Low doses of beta-carotene and lutein inhibit AOM-induced rat colonic ACF formation but high doses augment ACF incidence

Epidemiological studies suggest that carotenoids such as beta-carotene and lutein play an important role in reducing the risk for several cancers. However, in colon cancer there is ambiguity with regard to the role of these compounds in that both preventive effects and tumor promotion have been observed. In the present study we observed that male F344 rats were able to tolerate up to 2,500 ppm of beta-carotene as well as of lutein. We have then assessed the chemopreventive efficacy of beta-carotene and lutein at dose levels of approximately 4 and 8% of the 2,500 ppm tolerated dose (TD) and also approximately 40 and 80% of the TD on azoxymethane (AOM)-induced colon carcinogenesis, using aberrant crypt foci (ACF) as a surrogate biomarker for colon cancer. Throughout the experiments, 5-week-old male F344 rats were fed the control diet (modified AIN-76A) or experimental diets containing 100 or 200 ppm (approximately 4 or 8% of the 2,500 ppm TD), or 1,000 or 2,000 ppm ( approximately 40 or 80% of the 2,500 ppm TD) of beta-carotene and lutein (n=10 rats/group). After 2 weeks on the experimental or control diets, all animals were injected with AOM (15 mg/kg body wt., once weekly for 2 weeks). At 14 weeks of age, all rats were killed, and their colons were evaluated for ACF. Administration of 100 or 200 ppm of beta-carotene inhibited AOM-induced total colonic ACF formation by 24% (p<0.01) and 36% (p<0.001), respectively, whereas lutein at 200 ppm produced a 27% inhibition (p<0.01) yet had no significant effect at the 100 ppm dose level. Surprisingly, administration of 1,000 or 2,000 ppm of beta-carotene and lutein increased colonic ACF formation in a dose-dependent manner, i.e., to 124% and 144% for the former and 110% and 159% for the latter. These results clearly suggest that further studies are warranted to determine whether the increase in ACF incidence by high doses of beta-carotene and lutein will also lead to an increase in tumor outcome. Taken together these data indicate that the chemopreventive activity of beta-carotene and lutein against colon carcinogenesis depends on the dose level.

Lutein and Zeaxanthin and Their Potential Roles in Disease Prevention

Lutein and zeaxanthin are xanthophyll carotenoids found particularly in dark-green leafy vegetables and in egg yolks. They are widely distributed in tissues and are the principal carotenoids in the eye lens and macular region of the retina. Epidemiologic studies indicating an inverse relationship between xanthophyll intake or status and both cataract and age-related macular degeneration suggest these compounds can play a protective role in the eye. Some observational studies have also shown these xanthophylls may help reduce the risk of certain types of cancer, particularly those of the breast and lung. Emerging studies suggest as well a potential contribution of lutein and zeaxanthin to the prevention of heart disease and stroke. Even as the evidence for a role of lutein and zeaxanthin in disease prevention continues to evolve, particularly from human studies directed to their bioavailability, metabolism, and dose-response relationships with intermediary biomarkers and clinical outcomes, it is worth noting that recommendations to consume foods rich in xanthophylls are consistent with current dietary guidelines.

Double-masked, placebo-controlled, randomized trial of lutein and antioxidant supplementation in the intervention of atrophic age-related macular degeneration: the Veterans LAST study (Lutein Antioxidant Supplementation Trial)

BACKGROUND

Age-related macular degeneration (ARMD) is the leading cause of vision loss in aging Westem societies. The objective of the lutein antioxidant supplementation trial (LAST) is to determine whether nutritional supplementation with lutein or lutein together with antioxidants, vitamins, and minerals, improves visual function and symptoms in atrophic ARMD.

METHODS

The study was a prospective, 12-month, randomized, double-masked, placebo-controlled trial conducted at an urban midwestern Veterans Administration Hospital from August 1999 to May 2001. Ninety patients with atrophic ARMD were referred by ophthalmologists at two Chicago-area veterans medical facilities. Patients in Group 1 received lutein 10 mg (L); in Group 2, a lutein 10 mg/antioxidants/vitamins and minerals broad spectrum supplementation formula (L/A); and in Group 3, a maltodextrin placebo (P) over 12 months.

RESULTS

In Groups 1 L and 2 L/A, mean eye macular pigment optical density increased approximately 0.09 log units from baseline, Snellen equivalent visual acuity improved 5.4 letters for Group 1 L and 3.5 letters for Group 2 L/A, and contrast sensitivity improved. There was a net subjective improvement in Amsler grid in Group 1 L. VFO-14 questionnaires conceming subjective glare recovery were nearly significant at 4 months for Group 2 L/A. Patients who received the placebo (Group 3) had no significant changes in any of the measured findings.

CONCLUSION

In this study, visual function is improved with lutein alone or lutein together with other nutrients. Further studies are needed with more patients, of both genders, and for longer periods of time to assess long-term effects of lutein or lutein together with a broad spectrum of antioxidants, vitamins, and minerals in the treatment of atrophic age-related macular degeneration.

[Oxidative stress in a model for experimental diabetic retinopathy: treatment with antioxidants]

PURPOSE

Diabetic retinopathy is the primary cause of blindness in developed countries, and though strict glycemic control is desirable to prevent complications, this is not always achievable. Thus, adjunctive therapies are needed to help in preventing or delaying the onset of diabetic complications. We have studied the biochemical and functional changes in the retina of diabetic mice, and the ability of ebselen and lutein, two antioxidants, to reverse these effects, using as a comparison the effect of insulin therapy.

METHODS

Alloxan injection was used to achieve hyperglycemia. Malondialdehyde (MDA) concentration in blood and glutathione peroxidase (GPx) activity in eye homogenate were measured. Serial electroretinograms (ERG) were recorded.

RESULTS

MDA concentration in the blood was high in diabetic animals. GPx activity in eye homogenate decreased in the diabetic conditions. Maximal electroretinogram amplitude decreased in diabetic animals with respect to controls. Ebselen and lutein restored MDA levels, GPx activity and ERG amplitude, and had no effect on glycemia.

CONCLUSION

These results call for further studies on ebselen or lutein as adequate adjunctive therapies for diabetes.

Lutein, but not alpha-tocopherol, supplementation improves visual function in patients with age-related cataracts: a 2-y double-blind, placebo-controlled pilot study

OBJECTIVE

We investigated the effect of long-term antioxidant supplementation (lutein and alpha-tocopherol) on serum levels and visual performance in patients with cataracts.

METHODS

Seventeen patients clinically diagnosed with age-related cataracts were randomized in a double-blind study involving dietary supplementation with lutein (15 mg; n = 5), alpha-tocopherol (100 mg; n = 6), or placebo (n = 6), three times a week for up to 2 y. Serum carotenoid and tocopherol concentrations were determined with quality-controlled high-performance liquid chromatography, and visual performance (visual acuity and glare sensitivity) and biochemical and hematologic indexes were monitored every 3 mo throughout the study. Changes in these parameters were assessed by General Linear Model (GLM) repeated measures analysis.

RESULTS

Serum concentrations of lutein and alpha-tocopherol increased with supplementation, although statistical significance was reached only in the lutein group. Visual performance (visual acuity and glare sensitivity) improved in the lutein group, whereas there was a trend toward the maintenance of and decrease in visual acuity with alpha-tocopherol and placebo supplementation, respectively. No significant side effects or changes in biochemical or hematologic profiles were observed in any of the subjects during the study.

CONCLUSIONS

Visual function in patients with age-related cataracts who received the lutein supplements improved, suggesting that a higher intake of lutein, through lutein-rich fruit and vegetables or supplements, may have beneficial effects on the visual performance of people with age-related cataracts.

Influence of short-term antioxidant supplementation on macular function in age-related maculopathy: a pilot study including electrophysiologic assessment

PURPOSE

To evaluate the influence of short-term antioxidant supplementation on retinal function in age-related maculopathy (ARM) patients by recording focal electroretinograms (FERGs).

DESIGN

Nonrandomized, comparative clinical trial.

PARTICIPANTS

Thirty patients with early ARM and visual acuity >/=20/30, divided into two groups, similar for age and disease severity: antioxidant group (ARM-A, n = 17) and no treatment group (ARM-NT, n = 13). Eight age-matched normal subjects divided into antioxidant (N-A, n = 4) or no treatment (N-NT, n = 4) groups.

METHODS

ARM-A patients and N-A patients had oral supplementation of lutein, 15 mg; vitamin E, 20 mg; and nicotinamide, 18 mg, daily for 180 days, whereas ARM-NT patients and N-NT patients had no dietary supplementation during the same period. Eight of the 17 ARM-A patients took supplementation for an additional 180-day period. In all patients and normal subjects, FERG assessment was performed at the study entry (baseline) and after 180 days. Further testing was performed at 360 days for the eight ARM-A patients taking supplements and for one ARM-A patient who had discontinued supplementation after 180 days. FERGs were recorded in response to a 41-Hz sinusoidally modulated uniform field (93.5% modulation depth) presented to the macular region (18 degrees ) on a light-adapting background. In a subgroup of patients (11 ARM-A and 5 ARM-NT), whose responses had suitable signal-to-noise ratios, FERGs were also recorded at different stimulus modulation depths between 8.25% and 93.5%.

MAIN OUTCOME AND MEASURES

Amplitude (in micro V) and phase (in degrees) of the FERG fundamental harmonic component. FERG modulation thresholds, estimated from the value of log modulation depth yielding a criterion response.

RESULTS

At 180 days, FERGs of ARM-A patients and N-A patients were increased in amplitude (mean change, 0.11 and 0.15 log micro V, respectively, P </= 0.01) compared with baseline values, whereas no significant changes in FERG amplitudes of ARM-NT patients and N-NT patients were found (mean change, -0.004 and -0.023 log micro V, respectively). In all groups no changes in the FERG phase were found. FERG modulation thresholds decreased with respect to baseline values (mean change, -0.36 log units, P < 0.01) in ARM-A patients, whereas no significant change (mean change, 0.07 log units) in ARM-NT patients was seen. At 360 days, FERGs of ARM-A patients taking supplementation were still increased in amplitude with respect to baseline (P < 0.05) but did not differ from those recorded at 180 days. In the patient who had discontinued supplementation, FERG amplitude decreased from the 180 days value, approaching that recorded at baseline.

CONCLUSIONS

Although this study provides no evidence for the long-term benefit of antioxidants in ARM, the results suggest that increasing the level of retinal antioxidants might influence macular function early in the disease process, as well as in normal aging.

Carotenoids and protection against solar UV radiation

Upon exposure to UV light photooxidative reactions are initiated which are damaging to biomolecules and affect the integrity of cells and tissues. Photooxidative damage plays a role in pathological processes and is involved in the development of disorders affecting the skin. When skin is exposed to UV light, erythema is observed as an initial reaction. Carotenoids like beta-carotene or lycopene are efficient antioxidants scavenging singlet molecular oxygen and peroxyl radicals generated in during photooxidation. When beta-carotene was applied as such or in combination with alpha-tocopherol for 12 weeks, erythema formation induced with a solar light simulator was diminished from week 8 on. Similar effects were also achieved with a diet rich in lycopene. Ingestion of tomato paste corresponding to a dose of 16 mg lycopene/ day over 10 weeks led to increases in serum levels of lycopene and total carotenoids in skin. At week 10, erythema formation was significantly lower in the group that ingested the tomato paste as compared to the control group. No significant difference was found at week 4 of treatment. Thus, protection against UV light-induced erythema can be achieved by ingestion of a commonly consumed dietary source of lycopene. Such protective effects of carotenoids were also demonstrated in cell culture. The in-vitro data indicate that there is an optimal level of protection for each carotenoid.

[Antioxidants to slow aging, facts and perspectives]

FREE RADICALS AND THE THEORY OF AGING: Severe oxidative stress progressively leads to cell dysfunction and ultimately cell death. Oxidative stress is defined as an imbalance between pro-oxidants and/or free radicals on the one hand, and anti-oxidizing systems on the other. The oxygen required for living may indirectly be responsible for negative effects; these deleterious effects are due to the production of free radicals, which are toxic for the cells (superoxide anions, hydroxyl radicals, peroxyl radicals, hydrogen peroxide, hydroperoxides and peroxinitrite anions). Free radical attacks are responsible for cell damage and the targeted cells are represented by the cell membranes, which are particularly rich in unsaturated fatty acids, sensitive to oxidation reactions; DNA is also the target of severe attacks by these reactive oxygen species (ROS).

THE DEFENCE SYSTEMS

These are represented by the enzymes and free radical captors. The latter are readily oxidizable composites. The free radical captor or neutralization systems of these ROS use a collection of mechanisms, vitamins (E and C), enzymes [superoxide dismutase (SOD), glutathion peroxidase (GPx) and others], and glutathion reductase (GSH), capable of neutralizing peroxinitrite. The efficacy of this system is dependent on the genome for the enzymatic defence systems, and on nutrition for the vitamins. Some strategies aimed at reducing oxidative stress-related alterations have been performed in animals. However, only a few can be used and are efficient in humans, such as avoidance of unfavourable environmental conditions (radiation, dietary carcinogens, smoking...) and antioxidant dietary supplementation.

DIETARY SUPPLEMENTATION

Epidemiological data suggest that antioxidants may have a beneficial effect on many age-related diseases: atherosclerosis, cancer, some neurodegenerative and ocular diseases. However, the widespread use of supplements is hampered by several factors: the lack of prospective and controlled studies; insufficient knowledge on the pro-oxidant, oxidant and ant-oxidant properties of the various supplements; growing evidence that free radicals are not only by-products, but also play an important role in cell signal transduction, apoptosis and infection control.

RECOMMENDATIONS

Although current data indicate that antioxidants cannot prolong maximal life span, the beneficial impact of antioxidants on various age-related degenerative diseases may forecast an improvement in life span and enhance quality of life. The current lack of sufficient data does not permit the systematic recommendation of anti-oxidants. Nevertheless, antioxidant-rich diets with fruit and vegetables should be recommended.

The body of evidence to support a protective role for lutein and zeaxanthin in delaying chronic disease. Overview

Recent evidence introduces the possibility that lutein and zeaxanthin may protect against the development of the two common eye diseases of aging, cataract and macular degeneration. This potential and the lack of other effective means to slow the progression of macular degeneration have fueled high public interest in the health benefits of lutein and zeaxanthin and the proliferation of supplements containing them on pharmacy shelves. An understanding of the biologic consequences of limiting or supplementing with these carotenoids is only beginning to emerge. Some epidemiologic evidence supports a role in eye disease and, to a lesser extent, cancer and cardiovascular disease. However, the overall body of evidence is insufficient to conclude that increasing levels of lutein and zeaxanthin, specifically, will confer an important health benefit. Future advances in scientific research are required to gain a better understanding of the biologic mechanisms of their possible role in preventing disease. Additional research is also required to understand the effect of their consumption, independent of other nutrients in fruits and vegetables, on human health. The newly advanced ability to measure levels of lutein and zeaxanthin in the retina in vivo creates a unique opportunity to contribute some of this needed evidence.

Macular pigment and lutein supplementation in choroideremia

Choroideremia is an incurable X-linked retinal degeneration caused by mutations in the gene encoding Rab escort protein-1. A group of clinically defined and genotyped patients were studied to determine: (1) the degree of rod and cone dysfunction and structural abnormality in the central retina and the level of macular pigment; and (2) the response of macular pigment and foveal vision to a 6 month trial of supplementation with oral lutein (at 20 mg per day). Rod and cone-mediated function was measured with dark-adapted static perimetry; in vivo retinal structure was determined with optical coherence tomography; and macular pigment optical density was measured with heterochromatic flicker photometry. In this cohort of patients (ages 15-65 years), both rod- and cone-mediated central function declined with age as did central retinal thickness. Macular pigment levels did not differ between patients and male control subjects. Supplementation of oral lutein in a subset of patients led to an increase in serum lutein and macular pigment levels; absolute foveal sensitivity did not change. It is concluded that macular pigment density can be augmented by oral intake of lutein in patients with choroideremia. There was no short-term change in the central vision of the patients on the supplement, but long-term influences of lutein supplementation on disease natural history warrant further study.

Serum iron, transferrin saturation, ferritin, and dietary data in age-related macular degeneration

Iron (Fe) is a tightly metabolically controlled mineral and growth factor for all living cells. Iron not bound in erythrocyte hemoglobin is transported by the plasma iron transport protein transferrin (Tf) and bound within cells by ferritin. Apo-Tf and apo-hemopexin are also known to be made locally in the retina. Free Fe is cytotoxic, promotes oxidation/lipid peroxidation, has been implicated as a risk factor in cardiac disease, and is itself associated with age-related macular degeneration (ARMD), the leading cause of blindness in aging western societies. The authors evaluated Fe overload serum markers and dietary intake in patients with atrophic ARMD. After obtaining informed consent, an Fe panel consisting of serum Fe, total Fe binding capacity (TIBC), and ferritin was performed on 75 veterans (70 men, five women) with an average age of 75 years with a diagnosis of atrophic ARMD by combined criteria of International Retinal Classification and psychophysical/symptom abnormalities. Tf saturation was calculated by dividing serum Fe concentration by TIBC. Dietary iron with and without supplementation and vitamin C intake were determined for 86 patients using the Harvard School of Public Health/Department of Nutrition Food Frequency Questionnaire. Statistically significant correlations (P <0.1) were found between serum and dietary Fe (r = -.26), between serum Fe and serum ferritin (r =.34), and between dietary Fe and dietary vitamin C (r =.30). The data on mostly male geriatric veterans with atrophic ARMD indicate that single time-point assessment of systemic Fe status and dietary Fe is not useful. However, serial multiple-year data, correlating Fe markers with disease, may still be important. Also, because Fe transport proteins do not cross the blood-retina barrier, the local cellular toxic effects of Fe must also be considered.

Effect of vitamin E, vitamin C, and beta-carotene on stroke risk

In a recent prospective observational study, vitamins C and E and beta-carotene did not elicit protective effects on stroke risk. Lutein, however, may elicit such protection. Nevertheless, these nutrients may be important modulators of the outcome after the occurrence of a stroke. At present, optimal control of the classic stroke risk factors in combination with increased consumption of fruits, vegetables, and antioxidant nutrients may represent the safest and most efficient strategy to control stroke risk.

Carotenoids and colon cancer

BACKGROUND

Carotenoids have numerous biological properties that may underpin a role for them as chemopreventive agents. However, except for beta-carotene, little is known about how dietary carotenoids are associated with common cancers, including colon cancer.

OBJECTIVE

The objective of this study was to evaluate associations between dietary alpha-carotene, beta-carotene, lycopene, lutein, zeaxanthin, and beta-cryptoxanthin and the risk of colon cancer.

DESIGN

Data were collected from 1993 case subjects with first primary incident adenocarcinoma of the colon and from 2410 population-based control subjects. Dietary data were collected from a detailed diet-history questionnaire and nutrient values for dietary carotenoids were obtained from the US Department of Agriculture-Nutrition Coordinating Center carotenoid database (1998 updated version).

RESULTS

Lutein was inversely associated with colon cancer in both men and women [odds ratio (OR) for upper quintile of intake relative to lowest quintile of intake: 0.83; 95% CI: 0.66, 1.04; P = 0.04 for linear trend]. The greatest inverse association was observed among subjects in whom colon cancer was diagnosed when they were young (OR: 0.66; 95% CI: 0.48, 0.92; P = 0.02 for linear trend) and among those with tumors located in the proximal segment of the colon (OR: 0.65; 95% CI: 0.51, 0.91; P < 0.01 for linear trend). The associations with other carotenoids were unremarkable.

CONCLUSION

The major dietary sources of lutein in subjects with colon cancer and in control subjects were spinach, broccoli, lettuce, tomatoes, oranges and orange juice, carrots, celery, and greens. These data suggest that incorporating these foods into the diet may help reduce the risk of developing colon cancer.

Dietary lutein from marigold extract inhibits mammary tumor development in BALB/c mice

High levels of dietary lutein can inhibit mammary tumor growth in mice. However, the antitumor effect of low levels of dietary lutein on mammary tumors is unavailable. Female BALB/c mice and the WAZ-2T (-SA) mammary tumor cell line were used in two experiments. A preliminary tumor cell dose titration study (Experiment 1) was designed to determine the inoculation dose to produce approximately 65% tumor incidence. Mice (n = 10/dose) were inoculated with 0 to 1 x 10(6) tumor cells in the right inguinal mammary fat pad. A tumor cell load of 2.5 x 10(3) cells/inoculation produced approximately 65% tumor incidence. This dose was used in a subsequent study (Experiment 2) of the efficacy of dietary lutein against mammary tumor development. Mice (n = 20/treatment) were fed a semisynthetic diet containing 0, 0.002, 0.02, 0.2 or 0.4% lutein from marigold extract. After 14 d, all mice were inoculated with 2.5 x 10(3) tumor cells, and tumor growth was measured daily for 70 d at which time blood, liver, spleen and tumors were obtained. Lutein + zeaxanthin uptake increased dose-dependently (P < 0.05) with dietary lutein levels from 0 to 0.02% (spleen) or 0.2% (plasma, liver and tumor). Low levels (0.002 and 0.02%) of dietary lutein lowered (P < 0.05) mammary tumor incidence, tumor growth and lipid peroxidation, and increased tumor latency, whereas higher dietary levels (0.2 or 0.4%) were less effective. Therefore, very low amounts of dietary lutein (0.002%) can efficiently decrease mammary tumor development and growth in mice.

Lutein, lycopene, and their oxidative metabolites in chemoprevention of cancer

Numerous epidemiological studies have demonstrated that consuming large quantities of fruits and vegetables reduces the risk for several types of human cancers. Carotenoids are abundant in fruits and vegetables and have been extensively studied as cancer preventive agents. A proposed mechanism of action for the protective effect of carotenoids against cancer is based on their antioxidant capability. Recently, we have isolated and characterized 14 new carotenoids, including seven metabolites from the extracts of human serum/plasma. This brings the total number of identified blood carotenoids to 21. Lutein and lycopene, abundant in most fruits and vegetables as well as human serum, have been shown to possess strong antioxidant capability. Among the metabolites of lutein, four results from oxidation and two from non-enzymatic dehydration. The metabolite of lycopene has been identified as 5,6-dihydroxy-5,6-dihydrolycopene, which apparently results from oxidation of lycopene to an intermediate, lycopene epoxide. This intermediate may undergo metabolic reduction to form the lycopene metabolite. Although in vivo oxidation of lutein to its metabolites has been demonstrated based on data obtained from two human studies, in vivo oxidation of lycopene to its metabolite has not yet been established. Recent preliminary studies involving healthy subjects ingesting purified lutein and zeaxanthin (a dietary dihydroxycarotenoid isomeric to lutein) are presented. We propose a possible antioxidant mechanism of action for lutein and lycopene that leads to formation of the oxidation products of these promising chemopreventive agents.