Long-term effects of triptolide on spermatogenesis, epididymal sperm function, and fertility in male rats

Prior studies had suggested that triptolide, a diterpene triepoxide isolate d from a Chinese medicinal plant, might be an attractive candidate as a pos t-testicular male contraceptive agent. Despite the promise that triptolide would not affect testis function, nagging concerns remained that a delayed onset of testicular effect might exist. The objectives of this study were t o assess the effects of relatively longer treatment duration of triptolide on fertility, spermatogenesis, and epididymal sperm pathophysiology; and to evaluate the reversibility of these effects after the cessation of treatme nt. Adult male Sprague-Dawley rats were fed daily with either 30% gum acaci a as a vehicle control (n = 12) or 100 mu g/kg body weight (BW) of triptoli de for 82 days (n = 12) followed by a recovery period of up to 14 weeks (n = 6). At the end of the treatment period, all rats treated with triptolide were sterile. Cauda epididymal sperm content decreased by 84.8% and sperm m otility was reduced to zero. In addition, virtually all cauda epididymal sp erm in the triptolide-treated group exhibited severe structural abnormaliti es. The most striking changes observed were head-tail separation, premature chromatin decondensation of sperm nuclei, a complete absence of the plasma membrane of the entire middle and principle pieces, disorganization of the mitochondrial sheath, and aggregation of many sperm tails. Longer treatmen t duration of triptolide also affected spermatogenesis, with marked variabi lity in the response of individual animals. The degree of damage ranged fro m apparently normal-looking seminiferous tubules to flattened seminiferous epithelium lined by a single layer of cells consisting of Sertoli cells and a few spermatogonia. Affected tubules exhibited intraepithelial vacuoles o f varying sizes, multinucleated giant cells, germ cell exfoliation, and tub ular atrophy. Recovery occurred as early as 6 weeks after cessation of trea tment. By 14 weeks, 4 out of 6 triptolide-treated males were fertile and th e females that were impregnated by 3 out of 4 triptolide-treated male rats produced apparently normal litters. These results suggest that triptolide h as 2 phenotypic effects on mature and maturing germ cells. The first action appears earlier and manifests mainly in epididymal sperm, The second actio n presumably is directly on germ cells in testis and causes a variable impa irment of spermatogenesis that may not be completely reversible. It is uncl ear if the earlier effect is a delayed manifestation of subtle testicular i njury or post-testicular action.