Anti-mitochondrial flavoprotein autoantibodies of patients with myocarditis and dilated cardiomyopathy (anti-M7): interaction with flavin-carrying proteins, effect of vitamin B2 and epitope mapping

Abstract

Vitamin B2 and flavin cofactors are transported tightly bound to immunoglobulin in human serum. We reasoned that anti-mitochondrial flavoprotein autoantibodies (alpha Fp-AB) present in the serum of patients with myocarditis and cardiomyopathy of unknown aetiology may form immunoglobulin aggregates with these serum proteins. However, immunodiffusion and Western blot assays demonstrated that the flavin-carrying proteins were not recognized by alpha Fp-AB. Apparently the flavin moiety in the native protein conformation was inaccessible to alpha Fp-AB. This conclusion was supported by the absence of an immunoreaction between the riboflavin-binding protein from egg white and alpha FP-AB. Intravenous application of vitamin B2 to rabbits immunized with 6-hydroxy-D-nicotine oxidase, a bacterial protein carrying covalently attached FAD, did not neutralize alpha Fp-AB which had been raised in the serum of the animals. FAD-carrying peptides generated from 6-hydroxy-D-nicotine oxidase by trypsin and chymotrypsin treatment were not recognized by the alpha Fp-AB, but those generated by endopeptidase Lys were. This demonstrates that the epitope recognized by alpha Fp-AB comprises, besides the flavin moiety, protein secondary structure elements.

A NADH Dehydrogenase Ubiquinone Flavoprotein is Decreased in Patients with Dilated Cardiomyopathy

“…Flavoproteins are involved in a wide array of biological processes, including, but by no means limited to, bioluminescence, removal of radicals contributing to oxidative stress, photosynthesis, DNA repair, and apoptosis. Recently, Stähle et al reported that anti-mitochondrial flavoprotein autoantibodies are present in the serum of patients with myocarditis and DCM (6). To investigate the mechanism in these patients, the tissue concentration of NADH dehydrogenase ubiquinone flavoprotein (NDUFV1) of the mitochondrial Complex I, and SDHA of Complex II were examined using subendomyocardial biopsy samples in patients with DCM.…”

Analysis of mitochondrial antigens reveals inner membrane succinate dehydrogenase flavoprotein subunit as autoantigen to antibodies in anti-M7 sera

“…The mature bovine SucDH‐Fp subunit has a molecular weight of 68 130 [20] and may be identified by its flavin fluorescence [14]. This work demonstrates that the autoantigen recognized by the αFp antibody described for anti‐M7 sera [11,12] represents the SucDH‐Fp. The failure to resolve the SucDH‐Fp as a fluorescent spot by two‐dimensional PAGE may be due to an impaired isoelectric focusing of the components of the SucDH complex by the pH gradient of the first dimension.…”

“…Rat liver inner mitochondrial membrane proteins and bovine heart mitochondrial proteins were separated by SDS‐PAGE on 10% polyacrylamide gels, soaked in 10% acetic acid and inspected on an UV‐transilluminator. The bacterial 6‐hydroxy‐ D ‐nicotine oxidase (6HDNO) protein was used as a control for protein‐bound flavin fluorescence [12]. The fluorescent band was marked and the gel stained with Coomassie blue (Fig.…”

“…Klein and Berg [9] described antimitochondrial antibodies (anti‐M7) [10] in patients with myocarditis and idiopathic dilated cardiomyopathy (IDCM) directed against an aproximately 68 kDa antigen of the inner mitochondrial membrane, present in both bovine heart mitochondria and rat liver mitochondria. These sera contain antiflavoprotein (αFp) antibodies directed against enzymes with covalently bound flavin of bacterial or mammalian mitochondrial origin [11,12]. The heart mitochondrial membrane antigen detected on Western blots by these sera probably represents the SucDH flavoprotein (Fp) subunit [11], which is the only protein with covalently attached FAD in cardiomyocytes.…”

Detection of citrate synthase-reacting autoantibodies after heart transplantation: an epitope mapping study

“…However, we did not find any records of test on autoantibodies against mitochondrial inner-membrane enzymes in cardiac transplant patients [21], although these have been previously described in the pathomechanism of other diseases with autoimmune backgrounds, such as primary biliary cirrhosis and anti-glomerular basement membrane disease [22,23,24]. In this study our aim was to detect the presence and isotype of citrate synthase-specific autoantibodies, one of these anti-mitochondrial autoantibodies, in heart transplant patients.…”