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G Leonarduzzi

Publications and source records attributed to G Leonarduzzi.

29 records · Page 2Linked to original sources
PubMed1995

Hepatocellular metabolism of 4-hydroxy-2,3-nonenal is impaired in conditions of chronic cholestasis.

4-Hydroxy-2,3-nonenal is a major aldehydic end-product of lipid peroxidation known to exert several biological and cytotoxic effects and to be produced during conditions of chronic cholestasis. Here we report that viable hepatocytes isolated from cholestatic livers of bile duct-ligated rats (BDL hepatocytes) show a significantly lower rate of HNE metabolism than control cells. This feature is likely to be the consequence of a significant inhibition in the activity of HNE-metabolizing cytosolic glutathione-S-transferase and alcohol dehydrogenase in BDL hepatocytes. Particulate NADP-dependent aldehyde dehydrogenase was also inhibited. No significant change was found for aldehyde reductase activity. A decreased hepatocellular metabolism of HNE can expose liver parenchymal and non-parenchymal cells to cytotoxic as well as pro-inflammatory and pro-fibrogenic effects of HNE, contributing to the development of chronic cholestatic liver damage.

Alcohol Dehydrogenase↗
PubMed1995

Enrichment with arachidonic acid increases the sensitivity of hepatoma cells to the cytotoxic effects of oxidative stress.

Hepatoma cells are, at most, moderately sensitive to oxidative stress. An important cause of this lack of sensitivity is the decreased content of polyunsaturated fatty acids in comparison with normal cells. These fatty acids are one cellular target of oxygen radicals, by which they are broken down into several toxic carbonyl compounds. If the membrane phospholipids of tumor cells are enriched with polyunsaturated fatty acids, such as arachidonic acid, they become able to undergo lipid peroxidation in the presence of prooxidants. This effect is studied in the highly deviated Yoshida AH-130 ascites hepatoma and in two rat hepatoma cell lines. In parallel to their increased lipid peroxidation, cells enriched with arachidonic acid and exposed to ascorbic acid/FeSO4 showed lower viability and growth than unenriched ones.

Aldehydes↗
PubMed1994

Role of aldehyde metabolizing enzymes in mediating effects of aldehyde products of lipid peroxidation in liver cells.

It is well established that many types of tumor cells have reduced lipid peroxidation capacity compared to their normal counterparts. Changes in the activity of enzymes metabolizing aldehydes produced by lipid peroxidation have also been reported in a variety of tumor cells. We have investigated the relationship between changes in lipid peroxidation and changes in aldehyde-metabolizing enzymes in normal hepatocytes and two representative rat hepatoma cell lines, McA-RH-7777 and JM2. Compared to hepatocytes, both 7777 and JM2 cells have significantly lower basal and prooxidant-induced levels of lipid peroxidation than normal hepatocytes. Using 4-hydroxynonenal (4-HNE) as substrate, both cell lines also have significantly reduced activities of alcohol dehydrogenase (ADH) and glutathione S-transferase (GST) compared to hepatocytes. JM2 cells have significantly increased aldehyde dehydrogenase (ALDH) and aldehyde reductase (ALRD) activities with 4-HNE. In 7777 cells the ALDH and ALRD activities are not different from hepatocytes. The changes in enzyme activity are inversely correlated with the sensitivity of cells to 4-HNE. JM2 cells, with increased ALDH and ALRD and decreased ADH and GST, are much more resistant to the toxic effects of 4-HNE than 7777 cells. Normal hepatocytes and JM2 cells are approximately equally resistant to 4-HNE even though hepatocytes rely primarily on GST-mediated aldehyde conjugation to metabolize 4-HNE. Coupled with previous results from our laboratories, the overall increased sensitivity of certain hepatoma cells to lipid aldehydes appears due to decreased ability of these hepatoma cells to remove toxic products of lipid peroxidation. Moreover, hepatoma cells with increased levels of aldehyde dehydrogenase and aldehyde reductase appear most like hepatocytes in their ability to metabolize lipid aldehydes.

Aldehyde Dehydrogenase↗
PubMed1993

Constitutive and inducible profile of glutathione S-transferase subunits in biliary epithelial cells and hepatocytes isolated from rat liver.

The constitutive and inducible cytosolic glutathione S-transferase (EC 2.5.1.18) subunit compositions of parenchymal cells (hepatocytes) and biliary epithelial cells (BEC) from rat liver have been quantitatively analysed using reverse-phase h.p.l.c. Hepatocytes, analysed in the absence of non-parenchymal cells, expressed constitutively the following subunits, in order of their concentration: 3, 4, 2, 1a, 1b, 8, 6 and 10. BEC express constitutively only four of the GST subunits expressed by hepatocytes and these are, in order of their concentration: subunits 2, 7, 4 and 3. Notable differences from hepatocytes are that BEC completely lack the Alpha-class subunits 1a and 1b that are major subunits in hepatocytes, Mu-class subunits make up a very low proportion of the total, and the Pi-class subunit 7 is a major subunit in BEC, whereas it is essentially absent from hepatocytes. For the first time, the effects of the inducing agents phenobarbitone (PB), beta-naphthoflavone (beta-NF) and ethoxyquin (EQ) have been characterized in a comprehensive and quantitative manner in both cell types. PB, beta-NF and EQ increased total GST protein in hepatocytes by approx. 2-fold, 3-fold and 4-fold respectively. Subunits significantly induced in hepatocytes were (in order of fold-induction): by PB, 1b > 8 > 3 > 2 > 4; by beta-NF, 1b > 8 > 2 > 3 > 4; and by EQ, 7 > 1b > 10 > 8 > 3 > 2 > 1a > 4. In BEC, neither PB nor beta-NF had significant effects on the total amount of GST protein, although PB did significantly induce subunit 3 at the expense of other subunits. EQ increased total GST protein nearly 5-fold in BEC, subunits 7 and 3 being induced dramatically above constitutive levels.

Animals↗
PubMed1993

Modulation of hepatic fibrogenesis by antioxidants.

The oxidative damage of liver tissue appears to favour a fibrogenic process, through the stimulation of TGF beta 1 and procollagen gene expression. The latter effect has been also showed by a well defined end-product of lipid peroxidation, 4-hydroxy-2,3-nonenal in human Ito cell culture. "In vivo" and "in vitro" data give evidence of a strong down modulation of TGF beta 1 and collagen expression afforded by supplementation with different antioxidant molecules.

Animals↗
PubMed1992

Vitamin E dietary supplementation inhibits transforming growth factor beta 1 gene expression in the rat liver.

Overexpression of transforming growth factor beta 1 (TGF beta 1) and increased transcription of pro-collagen type I, are known to represent major events implicated in the development of liver fibrosis under either experimental or clinical conditions. Here we report that long-term dietary vitamin E supplementation in animals undergoing an experimental model of liver fibrosis (induced by chronic treatment of rats with carbon tetrachloride) results in a net inhibition of both hepatic TGF beta 1 and alpha 2 (I) procollagen mRNA levels. Moreover, of striking interest is the observation that vitamin E supplementation per so down-modulates basal levels of TGF beta 1 mRNA in the liver of untreated animals, suggesting that a dietary regimen rich in vitamin E may potentially interfere with both the initiation and progression of the fibrosclerotic processes.

Animals↗
PubMed1992

Vitamin E dietary supplementation protects against carbon tetrachloride-induced chronic liver damage and cirrhosis.

Previous studies have shown that alpha-tocopherol (vitamin E) pretreatment of experimental animals can protect against acute liver necrosis induced by carbon tetrachloride. In this study we investigated whether the increase of vitamin E liver content by dietary supplementation influences chronic liver damage and cirrhosis induced by carbon tetrachloride in the rat. Our data indicate that vitamin E supplementation did not interfere with the growth rate of the animals and increased about threefold the liver's content of the vitamin. Vitamin E supplementation significantly reduced oxidative liver damage, but it was not effective in protecting against development of fatty liver and did not interfere with metabolic activation of carbon tetrachloride. Moreover, vitamin E-fed animals showed incomplete but significant prevention of liver necrosis and cirrhosis induced by carbon tetrachloride. This has been shown by means of histological examination, analysis of serum parameters and biochemical evaluation of collagen content. These results show that an increased liver content of vitamin E can afford a significant degree of protection against carbon tetrachloride-induced chronic liver damage and cirrhosis.

Animals↗
PubMed1990

CCl4-induced increase of hepatocyte free arachidonate level: pathogenesis and contribution to cell death.

A significant increase of the intracellular level of free arachidonic acid was observed in intact rat hepatocytes after poisoning with very low concentrations of CCl4 (0.129-0.172 mM), shown not to exert direct solvent effect. It seems likely that activation of phospholipase A2 (PLA2) is the mechanism mainly responsible for the rise of cytosolic arachidonate, since the latter is prevented by the PLA2 inhibitors indomethacin and mepacrine. The CCl4-induced delay of arachidonic acid incorporation within the cell membrane phospholipids partly contributes to its intracellular accumulation in the early phases of the poisoning. The lack of any significant protection by metabolic inhibitors (SKF 525A, metyrapone), antioxidant compounds (promethazine, diphenylphenylenediamine DPPD) or antioxidant procedures (rat pretreatment with vitamin E) leads to exclude an involvement of CCl4 biotransformation in the increase of intracellular free arachidonate. Finally, the PLA2 inhibitors employed in this study did not afford protection against the enzymic leakage of CCl4-treated hepatocytes.

Animals↗
PubMed1990

Studies on the antioxidant and free radical scavenging properties of IdB 1016 a new flavanolignan complex.

Silybin has been complexed in 1:1 ratio with phosphatidyl choline to give IdB 1016 in order to increase its bioavailability. The antioxidant and free radical scavenger action of this new form of silybin has been evaluated. One hour after the intragastric administration to rats of IdB 1016 (1.5 g/kg b.wt.) the concentration of silybin in the liver microsomes was estimated to be around 2.5 micrograms/mg protein corresponding to a final concentration in the microsomal suspension used of about 10 microM. At these levels IdB decreased by about 40% the lipid peroxidation induced in microsomes by NADPH, CCl4 and cumene hydroperoxide, probably by acting on lipid derived radicals. Spin trapping experiments showed, in fact, that the complexed form of silybin was able to scavenge lipid dienyl radicals generated in the microsomal membranes. In addition, IdB 1016 was also found to interact with free radical intermediates produced during the metabolic activation of carbon tetrachloride and methylhydrazine. These effects indicate IdB 1016 as a potentially protective agent against free radical-mediated toxic damage.

Administration, Oral↗