The effect of dietary fatty acid composition on liver retinyl ester (vitamin A ester) composition in the rat

Genetic Characterization of Rat Hepatic Stellate Cell Line PAV-1

The rat hepatic stellate cell line PAV-1 was established two decades ago and proposed as a cellular model to study aspects of hepatic retinoic acid metabolism. This cell line exhibits a myofibroblast-like phenotype but also has the ability to store retinyl esters and synthesize retinoic acid from its precursor retinol. Importantly, when cultured with palmitic acid alone or in combination with retinol, the cells switch to a deactivated phenotype in which the proliferation and expression of profibrogenic marker genes are suppressed. Despite these interesting characteristics, the cell line has somehow fallen into oblivion. However, based on the fact that working with in vivo models is becoming increasingly complicated, genetically characterized established cell lines that mimic aspects of hepatic stellate cell biology are of fundamental value for biomedical research. To genetically characterize PAV-1 cells, we performed karyotype analysis using conventional chromosome analysis and multicolor spectral karyotyping (SKY), which allowed us to identify numerical and specific chromosomal alteration in PAV-1 cells. In addition, we used a panel of 31 species-specific allelic variant sites to define a unique short tandem repeat (STR) profile for this cell line and performed bulk mRNA-sequencing, showing that PAV-1 cells express an abundance of genes specific for the proposed myofibroblastic phenotype. Finally, we used Rhodamine-Phalloidin staining and electron microscopy analysis, which showed that PAV-1 cells contain a robust intracellular network of filamentous actin and process typical ultrastructural features of hepatic stellate cells.

A minute dose of 14C-{beta}-carotene is absorbed and converted to retinoids in humans

Our objective was to quantify the absorption and conversion to retinoids of a 1.01-nmol, 3.7-kBq oral dose of (14)C-beta-carotene in 8 healthy adults. The approach was to quantify, using AMS, the elimination of (14)C in feces for up to 16 d after dosing and in urine for up to 30 d after dosing. The levels of total (14)C in undiluted serial plasma samples were measured for up to 166 d after dosing. Also, the levels of (14)C in the retinyl ester (RE), retinol (ROH), and beta-carotene fractions that were isolated from undiluted plasma using HPLC were measured. The apparent digestibility of the (14)C was 53 +/- 13% (mean +/- SD), based on the mass balance data, and was generally consistent with the area under the curve for zero to infinite period of (14)C that was eliminated in the feces collections made up to 7.5 d after dosing. Metabolic fecal elimination, calculated as the slope per day (% (14)C-dose/collection from d 7.5 to the final day), was only 0.05 +/- 0.02%. The portion of the (14)C dose eliminated via urine was variable (6.5 +/- 5.2%). Participants [except participant 6 (P6)] had a distinct plasma peak of (14)C at 0.25 d post-dose, preceded by a shoulder at approximately 0.1 d, and followed by a broad (14)C peak that became indistinguishable from baseline at approximately 40 d. Plasma (14)C-RE accounted for most of the absorbed (14)C early after dosing and P1 had the longest delay in the first appearance of (14)C-RE in plasma. The data suggest that plasma RE should be considered in estimating the ROH activity equivalent of ingested beta-carotene.

Intestinal β-carotene 15,15′-dioxygenase activity is markedly enhanced in copper-deficient rats fed on high-iron diets and fructose

The purpose of the present work was to examine effects of the Cu–Fe interaction on intestinal β-carotene 15,15′-dioxygenase activity when a wide range of dietary Fe (deficiency to excess) was used in relation to Cu status of rats. The effect of dietary carbohydrates was also examined since they play a role in the Cu–Fe interactionin vivo. Weanling male Sprague-Dawley rats (n72) were divided into twelve dietary groups, which were fed on either low-, normal-, or high-Fe levels (0·9, 9·0, and 90·0 mmol Fe/kg diet respectively) combined with Cu-adequate or -deficient levels (0·94 and 0·09 mmol Cu/kg diet respectively) and with starch or fructose in the diets. The data showed that both Fe concentration and β-carotene 15,15′-dioxygenase activity in small intestinal mucosa were enhanced with increasing dietary Fe and with Cu deficiencyv. Cu adequacy. Dietary fructose did not aggravate the Fe-enhancement, related to Cu deficiency, in the small intestine; however, fructose increased the intestinal dioxygenase activity in rats fed on normal- or high-Fe diets when compared with starch controls. Thus, the highest intestinal dioxygenase activity associated with the lowest hepatic retinol (total) concentration was found in rats fed on the Cu-deficient, high-Fe, fructose-based diet. Finally, a positive linear relationship was found between the dioxygenase activity and Fe concentration in intestinal mucosa. In conclusion, the data indicate that β-carotene 15,15′-dioxygenase activity requires Fe as cofactorin vivoand the enzyme is modulated by the three dietary components: Cu, Fe, and fructose.

Carotenoid and retinoid metabolism: insights from isotope studies

Use of isotopes as tracers has had an important role in elucidating key features of vitamin A and retinoid metabolism in animal models and humans. Their use has shown that beta-carotene absorption is variable, and that the appearance of beta-carotene and its metabolites in the blood by time since dosing follows characteristic patterns. Retinol formed from beta-carotene shows a different pattern, as does lutein. In this article, we summarize and discuss insights and some surprises into the absorption and metabolism of vitamin A, beta-carotene, and lutein that were gained with the use of isotope tracers in humans, rats, and cells as models.

PAV-1, a new rat hepatic stellate cell line converts retinol into retinoic acid, a process altered by ethanol

During liver fibrogenesis or long term culture, hepatic stellate cells (HSCs) evolved from "quiescent" to activated phenotype called "myofibroblast-like", a transition prevented by retinoic acid (RA). Little is known about RA generation by HSCs. Our study aimed to check the ability of these cells to produce RA from retinol (Rol) and the alterations of this metabolic step by ethanol. To study this metabolic pathway, primary cultures of HSCs represent the most physiological model but technically suffer several drawbacks. To circumvent these problems, an immortalized rat HSC line (named PAV-1) has been established. We validated PAV-1 cell line as a convenient model to study retinoids metabolism by HSCs. Then, we showed that PAV-1 cells express Rol-binding proteins (RBPs), enzymes and nuclear receptors involved in RA signaling pathway. We also demonstrated in situ generation of functional all-trans-RA (ATRA), using transient transfections with a RA-sensitive reporter gene, in situ modulation of tissue transglutaminase (tTG) activity and HPLC experiments. This production was Rol dose-dependent; 4-methylpyrazole, citral, and ethanol-inhibited which argues in favor of an enzymatic process.In conclusion, we first demonstrate in situ RA generation from Rol in a newly immortalized rat HSC line, named PAV-1. Inhibition of RA production by ethanol in PAV-1 and recent data, suggesting fundamental role of RA to prevent fibrosis development in the liver, allow us to hypothesize that Rol metabolism could be a primary target for ethanol during development of hepatic fibrosis.

Characterization of liver stellate cell retinyl ester storage

The stellate cells of the liver are the main storage site of retinyl esters in the body. During cultivation in vitro of stellate cells isolated from rat and rabbit livers were observed that the cells rapidly loose their retinyl ester content. Freshly isolated stellate cells contain about 144 nmol of total retinol/mg of protein, while cells cultivated for 14 days contained below 0.1 nmol/mg of protein. When 3-day-old cultures were incubated for 6 h with 2 microM retinol, the cellular content increased from 5.6 to approx. 9.4 nmol of total retinyl esters/mg of protein. In contrast, little retinyl ester accumulated in 10-20-day-old cultures incubated with 2 microM retinol. At 50 microM retinol, however, the retinyl ester level did increase both with 3-day-old cultures and 10-20-day-old cultures. In parallel experiments with cultured fibroblasts esterification characteristics similar to those seen in older cultures of stellate cells were observed. When 10-day-old cultures of stellate cells were incubated with retinol alone, or in combination with palmitic acid, linoleic acid or oleic acid, the total storage of retinyl esters increased by 20-150%. In most cases, the fatty acid supplemented in the medium was found to be the dominant fatty acid esterified with retinol. Cultures of stellate cells were then exposed to a physiological concentration (1.3 microM) of radioactive retinol free in solution or bound to retinol-binding protein. With 3-day-old cultures, as well as older cultures, the cellular content of unesterified retinol was 10-20 times higher when free retinol was added compared with addition of retinol bound to retinol-binding protein. However, 2-3-fold as much radioactive retinyl esters were recovered in cells incubated with retinol-retinol-binding protein compared with retinol free in solution. These results show that retinol delivered to stellate cells from retinol-binding protein is preferentially esterified, and that the complex is handled differently to free retinol by the stellate cells.

[Factors influencing the vitamin A concentration in the liver of cattle]

Nineteen long-term individual- and group-feeding experiments with 180 male calves, 338 growing bulls, 302 heifers, and 344 dairy cows were carried out in order to measure the influence of feeding (straw, silages or green fodder as roughages) and different vitamin-A supplies (0-40,000 IU per 100 kg body weight per day in growing cattle or 0-120,000 IU per dairy cow per day) on liver vitamin-A concentration. All together, 2,127 biopsies from livers were taken for retinol analysis. At the end of six growth experiments animals were slaughtered. Liver vitamin-A concentration of calves depends on their term at birth and is associated with the carotene intake of their mothers. The carotene content of feeds and the vitamin-A supply are the most important influencing factors on liver vitamin-A concentration of growing and lactating cattle. On the average, livers of calves fed with colostrum contained 100-200 IU, those of growing cattle fed with grass and legumes or with silages contained 200-300 or 100-200 IU resp., and those of cows fed with green fodder or silage contained 300-600 or 100-300 IU vitamin A resp. per g fresh liver. There were also values outside of the variations mentioned above. The vitamin-A storage capacity of liver and the effects of oral and parenteral vitamin-A supply to depleted calves and growing cattle were also tested.

Effect of dietary fat on Ito cell activation by chronic ethanol intake: a long-term serial morphometric study on alcohol-fed and control rats

We studied the effects of long-term ethanol ingestion and dietary fat on Ito cell activation morphometrically in rats. Sixteen pairs of Wistar male rats were divided into two groups, one fed tallow and the other fed corn oil as the source of dietary fat. Each group of rats were pair-fed a nutritional adequate liquid diet containing either corn oil (CF) or tallow (TF) as fat as well as protein and carbohydrate. Half of each group received ethanol, the rest were pair-fed isocaloric amounts of dextrose via an implanted gastric tube for up to 5 months. Morphometric analysis of the change in fat and rough endoplasmic reticulum (RER) of Ito cells was performed on electron micrographs obtained from monthly biopsies including baseline. Ito cell activation was assessed by a decrease in the ratio of fat/RER in Ito cells. The ratio of fat/RER in Ito cells of alcoholic rats fed the CF diet (CFA) gradually decreased. The ratio was found to be lower than in the pair-fed control rats (CFC) at 5 months of feeding. CFA: 1.74 +/- 0.57, vs. 7.46 +/- 2.05, respectively, p less than 0.05, mean +/- SE). Ito cell fat also significantly decreased at 5 months of feeding (p less than 0.05). The fat/RER ratio in CFA significantly decreased only subsequent to the development of fatty change, necrosis, and inflammation followed by fibrosis of the liver. In contrast, the TFA rats did not show a significant decrease in the fat/RER ratio in the Ito cells throughout the study, while TFC rats showed an increase in the fat/RER ratio.(ABSTRACT TRUNCATED AT 250 WORDS)

Fatty acyl CoA-dependent and -independent retinol esterification by rat liver and lactating mammary gland microsomes

Retinol esterification was examined in microsomes from rat liver and lactating mammary gland as a function of the form of retinol substrate, dependence on fatty acyl CoA, and sensitivity to phenylmethylsulfonyl fluoride (PMSF). Retinol bound to cellular retinol-binding protein (CRBP) or dispersed in solvent was esterified in a fatty acyl CoA-independent, PMSF-sensitive reaction, consistent with lecithin:retinol acyltransferase (LRAT) activity. LRAT activity exhibited the same Km (2 microM retinol) between tissues but a higher Vmax in liver as compared to that in mammary gland (47 vs 8 pmol/min/mg microsome protein, respectively). Solvent-dispersed retinol was also esterified in a fatty acyl CoA-dependent, PMSF-resistant reaction, consistent with acyl CoA:retinol acyltransferase (ARAT) activity. Retinol bound to CRBP was not a good substrate for this reaction. ARAT activity displayed a similar Vmax (300 pmol/min/mg microsome protein) between tissues but Km values of 15 and 5 microM for retinol and fatty acyl CoA in mammary gland as compared to 30 and 25 microM, respectively, in the liver. Thus, when substrate was near or below Km, retinol esterification occurred predominantly by LRAT in the liver and ARAT in the mammary gland, respectively. The concentration of CRBP in the cytosol, determined by Western blotting, was approximately 2 microM in the liver but was almost nondetectable in the mammary gland. These data suggest that retinol esterification is regulated via different mechanisms in liver and mammary gland and support a specific role for CRBP in the liver.