Tauroursodeoxycholic acid protects retinal neural cells from cell death induced by prolonged exposure to elevated glucose

Unveiling the gut-eye axis: how microbial metabolites influence ocular health and disease

The intricate interplay between the gut microbiota and ocular health has surpassed conventional medical beliefs, fundamentally reshaping our understanding of organ interconnectivity. This review investigates into the intricate relationship between gut microbiota-derived metabolites and their consequential impact on ocular health and disease pathogenesis. By examining the role of specific metabolites, such as short-chain fatty acids (SCFAs) like butyrate and bile acids (BAs), herein we elucidate their significant contributions to ocular pathologies, thought-provoking the traditional belief of organ sterility, particularly in the field of ophthalmology. Highlighting the dynamic nature of the gut microbiota and its profound influence on ocular health, this review underlines the necessity of comprehending the complex workings of the gut-eye axis, an emerging field of science ready for further exploration and scrutiny. While acknowledging the therapeutic promise in manipulating the gut microbiome and its metabolites, the available literature advocates for a targeted, precise approach. Instead of broad interventions, it emphasizes the potential of exploiting specific microbiome-related metabolites as a focused strategy. This targeted approach compared to a precision tool rather than a broad-spectrum solution, aims to explore the therapeutic applications of microbiome-related metabolites in the context of various retinal diseases. By proposing a nuanced strategy targeted at specific microbial metabolites, this review suggests that addressing specific deficiencies or imbalances through microbiome-related metabolites might yield expedited and pronounced outcomes in systemic health, extending to the eye. This focused strategy holds the potential in bypassing the irregularity associated with manipulating microbes themselves, paving a more efficient pathway toward desired outcomes in optimizing gut health and its implications for retinal diseases.

Gut microbiome in diabetic retinopathy: A systematic review and meta-analysis

CONTEXT

Changes in the gut microbiome are linked with Type 2diabetes mellitus (T2DM) development, but alterations in patients with diabetic retinopathy (DR) are still being debated.

OBJECTIVE

To investigate the differences in biodiversity and relative abundance of gut microbiome between patients with DR and T2DM.

METHODS

A comprehensive search was performed in five electronic databases (PubMed, EMBASE, Cochrane Central Register of Controlled Trials, Web of Science, and CNKI) from the inception of each database through to August 2023. The standardized mean difference (SMD) and its 95% confidence interval (CI) were estimated using Stata 15.1. Furthermore, the alpha diversity index and relative abundance of the gut microbiome were calculated. The Egger test determined publication bias in the literature.

RESULTS

Seven case-control studies were included in the final dataset, comprising 195 patients with DR and 211 patients with T2DM. Compared to T2DM patients, patients in the DR group had a reduced but not significantly different α-diversity. The analysis of microbial composition at the phylum level revealed a marked increase in the relative abundance of Bacteroidetes(ES = 23.27, 95%CI[8.30, 38.23], P = 0.000) and a decline in Firmicutes(ES = 47.05, 95%CI[36.58, 57.52], P = 0.000), Proteobacteria (ES = 11.08, 95%CI[6.08, 16.07], P = 0.000) and Actinobacteria (ES = 10.43, 95%CI[1.64, 19.22], P = 0.001) in patients with DR when compared to those with T2DM.

CONCLUSIONS

An association exists between alterations in the gut microbiome of T2DM and the development and progression of DR. This suggests that re-establishing homeostasis of the gut microbiome could be a potential way to prevent or treat DR and requires further confirmation in future studies.

REGISTRATION DATABASE

Prospero.

REGISTRATION NUMBER

CRD42023455280.

Effect of age on metabolomic changes in a model of paclitaxel-induced peripheral neurotoxicity

BACKGROUND AND AIMS

Chemotherapy-induced peripheral neurotoxicity (CIPN) is one of the most common dose-limiting side effects of paclitaxel (PTX) treatment. Many age-related changes have been hypothesized to underlie susceptibility to damage or impaired regeneration/repair after nerve injury. The results of these studies, however, are inconclusive and other potential biomarkers of nerve impairment need to be investigated.

METHODS

Twenty-four young (2 months) and 24 adult (9 months) Wistar male rats were randomized to either PTX treatment (10 mg/kg i.v. once/week for 4 weeks) or vehicle administration. Neurophysiological and behavioral tests were performed at baseline, after 4 weeks of treatment and 2-week follow-up. Skin biopsies and nerve specimens collected from sacrificed animals were examined for intraepidermal nerve fiber (IENF) density assessment and nerve morphology/morphometry. Blood and liver samples were collected for targeted metabolomics analysis.

RESULTS

At the end of treatment, the neurophysiological studies revealed a reduction in sensory nerve action potential amplitude (p < .05) in the caudal nerve of young PTX-animals, and in both the digital and caudal nerve of adult PTX-animals (p < .05). A significant decrease in the mechanical threshold was observed only in young PTX-animals (p < .001), but not in adult PTX-ones. Nevertheless, both young and adult PTX-rats had reduced IENF density (p < .0001), which persisted at the end of follow-up period. Targeted metabolomics analysis showed significant differences in the plasma metabolite profiles between PTX-animals developing peripheral neuropathy and age-matched controls, with triglycerides, diglycerides, acylcarnitines, carnosine, long chain ceramides, sphingolipids, and bile acids playing a major role in the response to PTX administration.

INTERPRETATION

Our study identifies for the first time multiple related metabolic axes involved in PTX-induced peripheral neurotoxicity, and suggests age-related differences in CIPN manifestations and in the metabolic profile.

Tauroursodeoxycholic acid: a bile acid that may be used for the prevention and treatment of Alzheimer's disease

Alzheimer's disease (AD) is a prevalent neurodegenerative disease that has become one of the main factors affecting human health. It has serious impacts on individuals, families, and society. With the development of population aging, the incidence of AD will further increase worldwide. Emerging evidence suggests that many physiological metabolic processes, such as lipid metabolism, are implicated in the pathogenesis of AD. Bile acids, as the main undertakers of lipid metabolism, play an important role in the occurrence and development of Alzheimer's disease. Tauroursodeoxycholic acid, an endogenous bile acid, has been proven to possess therapeutic effects in different neurodegenerative diseases, including Alzheimer's disease. This review tries to find the relationship between bile acid metabolism and AD, as well as explore the therapeutic potential of bile acid taurocursodeoxycholic acid for this disease. The potential mechanisms of taurocursodeoxycholic acid may include reducing the deposition of Amyloid-β protein, regulating apoptotic pathways, preventing tau hyperphosphorylation and aggregation, protecting neuronal synapses, exhibiting anti-inflammatory properties, and improving metabolic disorders. The objective of this study is to shed light on the use of tauroursodeoxycholic acid preparations in the prevention and treatment of AD, with the aim of identifying effective treatment targets and clarifying various treatment mechanisms involved in this disease.

Bile acid metabolites predict multiple sclerosis progression and supplementation is safe in progressive disease

Background

Bile acid metabolism is altered in multiple sclerosis (MS) and tauroursodeoxycholic acid (TUDCA) supplementation ameliorated disease in mouse models of MS.

Methods

Global metabolomics was performed in an observational cohort of people with MS followed by pathway analysis to examine relationships between baseline metabolite levels and subsequent brain and retinal atrophy. A double-blind, placebo-controlled trial, was completed in people with progressive MS (PMS), randomized to receive either TUDCA (2g daily) or placebo for 16 weeks. Participants were followed with serial clinical and laboratory assessments. Primary outcomes were safety and tolerability of TUDCA, and exploratory outcomes included changes in clinical, laboratory and gut microbiome parameters.

Results

In the observational cohort, higher primary bile acid levels at baseline predicted slower whole brain, brain substructure and specific retinal layer atrophy. In the clinical trial, 47 participants were included in our analyses (21 in placebo arm, 26 in TUDCA arm). Adverse events did not significantly differ between arms (p=0.77). The TUDCA arm demonstrated increased serum levels of multiple bile acids. No significant differences were noted in clinical or fluid biomarker outcomes. Central memory CD4+ and Th1/17 cells decreased, while CD4+ naïve cells increased in the TUDCA arm compared to placebo. Changes in the composition and function of gut microbiota were also noted in the TUDCA arm compared to placebo.

Conclusion

Bile acid metabolism in MS is linked with brain and retinal atrophy. TUDCA supplementation in PMS is safe, tolerable and has measurable biological effects that warrant further evaluation in larger trials with a longer treatment duration.

Neuroprotective Effect of Tauroursodeoxycholic Acid (TUDCA) on In Vitro and In Vivo Models of Retinal Disorders: A Systematic Review

BACKGROUND

Tauroursodeoxycholic acid (TUDCA) is a naturally produced hydrophilic bile acid that has been used for centuries in Chinese medicine. Numerous recent in vitro and in vivo studies have shown that TUDCA has neuroprotective action in various models of retinal disorders.

OBJECTIVE

To systematically review the scientific literature and provide a comprehensive summary on the neuroprotective action and the mechanisms involved in the cytoprotective effects of TUDCA.

METHODS

A systematic review was conducted in accordance with the PRISMA (The Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. Systematic literature search of United States National Library of Medicine (PubMed), Web of Science, Embase, Scopus and Cochrane Library was performed, which covered all original articles published up to July 2022. The terms, "TUDCA" in combination with "retina", "retinal protection", "neuroprotection" were searched. Possible biases were identified with the adopted SYRCLE's tool.

RESULTS

Of the 423 initially gathered studies, 24 articles met inclusion/exclusion criteria for full-text review. Six of them were in vitro experiments, 17 studies reported in vivo data and one study described both in vitro and in vivo data. The results revealed the effect of TUDCA on different retinal diseases, such as retinitis pigmentosa (RP), diabetic retinopathy (DR), retinal degeneration (RD), retinal ganglion cell (RGC) injury, Leber's hereditary optic neuropathy (LHON), choroidal neovascularization (CNV), and retinal detachment (RDT). The quality scores of the in vivo studies were ranged from 5 to 7 points (total 10 points), according to SYRCLE's risk of bias tool. Both in vitro and in vivo data suggested that TUDCA could effectively delay degeneration and apoptosis of retinal neurons, preserve retinal structure and function, and its mechanism of actions might be related with inhibiting apoptosis, decreasing inflammation, attenuating oxidative stress, suppressing endoplasmic reticulum (ER) stress, and reducing angiogenesis.

CONCLUSION

This systematic review demonstrated that TUDCA has neuroprotective effect on in vivo and in vitro models of retinal disorders, reinforcing the currently available evidence that TUDCA could be a promising therapeutic agent in retinal diseases treatment. However, well designed clinical trials are necessary to appraise the efficacy of TUDCA in clinical setting.

Evaluating the potential of tauroursodeoxycholic acid as add-on therapy in amelioration of streptozotocin-induced diabetic kidney disease

The bile acid tauroursodeoxycholic acid (TUDCA) is of natural origin and is used in traditional Chinese medicine for centuries. Earlier its use was limited to biliary disorders but owing to its pleiotropic effects dietary TUDCA supplementation is under clinical trials for diseases including type 1 and 2 diabetic complications. The current study aims to evaluate the potential and underlying molecular mechanism of the TUDCA as a monotherapy and as an add-on therapy to telmisartan, an angiotensin II type 1 receptor (AT1R) blocker against diabetic kidney disease (DKD). We employed both in-vitro and in-vivo approaches where NRK-52E cells were incubated with high glucose, and DKD was induced in Wistar rats using streptozotocin (55 mg/kg, i.p.). After 4 weeks, animals were administered with TUDCA (250 mg/kg, i.p.), telmisartan (10 mg/kg, p.o.), and their combination for 4 weeks. Plasma was collected for the biochemical estimation and kidneys were used for immunoblotting, PCR, and histopathological analysis. Similarly, for in-vitro experiments, cells were exposed to 1000 μM of TUDCA and 10 μM of telmisartan, and their combination, followed by cell lysate collection and immunoblotting analysis. We observed that the addition of TUDCA to conventional telmisartan treatment was more effective in restoring the renal function decline and suppressing the apoptotic and fibrotic signaling as compared to monotherapies of AT1R blocker and ER stress inhibitor. The results implicate the utility of traditionally used TUDCA as a potential renoprotective compound. Since, both TUDCA and telmisartan are approved for clinical usage, thus concomitant administration of them could be a novel therapeutic strategy against DKD.

Retinal Neurodegeneration in Euglycemic Hyperinsulinemia, Prediabetes, and Diabetes

Diabetic retinopathy (DR) is a challenging public health problem mainly because of its growing prevalence and risk of blindness. In general, our current knowledge and practice have failed to prevent the onset or progression of DR to sight-threatening complications. While there are treatment options for sight-threatening complications of DR, it is crucial to pay more attention to the early stages of DR to decrease its prevalence. Growing evidence suggests many pathologic changes occur before clinical presentations of DR in euglycemic hyperinsulinemia, prediabetes, and diabetes. These pathological changes occur in retinal neurons, glia, and microvasculature. A new focus on these preclinical pathologies - especially on hyperinsulinemia - may provide further insight into disease mechanisms, endpoints for clinical trials, and druggable targets in early disease. Here, we review the current evidence on the pathophysiological changes reported in preclinical DR and appraise preventive and treatment options for DR.

Effect of Tauroursodeoxycholic Acid on Inflammation after Ocular Alkali Burn

Inflammation is the main cause of corneal and retinal damage in an ocular alkali burn (OAB). The aim of this study was to investigate the effect of tauroursodeoxycholic acid (TUDCA) on ocular inflammation in a mouse model of an OAB. An OAB was induced in C57BL/6j mouse corneas by using 1 M NaOH. TUDCA (400 mg/kg) or PBS was injected intraperitoneally (IP) once a day for 3 days prior to establishing the OAB model. A single injection of Infliximab (6.25 mg/kg) was administered IP immediately after the OAB. The TUDCA suppressed the infiltration of the CD45-positive cells and decreased the mRNA and protein levels of the upregulated TNF-α and IL-1β in the cornea and retina of the OAB. Furthermore, the TUDCA treatment inhibited the retinal glial activation after an OAB. The TUDCA treatment not only ameliorated CNV and promoted corneal re-epithelization but also attenuated the RGC apoptosis and preserved the retinal structure after the OAB. Finally, the TUDCA reduced the expression of the endoplasmic reticulum (ER) stress molecules, IRE1, GRP78 and CHOP, in the retinal tissues of the OAB mice. The present study demonstrated that the TUDCA inhibits ocular inflammation and protects the cornea and retina from injury in an OAB mouse model. These results provide a potential therapeutic intervention for the treatment of an OAB.

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.

Neuroprotective Effects of Tauroursodeoxicholic Acid Involves Vascular and Glial Changes in Retinitis Pigmentosa Model

Purpose

Retinitis pigmentosa is primarily characterized by a massive photoreceptor loss. But a global retinal remodeling occurs in later stages of the disease. At that phase, glial cells and retinal vasculature are also strongly affected. The main aim of the present work is to assess if the bile acid Tauroursodeoxicholic acid (TUDCA), which has a demonstrated neuroprotective effect in numerous neurodegenerative diseases, is able to prevent glial and vascular degeneration in the P23H rat retina.

Methods

Homozygous P23H (line 3) animals were injected weekly with a TUDCA (500 mg/kg, i.p.) or vehicle solution, from the postnatal day (P) 21 to P120. Sprague-Dawley rats (SD) were used as control. Retinal cross-sections and wholemounts were immunostained using different glial and vascular markers and visualized with confocal microscopy. Retinal blood vessels were stained with nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase histochemistry and retinal vascular networks were drawn by hand using a camera lucida.

Results

At P120, the photoreceptor degeneration observed in P23H rats was accompanied by a reduction in the vascular network density and complexity at the deep capillary plexus. In addition, astrocytes showed gliotic features and the outer processes of Müller cells displayed an aberrant distribution in ring-shaped structures. When treated with TUDCA, P23H rats displayed better-preserved vessels and capillary loops in the deep capillary plexus which are associated with the partial preservation of photoreceptors. TUDCA treatment also increased the number of astrocytes and reduced the presence of Müller cell process clusters in the outer retina.

Conclusion

This work suggests that, besides its neuroprotective effect on photoreceptor cells, TUDCA treatment also protects from vascular and glial degeneration, a fact that encourages the use of TUDCA as a powerful therapy for neurodegenerative diseases.

Comparative Analysis of Urso- and Tauroursodeoxycholic Acid Neuroprotective Effects on Retinal Degeneration Models

Ursodeoxycholic (UDCA) and tauroursodeoxycholic (TUDCA) acids have shown neuroprotective properties in neurodegenerative diseases, but differential effects of the two bile acids have been poorly explored. The aim of this study was to evaluate the neuroprotective effects of UDCA versus TUDCA in a neuroretinal degeneration model and to compare transcriptionally regulated pathways. The WERI-Rb-1 human cone-like cell line and retinal explants were exposed to albumin and TUDCA or UDCA. Viability, cell death, and microglial activation were quantified. Transcriptionally regulated pathways were analyzed after RNA sequencing using the edgeR bioconductor package. Pre-treatment of cone-like cells with UDCA or TUDCA significantly protected cells from albumin toxicity. On retinal explants, either bile acid reduced apoptosis, necroptosis, and microglia activation at 6 h. TUDCA induced the regulation of 463 genes, whilst 31 genes were regulated by UDCA. Only nineteen common genes were regulated by both bile acids, mainly involved in iron control, cell death, oxidative stress, and cell metabolism. As compared to UDCA, TUDCA up-regulated genes involved in endoplasmic reticulum stress pathways and down-regulated genes involved in axonal and neuronal development. Either bile acid protected against albumin-induced cell loss. However, TUDCA regulated substantially more neuroprotective genes than UDCA.

From dried bear bile to molecular investigation: A systematic review of the effect of bile acids on cell apoptosis, oxidative stress and inflammation in the brain, across pre-clinical models of neurological, neurodegenerative and neuropsychiatric disorders

Bile acids, mainly ursodeoxycholic acid (UDCA) and its conjugated species glycoursodeoxycholic acid (GUDCA) and tauroursodeoxycholic acid (TUDCA) have long been known to have anti-apoptotic, anti-oxidant and anti-inflammatory properties. Due to their beneficial actions, recent studies have started to investigate the effect of UDCA, GUDCA, TUDCA on the same mechanisms in pre-clinical models of neurological, neurodegenerative and neuropsychiatric disorders, where increased cell apoptosis, oxidative stress and inflammation in the brain are often observed. A total of thirty-five pre-clinical studies were identified through PubMed/Medline, Web of Science, Embase, PsychInfo, and CINAHL databases, investigating the role of the UDCA, GUDCA and TUDCA in the regulation of brain apoptosis, oxidative stress and inflammation, in pre-clinical models of neurological, neurodegenerative and neuropsychiatric disorders. Findings show that UDCA reduces apoptosis, reactive oxygen species (ROS) and tumour necrosis factor (TNF)-α production in neurodegenerative models, and reduces nitric oxide (NO) and interleukin (IL)-1β production in neuropsychiatric models; GUDCA decreases lactate dehydrogenase, TNF-α and IL-1β production in neurological models, and also reduces cytochrome c peroxidase production in neurodegenerative models; TUDCA decreases apoptosis in neurological models, reduces ROS and IL-1β production in neurodegenerative models, and decreases apoptosis and TNF-α production, and increases glutathione production in neuropsychiatric models. In addition, findings suggest that all the three bile acids would be equally beneficial in models of Huntington's disease, whereas UDCA and TUDCA would be more beneficial in models of Parkinson's disease and Alzheimer's disease, while GUDCA in models of bilirubin encephalopathy and TUDCA in models of depression. Overall, this review confirms the therapeutic potential of UDCA, GUDCA and TUDCA in neurological, neurodegenerative and neuropsychiatric disorders, proposing bile acids as potential alternative therapeutic approaches for patients suffering from these disorders.

Gut Microbes and Eye Disease

Microbial symbionts in the gut are increasingly recognized as having important effects on health and disease, but have only recently begun to be linked to diseases of the eye. We review current research on the intestinal microbiota's relationship to ocular disease, focusing on autoimmune uveitis, diabetic retinopathy, age-related macular degeneration, and primary-open angle glaucoma. We discuss findings and limitations of this exciting new area of ophthalmology research and explore possible future disease-modifying treatments.

Risk Factors for Retinal Ganglion Cell Distress in Glaucoma and Neuroprotective Potential Intervention

Retinal ganglion cells (RGCs) are a population of neurons of the central nervous system (CNS) extending with their soma to the inner retina and with their axons to the optic nerve. Glaucoma represents a group of neurodegenerative diseases where the slow progressive death of RGCs results in a permanent loss of vision. To date, although Intra Ocular Pressure (IOP) is considered the main therapeutic target, the precise mechanisms by which RGCs die in glaucoma have not yet been clarified. In fact, Primary Open Angle Glaucoma (POAG), which is the most common glaucoma form, also occurs without elevated IOP. This present review provides a summary of some pathological conditions, i.e., axonal transport blockade, glutamate excitotoxicity and changes in pro-inflammatory cytokines along the RGC projection, all involved in the glaucoma cascade. Moreover, neuro-protective therapeutic approaches, which aim to improve RGC degeneration, have also been taken into consideration.

Tauroursodeoxycholic Acid Protects Retinal and Visual Function in a Mouse Model of Type 1 Diabetes

PURPOSE

Previous studies demonstrated that systemic treatment with tauroursodeoxycholic acid (TUDCA) is protective in in vivo mouse models of retinal degeneration and in culture models of hyperglycemia. This study tested the hypothesis that TUDCA will preserve visual and retinal function in a mouse model of early diabetic retinopathy (DR).

METHODS

Adult C57BL/6J mice were treated with streptozotocin (STZ) and made diabetic at 8-10 weeks of age. Control and diabetic mice were treated with vehicle or TUDCA starting 1 or 3 weeks after induction of diabetes, and were assessed bimonthly for visual function via an optomotor response and monthly for retinal function via scotopic electroretinograms.

RESULTS

Diabetic mice showed significantly reduced spatial frequency and contrast sensitivity thresholds compared to control mice, while diabetic mice treated early with TUDCA showed preservation at all timepoints. A-wave, b-wave, and oscillatory potential 2 (OP2) amplitudes decreased in diabetic mice. Diabetic mice also exhibited delays in a-wave and OP2-implicit times. Early TUDCA treatment ameliorated a-wave, b-wave, and OP2 deficits. Late TUDCA treatment showed reduced preservation effects compared to early treatment.

CONCLUSIONS

Early TUDCA treatment preserved visual function in an STZ-mouse model of Type I diabetes. These data add to a growing body of preclinical research that may support testing whether TUDCA may be an effective early clinical intervention against declining visual function caused by diabetic retinopathy.

Mitochondrial Dysfunction and Endoplasmic Reticulum Stress in Age Related Macular Degeneration, Role in Pathophysiology, and Possible New Therapeutic Strategies

Age related macular degeneration (AMD) is the main cause of legal blindness in developed countries. It is a multifactorial disease in which a combination of genetic and environmental factors contributes to increased risk of developing this vision-incapacitating condition. Oxidative stress plays a central role in the pathophysiology of AMD and recent publications have highlighted the importance of mitochondrial dysfunction and endoplasmic reticulum stress in this disease. Although treatment with vascular endothelium growth factor inhibitors have decreased the risk of blindness in patients with the exudative form of AMD, the search for new therapeutic options continues to prevent the loss of photoreceptors and retinal pigment epithelium cells, characteristic of late stage AMD. In this review, we explain how mitochondrial dysfunction and endoplasmic reticulum stress participate in AMD pathogenesis. We also discuss a role of several antioxidants (bile acids, resveratrol, melatonin, humanin, and coenzyme Q10) in amelioration of AMD pathology.

Oral Ursodeoxycholic Acid Crosses the Blood Retinal Barrier in Patients with Retinal Detachment and Protects Against Retinal Degeneration in an Ex Vivo Model

Rhegmatogenous retinal detachment (RD) is a threatening visual condition and a human disease model for retinal degenerations. Despite successful reattachment surgery, vision does not fully recover, due to subretinal fluid accumulation and subsequent photoreceptor cell death, through mechanisms that recapitulate those of retinal degenerative diseases. Hydrophilic bile acids are neuroprotective in animal models, but whether they can be used orally for retinal diseases is unknown. Ursodeoxycholic acid (UDCA) being approved for clinical use (e.g., in cholestasis), we have evaluated the ocular bioavailability of oral UDCA, administered to patients before RD surgery. The level of UDCA in ocular media correlated with the extent of blood retinal barrier disruption, evaluated by the extent of detachment and the albumin concentration in subretinal fluid. UDCA, at levels measured in ocular media, protected photoreceptors from apoptosis and necrosis in rat retinal explants, an ex vivo model of RD. The subretinal fluid from UDCA-treated patients, collected during surgery, significantly protected rat retinal explants from cell death, when compared to subretinal fluid from control patients. Pan-transcriptomic analysis of the retina showed that UDCA upregulated anti-apoptotic, anti-oxidant, and anti-inflammatory genes. Oral UDCA is a potential neuroprotective adjuvant therapy in RD and other retinal degenerative diseases and should be further evaluated in a clinical trial.

Pharmacological and Metabolic Significance of Bile Acids in Retinal Diseases

Bile acids (BAs) are amphipathic sterols primarily synthesized from cholesterol in the liver and released in the intestinal lumen upon food intake. BAs play important roles in micellination of dietary lipids, stimulating bile flow, promoting biliary phospholipid secretion, and regulating cholesterol synthesis and elimination. Emerging evidence, however, suggests that, aside from their conventional biological function, BAs are also important signaling molecules and therapeutic tools. In the last decade, the therapeutic applications of BAs in the treatment of ocular diseases have gained great interest. Despite the identification of BA synthesis, metabolism, and recycling in ocular tissues, much remains unknown with regards to their biological significance in the eye. Additionally, as gut microbiota directly affects the quality of circulating BAs, their analysis could derive important information on changes occurring in this microenvironment. This review aims at providing an overview of BA metabolism and biological function with a focus on their potential therapeutic and diagnostic use for retinal diseases.

Bile acid metabolism is altered in multiple sclerosis and supplementation ameliorates neuroinflammation

Multiple sclerosis (MS) is an inflammatory demyelinating disorder of the CNS. Bile acids are cholesterol metabolites that can signal through receptors on cells throughout the body, including in the CNS and the immune system. Whether bile acid metabolism is abnormal in MS is unknown. Using global and targeted metabolomic profiling, we identified lower levels of circulating bile acid metabolites in multiple cohorts of adult and pediatric patients with MS compared with controls. In white matter lesions from MS brain tissue, we noted the presence of bile acid receptors on immune and glial cells. To mechanistically examine the implications of lower levels of bile acids in MS, we studied the in vitro effects of an endogenous bile acid, tauroursodeoxycholic acid (TUDCA), on astrocyte and microglial polarization. TUDCA prevented neurotoxic (A1) polarization of astrocytes and proinflammatory polarization of microglia in a dose-dependent manner. TUDCA supplementation in experimental autoimmune encephalomyelitis reduced the severity of disease through its effects on G protein-coupled bile acid receptor 1 (GPBAR1). We demonstrate that bile acid metabolism was altered in MS and that bile acid supplementation prevented polarization of astrocytes and microglia to neurotoxic phenotypes and ameliorated neuropathology in an animal model of MS. These findings identify dysregulated bile acid metabolism as a potential therapeutic target in MS.

Decreased Physiological Serum Total Bile Acid Concentrations in Patients with Type 2 Diabetic Peripheral Neuropathy

PURPOSE

Bile acids, amphipathic cholesterol metabolites, have been reported to have cytoprotective and neuroprotective effects in humans and animal models. The relationship of physiological serum total bile acid (TBA) levels with diabetic peripheral neuropathy (DPN), however, has not been determined. The purpose of this study was to investigate the relationship between physiological serum TBA and DPN.

PATIENTS AND METHODS

In total, 856 patients with type 2 diabetes mellitus (T2DM) aged 20-89 years were enrolled in this cross-sectional study. Serum TBA was measured, and its relationship with DPN and other parameters was analyzed.

RESULTS

T2DM patients with DPN had significantly lower serum TBA compared with those without (P<0.01). Serum TBA was negatively associated with glycated hemoglobin A1C, plateletcrit, fibrinogen, urine albumin-to-creatinine ratio, vibration perception thresholds, and prevalence of DPN, peripheral arterial disease, and diabetic foot ulceration after adjustment for age, sex, and body mass index (P<0.01 or P<0.05). A graded association with prevalence of DPN and increase in serum TBA quartiles was observed (P for trend <0.01), and there was an 48.2% decreased risk of DPN in the highest quartile of serum TBA versus the lowest quartile (95% CI 0.299-0.617; P=0.000) after multivariate adjustment. Receiver-operating characteristic analysis revealed that the optimal cutoff point of serum TBA to indicate DPN was 2.85 μmol/L (sensitivity 77.6% and specificity 45.6%).

CONCLUSION

These findings suggest that lower physiological serum TBA level may be associated with the prevalence of DPN in T2DM patients and may be a potential biomarker for DPN.

Tauroursodeoxycholic acid attenuates neuronal apoptosis via the TGR5/ SIRT3 pathway after subarachnoid hemorrhage in rats

Background

Neuronal apoptosis plays a critical event in the pathogenesis of early brain injury after subarachnoid hemorrhage (SAH). This study investigated the roles of Tauroursodeoxycholic acid (TUDCA) in attenuate neuronal apoptosis and underlying mechanisms after SAH.

Methods

Sprague–Dawley rats were subjected to model of SAH and TUDCA was administered via the internal carotid injection. Small interfering RNA (siRNA) for TGR5 were administered through intracerebroventricular injection 48 h before SAH. Neurological scores, brain water content, Western blot, TUNEL staining and immunofluorescence staining were evaluated.

Results

TUDCA alleviated brain water content and improved neurological scores at 24 h and 72 h after SAH. TUDCA administration prevented the reduction of SIRT3 and BCL-2 expressions, as well as the increase of BAX and cleaved caspase-3.Endogenous TGR5 expression were upregulated after SAH and treatment with TGR5 siRNA exacerbated neurological outcomes after SAH and the protective effects of TUDCA at 24 h after SAH were also abolished by TGR5 siRNA.

Conclusions

Our findings demonstrate that TUDCA could attenuated neuronal apoptosis and improve neurological functions through TGR5/ SIRT3 signaling pathway after SAH. TUDCA may be an attractive candidate for anti-apoptosis treatment in SAH.

Plasma metabolomics supports the use of long-duration cardiac arrest rodent model to study human disease by demonstrating similar metabolic alterations

Cardiac arrest (CA) is a leading cause of death and there is a necessity for animal models that accurately represent human injury severity. We evaluated a rat model of severe CA injury by comparing plasma metabolic alterations to human patients. Plasma was obtained from adult human control and CA patients post-resuscitation, and from male Sprague–Dawley rats at baseline and after 20 min CA followed by 30 min cardiopulmonary bypass resuscitation. An untargeted metabolomics evaluation using UPLC-QTOF-MS/MS was performed for plasma metabolome comparison. Here we show the metabolic commonality between humans and our severe injury rat model, highlighting significant metabolic dysfunction as seen by similar alterations in (1) TCA cycle metabolites, (2) tryptophan and kynurenic acid metabolites, and (3) acylcarnitine, fatty acid, and phospholipid metabolites. With substantial interspecies metabolic similarity in post-resuscitation plasma, our long duration CA rat model metabolically replicates human disease and is a suitable model for translational CA research.

Tauroursodeoxycholic Acid Protects Retinal Pigment Epithelial Cells from Oxidative Injury and Endoplasmic Reticulum Stress In Vitro

Retinal degeneration is characterized by the dysfunction of retinal cells. Oxidative and endoplasmic reticulum (ER) stress play an important role in the pathogenesis and progression of retinal degeneration. Tauroursodeoxycholic acid (TUDCA) has been demonstrated to have protective effects in in vitro and in vivo retinal degeneration models. To fully understand the molecular mechanisms of TUDCA’s protection, we first treated human retinal pigment epithelial (RPE) cells, ARPE-19, with H₂O₂ or H₂O₂ plus TUDCA for 24 h. RPE cells co-exposed to TUDCA had higher cell viability and lower cell death rate compared to cells exposed to H₂O₂ alone. TUDCA significantly increased antioxidant capacity in H₂O₂-treated RPE cells by decreasing the generation of reactive oxygen species (ROS) and Malondialdehyde (MDA), upregulating the expression of antioxidant genes, and increasing the generation of glutathione (GSH). TUDCA also inhibited inflammation in H₂O₂-challenged RPE cells by decreasing the expression of proinflammatory cytokines. Furthermore, TUDCA suppressed thapsigargin-induced ER stress in RPE cells, as demonstrated by decreased the expression of CCAAT-enhancer-binding protein homologous protein (CHOP) and apoptosis. Our present study suggests that TUDCA can protect RPE cells against oxidative damage, inflammation, and ER stress and may benefit patients with retinal degeneration.

Inhibiting ER Stress Weakens Neuronal Pyroptosis in a Mouse Acute Hemorrhagic Stroke Model

Intracerebral hemorrhage (ICH) is a form of stroke, characterized by high morbidity and mortality and currently lacks specific therapy. ICH leads to endoplasmic reticulum (ER) stress, which can induce neurological impairment through crosstalk with programmed cell death (PCD). Pyroptosis, a newly discovered form of PCD, has received attention because of its close relationship with some certain diseases, such as traumatic brain injury and ischemic and hemorrhagic stroke. However, the relationship between ER stress and pyroptosis in ICH remains unclear. In this study, we investigated the role of ER stress in evoking neuronal pyroptosis and related mechanisms in a mouse ICH model. We used tauroursodeoxycholic acid (TUDCA) to inhibit ER stress and observed that TUDCA reduces neuronal pyroptosis and has a neuroprotective role. We explored the potential mechanisms underlying the regulation of neuronal pyroptosis by ER stress through testing the expression of interleukin-13 (IL-13). We found that ER stress inhibition alleviates neuronal pyroptosis through decreasing the expression of IL-13 after ICH. In summary, this study revealed that IL-13 is involved in ER stress-induced neuronal pyroptosis after ICH, pointing to IL-13 as a novel therapeutic target for ICH treatment.

Cigarette smoke induces endoplasmic reticulum stress and suppresses efferocytosis through the activation of RhoA

Impaired efferocytosis is a key mechanism of inflammatory lung diseases, including chronic obstructive pulmonary disease and cystic fibrosis. Cigarette smoking activates RhoA and impairs efferocytosis in alveolar macrophages, but the mechanism has not been fully elucidated. We investigated the role of endoplasmic reticulum (ER) stress induced by cigarette smoking in the disruption of efferocytosis. Both tunicamycin (10 μg/ml) and thapsigargin (0.1 and 1 μM), which are ER stress inducers, suppressed efferocytosis in J774 cells, and a Rho-associated coiled-coil-forming kinase (ROCK) inhibitor (Y27632) reversed this effect. We validated the effect of tunicamycin on efferocytosis in experiments using RAW264.7 cells. Then, we investigated the role of the unfolded protein response (UPR) in efferocytosis impaired by ER stress. A PERK inhibitor (GSK2606414) restored the efferocytosis that had been impaired by TM, and an eIF2α dephosphorylation inhibitor (salubrinal) suppressed efferocytosis. Cigarette smoke extract (CSE) induced ER stress in J774 macrophages and RhoA activation in J774 cells, and the CSE-induced ROCK activity was successfully reversed by GSK2606414 and tauroursodeoxycholic acid. Finally, we confirmed that ER stress suppresses efferocytosis in murine alveolar macrophages and that GSK2606414 could rescue this process. These data suggest that cigarette smoke-induced ER stress and the UPR play crucial roles in RhoA activation and suppression of efferocytosis in the lung.

Tauroursodeoxycholate-Bile Acid with Chaperoning Activity: Molecular and Cellular Effects and Therapeutic Perspectives

Tauroursodeoxycholic acid (TUDCA) is a naturally occurring hydrophilic bile acid that has been used for centuries in Chinese medicine. Chemically, TUDCA is a taurine conjugate of ursodeoxycholic acid (UDCA), which in contemporary pharmacology is approved by Food and Drug Administration (FDA) for treatment of primary biliary cholangitis. Interestingly, numerous recent studies demonstrate that mechanisms of TUDCA functioning extend beyond hepatobiliary disorders. Thus, TUDCA has been demonstrated to display potential therapeutic benefits in various models of many diseases such as diabetes, obesity, and neurodegenerative diseases, mostly due to its cytoprotective effect. The mechanisms underlying this cytoprotective activity have been mainly attributed to alleviation of endoplasmic reticulum (ER) stress and stabilization of the unfolded protein response (UPR), which contributed to naming TUDCA as a chemical chaperone. Apart from that, TUDCA has also been found to reduce oxidative stress, suppress apoptosis, and decrease inflammation in many in-vitro and in-vivo models of various diseases. The latest research suggests that TUDCA can also play a role as an epigenetic modulator and act as therapeutic agent in certain types of cancer. Nevertheless, despite the massive amount of evidence demonstrating positive effects of TUDCA in pre-clinical studies, there are certain limitations restraining its wide use in patients. Here, molecular and cellular modes of action of TUDCA are described and therapeutic opportunities and limitations of this bile acid are discussed.

Spermine oxidase: A promising therapeutic target for neurodegeneration in diabetic retinopathy

Diabetic Retinopathy (DR), is a significant public health issue and the leading cause of blindness in working-aged adults worldwide. The vision loss associated with DR affects patients' quality of life and has negative social and psychological effects. In the past, diabetic retinopathy was considered as a vascular disease; however, it is now recognized to be a neuro-vascular disease of the retina. Current therapies for DR, such as laser photocoagulation and anti-VEGF therapy, treat advanced stages of the disease, particularly the vasculopathy and have adverse side effects. Unavailability of effective treatments to prevent the incidence or progression of DR is a major clinical problem. There is a great need for therapeutic interventions capable of preventing retinal damage in DR patients. A growing body of evidence shows that neurodegeneration is an early event in DR pathogenesis. Therefore, studies of the underlying mechanisms that lead to neurodegeneration are essential for identifying new therapeutic targets in the early stages of DR. Deregulation of the polyamine metabolism is implicated in various neurodegenerative diseases, cancer, renal failure, and diabetes. Spermine Oxidase (SMOX) is a highly inducible enzyme, and its dysregulation can alter polyamine homeostasis. The oxidative products of polyamine metabolism are capable of inducing cell damage and death. The current review provides insight into the SMOX-regulated molecular mechanisms of cellular damage and dysfunction, and its potential as a therapeutic target for diabetic retinopathy. Structural and functional changes in the diabetic retina and the mechanisms leading to neuronal damage (excitotoxicity, loss of neurotrophic factors, oxidative stress, mitochondrial dysfunction etc.) are also summarized in this review. Furthermore, existing therapies and new approaches to neuroprotection are discussed.

Subcutaneous delivery of tauroursodeoxycholic acid rescues the cone photoreceptors in degenerative retina: A promising therapeutic molecule for retinopathy

Inherited retinal degeneration (RD) comprises a heterogeneous group of retinopathies that rank among the main causes of blindness. Tauroursodeoxycholic acid (TUDCA) is taurine conjugate hydrophilic bile acid that demonstrates profound protective effects against a series of neurodegenerative diseases related to oxidative stress. This study sought to evaluate the TUDCA induced effects of on a pharmacologically induced RD animal model by electroretinogram (ERG) examination, behavior tests, morphological analysis and immunochemistry assay. Massive photoreceptor degeneration in mice retina was induced by an intraperitoneal administration of N-methyl-N-nitrosourea(MNU). Subcutaneous delivery of TUDCA inhibits effectively the photoreceptor loss and visual impairments in the MNU administered mice. In the retinal flat-mounts of TUDCA treated mice, the cone photoreceptors were efficiently preserved. Furthermore, the multi-electrodes array (MEA) was used to detect the firing activities of retinal ganglion cells within the inner retinal circuits. TUDCA therapy could restrain the spontaneous firing response, enhance the light induced firing response, and preserve the basic configurations of ON-OFF signal pathway in degenerative retinas. Our MEA assay provided an example to evaluate the potency of pharmacological compounds on retinal plasticity. TUDCA affords these protective effects by modulating apoptosis and alleviating oxidative stress in the degenerative retina. In conclusion, TUDCA therapy can ameliorate the photoreceptor degeneration and rectify the abnormities in visual signal transmission. These findings suggest that TUDCA might act as a potential medication for these retinopathies with progressive photoreceptor degeneration.

Progesterone, Lipoic Acid, and Sulforaphane as Promising Antioxidants for Retinal Diseases: A Review

Oxidative stress has been documented to be a key factor in the cause and progression of different retinal diseases. Oxidative cellular unbalance triggers a sequence of reactions which prompt cell degeneration and retinal dysfunction, both hallmarks of several retinal pathologies. There is no effective treatment, yet, for many retinal diseases. Antioxidant treatment have been pointed out to be an encouraging palliative treatment; the beneficial effects documented involve slowing the progression of the disease, a reduction of cell degeneration, and improvement of retinal functions. There is a vast information corpus on antioxidant candidates. In this review, we expose three of the main antioxidant treatments, selected for their promising results that has been reported to date. Recently, the sulforaphane, an isothiocyanate molecule, has been unveiled as a neuroprotective candidate, by its antioxidant properties. Progesterone, a neurosteroid has been proposed to be a solid and effective neuroprotective agent. Finally, the lipoic acid, an organosulfur compound, is a well-recognized antioxidant. All of them, have been tested and studied on different retinal disease models. In this review, we summarized the published results of these works, to offer a general view of the current antioxidant treatment advances, including the main effects and mechanisms described.

High Dose and Delayed Treatment with Bile Acids Ineffective in RML Prion-Infected Mice

Prion diseases are a group of neurodegenerative diseases associated with the misfolding of the cellular prion protein (PrP^C) into the infectious form (PrP^Sc). There are currently no treatments for prion disease. Bile acids have the ability to protect hepatocytes from apoptosis and are neuroprotective in animal models of other protein-folding neurodegenerative diseases, including Huntington's, Parkinson's, and Alzheimer's disease. Importantly, bile acids are approved for clinical use in patients with cirrhosis and have recently been shown to be safe and possibly effective in pilot trials of patients with amyotrophic lateral sclerosis (ALS). We previously reported that the bile acid ursodeoxycholic acid (UDCA), given early in disease, prolonged incubation periods in male RML-infected mice. Here, we expand on this result to include tauro-ursodeoxycholic acid (TUDCA) treatment trials and delayed UDCA treatment. We demonstrate that despite a high dose of TUDCA given early in disease, there was no significant difference in incubation periods between treated and untreated cohorts, regardless of sex. In addition, delayed treatment with a high dose of UDCA resulted in a significant shortening of the average survival time for both male and female mice compared to their sex-matched controls, with evidence of increased BiP, a marker of apoptosis, in treated female mice. Our findings suggest that treatment with high-dose TUDCA provides no therapeutic benefit and that delayed treatment with high-dose UDCA is ineffective and could worsen outcomes.

Neuroprotective strategies for retinal disease

Diseases that affect the eye, including photoreceptor degeneration, diabetic retinopathy, and glaucoma, affect 11.8 million people in the US, resulting in vision loss and blindness. Loss of sight affects patient quality of life and puts an economic burden both on individuals and the greater healthcare system. Despite the urgent need for treatments, few effective options currently exist in the clinic. Here, we review research on promising neuroprotective strategies that promote neuronal survival with the potential to protect against vision loss and retinal cell death. Due to the large number of neuroprotective strategies, we restricted our review to approaches that we had direct experience with in the laboratory. We focus on drugs that target survival pathways, including bile acids like UDCA and TUDCA, steroid hormones like progesterone, therapies that target retinal dopamine, and neurotrophic factors. In addition, we review rehabilitative methods that increase endogenous repair mechanisms, including exercise and electrical stimulation therapies. For each approach, we provide background on the neuroprotective strategy, including history of use in other diseases; describe potential mechanisms of action; review the body of research performed in the retina thus far, both in animals and in humans; and discuss considerations when translating each treatment to the clinic and to the retina, including which therapies show the most promise for each retinal disease. Despite the high incidence of retinal diseases and the complexity of mechanisms involved, several promising neuroprotective treatments provide hope to prevent blindness. We discuss attractive candidates here with the goal of furthering retinal research in critical areas to rapidly translate neuroprotective strategies into the clinic.

Global untargeted serum metabolomic analyses nominate metabolic pathways responsive to loss of expression of the orphan metallo β-lactamase, MBLAC1

The C. elegans gene swip-10 encodes an orphan metallo β-lactamase that genetic studies indicate is vital for limiting neuronal excitability and viability. Sequence analysis indicates that the mammalian gene Mblac1 is the likely ortholog of swip-10, with greatest sequence identity localized to the encoded protein's single metallo β-lactamase domain. The substrate for the SWIP-10 protein remains unknown and to date no functional roles have been ascribed to MBLAC1, though we have shown that the protein binds the neuroprotective β-lactam antibiotic, ceftriaxone. To gain insight into the functional role of MBLAC1 in vivo, we used CRISPR/Cas9 methods to disrupt N-terminal coding sequences of the mouse Mblac1 gene, resulting in a complete loss of protein expression in viable, homozygous knockout (KO) animals. Using serum from both WT and KO mice, we performed global, untargeted metabolomic analyses, resolving small molecules via hydrophilic interaction chromatography (HILIC) based ultra-performance liquid chromatography, coupled to mass spectrometry (UPLC-MS/MS). Unsupervised principal component analysis reliably segregated the metabolomes of MBLAC1 KO and WT mice, with 92 features subsequently nominated as significantly different by ANOVA, and for which we made tentative and putative metabolite assignments. Bioinformatic analyses of these molecules nominate validated pathways subserving bile acid biosynthesis and linoleate metabolism, networks known to be responsive to metabolic and oxidative stress. Our findings lead to hypotheses that can guide future targeted studies seeking to identify the substrate for MBLAC1 and how substrate hydrolysis supports the neuroprotective actions of ceftriaxone.

Involvement of ciliary neurotrophic factor in early diabetic retinal neuropathy in streptozotocin-induced diabetic rats

Objective

Ciliary neurotrophic factor (CNTF) has been evaluated as a candidate therapeutic agent for diabetes and its neural complications. However, its role in diabetic retinopathy has not been fully elucidated.

Methods

This is a randomized unblinded animal experiment. Wistar rats with streptozocin (STZ)-induced diabetes were regularly injected with CNTF or vehicle control in their vitreous bodies beginning at 2 weeks after STZ injection. A total of five injections were used. In diabetic rats, the levels of CNTF and neurotrophin-3 (NT-3) were evaluated by enzyme-linked immunosorbent assays (ELISA) and real-time PCR. The abundance of tyrosine hydroxylase (TH) and β-III tubulin was detected by western blot. Transferase-mediated dUTP nick-end labeling staining (TUNEL) was used to detect cell apoptosis in the retinal tissue. The activation of caspase-3 was also measured.

Results

The protein and mRNA levels of CNTF in diabetic rat retinas were reduced compared to control rats. In addition, retinal ganglion cells (RGCs) and dopaminergic amacrine cells appeared to undergo degeneration in diabetic rat retinas, as revealed by transferase-mediated dUTP nick-end labeling staining (TUNEL). Tyrosine hydroxylase (TH) and β-III tubulin protein levels also decreased significantly. Intraocular administration of CNTF rescued RGCs and dopaminergic amacrine cells from neurodegeneration and counteracted the downregulation of β-III tubulin and TH expression, thus demonstrating its therapeutic potential.

Conclusion

Our study suggests that early diabetic retinal neuropathy involves the reduced expression of CNTF and can be ameliorated by an exogenous supply of this neurotrophin.

Tauroursodeoxycholic acid binds to the G-protein site on light activated rhodopsin

The heterotrimeric G-protein binding site on G-protein coupled receptors remains relatively unexplored regarding its potential as a new target of therapeutic intervention or as a secondary site of action by the existing drugs. Tauroursodeoxycholic acid bears structural resemblance to several compounds that were previously identified to specifically bind to the light-activated form of the visual receptor rhodopsin and to inhibit its activation of transducin. We show that TUDCA stabilizes the active form of rhodopsin, metarhodopsin II, and does not display the detergent-like effects of common amphiphilic compounds that share the cholesterol scaffold structure, such as deoxycholic acid. Computer docking of TUDCA to the model of light-activated rhodopsin revealed that it interacts using similar mode of binding to the C-terminal domain of transducin alpha subunit. The ring regions of TUDCA made hydrophobic contacts with loop 3 region of rhodopsin, while the tail of TUDCA is exposed to solvent. The results show that TUDCA interacts specifically with rhodopsin, which may contribute to its wide-ranging effects on retina physiology and as a potential therapeutic compound for retina degenerative diseases.

Synergistic neuroprotective effects of Geniposide and ursodeoxycholic acid in hypoxia-reoxygenation injury in SH-SY5Y cells

Endoplasmic reticulum stress (ERS) and autophagy activation play important roles in the process of cerebral ischemia/reperfusion (I/R) injury. The synergistic protective effects of Geniposide and ursodeoxycholic acid against cellular apoptosis caused by oxygen-glucose deprivation-reoxygenation (OGD/R) were investigated using a Cell Counting Kit-8 assay, lactate dehydrogenase (LDH) assay, flow cytometry, quantitative polymerase chain reaction (qPCR), and western blotting to examine cellular viability, apoptosis, reactive oxygen species (ROS) levels, mRNA and protein levels, respectively, in relation to ERS and autophagy. We found that pretreatment with Geniposide improved cellular viability. Moreover, treatment with a combination of Geniposide and Tauroursodeoxycholic acid (TUDCA) (GT) protected injured cells better than Geniposide alone. Further studies showed that the increase in cellular ROS levels, and the overexpression of mRNA and proteins related to OGD/R-induced ERS and autophagy, were both counteracted by GT. Our study indicates that the protective effects of GT on OGD/R-induced apoptosis in SH-SY5Y cells are associated with the inhibition of ERS and autophagy.

Prophylactic role of taurine and its derivatives against diabetes mellitus and its related complications

Taurine is a conditionally essential amino acid present in the body in free form. Mammalian taurine is synthesized in the pancreas via the cysteine sulfinic acid pathway. Anti-oxidation and anti-inflammation are two main properties through which it exerts its therapeutic effects. Many studies have shown its excellent therapeutic potential against diabetes mellitus and related complications like diabetic neuropathy, retinopathy, nephropathy, hematological dysfunctions, reproductive dysfunctions, liver and pancreas related complications etc. Not only taurine, a number of its derivatives have also been reported to be important in ameliorating diabetic complications. The present review has been aimed to describe the importance of taurine and its derivatives against diabetic metabolic syndrome and related complications.

Controlled delivery of tauroursodeoxycholic acid from biodegradable microspheres slows retinal degeneration and vision loss in P23H rats

Successful drug therapies for treating ocular diseases require effective concentrations of neuroprotective compounds maintained over time at the site of action. The purpose of this work was to assess the efficacy of intravitreal controlled delivery of tauroursodeoxycholic acid (TUDCA) encapsulated in poly(D,L-lactic-co-glycolic acid) (PLGA) microspheres for the treatment of the retina in a rat model of retinitis pigmentosa. PLGA microspheres (MSs) containing TUDCA were produced by the O/W emulsion-solvent evaporation technique. Particle size and morphology were assessed by light scattering and scanning electronic microscopy, respectively. Homozygous P23H line 3 rats received a treatment of intravitreal injections of TUDCA-PLGA MSs. Retinal function was assessed by electroretinography at P30, P60, P90 and P120. The density, structure and synaptic contacts of retinal neurons were analyzed using immunofluorescence and confocal microscopy at P90 and P120. TUDCA-loaded PLGA MSs were spherical, with a smooth surface. The production yield was 78%, the MSs mean particle size was 23 μm and the drug loading resulted 12.5 ± 0.8 μg TUDCA/mg MSs. MSs were able to deliver the loaded active compound in a gradual and progressive manner over the 28-day in vitro release study. Scotopic electroretinografic responses showed increased ERG a- and b-wave amplitudes in TUDCA-PLGA-MSs-treated eyes as compared to those injected with unloaded PLGA particles. TUDCA-PLGA-MSs-treated eyes showed more photoreceptor rows than controls. The synaptic contacts of photoreceptors with bipolar and horizontal cells were also preserved in P23H rats treated with TUDCA-PLGA MSs. This work indicates that the slow and continuous delivery of TUDCA from PLGA-MSs has potential neuroprotective effects that could constitute a suitable therapy to prevent neurodegeneration and visual loss in retinitis pigmentosa.

Oxidative stress and diabetic retinopathy: development and treatment

Diabetic retinopathy (DR) is the most common microvascular complication in diabetic patients and one of the main causes of acquired blindness in the world. From the 90s until date, the incidence of this complication has increased. Reactive oxygen species (ROS) is a free radical with impaired electron that usually participates in the redox mechanisms of some body molecules such as enzymes, proteins, and so on. In normal biological conditions, ROS is maintained in equilibrium, however its overproduction can lead to biological process called oxidative stress and this is considered the main pathogenesis of DR. The retina is susceptible to ROS because of high-energy demands and exposure to light. When the balance is broken, ROS produces retinal cell injury by interacting with the cellular components. This article describes the possible role of oxidative stress in the development of DR and proposes some treatment options based on its stages. The review of the topic shows that blindness caused by DR can be avoided by early detection and timely treatment.

Ursodeoxycholic Acid Attenuates Endoplasmic Reticulum Stress-Related Retinal Pericyte Loss in Streptozotocin-Induced Diabetic Mice

Loss of pericytes, an early hallmark of diabetic retinopathy (DR), results in breakdown of the blood-retinal barrier. Endoplasmic reticulum (ER) stress may be involved in this process. The purpose of this study was to examine the effects of ursodeoxycholic acid (UDCA), a known ameliorator of ER stress, on pericyte loss in DR of streptozotocin- (STZ-) induced diabetic mice. To assess the extent of DR, the integrity of retinal vessels and density of retinal capillaries in STZ-induced diabetic mice were evaluated. Additionally, induction of ER stress and the unfolded protein response (UPR) were assessed in diabetic mice and human retinal pericytes exposed to advanced glycation end products (AGE) or modified low-density lipoprotein (mLDL). Fluorescein dye leakage during angiography and retinal capillary density were improved in UDCA-treated diabetic mice, compared to the nontreated diabetic group. Among the UPR markers, those involved in the protein kinase-like ER kinase (PERK) pathway were increased, while UDCA attenuated UPR in STZ-induced diabetic mice as well as AGE- or mLDL-exposed retinal pericytes in culture. Consequently, vascular integrity was improved and pericyte loss reduced in the retina of STZ-induced diabetic mice. Our findings suggest that UDCA might be effective in protecting against DR.

Bile Acids in Neurodegenerative Disorders

Bile acids, a structurally related group of molecules derived from cholesterol, have a long history as therapeutic agents in medicine, from treatment for primarily ocular diseases in ancient Chinese medicine to modern day use as approved drugs for certain liver diseases. Despite evidence supporting a neuroprotective role in a diverse spectrum of age-related neurodegenerative disorders, including several small pilot clinical trials, little is known about their molecular mechanisms or their physiological roles in the nervous system. We review the data reported for their use as treatments for neurodegenerative diseases and their underlying molecular basis. While data from cellular and animal models and clinical trials support potential efficacy to treat a variety of neurodegenerative disorders, the relevant bile acids, their origin, and the precise molecular mechanism(s) by which they confer neuroprotection are not known delaying translation to the clinical setting.

Effects of bile acids on neurological function and disease

Bile acids are synthesized from cholesterol and are known to be involved with the emulsification and digestion of dietary lipids and fat-soluble vitamins. Outside of this role, bile acids can act as cell signaling effectors through binding and activating receptors on both the cell membrane and nucleus. Numerous reports have investigated these signaling pathways in conditions where the liver is damaged. More recently, effort has been made to investigate the role of bile acids in diseases outside of those associated with liver damage. This review summarizes recent findings on the influences that bile acids can exert in normal neurological function and their contribution to diseases of the nervous system, with the intent of highlighting the role of these metabolites as potential players in neurological disorders.-McMillin, M., DeMorrow, S. Effects of bile acids on neurological function and disease.

Mechanisms involved in the development of diabetic retinopathy induced by oxidative stress

BACKGROUND

Diabetic retinopathy (DR) is one of the main complications in patients with diabetes and has been the leading cause of visual loss since 1990. Oxidative stress is a biological process resulting from excessive production of reactive oxygen species (ROS). This process contributes to the development of many diseases and disease complications. ROS interact with various cellular components to induce cell injury. Fortunately, there is an antioxidan t system that protects organisms against ROS. Indeed, when ROS exceed antioxidant capacity, the resulting cell injury can cause diverse physiological and pathological changes that could lead to a disease like DR.

OBJECTIVE

This paper reviews the possible mechanisms of common and novel biomarkers involved in the development of DR and explores how these biomarkers could be used to monitor the damage induced by oxidative stress in DR, which is a significant complication in people with diabetes.

CONCLUSION

The poor control of glucemy in pacients with DB has been shown contribute to the development of complications in eyes as DR.

Protection of tauroursodeoxycholic acid on high glucose-induced human retinal microvascular endothelial cells dysfunction and streptozotocin-induced diabetic retinopathy rats

ETHNOPHARMACOLOGICAL RELEVANCE

Tauroursodeoxycholic acid (TUDCA), one of the main ingredients from bear gall which hold "Clearing heat and detoxification, Removing liver fire for improving eyesight" functions, is formed by the conjugation of ursodeoxycholic acid (UDCA) with taurine. However, the limited information of TUDCA on protecting diabetic retinopathy (DR) has been known. The present study was conducted to evaluate the protection of TUDCA on high glucose-induced human retinal microvascular endothelial cells (HRMECs) dysfunction and streptozotocin (STZ)-induced diabetic retinopathy (DR) rats and the possible mechanism underlying was also explored.

MATERIALS AND METHODS

The proliferation of high glucose-induced HRMECs was determined by MTT assay. DR rats' model was established by an administration of high-glucose-fat diet and an intraperitoneal injection of STZ (30mg/kg). The cell supernatant and rats' serum were collected for the assays of NO content by ELISA kits. Retinas were stained with hematoxylin and eosin (HE) to observe pathological changes. Immunohistochemical assay was applied to examine the protein expression of ICAM-1, NOS, NF-κB p65 and VEGF in rat retinas. Furthermore, western blot analysis was carried out to examine the protein expression of ICAM-1, NOS, NF-κB p65 and VEGF in high glucose-induced HRMECs.

RESULTS

After treating with TUDCA, high glucose-induced HRMECs proliferation could be significantly inhibited. TUDCA (5.0μM, 25.0μM and 125.0μM) could decrease NO content in high glucose-induced HRMECs. Furthermore, TUDCA (500mg/kg/d and 250mg/kg/d) also decrease NO content in serum of DR rats. Additionally, both immunocytochemistry analysis and western blot analysis showed that the over-expression of ICAM-1, NOS, NF-κB p65 and VEGF were significantly decreased by TUDCA.

CONCLUSION

The data indicated that TUDCA could ameliorate DR by decreasing NO content and down-regulating the protein expression of ICAM-1, NOS, NF-κB p65 and VEGF. Thus, our experimental results suggested that TUDCA might be a potential drug for the prevention and treatment of DR.

Chronology of UPR activation in skeletal muscle adaptations to chronic contractile activity

The mitochondrial and endoplasmic reticulum unfolded protein responses (UPR(mt) and UPR(ER)) are important for cellular homeostasis during stimulus-induced increases in protein synthesis. Exercise triggers the synthesis of mitochondrial proteins, regulated in part by peroxisome proliferator activator receptor-γ coactivator 1α (PGC-1α). To investigate the role of the UPR in exercise-induced adaptations, we subjected rats to 3 h of chronic contractile activity (CCA) for 1, 2, 3, 5, or 7 days followed by 3 h of recovery. Mitochondrial biogenesis signaling, through PGC-1α mRNA, increased 14-fold after 1 day of CCA. This resulted in 10-32% increases in cytochrome c oxidase activity, indicative of mitochondrial content, between days 3 and 7, as well as increases in the autophagic degradation of p62 and microtubule-associated proteins 1A/1B light chain 3A (LC3)-II protein. Before these adaptations, the UPR(ER) transcripts activating transcription factor-4, spliced X-box-binding protein 1, and binding immunoglobulin protein were elevated (1.3- to 3.8-fold) at days 1-3, while CCAAT/enhancer-binding protein homologous protein (CHOP) and chaperones binding immunoglobulin protein and heat shock protein (HSP) 70 were elevated at mRNA and protein levels (1.5- to 3.9-fold) at days 1-7 of CCA. The mitochondrial chaperones 10-kDa chaperonin, HSP60, and 75-kDa mitochondrial HSP, the protease ATP-dependent Clp protease proteolytic subunit, and the regulatory protein sirtuin-3 of the UPR(mt) were concurrently induced 10-80% between days 1 and 7 To test the role of the UPR in CCA-induced remodeling, we treated animals with the endoplasmic reticulum stress suppressor tauroursodeoxycholic acid and subjected them to 2 or 7 days of CCA. Tauroursodeoxycholic acid attenuated CHOP and HSP70 protein induction; however, this failed to impact mitochondrial remodeling. Our data indicate that signaling to the UPR is rapidly activated following acute contractile activity, that this is attenuated with repeated bouts, and that the UPR is involved in chronic adaptations to CCA; however, this appears to be independent of CHOP signaling.

Selective A2A receptor antagonist prevents microglia-mediated neuroinflammation and protects retinal ganglion cells from high intraocular pressure-induced transient ischemic injury

Glaucoma is a leading cause of vision loss and blindness worldwide, characterized by chronic and progressive neuronal loss. Reactive microglial cells have been recognized as a neuropathologic feature, contributing to local inflammation and retinal neurodegeneration. In a recent in vitro work (organotypic cultures), we demonstrated that blockade of adenosine A2A receptor (A2AR) prevents the neuroinflammatory response and affords protection to retinal ganglion cells (RGCs) against exposure to elevated hydrostatic pressure (EHP), to mimic elevated intraocular pressure (IOP), the main risk factor for glaucoma development. Herein, we investigated whether a selective A2AR antagonist (SCH 58261) could modulate retinal microglia reactivity and their inflammatory response. Furthermore, we took advantage of the high IOP-induced transient ischemia (ischemia-reperfusion, I-R) animal model to evaluate the protective role of A2AR blockade in the control of retinal neuroinflammation and neurodegeneration. Primary microglial cell cultures were challenged either with lipopolysaccharide or with EHP, in the presence or absence of A2AR antagonist SCH 58261 (50 nM). In addition, I-R injury was induced in adult Wistar rats after intravitreal administration of SCH 58261 (100 nM, 5 μL). Our results showed that SCH 58261 attenuated microglia reactivity and the increased expression and release of proinflammatory cytokines. Moreover, intravitreal administration of SCH 58261 prevented I-R-induced cell death and RGC loss, by controlling microglial-mediated neuroinflammatory response. These results prompt the proposal that A2AR blockade may have great potential in the management of retinal neurodegenerative diseases characterized by microglia reactivity and RGC death, such as glaucoma and ischemic diseases.

Tauroursodeoxycholic acid prevents hearing loss and hair cell death in Cdh23(erl/erl) mice

Sensorineural hearing loss has long been the subject of experimental and clinical research for many years. The recently identified novel mutation of the Cadherin23 (Cdh23) gene, Cdh23(erl/erl), was proven to be a mouse model of human autosomal recessive nonsyndromic deafness (DFNB12). Tauroursodeoxycholic acid (TUDCA), a taurine-conjugated bile acid, has been used in experimental research and clinical applications related to liver disease, diabetes, neurodegenerative diseases, and other diseases associated with apoptosis. Because hair cell apoptosis was implied to be the cellular mechanism leading to hearing loss in Cdh23(erl/erl) mice (erl mice), this study investigated TUDCA's otoprotective effects in erl mice: preventing hearing impairment and protecting against hair cell death. Our results showed that systemic treatment with TUDCA significantly alleviated hearing loss and suppressed hair cell death in erl mice. Additionally, TUDCA inhibited apoptotic genes and caspase-3 activation in erl mouse cochleae. The data suggest that TUDCA could be a potential therapeutic agent for human DFNB12.