Emodin inhibits human sperm functions by reducing sperm [Ca2+]i and tyrosine phosphorylation

Emodin, a bioactive anthraquinone widely used in Chinese traditional medicine, disrupts mouse testicular gene expression in vivo. In this study, we investigated the toxicity of emodin to human sperm in vitro. Different doses of emodin (25, 50, 100, 200 and 400 μM) were applied to ejaculated human sperm. The results indicated that 100, 200 and 400 μM emodin significantly inhibited the total motility, progressive motility and linear velocity of human sperm. In addition, sperm's ability to penetrate viscous medium together with progesterone induced capacitation and acrosome reaction was also adversely affected by emodin. In contrast, emodin did not affect sperm viability. Furthermore, intracellular Ca2+ concentration ([Ca2+]i) and tyrosine phosphorylation, which serve as key regulators of sperm function, were dose-dependently reduced by emodin (50-400 μM). These results suggest that emodin inhibits human sperm functions by reducing sperm [Ca2+]i and suppressing tyrosine phosphorylation in vitro.