Human-relevant co-exposure to 6:2 Cl-PFESA and PFHxS impairs sperm motility and blood-testis barrier integrity in male mice: Evaluation of combined effects

Our recent large-scale population study demonstrated that several per- and polyfluoroalkyl substances (PFAS) are potential risk factors for sperm quality—with perfluorohexane sulfonate (PFHxS) and 6:2 chlorinated polyfluorinated ether sulfonate (6:2 Cl-PFESA) emerging as the strongest effect contributors to asthenospermia, yet their causal relationships remain unclear. Here, we provide in vivo experimental evidence and evaluation of the combined effects of 6:2 Cl-PFESA and PFHxS under human-relevant exposure. Male ICR mice were orally exposed to each compound alone or in combination for 35 days, covering one full spermatogenic cycle. Both single and combined exposures were associated with alterations of the male reproductive axis, including reduced serum testosterone and elevations in the gonadotropins luteinising hormone (LH) and follicle-stimulating hormone (FSH), and in sex hormone-binding globulin (SHBG). Testicular injury included disturbed seminiferous architecture, decreased sperm motility, and increased germ-cell apoptosis. Transcriptomics highlighted pathways related to cell adhesion, junctional integrity, and apoptosis, and Western blotting and TUNEL confirmed blood-testis barrier (BTB) protein disruption and increased germ-cell apoptosis. Toxic potency differed by endpoint, with endpoint-specific patterns across endocrine, BTB, and motility outcomes. Combined-effect analysis identified a positive non-additive interaction for LH, whereas most BTB-associated proteins showed no statistically significant interaction despite endpoint-specific deviations from the concentration-addition expectation. Collectively, these findings indicate that human-relevant co-exposure to 6:2 Cl-PFESA and PFHxS is associated with asthenospermia-related sperm and testicular alterations. The converging phenotypic, molecular, and functional findings support BTB impairment and germ-cell apoptosis as plausible contributing processes, yet the precise mechanisms still need further investigation.