Excentral cleavage of beta-carotene in vivo in a healthy man.

BACKGROUND: Excentral cleavage of beta-carotene to retinoids and apocarotenoids occurs in vitro and in animal models. Whether it occurs in humans is unclear. OBJECTIVE: We tested the hypothesis of whether humans can cleave beta-carotene excentrally. DESIGN: A healthy man was given an oral dose of all-trans [10,10',11,11'-(14)C]-beta-carotene (1.01 nmol; 100 nCi). Its fate and that of its metabolites were measured in serial plasma samples. Its fate in feces and urine was also measured over time. Selected plasma samples were spiked with reference standards of retinol, beta-apo-12'-carotenal, beta-apo-8'-carotenal, 13-cis-retinoic acid, all-trans-retinoic acid, beta-carotene-5,6-epoxide, all-trans-beta-carotene, and retinyl palmitate and subjected to reverse-phase HPLC fractionation. The plasma, plasma fractions, urine, and feces were measured for (14)C with the use of accelerator mass spectrometry. RESULTS: Sixty-five percent of administered (14)C was absorbed, and 15.7% was eliminated in urine during the first 21 d after dosing. (14)C-beta-carotene and (14)C-retinyl palmitate appeared in plasma 0.25 d after the dose. (14)C-beta-carotene and (14)C-retinol both appeared at 0.5 d only. On day 3 after the dose, 2 large (14)C peaks appeared in plasma: one matched the retention time of beta-apo-8'-carotenal, and the other did not match any of the reference standards used. The delayed appearance of (14)C-beta-apo-8'-carotenal in plasma suggests that the excentral cleavage occurred after the (14)C-beta-apo-8'-carotene was absorbed into the body. CONCLUSION: These data suggest that excentral cleavage of ingested beta-carotene occurs in vivo in humans. Confirmation of that possibility and further study to identify and characterize additional metabolites are needed.

Dietary evaluation and attenuation of relative risk: multiple comparisons between blood and urinary biomarkers, food frequency, and 24-hour recall questionnaires: the DEARR study.

Estimates of diet-disease relative risks (RRs) suffer from inaccuracies introduced by dietary measurement errors. Using the "method of triads," by which the validity coefficient (VC) of the dietary assessment method and "true" long-term intake could be estimated from 3 pairwise correlations between the FFQ, the reference method, and the biomarker, the authors evaluated the performance of a newly developed FFQ. Over a period of 13 mo (September 2000 to September 2001), 161 participants completed 3 FFQs and six 24-h recalls (24HRs), and supplied 2 blood samples and three 24-h urine collections. For protein, beta-carotene, and folic acid, the VCs of the FFQ with the "true intake" (0.77, 0.65, and 0.72, respectively) were relatively higher than the VCs of 24HRs (0.68, 0.60 and 0.39, respectively). Among the biomarkers, the VCs of serum beta-carotene and folic acid with the "true intake" (0.65 and 0.65) were higher than the VCs of urinary nitrogen and alpha-tocopherol (0.44 and 0.34, respectively). The DEARR study showed that the newly developed FFQ is a valid and reproducible instrument for assessing dietary intake. The VCs obtained can be used for future adjustment of diet-disease RR estimates in this population.

Absorption and retinol equivalence of beta-carotene in humans is influenced by dietary vitamin A intake.

The effect of vitamin A supplements on metabolic behavior of an oral tracer dose of [14C]beta-carotene was investigated in a longitudinal test-retest design in two adults. For the test, each subject ingested 1 nmol of [14C]beta-carotene (100 nCi) in an emulsified olive oil-banana drink. Total urine and stool were collected for up to 30 days; concentration-time patterns of [14C]beta-carotene, [14C]retinyl esters, and [14C]retinol were determined for 46 days. On Day 53, the subjects were placed on a daily vitamin A supplement (10000 IU/day), and a second dose of [14C]beta-carotene (retest) was given on Day 74. All 14C determinations were made using accelerator mass spectrometry. In both subjects, the vitamin A supplementation was associated with three main effects: 1). increased apparent absorption: test versus retest values rose from 57% to 74% (Subject 1) and from 52% to 75% (Subject 2); 2). an approximately 10-fold reduction in urinary excretion; and 3). a lower ratio of labeled retinyl ester/beta-carotene concentrations in the absorptive phase. The molar vitamin A value of the dose for the test was 0.62 mol (Subject 1) and 0.54 mol (Subject 2) vitamin A to 1 mol beta-carotene. Respective values for the retest were 0.85 and 0.74. These results show that while less cleavage of beta-carotene occurred due to vitamin A supplementation, higher absorption resulted in larger molar vitamin A values.

Long-term kinetic study of beta-carotene, using accelerator mass spectrometry in an adult volunteer.

We present a sensitive tracer method, suitable for in vivo human research, that uses beta-[(14)C]carotene coupled with accelerator mass spectrometry (AMS) detection. Using this approach, the concentration-time course of a physiological (306 microgram 200 nCi) oral dose of beta-[(14)C]carotene was determined for 209 days in plasma. Analytes included beta-[(14)C]carotene, [(14)C]retinyl esters, [(14)C]retinol, and several [(14)C]retinoic acids. There was a 5.5-h lag between dosing and the appearance of (14)C in plasma. Labeled beta-carotene and [(14)C]retinyl esters rose and displayed several maxima with virtually identical kinetic profiles over the first 24-h period; elevated [(14)C]retinyl ester concentrations were sustained in the plasma compartment for >21 h postdosing. The appearance of [(14)C]retinol in plasma was also delayed 5.5 h postdosing and its concentration rose linearly for 28 h before declining. Cumulative urine and stool were collected for 17 and 10 days, respectively, and 57.4% of the dose was recovered in the stool within 48 h postdosing. The stool was the major excretion route for the absorbed dose. The turnover times (1/k(el)) for beta-carotene and retinol were 58 and 302 days, respectively. Area under the curve analysis of the plasma response curves suggested a molar vitamin A value of 0.53 for beta-carotene, with a minimum of 62% of the absorbed beta-carotene being cleaved to vitamin A.In summary, AMS is an excellent tool for defining the in vivo metabolic behavior of beta-carotene and related compounds at physiological concentrations. Further, our data suggest that retinyl esters derived from beta-carotene may undergo hepatic resecretion with VLDL in a process similar to that observed for beta-carotene.

Effect of repeated exercise on urinary 8-hydroxy-deoxyguanosine excretion in humans.

The purpose of this study was to investigate the effect of repeated exercise on oxidative damage to DNA in 10 well trained long distance runners who participated in an 8-day training camp. The average running distance during the camp was 30 +/- 3 km/day. The amount of urinary 8-hydroxy-deoxyguanosine (8-OHdG) excretion was used to estimate the oxidative DNA damage. Urine samples were collected for both a 3-day control period as well as throughout the camp. Blood samples were drawn after overnight fasting both before and after the camp. Urinary 8-OHdG excretion was significantly increased during the camp compared to the control period (265.7 +/- 75.5 vs. 335.6 +/- 107.4 pmol/kg/day, P < 0.05). The content of 8-OHdG in the lymphocyte DNA on the day after finishing the camp did not differ from that before the camp. Plasma TBARS, LDH, CK, CK-MB, and myoglobin significantly rose after the camp (P < 0.05). The plasma beta-carotene levels tended to rise after the camp, while the plasma alpha-tocopherol levels increased significantly after the camp (P < 0.05). These results indicate that repeated exercise augments oxidative stress and the DNA is also injured by exercise-induced reactive oxygen species. However, the oxidative damage to DNA is not accumulated by consecutive exercise, although it is sustained as long as the exercise is repeated.