Reactive oxygen species generation and human spermatozoa: The balance of benefit and risk

Abstract

Although the generation of reactive oxygen species is an activity normally associated with phagocytic leucocytes, mammalian spermatozoa were, in fact, the first cell type in which this activity was described. In recent years it has become apparent that spermatozoa are not the only nonphagocytic cells to exhibit a capacity for reactive oxygen species production, because this activity has been detected in a wide variety of different cells including fibroblasts, mesangial cells, oocytes, Leydig cells, endothelial cells, thyroid cells, adipocytes, tumour cells and platelets. Since the capacity to generate reactive oxygen species is apparently so widespread, the risk-benefit equation for these potentially pernicious molecules becomes a matter of intense interest. In the case of human spermatozoa, the risk of manufacturing reactive oxygen metabolites is considerable because these cells are particularly vulnerable to lipid peroxidation. Indeed, there is now good evidence to indicate that oxygen radicals are involved in the initiation of peroxidative damage to the sperm plasma membrane, seen in many cases of male infertility. This risk is off-set by recent data suggesting that superoxide anions and hydrogen peroxide also participate in the induction of key biological events such as hyperactivated motility and the acrosome reaction. Thus, human spermatozoa appear to use reactive oxygen species for a physiological purpose and have the difficult task of ensuring the balanced generation of these potentially harmful, but biologically important, modulators of cellular function.

Effect of leukocytospermia and processing by discontinuous density gradient on sperm nuclear DNA fragmentation and mitochondrial activity

“…Imbalances between ROS production and semen antioxidant capacity will lead to oxidative stress [9,10], which will ultimately result in oxidation of membrane polyunsaturated fatty acids [14,15], loss of mitochondrial membrane potential [16], and single and double strand DNA fragmentation [17].…”

“…While baseline ROS concentration is essential during sperm capacitation and acrosome reaction [7,8], excessive ROS production will lead to oxidative stress [9,10], which in turn will decrease sperm functional integrity (mitochondrial activity, sperm-egg binding, and DNA integrity, for example) [11,12].…”

Role of reactive oxygen species in the pathophysiology of human reproduction

“…The LPO cascade occurs in two fundamental stages: initiation and propagation. The hydroxyl radical (OH • ) is a powerful initiator of LPO (65). Most membrane PUFA have unconjugated double bonds that are separated by methylene groups.…”

“…This by-product has been used in biochemical assays to monitor the degree of peroxidative damage sustained by spermatozoa (65). The results of such an assay exhibit an excellent correlation with the degree to which sperm function is impaired in terms of motility and the capacity for sperm-oocyte fusion (36).…”

Protective effects of exogenous gangliosides on ROS-induced changes in human spermatozoa

“…5,6 Polyunsaturated fatty acids are particularly prone to oxidative attack, as the presence of a double bond weakens C-H bonds on adjacent carbon atoms and facilitates hydrogen abstraction, which initiates a lipid peroxidation cascade. [6][7][8] The limited enzymatic antioxidative defence system in spermatozoa also increases their susceptibility to oxidative stress.…”