Biologic mechanisms of the protective role of lutein and zeaxanthin in the eye

Outdoor cultivation of microalgae for carotenoid production: current state and perspectives

Microalgae are a major natural source for a vast array of valuable compounds, including a diversity of pigments, for which these photosynthetic microorganisms represent an almost exclusive biological resource. Yellow, orange, and red carotenoids have an industrial use in food products and cosmetics as vitamin supplements and health food products and as feed additives for poultry, livestock, fish, and crustaceans. The growing worldwide market value of carotenoids is projected to reach over US$1,000 million by the end of the decade. The nutraceutical boom has also integrated carotenoids mainly on the claim of their proven antioxidant properties. Recently established benefits in human health open new uses for some carotenoids, especially lutein, an effective agent for the prevention and treatment of a variety of degenerative diseases. Consumers' demand for natural products favors development of pigments from biological sources, thus increasing opportunities for microalgae. The biotechnology of microalgae has gained considerable progress and relevance in recent decades, with carotenoid production representing one of its most successful domains. In this paper, we review the most relevant features of microalgal biotechnology related to the production of different carotenoids outdoors, with a main focus on beta-carotene from Dunaliella, astaxanthin from Haematococcus, and lutein from chlorophycean strains. We compare the current state of the corresponding production technologies, based on either open-pond systems or closed photobioreactors. The potential of scientific and technological advances for improvements in yield and reduction in production costs for carotenoids from microalgae is also discussed.

Partial synthesis of (3R,6'R)-alpha-cryptoxanthin and (3R)-beta-cryptoxanthin from (3R,3'R,6'R)-lutein

(3R,3'R,6'R)-Lutein (1), (3R,3'R)-zeaxanthin (2), (3R,6'R)-alpha-cryptoxanthin (3), and (3R)-beta-cryptoxanthin (4) are among dietary hydroxycarotenoids that have been identified in human serum, milk, and ocular tissues. While 1 containing 6% of 2 is commercially available, industrial production of optically active 3 and 4 has not yet been accomplished. Several processes have been developed that transform 1 into 3, 4, and minor quantities of (3R,5'RS,6'R)-3',4'-didehydro-5',6'-dihydro-beta,beta-caroten-3-ol (5) (a regioisomer of 3). In one process, lutein (1) was cleanly deoxygenated to 3 in the presence of trifluoroacetic acid (TFA) and Me3N.BH3 in CH2Cl2 at ambient temperature in nearly 90% yield. Reaction of lutein (1) with a Lewis acid (AlCl3, ZnBr2, ZnI2) and a hydride donor (Me3N.BH3, Na[BH3(OCOCF3)], NaCNBH3) in solvents such as CH2Cl2, THF, and TBME produced similar results. In a two-step process, high-temperature acid-catalyzed dehydration of 1 (propanol/water/acid, 90 degrees C) gave a mixture of anhydroluteins 6, 7, and 8 in 86% yield. In the second step, these dehydration products underwent ionic hydrogenation with TFA/Me3N.BH3 in CH2Cl2 to afford a mixture of 3 and 4 in nearly 80% yield that contained only 1% of 5.

Outdoor cultivation of lutein-rich cells of Muriellopsis sp. in open ponds

The growth performance of the chlorophycean microalga Muriellopsis sp. outdoors in open tanks agitated with a paddlewheel and its ability to accumulate carotenoids have been evaluated throughout the year. The cells grown in the open system had free lutein as the main carotenoid, with violaxanthin, beta-carotene, and neoxanthin also present. Lutein content of the dry biomass ranged from 0.4 to 0.6%, depending on the growth and environmental conditions. In addition, the biomass of Muriellopsis sp. had a high content in both protein and lipids with about half of the fatty acids being of the polyunsaturated type, with alpha-linolenic acid accounting for almost 30% of the total fatty acids. The effect of determinant parameters on the performance of the cultures in open tanks was evaluated. Operating conditions that allow the maintenance of productive cultures were established under semicontinuous regime for 9 months throughout the year. Biomass and lutein yields in the open system were not far from those in closed tubular photobioreactors, and reached productivity values of 20 g dry biomass, containing around 100 mg lutein m(-2) day(-1) in summer. The outdoor culture of Muriellopsis sp. in open ponds thus represents a real alternative to established systems for the production of lutein.

Guest editorial: Notes on the macular pigment

Potential functions of the macular pigment are reviewed. Its role as a protector of the retina in respect of the blue-light hazard, and its relation to the rods and the cones, are examined. It is tentatively suggested that its presence in the human retina originated in the wild as a result of diet and not as a special evolutionary process: the pigment does not appear to be able to offer any significant photic protection, and the effect on chromatic aberration, as recently reported, may be negligible. Its relation to the spectral placing of photopigments is also examined.

Antioxidants in cystic fibrosis. Conclusions from the CF antioxidant workshop, Bethesda, Maryland, November 11-12, 2003

Although great strides are being made in the care of individuals with cystic fibrosis (CF), this condition remains the most common fatal hereditary disease in North America. Numerous links exist between progression of CF lung disease and oxidative stress. The defect in CF is the loss of function of the transmembrane conductance regulator (CFTR) protein; recent evidence that CFTR expression and function are modulated by oxidative stress suggests that the loss may result in a poor adaptive response to oxidants. Pancreatic insufficiency in CF also increases susceptibility to deficiencies in lipophilic antioxidants. Finally the airway infection and inflammatory processes in the CF lung are potential sources of oxidants that can affect normal airway physiology and contribute to the mechanisms causing characteristic changes associated with bronchiectasis and loss of lung function. These multiple abnormalities in the oxidant/antioxidant balance raise several possibilities for therapeutic interventions that must be carefully assessed.

Differential effects of carotenoids on lipid peroxidation due to membrane interactions: X-ray diffraction analysis

The biological benefits of certain carotenoids may be due to their potent antioxidant properties attributed to specific physico-chemical interactions with membranes. To test this hypothesis, we measured the effects of various carotenoids on rates of lipid peroxidation and correlated these findings with their membrane interactions, as determined by small angle X-ray diffraction approaches. The effects of the homochiral carotenoids (astaxanthin, zeaxanthin, lutein, beta-carotene, lycopene) on lipid hydroperoxide (LOOH) generation were evaluated in membranes enriched with polyunsaturated fatty acids. Apolar carotenoids, such as lycopene and beta-carotene, disordered the membrane bilayer and showed a potent pro-oxidant effect (>85% increase in LOOH levels) while astaxanthin preserved membrane structure and exhibited significant antioxidant activity (40% decrease in LOOH levels). These findings indicate distinct effects of carotenoids on lipid peroxidation due to membrane structure changes. These contrasting effects of carotenoids on lipid peroxidation may explain differences in their biological activity.

Predictors of optical density of lutein and zeaxanthin in retinas of older women in the Carotenoids in Age-Related Eye Disease Study, an ancillary study of the Women's Health Initiative

BACKGROUND

Lifestyle, diet, and physical and health predictors of xanthophyll carotenoids in the retina are poorly understood.

OBJECTIVE

We aimed to investigate the predictors of the density of lutein and zeaxanthin in the macula of the retina.

DESIGN

Macular pigment optical density (MPOD) was measured by heterochromatic flicker photometry. Relations to dietary lutein and zeaxanthin and to other predictors were measured in 1698 women aged 53-86 y. The women were members of observational study cohorts of the Women's Health Initiative at Iowa City, IA, Madison, WI, or Portland, OR, and participated in the Carotenoids in Age-Related Eye Disease Study (2001-2004).

RESULTS

MPOD at 0.5 degrees from the foveal center was 30% higher in women in the highest quintile for lutein and zeaxanthin intake [x (+/-SD): 0.40 +/- 0.21] than in women in the lowest quintile (0.31 +/- 0.21) and 20% higher after adjustment for other predictors. Dietary intake of lutein, zeaxanthin, fiber, and polyunsaturated fatty acids (% of energy) together explained 3% of the variability in MPOD. Higher waist circumference and diabetes, which are related to lower MPOD, together with study site explained an additional 5% of variation. The total explained variability increased to 12% when lutein and zexanthin concentrations obtained from the serum, which were collected 4-7 y earlier, were added to the model.

CONCLUSIONS

MPOD is directly related to dietary intake of lutein and zeaxanthin but even more strongly to serum concentrations, which may reflect unmeasured physical and medical factors that influence the uptake, distribution, and utilization of lutein and zeaxanthin. Higher abdominal body fat and diabetes are related to lower MPOD. Unknown predictors of retinal carotenoids remain.

Oxidation, antioxidants and cataract formation: a literature review

PURPOSE

This review aims to provide a literature survey of the association between photo-oxidation of lens proteins and lipid peroxidation with the genesis of age-related cataract in laboratory studies using rodent models, in epidemiological and interventional studies in humans.

MATERIALS AND METHODS

A Medline search using initial search terms lens, oxidation, antioxidant, and diet was employed to search for research papers covering the areas noted above from 1995 to 2005. Literature cited in those papers was also reviewed to provide as comprehensive a coverage of research work as possible.

RESULTS

Lens protein photo-oxidation and lipid peroxidation are widely acknowledged as important steps in age-related cataractogenesis. Dietary antioxidants are central in retarding cataractogenesis, although most evidence for this is gained from laboratory-based work on relatively unphysiologic rodent cataract models, using antioxidant regimes that could not be sustained in clinical practice. Most research in humans is retrospective epidemiology although some interventional research has been undertaken, with mixed results.

CONCLUSIONS

Dietary antioxidants are likely to be important in retarding cataractogenesis in older animals and in humans. Work on companion animals could provide a valuable stepping stone between rodent-based laboratory work and human interventional studies.

Distribution of macular xanthophylls between domains in a model of photoreceptor outer segment membranes

A model of photoreceptor outer segment (POS) membranes has been proposed, consisting of an equimolar ternary mixture of 1-palmitoyl-2-docosahexaenoylphosphatidylcholine/distearoylphosphatidylcholine/cholesterol. It was shown that, as in membranes made from the raft-forming mixture, in the model of POS membranes, two domains are formed: the raft domain (detergent resistant membranes, DRM), and the bulk domain (detergent soluble membranes, DSM). Saturation-recovery EPR discrimination by oxygen transport method also demonstrated the presence of two domains in this model system in situ at a wide range of temperatures (10-55 degrees C), showing additionally that neither lutein nor zeaxanthin at 1 mol% affect the formation of these domains. These membrane domains have been separated using cold Triton X-100 extraction from a model of POS membranes containing 1 mol% of either lutein or zeaxanthin. The results indicated that the macular xanthophylls lutein and zeaxanthin are substantially excluded from DRM and remain concentrated in DSM, a domain enriched in highly unsaturated docosahexaenoyl acid which is abundant in retina membranes. The concentration of xanthophylls in DRM and DSM calculated as the mol ratio of either xanthophyll to total lipid (phospholipid+cholesterol) was 0.0028 and 0.0391, respectively. Thus, xanthophylls are about 14 times more concentrated in DSM than in DRM. No significant difference in the distribution of lutein and zeaxanthin was found. The obtained results suggest that in POS membranes macular xanthophylls should also be concentrated in domains enriched in polyunsaturated chains.

Consumption of one egg per day increases serum lutein and zeaxanthin concentrations in older adults without altering serum lipid and lipoprotein cholesterol concentrations

Lutein and zeaxanthin accumulate in the macular pigment of the retina, and are reported to be associated with a reduced incidence of age-related macular degeneration. A rich source of lutein and zeaxanthin in the American diet is the yolk of chicken eggs. Thus, the objective of the study was to investigate the effect of consuming 1 egg/d for 5 wk on the serum concentrations of lutein, zeaxanthin, lipids, and lipoprotein cholesterol in individuals >60 y of age. In a randomized cross-over design, 33 men and women participated in the 18-wk study, which included one run-in and one washout period of no eggs prior to and between two 5-wk interventions of either consuming 1 egg or egg substitute/d. Serum lutein 26% (P < 0.001) and zeaxanthin 38% (P < 0.001) concentrations increased after 5-wk of 1 egg/d compared with the phase prior to consuming eggs. Serum concentrations of total cholesterol, LDL cholesterol, HDL cholesterol, and triglycerides were not affected. These findings indicate that in older adults, 5 wk of consuming 1 egg/d significantly increases serum lutein and zeaxanthin concentrations without elevating serum lipids and lipoprotein cholesterol concentrations.

Enhanced bioavailability of zeaxanthin in a milk-based formulation of wolfberry (Gou Qi Zi; Fructus barbarum L.)

The carotenoid zeaxanthin is concentrated within the macula. Increased macular zeaxanthin is suggested to lower the risk of age-related macular degeneration. The small red berry, wolfberry (Fructus barbarum L.; Gou Qi Zi and Kei Tze), is one of the richest natural sources of zeaxanthin. However, carotenoid bioavailability is low, and food-based products with enhanced bioavailability are of interest. The present study investigated zeaxanthin bioavailability from three wolfberry formulations. Berries were homogenised in hot (80 degrees C) water, warm (40 degrees C) skimmed milk and hot (80 degrees C) skimmed milk, with freeze drying of each preparation into a powdered form. A zeaxanthin-standardised dose (15 mg) of each was consumed, in randomised order, together with a standardised breakfast by twelve healthy, consenting subjects in a cross-over trial, with a 3-5-week washout period between treatments. Blood samples were taken via a venous cannula immediately before (fasting) and 2, 4, 6, 7, 8 and 10 h post-ingestion. Zeaxanthin concentration in the triacylglycerol-rich lipoprotein fraction of plasma was measured by HPLC. Results showed that triacylglycerol-rich lipoprotein zeaxanthin peaked at 6 h post-ingestion for all formulations. Zeaxanthin bioavailability from the hot milk formulation was significantly higher (P < 0.001) than from the others. Mean area under the curve (n 12) results were 9.73 (sem 2.45), 3.24 (sem 0.72) and 3.14 (sem 1.09) nmol x h/l for the hot milk, warm milk and hot water formulations, respectively. Results showed clearly that homogenisation of wolfberry in hot skimmed milk results in a formulation that has a 3-fold enhanced bioavailability of zeaxanthin compared with both the 'classical' hot water and warm skimmed milk treatment of the berries.

Antioxidant activity of Botryococcus braunii extract elucidated in vitro models

Botryococcus braunii is a green colonial microalga that is used mainly for the production of hydrocarbons, exopolysaccharides, and carotenoids. In the present study, the antioxidant properties of acetone extracts of B. braunii were evaluated using in vitro model systems such as 1,1-diphenyl-2-picrylhydrazyl (DPPH), hydroxy radical scavenging, and lipid peroxidation in human low-density lipoprotein and rat tissues. Acetone extracts of B. braunii (equivalent to 10 ppm total carotenoid) exhibited 71 and 67% antioxidant activity in DPPH and hydroxyl radical scavenging model systems, respectively. Similarly, the extract also showed 72, 71, and 70% antioxidant activity in the liver, brain, and kidney of rats. Low-density lipoprotein oxidation induced by Cu2+ ions was also protected (22, 38, and 51%) by the algal extract in a dose-dependent manner (4, 6, and 8 ppm levels of total carotenoid). Thiobarbituric acid reactive substances concentration in the blood, liver, and kidney of rats was also significantly decreased in B. braunii treated samples compared with those of control. Carotenoids (violaxanthin, astaxanthin, lutein, zeaxanthin, chlorophylls a and b, and alpha, beta-carotene) identified in the B. braunii acetone extract may be exhibiting antioxidant activity. Among the carotenoids, lutein represents more than 75% of the total carotenoids. B. braunii extract was shown to be effective for protecting biological systems against various oxidative stresses in vitro. This is the first report on the antioxidant properties of B. braunii.

beta-Carotene accumulation induced by the cauliflower Or gene is not due to an increased capacity of biosynthesis

The cauliflower (Brassica oleracea L. var. botrytis) Or gene is a rare carotenoid gene mutation that confers a high level of beta-carotene accumulation in various tissues of the plant, turning them orange. To investigate the biochemical basis of Or-induced carotenogenesis, we examined the carotenoid biosynthesis by evaluating phytoene accumulation in the presence of norflurazon, an effective inhibitor of phytoene desaturase. Calli were generated from young seedlings of wild type and Or mutant plants. While the calli derived from wild type seedlings showed a pale green color, the calli derived from Or seedlings exhibited intense orange color, showing the Or mutant phenotype. Concomitantly, the Or calli accumulated significantly more carotenoids than the wild type controls. Upon treatment with norflurazon, both the wild type and Or calli synthesized significant amounts of phytoene. The phytoene accumulated at comparable levels and no major differences in carotenogenic gene expression were observed between the wild type and Or calli. These results suggest that Or-induced beta-carotene accumulation does not result from an increased capacity of carotenoid biosynthesis.

Accumulation of macular xanthophylls in unsaturated membrane domains

The distribution of macular xanthophylls, lutein and zeaxanthin, between domains formed in membranes made from an equimolar ternary mixture of dioleoylphosphatidylcholine/sphingomyelin/cholesterol, called a raft-forming mixture, was investigated. In these membranes, two domains are formed: the raft domain enriched in saturated lipids and cholesterol (detergent-resistant membranes, DRM), and the bulk domain enriched in unsaturated lipids (detergent-soluble membranes, DSM). These membrane domains have been separated using cold Triton X-100 extraction from membranes containing 1 mol% of either lutein or zeaxanthin. The results indicated that xanthophylls are substantially excluded from DRM and remain concentrated in DSM. Concentrations of xanthophylls in DRM and DSM calculated as the mole ratio of either xanthophyll to phospholipid were 0.005 and 0.03, respectively, and calculated as the mole ratio of either xanthophyll to total lipid (phospholipid + cholesterol) were 0.003 and 0.025, respectively. Thus, xanthophylls are over eight times more concentrated in DSM than in DRM. No significant difference in the distribution of lutein and zeaxanthin was found. It was also demonstrated using saturation-recovery EPR that at 1 mol%, neither lutein nor zeaxanthin affect the formation of membrane domains. The location of xanthophylls in domains formed from unsaturated lipids is ideal if they are to act as a lipid antioxidant, which is the most accepted mechanism through which lutein and zeaxanthin protect the retina from age-related macular diseases.

Inhibition of nNOS and COX-2 expression by lutein in acute retinal ischemia

OBJECTIVE

Lutein is a major nutrient in the retina. Lutein has an antioxidative effect and protects against macular degeneration and retinal degenerative disease. However, the mechanism of lutein is not clear in retinal degeneration, and a role for lutein is not known in ischemic injury. In this study, an ischemia-induced rat retina was examined to determine the effect of the lutein on ischemic retinal cell death.

METHODS

We used a transient ischemia model of high intraocular pressure in the rat. Lutein (Kemin Foods, LC) was injected into the intraperitoneal or intravitreous before ischemia. Retinal degeneration was observed by light microscopy 24 h after ischemia. Expressions of neuronal nitric oxide synthase (nNOS) and cyclo-oxygenase-2 (COX-2) were detected by western blot analysis at various times after retinal ischemia.

RESULTS

The nNOS and COX-2 expression levels were increased early in ischemic control retinas, but these increases were inhibited by lutein. In addition, the inhibitory effect of lutein was observed to be dose dependent. Further, ischemia-induced cell death was inhibited by lutein. Lutein-injected ischemic retina appeared similar to normal retina.

CONCLUSION

This study investigated the protective effect of lutein on retinal ischemia and the inhibitory effect of nNOS and COX-2 expressions. These results suggest that a supplement with lutein may have the potential to inhibit ischemic cell death by this mechanism in the neural retina.

Engineering ketocarotenoid biosynthesis in potato tubers

Consumption of astaxanthin is increasingly associated with a range of health benefits. Attempts to engineer ketocarotenoid biosynthesis in plants have been successful although there are no reports of nutritionally significant levels of astaxanthin in plant storage organs. Thus, in this study, ketocarotenoid biosynthesis was engineered in potato tubers. Both Solanum tuberosum and Solanum phureja transgenic lines were produced that expressed an algal bkt1 gene, encoding a beta-ketolase, and accumulated ketocarotenoids. Two major ketocarotenoids were detected, ketolutein and astaxanthin. The level of unesterified astaxanthin reached ca. 14 microg g(-1) DW in some bkt1 expressing lines of S. phureja but was much lower in the S. tuberosum background. Co-transformation of S. tuberosum with crtB, encoding phytoene synthase, and the bkt1 gene was achieved in order to determine whether this would enhance the levels of S. tuberosum ketocarotenoid.

Age-related maculopathy and the impact of blue light hazard

The pathogenesis of age-related maculopathy (ARM), the most common cause of visual loss after the age of 60 years, is indeed a complicated scenario that involves a variety of hereditary and environmental factors. The pathological cellular and molecular events underlying retinal photochemical light damage, including photoreceptor apoptosis, have been analysed in experimental animal models. Studies of age-related alterations of the retina and photoreceptors, the accumulation of lipofuscin in retinal pigment epithelium (RPE) cells, and the formation of drusen have greatly contributed to our knowledge. A new concept of an inflammatory response to drusen has emerged, suggesting immunogenic and systemic reactions in Bruch's membrane and the subretinal space. Oxidative stress and free radical damage also impact on the photoreceptors and RPE cells in the ageing eye. Based on the photoelectric effect, a fundamental concept in quantum physics, the consequences of high-energy irradiation have been analysed in animal models and cell culture. Short-wavelength radiation (rhodopsin spectrum), and the blue light hazard (excitation peak 440 nm), have been shown to have a major impact on photoreceptor and RPE function, inducing photochemical damage and apoptotic cell death. Following cataract surgery, there is a dramatic change in ocular transmittance. In aphakic or pseudophakic eyes (with clear intraocular lenses), high-energy (blue) and ultraviolet-A radiation strikes the retina. Epidemiological data indicate a significantly increased 5-year incidence of late ARM in non-phakic eyes compared with phakic eyes. In recent years, putative prophylactic measures against ARM have emerged. The implantation of 'yellow' intraocular lenses (IOLs) that absorb high-energy blue radiation is, from a theoretical point of view, the most rational approach, and, from a practical point of view, is easy to accomplish. With increasing age, RPE cells accumulate lipofuscin (chromophore A2E). It is noteworthy that the yellow IOL not only protects A2E-laden human RPE cells from blue light (peak 430 nm) damage, but also alleviates the detrimental effects of green (peak 550 nm) and white light. A prophylactic treatment using antioxidants is aimed at counteracting oxidative stress and free radical cellular damage. The Age-Related Eye Disease Study (AREDS), a randomized clinical trial, showed a significantly lower incidence of late ARM in a cohort of patients with drusen maculopathy treated with high doses of antioxidants than in a placebo group. In recent years, considerable progress in retinal research has been achieved, creating a platform for the search for new prophylactic and therapeutic measures to alleviate or prevent photoreceptor and RPE degeneration in ARM.

Hydrolysis of zeaxanthin esters by carboxyl ester lipase during digestion facilitates micellarization and uptake of the xanthophyll by Caco-2 human intestinal cells

Zeaxanthin (Zea) and lutein are the only dietary carotenoids that accumulate in the macular region of the retina and lens. It was proposed that these carotenoids protect these tissues against photooxidative damage. Few plant foods are enriched in Zea, and information about the bioavailability of Zea from these foods and its accumulation in ocular tissues is limited. The amounts of free Zea and its mono- and diesters were measured for several plant foods that have relatively high concentrations of this xanthophyll. Wolfberry had the greatest concentration of Zea with a diester that accounts for 95% of the total. Free, mono-, and diesters of Zea were present in orange and red peppers, whereas only Zea monoesters were detected in squash. Zea esters were partially hydrolyzed by carboxyl ester lipase (CEL) during simulated digestion. The efficiency of micellarization was dependent on speciation with combined means of free Zea, Zea monoesters, Zea diesters from the digested foods of 81 +/- 8, 44 +/- 5, and 11 +/- 4%, respectively. When exposed to micelles generated during digestion of the test foods, Zea uptake by Caco-2 cells was proportional to the medium content (11-14%). Free Zea was the most abundant form in Caco-2 cells, although Zea monoesters also were detected (<8 +/- 0.7% vs. free Zea). CEL enhanced Zea uptake from micelles (12.3-fold; P < 0.05) by hydrolyzing Zea esters. After cell uptake, concentrations of free and monoesterified Zea remained relatively stable. These data suggest that dietary Zea esters are hydrolyzed by CEL during the small intestinal phase of digestion and that this conversion enhances Zea bioavailability.

A hypothesis to suggest that light is a risk factor in glaucoma and the mitochondrial optic neuropathies

The authors propose that light entering the eye interacts with retinal ganglion cell (RGC) axon mitochondria to generate reactive oxygen intermediates (ROI) and that when these neurons are in an energetically low state, their capacity to remove these damaging molecules is exceeded and their survival is compromised. They suggest that in the initial stages of glaucoma, RGCs exist at a low energy level because of a reduced blood flow at the optic nerve head and that in the mitochondrial optic neuropathies (MONs), this results from a primary, genetic defect in aerobic metabolism. In these states RGCs function at a reduced energy level and incident light on the retina becomes a risk factor. Preliminary laboratory studies support this proposition. Firstly, the authors have shown that light is detrimental to isolated mitochondria in an intensity dependent manner. Secondly, light triggers apoptosis of cultured, transformed RGCs and this effect is exacerbated when the cells are nutritionally deprived. Detailed studies are under way to strengthen the proposed theory. On the basis of this proposal, the authors suggest that patients with optic neuropathies such as glaucoma or at risk of developing a MON may benefit from the use of spectral filters and reducing the intensity of light entering the eye.

Evidence for the use of nutritional supplements and herbal medicines in common eye diseases

PURPOSE

To provide a perspective by reviewing the evidence for the role of nutritional supplements and herbal medicines in the common causes of visual impairment.

DESIGN

Retrospective literature review.

METHODS

Published studies and information found in PubMed, International Bibliographic Information of Dietary Supplements, and selected websites were reviewed for the role of nutritional and herbal medicines in the treatment of age-related macular degeneration, cataract, diabetic retinopathy, and glaucoma. The studies were evaluated systematically for their study design, study population, benefits, risks, biases, and criteria for the categorization of the level of evidence.

RESULTS

The available evidence does support the use of certain vitamins and minerals in patients with certain forms of age-related macular degeneration. For cataracts, the available evidence does not support these supplements to prevent or treat cataracts in healthy individuals. For diabetic retinopathy and glaucoma, the available evidence does not support the use of these supplements. In the category of herbal medicines, the available evidence does not support the use of herbal medicines for any of these ocular diseases.

CONCLUSION

Because of the widespread use of nutritional supplements and herbal medicines, ophthalmologists should be aware of their use so that they can inform patients properly when the supplements and herbal medicine are being used for eye disease.

Improved high performance liquid chromatographic method for determination of carotenoids in the microalga Chlorella pyrenoidosa

Microalgae have become an important commercial source of carotenoids and microalgae-derived functional foods are consumed by people worldwide. Therefore, an HPLC method was developed to discern the variety and content of carotenoids in the microalga Chlorella pyrenoidosa. The microalga sample was powdered, extracted, saponified and subjected to HPLC analysis. A mobile phase of methanol-acetonitrile-water (84:14:2, v/v/v) (A) and methylene chloride (100%) (B) with the following gradient elution was developed: 100% A and 0% B in the beginning, maintained for 14 min, decreased to 95% A in 25 min, 75% A in 30 min, 74% A in 35 min, 45% A in 50 min and returned to 100% A in 55 min. A total of 32 carotenoids were resolved within 49 min by using a C30 column with flow rate at 1 mL/min and detection at 450 nm. An internal standard beta-apo-8'-carotenal was used to quantify all the carotenoids. All-trans-lutein was present in exceptionally large amount (125034.4 microg/g), followed by cis isomers of lutein (27975.3 microg/g), all-trans-alpha-carotene (2465.8 microg/g), zeaxanthin (2170.3 microg/g), cis isomers of beta-carotene (2159.3 microg/g), all-trans-beta-carotene (2155.0 microg/g), cis isomers of alpha-carotene (1766.7 microg/g), beta-cryptoxanthin (334.9 microg/g), neoxanthin and its cis isomers (199.7 microg/g), neochrome (65.2 microg/g), auroxanthin (38.5 microg/g) and violaxanthin and its cis isomers (38.1 microg/g).

Synthetic carotenoid derivatives prevent photosensitised killing of retinal pigment epithelial cells more effectively than lutein

We studied the photosensitised killing of retinal pigment epithelial (RPE) cells using two photosensitisers that localise in lysosomes. The ARPE-19 cell line was photosensitised using either acridine orange or cis-di(4-sulfonatophenyl)diphenylporphine. We then measured the amount of photoprotection provided to RPE cells by five synthetic carotenoid derivatives and by lutein. The synthetic carotenoid derivatives studied were the Girard's reagent P derivative (GRP) of retinal (GRP-retinal), the GRP derivative of beta-apo-8'-carotenal (GRP-carotenal), the Girard's reagent T derivative of beta-apo-8'-carotenal (GRT-carotenal), the GRP derivative of canthaxanthin ((GRP)2-canthaxanthin) and the dansyl hydrazine derivative of beta-apo-8'-carotenal (dansyl-carotenal). We found that GRP-carotenal, GRT-carotenal (GRP)2-canthaxanthin and dansyl-carotenal were effective photoprotectors. All of these carotenoids had large singlet-oxygen quenching constants and had chemical structures designed to localise either in mitochondria or in lysosomes. In contrast, lutein and GRP-retinal were not effective photoprotectors. The failure of GRP-retinal to provide significant photoprotection may have been due to its relatively low singlet-oxygen quenching constant. Lutein is a potent singlet-oxygen quencher, but may not have provided significant photoprotection in this model because the lutein may have had a different subcellular distribution than the photosensitisers used.

Emerging biological therapies for age-related macula degeneration

Age-related macular degeneration (AMD) has emerged as the dominant cause of irretrievable visual loss in most developed countries achieving increasing longevity. The major cause of rapid and severe visual loss is the development of choroidal neovascularisation under the macula (exudative or wet AMD). Physical treatments, especially thermal laser and photodynamic therapy following intravenous verteporfin, have made statistically significant but modest progress in limiting visual loss, whereas surgical translocation of the macula and even light or electrically sensitive retinal implants are spectacular, but likely to only ever benefit a few. Intravitreal fine needle injections and slow release implants of steroid derivatives have opened new areas for investigation. The blocking of endothelial receptors for vascular endothelial growth factor by RNA-based aptamer or immune-protected antibody fragments has been the subject of intensive scientific development and large scale clinical trials. This approach may expand the range of AMD patients amenable to treatment. Additional therapeutic gains await measures to modify photoreceptor cell loss and subretinal fibrosis involving the retinal pigment epithelium as well as prevention or treatment for pigment epithelial detachment. Epidemiological associations with smoking and diet, and antioxidant dietary supplements offer important strategies for prevention.

Quantitative measurement of 3′-oxolutein from human retina by normal-phase high-performance liquid chromatography coupled to atmospheric pressure chemical ionization mass spectrometry

3-Hydroxy-beta,epsilon-carotene-3'-one (3'-oxolutein) is the major oxidative metabolite of dietary carotenoids in the retina of the human eye. Elucidating the biochemical mechanism of its formation may provide helpful insight into the pathogenesis of age-related macular degeneration; however, it is found in relatively low quantities that require highly sensitive methods for quantitation from individual retinas. Normal-phase high-performance liquid chromatography coupled to atmospheric pressure chemical ionization mass spectrometry allowed us to do quantitative analysis of 3'-oxolutein from central and peripheral retinas obtained from individual human donors. The limit of quantification for 3'-oxolutein in human retina at a signal-to-noise ratio of 10 was 6 pg. The precision of the assay yielded a coefficient of variation ranging from 4.7 to 7.4% and accuracies of 106-108%. A statistically significant (R = 0.99, p < or = 0.001) linear working range was achieved between 5 and 7200 pg. The 3'-oxolutein contents from 8-mm punches of the central macula and peripheral retina were found to be 375+/-192 and 191+/-95 pg/tissue, respectively.

Lutein: A Valuable Ingredient of Fruit and Vegetables

Lutein is a human serum carotenoid which is not synthesized by humans and thus must be obtained by the ingestion of food containing it such as fruits and vegetables. Lutein is present in different forms in those foods as all-trans-lutein, cis-lutein, epoxi-lutein, and lutein linked to proteins. It discusses if the intake of lutein or diets supplemented with lutein or diets rich in fruits and vegetables are important in the prevention of diseases like some cancers, cardiovascular diseases, etc., that may be affected by the antioxidant effect of lutein; or in the prevention of age-related macular degeneration and other eye diseases. The concentration of lutein in fruits and vegetables depends on the species. We've included the concentration of lutein in 74 species reported by different authors since 1990. Currently the quantification of lutein is mainly performed by HPLC, but more investigations into a quantification method for lutein, lutein isomers, and epoxi-lutein are necessary. Improvement of lutein extraction methods is important as well. Methods commonly used in the vegetable and fruit industry like heat treatment, storage conditions, etc. can change lutein concentrations; other factors depend on the plant, for instance the variety, the stage of maturity, etc.

Use of a 13C tracer to investigate lutein as a ligand for plasma transthyretin in humans

The selective accumulation of lutein in the macula of the human retina is likely to be mediated by specific transport and/or binding proteins. Our objective was to determine whether transthyretin (TTR) is a plasma transport protein for lutein. We used a biosynthetic 13C-lutein tracer and GC-combustion interfaced-isotope ratio MS to gain the requisite sensitivity to detect the minute amounts of lutein expected as a physiological ligand for TTR. Subjects (n = 4) each ingested 1 mg of 13C-lutein daily for 3 d and donated blood 24 h after the final dose. For three subjects, the plasma TTR-retinol-binding protein (RBP) complex was partially purified by anion-exchange (diethylaminoethyl, DEAE) chromatography and then dissociated by hydrophobic-interaction chromatography to yield the TTR component. For subject 4, the initial DEAE purification step was omitted and total plasma TTR (RBP-bound and free) was isolated by hydrophobic-interaction chromatography. In each case, the crude TTR fractions were then purified to homogeneity by RBP-Sepharose affinity chromatography. Pure TTR was extracted with chloroform, and unlabeled lutein was added to the extract as a carrier. The mean 13C/12C ratio (expressed in delta notation, delta13C) of the lutein fraction isolated from the plasma TTR extracts of the four subjects was -30.53 +/- 3.29 per thousand. The delta13C value of the unlabeled lutein carrier was -30.97 +/- 0.27per thousand. Thus, no 13C enrichment was detected in association with TTR. We conclude that lutein is not associated with TTR in human plasma after being ingested in physiological amounts.

Molecular characterization of marker-free transgenic lines of indica rice that accumulate carotenoids in seed endosperm

A single Agrobacterium strain harbouring two binary plasmids was successfully used for the first time to develop a marker-free transgenic rice of improved nutritional value. Sixty-eight T0 co-transformants were obtained in three indica rice cultivars--two popular high-yielding Bangladeshi varieties (BR28 and BR29), and one high-iron rice cultivar (IR68144). Marker-free lines were obtained from 14 out of 24 selected co-transformants screened in the T1 generation. The accumulation of total carotenoids in polished T2 rice seeds of the primary transgenic VPBR29-17-37 reached levels of up to 3.0 microg/g, with the level of beta-carotene reaching 1.8 microg/g. In the cultivars BR28 and IR68144, total carotenoid levels in the transformants reached 2.0 microg/g of polished rice seeds. The levels of lutein and other carotenoids in the seeds were also significantly enhanced. T1 plants obtained from primary transgenics with simple gene-integration patterns tended to have a lower carotenoid content than the original parental lines. This study describes the development of marker-free transgenic rice lines containing high levels of carotenoids, and addresses the relationship between the rearrangement of transgenes and the presence of metabolic end products in transgenic rice.

Genotypic differences in chlorophyll, lutein, and beta-carotene contents in the fruits of actinidia species

Chlorophyll, lutein, and beta-carotene contents in Actinidia fruits were determined by high-performance liquid chromatography in various genotypes, including five Actinidia deliciosa, seven Actinidia chinensis, two Actinidia rufa, five Actinidia arguta, and three interspecific hybrids. The concentrations of chlorophyll, lutein, and beta-carotene in the fruit of A. deliciosa Hayward were 1.65, 0.418, and 0.088 mg/100 g fresh weight, respectively. Of A. deliciosa cultivars, Koryoku showed significantly higher concentrations in chlorophyll, lutein, and beta-carotene than Hayward. In most cultivars of A. chinensis, although both chlorophyll and lutein contents were significantly lower than in Hayward, the beta-carotene content tended to be slightly higher. In A. rufa, A. arguta, and their interspecific hybrids, the contents of chlorophyll, lutein, and beta-carotene were much higher than in Hayward. In particular, these fruits were found to be the richest dietary source of lutein among commonly consumed fruits.

Invited Review: Fluphenazine Augments Retinal Oxidative Stress

Recently, fluphenazine, a phenothiazine neuroleptic, has been associated with idiosyncratic retinopathy. Neuroleptic-induced retinopathy appears to be isolated to only a few structurally related phenothiazines, suggesting that the causality is not the result of dopamine antagonism. The chemical structure of fluphenazine is very similar to that of chlorpromazine and thioridazine, agents known to produce retinopathy. Like chlorpromazine and thioridazine, fluphenazine may be oxidized by retinal cytochrome P450 and/or myeloperoxidase to an electrophile, producing injury in susceptible patients.

Studies on canthaxanthin in lipid membranes

Polar carotenoid pigment - canthaxanthin - has been found to interfere with the organization of biological membranes, in particular of the retina membranes of an eye of primates. The organization of lipid membranes formed with dipalmitoylphosphatidylcholine (DPPC) and egg yolk phosphatidylcholine containing canthaxanthin was studied by means of several techniques including: electronic absorption spectroscopy, linear dichroism, X-ray diffractometry, (1)H-NMR spectroscopy and FTIR spectroscopy. It appears that canthaxanthin present in the lipid membranes at relatively low concentration (below 1 mol% with respect to lipid) modifies significantly physical properties of the membranes. In particular, canthaxanthin (i) exerts restrictions to the segmental molecular motion of lipid molecules both in the headgroup region and in the hydrophobic core of the bilayer, (ii) promotes extended conformation of alkyl lipid chains, (iii) modifies the surface of the lipid membranes (in particular in the gel state, L(beta )) and promotes the aggregation of lipid vesicles. It is concluded that canthaxanthin incorporated into lipid membranes is distributed among two pools: one spanning the lipid bilayer roughly perpendicularly to the surface of the membrane and one parallel to the membrane, localized in the headgroup region. The population of the horizontal fraction increases with the increase in the concentration of the pigment in the lipid phase. Such a conclusion is supported by the linear dichroism analysis of the oriented lipid multibilayers containing canthaxanthin: The mean angle between the dipole transition moment and the axis normal to the plane of the membrane was determined as 20+/-3 degrees at 0.5 mol% and 47+/-3 degrees at 2 mol% canthaxanthin. The analysis of the absorption spectra of canthaxanthin in the lipid phase and (1)H-NMR spectra of lipids point to the exceptionally low aggregation threshold of the pigment in the membrane environment (approximately 1 mol%). All results demonstrate a very strong modifying effect of canthaxanthin with respect to the dynamic and structural properties of lipid membranes.

Storage Stability of Lutein During Ripening of Cheddar Cheese

Lutein (3,3'-dihydroxy-alpha-carotene) has been identified as a dietary factor that can delay the onset of age-related macular degeneration (AMD). However, available food sources of lutein contain only modest amounts of the carotenoid. Food fortification with lutein extract has been identified as a low-budget approach to prevent the onset or progression of AMD. The objectives of this study were to 1) incorporate various amounts of lutein into Cheddar cheese; 2) examine the color, pH, microbiological, and sensory characteristics of the Cheddar cheese during storage; and 3) analyze the stability of lutein during the cheese maturation process. Lutein extracted from corn was added to Cheddar cheese in quantities of 1, 3, and 6 mg per serving size. Measurements of the lutein stability were carried out by HPLC using a YMC C30 carotenoid column. Microbiological analyses of cheese samples included aerobic plate count, coliform, and yeast/mold counts. The color attributes a* and b* were significantly different between the treatment and control groups; however, no significant difference was observed in L* value and pH. Significant differences among 1, 3, and 6 mg lutein-enriched cheeses were observed in the aerobic plate count and yeast/mold compared with the control. Cheese samples contained no detectable levels of coliforms (< 10 cfu/g). The HPLC data showed quantitative recovery of lutein during the storage period, and no lutein degradation products were identified. These results indicate that lutein, a functional additive with purported ability to prevent or reduce the onset of AMD, can be incorporated into cheese adding value to this product.

Synergistic effects of zeaxanthin and its binding protein in the prevention of lipid membrane oxidation

There is growing evidence that high levels of the macular xanthophyll carotenoids lutein and zeaxanthin may be protective against visual loss due to age-related macular degeneration, but the actual mechanisms of their protective effects are still poorly understood. We have recently purified, identified and characterized a pi isoform of glutathione S-transferase (GSTP1) as a zeaxanthin-binding protein in the macula of the human eye which specifically and saturably binds to the two forms of zeaxanthin endogenously found in the foveal region. In this report, we studied the synergistic antioxidant role of zeaxanthin and GSTP1 in egg yolk phosphatidylcholine (EYPC) liposomes using hydrophilic 2,2'-azobis(2-methyl-propionamidine) dihydrochloride (AAPH) and lipophilic 2,2'-azobis(2,4-dimethylvaleronitrile) (AMVN) as lipid peroxyl radical generators. The two zeaxanthin diastereomers displayed synergistic antioxidant effects against both azo lipid peroxyl radical generators when bound to GSTP1. In the presence of GSTP1, nondietary (3R,3'S-meso)-zeaxanthin was observed to be a better antioxidant than dietary (3R,3'R)-zeaxanthin. This effect was found to be independent of the presence of glutathione. Carotenoid degradation profiles indicated that the zeaxanthin diastereomers in association with GSTP1 were more resistant to degradation which may account for the synergistic antioxidant effects.

Fasting plasma zeaxanthin response to Fructus barbarum L. (wolfberry; Kei Tze) in a food-based human supplementation trial

Age-related macular degeneration (AMD) is a common disorder that causes irreversible loss of central vision. Increased intake of foods containing zeaxanthin may be effective in preventing AMD because the macula accumulates zeaxanthin and lutein, oxygenated carotenoids with antioxidant and blue light-absorbing properties. Lycium barbarum L. is a small red berry known as Fructus lycii and wolfberry in the West, and Kei Tze and Gou Qi Zi in Asia. Wolfberry is rich in zeaxanthin dipalmitate, and is valued in Chinese culture for being good for vision. The aim of this study, which was a single-blinded, placebo-controlled, human intervention trial of parallel design, was to provide data on how fasting plasma zeaxanthin concentration changes as a result of dietary supplementation with whole wolfberries. Fasting blood was collected from healthy, consenting subjects; fourteen subjects took 15 g/d wolfberry (estimated to contain almost 3 mg zeaxanthin) for 28 d. Repeat fasting blood was collected on day 29. Age- and sex-matched controls (n 13) took no wolfberry. Responses in the two groups were compared using the Mann-Whitney test. After supplementation, plasma zeaxanthin increased 2.5-fold: mean values on day 1 and 29 were 0.038 (sem 0.003) and 0.096 (sem 0.009) micromol/l (P<0.01), respectively, for the supplementation group; and 0.038 (sem 0.003) and 0.043 (sem 0.003) micromol/l (P>0.05), respectively, for the control group. This human supplementation trial shows that zeaxanthin in whole wolfberries is bioavailable and that intake of a modest daily amount markedly increases fasting plasma zeaxanthin levels. These new data will support further study of dietary strategies to maintain macular pigment density.

The Macular Xanthophylls

The macular pigments are predominantly composed of three carotenoids: lutein, zeaxanthin, and meso-zeaxanthin. These carotenoids are concentrated and distributed in a selective manner. The properties of these pigments are further explored along with their methods of uptake, stabilization, and storage. The dual nature of these pigments as filters and antioxidants are elaborated upon in relation to their protective effects upon the macula, specifically in age-related macular degeneration. Evidence suggests that increased levels of macular pigment are correlated with a decreased risk of age-related macular degeneration. Many have sought to exploit this therapeutic relation. Studies reveal that oral supplementation with lutein and zeaxanthin can increase the levels of macular pigments in the retina and plasma. The effects of such supplementation on actual ocular function have yet to be fully addressed. New and standardized methods of assessing macular pigment density are discussed and future areas of research to further our understanding of macular xanthophylls as they pertain to age-related macular degeneration are highlighted.

Obesity, Lutein Metabolism, and Age-Related Macular Degeneration: A Web of Connections

Age-related macular degeneration (AMD) is a major cause of visual impairment in the United States. Currently there is no effective cure for this disease. Risk factors include decreased lutein and zeaxanthin status and obesity. Obesity is also an increasing public health concern. The alarming increase in the prevalence of obesity further exacerbates the public health concern of AMD. The mechanism by which obesity increases the risk of AMD may be related to the physiologic changes that occur with this condition. These include increased oxidative stress, changes in the lipoprotein profile, and increased inflammation. These changes would also result in an increased destruction and a decreased circulatory delivery of lutein and zeaxanthin to the macula of the eye. Therefore, the mechanism by which obesity is related to AMD risk may be through indirect effects on changes in lutein and zeaxanthin status and metabolism.

Production of Dunaliella salina biomass rich in 9-cis-β-carotene and lutein in a closed tubular photobioreactor

Performance of Dunaliella salina cultures outdoors in a closed tubular photobioreactor has been assessed. Optimization of conditions involved verification of the effect of several determining factors on the yield of both biomass and carotenoids. Maximal biomass productivity (over 2g (dry weight) m(-2) d(-1) or 80 gm(-3) d(-1)) was achieved at 38 cm s(-1), flow rate; 2 x 10(9) cells l(-1), initial population density; 25 degrees C, temperature; semi-continuous regime, keeping a cell density interval between 2 x 10(9) and over 4 x 10(9) cells l(-1). Coverage of the tubular loop with a sunshade screen to avoid light-induced damage of cells was essential to maintain growth performance. The cellular beta-carotene level increased significantly during the light period, as also did that of lutein. The rise in the beta-carotene level could be accounted by the 9-cis-isomer, with all-trans-beta-carotene remaining steady during the light period. By sunset, the ratio between 9-cis- and all-trans-isomers of beta-carotene amounted to 1.5, with over 60% of total beta-carotene corresponding to the 9-cis-isomer. Removal of sunshade enhanced carotenoid accumulation by cells to reach up to 10% of dry biomass. Cultivation of Dunaliella in closed tubular photobioreactor, thus represents a suitable approach for the production of a high-quality microalgal biomass enriched in the valuable 9-cis-isomer of beta-carotene and lutein.

Lutein absorption is facilitated with cosupplementation of ascorbic acid in young adults

The objectives of this study were to evaluate the bioavailability of crystalline lutein supplements and compare lutein uptake and clearance in humans simultaneously supplemented with either vitamin C or E. The design was an intervention in which area under the curve (AUC) of lutein was compared with and without each of the supplements. Blood samples were drawn at 0, 2, 4, 6, 8, 12, 16, 24, 32, 60, 128, and 504 hours after the dose to measure serum lutein concentration. Four men and five women, aged 26.6+/-2.6 years, participated in this study. Treatments consisted of 18 mg lutein softgel supplements given either alone (L) or with 2 g vitamin C (LC) or 800 IU vitamin E (LE). Comparison of AUCs for the three treatments was examined using analysis of variance. Individual variations, both between and within subjects, 190- and 70-fold, respectively, were very high. AUC analyses for the first 128 hours postdosing; 2.93+/-1.93, 5.37+/-5.0, and 4.11+/-3.04 micromol . hr/L for L, LC, and LE treatments, respectively; were not significantly different. However, by fitting a multiple regression model of serum concentration over time, lutein is absorbed faster with simultaneous supplementation of vitamin C ( P </=.026). In conclusion, bioavailability of crystalline lutein from supplements varies greatly both within and between subjects and therefore reformulation should be considered. Cosupplementation with another antioxidant may facilitate absorption.

Bioactivity and protective effects of natural carotenoids

Carotenoids comprise a class of natural fat-soluble pigments which are found in numerous fruits and vegetables. The consumption of a diet rich in carotenoids has been epidemiologically correlated with a lower risk for several diseases. The antioxidant activity of carotenoids and biochemical properties influencing signaling pathways have been discussed as basic mechanisms of prevention. Conflicting data from intervention studies with beta-carotene to prevent cancers and cardiovascular disorders have challenged the concept. However, there is convincing evidence that carotenoids are important components of the antioxidant network. Photooxidative damage is suggested to be involved in the pathobiochemistry of several diseases affecting the skin and the eye, and carotenoids may protect light-exposed tissues. Lutein and zeaxanthin are the predominant carotenoids of the retina and are considered to act as photoprotectants preventing retinal degeneration. The unique distribution, localization and high levels of both carotenoids within the macula lutea as well as their physicochemical properties make them suitable candidates for photoprotection. beta-Carotene is used as an oral sun protectant for the prevention of sunburn and has been shown to be effective either alone or in combination with other carotenoids or antioxidant vitamins. Protective effects are also achieved with a diet rich in lycopene.

Xanthophylls and alpha-tocopherol decrease UVB-induced lipid peroxidation and stress signaling in human lens epithelial cells

Epidemiological studies suggest that consumption of vegetables rich in the xanthophylls lutein (LUT) and zeaxanthin (ZEA) reduces the risk for developing age-related cataract, a leading cause of vision loss. Although LUT and ZEA are the only dietary carotenoids present in the lens, direct evidence for their photoprotective effect in this organ is not available. The present study examined the effects of xanthophylls and alpha-tocopherol (alpha-TC) on lipid peroxidation and the mitogen-activated stress signaling pathways in human lens epithelial (HLE) cells following ultraviolet B light (UVB) irradiation. When presented with LUT, ZEA, astaxanthin (AST), and alpha-TC as methyl-beta-cyclodextrin complexes, HLE cells accumulated the lipophiles in a concentration- and time-dependent manner with uptake of LUT exceeding that of ZEA and AST. Pretreatment of cultures with either 2 micromol/L xanthophyll or 10 micromol/L alpha-TC for 4 h before exposure to 300 J/m(2) UVB radiation decreased lipid peroxidation by 47-57% compared with UVB-treated control HLE cells. Pretreatment with the xanthophylls and alpha-TC also inhibited UVB-induced activation of c-JUN NH(2)-terminal kinase (JNK) and p38 by 50-60 and 25-32%, respectively. There was substantial inhibition of UVB-induced JNK and p38 activation for cells containing <0.20 and approximately 0.30 nmol xanthophylls/mg, respectively, whereas >2.3 nmol alpha-TC/mg protein was required to significantly decrease UVB-induced stress signaling. These data suggest that xanthophylls are more potent than alpha-TC for protecting human lens epithelial cells against UVB insult.

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.

Carotenoid and retinoid metabolism: insights from isotope studies

Use of isotopes as tracers has had an important role in elucidating key features of vitamin A and retinoid metabolism in animal models and humans. Their use has shown that beta-carotene absorption is variable, and that the appearance of beta-carotene and its metabolites in the blood by time since dosing follows characteristic patterns. Retinol formed from beta-carotene shows a different pattern, as does lutein. In this article, we summarize and discuss insights and some surprises into the absorption and metabolism of vitamin A, beta-carotene, and lutein that were gained with the use of isotope tracers in humans, rats, and cells as models.

Assessment of lutein bioavailability from meals and a supplement using simulated digestion and caco-2 human intestinal cells

Lutein and zeaxanthin are selectively accumulated in the lens and macular region of the retina. It was suggested that these xanthophylls protect ocular tissues from free-radical damage that can cause cataracts and age-related macular degeneration. Insights regarding the absorption of dietary xanthophylls for delivery to ocular tissues are limited. Our primary objective was to examine factors affecting the transfer of lutein from foods to absorptive intestinal epithelial cells during digestion. Lutein and other carotenoids present in spinach purée and lutein from a commercial supplement were relatively stable during in vitro digestion. Micellarization of lutein and zeaxanthin during the small intestinal phase of digestion exceeded that of beta-carotene and was greater for xanthophylls in oil-based supplements than in spinach. Apical uptake of lutein from micelles by Caco-2 human intestinal cells was linear for at least 8 h, and accumulation from synthetic micelles exceeded that from micelles generated during simulated digestion. Stimulation of chylomicron synthesis resulted in the secretion of 7.6 +/- 0.1% of cellular lutein into the triglyceride-rich fraction in the basolateral chamber. These data support the use of simulated digestion and the Caco-2 cell model as effective tools for identifying factors affecting absorption of dietary carotenoids.

Antioxidants and Prevention of Chronic Disease

The generation of reactive oxygen species (ROS) and other free radicals (R) during metabolism is a necessary and normal process that ideally is compensated for by an elaborate endogenous antioxidant system. However, due to many environmental, lifestyle, and pathological situations, excess radicals can accumulate, resulting in oxidative stress. Oxidative stress has been related to cardiovascular disease, cancer, and other chronic diseases that account for a major portion of deaths today. Antioxidants are compounds that hinder the oxidative processes and thereby delay or prevent oxidative stress. This article examines the process of oxidative stress and the pathways by which it relates to many chronic diseases. We also discuss the role that endogenous and exogenous antioxidants may play in controlling oxidation and review the evidence of their roles in preventing disease.

Gene duplication in the carotenoid biosynthetic pathway preceded evolution of the grasses

Despite ongoing research on carotenoid biosynthesis in model organisms, there is a paucity of information on pathway regulation operating in the grasses (Poaceae), which include plants of world-wide agronomic importance. As a result, efforts to either breed for or metabolically engineer improvements in carotenoid content or composition in cereal crops have led to unexpected results. In comparison to maize (Zea mays), rice (Oryza sativa) accumulates no endosperm carotenoids, despite having a functional pathway in chloroplasts. To better understand why these two related grasses differ in endosperm carotenoid content, we began to characterize genes encoding phytoene synthase (PSY), since this nuclear-encoded enzyme appeared to catalyze a rate-controlling step in the plastid-localized biosynthetic pathway. The enzyme had been previously associated with the maize Y1 locus thought to be the only functional gene controlling PSY accumulation, though function of the Y1 gene product had never been demonstrated. We show that both maize and rice possess and express products from duplicate PSY genes, PSY1 (Y1) and PSY2; PSY1 transcript accumulation correlates with carotenoid-containing endosperm. Using a heterologous bacterial system, we demonstrate enzyme function of PSY1 and PSY2 that are largely conserved in sequence except for N- and C-terminal domains. By database mining and use of ortholog-specific universal PCR primers, we found that the PSY duplication is prevalent in at least eight subfamilies of the Poaceae, suggesting that this duplication event preceded evolution of the Poaceae. These findings will impact study of grass phylogeny and breeding of enhanced carotenoid content in an entire taxonomic group of plant crops critical for global food security.

Lutein, zeaxanthin, macular pigment, and visual function in adult cystic fibrosis patients

BACKGROUND

Pancreatic insufficiency in cystic fibrosis (CF), even with replacement pancreatic enzyme therapy, is often associated with decreased carotenoid absorption. Because the macular pigment of the retina is largely derived from 2 carotenoids, lutein and zeaxanthin, the decreased serum concentrations seen in CF may have consequences for ocular and retinal health

OBJECTIVES

Our aims were to determine plasma carotenoid concentrations, determine absorption and distribution of macular pigment, and assess retinal health and visual function in CF patients.

DESIGN

In 10 adult CF patients (ages 21-47 y) and 10 age- and sex-matched healthy control subjects, we measured macular pigment density in vivo, measured serum lutein and zeaxanthin concentrations, and comprehensively assessed visual performance (including contrast sensitivity, color discrimination, and retinal function) under conditions of daylight illumination.

RESULTS

Serum lutein and zeaxanthin were significantly reduced (P < 0.005) in CF patients ( +/- SD: 87 +/- 36.1 and 27 +/- 15.8 nmol/L, respectively) compared with control subjects (190 +/- 72.1 and 75 +/- 23.6 nmol/L, respectively). Although macular pigment optical density was significantly lower (P < 0.0001) in the CF group (0.24 +/- 0.11) than in the control group (0.53 +/- 0.12), no significant differences in visual function were observed.

CONCLUSIONS

Adults with CF have dramatically low serum and macular concentrations of carotenoids (lutein and zeaxanthin), but their ocular status and visual function are surprisingly good. The clinical implications of low plasma concentrations of carotenoids in CF are yet to be clarified.