Total Antioxidant Capacity Of Ethanolic Extract Of Hippocretea Welwitschii Oliv

1.0 Introduction

Free radicals (reactive oxygen species and reactive nitrogen species) have been implicated in a large number of pathological and disease conditions as well as in the aging process (Valdez et al., 2000). Evidences have suggested that the role of these free radical species especially the reactive oxygen species in the etiology and development of these pathological conditions may be through their oxidative damage to cells. However, other researches supported the idea that the destabilization of free radical generating pathways could play a role in causes and consequence of some diseased conditions (Mates et al., 1999). The oxidative stress experienced by a tissue or cell results from the negative imbalance between the production and removal of potentially damaging reactive oxygen species (Ros).

The removal rate is mostly controlled by a variety of antioxidants e.g glutathione, catalase, superoxide dismutase, Tocopherols (vitamin E, ascorbic acid (vitamin C) etc. The reduce rate of removal of reactive oxygen species may be due to reduce level of quantity and activity of these antioxidants. However, the low molecular weight antioxidants have been shown to be present in the various parts of different plants such as (khan et al., 2010). Hence plants are good sources of antioxidants to supplement the natural antioxidants of the body. Several studies have reported different total antioxidant capacity for various plants (bhalodi et al., 2008)

1.1 Aim

The purpose of this study is to;

Determine the total antioxidant capacity of hippocratea welwitshii oliv in albino wistar rats.

1.2 Literature Review

1.2.1 Free Radicals

Free radicals are defined as molecules having an unpaired electron in the outer orbit. (Gilbert, 2000). They are generally unstable and very reactive. Examples of oxygen free radicals are superoxide (02), hydroxyl (OH), peroxyl (RO2•),alkoxyl (RO•), and hydroperoxyl (HO2• ) radicals. Nitric oxide (NO) and nitrogen dioxide (•NO2) are two nitrogen free radicals. Oxygen and nitrogen free radicals can be converted to other non-radical reactive species, such as hydrogen peroxide(H2O2), hypochlorous acid (HOCl), hypobromous acid (HOBr), and peroxynitrite (ONOO) .(Pham et al., 2008). ROS, reactive nitrogen species (RNS), and reactive chlorine species are produced in animals and humans under physiologic and pathologic conditions. (Evans et al., 2001). Thus, ROS and RNS include radical and non-radical species.

1.2.2 Oxidative Stress

Oxidative stress reflects an imbalance between the systemic manifestation of reactive oxygen species and a biological system’s ability to readily detoxify the reactive intermediates or to repair the resulting damage (Halliwell and Glutteridge,2007). 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(deoxyribonucleic acid) DNA. some reactive oxidative species act as cellular messengers in redox signaling. Thus, oxidative stress can cause disruptions in normal mechanisms of cellular signaling. (Halliwell and Glutteridge,2007).

In humans, oxidative stress is thought to be involved in the development of cancer, Parkinson’s disease, Alzheimer’s disease, atherosclerosis, heart failure, myocardial infarction, Sickle Cell Disease, infection (Valko et al., 2007).However, reactive oxygen species can be beneficial, as they are used by the immune system as a way to attack and kill pathogens.(Segal,2005).

1.2.3 Antioxidants

Antioxidants are molecules that can neutralize free radicals by accepting or donating electron(s) to eliminate the unpaired electrons of the free radical. The antioxidant molecules may directly react with the reactive radicals and destroy them, while they may become new free radicals which are less active, longer-lived and less dangerous than those radicals they have neutralized (Jian-Ming Lü et al, 2010). Cells, tissues, and body fluids are equipped with these powerful defense systems that help counteract oxidative challenge.

To maintain a steady-state of metabolites and functional integrity in the aerobic environment antioxidant defense is organized at 3 principal levels of protection prevention, interception, and repair (Seis, 2007). Matching the diversity of prooxidants, the antioxidant molecules comprises a widespread array of systems which include the enzymatic (e.g superoxide dismutases, glutathione peroxidases, catalases etc) and non enzymatic (low molecular weight e.g vitamin C & E, gluthatione, etc) antioxidants

1.2.4 Functions / Uses Of Antioxidants

An antioxidant is a molecule that inhibits the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons or hydrogen from a substance to an oxidizing agent. Oxidation reactions can produce free radicals. In turn, these radicals can start chain reactions. When the chain reaction occurs in a cell, it can cause damage or death to the cell. Antioxidants terminate these chain reactions by removing free radical intermediates, and inhibit other oxidation reactions. They do this by being oxidized themselves, so antioxidants are often reducing agents such as thiols, ascorbic acid, or polyphenols. (Sies et al., 1997).

1.2.5 Antioxidant Metabolites

Antioxidants are classified into two broad divisions, depending on whether they are soluble in water (hydrophilic) or in lipids (lipophilic). In general, water-soluble antioxidants react with oxidants in the cell cytosol and the blood plasma, while lipid-soluble antioxidants protect cell membranes from lipid peroxidation. (Sies et al., 1997). These compounds may be synthesized in the body or obtained from the dirt. (Vertuani et al., 2004). The different antioxidants are present at a wide range of concentrations in body fluids and tissues, with some such as glutathione or ubiquinone mostly present within cells, while others such as uric acid are more evenly distributed. Some antioxidants are only found in a few organisms and these compounds can be important in pathogens and can be virulence factors. (Miler et al., 1997).

The relative importance and interactions between these different antioxidants is a very complex question, with the various metabolites and enzyme systems having synergistic and interdependent effects on one another. (Chaudière et al., 1997). The action of one antioxidant may therefore depend on the proper function of other members of the antioxidant system.( Vertuani et al., 2004). The amount of protection provided by any one antioxidant will also depend on its concentration, its reactivity towards the particular reactive oxygen species being considered, and the status of the antioxidants with which it interacts.( Vertuani et al., 2004).

Some compounds contribute to antioxidant defense by chelating transition metals and preventing them from catalyzing the production of free radicals in the cell. Particularly important is the ability to sequester iron, which is the function of iron-binding proteins such as transferrin and ferritin.(Imlay et al., 2003) Selenium and zinc are commonly referred to as antioxidant nutrients, but these chemical elements have no antioxidant action themselves and are instead required for the activity of some antioxidant enzymes, as is discussed below.