Action of alpha-tocopherol on the enzymes of the electron transport chains in the liver microsomes of irradiated rats

Five days following single whole-body gamma irradiation of rats (8.5 Gy) the rate of NADPH and NADH oxidation, the activity of NADPH-cytochrome P-450 and NADH-cytochrome b5 reductases, and the content of cytochromes P-450 and b5 were found to decrease. The intragastric administration of alpha-tocopherol (100 mg/kg, two times a day) produced a normalizing effect.     

Regulation of lipid peroxidation induced by cumene hydroperoxide in the liver mitochondria of irradiated rats

A study was made of the accumulation of lipoperoxidation products and O2- generation induced by cumene hydroperoxide in mitochondria of irradiated rat liver. O2- generation and formation of lipoperoxidation products were found to be connected with the function of mitochondrial P-450 cytochrome. During the first 24 h following X-irradiation of rats with a dose of 10 Gy, the rate of O2- generation sharply increased and mitochondria could not regulate the intensity of lipoperoxidation with incubation medium tonicity being altered.     

Neutral and polar lipid metabolism in liver microsomes of growing rats fed a calcium-deficient diet

We studied the incorporation of (14)C-labeled fatty acids and glycerol into different classes of glycerolipids in an in vitro system containing liver microsomes from growing Wistar rats fed a calcium-deficient (CaD; 0.5 g/kg) diet for a 60-day period. Desaturase activities and incorporation of the elongation-desaturation metabolites into specific neutral and polar glycerolipids were also studied and correlated with the activities of various enzymes involved in complex lipid metabolism (acyl-CoA synthase, acyl-CoA hydrolase, DAG-acyltransferase, DAG-kinase, lysophospatidate-acyl-CoA transferase, phosphatidate-phosphohydrolase and phospholipase A(2)). Low calcium condition led to a significant increase in the incorporation (relative amounts and specific activities) of both labeled fatty acids and glycerol with a preferential increase of labeling in neutral lipids rather than in phospholipids. Acyl-CoA synthetase, diacylglycerol acyltransferase and diacylglycerol-3-P acyltransferase activities were increased in low calcium microsomes while diacylglycerol kinase, phospholipase A(2) and palmitoyl-, stearoyl-, linoleyl-, alpha-linolenyl, and eicosatrienoyl-desaturases were decreased. The modifications observed in the interlipid and lipid/protein relationships, enzyme activities, and pattern of incorporation of labeled precursors into each glycerolipid class, suggest that decreased intake of calcium should be considered as a harmful risk factor for the development of cardiovascular diseases.     

Effect of N-stearoylethanolamine and ionizing radiation on lipid components of the liver and heart microsomes in rats

The influence of irradiation and NSE on the microsomal lipid composition of the rat liver and heart was studied. It was shown, that radiation treatment in a dose of 2 Gy had not a significant affect on the heart phospholipid composition, whereas in the liver the amounts of the phosphatidylethnolamine and phosphatidylinositol were increased and the amounts of the phosphatidylcholine and sphyngomieline were decreased. NSE did not impact on these characteristics. The alterations of the plasmalogen/diacyl forms ratio of the PC and PE also took place only in the liver microsome. The analysis of the fatty acids esterified to phospholipids showed similar situation: the fatty acids of the heart microsome less were changed than those of the liver microsome undergo irradiation. The amount of arachidonic acid rise after the adding of NSE to rats. Investigation of the important component of biological membranes--cholesterol and its esters also showed that the liver tissue is more vulnerable to irradiation than the heart. NSE led to insignificant increase of the not esterified cholesterol in the liver. As a result of the present work we may conclude that the liver microsome is more vulnerable than the heart under X-ray radiation and NSE has protective effect in these conditions.     

Effect of radioprotectors on lipid peroxidation in liver microsomes induced by ultraviolet irradiation of the skin in rats

The modifying effect of radioprotectors (serotonin, cysteamine, ionol) on lipid peroxidation intensification of liver microsomes caused by rat skin ultraviolet radiation has been studied. A possible mechanism of action of these compounds on the investigated indexes during their preventive injection is under discussion.     

Relation between lipid polymorphism and transbilayer movement of lipid in rat liver microsomes

We have studied the effects of trinitrophenylation on the transbilayer movement of phosphatidylcholine and the macroscopic lipid structure in rat liver microsomal membranes. The transbilayer movement of phosphatidylcholine was investigated using the PC-specific transfer protein. ³¹P-NMR was employed to monitor the phospholipid organization in intact microsomal vesicles. The results indicate that modification of microsomes with trinitrobenzenesulfonic acid enhances the transbilayer movement of phosphatidylcholine at 4°C. Furthermore, phosphatidylethanolamine headgroup trinitrophenylation in microsomes increases the isotropic component in the ³¹P-NMR spectra even at 4°C, possibly representing the appearance of intermediate non-bilayer lipid structures. The observed parallel between these data suggests that phosphatidylethanolamine molecules in the microsomal membrane, probably in combination with a protein component, are able to destabilize the bilayer organization, thereby facilitating the transmembrane movement of phospholipids.     

Impaired glycosylation in liver microsomes of orotic-acid-fed rats

In rats fed orotic acid, the incorporation in liver subcellular fractions of sugars injected intraperitonealy is altered only for mannose, but not for fucose or galactose. Direct determinations of several glycosyltransferases are done in smooth and rough microsomes: fucosyl-, glactosyl-, N-acetylglucosaminyltransferase activities are at quite similar levels in normal and fatty livers. By contrast, sialyltransferase activity is increased (+50%) in smooth microsomes of fatty livers, while mannosyltransferase activity is inhibited by 30%. These alterations are not caused by interfering reactions pyrophosphatases or proteases). For the mannosyltransferase activity, the inhibition is found in the dolichylphorylmannose intermediates. Kinetic studies suggest that there is deficiency of both enzyme and endogenous dolichyl phosphate.     

Senescence-associated decrease of NADPH-induced lipid peroxidation in rat liver microsomes

Senescence is associated with decrease in the NADPH-induced lipid peroxidation in liver homogenate as well as rough and smooth microsomes of female rats. In the microsomal fractions, sensitivity to NADPH-induced lipid peroxidation is high in young adults (3-month-old), decreases in middle aged (12-month-old) and reaches lowest levels in senescent (30-month-old) rats. Increasing the concentration of co-factors or time of incubation does not alter this resistance observed in the senescent rats. Major factors responsible for this resistance in senescent rats seem to be low levels of substrate in the c reductase, cytochrome P-450 and high cholesterol:phospholipid ratios besides enhanced levels of superoxide dismutase, alpha-tocopherol and reduced glutathione.     

Effect of thiols on lipid peroxidation in rat liver microsomes

The stimulatory or inhibitory effects of various thiol compounds on in vitro lipid peroxidation by iron-ascorbate in rat liver microsomes were determined. Glutathione had no measurable pro-oxidant capacity, in contrast, it protected against lipid peroxidation. N-Acetyl l-cysteine and S-methyl-glutathione had no effect on in vitro lipid peroxidation. l-Cysteine stimulated lipid peroxidation and also of d-penicillamine and dl-dithiothreitol the pre-oxidant capacity predominated the anti-oxidant capacity. Cysteamine afforded a pronounced protection against in vitro lipid peroxidation. In contrast to the labile character of the glutathione dependent protection, the protection by cysteamine was not affected by heat-pretreatment of the liver microsomes or alkylating protein sulfhydryl groups by N-ethyl maleimide. Again in contrast to glutathione, the protection against in vitro microsomal lipid peroxidation by cysteamine was not reduced after in vivo lipid peroxidation induced by CC14. This suggests that even after the process of lipid peroxidation has been started, administration of cysteamine might still be beneficial.     

NADPH-dependent inhibition of lipid peroxidation in rat liver microsomes.

Microsomal NADPH-driven electron transport is known to initiate lipid peroxidation by activating oxygen in the presence of iron. This pro-oxidant effect can mask an antioxidant function of NADPH-driven electron transport in microsomes via vitamin E recycling from its phenoxyl radicals formed in the course of peroxidation. To test this hypothesis we studied the effects of NADPH on the endogenous vitamin E content and lipid peroxidation induced in liver microsomes by an oxidation system independent of iron: an azo-initiator of peroxyl radicals, 2,2'-azobis (2,4-dimethylvaleronitrile), (AMVN), in the presence of an iron chelator deferoxamine. We found that under conditions NADPH: (i) inhibited lipid peroxidation; (ii) this inhibitory effect was less pronounced in microsomes from vitamin E-deficient rats than in microsomes from normal rats; (iii) protected vitamin E from oxidative destruction; (iv) reduced chromanoxyl radicals of vitamin E homologue with a 6-carbon side-chain, chromanol-alpha-C-6. Thus NADPH-driven electron transport may function both to initiate and/or inhibit lipid peroxidation in microsomes depending on the availability of transition metal catalysts.     

Lipogenesis and gluconeogenesis in the liver of irradiated rats

The incorporation of 14C from [U-14C] glucose and 3H from 3H2O into the total lipids fatty acids and glycogen of the liver incorporation of 3H from 3H2O into blood glucose was studied in rats totally irradiated in a dose of 14.4 Gy. It is shown that in the liver of irradiated rats glucose is accumulated in considerable amounts as glycogen but it is slightly used as a source of carbon for lipid synthesis. The study of 3H incorporation shows that irradiation stimulates glucogenesis, glyconeogenesis and lipogenesis in the liver.     

Alteration of arachidonic acid metabolism with spleen microsomes of irradiated rats

Arachidonic acid is metabolized by a rat spleen microsomes cyclooxygenase into prostaglandin D₂, thromboxane B₂, 12-hydroxy-5, 8, 10-heptadecadienoic acid and by a lipoxygenase into 12-hydroxy-5, 8, 10, 14-eicosatetraenoic acid and other unidentified compounds as analyzed by a radiometric thin-layer chromatography method and by gas-chromatography-mass spectrometry. This conversion is modified when spleen microsomes are obtained from whole body irradiated rats. Furthermore, if exogenous cofactors are added to the incubation medium, other changes appear that are different for the lipoxygenase and the cyclooxygenase activities. The results suggest a regulatory role of cofactors on both enzymes and/or a modification of sensitivity of the microsomal fraction from irradiated rats to effectors.     

Dihydroxyfumaric acid induced lipid peroxidation in rat liver microsomes.

Dihydroxyfumaric acid induced lipid peroxidation in rat liver microsomes. This reaction was heat-insensitive contrary to the mitochondrial peroxidation reported in the previous paper, and was enhanced by p-chloromercuribenzoate. Additions of Fe²⁺ and Fe³⁺ stimulated both the lipid peroxidation and the disappearance of dihydroxyfumaric acid. On the other hand, addition of Mn²⁺ or Cu²⁺, which stimulated the disappearance of dihydroxyfumaric acid, inhibited the lipid peroxidation. Hydroxyl radical scavengers, superoxide dismutase and catalase had no effect on this lipid peroxidation and dihydroxyfumaric acid disappearance. The cytochrome p-450 content decreased about 70 % in parallel with the lipid peroxidation.     

Ubiquinone-9 of the flagellates Crithidia oncopelti and Astasia longa

The content of ubiquinones (Co Q) of the Astasia longa and Crithidia oncopelti protozoa was studied. The protozoa were grown on an artificial nutrient broth. The cells were separated, washed, freeze-dried, and refluxed with KOH and pyrogallol in ethanol media. The hydrolyzate was concentrated. The residue was stored at -20 degrees and filtered. An ubiquinone fraction was isolated from the filtrate by TLC on silica gel. Identification of the ubiquinone homologues was carried out by reverse phase TLC and mass spectrometry. Ubiquinones were quantitated with respect to the difference in the density between the oxidized and reduced forms of Co Q at 275 nm. The A. longa and C. oncopelti flagellates were shown to contain ubiquinone-9 (Co Q9) at a concentration of 0.48 and 1.14 mumole/g dry cells, respectively. The higher Co Q level in zooflagellates as compared to that in phytoflagellates is discussed.     

Inhibition by polyamines of lipid peroxide formation in rat liver microsomes.

Both NADPH- and ascorbic acid-dependent lipid peroxidations were inhibited by spermine, the degree of inhibition being greater with the former peroxidation. The effective concentration of spermine required for inhibition was higher when larger amounts of microsomes were used. However, the activities of NADPH-cytochrome c reductase and NADPH-peroxidase were not influenced by spermine. These results suggest that spermine inhibits lipid peroxidation by binding to phospholipids in the microsomes.