Synthetic antioxidants, their classification by chemical nature and mechanism of action (Review)

Abstract

The challenge of equally importance in modern medicinal chemistry and pharmacy is the chemical regulation of numerous pathological conditions caused by the development of oxidative stress in a living organism, and researches the biochemical mechanisms inhibiting free radical processes. The present review considers the general characteristics of the oxidative and antioxidant systems of the organism, their role in the formation and correction of oxidative stress. It also summarizes the main types of antioxidants, and their mechanisms of action. Oxidative stress is defined as a physiological state which occurs as a result of imbalance between redox processes in the body, in particular the formation of reactive oxygen species, and the antioxidant defense system functioning. Unfavorable exogenous and endogenous factors effects on biological tissues and the living organisms as a whole may be associated with the development of oxidative stress and leads to oxidative modification of biomolecules, in particular, lipids, proteins and DNA. An antioxidant is a substance which at low concentrations delays or prevents oxidation of a substrate. The recent studies emphasizes the importance of antioxidants mechanisms understanding which allows to determine the biological meaning of antioxidants, their possible uses, their production by organic synthesis or biotechnological methods, and the standardization of the antioxidant activity evaluation techniques. The classifications of antioxidants by their chemical nature and mechanism of action are overviewed. Antioxidant compounds are considered to act through several chemical mechanisms: hydrogen atom transfer, single electron transfer, and the ability to chelate transition metals. While regardless of the reaction mechanism, the antioxidant is oxidized and forms a new radical which can behave in different ways when interacting with the biological target it protects. The main synthetic antioxidants used in modern medical practice for the treatment and prevention of diseases associated with oxidative stress are studied. Antioxidants are classified into drugs of direct and indirect action. The first group compounds directly eliminate free radicals. They are evaluated to be effective both in vivo and in vitro . Indirect antioxidants are effective only in a living organism, because they include substances involved into the synthesis of direct antioxidants or antioxidant enzymes. It is shown that synthetic antioxidants can certainly play an important role in treatment of many disorders, thus, the knowledge of the antioxidants` mechanisms of action is essential for the novel strategies development for the directed synthesis, screening and chemical optimization of biologically active substances as potential effective drug candidate possessing antioxidant effect. Key words: oxidative stress, antioxidants, antioxidant enzymes, synthetic antioxidants.