Loss of tolerance in C57BL/6 mice to the autoantigen E2 subunit of pyruvate dehydrogenase by a xenobiotic with ensuing biliary ductular disease

Abstract

There have been important advances in defining effector mechanisms for several human autoimmune diseases. However, for most human autoimmune diseases, the induction stage is less well defined and there are very few clues on etiology. Our laboratory has focused on defining the molecular basis of autoantibody recognition and epitope modification in primary biliary cirrhosis (PBC). Our work has demonstrated that antibodies to mitochondria (AMA), the hallmark of disease, are directed against a very conserved site of pyruvate dehydrogenase (PDCE2). We have also demonstrated that several chemical xenobiotics, chosen based on quantitative structural activity relationship analysis and rigorous epitope analysis, when coupled to the lysine residue that normally binds the lipoic acid co-factor of PDC-E2, reacts as well or better to PBC sera than native autoantigen. In the present studies, we immunized C57BL/6 mice with one such xenobiotic, 2-octynoic acid (2OA), coupled to bovine serum albumin (BSA) and followed mice for 24 weeks. Animals were studied for appearance of histologic lesions as well as appearance of antibodies to PDC-E2, serum levels of TNF-α and IFN-γ and splenic and liver lymphoid phenotyping by flow cytometry. Mice immunized with 2OA manifest autoimmune cholangitis, typical mitochondrial autoantibodies, increased liver lymphoid cell numbers, an increase in CD8+ liver infiltrating cells, particularly CD8+ T cells that co-express CD44, and finally an elevation of serum TNF-α and IFN-γ. In conclusion, these data provide a persuasive argument in favor of an environmental origin for human PBC.

Infectious Agents and Xenobiotics in the Etiology of Primary Biliary Cirrhosis

“…One such halogenated compounds has been shown to induce AMA production in rabbits without requiring the peptide backbone of PDC-E2 [129] but failed to produce liver lesions (possibly in agreement with observations in humans where AMA is present several years prior to the appearance of liver injury) and disappeared when the stimulus was discontinued [130]. A different approach reported the induction of PBC-like liver lesions following longer follow-ups in guinea pigs [125] while a further study reported two new xenobiotic-induced PBC murine models based on the immunization with 2-octynoic acid of NOD.1101 [126] or C57BL/6 [127] mice. These two most recent models share the breakdown of tolerance in the absence of PDC-E2 molecules but fail to manifest the progression to liver cirrhosis.…”

“…The PDC-E2 structure exposes lipoic acid at the exterior of the protein complex making it accessible to chemical modification [123]. The role of xenobiotics in PBC is supported by serum reactivity against specific organic compounds with structures similar to lipoic acid [124]; further, two of these compounds (6-bromohexanoate and 2-octynoic acid) are capable of inducing AMA and PBC-like liver lesions in guinea pigs [125] and NOD.1101 [126] or C57BL/6 [127] mice, respectively. The ability of N. aromaticivorans to metabolize chemical compounds might link xenobiotics and bacteria in the etiology of PBC, as discussed in the previous paragraph.…”

Primary Biliary Cholangitis: Its Pathological Characteristics and Immunopathological Mechanisms

“…Mice immunized with 2 -octynoic acid serve as a unique PBC animal model showing autoimmune cholangitis, typical anti-mitochondrial autoantibodies, and elevated numbers of liver lymphoid cells with an increase in the number of CD8 ( + ) cells in the liver (Fig. 3 A, B) (42). However, difficulties are associated with demonstrating the localization of 2 -octynoic acid in the liver because of its small molecular size.…”

Xenobiotic Induced Model of Primary Biliary Cirrhosis

“…B6 Idd10 Idd18r2) mice immunised with 2-octynoic acid Unauthenticated Download Date | 5/9/18 8:02 AM (2-OA), coupled to BSA, had high AMA titers, portal inflammation, and cholangitis similar to human PBC (14).…”