Depletion of liver and esophageal epithelium vitamin A after chronic moderate ethanol consumption in rats: inverse relation to zinc nutriture

Alcohol exposure in utero perturbs retinoid homeostasis in adult rats

BACKGROUND

Maternal alcohol exposure and adult alcohol intake have been shown to perturb the metabolism of various micro- and macro-nutrients, including vitamin A and its derivatives (retinoids). Therefore, it has been hypothesized that the well-known detrimental consequences of alcohol consumption may be due to deregulations of the metabolism of such nutrients rather than to a direct effect of alcohol. Alcohol exposure in utero also has long-term harmful consequences on the health of the offspring with mechanisms that have not been fully clarified. Disruption of tissue retinoid homeostasis has been linked not only to abnormal embryonic development, but also to various adult pathological conditions, including cancer, metabolic disorders and abnormal lung function. We hypothesized that prenatal alcohol exposure may permanently perturb tissue retinoid metabolism, predisposing the offspring to adult chronic diseases.

METHODS

Serum and tissues (liver, lung and prostate from males; liver and lung from females) were collected from 60-75 day-old sprague dawley rats born from dams that were: (I) fed a liquid diet containing 6.7% alcohol between gestational day 7 and 21; or (II) pair-fed with isocaloric liquid diet during the same gestational window; or (III) fed ad libitum with regular rat chow diet throughout pregnancy. Serum and tissue retinoid levels were analyzed by reverse-phase high-performance liquid chromatography (HPLC). Serum retinol-binding protein (RBP) levels were measured by western blot analysis, and liver, lung and prostate mRNA levels of lecithin-retinol acyltransferase (LRAT) were measured by qPCR.

RESULTS

Retinyl ester levels were significantly reduced in the lung of both males and females, as well as in the liver and ventral prostate of males born from alcohol-fed dams. Tissue LRAT mRNA levels remained unchanged upon maternal alcohol treatment.

CONCLUSIONS

Prenatal alcohol exposure in rats affects retinoid metabolism in adult life, in a tissue- and sex-dependent manner. We propose that the alcohol-induced perturbations of vitamin A metabolism may predispose to detrimental consequnces on adult health.

Retinoids and nuclear retinoid receptors in white and brown adipose tissues: physiopathologic aspects

Vitamin A, ingested either as retinol or β-carotene from animal- or plant-derived foods respectively, is a nutrient essential for many biological functions such as embryonic development, vision, immune response, tissue remodeling, and metabolism. Its main active metabolite is all

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.

Vitamin A deficiency injures liver parenchyma and alters the expression of hepatic extracellular matrix

Vitamin A is an essential lipid-soluble nutrient that is crucial for morphogenesis and adult tissue maintenance. The retinoid homeostasis in the liver depends on a regular supply of vitamin A from an adequate dietary intake to preserve the normal organ structure and functions. This study focuses on the effect of vitamin A deficiency on the morphology and extracellular proteins expression of the liver in adult Wistar rats. Animals were fed with a normal (control group) or deficient vitamin A diet for 3 months. At the end of the experimental period, histological examination of the livers under light and electron microscopy revealed that vitamin A deficiency produced a loss of hepatocyte cord disposition with an irregular parenchymal organization. Abundant fat droplets were present in the cytoplasm of the hepatocytes. Elongated myofibroblastic-like cells with an irregular cytoplasmic process and without lipid droplets could be seen at the perisinusoidal space, where an elevated intensity of alpha smooth muscle actin (alpha-SMA) was observed. These results suggest that an activation of hepatic stellate cells (HSCs) occurred. Moreover, immunochemical methods revealed that vitamin A deficiency led to an increased expression of hepatic fibronectin, laminin and collagen type IV. We propose that vitamin A deprivation caused liver injury and that HSCs underwent a process of activation in which they produced alpha-SMA and synthesized extracellular components. These changes may be a factor predisposing to liver fibrosis. In consequence, vitamin A deprivation could affect human and animal health.

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)

Effects of acute ethanol doses or dietary phenobarbitol with carbon tetrachloride exposure on vitamin A status of rats

Hepatotoxins such as ethanol and CCl4 are known to adversely affect vitamin A metabolism, although the effects of acute exposure to these agents have received less evaluation. The purpose of this study was to determine the effects of vitamin A status after a series of acute ethanol doses or a series of CCl4 inhalation challenges with concurrent phenobarbital exposure in the diet of rats. The depressed hepatic vitamin A seen after one ethanol dose was not sustained after repeated dosings. However, the significantly increased urine and liver radiolabeled vitamin A recovery after three acute ethanol exposure periods suggests adaptive physiologic and metabolic changes after the initial dose. The results of repeated CCl4/phenobarbital dosings on vitamin A status paralleled, for the most part, the ethanol results. Thus, the initial acute exposure of hepatotoxic agents causes metabolic changes that are not fully sustained as the animal adapts to these challenges.

Vitamin A status of alcoholics upon admission and after two weeks of hospitalization

The purpose of this study was to determine the vitamin A status of alcoholics upon admission and after a brief in-patient stay. Fasting blood was drawn from 28 randomly selected subjects who were presumed to represent a wide range of liver disease severity. Admission laboratory tests revealed hypozincemia in 14.8% of subjects, while serum retinol and retinol-binding protein (RBP) were depressed below normal range in 15 (57.1%) and 7 (25%) of the subjects, respectively. Significant linear correlations were found between serum retinol and RBP (r = 0.90, p < or = 0.0001), serum retinol and albumin (r = 0.76, p < or = 0.0001), serum retinol and serum zinc (r = 0.56, p < or = 0.0003), and serum retinol and serum triglycerides (r = 0.42, p < or = 0.006). All subjects with elevated serum bilirubin levels demonstrated depressed serum retinol levels. However, elevated molar ratios of retinol to RBP suggest that the carrying capacity of RBP was at times exceeded, even with low serum retinol levels. Follow-up of 12 subject after 2 weeks of hospitalization revealed significant individual changes in blood chemistry, but no general trends. Although this study emphasizes the need for individual evaluation and treatment, elevated bilirubin levels may be indicative of low serum retinol levels in the alcoholic. Caution in levels of vitamin A therapy in these cases is advised, and consideration should instead be given to beta-carotene supplementation.

Effects of ethanol and carbon tetrachloride upon vitamin A status of rats

The effects of ethanol and carbon tetrachloride (CCl4) upon tissue vitamin A, liver lipids, liver cytochrome P450 and hepatic morphology were investigated. It was anticipated that CCl4 treatment would have more severe effects upon vitamin A status because CCl4 provides greater hepatic injury than does ethanol. After a 2-week standardization feeding period, young male rats were divided into four groups. For 5 weeks one group of rats (n = 17) received ethanol in liquid diets (30% of calories) while another (n = 8) was exposed to CCl4 inhalation twice a week along with phenobarbital in the diet. All groups received the National Regulatory Commission recommended level for vitamin A. Comparison of ethanol and its pair-fed control group (n = 17) revealed: decreased hepatic vitamin A, no change in serum vitamin A, increased percentage of liver lipid, and cytochrome P450 with moderate fat accumulation in hepatocytes. Comparison of the CCl4-phenobarbital group with pair-fed controls (n = 8) showed: increased serum vitamin A, decreased hepatic vitamin A, increased cytochrome P450, marked hepatic fat accumulation, hepatic cell necrosis, and early cirrhosis. Thus, CCl4 (with phenobarbitol), which is a more potent hepatotoxin as evidenced by a more elevated cytochrome P450 and distorted liver morphology, not only reduced liver vitamin A, but also increased serum vitamin A. The extent of substrate and/or organ specificity remains to be elucidated.

Alcohol, liver, and nutrition

Until two decades ago, dietary deficiencies were considered to be the major reason why alcoholics developed liver disease. As the overall nutrition of the population improved, more emphasis was placed on secondary malnutrition. Direct hepatotoxic effects of ethanol were also established, some of which were linked to redox changes produced by reduced nicotinamide adenine dinucleotide (NADH) generated via the alcohol dehydrogenase (ADH) pathway. It was also determined that ethanol can be oxidized by a microsomal ethanol oxidizing system (MEOS) involving cytochrome P-450: the newly discovered ethanol-inducible cytochrome P-450 (P-450IIE1) contributes to ethanol metabolism, tolerance, energy wastage (with associated weight loss), and the selective hepatic perivenular toxicity of various xenobiotics. P-450 induction also explains depletion (and enhanced toxicity) of nutritional factors such as vitamin A. Even at the early fatty-liver stage, alcoholics commonly have a very low hepatic concentration of vitamin A. Ethanol administration in animals was found to depress hepatic levels of vitamin A, even when administered with diets containing large amounts of the vitamin, reflecting, in part, accelerated microsomal degradation through newly discovered microsomal pathways of retinol metabolism, inducible by either ethanol or drug administration. The hepatic depletion of vitamin A was strikingly exacerbated when ethanol and other drugs were given together, mimicking a common clinical occurrence. Hepatic retinoid depletion was found to be associated with lysosomal lesions and decreased detoxification of chemical carcinogens. To alleviate these adverse effects, as well as to correct problems of night blindness and sexual inadequacies, the alcoholic patient should be provided with vitamin A supplementation. Such therapy, however, is complicated by the fact that in excessive amounts vitamin A is hepatotoxic, an effect exacerbated by long-term ethanol consumption. This results in striking morphologic and functional alterations of the mitochondria with leakage of mitochondrial enzymes, hepatic necrosis, and fibrosis. Thus, treatment with vitamin A and other nutritional factors (such as proteins) is beneficial but must take into account a narrowed therapeutic window in alcoholics who have increased needs for such nutrients, but also display an enhanced susceptibility to their adverse effects. Massive doses of choline also exerted some toxic effects and failed to prevent the development of alcoholic cirrhosis. Acetaldehyde (the metabolite produced from ethanol by either ADH or MEOS) impairs hepatic oxygen utilization and forms protein adducts, resulting in antibody production, enzyme inactivation, and decreased DNA repair. It also enhances pyridoxine and perhaps folate degradation and stimulates collagen production by the vitamin A storing cells (lipocytes) and myofibroblasts.(ABSTRACT TRUNCATED AT 400 WORDS)

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

The inability of the 'ethanol/high vitamin A Lieber-DeCarli diet' to induce liver fibrosis in two different rat strains was further evaluated by determining changes in parameters of liver cell damage and of retinoid and lipid metabolism. In the ethanol/vitamin A-treated group, slight but constant hepatic cell damage, as indicated by elevated alanine aminotransferase, aspartate aminotransferase and glutamate dehydrogenase activities in blood, was already observed at 6 months and maintained until the time of death at 16 months. Serum gamma-glutamyl transaminase activities were not raised. Moderate parenchymal liver cell damage was not accompanied by fibrosis. Hypertriglyceridemia or hypercholesterolemia were observed at 6-16 months of chronic alcohol administration. This response was strain dependent. In ethanol-treated rats of both strains, total liver retinoids and serum retinol concentrations were not altered. Therefore, the hypothesis that interaction between alcohol and retinoids is a major factor in the pathogenesis of alcoholic liver disease, needs to be reconsidered.

Vitamin A deficiency. New knowledge on diagnosis, consequences and therapy

Due to the rapid development of biochemical analyses in the last 10 years different substances like vitamin A, with an apparent clarified metabolism and action, were re-estimated. As a result, new knowledge was presented which could be essential for human health. Some details and consequences are reviewed in this paper. Marginal deficiency, which also may occur in industrialized nations, cannot be determined with certainty by usual blood analyses. The reasons for marginal deficiency are either different diseases or unbalanced nutrition. From epidemiological research it is argued that low vitamin A intake is associated with a higher incidence of cancer in different tissues. However, vitamin A may lead by over-dosing to toxic side effects. There exists a possibility that vitamin A is teratogenic also in humans. Thus, for safety reasons, woman who can become pregnant should not be advised to supplement the vitamin more than twice the RDA of the US Food and Nutrition Board for pregnant women (10,000 I.U./day) if there is no clear-cut indication. On the other hand there are indications that malformations may also caused by vitamin A deficiency.

In vitro stimulation of rat liver retinyl ester hydrolase by ethanol

Retinyl ester hydrolase (REH), the enzyme which converts retinyl esters to retinol, was partially characterized from whole liver homogenates of rats using an HPLC method with quantitation of retinol product. Optimal results were obtained by incubation of 1 mg of whole homogenate protein with 900 microM all-trans-retinyl palmitate and 275 mM 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate in a 0.1 M Tris-maleate buffer, pH 7.0, for 1 h at 37 degrees C. The enzyme assay proved to be sensitive and reproducible, with an interanimal coefficient of variation of 13% (n = 7). Because ethanol has been shown to mobilize vitamin A from the liver, we tested its effect on REH activity at several concentrations. In concentrations ranging from 0.01 to 0.5 M, ethanol added in vitro caused a concentration related increase in REH activity (from 20 to 86% above baseline activity). This increase was specific to ethanol as acetaldehyde, 1-propanol, and t-butanol either did not change or significantly decreased REH activity over the range of concentrations tested. The range of concentrations of ethanol causing stimulation in our assays was within the range of concentrations seen in the blood of rats after acute ethanol ingestion. Stimulation of REH activity could explain, in part, the well-known effects of ethanol on mobilization of vitamin A from liver stores.

Effect of ethanol and vitamin A deficiency on epithelial cell proliferation and structure in the rat esophagus

An increased risk of cancer of the esophagus has been reported in alcoholics and in populations with low dietary vitamin A consumption. As cancer is a disorder of cell proliferation and differentiation, we have assessed the combined effects of ethanol and vitamin A deficiency on cell proliferation and structure of the esophagus. Weanling male rats were fed liquid diets with either a standard amount of vitamin A or lacking vitamin A for 8 wk. Littermates were pair-fed the same diets with carbohydrate (36% of calories) replaced by ethanol. Rats were given [3H]thymidine 1 h before death, and the labeling index of the proliferative basal cells was determined on radioautographs. In rats fed the normal vitamin A diet with or without ethanol, plasma vitamin A was normal. Hepatic vitamin A was markedly decreased, whereas esophageal vitamin A was increased after ethanol feeding. Ethanol feeding resulted in a twofold increase in basal cell labeling index (14.6 +/- 0.7 vs. 6.8 +/- 0.8; p less than 0.001). The thickness of the epithelium and the morphology of basal cells were not altered by ethanol feeding. In rats fed the vitamin A-deficient diet with or without ethanol, plasma vitamin A was extremely low, and hepatic and esophageal vitamin A were unmeasurable. The epithelium was thin (with a 50% reduction in thickness) and showed abnormalities of basal cells and increased production of keratohyalin granules, changes suggesting a disorder in the epithelial differentiation. This altered differentiation caused by vitamin A deficiency was not affected by ethanol consumption. Ethanol feeding again resulted in an increase in the basal cell labeling index (13.2 +/- 1.6 vs. 4.8 +/- 0.7; p less than 0.001). Vitamin A deficiency had no effect on basal cell proliferation. Therefore, the stimulatory effect of ethanol on cell proliferation is independent of vitamin A deficiency. Nevertheless, the combined actions of ethanol and vitamin A deficiency may have a synergistic effect on the susceptibility of the esophagus to carcinogens.