EFFECT OF CHLOROFORM- METHANOL EXTRACT OF TETRACARPIDIUM CONOPHORUM NUTS (WALNUTS) ON OXIDATIVE STRESS MARKERS IN HYDROGEN PEROXIDE INDUCED WISTAR ALBINO RATS

ABSTRACT

This work was done to ascertain the efficacy of the seed of Tetracarpidium conophorum on hydrogen peroxide induced oxidative stress in Wistar albino rats. Thirty five (35) male wistar albino rats weighing (120- 140g) were distributed into seven (7) groups of five  rats each. Groups 2-6 were administered with hydrogen peroxide (1.0 ml/kg), while group 1 served as the normal control while group 2 serves as positive control Groups 3, 4, 5 and 6 were treated with vitamin C (100 mg/kg), 200, 400 and 800 mg/kg of the  extract respectively for five days, Group 7 was administered 800 mg/kg b.w of the extract only. Blood was collected from the  animals  on  the  7th   day  through  occular  puncture  for  assay  of  some  biochemical parameters.  The qualitative  and quantitative  analysis  of the seed extract were  determined using standard methods and showed that the extract contained terpenoids (4.36 ± 0.06 mg/g), Tannins (1.89 ± 0.11 mg/g), alkaloids (20.31 ± 0.30mg/g) and cardiac glycosides (12. 45 ± 0.08 mg/g), anthraquinones, saponins and steroids were not detected in the extract. Vitamins constituents of the extract were vitamin A (10.55 ± 2.67 mg/ 100g), vitamin C (13.09 ± 0.23 mg/ 100g) and vitamin E (5.77 ± 0.08 mg/ 100g). The mineral  constituents  indicated  the presence of mg (133.59 ± 0.11 mg/ 100g), Ca (118.90 ± 0.01 mg/ 100g), Fe (3.67 ± 0.07 mg/ 100g), Zn (2.22 ± 0.01 mg/ 100g), Cu (1.54 ± 0.78 mg/ 100g). The acute toxicity test of the extract  showed  no  toxicity  up  to  5000  mg/  kg  b.w.  Serum  ALT  activity  significantly decreased (p< 0.05) in all the test groups compared to group 2. Serum AST and ALP activity decreased  significantly  (p< 0.05)  in all the test  groups  except  group  6  for ALP  activity compared to the enzyme activities of normal and positive controls. A significant decrease (p< 0.05)  was  observed  in  the  serum  MDA  concentration  of  rats  in  the  test  groups  when compared to the group 2. A significant increase (p < 0.05) was observed in the serum GPx activity of groups 4, 6 and 7 compared to the GPx activity of group 2  rats.  There was a significant increase (p < 0.05)  in groups 4 and 7 compared to group 2. The serum cholesterol concentration showed a significant decrease (p < 0.05) in the test groups relative to those of the controls. There was a significant decrease (p < 0.05) in the serum LDL and TAGs of rats in the  test  groups  when  compared  to  the  controls.  The  serum  HDL  of groups  5  and 7 increased significantly (p < 0.05) compared to the normal control and the positive control. The effect of the extract on lipid profile showed that it increased HDL at a concentration of 400mg/kg  body.  These  antioxidant  enzymes  results  support  the  claims  made  by  several scientists that the plant could be used to scavenge free radicals in the system which often lead to the risk of various diseases.

1.1      Background of the study

CHAPTER ONE

INTRODUCTION

The use of various fruits, vegetables, nuts and various parts of plants in  traditional medicine is as old as man (Evans, 2002). This lies outside the mainstream  of orthodox or Western medicine, it has been estimated that two thirds of the world population (mainly in developing  countries)  rely  on  traditional  medicine  as  their  primary  form  of  health  care (Sumner,  2000).  The  use  of  traditional  medicine  cannot  fade  out  in  the  treatment  and management of diseases in the African continent  and this could be attributed to the socio- cultural, socio-economic,  lack of  basic health care and qualified  personnel (Elujoba et al.,

2005).  Plants  contain  active  components  such  as anthraquinones,  flavonoids,  glycosides, saponins, tannins, etc which posses medicinal properties that are harnessed for the treatment of  different  diseases  (Chevalier,  2000).  The  active  ingredients  for  a  vast  number  of pharmaceutically  derived  medications  contain  the healing  properties  known as the active principles   and  are  found  to  differ  from  plant  to   plant  (Chevalier,   2000).Nuts   vary considerably  in their  nutrient  content  and are  sources of vitamins,  antioxidants,  proteins, essential  amino  acids,  etc.  (Fasuyi,  2006).  They  are  included  in meals  mainly  for  their nutritional values. However, some are reserved for their medicinal values such as increase in brain health, decreased   depression, increase in antioxidant levels; thus, helping to mop up free radicals  which have been implicated in a number of diseases (Oladiyi et al., 2007).

In  a  normal  cell,  there  is  an  appropriate  pro-oxidant/antioxidant  balance.  However  this balance can be shifted towards the prooxidant following the ingestion of certain chemicals or drugs when the levels of antioxidants are low; this gives rise to oxidative stress and results in cell  damage  if  prolonged  or  massive  (Murray  et  al.,  2009).  Thus oxidative  stress  is  a metabolic perturbation of homeostasis.  On the other hand,  antioxidants are a complex and diverse group of molecules that protect key biological sites from oxidative damage (Murray et   al.,   2009).Lipid   peroxidation   is   a   degenerative   process   involving   peroxidative decomposition of unsaturated fatty acids mediated by free radical or reactive oxygen species (Gutteridge  and Halliwell, 1995).

Recently oxidative stress has been linked to many age associated diseases including  heart diseases, cancer, atherosclerosis  as well as brain disorders (Singh et al., 1995). It can also lead to inhibition of some metabolic enzymes (Devasagayam et al., 2004).

Fortunately, aerobic organism have evolved very effective defense system against oxidative assault, this is due to the consistency of both hydrophilic (GSH, Vit C) and lipophilic (Vit E,

Carotenoid pigment) antioxidant compounds or scavengers and specific antioxidant enzymes including  superoxide  dismutase,  catalase,  glutathione  peroxidase,  glutathione  reductase. Epidemiological studies have shown strong correlation between plasma antioxidant vitamin levels and mortality rates from heart disease (Schafer and Buettner, 2001).

Hence, oxidative stress is one of the common causes of health disorders posing a great threat to global health care. Medicinal plants are currently being used in various parts of the world especially in the civilized world in the treatment of several diseases such as  artherosclerosis, heart disease, brain disorder etc (Ajaiyeoba and Fadare, 2006).

Most nuts contain antioxidant  enzymes as well as antioxidant  vitamins (A, C,  E). Tetracarpidium conophorum nuts used as snack in various countries of the world have been shown to have positive effects on oxidative stress (Oke, 1995).Due to their ability to increase poly unsaturated fatty acids, good cholesterol (HDL) antioxidant vitamins in several parts of the world.Hence there is need to investigate the effect of chloroform-methanol extract of T. conophorum  nuts  on  hydrogen  peroxide  induced  oxidative  stress  markers  and  possibly advocate their inclusion in food preparations for everyone and especially for the elderly and this has necessitated this research.

1.2      Tetracarpidium conophorum

Tetracarpidium conophorum (Walnut) consists of families of Juglandaceae (English Walnut), Euphorbiaceae  (African  Walnut)  and  Olacaceae  (African  Walnut  (Dalziel)  1937).  Each family has its own peculiar characteristics but they have some things in common such as the nuts. Juglandaceae, is mostly found   in Southeast Europe to Japan and more widely in the New world. Tetracarpidium  conophorum  (family  Euphorbiaceae)  is found in Nigeria  and Cameroun while coula edulis (family Olacaceae) which is also referred to as African Walnut is found in Congo, Gabon and Liberia (Wikipedia, 2008).

Tetracarpidium conophorum is a climbing shrub 10-20 feet long, it is known in the Southern Nigeria as Ukpa (Igbo), Western Nigeria as awusa or asala (Yoruba). It is known in the littoral and the Western Cameroun as Kaso or ngak (Dalziel, 1937). It is found in Uyo, Akamkpa, Akpabuyo, Lagos, Kogi, Ogbomoso and Ibadan. The plant is cultivated principally for the nuts which are cooked and consumed as snacks (Oke, 1995).

The plant is glabrous with deciduous male flowers leaving the females at the base of  the raceme (Petrova, 1980).

A bitter taste is usually observed upon drinking water immediately after eating the nuts.  This  could  be  attributed  to  the  presence  of  chemical  substances  such  as  alkaloid (Ayodele, 2003). The seeds contain ascorbic acid and heavy metals, amino  acids and fatty acids (Oyenuga, 1997) reported on the amino acid and fatty acid compositions of the nuts and on the use of its leaf juice have been used  for the  treatment  of prolonged  and constant hiccups.

1.2.1    Scientific classification of Tetracarpidium conophorum

Kingdom:                     Plantae Division:                       Magnoliophyta Class:                            Magnoliopsida Order:                           Malpighiales Family:                         Janiroidea Genus:                          Tetracarpidium Species:                       conophorum

Govarts (2003)

1.2.2    Medicinal, Nutritional and Industrial importance of Tetracarpidium conophorum

1.2.2.1 Medicinal uses of Tetracarpidum conophorum (Walnuts)

Tetracarpidium conophorum is a medicinal plant widely cultivated for the production of its seeds. The seed have been implicated in Southern Nigeria ethno  medicine as a male fertility agent (Ajaiyeoba and Fadare, 2006). The seed is used in the treatment of indigestion, constipation and diarrhea (Wolters, 2009). The seed is a good source of vitamins. Alkaloids are the most efficient plant substances used therapeutically. Pure isolated alkaloids and the synthetic  derivatives  are  used  as  the  basic  medicinal  agent  because  of  their  analgesic, antispadomic and bacterial properties. This is why the seed is believed to stop asthma and is prescribed to be taken between bouts of asthma, but not for acute asthma. It is used for the elderly as a  constipation  cure (Wikipedia,  2009). The presence of tannins  in the seed of Tetracarpidium conophorum can support its strong use for healing of haemorrhoids, frost bite and varicose ulcers in herbal medicine (Igboko, 1983, Maduiyi, 1983).

Walnuts have been reported as having Chelating ability which in turn could account for its high antioxidant activity which have been compared to the use of dimercapto- succinic acid  (DMSA).  2, 3- dimercapto  -1- propanesulfonic  acid  (DMPS)  and  alpha  lipoic  acid (ALA) (Muanya, 2012).

Walnuts are a good source of protein, vitamin C, folic acid and vitamin E, they also have an extremely high level of polyunsaturated fat and are a good source of omega 3- fatty acids (Cortes et al.,  2006) such as  linoleic acid, alpha-linolenic acid (ALA) and arachidonic acids. Regular intake of Walnuts in the diet helps to lower, total as well as  LDL or ‘bad cholesterol’ and increases HDL or “good cholesterol” levels in the blood. Walnuts are a rich source of many phytochemical substances that may contribute to their overall anti- oxidant activity,  including  melatonin,  ellagic  acid,  Vitamin  E,   Carotenoid  and  poly  phenolic compounds.   These   Compounds   have   potential   health   effects   against   Cancer,   aging, inflammation and neurological diseases (Reiter et al., 2005).Walnuts Oil has flavourful nutty aroma and excellent  astringent  properties,  applied  locally,  it helps to keep  the skin well protected  from dryness.  It has also  been used  in cooking  and as ‘carrier  or base oil’ in traditional  medicines  in  massage  therapy,  aromatherapy  in  pharmaceutical  and  cosmetic industry (Fortin, 1996).

1.2.2.2 Nutritional uses of Tetracarpidium conophorum (Walnuts)

Walnuts are excellent sources of vitamin E, not in the alpha tocopherol but in the gamma-tocopherol,  particularly  in studies  of cardio  vascular  health of men,  this  gamma-

tocopherol form has been found to provide significant protection from heart problems and maintaining the integrity of cell membranes of mucous membranes and skin by protecting it from harmful oxygen radicals. (Blomhoff  et al., 2006).

Some phytonutrients found in walnut for example, the quinine juglone are found in virtually no other commonly eaten food. Others’ such as the tannin-tellimagrandin  or the flavonol morin are also rare and valuable as antioxidants and anti inflammatory nutrients. These anti- inflammatory and anti- oxidant phytonutrients also help explain the decreased risk of certain cancers- including prostate cancer and breast cancer (Fukuda et al., 2003). Walnut are packed with many important B- Complex groups of vitamins such as riboflavin, niacin, thiamine, pantothenic acid, Vitamin B6, and Folates.

They are also a rich source of mineral salts such as mangenese, copper, potassium,

calcium, iron, magnesium, zinc and selenium. Copper is a cofactor for many vital enzymes, including cytochrome  c- oxidase  and superoxide  dismutase.  Zinc is a co-  factor in many enzymes that regulate growth and development, sperm generation, digestion and nucleic acid synthesis. Selenium is an important micro nutrient which  functions as a co-factor for anti- oxidant enzymes such as glutathione peroxidases. (Esminger   et al., 1983). Walnuts oil has flavourful nutty aroma used in salad dressings and also used as an edible oil in cooking.

1.2.2.3 Industrial uses of Tetracarpiduim conophorum (Walnuts)

Locally, the oil has been used as a moisturizer to keep the skin well protected from dryness. The bark is used as dye in clothing and textile industry because it contains a juice that will readily stain anything it comes into contact with. Walnut  hulls contain phenolic compounds  (ferulic  acid,  vanillic  acid,  coumaric  acid,  syringic  acid,  myricetrin  juglone (Cosmulesc et al., 2010) and regiolone (Liu et al., 2007). Black Walnut heartwood is heavy, hard strong and durable with a chocolate brown colour.  Walnut shells  are used as thickener in paint and plastic industry, a filler in explosives and for cleaning and polishing, used as abrasive element in home soap making (Liu et al., 2007).The floor of the Globe Theatre in Elizabethan  London was  made of Walnut shells and compacted  down to a very hard and polishable surface.

1.3      Oxidative Stress

Oxidative  stress  is  an  imbalance  between  the  systemic  manifestation  of  reactive oxygen  species   and  a  biological   system’s   inability  to  readily  detoxify   the  reactive intermediates  or to repair the resulting  damage  (Murray et al.,2009).  Disturbances  in the

normal redox state of cells can cause toxic effects through the production of peroxides and free radicals that damage all components of the cell including proteins, lipids and DNA.

In humans and animals, oxidative stress is thought to be involved in the development of many diseases or may exacerbate their symptoms (Proctor et al.,  1984,  Proctor, 1989) These   include   cancer,   (Halliwell,   2001),   Parkinson’s   disease,   Alzeihmer’s   disease, atherosclerosis, heart failure, myocardial infarction, schizophrenia, Bipolar disorder, fragile X syndrome, sickle cell disease, autism and chronic fatigue syndrome (Gwen et al.,2005).

Oxidative stress is a term used to refer to the shift towards the pro-oxidants in the pro- oxidative/  antioxidants  balance  that  can  occur  as  a  result  of  an  increase  in  oxidative metabolism (Manda et al., 2009). ROS reactions with biomolecules such as lipid, protein and DNA, produce different types of secondary radicals like lipids radicals, non-sugar and base derived radicals, amino acid radicals depending upon the  nature of the ROS (Niki et al.,

2005). These radicals in the presence of oxygen are converted to peroxyl radicals.  Peroxyl radicals are critical in biosystems, these reactions exert oxidative stress on the cells, tissues and organs of the body. The biological implications of such reactions  depends on several factors like site of generation, nature of the substrate, activation of repair mechanisms, redox status among many others (Koppeno, 1993; Goldstein et al., 1993).

1.3.1 Chemical and biological effects of oxidative stress.

Chemically,  oxidative  stress  is  associated  with  increased  production  of  oxidizing species  or  a  significant  decrease  in  the  effectiveness  of  antioxidant  defenses,  such  as glutathione (Schafer and Buettner, 2001). The effects of oxidative stress depend upon the size of these  changes,  with a cell being able to overcome  small  perturbations  and  regain  its original state. However, more severe oxidative stress can cause cell death and even moderate oxidation can trigger apoptosis, while more intense stresses may cause necrosis (Lennon et al., 1991).

Production of reactive oxygen species is a particularly destructive aspect of oxidative stress. Such species include free radicals and peroxides. Some of the less reactive of these species (such as superoxide)  can be converted  by oxidoreduction  reactions with transition metals or other redox cycling compounds (including quinines) into more aggressive radicals that can cause extensive cellular damage (Valko et al., 2005). The major portion of long term effects is inflicted by damage on DNA (Evans and  Cooke, 2004). Most of these oxygen – derived species are produced at a low level by normal aerobic metabolism. Normal cellular defense  mechanisms  destroy most  of  these.  Likewise,  any damage  to  cells  is constantly

repaired. However, under the severe levels of oxidative stress that cause necrosis, the damage causes ATP depletion, preventing controlled apoptotic death and causing the cell to simply fall apart (Lelli et al., 1998, Lee and Shacter, 1999).

1.3.2    Oxidative stress and diseases

Oxidative stress is suspected to be implicated in neurodegenerative diseases including Lou Gehrig’s disease, Parkinson’s disease, Alzheimer’s disease, and  Huntington’s  disease (Patel and Chu 2011). Indirect evidence via monitoring biomarkers such as reactive oxygen species, and reactive nitrogen species production, antioxidant defense  mechanism indicates that oxidative damage may be involved in the pathogenesis of these diseases (Nunomura et al., 2005), while cumulative  oxidative  stress with disrupted  mitochondrial  respiration  and mitochondrial damage are related  with Alzheimer’s disease, Parkinson’s disease, and other neurodegenerative diseases (Ramalingam and Kim, 2012).

Oxidative  stress  is  thought  to  be  linked  to  certain  cardiovascular  disease,  since oxidation of LDL in the vascular endothelium is a precursor to plaque formation. Oxidative stress also plays a role in the ischemic cascade due to oxygen reperfusion injury following hypoxia. This cascade includes both strokes and heart attacks. Oxidative stress has also been implicated in chronic fatigue syndrome (Nijs et al., 2006). Oxidative stress also contributes to tissue injury following irradiation and hyperoxia as well as in diabetes.

1.3.3    Free Radical generations / Reactive oxygen species.

Free radicals can be defined  as those atoms or molecules  containing one or  more unpaired electrons in their outer most shell and mostly is very reactive due to the presence of these unpaired  electron(s)  (Knight,  1998), Reactive oxygen species (ROS)  is a collective name  given  to  both  oxygen  free  radicals  and  non oxygen  free  radicals  (Mittler,  2002). Reactive oxygen species can also be used to refer to a group of oxidants.

1.3.3.1 Sources of Free radicals

1. Electron Transport Chain

Production   of  superoxide   and  hydrogen   peroxide   usually  takes  place   in   the mitochondria of a cell (Valko et al., 2004; Nelson et al., 2006). The mitochondria electron transport chain is the main source of ATP in the mammalian cell; hence, it is essential for life. During energy transduction, a small number of electrons “leak” to oxygen prematurely,

forming   the   oxygen   free   radical   superoxide,   which   has   been   implicated   in   the pathophysiology of a variety of diseases (Valko et al., 2007).

2.  Stress responses and defence pathways. (Phagocytosis)

Reactive oxygen species are nature’s response to external and internal stimuli. This is done in most cases to defend the body against foreign pathogenic and or parasitic invasion for instance; the killing of parasites during disease and infection states has been hypothesized. The hydroxyl radical, OH, is the neutral form of the hydroxide ion. The hydroxyl radical has a high reactivity, making it a very dangerous radical with a  very short in vivo half- life of

approximately 10-9  s (Pastor et al., 2000). Thus, when produced in vivo, OH reacts close to

its site of formation. Cellular productions of these ROS are enhanced during stress and can posed threat to cells, but it is also thought that ROS act as signals for the activation of stress- response  and  defence  pathways  (Mittler,  2002).  Thus,  ROS  can  be  viewed  as  cellular indicators  of stress  and  as secondary  messengers  involved  in the stress-  response  signal transduction  pathway (Valko  et al., 2005). Over- accumulation  of  ROS can result in cell death (Toykuni, 1999). ROS-induced cell death can result from oxidative processes such as membrane  lipid  peroxidation,  protein  oxidation,  enzyme  inhibition  and  DNA  and  RNA damage (Etsuo et al., 1991).

3.  Metal catalysts

Metals such as iron, copper, chromium, vanadium and cobalt are capable of  redox cycling in which a single electron may be accepted or donated by the metal.  This action catalyzes reactions that produce reactive radicals and can produce reactive  oxygen species (Pratviel, 2012). The most important reactions are probably Fenton’s reaction and the Haber- Weiss  reaction,  in which  hydroxyl  radical  is produced  from  reduced  iron and  hydrogen peroxide. The hydroxyl radical then can lead to  modifications  of amino acids (e.g. meta- tyrosine  and  ortho-tyrosine  formation  from  phenylalanine),  carbohydrates,  initiate  lipid peroxidation, and oxidized nucleobases. Most enzymes that produce reactive oxygen species contain  one  of  these  metals.  The  presence  of  such  metals  in  biological  systems  in  an uncomplexed  form (not in a  protein or other protective  metal complex)  can significantly increase  the  level  of  oxidative  stress.  In  humans,  hemochromatosis  is  associated  with increased  tissue  iron levels,  Wilson’s  disease  with  increased  tissue  levels of copper  and chronic manganism with exposure to manganese ores. The reaction of transition metals with proteins oxidated by reactive oxygen species or reactive nitrogen species can yield reactive

xxii

products that accumulate  over time and contribute  to aging and disease.  For example,  in Alzheimer’s  patients,  peroxidized  lipids  and  proteins  accumulate  in  lysosomes  of  the patient’s brain cells (Devasagayam et al., 2004)

4. Non- metal catalysts

Certain organic  compounds  in addition to  metal  redox catalysts  can also  produce reactive  oxygen  species.  One  of  the  most  important  classes  of  these  are  the  quinines. Quinines can redox cycle with their conjugate semiquinones  and  hydroquinones,  in some cases catalyzing  the production of superoxide  from dioxygen  or hydrogen  peroxide  from superoxide. Oxidative stress generated by the reducing agent uric acid may be involved in the Lesch- Nyhan syndrome, stroke, and metabolic syndrome. Likewise, production of reactive oxygen species in the presence of homocysteine  may figure in homocystinuria,  as well as atherosclerosis, stroke, and Alzheimers.

1.4      Hydrogen Peroxide (H2O2)

Hydrogen peroxide is a lipid soluble radical or oxidant formed by dismutation by the enzyme  SOD  in  the  inactivation  of  destructive  superoxide  ions  by  converting  them  to hydrogen  peroxide  which  is  in turn  transformed  into  water  and  oxygen  by  the  enzyme catalase. Peroxisomes are known to produce H2O2, but not O2, under physiologic conditions (Valko et al., 2004). Peroxisomes  are major sites of oxygen  consumption  in the cell and participate  in  several  metabolic  functions  that  use  oxygen.  Oxygen  consumption  in  the peroxisome leads to H2O2   production, which is then used to oxidize a variety of molecules (Forman et al., 2010). This organelle also  contains  catalase, which decomposes  hydrogen peroxide  and  presumably  prevents   accumulation   of  this  toxic  compound.   Thus,  the peroxisome  maintains  a  delicate  balance  with  respect  to  the  relative  concentrations  or activities of these enzymes to ensure no net production of ROS (Juranek and Bezek, 2005). When peroxisomes are damaged and their H2O2 consuming enzymes down regulated, H2O2 releases into the cytosol which is significantly contributing to oxidative stress (Juranek and Bezek,  2005).  Proteins can undergo direct and indirect damage following interaction with ROS resulting into peroxidation, changes in their tertiary structure, proteolytic degradation, protein- protein cross linkages and fragmentation (Yu, 1994). Although,  DNA is a stable, well- protected molecule, ROS can interact with it and cause several types of damage such as modification of DNA bases, single and double strand DNA breaks, loss of purines (apurinic

sites), damage to the deoxyribose sugar, DNA- protein cross linkage and damage to the DNA

repair system (Droge, 2002).

1.5      Lipid Peroxidation

Lipid peroxidation is a well-established  mechanism of cellular injury in both plants and animals, and is used as an indicator of oxidative stress in cells and tissues.  It is the process in which free radicals “steal” electrons from the lipids in cell membranes, resulting in cell damage. This process proceeds by a free radical chain  reaction mechanism (Marnett,

1999).  Lipid  peroxidation  is  an autocatalytic  free  radical-  medicated  destructive  process whereby poly-unsaturated  fatty acids in cell membranes undergo degradation to  form lipid hydroperoxides  (Moore  and  Robert,  1998).  Lipid  peroxidation  of  cellular  structures,  a consequence  of  increased  oxygen  free  radicals,  is  thought  to  play an  important  role  in atherosclerosis  and micro vascular complications  of diabetes mellitus  which is consequent from  oxidative  stress  (Soliman,  2008).Lipid  peroxidation  triggers the  loss  of  membrane integrity,  causing  increased  cell  permeability,  enzyme  inactivation,  structural  damage  to DNA and cell death (Halliwell, 1992). Initiation is the step in which a fatty acid radical is produced. The most notable initiators in living cells are reactive oxygen species (ROS), such as OH and HO, which combines with a hydrogen atom to make water and a fatty acid radical. The fatty acid  radical  is not a  very stable  molecule,  so  it reacts  readily with molecular oxygen, thereby creating a  peroxyl- fatty acid radical. This too is an unstable  specie that reacts with another free fatty acid, producing a different fatty acid radical and lipid peroxide, or cyclic peroxide if it had reacted with itself (Koppeno, 1993; Goldstein et al., 1993). This cycle continues,  as the new fatty acid radical reacts in the same way. Lipid peroxides are unstable and decompose to form a complex series of compounds including reactive carbonyl compounds.

When a radical reacts with a non- radical, it always produces another radical, which is why the process is called a “chain reaction mechanism”. The radical reaction stops when two radicals react and produce a non- radical specie (Juranek and Bezek,  2005). This happens only  when  the  concentration  of  radical  species  is  high  enough  for  there  to  be  a  high probability of collision of two radicals. Hence, the generation of free radicals lead to lipid peroxidation and formation of severe damage in tissues (Soliman, 2008). Cellular membranes are  vulnerable  to  the  oxidation  by  ROS  due  to  the  presence  of  high  concentration  of unsaturated fatty acids in their lipid components. ROS reactions with membrane lipids cause lipid peroxidation, resulting in formation of lipid hydroperoxide (LOOH) which can further decompose to an aldehyde such as malondialdehyde,  4- hydroy nonenal (4-HNE) or  form cyclic endoperoxide, and hydrocarbons (Trangvarasittichai et al., 2009).

Living  organisms  have  evolved  different  molecules  that  speed  up  termination  by catching  free  radicals  and,  therefore,  protecting  the  cell membrane.  One  important  such antioxidant  is vitamin E. Other anti- oxidants made within the body  include the enzymes superoxide dismutase, catalase and perioxidase. If not terminated fast enough, there will be damage to the cell membrane, which consists mainly of lipids (Seiler et al., 2008).

1.5.1    Malondialdehyde

By-products  of lipid peroxidation  such as conjugated  dienes  and  malondialdehyde (MDA). MDA is generated as a relatively stable end product from the oxidative degradation of poly- unsaturated fatty acids (PUFA). This free radical- driven lipid peroxidation has been causatively implicated in the aging process, atherosclerosis, Alzheimer’s disease and cancer (Niki et al., 2005). Serum MDA has been used as a biomarker of lipid peroxidation and has served   as   an   indicator   of   free   radical   damage   (Tangvarasittichai   et   al.,   2009). Malondialedehyde is a highly reactive three carbon dialdehyde that occurs naturally and exits primarily in an enol form. It is a toxic compound that reacts with DNA to form covalently- bonded  adducts  with  deoxyadenosine  and  deoxyguanosine,  an  event  that  can  cause  a mutagenic transformation within DNA (Nordberg and Amer, 2001). Additionally,  Malondialedehyde   can  interact  with  several  functional  groups  on proteins  and  lipoproteins,  altering  their  chemical  behaviour  and  possibly  contributing  to carcinogenesis  and  mutagenesis  (Ogugua  and  Ikejiaku,  2005).  Due  to  its highly reactive nature, Malondialedehyde also functions as an electrophile that can cause toxic stress within the cell and is, therefore, a potent marker for measuring the overall level of oxidative stress within an organism (Conn, 1995; Del- Rio et al., 2005; Soliman, 2008; Tangvarasittichai et al., 2009).

₦5,000.00 – DOWNLOAD FULL PROJECT DOWNLOAD FULL PROJECT Added to cart

---

---

---

---

Related Project Topics :