Oxygen uptake by mitochondria in demembranated human spermatozoa: A reliable tool for the evaluation of sperm respiratory efficiency

In this work we report a relatively simple and fast method for analysing oxygen consumption and therefore mitochondrial functionality, in individual human ejaculates. This oxygraphic method requires a low number of cells, is highly reproducible and linearly correlates with sperm concentration. Our results have shown that oxygen uptake by mitochondria of demembranated sperm cells from normozoospermic subjects is significantly stimulated by a large set of respiratory substrates and ADP. The respiratory control ratio (RCR) values indicate a good coupling between respiration and phosphorylation by sperm mitochondria and thus a well preserved integrity of the mitochondria themselves. Interestingly, whereas the rates of oxygen uptake, as expected, changed with different sperm concentrations, the RCR values remained constant, thus demonstrating a linear response of the assay. In asthenozoospermic subjects, however, a significant decrease in the sperm respiratory efficiency was found. In our opinion, the implications of this study are the following. On the one hand, a careful and detailed investigation of the mitochondrial bioenergetics of sperm will provide more insight into the basic biology of the spermatozoon with the aim of obtaining more information on the role of sperm mitochondria in motility and on the overall quality of the gametes. On the other hand, we are confident that this relatively simple and fast assay, requiring a limited amount of sperm cells, can be used as a routine semen analysis in clinical investigation