Oxidative stress has been implicated as a cause of various diseases such as anaemia. We found that the SOD1 [Cu,Zn-SOD (superoxide dismutase)] gene deficiency causes anaemia, the production of autoantibodies against RBCs (red blood cells) and renal damage. In the present study, to further understand the role of oxidative stress in the autoimmune response triggered by SOD1 deficiency, we generated mice that had the hSOD1 (human SOD1) transgene under regulation of the GATA-1 promoter, and bred the transgene onto the SOD1(-/-) background (SOD1(-/-);hSOD1(tg/+)). The lifespan of RBCs, levels of intracellular reactive oxygen species, and RBC content in SOD1(-/-);hSOD1(tg/+) mice, were approximately equivalent to those of SOD1(+/+) mice. The production of antibodies against lipid peroxidation products, 4-hydroxy-2-nonenal and acrolein, as well as autoantibodies against RBCs and carbonic anhydrase II were elevated in the SOD1(-/-) mice, but were suppressed in the SOD1(-/-);hSOD1(tg/+) mice. Renal function, as judged by blood urea nitrogen, was improved in the transgenic mice. These results rule out the involvement of a defective immune system in the autoimmune response of SOD1-deficient mice, because SOD1(-/-);hSOD1(tg/+) mice carry the hSOD1 protein only in RBCs. Metabolomic analysis indicated a shift in glucose metabolism to the pentose phosphate pathway and a decrease in the energy charge potential of RBCs in SOD1-deficient mice. We conclude that the increase in reactive oxygen species due to SOD1 deficiency accelerates RBC destruction by affecting carbon metabolism and increasing oxidative modification of lipids and proteins. The resulting oxidation products are antigenic and, consequently, trigger autoantibody production, leading to autoimmune responses.

Several lines of evidence indicate that the nonenzymatic oxidative modification of proteins and the subsequent accumulation of the modified proteins have been found in cells during aging and oxidative stress and in various pathological states, including premature diseases, muscular dystrophy, rheumatoid arthritis, and atherosclerosis. Our previous work suggested the existence of molecular mimicry between antibodies raised against hydroxy-2-nonenal (HNE)-modified protein and anti-DNA autoantibodies, a serologic hallmark of systemic lupus erythematosus (SLE). In the present study, we investigated the possible involvement of HNE-modified proteins as the endogenous source of the anti-DNA antibodies. Accumulation of the antigen recognized by the antibody against the HNE-modified protein was observed in the nucleus of almost all of the epidermal cells from patients with autoimmune diseases, including SLE. The SLE patients also showed significantly higher serum levels of the anti-HNE titer than healthy individuals. To determine if a specific anti-DNA response could be initiated by the HNE-derived epitopes, we immunized BALB/c mice with the HNE-modified protein and observed a progressive increase in the anti-DNA response. Moreover, we generated the monoclonal antibodies, showing recognition specificity toward DNA, and found that they can bind to two structurally distinct antigens (i.e. the native DNA and protein-bound 4-oxo-2-nonenal). The findings in this study provide evidence to suspect an etiologic role for lipid peroxidation in autoimmune diseases.Several lines of evidence indicate that the nonenzymatic oxidative modification of proteins and the subsequent accumulation of the modified proteins have been found in cells during aging and oxidative stress and in various pathological states, including premature diseases, muscular dystrophy, rheumatoid arthritis, and atherosclerosis (1, 2). It has also been suggested that many of the effects of cellular dysfunction under oxidative stress are mediated by the products of nonenzymatic reactions, such as the peroxidative degradation of polyunsaturated fatty acids (3, 4). Lipid peroxidation leads to the formation of a broad array of different products with diverse and powerful biological activities. Among them are a variety of different aldehydes. The primary products of lipid peroxidation, lipid hydroperoxides, can undergo carbon-carbon bond cleavage via alkoxyl radicals in the presence of transition metals, giving rise to the formation of short chain, unesterified aldehydes of 3-9 carbons in length, and a second class of aldehydes still esterified to the parent lipid (5). These aldehydes generated during the lipid peroxidation have been implicated as causative agents in cytotoxic processes initiated by the exposure of biological systems to oxidizing agents.Some of the lipid peroxidation products exhibit a facile reactivity with proteins, generating a variety of intra-and intermolecular covalent adducts. Such adducts could be the targets of B cell-mediated immune responses a...

4-Hydroxy-2-nonenal (HNE), a racemic mixture of 4R-and 4S-enantiomers, is a major product of lipid peroxidation and is believed to be largely responsible for the cytopathological effects observed during oxidative stress. HNE reacts with histidine to form a stable HNE-histidine Michael addition-type adduct possessing three chiral centers in the cyclic hemiacetal structure. We have previously raised the mAbs, anti-R mAb 310 and anti-S mAb S412, that enantioselectively recognized the R-HNE-histidine and R-HNEhistidine adducts, respectively, and demonstrated the presence of both epitopes in vivo. In the present study, to further investigate the anti-HNE immune response, we analyzed the variable genes and primary structure of these Abs and found that the sequence of R310 was highly homologous to anti-DNA autoantibodies, the hallmark of systemic lupus erythematosus. An x-ray crystallographic analysis of the R310 Fab fragment showed that the R-HNEhistidine adduct binds to a hydrophobic pocket in the antigenbinding site. Despite the structural identity to the anti-DNA autoantibodies, however, R310 showed only a slight crossreactivity with the native double-stranded DNA, whereas the Ab immunoreactivity was dramatically enhanced by the treatment of the DNA with 4-oxo-2-nonenal (ONE), an analog of HNE. Moreover, the 7-(2-oxo-heptyl)-substituted 1,N 2 -etheno-type ONE-2 -deoxynucleoside adducts were identified as alternative epitopes of R310. Molecular mimicry between the R-HNE-histidine configurational isomers and the ONE-DNA base adducts is proposed for the dual crossreactivity.4-hydroxy-2-nonenal ͉ anti-DNA autoantibody ͉ lipid peroxidation ͉ oxidative stress ͉ systemic lupus erythematosus I t is estimated that most of the proteins in the human body are posttranslationally modified. Such modifications include phosphorylation, methylation, and glucosylation. They are enzymemediated and homeostatically important, either to carry out a particular structural or functional role or to allow the efficient recycling of the amino acid constituents. However, several lines of evidence indicate that the nonenzymatic oxidative modification of proteins and the subsequent accumulation of the modified proteins have been found in cells during aging and oxidative stress and in various pathological states, including premature diseases, muscular dystrophy, rheumatoid arthritis, and atherosclerosis (1). The important agents that give rise to the modification of proteins are represented by oxidized lipid metabolites, such as 2-alkenals, 4-hydroxy-2-alkenals, and ketoaldehydes (2, 3). These metabolites are considered important mediators of cell damage because of their ability to covalently modify biomolecules, which can disrupt important cellular functions and can cause mutations (2).4-Hydroxy-2-nonenal (HNE), a racemic mixture of 4R-and 4S-enantiomers, is a major product of lipid peroxidation and is believed to be largely responsible for the cytopathological effects observed during oxidative stress (2). HNE exerts these effects because of its...