Chronic ethanol treatment: dolichol and retinol distribution in isolated rat liver cells

All trans retinoic acid modulates TNF-α and CYP2E1 pathways and enhances regression of ethanol-induced fibrosis markers in hepatocytes and HSCs in abstaining rodent model

Context: Our previous studies showed that all trans retinoic acid (ATRA) ameliorates alcohol-induced toxicity. Hence, we evaluated the efficacy of ATRA and abstention in the regression of alcohol-induced hepatotoxicity. Materials and methods: After ethanol administration to rats for 90 days, the regression of alcohol-induced toxicity was studied by supplementing ATRA at a dose of 100 μg/kg body weight for 30 days. It was also compared with animals in abstention. Results and discussion: Ethanol administration enhanced oxidative stress, activated HSCs and increased collagen deposition. All these alterations were reversed to a certain extent by ATRA supplementation. Conclusions: ATRA had better efficacy than just abstention in reducing ethanol-induced toxicity. The mechanism might be downregulation of CYP2E1, leading to reduced oxidative stress in the hepatocytes and thus impeding NFκB activation, cytokine production, activation of HSC and resulting in the reduction of inflammation and remodelling of fibrosis by modulating MMP and TIMP.

Methods for Isolation and Purification of Murine Liver Sinusoidal Endothelial Cells: A Systematic Review

To study the biological functions of liver sinusoidal endothelial cells (LSEC) and to identify their interplay with blood or liver cells, techniques allowing for the isolation and purification of LSEC have been developed over the last decades. The objective of the present review is to summarize and to compare the efficiency of existing methods for isolating murine LSEC. Toward this end, the MEDLINE database was searched for all original articles describing LSEC isolation from rat and mouse livers. Out of the 489 publications identified, 23 reported the main steps and outcomes of the procedure and were included in our review. Here, we report and analyse the technical details of the essential steps of the techniques used for LSEC isolation. The correlations between the prevalence of some steps and the efficiency of LSEC isolation were also identified. We found that centrifugal elutriation, selective adherence and, more recently, magnetic-activated cell sorting were used for LSEC purification. Centrifugal elutriation procured high yields of pure LSEC (for rats 30-141.9 million cells for 85-98% purities; for mice 9-9.25 million cells for >95% purities), but the use of this method remained limited due to its high technical requirements. Selective adherence showed inconsistent results in terms of cell yields and purities in rats (5-100 million cells for 73.7-95% purities). In contrast, magnetic-activated cell sorting allowed for the isolation of highly pure LSEC, but overall lower cell yields were reported (for rats 10.7 million cells with 97.6% purity; for mice 0.5-9 million cells with 90-98% purities). Notably, the controversies regarding the accuracy of several phenotypic markers for LSEC should be considered and their use for both magnetic sorting and characterization remain doubtful. It appears that more effort is needed to refine and standardize the procedure for LSEC isolation, with a focus on the identification of specific antigens. Such a procedure is required to identify the molecular mechanisms regulating the function of LSEC and to improve our understanding of their role in complex cellular processes in the liver.

The adverse effects of alcohol on vitamin A metabolism

The objective of this review is to explore the relationship between alcohol and the metabolism of the essential micronutrient, vitamin A; as well as the impact this interaction has on alcohol-induced disease in adults. Depleted hepatic vitamin A content has been reported in human alcoholics, an observation that has been confirmed in animal models of chronic alcohol consumption. Indeed, alcohol consumption has been associated with declines in hepatic levels of retinol (vitamin A), as well as retinyl ester and retinoic acid; collectively referred to as retinoids. Through the use of animal models, the complex interplay between alcohol metabolism and vitamin A homeostasis has been studied; the reviewed research supports the notion that chronic alcohol consumption precipitates a decline in hepatic retinoid levels through increased breakdown, as well as increased export to extra-hepatic tissues. While the precise biochemical mechanisms governing alcohol's effect remain to be elucidated, its profound effect on hepatic retinoid status is irrefutable. In addition to a review of the literature related to studies on tissue retinoid levels and the metabolic interactions between alcohol and retinoids, the significance of altered hepatic retinoid metabolism in the context of alcoholic liver disease is also considered.

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.

Role of ethanol in the regulation of hepatic stellate cell Function

Evidence has accumulated to suggest an important role of ethanol and/or its metabolites in the pathogenesis of alcohol-related liver disease. In this review, the fibrogenic effects of ethanol and its metabolites on hepatic stellate cells (HSCs) are discussed. In brief, ethanol interferes with retinoid metabolism and its signaling, induces the release of fibrogenic cytokines such as transforming growth factor β-1 (TGFβ-1) from HSCs, up-regulates the gene expression of collagen I and enhances type I collagen protein production by HSCs. Ethanol further perpetuates an activated HSC phenotype through extracellular matrix remodeling. The underlying pathophysiologic mechanisms by which ethanol exerts these pro-fibrogenic effects on HSCs are reviewed.

Protein and m-RNA expression of farnesyl-transferases, RhoA and RhoB in rat liver hepatocytes: action of perillyl alcohol and vitamin A in vivo

We analysed the action, in rats in vivo, of the protein isoprenylation inhibitor perillyl alcohol (POH) and that of vitamin A, alone or in association, on m-RNA and protein expression of farnesyltransferases (FTases alpha and beta subunits) and their protein substrates RhoA and RhoB, in isolated hepatocytes. Combined administration of POH and vitamin A induced a sharp decrease in FTase alpha protein after 96 h, suggesting an involvement not only of farnesyltransferases but also of geranylgeranyltransferases, which share the FTase alpha protein. FTase beta protein did not decrease. POH plus vitamin A, in contrast with POH or vitamin A alone, induced a decrease in RhoB protein, probably because of different cleavages. No modification was observed in RhoA protein. Vitamin A alone increased RhoB m-RNA and protein expression. As one of the functions of RhoB is cell polarisation, these data support our previous hypothesis of a polarised transport of vitamin A from hepatocytes to hepatic stellate cells. As the behaviours of m-RNAs and proteins in this study were often different, cytoplasmic metabolic pathways must be considered for the parameters studied. The behaviour of Rho B, which is thought to have an antioncogene function, is discussed in view of its isoprenylated forms in the membranes. These preliminary findings stress the need, when studying the association of two isoprenoids in cancer therapy, to consider normal as well as tumour-bearing animals.

Morphological and oxidative alterations on Sertoli cells cytoskeleton due to retinol-induced reactive oxygen species

Retinol (vitamin A) is involved in several cellular processes, like cell division, differentiation, transformation and apoptosis. Although it has been shown that retinol is a limitant factor for all these processes, the precise mechanisms by which retinol acts are still unknown. In the present study we hypothesised that alterations in the cytoskeleton of Sertoli cells induced by retinol supplementation could indicate an adaptive maintenance of its functions, since it plays an important role in the transformation process that we observed. Previous results demonstrated that Sertoli cells treated with retinol showed an oxidative imbalance, that leads the cell to two phenotypes: apoptosis or transformation. Our group has identified characteristics of Sertoli cells transformed by retinol which results in normal cell functions modification. In the present study the actin filament fluorescence assay and the deformation coefficient showed a modification in the morphology induced by retinol. We also observed an oxidative alteration in isolated cytoskeleton proteins and did not show alterations when these proteins are analyzed by electrophoreses. Our results showed an increase in mitochondria superoxide production and a decrease in nitric oxide levels. All results were partially or completely reverted by co-treatment of the antioxidant Trolox. These findings suggest that the cytoskeleton components suffer individual alterations in different levels and that these alterations generate a global phenotype modification and that these processes are probably ROS dependent. We believe that the results from this study indicate an adaptation of the cytoskeleton to oxidative imbalance since there was not a loss of its function.

Association of Thioacetamide and Ethanol Treatment: Dolichol and Retinol in Isolated Rat Liver Cells

Our aim was to study the distribution of dolichol, dolichol isoprenoids, and retinol in hepatocytes, Kupffer, sinusoidal endothelial and two subfractions of hepatic stellate cells, --Ito-1 and Ito-2--, after chronic treatment of rats for 2 and 4 months with a low dosage of thioacetamide associated with ethanol. Each type of cell responded differently to the two hepatotoxins. Overall, ethanol rarely affected the action of thioacetamide. Some new information emerges with regard to these hepatotoxins in comparison with the effects exerted by each of the drugs separately: treatment with thioacetamide plus ethanol determined an early decrease in dolichol in Kupffer cells (about 13% and 50% after 2 and 4 months, respectively). Moreover, after liver damage, a load of vitamin A evidenced altered percentages of the form of dolichol with eighteen isoprene units; these percentages were modified by all treatments in all cell types. The results confirm that dolichol is the preferred target of oxidative stress and suggest a relationship between dolichol and retinol metabolisms, and a possible new role of dolichol precursors, of prenyltransferases and of retinol metabolites in liver pathology.

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

This study examines how treatment with a single dose of thioacetamide, a known experimental hepatotoxin, alters the content of dolichol, dolichol isoprene units and retinol in isolated rat parenchymal and non-parenchymal liver cells at different times and when the animals are supplemented with Vitamin A. Thioacetamide (300 mg/kg i.p.) was administered in a single injection to rats, sacrificed at intervals of 0.5, 1, 2, 3, 4, 15 and 30 days. Rats supplemented, following thioacetamide, with Vitamin A, 3 days before sacrifice showed increased mortality and cellular necrosis on the third and fourth days. Parameters indicating tissue necrosis returned to normal values in surviving animals. Dolichol and retinol content showed a variable, reversible decrease, with normal levels being restored in 15-30 days. After Vitamin A, dolichol content only in hepatic stellate cells (HSC) was lower then the controls 3 and 4 days after thioacetamide treatment, in parallel with the decrease of retinol storage. The percentage of dolichol-18 is not modified by thioacetamide alone. When supplemented with Vitamin A the percentage of dolichol-18 always decreased after thioacetamide, showing that damage was still present. Mechanisms that might be operative in liver cells are briefly discussed. This approach would provide an indication to investigate how the length of the dolichol chain is determined.