The involvements of intracellular basal calcium and membrane potential in para-phenylenediamine-impaired sperm function

Background: Para-phenylenediamine (PPD) is a crystalline solid that belongs to the aromatic amine group, widely used in the manufacturing of various dyes. PPD exhibits toxic effects on female hormone stability, ovarian function, and embryo development. Although studies have shown that PPD exposure can damage oocyte quality in female mice, research on its effects on male reproductive capability, particularly on human sperm quality and function, is limited. The purpose of this study was to investigate the effect of PPD on male semen and explore its mechanism.

Methods: Computer-assisted sperm analysis system and eosin-aniline black method were conducted to detect sperm motility and viability; sperm function was analyzed by tyrosine phosphorylation immunofluorescence staining, sperm mucus penetration capacity assay, and sperm acrosome reaction incidence; reactive oxygen species (ROS) and DNA damage were analyzed by specific kits; the transient calcium, intracellular basal calcium, and membrane potential were detected by multi-functional microplate reader after Fluo-4, Fura-10 AM and DiSC3(5) staining.

Results: PPD was shown to have a dose-dependent impact on both the motility and viability of human sperm. Furthermore, the ability of sperm to capacitate, penetrate viscous substances, and undergo acrosome reaction exhibited significant impairments in various aspects of sperm function. The impact of PPD on sperm is comparable to its effects on other bodily systems. Spermatozoon toxicity caused by PPD was found to be associated with increased levels of ROS and DNA damage, which indicated that oxidative stress plays a role in this process. Although the transient calcium response to PPD and progesterone was not disturbed, intracellular basal calcium was increased and membrane potential was depolarized after exposure of human sperm to PPD.

Conclusions: In summary, our findings suggest that increased intracellular basal calcium, hyperpolarization in the membrane potential of damaged sperm, and oxidative stress might be the underlying reasons for the decline in semen quality and dysfunction of sperm following PPD exposure.