Pyroptosis is not an ordinary death. It is a programmed, highly inflammatory form of cell suicide that serves as an alarm system for the immune system. It is triggered when pathogen-associated or danger-associated molecular patterns are detected in the cytosol, the fluid interior of the cell. Upon sensing these threats, caspase-1 in humans and mice, along with caspase-4, caspase-5 in humans and caspase-11 in mice, cleaves a protein called gasdermin D, or GSDMD. This cleavage releases the N-terminal fragment of GSDMD, which migrates to the cell membrane and oligomerizes into pores. These pores disrupt the osmotic balance of the cell, allowing water to rush in, causing the cell to swell, burst and spill its inflammatory contents, including the potent cytokine interleukin-1β, into the surrounding tissue.

While this fiery demise is useful for containing infection, overactive pyroptosis is a driver of disease. Excessive pyroptotic cell death has been implicated in atherosclerosis, arthritis, Alzheimer’s disease, HIV and various types of cancer. This has made the inflammatory caspases attractive drug targets, and caspase inhibitors have captured the attention of scientists and clinicians alike. Yet developing safe and clinically effective caspase inhibitors has proven remarkably difficult. The central problem is selectivity. Caspases are a family of proteases with overlapping substrate preferences, which makes it difficult to inhibit one member without affecting others. Many existing inhibitors block caspases involved in both pyroptosis and apoptosis, the quiet, non-inflammatory form of cell death that is essential for development and immunity. Worse, inhibiting caspase-8 can sensitize cells to necroptosis, another damaging form of cell death, potentially trading one pathology for another.

To escape this trap, Groborz and colleagues took a rational, chemistry-driven approach. They exploited the known substrate preferences of individual caspases to synthesize a library of roughly one hundred tetrapeptides, each attached to an acyloxymethyl ketone, or AOMK, group. These reactive chemical groups allow the tetrapeptides to bind covalently and irreversibly to the active sites of their target caspases, ensuring durable inhibition. From this library, several candidates emerged that suppressed cell death driven by caspase-1, caspase-4 and caspase-11 while leaving staurosporine-induced apoptosis untouched. One of the most potent, named KGR-3, stood out as a strong inhibitor of caspase-1 and caspase-4.

The detailed characterization of KGR-3 revealed just how precisely it worked. The compound blocked pyroptosis by preventing the cleavage of GSDMD, thereby stopping pore formation at its source. It also attenuated the release of interleukin-1β and lactate dehydrogenase, a standard marker of membrane rupture, in response to activation of the NLRP3 and NLRP1 inflammasomes, the multiprotein complexes that activate caspase-1. Crucially, KGR-3 did not interfere with hallmarks of apoptosis such as caspase-1-induced blebbing or caspase-3 cleavage, nor did it affect necrosis triggered by listeriolysin O, a bacterial toxin. Cells treated with KGR-3 not only avoided death; their swelling and lysis were suppressed and they continued to grow and divide. The inhibitor appeared to grant cells a genuine reprieve rather than merely delaying the inevitable.

Yet a puzzling observation threatened to undermine the whole story. KGR-3 and its chemical siblings showed limited permeability in healthy cells, meaning they should not have been able to reach the intracellular caspases they so effectively inhibited. This paradox led the authors to a bold hypothesis: pyroptosis itself facilitates inhibitor uptake. Like a Trojan horse being wheeled through the gates of a besieged city, the caspase inhibitors were exploiting the very pores formed during pyroptosis to slip inside and reach the caspases driving the process. To test this idea, the researchers used propidium iodide and YOYO-1, two small fluorescent molecules that normally cannot cross intact membranes. Both entered cells in a GSDMD-dependent manner, providing strong evidence that gasdermin pores admit small molecules from the outside.

The story became even more sophisticated when the researchers examined what happened to the membrane damage inflicted along the way. In KGR-3-treated cells, GSDMD-induced membrane injury was repaired by the endosomal sorting complexes required for transport, known as the ESCRT machinery. This repair system is a conserved cellular mechanism that seals small membrane wounds. When the researchers expressed dominant-negative versions of the ESCRT proteins VPS4A and CHMP3, KGR-3 lost its protective effect, and pyroptosis proceeded. This finding challenges the simple binary view of pyroptosis as an irreversible commitment to death. Instead, it suggests a pharmacologically accessible window between the initiation of pyroptosis and final lysis, a period during which GSDMD pores disrupt the membrane enough to admit the drug, but not so extensively that repair by ESCRT becomes impossible. Recent research has independently highlighted the reversibility of GSDMD pore formation and shown that ESCRT can limit pyroptosis and cytokine secretion after inflammasome activation, lending further support to this model.

There is also an elegant pharmacological lesson hidden in the poor permeability of these compounds. In traditional drug development, limited cell permeability is considered a weakness. Here, it becomes a feature. Because the inhibitors can only enter cells whose membranes have already been breached by gasdermin pores, they are restricted to unhealthy cells, those actively undergoing pyroptosis, and are excluded from healthy neighbors. This built-in targeting mechanism could limit the off-target effects that have plagued broader caspase inhibitors, offering a new design principle: drugs need not always be membrane permeable if the disease state itself creates the doorway. The study thus overturns the conventional assumption that any drug aimed at an intracellular target must be able to cross an intact plasma membrane.

Translating the concept into animals required further chemical refinement. KGR-3 itself showed limited efficacy in vivo, but another tetrapeptide from the library, KGR-53, proved more promising. It was selected for animal testing because of its potent inhibition of caspase-11, a key mediator of endotoxic shock induced by lipopolysaccharide in mice. Because negatively charged compounds are transported inefficiently through GSDMD pores, the team designed a derivative called KGR-53P that lacks a negative charge. This optimized compound inhibited GSDMD cleavage and blocked the caspase-1- and caspase-11-dependent secretion of interleukin-1β and interleukin-18, while leaving both intrinsic and extrinsic apoptosis intact. In a mouse model of endotoxic shock, a condition driven by runaway caspase-11 activity, this selectivity could prove decisive.

The work is not without caveats, as Henry and O’Neill note in their highlight. First, the entry of KGR-3 through GSDMD pores has not been directly visualized. Although the GSDMD-dependent uptake of propidium iodide and YOYO-1 strongly implies that the pores serve as entry routes for small molecules, attempts to image KGR-3 itself failed because fluorescent tagging compromised the compound’s potency, permeability or toxicity. Second, KGR-53 showed evidence of liver toxicity in vivo, and it remains unclear whether this toxicity stems from the AOMK chemistry, an off-target effect or an entirely different mechanism. These open questions will shape the next phase of research. Even so, the conceptual advance is considerable. If the window between pyroptosis initiation and lysis can be reliably exploited, a new class of anti-inflammatory drugs could emerge that intervene only where inflammation is already burning, leaving healthy tissue untouched. The gates that pyroptosis opens may, in the end, become the route by which medicine tames it.

Subject of Research: Selective inflammatory caspase inhibitors that enter cells through gasdermin D pores to inhibit pyroptosis

Article Title: A Trojan horse story: does pyroptosis open the gates to its own inhibition?

Article References: Henry, Ó. C., & O’Neill, L. A. J. (2026). A Trojan horse story: does pyroptosis open the gates to its own inhibition?. Cell Research. https://doi.org/10.1038/s41422-026-01302-z

Image Credits: AI Generated

DOI: 10.1038/s41422-026-01302-z

Keywords: pyroptosis, gasdermin D, inflammatory caspases, caspase-1, caspase-11, GSDMD, ESCRT, inflammasome, cell death, innate immunity, drug design, inflammation

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