Brian M. Besch

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.

Retinal accumulation of zeaxanthin, lutein, and β-carotene in mice deficient in carotenoid cleavage enzymes

Abstract Carotenoid supplementation can prevent and reduce the risk of age‐related macular degeneration (AMD) and other ocular disease, but until now, there has been no validated and well‐characterized mouse model which can be employed to investigate the protective mechanism and relevant metabolism of retinal carotenoids. &bgr;‐Carotene oxygenases 1 and 2 (BCO1 and BCO2) are the only two carotenoid cleavage enzymes found in animals. Mutations of the bco2 gene may cause accumulation of xanthophyll carotenoids in animal tissues, and BCO1 is involved in regulation of the intestinal absorption of carotenoids. To determine whether or not mice deficient in BCO1 and/or BCO2 can serve as a macular pigment mouse model, we investigated the retinal accumulation of carotenoids in these mice when fed with zeaxanthin, lutein, or &bgr;‐carotene using an optimized carotenoid feeding method. HPLC analysis revealed that all three carotenoids were detected in sera, livers, retinal pigment epithelium (RPE)/choroids, and retinas of all of the mice, except that no carotenoid was detectable in the retinas of wild type (WT) mice. Significantly higher amounts of zeaxanthin and lutein accumulated in the retinas of BCO2 knockout (bco2‐/‐) mice and BCO1/BCO2 double knockout (bco1‐/‐/bco2‐/‐) mice relative to BCO1 knockout (bco1‐/‐) mice, while bco1‐/‐ mice preferred to take up &bgr;‐carotene. The levels of zeaxanthin and lutein were higher than &bgr;‐carotene levels in the bco1‐/‐/bco2‐/‐ retina, consistent with preferential uptake of xanthophyll carotenoids by retina. Oxidative metabolites were detected in mice fed with lutein or zeaxanthin but not in mice fed with &bgr;‐carotene. These results indicate that bco2‐/‐ and bco1‐/‐/bco2‐/‐ mice could serve as reasonable non‐primate models for macular pigment function in the vertebrate eye, while bco1‐/‐ mice may be more useful for studies related to &bgr;‐carotene. HighlightsBCO1 and BCO2 regulate carotenoid delivery into the mouse retina.Zeaxanthin and lutein are preferentially accumulated in the mouse retina.Bco2‐/‐ mice can serve as “macular pigment mice” in study of eye disease prevention.

Protein-Flavonoid Interaction Studies by a Taylor Dispersion Surface Plasmon Resonance (SPR) Technique: A Novel Method to Assess Biomolecular Interactions

Flavonoids are common polyphenolic compounds widely distributed in fruits and vegetables. These pigments have important pharmacological relevance because emerging research suggests possible anti-cancer and anti-inflammatory properties as well other beneficial health effects. These compounds are relatively hydrophobic molecules, suggesting the role of blood transport proteins in their delivery to tissues. In this study, we assess the binding interactions of four flavonoids (kaempferol, luteolin, quercetin, and resveratrol) with human serum albumin (HSA), the most abundant protein in the blood, and with glutathione S-transferase pi isoform-1 (GSTP1), an enzyme with well-characterized hydrophobic binding sites that plays an important role in detoxification of xenobiotics with reduced glutathione, using a novel Taylor dispersion surface plasmon resonance (SPR) technique. For the first time, HSA sites revealed a high-affinity binding site for flavonoid interactions. Out of the four flavonoids that we examined, quercetin and kaempferol showed the strongest equilibrium binding affinities (KD) of 63 ± 0.03 nM and 37 ± 0.07 nM, respectively. GSTP1 displayed lower affinities in the micromolar range towards all of the flavonoids tested. The interactions of flavonoids with HSA and GSTP1 were studied successfully using this novel SPR assay method. The new method is compatible with both kinetic and equilibrium analyses.

Association of Exfoliation Syndrome With Risk of Indirect Inguinal Hernia: The Utah Project on Exfoliation Syndrome

Importance Exfoliation syndrome (XFS) is a systemic connective tissue disease, and abnormal connective tissue metabolism is implicated in inguinal hernias (IH). Associating XFS with comorbid conditions may illuminate their underlying pathophysiology and affect clinical screening and treatment. Exfoliation syndrome involves altered systemic extracellular matrix (ECM) homeostasis involving elastin metabolism. Hernias occur owing to abnormal ECM synthesis, metabolism, or repair. Inguinal hernias involve weakening or rupture of the abdominal/groin wall. Objective To determine an association between patients with XFS and patients with IH in Utah, possibly differing between direct or indirect hernia. Design, Setting, and Participants Cross-sectional study in a large health care system of Utah hospitals and clinics. Conditional logistic regression odds ratios were used to estimate risk of XFS in patients with IH overall and by subtype (direct or indirect) compared with control individuals. Codes specific to direct and indirect IH with additional medical records review of 186 procedures were used to classify IH subtypes that were not prespecified. Bootstrap resampling with jackknife estimation used to calculate 95% confidence intervals. The model accounted for matching on sex and age and adjusted for body mass index and tobacco use. Population-based sample using medical records from 1996 to 2015 that identified 2594 patients 40 years or older on January 1, 1996, with surgical IH repair and 12 966 random control patients with no IH history matched 5:1 on sex and birth year. Data were analyzed between September 10, 2017, and October 23, 2017. Main Outcomes and Measures Exfoliation syndrome outcome defined by diagnosis codes for XFS or exfoliation glaucoma from 1996 to 2015. Results Participants were primarily white (2532 of 2594 patients, [96.1%]; 12 454 of 12 966 control individuals [97.6%]) and non-Hispanic (2396 of 2594 patients [92.4%]); 250 participants were women (9.6%). Of study participants, 22 patients with IH and 43 control individuals were diagnosed as having XFS, respectively. Patients with IH had a 2.3-fold risk for an XFS diagnosis compared with control individuals (95% CI, 1.4-3.5; P = .03), and XFS risk with indirect IH appeared especially pronounced. Conclusions and Relevance Inguinal hernia was associated with an increased risk of XFS in this Utah population. Further work is needed to understand the pathophysiology, genetics, and environmental factors contributing to both diseases.

Carotenoids and Age-Related Macular Degeneration

Abstract Carotenoids, specifically the xanthophylls lutein and zeaxanthin, are compounds typically found in fruits and dark leafy vegetables that are thought to provide a protective role in ocular health via their antioxidant properties as well as their ability to filter blue–violet light in the visible spectrum. The human macula contains a high content of these carotenoids that are concentrated by the action of specific binding proteins. These include StARD3, which binds lutein, and GSTP1, which binds zeaxanthin and its dietary metabolite meso-zeaxanthin. In the human macula, these three carotenoids are observed in an equal ratio. Studies on macular pigment optical density (MPOD) suggest the progression of diseases such as age-related macular degeneration (AMD) and cataract may be delayed by increased dietary carotenoid consumption and/or supplementation. Thus, quantifying and monitoring MPOD is important in tracking ocular health; several noninvasive measurement techniques have been developed, including heterochromatic flicker photometry and resonance Raman spectroscopy.