Studies on 4-hydroxynonenal modified human serum albumin: implications in systemic lupus erythematosus and rheumatoid arthritis

Abstract

Peroxidation of membrane-derived phospholipids is a well-known biochemical consequence of reactive oxygen species (ROS). Lipid peroxidation proceeds by a free radical chain reaction mechanism and yield hydroperoxides as major initial reaction products. Subsequently, decomposition of lipid hydroperoxides generates a number of breakdown products that display a wide variety of damaging actions. Compared to free radicals, the lipid peroxidation products are stable and can diffuse within or even escape from the cell and attack targets far from the site of the original event. Therefore, they are not only the end-products and remnants of lipid peroxidation, but also may act as second cytotoxic messengers for the primary reactions. Products of lipid peroxidation have, therefore, commonly been used as biomarkers of oxidative stress/damage. Lipid peroxidation generates a variety of relatively stable decomposition end products particularly aldehydes, such as 4-hydroxynonenal (HNE), acrolein, malondialdehyde (MDA), crotonaldehyde etc. Aldehydes derived from lipid peroxidation have been implicated as causative agents in cytotoxic processes initiated by the exposure of biological systems to oxidizing agents. HNE is among the most abundant and cytotoxic of these aldehydes. HNE bind covalently with nucleophilic amino groups of proteins to form HNE-modified protein adducts. The formation of adducts on proteins has wide-ranging and profound functional consequences not only in terms of damage to cellular macromolecules, but also in terms of regulatory effects, via the formation of aldehyde protein adducts. HNE can impact several cellular processes, including inhibition of key enzymes and disruption of ion transporters. Covalent binding of lipid peroxidation derived aldehyde with endogenous macromolecules including proteins may not only alter their physiological functions, but also produce structural modifications generatingneoantigens, which may consequently elicit an autoimmune response leading to autoimmune disease (AD).