Lipid peroxidation in tissue and in tissue fractions represents a degradative process, which is the consequence of the production and the propagation of free radical reactions primarily involving membrane polyunsaturated fatty acids, and has been implicated in the pathogenesis of numerous diseases, including systemic lupus erythematosus (SLE). We have found that bovine serum albumin incubated with peroxidized polyunsaturated fatty acids significantly cross-reacted with the sera from MRLlpr mice, a representative murine model of SLE. To identify the active substances responsible for the generation of autoantigenic epitopes recognized by the SLE sera, we performed the activity-guiding separation of a principal source from 13-hydroperoxy-9Z,11E-octadecadienoic acid and identified 4-oxo-2-nonenal (ONE), a highly reactive aldehyde originating from the peroxidation of 6 polyunsaturated fatty acids, as the source of the autoantigenic epitopes. When the age-dependent change in the antibody titer against the ONE-modified protein was measured in the sera from MRL-lpr mice and control MRL-MpJ mice, all of the MRL-lpr mice developed an anti-ONE titer, which was comparable with the anti-DNA titer. Strikingly, a subset of the anti-DNA monoclonal antibodies generated from the SLE mice showing recognition specificity toward DNA cross-reacted with the ONE-specific epitopes. Furthermore, these dual-specific antibodies rapidly bound and internalized into living cells. These findings raised the possibility that the enhanced lipid peroxidation followed by the generation of ONE may be involved in the pathogenesis of autoimmune disorders.

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.

Carbon tetrachloride (CCl(4): 4 ml/kg body weight as a 1:1 mixture of CCl(4) and mineral oil) was orally administered to rats. After 12 h the activity of plasma AST (aspartate aminotransferase) and ALT (alanine aminotransferase) was significantly higher than that of the control group and plasma AST and ALT activities increased thereafter. These results indicated that the necrotic process was active at about 12 h and developed thereafter. After 2-24 h of CCl(4) administration, the hepatic level of vitamin C, the most sensitive indicator of oxidative stress, decreased significantly, indicating that oxidative stress was significantly enhanced as early as 2 h after CCl(4) intoxication and thereafter. Phosphorylated JNK (c-Jun NH(2)-terminal kinase) and phospho-ERK1/2 (extracellular signal-regulated kinase1/2) were significantly increased transiently 1-3 h after treatment with CCl(4), while phosphorylated p38 decreased significantly 1-24 h after CCl(4) treatment. These results indicated that the change in MAPKs (mitogen activated protein kinases) slightly preceded that in vitamin C, the most sensitive chemical indicator of oxidative stress.

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...

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