Vitamin A absorption in cystic fibrosis: risk of hypervitaminosis A.

Vitamin A status was examined in nine adult cystic fibrosis patients and six adult control subjects, together with an assessment of their ability to absorb 10,000 IU of retinyl palmitate from a test meal, taken with appropriate pancreatic enzyme supplements. Median baseline values for plasma retinol and carotene, as well as median serum retinol binding protein concentrations, were significantly lower in cystic fibrosis patients than in control subjects. One cystic fibrosis patient had a raised fasting plasma retinyl ester concentration suggestive of chronic hypervitaminosis A, but no symptoms of toxicity. Measures of vitamin A absorption were also significantly lower in cystic fibrosis patients, although there was considerable overlap with control values. No correlation was observed between measures of baseline status and vitamin A absorption. Measurement of plasma retinyl esters may be an appropriate investigation in those patients considered to be at risk of chronic hypervitaminosis A.     

Role of hepatic vitamin A and lipocyte distribution in experimental hepatic fibrosis

ABSTRACT— Lipocytes are the major site of hepatic vitamin A storage, and they have been demonstrated to lose their vitamin A content in the process of hepatic fibrosis. To investigate the relationship between hepatic vitamin A content and the degree of hepatic fibrosis, we measured levels of retinyl palmitate and retinol in the CCl₄-induced fibrotic liver using high-performance liquid chromatography. We estimated hepatic collagen content using a spectrophotometric analysis with sirius red, and also by measuring hydroxyproline levels. Lipocytes were detected by an immunoperoxidase method with anti-desmin antibody, and were counted morphometrically through a Texture Analyzing System. A significant negative correlation was observed between the level of retinyl palmitate and collagen content (r = –0.64) as well as the hydroxyproline level (r = –0.69) in the CCl₄-induced fibrotic liver. In the process of fibrosis, hepatic retinol levels were elevated in association with a decrease in retinyl palmitate. In particular in the early stage of fibrosis, lipocytes increased remarkably in number in fibrotic areas in spite of a decrease in total hepatic vitamin A. The present study suggests that an increase in hepatic retinol as well as a decrease in retinyl palmitate may facilitate the process of hepatic fibrosis produced by lipocytes.     

Amounts and types of fatty acids in meals affect the pattern of retinoids secreted in human chylomicrons after a high-dose preformed vitamin A intake

High doses of preformed vitamin A are commonly used to correct vitamin A deficiency. Newly absorbed vitamin A is secreted mainly as retinyl esters in chylomicrons. The effect of changing types and amounts of fatty acids on fatty acid composition of chylomicron retinoid esters when a high dose of vitamin A is ingested have not been studied previously. In the present study, 10 healthy young men ingested, in a random order, mixed meals containing 15,000 retinol equivalents (RE) of vitamin A (as retinyl palmitate) and either no fat or 40 g of fat provided as butter, olive oil, or sunflower oil. Fasting and postprandial blood samples were obtained for 7 hours after meals. Free retinol and the main retinyl esters (retinyl palmitate/oleate, stearate, and linoleate) were measured in chylomicrons by high-performance liquid chromatography (HPLC). Chylomicron retinyl palmitate/oleate and retinyl stearate concentrations significantly increased after intake of the 4 test meals. Conversely, chylomicron retinyl linoleate and chylomicron free retinol significantly increased only after the sunflower and the fat-free meals, respectively. The main retinoid secreted in chylomicrons after the intake of the fat-rich meals was retinyl palmitate/oleate, accounting for 63% to 79% of total RE, but it was free retinol after the fat-free meal (51% of total RE). Thus, the retinoid pattern secreted in chylomicrons after the intake of a high dose of preformed vitamin A depends on type and amounts of fatty acids ingested. To explain this result we suggest that the esterification process of retinol in the enterocyte by lecithin:retinol acyltransferase can be overwhelmed by a high load of vitamin A. Consequently, a significant proportion of the retinol is esterified by acyl coenzyme A:retinol acyltransferase (ARAT) with ingested fatty acids, explaining the appearance of retinyl linoleate in chylomicrons after the sunflower oil meal. If a high dose of preformed vitamin A is ingested with a fat-free meal, a significant proportion of retinol is not esterified, owing to the lack of fatty acids for ARAT, which explains the appearance of free retinol in chylomicrons.     

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.     

Metabolism of all-trans-[11-3H]retinyl acetate in the testes of young rats

All-trans-[11-3H]retinyl acetate was injected directly into the testes of young rats and testicular and liver metabolites were analyzed by HPLC at 6, 24 and 72 h post injection. All-trans-retinyl acetate was hydrolyzed to retinol and further metabolized to polar compounds and a trace of retinoic acid, or reesterified to various retinyl esters including retinyl palmitate and retinyl stearate. Thus, retinyl ester hydrolyzing and esterifying enzymes are present in the testes of young rats. Eleven, twelve and ten radioactive peaks were observed at 6, 24 and 72 h, respectively. The amount of radioactivity in retinyl palmitate and retinyl stearate increased with time and reached 24 and 4%, respectively, by 72 h. Although retinol predominated, retinyl palmitate was the major esterified form in testis. The amount of radioactivity in retinol and retinyl acetate decreased with time and increased in unidentified metabolites and retinyl esters. An insignificant amount of radioactivity was found in liver. We conclude from these results that some vitamin A is stored/accumulated in the testes as retinyl esters in order to support the process of spermatogenesis and other physiological functions and that the retinol esterifying enzyme is quite active in the testes of young rats.     

Plasma kinetics of oral retinol in cancer patients

Concurrent with a phase I trial of retinol in patients with advanced cancer, we studied the plasma kinetics of both retinol and its major metabolites, retinyl palmitate and retinyl stearate. Retinol was administered to 12 patients in daily oral doses of 60,000, 100,000, 150,000, or 200,000 units/m2. Patients remained on treatment until the development of dose-limiting toxic effects or disease progression. Retinoid plasma kinetics were studied on the first day of treatment, at Weeks 2 and 4, and every 2-3 months thereafter as long as the patient remained on therapy. A high-performance liquid chromatography assay was used to quantitate the plasma concentration of both retinol and its fatty acid esters. There was no significant change in the plasma retinol concentration up to 24 hours after a single oral dose of retinol (P greater than 0.05). However, the plasma concentration of retinyl palmitate and retinyl stearate markedly increased with a mean time to peak plasma concentration of 4.3 +/- 0.7 hours. Retinyl palmitate rapidly disappeared from the plasma with an initial phase half-life of 2.2 +/- 0.9 hours. The terminal phase half-life appeared prolonged and could not be accurately determined. Retinyl stearate was detected in the plasma of all patients with plasma concentrations paralleling and ranging from 20% to 40% those of retinyl palmitate. With prolonged retinol administration, peak plasma retinyl palmitate concentrations increased with both increasing retinol dose (P less than 0.001) and increasing duration of treatment (P = 0.001). In three patients with low pretreatment plasma retinol concentrations, daily retinol administration was associated with a rise in plasma retinol concentration. Because only one patient developed serious toxic effects and all patients had markedly increased plasma concentrations of retinyl esters, no conclusion could be made about the relationship between plasma retinyl ester concentration and retinol toxicity.     

Hepatic stores of retinol and retinyl esters in elderly people

Post-mortem concentrations of hepatic retinol and retinyl esters were determined in 40 subjects aged over 65 years to assess the effects of disease and malnutrition on vitamin A reserves. Three groups of patients (mean age 79.6 years) were studied: (1) previously healthy, (2) chronically ill, (3) chronically ill and wasted. There was no significant difference in height or age between the groups, but group 3 was lighter than both group 1 (P less than 0.001) and group 2 (P less than 0.05). Free retinol and retinyl esters were measured by high pressure liquid chromatography, and the total hepatic retinol calculated. Analysis of variance showed that the three groups differed significantly (P less than 0.02) with regard to total retinol, retinyl palmitate and total retinyl ester content.     

Transfer of retinol from parenchymal to stellate cells in liver is mediated by retinol-binding protein.

Newly absorbed chylomicron remnant retinyl ester is endocytosed by parenchymal liver cells, and retinol is subsequently transferred to perisinusoidal stellate cells in liver. In the present study we have used several approaches to elucidate the mechanism for the paracrine transfer of retinol between liver parenchymal and stellate cells. In one series of experiments, chylomicrons labeled with [3H]retinyl palmitate or with retinyl [3H]palmitate were injected intravenously into rats. It was shown that the retinol as well as the palmitate moiety were initially taken up in parenchymal liver cells. However, only the retinol moiety was detected in stellate cells, indicating that the retinyl ester is hydrolyzed before retinol is transferred to stellate cells. It is well known that parenchymal liver cells secrete retinol bound to retinol-binding protein (RBP), and we have recently found that stellate cells do have RBP receptors. Here we report that antibodies against RBP completely block the transfer of retinol from parenchymal to stellate cells. These findings indicate that following uptake of chylomicron remnant retinyl ester in parenchymal cells, the retinyl ester is hydrolyzed, and retinol secreted from parenchymal cells on RBP is taken up by stellate cells by means of RBP receptors.     

Role of triglyceride-rich lipoproteins from the liver and intestine in the etiology of postprandial peaks in plasma triglyceride concentration

Plasma triglyceride concentration in human subjects peaks once, twice or three times in the twelve-hour period following the ingestion of a fat-rich meal. Triglyceride-rich lipoproteins (TRL) containing apolipoprotein (apo)B-48 (of intestinal origin), and TRL containing apoB-100 (predominantly of hepatic origin) both contribute to postprandial changes in plasma triglyceride concentration. To test the hypothesis that earlier peaks in postprandial triglyceridemia are due predominantly to the secretion of TRL from the intestine, while later peaks are due to the secretion of TRL from the liver, TRL apoB-48, TRL apoB-100 and retinyl ester (a marker of intestinal lipoproteins) were measured in plasma samples from subjects fed a fat-rich meal (1 g fat/kg body wt). Data from seven subjects (four fed 40 retinol equivalents vitamin A/kg body wt, three fed 20 retinol equivalents vitamin A/kg body wt, with the fat meal), showed that postprandial peaks in plasma triglyceride were always associated with increases in plasma retinyl ester concentration. In four subjects, who were selected because they had two clearly defined postprandial triglyceride peaks, the plasma concentration of TRL triglyceride, apoB-48, apoE and apoC increased in conjunction with both the earlier (three hour) and later (nine hour) peaks in plasma triglyceride. Increase in TRL apoB-100 was associated with both peaks in two of the four subjects. Our data suggest that 1) TRL from the liver and intestine contribute to both earlier and later peaks in postprandial triglyceridemia; and 2) the rate of appearance of TRL from the intestine is not constant after dietary fat absorption.     

Effects of vitamin A and ethanol on liver plasma membrane fluidity

To study possible mechanisms whereby vitamin A and ethanol may affect liver plasma membranes, rats were fed liquid diets containing either 6 international units of vitamin A per kcal or 5 times more, with or without ethanol (36% of total energy as isocaloric substitution for carbohydrate). Vitamin A supplementation resulted in 2- to 3-fold increases of liver plasma membrane free retinol (p less than 0.005) and retinyl esters (p less than 0.001), particularly esters of palmitate and oleate, whereas cholesterol esters did not change. The fluorescent probe 1,6-diphenyl-1,3,5-hexatriene revealed decreased fluidity as measured by an increase in fluorescence polarization which correlated significantly with retinyl palmitate plus oleate content in membranes. In rats fed ethanol chronically, we first verified our previous observation of a decrease in liver plasma membrane fluorescence polarization. We now find this effect to be associated with (and possibly due to) an increase of cholesterol ester content. In linear regression analysis, the change in fluorescence polarization correlated positively with vitamin A (p less than 0.02) and negatively with cholesterol ester contents (p less than 0.001). Ethanol feeding partially offset the effect of vitamin A supplementation on fluorescence polarization. We conclude from these observations that liver plasma membranes contain a significant amount of vitamin A, that vitamin A supplementation increases membrane fluorescence polarization and that chronic ethanol administration can interfere with this effect.     

Comparison of indices of vitamin A status in children with chronic liver disease

Malabsorption of fat-soluble vitamins is a major complication of chronic cholestatic liver disease. The most accurate way to assess vitamin A status in children who have cholestasis is unknown. The goal of this study was to assess the accuracy of noninvasive tests to detect vitamin A deficiency. Children with chronic cholestatic liver disease (n = 23) and noncholestatic liver disease (n = 10) were studied. Ten cholestatic patients were identified as vitamin A-deficient based on the relative dose response (RDR). Compared with the RDR, the sensitivity and specificity to detect vitamin A deficiency for each test was, respectively: serum retinol, 90% and 78%; retinol-binding protein (RBP), 40% and 91%; retinol/RBP molar ratio, 60% and 74%; conjunctival impression cytology, 44% and 48%; slit-lamp examination, 20% and 66%; tear film break-up time, 40% and 69%; and Schirmer's test, 20% and 78%. We developed a modified oral RDR via oral coadministration of d-alpha tocopheryl polyethylene glycol-1000 succinate and retinyl palmitate. This test had a sensitivity of 80% and a specificity of 100% to detect vitamin A deficiency. In conclusion, vitamin A deficiency is relatively common in children who have chronic cholestatic liver disease. Our data suggest that serum retinol level as an initial screen followed by confirmation with a modified oral RDR test is the most effective means of identifying vitamin A deficiency in these subjects.     

In vivo uptake of chylomicron [3H]retinyl ester by rat liver: evidence for retinol transfer from parenchymal to nonparenchymal cells.

We have studied hepatic uptake of chylomicron retinyl ester. Chylomicrons were obtained from intestinal lymph of rats that were given retinol in groundnut oil by intraduodenal injection. When lymph was injected intravenously into normal rats, the radioactivity was cleared from blood with t1/2 approximately equal to 10 min. Retinyl ester was taken up initially by the liver, which, after 30 min, contained 80-90% of the radioactivity injected. Initially, most of the radioactivity was in hepatocytes, but after 30 min it disappeared from these cells and reappeared in nonparenchymal liver cells. After 2 hr these cells contained more radioactivity than the hepatocytes. When lymph was injected into vitamin A-deficient rats or rats given vitamin A in the form of retinoic acid, the plasma clearance and initial hepatic uptake of radioactivity were similar to that found in control animals. However, the nonparenchymal cells in these animals did not accumulate radioactivity. The current data suggest that vitamin A (in chylomicron remnants) is taken up initially by hepatocytes and then is released from these cells and delivered mainly to nonparenchymal liver cells in normal animals. In vitamin A-deficient rats, the vitamin is transferred from the hepatocytes to extrahepatic tissues.     

Retinol storage in the rat liver after daily intramuscular administration of physiological doses of a vitamin A oil emulsion

We have recently shown the kinetic behavior of liver retinyl esters in rats with adequate vitamin A levels receiving oral vitamin supplementation. In the present work we have studied the effects of intramuscular administration of a vitamin A preparation on the metabolism of vitamin A in the rat. Retinol administered intramuscularly to rats in the form of an emulsion brought about a significant increase in the serum and liver concentration of vitamin A; this increase was slightly less than in orally treated rats. In each group, retinyl palmitate constituted 80-85% of the total retinyl esters, followed by stearate (9-13%), laurate, palmitoleate, myristate, linoleate and pentadecanoate making up 3-10%. The subcellular localization of all retinyl esters is similar and dependent on age but not on the route of administration. These results indicate that although the best hepatic storage is achieved with an orally administered vitamin A emulsion, the intramuscular administration of a physiological dose might provide an effective supplementation method if oral vitamin A is contraindicated.     

Vitamin A toxicity in a physical culturist patient: a case report and review of the literature

Excessive intake of vitamin A may produce acute or chronic toxicity. Vitamin A can be consumed in foods, fortified products and supplements. We present a case of a young physical culturist man who was referred to our Unit because of chronic liver disease of unknown origin. The patient had a history of increased vitamin A intake from natural source with the addition of high dose of vitamin A supplements with the purpose of improving his muscular development. Our patient showed chronic liver disease with severe fibrosis, signs of portal hypertension and marked hyperplasia of Ito cells. In conclusion, chronic vitamin A toxicity may produce severe liver damage and should be recognized in the differential diagnosis of chronic liver diseases.     

Pathways of vitamin A delivery to the embryo: insights from a new tunable model of embryonic vitamin A deficiency

Circulating retinoids (vitamin A and its derivatives) are found predominantly as retinol bound to retinol-binding protein (RBP), which transports retinol from liver stores to target tissues, or as retinyl ester incorporated in lipoproteins of dietary origin. The transport of retinoids from maternal to fetal circulation is poorly understood, especially under conditions of inadequate dietary vitamin A intake. Here we present RBP-/- mice as a tunable model of embryonic vitamin A deficiency. This model has enabled us to analyze metabolic links between maternal nutrition and retinoid delivery to the fetus. Our data show that retinol-RBP is the primary contributor to fetal development, whereas retinyl ester are largely responsible for accumulation of fetal retinoid stores. Furthermore, these studies indicate the importance of embryonic RBP in distributing vitamin A to certain developing tissues under restrictive diets. We also show differences among developing tissues in their dependency on the embryonic retinol-RBP pathway. Finally, we demonstrate that accumulation of embryonic vitamin A stores does not depend on the expression of RBP in the fetal liver.     

Retinyl palmitate reduces hepatic fibrosis in rats induced by dimethylnitrosamine or pig serum

Background/Aims: Lipid peroxidation has been found to be associated with Ito cell activation. Ito cells are the principal collagen-producing cells and the main storage sites of retinoids. However, the relationship between retinoids and hepatic fibrosis is complex. The aim of this study was to elucidate the role of retinoids as a fibrosuppressant: the effects of retinoids on hepatic fibrosis induced in rats by dimethylnitrosamine or pig serum, as well as on rat Ito cells in primary culture, were examined in order to assess the antioxidant activity of retinoids.Methods: Male Wistar rats were given a single injection of 40 mg/kg dimethylnitrosamine or 0.5 ml PS twice weekly for 10 weeks. In each model, rats were treated with retinyl palmitate for 2 weeks before hepatotoxin treatments or for the last 2 weeks of the treatments. The cumulative amount of retinyl palmitate administered in each experiment was 2, 10, or 20×10⁴ IU/rat.Results: Retinyl palmitate treatment before or after administration of dimethylnitrosamine or pig serum suppressed the induction of hepatic fibrosis, restored hepatic retinyl palmitate levels, prevented increases in hepatic levels of collagen and malondialdehyde, a product of lipid peroxidation, and prevented increases in deposition of type III collagen and the number of α-smooth muscle actin (α-SMA) positive-Ito cells in the liver. Retinyl palmitate supplementation resulted in a dose-dependent reduction of α-SMA expression and an oxidative burst in cultured Ito cells. In addition, retinyl palmitate inhibited Fe²⁺/adenosine 5′-diphosphate-induced lipid peroxidation in rat liver mitochondria and showed radical scavenging activity.Conclusions: These findings suggest that retinyl palmitate may suppress the induction of hepatic fibrosis, at least in part, by the inhibition of Ito cell activation through its antioxidant activity.     

Hepatic hydrothorax associated with vitamin a toxicity

We report the first case of an adult presenting with respiratory symptoms caused by hepatic hydrothorax secondary to vitamin A intoxication. The patient was a 52-year-old woman who presented to the hospital with progressive dyspnea. Evaluation demonstrated mild elevation of her liver function tests, ascites, and a right pleural effusion. The patient consumed a variety of vitamins, including vitamin A. Her estimated vitamin A intake was at least 162,300,000 international units (IU) during 18 years. She dramatically escalated her dose the year before admission for a total acute dose of 98,550,000 IU, with a daily intake of 270,000 IU. The recommended daily allowance is 4,000 IU. A transjugular liver biopsy revealed histopathologic changes consistent with vitamin A toxicity: hypertrophy and hyperplasia of hepatic stellate cells, focal pericellular fibrosis, mild perivenular fibrosis, and minimal, predominantly microvesicular steatosis. Despite the absence of cirrhosis, pressure readings demonstrated portal hypertension. During her hospitalization, the patient's symptoms and biochemical profile improved. As the large and generally unregulated United States dietary supplement industry continues to grow, it is increasingly likely that individuals will present with the signs and symptoms of vitamin excess rather than vitamin deficiency. Physicians need to remain alert to the varied presentations and toxic manifestations of excessive vitamin use.     

Effects of a vitamin-A-free diet on tissue vitamin A concentration and dark adaptation of aging rats

Changes in serum, hepatic, and ocular vitamin A levels were followed in 9-month-old Long Evans rats fed either a vitamin-A-free or vitamin-A-sufficient diet for up to 18 months. After 18 months, hepatic total vitamin A fell exponentially from 2542 +/- 433 to 48 +/- 12 micrograms/g wet weight, but these stores maintained normal serum retinol and ocular total vitamin A concentrations in vitamin-A-deprived rats. However, retinal dark-adaptation time, a functional indicator of photoreceptor integrity, was prolonged in elderly vitamin-A-deprived rats as compared to vitamin-A-sufficient controls (p less than 0.05). Aging appeared to be the most important factor that depressed the rate of dark adaptation, with vitamin A status having a secondary effect. The proportion of total ocular retinaldehyde decreased (p less than 0.05) and the concentration of retinyl ester increased (p less than 0.05) in the eyes of 27-month-old vitamin-A-deprived rats compared to age-matched vitamin-A-sufficient animals. Possible mechanisms of visual dysfunction include abnormal retinal rhodopsin recycling caused by a dependence on newly absorbed dietary vitamin A (e.g., chylomicron). Alternatively, in the vitamin-A-deprived rat, decreased hepatic oxidation of pentobarbital (used for electroretinographic anesthesia) could prolong retinal anesthetic exposure and either directly depress neural transmission or indirectly alter transmission by affecting rhodopsin recycling.     

Massive vitamin A intoxication with ascites and pleural effusion

Vitamin A intoxication was diagnosed in a 14-year-old girl who presented with massive exudative ascites and right pleural effusion, impaired liver enzymes, and hypertriglyceridemia. Electron microscopy of liver biopsy material demonstrated numerous perisinusoidal lipid-filled Ito cells. The patient had taken 100-200,000 I.U. vitamin A per day for 15 months. Serum vitamin A level remained elevated for 4 months after vitamin discontinuation. The unusual severity of portal hypertension was documented by a high wedged hepatic vein pressure level. The ascites occurred 2 months after vitamin A had been discontinued, probably owing to particularly slow mobilization of large hepatic stores of vitamin A. Portal hypertension disappeared after a 6-month low vitamin A diet, but the liver biopsy failed to demonstrate any decrease in number or size of Ito cells, suggesting that lipid venous obstruction is unlikely to be the only mechanism responsible for portal hypertension in vitamin A-induced liver disease.