MOCK TEACHING UiTMMOCK TEACHING UiTM

““REVIEW OF OXIDANTS REVIEW OF OXIDANTS AND ANTIOXIDANTS”AND ANTIOXIDANTS”

NURHAFZAN ANIS ISMAILNURHAFZAN ANIS ISMAIL

Trend of going back to nature is getting popular.

Increasing demand for natural health supplements (e.g.: vitamins and herbal remedies) since modern medicine and synthetic drugs have not been totally successful in solving health problems.

Malaysians spent an average of US$17.30 a month on health supplements.

Current domestic market for herbs and medicinal plants is estimated to be worth USD1.2 billion with an annual growth rate of 15% to 20% (Malaysian Herbal Corporation).

INTRODUCTION

What are oxidants Substances that have the ability to

oxidize other substances are said to be oxidative and are also known as oxidizing agents, oxidants or oxidizers.

Oxidation describes the loss of an electron by a molecule, atom or ion.

However, oxidation is better defined as an increase in oxidation number.

Therefore, the oxidant removes electrons from the other substances and is thus reduced itself.

Oxidants are usually chemical substances with elements in high oxidation number (e.g.: hydrogen peroxide) or highly electron negative substances that can gain one or two extra electrons by oxidizing a substance.

Examples of oxidantsReactive Oxygen Species

(ROS) Superoxide radical (O2-2) – The best

known oxygen radical. Half-life of 1 10-6 seconds. Can lead to formation of other ROS-hydroxyl, hydrogen peroxide, peroxyl.

Hydrogen peroxide (H2O2) – It is not a radical. Relatively stable as compared to the other ROS. High diffusion potential. Not every potent by itself but hydrophobic membranes.

Hydroxyl radical (OH-) – Most potent oxygen radical. Half-life of 1 10-9 seconds. Area of interaction about 2 molecules diameters. Reacts readily with lipids. Produced by the Fenton reaction and the Haber-Weiss reaction.

Single oxygen (1O2) – Not really a free radical. The unpaired electron in the outermost orbital is transferred to a higher energy state. Powerful oxidising agent. Half-life of 1 10-6 seconds.

Peroxyl radical – It is free radical. Low oxidising relative to hydroxyl but greater diffusibility. Half-life of 1 10-2 seconds.

Alkoxyl radical – It is a free radical. Greater oxidising capability than peroxyl but less than hydroxyl. Half-life of 1 10-6 seconds.

Perhydroxy radical (HO2) – Strong oxidant and more lipid soluble.

Examples of oxidants

Sources of oxidants Radiation – Ionizing radiation, x-ray and

gamma rays produce ROS in their reaction with water.

Metabolism – Compounds undergo metabolism in the body (liver). During the process of metabolism of certain compounds e.g.: doxorubicin (redox-cycling), ROS is produced.

Mitochondrial respiration – The mitochondrial produces energy for the cells. It involves transfer of electrons through the mitochondrial electrons transport chain. Some leakage occurs and ROS are produced. Maybe the largest of superoxide and hydrogen peroxide. It is estimated that 1% of the oxygen used in respiration is converted to ROS.

Sources of oxidants Phagocytosis – The white blood cells

(e.g.: neutrophilis) are responsible for defences against infection. The neutrophilis engulf the infecting organism and kill them by releasing ROS.

Peroxisomes – Organelles in the cell that produce hydrogen peroxide.

Xanthine oxidase (XO) – It is an enzyme. In certain reactions catalysed by XO, superoxide is produced.

Industrial and atmospheric pollutants – Reaction of certain pollutants in the atmosphere lead to the production of reactive oxygen species e.g.: tobacco smoke.

What are oxidants Chemical that reduces the rate of

particular oxidation reactions in a specific context, where oxidation reactions are chemical reactions that involve the transfer of electrons from a substance to an oxidising agent – WIKIPEDIA

Substances that may protect cells from the damage caused by unstable molecules known as free radicals. Free radical damage may lead to a cancer. Antioxidants interact with and stabilize free radicals and may prevent some of the damage free radicals otherwise might cause – National Cancer Institute, USA

Types of antioxidants ENDOGENOUS:

Glutahione (GSH, also present in foods)

Fe-catalase Mn, Cu, Zn-superoxide dismutase

(SOD) Uric acid Lipoic acid

DIETARY AND EXOGENOUS: Tocopherols and tocotrienols

(vitamin E) Ascorbate (vitamin C) Vitamin A and carotenoids Phytochemicals with antioxidant

activity Food antioxidants (BHA, BHT,

TBHQ, propyl gallate, rosemary extract)

Examples of antioxidants ENZYMES:

Superoxide dismutase (SOD) – 10,000 times faster in presence of the enzyme different types- Cu/Zn SOD, Mn SOD. Highest level in liver, adrenal gland, kidney and spleen.

O2- + O2- + 2H H2O2 + O2

Glutathione peroxide – Removal of hydrogen peroxide. Act better in low levels of hydrogen peroxide. 2 types: selenium dependent and selenium independent (Organic hydroperoxides)2GSH + H2O2 GSSG + 2H2O

Examples of antioxidants Catalase – Removal of hydrogen

peroxide. Usually acts at higher concentrations of hydrogen peroxide liver, kidney and red blood cells have high levels.

Tocopherol (Vitamin E) – Most widely distributed antioxidant in nature. Found in both plants and animals. At least 8 isomer- most widely known is alpha-tocopherol. Also most potent isomer. Very effective in lipid environment.

Vitamin C (Ascorbic acid) – Hydrophilic. Free radical scavenger. Functions better in an aqueous environment. Reacts with ROS but also helps to recycle oxidised vitamin E. Good protection against plasma lipid peroxidation. Can also act as prooxidant. Vitamin E and C work synergistically.

Antioxidants SourcesVitamin A and Carotenoids Carrots, broccoli, sweet potatoes,

tomatoes, peaches and apricots.Vitamin C Citrus fruits like oranges and lime etc.

green peppers, broccoli, leafy vegetables and tomatoes.

Vitamin E Nuts and seeds, whole grains, green leafy vegetables, vegetable and liver oil.

Some common phytochemicals

Flavonoids (soy, red grapes, tea)Lycopene (tomatoes)Lutein (dark green vegetables e.g.: spinach)Lignan (flax seed, oatmeal, barley)

Vitamin-like antioxidants Coenzyme Q10 (CoQ10)

Glutathione

Examples of antioxidants

Glutathione (GSH) – It is a tripeptide- made up of glutamate, cysteinyl-glycine. Most abundant thiol in mammals. Used as a measure of oxidative stress, levels change with age, time of day (Diurnal variation), nutritive state etc.

Uric acid – Good scavenger of free radicals, especially hydroxyl radical.

Carotenoids – Scavenger of free radicals. Beta-carotene: found in carrots. Lycopene: found in tomatoes. Red Palm oil.

Polyphenols (flavonoids) – Found in plants, timber, red wine (Resveratrol).

Ubiquinone (Coenzyme Q10) – Good scavenger of superoxide radicals.

Examples of antioxidants

Examples of antioxidantsSecondary defenses against

oxidative stress Lipolytic enzymes – Phospholipase A2- repair of peroxidised lipids

Proteolytic enzymes – Preferentially degrading oxidised proteins and thus preventing their accumulation.

ADVANTAGES AND DISADVANTAGES OF NATURAL AND SYNTHETIC ANTIOXIDANTS

Synthetic Antioxidants Natural AntioxidantsInexpensive Expensive

Widely applied Use restricted to some products

Medium to high antioxidant activity Wide ranging antioxidant activity

Increasing safety concern Perceived as innocuous substances

Use banned for some of them Increasing use and expanding applications

Low water solubility Broad range of solubility

Decreasing interest Increasing interest

METHOD OF PRODUCING STABLE FOODS/PRODUCTS WITHOUT ADDING

ANTIOXIDANTS

Techniques MethodsElimination of oxygen Packaging under nitrogen; packaging in

vacuum; packaging with an oxygen scavenger.

Elimination of sensitive substances Replacement of polyunsaturated oils with oils which less unsaturated and more stable, such as olive oil or palm oil.

Decreasing the rate of oxidation Storage at low temperature; storage in the dark; use of fats and oils that contain low levels of oxidation promoters (e.g.: oxidised products and heavy metals); use of ingredient that are naturally rich in antioxidants.

Consequences of the action of oxidants

Damage to proteins – Oxidation of proteins will lead to fragmentation of proteins (e.g.: albumin), aggregation and susceptibility to protein digestion.

Damage to carbohydrates – Oxidation of carbohydrates such as glucose and other monosaccharide can produce oxidised compounds that can interact with proteins and from new structures.

Damage to lipids – Lipids are a very important constituent of cell membranes. Cell membranes are made up of a lipid bilayer. ROS species can produce peroxidation of lipid, through 3 stages process of initiation, propagation and termination.

Consequences of the action of oxidants

Lipid peroxidation is facilitated by metals such as Fe and Cu.Not only do lipids loose their properties but also there are other products such as aldehydes that are produced which are toxic to cells.

Damage to DNA – Can have serious implications, not just on the cell, but the whole body and also offspring. Can cause base alterations and strand breaks. The hydroxyl radical, especially can interact with thymine and cytosine. Greater effect in isolated DNA.

ARTHRITIS – Damage to the joint is said to be caused by the release of ROS. Leads to inflammation and swelling.

Consequences of the action of oxidants

DIABETES – Damage to the pancreas and some of the complications of diabetes is said to be caused by ROS. Damage to beta cells of the pancreas by ROS and complications of diabetes by glycation of proteins.

CANCER – One of the cause is said to be ROS and other free radicals. Cancer are said to be cause by ROS because of damage to the DNA. Cause of cancer may be physical, chemical or viral. The damage most likely is during the initiation or promotion stage. Low level of SOD found in tumour cells.

Consequences of the action of oxidants

ATHEROSCLEROSIS – The development of the atherosclerotic plaques are said to involve the action of ROS. Plaque deposits is related to the low density lipoprotein cholesterol (LDL). Oxidatively modified LDL is cytotoxic. It disrupts endothelial cell homeostasis and injures the arterial intima. It also promotes platelet aggregation.

AGEING – The free radical theory of ageing says that we age because of the reaction of free radicals on our skin and body. In animals, antioxidants shown to increase average life span but very little effecting maximum life span.

Others – Cataracts, Parkinson’s disease, Alzheimer’s disease.

SUMMARY Our body is constantly exposed to

oxidants. These can be endogenous or exogenous.

Body has available defences against oxidative stress. These can be endogenous or exogenous.

There may be a need in certain instances for supplements of antioxidants - age, life-style, pollution etc.

Eat more fruits and vegetables.

QUESTION AND ANSWER SESSION

THANK YOU FOR YOUR KIND ATTENTION