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Rintaro Yamanishi - One of the best experts on this subject based on the ideXlab platform.
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Ingested quercetin but not rutin increases accumulation of hepatic β‐carotene in BALB/c mice
Molecular Nutrition & Food Research, 2010Co-Authors: Noriko Bando, Naomi Muraki, Kaeko Murota, Junji Terao, Rintaro YamanishiAbstract:Beta-Carotene is a carotenoid with a range of reported health benefits besides vitamin A activity. If the enzymatic conversion of Beta-Carotene to retinal is suppressed in the digestive tract, residual Beta-Carotene that reaches the tissues increases. We evaluated the function of quercetin and rutin (quercetin-3-rutinoside) to increase the accumulation of Beta-Carotene in vitro and in vivo in BALB/c mice. When the conversion of Beta-Carotene by a preparation of the murine small intestine was measured in vitro, the addition of quercetin or rutin considerably inhibited the conversion. When the levels of hepatic Beta-Carotene and retinoids were measured among three groups of mice fed a diet supplemented with Beta-Carotene plus quercetin or rutin or Beta-Carotene alone (four to six mice per group), quercetin increased the level of Beta-Carotene and decreased the level of retinol, whereas rutin did not. These results demonstrate that quercetin can suppress the conversion of Beta-Carotene which develops in the cytosol of small intestinal epithelial cells, and that rutin whose rutinose-moiety prevents being absorbed in the small intestine cannot suppress the conversion in vivo. This study offers a novel insight into the interaction between flavonoids and carotenoids with respect to the health benefits from the latter.
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Ingested quercetin but not rutin increases accumulation of hepatic Beta-Carotene in BALB/c mice.
Molecular nutrition & food research, 2010Co-Authors: Noriko Bando, Naomi Muraki, Kaeko Murota, Junji Terao, Rintaro YamanishiAbstract:Beta-Carotene is a carotenoid with a range of reported health benefits besides vitamin A activity. If the enzymatic conversion of Beta-Carotene to retinal is suppressed in the digestive tract, residual Beta-Carotene that reaches the tissues increases. We evaluated the function of quercetin and rutin (quercetin-3-rutinoside) to increase the accumulation of Beta-Carotene in vitro and in vivo in BALB/c mice. When the conversion of Beta-Carotene by a preparation of the murine small intestine was measured in vitro, the addition of quercetin or rutin considerably inhibited the conversion. When the levels of hepatic Beta-Carotene and retinoids were measured among three groups of mice fed a diet supplemented with Beta-Carotene plus quercetin or rutin or Beta-Carotene alone (four to six mice per group), quercetin increased the level of Beta-Carotene and decreased the level of retinol, whereas rutin did not. These results demonstrate that quercetin can suppress the conversion of Beta-Carotene which develops in the cytosol of small intestinal epithelial cells, and that rutin whose rutinose-moiety prevents being absorbed in the small intestine cannot suppress the conversion in vivo. This study offers a novel insight into the interaction between flavonoids and carotenoids with respect to the health benefits from the latter.
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β carotene and β cryptoxanthin but not lutein evoke redox and immune changes in raw264 murine macrophages
Molecular Nutrition & Food Research, 2009Co-Authors: Sakurako Katsuura, Noriko Bando, Tomomi Imamura, Rintaro YamanishiAbstract:The mechanism of immunological benefits induced by carotenoids has not been fully elucidated. Here, we investigated some of the immunity-related properties of Beta-Carotene and two other carotenoids, beta-cryptoxanthin, and lutein, on the murine macrophages cell line RAW264. Beta-Carotene added to the culture medium accumulated in the cells in a time- and dose-dependent manner. The accumulation was positively correlated with cellular lipid peroxidation, demonstrating the pro-oxidative activity of Beta-Carotene, and also with the synthesis of glutathione, an intracellular antioxidant. Conversely, accumulation of Beta-Carotene was negatively correlated with the transcription of immune-active molecules, such as IL-1beta, IL-6, and IL-12 p40, in cells stimulated by LPS and INF-gamma. The transcription of the pro-inflammatory cytokines IL-1beta and IL-6 was more sensitive to the accumulation of Beta-Carotene than was IL-12 p40. The accumulation of beta-cryptoxanthin in cells resulted in effects similar to those of Beta-Carotene. However, lutein accumulated minimally and did not significantly affect the cells. These results demonstrate that Beta-Carotene, and beta-cryptoxanthin as well, can accumulate in RAW264 cells and induce changes in intracellular redox status, which in turn regulate the immune function of macrophages.
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β‐Carotene and β‐cryptoxanthin but not lutein evoke redox and immune changes in RAW264 murine macrophages
Molecular nutrition & food research, 2009Co-Authors: Sakurako Katsuura, Noriko Bando, Tomomi Imamura, Rintaro YamanishiAbstract:The mechanism of immunological benefits induced by carotenoids has not been fully elucidated. Here, we investigated some of the immunity-related properties of Beta-Carotene and two other carotenoids, beta-cryptoxanthin, and lutein, on the murine macrophages cell line RAW264. Beta-Carotene added to the culture medium accumulated in the cells in a time- and dose-dependent manner. The accumulation was positively correlated with cellular lipid peroxidation, demonstrating the pro-oxidative activity of Beta-Carotene, and also with the synthesis of glutathione, an intracellular antioxidant. Conversely, accumulation of Beta-Carotene was negatively correlated with the transcription of immune-active molecules, such as IL-1beta, IL-6, and IL-12 p40, in cells stimulated by LPS and INF-gamma. The transcription of the pro-inflammatory cytokines IL-1beta and IL-6 was more sensitive to the accumulation of Beta-Carotene than was IL-12 p40. The accumulation of beta-cryptoxanthin in cells resulted in effects similar to those of Beta-Carotene. However, lutein accumulated minimally and did not significantly affect the cells. These results demonstrate that Beta-Carotene, and beta-cryptoxanthin as well, can accumulate in RAW264 cells and induce changes in intracellular redox status, which in turn regulate the immune function of macrophages.
Helmut Sies - One of the best experts on this subject based on the ideXlab platform.
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Interaction of Peroxynitrite with Carotenoids in Human Low Density Lipoproteins
Archives of biochemistry and biophysics, 2000Co-Authors: Oleg M. Panasenko, Victor S Sharov, Karlis Briviba, Helmut SiesAbstract:Interaction of peroxynitrite, the product of the reaction between nitric oxide and superoxide, with carotenes (lycopene, alpha-carotene, and Beta-Carotene) and oxocarotenoids (beta-cryptoxanthin, zeaxanthin, and lutein) was studied both in homogeneous solution and in human low-density lipoproteins (LDL). All carotenoids prevented the formation of rhodamine 123 from dihydrorhodamine 123 caused by peroxynitrite, suggesting that the carotenoids react with peroxynitrite. Oxocarotenoids were as effective as biothiols, known scavengers of peroxynitrite, whereas lycopene, alpha-carotene, and Beta-Carotene exhibited a considerably more pronounced effect. Moreover, peroxynitrite caused a loss of carotenoids in LDL as was revealed by HPLC. The concentration of peroxynitrite causing half-maximal loss of carotenoids in LDL ranged from 13 +/- 3 to 68 +/- 3 microM for lycopene and lutein, respectively. Again, oxocarotenoids were less reactive in this system. A correlation between efficiency of carotenoids in the competitive assay with dihydrorhodamine 123 and the concentration of peroxynitrite causing half-maximal loss of carotenoids in LDL was observed (r(2) = 0.91). These findings suggest that carotenoids can efficiently react with peroxynitrite and perform the role of scavengers of peroxynitrite in vivo.
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all trans β carotene preferentially accumulates in human chylomicrons and very low density lipoproteins compared with the 9 cis geometrical isomer
Journal of Nutrition, 1995Co-Authors: Wilhelm Stahl, Wolfgang Schwarz, Jutta Von Laar, Helmut SiesAbstract:: Following ingestion of a Beta-Carotene isomer mixture (Betatene) containing nearly equal amounts of all-trans and 9-cis Beta-Carotene (all-trans/9-cis Beta-Carotene ratio approximately 1.5), concentrations of all-trans Beta-Carotene increased for 6 or 8 h in the chylomicron fraction of plasma from four of seven human subjects. A substantially lower increase in the 9-cis Beta-Carotene concentration was observed, with the accumulation of the all-trans isomer being 10- to 50-fold higher than that of the 9-cis isomer, calculated on the basis of the Beta-Carotene isomer pattern in the ingested mixture. A similar effect was observed in the VLDL fraction. Three of the seven subjects did not respond to Beta-Carotene ingestion. In the subjects that did respond, the all-trans/9-cis Beta-Carotene ratios in chylomicrons and VLDL suggest an efficient isomer-selective mechanism for intestinal uptake across the mucosa or very rapid elimination into tissues.
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human serum concentrations of all trans β and α carotene but not 9 cis β carotene increase upon ingestion of a natural isomer mixture obtained from dunaliella salina betatene
Journal of Nutrition, 1993Co-Authors: Wilhelm Stahl, Wolfgang Schwarz, Helmut SiesAbstract:: The uptake of all-trans and 9-cis Beta-Carotene and of alpha-carotene from a natural carotene preparation from Dunaliella salina, Betatene, was studied in humans. All-trans Beta-Carotene and alpha-carotene were absorbed well and showed the expected biokinetics with serum peak concentrations between 24 and 48 h. The mean increase in serum concentrations of alpha-carotene was 5.6% of the increase of all-trans Beta-Carotene, reflecting the composition of these carotenoids in Betatene. 9-cis Beta-Carotene, however, was not detected in human serum, even after repeated doses. This could be due to preferential absorption of all-trans Beta-Carotene, rapid distribution of 9-cis Beta-Carotene into the tissue, or the presence of isomerase activity processing 9-cis to all-trans Beta-Carotene.
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Separation of Beta-Carotene and lycopene geometrical isomers in biological samples.
Clinical chemistry, 1993Co-Authors: Wilhelm Stahl, A. R. Sundquist, Michael Hanusch, W Schwarz, Helmut SiesAbstract:The analysis of Beta-Carotene and lycopene, the two predominant carotenoids in human serum and tissues, was extended to the level of geometrical (cis-trans) isomers by using an improved reversed-phase HPLC methodology. We separated five geometrical isomers of Beta-Carotene and seven of lycopene in human serum and tissues. 13-cis-Beta-Carotene was identified as the predominant cisisomer in human serum, contributing about 5% to total Beta-Carotene. In tissue, however, considerable amounts of 9-cis- and traces of 15-cis-Beta-Carotene were also detected. In contrast to Beta-Carotene, the lycopene isomer patterns in human serum and tissues are quite similar.
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Cellular levels of all-trans-Beta-Carotene under the influence of 9-cis-Beta-Carotene in FU-5 rat hepatoma cells.
Biological chemistry Hoppe-Seyler, 1993Co-Authors: Motoko Oarada, Wilhelm Stahl, Helmut SiesAbstract:After incubation of FU-5 hepatoma cells for 46.5 h with synthetic all-trans-Beta-Carotene (3.5 microM) dissolved in tetrahydrofuran, the Beta-Carotene level in the cells amounted to 0.24 nmol/mg protein. No interconversion from all-trans to cis isomers occurred during incubation. Upon incubation with 3.5 microM synthetic 9-cis-Beta-Carotene, only 0.03 nmol 9-cis-Beta-Carotene/mg protein was detected in the cells. With a mixture of synthetic all-trans- (3.5 microM) and 9-cis-Beta-Carotene (1.0 microM), 0.09 nmol all-trans- and 0.02 nmol 9-cis-Beta-Carotene/mg protein were incorporated into the cells. These data suggest that 9-cis-Beta-Carotene and/or its decomposition products inhibited the uptake or influenced the metabolism of all-trans-Beta-Carotene. Thus, the lack of an increase in human serum levels of 9-cis-Beta-Carotene upon intake of a mixture of all-trans- and cis-Beta-Carotene isomers dissolved in soybean oil, Betatene (Stahl et al. (1993) J. Nutr. 123, 847-851), may be due to particular biokinetic or metabolic parameters for cis isomers of Beta-Carotene as compared to all-trans-Beta-Carotene.
Sherry A Tanumihardjo - One of the best experts on this subject based on the ideXlab platform.
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cassava with enhanced β carotene maintains adequate vitamin a status in mongolian gerbils meriones unguiculatus despite substantial cis isomer content
British Journal of Nutrition, 2009Co-Authors: Julie A Howe, B Maziyadixon, Sherry A TanumihardjoAbstract:Efforts to increase Beta-Carotene in cassava have been successful, but the ability of high-Beta-Carotene cassava to prevent vitamin A deficiency has not been determined. Two studies investigated the bioefficacy of provitamin A in cassava and compared the effects of carotenoid content and variety on vitamin A status in vitamin A-depleted Mongolian gerbils (Meriones unguiculatus). Gerbils were fed a vitamin A-free diet 4 weeks prior to treatment. In Expt 1, treatments (ten gerbils per group) included 45 % high-Beta-Carotene cassava, Beta-Carotene and vitamin A supplements (intake matched to high-Beta-Carotene cassava group), and oil control. In Expt 2, gerbils were fed cassava feeds with 1.8 or 4.3 nmol provitamin A/g prepared with two varieties. Gerbils were killed after 4 weeks. For Expt 1, liver vitamin A was higher (P < 0.05) in the vitamin A (1.45 (sd 0.23) micromol/liver), lower in the control (0.43 (sd 0.10) micromol/liver), but did not differ from the Beta-Carotene group (0.77 (sd 0.12) micromol/liver) when compared with the high-Beta-Carotene cassava group (0.69 (sd 0.20) micromol/liver). The bioconversion factor was 3.7 microg Beta-Carotene to 1 microg retinol (2 mol:1 mol), despite 48 % cis-Beta-Carotene [(Z)-Beta-Carotene] composition in cassava. In Expt 2, cassava feed with 4.3 nmol provitamin A/g maintained vitamin A status. No effect of cassava variety was observed. Serum retinol concentrations did not differ. Beta-Carotene was detected in livers of gerbils receiving cassava and supplements, but the cis-to-trans ratio in liver differed from intake. Biofortified cassava adequately maintained vitamin A status and was as efficacious as Beta-Carotene supplementation in the gerbil model.
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carotenoid biofortified maize maintains adequate vitamin a status in mongolian gerbils
Journal of Nutrition, 2006Co-Authors: Julie A Howe, Sherry A TanumihardjoAbstract:Efforts to biofortify maize with provitamin A carotenoids have been successful, but the impact on vitamin A (VA) status has not been determined. We conducted two studies that investigated the bioefficacy of provitamin A carotenoids from maize and compared maize percentage and carotenoid concentrations on VA status in VA-depleted Mongolian gerbils (Meriones unguiculatus). Gerbils (n = 40/study) were fed a white maize diet 4 wk prior to treatment. In study 1, treatments (n = 10/group) included oil control, 60% high-Beta-Carotene maize, and Beta-Carotene or VA supplements (matched to high-Beta-Carotene maize). In study 2, gerbils were fed 30 or 60% orange or yellow maize diets. Gerbils were killed after 4 wk. In study 1, liver VA concentrations, compared with the high-Beta-Carotene maize group (0.25 +/- 0.15 micromol/g), were higher in the VA group (0.56 +/- 0.15 micromol/g, P < 0.05), lower in the control (0.10 +/- 0.04 micromol/g, P < 0.05), and did not differ in the Beta-Carotene group (0.25 +/- 0.08 micromol/g). Bioconversion was approximately 3 microg Beta-Carotene to 1 mug retinol (1.5 mol Beta-Carotene to 1 mol retinol). The liver Beta-Carotene content was greater in the high-Beta-Carotene maize group (26.4 +/- 6.0 nmol) than in the Beta-Carotene supplement group (14.1 +/- 6.0 nmol; P < 0.05). In study 2, the gerbils' VA status improved with increasing dietary Beta-Carotene. Liver VA in gerbils fed orange maize was greater than in those fed yellow maize, regardless of maize percentage (P < 0.05). Biofortified maize adequately maintained VA status in Mongolian gerbils and was as efficacious as Beta-Carotene supplementation. In populations consuming maize as a staple food, using orange instead of white maize could dramatically affect VA status.
Noriko Bando - One of the best experts on this subject based on the ideXlab platform.
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Ingested quercetin but not rutin increases accumulation of hepatic β‐carotene in BALB/c mice
Molecular Nutrition & Food Research, 2010Co-Authors: Noriko Bando, Naomi Muraki, Kaeko Murota, Junji Terao, Rintaro YamanishiAbstract:Beta-Carotene is a carotenoid with a range of reported health benefits besides vitamin A activity. If the enzymatic conversion of Beta-Carotene to retinal is suppressed in the digestive tract, residual Beta-Carotene that reaches the tissues increases. We evaluated the function of quercetin and rutin (quercetin-3-rutinoside) to increase the accumulation of Beta-Carotene in vitro and in vivo in BALB/c mice. When the conversion of Beta-Carotene by a preparation of the murine small intestine was measured in vitro, the addition of quercetin or rutin considerably inhibited the conversion. When the levels of hepatic Beta-Carotene and retinoids were measured among three groups of mice fed a diet supplemented with Beta-Carotene plus quercetin or rutin or Beta-Carotene alone (four to six mice per group), quercetin increased the level of Beta-Carotene and decreased the level of retinol, whereas rutin did not. These results demonstrate that quercetin can suppress the conversion of Beta-Carotene which develops in the cytosol of small intestinal epithelial cells, and that rutin whose rutinose-moiety prevents being absorbed in the small intestine cannot suppress the conversion in vivo. This study offers a novel insight into the interaction between flavonoids and carotenoids with respect to the health benefits from the latter.
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Ingested quercetin but not rutin increases accumulation of hepatic Beta-Carotene in BALB/c mice.
Molecular nutrition & food research, 2010Co-Authors: Noriko Bando, Naomi Muraki, Kaeko Murota, Junji Terao, Rintaro YamanishiAbstract:Beta-Carotene is a carotenoid with a range of reported health benefits besides vitamin A activity. If the enzymatic conversion of Beta-Carotene to retinal is suppressed in the digestive tract, residual Beta-Carotene that reaches the tissues increases. We evaluated the function of quercetin and rutin (quercetin-3-rutinoside) to increase the accumulation of Beta-Carotene in vitro and in vivo in BALB/c mice. When the conversion of Beta-Carotene by a preparation of the murine small intestine was measured in vitro, the addition of quercetin or rutin considerably inhibited the conversion. When the levels of hepatic Beta-Carotene and retinoids were measured among three groups of mice fed a diet supplemented with Beta-Carotene plus quercetin or rutin or Beta-Carotene alone (four to six mice per group), quercetin increased the level of Beta-Carotene and decreased the level of retinol, whereas rutin did not. These results demonstrate that quercetin can suppress the conversion of Beta-Carotene which develops in the cytosol of small intestinal epithelial cells, and that rutin whose rutinose-moiety prevents being absorbed in the small intestine cannot suppress the conversion in vivo. This study offers a novel insight into the interaction between flavonoids and carotenoids with respect to the health benefits from the latter.
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β carotene and β cryptoxanthin but not lutein evoke redox and immune changes in raw264 murine macrophages
Molecular Nutrition & Food Research, 2009Co-Authors: Sakurako Katsuura, Noriko Bando, Tomomi Imamura, Rintaro YamanishiAbstract:The mechanism of immunological benefits induced by carotenoids has not been fully elucidated. Here, we investigated some of the immunity-related properties of Beta-Carotene and two other carotenoids, beta-cryptoxanthin, and lutein, on the murine macrophages cell line RAW264. Beta-Carotene added to the culture medium accumulated in the cells in a time- and dose-dependent manner. The accumulation was positively correlated with cellular lipid peroxidation, demonstrating the pro-oxidative activity of Beta-Carotene, and also with the synthesis of glutathione, an intracellular antioxidant. Conversely, accumulation of Beta-Carotene was negatively correlated with the transcription of immune-active molecules, such as IL-1beta, IL-6, and IL-12 p40, in cells stimulated by LPS and INF-gamma. The transcription of the pro-inflammatory cytokines IL-1beta and IL-6 was more sensitive to the accumulation of Beta-Carotene than was IL-12 p40. The accumulation of beta-cryptoxanthin in cells resulted in effects similar to those of Beta-Carotene. However, lutein accumulated minimally and did not significantly affect the cells. These results demonstrate that Beta-Carotene, and beta-cryptoxanthin as well, can accumulate in RAW264 cells and induce changes in intracellular redox status, which in turn regulate the immune function of macrophages.
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β‐Carotene and β‐cryptoxanthin but not lutein evoke redox and immune changes in RAW264 murine macrophages
Molecular nutrition & food research, 2009Co-Authors: Sakurako Katsuura, Noriko Bando, Tomomi Imamura, Rintaro YamanishiAbstract:The mechanism of immunological benefits induced by carotenoids has not been fully elucidated. Here, we investigated some of the immunity-related properties of Beta-Carotene and two other carotenoids, beta-cryptoxanthin, and lutein, on the murine macrophages cell line RAW264. Beta-Carotene added to the culture medium accumulated in the cells in a time- and dose-dependent manner. The accumulation was positively correlated with cellular lipid peroxidation, demonstrating the pro-oxidative activity of Beta-Carotene, and also with the synthesis of glutathione, an intracellular antioxidant. Conversely, accumulation of Beta-Carotene was negatively correlated with the transcription of immune-active molecules, such as IL-1beta, IL-6, and IL-12 p40, in cells stimulated by LPS and INF-gamma. The transcription of the pro-inflammatory cytokines IL-1beta and IL-6 was more sensitive to the accumulation of Beta-Carotene than was IL-12 p40. The accumulation of beta-cryptoxanthin in cells resulted in effects similar to those of Beta-Carotene. However, lutein accumulated minimally and did not significantly affect the cells. These results demonstrate that Beta-Carotene, and beta-cryptoxanthin as well, can accumulate in RAW264 cells and induce changes in intracellular redox status, which in turn regulate the immune function of macrophages.
John W Erdman - One of the best experts on this subject based on the ideXlab platform.
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Mongolian Gerbils (Meriones unguiculatus) Absorb β-Carotene Intact from a Test Meal
Journal of Nutrition, 1994Co-Authors: Joann. Pollack, Joy M. Campbell, Susan M. Potter, John W ErdmanAbstract:: Because a yellow color has been observed in the fat pads of Mongolian gerbils fed a nonpurified diet, we designed the current study to determine whether adult male gerbils would absorb Beta-Carotene intact from a test meal. Thirty-five gerbils (80-90 g) were adapted to the laboratory and fed a standard purified diet free of Beta-Carotene for 16-19 d. Gerbils were then fed a test meal consisting of 279 nmol of Beta-Carotene as 10% water-soluble beadlets suspended in 0.5 mL of Ensure. Gerbils (n = 5) were killed at 0, 2, 4, 6, 12, 24 or 72 h after the test meal, blood was obtained by cardiac puncture, and tissues were taken for Beta-Carotene analysis. No Beta-Carotene was detected in serum at 0 or 72 h, whereas Beta-Carotene was present at all other sampling times. Serum Beta-Carotene peaked at 4 h, at a level of 88 nmol/L. Beta-Carotene was detected in the liver of all groups; however, the concentration increased from -34 pmol/g to a maximum concentration of 926 pmol/g at 24 h after the test meal. Other tissues also contained Beta-Carotene. The results demonstrate that Mongolian gerbils, like ferrets and preruminant calves, absorb Beta-Carotene intact when Beta-Carotene is provided at a physiological level in a test meal. This species may be particularly useful for evaluation of the role of antioxidants, such as Beta-Carotene, in LDL oxidation.
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The relationship between plasma, leukocyte and leukocyte membrane Beta-Carotene concentrations in bovine animals
Nutrition Research, 1991Co-Authors: Nicholas J. Bruns, Eric T. Gugger, Patricia V Johnston, John W ErdmanAbstract:Abstract Blood was obtained at the time of slaughter from 14 mature bovine animals. Plasma, leukocyte and leukocyte membranes were harvested from each blood sample and Beta-Carotene concentrations were determined. Plasma Beta-Carotene concentrations ranged from 32.4 to 115.5 nmoles/dl (17.4 to 62.0 ug/dl) with a mean concentration of 73.2 nmoles/dl (39.3 ug/dl). Whole leukocyte Beta-Carotene concentrations in these same animals ranged from 0.07 to 0.31 nmoles/g weight (mean=0.17 nmoles/g). Leukocyte membrane Beta-Carotene concentrations ranged from 0.74 pmole/g to 0.29 n mole/g (mean 0.15 nmole/g). There was a linear relationship between plasma and leukocyte Beta-Carotene concentrations with a correlation coefficient of .82. A linear relationship also existed between plasma and leukocyte membrane Beta-Carotene concentrations (correlation coefficient=.78) and between leukocyte and leukocyte membrane Beta-Carotene concentrations (correlation coefficient=.65). Thus, Beta-Carotene is present in bovine leukocyte and leukocyte membranes and a linear relationship exists between plasma levels and Beta-Carotene content in these cells and cell membranes.