Kinetics of the inhibition and recovery of spermatogenesis induced by treatment with WIN 18,446, a male contraceptive, in mice.

Background: Retinoic acid (RA) is essential for spermatogenesis. Genetic deletion of the retinoic acid synthesizing enzymes, Aldh1a1/1a2, in the testes causes infertility in mice. An inhibitor of the ALDH1A1/1A2 enzymes, WIN 18,446 reversibly inhibit spermatogenesis and is a promising approach to male contraception. Previously we reported that a 4-week treatment of WIN 18,446 inhibits spermatogenesis and 9-week recovery from treatment normalized fertility of treated mice. However, the precise kinetics of this process has not been studied.

Objectives: To extend our knowledge of kinetics of ALDH1A inhibition, we studied the changes in the seminiferous epithelium and retinoic acid synthesis capacity of the testes during 4 weeks of WIN 18,446 treatment and during 9 weeks of recovery.

Materials and methods: Male mice were fed a diet containing WIN 18,446 for 4 weeks followed by a normal diet for up to 8 weeks. Frequently, during the treatment and recovery period, five mice were euthanized, and testes were analyzed for testicular histology and retinoic acid synthesis capacity and compared with controls.

Results: Testes weights progressively decreased, and the seminiferous epithelium deteriorated over the time with WIN 18,446 treatment and returned to normal after 8 weeks. Retinoic acid synthesis capacity was significantly inhibited 3 days after the WIN 18,446 treatment and recovered after 7 days of no treatment. After 4 weeks of treatment, complete blockage of spermatogenesis with only spermatogonia and Sertoli cells was observed. The RA biosynthetic capacity of the testes was significantly reduced before the disruption of spermatogenesis was observed and recovered prior to the reinitiation of spermatogonial differentiation.

Conclusions: Effects of ALDH1A inhibition on spermatogenesis are reversible. Our observation that strong inhibition of ALDH1A disrupts the seminiferous epithelium prior to the completion of a full cycle of spermatogenesis suggests that episodic inhibition of ALDH1A may function as a male contraceptive.