Retinoid metabolism in the small intestine during development of liver cirrhosis

Background and Aims:  Retinoids are important mediators of cellular differentiation and proliferation in various epithelia of the body including the small intestine. Though alterations in intestinal epithelial cell proliferation have been noted in liver cirrhosis, mechanisms involved in the process are not well understood. This study examined the levels of various retinoids and retinoid-metabolizing enzymes in the small intestine during development of liver cirrhosis.
Methods:  Four groups of animals were used (control, phenobarbitone control, thioacetamide and carbon tetrachloride treatment). Twice-weekly intragastric or i.p. administration of carbon tetrachloride or thioacetamide, respectively, produced liver cirrhosis after 3 months, which was confirmed through histology and serum markers. Retinoid levels were measured by high-performance liquid chromatography.
Results:  A decrease in the levels of retinal, retinoic acid and retinol was evident in the intestine by 3 months, when cirrhosis was evident histologically, and these remained low until 6 months. A decrease in the activities of retinaldehyde oxidase, retinaldehyde reductase and retinol dehydrogenase was also seen in intestine from cirrhotic rats.
Conclusion:  These results suggest that altered retinoid metabolism in the intestine of cirrhotic rats might have an influence on changes in intestinal epithelial cell differentiation, seen in liver cirrhosis.     

Decreasing serum concentrations of all-trans, 13-cis retinoic acids and retinol during fasting and caloric restriction

OBJECTIVES: To investigate the effects of caloric restriction on the serum concentrations of retinoids in man. DESIGN: Samples were drawn before and during caloric restriction by fasting or 4-6 weeks after gastric surgery. SUBJECTS: The fasting group included 17 healthy subjects (11 women and six men) and 16 obese patients (10 women and six men) who underwent bariatric surgery (vertical banded gastroplasty). MAIN OUTCOME MEASURES: Serum concentrations of all-trans, 13-cis, 4-oxo-13-cis retinoic acids and retinol. RESULTS: The serum concentrations of retinol, all-trans and 13-cis retinoic acids decreased by about 20% after 5 days of fasting. After gastroplasty, the serum concentration of retinol, all-trans, 13-cis retinoic acids, retinol-binding protein and transthyretin also decreased to a similar extent after 1 month. In both groups we found a correlation between the delta values of 13-cis retinoic acid and its metabolite 4-oxo-13-cis retinoic acid. In all subjects there were also correlations between the delta values of the retinoids. However, these correlations were comparatively weak (e.g. r2 = 0.36 for retinol--all-trans retinoic acid). The change in retinoid concentrations did not correlate to the change of weight or body mass index. CONCLUSION: Our results support the hypothesis that serum retinol is one of the determinants of serum concentrations of all-trans and 13-cis retinoic acid and that the catabolism of 13-cis retinoic acid is not affected by fasting. However, in the individual case, S-Retinol is a poor predictor of S-All-trans retinoic acid.     

Early effects of high doses of retinol (vitamin A) on the in situ cellular metabolism in rat liver

Abstract: Understanding of the possible toxicity associated with hypervitaminosis A becomes increasingly important in view of the popularity of vitamin A supplementation. Hypervitaminosis A for many years may eventually lead to hepatocellular damage. In the present study, rats were treated for 7 days with high doses of retinol to study the early effects on the metabolism of different types of liver cells using (enzyme) histochemistry, immunohistochemistry and electron microscopy. Excessive intake of vitamin A activates Kupffer cells and induces accumulation of lipid droplets in fat-storing cells as well as proliferation of these cells. Moreover, it affects the metabolic heterogeneity in the liver lobules, but does not lead to apparent cell damage. Based on the changes in marker enzymes for different metabolic processes, it is concluded that the capacity for breakdown of purines, the antioxidant capacity, the potential for phagocytosis and the regulation of ammonia levels were largely decreased. Increased alkaline phosphatase activity in hepatocytes pointed to an activated process of transport of retinol esters over the bile canalicular membrane. The possible causes of these metabolic changes have been described in the discussion.     

Gastric injury induced by ethanol and ischemia-reperfusion in the rat

This study determined the role that oxygen-derived free radicals played in the production of gastric injury in rats challenged orally with concentrated ethanol or subjected to vascular compromise. In the ethanol study, rats were pretreated with a variety of free radical scavengers or enzyme inhibitors prior to exposing the stomach to 100% ethanol. At sacrifice, the degree of macroscopic damage to the glandular gastric mucosa was quantified. In separate studies, the effects of ethanol on gastric mucosal levels of enaldehydes (malondialdehyde and 4-hydroxynonenal) were examined as an index of lipid peroxidation. Superoxide dismutase and catalase pretreatment were without benefit in reducing injury in our ethanol model, excluding potential contributory roles for the superoxide anion or hydrogen peroxide, respectively. Dimethyl sulfoxide and desferoxamine were likewise without protective capabilities, eliminating a role for the hydroxyl radical. Allopurinol, a xanthine oxidase inhibitor, provided no protection under acute conditions, even though partial protection was noted when administered chronically. Further, enaldehyde levels were not increased over control levels in alcohol-exposed mucosa, indicating no enhanced lipid peroxide formation. In contrast, in animals in which ischemia to the stomach was induced followed by reperfusion, marked gastric injury was observed in combination with enhanced enaldehyde levels. Prevention of enaldehyde formation by a 21-aminosteroid concomitantly prevented injury induced by ischemia-reperfusion. These findings support the conclusion that ischemia-reperfusion injury to the stomach is an oxygen-derived free radical process whereas ethanol-induced injury clearly involved some other process. Although allopurinal was partially protective against ethanol damage when administered chronically, observations in other models of injury suggest that this action is independent of its inhibitory effect on xanthine oxidase.     

First pass metabolism of ethanol is strikingly influenced by the speed of gastric emptying

Background—Ethanol undergoes a first passmetabolism (FPM) in the stomach and liver. Gastric FPM of ethanolprimarily depends on the activity of gastric alcohol dehydrogenase(ADH). In addition, the speed of gastric emptying (GE) may modulateboth gastric and hepatic FPM of ethanol.
Aims—To study the effect of modulation of GE onFPM of ethanol in the stomach and liver.
Methods—Sixteen volunteers (eight men andeight women) received ethanol (0.225 g/kg body weight) orally andintravenously, and the areas under the ethanol concentration timecurves were determined to calculate FPM of ethanol. In seven of thesesubjects, FPM of ethanol was measured after the intravenousadministration of 10 mg metoclopramide (MCP) and 20 mgN-butylscopolamine (NBS) in separate experiments to eitheraccelerate or delay GE. GE was monitored sonographically by integrationof the antral area of the stomach every five minutes for 90 minutesafter oral ethanol intake. In addition, gastric biopsy specimens weretaken to determine ADH activity and phenotype, as well as to evaluategastric histology. Blood was also drawn for ADH genotyping.
Results—GE time was significantly delayed by theadministration of NBS as compared with controls (p<0.0001) and ascompared with the administration of MCP (p<0.0001). This wasassociated with a significantly enhanced FPM of ethanol with NBScompared with MCP (p = 0.0004). A significant correlation was notedbetween GE time and FPM of ethanol (r = 0.43, p = 0.0407).Gastric ADH activity did not significantly correlate with FPM of ethanol.
Conclusion—FPM of ethanol is strikingly modulatedby the speed of GE. Delayed GE increases the time of exposure ofethanol to gastric ADH and may therefore increase gastric FPM ofethanol. In addition, hepatic FPM of ethanol may also be enhanced asthe result of slower absorption of ethanol from the small intestine. Thus a knowledge of GE time is a major prerequisite for studying FPM ofethanol in humans.

Keywords:first pass metabolism of ethanol; gastric emptying; alcohol dehydrogenase; ethanol metabolism; stomach

     

Influence of aging on ethanol and acetaldehyde oxidation in female rat liver

Rates of ethanol metabolism by alcohol dehydrogenase, the microsomal ethanol oxidizing system (MEOS), and catalase were similar in liver preparations from young (4-5 months) and old (24-27 months) female Fischer 344 rats. On the other hand, rates of acetaldehyde metabolism by mitochondrial aldehyde dehydrogenase (ALDH) were 15-20% lower in livers of old rats than in those of younger ones. Results with the ALDH inhibitor cyanamide indicated that a decline in ALDH activity of this magnitude would not increase acute ethanol hepatotoxicity.     

Effects of ethanol and its metabolites on collagen synthesis by cultured rat liver cells

The effects of ethanol and its metabolites on collagen synthesis in cultured rat Ito cells and hepatocytes were studied. In cultured Ito cells, collagen synthetic ability reached peak values after incubation for 24 h and after 8 h in cultured hepatocytes. The distribution patterns of 14C-activity in each collagen fraction were quite different between the two cell types. About 80% of the activity was found in the degraded collagen fraction in the cultured hepatocytes, indicating a rapid turn-over of collagen protein in this cell type. In the Ito cells, the activity in the intact collagen was about 50%. Ethanol and its metabolites added to the incubation medium did not stimulate collagen synthesis in either cell type; rather, they inhibited it. Collagen metabolism in the cells to which ethanol or its metabolites had been added was slower than in the control medium. These results indicate that the pathogenesis of alcoholic liver fibrosis is not simple and that interaction or modulation of cell function in different types of cells should be considered when examining the mechanisms of fibrogenesis in alcoholic liver fibrosis.     

Inhibition of fatty acid oxidation and in normal and hypoxic perfused rat hearts by 2-tetradecylglycidic acid.

Studies with a new fatty acid oxidation inhibitor, 2-tetradecylglycidic acid, showed that half-maximal inhibition of oleate oxidation occurred at concentrations of 3 × 10⁻⁶m. 2-Tetradecylglycidic acid also inhibited endogenous fatty acid oxidation, but had little effect on octanoate oxidation. The inhibition of long chain fatty acid oxidation produced by 2-tetradecylglycidic acid depended on its time exposure to the hearts. At low work loads it had no effect on left ventricular pressure development or aortic output, but was inhibitory at high work loads when the capacity for glucose oxidation was exceeded.The relationship of oleate concentration (with 2% albumin present) to pyridine nucleotide fluorescence and to the stimulation of oxygen consumption was examined using hearts perfused with glucose. Pyridine nucleotide fluorescence and oxygen consumption were both increased, with half-maximal effects occurring at 0.08 mm and 0.2 mm oleate, respectively. Oleate addition, both in the absence and presence of insulin, increased oxygen consumption to a greater degree than expected from the theoretical decrease of the $\text{P}\text{O}$ ratio associated with fatty acid oxidation. At fatty acid/albumin molar ratios of 2.5 or greater, contractility was impaired and oxygen consumption increased even further. Pyridine nucleotides remained reduced indicating the absence of an uncoupling effect on oxidative phosphorylation. The oxygen wasting effect of fatty acids is interpreted as caused by long chain fatty acyl-CoA formation and hydrolysis.In working heart preparations made hypoxic by lowering the perfusate oxygen content to about 35%, addition of 1 mm oleate to the perfusate resulted in a reversible decrease in left ventricular pressure development and aortic output. Perfusion with 5 × 10⁻⁵m 2-tetradecylglycidic acid for 40 min before oleate addition prevented this deleterious effect of oleate during hypoxia. Photographs of the surface pyridine nucleotide fluorescence showed that addition of oleate to the hypoxic heart resulted in an increase in the size and number of anoxic areas. Subsequent addition of 10⁻⁵m 2-tetradecylglycidic acid caused the anoxic areas to disappear. These results indicate that the deleterious effects of fatty acids on the hypoxic myocardium are due to an increased oxygen demand resulting from accelerated fatty acid oxidation.     

Ciprofloxacin decreases the rate of ethanol elimination in humans

BACKGROUND: Extrahepatic ethanol metabolism is postulated to take place via microbial oxidation in the colon, mediated by aerobic and facultative anaerobic bacteria. AIMS: To evaluate the role of microbial ethanol oxidation in the total elimination rate of ethanol in humans by reducing gut flora with ciprofloxacin. METHODS: Ethanol was administered intravenously at the beginning and end of a one week period to eight male volunteers. Between ethanol doses volunteers received 750 mg ciprofloxacin twice daily. RESULTS: A highly significant (p=0.001) reduction in the ethanol elimination rate (EER) was detected after ciprofloxacin medication. Mean (SEM) EER was 107.0 (5.3) and 96.9 (4.8) mg/kg/h before and after ciprofloxacin, respectively. Faecal Enterobacteriaceae and Enterococcus sp. were totally absent after medication, and faecal acetaldehyde production capacity was significantly (p<0.05) decreased from 0.91 (0.15) to 0.39 (0.08) nmol/min/mg protein. Mean faecal alcohol dehydrogenase (ADH) activity was significantly (p<0. 05) decreased after medication, but ciprofloxacin did not inhibit human hepatic ADH activity in vitro. CONCLUSIONS: Ciprofloxacin treatment decreased the ethanol elimination rate by 9.4%, with a concomitant decrease in intestinal aerobic and facultative anaerobic bacteria, faecal ADH activity, and acetaldehyde production. As ciprofloxacin has no effect on liver blood flow, hepatic ADH activity, or cytochrome CYP2E1 activity, these effects are probably caused by the reduction in intestinal flora.     

Serum retinoic acid, retinol and retinyl palmitate levels in patients with lung cancer

OBJECTIVES: Epidemiological studies have shown an inverse relationship between dietary vitamin A intake and the risk of developing lung cancer. The aim of this study was to investigate the vitamin A status in patients with lung cancer, by determining the serum levels of retinoic acid, retinol and retinyl palmitate. METHODS: In total, 36 patients with lung cancer and 27 controls were assessed. Of the patients 14 had squamous cell carcinoma, 3 adenocarcinoma, 15 non-small cell lung cancer and 4 small cell lung cancer. Serum retinoic acid, retinol and retinyl palmitate levels were determined with HPLC and UV detection, after liquid extraction. RESULTS: Serum retinol levels did not differ between patients (733.5 +/- 326.4 ng/mL) and controls (734.5 +/- 337.1 ng/mL). The retinyl palmitate concentration tended to be lower in patients (14.3 +/- 9.7 ng/mL) than in controls (16.7 +/- 13.7 ng/mL). The serum retinoic acid levels were significantly lower in patients (1.9 +/- 0.6 ng/mL) than in controls (2.5 +/- 1.1 ng/mL, P < 0.05). A positive correlation was observed between the retinol and retinoic acid levels and retinyl palmitate and retinoic acid levels. CONCLUSIONS: The lower levels of retinoic acid in patients with lung cancer suggest there may be a deficiency or impairment in retinol metabolism in these patients. Further studies with larger numbers of patients are needed to evaluate the possible relationship between serum retinoid levels and lung cancer.     

维甲酸对胃癌生长和肝转移抑制作用的实验研究

[目的]研究维甲酸（RA）对裸鼠原位荷人胃癌细胞BGC-803移植瘤和肝转移的抑制作用。[方法]建立人胃癌裸鼠原位种植肝转移模型,分为2组,对照组和RA组,种植后第5天开始,分别自腹腔注射0．85％氯化钠、RA（1mg／kg）,每日1次,第8周处死动物,检测抑瘤率、胃癌细胞凋亡指数（AD,观察肿瘤细胞肝转移以及金属基质蛋白酶2（MMP-2）、增殖细胞核抗原（PCNA）的表达情况。[结果]RA组的抑瘤率为37．8％。与对照组相比,RA组胃癌生长、肝转移受到明显抑制（P〈0．05）,AI明显增高（P〈0．05）,MMP-2、PCNA的表达降低。[结论]RA对胃癌生长和肝转移的抑制可能通过诱导胃癌细胞凋亡、抑制细胞增殖以及肿瘤细胞外基质降解实现的。     

Inhibition of fatty acid oxidation and decrease of oxygen consumption of working rat heart by 4-bromocrotonic acid

Nonesterified fatty acids (NEFA), glucose and lactate are major fuels for myocardial energy production. The ratio of energy produced and oxygen consumed, which can be expressed as ATP/O ratio, is different for each substrate: e.g. 3.17 for glucose and 2.83 for palmitate. Direct measurements, however, have shown that the difference of oxygen consumption is about twice as great as theoretically expected. This difference is of little significance under aerobic conditions, but may be important when oxygen supply is restricted. Numerous attempts have been made to reduce oxygen consumption by activating carbohydrate oxidation or inhibiting fatty acid metabolism. As the rate of fatty acid oxidation has been shown to depend on arterial concentrations of NEFA and albumin, this may be one point of control. Further approaches such as increasing the arterial levels of glucose, insulin and potassium, have been controversially discussed. As 4-bromocrotonic acid has been found to inhibit the fatty acid oxidation in isolated rat heart mitochondria [8], this might be an effective agent to save oxygen by reducing the rate of fatty acid oxidation in intact hearts.     

Protective role of melatonin and retinol palmitate in oxidative stress and hyperlipidemic nephropathy induced by adriamycin in rats

Abstract: We have studied the effects of melatonin and retinol palmitate (RP) on the nephropathy and oxidative stress induced by a single and high dose of adriamycin (AD) in Wistar male rats. A dose of melatonin (75 μg/ kg/day) and a dose of RP (0.25 g oily solution/kg/day, sc) were injected 3 and 9 days before and after the administration of AD (25 mg/kg, i.p.), respectively. After the decapitation, samples were taken from the neck vascular trunk in order to determine the triglycerides, total cholesterol, phospholipids, HDL-cholesterol, total proteins, urea, lipoperoxides, and reduced glutathione (GSH). We estimated the lipoperoxide and glutathione (GSH) contents in renal homogenates, and the excretion of proteins in urine over a 24 hr period. The administration of AD caused significant increases in proteinuria and in the other parameters studied [lipids (triglycerides, total cholesterol, phospholipids, and HDL-cholesterol), nonprotein nitrogen compounds, and lipoperoxides]. AD increased the lipoperoxide content, but it decreased the GSH content in the kidney. Both melatonin and RP, although melatonin more significantly, decreased the intensity of the changes produced by the administration of AD alone. In fact, melatonin was quite efficient in reducing the formation of lipoperoxides, restoring renal GSH content and decreasing remarkably the severity of proteinuria. These results support the powerful antioxidant action of melatonin at renal level and a lower antioxidant action of retinol. Likewise, these data reinforce the hypothesis which supports the pathogenetic role and the close relation between the oxidative stress and the expression of the nephropathy induced by AD. However, in spite of this obvious antioxidant effect of melatonin in the kidney, additional studies are required to establish accurately the role of this pineal indole in the regulation and dynamics of the antioxidative defense enzyme system, which neutralizes the damaging effect of free radicals, both endogenous and exogenous, in this organ.     

Oxidation of ethanol in the rat brain and effects associated with chronic ethanol exposure

It has been reported that chronic and acute alcohol exposure decreases cerebral glucose metabolism and increases acetate oxidation. However, it remains unknown how much ethanol the living brain can oxidize directly and whether such a process would be affected by alcohol exposure. The questions have implications for reward, oxidative damage, and long-term adaptation to drinking. One group of adult male Sprague–Dawley rats was treated with ethanol vapor and the other given room air. After 3 wk the rats received i.v. [2-¹³C]ethanol and [1, 2-¹³C₂]acetate for 2 h, and then the brain was fixed, removed, and divided into neocortex and subcortical tissues for measurement of ¹³C isotopic labeling of glutamate and glutamine by magnetic resonance spectroscopy. Ethanol oxidation was seen to occur both in the cortex and the subcortex. In ethanol-naïve rats, cortical oxidation of ethanol occurred at rates of 0.017 ± 0.002 µmol/min/g in astroglia and 0.014 ± 0.003 µmol/min/g in neurons, and chronic alcohol exposure increased the astroglial ethanol oxidation to 0.028 ± 0.002 µmol/min/g (P = 0.001) with an insignificant effect on neuronal ethanol oxidation. Compared with published rates of overall oxidative metabolism in astroglia and neurons, ethanol provided 12.3 ± 1.4% of cortical astroglial oxidation in ethanol-naïve rats and 20.2 ± 1.5% in ethanol-treated rats. For cortical astroglia and neurons combined, the ethanol oxidation for naïve and treated rats was 3.2 ± 0.3% and 3.8 ± 0.2% of total oxidation, respectively. ¹³C labeling from subcortical oxidation of ethanol was similar to that seen in cortex but was not affected by chronic ethanol exposure.     

Effect of chronic ethanol administration on iron metabolism in the rat

This study shows that the ingestion of ethanol provokes alterations in iron metabolism which may lead to iron overload. Impaired release of reticuloendothelial iron was shown by a decrease of the maximum red blood cell utilization when radioactive iron was supplied as colloidal iron. An impairment in the erythropoietic activity of ethanol-treated animals was also observed, as can be seen from the reduced plasma iron turnover and red blood cell utilization within 24 h of iron administration. A rise in marrow transit time was also observed. In ethanol-treated rats there was an increase in the amount of iron retained both in the liver and the spleen. This was observed in both sexes and also in the offspring from ethanol-treated mothers.     

Subcellular changes and apoptosis induced by ethanol in rat liver

The livers of rats given ethanol for 5 weeks showed marked structural alterations of hepatocytes of acinar zone 3 including mitochondrial pleomorphism, increased smooth endoplasmic reticulum and deposition of small (less than 0.5 micron) lipid droplets. In addition, apoptotic bodies involving altered parenchymal cells were frequently observed, together with prominent mononuclear infiltrates adjacent to the terminal hepatic veins. It is suggested that 'age' of liver cells may play a role in the preferential perivenular localization of early ethanol-induced liver damage.     

Human leukemic K562 cells treated with cytosine arabinoside: enhancement of erythroid differentiation by retinoic acid and retinol

Abstract: Human leukemia K562 cells can be induced to erythroid differentiation when treated with a variety of compounds, including hemin, cytosine arabinoside and 5-azacytidine. Following erythroid induction, K562 cells express at high level γ-globin and accumulate both Hb Portland and Hb Gower 1. In this paper we determined whether a combination treatment of K562 cells with suboptimal concentrations of cytosine arabinoside and retinoids lead to full expression of differentiated functions. Cell growth kinetics studies, intracellular detection of hemoglobin by benzidine staining and hemoglobin analysis by cellulose acetate were performed. The results obtained show that (a) retinoic acid and retinol are not able to induce differentiaton of K562 cells and (b) cytosine arabinoside induces differentiation only when used at 100–300 nmol/l concentrations. In addition, our data demonstrate that erythroid differentiation of K562 occurs when 40 μmol/l of retinoic acid or retinol are added together with 75 nmol/l cytosine arabinoside.     

Inhibition of palmitoylcarnitine oxidation by pyruvate in rat heart mitochondria

The oxidation of 1-14C-palmitoylcarnitine by rat heart mitochondria has been measured by assessing both the disappearance of substrate and the appearance of labelled products. Pyruvate inhibited palmitoylcarnitine oxidation by about 40%. Fifty percent inhibition occurred at about 20 mumol/L pyruvate. The inhibitory effect of pyruvate required entry of pyruvate into mitochondria since it did not occur in the presence of alpha-cyano-4-hydroxycinnamic acid, an inhibitor of the mitochondrial pyruvate transporter. The inhibitory effect of pyruvate also required an active pyruvate dehydrogenase. These studies indicate a mechanism that may be important in the replacement of fatty acids by carbohydrate as fuels of respiration of the heart during the transition from the starved to the fed state.