Section 2 Antioxidants

*Free Radical Medicine and Biology*

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**73**

**Chapter 5**

**Abstract**

*Yi Fang and Rongzhen Zhong*

Effects of Oxidative Stress on

Spermatozoa and Male Infertility

Oxidative stress occurs when the production of potentially destructive reactive oxygen species (ROS) exceeds the body's own natural antioxidant defences, resulting in cellular damage. Spermatozoa oxidative stress is intimately linked to several reproductive pathologies including the failure of spermatozoa cryopreservation and spermatozoa-egg recognition and fertilization. In this light, this review focuses on (i) the effects of oxidative stress on spermatozoa and application of antioxidants; (ii) production of ROS during cryopreservation; and (iii) oxidative stress in male infertility. This literature describes both a physiological and a pathological role of ROS in fertility. A delicate balance between ROS necessary for physiological activity and antioxidants to protect from cellular oxidative injury is essential for fertility.

**Keywords:** spermatozoa, oxidative stress, antioxidants, cryopreservation, infertility

Oxidative stress occurs when a system has an imbalance between oxidation and

—) anion, and H2O2.

reduction reactions, leading to generation of excess oxidants or molecules that accept an electron from another reactant [1]. A free radical is a molecule or element with an unpaired electron that is extremely reactive in an attempt to reach an electronically stable state. ROS are free radical derivatives of oxygen (O2) containing molecules. Some of the clinically important ROS identified include peroxyl

Nitrogen compounds such as nitric oxide (NO) and peroxynitrite anion (ONOO) also appear to play a role in oxidation and reduction reactions. Common molecules that receive the unpaired electron are lipids in membranes and carbohydrates in nucleic acids [2]. This leads to potential cellular membrane and DNA damage when

The process of mitochondrial oxidative phosphorylation uses nicotinamide adenine dinucleotide (NADH) as an electron donor and O2 as an electron acceptor in the electron transport chain, coupling both reduction and oxidation reactions with the synthesis of adenosine triphosphate (ATP), and about 1–5% O2 transformed into ROS [3]. Another intrinsic source of spermatic ROS production is cytoplasmic glucose-6-phosphate dehydrogenase (G-6-PDH). This cytoplasmic source of ROS

**1. Effects of oxidative stress on spermatozoa**

(·ROO—) and hydroxyl (·OH—) radicals, superoxide (·O2

ROS are greater than the antioxidant-carrying capacity (**Figure 1**).

**1.1 What is oxidative stress?**

**1.2 Production of ROS**
