Antioxidant Categories and Mode of Action

*Manal Azat Aziz, Abdulkareem Shehab Diab and Abeer Abdulrazak Mohammed*

### **Abstract**

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 enzymes, free radicals, antioxidant mechanisms

#### **1. Introduction**

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 hydroxyl radical (OH• ), perhydroxyl radical (HO2 • ), hypochlorous acid (HOCl), superoxide anion radical (O2 •¯), hydrogen peroxide (H2O2), singlet oxygen (1 O2), nitric oxide radical (NO• ), hypochlorite radical (OCl• ), peroxynitrite (ONOO), and different lipid peroxides. RNS are derived from nitric oxide by the reaction with O2 •¯ to form ONOO¯ , 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

#### **Figure 1.**

*Reactive oxygen species (ROS) generation by endogenous and exogenous sources can lead to oxidative damage and accumulation of proteins, lipids and DNA, when defensive (repair) mechanisms of the body become weak. These ROS also modulate the signal transduction pathways, which result in organelle damage, and changes in gene expression followed by altered responses of the cells, which finally results into aging. Adapted from Pandey and Rizvi [5].*

chelating, and free radical scavenging actions to keep the ROS homeostasis at a low level. In addition, dietary antioxidants can assist to keep an adequate antioxidant status in the body. Nevertheless, during environmental stress and cell dysfunction, levels of ROS can increase dramatically and cause significant cellular damage in the body. Consequently, oxidative stress significantly contributes to the pathogenesis of different diseases, such as heart disease, inflammatory disease, cancer, diabetes mellitus, Alzheimer's disease, autism, and to the aging process (**Figure 1**) [3–5]. The chapter clarifies oxidative stress. Then classify the antioxidants and their applications. Finally, we describe antioxidants' mode of action and how they prevent the cell damage.
