Non-enzymatic and enzymatic lipid peroxidation of microsomes and nuclei obtained from rat liver

Steatosis-induced proteins adducts with lipid peroxidation products and nuclear electrophilic stress in hepatocytes

Accumulating evidence suggests that fatty livers are particularly more susceptible to several pathological conditions, including hepatic inflammation, cirrhosis and liver cancer. However the exact mechanism of such susceptibility is still largely obscure. The current study aimed to elucidate the effect of hepatocytes lipid accumulation on the nuclear electrophilic stress. Accumulation of intracellular lipids was significantly increased in HepG2 cells incubated with fatty acid (FA) complex (1 mM, 2:1 oleic and palmitic acids). In FA-treated cells, lipid droplets were localized around the nucleus and seemed to induce mechanical force, leading to the disruption of the nucleus morphology. Level of reactive oxygen species (ROS) was significantly increased in FA-loaded cells and was further augmented by treatment with moderate stressor (CoCl₂). Increased ROS resulted in formation of reactive carbonyls (aldehydes and ketones, derived from lipid peroxidation) with a strong perinuclear accumulation. Mass-spectroscopy analysis indicated that lipid accumulation per-se can results in modification of nuclear protein by reactive lipid peroxidation products (oxoLPP). 235 Modified proteins involved in transcription regulation, splicing, protein synthesis and degradation, DNA repair and lipid metabolism were identified uniquely in FA-treated cells. These findings suggest that steatosis can affect nuclear redox state, and induce modifications of nuclear proteins by reactive oxoLPP accumulated in the perinuclear space upon FA-treatment.

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Effects of fatty acids on modification of nuclear proteins in hepatocytes was studied.

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Lipid accumulation was associated with abnormal nuclear morphology.

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Lipid accumulation promoted mitochondrial activity and enhanced ROS generation.

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Nuclear proteins were modified by lipid peroxidation products.

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Data suggest nuclear stress as a mechanism for fatty liver disease progression.

Arachidonic acid hydroperoxide stimulates lipid peroxidation in rat liver nuclei and chromatin fractions

Arachidonic acid, the most abundant polyunsaturated fatty acid in rat liver nuclei phospholipids is a major target of free radical attack, which induces lipid peroxidation. The non-enzymatic lipid peroxidation process in intact rat liver nuclei and in several chromatin fractions indicated that the most sensitive fatty acid for peroxidation is arachidonic acid C20:4 n-6. In this study, the effect of different amounts of arachidonic acid hydroperoxide on the lipid peroxidation of rat liver nuclei and chromatin fractions was studied; rat liver nuclei and chromatin fractions deprived of exogenous added hydroperoxide were utilized as control. The addition of arachidonic acid hydroperoxide to liver nuclei produces a marked increase in light emission that was hydroperoxide concentration dependent. The maximal peak of chemiluminescence displayed by the different chromatin fractions analyzed was observed between 20 and 80 min of incubation. The highest value of light emission was displayed by the high-density chromatin fractions, the 27.5 K fraction showed intermediate values of light emission, whereas the lowest density fraction produced very low chemiluminescence. A high correlation between arachidonic acid hydroperoxide concentration and chemiluminescence in the different chromatin fractions was observed.

Role of free radicals in aseptic loosening of hip arthroplasty

Fibrous pseudocapsule around hip implants is an invariable finding at revision operations and is believed to release inflammatory mediators that stimulate bone resorption. Reactive oxygen species have been proposed to be causative factors in various disorders with tissue fibrosis. We were interested in investigating whether aseptic loosening is connected with high oxidative stress, and in showing the underlying mechanism of periprosthetic fibrosis and its role in loosening. Levels of oxidative stress markers reduced (GSH) and oxidized (GSSG) gluthatione and malondialdehyde (MDA) were assayed in 28 loose hips and in 12 stable hips revised for high rate of wear and osteolysis. Collagen in the periprosthetic tissues was measured as hydroxyproline content. Osteolysis and polyethylene wear were graded. Increased oxidative stress measured by low GSH/GSSG ratio as well as by increased MDA level was established in patients compared to controls. Oxidative stress markers intercorrelated significantly. MDA and both GSH and GSSG levels correlated significantly with hydroxyproline level. Levels of GSSG and MDA were higher in hips with greater polyethylene wear. The results suggest that high oxidative stress may play a role in formation of a fibrous membrane observed at revision of loose hips. The fibrous pseudocapsule is probably related to high intraarticular pressure and expansion of the effective joint space. This study may elicit some aspects of the pathogenesis of aseptic hip loosening and aid in future investigations aiming at prevention of this complication.

Effect of dietary high-oleic-acid oils that are rich in antioxidants on microsomal lipid peroxidation in rats

In contrast to other metabolic functions, the role of dietary antioxidants and oil on microsomal lipid oxidation has been less extensively studied. This study examines ascorbate-Fe(2+) and NADPH-induced lipid peroxidation of hepatic microsomes of rats that were fed for three weeks high-oleic-acid oils (high-oleic sunflower oil, HOSO; olive oil, OO; or olive pomace oil, OPO) containing different concentrations of the antioxidants alpha-tocopherol, erythrodiol, and oleanolic acid. The fatty acid composition of hepatic microsomes of Wistar rats that were fed for three weeks with the above-mentioned oils had lower proportions of C16:0, C18:2n6, and C22:6n3 and higher proportions of C18:0 and C18:1n9 than rats fed the control diet. Light emission by hepatic microsomes increased, in the first 180 min, 2-fold after ascorbate-Fe(2+) addition compared with NADPH addition. Both increases were less pronounced in microsomes of OPO-fed rats and to a smaller extent in microsomes of OO-fed rats. Smaller increases in light emission were associated positively with higher concentrations of dietary alpha-tocopherol, erythrodiol, and oleanolic acid but were not associated with changes in fatty acid composition of hepatic microsomes. Addition of alpha-tocopherol, erythrodiol, or oleanolic acid decreased light emission of hepatic microsomes with a greater inhibition in microsomes of rats fed the control diet. Our data suggest that erythrodiol and oleanolic acids partly explain the protective effect of dietary OPO on microsomal lipid peroxidation in rats.