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Thermal isomerization of synthetic all-(E)-beta-carotene yielded a multi-component mixture composed of more than sixteen (Z)-beta-carotenes and two thermo-cyclized isomers. They were separated and purified by high-performance liquid chromatography. Ten of these were characterized by spectroscopic methods as four mono-(Z)-, five di-(Z)-, and one tri-(Z)-beta-carotenes; the 7-(Z)-, 9-(Z)-, 13-(Z)-, 15-(Z)-, 9.13-(Z)-, 9.15-(Z)-, 9.13'-(Z)-, 13.15-(Z)-, 7.13'-(Z)-, and 9.9'.13-(Z)-isomers were included. Stereochemistry of six additional (Z)-isomers obtained is, as yet, unknown, though one of them might have the 9.9'-(Z)-geometry in the molecule. This is the first report on the formation and identification of the 'sterically hindered' 7-(Z)-isomers as well as the (5 leads to 10)-thermo-cyclized products in the field of alicyclic carotenoids.
OBJECTIVE: This study examined the relationship between pretrial serum concentrations of retinol, beta-carotene, beta-cryptoxanthin, and lutein/zeaxanthin and the subsequent risk of developing esophageal squamous cell carcinoma and gastric cardia or non-cardia adenocarcinoma in subjects selected from a randomized nutritional intervention trial in Linxian, China, a region with epidemic rates of esophageal and gastric cardia cancer. METHODS: We used a stratified case-cohort design to select cohort members for inclusion in this study. In all we measured serum concentrations of the above vitamins in 590 esophageal, 395 gastric cardia, and 87 gastric non-cardia case subjects as well as in 1053 control subjects. Relative risks (RRs) were estimated using Cox proportional hazards models. RESULTS: Median values in our cohort were low for serum retinol (33.6 microg/dl), beta-carotene (4.3 microg/dl), and beta-cryptoxanthin (3.5 microg/dl), but were high for lutein/zeaxanthin (40.0 microg/dl). Gastric cardia cancer incidence fell 10% for each quartile increase in serum retinol (RR = 0.90, 95% CI = 0.83-0.99). For esophageal cancer, an inverse association with retinol levels was found only in male non-smokers (RR = 0.79 per quartile increase, 95% CI = 0.63-0.99). For gastric non-cardia cancer, an inverse association was limited to subjects 50 years old or younger (RR = 0.58 per quartile, 95% CI = 0.31-0.96). For beta-cryptoxanthin there was a borderline significant protective association for gastric non-cardia cancer (RR = 0.88 per quartile, 95% CI = 0.76-1.0). In contrast, we found the incidence of gastric non-cardia cancer increased (RR = 1.2 per quartile, 95% CI = 1.0-1.3) with increasing concentration of serum lutein/zeaxanthin. CONCLUSIONS: In this population, we found that low retinol and high lutein/zeaxanthin concentrations increased the risks of gastric cardia and gastric non-cardia cancer respectively. We found that there were no strong associations between any of the other analytes and any of the cancer sites.
Inhibitory effect of four carotenoids prevalent in human blood and tissues against the formation of colonic aberrant crypt foci was examined in Sprague-Dawley rats. They received three intrarectal doses of N-methylnitrosourea in weak 1, and a daily gavage of de-escalated doses of carotenoids during weeks 2 and 5. Lycopene, lutein, alpha-carotene and palm carotenes (a mixture of alpha-carotene, beta-carotene and lycopene) inhibited the development of aberrant crypt foci quantitated at week 6, but beta-carotene did not. The results suggested that lycopene and lutein in small doses may potentially prevent colon carcinogenesis.
Isomerization of carotenoids, which is often encountered in food processing under the influence of temperature and light, may play a role in the observed protective effects of this group of secondary plant products. Investigation of in vitro antioxidant activity of prominent carotenoid geometrical isomers was undertaken in light of recent reports illustrating a large percentage of carotenoid (Z)-isomers in biological fluids and tissues. Alpha-carotene, beta-carotene, lycopene, and zeaxanthin were isolated from foods or supplements and subsequently photoisomerized with iodine as a catalyst. Major Z-isomers of each carotenoid were fractionated by semipreparative C(30) HPLC. In vitro antioxidant activity of all isomers collected was measured photometrically using the Trolox equivalent antioxidant capacity (TEAC) assay. TEAC values of 17 geometrical isomers investigated ranged from 0.5 to 3.1 mmol/L. Three unidentified (Z)-isomers of lycopene showed the highest antioxidant activity, being significantly higher than the result for (all-E)-lycopene, which had approximately two times the activity of (all-E)-beta-carotene. On the other hand, (9Z)-zeaxanthin had a more than 80% lower TEAC value compared to that of (all-E)-lycopene. These results allow for the in vivo relevance of (Z)-isomers of carotenoids to be considered.
BACKGROUND: Fat-soluble vitamin E and carotenoids are regarded as being protective against chronic diseases. Little is known about the effect of dietary fat on the bioavailability of these compounds. OBJECTIVE: The objective of this study was to assess the effect of the amount of dietary fat on plasma concentrations of vitamin E and carotenoids after supplementation with these compounds. DESIGN: During two 7-d periods, 4 groups of 14-15 volunteers received daily, with a low-fat hot meal, 1 of 4 different supplements: vitamin E (50 mg), alpha- plus beta-carotene (8 mg), lutein esters (8 mg lutein), or placebo. The supplements were provided in a low- or high-fat spread supplied in random sequence during either of the 2 experimental periods. RESULTS: As anticipated, plasma concentrations of vitamin E, alpha- and beta-carotene, and lutein were significantly higher in the supplemented groups than in the placebo group. The amount of dietary fat consumed with the hot meal (3 or 36 g) did not affect the increases in plasma concentrations of vitamin E (20% increase with the low-fat spread and 23% increase with the high-fat spread) or alpha- and beta-carotene (315% and 139% with the low-fat spread and 226% and 108% with the high-fat spread). The plasma lutein response was higher when lutein esters were consumed with the high-fat spread (207% increase) than with the low-fat spread (88% increase). CONCLUSION: Optimal uptake of vitamin E and alpha- and beta-carotene requires a limited amount of fat whereas the amount of fat required for optimal intestinal uptake of lutein esters is higher. 2000;71:-93.
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It is important that the factors influencing functional carotenoid absorption be made clear. The effect of rat diets containing different combinations of dietary protein, fat, and beta-carotene levels on beta-carotene absorption was evaluated. In the mid-level beta-carotene diet groups (1.8 mg beta-carotene/100 g diet), the retinol content in the liver and the ratio of the liver retinol content to the beta-carotene intake (namely, retinol accumulation rate) were both greater in the mid-level dietary protein groups (20 g protein/100 g diet) than in lower dietary protein groups (5 g protein/100 g diet), but were not affected by dietary fat level (10 g or 2 g fat/100 g diet). The liver beta-carotene content and its accumulation rate were lower in the mid-level dietary fat groups (10 g fat/100 g diet). beta-carotene 15,15'-dioxygenase (CDO) activity in the small intestine increased in the mid-level dietary protein groups, which resulted in an increase in the content of liver retinol converted from dietary beta-carotene. With respect to the mid-level dietary fat groups, the fecal beta-carotene excretion rate (%) increased. The low beta-carotene diet groups (0.006 mg beta-carotene/100 g diet) showed a higher serum retinol accumulation rate, CDO activity, and liver beta-carotene accumulation rate than the mid-level beta-carotene diet groups. These results suggest the marked effect of protein, fat, and beta-carotene level in diets on the absorption and metabolism of beta-carotene.
Changes in concentrations of milk and serum carotenoids, retinol, and alpha-tocopherol of five healthy, well-nourished, lactating women were measured over a 28-d supplementation trial with 30 mg beta-carotene and for 4 wk thereafter. Beta-carotene supplementation increased mean beta-carotene concentrations in milk and serum 6.4- and 7.4-fold, respectively. Concentrations of other major carotenoids, retinol, and alpha-tocopherol did not change substantially in either milk or serum. Uptake of beta-carotene into both serum and milk followed apparent first-order kinetics, occurring more rapidly into serum (t(1/2) = 5.5 d) than into milk (t(1/2) = 9 d). After supplementation, milk and serum beta-carotene concentrations decayed slowly, reaching approximately twofold initial concentrations by 4 wk. Kinetics of uptake and decay in milk beta-carotene concentrations paralleled those in serum. The data show that short-term supplementation of healthy, lactating mothers with purified beta-carotene at approximately fivefold the average daily dietary intake substantially increased milk and serum beta-carotene concentrations while not interfering with concentrations of other carotenoids, retinol, or alpha-tocopherol in milk or serum. Thus, an increased intake of beta-carotene by healthy, lactating women increases the supply of milk beta-carotene available to their breast-feeding infants.
Two major carotenoids of the stick insect were reinvestigated and shown to be beta,beta-caroten-2-ol and beta,beta-carotene-2,2'-diol and not isocryptoxanthin (beta,beta-carotin-4-ol) and isozeaxaanthin (beta,beta-carotene-4,4'-diol). Both pigments are esterified with fatty acids. The identification is based on cochromatography with authentic 2-, 3- and 4-isomers of the mono- and dihydroxy pigment, mass spectra, and chemical behaviour. In acid solution beta-beta-carotene-2,2'-diol is specifically dehydrogenated and rearranged to ketones with retro structures in analogy to the reactionof beta,beta-caroten-2-ol as recently reported. The final product of the diol is 4,5-dihydro-4,5'-retro-beta,beta-carotene-2,2'-dione. This is the first demonstration of beta,beta-carotene-2,2'-diol in an animal.
Seasonal variations in beta carotene intake and low levels of beta carotene and vitamin A in blood plasma were found in cows fed ration based mainly on maize silage. The supplementation of daily winter rations with 300 mg Rovimix-beta carotene per cow, beginning 14 days before parturition and 60 days after calving increased slighty the beta carotene and vitamin A concentrations of blood plasma and improved some fertility indices: the number of inseminations per cow was reduced and the percentage of conception rate was significantly higher. It may be assumed that beta carotene content in feeds and it's utilization rate generally reflected in beta carotene blood plasma level and in the improvement of fertility.
1H-NMR technique was applied to study liposomes formed with egg-yolk phosphatidylcholine containing as an additional component two carotenoid pigments: beta-carotene or zeaxanthin (dihydrohy-beta-carotene). A strong rigidifying effect of zeaxanthin but not of beta-carotene with respect to hydrophobic core of lipid bilayer was concluded from the carotenoid-dependent broadening of the NMR lines assigned to -CH2- groups and terminal -CH3 groups of lipid alkyl chains. A similar effect of zeaxanthin with respect to polar headgroups was concluded on the basis of the effect of the pigment on the shape of NMR lines attributed to -N+(CH3)3 groups. In contrast, beta-carotene increases motional freedom of lipid polar headgroups. The inclusion of both carotenoids to liposomes resulted in the enhanced penetration of Pr3+ ions to the polar zone of the external layer of a membrane monitored by the splitting of the -N+(CH3)3 signal, the effect of beta-carotene being much more pronounced. Differences in the effect on membrane structure and molecular dynamics observed for beta-carotene and its polar derivative are discussed in terms of organization of a carotenoid-containing lipid membrane.
The chemopreventive effects of beta-carotene are usually attributed to its antioxidant properties. To determine the effects of beta-carotene supplementation on different parameters of oxidative metabolism, 15 normal young male subjects (18-30 yrs) were placed on a carotenoid-free liquid diet for two weeks prior to entry into the study. Blood was then measured for five carotenoids, retinol, retinyl palmitate, retinol-binding protein, alpha-tocopherol, vitamin C, zinc, lipid peroxides, and neutrophil superoxide production. Absorption tests were performed with 15 mg of beta-carotene to determine absorption curves for each subject. Subjects were then divided into two groups and given either 15 (n = 7) or 120 (n = 8) mg of beta-carotene daily for four weeks along with the same carotenoid-free liquid diet. The absorption test and the blood measurements were repeated. After repletion with beta-carotene, serum lipid peroxide levels decreased in both groups (p less than 0.05), but no other changes were noted in either the neutrophil superoxide production or in the levels of any of the vitamins measured. In contrast to vitamin E, the superoxide scavenging ability of beta-carotene apparently does not contribute to its effects in lowering serum lipid peroxide levels.
Fishermen from Kerala (India) who chewed tobacco-containing betel quids daily (17.2 +/- 9.6 quids per day) and had well-developed oral leukoplakias with elevated frequencies of micronucleated cells participated in a short-term intervention trial. Beta-carotene (180 mg/week) (Group I), beta-carotene (180 mg/week) plus vitamin A (100,000 IU/week) (Group II), and placebo (Group III) capsules were given twice weekly for 6 months under strict supervision. The remission of oral leukoplakias, the inhibition of new leukoplakias, and the reduction of micronucleated oral mucosal cells were recorded at the 3rd and 6th months of the trial period. After 3 months, the frequency of micronucleated cells was significantly reduced in Group I (from 4.09% to 1.1% in areas of leukoplakia, and from 4.1% to 1.0% in the normal mucosa). At this time, remission of oral leukoplakias did not differ significantly from that observed in the placebo group. After 6 months of treatment, remission of leukoplakias in Group I (14.8%) and Group II (27.5%) differed significantly from that seen in Group III (3.0%). The development of new leukoplakias during the 6-month period was strongly inhibited in Group II (7.8%), and to a lesser degree in Group I (14.8%), as compared to Group III (21.2%). During the trial period, all participants continued to chew tobacco-containing betel quids in their accustomed manner. Thus, remission and inhibition of new oral leukoplakias and reduction of micronucleated mucosal cells occurred in the groups receiving beta-carotene and beta-carotene plus vitamin A during the continuous presence of carcinogens derived from tobacco and areca nut.
In this report we describe the development of a method for the concurrent reversed-phase high-performance liquid chromatographic separation and photodiode array detection of human plasma retinol, tocopherols and carotenes. For a single sample injection, retinol, retinyl acetate, alpha-tocopherol, gamma-tocopherol, alpha-tocopheryl acetate, all-trans-alpha-carotene and all-trans-beta-carotene, as well as the mono-cis geometrical isomers of beta-carotene were separated and detected. Analytical separations were performed at a subambient temperature (0 degree C) over a Suplex pKb-100 reversed-phase analytical column with an isocratic mobile phase of methanol-methyl tert.-butyl ether-water (80:20:5, v/v/v) at a flow-rate of 0.8 ml/min for 60 min. Standards and samples were reconstituted in ethanol, and typically, 50 microliters was injected for analysis. By HPLC, compounds of interest were clearly resolved and detectable at the picomole level.
A chemical model system was used to study peroxyl radical trapping reactions of beta-carotene (1) that may contribute to its antioxidant action in biological systems. Peroxyl radicals generated in hexane by thermolysis of azobis(2,4-dimethylvaleronitrile) (AMVN) at 37 degrees C oxidized 1 to 5,6-epoxy-beta,beta-carotene (2) and a previously unreported product, 15,15'-epoxy-beta,beta-carotene (6), in addition to several unidentified polar products. The epoxide products were purified by high-performance liquid chromatography and characterized by UV-vis spectroscopy, mass spectrometry, and 1H NMR. Epoxides 2 and 6 and the polar products were formed together from the initial stages of the reaction. As the reaction progressed, the epoxides were oxidized further to more polar products. Although epoxides 2 and 6 were formed at similar rates, 2 was oxidized more rapidly than 6. Incubations with [14C]-1 indicate that at their maximum concentrations 2 and 6 account for approximately 20% of the radiolabeled oxidation products. Epoxide formation may result from peroxyl radical addition to the polyene chain to form a resonance-stabilized peroxyl radical adduct. Peroxide bond scission would yield the epoxide and release an alkoxyl radical. Although this two-step sequence produces no net radical trapping, it could produce a kinetically significant inhibition of peroxyl radical propagation and account, in part, for the antioxidant properties of 1. Epoxides 2 and 6 are structurally distinct from retinoids, which are the metabolic products of 1, and therefore may be useful biochemical markers for its antioxidant actions.
Absorption and storage of [14C]beta-carotene in control and beta-carotene-fed (BC-fed) rats were determined. Pre-feeding with beta-carotene for 2 weeks caused a 1.9-fold stimulation of its own absorption as well as its conversion to retinyl esters, whereas the absorption of [3H]retinyl acetate was unaffected. The liver and the lungs accounted for 60% and 30%, respectively, of the total recovered 14C radioactivity in both control and BC-fed groups. Beta-carotene accounted for 80-87% of the recovered 14C radioactivity in both the liver and the lung. Subcellular distribution of [14C]beta-carotene in both control and BC-fed groups revealed that the cytosol was the major fraction accounting for 44.4% and 26.8% of the radioactivity in the liver and lungs, respectively. Distribution of beta-carotene among liver parenchymal (PC) and stellate cells (STC) was determined in the two groups. Based on radioactivity, the PC and STC contained 22% and 78% of the total, respectively, in the control group; the corresponding values for the PC and STC in the BC-fed group were 48% and 52% of the total radioactivity, respectively. Based on the beta-carotene concentration following chronic beta-carotene feeding, PC contained 75.5% while the STC had 24.5% of the total beta-carotene. Thus, parenchymal cells seem to be the major hepatic storage site for dietary beta-carotene after chronic feeding.
A two-month double-blind, placebo-controlled supplementation study of oral beta-carotene (20 mg daily) was conducted. Two hundred and twenty two 30-69 year old men were randomized into either a beta-carotene or placebo group, and serum samples were obtained at baseline, follow-up (2 months), and up to 12 weeks post-supplementation. Serum beta-carotene increased on average 10-fold in the beta-carotene group, from 0.53 +/- 0.32 mumol/l (mean +/- SD) at baseline to 4.99 +/- 2.47 mumol/l at follow-up (P less than 0.0001), and beta-carotene levels remained elevated up to 12 weeks post-supplementation (0.61 +/- 0.15 mumol/l). No changes in serum retinol, alpha-tocopherol, or total cholesterol were observed. At baseline, serum beta-carotene levels were positively correlated with dietary beta-carotene (r = 0.29) and inversely correlated with body mass index and serum gamma-glutamyltransferase (r = -0.33 and r = -0.40, respectively). The inverse association with body mass index and serum gamma-glutamyltransferase persisted during active supplementation, whereas the positive association with dietary beta-carotene disappeared. In multivariate analysis, serum cholesterol was also positively associated with serum beta-carotene levels both before and after supplementation. Baseline serum beta-carotene was the factor most strongly associated (positively) with serum beta-carotene after supplementation. Our study highlights the importance of several factors which affect serum beta-carotene.