Lutein and zeaxanthin isomers may attenuate photo-oxidative retinal damage via modulation of G protein-coupled receptors and growth factors in rats

Zeaxanthin dipalmitate-enriched wolfberry extract improves vision in a mouse model of photoreceptor degeneration

Zeaxanthin dipalmitate (ZD) is a chemical extracted from wolfberry that protects degenerated photoreceptors in mouse retina. However, the pure ZD is expensive and hard to produce. In this study, we developed a method to enrich ZD from wolfberry on a production line and examined whether it may also protect the degenerated mouse retina. The ZD-enriched wolfberry extract (ZDE) was extracted from wolfberry by organic solvent method, and the concentration of ZD was identified by HPLC. The adult C57BL/6 mice were treated with ZDE or solvent by daily gavage for 2 weeks, at the end of the first week the animals were intraperitoneally injected with N-methyl-N-nitrosourea to induce photoreceptor degeneration. Then optomotor, electroretinogram, and immunostaining were used to test the visual behavior, retinal light responses, and structure. The final ZDE product contained ~30mg/g ZD, which was over 9 times higher than that from the dry fruit of wolfberry. Feeding degenerated mice with ZDE significantly improved the survival of photoreceptors, enhanced the retinal light responses and the visual acuity. Therefore, our ZDE product successfully alleviated retinal morphological and functional degeneration in mouse retina, which may provide a basis for further animal studies for possible applying ZDE as a supplement to treat degenerated photoreceptor in the clinic.

Antioxidants and Mechanistic Insights for Managing Dry Age-Related Macular Degeneration

Age-related macular degeneration (AMD) severely affects central vision due to progressive macular degeneration and its staggering prevalence is rising globally, especially in the elderly population above 55 years. Increased oxidative stress with aging is considered an important contributor to AMD pathogenesis despite multifaceted risk factors including genetic predisposition and environmental agents. Wet AMD can be managed with routine intra-vitreal injection of angiogenesis inhibitors, but no satisfactory medicine has been approved for the successful management of the dry form. The toxic carbonyls due to photo-oxidative degradation of accumulated bisretinoids within lysosomes initiate a series of events including protein adduct formation, impaired autophagy flux, complement activation, and chronic inflammation, which is implicated in dry AMD. Therapy based on antioxidants has been extensively studied for its promising effect in reducing the impact of oxidative stress. This paper reviews the dry AMD pathogenesis, delineates the effectiveness of dietary and nutrition supplements in clinical studies, and explores pre-clinical studies of antioxidant molecules, extracts, and formulations with their mechanistic insights.

Lutein Production and Extraction from Microalgae: Recent Insights and Bioactive Potential

Microalgae have been reported to be excellent producers of bioactive molecules. Lutein is a pigment reported to have various beneficial effects for humans, and especially for eye well-being. In the current review, we summarize various methods that have been developed to optimize its extraction and bioactivities reported for human health. Several protective effects have been reported for lutein, including antioxidant, anticancer, anti-inflammatory, and cardioprotective activity. This review also reports attempts to increase lutein production by microalgae by changing culturing parameters or by using pilot-scale systems. Genetic engineering lutein production is also discussed. Considering the increasing aging of the worldwide population will create an increased need for lutein, a viable economic and eco-sustainable method to produce lutein is needed to face this market demand.

Current applications of solid lipid nanoparticles and nanostructured lipid carriers as vehicles in oral delivery systems for antioxidant nutraceuticals: A review

Antioxidant nutraceuticals can be found in several dietary sources and have been utilized for various medical benefits including health promotion, disease prevention, and support for treatment of acute and/or chronic diseases. Nonetheless, there are some limitations in delivering antioxidants via oral administration such as low solubility and permeability, pH and enzyme degradation, and instability of the compounds along the gastrointestinal tract leading to low bioavailability. In order to tackle these challenges, the utilization of lipid nanoparticles has numerous advantages to the escalating delivery system of antioxidants in nutraceuticals across the gastrointestinal tract barrier. Nowadays, several types of lipid nanoparticles can be used in antioxidant nutraceutical delivery systems through the oral route, namely solid lipid nanoparticles and nanostructured lipid carriers. This review article aims to provide notable information on the importance and applications of lipid nanoparticles in antioxidant delivery systems from nutraceuticals by an oral route. The mechanism in enhancing antioxidant compound transport across the gastrointestinal tract can occur by elevating loading capacity, improving chemical and physical stability, and increasing its bioavailability. To date, lipid nanoparticle vehicles have been developed to improve the delivery of antioxidant compounds to enhance bioavailability via oral routes. Lipid nanoparticles have remarkable benefits in delivering antioxidant nutraceuticals via oral administration. Hence, scale-up and commercialization of antioxidant nutraceutical-loaded lipid nanoparticles have been a potential technology in recent years. Subsequently, several vegetable and natural oils with antioxidant activity can also be utilized for nanoparticle formulation lipid components to increase nutraceuticals' antioxidant properties and bioavailability.

Plant bioactive compounds alleviate photoinduced retinal damage and asthenopia: Mechanisms, synergies, and bioavailability

The retina, an important tissue of the eye, is essential in visual transmission and sustaining adequate eyesight. However, oxidative stress and inflammatory reactions can harm retinal structure and function. Recent studies have demonstrated that exposure to light can induce oxidative stress and inflammatory reactions in retinal cells, thereby facilitating the progression of retinal damage-related diseases and asthenopia. Plant bioactive compounds such as anthocyanin, curcumin, resveratrol, lutein, zeaxanthin, epigallocatechin gallate, and quercetin are effective in alleviating retinal damage and asthenopia. Their strong oxidation resistance and unique chemical structure can prevent the retina from producing reactive oxygen species and regulating eye muscle relaxation, thus alleviating retinal damage and asthenopia. Additionally, the combination of these active ingredients produces a stronger antioxidant effect. Consequently, understanding the mechanism of retinal damage caused by light and the regulation mechanism of bioactive compounds can better protect the retina and reduce asthenopia.

Lutein/Zeaxanthin Isomers and Quercetagetin Combination Safeguards the Retina from Photo-Oxidative Damage by Modulating Neuroplasticity Markers and the Nrf2 Pathway

Exposure to light-emitting diode (LED) light is a primary cause of retinal damage, resulting in vision loss. Several plant-derived substances, such as lutein and quercetagetin (QCG), show promise in supporting eye health. In this study, the impact of lutein/zeaxanthin (L/Z, Lutemax 2020) and QCG were evaluated individually and together in a rat model of LED-induced retinal damage. A total of 63 Wistar rats were allocated into nine groups (n = 7). For 28 days, the rats received L/Z (10 or 20 mg/kg BW), quercetin (QC, 20 mg/kg BW), QCG (10 or 20 mg/kg BW), or a mixture of different lutein and QCG dosages, after which they were exposed to LED light for 48 h. LED exposure led to a spike in serum malondialdehyde (MDA) and inflammatory cytokines, as well as an increase in retinal NF-κB, ICAM, GFAP, and MCP-1 levels (p < 0.0001 for all). It also reduced serum antioxidant enzyme activities and retinal Nrf2, HO-1, GAP43, NCAM, and outer nuclear layer (ONL) thickness (p < 0.0001 for all). However, administering L/Z and QCG, particularly a 1:1 combination of L/Z and QCG at 20 mg/kg, effectively reversed these changes. The treatment suppressed NF-κB, ICAM, GFAP, and MCP-1 while enhancing Nrf2, HO-1, GAP43, and NCAM and preventing ONL thickness reduction in LED-induced retinal damage rats. In conclusion, while LED light exposure caused retinal damage, treatment with L/Z, QC, and QCG, particularly a combined L/Z and QCG regimen, exhibited protective effects on the retina. This is possibly due to the modulation of neuroplasticity markers and nuclear transcription factors in the rats' retinal cells.

Transcriptome Analysis of Retinal and Choroidal Pathologies in Aged BALB/c Mice Following Systemic Neonatal Murine Cytomegalovirus Infection

Our previous studies have shown that systemic neonatal murine cytomegalovirus (MCMV) infection of BALB/c mice spread to the eye with subsequent establishment of latency in choroid/RPE. In this study, RNA sequencing (RNA-Seq) analysis was used to determine the molecular genetic changes and pathways affected by ocular MCMV latency. MCMV (50 pfu per mouse) or medium as control were injected intra-peritoneally (i.p.) into BALB/c mice at <3 days after birth. At 18 months post injection, the mice were euthanized, and the eyes were collected and prepared for RNA-Seq. Compared to three uninfected control eyes, we identified 321 differentially expressed genes (DEGs) in six infected eyes. Using the QIAGEN Ingenuity Pathway Analysis (QIAGEN IPA), we identified 17 affected canonical pathways, 10 of which function in neuroretinal signaling, with the majority of DEGs being downregulated, while 7 pathways function in upregulated immune/inflammatory responses. Retinal and epithelial cell death pathways involving both apoptosis and necroptosis were also activated. MCMV ocular latency is associated with upregulation of immune and inflammatory responses and downregulation of multiple neuroretinal signaling pathways. Cell death signaling pathways are also activated and contribute to the degeneration of photoreceptors, RPE, and choroidal capillaries.

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.

Inherited Retinal Dystrophies: Role of Oxidative Stress and Inflammation in Their Physiopathology and Therapeutic Implications

Inherited retinal dystrophies (IRDs) are a large group of genetically and clinically heterogeneous diseases characterized by the progressive degeneration of the retina, ultimately leading to loss of visual function. Oxidative stress and inflammation play fundamental roles in the physiopathology of these diseases. Photoreceptor cell death induces an inflammatory state in the retina. The activation of several molecular pathways triggers different cellular responses to injury, including the activation of microglia to eliminate debris and recruit inflammatory cells from circulation. Therapeutical options for IRDs are currently limited, although a small number of patients have been successfully treated by gene therapy. Many other therapeutic strategies are being pursued to mitigate the deleterious effects of IRDs associated with oxidative metabolism and/or inflammation, including inhibiting reactive oxygen species’ accumulation and inflammatory responses, and blocking autophagy. Several compounds are being tested in clinical trials, generating great expectations for their implementation. The present review discusses the main death mechanisms that occur in IRDs and the latest therapies that are under investigation.

Nerve Growth Factor Promotes Retinal Neurovascular Unit Repair: A Review

Purpose: The purpose of this paper is to investigate how the imbalance of neurogenic factor (NGF) and its precursor (pro-NGF) mediates structural and functional impairment of retinal neurovascular unit (RNVU) that plays a role in retinal degenerative diseases.Methods: A literature search of electronic databases was performed.Results: The pro-apoptotic effect of pro-NGF and the pro-growth effect of NGF are essential for the pathological and physiological activities of RNVU. Studies show that NGF-based treatment of retinal degenerative diseases, including glaucoma, age-related macular degeneration, retinitis pigmentosa, and diabetic retinopathy, has achieved remarkable efficacy.Conclusions: RNVU plays a complex and multifaceted role in retinal degenerative diseases. The exploration of the differential signaling expression of proNGF-NGF homeostasis under physiological and pathological conditions, and the corresponding pathological processes induced by its regulation, has prompted us to focus on earlier retinal neuroprotective therapeutic strategies to prevent retinal degenerative diseases.

Environmentally-driven metabolite and lipid variations correspond to altered bioactivities of black wolfberry fruit

Black wolfberry is a commonly cultivated woody plant in China, and is rich in nutrients that are beneficial for human. To characterize the endogenous metabolite differences among black wolfberry fruits grown in different geographical regions, mass spectrometry-based metabolomic and lipidomic analyses were performed in black wolfberry grown in nine locations throughout five provinces in China, from which 204 primary and specialized metabolites, and 267 lipids were identified in their fruits. Three samples from Alxa Left Banner, Jinta, and Minqin showed dramatically altered metabolite profiles, displaying higher levels of phenolic acids, soluble sugars and flavonoids, but lower levels of tricarboxylic acid cycle intermediates and aromatic amino acids. Moreover, the lipid profile of the Alxa Left Banner sample was strikingly distinct from all other samples, with high levels of monogalactosyl diacylglycerol and sulfoquinovosyl diacylglycerol, which are positively correlated with their anti-inflammatory capacities. These findings thus prompt for further studies on black wolfberry fruit for their health benefits.

Therapeutic effect of Keap1-Nrf2-ARE pathway-related drugs on age-related eye diseases through anti-oxidative stress

Age-related eye diseases, including cataract, glaucoma, diabetic retinopathy (DR), and age-related macular degeneration (AMD), are the leading causes of vision loss in the world. Several studies have shown that the occurrence and development of these diseases have an important relationship with oxidative stress in the eye. The Keap1-Nrf2-ARE pathway is a classical pathway that resists oxidative stress and inflammation in the body. This pathway is also active in the development of age-related eye diseases. A variety of drugs have been shown to treat age-related eye diseases through the Keap1-Nrf2-ARE (Kelch-like ECH-Associating protein 1- nuclear factor erythroid 2 related factor 2-antioxidant response element) pathway. This review describes the role of oxidative stress in the development of age-related eye diseases, the function and regulation of the Keap1-Nrf2-ARE pathway, and the therapeutic effects of drugs associated with this pathway on age-related eye diseases.

Wolfberry-derived zeaxanthin dipalmitate delays retinal degeneration in a mouse model of retinitis pigmentosa through modulating STAT3, CCL2 and MAPK pathways

Retinitis pigmentosa (RP) is a group of inherited photoreceptor degeneration diseases that causes blindness without effective treatment. The pathogenesis of retinal degeneration involves mainly oxidative stress and inflammatory responses. Zeaxanthin dipalmitate (ZD), a wolfberry-derived carotenoid, has anti-inflammatory and anti-oxidative stress effects. Here we investigated whether these properties of ZD can delay the retinal degeneration in rd10 mice, a model of RP, and explored its underlying mechanism. One shot of ZD or control vehicle was intravitreally injected into rd10 mice on postnatal day 16 (P16). Retinal function and structure of rd10 mice were assessed at P25, when rods degenerate substantially, using a visual behavior test, multi-electrode-array recordings and immunostaining. Retinal pathogenic gene expression and regulation of signaling pathways by ZD were explored using transcriptome sequencing and western blotting. Our results showed that ZD treatment improved the visual behavior of rd10 mice and delayed the degeneration of retinal photoreceptors. It also improved the light responses of photoreceptors, bipolar cells and retinal ganglion cells. The expression of genes that are involved in inflammation, apoptosis and oxidative stress were up-regulated in rd10 mice, and were reduced by ZD. ZD further reduced the activation of two key factors, signal transducer and activator of transcription 3 and chemokine (C-C motif) ligand 2, down-regulated the expression of the inflammatory factor GFAP, and inhibited extracellular signal regulated protein kinases and P38, but not the JNK pathways. In conclusion, ZD delays the degeneration of the rd10 retina both morphologically and functionally. Its anti-inflammatory function is mediated primarily through the signal transducer and activator of transcription 3, chemokine (C-C motif) ligand 2 and MAPK pathways. Thus, ZD may serve as a potential clinical candidate to treat RP.

Different Doses of β-Cryptoxanthin May Secure the Retina from Photooxidative Injury Resulted from Common LED Sources

Retinal damage associated with loss of photoreceptors is a hallmark of eye diseases such as age-related macular degeneration (AMD) and diabetic retinopathy. Potent nutritional antioxidants were previously shown to abate the degenerative process in AMD. β-Cryptoxanthin (BCX) is an essential dietary carotenoid with antioxidant, anti-inflammatory, and provitamin A activity. It is a potential candidate for developing intervention strategies to delay the development/progression of AMD. In the current study, the effect of a novel, highly purified BCX oral formulation on the rat retinal damage model was evaluated. Rats were fed with BCX for four weeks at the doses of 2 and 4 mg/kg body weight in the form of highly bioavailable oil suspension, followed by retinal damage by exposing to the bright light-emitting diode (LED) light (750 lux) for 48 hrs. Animals were sacrificed after 48 hours, and eyes and blood samples were collected and analyzed. BCX supplementations (2 and 4 mg/kg) showed improvements in the visual condition as demonstrated by histopathology of the retina and measured parameters such as total retinal thickness and outer nuclear layer thickness. BCX supplementation helped reduce the burden of oxidative stress as seen by decreased serum and retinal tissue levels of malondialdehyde (MDA) and restored the antioxidant enzyme activities in BCX groups. Further, BCX supplementation modulated inflammatory markers (IL-1β, IL-6, and NF-κB), apoptotic proteins (Bax, Bcl-2, caspase 3), growth proteins and factors (GAP43, VEGF), glial and neuronal proteins (GFAP, NCAM), and heme oxygenase-1 (HO-1), along with the mitochondrial stress markers (ATF4, ATF6, Grp78, Grp94) in the rat retinal tissue. This study indicates that oral supplementation of BCX exerts a protective effect on light-induced retinal damage in the rats via reducing oxidative stress and inflammation, also protected against mitochondrial DNA damage and cellular death.

Microglia Activation and Inflammation During the Death of Mammalian Photoreceptors

Photoreceptors are highly specialized sensory neurons with unique metabolic and physiological requirements. These requirements are partially met by Müller glia and cells of the retinal pigment epithelium (RPE), which provide essential metabolites, phagocytose waste, and control the composition of the surrounding microenvironment. A third vital supporting cell type, the retinal microglia, can provide photoreceptors with neurotrophic support or exacerbate neuroinflammation and hasten neuronal cell death. Understanding the physiological requirements for photoreceptor homeostasis and the factors that drive microglia to best promote photoreceptor survival has important implications for the treatment and prevention of blinding degenerative diseases like retinitis pigmentosa and age-related macular degeneration.