HFPOs were engineered with oxygen atoms inserted into their fluorinated carbon chains, a modification intended to make the molecules more degradable and less persistent than PFOA and PFOS. That promise has not held up. Rodent studies have shown that HFPO-dimer acid, better known as GenX, lingers in blood and liver with extended half-lives and crosses the placenta, while HFPO-trimer acid is absorbed rapidly, excreted slowly and accumulates even more strongly than PFOA. Human biomonitoring has confirmed the concern: residents of North Carolina exposed through contaminated drinking water carry HFPO-DA in their blood, and people living near fluorochemical plants in China have been found with HFPO-TA in their serum at concentrations reaching hundreds of nanograms per milliliter. Animal experiments have linked these compounds to liver mitochondrial disruption, cardiovascular toxicity in zebrafish embryos, damage to the blood-testis barrier and impaired spermatogenesis, but whether they directly compromise human sperm function remained an open question until now.

To answer it, the team obtained semen samples from thirty healthy donors meeting World Health Organization criteria for normal sperm, purified the cells and exposed them to graded concentrations of HFPO-DA, HFPO-TeA and HFPO-TA under physiological conditions. Computer-assisted sperm analysis revealed a consistent pattern: total and progressive motility declined significantly within hours of exposure across all three compounds, and viability dropped at the higher doses. The effects were not limited to gross movement. When the researchers assessed the acrosome reaction, the explosive release of enzymes that allows sperm to penetrate the egg’s outer coat, they found that HFPO-TA suppressed both spontaneous and progesterone-triggered reactions in a dose-dependent manner, while HFPO-TeA and HFPO-DA interfered with the progesterone-induced response. A viscous-medium penetration assay, a standard proxy for the hyperactivated swimming needed to navigate the female reproductive tract, showed sharply reduced penetration capacity, and high-speed imaging of flagellar waveforms revealed blunted beat amplitude and disrupted asymmetric beating patterns characteristic of capacitated sperm.

Transmission electron microscopy then exposed the structural carnage behind these functional failures. Sperm exposed for two hours to mid-range concentrations of the compounds showed swollen and disintegrating acrosomal membranes, misaligned mitochondria in the neck region, fragmented mitochondrial cristae and vacuolization of the mitochondrial sheath that wraps the flagellum. Even more striking, all three HFPOs disorganized the peripheral dense fibers, and HFPO-TeA and HFPO-TA severely scrambled the axoneme itself, the elegant ‘9+2’ array of microtubules that powers flagellar beating. Because mature sperm are transcriptionally silent and carry minimal DNA repair machinery or antioxidant defenses, such structural damage cannot be repaired by the cell; it accumulates until function collapses.

The functional consequences of that damage were quantified with fluorescent probes. Total intracellular reactive oxygen species rose to 150 to 170 percent of control levels after exposure to medium concentrations of HFPO-TeA and HFPO-TA, but the mitochondrial compartment fared far worse: mitochondrial superoxide climbed to 1.7 to 2.0 times control values. Mitochondrial membrane potential, the electrical gradient that drives ATP synthesis, depolarized by a factor of 1.4 to 1.6, and HFPO-TA triggered a 2.1-fold collapse in sperm ATP production. The team then turned to Mitoquinone, or MitoQ, an antioxidant that accumulates specifically inside mitochondria. Pretreating sperm with 100 nanomolar MitoQ significantly blunted the losses in total and progressive motility, reduced both total and mitochondrial ROS, and preserved membrane potential, providing pharmacological proof that mitochondrial oxidative stress sits at the heart of the toxicity.

Calcium emerged as the other half of the story. Using the fluorescent indicator Fluo-4 AM and real-time recording, the researchers observed that HFPO-DA, HFPO-TeA and HFPO-TA each triggered a rapid transient surge of intracellular calcium within seconds of exposure, followed by stabilization near baseline. When sperm were pretreated with NNC 55-0396, a CatSper channel inhibitor, the HFPO-induced calcium peaks were markedly attenuated, identifying the sperm-specific CatSper channel as the gateway for the influx. The parallels with progesterone, the physiological activator of CatSper in the female tract, were unmistakable. HFPO exposure alone produced calcium flux patterns resembling progesterone stimulation, yet pre-exposure to the chemicals suppressed subsequent progesterone-induced calcium responses in a concentration-dependent fashion. When HFPOs and progesterone were co-administered, the combined calcium peaks exceeded those of HFPO alone but fell short of the sum of the individual responses, suggesting the compounds act as partial agonists at CatSper, competing with progesterone and desensitizing sperm to its signal.

Time-resolved imaging revealed the sequence linking calcium to mitochondrial collapse. Cytosolic calcium peaked within roughly twenty seconds of HFPO stimulation, while mitochondrial calcium, tracked with a targeted probe, began rising within about eighty seconds and then accumulated progressively rather than stabilizing. This biphasic pattern, an acute transient followed by sustained overload, indicates that HFPOs first open the CatSper floodgate and that the resulting calcium is then shunted into mitochondria through the mitochondrial calcium uniporter, overwhelming the organelles. Calcium overload in mitochondria is a well-known trigger for excessive ROS generation, membrane depolarization and apoptotic signaling, and the new data place human sperm squarely within that pathological cascade.

To map the molecular fingerprints of each homologue, the team deployed integrated metabolomics and proteomics. Untargeted metabolomic profiling identified hundreds of differentially regulated metabolites per compound and revealed distinct pathway disruptions: HFPO-DA perturbed phenylalanine, amino sugar and sphingolipid metabolism; HFPO-TeA altered alanine, aspartate and glutamate metabolism, primarily through L-aspartic acid; and HFPO-TA skewed glycerophospholipid metabolism and arginine biosynthesis, mainly through glutamic acid. Quantitative proteomics, capturing more than 7,400 proteins, showed that all three compounds converged on calcium signaling, sphingolipid signaling, apoptosis and fatty acid metabolism, while each left its own signature: HFPO-DA uniquely affected nitrogen metabolism and oxidative phosphorylation, HFPO-TeA selectively perturbed carbon metabolism, and HFPO-TA predominantly impacted cell adhesion molecules and the TCA cycle. These compound-specific profiles explain why the three homologues showed divergent toxic potencies despite damaging the same fundamental sperm processes.

The authors are careful to frame the study’s scope. The experimental concentrations, spanning 5 to 500 micromolar for HFPO-DA and 5 to 100 micromolar for HFPO-TA and HFPO-TeA, exceed the highest reported human serum levels by roughly six- to one-thousand-fold, and the in vitro acute exposure model cannot replicate the chronic, low-dose, cumulative exposure typical of real-world contamination. The proposed competitive interaction between HFPOs and progesterone at CatSper also remains inferential until direct binding studies, patch-clamp recordings or molecular docking can be performed. Nevertheless, the mechanistic chain the study establishes, from CatSper-mediated calcium influx to mitochondrial calcium overload, oxidative stress, ATP depletion and loss of motility and fertilization competence, offers a compelling explanation for epidemiological findings linking PFAS body burdens to reduced sperm density, motility and testosterone in populations across Denmark, Italy and China. As HFPOs continue to accumulate in water, wildlife and human blood worldwide, the research adds male fertility to the growing list of health risks posed by the replacements for the forever chemicals they were meant to replace.

Subject of Research: Toxic effects of HFPO perfluoroalkyl substitutes on human sperm calcium signaling and mitochondrial function

Article Title: HFPO homologue exposure impairs human sperm function via calcium dyshomeostasis and mitochondrial dysfunction

Article References: Le, M., Xue, J., Ding, J., Wu, L., Yuan, Y., Zheng, L., Hu, L., & Zhang, D. (2026). HFPO homologue exposure impairs human sperm function via calcium dyshomeostasis and mitochondrial dysfunction. Journal of Advanced Research. https://doi.org/10.1016/j.jare.2026.10.013

Image Credits: AI Generated

DOI: 10.1016/j.jare.2026.10.013

Keywords: PFAS, HFPO, GenX, male fertility, sperm motility, CatSper, calcium signaling, mitochondrial dysfunction, reactive oxygen species, acrosome reaction, reproductive toxicology, endocrine disruptors