Origin of ROS in Male Reproductive System 21321 ROS Production by Spermatozoa

Many studies had proved that human spermatozoa are vulnerable to oxidative stress created by ROS [68]. Human spermatozoa have the ability to generate ROS, especially H2O2 that is important for sperm capacitation through the tyrosine phosphorylation reactions. H2O2 has the ability to suppress tyrosine phosphatase activity and indirectly stimulate cAMP production by adenylyl cyclase [68, 69]. cAMP is required for tyrosine phosphorylation stimulation. The effect of tyrosine phospho-rylation on sperm capacitation was found in human and other species [68-70].

21.3.2.2 Role of NADPH and NADPH Oxidase Activity

Two possible mechanisms had been proposed regarding the production of ROS by human spermatozoa; these are the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase system at the level of the sperm plasma membrane and nicotin-amide adenine dinucleotide (NADH)-dependent oxido-reductase (diphorase) at the level of mitochondria [71] . Many research groups have reported the presence of NADPH oxidase-like activity, at the human sperm plasma membrane. This activity has subsequent consequences of induced OS on spermatozoa [72] . The presence of large number of mitochondria in spermatozoa is necessary to provide a constant source of energy for their motility. However, the increased number of damaged mitochondria in spermatozoa may elevate the production of ROS which in turn disrupt the function of the spermatozoa [73].

21.3.2.3 Retained Cytoplasma

High levels of ROS are generated by immature germ cells, damaged spermatozoa, and those with retention of residual cytoplasm [74]. In addition, ROS production by spermatozoa has been associated with midpiece abnormalities, cytoplasmic droplets, and spermatozoa immaturity [75-77]. It has been shown that the retention of residual cytoplasm in the sperm midpiece after spermeation is responsible for excess ROS generation by spermatozo [77] Immature spermatozoa are also a well-characterized source of ROS which may alter the semen quality. The major ROS type produced by immature spermatozoa are superoxide anion (O2"~) and hydrogen peroxide (H2O2) [78, 79] . 2

Stimulation of ROS generation by sperm residual cytoplasm is elevated due to high levels of NADPH produced by the enzyme glucose-6-phosphate dehydrogenase (G6PD), which is exhibited in sperm residual cytoplasm. Therefore, the retention of residual cytoplasm creates a situation in which sufficient substrate would be available to support excessive NADPH-dependent ROS generation [77, 80, 81].

Spermatozoa may be damaged during transferring from the seminiferous tubules to the epididymis due to high ROS generation by immature, morphologically abnormal spermatozoa with cytoplasmic residues such as those confronted in teratozoo-spermic semen [82]. However, immature spermatozoa, sperm with cytoplasmic droplets at the midpiece and leukocytes, are the major ROS producers in semen [83], Single study [84] demonstrated that sperm morphology was not found to be associated with oxidative stress. However, retained cytoplasmic residues in the sperm may be an important source of ROS in both primary and secondary infertile men [85].

21.3.2.4 ROS Production by Leukocytes

Leukocytes are found in the male reproductive tract and human ejaculates [85]; they play an immunological role against pathogens as well as phagocytic clearance of abnormal sperm [86]. The leucocytes produce ROS as a result of their activity [59]. Male subfertility and infertility have been correlated with reproductive tract inflammation and the presence of leukocytes in ejaculate ] 13, 87]. Patients exhibiting leukocytospermia secondary to infection or as consequence of a paraplegia showed high level of oxidative stress in their ejaculates [39]

Plante et al. [88] reported that activated leukocytes can produce 100-fold higher amounts of ROS than nonactivated leukocytes. Inflammation and infections activate leukocytes [89]. High levels of ROS produced by leukocytes [90] or during separating spermatozoa from seminal plasma for assisted reproduction will increase the incidence of spermatozoa damage [13] , This spermatozoal damages may include chromatin alterations [91], poor motility [92], and inhibition of the mitochondrial function [93] .

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