The Lipoic Acid Containing Components of the 2-Oxoacid Dehydrogenase Complexes Mimic Trifluoroacetylated Proteins and Are Autoantigens Associated with Halothane Hepatitis

Abstract

Anti-CF3CO antibodies, monospecific toward trifluoroacetylated proteins (CF3CO-proteins), which are elicited in experimental animals and humans exposed to the anesthetic agent halothane, cross-react with an unknown protein of approximately 52 kDa, constitutively expressed in tissues of experimental animals and humans not previously exposed to the agent. Using anti-CF3CO antibody, the protein(s) of 52 kDa could be immunoprecipitated from solubilized rat heart homogenate. Two-dimensional gel electrophoretic analysis revealed the presence of distinct major (P1, P2) and minor (P3, P4, P5) protein components with apparent molecular masses of 52 kDa. From each of the components P1 and P2, the amino acid sequences of three peptides were determined and found to exhibit 100% identity with the corresponding amino acid sequences of the E2 subunit of the rat 2-oxoglutarate dehydrogenase complex (OGDC). Additionally to the E2 subunit of OGDC, anti-CF3CO antibody also recognized on immunoblots the purified E2 subunit of the branched chain 2-oxoacid dehydrogenase complex (BCOADC) and protein X, a constituent of the pyruvate dehydrogenase complex (PDC), in a manner sensitive to competition by N6-(trifluoroacetyl)-L-lysine (CF3CO-Lys), 6(RS)-lipoic acid, and N6-(6(RS)-lipoyl)-L-lysine (lipoyl-Lys). Furthermore, a discrete population of autoantibodies was identified in sera of patients with halothane hepatitis which could not discriminate between the lipoylated target epitope present on the E2 subunit of OGDC and epitopes on CF3CO-RSA, used as model for CF3CO-proteins. These data suggest that the autoantigenicity of these proteins in halothane hepatitis is based on the molecular mimicry of CF3CO-Lys by lipoic acid, the prosthetic group common to protein X and the E2 subunits of OGDC and BCOADC.

Induction of Primary Biliary Cirrhosis in Guinea Pigs following Chemical Xenobiotic Immunization

“…The chronic presence of the self-protein would then serve to perpetuate the immune response initiated by the xenobiotically modified self-protein and lead to autoimmunity. In support of this hypothesis, patients exposed to halothane, whose trifluoroacetyl metabolite covalently links to lysine on cytochrome p450 2E1, develop anti-trifluoroacetyl Abs that are also cross-reactive to lipoylated PDC-E2 (24). In addition, we have identified a number of lipoic acid mimeotopes that are recognized by AMA-positive PBC sera (3,4,8).…”

Comparative Immunoreactivity of Anti-trifluoroacetyl (TFA) Antibody and Anti-lipoic Acid Antibody in Primary Biliary Cirrhosis: Searching for a Mimic

“…In addition, trifluoracetylated lysine, (6RS)-lipoic acid as well as the lipoylated peptide ETDK (lipoyl) ATIG of the PDC-E2 inner lipoyl domain specifically inhibited the recognition of PDC-E2 trifluoroacetylated rabbit serum albumin (TFA-RSA), and human liver TFA-proteins with anti-TFA antibody. Similar inhibition of recognition of the other E2 subunits of the 2-oxoacid dehydrogenase complexes by anti-TFA antibody has been demonstrated [14]. Furthermore, using a molecular modelling approach, the determination of Connolly dot surfaces of energy minimized conformations of TFA-Lysine, as well as the 6S and 6R enantiomers of lipoic acid analysis showed that these three compounds have a high degree of structural relatedness revealed by the calculated union surface [13].…”

“…The cross-reactivity of antibodies made against TFA-conjugated proteins (with specificity for the hapten-derivative of N6-trifluoroacetyl-L-lysine), with the E2 subunit of pyruvate dehydrogenase complex, suggests that the epitopes on PDC-E2 molecularly mimic those of the TFA-proteins. Further, only the lipoylated form of the recombinant inner domain of the human PDC-E2, but not the unlipoylated form, was recognized by the antibody denoting the importance of the lipoate molecule in such interactions [13][14][15][16]. In addition, trifluoracetylated lysine, (6RS)-lipoic acid as well as the lipoylated peptide ETDK (lipoyl) ATIG of the PDC-E2 inner lipoyl domain specifically inhibited the recognition of PDC-E2 trifluoroacetylated rabbit serum albumin (TFA-RSA), and human liver TFA-proteins with anti-TFA antibody.…”

Mitochondrial stress protein recognition of inactivated dehydrogenases during mammalian cell death

“…Proximal tubule cell death, visualized as an exfoliation into the tubule lumen, was maximal between 18 and 48 h after the dose was administered. Immunoreactive cell debris was cleared progressively and was localized exclusively to the lumen by 72 h. ( (36,37).…”