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BACKGROUND: The results of epidemiologic studies have consistently shown associations between dietary intake or plasma carotenoid status and incidence of cancers and cardiovascular and eye diseases. OBJECTIVE: The aim was to assess whether vegetable-borne carotenoids (lycopene, lutein, and beta-carotene) compete for intestinal absorption and whether this affects the plasma status of carotenoids in the medium term (ie, after 3 wk). DESIGN: During 3-wk periods separated by 3-wk washout periods, 20 women were supplemented with either 96 g tomato puree/d (14.98 mg lycopene + 1.50 mg beta-carotene), 92 g cooked chopped spinach/d (11.93 mg lutein + 7.96 mg beta-carotene), 96 g tomato puree/d + 92 g chopped spinach/d, 96 g tomato puree/d + 2 lutein pills (12 mg lutein), or 92 g chopped spinach/d + 1 lycopene pill (15 mg lycopene). Plasma carotenoids were measured before and after each supplementation period. The subjects also participated in postprandial experiments in which they ingested meals containing double amounts of the supplements described above. Carotenoids were measured in chylomicrons to assess the interaction of carotenoids on absorption. RESULTS: Adding a second carotenoid to a meal that provided a first carotenoid diminished the chylomicron response to the first carotenoid. However, cosupplementation with a second carotenoid of a diet supplemented with a first carotenoid did not diminish the medium-term plasma response to the first carotenoid. CONCLUSION: Consumption of carotenoids from different vegetable sources does not diminish plasma carotenoid concentrations in the medium term, despite the finding in postprandial testing of competitive inhibitory interactions among different carotenoids. [ABSTRACT FROM AUTHOR]

Objectives: To seek insights into the relationship between chewing, appetite, food intake and gut hormones, and to consider potentially useful recommendations to promote benefits of chewing for weight management., Materials and Methods: Papers were obtained from two electronic databases (Medline and Cochrane), from searches of reference lists, and from raw data collected from the figures in the articles. A total of 15 papers were identified that detailed 17 trials. All 15 papers were included in the systematic review; however, a further five studies were excluded from the meta-analysis because appropriate information on hunger ratings was not available. The meta-analysis was conducted on a total of 10 papers that detailed 13 trials., Results: Five of 16 experiments found a significant effect of chewing on satiation or satiety using self-report measures (visual analogue scales, VASs). Ten of 16 experiments found that chewing reduced food intake. Three of five studies showed that increasing the number of chews per bite increased relevant gut hormones and two linked this to subjective satiety. The meta-analysis found evidence of both publication bias and between study heterogeneity (IA(2) = 93.4%, tau(2) = 6.52, p < 0.001) which decreased, but remained, when covariates were considered. Analysis of the heterogeneity found a substantial effect of the fasting period where the duration of fasting influenced the decrease in hunger due to chewing. Prolonged mastication significantly reduces self-reported hunger levels (hunger: − 2.31 VAS point, 95% CI [− 4.67, − 1.38], p < 0.001)., Conclusions: Evidence currently suggests that chewing may decrease self-reported hunger and food intake, possibly through alterations in gut hormone responses related to satiety. Although preliminary, the results identify a need for additional research in the area. Focused, uniform, experimental designs are required to clearly understand the relationships that exist between mastication, appetite, satiety, food intake and, ultimately, body weight.

We aimed to provide basic data on the processing of vitamin A and E in the human gastrointestinal tract and to assess whether the size of emulsion fat globules affects the bioavailability of these vitamins. Eight healthy men received intragastrically two lipid formulas differing in their fat-globule median diameter (0.7 vs. 10. 1 microm. Formulas provided 28 mg vitamin A as retinyl palmitate and 440 mg vitamin E as all-rac alpha-tocopherol. Vitamins were measured in gastric and duodenal aspirates, as well as in chylomicrons, during the postprandial period. The gastric emptying rate of lipids and vitamin A and E was similar. The free retinol/total vitamin A ratio was not significantly modified in the stomach, whereas it was dramatically increased in the duodenum. The proportion of ingested lipid and vitamins was very similar in the duodenal content. The chylomicron response of lipids and vitamins was not significantly different between the two emulsions. Our main conclusions are as follows: 1) there is no significant metabolism of vitamin A and E in the human stomach, 2) the enzyme(s) present in the duodenal lumen is significantly involved in the hydrolysis of retinyl esters, and 3) the size of emulsion fat globules has no major effect on the overall absorption of vitamin A and E.

Vitamin A (retinol) and its active derivatives (retinoic acids) are essential for growth and development of the mammalian fetus. Maternally derived retinol must pass the placenta to reach the developing fetus. Despite its apparent importance, little is known concerning placental transfer and metabolism of retinol, and particularly of placental production and storage of retinyl esters. To elucidate this metabolic pathway, we incubated, in the presence of retinol, 1) human full-term placental explants and 2) primary cultures of major cells types contributing to placental function: trophoblasts and villous mesenchymal fibroblasts. We used HPLC to determine the types and concentrations of retinyl esters produced by these explants and cells. About 14% of total cellular retinol in placental explants was esterified. The most abundant esters were myristate and palmitate. Primary cell cultures showed that fibroblasts efficiently produced retinyl esters, but trophoblasts did not. In both types of experiments, no retinyl esters were detected in the culture medium, suggesting that retinyl esters were produced for storage purpose. These results suggest that villous mesenchymal fibroblasts are primary sites of retinol esterification and storage in the placenta.

The present study examined whether the intestinal microflora could affect the bioavailability and vitamin A activity of dietary alpha- and beta-carotene in the rat. In the first set of experiments, we used conventional, germ-free (axenic), and human-flora-associated (heteroxenic) rats. In a second series, conventional rats were treated with either an antibiotic mixture or a potent inhibitor of gastric secretion (Omeprazole). All animals were first depleted of vitamin A over 4 weeks and then were fed on a sterilized diet supplemented with 14 mg beta-carotene and 3 mg alpha-carotene/kg for 2 weeks. In both experiments, a reduction in the intestinal microflora resulted in an increased storage of beta-carotene, alpha-carotene and vitamin A in the liver. Neither the nature of the metabolism of the intestinal microflora (aerobic or anaerobic) nor treatment with omeprazole, to modify intestinal pH, induced a significant effect on the measured variables. When incubated with 15 mumol beta-carotene/l for 72 h, neither the anaerobic nor the aerobic sub-fractions obtained from rat or human faeces contributed to beta-carotene degradation or to vitamin A synthesis. These findings suggest that reduction in gut microflora results in a better utilization of alpha- and beta-carotene by rats, although bacteria do not have a direct effect on the bioavailability of these pigments.

Several lines of evidence suggest that carotenoids may have a beneficial effect on health as a result of their antioxidant properties. In addition to beta-carotene, five other carotenoids are recovered in noticeable amounts from human plasma and tissues. Although the effect of beta-carotene on in vivo lipid peroxidation has been documented, few data are available on the effects of the other carotenoids. We evaluated the ability of the main human carotenoids to reduce lipid peroxidation by determining the correlations between plasma carotenoid concentration and plasma antioxidant capacity (in 79 healthy volunteers) and between carotenoid status and breath pentane excretion (in a subgroup of 24 subjects). Carotenoid intake was assessed by means of a 3-day food recall. Carotenoid status was evaluated by measurement of beta-carotene, lycopene, lutein/zeaxanthin, and alpha-carotene in plasma and buccal mucosal cells. Antioxidant status was evaluated by measurement of the total antioxidant capacity of the plasma. Oxidative stress status was evaluated by breath pentane measurements. Food recall data and the carotenoid concentrations in plasma and buccal mucosal cells showed that the subjects had normal carotenoid intake and normal carotenoid status. The total antioxidant capacity of the plasma was not related to the concentration of any specific carotenoid. The level of expired air pentane was not related to the carotenoid status of the subjects. These results show that normal concentrations of carotenoids in plasma and tissues are not correlated with these clinical markers of antioxidant and oxidative stress status.

Body retinoids are stored in the lipid droplets of hepatic stellate (Ito) cells. In chronic liver disease, the stellate cells differentiate into myofibroblast-like cells, a process whereby they lose their retinoid-containing lipid droplets. We studied the relation between liver retinoid content, the number of lipid droplets per stellate cell, and the number of stellate cells per mm2 in human alcoholic liver disease. Semithin sections of liver biopsies from normal subjects and patients with early (steatosis, inflammation, and mild fibrosis) and late (cirrhosis and cirrhosis with acute alcoholic hepatitis) alcoholic liver disease were morphometrically evaluated. Liver retinoid content was determined by HPLC. In normal patients, liver retinoid content was 901 +/- 213 IU/g of liver (mean +/- SEM). There was a decrease in liver retinoid content in early alcoholic liver disease (409 +/- 50 IU/g) and a further reduction in cirrhosis (153 +/- 50 IU/g). In patients with acute alcoholic hepatitis, retinoid content was strikingly low (5.2 +/- 1.8 IU/g). There was a progressive decrease in the number of stellate cells per mm2 associated with progressive liver damage. We found a fair correlation between the number of stellate cells per mm2 and liver retinoid content in all patient groups (overall correlation: 0.71). In normal subjects, the mean number of lipid droplets per stellate cell was 7.4 +/- 0.7. In patients with early alcoholic liver disease and in patients with alcoholic cirrhosis, this value was increased to 13.6 +/- 0.8 and 10.4 +/- 2.0, respectively. In patients with acute alcoholic hepatitis, only a few lipid droplets were present (4.2 +/- 0.5). There was a good correlation between liver retinoid content and mean number of lipid droplets in normal patients (r = 0.58). In alcoholic cirrhosis, however, correlation was poor (r = 0.34). In early alcoholic liver disease, the correlation was absent (r = 0.004). In conclusion, the major finding of our study is that the correlation between the mean number of lipid droplets per stellate cell and liver retinoid content varies according to the hepatic pathology considered. Marked lipid droplet accumulation occurs in stellate cells in early alcoholic liver disease and, to a lesser extent, in alcoholic cirrhosis, but there is no correlation between the mean number of lipid droplets per stellate cell and liver retinoid content. Therefore, not retinoids but probably lipids are responsible for the accumulation of lipid droplets. We also find that there is a fair correlation between the number of stellate cells per mm2 and liver retinoid content in all patient groups. Finally, we confirm the decrease in hepatic retinoid content that occurs in alcoholic liver disease in humans, even at the early stages of the disease.

beta-Carotene dioxygenase catalyzes the conversion of provitamin A carotenoids to vitamin A in mammalian tissues. Whether the enzyme can also cleave non-provitamin A carotenoids to retinoid analogs with biological activities is still unclear. We investigated (i) substrate specificities of beta-carotene dioxygenase toward provitamin A and non-provitamin A carotenoids and (ii) potential antagonistic effects of non-provitamin A carotenoids on beta-carotene conversion to vitamin A. Provitamin A substrates were 8 to 23% as active as beta-carotene. No polar metabolites were detected with canthaxanthin or zeaxanthin as substrates; these compounds efficiently inhibited the beta-carotene cleavage reaction by 71 and 40%, respectively. Kinetic studies indicated mixed inhibition for canthaxanthin (Ki = 1.6 microM) and non-competitive for zeaxanthin (Ki = 7.8 microM), suggesting that both compounds do not interact significantly with the active site of the enzyme. In vivo, dietary combinations of canthaxanthin and beta-carotene resulted in lower liver levels of both carotenoids and vitamin A and in a higher beta-carotene/vitamin A ratio as compared to groups supplemented with the compounds separately. This supports the view that canthaxanthin at high doses competes with beta-carotene for intestinal absorption and inhibits the conversion of beta-carotene to vitamin A. Thus, we suggest that although canthaxanthin is not a substrate for beta-carotene dioxygenase, it is likely to affect the activity of provitamin A carotenoids by direct interaction with the enzyme.

Myofibroblasts (MF) are a major effector cell type in liver fibrogenesis, where they are thought to derive from the activation of hepatic stellate cells. Cultured human MF, grown from liver explants, retain most of the in vivo characteristics of liver MF but are in limited supply. A continuous MF cell line would therefore be valuable in studying human liver fibrogenesis. For this purpose, we sought to immortalize human liver MF with polyoma virus large T antigen. MF were obtained from explants of human liver and transfected with a plasmid containing the coding sequence of polyoma virus large T antigen. This procedure yielded an activity growing cell line, designated GREF-X, which did not express large T antigen. Nevertheless, this cell line has been passaged repeatedly for almost 1 year and is thus likely immortalized. The morphology of GREF-X resembles that of primary liver MF. These cells have a doubling time of approximately 72 hours and are density-inhibited, and their growth is serum-dependent. Moreover, GREF-X cells do not grow in soft agar or induce tumors in nude mice, suggesting that they are not transformed. They stain positively for MF markers, such as smooth muscle alpha-actin and vimentin; express collagens type I, IV, V, and VI, fibronectin, and laminin: and secrete matrix-metalloproteinase-2. In addition, GREF-X cells are able to take up and esterify [3H]retinol, suggesting that they actually derive from hepatic stellate cells. Finally, these cells respond to transforming growth factor-beta 1, a major mediator of liver fibrogenesis, by increasing secretion of fibronectin and plasminogen activator-inhibitor type 1. Transient transfection experiments showed that plasminogen activator-inhibitor type 1 regulation, by transforming growth factor-beta 1, was transcriptional. We believe, therefore, that GREF-X would be a useful tool for studying the pathophysiology and pharmacology of liver fibrogenesis.

The purposes of this study were to determine the location of beta-carotene dioxygenase (EC 1.13.11.21) activity within the rat gastrointestinal tract, within the villus and within enterocytes, and to identify the metabolites produced in each intestinal fraction. In Wistar female rats, maximal activity was detected in the cytosol (74-93% of the total cellular activity) of mature functional enterocytes harvested from the jejunum (67% of the intestinal activity). The specific activity, expressed in pmol of retinoids/(h x mg protein) rose from 49 +/- 3 in the stem cells to 199 +/- 12 in the mature functional cells (P < 0.05). Thus the intestinal beta-carotene cleavage activity might be regulated during the enterocyte maturation process. By using HPLC with diode array and radioactive detectors, retinal, and in the presence of NAD+, retinoic acid, were identified as the only metabolites produced. No beta-12'-, 10'-, and 8'-apo-carotenals were detected, even when various enzyme sources were tested. These results suggest that the major, if not the sole, pathway for the formation of vitamin A from beta-carotene in the rat intestine is central cleavage.

Given the current interest in the cardiovascular complications of Mg deficiency, the aim of the present experiment was to investigate the effect of Mg deficiency on the time-course of lipoprotein oxidation and to assess whether short-term Mg deficiency results in vitamin E depletion that predisposes lipoproteins and tissues to subsequent oxidation. Weanling rats were pair-fed for 8 d with control and Mg-deficient diets respectively. Plasma triacylglycerol and alpha-tocopherol levels were significantly greater in Mg-deficient rats compared with control animals. The increase in plasma apolipoprotein B concentration indicated that a corresponding increase in plasma triacylglycerol-rich lipoproteins (TGRLP) occurred in Mg-deficient animals. Hyperlipaemia was associated with modifications in the composition of TGRLP. The proportion of triacylglycerols was elevated whereas that of cholesterol and protein was reduced, and Mg deficiency resulted in a slight significant reduction in alpha-tocopherol content. When the TGRLP fractions were subjected to in vitro Cu-induced oxidation the lipoprotein fractions from Mg-deficient rats were more susceptible to oxidative damage than lipoprotein fractions from control rats. Mg deficiency did not modify the alpha-tocopherol content of liver, heart and skeletal muscle. However, after exposure of tissue homogenates to Fe-induced lipid peroxidation, thiobarbituric acid-reactive substances were significantly higher in tissues from Mg-deficient rats compared with those from control rats. These results complement previous findings, showing that Mg deficiency increases the susceptibility of TGRLP and tissues to peroxidation and suggest that oxidative damage is not the result of a decrease in vitamin E antioxidant status.

When incorporated into liposomes made of phospholipids, retinyl palmitate is an adequate substrate for an acidic REH (aREH). In rat liver, this activity is mainly localized in the lysosomal fraction. Kinetic parameters have been determined for retinyl palmitate (Km = 315 microM; maximal rate = 22.1 nmol retinol/h per mg protein). The aREH activity is different from the lysosomal acidic cholesteryl ester hydrolase (aCEH): cholesteryl oleate does not inhibit aREH activity, neither do some aCEH specific inhibitors, and aREH does not hydrolyse cholesteryl ester. Involvement of aREH in the hydrolysis of lipid droplets retinyl esters in fat storing cells is discussed.

Previous studies have shown that rats exposed to 3,3',4,4'-tetrachlorobiphenyl (TCB) exhibit decreased liver vitamin A stores. The activity of retinyl ester hydrolase (REH), the enzyme responsible for the hydrolysis of the storage form of vitamin A (retinyl esters) into free retinol, may therefore be altered by TCB. This study was carried out to investigate the effect of TCB on vitamin A distribution and on REH activity in the rat. REH activity was measured in liver homogenates and microsomes (650 micrograms protein), in Tris-maleate buffer 0.1 M at pH 7.2 in the presence of 150 mM CHAPS and 1.5 mM retinyl palmitate dispersed in Triton X-100 0.2%. Using these conditions, the kinetic parameters of the enzyme were determined and the inter-animal variation coefficient (10%) allowed statistical comparisons between experimental groups. Male Wistar rats of sufficient or deficient vitamin A status were treated IP with 340 mumol of TCB/kg. Vitamin A levels were significantly depressed in liver. REH activity was decreased about 20%, and serum retinol was decreased about 50%, independent of the initial vitamin A status of the animals. Vitamin A levels in lungs and testes were also decreased, suggesting that TCB could interfere with vitamin A delivery to target organs. The negative effect of TCB on REH activity in vivo was also observed when TCB was added in vitro to the incubation medium at concentrations near to those expected after in vivo treatment. TCB is a non-competitive inhibitor of retinyl palmitate hydrolase.

Male Wistar rats of different vitamin A status (total depletion to moderate deficiency) were administered DDT (5 mg/kg/day) or vehicule (corn oil) i.p. daily for 14 days. Vitamin A-dependent protein mannosylation was measured either by in vivo incorporation of [3H]mannose into liver glycoprotein or by in vitro assay of incorporation of [14C]mannose into mannosylretinyl phosphate. Vitamin A deficiency resulted in a significantly impaired in vivo incorporation of mannose in liver glycoprotein but had no effect on the in vitro transport of mannose via retinyl phosphate. Although DDT induced an increase synthesis of liver proteins in smooth endoplasmic reticulum and caused a diminution of the hepatic vitamin A content, it did not affect vitamin A-dependent protein mannosylation.