Neuroprotective Effect of Curcumin Against Oxidative Damage in BV-2 Microglia and High Intraocular Pressure Animal Model

Protective Effect of Curcumin on the Tight Junction Integrity and Cellular Senescence in Human Retinal Pigment Epithelium of Early Diabetic Retinopathy

Diabetic retinopathy (DR) is a secondary complication of diabetes that can lead to visual impairment and blindness. The retinal pigment epithelium (RPE) is a monolayer of pigment cells that forms the blood-retinal barrier (BRB) via tight junction (TJ) proteins and plays a crucial role in the physiological function of the retina. Hyperglycemia induces RPE death and BRB breakdown, which accelerates the process of DR. Curcumin, an active extract of Curcuma longa , has anti-inflammatory, antioxidant, antiapoptotic, and neuroprotective properties. However, the effect of Curcumin on the BRB under high glucose conditions remains unknown. This study aimed to investigate the protective effects of Curcumin on RPE physiology in vitro and in vivo . Curcumin significantly alleviated cell viability inhibition under high glucose conditions. Moreover, high glucose reduced extracellular signal-regulated kinase and Akt pathways activation to diminish RPE cell growth but reversed by Curcumin treatment. Curcumin protected not only TJ integrity but also retinoid regeneration through TJ proteins and isomerase modulation in diabetic retina. Furthermore, Curcumin decreased the expression of angiogenic factor to inhibit retinal neovascularization. Finally, Curcumin treatment markedly reduced apoptosis during hyperglycemia. In conclusion, Curcumin can alleviate the progression of DR by promoting RPE survival, TJ integrity, retinoid isomerase activity, RPE senescence inhibition, and neovascularization. Therefore, Curcumin exhibits high potential for use as a therapeutic agent for early DR.

Oxidative stress in the eye and its role in the pathophysiology of ocular diseases

Oxidative stress occurs through an imbalance between the generation of reactive oxygen species (ROS) and the antioxidant defense mechanisms of cells. The eye is particularly exposed to oxidative stress because of its permanent exposure to light and due to several structures having high metabolic activities. The anterior part of the eye is highly exposed to ultraviolet (UV) radiation and possesses a complex antioxidant defense system to protect the retina from UV radiation. The posterior part of the eye exhibits high metabolic rates and oxygen consumption leading subsequently to a high production rate of ROS. Furthermore, inflammation, aging, genetic factors, and environmental pollution, are all elements promoting ROS generation and impairing antioxidant defense mechanisms and thereby representing risk factors leading to oxidative stress. An abnormal redox status was shown to be involved in the pathophysiology of various ocular diseases in the anterior and posterior segment of the eye. In this review, we aim to summarize the mechanisms of oxidative stress in ocular diseases to provide an updated understanding on the pathogenesis of common diseases affecting the ocular surface, the lens, the retina, and the optic nerve. Moreover, we discuss potential therapeutic approaches aimed at reducing oxidative stress in this context.

Inhibition of NOX4 with GLX351322 alleviates acute ocular hypertension-induced retinal inflammation and injury by suppressing ROS mediated redox-sensitive factors activation

Reactive oxygen species (ROS) overproduction plays an essential role in the etiology of ischemic/hypoxic retinopathy caused by acute glaucoma. NADPH oxidase (NOX) 4 was discovered as one of the main sources of ROS in glaucoma. However, the role and potential mechanisms of NOX4 in acute glaucoma have not been fully elucidated. Therefore, the current study aims to investigate the NOX4 inhibitor GLX351322 that targets NOX4 inhibition in acute ocular hypertension (AOH)-induced retinal ischemia/hypoxia injury in mice. Herein, NOX4 was highly expressed in AOH retinas, particularly the retinal ganglion cell layer (GCL). Importantly, the NOX4 inhibitor GLX351322 reduced ROS overproduction, inhibited inflammatory factor release, suppressed glial cell activation and hyperplasia, inhibited leukocyte infiltration, reduced retinal cell senescence and apoptosis in damaged areas, reduced retinal degeneration and improved retinal function. This neuroprotective effect is at least partially associated with mediated redox-sensitive factor (HIF-1α, NF-κB, and MAPKs) pathways by NOX4-derived ROS overproduction. These results suggest that inhibition of NOX4 with GLX351322 attenuated AOH-induced retinal inflammation, cellular senescence, and apoptosis by inhibiting the activation of the redox-sensitive factor pathway mediated by ROS overproduction, thereby protecting retinal structure and function. Targeted inhibition of NOX4 is expected to be a new idea in the treatment of acute glaucoma.

Immunomodulatory and Antioxidant Drugs in Glaucoma Treatment

Glaucoma, a group of diseases characterized by progressive retinal ganglion cell loss, cupping of the optic disc, and a typical pattern of visual field defects, is a leading cause of severe visual impairment and blindness worldwide. Elevated intraocular pressure (IOP) is the leading risk factor for glaucoma development. However, glaucoma can also develop at normal pressure levels. An increased susceptibility of retinal ganglion cells to IOP, systemic vascular dysregulation, endothelial dysfunction, and autoimmune imbalances have been suggested as playing a role in the pathophysiology of normal-tension glaucoma. Since inflammation and oxidative stress play a role in all forms of glaucoma, the goal of this review article is to present an overview of the inflammatory and pro-oxidant mechanisms in the pathophysiology of glaucoma and to discuss immunomodulatory and antioxidant treatment approaches.

Oxidative Stress: A Suitable Therapeutic Target for Optic Nerve Diseases?

Optic nerve disorders encompass a wide spectrum of conditions characterized by the loss of retinal ganglion cells (RGCs) and subsequent degeneration of the optic nerve. The etiology of these disorders can vary significantly, but emerging research highlights the crucial role of oxidative stress, an imbalance in the redox status characterized by an excess of reactive oxygen species (ROS), in driving cell death through apoptosis, autophagy, and inflammation. This review provides an overview of ROS-related processes underlying four extensively studied optic nerve diseases: glaucoma, Leber's hereditary optic neuropathy (LHON), anterior ischemic optic neuropathy (AION), and optic neuritis (ON). Furthermore, we present preclinical findings on antioxidants, with the objective of evaluating the potential therapeutic benefits of targeting oxidative stress in the treatment of optic neuropathies.

Suppression of MAPK/NF-kB and activation of Nrf2 signaling by Ajugarin-I in EAE model of multiple sclerosis

Multiple sclerosis (MS) is a debilitating neurodegenerative autoimmune disease of the central nervous system (CNS). The current study aimed to investigate the neuroprotective properties of Ajugarin-I (Aju-I) against the experimental autoimmune encephalomyelitis (EAE) model of MS and explored the underlying mechanism involved. The protective potential of Aju-I was first confirmed against glutamate-induced HT22 cells and hydrogen peroxide (H₂ O₂ )-induced BV2 cells. Next, an EAE model has been established to investigate the mechanisms of MS and identify potential candidates for MS treatment. The behavioral results demonstrated that Aju-I post-immunization treatment markedly reduced the EAE-associated clinical score, motor impairment, and neuropathic pain. Evans blue and fluorescein isothiocyanate extravasation in the brain were markedly reduced by Aju-I. It effectively restored the EAE-associated histopathological changes in the brain and spinal cord. It markedly attenuated EAE-induced inflammation in the CNS by reducing the expression levels of p-38/JNK/NF-κB but increased the expression of IkB-α. It suppressed oxidative stress by increasing the expression of Nrf2 but decreasing the expression of keap-1. It suppressed EAE-induced apoptosis in the CNS by regulating Bax/Bcl-2 and Caspase-3 expression. Taken together, this study suggests that Aju-I treatment exhibits neuroprotective properties in the EAE model of MS via regulation of MAPK/NF-κB, Nrf2/Keap-1, and Bcl2/Bax signaling.

Nanoparticles for the treatment of glaucoma-associated neuroinflammation

Recently, a considerable amount of literature has emerged around the theme of neuroinflammation linked to neurodegeneration. Glaucoma is a neurodegenerative disease characterized by visual impairment. Understanding the complex neuroinflammatory processes underlying retinal ganglion cell loss has the potential to improve conventional therapeutic approaches in glaucoma. Due to the presence of multiple barriers that a systemically administered drug has to cross to reach the intraocular space, ocular drug delivery has always been a challenge. Nowadays, studies are focused on improving the current therapies for glaucoma by utilizing nanoparticles as the modes of drug transport across the ocular anatomical and physiological barriers. This review offers some important insights on the therapeutic advancements made in this direction, focusing on the use of nanoparticles loaded with anti-inflammatory and neuroprotective agents in the treatment of glaucoma. The prospect of these novel therapies is discussed in relation to the current therapies to alleviate inflammation in glaucoma, which are being reviewed as well, along with the detailed molecular and cellular mechanisms governing the onset and the progression of the disease.

Recent Progress in Research on Mechanisms of Action of Natural Products against Alzheimer's Disease: Dietary Plant Polyphenols

Alzheimer's disease (AD) is an incurable degenerative disease of the central nervous system and the most common type of dementia in the elderly. Despite years of extensive research efforts, our understanding of the etiology and pathogenesis of AD is still highly limited. Nevertheless, several hypotheses related to risk factors for AD have been proposed. Moreover, plant-derived dietary polyphenols were also shown to exert protective effects against neurodegenerative diseases such as AD. In this review, we summarize the regulatory effects of the most well-known plant-derived dietary polyphenols on several AD-related molecular mechanisms, such as amelioration of oxidative stress injury, inhibition of aberrant glial cell activation to alleviate neuroinflammation, inhibition of the generation and promotion of the clearance of toxic amyloid-β (Aβ) plaques, inhibition of cholinesterase enzyme activity, and increase in acetylcholine levels in the brain. We also discuss the issue of bioavailability and the potential for improvement in this regard. This review is expected to encourage further research on the role of natural dietary plant polyphenols in the treatment of AD.

Treatment of Glaucoma with Natural Products and Their Mechanism of Action: An Update

Glaucoma is one of the leading causes of irreversible blindness. It is generally caused by increased intraocular pressure, which results in damage of the optic nerve and retinal ganglion cells, ultimately leading to visual field dysfunction. However, even with the use of intraocular pressure-lowering eye drops, the disease still progresses in some patients. In addition to mechanical and vascular dysfunctions of the eye, oxidative stress, neuroinflammation and excitotoxicity have also been implicated in the pathogenesis of glaucoma. Hence, the use of natural products with antioxidant and anti-inflammatory properties may represent an alternative approach for glaucoma treatment. The present review highlights recent preclinical and clinical studies on various natural products shown to possess neuroprotective properties for retinal ganglion cells, which thereby may be effective in the treatment of glaucoma. Intraocular pressure can be reduced by baicalein, forskolin, marijuana, ginsenoside, resveratrol and hesperidin. Alternatively, Ginkgo biloba, Lycium barbarum, Diospyros kaki, Tripterygium wilfordii, saffron, curcumin, caffeine, anthocyanin, coenzyme Q10 and vitamins B3 and D have shown neuroprotective effects on retinal ganglion cells via various mechanisms, especially antioxidant, anti-inflammatory and anti-apoptosis mechanisms. Extensive studies are still required in the future to ensure natural products' efficacy and safety to serve as an alternative therapy for glaucoma.

Retinal ganglion cell loss in an ex vivo mouse model of optic nerve cut is prevented by curcumin treatment

Retinal ganglion cell (RGC) loss is a pathologic feature common to several retinopathies associated to optic nerve damage, leading to visual loss and blindness. Although several scientific efforts have been spent to understand the molecular and cellular changes occurring in retinal degeneration, an effective therapy to counteract the retinal damage is still not available. Here we show that eyeballs, enucleated with the concomitant optic nerve cut (ONC), when kept in PBS for 24 h showed retinal and optic nerve degeneration. Examining retinas and optic nerves at different time points in a temporal window of 24 h, we found a thinning of some retinal layers especially RGC's layer, observing a powerful RGC loss after 24 h correlated with an apoptotic, MAPKs and degradative pathways dysfunctions. Specifically, we detected a time-dependent increase of Caspase-3, -9 and pro-apoptotic marker levels, associated with a strong reduction of BRN3A and NeuN levels. Importantly, a powerful activation of JNK, c-Jun, and ERK signaling (MAPKs) were observed, correlated with a significant augmented SUMO-1 and UBC9 protein levels. The degradation signaling pathways was also altered, causing a significant decrease of ubiquitination level and an increased LC3B activation. Notably, it was also detected an augmented Tau protein level. Curcumin, a powerful antioxidant natural compound, prevented the alterations of apoptotic cascade, MAPKs, and SUMO-1 pathways and the degradation system, preserving the RGC survival and the retinal layer thickness. This ex vivo retinal degeneration model could be a useful method to study, in a short time window, the effect of neuroprotective tools like curcumin that could represent a potential treatment to contrast retinal cell death.

Nutritional supplementation in the prevention and treatment of Glaucoma

Glaucoma is a chronic optic neuropathy that creates a significant burden on public health. Oxidative stress is hypothesised to play a role to glaucoma progression, and its reduction is being analysed as a therapeutic target. Dietary antioxidants play a crucial role in helping provide insight into this hypothesis. We reviewed 71 trials, interventional, I -vivo and I -vitro, including 11 randomised controlled trials, to determine if adjunctive nutritional supplementation could lead to a reduction in oxidative stress and prevent glaucomatous progression. Many laboratory findings show that vitamins and natural compounds contain an abundance of intrinsic antioxidative, neuroprotective and vasoprotective properties that show promise in the treatment and prevention of glaucoma. Although there is encouraging early evidence, most clincial findings are inconclusive. The group of B vitamins appear to have the greatest amount of evidence. Other compounds such as flavonoids, carotenoids, curcumin, saffron, CoQ10, Ggngko Biloba and Resveratrol however warrant further investigation in glaucoma patients. Studies of these antioxidants and other nutrients could create adjunctive or alternative preventative and treatment modalities for glaucoma to those currently available.

Withametelin, a novel phytosterol, alleviates neurological symptoms in EAE mouse model of multiple sclerosis via modulation of Nrf2/HO-1 and TLR4/NF-κB signaling

Multiple Sclerosis (MS) is a chronic inflammatory demyelinating disorder of the central nervous system (CNS) that remains incurable. Withametelin (WMT), a phytosterol, showed diverse biological activities isolated from the leaves of Datura innoxa. In the present study, we used an in vitro model of HT22 and BV-2 cell lines and an in vivo murine model of MS, experimental autoimmune encephalomyelitis (EAE), to explore the antioxidant and anti neuroinflammatory potential of WMT. The results showed that pretreatment with WMT markedly inhibited H₂O₂-induced cytotoxicity and oxidative stress in a dose-dependent manner. Correspondingly, WMT post-immunization treatment significantly attenuated EAE-induced clinical score, weight loss, neuropathic pain behaviors, and motor dysfunction. It markedly lowers EAE-induced elevated circulating leucocytes, spinal deformity, and splenomegaly. It strikingly inhibited the Evans blue and FITC extravasation in the brain. It remarkably reversed the EAE-induced histopathological alteration of the brain, spinal cord, eye, and optic nerve. It significantly intensified the antioxidant defense mechanism by improving the expression level of nuclear factor-erythroid-related factor-2 (Nrf2), heme-oxygenase-1 (HO-1) but reducing the expression level of the Kelch-like-ECH-associated-protein-1 (keap-1), inducible-nitric-oxide-synthase (iNOS) in the CNS. Likewise, it markedly suppressed neuroinflammation by reducing the expression level of toll-like-receptor 4 (TLR4), nuclear-factor-kappa-B (NF-κB), activator-protein-1 (AP-1) but increased the expression level IkB-α in the CNS. Furthermore, molecular dynamics simulations and MMPBSA binding free energies were determined to validate the dynamic stability of complexes and shed light on the atomic level intermolecular interaction energies. Taken together, this study showed that WMT has significant neuroprotective potential in EAE via modulation of Nrf2 mediated-oxidative stress and NF-κB mediated inflammation.

Long Non-coding RNA GAS5 Knockdown Attenuates H2O2-Induced Human Trabecular Meshwork Cell Apoptosis and Promotes Extracellular Matrix Deposition by Suppressing miR-29b-3p and Upregulating STAT3

The long non-coding RNA GAS5 (GAS5) is reportedly implicated in glaucoma. However, its significance in human trabecular meshwork cells (HTMCs) remains largely unclear. Here, we investigated the effect of GAS5 on the function of HTMCs and its interaction with miR-29b-3p in HTMCs. We established an H₂O₂-induced oxidative injury model using HTMCs. RT-qPCR or western blotting was performed to examine the expression of the indicated genes. Luciferase reporter assay was used to determine the interaction between GAS5, miR-29b-3p, miR-29b-3p, and STAT3. CCK8 assay was used to assess the proliferative rate of HTMCs. Exposure to H₂O₂ increased the expression of Bax, cleaved caspase-3, and extracellular matrix (ECM) proteins, accompanied by reduced Bcl-2 expression. These H₂O₂-induced changes were effectively alleviated by GAS5 knockdown with sh-GAS5. MiR-29b-3p was directly regulated by GAS5. The effect of sh-GAS5 on ECM protein expression was also observed with the miR-29b-3p mimic. STAT3 was directly regulated by miR-29b-3p. MiR-29b-3p silencing alleviated STAT3 inhibition, followed by the restoration of cell vitality, Bax, Bcl-2, and cleaved caspase-3 expression, and ECM deposition. Our study is the first experimental investigation to shed light on a novel molecular mechanism of the GAS5/miR-29b-3p/STAT3 axis in an H₂O₂-induced oxidative injury model using HTMCs, which may offer a promising therapeutic approach against glaucoma.

A Nature-Inspired Nrf2 Activator Protects Retinal Explants from Oxidative Stress and Neurodegeneration

Oxidative stress (OS) plays a key role in retinal dysfunctions and acts as a major trigger of inflammatory and neurodegenerative processes in several retinal diseases. To prevent OS-induced retinal damage, approaches based on the use of natural compounds are actively investigated. Recently, structural features from curcumin and diallyl sulfide have been combined in a nature-inspired hybrid (NIH1), which has been described to activate transcription nuclear factor erythroid-2-related factor-2 (Nrf2), the master regulator of the antioxidant response, in different cell lines. We tested the antioxidant properties of NIH1 in mouse retinal explants. NIH1 increased Nrf2 nuclear translocation, Nrf2 expression, and both antioxidant enzyme expression and protein levels after 24 h or six days of incubation. Possible toxic effects of NIH1 were excluded since it did not alter the expression of apoptotic or gliotic markers. In OS-treated retinal explants, NIH1 strengthened the antioxidant response inducing a massive and persistent expression of antioxidant enzymes up to six days of incubation. These effects resulted in prevention of the accumulation of reactive oxygen species, of apoptotic cell death, and of gliotic reactivity. Together, these data indicate that a strategy based on NIH1 to counteract OS could be effective for the treatment of retinal diseases.

Resveratrol attenuates retinal ganglion cell loss in a mouse model of retinal ischemia reperfusion injury via multiple pathways

BACKGROUND

Resveratrol (RES) is a natural polyphenol that has been shown to protect retinal ganglion cells (RGCs) following retinal ischemia reperfusion (I/R) injury. However, the molecular mechanisms of resveratrol function are yet to be fully elucidated. Thus, this study explored the potential mechanisms of resveratrol in vivo.

METHODS

A retinal ischemia reperfusion injury model was established in adult male C57BL/6 J mice. Intraperitoneal injection of resveratrol was administered continuously for 5 days. RGC survival was determined by immunofluorescence staining with Brn3a. Flash electroretinography (ERG) was conducted to assess visual function. Proteins of HIF-1a, VEGF, p38, p53, PI3K, Akt, Bax, Bcl2, and Cleaved Caspase3 were detected using Western blot.

RESULTS

RES administration significantly ameliorated retinal thickness damage and increased Brn3a stained RGCs 7 days after I/R injury. We also found that administration of RES remarkably inhibited the upregulation of mitochondrial apoptosis-related protein Bax and Cleaved Caspase3, as well as increased the expression of Bcl2. Furthermore, RES administration significantly suppressed the I/R injury-induced upregulation of the HIF-1a/VEGF and p38/p53 pathways, while activating the I/R injury-induced downregulation of the PI3K/Akt pathway. Moreover, RES administration remarkably improved retinal function after I/R injury-induced functional impairment.

CONCLUSIONS

Our data demonstrated that resveratrol can mitigate retinal ischemic injury induced RGC loss and retinal function impairment by inhibiting the HIF-1a/VEGF and p38/p53 pathways while activating the PI3K/Akt pathway. Therefore, our results further reinforce that resveratrol has potential for treating glaucoma.

How curcumin affects hyperglycemia-induced optic nerve damage: A short review

Considered to be one of the most important non-contagious systemic diseases worldwide, diabetes mellitus is still a topical issue on the health agenda with the problems it causes. Exposure to long-term hyperglycemia causes diabetic complications (diabetic neuropathy, nephropathy and retinopathy). The optic nerve can suffer damage by both diabetic retinopathy and neuropathy during diabetes, both because it is formed by axons of retinal ganglion cells and these axons belong to the central nervous system. The issue of hyperglycemia on the optic nerve have been described as diabetic papillopathy, posterior ischemic optic neuropathy, nonarteritic anterior ischemic optic neuropathy and optic atrophy in clinical studies. Experimental studies indicated axon-myelin degeneration in addition to microvascular and ultrastructural changes caused by the hyperglycemia-induced optic nerve damage. Although there are several proposed biochemical mechanisms to cause these damages, oxidative stress emerges as an important factor among them. Oxidative stress leads to pathological state on the nerve cells by affecting the DNA, protein and lipids at different levels. These are causing deterioration on nerve conduction velocity, myelin sheath and nerve structure, neurotrophic support system, glial cells and nerve function. Curcumin, as an important antioxidant, can be an ideal prophylactic agent to eliminate damages on optic nerve. Curcumin helps to regulate the balance of antioxidant and reactive oxygen species by targeting various molecules (NF-κB, STAT3, MAPK, Mfn2, Nrf2, pro-inflammatory cytokines). In addition, it shows healing or preventive effects on myelin sheath damage via regulating ferritin protein in oligodendrocytes. It is also effective in preventing neurovascular damage.

Natural Products: Evidence for Neuroprotection to Be Exploited in Glaucoma

Glaucoma, a leading cause of irreversible blindness worldwide, is an optic neuropathy characterized by the progressive death of retinal ganglion cells (RGCs). Elevated intraocular pressure (IOP) is recognized as the main risk factor. Despite effective IOP-lowering therapies, the disease progresses in a significant number of patients. Therefore, alternative IOP-independent strategies aiming at halting or delaying RGC degeneration is the current therapeutic challenge for glaucoma management. Here, we review the literature on the neuroprotective activities, and the underlying mechanisms, of natural compounds and dietary supplements in experimental and clinical glaucoma.

Obstacles against the Marketing of Curcumin as a Drug

Among the extensive public and scientific interest in the use of phytochemicals to prevent or treat human diseases in recent years, natural compounds have been highly investigated to elucidate their therapeutic effect on chronic human diseases including cancer, cardiovascular disease, and neurodegenerative disease. Curcumin, an active principle of the perennial herb Curcuma longa, has attracted an increasing research interest over the last half-century due to its diversity of molecular targets, including transcription factors, enzymes, protein kinases, growth factors, inflammatory cytokines, receptors, and it's interesting pharmacological activities. Despite that, the clinical effectiveness of the native curcumin is weak, owing to its low bioavailability and rapid metabolism. Preclinical data obtained from animal models and phase I clinical studies done in human volunteers confirmed a small amount of intestinal absorption, hepatic first pass effect, and some degree of intestinal metabolism, might explain its poor systemic availability when it is given via the oral route. During the last decade, researchers have attempted with new pharmaceutical methods such as nanoparticles, liposomes, micelles, solid dispersions, emulsions, and microspheres to improve the bioavailability of curcumin. As a result, a significant number of bioavailable curcumin-based formulations were introduced with a varying range of enhanced bioavailability. This manuscript critically reviews the available scientific evidence on the basic and clinical effects and molecular targets of curcumin. We also discuss its pharmacokinetic and problems for marketing curcumin as a drug.

Plant-Derived Antioxidants Protect the Nervous System From Aging by Inhibiting Oxidative Stress

Alzheimer's disease (AD) has become a major disease contributing to human death and is thought to be closely related to the aging process. The rich antioxidant substances in plants have been shown to play a role in delaying aging, and in recent years, significant research has focused on also examining their potential role in AD onset and progression. Many plant-derived antioxidant research studies have provided insights for the future treatment and prevention of AD. This article reviews various types of plant-derived antioxidants with anti-aging effects on neurons. Also it distinguishes the different types of active substances that exhibit different degrees of protection for the nervous system and summarizes the mechanism thereof. Plant-derived antioxidants with neuroprotective functions can protect various components of the nervous system in a variety of ways and can have a positive impact on interventions to prevent and alleviate AD. Furthermore, when considering neuroprotective agents, glial cells also contribute to the defense of the nervous system and should not be ignored.

Curcumin diminishes cisplatin-induced apoptosis and mitochondrial oxidative stress through inhibition of TRPM2 channel signaling pathway in mouse optic nerve

Background: Cisplatin (CiSP), a chemotherapeutic agent, is widely used to treat several types of cancers. However, its clinical use is limited due to adverse side effects caused by excessive production of reactive oxygen species (ROS) and death of neurons. The transient receptor potential (TRP) melastatin 2 (TRPM2) cation channel is activated by ADP-ribose (ADPR) and ROS. The protective effect of curcumin (CURCU) against CiSP-induced apoptosis and mitochondrial ROS through inhibition of TRP channels in several types of neuron except optic nerve, was recently reported. The aim of the current study is to clarify the protective effect of CURCU on CiSP-induced mitochondrial oxidative injury and TRPM2 activation in the mice optic nerve and SH-SY5Y human derived neuronal cells.Material and methods: The SH-SY5Y cells and mice were divided into four groups: Control, CURCU, CiSP, and CURCU + CiSP. The mice were treated for 14 days and the cells were incubated with CiSP and CURCU for 24 h.Results: CURCU and PARP-1 inhibitor (PJ34) treatments ameliorated CiSP-induced mitochondrial membrane depolarization, mitochondrial and cytosolic ROS levels and neuronal death in the optic nerve. In the patch-clamp of SH-SY5Y cells and laser confocal microscopy experiments of optic nerve, CURCU and TRPM2 blocker treatments also decreased ADPR-induced TRPM2 currents and cytosolic free calcium ion (Ca²⁺) concentration, suggesting a suppression of Ca²⁺ influx and neuronal death.Conclusion: CURCU prevents CiSP-induced optic nerve oxidative injury and cell death by suppressing mitochondrial ROS production via regulating TRPM2 signaling pathways. CURCU may serve as a potential therapeutic target against CiSP-induced toxicity in the optic nerve of CiSP-treated patients.

Curcumin Affects HSP60 Folding Activity and Levels in Neuroblastoma Cells

The fundamental challenge in fighting cancer is the development of protective agents able to interfere with the classical pathways of malignant transformation, such as extracellular matrix remodeling, epithelial–mesenchymal transition and, alteration of protein homeostasis. In the tumors of the brain, proteotoxic stress represents one of the main triggering agents for cell transformation. Curcumin is a natural compound with anti-inflammatory and anti-cancer properties with promising potential for the development of therapeutic drugs for the treatment of cancer as well as neurodegenerative diseases. Among the mediators of cancer development, HSP60 is a key factor for the maintenance of protein homeostasis and cell survival. High HSP60 levels were correlated, in particular, with cancer development and progression, and for this reason, we investigated the ability of curcumin to affect HSP60 expression, localization, and post-translational modifications using a neuroblastoma cell line. We have also looked at the ability of curcumin to interfere with the HSP60/HSP10 folding machinery. The cells were treated with 6, 12.5, and 25 µM of curcumin for 24 h, and the flow cytometry analysis showed that the compound induced apoptosis in a dose-dependent manner with a higher percentage of apoptotic cells at 25 µM. This dose of curcumin-induced a decrease in HSP60 protein levels and an upregulation of HSP60 mRNA expression. Moreover, 25 µM of curcumin reduced HSP60 ubiquitination and nitration, and the chaperonin levels were higher in the culture media compared with the untreated cells. Furthermore, curcumin at the same dose was able to favor HSP60 folding activity. The reduction of HSP60 levels, together with the increase in its folding activity and the secretion in the media led to the supposition that curcumin might interfere with cancer progression with a protective mechanism involving the chaperonin.

Nanotechnology for Medical and Surgical Glaucoma Therapy-A Review

Glaucoma is the second leading cause of blindness worldwide. Even though significant advances have been made in its management, currently available antiglaucoma therapies suffer from considerable drawbacks. Typically, the success and efficacy of glaucoma medications are undermined by their limited bioavailability to target tissues and the inadequate adherence demonstrated by patients with glaucoma. The latter is due to a gradual decrease in tolerability of lifelong topical therapies and the significant burden to patients of prescribed stepwise antiglaucoma regimens with frequent dosing which impact quality of life. On the other hand, glaucoma surgery is restricted by the inability of antifibrotic agents to efficiently control the wound healing process without causing severe collateral damage and long-term complications. Evolution of the treatment paradigm for patients with glaucoma will ideally include prevention of retinal ganglion cell degeneration by the successful delivery of neurotrophic factors, anti-inflammatory drugs, and gene therapies. Nanotechnology-based treatments may surpass the limitations of currently available glaucoma therapies through optimized targeted drug delivery, increased bioavailability, and controlled release. This review addresses the recent advances in glaucoma treatment strategies employing nanotechnology, including medical and surgical management, neuroregeneration, and neuroprotection.

Therapeutic potential of curcumin in eye diseases

Curcumin (diferuloylmethane) derived from the rhizome of Curcuma longa L. has been used for thousands of years in traditional Chinese medicine and Ayurvedic medicine in Asian countries to treat liver diseases, rheumatoid diseases, diabetes, atherosclerosis, infectious diseases and cancer. It exhibits a wide range of pharmacological properties, which include antioxidant, anti-inflammatory, antimutagenic, antimicrobial and anticancer activity. Herein the mechanisms of curcumin impact on oxidative stress, angiogenesis and inflammatory processes are described indicating that curcumin use may inhibit those pathological conditions and restore body homeostasis. Its effectiveness was also proved for major eye diseases. In this review, the influence of curcumin on eye diseases, such as glaucoma, cataract, age-related macular degeneration, diabetic retinopathy, corneal neovascularization, corneal wound healing, dry eye disease, conjunctivitis, pterygium, anterior uveitis are reported. The analysis of a number of clinical and preclinical investigations indicates that curcumin may be used as a therapeutic agent in the treatment of various eye disorders.

Curcumin: A new candidate for retinal disease therapy?

The retina is the neural portion and light-sensitive layer of the eye, which has been observed in most of the vertebrates. The retina is composed of light-sensitive cells that absorb light and convert it into neural signals. These signals are sent to the brain for visual recognition. It has been shown that many pathogenesis conditions, including inflammation, angiogenesis, oxidative stress, and imbalanced histone modifications in the retina are associated with initiation and progression of retinal diseases (ie, glaucoma, diabetic retinopathy, and age-related macular degeneration). Currently available treatments include laser surgery, freezing, stem-cell therapy, shrinking abnormal blood vessels. It has some limitations, such as invasive methods, high costs, and many side effects. Hence, finding a new therapeutic platform for stopping or slowing of the disease progression is required. Curcumin is a natural product, which is associated with a wide range of properties, such as antioxidant, anti-inflammatory, antiangiogenic, and antitumor activates. It exerts therapeutic effects via activation/inhibition cellular and molecular targets involved in various diseases, such as retinal diseases. Increasing evidence revealed that curcumin can be used as a therapeutic option in the treatment of different retinal diseases. Here, we summarized various clinical and preclinical studies that used curcumin as a therapeutic agent in the treatment of retinal disorders.

Effects of Curcumin on Microglial Cells

Microglia are innate immune system cells which reside in the central nervous system (CNS). Resting microglia regulate the homeostasis of the CNS via phagocytic activity to clear pathogens and cell debris. Sometimes, however, to protect neurons and fight invading pathogens, resting microglia transform to an activated-form, producing inflammatory mediators, such as cytokines, chemokines, iNOS/NO and cyclooxygenase-2 (COX-2). Excessive inflammation, however, leads to damaged neurons and neurodegenerative diseases (NDs), such as Parkinson's disease (PD), Alzheimer's disease (AD), Huntington's disease (HD), multiple sclerosis (MS) and amyotrophic lateral sclerosis (ALS). Curcumin is a phytochemical isolated from Curcuma longa. It is widely used in Asia and has many therapeutic properties, including antioxidant, anti-viral, anti-bacterial, anti-mutagenic, anti-amyloidogenic and anti-inflammatory, especially with respect to neuroinflammation and neurological disorders (NDs). Curcumin is a pleiotropic molecule that inhibits microglia transformation, inflammatory mediators and subsequent NDs. In this mini-review, we discuss the effects of curcumin on microglia and explore the underlying mechanisms.

Targeting Mitochondrial Dysfunction and Oxidative Stress in Activated Microglia using Dendrimer-Based Therapeutics

Mitochondrial oxidative stress is associated with many neurodegenerative diseases, such as traumatic brain injury (TBI). Targeted delivery of antioxidants to mitochondria has failed to translate into clinical success due to their nonspecific cellular localization, poor transport properties across multiple biological barriers, and associated side effects. These challenges, coupled with the complex function of the mitochondria, create the need for innovative delivery strategies. Methods: Neutral hydroxyl-terminated polyamidoamine (PAMAM) dendrimers have shown significant potential as nanocarriers in multiple brain injury models. N-acetyl cysteine (NAC) is a clinically used antioxidant and anti-inflammatory agent which has shown significant potency when delivered in a targeted manner. Here we present a mitochondrial targeting hydroxyl PAMAM dendrimer-drug construct (TPP-D-NAC) with triphenyl-phosphonium (TPP) for mitochondrial targeting and NAC for targeted delivery to mitochondria in injured glia. Co-localization and mitochondrial content of mitochondria-targeted and unmodified dendrimer were assessed in microglia and macrophages in vitro via immunohistochemistry and fluorescence quantification. Therapeutic improvements of TPP-D-NAC over dendrimer-NAC conjugate (D-NAC) and free NAC were evaluated in vitro in microglia under oxidative stress challenge. In vivo neuroinflammation targeting was confirmed in a rabbit model of TBI. Results: TPP-conjugated dendrimer co-localized significantly more with mitochondria than unmodified dendrimer without altering overall levels of cellular internalization. This targeting capability translated to significant improvements in the attenuation of oxidative stress by TPP-D-NAC compared to D-NAC and free NAC. Upon systemic administration in a rabbit TBI model, TPP-conjugated dendrimer co-localized specifically with mitochondria in activated microglia and macrophages in the white matter of the ipsilateral/injured hemisphere, confirming its BBB penetration and glial targeting capabilities. Conclusion: D-NAC has shown promising efficacy in many animal models of neurodegeneration, and this work provides evidence that modification for mitochondrial targeting can further enhance its therapeutic efficacy, particularly in diseases where oxidative stress-induced glial cell death plays a significant role in disease progression.

Topical Curcumin Nanocarriers are Neuroprotective in Eye Disease

Curcumin (1,7-bis-(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5dione) is a polyphenol extracted from turmeric that has long been advocated for the treatment of a variety of conditions including neurodegenerative and inflammatory disorders. Despite this promise, the clinical use of curcumin has been limited by the poor solubility and low bioavailability of this molecule. In this article, we describe a novel nanocarrier formulation comprising Pluronic-F127 stabilised D-α-Tocopherol polyethene glycol 1000 succinate nanoparticles, which were used to successfully solubilize high concentrations (4.3 mg/mL) of curcumin. Characterisation with x-ray diffraction and in vitro release assays localise curcumin to the nanocarrier interior, with each particle measuring <20 nm diameter. Curcumin-loaded nanocarriers (CN) were found to significantly protect against cobalt chloride induced hypoxia and glutamate induced toxicity in vitro, with CN treatment significantly increasing R28 cell viability. Using established glaucoma-related in vivo models of ocular hypertension (OHT) and partial optic nerve transection (pONT), topical application of CN twice-daily for three weeks significantly reduced retinal ganglion cell loss compared to controls. Collectively, these results suggest that our novel topical CN formulation has potential as an effective neuroprotective therapy in glaucoma and other eye diseases with neuronal pathology.

NGF and PI3K/Akt signaling participate in the ventral motor neuronal protection of curcumin in sciatic nerve injury rat models

OBJECTIVE

It has been reported that sciatic nerve injury (SNI) leads to degeneration, damage, and apoptosis of motor neurons. Nerve growth factor (NGF) plays a pivotal role in regeneration and reestablishment of neuronal function via activating PI3K/Akt survival signaling pathways. Curcumin owns neuroprotective effect following brain injury. In the present study, we attempt to investigate underlying mechanism of neuroprotective effect of curcumin through elucidating its correlation with NGF and PI3K/Akt signaling pathways in vitro and in vivo.

METHODS

PC-12 cells were exposed H₂O₂ in order to induce neuron cell injury and cells were then treated with curcumin. Caspase-3, NGF level and Akt phosphorylation were determined using flow cytometry and western blotting. Then, cells were treated with NGF specific siRNA followed by measurement of apoptosis, NGF and Akt phosphorylation levels. In animal model, rats were subjected to SNI and then randomly designated into four different groups: curcumin, curcumin + LY294002, curcumin + NGF shRNA, and negative controls and 12 rats in each group (n = 12). After four weeks of continuous treatment, tissue samples were obtained and subjected to TUNEL, NeuN double staining and western blotting.

RESULTS

Curcumin significantly reduced the number of apoptotic cells induced by H₂O₂ and this effect was associated with upregulation of TrkA, Akt and downregulation of p17. ProNGF level was significantly decreased while mature NGF level was increased with curcumin treatment. When NGF was suppressed, anti-apoptotic effect of curcumin was attenuated. In addition, inhibition of PI3K/Akt results in increased apoptotic rate compared to vehicles following curcumin treatment which was reflected by decreased p17, Ki67, and cyclin D1. Suppression of NGF and inhibition of PI3K led to increased neuron cell death through increasing proNGF and decreasing mNGF, Akt, TrkA, p75^NTR, and p17.

CONCLUSION

Our findings revealed that curcumin exerts its protective effect against injured neurons through stimulating NGF release which further activates TrkA and PI3K/Akt cell survival signaling.

Rational Basis for Nutraceuticals in the Treatment of Glaucoma

BACKGROUND

Glaucoma, the second leading cause of blindness worldwide, is a chronic optic neuropathy characterized by progressive retinal ganglion cell (RGC) axons degeneration and death. Primary open-angle glaucoma (OAG), the most common type, is often associated with increased intraocular pressure (IOP), however other factors have been recognized to partecipate to the patogenesis of the optic neuropathy. IOP-independent mechanisms that contribute to the glaucoma-related neurodegeneration include oxidative stress, excitotoxicity, neuroinflammation, and impaired ocular blood flow. The involvement of several and diverse factors is one of the reasons for the progression of glaucoma observed even under efficient IOP control with the currently available drugs.

METHODS

Current research and online content related to the potential of nutritional supplements for limiting retinal damage and improving RGC survival is reviewed.

RESULTS

Recent studies have suggested a link between dietary factors and glaucoma risk. Particularly, some nutrients have proven capable of lowering IOP, increase circulation to the optic nerve, modulate excitotoxicity and promote RGC survival. However, the lack of clinical trials limit their current therapeutic use. The appropriate use of nutraceuticals that may be able to modify the risk of glaucoma may provide insight into glaucoma pathogenesis and decrease the need for, and therefore the side effects from, conventional therapies.

CONCLUSION

The effects of nutrients with anti-oxidant and neuroprotective properties are of great interest and nutraceuticals may offer some therapeutic potential although a further rigorous evaluation of nutraceuticals in the treatment of glaucoma is needed to determine their safety and efficacy.

Protective Effects of Curcumin on Manganese-Induced BV-2 Microglial Cell Death

Curcumin, a bioactive component in tumeric, has been shown to exert antioxidant, anti-inflammatory, anticarcinogenic, hepatoprotective, and neuroprotective effects, but the effects of curcumin against manganese (Mn)-mediated neurotoxicity have not been studied. This study examined the protective effects of curcumin on Mn-induced cytotoxicity in BV-2 microglial cells. Curcumin (0.1-10 µM) dose-dependently prevented Mn (250 µM)-induced cell death. Mn-induced mitochondria-related apoptotic characteristics, such as caspase-3 and -9 activation, cytochrome c release, Bax increase, and Bcl-2 decrease, were significantly suppressed by curcumin. In addition, curcumin significantly increased intracellular glutathione (GSH) and moderately potentiated superoxide dismutase (SOD), both which were diminished by Mn treatment. Curcumin pretreatment effectively suppressed Mn-induced upregulation of malondialdehyde (MDA), total reactive oxygen species (ROS). Moreover, curcumin markedly inhibited the Mn-induced mitochondrial membrane potential (MMP) loss. Furthermore, curcumin was able to induce heme oxygenase (HO)-1 expression. Curcumin-mediated inhibition of ROS, down-regulation of caspases, restoration of MMP, and recovery of cell viability were partially reversed by HO-1 inhibitor (SnPP). These results suggest the first evidence that curcumin can prevent Mn-induced microglial cell death through the induction of HO-1 and regulation of oxidative stress, mitochondrial dysfunction, and apoptotic events.

Curcumin, A Potential Therapeutic Candidate for Anterior Segment Eye Diseases: A Review

Curcumin, the major curcuminoid of the turmeric, has been extensively used in many countries since ancient time for preventing and/or treating a multitude of diseases. This review is to illustrate the researches on the properties of curcumin and its potential therapeutic efficacy in major anterior segment eye diseases. The bio-medical potential of curcumin is restricted because of its low solubility and digestive bioavailability. This review will discuss promising research in improving curcumin bioavailability through structural modification. In vitro and in vivo research made progress in studying the beneficial effects of curcumin on major anterior segment eye diseases, including anti-angiogenesis effect in corneal diseases; anti-inflammation or anti-allergy effects in dry eye disease, conjunctivitis, anterior uveitis; anti-proliferation and pro-apoptosis effects in pterygium; anti-oxidative stress, anti-osmotic stress, anti-lipid peroxidation, pro-apoptosis, regulating calcium homeostasis, sequestrating free radicals, protein modification and degradation effects in cataracts; neuroprotective effects in glaucoma. Curcumin exhibited to be a potent therapeutic candidate for treating those anterior segment eye diseases.

HSP60 mediates the neuroprotective effects of curcumin by suppressing microglial activation

Curcumin has anti-inflammatory and antioxidant properties and has been widely used to treat or prevent neurodegenerative diseases. However, the mechanisms underlying the neuroprotective effects of curcumin are not well known. In the present study, the effect of curcumin on lipopolysaccharide (LPS)-stimulated BV2 mouse microglia cells was investigated using enzyme-linked immunosorbent assays of the culture medium and western blotting of cell lysates. The results showed that curcumin significantly inhibited the LPS-induced expression and release of heat shock protein 60 (HSP60) in the BV2 cells. The level of heat shock factor (HSF)-1 was upregulated in LPS-activated BV2 microglia, indicating that the increased expression of HSP60 was driven by HSF-1 activation. However, the increased HSF-1 level was downregulated by curcumin. Extracellular HSP60 is a ligand of Toll-like receptor 4 (TLR-4), and the level of the latter was increased in the LPS-activated BV2 microglia and inhibited by curcumin. The activation of TLR-4 is known to be associated with the activation of myeloid differentiation primary response 88 (MyD88) and nuclear factor (NF)-κB, with the subsequent production of proinflammatory and neurotoxic factors. In the present study, curcumin demonstrated marked suppression of the LPS-induced expression of MyD88, NF-κB, caspase-3, inducible nitric oxide synthase, tumor necrosis factor-α, interleukin (IL)-1β and IL-6 in the microglia. These results indicate that curcumin may exert its neuroprotective and anti-inflammatory effects by inhibiting microglial activation through the HSP60/TLR-4/MyD88/NF-κB signaling wpathway. Therefore, curcumin may be useful for the treatment of neurodegenerative diseases that are associated with microglial activation.

Inhibition of the classical pathway of the complement cascade prevents early dendritic and synaptic degeneration in glaucoma

Background

Glaucoma is a complex, multifactorial disease characterised by the loss of retinal ganglion cells and their axons leading to a decrease in visual function. The earliest events that damage retinal ganglion cells in glaucoma are currently unknown. Retinal ganglion cell death appears to be compartmentalised, with soma, dendrite and axon changes potentially occurring through different mechanisms. There is mounting evidence from other neurodegenerative diseases suggesting that neuronal dendrites undergo a prolonged period of atrophy, including the pruning of synapses, prior to cell loss. In addition, recent evidence has shown the role of the complement cascade in synaptic pruning in glaucoma and other diseases.

Results

Using a genetic (DBA/2J mouse) and an inducible (rat microbead) model of glaucoma we first demonstrate that there is loss of retinal ganglion cell synapses and dendrites at time points that precede axon or soma loss. We next determine the role of complement component 1 (C1) in early synaptic loss and dendritic atrophy during glaucoma. Using a genetic knockout of C1qa (D2.C1qa^-/- mouse) or pharmacological inhibition of C1 (in the rat bead model) we show that inhibition of C1 is sufficient to preserve dendritic and synaptic architecture.

Conclusions

This study further supports assessing the potential for complement-modulating therapeutics for the prevention of retinal ganglion cell degeneration in glaucoma.

Curcumin alleviates lung injury in diabetic rats by inhibiting nuclear factor-κB pathway

Curcumin is a polyphenolic compound that is extracted from Curcuma longa. It has broad anti-inflammation and anti-tumor activities. Curcumin was previously reported to exert beneficial effects on diabetes. However, the effect of curcumin on diabetes-induced lung injury is not yet clear. In this study, the effects of curcumin on lung injury induced by diabetes was explored using quantitative real time polymerase chain reaction (PCR), enzyme-linked immunosorbent assay (ELISA), immunohistochemistry and electrophoretic mobility shift assay. The results of this study showed that curcumin reduced oxidative stress level, inhibited the synthesis of nitric oxide and prostaglandin E2, and reduced inflammatory responses in the lungs of diabetic rats, thereby alleviating diabetes-induced lung injury. Further study of the mechanism revealed that curcumin inhibited the activation of nuclear factor (NF)-κB which is a key player in inflammatory responses. In summary, our study demonstrated that curcumin inhibited the activation of NF-κB in the lungs of diabetic rats, thus reducing pulmonary inflammatory responses and oxidative stress, and ultimately relieving diabetes-induced lung injury. This study suggests that curcumin may be a promising agent to alleviate diabetic lung injury and also provides theoretical foundation for the development of diabetes therapy.

Mutated myocilin and heterozygous Sod2 deficiency act synergistically in a mouse model of open-angle glaucoma

Glaucoma is a multifactorial optic neuropathy characterized by retinal ganglion cell (RGC) death and axonal degeneration leading to irreversible blindness. Mutations in the myocilin (MYOC) gene are the most common genetic factors of primary open-angle glaucoma. To develop a genetic mouse model induced by the synergistic interaction of mutated myocilin and another significant risk factor, oxidative stress, we produced double-mutant mice (Tg-MYOC(Y437H/+)/Sod2(+/-)) bearing human MYOC with a Y437H point mutation and a heterozygous deletion of the gene for the primary antioxidant enzyme, superoxide dismutase 2 (SOD2). Sod2 is broadly expressed in most tissues including the trabecular meshwork (TM) and heterozygous Sod2 knockout mice exhibit the reduced SOD2 activity and oxidative stress in all studied tissues. Accumulation of Y437H myocilin in the TM induced endoplasmic reticulum stress and led to a 45% loss of smooth muscle alpha-actin positive cells in the eye drainage structure of 10- to 12-month-old Tg-MYOC(Y437H/+)/Sod2(+/-) mice as compared with wild-type littermates. Tg-MYOC(Y437H/+)/Sod2(+/-) mice had higher intraocular pressure, lost about 37% of RGCs in the peripheral retina, and exhibited axonal degeneration in the retina and optic nerve as compared with their wild-type littermates. Single-mutant littermates containing MYOC(Y437H/+) or Sod2(+/-) exhibited no significant pathological changes until 12 months of age. Additionally, we observed elevated expression of endothelial leukocyte adhesion molecule-1, a human glaucoma marker, in the TM of Tg-MYOC(Y437H/+)/Sod2(+/-) mice. This is the first reported animal glaucoma model that combines expression of a glaucoma-causing mutant gene and an additional mutation mimicking a deleterious environment factor that acts synergistically.