Effect of Antioxidant Supplementation on Macular Pigment Optical Density and Visual Functions: A Systematic Review and Network Meta-Analysis of Randomized Controlled Trials

Antioxidants are bioactive molecules that function to scavenge free radicals and balance oxidative stress. Although all antioxidants can act as reactive oxygen species scavengers, their efficacy on eye health may vary. Moreover, the comparative effectiveness and potential additive effect between groups of antioxidants, hitherto, have not been systematically studied. A systematic review and network meta-analysis were conducted to investigate the comparative or additive effect of dietary antioxidant supplements on eye health. Four databases (PubMed, Embase, CINAHL, and Cochrane) were searched, and relevant randomized controlled trials were identified. Out of 60 articles selected for systematic review, 38 were included in the network meta-analysis, categorized into 8 distinct antioxidant-supplemented groups and placebo. All groups significantly increased macular pigment optical density and contrast sensitivity at low spatial frequency, whereas only the antioxidant mixture + lutein (L) + fatty acid combination exhibited significant improvements in visual acuity (hazard ratio = -0.15; 95% confidence interval: -0.28, -0.02) and L + zeaxanthin combination for photostress recovery time (hazard ratio = -5.75; 95% confidence interval: -8.80, -1.70). Especially, the L + zeaxanthin + fatty acid combination was ranked best for macular pigment optical density (surface under the cumulative ranking: 99.3%) and second best for contrast sensitivity at low spatial frequency (67.7%). However, these findings should be interpreted with caution due to low quality of evidence, primarily influenced by indirectness and potential publication bias. Overall, antioxidant supplementation was estimated to improve eye health parameters, whereas different combinations of antioxidants may also have varying effects on improving visual health from multiple perspectives. This study was registered at PROSPERO as CRD42022369250.

Therapeutic Potential of Leaves from Fridericia chica (Bonpl.) L. G. Lohmann: Botanical Aspects, Phytochemical and Biological, Anti-Inflammatory, Antioxidant and Healing Action

Plants of the species Fridericia chica (Bonpl.) L. G. Lohmann (Bignoniaceae), which are widely distributed in Brazil and named crajiru in the state of Amazonas, are known in folk medicine as a traditional medicine in the form of a tea for the treatment of intestinal colic, diarrhea, and anemia, among other diseases. The chemical analysis of extracts of the leaves has identified phenolic compounds, a class of secondary metabolites that provide defense for plants and benefits to the health of humans. Several studies have shown the therapeutic efficacy of F. chica extracts, with antitumor, antiviral, wound healing, anti-inflammatory, and antioxidant activities being among the therapeutic applications already proven. The healing action of F. chica leaf extract has been demonstrated in several experimental models, and shows the ability to favor the proliferation of fibroblasts, which is essential for tissue repair. The anti-inflammatory activity of F. chica has been clearly demonstrated by several authors, who suggest that it is related to the presence of 3-deoxyanthocyanidins, which is capable of inhibiting pro-inflammatory pathways such as the kappa B (NF-kB) nuclear transcription factor pathway. Another important effect attributed to this species is the antioxidant effect, attributed to phenolic compounds interrupting chain reactions caused by free radicals and donating hydrogen atoms or electrons. In conclusion, the species Fridericia chica has great therapeutic potential, which is detailed in this paper with the objective of encouraging new research and promoting the sum of efforts for the inclusion of herbal medicines in health systems around the world.

A Rare Dirhamnosyl Flavonoid and Other Radical-Scavenging Metabolites from Cynophalla mollis (Kunth) J. Presl and Colicodendron scabridum (Kunt) Seem. (Capparaceae) of Ecuador

The phytochemistry of Cynophalla mollis (Kunth) J. Presl and Colicodendron scabridum (Kunth), both belonging to the family Capparaceae, were investigated in this study for the first time. Lupeol, betulin, lutein, stachydrine and quercetin-3,4'-di-O-rhamnoside were isolated from C. mollis, whereas C. scabridum afforded lupeol, lutein, stachydrine, β-sitosterol, stigmasterol, betonicine and narcissoside. All these compounds were purified by preparative liquid chromatography, in both open column and instrumental (MPLC) separation systems. Preparative TLC was also applied. They were all identified by ¹ H- and ¹³ C-NMR experiments. The complete structure of the very rare flavonoid quercetin-3,4'-di-O-rhamnoside was fully elucidated through DEPT-135, COSY, HMQC and HMBC experiments, together with UV/VIS and FT-IR spectrophotometry. Complete NMR data for quercetin-3,4'-di-O-rhamnoside in deuterated methanol were presented here for the first time. All the extracts did not exert antioxidant activity at the maximum tested dose of 1 mg/mL. Three out of the nine isolated compounds exerted a good spectrum of antioxidant capacity, being narcissoside the most active against ABTS radicals, with SC₅₀ =12.43 μM. It was followed by lutein and quercetin-3,4'-di-O-rhamnoside, with 40.92 μM and 46.10 μM, respectively.

Histopathological and Biochemical Assessment of Neuroprotective Effects of Sodium Valproate and Lutein on the Pilocarpine Albino Rat Model of Epilepsy

Epilepsy is one of the most frequent neurological disorders characterized by an enduring predisposition to generate epileptic seizures. Oxidative stress is believed to directly participate in the pathways of neurodegenerations leading to epilepsy. Approximately, one-third of the epileptic patients who suffer from seizures do not receive effective medical treatment. Sodium valproate (SVP) is a commonly used antiepileptic drug (AED); however, it has toxic effects. Lutein (L), a carotenoid, has potent antioxidant and anti-inflammatory properties. The aim of this study was to determine the neuroprotective effect of sodium valproate (SVP) and lutein (L) in a rat model of pilocarpine- (PLC-) induced epilepsy. To achieve this aim, fifty rats were randomly divided into five groups. Group I: control, group II: received PLC (400 mg/kg intraperitoneally), group III: received PLC + SVP (500 mg/kg orally), group IV: received PLC + SVP + L (100 mg/kg orally), and group V: received (PLC + L). Racine Scale (RC) and latency period to onset seizure were calculated. After eight weeks, the hippocampus rotarod performance and histological investigations were performed. Oxidative stress was investigated in hippocampal homogenates. Results revealed that SVP and L, given alone or in combination, reduced the RC significantly, a significant delay in latency to PLC-kindling onset, and improved rotarod performance of rats compared with the PLC group. Moreover, L was associated with a reduction of oxidative stress in hippocampal homogenate, a significant decrease in serum tumor necrosis factor-alpha (TNF-α) level, and inhibition of cerebral injury and displayed antiepileptic properties in the PLC-induced epileptic rat model. Data obtained from the current research elucidated the prominent neuroprotective, antioxidant, and anti-inflammatory activities of lutein in this model. In conclusion, lutein cotreatment with AEDs is likely to be a promising strategy to improve treatment efficacy in patients suffering from epilepsy.

Tauroursodeoxycholic Acid (TUDCA)-Lipid Interactions and Antioxidant Properties of TUDCA Studied in Model of Photoreceptor Membranes

Tauroursodeoxycholic acid (TUDCA), a hydrophilic bile acid containing taurine conjugated with the ursodeoxycholic acid (UDCA), has been known and used from ancient times as a therapeutic compound in traditional Chinese medicine. TUDCA has recently been gaining significant interest as a neuroprotective agent, also exploited in the visual disorders. Among several mechanisms of TUDCA's protective action, its antioxidant activity and stabilizing effect on mitochondrial and plasma membranes are considered. In this work we investigated antioxidant activity of TUDCA and its impact on structural properties of model membranes of different composition using electron paramagnetic resonance spectroscopy and the spin labeling technique. Localization of TUDCA molecules in a pure POPC bilayer has been studied using a molecular dynamics simulation (MD). The obtained results indicate that TUDCA is not an efficient singlet oxygen (1O2 (1Δg)) quencher, and the determined rate constant of its interaction with 1O2 (1Δg) is only 1.9 × 105 M-1s-1. However, in lipid oxidation process induced by a Fenton reaction, TUDCA reveals substantial antioxidant activity significantly decreasing the rate of oxygen consumption in the system studied. In addition, TUDCA induces slight, but noticeable changes in the polarity and fluidity of the investigated model membranes. The results of performed MD simulation correspond very well with the experimental results.

Anti-Apoptotic Effects of Carotenoids in Neurodegeneration

Apoptosis, programmed cell death type I, is a critical part of neurodegeneration in cerebral ischemia, Parkinson’s, and Alzheimer’s disease. Apoptosis begins with activation of pro-death proteins Bax and Bak, release of cytochrome c and activation of caspases, loss of membrane integrity of intracellular organelles, and ultimately cell death. Approaches that block apoptotic pathways may prevent or delay neurodegenerative processes. Carotenoids are a group of pigments found in fruits, vegetables, and seaweeds that possess antioxidant properties. Over the last several decades, an increasing number of studies have demonstrated a protective role of carotenoids in neurodegenerative disease. In this review, we describe functions of commonly consumed carotenoids including lycopene, β-carotene, lutein, astaxanthin, and fucoxanthin and their roles in neurodegenerative disease models. We also discuss the underlying cellular mechanisms of carotenoid-mediated neuroprotection, including their antioxidant properties, role as signaling molecules, and as gene regulators that alleviate apoptosis-associated brain cell death.

EPR Studies on the Properties of Model Photoreceptor Membranes Made of Natural and Synthetic Lipids

The membranes of retina photoreceptors have unique lipid composition. They contain a high concentration of polyunsaturated docosahexaenoic acid, with six double bonds, and are enriched in phosphatidylethanolamines. Based on their phospholipid composition and cholesterol content, membranes of photoreceptors can be divided into three types: plasma membrane, young disks membranes, and old disks membranes. High amount of docosahexaenoic acid, abundant illumination, and high respiratory demands make these membranes sensitive to oxidative stress and lipid peroxidation. Human retinas are not easily available for research, therefore most research is done on bovine retinas. However, to follow, in a controlled manner, the changes in membrane properties caused by different factors it seems advisable to apply carefully prepared models of photoreceptor membranes. Using synthetic lipids we prepared liposome models of three types of photoreceptor membranes, and by means of electron paramagnetic resonance spectroscopy and spin labeling technique we compared polarity and fluidity of those model membranes with the properties of membranes consisting of natural lipids extracted from photoreceptor outer segments of bovine retinas. Additionally, we studied the effect of oxidation on the membrane properties in the presence and in the absence of zeaxanthin, which is an antioxidant naturally present in the human retina. The results show that there are significant differences in polarity and fluidity between all investigated membranes, which reflect differences in their lipid composition. The properties of the membranes made of natural photoreceptor outer segment lipids are most similar to the ones of the models of old disks membranes. Oxidation did not change the membrane properties significantly; however, a slight ordering effect was observed in liposomes made of natural photoreceptor outer segment lipids and in the model of old disks membranes. Zeaxanthin affected polarity and fluidity mostly in the model of old disks membranes. The results show that by careful selection and appropriate proportions of lipid mixtures, it is possible to obtain synthetic membranes of the properties similar to the natural ones.

Can Xanthophyll-Membrane Interactions Explain Their Selective Presence in the Retina and Brain?

Epidemiological studies demonstrate that a high dietary intake of carotenoids may offer protection against age-related macular degeneration, cancer and cardiovascular and neurodegenerative diseases. Humans cannot synthesize carotenoids and depend on their dietary intake. Major carotenoids that have been found in human plasma can be divided into two groups, carotenes (nonpolar molecules, such as β-carotene, α-carotene or lycopene) and xanthophylls (polar carotenoids that include an oxygen atom in their structure, such as lutein, zeaxanthin and β-cryptoxanthin). Only two dietary carotenoids, namely lutein and zeaxanthin (macular xanthophylls), are selectively accumulated in the human retina. A third carotenoid, meso-zeaxanthin, is formed directly in the human retina from lutein. Additionally, xanthophylls account for about 70% of total carotenoids in all brain regions. Some specific properties of these polar carotenoids must explain why they, among other available carotenoids, were selected during evolution to protect the retina and brain. It is also likely that the selective uptake and deposition of macular xanthophylls in the retina and brain are enhanced by specific xanthophyll-binding proteins. We hypothesize that the high membrane solubility and preferential transmembrane orientation of macular xanthophylls distinguish them from other dietary carotenoids, enhance their chemical and physical stability in retina and brain membranes and maximize their protective action in these organs. Most importantly, xanthophylls are selectively concentrated in the most vulnerable regions of lipid bilayer membranes enriched in polyunsaturated lipids. This localization is ideal if macular xanthophylls are to act as lipid-soluble antioxidants, which is the most accepted mechanism through which lutein and zeaxanthin protect neural tissue against degenerative diseases.

Effects of lutein and chlorophyll b on GSH depletion and DNA damage induced by cisplatin in vivo

Recent studies have proposed the use of low concentrations of phytochemicals and combinations of phytochemicals in chemoprevention to reduce cytotoxicity and simulate normal ingestion through diet. The purpose of the present study was to evaluate whether the DNA damage, chromosome instability, and oxidative stress induced by cisplatin (cDDP) are modulated by a combination of the natural pigments lutein (LT) and chlorophyll b (CLb). The protective effects observed for synergism between phytochemicals have not been completely investigated. The comet assay and micronucleus test were performed and the catalase activities and glutathione (GSH) concentrations were measured in the peripheral blood, bone marrow, liver, and kidney cells of mice. The comet assay and micronucleus test results revealed that the pigments LT and CLb were not genotoxic or mutagenic and that the pigments presented antigenotoxic and antimutagenic effects in the different cell types evaluated. This protective effect is likely related to antioxidant properties in peripheral blood cells through the prevention of cDDP-induced GSH depletion. Altogether our results show that the combination of LT and CLb, which are both usually present in the same foods, such as leafy green vegetables, can be used safely.

Membrane composition and dynamics: a target of bioactive virgin olive oil constituents

The endogenous synthesis of lipids, which requires suitable dietary raw materials, is critical for the formation of membrane bilayers. In eukaryotic cells, phospholipids are the predominant membrane lipids and consist of hydrophobic acyl chains attached to a hydrophilic head group. The relative balance between saturated, monounsaturated, and polyunsaturated acyl chains is required for the organization and normal function of membranes. Virgin olive oil is the richest natural dietary source of the monounsaturated lipid oleic acid and is one of the key components of the healthy Mediterranean diet. Virgin olive oil also contains a unique constellation of many other lipophilic and amphipathic constituents whose health benefits are still being discovered. The focus of this review is the latest evidence regarding the impact of oleic acid and the minor constituents of virgin olive oil on the arrangement and behavior of lipid bilayers. We highlight the relevance of these interactions to the potential use of virgin olive oil in preserving the functional properties of membranes to maintain health and in modulating membrane functions that can be altered in several pathologies. This article is part of a Special Issue entitled: Membrane Structure and Function: Relevance in the Cell's Physiology, Pathology and Therapy.

Eye nutrition in context: mechanisms, implementation, and future directions

Carotenoid-based visual cues and roles of carotenoids in human vision are reviewed, with an emphasis on protection by zeaxanthin and lutein against vision loss, and dietary sources of zeaxanthin and lutein are summarized. In addition, attention is given to synergistic interactions of zeaxanthin and lutein with other dietary factors affecting human vision (such as antioxidant vitamins, phenolics, and poly-unsaturated fatty acids) and the emerging mechanisms of these interactions. Emphasis is given to lipid oxidation products serving as messengers with functions in gene regulation. Lastly, the photo-physics of light collection and photoprotection in photosynthesis and vision are compared and their common principles identified as possible targets of future research.