LITERATURE REVIEW

Severe malnutrition is one of the most important underlying causes of child mortality in developing countries, particularly during the first 5 years of life (UNICEF, 2008). The major causes for this are poverty, world conflicts, lack of education, natural disasters and poor access to health (Leonor et al., 2011)

Undernutrition is a consequence of consuming little energy and other essential nutrients or using or excreting them more rapidly than they can be replaced (UNICEF, 2006). This state of malnutrition is often characterized by infections and diseases as it intensifies the effect of every disease (UNICEF, 2006). PEM is one of the most prevalent and devastating forms of malnutrition in the world (Whitney and Rolfes, 2008).

PEM is defined by the WHO as the cellular imbalance between the supply of nutrients and energy and the body's demand for them to ensure growth, maintenance, and specific functions (WHO, 1993). It can be caused, primarily, by an inadequate diet or, secondarily, by deficiency in gastrointestinal absorption and/or increase in demand, or even, by an excessive excretion of nutrients (Leonor et al., 2011). PEM usually manifests early in children between 6 months and 2 years of age and is associated with early weaning, delayed introduction of complementary foods, a low-protein diet and severe or frequent infections (Kwena et al., 2003). Nearly one-third of children in the developing world are malnourished (Ahmed et al., 2009). The spectrum of PEM ranges in severity from mild, through moderate to severe degrees. The mild and most of the cases of moderate PEM are subclinical and can only be detected by anthropometric and biochemical

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tests (El-Mougy, 1999). These early stages are characterized by growth failure and possibly some retardation of mental development (El-Mougy, 1999).

PEM appears in three principal clinical forms: marasmus, characterized by chronic wasting condition and a gross underweight status that is habitually associated with early weaning; kwashiorkor, characterized by moderate growth retardation, changes to hair and skin colour, oedema, moon face, and hepatosplenomegaly; and marasmic kwashiorkor, characterized by severe wasting and the presence of oedema. Marasmus appears by caloric and protein insufficiency, whereas kwashiorkor develops from protein deficiency (Waterlow, 1996).

PEM often coexist with micronutrient deficiencies (Bryan et al., 2004). Malnutrition results from multiple deficiencies not necessarily limited to lack of proteins or calories but also involving other associated or separated factors such as selenium, copper and zinc (Ballabriga, 1985).

2.1 Prevalence of PEM

Malnutrition remains one of the most common causes of morbidity and mortality among children throughout the world (WHO, 2002). It is responsible for at least half of the 7.6 million child‟s deaths each year in developing countries (Park et al., 2012).

Globally in 2011, an estimated 101 million children under 5 years of age were underweight, or approximately 16 per cent of children under 5. Underweight prevalence is highest in South Asia, which has a rate of 33 per cent, followed by sub-Saharan Africa, at 21 per cent. South Asia has 59 million underweight children, while sub-Saharan Africa has 30 million (UNICEF, 2013). In 2009, the WHO estimated that 27% of children in developing countries under the age of 5 years are malnourished. Approximately 178 million children (32% of children in the developing world) suffer from chronic malnutrition. Although the prevalence of childhood malnutrition is decreasing in Asia, countries in South Asia still have both the highest rates of malnutrition and

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the largest numbers of malnourished children. Indeed, the prevalence of malnutrition in India, Bangladesh, Afghanistan and Pakistan (38–51%) is much higher than in sub-Saharan Africa (26%) (Ahmed et al., 2009).

The prevalence of PEM is lowest during the first six months of life, due to the fact that breast feeding is the rule in this period and is considered satisfactory from the nutritional point of view (Osman et al., 1978). On the other hand, in the second six mouths of life, the incidence of malnutrition increases as breast milk becomes insufficient to meet all dietary requirements, and supplements given are mostly watery fluids of negligible nutritional value (Osman et al., 1978).

2.2 Assessment of Nutritional Status

Nutritional status assessment is the evaluation of an individual‟s health status from a nutrition perspective. It is a means by which the undernourished (or overnourished) child can be identified, the nutritional effect of therapy and the efficacy of nutritional interventions monitored and prevalence of under or overnutrition in a group established (Reilly, 1998).

There are four principal approaches to nutritional assessment: clinical, anthropometric, dietary and biochemical (Whitney and Rolfes, 2008).

2.2.1 Clinical assessment

Severe nutritional deprivation is easily detectable on clinical examination (Weaver, 1998). Physical findings like changes to hair and skin colour are most valuable in revealing problems for other assessment techniques, to confirm or in confirming other assessment measures such as anthropometric, dietary and biochemical nutritional Assessment (Weaver, 1998).

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2.2.2 Anthropometric assessment

Anthropometric measurement such as body weight and height reveal the nutritional status of an individual (Pinstrup et al., 1993). Anthropometrically, PEM is defined as measurements that fall below 2 standard deviations under the normal weight-for-height (Pinstrup et al., 1993). Wasting indicates recent weight loss, whereas stunting usually results from being chronically undernourished. In clinical practice, these anthropometric indices (body weight and height) are useful but can be limited (Potter et al., 1995). For example, when a child has fluid retention or large solid tumour, such condition can affect weight-based anthropometric indices. The mid-arm circumference and skin fold thickness has been proposed for the identification and classification of PEM of various degrees and severity (Potter et al., 1995).

The advantages of these anthropometric measurements are that they are simple, inexpensive, portable and suitable.

2.2.3 Dietary intake assessment

Assessment of nutritional status based on dietary intake provides a record of an individual‟s eating habits and food intake and can help identify possible nutrient imbalances (Whitney and Rolfes, 2008). Recording dietary intake can be done using various ways such as 24 hours recall, the usual intake record and food frequency questionnaire (Whitney and Rolfes, 2008). Food models or photos and measuring devices can also help to identify the type of foods and quantities consumed (Whitney and Rolfes, 2008).

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2.2.4 Biochemical assessment

Biochemical nutritional assessments are based on analysis of blood and urine samples, which contain nutrients, enzymes, and metabolites that reflect nutritional status. These analyses are especially useful in helping to detect subclinical malnutrition by uncovering early signs of malnutrition before the clinical signs of deficiency appear (Robinson, 1998).

2.3 Classification of PEM

In 1970, Wellcome classified PEM based on the presence or absence of oedema and the deficit of body weight.

Table 2.1: Wellcome’s Classification of PEM

State of malnutrition

Body weight % of standard

Oedema

Simple underweight

80 – 60%

Absent

Marasmus

< 60%

Absent

Kwashiorkor

80 – 60%

Present

Marasmic-kwashiorkor

< 60%

Present

Adapted from Wellcome (1970)

PEM is frequently classified on the basis of deficits of weight-for-age (w/a) or height-for-age (Gomez et al., 1956; Waterlow et al., 1977). In this system, children are classified into three groups according to malnutrition severity based on their weight compared to the weight average for their age. First degree or mild cases of malnutrition include children whose weights are 75– 90% of the average weight. Children with second degree or moderate cases have weights

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between 60–74% of the average, and children with third degree or severe malnutrition weigh less than 60% (Gomez et al., 1956).

Table 2.2: Gomez’s Classification of PEM

% of expected weight for age

Grade of PEM

75% - 90%

First degree

60 % - 74%

Second degree

< 60%

Third degree

Gomez Classification of PEM (Gomez et al, 1956)

The major disadvantage of this classification is that it assumes all children of certain age should have the same weight. It also includes actively malnourished children and those who are underweight as a result of malnutrition of the past. However, Gomez classification overestimates the prevalence of malnutrition (Kiju et al., 1991).

2.3.1 Marasmus

Marasmus is a clinical syndrome of severe PEM caused by severe deprivation of food over a long period of time (chronic PEM). It is characterized by extreme growth failure, wasted muscle and subcutaneous fat, with weight of 60% or less than that expected for age (Jelliffe and Jelliffe, 1991). Marasmus occurs most commonly in children from 6 to 18 months of age in all the over populated and impoverished areas of the world (Kwena et al., 2003). This is because children in those areas simply do not have enough to eat and subsist on diluted cereal drinks that supply scanty energy and protein of low quality; such food can barely sustain life and much less support

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growth (Kwena et al., 2003). Consequently, marasmic children look like little old people (just skin and bone) (Whitney and Rolfes, 2008).

2.3.2 Kwashiorkor

Kwashiorkor is a clinical syndrome of severe PEM caused by recent deprivation of food (acute PEM). Kwashiorkor is a Ghanaian word that refers to the birth position of a child and is used to describe the illness a child develops when the next one is born (Krawinkel, 2003). When a woman who has been nursing her first child bears a second child, she weans the first child so as to breastfed the second child. The first child suddenly switched from nutrient-dense, protein-rich milk to a starchy, protein-poor cereal and soon begins to sicken and die (Krawinkel, 2003). Kwashiorkor occurs most commonly in children between 18 months to two years of age (Krawinkel, 2003).

Kwashiorkor usually develops rapidly as a result of protein deficiency or more commonly, is precipitated by an illness such as measles or other infection (Krawinkel, 2003). Other factors such as aflatoxins (a fungal toxin found on grains stored in warm moist condition), may also contribute to the development of, or symptoms that accompany kwashiorkor (Krawinkel, 2003).

A loss of body weight and fat is usually not as severe in kwashiorkor as in marasmus, but some muscle wasting may occur (Krawinkel, 2003). Protein and hormones that previously maintained fluid balance diminish, and fluid leaks into the interstitial spaces. The child‟s limbs and abdomen becomes swollen with oedema, a distinguishing feature of kwashiorkor (Krawinkel, 2003). A fatty liver develops due to lack of the protein carrier that transports fat out of the liver (Krawinkel, 2003). The fatty liver lacks enzymes to clear metabolic toxins from the body, so their harmful effects are prolonged (Krawinkel, 2003). Inflammation in response to these toxins

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and infections further contributes to the oedema that accompanies kwashiorkor. Without sufficient tyrosine to make melanin, the child‟s hair loses its color, and inadequate protein synthesis leaves the skin patchy and scaly, often with sore that fail to heal. The lack of proteins to carry or store iron leaves iron free. Unbound iron is common in children with kwashiorkor and may contribute to their illness and death by promoting bacterial growth and free radical damage (Krawinkel, 2003).

2.3.3 Marasmic-kwashiorkor

Marasmic-kwashiorkor is characterized by both symptoms of marasmus and kwashiorkor such as oedema of kwashiorkor with the wasting of marasmus (Waterlow, 1996). Most often, the child suffers the effect of both malnutrition and infections (Whitney and Rolfes, 2008).

2.4 Complications of PEM

2.4.1 Infection

Infection is a major complication of PEM and may occur without the classical signs and symptoms (W.H.O, 2000). In PEM, antibodies that fight against invading bacteria are degraded to produce amino acids for other uses, leaving the malnourished child vulnerable to infections (Bloss et al., 2004). Blood proteins, including haemoglobin are no longer synthesized, so the child becomes anaemic and weak (Bloss et al., 2004). Infection can suppress appetite and directly affect nutrient metabolism, leading to poor nutrient utilization (Bloss et al., 2004).

2.4.2 Diarrhoea and dehydration

Dysentery, an infection of the digestive tract, causes diarrhoea, further depleting the body nutrients and fluids leading to dehydration (Reid, 2002). In marasmic child once infection sets in, kwashiorkor often follows, and the immune response weakens further (Reid, 2002).

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2.4.3 Heart failure

The combination of infections, fever, fluid imbalance and anaemia often leads to heart failure and occasionally sudden death (Wharton, 1991). Acute congestive heart failure occurs in children with PEM due to excess sodium intake. Moreover, heart failure in kwashiorkor, anaemia, vigorous refeeding and volume overload may also be involved (Wharton, 1991).

2.4.4 Hypothermia

Severe deprivation of food in children with PEM usually makes them to experience cold due to low energy level which is responsible for heat generation. Body temperature below 35.5oC may occur due to impaired thermoregulatory mechanism and severe infections (Torun and Chew, 1994).

2.5 Prevention and Treatment of PEM

The treatment of PEM is to feed children a ready to-use therapeutic food (RUTP) until they have gained adequate weight. In some cases, it may be possible to construct an appropriate therapeutic diet using locally available nutrients-dense foods with added micronutrients supplements. However, this approach requires very careful monitoring because nutrient adequacy is hard to achieve (W.H.O, 2007). Prevention of PEM requires provision of a good supply of food and prompt treatment of gastroenteritis with oral rehydration (Weaver, 1994). Prolonged breast feeding up to two years should be encouraged along with the use of locally available protein foods. Continuation of breast feeding during diarrhoea episodes should also be encouraged (Victora et al., 2000). Promotion of health education, immunization programs, family planning, and regular supervision of child‟s nutritional status are important tools in the early detection of moderate deficiency, allowing advice and treatment to be given well before occurance of severe

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malnutrition (Wharton and Weaver, 1998; Ojofeitimi et al., 2003). Infections are also common in severely malnourished children thus, antibiotics are often routinely recommended (WHO, 2000).

2.6 Free Radicals

Free radicals can be defined as reactive chemical species having a single unpaired electron in an outer orbit (Riley, 1994). This unstable configuration creates energy which is released through reactions with adjacent molecules, such as proteins, lipids, carbohydrates and nucleic acids. The majority of free radicals that damage biological systems are oxygen-free radicals, and these are more generally known as “reactive oxygen species” (ROS). These are the main byproducts formed in the cells of aerobic organisms, and can initiate autocatalytic reactions so that molecules to which they react are themselves converted into free radicals to propagate the chain of damage. ROS can be (i) generated during UV light irradiation and by X-rays and gamma rays (ii) produced during metal catalyzed reactions (iii) are present in the atmosphere as pollutants (iv) are produced by neutrophils and macrophages during inflammation and (iv) are by-products of mitochondrial catalyzed electron transport reactions, and various other mechanisms (Cadenas,1989).

The amount of free radical production is determined by the balance of many factors, and ROS are produced both endogenously and exogenously (Inoue et al., 2003). The endogenous sources of ROS include mitochondria, cytochrome P450 metabolism, peroxisomes and inflammatory cell

activation (Inoue et al., 2003). Examples of oxygen-derived free radicals include superoxide radical (O2.-), hydroxyl radicals (OH.) and nitric oxide (NO.). Hydrogen peroxide, although not a radical species is produced in the mitochondria as is its ROS precursor superoxide. It has been proposed that ubisemiquinone is the main reductant of oxygen in mitochondrial membranes and 15

the generation of superoxide within mitochondria is approximately 2–3 nmol/min per mg of protein (Inoue et al., 2003). The presence of ubiquinone indicates it to be the most important physiological source of this radical in living organisms (Inoue et al., 2003). Since mitochondria are the major site of free radical generation, they contain a variety of antioxidants including enzymes such as superoxide dismutase (SOD) and glutathione peroxidase (GPx) which are present on both sides of their membranes in order to minimize ROS induced stress (Cadenas and Davies 2000). There are also other cellular sources of superoxide radicals present such as the enzyme xanthine oxidase, which catalyzes the reaction of hypoxanthine to xanthine and xanthine to uric acid. In both steps, molecular oxygen is reduced, forming the superoxide anion followed by the generation of hydrogen peroxide (Valko et al., 2004). ROS can also be produced by a host of exogenous sources such as xenobiotics, chlorinated compounds, environmental agents, metals (redox and non-redox), ions, and radiation (Valko et al., 2006).

ROS can be both harmful and beneficial in biological systems depending on the environment (Lopaczynski and Zeisel 2001; Glade 2003). Beneficial effects of ROS involve, for example, the physiological roles in cellular responses to noxia such as defense against infectious agents, and in the function of a number of cellular signaling systems. In contrast, at high concentrations, ROS can mediate damage to cell structures, including lipid membranes, proteins and nucleic acids, and this damage is often referred to as “oxidative stress” (Poli et al 2004). The harmful effects of these free radicals (ROS) have been found in children with severe PEM which is responsible for cell damage leading to oedema, fatty liver and skin lesions (Golden et al., 1990), and are balanced by the action of antioxidants, some of which are enzymes present in the body (Halliwell, 1996). Despite the presence of the cell‟s antioxidant defense system to counteract oxidative damage from ROS, oxidative damage accumulates during the life cycle and has been

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implicated in aging and diseases such as cardiovascular disease, cancer, neurodegenerative disorders and other chronic conditions (Rahman, 2003). Antioxidants neutralize these damaging free radicals by quenching the reactive molecules, thereby protecting cells from endogenous and exogenous stressors and prolonging their life and vitality (Halliwell, 1996) .

2.7 Antioxidants

Antioxidant is a substance that when present at low concentration compared to that of an oxidizable substrate, would significantly delay or prevent oxidation of that substrate (Halliwell, 1995). The oxidizable substrate includes almost everything found in living cells including carbohydrates, DNA, lipids and proteins (Lequeux et al., 2010). Antioxidants are a conspicuous first line of defense against free radicals and are able to counteract or at least slow all major steps in the process of free radical induction of cancer (Rahman, 2003).

Antioxidants are broadly divided into enzymatic antioxidants and non-enzymatic antioxidants. Enzymatic antioxidants include the superoxide dismutase, glutathione peroxidase and catalase (Klaunig and Kamendulis, 2004). Superoxide dismutase and glutathione peroxidase, which are present in cytosol and mitochondria, reduce the superoxide anion to hydrogen peroxide and water, and remove the majority of hydrogen peroxide, respectively, while, catalase located in the peroxisomes, also removes high levels of hydrogen peroxide (Fridovich, 1986). Non-enzymatic antioxidants which include vitamin A, C, E, trace elements such as zinc, copper and selenium, reduced glutathione, and coenzyme Q function to quench reactive oxygen species (Clarkson and Thompson 2000).

These antioxidant enzymes are synthesized by the body to keep the concentration of the free radicals at a non-harmful level but the trace elements (Selenium, Zinc, and Copper) needed as cofactors must be supplied by the diet. Selenium (Se) is a cofactor for glutathione peroxidase 17

(Chan et al., 1998). The superoxide dismutase present in the cytosol contains zinc (Zn) and copper (Cu) (Fridovich, 1986).

2.7.1 The need for antioxidants defense

Most biologically relevant free radicals are derived from oxygen and nitrogen and the so-called ROS and Reactive Nitrogen Species (RNS) (Peter, 2007). Both these elements are essential but in certain circumstances are converted into free radicals which are highly unstable and their reactive capacity makes them capable of damaging biologically relevant molecules such as proteins, lipid or carbohydrates (Peter, 2007). Antioxidants are molecules that retard or prevent the oxidation of other compounds (Halliwell, 1995). Not only soluble antioxidants but also complex enzymatic systems such as catalase, superoxide dismutase and some peroxidases may be used by cells to avoid undesired oxidations (Angelo, 2009). Sarvajeet and Narendra (2010) reported that the ROS affect many cellular functions by damaging nucleic acids, oxidizing proteins and causing lipid peroxidation. it is important to note that whether ROS will act as damaging, protective or signaling factors depends on the delicate equilibrium between ROS production and scavenging at the proper site and time. Oxidative stress occurs when this critical balance is disrupted due to depletion of antioxidants or excess accumulation of ROS, or both (Scandalios, 2005).

2.7.2 Mechanisms of antioxidant functions

Antioxidants are effective through various mechanisms including: 1) preventive antioxidants, 2) free radical scavengers, 3) sequestration of elements by chelation and

4) quenching active oxygen species (McDowell et al., 2007).

Preventive antioxidants:

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These antioxidants suppress formation of free radicals; for example catalase (Fe containing) and glutathione peroxidase (Se containing), two antioxidant enzymes, decompose hydrogen peroxide, preventing the formation of oxygen radicals (McDowell et al., 2007).

Free radical scavengers:

These antioxidants confer stability to the „reactive‟ species by donation of an electron and become oxidized themselves to form a more stable radical. For example α-tocopherol (vitamin E) scavenges peroxyl radicals and is converted to a tocopherol radical. Illustrating antioxidant interactions, the vitamin E becomes “reactivated” by ascorbic acid donating an electron which in turn forms an ascorbate radical in the process (McDowell et al., 2007).

Sequestration of metal by chelation:

Although trace minerals are important dietary constituents, they can act as pro-oxidants (promote free radical formation). Since trace minerals such as Fe and Cu can propagate the formation of more reactive radicals they are kept bound to transport proteins such as transferrin or ceruloplasmin, as this renders them less available to contribute to radical or pro-oxidant formation (McDowell et al., 2007).

Quenching of active oxygen species:

Antioxidants can convert active oxygen species to more stable forms, for example, superoxide dismutase (Zn and Cu containing), carotenoids and vitamin E stabilize singlet oxygen radicals, forming less reactive hydrogen peroxide (McDowell et al., 2007).

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2.7.3 Enzymatic antioxidants and their cofactors

Glutathione peroxidase

There are two forms of this enzyme, one which is selenium-dependent and the other, which is selenium-independent (glutathione-S-transferase, GST) (Mates et al., 1999). The differences are due to the number of subunits, catalytic mechanism and the bonding of selenium at the active centre, and glutathione metabolism is one of the most important antioxidative defense mechanisms present in the cells. There are four different Se-dependent glutathione peroxidases present in humans (Chaudière and Ferrari-Iliou, 1999) and these are known to add two electrons to reduce peroxides by forming selenoles (Se-OH) 9and the antioxidant properties of these seleno-enzymes allow them to eliminate peroxides as potential substrates for the Fenton reaction. Selenium-dependent glutathione peroxidase acts in association with tripeptide glutathione (GSH), which is present in high concentrations in cells and catalyzes the conversion of hydrogen peroxide or organic peroxide to water or alcohol while simultaneously oxidizing GSH. It also competes with catalase for hydrogen peroxide as a substrate and is the major source of protection against low levels of oxidative stress (Chaudière and Ferrari-Iliou 1999).

Catalase

This enzyme is present in the peroxisome of aerobic cells and is very efficient in promoting the conversion of hydrogen peroxide to water and molecular oxygen (Mates et al., 1999). Catalase has one of the highest turnover rates of all enzymes: one molecule of catalase can convert approximately 6 million molecules of hydrogen peroxide to water and oxygen every minute (Mates et al., 1999).