Toxic potential of dietary genistein isoflavone and beta-lapachone on capacitation and acrosome reaction of epididymal spermatozoa.

We determined if acrosomal reaction was influenced by exposure of sperm cells to two dietary phytochemicals, genistein isoflavone and beta-lapachone, using the rat model. Spermatozoa were capacitated in capacitating medium with or without genistein isoflavone and beta-lapachone, and the percentage of posttreatment acrosome reaction compared with controls was assessed with two fluorescent probes, chlortetracycline (CTC) and fluorescein isothiocyanate- Pisum sativum ag-glutinin conjugate (FITC-PSA). Spermatozoa were permeabilized in ethanol and labeled with the FITC-PSA or CTC to determine the acrosome status. The results revealed that calcium ionophore could induce acrosome reaction in spermatozoa and that acrosome-reacted sperm cells showed obvious darkness in the head region, whereas acrosome-intact sperm displayed bright fluorescence over the entire sperm head. The basic response and pattern of acrosome reaction status were significantly similar in both CTC and FITC assays and in both treatment (genistein and beta-lapachone) groups. It was observed that higher doses of both genistein and beta-lapachone significantly suppressed acrosome reaction and that this inhibitory effect was both dose- and time-dependent. It was stipulated that the observed genistein inhibition of acrosome reaction could be due to suppression of protein kinase C, and that beta-lapachone could inhibit acrosome reaction through direct cytotoxic effects on sperm cell membrane at higher doses. However, light microscopic examination indicated that both phytochemicals had no significant effect on sperm morphology. It is concluded that, in view of the fact that acrosome reaction is a physiological prerequisite for fertilization of most mammalian eggs, both genistein and beta-lapachone could potentially suppress male fertility via suppression of acrosome reaction at higher doses, but could enhance fertility by promoting acrosome reaction at lower doses. This bimodal mode of action of both phytochemicals could offer a potentially new dimension in the search for causes of male infertility and possibly for male contraceptive development.