Sperm chromatin structure is altered in cynomolgus monkeys with environmentally relevant blood lead levels

Exposure to lead has been associated with a variety of adverse reproductive outcomes such as spontaneous abortion, impaired fecundity, and sterility. Although decreased sperm counts and serum testosterone levels have been found in men with occupational lead exposure, animal experiments suggest that fertility may be impaired at blood lead levels that have no apparent effect on reproductive hormone levels or sperm concentration. Consequently, this study investigated the effect of chronic lead treatment on semen quality in healthy cynomolgus monkeys aged 15-20 years with mean (+/-SD) blood lead levels of 10 +/- 3 micrograms/dL (range 6-20 micrograms/dL, n = 4) and 56 +/- 49 micrograms/dL (range 22-148 micrograms/dL, n = 7) compared to a reference group with blood lead levels < 1.0 microgram/dL (n = 8). Blood and semen samples were collected once from each monkey in five different months. Serum testosterone levels were determined by radioimmunoassay, and lead effects on chromatin structure were analyzed by flow cytometry. There were no effects of treatment on circulating levels of testosterone or parameters of semen quality such as sperm count, viability, motility, and morphology. However, significant (p < 0.03) treatment-related effects were seen on SD alpha t values in the treated vs control animals. Group comparisons also revealed that the effects of chronic lead exposure were significant (p < 0.05) for both lead-exposed groups compared to the reference group. We conclude that chronic lead exposure alters sperm chromatin structure at blood lead levels relevant to the human population and in the absence of effects on endocrine function and traditional measures of semen quality.