Chronic administration of ethanol with high vitamin A supplementation in a liquid diet to rats does not cause liver fibrosis. 2. Biochemical observations

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.

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.

Flupenthixol and cefotiam: effects on vitamin A metabolism in rats

We examined the alterations in vitamin A metabolism as a result of flupenthixol or cefotiam administration. The impact of these drugs on indices of vitamin A status was evaluated in Brown Norway and Long-Evans rats. Intramuscular drug administration for 28 d resulted in a decline in systemic retinol. Changes in circulating retinol with time for chronic dosing showed drug treatment (P<0.001) and time (P<0.03) to be significant factors, but rat strain (P=0.33) was not a significant factor. Flupenthixol was the most active retinol-lowering compound (P<0.005). At the end of the 28 d period, hepatic retinyl ester hydrolase activity was greater in drug-treated rats than in controls (P<0.05). With regard to effects on liver reserves: (1) flupenthixol treatment resulted in vitamin A depletion (P<0.05); (2) cefotiam treatment stimulated vitamin A accumulation; (3) distinctive patterns of retinol and its esters were seen in response to treatment. It is reasonable to assume that the drugs interfere with vitamin A in at least two ways: (1) lowering of plasma retinol, an early event in the interaction, may be caused by inhibition of hepatic holo-retinol-binding protein secretion or stimulation of clearance, or both; (2) when plasma retinol levels are persistently low, and as the hepatic deposits of the xenobiotics build up, there are changes in the vitamin A pool size and composition of the liver. Candidate enzymes are retinyl ester hydrolase and cytochrome P450. The relationship between these two events will be studied in further detail.

Role of vitamin A in liver fibrosis

The relationship between vitamin A and liver fibrosis was studied with a CCl4-induced fibrosis model in rats. Depending on the time of administration, vitamin A can potentiate or reduce fibrosis: when present during CCl4-treatment parenchymal cell damage and fibrosis were enhanced, whereas vitamin A post-treatment strongly reduced fibrosis. Enhanced fibrosis was also found in rats with low hepatic retinoid levels. Administration of beta-carotene during CCl4-treatment reduced several signs of fibrosis. The notion that liver retinoids play an important role in hepatic fibrogenesis is discussed.

Simultaneous determination of retinyl esters and retinol in human livers by reversed-phase high-performance liquid chromatography

A high-performance liquid chromatographic method for the simultaneous determination of retinol and retinyl esters in human liver samples is presented. The free retinol and the prevalent retinyl esters (retinyl palmitate, oleate and stearate) are resolved within less than 30 min, using an octasilyl (C8)-substituted column and an isocratic elution with methanol-water as mobile phase. This method allows to determine in duplicate all retinyl ester concentrations in small liver samples (3-10 mg of fresh tissue). The results obtained from thirteen patients without liver disease are described.

Alcohol in combination with malnutrition causes increased liver fibrosis in rats

Rats were malnourished for 12 months with a highly inadequate fat-rich, calorie-sufficient but otherwise poly-deficient liquid diet composed of mashed potatoes with mayonnaise, comparable with the nutritional intake of many chronic alcoholics. When alcohol was incorporated into this diet, administered as whisky in drinking water available ad libitum, the livers of all eight rats showed increased fibrosis and cirrhosis as compared to the livers of the eight non-alcohol-treated, isocalorically fed, paired control rats. Alcohol-treated rats developed fibrosis and cirrhosis on a dietary fat content of 38% of total caloric intake and low blood alcohol levels, ranging from 50 to 126 mg/dl, due to gradual intake over the day and to low absolute intake (mean 11.9 +/- 0.6 g/kg per day). None of the rats died spontaneously. Malnutrition is likely to be an important factor in the development of the fibrosis of alcoholic liver disease, and this rat model may be used to study aspects of the pathogenesis.

Regulatory potential of ethanol and retinoic acid on human monocyte functions

Retinoic acid (RA), a metabolic product of vitamin A, has been shown to affect a variety of immune functions, including monocytes. Monocyte functions and mediator production are also modulated by ethanol exposure. This study demonstrates that therapeutic doses of RA (0.1-10 microM) significantly increase transforming growth factor-beta (TGF beta) production both in THP-1, human myelomonocytic cells, and in human peripheral blood monocytes. We have previously reported TGF beta induction by ethanol in human M theta. Combination of RA stimulation with acute in vitro ethanol treatment, however, resulted in significantly lower M theta TGF beta production than TGF beta levels induced by RA alone (p < 0.003). Down-regulation of M theta TGF beta production by ethanol was tested at the concentration range of 25-150 mM and occurred both at high and low RA concentrations (10-0.1 microM). In contrast to its inhibitory effect on RA-induced M theta TGF beta production, ethanol augmented TGF beta production induced by muramyl dipeptide (20 micrograms/ml), suggesting that ethanol can either up- or down-regulate M theta TGF beta production, depending on the costimulatory factors. RA also induced a moderate increase in M theta tumor necrosis factor-alpha (TNF alpha) production, which was down-regulated by ethanol both at the level of secreted and cell-associated TNF alpha. In addition to regulation of cytokine production, both RA and ethanol decreased expression of CD4 on THP-1 cells. The degree of inhibition of CD4 expression by RA was more significant than by ethanol, but RA-induced decrease in CD4 expression was not significantly affected by the combined stimulation with ethanol.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of hepatic fibrogenesis: a review of pharmacologic candidates

Therapeutic attempts with anti-fibrotic drugs are still at an experimental stage. The clinical efficacies of most agents listed in Table II have not been proved. Some potential agents, such as colchicine, analogues of PGE, gamma-interferon, inhibitors of prolyl hydroxylase, malotilate, and PUL, must be further evaluated in controlled clinical trials. In addition, almost all anti-fibrotic agents, except HOE 077, are neither liver-nor fibrosis-specific. Some site-directed (targeted) drug delivery systems, drug-loaded vesicle carrier systems, like liposomes and erythrocyte ghosts, which selectively affect the extracellular matrix-producing cells, may improve efficacy and reduce adverse effects if they can be carriers for anti-fibrotic agents. Developments in biochemistry, immunohistochemistry, and molecular biology have considerably advanced our understanding of pathogenic mechanisms of hepatic fibrosis. With the development of available pathologic and serologic markers for ongoing fibrogenesis, experimental and clinical anti-fibrotic trials have become more active. Some therapeutic strategies have chosen targets for interference in collagen metabolism. In vivo inhibition of Ito cell activation has been a focus for the anti-fibrotic studies (70). In the present review an update of pharmacologic intervention in the process of metabolic pathways of collagen, the main extracellular matrices in both interstitium and basement membrane, has been summarized. Several drugs or biochemical agents that act on different steps of collagen synthesis, crosslinking, and breakdown are listed and discussed briefly. Moreover, agents that inhibit other matrix components are also involved in the review.(ABSTRACT TRUNCATED AT 250 WORDS)

Vitamin A deficiency potentiates carbon tetrachloride-induced liver fibrosis in rats

Earlier studies have shown that retinoid administration suppresses the generation of hepatic fibrosis and stimulates its regression in normal (i.e., vitamin A-sufficient) carbon tetrachloride-treated rats. This study focuses on the possible role of a marginal or deficient vitamin A status on carbon tetrachloride-induced fibrosis. This experimental study in rats shows that vitamin A status, reflected by hepatic retinoid content (retinol and retinyl esters), modulates the development of hepatic fibrosis induced by carbon tetrachloride. In rats with low hepatic retinoid levels (12 +/- 0.9 micrograms/gm liver), carbon tetrachloride-induced liver fibrosis was more pronounced than in rats with sufficient hepatic retinoid levels (1,065 +/- 327 micrograms/gm liver). Enhanced liver fibrogenesis was confirmed both morphologically and by a higher hydroxyproline content of the liver. It was associated with a reduced liver weight and the development of parenchymal regeneration nodules. Furthermore, carbon tetrachloride treatment itself reduced the hepatic retinoid content in rats independently of the liver vitamin A status before treatment and increased serum retinol levels in vitamin A-sufficient rats. The results show that the vitamin A status of the liver plays an important role in hepatic fibrogenesis. Low hepatic vitamin A levels, which can be the result not only of low dietary intake but also of interference with vitamin A metabolism by agents such as ethanol and carbon tetrachloride, may be a risk factor for the development of liver fibrosis. We suggest that retinoids modulate collagen synthesis and deposition irrespective of the degree of hepatocellular necrosis induced by carbon tetrachloride.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic administration of ethanol with high vitamin A supplementation in a liquid diet to rats does not cause liver fibrosis. 1. Morphological observations

Rats of two strains (BN/BiRij and WAG/Rij) were fed the ethanol-containing Lieber-De Carli liquid diet supplemented with high amounts of vitamin A for 16 months. In contrast to Lieber and co-workers, who showed liver fibrosis developing within 9 months on the same diet in Sprague-Dawley rats, we were unable to demonstrate a histological and biochemical increase in liver collagen in either strain. Steatosis was present to a varying degree in both strains in ethanol-treated rats, but also in control animals. Considerable liver inflammation with focal necrosis accompanied by severe systemic inflammation was observed in 60% of the ethanol-treated WAG rats. This suggests that, at least in rats, the main effects of chronic ethanol consumption on the liver may be secondary to interference with host resistance to infections. The ethanol-high vitamin A Lieber-De Carli liquid diet does not necessarily elicit fibrosis or other characteristic histological abnormalities of human alcoholic liver disease.