Human ocular carotenoid-binding proteins

The Role of Glutathione in Age-Related Macular Degeneration (AMD)

Age-related macular degeneration (AMD) is a chronic disease that usually develops in older people. Pathogenetic changes in this disease include anatomical and functional complexes. Harmful factors damage the retina and macula. These changes may lead to partial or total loss of vision. The disease can occur in two clinical forms: dry (the progression is slow and gentle) and exudative (wet-progression is acute and severe), which usually starts in the dry form; however, the coexistence of both forms is possible. The etiology of AMD is not fully understood, and the precise mechanisms of the development of this illness are still unknown. Extensive genetic studies have shown that AMD is a multi-factorial disease and that genetic determinants, along with external and internal environmental and metabolic-functional factors, are important risk factors. This article reviews the role of glutathione (GSH) enzymes engaged in maintaining the reduced form and polymorphism in glutathione S-transferase theta-1 (GSTT1) and glutathione S-transferase mu-1 (GSTM1) in the development of AMD. We only chose papers that confirmed the influence of the parameters on the development of AMD. Because GSH is the most important antioxidant in the eye, it is important to know the influence of the enzymes and genetic background to ensure an optimal level of glutathione concentration. Numerous studies have been conducted on how the glutathione system works till today. This paper presents the current state of knowledge about the changes in GSH, GST, GR, and GPx in AMD. GST studies clearly show increased activity in ill people, but for GPx, the results relating to activity are not so clear. Depending on the research, the results also suggest higher and lower GPx activity in patients with AMD. The analysis of polymorphisms in GST genes confirmed that mutations lead to weaker antioxidant barriers and may contribute to the development of AMD; unfortunately, a meta-analysis and some research did not confirm that connection. Unspecific results of many of the parameters that make up the glutathione system show many unknowns. It is so important to conduct further research to understand the exact mechanism of defense functions of glutathione against oxidative stress in the human eye.

A narrative review on dietary components and patterns and age-related macular degeneration

Age-related macular degeneration (AMD) is one of the most prevalent eye diseases among the ageing population worldwide. It is a leading cause of blindness in individuals over 55, particularly in industrialised Western countries. The prevalence of AMD increases with age, and genetic factors and environmental influences are believed to contribute to its development. Among the environmental factors, diet plays a significant role in AMD. This review explores the association between dietary components, dietary patterns and AMD. Various nutrients, non-nutrient substances and dietary models that have the potential to counteract oxidative stress and inflammation, which are underlying mechanisms of AMD, are discussed. Consuming fruits, vegetables, fish and seafood, whole grains, olive oil, nuts and low-glycaemic-index foods has been highlighted as beneficial for reducing the risk of AMD. Adhering to the Mediterranean diet, which encompasses these elements, can be recommended as a dietary pattern for AMD. Furthermore, the modulation of the gut microbiota through dietary interventions and probiotics has shown promise in managing AMD.

Protein-Mediated Carotenoid Delivery Suppresses the Photoinducible Oxidation of Lipofuscin in Retinal Pigment Epithelial Cells

Lipofuscin of retinal pigment epithelium (RPE) cells is a complex heterogeneous system of chromophores which accumulates as granules during the cell's lifespan. Lipofuscin serves as a source of various cytotoxic effects linked with oxidative stress. Several age-related eye diseases such as macular degeneration of the retina, as well as some severe inherited eye pathologies, are accompanied by a significant increase in lipofuscin granule concentration. The accumulation of carotenoids in the RPE could provide an effective antioxidant protection against lipofuscin cytotoxic manifestations. Given the highly lipophilic nature of carotenoids, their targeted delivery to the vulnerable tissues can potentially be assisted by special proteins. In this study, we demonstrate how protein-mediated delivery of zeaxanthin using water-soluble Bombyx mori carotenoid-binding protein (BmCBP-ZEA) suppresses the photoinducible oxidative stress in RPE cells caused by irradiation of lipofuscin with intense white light. We implemented fluorescence lifetime imaging of the RPE cell culture ARPE-19 fed with lipofuscin granules and then irradiated by white light with and without the addition of BmCBP-ZEA. We demonstrate that after irradiation the mean fluorescence lifetime of lipofuscin significantly increases, while the presence of BmCBP-ZEA at 200 nM concentration suppresses the increase in the average lifetime of lipofuscin fluorescence, indicating an approx. 35% inhibition of the oxidative stress. This phenomenon serves as indirect yet important evidence of the efficiency of the protein-mediated carotenoid delivery into pigment epithelium cells.

Changes in Aqueous Humor Lutein Levels of Patients with Cataracts after a 6-Week Course of Lutein-Containing Antioxidant Supplementation

PURPOSE

Oxidative damage is known to be an important cause of age-related cataracts and it has been suggested that administration of antioxidants, such as lutein, may delay the onset and progression of cataracts. Our previous investigation of human aqueous humor after the intake of a lutein-containing supplement demonstrated decreases in peroxidative products. This study evaluated the transportation of lutein into aqueous humor which is an important factor when measuring the antioxidant effects of lutein on the lens.

METHODS

This study enrolled 155 patients with binocular cataracts of the same grade. Serum and aqueous humor samples were collected during cataract surgery before (as pre-intake samples) and after 6 weeks of oral intake of Ocuvite + Lutein^® (as post-intake samples). Lutein levels were measured with high-performance liquid chromatography.

RESULTS

Lutein levels in both the serum and aqueous humor were significantly higher in the post-intake than the pre-intake samples. There were significant increases in the lutein levels in patients with lower pre-intake lutein serum levels. There was also a tendency for greater increases in patients with lower pre-intake aqueous humor lutein levels.

CONCLUSIONS

These results demonstrate that oral lutein supplementation increases lutein levels, which further induce decreases in peroxidation in the aqueous humor. Furthermore, lutein supplementation may be more effective in patients with lower serum lutein levels.

Lutein and Zeaxanthin and Their Roles in Age-Related Macular Degeneration-Neurodegenerative Disease

Lutein and zeaxanthin belong to the xanthophyll family of carotenoids, which are pigments produced by plants. Structurally, they are very similar, differing only slightly in the arrangement of atoms. Key sources of these carotenoids include kale, savoy cabbage, spinach, broccoli, peas, parsley, corn, and egg yolks. The recommended daily intake of lutein is approximately 10.0 mg and that of zeaxanthin is 2 mg. Lutein intake in adults varies, with average intakes being 1–2 mg/day. Due to the lack of synthesis of consumption of these compounds in humans, these substances are extremely important for the proper functioning of certain organs of the body (eye, skin, heart, intestines). Eating a lot of dark leafy vegetables and some fruits can help to prevent our bodies from developing diseases. The protective effects of carotenoids are mainly related to their defense against oxidative stress and their ability to scavenge free radicals. Lutein and zeaxanthin are the only dietary carotenoids that accumulate in the retina, specifically the macula, and are called macular pigments. These carotenoids are concentrated by the action of specific binding proteins such as StARD3, which binds lutein, and GSTP1, which binds zeaxanthin and its dietary metabolite, mesozeaxanthin. It has been shown that supportive therapy with lutein and zeaxanthin can have a beneficial effect in delaying the progression of eye diseases such as age-related macular degeneration (AMD) and cataracts. This article presents the current state of knowledge on the role of lutein and zeaxanthin, especially from human studies targeting their metabolism and bioavailability, with recommendations to consume xanthophyll-rich foods.

HDL is the primary transporter for carotenoids from liver to retinal pigment epithelium in transgenic ApoA-I-/-/Bco2-/- mice

Supplementation with antioxidant carotenoids is a therapeutic strategy to protect against age-related macular degeneration (AMD); however, the transport mechanism of carotenoids from the liver to the retina is still not fully understood. Here, we investigate if HDL serves as the primary transporter for the macular carotenoids. ApoA-I, the key apolipoprotein of HDL, was genetically deleted from BCO2 knockout (Bco2-/-) mice, a macular pigment mouse model capable of accumulating carotenoids in the retina. We then conducted a feeding experiment with a mixed carotenoid chow (lutein:zeaxanthin:β-carotene = 1:1:1) for one month. HPLC data demonstrated that the total carotenoids were increased in the livers but decreased in the serum, retinal pigment epithelium (RPE)/choroids, and retinas of ApoA-I-/-/Bco2-/- mice compared to Bco2-/- mice. In detail, ApoA-I deficiency caused a significant increase of β-carotene but not lutein and zeaxanthin in the liver, decreased all three carotenoids in the serum, blocked the majority of zeaxanthin and β-carotene transport to the RPE/choroid, and dramatically reduced β-carotene and zeaxanthin but not lutein in the retina. Furthermore, surface plasmon resonance spectroscopy (SPR) data showed that the binding affinity between ApoA-I and β-carotene ≫ zeaxanthin > lutein. Our results show that carotenoids are transported from the liver to the eye mainly by HDL, and ApoA-I may be involved in the selective delivery of macular carotenoids to the RPE.

Overflow phenomenon in serum lutein after supplementation: a systematic review supported with SNPs analyses

Lutein, a type of carotenoids, is found to delay the onset and progression of age-related macular degeneration (AMD). Several lutein supplementation studies showed that after an initial increase, lutein serum levels demonstrated a subsequent decrease despite continuous supplementation. In this systematic literature review, this obscure phenomenon was tried to be explained. The subsequent drop in lutein levels was postulated due to down-regulation of lutein receptors scavenger receptor class B type I (SR-BI) in the gastrointestinal tract, upregulation of lutein degrading enzyme β-carotene dioxygenase (BCDO2), or perhaps a combination of both. Some single nucleotides polymorphisms (SNPs) that could have influence on the occurrence of this phenomenon. To date, an exact scientific explanation for this phenomenon has not been established. Further research is needed to investigate this phenomenon in depth to reach an irrefutable explanation, giving that lutein is proven to be effective in delaying the onset and progression of AMD and its metabolism in the human body becomes of equal importance.

Factors Differentiating the Antioxidant Activity of Macular Xanthophylls in the Human Eye Retina

Macular xanthophylls, which are absorbed from the human diet, accumulate in high concentrations in the human retina, where they efficiently protect against oxidative stress that may lead to retinal damage. In addition, macular xanthophylls are uniquely spatially distributed in the retina. The zeaxanthin concentration (including the lutein metabolite meso-zeaxanthin) is ~9-fold greater than lutein concentration in the central fovea. These numbers do not correlate at all with the dietary intake of xanthophylls, for which there is a dietary zeaxanthin-to-lutein molar ratio of 1:12 to 1:5. The unique spatial distributions of macular xanthophylls—lutein, zeaxanthin, and meso-zeaxanthin—in the retina, which developed during evolution, maximize the protection of the retina provided by these xanthophylls. We will correlate the differences in the spatial distributions of macular xanthophylls with their different antioxidant activities in the retina. Can the major protective function of macular xanthophylls in the retina, namely antioxidant actions, explain their evolutionarily determined, unique spatial distributions? In this review, we will address this question.

From carotenoid intake to carotenoid blood and tissue concentrations - implications for dietary intake recommendations

There is uncertainty regarding carotenoid intake recommendations, because positive and negative health effects have been found or are correlated with carotenoid intake and tissue levels (including blood, adipose tissue, and the macula), depending on the type of study (epidemiological vs intervention), the dose (physiological vs supraphysiological) and the matrix (foods vs supplements, isolated or used in combination). All these factors, combined with interindividual response variations (eg, depending on age, sex, disease state, genetic makeup), make the relationship between carotenoid intake and their blood/tissue concentrations often unclear and highly variable. Although blood total carotenoid concentrations <1000 nmol/L have been related to increased chronic disease risk, no dietary reference intakes (DRIs) exist. Although high total plasma/serum carotenoid concentrations of up to 7500 nmol/L are achievable after supplementation, a plateauing effect for higher doses and prolonged intake is apparent. In this review and position paper, the current knowledge on carotenoids in serum/plasma and tissues and their relationship to dietary intake and health status is summarized with the aim of proposing suggestions for a "normal," safe, and desirable range of concentrations that presumably are beneficial for health. Existing recommendations are likewise evaluated and practical dietary suggestions are included.

A review of factors that affect carotenoid concentrations in human plasma: differences between Mediterranean and Northern diets

Carotenoids are naturally occurring pigments of autotroph organisms that have been related to many health benefits and this is not only because some of them are precursors of vitamin A. Individual or whole carotenoid consumption has been associated with a lower risk of developing cancer, cardiovascular and metabolic diseases among others. However, the blood levels of carotenoids vary largely from person to person due to different factors. Diet is the most important one because of the dietary patterns that different populations follow, the time of the year of consumption or the personal preferences. Nevertheless, the intrinsic host factors such as the absorption, distribution, metabolism and excretion genetic polymorphisms, the volume of distribution and the person's microbiota and others such as carotenoid interactions are also inducing this so called inter-individual variability. Besides, culinary methods and processing produce changes in the foods that directly affect carotenoid content and hence their blood profile. Different types of studies have been performed to understand the between-subject variation of the carotenoid profile in human plasma. This research is focused on this matter as levels of carotenoids in human plasma could be useful for the prediction of some diseases. The Mediterranean diet is probably the most carotenoid rich diet stemming from its high proportion of fruits and vegetables. Its differences with other diets and the effect on the carotenoid blood profile of the consumers are currently a very interesting topic of study.

Why is Zeaxanthin the Most Concentrated Xanthophyll in the Central Fovea?

Diet-based xanthophylls (zeaxanthin and lutein) are conditionally essential polar carotenoids preferentially accreted in high concentrations (1 mM) to the central retina, where they have the capacity to impart unique physiologically significant biophysical biochemical properties implicated in cell function, rescue, and survival. Macular xanthophylls interact with membrane-bound proteins and lipids to absorb/attenuate light energy, modulate oxidative stress and redox balance, and influence signal transduction cascades implicated in the pathophysiology of age-related macular degeneration. There is exclusive transport, sequestration, and appreciable bioamplification of macular xanthophylls from the circulating carotenoid pool to the retina and within the retina to regions required for high-resolution sensory processing. The distribution of diet-based macular xanthophylls and the lutein metabolite meso-zeaxanthin varies considerably by retinal eccentricity. Zeaxanthin concentrations are 2.5-fold higher than lutein in the cone-dense central fovea. This is an ~20-fold increase in the molar ratio relative to eccentric retinal regions with biochemically detectable macular xanthophylls. In this review, we discuss how the differences in the specific properties of lutein and zeaxanthin could help explain the preferential accumulation of zeaxanthin in the most vulnerable region of the macula.

The molecular aspects of absorption and metabolism of carotenoids and retinoids in vertebrates

Vitamin A is an essential nutrient necessary for numerous basic physiological functions, including reproduction and development, immune cell differentiation and communication, as well as the perception of light. To evade the dire consequences of vitamin A deficiency, vertebrates have evolved specialized metabolic pathways that enable the absorption, transport, and storage of vitamin A acquired from dietary sources as preformed retinoids or provitamin A carotenoids. This evolutionary advantage requires a complex interplay between numerous specialized retinoid-transport proteins, receptors, and enzymes. Recent advances in molecular and structural biology resulted in a rapid expansion of our understanding of these processes at the molecular level. This progress opened new avenues for the therapeutic manipulation of retinoid homeostasis. In this review, we summarize current research related to the biochemistry of carotenoid and retinoid-processing proteins with special emphasis on the structural aspects of their physiological actions. This article is part of a Special Issue entitled Carotenoids recent advances in cell and molecular biology edited by Johannes von Lintig and Loredana Quadro.

Nonresonant Raman spectroscopy of isolated human retina samples complying with laser safety regulations for in vivo measurements

Retinal diseases, such as age-related macular degeneration, are leading causes of vision impairment, increasing in incidence worldwide due to an aging society. If diagnosed early, most cases could be prevented. In contrast to standard ophthalmic diagnostic tools, Raman spectroscopy can provide a comprehensive overview of the biochemical composition of the retina in a label-free manner. A proof of concept study of the applicability of nonresonant Raman spectroscopy for retinal investigations is presented. Raman imaging provides valuable insights into the molecular composition of an isolated ex vivo human retina sample by probing the entire molecular fingerprint, i.e., the lipid, protein, carotenoid, and nucleic acid content. The results are compared to morphological information obtained by optical coherence tomography of the sample. The challenges of in vivo Raman studies due to laser safety limitations and predefined optical parameters given by the eye itself are explored. An in-house built setup simulating the optical pathway in the human eye was developed and used to demonstrate that even under laser safety regulations and the above-mentioned optical restrictions, Raman spectra of isolated ex vivo human retinas can be recorded. The results strongly support that in vivo studies using nonresonant Raman spectroscopy are feasible and that these studies provide comprehensive molecular information of the human retina.

Ocular Carotenoid Status in Health and Disease

Retinal carotenoids are dietary nutrients that uniquely protect the eye from light damage and various retinal pathologies. Their antioxidative properties protect the eye from many retinal diseases, such as age-related macular degeneration. As many retinal diseases are accompanied by low carotenoid levels, accurate noninvasive assessment of carotenoid status can help ophthalmologists identify the patients most likely to benefit from carotenoid supplementation. This review focuses on the different methods available to assess carotenoid status and highlights disease-related changes and potential nutritional interventions.

Immunohistological Study of Monkey Foveal Retina

The fovea centralis, an anatomically concave pit located at the center of the macula, is avascular, hypoxic, and characteristic of stem-cell niches of other tissues. We hypothesized that in the fovea, undifferentiated retinal-stem-cell-like cells may exist, and that neurogenesis may occur. Hence, we performed an immunohistological study using cynomolgus monkey retinas. After preparing frozen tissue sections of the retina including the foveal pit, immunostaining was performed for glial fibrillary acidic protein (GFAP), nestin, vimentin, neuron-specific class III β-tubulin (Tuj-1), arrestin 4, neurofilament, CD117, CD44, Ki67, and cellular retinaldehyde-binding protein (CRALBP), followed by fluorescence and/or confocal microscopy examinations. Immunostaining of the tissue sections enabled clear observation of strongly GFAP-positive cells that corresponded to the inner-half layer of the foveolar Müller cell cone. The surface layer of the foveal slope was partially costained with GFAP and vimentin. Tuj-1-positive cells were observed in the innermost layer of the foveolar retina, which spanned to the surrounding ganglion cell layer. Moreover, colocalization of Tuj-1 and GFAP was observed at the foveal pit. The coexpression of CD117 and CD44 was found in the interphotoreceptor matrix of the fovea. The foveolar cone stained positive for both nestin and arrestin 4, however, the photoreceptor layer outside of the foveola displayed weak staining for nestin. Colocalization of nestin and vimentin was observed in the inner half of the Henle layer, while colocalization of nestin and neurofilament was observed in the outer half, predominantly. Scattered Ki67-positive cells were observed in the cellular processes of the outer plexiform layer and the ganglion cell layer around the foveola. Immunostaining for CRALBP was negative in most parts of the GFAP-positive area. The Müller cell cone was divided into GFAP-strongly positive cells, presumably astrocytes, in the inner layer and nestin-positive/GFAP-weakly positive radial glia-like cells in the outer layer. These findings indicated that groups of such undifferentiated cells in the foveola might be involved in maintaining morphology and regeneration.

Mechanisms of Transport and Delivery of Vitamin A and Carotenoids to the Retinal Pigment Epithelium

Vision depends on the delivery of vitamin A (retinol) to the retina. Retinol in blood is bound to retinol-binding protein (RBP). Retinal pigment epithelia (RPE) cells express the RBP receptor, STRA6, that facilitates uptake of retinol. The retinol is then converted to retinyl esters by the enzyme lecithin:retinol acyltransferase. The esters are the substrate for RPE65, an enzyme that produces 11-cis retinol, which is converted to 11-cis retinaldehyde for transport to the photoreceptors to form rhodopsin. The dietary xanthophylls, lutein (LUT) and zeaxanthin (ZEA), accumulate in the macula of the eye, providing protection against age-related macular degeneration. To reach the macula, carotenoids cross the RPE. In blood, xanthophylls and β-carotene mostly associate with high-density lipoprotein (HDL) and low-density lipoprotein (LDL), respectively. Studies using a human RPE cell model evaluate the kinetics of cell uptake when carotenoids are delivered in LDL or HDL. For LUT and β-carotene, LDL delivery result in the highest rate of uptake. HDL is more effective in delivering ZEA (and meso-ZEA). This selective HDL-mediated uptake of ZEA, via a scavenger receptor and LDL-mediated uptake of LUT and β-carotene provides a mechanism for the selective accumulation of ZEA > LUT and xanthophylls over β-carotene in the macula.

(3R, 3'R)-zeaxanthin protects the retina from photo-oxidative damage via modulating the inflammation and visual health molecular markers

PURPOSE

Zeaxanthin protects the macula from ocular damage due to light or radiation by scavenging harmful reactive oxygen species. In the present study, zeaxanthin product (OmniXan®; OMX), derived from paprika pods (Capsicum annum; Family-Solanaceae), was tested for its efficacy in the rat retina against photooxidation.

METHODS

Forty-two male 8-week-old Wistar rats exposed to 12L/12D, 16L/8D and 24L/0D hours of intense light conditions were orally administrated either 0 or 100 mg/kg BW of zeaxanthin concentration. Retinal morphology was analyzed by histopathology, and target gene expressions were detected with real-time polymerase chain reaction methods.

RESULTS

OMX treatment significantly increased the serum zeaxanthin concentration (p < 0.001) and ameliorated oxidative damage by increasing the antioxidant enzyme activities in the retina induced by light (p < 0.001). OMX administration significantly upregulated the expression of genes, including Rhodopsin (Rho), Rod arrestin (SAG), Gα Transducin 1 (GNAT-1), neural cell adhesion molecule (NCAM), growth-associated protein 43 (GAP43), nuclear factor-(erythroid-derived 2)-like 2 (Nrf2) and heme oxygenase (HO-1) and decreased the expression of nuclear factor-κB (NF- κB) and GFAP by OMX treatment rats. The histologic findings confirmed the antioxidant and gene expression data.

CONCLUSIONS

This study suggests that OMX is a potent substance that can be used to protect photoreceptor cell degeneration in the retina exposed to intense light.

Mechanisms enhancing the protective functions of macular xanthophylls in the retina during oxidative stress

Macular xanthophylls (MXs) are distinguished from other dietary carotenoids by their high membrane solubility and preferential transmembrane orientation. Additionally, these properties enhance the chemical and physical stability of MXs in the eye retina, and maximize their protective activities. The effectiveness of MXs' protection is also enhanced by their selective accumulation in the most vulnerable domains of retinal membranes. The retina is protected by MXs mainly through blue-light filtration, quenching of the excited triplet states of potent photosensitizers, and physical quenching of singlet oxygen. To perform these physical, photo-related actions, the structure of MXs should remain intact. However, the conjugated double-bond structure of MXs makes them highly chemically reactive and susceptible to oxidation. Chemical quenching of singlet oxygen and scavenging of free radicals destroy their intact structure and consume MXs. Consequently, their physical actions, which are critical to the protection of retina, are diminished. Thus, it is timely and important to identify mechanisms whereby the chemical destruction (bleaching) of MXs in retinal membranes can be reduced. It was shown that nitroxide free radicals (spin labels) located in membranes protect MXs against destruction, and their effect is especially pronounced during the light-induced formation of singlet oxygen. That should extend and enhance their positive action in the retina through physical processes. In this review, we will discuss possible applications of this new strategy during ophthalmological procedures, which can cause acute bleaching of MXs and damage the retina through oxidative processes.

Supplementation with macular carotenoids improves visual performance of transgenic mice

Carotenoid supplementation can improve human visual performance, but there is still no validated rodent model to test their effects on visual function in laboratory animals. We recently showed that mice deficient in β-carotene oxygenase 2 (BCO2) and/or β-carotene oxygenase 1 (BCO1) enzymes can accumulate carotenoids in their retinas, allowing us to investigate the effects of carotenoids on the visual performance of mice. Using OptoMotry, a device to measure visual function in rodents, we examined the effect of zeaxanthin, lutein, and β-carotene on visual performance of various BCO knockout mice. We then transgenically expressed the human zeaxanthin-binding protein GSTP1 (hGSTP1) in the rods of bco2^-/- mice to examine if delivering more zeaxanthin to retina will improve their visual function further. The visual performance of bco2^-/- mice fed with zeaxanthin or lutein was significantly improved relative to control mice fed with placebo beadlets. β-Carotene had no significant effect in bco2^-/- mice but modestly improved cone visual function of bco1^-/- mice. Expression of hGSTP1 in the rods of bco2^-/-mice resulted in a 40% increase of retinal zeaxanthin and further improvement of visual performance. This work demonstrates that these "macular pigment mice" may serve as animal models to study carotenoid function in the retina.

A global perspective on carotenoids: Metabolism, biotechnology, and benefits for nutrition and health

Carotenoids are lipophilic isoprenoid compounds synthesized by all photosynthetic organisms and some non-photosynthetic prokaryotes and fungi. With some notable exceptions, animals (including humans) do not produce carotenoids de novo but take them in their diets. In photosynthetic systems carotenoids are essential for photoprotection against excess light and contribute to light harvesting, but perhaps they are best known for their properties as natural pigments in the yellow to red range. Carotenoids can be associated to fatty acids, sugars, proteins, or other compounds that can change their physical and chemical properties and influence their biological roles. Furthermore, oxidative cleavage of carotenoids produces smaller molecules such as apocarotenoids, some of which are important pigments and volatile (aroma) compounds. Enzymatic breakage of carotenoids can also produce biologically active molecules in both plants (hormones, retrograde signals) and animals (retinoids). Both carotenoids and their enzymatic cleavage products are associated with other processes positively impacting human health. Carotenoids are widely used in the industry as food ingredients, feed additives, and supplements. This review, contributed by scientists of complementary disciplines related to carotenoid research, covers recent advances and provides a perspective on future directions on the subjects of carotenoid metabolism, biotechnology, and nutritional and health benefits.

What do we know about the macular pigment in AMD: the past, the present, and the future

Carotenoids are lipophilic isoprenoid pigments with a common C₄₀H₅₆ core chemical structure that are naturally synthesized by many plants, algae, bacteria, and fungi. Humans and animals cannot synthesize carotenoids de novo and must obtain them solely through dietary sources. Among the more than 750 carotenoids in nature, only lutein, zeaxanthin, meso-zeaxanthin, and their oxidative metabolites selectively accumulate in the foveal region of the retina where they are collectively referred to as the macular pigment (MP) of the macula lutea. MP serves an ocular protective role through its ability to filter phototoxic blue light radiation and also via its antioxidant activity. These properties have led to the hypothesis that carotenoids may protect against the development of age-related macular degeneration (AMD), the most common cause of blindness in the aged population >60 years old. Epidemiological studies have supported this by showing that patients with lower concentrations of serum carotenoids and macular pigment optical density (MPOD) measurements are at a higher risk of developing AMD. Conversely, nutritional supplementation and diets rich in lutein and zeaxanthin readily impact MP concentrations and reduce the risk of progression to advanced AMD, and the AREDS2 supplement formulation containing 10 mg of lutein and 2 mg of zeaxanthin is the standard-of-care recommendation for individuals at risk for visual loss from advanced AMD. This article reviews the rich history of research on the MP dating back to the 1700s and outlines their potential for further therapeutic improvements for AMD in the future.

Analysis of Lutein, Zeaxanthin, and Meso-Zeaxanthin in the Organs of Carotenoid-Supplemented Chickens

The macular carotenoids (i.e., lutein (L), zeaxanthin (Z) and meso-zeaxanthin (MZ)) exhibit anti-inflammatory, antioxidant and optical properties that are believed to support human health and function. Studying the accumulation and distribution of these nutrients in tissues and organs, in addition to the eye, is an important step in understanding how these nutrients might support global human function and health (e.g., heart and brain). Chicken is an appropriate animal model with which to study the accumulation of these carotenoids in organs, as the relevant transport molecules and carotenoid binding proteins for L, Z and MZ are present in both humans and chickens. In this experiment, a sample of 3 chickens that were supplemented with L and MZ diacetate (active group) and a sample of 3 chickens that received a standard diet (control group) were analysed. Both groups were analysed for L, Z and MZ concentrations in the brain, eyes, heart, lung, duodenum/pancreas, jejunum/ileum, kidney and breast tissue. L, Z and MZ were identified in all the organs/tissues analysed from the active group. L and Z were identified in all of the organs/tissues analysed from the control group; while, MZ was identified in the eyes of these animals only. The discovery that MZ is accumulated in the tissues and organs of chickens supplemented with this carotenoid is important, given that it is known that a combination of L, Z and MZ exhibits superior antioxidant capacity when compared to any of these carotenoids in isolation.

Plasma long-chain omega-3 polyunsaturated fatty acids and macular pigment in subjects with family history of age-related macular degeneration: the Limpia Study

PURPOSE

In numerous epidemiological studies, omega-3 polyunsaturated fatty acids (PUFAs) have been associated with a decreased risk of age-related macular degeneration (AMD). Beyond their structural, functional and neuroprotective roles, omega-3 PUFAs may favour the retinal accumulation of lutein and zeaxanthin and thus increase macular pigment optical density (MPOD). We examined the associations of MPOD with plasma omega-3 PUFAs in subjects with family history of AMD.

METHODS

The Limpia study is a double-blind, placebo-controlled, prospective randomized clinical trial performed in 120 subjects. Subjects with at least one parent treated for neovascular AMD, aged 40-70, with a best corrected visual acuity (BCVA) >20/25, free of late AMD and other major eye conditions and with no use of supplement containing lutein or zeaxanthin the preceding year were recruited in Bordeaux and Dijon, France. At baseline, MPOD within 1° of eccentricity was measured by modified Heidelberg retinal analyser (Heidelberg, Germany) and plasma omega-3 PUFAs by gas chromatography. Medical history and lifestyle data were collected from a standardized questionnaire. Associations of MPOD with plasma omega-3 PUFAs were assessed at the baseline examination, using mixed linear models adjusted for age, gender, centre, body mass index, smoking, plasma high-density lipoprotein (HDL) cholesterol and lutein+zeaxanthin.

RESULTS

After multivariate adjustment, high MPOD was significantly associated with higher level of plasma docosapentaenoic acid (DPA) (β = 0.029, 95% CI: 0.003, 0.055; p = 0.03). Plasma alpha linolenic, eicosapentaenoic and docosahexaenoic acids were not significantly associated with MPOD.

CONCLUSION

In the Limpia study, high MPOD within 1° was significantly associated with higher plasma levels of omega-3 DPA.

All three human scavenger receptor class B proteins can bind and transport all three macular xanthophyll carotenoids

Carotenoids are plant pigment molecules that are potent antioxidants. Carotenoids cannot be synthesized de novo; therefore, their dietary intake and transport to various tissues are essential to harness their health benefits. Two of the three scavenger receptor class B (SRB) proteins, SR-B1 and CD36, have been implicated as carotenoid transporters in lower species and in various tissues of higher animals. The function of the third SRB protein, SR-B2, in carotenoid transport is unknown. Using surface plasmon resonance (SPR) analyses, we have determined that all three human SRB proteins are capable of binding the macular xanthophyll carotenoids; lutein, zeaxanthin, and meso-zeaxanthin. By over-expressing human SRB proteins in cells that do not endogenously express SRBs, we have determined that lutein uptake is enhanced in the presence of LDL and is mediated by SR-B1 and CD36. SR-B1, SR-B2, and CD36 were able to take up significant amounts of zeaxanthin as well as meso-zeaxanthin, and uptake was increased in the presence of HDL. Our analyses revealed no apparent differences in protein expression profiles of SRBs in central and peripheral regions of human donor tissues, indicating that carotenoid-binding proteins rather than transporters are likely to mediate selective accumulation of carotenoids into the macula.

RPE65 has an additional function as the lutein to meso-zeaxanthin isomerase in the vertebrate eye

Carotenoids are plant-derived pigment molecules that vertebrates cannot synthesize de novo that protect the fovea of the primate retina from oxidative stress and light damage. meso-Zeaxanthin is an ocular-specific carotenoid for which there are no common dietary sources. It is one of the three major carotenoids present at the foveal center, but the mechanism by which it is produced in the eye is unknown. An isomerase enzyme is thought to be responsible for the transformation of lutein to meso-zeaxanthin by a double-bond shift mechanism, but its identity has been elusive. We previously found that meso-zeaxanthin is produced in a developmentally regulated manner in chicken embryonic retinal pigment epithelium (RPE)/choroid in the absence of light. In the present study, we show that RPE65, the isomerohydrolase enzyme of the vertebrate visual cycle that catalyzes the isomerization of all-trans-retinyl esters to 11-cis-retinol, is also the isomerase enzyme responsible for the production of meso-zeaxanthin in vertebrates. Its RNA is up-regulated 23-fold at the time of meso-zeaxanthin production during chicken eye development, and we present evidence that overexpression of either chicken or human RPE65 in cell culture leads to the production of meso-zeaxanthin from lutein. Pharmacologic inhibition of RPE65 function resulted in significant inhibition of meso-zeaxanthin biosynthesis during chicken eye development. Structural docking experiments revealed that the epsilon ring of lutein fits into the active site of RPE65 close to the nonheme iron center. This report describes a previously unrecognized additional activity of RPE65 in ocular carotenoid metabolism.

Lutein Activates the Transcription Factor Nrf2 in Human Retinal Pigment Epithelial Cells

The degeneration of the retinal pigment epithelium caused by oxidative damage is a stage of development in age-related macular degeneration (AMD). The carotenoid lutein is a major macular pigment that may reduce the incidence and progression of AMD, but the underlying mechanism is currently not fully understood. Carotenoids are known to be direct antioxidants. However, carotenoids can also activate cellular pathways resulting in indirect antioxidant effects. Here, we investigate the influence of lutein on the activation of nuclear factor erythroid 2-related factor 2 (Nrf2) target genes in human retinal pigment epithelial cells (ARPE-19 cells) using lutein-loaded Tween40 micelles. The micelles were identified as a suitable delivery system since they were nontoxic in APRE-19 cells up to 0.04% Tween40 and led to a cellular lutein accumulation of 62 μM ± 14 μM after 24 h. Lutein significantly enhanced Nrf2 translocation to the nucleus 1.5 ± 0.4-fold compared to that of unloaded micelles after 4 h. Furthermore, lutein treatment for 24 h significantly increased the transcripts of NAD(P)H:quinone oxidoreductase 1 (NQO1) by 1.7 ± 0.1-fold, glutamate-cysteine ligase regulatory subunit (GCLm) by 1.4 ± 0.1-fold, and heme oxygenase-1 (HO-1) by 1.8 ± 0.3-fold. Moreover, we observed a significant enhancement of NQO1 activity by 1.2 ± 0.1-fold. Collectively, this study indicates that lutein not only serves as a direct antioxidant but also activates Nrf2 in ARPE-19 cells.

Comparison of macular pigment and serum lutein concentration changes between free lutein and lutein esters supplements in Japanese subjects

PURPOSE

To compare changes in macular pigment optical density (MPOD) and serum lutein concentration between free lutein and lutein esters supplements in healthy Japanese individuals.

METHODS

Twenty healthy subjects (age range, 22-47 years) were recruited into this prospective, randomized, doubled-blind comparative study. Individuals were evenly divided into two groups: free lutein group, supplementation with 10 mg of free lutein; or lutein esters group, supplementation with 20 mg of lutein esters equivalent to 10 mg of free lutein. Each participant took either type of oral lutein daily for 3 months. The serum lutein concentrations and MPOD levels were measured at baseline and 3 and 6 months after the start of supplementation.

RESULTS

There were no significant differences in the serum lutein concentrations and MPOD levels at baseline between the groups. The increased serum lutein concentration and MPOD levels at 3 months were respectively, 89% and 38% in the free lutein group and 97% and 17% in the lutein esters group. The serum lutein concentrations in both groups and MPOD levels in the free lutein group increased significantly (p < 0.05) from baseline. No significant differences in serum lutein concentrations and MPOD levels were seen between the groups. Three months after supplementation ended, the serum lutein concentration decreased; the MPOD remained elevated in both groups.

CONCLUSIONS

The serum lutein concentrations and MPOD levels increased significantly with either free lutein or lutein esters, and no significant differences were found between the two. Both were considered useful as lutein supplements.

Relationship between Concentrations of Lutein and StARD3 among Pediatric and Geriatric Human Brain Tissue

Lutein, a dietary carotenoid, selectively accumulates in human retina and brain. While many epidemiological studies show evidence of a relationship between lutein status and cognitive health, lutein’s selective uptake in human brain tissue and its potential function in early neural development and cognitive health have been poorly evaluated at a molecular level. The objective of this study was to evaluate the cross-sectional relationship between concentrations of brain lutein and StARD3 (identified as its binding protein in retinal tissue) among three age groups: infants (1–4 months, n = 10), older adults (55–86 years, n = 8), and centenarians (98–105 years, n = 10). Brain lutein concentrations were analyzed by high-performance liquid chromatography and StARD3 levels were analyzed by Western Blot analysis. The strong relationship in infant brains (r = 0.75, P < 0.001) suggests that lutein has a role in neural development. The relationship remained significant but weaker in older adults (r = 0.51, P < 0.05) and insignificant in centenarians (r = 0.08, P > 0.05), seven of whom had mild cognitive impairment (MCI) or dementia. These exploratory findings suggest an age-related decrease or abnormality of StARD3 activity in human brain. Given that StARD3 is also involved in cholesterol transportation, a process that is aberrant in neurodegenerative diseases, the potential protective function of lutein against these diseases remains to be explored.

An exploratory study evaluating the effects of macular carotenoid supplementation in various retinal diseases

Purpose

The aim of this study was to assess the impact of daily oral supplementation with Macushield (10 mg/d meso-zeaxanthin, 10 mg/d lutein, and 2 mg/d zeaxanthin) on eye health in patients with retinal diseases by assessing the macular pigment (MP) profile, the visual function, and the quality of life.

Methods

Fifty-one patients with various retinal diseases were supplemented daily and followed up for 6 months. The MP optical density was measured using the customized heterochromatic flicker photometry and dual-wavelength autofluorescence. Visual function was evaluated by assessing the change in best corrected visual acuity, contrast sensitivity, and glare sensitivity in mesopic and photopic conditions. Vision-related and general quality of life changes were determined using the National Eye Insititute- Visual Function Questionnaire-25 (NEI-VFQ-25) and EuroQoL-5 dimension questionnaires.

Results

A statistically significant increase in the MP optical density was observed using the dual-wavelength autofluorescence (P=0.04) but not with the customized heterochromatic flicker photometry. Statistically significant (P<0.05) improvements in glare sensitivity in low and medium spatial frequencies were observed at 3 months and 6 months. Ceiling effects confounded other visual function tests and quality of life changes.

Conclusion

Supplementation with the three carotenoids enhances certain aspects of visual performance in retinal diseases.

Lutein suppresses inflammatory responses through Nrf2 activation and NF-κB inactivation in lipopolysaccharide-stimulated BV-2 microglia

SCOPE

In this study, the effects of lutein on neuroinflammation in lipopolysaccharide (LPS)-activated BV-2 microglia were investigated.

METHODS AND RESULTS

The production of proinflammatory cytokines tumor necrosis factor-α, interleukin-1β, and nitric oxide was measured in culture medium using enzyme immunoassay and Griess reagent, respectively. The expression of proteins was determined using Western blot. Pretreatment with lutein (50 μM) prior to LPS (1 μg/mL, 12 h) stimulation resulted in a significant inhibition of inducible nitric oxide synthase and cyclooxygenase-2 expression, as well as tumor necrosis factor-α, interleukin-1β, and nitric oxide production (p < 0.05). Further experiments demonstrated that lutein suppressed LPS-induced NF-κB activation by inhibiting the phosphorylation of p38 kinase, c-Jun N-terminal kinase (JNK), and Akt kinase (p < 0.05). Moreover, lutein markedly quenched reactive oxygen species and promoted antioxidant protein expression including heme oxygenase-1 and

NAD(P)H

quinone oxidoreductase by enhancing the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) mediated NF-E2-related factor 2 (Nrf2) activation (p < 0.05).

CONCLUSION

These results suggest that lutein attenuates neuroinflammation in LPS-activated BV-2 microglia partly through inhibiting p38-, JNK-, and Akt-stimulated NF-κB activation and promoting ERK-induced Nrf2 activation, suggesting that lutein has great potential as a nutritional preventive strategy in inflammation-related neurodegenerative disorders.

Surface plasmon resonance (SPR)-based biosensor technology for the quantitative characterization of protein-carotenoid interactions

The surface plasmon resonance (SPR) biosensor method is a highly sensitive, label-free technique to study the non-covalent interactions of biomolecules, especially protein-protein and protein-small molecule interactions. We have explored this robust biosensor platform to study the interactions of carotenoid-binding proteins and their carotenoid ligands to assess the specificity of interaction, kinetics, affinity, and stoichiometry. These characterizations are important to further study uptake and transport of carotenoids to targeted tissues such as the macula of the human eye. In this review, we present an overview of the SPR method and optimization of assay conditions, and we discuss the particular challenges in studying carotenoid-protein interactions using SPR.

Effect of supplemental lutein and zeaxanthin on serum, macular pigmentation, and visual performance in patients with early age-related macular degeneration

Purpose. To compare the 2-year effect of multiple doses of lutein/zeaxanthin on serum, macular pigmentation, and visual performance on patients with early age-related macular degeneration (AMD). Methods. In this randomized, double-blinded, and placebo-controlled trial, 112 early AMD patients randomly received either 10 mg lutein, 20 mg lutein, a combination of lutein (10 mg) and zeaxanthin (10 mg), or placebo daily for 2 years. Serum concentration of lutein/zeaxanthin, macular pigment optical density (MPOD), visual functions including best-spectacle corrected visual acuity (BCVA), contrast sensitivity (CS), flash recovery time (FRT), and vision-related quality of life (VFQ25) was quantified. Results. Serum lutein concentration and MPOD significantly increased in all the active treatment groups. Supplementation with 20 mg lutein was the most effective in increasing MPOD and CS at 3 cycles/degree for the first 48 weeks. However, they both significantly increased to the same peak value following supplementation with either 10 mg or 20 mg lutein during the intervention. No statistical changes of BCVA or FRT were observed during the trial. Conclusions. Long-term lutein supplementation could increase serum lutein concentration, MPOD, and visual sensitivities of early AMD patients. 10 mg lutein daily might be an advisable long-term dosage for early AMD treatment.

Nutritional supplements in age-related macular degeneration

Age-related macular degeneration (AMD) is the most frequent cause of blindness in the Western World. While with new therapies that are directed towards vascular endothelial growth factor (VEGF), a potentially efficient treatment option for the wet form of the disease has been introduced, a therapeutic regimen for dry AMD is still lacking. There is evidence from several studies that oral intake of supplements is beneficial in preventing progression of the disease. Several formulations of micronutrients are currently available. The present review focuses on the role of supplements in the treatment and prevention of AMD and sums up the current knowledge about the most frequently used micronutrients. In addition, regulatory issues are discussed, and future directions for the role of supplementation in AMD are highlighted.

Recent progress in molecular genetic studies on the carotenoid transport system using cocoon-color mutants of the silkworm

The existence of tissue-specific delivery for certain carotenoids is supported by genetic evidence from the silkworm Bombyx mori and the identification of cocoon color mutant genes, such as Yellow blood (Y), Yellow cocoon (C), and Flesh cocoon (F). Mutants with white cocoons are defective in one of the steps involved in transporting carotenoids from the midgut lumen to the middle silk gland via the hemolymph lipoprotein, lipophorin, and the different colored cocoons are caused by the accumulation of specific carotenoids into the middle silk gland. The Y gene encodes carotenoid-binding protein (CBP), which is expected to function as the cytosolic transporter of carotenoids across the enterocyte and epithelium of the middle silk gland. The C and F genes encode the C locus-associated membrane protein, which is homologous to a mammalian high-density lipoprotein receptor-2 (Cameo2) and scavenger receptor class B member 15 (SCRB15), respectively; these membrane proteins are expected to function as non-internalizing lipophorin receptors in the middle silk gland. Cameo2 and SCRB15 belong to the cluster determinant 36 (CD36) family, with Cameo2 exhibiting specificity not only for lutein, but also for zeaxanthin and astaxanthin, while SCRB15 seems to have specificity toward carotene substrates such as α-carotene and β-carotene. These findings suggest that Cameo2 and SCRB15 can discriminate the chemical structure of lutein and β-carotene from circulating lipophorin during uptake. These data provide the first evidence that CD36 family proteins can discriminate individual carotenoid molecules in lipophorin.

Photo-damage, photo-protection and age-related macular degeneration

The course of Age-related Macular Degeneration (AMD) is described as the effect of light (400–580 nm) on various molecular targets in photoreceptors and the retinal pigment epithelium (RPE). Photo-damage is followed by inflammation, increasing oxidative stress and, probably, unveiling new photosensitive molecules.

Solubilization and stabilization of macular carotenoids by water soluble oligosaccharides and polysaccharides

Xanthophyll carotenoids zeaxanthin and lutein play a special role in the prevention and treatment of visual diseases. These carotenoids are not produced by the human body and must be consumed in the diet. On the other hand, extremely low water solubility of these carotenoids and their instability restrict their practical application as components of food or medicinal formulations. Preparation of supramolecular complexes of zeaxanthin and lutein with glycyrrhizic acid, its disodium salt and the natural polysaccharide arabinogalactan allows one to minimize the aforementioned disadvantages when carotenoids are used in food processing as well as for production of therapeutic formulations with enhanced solubility and stability. In the present study, the formation of supramolecular complexes was investigated by NMR relaxation, surface plasmon resonance (SPR) and optical absorption techniques. The complexes increase carotenoid solubility more than 1000-fold. The kinetics of carotenoid decay in reactions with ozone molecules, hydroperoxyl radicals and metal ions were measured in water and organic solutions, and significant increases in oxidation stability of lutein and zeaxanthin in arabinogalactan and glycyrrhizin complexes were detected.

The Effect of BCMO1 Gene Variants on Macular Pigment Optical Density in Young Healthy Caucasians

Background: Serum lutein (L) and zeaxanthin (Z) positively correlate with macular pigment optical density (MPOD); hence, the latter is a valuable indirect tool for measuring L and Z content in the macula. L and Z have been attributed antioxidant capacity and protection from certain retinal diseases but their uptake within the eye is thought to depend on genetic, age, and environmental factors. In particular, gene variants within beta-carotene monooxygenase (BCMO1) are thought to modulate MPOD in the macula.

Objectives: To determine the effect of BCMO1 single nucleotide polymorphisms (SNPs) rs11645428, rs6420424, and rs6564851 on MPOD in a cohort of young healthy participants of Caucasian origin with normal ocular health.

Design: In this cohort study, MPOD was assessed in 46 healthy participants (22 male and 24 female) with a mean age of 23.8 ± 4.0 years (range 19–33). The three SNPs, rs11645428, rs6420424, rs6564851 that have established associations with MPOD were determined using MassEXTEND (hME) Sequenom assay. One-way analysis of variance was performed on groups segregated into homozygous and heterozygous BCMO1 genotypes. Correlations between body mass index (BMI), iris color, gender, central retinal thickness (CRT), diet, and MPOD were investigated.

Results: Macular pigment optical density neither significantly varied with BCMO1 rs11645428 (F_2,41 = 0.70, p = 0.503), rs6420424 (F_2,41 = 0.21, p = 0.801) nor rs6464851 homozygous or heterozygous genotypes (F_2,41 = 0,13, p = 0.88), in this young healthy cohort. The combination of these three SNPs into triple genotypes based on plasma conversion efficiency did not affect MPOD (F_2,41 = 0.07, p = 0.9). There was a significant negative correlation with MPOD and CRT (r = −0.39, p = 0.01) but no significant correlation between BMI, iris color, gender, and MPOD.

Conclusion: Our results indicate that macular pigment deposition within the central retina is not dependent on BCMO1 gene variants in young healthy people. We propose that MPOD is saturated in younger persons and/or other gene variant combinations determine its deposition.

Macular telangiectasia--changes in macular pigment optical density during a 5-year follow-up

PURPOSE

To quantitatively analyze the distribution of macular pigment (MP) over a period of 5 years and for monitoring progression of macular telangiectasia.

METHODS

Macular pigment concentration (autofluorescence, excitation wavelengths: 488 and 514 nm) was determined at baseline and after 5 years in 43 eyes of 22 subjects (46-80 years; mean, 65.6 years; 10 men) participating in the macular telangiectasia project.

RESULTS

Mean MP density at 0.5° declined in the segment (one eighth of a circle) with the highest MP optical density (-0.04 density units; P= 0.015), where density units (DU), and also averaged in the 2 segments that divided segments with detectable MP from those in which MP was no longer detectable (-0.04 density units; P = 0.0005). In the first segment mentioned, 2° values decreased to a lesser extent and not significantly. The diameter of MP loss expanded horizontally from 2.64 mm to 2.74 mm (P = 0.0001) but not vertically. Macular pigment density in the "halo" of peripheral MP at a mean of 5.44° (4.53-6.21°) increased (+0.01 DU; P= 0.01).

CONCLUSION

Five years of follow-up resulted in central (0.5°) reduction and peripheral (4.53-6.21°) accumulation of MP. Longer period of follow-up may disclose significant changes in paracentral locations. The area of central MP loss expands in particular in a horizontal direction and less vertically. Centrifugal movement of MP during disease may explain our findings.

Macular xanthophylls, lipoprotein-related genes, and age-related macular degeneration

Plant-based macular xanthophylls (MXs; lutein and zeaxanthin) and the lutein metabolite meso-zeaxanthin are the major constituents of macular pigment, a compound concentrated in retinal areas that are responsible for fine-feature visual sensation. There is an unmet need to examine the genetics of factors influencing regulatory mechanisms and metabolic fates of these 3 MXs because they are linked to processes implicated in the pathogenesis of age-related macular degeneration (AMD). In this work we provide an overview of evidence supporting a molecular basis for AMD-MX associations as they may relate to DNA sequence variation in AMD- and lipoprotein-related genes. We recognize a number of emerging research opportunities, barriers, knowledge gaps, and tools offering promise for meaningful investigation and inference in the field. Overviews on AMD- and high-density lipoprotein (HDL)-related genes encoding receptors, transporters, and enzymes affecting or affected by MXs are followed with information on localization of products from these genes to retinal cell types manifesting AMD-related pathophysiology. Evidence on the relation of each gene or gene product with retinal MX response to nutrient intake is discussed. This information is followed by a review of results from mechanistic studies testing gene-disease relations. We then present findings on relations of AMD with DNA sequence variants in MX-associated genes. Our conclusion is that AMD-associated DNA variants that influence the actions and metabolic fates of HDL system constituents should be examined further for concomitant influence on MX absorption, retinal tissue responses to MX intake, and the capacity to modify MX-associated factors and processes implicated in AMD pathogenesis.

Effect of age and other factors on macular pigment optical density measured with resonance Raman spectroscopy

BACKGROUND

Macular pigment is a defense system against phototoxic damage of the retina by visible light. It is still under debate whether or not macular pigment optical density (MPOD) levels decline with age, because the age effect varied depending on the technique used to measure MPOD levels. Resonance Raman spectroscopy (RRS) is an objective method to measure MPOD, and studies using RRS showed a drastic age-related decline of MPOD levels; however, since RRS measurements are influenced by cataracts, it has been argued that the age-related decline of RRS measurements is an artifact from lens changes in aged subjects. In the present study, MPOD levels were measured with RRS in pseudophakic eyes, and the effects of age and other factors on MPOD levels were investigated.

METHODS

The subjects included 144 patients with no fundus disorders who received cataract surgery with untinted intraocular lens implantation. MPOD levels were measured in 144 eyes using integral RRS 1 day post surgery. Factors potentially associated with MPOD levels such as age, gender, smoking habits, body mass index, diabetes, glaucoma, axial length, pupil diameter, spherical equivalent refractive error, and foveal thickness were examined by multiple regression analysis.

RESULTS

The macular pigment RRS levels ranged from 776 to 11,815 Raman counts, with an average level of 4,375 ± 1,917 (standard deviation [SD]) Raman counts. Multiple regression analysis revealed that age and axial length were significantly correlated with low MPOD values (regression coefficient of -59 for age and -404 for axial length, respectively). No significant correlations were observed for other factors.

CONCLUSIONS

After removing the potentially confounding effect of age-related lens yellowing on the RRS measurements, age remained a significant patient parameter for lowered MPOD levels. MPOD levels were found to decline by more than 10 % each decade. Axial length was also a negative predictor of MPOD levels. Since the present study included only patients aged 50 years and older, the effects of age and other factors on MPOD levels for younger subjects remain unknown.

Photochemical and optical properties of water-soluble xanthophyll antioxidants: aggregation vs complexation

Xanthophyll carotenoids can self-assemble in aqueous solution to form J- and H-type aggregates. This feature significantly changes the photophysical and optical properties of these carotenoids, and has an impact on solar energy conversion and light induced oxidative damage. In this study we have applied EPR and optical absorption spectroscopy to investigate how complexation can affect the aggregation ability of the xanthophyll carotenoids zeaxanthin, lutein, and astaxanthin, their photostability, and antioxidant activity. It was shown that complexation with the polysaccharide arabinogalactan (AG) polymer matrix and the triterpene glycoside glycyrrhizin (GA) dimer reduced the aggregation rate but did not inhibit aggregation completely. Moreover, these complexants form inclusion complexes with both monomer and H-aggregates of carotenoids. H-aggregates of carotenoids exhibit higher photostability in aqueous solutions as compared with monomers, but much lower antioxidant activity. It was found that complexation increases the photostability of both monomers and the aggregates of xanthophyll carotenoids. Also their ability to trap hydroperoxyl radicals increases in the presence of GA as the GA forms a donutlike dimer in which the hydrophobic polyene chain of the xanthophylls and their H-aggregates lies protected within the donut hole, permitting the hydrophilic ends to be exposed to the surroundings.

Carotenoids as possible interphotoreceptor retinoid-binding protein (IRBP) ligands: a surface plasmon resonance (SPR) based study

Uptake, transport and stabilization of xanthophylls in the human retina are important components of a complex multistep process that culminates in a non-uniform distribution of these important nutrients in the retina. The process is far from understood; here, we consider the potential role of interphotoreceptor retinoid-binding protein (IRBP) in this process. IRBP is thought to facilitate the exchange of 11-cis-retinal, 11-cis-retinol and all-trans-retinol between the retinal pigment epithelium (RPE), photoreceptors and Müller cells in the visual cycle. Structural and biochemical studies suggest that IRBP has a variety of nonequivalent ligand binding sites that function in this process. IRBP is multifunctional, being able to bind a variety of physiologically significant molecules including fatty acids in the subretinal space. This wide range of binding activities is of particular interest because it is unknown whether the lutein and zeaxanthin found in the macula originate from the choroidal or retinal circulations. If from the choroidal circulation, then IRBP is a likely mediator for their transport across the interphotoreceptor matrix. In this report, we explore the binding interactions of retinoids, fatty acids, and carotenoids with IRBP using surface plasmon resonance (SPR)-based biosensors. IRBP showed similar affinity toward retinoids and carotenoids (1-2 μM), while fatty acids had approximately 10 times less affinity. These results suggest that further studies should be carried out to evaluate whether IRBP has a physiologically relevant role in binding lutein and zeaxanthin in the interphotoreceptor matrix.