Development of an Image Analysis System to Monitor the Retention of Residual Cytoplasm by Human Spermatozoa: Correlation With Biochemical Markers of the Cytoplasmic Space, Oxidative Stress, and Sperm Function

Abstract

A method has been developed for quantifying the residual cytoplasm present in the midpiece of human spermatozoa, based upon the imaging of NADH oxidoreductase activity. This procedure used NADH and nitroblue tetrazolium as electron donor and acceptor, respectively, and resulted in the discrete staining of the entire midpiece area, including the residual cytoplasm. Image analysis techniques were then used to generate binary images of the midpiece, from which objective measurements of this cellular domain could be undertaken. Such data were found to be highly correlated with biochemical markers of the cytoplasmic space, such as creatine kinase (CK) and glucose‐6‐phosphate dehydrogenase (G‐6‐PDH), in sperm populations depleted of detectable leukocyte contamination. Morphometric analysis of the sperm midpiece was also found to reflect semen quality in that it predicted the proportion of the ejaculate that would be recovered from the high‐density region of Percoll gradients and was negatively correlated with the movement and morphology of the spermatozoa in semen. Variation in the retention of excess residual cytoplasm was also associated with differences in the functional competence of washed sperm preparations, both within and between ejaculates. Thus, within‐ejaculate comparisons of high‐ and low‐density sperm subpopulations revealed a relative disruption of sperm function in the low‐density fraction. This disruption was associated with the presence of excess residual cytoplasm in the midpiece, high concentrations of cytoplasmic enzymes, and the enhanced‐generation reactive oxygen species (ROS). Functional differences between individual high‐density Percoll preparations were also negatively correlated with the area of the midpiece and the corresponding capacity of the spermatozoa to generate ROS. These findings suggest that one of the factors involved in the etiology of defective sperm function is the incomplete extrusion of germ cell cytoplasm during spermiogenesis as a consequence of which the spermatozoa experience a loss of function associated with the induction of oxidative stress.

The Role of Melatonin to Ameliorate Oxidative Stress in Sperm Cells

“…Creatinine kinase (CK) and G6PDH were used as biomarkers of this retention [33][34][35][36]. In addition, it has been reported that in an environment of increased RONS levels, immature sperm can cause OS in neighboring mature ones during their transit through the epididymis [37][38][39]. Also, mature sperm could be an additional source of RONS due to cellular metabolism [40].…”

“…There is a positive correlation between RONS production, anomalies in sperm morphology, and DNA damage [31,38,49]. High levels of expression of the isoform of NADPH oxidase (NOX)-NOX5, generators of RONS in sperm-have been reported in both teratozoospermia [50] and asthenozoospermic human ejaculates [37].…”