Gondwanaland
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Looking into lipid peroxidation derived 4-hydroxynonenal (4-HNE), which is ihibited by carnosine:
http://www.sciencedirect.com/science/article/pii/S2213231714001359
Reactive oxygen species (ROS), such as superoxide anion, hydrogen peroxide, hydroxyl radicals, singlet oxygen, and lipid peroxyl radicals, are ubiquitous and considered as byproducts of aerobic life [1]. Most of these chemically reactive molecules are short-lived and react with surrounding molecules at the site of formation while some of the more stable molecules diffuse and cause damages far away from their sites of generation. Overproduction of these ROS, termed oxidative stress, may provoke oxidation of polyunsaturated fatty acids (PUFAs) in cellular membranes through free radical chain reactions and form lipid hydroperoxides as primary products [2]; some of these primary oxidation products may decompose and lead to the formation of reactive lipid electrophiles. Among these lipid peroxidation (LPO) products, 4-hydroxy-2-nonenals (4-HNE) represents one of the most bioactive and well-studied lipid alkenals [3]. 4-HNE can modulate a number of signaling processes mainly through forming covalent adducts with nucleophilic functional groups in proteins, nucleic acids, and membrane lipids. These properties have been extensively summarized in some excellent reviews [4–10].
Mitochondria are vital for cellular bioenergetics and regarded as the major cellular site for ROS production [11].
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Selective Inactivation of α-Ketoglutarate Dehydrogenase and Pyruvate Dehydrogenase: Reaction of Lipoic Acid with 4-Hydroxy-2-nonenal
Biochemistry, 1998, 37 (45), pp 15835–15841
Abstract
Previous research has established that 4-hydroxy-2-nonenal (HNE), a highly toxic product of lipid peroxidation, is a potent inhibitor of mitochondrial respiration. HNE exerts its effects on respiration by inhibiting α-ketoglutarate dehydrogenase (KGDH). Because of the central role of KGDH in metabolism and emerging evidence that free radicals contribute to mitochondrial dysfunction associated with numerous diseases, it is of great interest to further characterize the mechanism of inhibition. In the present study, treatment of rat heart mitochondria with HNE resulted in the selective inhibition of KGDH and pyruvate dehydrogenase (PDH), while other NADH-linked dehydrogenases and electron chain complexes were unaffected. KGDH and PDH are structurally and catalytically similar multienzyme complexes, suggesting a common mode of inhibition. To determine the mechanism of inhibition, the effects of HNE on purified KGDH and PDH were examined. These studies revealed that inactivation by HNE was greatly enhanced in the presence of substrates that reduce the sulfur atoms of lipoic acid covalently bound to the E2 subunits of KGDH and PDH. In addition, loss of enzyme activity induced by HNE correlated closely with a decrease in the availability of lipoic acid sulfhydryl groups. Use of anti-lipoic acid antibodies indicated that HNE modified lipoic acid in both purified enzyme preparations and mitochondria and that this modification was dependent upon the presence of substrates. These results therefore identify a potential mechanism whereby free radical production and subsequent lipid peroxidation lead to specific modification of KGDH and PDH and inhibition of NADH-linked mitochondrial respiration.