Altered toxicological endpoints in humans from common quaternary ammonium compound disinfectant exposure

Humans are frequently exposed to Quaternary Ammonium Compounds (QACs). QACs are ubiquitously used in medical settings, restaurants, and homes as cleaners and disinfectants. Despite their prevalence, nothing is known about the health effects associated with chronic low-level exposure. Chronic QAC toxicity, only recently identified in mice, resulted in developmental, reproductive, and immune dysfunction. Cell based studies indicate increased inflammation, decreased mitochondrial function, and disruption of cholesterol synthesis. If these findings translate to human toxicity, multiple physiological processes could be affected. This study tested whether QAC concentrations could be detected in the blood of 43 human volunteers, and whether QAC concentrations influenced markers of inflammation, mitochondrial function, and cholesterol synthesis. QAC concentrations were detected in 80 % of study participants. Blood QACs were associated with increase in inflammatory cytokines, decreased mitochondrial function, and disruption of cholesterol homeostasis in a dose dependent manner. This is the first study to measure QACs in human blood, and also the first to demonstrate statistically significant relationships between blood QAC and meaningful health related biomarkers. Additionally, the results are timely in light of the increased QAC disinfectant exposure occurring due to the SARS-CoV-2 pandemic.

MAIN FINDINGS

This study found that 80 % of study participants contained QACs in their blood; and that markers of inflammation, mitochondrial function, and sterol homeostasis varied with blood QAC concentration.

Oligomerized CARD16 promotes caspase-1 assembly and IL-1β processing

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CARD16 is the most abundant CARD-only protein in hematopoietic cells.

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Unlike CARD17, CARD16 oligomerizes to form a filament-like structure.

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The filament-like structure formed by CARD16 promotes caspase 1 (CASP1) assembly.

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CASP1-dependent IL-1β processing is enhanced by CARD16.

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CARD16 colocalizes in ASC-speck by interacting with ASC.

Increasing evidence indicates that caspase recruitment domain (CARD)-mediated caspase-1 (CASP1) assembly is an essential process for its activation and subsequent interleukin (IL)-1β release, leading to the initiation of inflammation. Both CARD16 and CARD17 were previously reported as inhibitory homologs of CASP1; however, their molecular function remains unclear. Here, we identified that oligomerization activity allows CARD16 to function as a CASP1 activator. We investigated the molecular characteristics of CARD16 and CARD17 in transiently transfected HeLa cells. Although both CARD16 and CARD17 interacted with CASP1CARD, only CARD16 formed a homo-oligomer. Oligomerized CARD16 formed a filament-like structure with CASP1CARD and a speck with apoptosis-associated speck-like protein containing a CARD. A filament-like structure formed by CARD16 promoted CASP1 filament assembly and IL-1β release. In contrast, CARD17 did not form a homo-oligomer or filaments and inhibited CASP1-dependent IL-1β release. Mutated CARD16_D27G, mimicking the CARD17 amino acid sequence, formed a homo-oligomer but failed to form a filament-like structure. Consequently, CARD16_D27G weakly promoted CASP1 filament assembly and subsequent IL-1β release. These results suggest that oligomerized CARD16 promotes CARD-mediated molecular assembly and CASP1 activation.