Protective effect of black tea against ethanol-induced oxidative modifications of liver proteins and lipids.

OBJECTIVE: Black tea has been recently ascertained as a source of water-soluble antioxidants that may enhance cellular antioxidant abilities. The present study was designed to investigate the efficacy of the preventive effect of black tea on oxidative modifications of liver lipids and proteins of 2-month-old rats intoxicated chronically (28 days) with ethanol. METHOD: Lipid peroxidation was estimated by measurement of lipid hydroperoxides, malondialdehyde, and 4-hydroxynonenal by high-performance liquid chromatography (HPLC) and by spectrophotometric determination of conjugated dienes. The markers of protein oxidative modification products-bistyrosine and tryptophan-were quantified by spectrofluorimetry, whereas levels of amino, sulfhydryl, and carbonyl groups were estimated spectrophotometrically. RESULTS: Ethanol intoxication caused changes in liver antioxidant abilities that led to the generation of oxidative stress and, consequently, to the significant increase in products of lipid and protein oxidative modification. Enhanced lipid peroxidation was confirmed by assessment of the concentration of lipid peroxidation products measured at all examined levels. Protein modifications were evidenced by increase in levels of bistyrosine and carbonyl groups and by decrease in concentration of tryptophan and levels of sulfhydryl and amino groups. The metabolic consequences of oxidative modifications of lipids and proteins were reduced by cathepsin B activity and translocation of this lysosomal protease into cytosol as well as markers of liver damage-alanine aminotransferase (ALT) and aspartate aminotransferase (AST)-into the blood serum. Administration of black tea to ethanol-intoxicated rats partially protected antioxidant parameters and, remarkably, prevented the significant increase in concentrations of all measured lipid peroxidation products. Moreover, the levels of markers of the protein-modification process were similar to those of the control group. Protection of biological membranes by black tea prevents changes in the permeability of these membranes and translocation of the examined enzymes. CONCLUSIONS: Our findings indicate that black tea protects proteins and lipids against oxidative modification induced by chronic ethanol intoxication, which preserves changes in redox and proteolytic homeostasis.

[Coenzyme Q10: its biosynthesis and biological significance in animal organisms and in humans]. / Koenzym Q10--biosynteza i znaczenie biologiczne w organizmach zwierzat i czlowieka.

Coenzyme Q10 (ubiquinone) is a naturally occurring compound widely distributed in animal organisms and in humans. The primary compounds involved in the biosynthesis of ubiquinone are 4-hydroxybenzoate and the polyprenyl chain. An essential role of coenzyme Q10 is as an electron carrier in the mitochondrial respiratory chain. Moreover, coenzyme Q10 is one of the most important lipophilic antioxidants, preventing the generation of free radicals as well as oxidative modifications of proteins, lipids, and DNA, it and can also regenerate the other powerful lipophilic antioxidant, alpha-tocopherol. Antioxidant action is a property of the reduced form of coenzyme Q10, ubiquinol (CoQ10H2), and the ubisemiquinone radical (CoQ10H*). Paradoxically, independently of the known antioxidant properties of coenzyme Q10, the ubisemiquinone radical anion (CoQ10-) possesses prooxidative properties. Decreased levels of coenzyme Q10 in humans are observed in many pathologies (e.g. cardiac disorders, neurodegenerative diseases, AIDS, cancer) associated with intensive generation of free radicals and their action on cells and tissues. In these cases, treatment involves pharmaceutical supplementation or increased consumption of coenzyme Q10 with meals as well as treatment with suitable chemical compounds (i.e. folic acid or B-group vitamins) which significantly increase ubiquinone biosynthesis in the organism. Estimation of coenzyme Q10 deficiency and efficiency of its supplementation requires a determination of ubiquinone levels in the organism. Therefore, highly selective and sensitive methods must be applied, such as HPLC with UV or coulometric detection.