Protective Mechanisms Operative in Spermatozoa

If the antioxidants present in epididymal and seminal plasma do not successfully intercept ROS, or if excessive ROS are generated by the spermatozoa themselves, then oxygen radical-induced damage and the initiation and propagation of the lipid peroxidation chain reaction may take place. If this happens, then the spermatozoon has to respond by removing and neutralizing the lipid peroxide. The removal is effected by phospholipase A2 (PLA2) which responds to the presence of a peroxidized fatty acid by moving into the plasma/mitochondrial membrane and cleaving out the offending peroxide. The fatty acids esterified to the sn-2 position of the glycerol backbone of sperm phospholipids are highly unsaturated (largely arachidonic and docosohexaenoic acid) and therefore very vulnerable to free radical attack because the carbon hydrogen dissociation energies are lowest at the bis-allylic methylene group [39]. As a result, the hydrogen abstraction event that initiates lipid peroxidation is promoted. Once the lipid peroxide has been cleaved by PLA2, two downstream events must now occur. First, the parent phospholipid (now a lysophospholipid) has to be repaired by replacing the lost fatty acid through the action of an acyl transferase. The plasmalogen fraction of the phospholipid pool appears to be particularly susceptible to peroxidative attack [23] and is the preferential target for acyl transferase activity [36]. Second, once the peroxidized fatty acid has been cleaved by PLA2, it can then be processed by GPX and/or thioredoxin reductase [40] in order to convert the toxic lipid peroxide to a harmless fatty alcohol. In addition, toxic lipid peroxides can be removed from the cell following PLA2 cleavage and transfer to albumin in the extracellular medium, as a consequence of the lipid binding characteristics of albumin. The latter is highly effective at protecting spermatozoa from oxidative stress by virtue of its ability to bind and neutralize cytotoxic lipid hydroperoxides generated as a consequence of sperm oxidative metabolism [39, 41]. Nevertheless, since PUFA content and oxygen radical production in mature spermatozoa are relatively low and homogenously distributed among the sperm population, at constant temperature and pO2, the rate-limiting factor that governs the rate of lipid peroxidation and sperm motile lifespan and function is intracellular antioxidant enzymatic activity.

Pregnancy Guide

Pregnancy Guide

A Beginner's Guide to Healthy Pregnancy. If you suspect, or know, that you are pregnant, we ho pe you have already visited your doctor. Presuming that you have confirmed your suspicions and that this is your first child, or that you wish to take better care of yourself d uring pregnancy than you did during your other pregnancies; you have come to the right place.

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