SUSCEPTIBILITY OF HUMAN SPERM TO IN-SITU DNA DENATURATION IS STRONGLYCORRELATED WITH DNA STRAND BREAKS IDENTIFIED BY SINGLE-CELL ELECTROPHORESIS

Susceptibility of mammalian sperm DNA to low pH-or heat-induced denatu ration in situ has shown very strong dose-response relationships with animal and human exposure to chemical and physical toxicants and also fertility potential. In this study, 23 human semen samples representin g a wide range in percentage (7-86%) of sperm exhibiting abnormally hi gh susceptibility of DNA in situ to denaturation were studied for the integrity of their DNA using alkaline comet assay (single-cell microge l electrophoresis, pH 10.0). The percentage of comets observed for the se samples ranged from 5 to 95%; these data correlated strongly with t he percentage of sperm with increased DNA denaturability (r = 0.973; P < 0.001). Labeling of 3' ends of nicked DNA sites with 5-bromo-2'-deo xyuridine 5'-triphosphate (BrdUTP) followed by tagging with FITC-BrdUT P monoclonal antibody and how cytometry also indicated significantly s trong correlations of BrdUTP incorporation with both abnormal suscepti bility of DNA to denaturation (r = 0.859, P < 0.001) and comet assay ( r = 0.812, P < 0.001). The relationship among susceptibility of sperm chromatin to acid denaturation in situ, BrdUTP incorporation, and form ation of comets suggests that DNA fragmentation monitored by these ass ays may have important physiological relevance in terms of sperm quali ty and fertility potential. (C) 1997 Academic Press.