EtCBN-associated olfactory dysfunction involves Irf7 signaling and a microbiota-metabolite axis

Liquid crystal monomers (LCMs) are emerging environmental contaminants with neurotoxic potential; however, their impact on olfactory function, a key early indicator of neurodegenerative diseases, is unknown. Here, we observed that exposure to LCM mixtures at an environmentally relevant dose (180 μg/kg) was associated with olfactory deficits in mice. Further investigation focused on a prevalent LCM monomer (EtCBN) found in indoor dust, a compound known to disrupt endothelial cell proliferation, as a key component of this effect. Mice exposed to environmentally relevant (20 μg/kg) or elevated (200 μg/kg) EtCBN for 12 weeks exhibited significant olfactory impairment, supported by behavioral deficits, magnetic resonance imaging (MRI)-based olfactory bulb atrophy, histopathological changes, and neuroinflammation. Molecular docking predicted that EtCBN may interact with Irf7 with a binding energy of -4.86 kcal/mol, suggesting a potential interaction that could serve as a candidate molecular initiating event (MIE). This interaction was associated with elevated IL-1β and TNF-α levels and may be linked to the onset of neuroinflammation. In addition, a reduced abundance of Dubosiella was found to correlate with phenylalanine accumulation, potentially further contributing to Irf7 activation through a microbiota-metabolite-inflammation axis. Fecal microbiota transplantation (FMT) and probiotic supplementation provided evidence suggesting a role for the intestinal microbiota. Exogenous nicotinamide adenine dinucleotide (NAD⁺) was observed to be associated with mitigation of these effects. Together, these findings are consistent with a proposed adverse outcome pathway (AOP) framework that suggests a link between the EtCBN-Irf7 interaction and LCM-associated neurotoxicity, offering potential mechanistic insights and therapeutic targets for olfactory dysfunction.