The neuroprotective effect of melatonin in glutamate excitotoxicity of R28 cells and mouse retinal ganglion cells

Neuroprotective Effects of Astragalus Polysaccharide on Retina Cells and Ganglion Cell Projection in NMDA-Induced Retinal Injury

PURPOSE

Astragalus polysaccharide (APS), a water-soluble heteropolysaccharide, possesses immunomodulatory, anti-inflammatory, and cardioprotective properties. This study investigates the neuroprotective potential of APS in a model of N-Methyl-d-aspartic acid (NMDA)-induced retinal neurodegeneration, aiming to explore its potential as a treatment for retinal degenerative diseases.

METHODS

Retinal function was evaluated using electroretinography (ERG), optomotor reflex (OMR), and flash visual evoked potentials (FVEP). Retinal inflammatory responses were examined through immunohistochemistry, western blotting (WB), and quantitative reverse transcription PCR (qRT-PCR). To assess the integrity of visual projections, an intravitreal injection of adeno-associated virus (AAV) was employed to trace the projections of retinal ganglion cells (RGCs) to the visual centers.

RESULTS

APS treatment conferred protection to retinal cells, as indicated by ERG and OMR assessments. And APS intervention mitigated NMDA-induced apoptosis, evidenced by a decrease in TUNEL-positive cells. Furthermore, APS treatment attenuated the NMDA-induced reduction in RGC projections to the visual centers, including the superior colliculus and lateral geniculate nucleus, as demonstrated by AAV tracing.

CONCLUSIONS

Our findings reveal that APS shields the retina from NMDA-induced damage by inhibiting the NF-κB signaling pathway and reduces the detrimental effects of NMDA on RGC projections to the visual centers. These findings propose APS as a potential novel therapeutic agent for the treatment of retinal diseases.

Exploring the association between melatonin and nicotine dependence (Review)

Due to the addictive qualities of tobacco products and the compulsive craving and dependence associated with their use, nicotine dependence continues to be a serious public health concern on a global scale. Despite awareness of the associated health risks, nicotine addiction contributes to numerous acute and chronic medical conditions, including cardiovascular disease, respiratory disorders and cancer. The nocturnal secretion of pineal melatonin, known as the 'hormone of darkness', influences circadian rhythms and is implicated in addiction‑related behaviors. Melatonin receptors are found throughout the brain, influencing dopaminergic neurotransmission and potentially attenuating nicotine‑seeking behavior. Additionally, the antioxidant properties of melatonin may mitigate oxidative stress from chronic nicotine exposure, reducing cellular damage and lowering the risk of nicotine‑related health issues. In addition to its effects on circadian rhythmicity, melatonin acting via specific neural receptors influences sleep and mood, and provides neuroprotection. Disruptions in melatonin signaling may contribute to sleep disturbances and mood disorders, highlighting the potential therapeutic role of melatonin in addiction and psychiatric conditions. Melatonin may influence neurotransmitter systems involved in addiction, such as the dopaminergic, glutamatergic, serotonergic and endogenous opioid systems. Preclinical studies suggest the potential of melatonin in modulating reward processing, attenuating drug‑induced hyperactivity and reducing opioid withdrawal symptoms. Chronotherapeutic approaches targeting circadian rhythms and melatonin signaling show promise in smoking cessation interventions. Melatonin supplementation during periods of heightened nicotine cravings may alleviate withdrawal symptoms and reduce the reinforcing effects of nicotine. Further research is required however, to examine the molecular mechanisms underlying the melatonin‑nicotine association and the optimization of therapeutic interventions. Challenges include variability in individual responses to melatonin, optimal dosing regimens and identifying biomarkers of treatment response. Understanding these complexities could lead to personalized treatment strategies and improve smoking cessation outcomes.

Neuroprotective effects of resveratrol on retinal ganglion cells in glaucoma in rodents: A narrative review

Glaucoma, an irreversible optic neuropathy, primarily affects retinal ganglion cells (RGC) and causes vision loss and blindness. The damage to RGCs in glaucoma occurs by various mechanisms, including elevated intraocular pressure, oxidative stress, inflammation, and other neurodegenerative processes. As the disease progresses, the loss of RGCs leads to vision loss. Therefore, protecting RGCs from damage and promoting their survival are important goals in managing glaucoma. In this regard, resveratrol (RES), a polyphenolic phytoalexin, exerts antioxidant effects and slows down the evolution and progression of glaucoma. The present review shows that RES plays a protective role in RGCs in cases of ischemic injury and hypoxia as well as in ErbB2 protein expression in the retina. Additionally, RES plays protective roles in RGCs by promoting cell growth, reducing apoptosis, and decreasing oxidative stress in H2O2-exposed RGCs. RES was also found to inhibit oxidative stress damage in RGCs and suppress the activation of mitogen-activated protein kinase signaling pathways. RES could alleviate retinal function impairment by suppressing the hypoxia-inducible factor-1 alpha/vascular endothelial growth factor and p38/p53 axes while stimulating the PI3K/Akt pathway. Therefore, RES might exert potential therapeutic effects for managing glaucoma by protecting RGCs from damage and promoting their survival.

Ripa-56 protects retinal ganglion cells in glutamate-induced retinal excitotoxic model of glaucoma

Glaucoma is a prevalent cause of blindness globally, characterized by the progressive degeneration of retinal ganglion cells (RGCs). Among various factors, glutamate excitotoxicity stands out as a significant contributor of RGCs loss in glaucoma. Our study focused on Ripa-56 and its protective effect against NMDA-induced retinal damage in mice, aiming to delve into the potential underlying mechanism. The R28 cells were categorized into four groups: glutamate (Glu), Glu + Ripa-56, Ripa-56 and Control group. After 24 h of treatment, cell death was assessed by PI / Hoechst staining. Mitochondrial membrane potential changes, apoptosis and reactive oxygen species (ROS) production were analyzed using flow cytometry. The alterations in the expression of RIP-1, p-MLKL, Bcl-2, BAX, Caspase-3, Gpx4 and SLC7A11 were examined using western blot analysis. C57BL/6j mice were randomly divided into NMDA, NMDA + Ripa-56, Ripa-56 and control groups. Histological changes in the retina were evaluated using hematoxylin and eosin (H&E) staining. RGCs survival and the protein expression changes of RIP-1, Caspase-3, Bcl-2, Gpx4 and SLC7A11 were observed using immunofluorescence. Ripa-56 exhibited a significant reduction in the levels of RIP-1, p-MLKL, Caspase-3, and BAX induced by glutamate, while promoting the expression of Bcl-2, Gpx-4, and SLC7A1 in the Ripa-56-treated group. In our study, using an NMDA-induced normal tension glaucoma mice model, we employed immunofluorescence and H&E staining to observe that Ripa-56 treatment effectively ameliorated retinal ganglion cell loss, mitigating the decrease in retinal ganglion cell layer and bipolar cell layer thickness caused by NMDA. In this study, we have observed that Ripa-56 possesses remarkable anti- necroptotic, anti-apoptotic and anti-ferroptosis properties. It demonstrates the ability to combat not only glutamate-induced excitotoxicity in R28 cells, but also NMDA-induced retinal excitotoxicity in mice. Therefore, Ripa-56 could be used as a potential retinal protective agent.

Misalignment of Circadian Rhythms in Diet-Induced Obesity

The biological clocks of the circadian timing system coordinate cellular and physiological processes and synchronize them with daily cycles. While the central clock in the suprachiasmatic nucleus (SCN) is mainly synchronized by the light/dark cycles, the peripheral clocks react to other stimuli, including the feeding/fasting state, nutrients, sleep-wake cycles, and physical activity. During the disruption of circadian rhythms due to genetic mutations or social and occupational obligations, incorrect arrangement between the internal clock system and environmental rhythms leads to the development of obesity. Desynchronization between the central and peripheral clocks by altered timing of food intake and diet composition leads to uncoupling of the peripheral clocks from the central pacemaker and to the development of metabolic disorders. The strong coupling of the SCN to the light-dark cycle creates a situation of misalignment when food is ingested during the "wrong" time of day. Food-anticipatory activity is mediated by a self-sustained circadian timing, and its principal component is a food-entrainable oscillator. Modifying the time of feeding alone greatly affects body weight, whereas ketogenic diet (KD) influences circadian biology, through the modulation of clock gene expression. Night-eating behavior is one of the causes of circadian disruption, and night eaters have compulsive and uncontrolled eating with severe obesity. By contrast, time-restricted eating (TRE) restores circadian rhythms through maintaining an appropriate daily rhythm of the eating-fasting cycle. The hypothalamus has a crucial role in the regulation of energy balance rather than food intake. While circadian locomotor output cycles kaput (CLOCK) expression levels increase with high-fat diet-induced obesity, peroxisome proliferator-activated receptor-alpha (PPARα) increases the transcriptional level of brain and muscle aryl hydrocarbon receptor nuclear translocator (ARNT)-like 1 (BMAL1) in obese subjects. In this context, effective timing of chronotherapies aiming to correct SCN-driven rhythms depends on an accurate assessment of the SCN phase. In fact, in a multi-oscillator system, local rhythmicity and its disruption reflects the disruption of either local clocks or central clocks, thus imposing rhythmicity on those local tissues, whereas misalignment of peripheral oscillators is due to exosome-based intercellular communication.Consequently, disruption of clock genes results in dyslipidemia, insulin resistance, and obesity, while light exposure during the daytime, food intake during the daytime, and sleeping during the biological night promote circadian alignment between the central and peripheral clocks. Thus, shift work is associated with an increased risk of obesity, diabetes, and cardiovascular diseases because of unusual eating times as well as unusual light exposure and disruption of the circadian rhythm.