Antioxidant Activity of Mangrove free essay sample

All forms of life maintain a reducing environment within their cells. This reducing environment is preserved by enzymes that maintain the reduced state through a constant input of metabolic energy. Disturbances in this normal redox state can cause toxic effects through the production of peroxides and free radicals that damage all components of the cell, including proteins,  lipids, and  DNA. Oxidative stress occurs when free radicals, which are not neutralized by antioxidants, go on create more volatile free radicals and damage cell walls, vessel walls, proteins, fats and even the nucleus of our cells. A free radical or reactive species is any chemical species capable of independent existence possessing one or more unpaired electrons. Biological free radicals are thus highly unstable molecules that have electrons available to react with various organic substrates. The reactive species generally include ROS and RNS, though reactive chlorine species also part of the reactive species. Reactive oxygen species  (ROS) are chemically reactive molecules containing oxygen. Examples include  oxygen  ions  and  peroxides. ROS form as a natural byproduct of the normal metabolism of  oxygen  and have important roles in  cell signaling  and  homeostasis. Normally, cells defend themselves against ROS damage with  enzymes  such as  alpha-1-microglobulin,  superoxide dismutase,  catalases,  lactoperoxidase, glutathione peroxidase  and  peroxiredoxins. Small molecule antioxidants such as  ascorbic acid  (vitamin C),  tocopherol  (vitamin E),  uric acid, and  glutathione also play important roles as cellular antioxidants. Reactive Nitrogen Species (RNS)  are radical nitrogen-based molecules that can act to facilitate nitrosylation reactions. Reactive Nitrogen Species (RNS) include nitrous oxide, peroxynitrate, nitrosyl cation, nitrous acid, etc. Many free radicals are the result of naturally occurring processes such as oxygen metabolism and inflammatory processes. For example, when cells use oxygen to generate energy, free radicals are created as a consequence of ATP production by the mitochondria. Exercise can increase the levels of free radicals as can environmental stimuli such as ionizing radiation (from industry, sun exposure, cosmic rays, and medical X-rays), environmental toxins, altered atmospheric conditions (e.g. , ozone and nitrous oxide (primarily from automobile exhaust). Lifestyle stressors such as cigarette smoking and excessive alcohol consumption are also known to affect levels of free radicals. Some of the important reactive species are superoxide (O2. –), shydrogen peroxide (H2O2), hydroxyl radicals (OH. ), nitric oxide (NO. ), etc. An extensive, highly effective group of protective agents and defense mechanisms referred to collectively as the  Antioxidant Defense System  (ADS), acts to regulate oxidative reactions. There are two types of antioxidant systems i. e.enzymatic and non enzymatic antioxidant system develop in plants. Enzymatic system includes superoxide dismutase, glutathione peroxidase, glutathione reductase, catalases, etc. These form the body’s endogenous defense mechanisms to help protect against free radical-induced cell damage. They require micronutrient cofactors such as  selenium, iron, copper, zinc, and manganese for their activity. Non-enzymatic system include such as  ascorbic acid  (Vitamin C), polyphenols  ,  tocopherols, etc. Vitamin C is the most important water-soluble antioxidant in extracellular fluids. Vitamin C helps to neutralize ROS in the water or aqueous phase before it can attack the lipids. Vitamin E is the most important lipid soluble antioxidant. It is important as the chain-breaking antioxidant within the cell membrane. It can protect the membrane fatty acids from lipid peroxidation. Vitamin C in addition is capable of regenerating vitamin E. Beta carotene and other carotenoids also have antioxidant properties. In human, some of the notable diseases caused due to oxidative stress include heart disease is the leading cause of death worldwide. Heart disease risk is raised by several factors including high  cholesterol  levels,  high blood pressure, cigarette smoking, and  diabetes (Sundararajan et al. , 2006; Tawaha et al. , 2007; Nanasombat and Teckchuen, 2009). These promote  atherosclerosis. Atherosclerosis refers to formation of hardened walls of the arteries that impairs blood flow to the heart and other vital organs. Cancer kills millions worldwide. Diet may be the cause for cancer in as much as 35% of all human cancers. Low antioxidant intake in diet may also be responsible. Low dietary intake of fruits and vegetables doubles the risk of most types of cancers. Pro-oxidants, or those who generate free radicals, stimulate cell division and these form the beginnings of mutagenesis and tumor formation. When a cell with a damaged DNA strand divides, it gives rise to disturbed and deformed clusters of cells that form the cancer. In addition, cigarette smoking and chronic inflammation lead to strong free radical generation that seems to be the reason for many cancers. The respiratory system is a well known target for free radical insult. This comes from endogenous factors as well as exposure to air pollutants and toxins, cigarette smoke etc. Recent studies suggest that free radicals may be involved in the development of pulmonary disorders such as  asthma. Antioxidants have been seen to reduce the development of asthmatic symptoms. Vitamin C, vitamin E, and  beta carotene supplementation has been associated with improved lung function. Free radicals can also damage nerves and the  brain. Formation of  cataracts  is believed to involve damage to lens protein by free radicals. This leads to opacity of the lens. Cataract  formation may be slowed with the regular consumption of supplemental antioxidants like vitamin E, vitamin C, and the carotenoids. Other diseases like Diabetes, Rheumatoid  arthritis  etc. are also associated with low antioxidant levels in blood. Several standard established antioxidant drugs such as butylhydroxytoluene (BHT) and rutin have been reported to be toxic to living cells (Madhavi et al, 1995, Bursal amp; Gulcin, 2011, Gocer et al, 2011). BHT drugs are known to be the most prevalent and approved antioxidant scavengers worldwide, have equally been reported to be toxic to the lungs, even at a lower concentration. As oxidative stress causes many human diseases, the use of natural antioxidants is intensively studied. Antioxidants are widely used in  dietary supplements  and have been investigated for the prevention of diseases such as cancer,  coronary heart disease  and even  altitude sickness. Plant contains a variety of phytochemical such as phenols, steroids, tannins, saponins, carbohydrates, etc having antioxidant activity that can be used for the removal of human diseases caused due to the oxidative stress. As part of their adaptation from marine life, terrestrial plants develop antioxidant system producing different phytochemicals such as  ascorbic acid  , polyphenols  and  tocopherols having antioxidant property. Mangrove plants are found to have medicinal values and have been used traditionally by local medical practitioners in worldwide. In nature, more than 65 species of mangrove plants, 18 species are found to be widely used by local medical practitioners in many countries like Africa, South East Asia, South America and Australia. These 12 species viz. Acanthus clicifolius, Aegiceras majus, Avicennia africana, A. marina, A. officinalis, Ceriops caudolleana, Exocoecaria agallocha, Kandelia rhecdi, Nypa fruticans, Rhizophora mangle, R. mcronata and Sonneratia caseolaris are used to cure some deeded diseases like leprosy, elephantiasis, tuberculosis, malaria, dysentery, ulcers and some skin diseases. Balsco et al,1976 and Banerjee and Gosh,1998 reported that 27 out of 65 species of mangrove are present in India respectively. The mangroves are the coastal tropical forest; grow in the intertidal deltaic areas, having higher salt concentration. Some species such as the Grey Mangrove can also tolerate the storage of large amounts of salt in their leaves – which are discarded when the salt load is too high. Mangroves can also restrict the opening of their stomata. This allows the mangrove to conserve its fresh water, ability vital to its survival in a saline environment. Mangroves are able to turn their leaves to reduce the surface area of the leaf exposed to the hot sun. This enables them to reduce water loss through evaporation. A distinctive feature of mangroves is their far-reaching, exposed roots. While these roots come in many different shapes and sizes, they all perform an important function – structural support in the soft soils. Some species of mangroves have pneumataphores, which are above-ground roots. These are filled with spongy tissue and peppered with small holes that offer structural support and allow oxygen to be transferred to the roots trapped below ground in the anaerobic (low oxygen) soils. The roots of many mangrove species are also adapted to stop the intake of a lot of the salt from the water before it reaches the plant. Some mangrove species have evolved to produce seeds that float. The tide acts as the method of dispersal to avoid crowding of young plants. Other mangrove species are viviparous. They retain their seeds until after it has germinated and a long, cylindrical propagule has formed. When it has matured to this stage, the parent tree drops it into the water, where it remains dormant until it finds the soil and is able to put out roots. Referring to the facts cited above the present study was designed with the following objectives. OBJECTIVES Selection of mangrove plants for antioxidant activity on the basis of their ethenomedicinal importance. 2. Preparation of mangrove plant extracts by successive extraction methods. 3. Phytochemical evaluation of the mangrove plant extracts. 4. Evaluation of antioxidant activity following in vitro assay techniques. Normally free radical formation is controlled naturally by various beneficial compounds known as antioxidants. When there is deficiency of these antioxidants damage due to free radicals can become cumulative and debilitating. Antioxidants are capable of stabilizing, or deactivating, free radicals before they attack cells. Some of the important reactive species and their biological effects are superoxide anion, hydrogen peroxide, peroxynitrite, hydroxyl radicals, etc. The free radical superoxide is generated from O2 by multiple pathways. They can be summarized into following categories, such as: i) NADPH oxidation by NADPH oxidase; ii) oxidation of xanthine or hypoxanthine by xanthine oxidase; iii) oxidation of reducing equivalents (e. g., nicotinamide adenine dinucleotide [reduced NADH], NADPH, and FADH2 [FAD reduced]) via the mitochondrial electron transport system; iv) autoxidation of monamines (e. g. , dopamine, epinephrine, and norepinephrine), flavins, and hemoglobin in the presence of trace amounts of transition metals; v) one-electron reduction of O2 by cytochrome P-450. Superoxide anion (O2-) is a reactive oxygen species that reacts quickly with nitric oxide (NO) in the vasculature. The reaction p roduces peroxynitrite and depletes the bioactivity of NO. This is important because NO is a key mediator in many important vascular functions including regulation of smooth muscle tone and blood pressure, platelet activation, and vascular cell signaling (Guzik et al, 2002). Peroxynitrite itself is a highly reactive species which can directly react with various biological targets and components of the cell including lipids, thiols, amino acid residues, DNA bases, and low-molecular weight antioxidants (ODonnell et al, 1999). Peroxynitrite can react directly with proteins that contain transition metal centers. Therefore, it can modify proteins such as hemoglobin, myoglobin, and cytochrone c by oxidizing ferrous heme into its corresponding ferric forms. Peroxynitrite may also be able to change protein structure through the reaction with various amino acids in the peptide chain. Hydrogen peroxide (H2O2) is a two-electron reduction state, formed by dismutation of †¢O2- or by direct reduction of O2. It is lipid soluble and thus able to diffuse across membranes. Hydrogen peroxide and superoxide radical (O2. –) by themselves are relatively less damaging, but they can form species such as hydroxyl radicals.