Pharmacokinetics of beta-carotene and canthaxanthin after ingestion of individual and combined doses by human subjects

Factors affecting the fate of β-carotene in the human gastrointestinal tract: A narrative review

Carotenoids and their metabolites play crucial roles in human health such as in immunity, cell differentiation, embryonic development, maintenance of plasma membrane integrity, and gastrointestinal functions, in addition to counteracting night blindness and other eye-related diseases. However, carotenoid bioavailability is highly variable and often low. The bioavailability of β-carotene, among the most frequently consumed carotenoid from the diet, is determined by food matrix related factors such as carotenoid dose, its location in food the matrix, the physical state in food, the presence of other food compounds in the matrix such as dietary fiber, dietary lipids, other micronutrients present such as minerals, and food processing, influencing also the size of food particles, and the presence of absorption inhibitors (fat replacers and anti-obesity drugs) or enhancers (nano-/micro-formulations). However, also host-related factors such as physiochemical interactions by gastrointestinal secretions (enzyme and salts) and other host-related factors such as surgery, age, disease, obesity, and genetic variations have shown to play a role. This review contributes to the knowledge regarding factors affecting the bioavailability of β-carotene (food and host-relegated), as well as highlights in vitro models employed to evaluate β-carotene bioavailability aspects.

Bioaccessibility of carotenoids from plant and animal foods

The frequent consumption of carotenoid-rich foods has been associated with numerous health benefits, such as the supply of provitamin A. To exert these health benefits, carotenoids need to be efficiently liberated from the food matrix, micellized in the small intestine, taken up by the enterocytes and absorbed into the human blood stream. Enormous efforts have been made to better understand these processes. Because human studies are costly, labor-intense and time-consuming, the evaluation of carotenoid liberation and micellization at the laboratory scale using simulated in vitro digestion models has proven to be an important tool for obtaining preliminary results prior to conducting human studies. In particular, the liberation from the food matrix and the intestinal micellization can be mimicked by simulated digestion, yielding an estimate of the so-called bioaccessibility of a carotenoid. In the present review, we provide an overview of the carotenoid digestion process in vivo, the currently used in vitro digestion models and the outcomes of previous bioaccessibility studies, with a special focus on correlations with concomitantly conducted human studies. Furthermore, we advocate for the on-going requirement of better standardized digestion protocols and, in addition, we provide suggestions for the complementation of the acquired knowledge and current nutritional recommendations. © 2018 Society of Chemical Industry.

Dietary canthaxanthin reduces xanthophyll uptake and red coloration in adult red-legged partridges

Carotenoids give color to conspicuous animal signals that are often the product of sexual selection. Knowledge of the mechanisms involved in carotenoid-based signaling is critical to understanding how these traits evolve. However, these mechanisms remain only partially understood. Carotenoids are usually viewed as scarce dietary antioxidants whose allocation to ornaments may trade off against health. This trade-off would ensure its reliability as a signal of individual quality. In the case of red (keto)carotenoids, the literature suggests that some species may show constraints in their uptake. Canthaxanthin is one of the most common ketocarotenoids in red ornaments of animals. It is often commercially used as a dietary supplement to obtain redder birds (e.g. poultry). We increased the dietary canthaxanthin levels in captive red-legged partridges (Alectoris rufa). This species shows red non-feathered parts mostly pigmented by another common ketocarotenoid: astaxanthin. We studied the impact on the uptake of carotenoids and vitamins and, finally, on coloration. We also tested the potential protective effect of canthaxanthin when exposing birds to a free radical generator (diquat). Canthaxanthin did not apparently protect birds from oxidative stress, but interfered with the absorption of yellow carotenoids (lutein and zeaxanthin). Zeaxanthin is a precursor of astaxanthin in enzymatic pathways, and their levels in tissues and eggs were lower in canthaxanthin-supplied birds. This led to lower astaxanthin levels in ornaments and paler coloration. As far as we know, this is the first report of a carotenoid supplementation decreasing animal coloration. The results have implications for understanding carotenoid-based signaling evolution, but also for improving husbandry/experimental procedures.

Host-related factors explaining interindividual variability of carotenoid bioavailability and tissue concentrations in humans

Carotenoid dietary intake and their endogenous levels have been associated with a decreased risk of several chronic diseases. There are indications that carotenoid bioavailability depends, in addition to the food matrix, on host factors. These include diseases (e.g. colitis), life-style habits (e.g. smoking), gender and age, as well as genetic variations including single nucleotide polymorphisms that govern carotenoid metabolism. These are expected to explain interindividual differences that contribute to carotenoid uptake, distribution, metabolism and excretion, and therefore possibly also their association with disease risk. For instance, digestion enzymes fostering micellization (PNLIP, CES), expression of uptake/efflux transporters (SR-BI, CD36, NPC1L1), cleavage enzymes (BCO1/2), intracellular transporters (FABP2), secretion into chylomicrons (APOB, MTTP), carotenoid metabolism in the blood and liver (LPL, APO C/E, LDLR), and distribution to target tissues such as adipose tissue or macula (GSTP1, StARD3) depend on the activity of these proteins. In addition, human microbiota, e.g. via altering bile-acid concentrations, may play a role in carotenoid bioavailability. In order to comprehend individual, variable responses to these compounds, an improved knowledge on intra-/interindividual factors determining carotenoid bioavailability, including tissue distribution, is required. Here, we highlight the current knowledge on factors that may explain such intra-/interindividual differences.

Lipid peroxides as endogenous oxidants forming 8-oxo-guanosine and lipid-soluble antioxidants as suppressing agents

The oxidation of guanosine to 8-oxo-2'-deoxyguanosine (8-oxo-dG) in DNA is closely associated with induction of various diseases, but the endogenous oxidant species involved remains unclear. Hydrogen peroxides (H2O2) have been considered to be the oxidant, while lipid peroxides are another possible oxidant because generated easily in bio-membranes surrounding DNA. The oxidant potency was compared between lipid peroxides and H2O2. Linoleic acid hydroperoxides (LOOH) formed 8-oxo-dG at a higher level than H2O2 in guanosine or double-stranded DNA. In the presence of a physiological concentration of Fe(2+) to produce hydroxyl radicals, LOOH was also a stronger oxidant. In a lipid micelle, LOOH markedly produced 8-oxo-dG at a concentration one-tenth of that of H2O2. Upon adding to rat hepatic mitochondria, phosphatidylcholine hydroperoxides produced 8-oxo-dG abundantly. Employing HepG2 cells after pretreated with glutathione peroxidase inhibitor, LOOH formed 8-oxo-dG more abundantly than H2O2. Then, antioxidants to suppress the 8-oxo-dG formation were examined, when the nuclei of pre-incubated HepG2 with antioxidants were exposed to LOOH. Water-soluble ascorbic acid, trolox, and N-acetyl cysteine showed no or weak antioxidant potency, while lipid-soluble 2,6-dipalmitoyl ascorbic acid, α-tocopherol, and lipid-soluble phytochemicals exhibited stronger potency. The present study shows preferential formation of 8-oxo-dG upon LOOH and the inhibition by lipid-soluble antioxidants.

Green extraction methods and environmental applications of carotenoids-a review

This review covers and discusses various aspects of carotenoids including their chemistry, classification, biosynthesis, extraction methods (conventional and non-conventional), analytical techniques and biological roles in living beings.

Effect of lycopene supplementation on oxidative stress: an exploratory systematic review and meta-analysis of randomized controlled trials

Lycopene is a potentially useful compound for preventing and treating cardiovascular diseases and cancers. Studies on the effects of lycopene on oxidative stress offer insights into its mechanism of action and provide evidence-based rationale for its supplementation. In this analysis, randomized controlled trials of the effects of oral lycopene supplementation on any valid outcomes of oxidative stress were identified and pooled through a search of international journal databases and reference lists of relevant publications. Two reviewers extracted data from each of the identified studies. Only studies of sufficient quality were included. Twelve parallel trials and one crossover trial were included in the systematic review, and six trials provided data for quantitative meta-analysis. Our results indicate that lycopene supplementation significantly decreases the DNA tail length, as determined using comet assays, with a mean difference (MD) of -6.27 [95% confidence interval (CI) -10.74, -1.90] (P=.006) between the lycopene intervention groups and the control groups. Lycopene supplementation does not significantly prolong the lag time of low-density lipoprotein (MD 3.76 [95% CI -2.48, 10.01]; P=.24). Lycopene possibly alleviates oxidative stress; however, biomarker research for oxidative stress needs be more consistent with the outcomes in lycopene intervention trials for disease prevention.

Bioavailability of micronutrients: stable isotope techniques to develop effective food-based strategies to combat micronutrient deficiencies

BACKGROUND

The prevalence of micronutrient deficiencies, in particular those of iron, vitamin A, iodine, and zinc, is unacceptably high, especially among infants, children, and women of childbearing age in developing countries. Effective food-based strategies to combat these public health problems are therefore urgently needed.

OBJECTIVE

As only a fraction of dietary iron, zinc, and provitamin A carotenoids is absorbed and utilized, i.e., bioavailable, access to information on micronutrient bioavailability is crucial in the development of food fortification strategies and interventions based on dietary diversification.

METHODS

Review of literature.

RESULTS AND CONCLUSIONS

This overview highlights the usefulness of stable isotope techniques to assess the bioavailability of nonheme iron and provitamin A carotenoids and the importance of generating data on micronutrient bioavailability to move the agenda forward.

Pharmacokinetics and first-pass metabolism of astaxanthin in rats

Astaxanthin is a carotenoid with antioxidant, anti-cancer and anti-inflammatory properties. The pharmacokinetics of astaxanthin after its intravenous (5, 10, and 20 mg/kg) and oral (100 and 200 mg/kg) administration and its first-pass extraction ratios after its intravenous, intraportal or intragastric (20 mg/kg) administration were evaluated in rats. The pharmacokinetic parameters of astaxanthin were dose dependent after its intravenous administration, due to the saturable hepatic metabolism of astaxanthin, but dose independent after oral administration. The gastrointestinal absorption of astaxanthin followed the flip-flop model. The hepatic and gastrointestinal first-pass extraction ratios of astaxanthin were approximately 0·490 and 0·901, respectively. Astaxanthin was metabolised primarily by hepatic cytochrome P-450 1A1/2 in rats. Astaxanthin was unstable up to 4 h incubation in four rat gastric juices and up to 24 h incubation in various buffer solutions having a pH of 1-13. The tissue/plasma ratios of astaxanthin at 8 and 24 h after its oral administration (100 mg/kg) were greater than unity for all tissues studied, except in the heart, at 8 h, indicating that the rat tissues studied had high affinity for astaxanthin.

Plasma carotenoids as biomarkers of intake of fruits and vegetables: ecological-level correlations in the European Prospective Investigation into Cancer and Nutrition (EPIC)

OBJECTIVE

The aim of this study was to assess the ability of a single 24-h dietary recall (24HDR) and food questionnaires (FQ) to predict plasma carotenoid levels at the ecological level by assessing the relationship between mean plasma carotenoid levels and mean intake of fruit and vegetables measured by 24HDR and FQ across 16 European regions.

DESIGN

A random subsample of 3089 subjects was included, stratified by age and gender. They provided blood samples and dietary information between 1992 and 2000 as part of the European Prospective Investigation into Cancer and Nutrition.

RESULTS

Using Spearman's correlation coefficients, the correlations between mean regional 24HDR fruit and vegetable variables and corresponding mean plasma carotenoid levels were generally higher than the correlations using FQ means. The highest correlation was between the 24HDR citrus fruit variable and beta-cryptoxanthin (r = 0.90). For 24HDR, total fruits and vegetables were highly correlated with lutein, zeaxanthin, and beta-cryptoxanthin (r = 0.83-0.87), while vegetables were more closely related with lutein (r = 0.69) and zeaxanthin (r = 0.68), and fruits correlated with zeaxanthin (r = 0.87) and beta-cryptoxanthin (r = 0.84). Root vegetables (r = 0.81) and total carrots (r = 0.71) were well correlated with alpha-carotene. In the multivariate models adjusting for age, body mass index, and season, and using observations of means stratified by sex and region, the association was generally higher for 24HDR compared to FQ.

CONCLUSION

Mean regional intakes of fruits and vegetables in several European countries were closely correlated with corresponding mean plasma levels of individual carotenoids. Fruits and vegetables measured by 24HDR were generally better able to predict plasma carotenoids at the ecological level.

Modification of lymphocyte DNA damage by carotenoid supplementation in postmenopausal women

BACKGROUND

Oxidative stress has been implicated in the pathogenesis of chronic diseases related to aging such as cancer and cardiovascular disease. Carotenoids could be a part of a protective strategy to minimize oxidative damage in vulnerable populations, such as the elderly.

OBJECTIVE

Our aim was to determine the protective effect of carotenoids against DNA damage.

DESIGN

A randomized, double-blind, placebo-controlled intervention study was conducted. Thirty-seven healthy, nonsmoking postmenopausal women aged 50-70 y were randomly assigned to 1 of 5 groups and were instructed to consume a daily dose of mixed carotenoids (beta-carotene, lutein, and lycopene; 4 mg each), 12 mg of a single carotenoid (beta-carotene, lutein, or lycopene), or placebo for 56 d. Plasma carotenoid concentrations were analyzed by using HPLC, and lymphocyte DNA damage was measured by using a single-cell gel electrophoresis (comet) assay.

RESULTS

At day 57, all carotenoid-supplemented groups showed significantly lower endogenous DNA damage than at baseline (P < 0.01), whereas the placebo group did not show any significant change. Significantly less (P < 0.05) endogenous DNA damage was found as early as day 15 in the mixed carotenoid (P < 0.01) and beta-carotene (P < 0.05) groups.

CONCLUSIONS

The results indicate that carotenoid supplementation decreases DNA damage and that a combination of carotenoids (4 mg each of lutein, beta-carotene, and lycopene), an intake that can be achieved by diet, or a larger dose (12 mg) of individual carotenoids exerts protection against DNA damage.

Plasma appearance of unesterified astaxanthin geometrical E/Z and optical R/S isomers in men given single doses of a mixture of optical 3 and 3'R/S isomers of astaxanthin fatty acyl diesters

Appearance, pharmacokinetics and distribution of astaxanthin all-E-, 9Z- and 13Z-geometrical and (3R,3'R)-, (3R,3'S)- and (3S,3'S)-optical isomers in plasma fractions were studied in three middle-aged male volunteers (41-50 years) after ingestion of a single meal containing first a 10-mg dose equivalent of astaxanthin from astaxanthin diesters, followed by a dose of 100 mg astaxanthin equivalents after 4 weeks. Direct resolution of geometrical isomers and optical isomers of astaxanthin dicamphanates by HPLC after saponification showed that the astaxanthin consisted of 95.2% all-E-, 1.2% 9Z- and 3.6% 13Z-astaxanthin, of (3R,3'R)-, (3R,3'S; meso)- and (3S,3'S)-astaxanthin in a 31:49:20 ratio. The plasma astaxanthin concentration-time curves were measured during 76 h. Astaxanthin esters were not detected in plasma. Maximum levels of astaxanthin (C(max)=0.28+/-0.1 mg/l) were reached 11.5 h after administration and the plasma astaxanthin elimination half-life was 52+/-40 h. The C(max) at the low dose was 0.08 mg/l and showed that, the dose response was non-linear. The (3R,3'R)-astaxanthin optical isomer accumulated selectively in plasma compared to the (3R,3'S)- and (3S,3'S)-isomers, and comprised 54% of total astaxanthin in the blood and only 31% of total astaxanthin in the administered dose. The astaxanthin Z-isomers were absorbed selectively into plasma and comprised approximately 32% of total astaxanthin 6-7.5 h postprandially. The proportion of all-E-astaxanthin was significantly higher in the very low density lipoproteins and chylomicrons (VLDL/CM) plasma lipoprotein fraction than in the high density lipoproteins (HDL) and low denisty lipoproteins (LDL) fractions (P<0.05). The results indicate that a selective process increase the relative proportion of astaxanthin Z-isomers compared to the all-E-astaxanthin before uptake in blood and that the astaxanthin esters are hydrolyzed selectively during absorption.

Carotenoid bioavailability is higher from salads ingested with full-fat than with fat-reduced salad dressings as measured with electrochemical detection

BACKGROUND

The amount of dietary fat required for optimal bioavailability of carotenoids in plant matrices is not clearly defined.

OBJECTIVE

The objective was to quantify the appearance of carotenoids in plasma chylomicrons after subjects ingested fresh vegetable salads with fat-free, reduced-fat, or full-fat salad dressings.

DESIGN

The subjects (n = 7) each consumed 3 salads consisting of equivalent amounts of spinach, romaine lettuce, cherry tomatoes, and carrots with salad dressings containing 0, 6, or 28 g canola oil. The salads were consumed in random order separated by washout periods of > or =2 wk. Blood samples were collected hourly from 0 to 12 h. Chylomicrons were isolated by ultracentrifugation, and carotenoid absorption was analyzed by HPLC with coulometric array detection.

RESULTS

After ingestion of the salads with fat-free salad dressing, the appearance of alpha-carotene, beta-carotene, and lycopene in chylomicrons was negligible. After ingestion of the salads with reduced-fat salad dressing, the appearance of the carotenoids in plasma chylomicrons increased relative to that after ingestion of the salads with fat-free salad dressing (P < 0.04). Similarly, the appearance of the carotenoids in plasma chylomicrons was higher after the ingestion of salads with full-fat than with reduced-fat salad dressing (P < 0.02).

CONCLUSIONS

High-sensitivity HPLC with coulometric array detection enabled us to quantify the intestinal absorption of carotenoids ingested from a single vegetable salad. Essentially no absorption of carotenoids was observed when salads with fat-free salad dressing were consumed. A substantially greater absorption of carotenoids was observed when salads were consumed with full-fat than with reduced-fat salad dressing.

Vegetable-borne lutein, lycopene, and beta-carotene compete for incorporation into chylomicrons, with no adverse effect on the medium-term (3-wk) plasma status of carotenoids in humans

BACKGROUND

The results of epidemiologic studies have consistently shown associations between dietary intake or plasma carotenoid status and incidence of cancers and cardiovascular and eye diseases.

OBJECTIVE

The aim was to assess whether vegetable-borne carotenoids (lycopene, lutein, and beta-carotene) compete for intestinal absorption and whether this affects the plasma status of carotenoids in the medium term (ie, after 3 wk).

DESIGN

During 3-wk periods separated by 3-wk washout periods, 20 women were supplemented with either 96 g tomato purée/d (14.98 mg lycopene + 1.50 mg beta-carotene), 92 g cooked chopped spinach/d (11.93 mg lutein + 7.96 mg beta-carotene), 96 g tomato purée/d + 92 g chopped spinach/d, 96 g tomato purée/d + 2 lutein pills (12 mg lutein), or 92 g chopped spinach/d + 1 lycopene pill (15 mg lycopene). Plasma carotenoids were measured before and after each supplementation period. The subjects also participated in postprandial experiments in which they ingested meals containing double amounts of the supplements described above. Carotenoids were measured in chylomicrons to assess the interaction of carotenoids on absorption.

RESULTS

Adding a second carotenoid to a meal that provided a first carotenoid diminished the chylomicron response to the first carotenoid. However, cosupplementation with a second carotenoid of a diet supplemented with a first carotenoid did not diminish the medium-term plasma response to the first carotenoid.

CONCLUSION

Consumption of carotenoids from different vegetable sources does not diminish plasma carotenoid concentrations in the medium term, despite the finding in postprandial testing of competitive inhibitory interactions among different carotenoids.

No significant effects of lutein, lycopene or beta-carotene supplementation on biological markers of oxidative stress and LDL oxidizability in healthy adult subjects

OBJECTIVE

The objective of this study was to determine the effect of individual carotenoid supplementation on biochemical indices of oxidative status in apparently healthy adult males.

METHODS

The study was a placebo controlled single blind study. Healthy male volunteers (n= 175) were assigned to four groups. They received daily supplements of beta-carotene (15 mg), lutein (15 mg), lycopene (15 mg) and placebo for three months. The effects of the supplementation on antioxidant status were monitored by plasma carotenoid, vitamin C and A levels, glutathione (GSH and GSSG) concentrations, protein SH groups. erythrocyte antioxidant enzyme activities (Cu-Zn SOD, Se-GSH-Px) and susceptibility of LDL to copper-induced oxidation.

RESULTS

beta-carotene, lycopene and lutein supplementation led to significant plasma and LDL increases in each of these carotenoids, without modifications of other carotenoid levels in plasma or in LDL. The supplementation failed to enhance the resistance of LDL to oxidation or to modify the LDL polyunsaturated/ saturated fatty acid ratio. Vitamin C, GSH, protein SH groups and antioxidant metalloenzyme activities were also unchanged.

CONCLUSION

We did not observe beneficial or adverse effects of lutein, lycopene or beta-carotene supplementation on biomarkers of oxidative stress. In apparently healthy subjects, carotenoid supplementation does not lead to significantly measurable improvement in antioxidant defenses.

Intestinal absorption of beta-carotene ingested with a meal rich in sunflower oil or beef tallow: postprandial appearance in triacylglycerol-rich lipoproteins in women

BACKGROUND

Evidence indicates that different types of fat have different effects on the postprandial plasma triacylglycerol response. Therefore, the type of fat may influence the appearance of beta-carotene in postprandial triacylglycerol-rich lipoproteins, which is used as an indicator of intestinal beta-carotene absorption.

OBJECTIVE

We compared in female subjects the appearance of beta-carotene in plasma triacylglycerol-rich lipoproteins after beta-carotene was ingested with a meal containing sunflower oil or beef tallow.

DESIGN

Women (n = 11) each ingested 2 different vitamin A-free, fat-rich meals that were supplemented with beta-carotene (47 micromol) and contained equivalent amounts (60 g) of sunflower oil or beef tallow. Blood samples were collected hourly from 0 to 10 h; additional samples were collected at selected intervals until 528 h. In a subgroup of the women (n = 7), plasma chylomicrons and 3 subfractions of VLDLs were separated by cumulative rate ultracentrifugation.

RESULTS

The appearance of beta-carotene in chylomicrons and in each VLDL subfraction was lower after ingestion with the meal containing sunflower oil than after ingestion with the meal containing beef tallow (P < 0.03). In chylomicrons, the area under the concentration-versus-time curve (AUC) for beta-carotene was 38.1 +/- 13.6% lower (P < 0.03); in contrast, the AUC for triacylglycerol was higher (P < 0.05) after the sunflower-oil-rich meal than after the beef-tallow-rich meal.

CONCLUSIONS

Ingestion of beta-carotene with a meal rich in sunflower oil as compared with a meal rich in beef tallow results in lower appearance of beta-carotene and greater appearance of triacylglycerol in triacylglycerol-rich lipoproteins.

Dietary factors that affect the bioavailability of carotenoids

Carotenoids are thought to contribute to the beneficial effects of increased vegetable consumption. Various dietary factors have an effect on the bioavailability of carotenoids. The type of food matrix in which carotenoids are located is a major factor. The bioavailability of beta-carotene from vegetables in particular has been shown to be low (14% from mixed vegetables) compared with that of purified beta-carotene added to a simple matrix (e.g., salad dressing), whereas for lutein, the difference is much smaller (relative bioavailability of 67% from mixed vegetables). Processing, such as mechanical homogenization or heat treatment, has the potential to enhance the bioavailability of carotenoids from vegetables (from 18% to a sixfold increase). The amount of dietary fat required to ensure carotenoid absorption seems low (approximately 3-5 g per meal), although it depends on the physicochemical characteristics of the carotenoids ingested. Unabsorbable, fat-soluble compounds reduce carotenoid absorption, and interaction among carotenoids may also result in a reduced carotenoid bioavailability. Research into the functional benefits of carotenoids should consider the fact that the bioavailability of beta-carotene in particular is one order of magnitude higher when provided as a pure compound added to foods than when it is present naturally in foods.

Use of a 13C tracer to quantify the plasma appearance of a physiological dose of lutein in humans

Increased intake of lutein from vegetables promotes increased density of the macular pigment and therefore may protect against age-related macular degeneration. Our objective was to use a 13C tracer and high-precision gas chromatography-combustion interfaced-isotope ratio mass spectrometry (GC-C-IRMS) to investigate metabolism of a lutein dose equivalent to that absorbed from vegetables. Biosynthetic per-labeled (>99% 13C) lutein was purified from a commercially available extract of algal biomass. Subjects (n = 4) ingested 3 mg of [13C]lutein with a standardized low-carotenoid breakfast. Blood samples were collected at baseline and then hourly for 12 h; additional blood samples were drawn at 16, 24, 48, 72, 96, 192, 360, and 528 h. To produce perhydro-beta-carotene suitable for analysis by GC-C-IRMS, the plasma lutein fraction was hydrogenated on palladium-on-carbon catalyst with acid-catalyzed hydrogenolysis. The stable carbon isotope (13C/12C) ratio measured by GC-C-IRMS was used to calculate the plasma concentration of [13C]lutein. There was a rapid increase in [13C]lutein in plasma until peak enrichment at 16 h followed by a decline to the next measurement at 24 h. At 528 h, small changes in 13C enrichment from baseline could still be measured in plasma lutein. High-precision GC-C-IRMS enables complete definition of the appearance and disappearance of [13C]lutein in plasma after ingestion of a dose similar to that absorbed from foods.

Carotenoid interactions

Interactions between carotenoids during absorption and during postabsorptive metabolism have been demonstrated or suggested in animal and human feeding or supplementation studies, as well as in in vitro studies of intestinal beta-carotene cleavage. Much of the evidence suggests an interaction between beta-carotene and oxycarotenoids such as canthaxanthin and lutein, and between the hydrocarbon carotenoids beta-carotene and lycopene. The evidence is equivocal, however, with discrepant findings between studies, both in magnitude and in direction of the interactions observed. This review discusses studies of carotenoid interactions and explores the possible underlying mechanisms and implications of these interactions. The most likely explanations for carotenoid interactions appear to be competition for incorporation into micelles, carotenoid exchange between lipoproteins in the postprandial state, and inhibition of provitamin A (beta-carotene) cleavage.

Supplementation with canthaxanthin affects plasma and tissue distribution of alpha- and gamma-tocopherols in mice

The effects of oral doses of canthaxanthin on tissue distribution of alpha- and gamma-tocopherols were investigated in three experiments in male and female Balb/c mice. Mice were assigned to receive canthaxanthin [7 or 14 microg/(g body weight.d)] or placebo (olive oil) by gavage for different periods of time (0, 1, 2, 4 and 6 wk). A 2 wk-treatment with canthaxanthin resulted in incorporation of the carotenoid in all tissues analyzed, including liver, spleen, kidney, lung and heart. In liver, the maximum accumulation of the carotenoid was reached after 2 wk of dosing in female mice and after 6 wk in male mice. Canthaxanthin incorporation was accompanied by changes in alpha- and gamma-tocopherol concentrations in plasma and tissues. These included the following: 1) a significant increase (P < 0.001) in alpha-tocopherol concentration in spleen (21 and 27% in male and female mice, respectively) after 2 wk and in liver ( approximately 50% in both male and female mice) after 6 wk; 2) a significant decrease in gamma-tocopherol concentration in plasma (P < 0.05) and tissues (P < 0.001) after 2 wk of treatment. In female mice, this decrease was 55% in plasma, 43% in liver, 44% in kidney, 71% in lung and 70% in heart. In male mice, the decrease was observed only in plasma (30%), kidney (54%) and heart (46%). In liver, the decrease in gamma-tocopherol concentration was both dose- and time-dependent and significantly (P < 0.001) greater in female than in male mice. We conclude that dietary administration of canthaxanthin modifies tocopherol status in murine tissues.

Prooxidant actions of carotenoids in biologic systems

The potential for carotenoids to modulate chronic disease risk is currently under investigation, and renewed interest has been placed on achieving a better understanding of the mechanisms of action of carotenoids in biologic systems. Available data currently show that the antioxidant activity of these compounds may shift into prooxidant activity, depending on the redox potential of the carotenoid molecules as well as on the biologic environment in which they act. The prooxidant potency of these compounds is determined by several factors, including oxygen tension, carotenoid concentration, and interactions with other antioxidants. Prooxidant activity can induce either beneficial or harmful results in biologic systems and influence the development of human chronic diseases.

Bioavailability and bioconversion of carotenoids

Factors that influence the bioavailability of carotenoids and their bioconversion to retinol are species of carotenoids, molecular linkage, amount of carotenoids consumed in a meal, matrix in which the carotenoid is incorporated, effectors of absorption and bioconversion, nutrient status of the host, genetic factors, host related factors, and mathematical interactions. In this paper, current knowledge of these factors is examined. Although data are not sufficiently comparable to allow an extensive systematic comparison of results, a number of conclusions can be drawn from the information available.

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.

In vitro and in vivo inhibition of beta-carotene dioxygenase activity by canthaxanthin in rat intestine

beta-Carotene dioxygenase catalyzes the conversion of provitamin A carotenoids to vitamin A in mammalian tissues. Whether the enzyme can also cleave non-provitamin A carotenoids to retinoid analogs with biological activities is still unclear. We investigated (i) substrate specificities of beta-carotene dioxygenase toward provitamin A and non-provitamin A carotenoids and (ii) potential antagonistic effects of non-provitamin A carotenoids on beta-carotene conversion to vitamin A. Provitamin A substrates were 8 to 23% as active as beta-carotene. No polar metabolites were detected with canthaxanthin or zeaxanthin as substrates; these compounds efficiently inhibited the beta-carotene cleavage reaction by 71 and 40%, respectively. Kinetic studies indicated mixed inhibition for canthaxanthin (Ki = 1.6 microM) and non-competitive for zeaxanthin (Ki = 7.8 microM), suggesting that both compounds do not interact significantly with the active site of the enzyme. In vivo, dietary combinations of canthaxanthin and beta-carotene resulted in lower liver levels of both carotenoids and vitamin A and in a higher beta-carotene/vitamin A ratio as compared to groups supplemented with the compounds separately. This supports the view that canthaxanthin at high doses competes with beta-carotene for intestinal absorption and inhibits the conversion of beta-carotene to vitamin A. Thus, we suggest that although canthaxanthin is not a substrate for beta-carotene dioxygenase, it is likely to affect the activity of provitamin A carotenoids by direct interaction with the enzyme.

Ingestion by men of a combined dose of beta-carotene and lycopene does not affect the absorption of beta-carotene but improves that of lycopene

A double-blind study was conducted in 10 healthy men to investigate serum beta-carotene and lycopene responses after ingestion of individual and combined doses of beta-carotene (BC) and lycopene. On each dosing day, a baseline blood sample was drawn, followed by an oral dose of 0.11 mmol (60 mg) of either all-trans BC or all-trans lycopene or by a combined oral dose of 0.11 mmol each. Subjects were tested with each of the three doses. The dose type was randomized. Blood (10 mL) was drawn at 1, 3, 5, 7, 9, 12 and 24 h after dosing. At 2 and 4 wk after the first dose, the protocol was repeated with the other doses. After ingestion of the BC dose, serum BC concentrations significantly decreased from baseline at 1 and 3 h followed by a continuous increase from baseline that was significant at 12 and 24 h (P < 0.01). Serum lycopene concentrations significantly increased from baseline at 5 h after the lycopene dose (P < 0.008) and returned to baseline thereafter. Ingestion of a combined dose of BC and lycopene resulted in a significant increase in serum concentrations of both BC and lycopene at 24 h (P < 0.05). The 24-h area under the curve (AUC) for BC was not different when BC was ingested alone or with lycopene, whereas the 24-h AUC for lycopene was significantly greater when lycopene was ingested with BC than when ingested alone (P < 0.05). Our data suggest that ingestion of a combined dose of BC and lycopene has little effect on the absorption of BC but improves that of lycopene in men.

Accumulation and clearance of capsanthin in blood plasma after the ingestion of paprika juice in men

The pharmacokinetics of dietary capsanthin was measured in four male volunteers to assess the bioavailability of oxygenated carotenoids (xanthophylls). Capsanthin was used because this carotenoid was not detected in the men's plasma before ingestion of paprika juice. Supplementing capsanthin-rich paprika juice for 1 wk (equivalent to three doses of 5.4 micromol capsanthin/d; 16.2 micromol/d), the level of capsanthin reached a plateau (0.10-0.12 micromol/L) between d 2 and 7 and was not detectable by d 16. Capsanthin was distributed in the plasma lipoproteins (VLDL, 13 +/- 3%; LDL , 44 +/- 3%; HDL, 43 +/- 3%) at the end of the experiment. In a separate experiment involving the single ingestion of paprika juice (equivalent to 34.2 micromol capsanthin) in the same men, the plasma concentration of capsanthin ranged from 0.10 to 0.29 micromol/L at 8 h after ingestion. In contrast, the elevation of the plasma concentration of an acyclic hydrocarbon carotenoid, lycopene, by a single ingestion of tomato soup (equivalent to 186.3 micromol lycopene) in the same subjects was minimal (0.02-0.06 micromol/L). The areas under the curves (AUC) for capsanthin between 0 and 74 h and for lycopene between 0 and 72 h were 4.68 +/- 1.22 and 0.81 +/- 0.17(micromol.h)/L, respectively. The half-lives (t1/2) were calculated to be 20.1 +/- 1.3 and 222 +/- 15 h for capsanthin and lycopene, respectively. We conclude that the clearance of capsanthin is much faster than that of lycopene, although capsanthin is transported into plasma lipoproteins in larger amounts. This polar carotenoid may be metabolized in the human body more rapidly than lycopene. These data justify further research on the physiological functions of capsanthin and other xanthophylls.

Effects of supplemental beta-carotene, cigarette smoking, and alcohol consumption on serum carotenoids in the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study

We determined whether serum carotenoid or retinol concentrations were altered by beta-carotene supplementation in the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study and whether such effects were modified by alcohol consumption or cigarette use. Participants in this substudy were 491 randomly selected men aged 58-76 y from the metropolitan Helsinki study center [237 receiving supplemental beta-carotene (20 mg/d) and 254 not receiving such supplementation]. Dietary carotenoids, retinol, and alcohol, and serum beta-carotene, alpha-tocopherol, retinol, and cholesterol were assessed at baseline. After an average of 6.7 y of supplementation, serum was collected and carotenoid, retinol, and alpha-tocopherol concentrations were determined by HPLC. Serum carotenoid fractions were highly correlated with each other (P < or = 0.0001). Compared with the unsupplemented group, the beta-carotene group had significantly higher serum concentrations of beta-carotene (1483%), alpha-carotene (145%), and beta-cryptoxanthin (67%) (P < or = 0.0001). Retinol concentrations were 6% higher (P = 0.03) and lutein was 11% lower (P = 0.02) in the supplemented group. Serum lycopene, zeaxanthin, and alpha-tocopherol did not differ according to beta-carotene-supplementation status. Although these beta-carotene-group differences were not significantly altered by amount of alcohol consumption, higher consumption (> 12.9 g/d, median) was related to lower (10-38%) concentrations of carotenoids, particularly beta-carotene, alpha-carotene, and beta-cryptoxanthin, in both the supplemented and unsupplemented groups. Smoking status did not significantly influence the supplementation-related differences in serum carotenoid and retinol values but concentrations of carotenoids were generally highest in participants who quit smoking while in the study and lowest in current smokers of > or = 20 cigarettes/d. This study showed that serum concentrations of non-beta-carotene carotenoids are altered by long-term beta-carotene supplementation and confirms the adverse effects of alcohol and cigarette smoking on serum carotenoids.