Effect of a load of Vitamin A after acute thioacetamide intoxication on dolichol, dolichol isoprenoids and retinol content in isolated rat liver cells

Polyprenols from Taxus chinensis var. mairei prevent the development of CCl₄-induced liver fibrosis in rats

ETHNOPHARMACOLOGICAL RELEVANCE

The aim of this study was to investigate the anti-fibrotic effects and the possible underlying mechanisms of taxus polyprenols (TPs) isolated from the needles of Taxus chinensis var. mairei.

MATERIALS AND METHODS

The animals were randomly divided into normal control with vehicles only (olive oil), rat model given CCl₄ only, CCl₄+low TPs (48 mg/kg), CCl₄+medium TPs (120 mg/kg), CCl₄+high TPs (300 mg/kg), and CCl₄+Polyene phosphatidylcholine (PP, 120 mg/kg). The rat model of liver fibrosis was induced by subcutaneous injection of 40% (v/v) of CCl₄ diluted in olive oil (3 mL/kg body weight) twice per week for 8 weeks. Liver histopathological study was performed. Aspartate transaminase (AST), alanine transaminase (ALT), alkaline phosphatase (ALP) and albumin (ALB) of the serum were determined for evaluating the liver function. In order to reveal the possible mechanisms of the anti-fibrotic effects, oxidative stress level, hepatic collagen metabolism, and hepatic stellate cells (HSCs) activation were investigated. Furthermore, the mRNA expression of the fibrotic-related factors was measured by the quantitative real-time RT-PCR.

RESULTS

TPs successfully attenuated liver injury induced by CCl₄ shown by histopathological sections of livers and improved liver function as indicated by decreased ALT, AST and ALP levels and increased ALB levels in serum of the rats. TPs significantly increased the hepatic Cu/Zn SOD and GSH-Px activities along with GSH content while a remarkable decrease in MDA content. Both immunohistochemical staining and mRNA expression levels of α-SMA indicated a profound suppression of HSCs activation. Furthermore, it significantly inhibited the mRNA expression of the pro-fibrotic cytokines Col α1(I), Col α1(Ш), MMP-2, TIMP-1, TIMP-2, PDGF-β, TGF-β1, CTGF and TNF-α and restored the hepatoprotective factor HGF.

CONCLUSION

These results suggest that the protective effects of TPs in chronic CCl₄-induced liver fibrosis might be related with the reduction of oxidative damage, the inhibition of HSCs activation, the down-regulation of pro-fibrogenic stimuli and the protection of hepatocytes.

Chronic High Doses of Thioacetamide Followed by Vitamin A Modify Dolichol, Dolichol Isoprenoids, and Retinol Content in Rat Liver Cells

Our line of researches follows the hypothesis that dolichol and retinol metabolism might be interrelated and involved in liver fibrosis. To this end, in this study rats were subjected to chronic treatment with thioacetamide (TAA) (300 mg/L liquid diet) for 1 and 2 months and, after liver damage had occurred, supplemented with vitamin A before sacrifice. Dolichol, dolichol isoprene units, and retinol content were determined in isolated parenchymal and sinusoidal liver cells (hepatic stellate cells; Kupffer cells; sinusoidal endothelial cells). Dolichol increased in hepatocytes after TAA treatment, with or without vitamin A. Dolichol decreased in the other cells. Retinol in general decreased. In hepatocytes, retinol decreased only on normal nutrition, while the vitamin A load was taken up normally. The percentages of dolichol isoprene units (Dol-16 to Dol-20, in rats) confirm that Dol-18, which was not modified in percentage by TAA on normal nutrition, did not increase after vitamin A, as it did in control cells (7-12%). The behavior of Dol-18 was similar in all the cells studied. Vitamin A might reveal a latent damage produced by TAA on dolichol homologues. These data support previous hypotheses that the action of TAA depends on the administration modality, the dosage, and the diet, and that Dol-18 might have different functions and compartmentalization in the cells. Furthermore, the results support the hypothesis that dolichol chain length might be interrelated with retinol metabolism, perhaps through their metabolites.

Rat HMGCoA reductase activation in thioacetamide-induced liver injury is related to an increased reactive oxygen species content

BACKGROUND/AIMS

In thioacetamide-induced liver injury a modification of isoprenoid content and an increase of reactive oxygen species has been described. We have examined how reactive oxygen species influence the 3-hydroxy-3-methylglutaryl coenzyme A reductase, the rate limiting enzyme of the isoprenoid biosynthetic pathway, to verify if changes of that enzyme activity are involved in the changed lipid composition of the liver.

METHODS

In chronic and acute thioacetamide-treated rat liver we measured the reactive oxygen species content, the activation state and K(M), the level and degradation rate of the hepatic reductase, its short term regulatory enzymes and the liver lipid profile.

RESULTS

In thioacetamide-treated rat liver, the reactive oxygen species content is high and the reductase is fully activated with no modifications in its K(M) and its short term regulatory enzymes. The reductase level is reduced in chronic thioacetamide treated rats and its degradation rate is altered.

CONCLUSIONS

The data show a relationship between reactive oxygen species production and altered 3-hydroxy-3-methylglutaryl coenzyme A reductase activity. It is suggested that reducing the levels of reactive oxygen species may improve the altered lipid profile found in liver injury.