Activity Of Beta-carotene Research Articles

Comparative Biologic Activity of Beta-Carotene and Vitamin A

Comparative Biologic Activity of Beta-Carotene and Vitamin A

Micellar oleic and eicosapentaenoic acid but not linoleic acid influences the β-carotene uptake and its cleavage into retinol in rats

Improving the bioavailability of beta-carotene is vital to manage vitamin A deficiency. The influence of micellar oleic (OA), linoleic (LA) and eicosapentaenoic (EPA) acids on plasma beta-carotene response and its conversion to retinol has been studied in rats employing single (9 h time course) and repeated (10 days) dose administrations. After a single dose, the levels (area under the curve) of plasma beta-carotene and retinyl palmitate in OA and EPA groups were higher (p < 0.05) by 13, 7 and 11, 6 folds than LA group. The liver beta-carotene level in OA and EPA groups were higher (p < 0.05) by 3 and 1.2 folds than LA group. After repeated dose, the plasma beta-carotene and retinyl palmitate levels in OA (6.2%, 51.7%) and EPA (25.4%, 17.23%) groups were higher (p < 0.05) than LA group. The liver beta-carotene level in OA (21.2%) and EPA (17.6%) groups were higher (p < 0.05) than LA group. In both the experiments, the activity of beta-carotene 15,15'-dioxygenase in the intestinal mucosa and plasma triglyceride levels were also higher in OA and EPA groups than LA group. beta-Carotene excreted through urine and feces of OA and EPA groups was lower than the LA group. These results demonstrate an improved absorption and metabolism of beta-carotene when fed mixed micelles with OA or EPA compared with LA. Although the mechanism involved in selective absorption of fatty acids needs further studies, intestinal beta-carotene uptake and its conversion to vitamin A can be modulated using specific fatty acids.

Assessment of Antioxidative Activity of Lipid- and Water-Soluble Vitamins in Human Whole Blood. Comparative Analysis Between a Biological Test and Chemical Methods

Assessment of the antioxidant activity of vitamins and other compounds is of interest in the understanding of their in vivo effects. In this study, we have investigated the activity of several lipid and water-soluble vitamins in human whole blood. Measurements were carried out using a biological test that enables the evaluation of both red blood cells and plasma resistance against free radical activity induced by 2,2'-azobis (2-amidinopropane)hydrochloride (AAPH). Antioxidant activity of vitamins has been determined by using the biological test versus chemical methods (chemiluminescence, DMPD radical). We have observed strong anti-oxidant potentials for vitamins B6 and B9 with biological tests, but not with chemical methods. At 10 microM, the vitamin B9 efficiency in inhibiting radical-induced red blood cell hemolysis was almost three times higher than vitamin C efficiency and two times higher than alpha-tocopherol efficiency. Antioxidant activity was not observed for vitamins B1 or B2, nor for retinol. The weak activity of beta-carotene still remains to be investigated particularly in relation to oxygen pressure. Our study demonstrated that the biological test is more useful than the chemical methods employed in this instance, for the evaluation of antioxidant capacity of lipophilic and putatively biologically active compounds.

Rate of free-radical oxidation of C18 diene and triene fatty acids in aqueous micellar solutions and effectiveness of beta-carotene as an inhibitor of their oxidation.

The rate of accumulation of conjugated dienes of polyunsaturated fatty acids was measured during free-radical oxidation of linoleic acid (18:2n-6, LA), alpha-linolenic acid (18:3n-3, alpha-LNA), and gamma-linolenic acid (18:3n-6, gamma-LNA) initiated by 2,2;-azo-bis-(2-amidinopropane) hydrochloride in aqueous micellar solutions of sodium dodecyl sulfate and sodium cholate. It was shown that, unlike homogeneous solutions, the oxidative stability of PUFAs in aqueous dispersions increased with an increase in the extent of unsaturation. The rate of LA oxidation was more than tenfold greater than that of alpha- and gamma-LNA. The antioxidant activity of beta-carotene, in contrast to homogeneous solutions, in both micellar systems studied depended on the degree of PUFA unsaturation. We found that 5 micro M beta-carotene effectively inhibited the LA oxidation (almost by 90%), whereas the oxidation of alpha-LNA and gamma-LNA was not inhibited by beta-carotene even at much greater concentration (30 micro M). The paradoxical discrepancy between the extent of unsaturation and the PUFA oxidation rate, as well as a decrease in the efficiency of beta-carotene-dependent inhibition of oxidation of more polyunsaturated fatty acids in reactions conducted in aqueous dispersions is consistent with the model according to which the peroxyl radicals of LA and fatty acids with the double-bond number greater than two exhibit different polarity.

Variability in conversion of β-carotene to vitamin A in men as measured by using a double-tracer study design

The vitamin A activity of beta-carotene is variable and surprisingly low in women. The reasons for this are not well understood. The vitamin A activity of beta-carotene in men is still uncertain. Contributions of dietary factors compared with individual traits are largely unknown. Our objective was to measure the intrinsic variability in the vitamin A activity of beta-carotene among healthy, well-fed men living in a controlled environment. We used a double-tracer test-retest design. We dosed 11 healthy men orally with 30 micromol hexadeuterated (D6) retinyl acetate (all-trans-19,19,19,20,20,20-[2H6]retinyl acetate) and then with 37 micromol D6 beta-carotene (19,19,19,19',19',19'-[2H6]beta-carotene) 1 wk later. Doses were taken with breakfasts containing 16 g fat. We measured D6 retinol, D6 beta-carotene, and trideuterated (D3) retinol (derived from D6 beta-carotene) concentrations in plasma. Areas under the plasma concentration x time since dosing curves (AUCs) were determined for D6 retinol, D6 beta-carotene, and D3 retinol. All men had detectable D6 retinol concentrations in plasma. The mean (+/-SE) absorption of D6 beta-carotene in all subjects was 2.235 +/- 0.925%, and the mean conversion ratio was 0.0296 +/- 0.0108 mol retinol to 1 mol beta-carotene. Only 6 of 11 men had sufficient plasma concentrations of D6 beta-carotene and D3 retinol that we could measure. The mean absorption of D6 beta-carotene in these 6 subjects was 4.097 +/- 1.208%, and the mean conversion ratio was 0.0540 +/- 0.0128 mol retinol to 1 mol beta-carotene. The vitamin A activity of beta-carotene, even when measured under controlled conditions, can be surprisingly low and variable.