Methylimidazolium Ionic Liquids as Persistent Xenobiotics: Mitochondrial Injury and PDC-E2 Modification Relevant to Autoimmune Liver Disease

Introduction: Methylimidazolium ionic liquids (MILs) are synthetic solvents increasingly used in industrial applications, including biofuel production. Although initially promoted as “green solvents” because of their low volatility and recyclability, growing evidence indicates that some MILs are environmentally persistent and may pose risks to human health. We investigated whether the 8-carbon MIL 1-octyl-3-methylimidazolium (M8OI), identified as an environmental contaminant with evidence of human exposure, may trigger mechanisms relevant to primary biliary cholangitis (PBC), an autoimmune liver disease directed against mitochondrial autoantigens.

Methods: The effects of M8OI were examined in rat liver progenitor B-13 cells and HepaRG human hepatic progenitor-like cells. Environmental persistence and biodegradation of MILs were assessed alongside cellular toxicity studies. Mitochondrial morphology, oxygen consumption rate by Seahorse extracellular flux analysis, reactive oxygen species generation, and cell death were evaluated to define the mechanism of toxicity. In HepaRG cells, PDC-E2 localisation, changes in the PDC-E2 immunoblotting pattern, and metabolism of M8OI were investigated.

Results: MILs demonstrated marked environmental resilience, supporting their classification as persistent xenobiotics. In B-13 cells and HepaRG cells, M8OI induced mitochondrial morphological changes and inhibited mitochondrial respiration, with evidence of complex I inhibition, leading to oxidative stress and cell death. In HepaRG cells, M8OI was metabolised, PDC-E2 translocated from mitochondria to the cell membrane, and a novel PDC-E2 band appeared, suggesting xenobiotic-induced modification. These findings support the possibility that an M8OI metabolite modifies PDC-E2, potentially replacing lipoic acid within its lipoyl-binding domain and thereby altering antigenicity. Such modified PDC-E2 may be expressed on the surface of apoptotic bodies, representing a possible mechanism linking xenobiotic exposure to loss of immune tolerance.

Conclusions: MILs may represent under-recognised persistent xenobiotics with potential relevance to mechanisms contributing to PBC and autoimmune liver injury.