ANTIOXIDANT AN OVERVIEW
Sanjay Singh Bhandari *, Mahaveer Prasad Kabra, Raman Gupta, Ami Sharma
Kota College of Pharmacy, SP-1, RIICO Industrial Area, Ranpur,
Jhalawar road, Kota, Rajasthan, India – 324009
Damage to cells caused by free radicals is believed play a central role in the aging process and in disease progression. Antioxidants are our first line of defense against free radical damage, and are critical for maintaining optimum health and well being. The need for antioxidants becomes even more critical with increased exposure to free radicals. Pollution, cigarette smoke, drugs, illness, stress, and even exercise can increase free radical exposure. Because so many factors can contribute to oxidative stress, individual assessment of susceptibility becomes important. Many experts believe that the Recommended Dietary Allowance (RDA) for specific antioxidants may be inadequate and, in some instances, the need may be several times the RDA. As part of a healthy lifestyle and a well-balanced, wholesome diet, antioxidant supplementation is now being recognized as an important means of improving free radical protection.
REFERENCE ID: PHARMATUTOR-ART-1762
Antioxidants are chemical compounds that can bind to free oxygen radicals preventing these radicals from damaging healthy cells.
Substances that have the ability to oxidize other substances are said to be oxidative and are known as oxidizing agents, oxidants, or oxidizers. Put another way, the oxidant removes electrons from another substance, and is thus itself reduced. And, because it "accepts" electrons, it is also called an electron acceptor.
Oxidants are usually chemical substances with elements in high oxidation numbers (e.g., H2O2, MnO−4, CrO3, Cr2O2−7, OsO4) or highly electronegative substances that can gain one or two extra electrons by oxidizing a substance (O, F, Cl, Br).(1)
Substances that have the ability to reduce other substances are said to be reductive and are known as reducing agents, reductants, or reducers. In other words, the reductant transfers electrons to another substance, and is thus itself oxidized. And, because it "donates" electrons it is also called an electron donor.
Reductants in chemistry are very diverse. Electropositive elemental metals, such as lithium, sodium, magnesium, iron, zinc, or aluminium, are good reducing agents. These metals donate or give away electrons readily. Hydride transfer reagents, such as NaBH4 and LiAlH4, are widely used in organic chemistry, primarily in the reduction of carbonyl compounds to alcohols. Another method of reduction involves the use of hydrogen gas (H2) with a palladium, platinum, or nickel catalyst. These catalytic reductions are primarily used in the reduction of carbon-carbon double or triple bonds.(2)
C) A brief look at chemical bonding:
To understand the way that free radicals and antioxidants interact, you must first understand a bit about cells and molecules. So here's a (very) brief refresher course in Physiology/Chemistry 101: The human body is composed of many different types of cells. Cells are composed of many different types of molecules. Molecules consist of one or more atoms of one or more elements joined by chemical bonds.
As you probably remember from your old high school days, atoms consist of a nucleus, neutrons, protons and electrons. The number of protons (positively charged particles) in the atoms nucleus determines the number of electrons (negatively charged particles) surrounding the atom. Electrons are involved in chemical reactions and are the substance that bonds atoms together to form molecules. Electrons surround, or "orbit" an atom in one or more shells. The innermost shell is full when it has two electrons. When the first shell is full, electrons begin to fill the second shell. When the second shell has eight electrons, it is full, and so on.
The most important structural feature of an atom for determining its chemical behavior is the number of electrons in its outer shell. A substance that has a full outer shell tends not to enter in chemical reactions (an inert substance). Because atoms seek to reach a state of maximum stability, an atom will try to fill its outer shell by:
Gaining or losing electrons to either fill or empty its outer shell Sharing its electrons by bonding together with other atoms in order to complete its outer shell Atoms often complete their outer shells by sharing electrons with other atoms. By sharing electrons, the atoms are bound together and satisfy the conditions of maximum stability for the molecule.
D) How free radicals are formed:
Normally, bonds don’t split in a way that leaves a molecule with an odd, unpaired electron. But when weak bonds split, free radicals are formed. Free radicals are very unstable and react quickly with other compounds, trying to capture the needed electron to gain stability. Generally, free radicals attack the nearest stable molecule, "stealing" its electron. When the "attacked" molecule loses its electron, it becomes a free radical itself, beginning a chain reaction. Once the process is started, it can cascade, finally resulting in the disruption of a living cell.
Some free radicals arise normally during metabolism. Sometimes the body’s immune system’s cells purposefully create them to neutralize viruses and bacteria. However, environmental factors such as pollution, radiation, cigarette smoke and herbicides can also spawn free radicals. Normally, the body can handle free radicals, but if antioxidants are unavailable, or if the free-radical production becomes excessive, damage can occur. Of particular importance is that free radical damage accumulate.(3, 4)
E) How antioxidants may prevent against free radical damage:
The vitamins C and E are thought to protect the body against the destructive effects of free radicals. Antioxidants neutralize free radicals by donating one of their own electrons, ending the electron-"stealing" reaction. The antioxidant nutrients themselves don’t become free radicals by donating an electron because they are stable in either form they act as scavengers, helping to prevent cell and tissue damage that could lead to cellular damage and disease.
Vitamin E: - The most abundant fat-soluble antioxidant in the body. One of the most efficient chain-breaking antioxidants available. Primary defender against oxidation. Primary defender against lipid per oxidation (creation of unstable molecules containing more oxygen than is usual).
Vitamin C: - The most abundant water-soluble antioxidant in the body. Acts primarily in cellular fluid. Of particular note in combating free-radical formation caused by pollution and cigarette smoke. Also helps return vitamin E to its active form.
Oxidants occur naturally as part of the normal body process; however harmful oxidants or free radicals, which are forms of oxygen, can cause damage to body cells. If free radicals are not neutralized they can work against the immune system and develop degenerative diseases.(5, 6)
High levels of oxidants are contained in substances such Drugs-
The desire to take medicine is perhaps the greatest failure which distinguishes man from animals.
Chemicals contained in food i.e.:-
Antibiotics- Used to supplement animal feeds as animal growth promoters
Pesticides, fungicides, herbicides and chemical fertilizers(e.g. nitrates) -Used on fruit and vegetables, some fruit and vegetables are sprayed up to seven times before harvesting Emulsifiers, flower treatment agents, mould growth retardants.
Preservatives and improvers- Used as additives in bread
Colorants preservatives and artificial sweeteners –Used in processed canned food and drinks e.g. Aspartame
Salt–This added either as salt, or in the form of sodium, to many processed foods
Chemicals in food packaging –Chemicals which can leach into food are added to plastic to make them soft and flexible and fire retardant. e.g. Bisphenol
A. They are also found in plastic seals inside metal twist–on, twist–off lids e.g. Semicarbazide
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