Common ‘Forever Chemical’ PFNA Found to Ignite Gut Inflammation at Tiny Doses

A new study has revealed that perfluorononanoic acid, or PFNA, one of the most frequently detected ‘forever chemicals’ in human blood, can dramatically worsen intestinal inflammation at doses far below those typically used in laboratory toxicology. The research, published in the Journal of Advanced Research by a team at Zhejiang University, identifies a previously unrecognized molecular pathway through which this ubiquitous pollutant amplifies inflammatory bowel disease, and points to a natural plant compound that may counteract the damage.

PFAS compounds, often called forever chemicals because of their extraordinary persistence in the environment and the human body, have been used for decades in nonstick coatings, water repellents, and industrial processes. When the older compounds PFOA and PFOS were phased out following widespread reports of health hazards, PFNA and its chemical cousin PFDA were adopted as primary substitutes because of their similar physicochemical properties. These replacements are now routinely detected in surface waters, sediments, and even Arctic soils, and they rank among the most commonly found PFAS congeners in human serum samples worldwide.

The Zhejiang University team, led by Kean Lu, Zhenyan Cui, Yihua Wu, and Dajing Xia, set out to address a critical gap in environmental health science. Most previous studies of PFAS toxicity employed doses far exceeding the levels that humans actually encounter in daily life. Because epidemiological research has already linked PFAS exposure to elevated risk of inflammatory bowel disease, or IBD, and because IBD incidence is rising rapidly in newly industrialized regions, understanding how environmentally realistic exposures translate into gut inflammation has become a pressing scientific priority.

The researchers compared three PFAS compounds, PFOA, PFNA, and PFDA, in mouse peritoneal macrophages, the immune cells that act as central effectors in the inflammatory cascade of IBD. The results were strikingly compound-specific. PFOA showed no significant effect on the inflammatory cytokines IL-1β and IL-18 across the entire tested concentration range. PFDA produced a more general increase in inflammatory signaling at higher concentrations. But PFNA stood out: at remarkably low concentrations of 0.1 to 1 micromolar, it drove dose-dependent increases in both IL-1β and IL-18, the signature effector cytokines of the NLRP3 inflammasome, a multiprotein complex widely recognized as a central driver of IBD progression.

Delving into the mechanism, the team discovered that low-dose PFNA selectively activated the noncanonical NLRP3 inflammasome pathway, which depends on the enzyme caspase-11 rather than the more commonly studied caspase-1. Within the low concentration range, PFNA dose-dependently increased caspase-11 expression and triggered the downstream cascade: upregulation of NLRP3, cleavage of caspase-1, and activation of gasdermin D, the protein that forms pores in cell membranes during inflammatory cell death. Notably, at high concentrations PFNA shifted behavior entirely, activating caspase-8 and caspase-3 and pushing cells toward apoptosis instead, a biphasic dose-response pattern the authors suggest may reflect crosstalk between inflammatory and apoptotic caspases or a hormetic effect of PFAS compounds.

To confirm that caspase-11 was genuinely the upstream driver, the researchers silenced the caspase-11 gene with small interfering RNAs. Knockdown significantly suppressed the entire PFNA-induced inflammatory program, reducing NLRP3, cleaved caspase-1, gasdermin D, and the mature forms of IL-1β and IL-18, while restoring cell viability. A pancaspase inhibitor, Z-VAD-FMK, produced similar protection. Molecular docking simulations then suggested a physical basis for the interaction: PFNA appeared to bind within the pro-caspase-11 protein, forming a hydrogen bond with the arginine residue ARG-360, with a calculated binding energy of −8.40 kilocalories per mole. Molecular dynamics simulations over 100 nanoseconds showed the PFNA–caspase-11 complex remained structurally stable, and more stable than the corresponding PFNA–caspase-1 complex, supporting a preferential association with caspase-11. The authors caution, however, that these computational findings are preliminary and require direct experimental validation.

The relevance to human health hinges on dose. Population studies indicate that PFAS concentrations in human serum range from 20 nanomolar to 215 micromolar, with PFNA levels reaching up to 352 nanomolar, squarely within the range where the study observed maximal inflammasome activation. Even more alarming, recent work published in Nature Microbiology demonstrated that human gut bacteria efficiently bioaccumulate PFNA, achieving intracellular concentrations 25- to 60-fold higher than environmental exposure levels. This suggests the gut microbiome may act as a reservoir, concentrating the chemical locally and enhancing its bioavailability to the intestinal lining, meaning that local gut concentrations could substantially exceed both environmental background and serum levels.

To test the findings in living animals, the team established a chronic colitis model in mice using three cycles of DSS treatment, a protocol that mimics the relapsing-remitting course of human IBD. Mice received PFNA orally at 1.01 micrograms per kilogram per day for 24 days, a dose derived from the tolerable daily intake proposed in human risk assessments. The results were unambiguous. PFNA-exposed mice showed significantly shortened colons, extensive inflammatory cell infiltration, crypt loss, and elevated histopathological scores. Colon tissue displayed upregulated pro-caspase-11, cleaved caspase-11, and the full downstream NLRP3 pathway, while serum levels of IL-1β and IL-18 rose sharply, confirming systemic inflammasome-mediated cytokine release. Immunofluorescence revealed increased numbers of F4/80-positive macrophages carrying active cleaved caspase-1, directly implicating these cells in the pathology.

Crucially, the study also identified a potential intervention. Myricetin, a natural flavonoid found in berries, tea, and various fruits and vegetables, was administered to a subset of mice starting on day 9, a delayed protocol designed to model how patients begin treatment after disease onset. Myricetin treatment significantly inhibited PFNA-induced colon shortening, ameliorated tissue damage, reduced inflammatory infiltration, and lowered serum cytokine levels. At the molecular level, it suppressed caspase-11 expression and cleavage along with the entire downstream NLRP3 cascade. In vitro, pretreating macrophages with myricetin before PFNA exposure similarly restored cell viability and dampened inflammatory signaling. The authors note that myricetin has previously been shown to inhibit NLRP3 activation through modulation of ASC and NLRP3 ubiquitination, and to suppress upstream NF-κB signaling and oxidative stress, though the present data cannot yet distinguish whether it directly targets caspase-11 or acts through these upstream pathways.

The researchers frame their findings within an adverse outcome pathway-like framework, linking a molecular initiating event, the interaction of PFNA with caspase-11, through the key event of NLRP3 inflammasome activation, to the adverse outcome of aggravated intestinal inflammation. This structure provides a template for investigating other PFAS members, whose mechanisms appear to differ: the team’s earlier work showed that PFDA exacerbates IBD through the cGAS/STING/NF-κB axis instead. The study does carry limitations. Only male mice were included, so conclusions may not generalize to females given known sex differences in PFAS toxicokinetics, and antibody limitations prevented direct visualization of caspase-11 localization in colon tissue. Nevertheless, by demonstrating that a substitute forever chemical can inflame the gut at doses people actually encounter, and by pointing to a dietary flavonoid as a possible shield, the work adds urgency to PFAS risk assessment and opens a concrete avenue for protecting the millions of people living with inflammatory bowel disease in an increasingly contaminated world.

Subject of Research: How low-dose PFNA exposure exacerbates intestinal inflammation through caspase-11-dependent noncanonical NLRP3 inflammasome activation in macrophages

Article Title: Low-dose PFNA exposure exacerbates intestinal inflammation via caspase-11-dependent noncanonical NLRP3 inflammasome activation in macrophages

Article References: Lu, K., Cui, Z., Fei, X., Zhang, J., Fang, S., Wang, Y., Chen, Y., Wu, Y., & Xia, D. (2026). Low-dose PFNA exposure exacerbates intestinal inflammation via caspase-11-dependent noncanonical NLRP3 inflammasome activation in macrophages. Journal of Advanced Research. https://doi.org/10.1016/j.jare.2026.09.005

Image Credits: AI Generated

DOI: 10.1016/j.jare.2026.09.005

Keywords: PFAS, PFNA, forever chemicals, inflammatory bowel disease, NLRP3 inflammasome, caspase-11, macrophages, myricetin, intestinal inflammation, environmental toxicology, gut microbiome, colitis