ANDROLOGY: THE EFFECT OF AGE ON THE EXPRESSION OF APOPTOSIS BIOMARKERS IN HUMAN SPERMATOZOA

Background: The negative impact of age on reproductive success has been well demonstrated for women, but age-related changes in the male reproductive system appear to be more subtle. Diminishing testicular function is indicated by a decline in testosterone levels, accompanied by an increase in gonadotropins. Some studies have shown increased age-related numerical and structural sperm chromosomal abnormalities, changes in sperm DNA methylation, and a higher mutational load. Epidemiologic data suggest that increasing male age may be associated with pregnancy loss and with a range of birth defects; the objective was to evaluate the impact of age on the expression of apoptotic biomarkers in human spermatozoa.
Materials and Methods: This study was a cross-sectional, prospective study. Healthy volunteers with proven fertility (n=25), stratified by age (range: 20 to 68 years) were subjected to examination of A.M. serum hormone levels [FSH, LH, Prolactin, AMH, T, sex hormone binding globulin (SHBG), and free androgen index (FAI)], basic semen parameters, and assessment of early [plasma membrane translocation of phosphatidylserine (PS)] and late (DNA fragmentation) sperm apoptotic markers by flow cytometry (using Annexin-V binding and Terminal-deoxynucleotidyl-transferase mediated deoxyuridine triphosphate fluorescence nick end labeling, TUNEL, respectively).
Main outcome measure: expression of apoptotic markers.
Results: The percentage of live sperm cells with plasma membrane translocation of PS (Annexin-V+/PI+) were significantly higher with advancing age (ANOVA, p=0.01). This significant association was further supported by a significant and positive correlation among these two parameters (r= 0.50, p<0.008). Although not significant, there was a clear trend for increased DNA fragmentation in the older groups (r=0.51). The age threshold for these observations appears to be 40 years. Advancing male age was positively correlated with FSH (r= 0.59, p<0.002), SHBG (r=. 63, p<0.01) and FAI (r= -0.67, p<0.01), and negatively correlated with sperm concentration (r= -0.52, p<0.01) and progressive motility (r=-0.67, p<0.01). There was no association between change in hormonal parameters and apoptosis biomarkers.
Conclusion: Advancing male age is associated with the expression of early apoptotic markers as evidenced by significantly increased plasma membrane translocation of PS, as well as with a more subtle proportion of sperm carrying DNA fragmentation. This study confirmed that male age is also associated with a decline in sperm concentration and motility.