In vitro exposure to metformin activates human spermatozoa at therapeutically relevant concentrations

BACKGROUND: Metformin, a drug used to treat type 2 diabetes, has gained attention for its multiple therapeutic applications. However, little is known about its effects on human sperm function at therapeutically relevant concentration. OBJECTIVES: The aim of this study was to elucidate the in vitro actions of metformin on human sperm function and explore the underlying mechanism of any effects. MATERIALS AND METHODS: Human ejaculated spermatozoa were treated with therapeutically relevant concentrations (0.25, 5, 10, 20, 40, and 80 microM) of metformin in vitro. Fertilization-essential functions of spermatozoa were examined, including viability, motility, capacitation, acrosome reaction, hyperactivation, and penetration ability. The signaling pathways mediated by 5'-AMP-activated protein kinase (AMPK), intracellular calcium concentration ([Ca(2+) ]i ), and tyrosine phosphorylation of spermatozoa were also measured. RESULTS: Although metformin did not affect sperm viability, motility, and [Ca(2+) ]i , it significantly increased the percentages of capacitated spermatozoa, acrosomal-reacted spermatozoa, and hyperactivated spermatozoa as well as penetration ability of human spermatozoa at the concentrations of 40 and 80 microM (P < .05). These concentrations of metformin also elevated the levels of phosphorylated AMPK and tyrosine phosphorylation in human spermatozoa. In addition, activation of AMPK by A769662 (an AMPK activator) had similar effects to metformin on human spermatozoa, while inhibition of AMPK by Compound C (an AMPK inhibitor) suppressed the enhancement of metformin on human spermatozoa. CONCLUSION: Our findings indicate that metformin activates human sperm function through an AMPK-related mechanism which increases tyrosine phosphorylation at therapeutically relevant concentrations, thereby suggesting its improvement on human sperm function when treating subfertile males of type 2 diabetes.