Absorption of canthaxanthin by the rat is influenced by total lipid in the intestinal lumen.

In this study the effect of luminal lipid on the absorption of canthaxanthin (CTX) was investigated using the lymph duct cannulated rat. Treatments were emulsions designed to deliver increasing amounts of olive oil (10, 30, 50, 70, or 90 mg/h) and CTX (12.5 nmol/h). Emulsions were continuously infused into the duodenum for 12 h, and lymph was collected during the final 6 h of infusion for analysis. As the amount of lipid in the emulsion increased, a linear increase in the absorption of CTX was observed. The recovery of CTX in the lymph when infused with 10 mg/h olive oil was 14.2 +/- 1.2% and with 90 mg/h was 26.9 +/- 5.7%. The efficiency of CTX absorption nearly doubled by increasing the amount of lipid infused with CTX. The correlation between lipid load and CTX absorbed was r= 0.85. We conclude that luminal lipid load affects CTX absorption.

Aldehyde reactivity with 2-thiobarbituric acid and TBARS in freeze-dried beef during accelerated storage.

When lipid oxidation is evaluated in freeze-dried beef, a yellow 450-nm-absorbing pigment develops during the 2-thiobarbituric acid (TBA) assay. TBA analysis and high performance liquid chromatography (HPLC) were applied to measure oxidative changes in salted freeze-dried beef patties (15% fat) initially during storage at 49°C. The TBA pink pigment (λ(max)=532 nm) was most pronounced in unstored salted freeze-dried beef, and yellow pigment (λ(max)=450 nm) predominated in stored samples. An in vitro study of TBA reactivity of different aldehydes, known to be secondary lipid oxidation products, showed that alkanals and alk-2-enals favored TBARS(450) formation, while alka-2,4-dienals favored TBARS(532). Values of TBARS(450) from 95°C TBA incubation were lower than those from 25°C incubation (P<0.05), indicating that the yellow chromophore from the aldehyde-TBA complex was less thermally stable than the pink pigment. 5-Hydroxymethyl-2-furfural, an aldehyde produced from Maillard reaction, also produced strong TBARS(450). Propional, butanal and 5-hydroxymethyl-2-furfural (HMF), were tentatively identified in freeze-dried beef during accelerated storage at 49°C, and have the potential to yield TBARS @450.

A comparison of lycopene and astaxanthin absorption from corn oil and olive oil emulsions.

The effect of different oils on the absorption of carotenoids was investigated in mesenteric lymph duct cannulated rats. Sixteen treatment emulsions containing increasing concentrations of either lycopene (LYC) or astaxanthin (AST) (5, 10, 15, 20 micromol/L) were prepared with olive oil or corn oil and continuously infused into the duodenum of the rat. Absorption of carotenoids into the mesenteric lymph duct was determined. Absorption of LYC and AST from both oils increased with the amount infused into the duodenum. The average recovery of AST in the lymph from the olive oil emulsion was 20% but was decreased to 13% from emulsions containing corn oil. Lycopene was not as well absorbed as AST. The average recovery of LYC was 6% from olive oil emulsions but only 2.5% when infused with corn oil. The LYC used in this study was isolated from tomato paste and was primarily in the all-trans form. We did not observe any significant isomerization of all-trans LYC to 9-cis LYC during absorption. We conclude that the type of oil with which a carotenoid is consumed can influence its absorption.

Iron and zinc supplementation improves indicators of vitamin A status of Mexican preschoolers.

BACKGROUND: The coexistence of multiple micronutrient deficiencies is a widespread public health problem in many regions of the world. Interactions between zinc deficiency and vitamin A metabolism have been reported but no longitudinal studies have evaluated the effect of iron deficiency on vitamin A. OBJECTIVE: The objective of this study was to investigate the effect of supplementation with iron, zinc, or both on vitamin A and its metabolically related proteins retinol binding protein (RBP) and transthyretin. DESIGN: The study was a longitudinal, double-blind, placebo-controlled trial in which 219 rural Mexican children aged 18-36 mo were randomly assigned to receive 20 mg Zn/d, 20 mg Fe/d, 20 mg Zn/d plus 20 mg Fe/d, or placebo. RESULTS: Six months after supplementation, plasma retinol increased in all supplemented groups. Compared with placebo, zinc supplementation was associated with significantly higher plasma retinol and transthyretin but the increase in RBP was not significant. Iron supplementation significantly increased plasma retinol, RBP, and transthyretin. Supplementation with zinc plus iron significantly increased plasma retinol but not RBP or transthyretin. Children deficient in zinc, iron, or vitamin A (as indicated by nutrient plasma concentration) at the beginning of the study had a significantly greater increase in retinol than did children with adequate nutrient status. CONCLUSIONS: Supplementation with zinc, iron, or both improved indicators of vitamin A status. The results of this study agree with previous observations of a metabolic interaction between zinc and vitamin A and suggest an interaction between iron and vitamin A metabolism.

Excess vitamin E decreases canthaxanthin absorption in the rat.

The recent attention given to the possible role of alpha-tocopherol (alpha-Toc) and carotenoids in the prevention and treatment of a variety of illnesses resulted in segments of the population increasing their consumption of these nutrient/antioxidants. Once consumed, alpha-Toc and carotenoids are thought to follow the same absorptive pathway and may influence each other's absorption, particularly when taken in large doses. The purpose of this study was to determine if alpha-Toc and the carotenoid, canthaxanthin (CTX), interact during absorption. Rats were intraduodenally infused with corn oil emulsions containing combinations of alpha-Toc (0 or 300 mumol/L) and CTX (5, 10, 15, 20 mumol/L) in a 2 x 4 factorial arrangement. Absorption was determined by measuring recovery of CTX and alpha-Toc in the mesenteric lymph. The amount of CTX in the lymph increased significantly with the amount infused into the duodenum. The overall efficiency of CTX absorption from emulsions without alpha-Toc averaged 12% with individual animals having a range of 8 to 18%. Efficiency of absorption was not related to concentration of CTX infused. When alpha-Toc (300 mumol/L) was added to the oil emulsion, the absorption of CTX was decreased by at least 50%. Recovery of alpha-Toc in the lymph averaged ca. 10% and was not affected by CTX. These results suggest that concurrent consumption of a large dose of alpha-Toc may influence carotenoid bioavailability.

Pectin and psyllium decrease the susceptibility of LDL to oxidation in guinea pigs.

These studies were undertaken to determine whether pectin (PE) and psyllium (PSY) intake affect the circulating levels of alpha-tocopherol and the susceptibility of low density lipoprotein (LDL) to oxidation. For that purpose, male Hartley guinea pigs were fed 19 g/100 g of a fat mix with a 2:1:1 ratio of saturated:polyunsaturated:monounsaturated fatty acids and 35 g/100 g total carbohydrate with 80% of the carbohydrate energy contributed by sucrose. Diets were identical in composition except for the fiber source: cellulose (control diet), PE, or PSY. Guinea pigs fed PE or PSY had 36% and 67% lower plasma cholesterol concentrations, respectively, compared with controls (P < 0.001). This plasma cholesterol lowering was associated with both very low density lipoproteins and LDL cholesterol fractions. Intake of PE or PSY resulted in 54% lower plasma triacylglycerol (TAG) concentrations compared with the control group (P < 0.001). LDL from PE and PSY fed guinea pigs contained fewer molecules of cholesteryl ester, and alpha-tocopherol concentrations in this particle were 49% and 66% higher, respectively, compared with controls. In addition, LDL from guinea pigs fed soluble fiber exhibited less susceptibility to oxidation than those from the control group, as determined by thiobarbituric acid-reactive substances formation. Hepatic free and esterified cholesterol were 32% lower and hepatic TAG was 25% lower in guinea pigs fed PE and PSY compared with controls. The data from these studies confirm that PE and PSY reverse the hyperlipidemia associated with high fat-sucrose diets and demonstrate a potential antioxidant effect of soluble fiber on circulating LDL.

Properties of retinoids. Structure, handling, and preparation.

Retinoids are unstable compounds being readily oxidized and/or isomerized to altered compounds, especially in the presence of oxidants including air, light, and excessive heat. They are labile toward strong acids and solvents that have dissolved oxygen or peroxides. In this review, procedures for handling and storage of retinoids and biological samples containing them have been described. The physical and chemical properties of retinoids have been reported. Simplified procedures for derivatizations and purification, and methods for quantitation of retinoids have been presented.

Varying dietary fat type of reduced-fat diets has little effect on the susceptibility of LDL to oxidative modification in moderately hypercholesterolemic subjects.

The effect of the fatty acid composition of reduced-fat diets on the in vitro oxidation of LDL was examined in 14 moderately hypercholesterolemic [low density lipoprotein (LDL) > 3.36 mmol/L] postmenopausal female and male subjects (age 44-78 y). Each subject consumed each of five reduced-fat diets [30 energy percent (E%) fat, 17 E% protein and 53 E% carbohydrate] enriched in beef tallow, canola oil, corn oil, olive oil or rice bran oil (20 E%) for 32-d periods. In vitro oxidation of LDL was assessed by incubating LDL with hemin and hydrogen peroxide, and measuring the time required for the reaction to reach maximum velocity (lag time). LDL lag times were 93.2 +/- 25.8, 95.9 +/- 26.4, 104.2 +/- 32.7, 108.0 +/- 26.6 and 113.1 +/- 24.0 min for corn oil, beef tallow, rice bran oil, canola oil and olive oil periods, respectively. When the data from all dietary phases were pooled, LDL alpha-tocopherol level (r = 0.30, P = 0.01) and plasma 18:1/18:2 ratio (r = 0.22, P = 0.08) were positively related to resistance of LDL to oxidation. Differences induced by the dietary perturbations in LDL content of beta-cryptoxanthin, lutein/zeaxanthin, lycopene, alpha-carotene or beta-carotene, and LDL particle size were not related to resistance of LDL to oxidation. In conclusion, in middle-aged and elderly moderately hypercholesterolemic subjects, the consumption of reduced-fat diets enriched in animal fat or vegetable oils with a relatively wide range of fatty acid profiles did not alter the in vitro susceptibility of LDL to oxidation. The advantages of reducing the saturated fat content of the diet were reflected in lower total and LDL cholesterol levels.

A comparison of lycopene and canthaxanthin absorption: using the rat to study the absorption of non-provitamin A carotenoids.

The purpose of this study was to validate the use of the mesenteric lymph duct cannulated rat to study the absorption of carotenoids which do not have provitamin A activity. The absorption of two carotenoids, a hydrocarbon carotenoid (lycopene) and a xanthophyll carotenoid (canthaxanthin), were investigated. In the first experiment, lipid emulsions containing lycopene (LYC) or canthaxanthin (CTX) were continuously infused into the duodenum, and lymph was collected for analysis at 2-h intervals. The time course for absorption of carotenoids and triacylglycerol (TAG) was similar. Carotenoids and TAG reached steady-state concentrations in the lymph by 6 h. There was no evidence for a delayed release of either carotenoid from the intestine relative to TAG. During a second experiment, emulsions containing increasing concentrations of LYC or CTX (5, 10, 15, 20 mumol/L) were infused. The LYC and CTX in the lymph increased in a dose-dependent manner. The average efficiency of CTX absorption was 16% while the efficiency of LYC absorption averaged only 6%. Efficiency of carotenoid absorption was not related to concentration infused. Finally, to test whether LYC and CTX interact during absorption both were added to a lipid emulsion at equal concentrations (20 mumol/L) and infused. The carotenoids did not significantly affect each other's absorption. These results demonstrate the usefulness of the rat as an animal model to study the absorption of non-provitamin A carotenoids.

Estimating derivatives of pharmacokinetic response curves with varying bandwidths.

A kernel-smoothing method with locally varying bandwidths for the nonparametric estimation of derivatives of a function is proposed for highly nonequidistant data as they occur in pharmacokinetic response curves. We construct estimates having the particular property that the derivative estimates correspond exactly to the corresponding derivatives of the curve estimate even under locally varying bandwidth choice. The effects on the estimation of peak location (characteristic points) are investigated. In an example, characteristic points are estimated for a recently developed in vivo isotope dilution assay for vitamin A (retinol) nutritional status. The in vivo kinetics of appearance and disappearance of isotopically labeled retinol can be described with the proposed method.

Fast minimicroassay of serum retinol (vitamin A) by capillary zone electrophoresis with laser-excited fluorescence detection.

In this paper, we present a fast minimicroassay of serum vitamin A by capillary zone electrophoresis with laser-excited fluorescence detection. A 60 cm x 50 microns I.D. fused-silica capillary was used for the separation, and the polymer coating was burned off 20 cm from the cathodic end to form a detection window. The buffer system consisted of 50 mM sodium phosphate plus 10 mM sodium chloride at pH 7.8. A helium-cadmium laser set at 325 nm was used for excitation, and the fluorescence of the vitamin A-retinol-binding protein complex was monitored at 465 nm using a photodiode. The stray and scattered radiation were removed by two special filters. Using this system, about 8 nl of serum sample were injected for direct analysis without any sample preparation. The analysis time for each sample was less than 6 min, and subfemtomole levels of vitamin A in human or animal blood could be easily detected. Therefore, the method is potentially useful for finger-prick vitamin A analysis, especially for babies and young children.

Fatty-acyl esters of retinol (vitamin A) in the liver of the harp seal (Phoca groenlandica), hooded seal (Cystophora cristata), and California sea lion (Zalophus californianus).

The fatty-acid composition of retinyl esters in the livers of two species of phocid seal, the harp seal (Phoca groenlandica, n = 20) and the hooded seal (Cystophora cristata, n = 15), and one species of otariid seal, the California sea lion (Zalophus californianus, n = 6), was determined. Vitamin A ranged in concentration from 4 to 1024 nmol retinol/g liver for the phocids and from 381 to 979 nmol/g liver for the otariids. In most of the livers, retinyl palmitate was not the principal ester, and the palmitate + stearate + oleate trio of retinyl esters represented less than 50% of the total. In all samples, the retinyl esters contained 20:1, 20:4, 20:5, and 22:6 in unusually large amounts. Retinyl esters tended to be richer than whole-liver lipids in 20:5 + 22:6, whereas whole-liver lipids were richer in 18:0 and 18:2. Therefore, the pool of acyl donors used for the esterification of retinol may be distinct from that used for other lipids. Birth-to-weaning changes were seen only in the harp seals. In the pups, the hepatic vitamin-A concentration increased 454%, while the proportion of 18:0 and 20:1 in the retinyl esters rose and that of 14:0 + 16:1 and 20:4 fell. Concomitantly, in their mothers, the proportion of 20:4 increased but that of 16:0 and 18:0 decreased.

Metabolism of carotenoid analogs in humans.

Single oral doses (100 mumol) in peanut oil of 4,4'-dimethoxy-beta-carotene, ethyl beta-apo-8'-carotenoate, and beta-apo-8'-carotenal were administered to healthy adult male subjects (n = 4-6). Blood samples were taken frequently thereafter, and serum carotenoids and retinoids were analyzed by HPLC. The metabolism of the three analogs was very different; 4,4'-dimethoxy-beta-carotene was oxidized at the 4 and 4' positions but apparently not cleaved, whereas ethyl beta-apo-8'-carotenoate was not detectably metabolized, and beta-apo-8'-carotenal was extensively converted to its corresponding acid, alcohol, and fatty acyl ester and detectably converted to retinyl ester and possibly to two shorter beta-apocarotenals. Serum concentrations of endogenous retinoids and carotenoids, except as noted above, were not affected in any case. Kinetically, the maximum serum concentrations, areas under the curve, and mean sojourn times for the three analogs differed by 50-, 270-, and 5-fold, respectively. For any given analog, however, the fractional standard deviations for these parameters were only 0.2-0.5.

Retinoids and carotenoids in bovine pineal gland.

The retinoids and carotenoids in bovine pineal gland were analyzed by high-performance liquid chromatographic methods. The major retinoid observed was all-trans retinol, with an average level of 579 pmol/g wet tissue. In agreement with a previous report, retinal was not detected; however, we could not detect any retinyl ester in bovine pineal gland. Methods similar to those used in studying metabolism of vitamin A in the bovine eye were used to study the esterification and isomerization reactions of retinoids in the pineal gland. Neither esterification nor isomerization reactions occurred. These results suggest that the key retinoids and enzymes involved in visual function are absent in the bovine pineal gland. The major carotenoid, which has not previously been reported in pineal gland, was beta-carotene at an average level of 1830 pmol/g wet tissue.