Chemistry and biochemistry of 4-hydroxynonenal, malonaldehyde and related aldehydes.

Free radicals, metals and antioxidants in oxidative stress-induced cancer

Publisher Summary This chapter discusses the role of free radicals and catalytic metal ions in human disease. The importance of transition metal ions in mediating oxidant damage naturally leads to the question as to what forms of such ions might be available to catalyze radical reactions in vivo . The chapter discusses the metabolism of transition metals, such as iron and copper. It also discusses the chelation therapy that is an approach to site-specific antioxidant protection. The detection and measurement of lipid peroxidation is the evidence most frequently cited to support the involvement of free radical reactions in toxicology and in human disease. A wide range of techniques is available to measure the rate of this process, but none is applicable to all circumstances. The two most popular are the measurement of diene conjugation and the thiobarbituric acid (TBA) test, but they are both subject to pitfalls, especially when applied to human samples. The chapter also discusses the essential principles of the peroxidation process. When discussing lipid peroxidation, it is essential to use clear terminology for the sequence of events involved; an imprecise use of terms such as initiation has caused considerable confusion in the literature. In a completely peroxide-free lipid system, first chain initiation of a peroxidation sequence in a membrane or polyunsaturated fatty acid refers to the attack of any species that has sufficient reactivity to abstract a hydrogen atom from a methylene group.

Role of free radicals and catalytic metal ions in human disease: an overview.

Nonalcoholic fatty liver disease (NAFLD) is present in up to one third of the general population and in the majority of patients with metabolic risk factors such as obesity and diabetes. Insulin resistance is a key pathogenic factor resulting in hepatic fat accumulation. Recent evidence demonstrates NAFLD in turn, exacerbates hepatic insulin resistance and often precedes glucose intolerance. Once hepatic steatosis is established, other factors including oxidative stress, mitochondrial dysfunction, gut-derived lipopolysaccharide and adipocytokines, may promote hepatocellular damage, inflammation and progressive liver disease. Confirmation of the diagnosis of NAFLD can usually be achieved by imaging studies, however staging the disease requires a liver biopsy. NAFLD is associated with an increased risk of all-cause death, probably because of complications of insulin resistance such as vascular disease, as well as due to cirrhosis and hepatocellular carcinoma, which occurs in a minority of patients. NAFLD is also now recognized to account for a substantial proportion of patients previously diagnosed with 'cryptogenic cirrhosis'. Diabetes, obesity and the necroinflammatory form of NAFLD known as non-alcoholic steatohepatitis, are risk factors for progressive liver disease. Current treatment relies on weight loss and exercise, although various insulin-sensitizing medications appear promising. Further research is needed to identify which patients will achieve the most benefit from therapy.

Nonalcoholic fatty liver disease.

Lipid peroxidation can be described generally as a process under which oxidants such as free radicals attack lipids containing carbon-carbon double bond(s), especially polyunsaturated fatty acids (PUFAs). Over the last four decades, an extensive body of literature regarding lipid peroxidation has shown its important role in cell biology and human health. Since the early 1970s, the total published research articles on the topic of lipid peroxidation was 98 (1970–1974) and has been increasing at almost 135-fold, by up to 13165 in last 4 years (2010–2013). New discoveries about the involvement in cellular physiology and pathology, as well as the control of lipid peroxidation, continue to emerge every day. Given the enormity of this field, this review focuses on biochemical concepts of lipid peroxidation, production, metabolism, and signaling mechanisms of two main omega-6 fatty acids lipid peroxidation products: malondialdehyde (MDA) and, in particular, 4-hydroxy-2-nonenal (4-HNE), summarizing not only its physiological and protective function as signaling molecule stimulating gene expression and cell survival, but also its cytotoxic role inhibiting gene expression and promoting cell death. Finally, overviews of in vivo mammalian model systems used to study the lipid peroxidation process, and common pathological processes linked to MDA and 4-HNE are shown.

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Lipid peroxidation: production, metabolism, and signaling mechanisms of malondialdehyde and 4-hydroxy-2-nonenal.

Myeloperoxidase (MPO), an abundant enzyme in phagocytes, has been implicated in the pathogenesis of various inflammatory diseases including atherosclerosis. The major oxidant produced by MPO, hypochlorous acid (HOCl), is able to modify a great variety of biomolecules by chlorination and/or oxidation. In this paper the reactions of lipids (preferentially unsaturated fatty acids and cholesterol) with either reagent HOCl or HOCl generated by the MPO-hydrogen peroxide-chloride system are reviewed. One of the major issues has been whether the reaction of HOCl with lipids of low density lipoprotein (LDL) yields predominantly chlorohydrins or lipid hydroperoxides. Electrospray mass spectrometry provided direct evidence that chlorohydrins rather than peroxides are the major products of HOCl- or MPO-treated LDL phosphatidylcholines. Nevertheless lipid peroxidation is a possible alternative reaction of HOCl with polyunsaturated fatty acids if an additional radical source such as pre-formed lipid hydroperoxides is available. In phospholipids carrying a primary amino group such as phosphatidylethanolamine chloramines are the preferred products compared to chlorohydrins. Cholesterol can be converted by HOCl to great variety of oxysterols besides three isomers of chlorohydrins. For the situation in vivo it appears that the type of reaction occurring between HOCl and lipids would very much depend on the circumstances, e.g. the pH and the presence of radical initiators. The biological effects of lipid chlorohydrins are not yet well understood. It has been shown that chlorohydrins of both unsaturated fatty acids as well as of cholesterol may cause lysis of target cells, possibly by disruption of membrane structures.

https://ojs.ptbioch.edu.pl/index.php/abp/article/download/3944/4283

The reactions of hypochlorous acid, the reactive oxygen species produced by myeloperoxidase, with lipids

Pathways of phospholipid oxidation by HOCL in human LDL detected by LC-MS

The aim of this study was to analyze the growth response of HeLa cells over a prolonged period of time to a single exposure of physiological and supraphysiological concentrations of 4-hydroxynonenal (HNE), a peroxidation product of omega-6-polyunsaturated fatty acids. Furthermore, the growth modulating effect of serum factors, particularly albumin, on the growth pattern was examined. The effects of HNE on the growth rate and viability of the cells, as well as on the incorporation of labelled amino acids were monitored daily over a period of four days. Fetal calf serum not only had a growth stimulating effect but also modulated the action of HNE. In neither respect was albumin able to substitute for serum indicating that the influence of serum was not exerted via an albumin-HNE conjugate. HNE had a clear dose-dependent effect and a distinction could be made between a supraphysiological concentration (100 microM), which was primarily cytotoxic and a physiological range (below 10 microM) which showed growth modulatory effects. These effects consisted of a transient inhibition in the initial phase of the cell growth, which under optimal conditions (in presence of serum) was followed by a period of increased proliferation, compared to untreated control cultures, until confluence was attained. It is suggested that HNE is not only a toxic product of lipid peroxidation, but a physiological growth regulating factor as well.

R. J. Schaur

Papers

Chemistry and biochemistry of 4-hydroxynonenal, malonaldehyde and related aldehydes.

The reactions of hypochlorous acid, the reactive oxygen species produced by myeloperoxidase, with lipids

Pathways of phospholipid oxidation by HOCL in human LDL detected by LC-MS

Stimulation of HeLa cell growth by physiological concentrations of 4-hydroxynonenal.

Possible involvement of myeloperoxidase in lipid peroxidation