Taurine protects against NMDA-induced retinal damage by reducing retinal oxidative stress

Taurine induces hormesis in multiple biological models: May have transformative implications for overall societal health

This paper represents the first integrative assessment and documentation of taurine-induced hormetic effects in the biological and biomedical areas, their dose response features, mechanistic frameworks, and possible public health, therapeutic and commercial applications. Taurine-induced hormetic effects are documented in a wide range of experimental models, cell types and for numerous biological endpoints, with most of these experimental findings being reported within the past five years. It is suggested that the concept of hormesis may have a transformative effect on taurine research and its public health and therapeutic applications.

Glycative stress as a cause of macular degeneration

People are living longer and rates of age-related diseases such as age-related macular degeneration (AMD) are accelerating, placing enormous burdens on patients and health care systems. The quality of carbohydrate foods consumed by an individual impacts health. The glycemic index (GI) is a kinetic measure of the rate at which glucose arrives in the blood stream after consuming various carbohydrates. Consuming diets that favor slowly digested carbohydrates releases sugar into the bloodstream gradually after consuming a meal (low glycemic index). This is associated with reduced risk for major age-related diseases including AMD, cardiovascular disease, and diabetes. In comparison, consuming the same amounts of different carbohydrates in higher GI diets, releases glucose into the blood rapidly, causing glycative stress as well as accumulation of advanced glycation end products (AGEs). Such AGEs are cytotoxic by virtue of their forming abnormal proteins and protein aggregates, as well as inhibiting proteolytic and other protective pathways that might otherwise selectively recognize and remove toxic species. Using in vitro and animal models of glycative stress, we observed that consuming higher GI diets perturbs metabolism and the microbiome, resulting in a shift to more lipid-rich metabolomic profiles. Interactions between aging, diet, eye phenotypes and physiology were observed. A large body of laboratory animal and human clinical epidemiologic data indicates that consuming lower GI diets, or lower glycemia diets, is protective against features of early AMD (AMDf) in mice and AMD prevalence or AMD progression in humans. Drugs may be optimized to diminish the ravages of higher glycemic diets. Human trials are indicated to determine if AMD progression can be retarded using lower GI diets. Here we summarized the current knowledge regarding the pathological role of glycative stress in retinal dysfunction and how dietary strategies might diminish retinal disease.

Taurine: a promising nutraceutic in the prevention of retinal degeneration

Taurine is considered a non-essential amino acid because it is synthesized by most mammals. However, dietary intake of taurine may be necessary to achieve the physiological levels required for the development, maintenance, and function of certain tissues. Taurine may be especially important for the retina. The concentration of taurine in the retina is higher than that in any other tissue in the body and taurine deficiency causes retinal oxidative stress, apoptosis, and degeneration of photoreceptors and retinal ganglion cells. Low plasma taurine levels may also underlie retinal degeneration in humans and therefore, taurine administration could exert retinal neuroprotective effects. Taurine has antioxidant, anti-apoptotic, immunomodulatory, and calcium homeostasis-regulatory properties. This review summarizes the role of taurine in retinal health and disease, where it appears that taurine may be a promising nutraceutical.

Active role of amino acid metabolism in early diagnosis and treatment of diabetic kidney disease

Diabetic Kidney Disease (DKD) is one of the significant microvascular consequences of type 2 diabetes mellitus with a complex etiology and protracted course. In the early stages of DKD, the majority of patients experience an insidious onset and few overt clinical symptoms and indicators, but they are prone to develop end-stage renal disease in the later stage, which is life-threatening. The abnormal amino acid metabolism is tightly associated with the development of DKD, which involves several pathological processes such as oxidative stress, inflammatory response, and immune response and is also closely related to autophagy, mitochondrial dysfunction, and iron death. With a focus on taurine, branched-chain amino acids (BCAAs) and glutamine, we explored the biological effects of various amino acid mechanisms linked to DKD, the impact of amino acid metabolism in the early diagnosis of DKD, and the role of amino acid metabolism in treating DKD, to offer fresh objectives and guidelines for later early detection and DKD therapy.

Exploring the current use of animal models in glaucoma drug discovery: where are we in 2023?

INTRODUCTION

Animal models are widely used in glaucoma-related research. Since the elevated intraocular pressure (IOP) is a major risk factor underlying the disease pathogenesis, animal models with high IOP are commonly used. However, models are also used to represent the clinical context of glaucomatous changes developing despite a normal IOP.

AREAS COVERED

Herein, the authors discuss the various factors that contribute to the quality of studies using animal models based on the evaluation of studies published in 2022. The factors affecting the quality of studies using animal models, such as the animal species, age, and sex, are discussed, along with various methods and outcomes of studies involving different animal models of glaucoma.

EXPERT OPINION

Translating animal research data to clinical applications remains challenging. Our observations in this review clearly indicate that many studies lack scientific robustness not only in their experiment conduct but also in data analysis, interpretation, and presentation. In this context, ensuring the internal validity of animal studies is the first step in quality assurance. External validity, however, is more challenging, and steps should be taken to satisfy external validity at least to some extent.

How to Increase Cellular Glutathione

Glutathione (GSH) has special antioxidant properties due to its high intracellular concentration, ubiquity, and high reactivity towards electrophiles of the sulfhydryl group of its cysteine moiety. In most diseases where oxidative stress is thought to play a pathogenic role, GSH concentration is significantly reduced, making cells more susceptible to oxidative damage. Therefore, there is a growing interest in determining the best method(s) to increase cellular glutathione for both disease prevention and treatment. This review summarizes the major strategies for successfully increasing cellular GSH stores. These include GSH itself, its derivatives, NRf-2 activators, cysteine prodrugs, foods, and special diets. The possible mechanisms by which these molecules can act as GSH boosters, their related pharmacokinetic issues, and their advantages and disadvantages are discussed.

Taurine: A Source and Application for the Relief of Visual Fatigue

According to reports, supplementation with appropriate doses of taurine may help to reduce visual fatigue. Presently, some progress has been made in research related to taurine in eye health, but the lack of systematic summaries has led to the neglect of its application in the relief of visual fatigue. This paper, therefore, provides a systematic review of the sources of taurine, including the endogenous metabolic and exogenous dietary pathways, as well as a detailed review of the distribution and production of exogenous taurine. The physiological mechanisms underlying the production of visual fatigue are summarized and the research progress of taurine in relieving visual fatigue is reviewed, including the safety of consumption and the mechanism of action in relieving visual fatigue, in order to provide some reference basis and inspiration for the development and application of taurine in functional foods for relieving visual fatigue.

NMR-based metabolomics approach to assess the ecotoxicity of prothioconazole on the earthworm (Eisenia fetida) in soil

Prothioconazole (PTC) is a widely used agricultural fungicide. In recent years, studies have confirmed that it exerts adverse effects on various species, including aquatic organisms, mammals, and reptiles. However, the toxicological effects of PTC on soil organisms are poorly understood. Here, we investigated the toxic effects, via oxidative stress and metabolic responses, of PTC on earthworms (Eisenia fetida). PTC exposure can induce significant changes in oxidative stress indicators, including the activities of superoxide dismutase (SOD) and catalase (CAT) and the content of glutathione (GSH), which in turn affect the oxidative defense system of earthworms. In addition, metabolomics revealed that PTC exposure caused significant changes in the metabolic profiles of earthworms. The relative abundances of 16 and 21 metabolites involved in amino acids, intermediates of the tricarboxylic acid (TCA) cycle and energy metabolism were significantly altered after 7 and 14 days of PTC exposure, respectively. Particularly, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that multiple different metabolic pathways could be disturbed after 7 and 14 days of PTC exposure. Importantly, these alterations in oxidative stress and metabolic responses in earthworms reveal that the effects of PTC on earthworms were time dependent, and vary with exposure time. In conclusion, this study highlights that the effects of PTC on soil organisms are of serious concern.

Taurine protects R28 cells from hypoxia/re-oxygenation-induced damage via regulation of mitochondrial energy metabolism

Oxidative-induced damage and hypoxia/re-oxygenation (H/R) injury are common causes of irreversible visual impairment. The goals of this study were to explore the effects of taurine on R28 cells under the two damage models and the underlying mechanisms. Low doses of taurine supplementation promoted cell viability, mitochondrial membrane potential (MMP), SOD levels, ATP contents and attenuated cytotoxicity and intracellular ROS generation of the R28 cells under the two kinds of damage. The expression level of GTPBP3, a mitochondrial-tRNA (mt-tRNA) modification enzyme that catalyzes the taurine involved modification, was decreased under the two damage and taurine could reverse the reduction. After knocking down GTPBP3, the R28 cells become vulnerable to damage. The viability, cytotoxicity, MMP and intracellular ROS level of knockdown cells changed more obviously under the H/R injury than those of control cell. We also found that knockdown of GTPBP3 significantly decreased mitochondrial energy metabolism by measuring the oxidative respiration rate by the Seahorse XFe24 extracellular flux analyzer. The protection of low doses of taurine disappeared on knockdown R28 cells, indicating that GTPBP3 is crucial in the protection mechanisms of taurine. However, the impacts of the reduction of GTPBP3 level can be reversed by relatively high doses of taurine, implying the protection effects of taurine were dose-dependent, and there were more complicated mechanisms remain to be explored. This study explored a new mechanism of the neuroprotective effects of taurine, which depend on the GTPBP3-mediated taurine modification of mt-tRNAs and the promotion of mitochondrial energy metabolism.

Neuroprotection Against NMDA-Induced Retinal Damage by Philanthotoxin-343 Involves Reduced Nitrosative Stress

N-methyl-D-aspartate receptor (NMDAR) overstimulation is known to mediate neurodegeneration, and hence represents a relevant therapeutic target for neurodegenerative disorders including glaucoma. This study examined the neuroprotective effects of philanthotoxin (PhTX)-343 against NMDA-induced retinal injury in rats. Male Sprague Dawley rats were divided into three groups; group 1 received phosphate buffer saline as the negative control, group 2 was injected with NMDA (160 nM) to induce retinal excitotoxic injury, and group 3 was pre-treated with PhTX-343 (160 nM) 24 h before NMDA exposure. All treatments were given intravitreally and bilaterally. Seven days post-treatment, rats were subjected to visual behaviour assessments using open field and colour recognition tests. Rats were then euthanized, and the retinas were harvested and subjected to haematoxylin and eosin (H&E) staining for morphometric analysis and 3-nitrotyrosine (3-NT) ELISA protocol as the nitrosative stress biomarker. PhTX-343 treatment prior to NMDA exposure improved the ability of rats to recognize visual cues and preserved visual functions (i.e., recognition of objects with different colours). Morphological examination of retinal tissues showed that the fractional ganglion cell layer thickness within the inner retina (IR) in the PhTX-343 treated group was greater by 1.28-fold as compared to NMDA-treated rats (p < 0.05) and was comparable to control rats (p > 0.05). Additionally, the number of retinal cell nuclei/100 μm² in IR for the PhTX-343-treated group was greater by 1.82-fold compared to NMDA-treated rats (p < 0.05) and was comparable to control group (p > 0.05). PhTX-343 also reduced the retinal 3-NT levels by 1.74-fold compared to NMDA-treated rats (p < 0.05). In conclusion, PhTX-343 pretreatment protects against NMDA-induced retinal morphological changes and visual impairment by suppressing nitrosative stress as reflected by the reduced retinal 3-NT level.

Protective role of taurine against oxidative stress (Review)

Taurine is a fundamental mediator of homeostasis that exerts multiple roles to confer protection against oxidant stress. The development of hypertension, muscle/neuro‑​associated disorders, hepatic cirrhosis, cardiac dysfunction and ischemia/reperfusion are examples of some injuries that are linked with oxidative stress. The present review gives a comprehensive description of all the underlying mechanisms of taurine, with the aim to explain its anti‑oxidant actions. Taurine is regarded as a cytoprotective molecule due to its ability to sustain normal electron transport chain, maintain glutathione stores, upregulate anti‑oxidant responses, increase membrane stability, eliminate inflammation and prevent calcium accumulation. In parallel, the synergistic effect of taurine with other potential therapeutic modalities in multiple disorders are highlighted. Apart from the results derived from research findings, the current review bridges the gap between bench and bedside, providing mechanistic insights into the biological activity of taurine that supports its potential therapeutic efficacy in clinic. In the future, further clinical studies are required to support the ameliorative effect of taurine against oxidative stress.

New solutions for old challenges in glaucoma treatment: is taurine an option to consider?

Glaucoma is a range of progressive optic neuropathies characterized by progressive retinal ganglion cell loss and visual field defects. It is recognized as a leading cause of irreversible blindness affecting more than 70 million people worldwide. Currently, reduction of intraocular pressure, a widely recognized risk factor for glaucoma development, is the only pharmacological strategy for slowing down retinal ganglion cell loss and disease progression. However, retinal ganglion cell death and visual field loss have been observed in normotensive glaucoma, suggesting that the disease process is partially independent of intraocular pressure. Taurine is one of the agents that have attracted attention of researchers recently. Taurine has been shown to be involved in multiple cellular functions, including a central role as a neurotransmitter, as a trophic factor in the central nervous system development, as an osmolyte, as a neuromodulator, and as a neuroprotectant. It also plays a role in the maintenance of the structural integrity of the membranes and in the regulation of calcium transport and homeostasis. Taurine is known to prevent N-methyl-D-aspartic acid-induced excitotoxic injury to retinal ganglion cells. A recently published study clearly demonstrated that taurine prevents retinal neuronal apoptosis both in vivo and in vitro. Protective effect of taurine may be attributed to direct inhibition of apoptosis, an activation of brain derived neurotrophic factor-related neuroprotective mechanisms and reduction of retinal oxidative and nitrosative stresses. Further studies are needed to fully explore the potential of taurine as a neuroprotective agent, so that it can be applied in clinical practice, particularly for the treatment of glaucoma. The objective of current review was to summarize recent evidence on neuroprotective properties of taurine in glaucoma.

Plasma metabolomic profiling of central serous chorioretinopathy

Our study aimed to investigate metabolites alterations in the blood plasma of central serous chorioretinopathy (CSC) patients and to identify the key biomarkers to increase the understanding of the mechanism of CSC at the molecular level. Quantitative and targeted metabolomics using liquid chromatography tandem-mass spectrometry (LCMS, Biocrates P500) assays were performed on plasma samples from the 42 subjects(CSC patients = 30, control = 12) enrolled at the Department of Ophthalmology of People's Hospital Peking University. A total of 61 altered metabolites were distinguished between CSC patients and controls. Taurine was selected as a candidate biomarker for CSC among 6 potential metobolites: taurine, glutamic acid, sarcosine, lactic acid, glutamine and C18_1. The P values of these potential metabolites were 1.01E-06, 7.35E-08, 1.27E-24, and 1.85E-10, 1.02E-05 and 8.59E-08, and the areas under the curve for them were 0.926, 0.991, 1.000, 0.900, 0.897 and 0.841, respectively. This study is the first to identify that taurine may be a biologically relevant biomarker for CSC and to provide a novel understanding of CSC.

DCMQA, a caffeoylquinic acid derivative alleviates NMDA-induced neurotoxicity via modulating GluN2A and GluN2B-containing NMDA receptors in vitro

Compound DCMQA (4, 5-O-dicaffeoyl-1-O-[4-malic acid methyl ester]-quinic acid) is a natural caffeoylquinic acid derivative isolated from Arctium lappa L. roots. Caffeoylquinic acid derivatives have been reported to possess neuroprotective effects through inhibiting oxidative stress and apoptosis in vitro. However, whether DCMQA exerts protective effects on N-methyl-D-aspartate (NMDA)-induced neurotoxicity and the underlying mechanism has not been elucidated. In this study, the results indicated that pretreatment of DCMQA prevented the loss of cell viability and attenuated the LDH leakage in SH-SY5Y cells exposed to NMDA. Hoechst 33342 staining and Annexin V-PI double staining illustrated that DCMQA suppressed NMDA-induced morphological damage and neuronal apoptosis. Moreover, DCMQA inhibited NMDA-mediated Ca²⁺ influx, excessive intracellular ROS generation and loss of mitochondrial membrane potential (MMP). Western blot analysis showed that DCMQA attenuated the Bax/Bcl-2 ratio, release of cytochrome c as well as expression of caspase-9 and caspase-3. Besides, DCMQA down-regulated GluN2B-containing NMDA receptors (NMDARs) and up-regulated GluN2A-containing NMDARs, promoted the disruption of nNOS and PSD95 as well as activation of CaMK II-α. Furthermore, computational docking study indicated that DCMQA possessed a good affinity for NMDARs. These results indicated that DCMQA protects SH-SY5Y cells against NMDA-induced neuronal damage. In addition, the underlying mechanisms of DCMQA-mediated neuroprotection are associated with modulating NMDARs and disruption of nNOS-PSD95 as well as the activation of CaMK II-α.

Magnesium acetyltaurate protects against endothelin-1 induced RGC loss by reducing neuroinflammation in Sprague dawley rats

Endothelin-1 (ET-1), a potent vasoconstrictor, plays a significant role in the pathophysiology of ocular conditions like glaucoma. Glaucoma is characterized by apoptotic loss of retinal ganglion cells (RGCs) and loss of visual fields and is a leading cause of irreversible blindness. In glaucomatous eyes, retinal ischemia causes release of pro-inflammatory mediators such as interleukin (IL)-1β, IL-6 and tumor necrosis factor (TNF)-α and promotes activation of transcription factors such as nuclear factor kappa B (NFKB) and c-Jun. Magnesium acetyltaurate (MgAT) has previously been shown to protect against ET-1 induced retinal and optic nerve damage. Current study investigated the mechanisms underlying these effects of MgAT, which so far remain unknown. Sprague dawley rats were intravitreally injected with ET-1 with or without pretreatment with MgAT. Seven days post-injection, retinal expression of IL-1β, IL-6, TNF-α, NFKB and c-Jun protein and genes was determined using multiplex assay, Western blot and PCR. Animals were subjected to retrograde labeling of RGCs to determine the extent of RGC survival. RGC survival was also examined using Brn3A staining. Furthermore, visual functions of rats were determined using Morris water maze. It was observed that pre-treatment with MgAT protects against ET-1 induced increase in the retinal expression of IL-1β, IL-6 and TNF-α proteins and genes. It also protected against ET-1 induced activation of NFKB and c-Jun. These effects of MgAT were associated with greater RGC survival and preservation of visual functions in rats. In conclusion, MgAT prevents ET-1 induced RGC loss and loss of visual functions by suppressing neuroinflammatory reaction in rat retinas.

Taurine/Pilocarpine Interaction in the Malnourished Rat Brain: A Behavioral, Electrophysiological, and Immunohistochemical Analysis

This study aimed to evaluate the possible protective role of taurine on anxiety-like behavior, brain electrical activity and glial cell immunoreactivity in well-nourished and malnourished rats that were treated with a subconvulsing dose of pilocarpine. Newborn Wistar rats were subjected to normal or unfavorable lactation conditions, represented by the suckling of litters with 9 or 15 pups, resulting in well-nourished and malnourished animals, respectively. Each nutritional group was split into five subgroups that were treated from postnatal day (PND) 35 to 55 with 300 mg/kg/day of taurine + 45 mg/kg/day of pilocarpine (group T + P), taurine only (group T), pilocarpine only (group P), vehicle control (group V), or not treated control (group naïve; Nv). At PND56-58, the groups were subjected to the elevated plus-maze behavioral tests. Glycemia was measured on PND59. Between PND60 and PND65, the cortical spreading depression (CSD) was recorded in the cerebral cortex, and the levels of malondialdehyde and microglial and astrocyte immunoreactivity were evaluated in the cortex and hippocampus. Our data indicate that treatment with taurine and pilocarpine resulted in anxiolytic-like and anxiogenic behavior, respectively, and that nutritional deficiency modulated these effects. Both treatments decelerated CSD propagation and modulated GFAP- and Iba1-containing glial cells. Pilocarpine reduced body weight and glycemia, and administration of taurine was not able to attenuate the effects of pilocarpine. The molecular mechanisms underlying taurine action on behavioral and electrophysiological parameters in the normal and altered brain remain to be further explored.