Conclusion: Specific modifications of the disulfide bond within the lipoic-acid-conjugated PDC-E2 moiety, i.e., by an electrophilic agent renders PDC-E2 immunogenic in a genetically susceptible host. (HEPATOLOGY 2013) Antimitochondrial autoantibodies (AMAs) to the E2 subunit of the pyruvate dehydrogenase complex (PDC-E2) are the serological hallmark of primary biliary cirrhosis (PBC).1-4 Previous analysis of the antibody specificity of anti-PDC-E2 revealed a number of subpopulations of anti-PDC-E2 antibodies that recognized either the PDC peptide, PDC peptide conjugated with lipoic acid,
or lipoic acid itself.5-7 Interestingly, PDC-E2-specific antibodies are present long before the onset of clinical symptoms and may represent a relic of initiating immunological events.8 Recent studies by quantitative structure-activity relationship (QSAR) analysis demonstrated that AMA-positive buy Pifithrin-�� PBC
sera, but not controls, reacted to a number Regorafenib in vivo of xenobiotic modified PDC-E2 structures,9-11 with a particularly striking level of reactivity against 6,8-bis(acetylthio) octanoic acid (SAc)-PDC-E2.12 This observation is critical because SAc is a modified form of lipoic acid in which both sulfur atoms of the disulfide bond of the lipoyl ring are modified by acetyl groups (Fig. 1), thereby maintaining PDC-E2 in a reduced state by preventing disulfide bond formation; this reduced state facilitates xenobiotic modification of PDC-E2.13 We hypothesized that the presence of antibodies directed against the SAc-PDC-E2 conjugate in sera from PBC patients suggests that this structure is involved in loss of tolerance. Such data would also support the thesis that chemical modification of self-proteins plays an important role in autoimmunity,7, 14-16 exemplified by minocycline-induced autoimmunity, whereby minocycline binding to self macromolecules produces immunogenic self antigens that become the target MCE公司 of disease-generating, crossreactive autoantibodies.17, 18 Thus, to address our hypothesis
and define the antibody reactivity to the SAc moiety, we studied the serological reactivity of 241 AMA-positive PBC patients, 34 AMA-negative PBC patients, 86 patients with primary sclerosing cholangitis (PSC), 95 patients with autoimmune hepatitis (AIH), and 60 healthy controls against SAc-conjugated bovine serum albumin (BSA), 2-octynoic acid (2OA)-conjugated BSA, recombinant PDC-E2 (rPDC-E2), and BSA itself. Importantly, we mapped specific reactivities of a nested subset of 24 AMA-positive SAc-BSA-positive PBC sera, including use of various affinity-purified antisera and inhibition studies. Interestingly, our data suggest that immunoglobulin M (IgM) reactivity to SAc reflects the footprints of xenobiotic modification of PDC-E2. Finally, we report herein that the IgM reactivity to SAc persists from early- to late-stage PBC with only minimal IgG reactivity.