Antioxidants: Sources and Modes of Actions

**3**

**Chapter 1**

**Abstract**

**1. Introduction**

hydroxyl radical (OH•

oxide radical (NO•

ONOO¯

superoxide anion radical (O2

of Action

Antioxidant Categories and Mode

Oxidative stress has received a considerable scientific attention as a mediator in the etiology of many human diseases. Oxidative stress is the result of an imbalance between free radicals and antioxidants. Cells can be damaged by free radicals that are considered to play a main role in the aging process and diseases development. Antioxidants are the first line of defense against the detrimental effects of free radical damage, and it is essential to maintain optimal health via different mechanisms of action. Types of antioxidants range from those generated endogenously by the body cells, to exogenous agents such as dietary supplements. Antioxidant insufficiency can be developed as a result of decreased antioxidant intake, synthesis of endogenous enzymes, or increased antioxidant utilization. To maintain optimal body function, antioxidant supplementation has become an increasingly popular practice through improving free radical protection. In this chapter, we first elucidate the oxidative stress, and then define the antioxidant and its categories. Finally, introduce the antioxidants mode of actions for cell protection from free radicals.

**Keywords:** oxidative stress, antioxidants, reactive oxygen species, antioxidant

), perhydroxyl radical (HO2

ent lipid peroxides. RNS are derived from nitric oxide by the reaction with O2

), hypochlorite radical (OCl•

Oxidative stress refers to the imbalance between oxidants and antioxidants within the body due to antioxidant deficiency or increased reactive oxygen species (ROS), reactive nitrogen species (RNA), and reactive sulfur species (RSS) production, which lead to potential cellular damage [1, 2]. ROS is a collective term that encompasses all highly reactive forms of oxygen, including free radicals. ROS categories include

•

, while RSS are easily produced from thiols through a reaction with ROS [3, 4]. Due to unpaired electrons of free radicals, these free radicals show high activity to react with other molecules in order to be neutralized. The free radicals have important functions in cell signaling, apoptosis, ion transportation, and gene expression [4]. Chemical reactivity of inactivated free radicals can damage all cellular macromolecules including carbohydrates, proteins, lipids, and nucleic acids. In general, cells are able to protect themselves against ROS damage via intracellular enzymatic reactions, metal

•¯), hydrogen peroxide (H2O2), singlet oxygen (1

), hypochlorous acid (HOCl),

), peroxynitrite (ONOO), and differ-

O2), nitric

•¯ to form

*Manal Azat Aziz, Abdulkareem Shehab Diab* 

*and Abeer Abdulrazak Mohammed*

enzymes, free radicals, antioxidant mechanisms
