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.

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 (K_D) 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.

Carotenoid supplementation may reduce the risk of age-related macular degeneration (AMD). These retinal nutrients are hydrophobic molecules obtained from the diet that are transported to the retina through high-density lipoprotein (HDL) complexes. HDL cholesterol is a recognized biomarker for AMD risk. This study examined the effect of carotenoid supplementation on circulating HDL cholesterol levels. Serum lipid profiles were measured in 20 participants from the Lutein and Zeaxanthin in Pregnancy (L-ZIP) trial, which enrolled 40 pregnant women. In addition to standard prenatal supplements, half received 10 mg of lutein and 2 mg of zeaxanthin daily from the first trimester, and half received a placebo. Carotenoid supplementation significantly increased HDL cholesterol in the third trimester, with no changes in total cholesterol, LDL cholesterol, or triglycerides (TG) across trimesters. To further evaluate individual carotenoids, serum lipids were analyzed in macular pigment transgenic mice fed lutein, zeaxanthin, or β-carotene for one month. All three carotenoids significantly increased HDL cholesterol and reduced TG levels, with the effect ranking as zeaxanthin > lutein > β-carotene. These findings suggest that carotenoid supplementation modulates the serum lipid profile—elevating HDL cholesterol and lowering TG—which may contribute to protection against AMD and other lipid-associated diseases.