions [2,6].
Later, others researchers complemented this characterization with new markers: CD13, CD44, CD54, 106 and Stro-1 [4] and the presentation of fibroblast cellular morphology [3,4].

MSCs have a great potential to the tissue repairment and regeneration in reconstructive plastic surgery, preventing ischemic lesions in skin flaps [7-14] and in skin grafts [15,16]. MSCs are capable of reducing severe atrophy, retraction, fibrosis and ulceration skin signals, caused by radiotherapy [17,18]. Combined with the lipoinjection in face and body defects and in rejuvenating esthetic treatments, MSCs raise in 35% the survival rate and the microvasculature from the injected fat [18]. Also, diabetic patients with ischemic wounds show greater survival rates and lower number of amputations in affected limbs, when treated with Adipose derived stem cells (ADSCs) [19]. The MSCs improved the skin healing at induced burns in rats [20,21]. In dermatology, the MSCs are being clinically used for inflammatory diseases [22-28], Graft-Versus-Host Disease [23,25], Chrown Disease [29], Systemic Sclerosis, Lupus or dermatomyositis [24,28,30].

When compared with the usage of Growing Factors, that like any drug has a limited half-life, the cellular therapy using MSCs, specially in its two subtypes - the Bone-Marrow Mesenchymal Stem Cells (BM-MSCs) and ADSCs - can bring greater benefits because of: their expansion capacity in cellular culture; stable phenotypic expression; and possibility of differentiating in specialized cells, that secrete and suppress cytokines and growing factors in the injury [13,31-33]. However, long expansion periods of the cellular culture, to achieve effective therapeutic doses, raise the possibility of infection from the host. Because of that, the ADSCs still have to be heavily studied to the application in the clinic routine [2]. This way, this study has as objective briefly review the literature about the usage of MSCs and its subtypes, the ADSCs, to improve the skin healing.

Discussion

The MSCs are capable to answer and adjust their functions, when exposed to cells or typical factors of the lesion environment [33,34]. They have an attraction capacity to the inflammation areas [33-35] or tumors, because of the molecules CCL21 or HMGB1, known as homing. In case of lacking of this signalization, they are attracted in order of preference to the lungs, liver and spleen [35]. The MSCs show chemotaxis in vitro by the Stromal Cell-Derived Factor (SDF1), Platelet-Derived Growth Factor (PDGF), Insulin-Like Growth Factor-1, Interleukin-8 (1L-8) and Tumor Necrosis Factor-α (TNFα). In murine models, the MSCs used in the systemic administration are capable of getting into the damaged tissues [14,34,36].

The MSCs act, in many levels, in the three healing phases: inflammatory, proliferative and remodeling phase. Current studies indicate that the differentiation of the MSCs, that contributed to the tissue regeneration, is limited by the small survival rate of these cells in the damaged area. However, the paracrine signaling to the cells from the injury is the main mechanism of the MSCs, reducing the inflammation, stimulating the angiogenesis and inducing the cell migration and proliferation [33,37]. Nevertheless, other authors suggest that the differentiation of the MSCs in keratinocytes and endothelial cells have the same function as the paracrine signaling to accelerate the neovascularization and the reepithelialization of wounds [32] (Figure 1 & 2).

Some studies suggest that immunosuppressive potential is the same of both types of MSCs, ADSCs and BM-MSCs, in an inflammatory environment. Their local administration inhibited the T cells recruitment and proliferation [37-41] and decrease Interferon-γ (lFNγ),Tumor Necrosis Factor-α (TNFα), 1L-6 and IL-1β expression in the skin grafts [39-41]. In the inflammatory phase (one to three days), the expression of anti-inflammatory cytokines 1L-4 and 1L-10 is increased while 1L-2 pro- inflammatory cytokines, TNF-α and 1FN-γ are decreased, causing less local inflammatory reaction [37,42]. MSCs can also regulate macrophage activation and convert phenotype expression of M1 macrophages to M2 anti-inflammatory macrophages [39-41], which accelerates the wound healing. Additionally, MSCs act over the innate immunity to prevent the rejection of transplanted allografts, inhibiting the complement system activation [39]. The decrease of TFN-α also helps the reepithelialization after the proliferation phase [43]. The antimicrobial action from the MSCs are also important to limit the infection occurrence [37].

With the utilization of cell therapy in the proliferative phase (14 days) the production of important growth factors is increased: Vascular Endothelial Growth Factor (VEGF), Basic Fibroblast Growth Factor (bFGF) [32,37,42,43], Epidermal Growth Factor (EGF), Keratinocyte Growth Factor (KGF), Hepatocyte Growth Factor (HGF), Platelet-Derived Growth Factor (PDGF) and Transforming Growth Factor-beta (TGF-β). Through their paracrine action, the MSCs raise the migration and proliferation of keratinocytes, endothelial and epithelial cells. The fibroblasts proliferation is also enhanced, as well as the blood vessels' formation. This way, there is a better growing of a more vigorous granulation tissue [33,37,42,43]. The angiogenesis is a very important factor to the wound's healing, and the VEGF and the Fibroblast Growth Factor (FGF) are very important angiogenic factors [32].

Through the paracrine signaling, from the MSCs in the remodeling phase (21 days to one year), the fibroblasts produce collagen fibers in greater quantity and density, generating an increase in wound tensile strength [37,42,43]. At the same time, there is a smaller wound contraction and increased matrix-metalloproteinases production, that control the collagen deposition exacerbation, improving the aesthetic result and keeping the skin's function [33,42,43]. MSCs also contribute to the scar's appropriate remodeling with the increased secretion of VEGF and HGF, the adequate balance between TGF-β1 and TGF-β3 [37] and the increase of bFGF and TGF-β which inhibit the Alpha-Smooth Muscle Actin (α-SMA) expression, responsible for myofibroblast phenotype [32].

Studies indicate that there is also the possibility of using BM-MSCs and ADSCs to protect the damaged tissues caused by the 1schemia-Reperfusion 1njury (1R1) and to decrease the dysfunction of organs undergoing ischemia. The ADSCs are able to protect axial flaps from the 1R1 with results as satisfactory as the ones obtained in procedures without ischemia, because of the improvement in the angiogenic response and the blood perfusion elevation [10]. Many studies use the ADSCs to prevent ischemic injuries in skin flaps [7-14], as others [15,16] used them to improve the quality of skin grafts.

Conclusion

The MSCs - both BM-MSCs and ADSCs - are capable to answer and module their functions, when exposed to cells or typical factors of the lesion environment, attracted by the cell signaling to the inflammation areas. The researches developed till the moment point the paracrine signaling as the main mechanism from the MSCs, decreasing the inflammation, benefiting the angiogenesis and inducing the cell migration and proliferation in the damaged area. The progress on the researches about the association of MSCs with reconstructive surgery practices indicates good and productive results, which can benefit the clinical practice in this field.

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