Oxidative stress and antioxidant mechanisms in human body

Abstract

The present review aims to high light on the oxidative stress, and prevention by internal antioxidants and external antioxidants by some natural products possessing antioxidant properties. Oxidative stress occurs when the balance between reactive oxygen species (ROS) formation and detoxification favors an increase in ROS levels, leading to disturbed cellular function. ROS causes damage to cellular macromolecules causing lipid peroxidation, nucleic acid, and protein alterations. Their formation is considered as a pathobiochemical mechanism involved in the initiation or progression phase of various diseases such as atherosclerosis, ischemic heart diseases, diabetes, and initiation of carcinogenesis or liver diseases. In order to maintain proper cell signaling, it is likely that a number of radical scavenging enzymes maintain a threshold level of ROS inside the cell. However, when the level of ROS exceeds this threshold, an increase in ROS production may lead to excessive signals to the cell, in addition to direct damage to key components in signaling pathways. ROS can also irreversibly damage essential macromolecules. Protein-bound thiol and non-protein-thiol are the major cytosolic low molecular weight sulfhydryl compound that acts as a cellular reducing and a protective reagent against numerous toxic substances including most inorganic pollutants, through the –SH group. Hence, thiol is often the first line of defense against oxidative stress. Flavonoids have been found to play important roles in the non-enzymatic protection against oxidative stress, especially in the case of cancer. Flavonoids have occurred widely in tea, fruit, red wine, vegetables, and cocoas. Flavonoids, including flavones, flavanone, flavonols, and isoflavones, are polyphenolic compounds which are widespread in foods and beverages, and possess a wide range of biological activities, of which anti-oxidation has been extensively explored. It can be concluded that oxidative stress causes irreversible damage in cellular macromolecules that leads to initiation of various diseases such as atherosclerosis, ischemic heart diseases, liver diseases, diabetes, and initiation of carcinogenesis. Antioxidants inhibit reactive oxygen species production and scavenging of free radicals. Therefore, the review recommends that high consumption of natural foods that are rich in antioxidants will provide more protection against toxic agents and related diseases.