Efficacy of a Spearmint (Mentha spicata L.) Extract as Nutritional Support in a Rat Model of Hypertensive Glaucoma.

Purpose: Glaucoma is an eye-brain axis disorder characterized by loss of retinal ganglion cells (RGCs). Although the role of intraocular pressure (IOP) elevation in glaucoma has been established, the reduction of oxidative stress and inflammation has emerged as a promising target for neuronal tissue-supporting glaucoma management. Therefore, we evaluated the effect of a proprietary spearmint extract (SPE) on RGC density, activity, and neuronal health markers in a rat model of hypertensive glaucoma. Methods: Animals were divided in four groups: untreated healthy control and three glaucomatous groups receiving orally administered vehicle, SPE-low dose, or SPE-high dose for 28 days. Ocular hypertension was induced through intracameral injection of methylcellulose at day 15. At day 29, rats underwent electroretinogram (ERG) recordings, and retinas were analyzed for RGC density and markers of neural trophism, oxidative stress, and inflammation. Results: SPE exerted dose-dependent response benefits on all markers except for IOP elevation. SPE significantly improved RGC-related ERG responses, cell density, neurotrophins, oxidative stress, and inflammation markers. Also, in SPE-high rats, most of the parameters were not statistically different from those of healthy controls. Conclusions: SPE, a plant-based, polyphenolic extract, could be an effective nutritional support for neuronal tissues. Translational Relevance: These results suggest that SPE not only may be a complementary approach in support to hypotensive treatments for the management of glaucoma but may also serve as nutritional support in other ocular conditions where antioxidant, anti-inflammatory, and neuroprotective mechanism are often disrupted.

Liposome-Mediated Delivery Improves the Efficacy of Lisosan G against Retinopathy in Diabetic Mice.

Nutraceuticals are natural substances whose anti-oxidant and anti-inflammatory properties may be used to treat retinal pathologies. Their efficacy is limited by poor bioavailability, which could be improved using nanocarriers. Lisosan G (LG), a fermented powder from whole grains, protects the retina from diabetic retinopathy (DR)-induced damage. For this study, we tested whether the encapsulation of LG in liposomes (LipoLG) may increase its protective effects. Diabetes was induced in mice via streptozotocin administration, and the mice were allowed to freely drink water or a water dispersion of two different doses of LG or of LipoLG. Electroretinographic recordings after 6 weeks showed that only the highest dose of LG could partially protect the retina from diabetes-induced functional deficits, while both doses of LipoLG were effective. An evaluation of molecular markers of oxidative stress, inflammation, apoptosis, vascular endothelial growth factor, and the blood-retinal barrier confirmed that the highest dose of LG only partially protected the retina from DR-induced changes, while virtually complete prevention was obtained with either dose of LipoLG. These data indicate that the efficacy of LG in contrasting DR is greatly enhanced by its encapsulation in liposomes and may lay the ground for new dietary supplements with improved therapeutic effects against DR.

Restored retinal physiology after administration of niacin with citicoline in a mouse model of hypertensive glaucoma.

Introduction: Much interest has been addressed to antioxidant dietary supplements that are known to lower the risk of developing glaucoma or delay its progression. Among them, niacin and citicoline protect retinal ganglion cells (RGCs) from degeneration by targeting mitochondria, though at different levels. A well-established mouse model of RGC degeneration induced by experimental intraocular pressure (IOP) elevation was used to investigate whether a novel combination of niacin/citicoline has better efficacy over each single component in preserving RGC health in response to IOP increase. Methods: Ocular hypertension was induced by an intracameral injection of methylcellulose that clogs the trabecular meshwork. Electroretinography and immunohistochemistry were used to evaluate RGC function and density. Oxidative, inflammatory and apoptotic markers were evaluated by Western blot analysis. Results: The present results support an optimal efficacy of niacin with citicoline at their best dosage in preventing RGC loss. In fact, about 50% of RGCs were spared from death leading to improved electroretinographic responses to flash and pattern stimulation. Upregulated levels of oxidative stress and inflammatory markers were also consistently reduced by almost 50% after niacin with citicoline thus providing a significant strength to the validity of their combination. Conclusion: Niacin combined with citicoline is highly effective in restoring RGC physiology but its therapeutic potential needs to be further explored. In fact, the translation of the present compound to humans is limited by several factors including the mouse modeling, the higher doses of the supplements that are necessary to demonstrate their efficacy over a short follow up period and the scarce knowledge of their transport to the bloodstream and to the eventual target tissues in the eye.

Natural History of Glaucoma Progression in the DBA/2J Model: Early Contribution of Müller Cell Gliosis.

Glaucoma is a chronic optic neuropathy characterized by progressive degeneration of retinal ganglion cells (RGCs). Elevated intraocular pressure (IOP) and the resulting mechanical stress are classically considered the main causes of RGC death. However, RGC degeneration and ensuing vision loss often occur independent of IOP, indicating a multifactorial nature of glaucoma, with the likely contribution of glial and vascular function. The aim of the present study was to provide a comprehensive evaluation of the time course of neuro-glial-vascular changes associated with glaucoma progression. We used DBA/2J mice in the age range of 2-15 months as a spontaneous model of glaucoma with progressive IOP elevation and RGC loss typical of human open-angle glaucoma. We found that the onset of RGC degeneration at 10 months of age coincided with that of IOP elevation and vascular changes such as decreased density, increased lacunarity and decreased tight-junction protein zonula occludens (ZO)-1, while hypoxia-inducible factor (HIF)-1α and vascular endothelial growth factor (VEGF) were already significantly upregulated at 6 months of age together with the onset of Müller cell gliosis. Astrocytes, however, underwent significant gliosis at 10 months. These results indicate that Müller cell activation occurs well before IOP elevation, with probable inflammatory consequences, and represents an early event in the glaucomatous process. Early upregulation of HIF-1α and VEGF is likely to contribute to blood retinal barrier failure, facilitating RGC loss. The different time courses of neuro-glial-vascular changes during glaucoma progression provide further insight into the nature of the disease and suggest potential targets for the development of efficient therapeutic intervention aside from IOP lowering.

Meldonium Inhibits Cell Motility and Wound-Healing in Trabecular Meshwork Cells and Scleral Fibroblasts: Possible Applications in Glaucoma.

Meldonium (MID) is a synthetic drug designed to decrease the availability of L-carnitine-a main player in mitochondrial energy generation-thus modulating the cell pathways of energy metabolism. Its clinical effects are mostly evident in blood vessels during ischemic events, when the hyperproduction of endogenous carnitine enhances cell metabolic activities, leading to increased oxidative stress and apoptosis. MID has shown vaso-protective effects in model systems of endothelial dysfunction induced by high glucose or by hypertension. By stimulating the endothelial nitric oxide synthetase (eNOS) via PI3 and Akt kinase, it has shown beneficial effects on the microcirculation and blood perfusion. Elevated intraocular pressure (IOP) and endothelial dysfunction are major risk factors for glaucoma development and progression, and IOP remains the main target for its pharmacological treatment. IOP is maintained through the filtration efficiency of the trabecular meshwork (TM), a porous tissue derived from the neuroectoderm. Therefore, given the effects of MID on blood vessels and endothelial cells, we investigated the effects of the topical instillation of MID eye drops on the IOP of normotensive rats and on the cell metabolism and motility of human TM cells in vitro. Results show a significant dose-dependent decrease in the IOP upon topic treatment and a decrease in TM cell motility in the wound-healing assay, correlating with an enhanced expression of vinculin localized in focal adhesion plaques. Motility inhibition was also evident on scleral fibroblasts in vitro. These results may encourage a further exploration of MID eye drops in glaucoma treatment.

Increased efficacy of dietary supplement containing wax ester-rich marine oil and xanthophylls in a mouse model of dry macular degeneration.

Age-related macular degeneration (AMD) is nowadays considered among the retinal diseases whose clinical management lacks established treatment approaches, mainly for its atrophic (dry) form. In this respect, the use of dietary patterns enriched in omega-3 and antioxidant xanthophylls has emerged as a promising approach to counteract dry AMD progression although the prophylactic potential of omega-3 of fish origin has been discussed. Whether enriched availability of omega-3 and xanthophylls may increase the effectiveness of diet supplementation in preventing dry AMD remains to be fully established. The present study aims at comparing the efficacy of an existing orally administered formulation based on lutein and fish oil, as a source of omega-3, with a novel formulation providing the combination of lutein and astaxanthin with Calanus oil (COil), which contains omega-3 together with their precursors policosanols. Using a mouse model of dry AMD based on subretinal injection of polyethylene glycol (PEG)-400, we assessed the comparative efficacy of both formulations on PEG-induced major hallmarks including oxidative stress, inflammation, glial reactivity and outer retinal thickness. Dietary supplementation with both mixtures has been found to exert a significant antioxidant and anti-inflammatory activity as reflected by the overall amelioration of the PEG-induced pathological hallmarks. Noteworthy, the formulation based on COil appeared to be more protective than the one based on fish oil, presumably because of the higher bioavailability of omega-3 in COil. These results support the use of dietary supplements combining omega-3 and xanthophylls in the prevention and treatment of AMD and suggest that the source of omega-3 might contribute to treatment efficacy.

Dietary Supplementation of Antioxidant Compounds Prevents Light-Induced Retinal Damage in a Rat Model.

Light-induced retinal damage (LD) is characterized by the accumulation of reactive oxygen species leading to oxidative stress and photoreceptor cell death. The use of natural antioxidants has emerged as promising approach for the prevention of LD. Among them, lutein and cyanidin-3-glucoside (C3G) have been shown to be particularly effective due to their antioxidant and anti-inflammatory activity. However, less is known about the possible efficacy of combining them in a multicomponent mixture. In a rat model of LD, Western blot analysis, immunohistochemistry and electroretinography were used to demonstrate that lutein and C3G in combination or in a multicomponent mixture can prevent oxidative stress, inflammation, gliotic and apoptotic responses thus protecting photoreceptor cells from death with higher efficacy than each component alone. Combined efficacy on dysfunctional electroretinogram was also demonstrated by ameliorated rod and cone photoreceptor responses. These findings suggest the rationale to formulate multicomponent blends which may optimize the partnering compounds bioactivity and bioavailability.

Preventive Efficacy of an Antioxidant Compound on Blood Retinal Barrier Breakdown and Visual Dysfunction in Streptozotocin-Induced Diabetic Rats.

In diabetic retinopathy (DR), high blood glucose drives chronic oxidative stress and inflammation that trigger alterations of the neurovascular balance finally resulting in vascular abnormalities and retinal cell death, which converge towards altered electroretinogram (ERG). In the last years, a growing body of preclinical evidence has suggested that nutrients with anti-inflammatory/antioxidant properties can be able to hamper DR progression since its very early stages. In the present study, we used a streptozotocin-induced rat model of DR, which mimics most aspects of the early stages of human DR, to test the preventive efficacy of a novel compound containing cyanidin-3-glucoside (C3G), verbascoside and zinc as nutrients with antioxidant and anti-inflammatory properties. Western blot, immunofluorescence and electroretinographic analyses demonstrated a dose-dependent inhibition of oxidative stress- and inflammation-related mechanisms, with a significant counterpart in preventing molecular mechanisms leading to DR-associated vasculopathy and its related retinal damage. Preventive efficacy of the compound on dysfunctional a- and b-waves was also demonstrated by electroretinography. The present demonstration that natural compounds, possibly as a consequence of vascular rescue following ameliorated oxidative stress and inflammation, may prevent the apoptotic cascade leading to ERG dysfunction, adds further relevance to the potential application of antioxidants as a preventive therapy to counteract DR progression.