Melatonin mitigates disrupted circadian rhythms, lowers intraocular pressure, and improves retinal ganglion cells function in glaucoma

Melatonin: Unveiling the functions and implications in ocular health

Melatonin, a versatile hormone produced by the pineal gland, has garnered considerable scientific interest due to its diverse functions. In the eye, melatonin regulates a variety of key processes like inhibiting angiogenesis by reducing vascular endothelial growth factor levels and protecting the blood-retinal barrier (BRB) integrity by enhancing tight junction proteins and pericyte coverage. Melatonin also maintains cell health by modulating autophagy via the Sirt1/mTOR pathways, reduces inflammation, promotes antioxidant enzyme activity, and regulates intraocular pressure fluctuations. Additionally, melatonin protects retinal ganglion cells by modulating aging and inflammatory pathways. Understanding melatonin's multifaceted functions in ocular health could expand the knowledge of ocular pathogenesis, and shed new light on therapeutic approaches in ocular diseases. In this review, we summarize the current evidence of ocular functions and therapeutic potential of melatonin and describe its roles in angiogenesis, BRB integrity maintenance, and modulation of various eye diseases, which leads to a conclusion that melatonin holds promising treatment potential for a wide range of ocular health conditions.

Protective effect of melatonin against metabolic disorders and neuropsychiatric injuries in type 2 diabetes mellitus mice

BACKGROUND

Type 2 diabetes mellitus (T2DM) is a metabolic disease characterized by hyperglycemia and progressive cognitive dysfunction, and our clinical investigation revealed that the plasma concentration of melatonin (Mlt) decreased and was closely related to cognition in T2DM patients. However, although many studies have suggested that Mlt has a certain protective effect on glucose and lipid metabolism disorders and neuropsychiatric injury, the underlying mechanism of Mlt against T2DM-related metabolic and cognitive impairments remains unclear.

PURPOSE

The aim of the present study was to investigate the therapeutic effect of Mlt on metabolic disorders and Alzheimer's disease (AD)-like neuropsychiatric injuries in T2DM mice and to explore the possible underlying molecular mechanism involved.

METHODS

A T2DM mouse model was established by a combination of a high-fat diet (HFD) and streptozotocin (STZ, 100 mg/kg, i.p.), and Mlt (5, 10 or 20 mg/kg) was intragastrically administered for six consecutive weeks. The serum levels of glycolipid metabolism indicators were measured, behavioral performance was tested, and the protein expression of key molecules involved in the regulation of synaptic plasticity, circadian rhythms, and neuroinflammation in the hippocampus was detected. Moreover, the fluorescence intensities of glial fibrillary acidic protein (GFAP), ionized calcium binding adapter molecule 1 (IBA-1), amyloid β-protein (Aβ) and phosphorylated Tau (p-Tau) in the hippocampus were also observed.

RESULTS

Treatment with Mlt not only improved T2DM-related metabolic disorders, as indicated by increased serum concentrations of fasting blood glucose (FBG), glycosylated hemoglobin (HbAlc), insulin (INS), total cholesterol (TC) and triglyceride (TG), improved glucose tolerance and liver and pancreas function but also alleviated AD-like neuropsychiatric injuries in a HFD/STZ-induced mouse model, as indicated by decreased immobility time in the tail suspension test (TST) and forced swimming test (FST), increased preference indices of novel objects or novel arms in the novel object recognition test (NOR) and Y-maze test (Y-maze), and improved platform positioning capability in the Morris water maze (MWM) test. Moreover, treatment with Mlt also improved the hyperactivation of astrocytes and microglia in the hippocampus of mice, accompanied by reduced expression of interleukin 1β (IL-1β), interleukin 6 (IL-6), tumor necrosis factor (TNF-α), Aβ, and p-Tau and increased expression of brain-derived neurotrophic factor (BDNF), Synapsin I, Synaptotagmin I, melatonin receptor 1B (MT1B), brain muscle arnt-like protein 1 (Bmal1), circadian locomotor output cycles kaput (Clock), period 2 (Per2), and cryptochrome 2 (Cry2).

CONCLUSION

Mlt alleviated T2DM-related metabolic disorders and AD-like neuropsychiatric injuries in a HFD/STZ-induced mouse model, possibly through a mechanism involving the regulation of glial activation and associated neuroinflammation and the balancing of synaptic plasticity and circadian rhythms in the hippocampus.

Temperature Self-Compensating Intelligent Wireless Measuring Contact Lens for Quantitative Intraocular Pressure Monitoring

Flexible bioelectronic devices that can perform real-time and accurate intraocular pressure (IOP) monitoring in both clinical and home settings hold significant implications for the diagnosis and treatment of glaucoma, yet they face challenges due to the open physiological environment of the ocular. Herein, we develop an intelligent wireless measuring contact lens (WMCL) incorporating a dual inductor-capacitor-resistor (LCR) resonant system to achieve temperature self-compensation for quantitative IOP monitoring in different application environments. The WMCL utilizes a compact circuitry design, which enables the integration of low-frequency and high-frequency resonators within a single layer of a sensing circuit without causing visual impairment. Mechanically guided microscale 3D encapsulation strategy combined with flexible circuit printing techniques achieves the surface-adaptive fabrication of the WMCL. The specific design of frequency separation imparts distinct temperature response characteristics to the dual resonators, and the linear combination of the dual resonators can eliminate the impact of temperature variations on measurement accuracy. The WMCL demonstrates outstanding sensitivity and linearity in monitoring the IOP of porcine eyes in vitro while maintaining satisfactory measurement accuracy even with internal temperature variations exceeding 10 °C. Overcoming the impact of temperature variations on IOP monitoring from the system level, the WMCL showcases immense potential as the next generation of all-weather IOP monitoring devices.

A Clinical, Pharmacological, and Formulation Evaluation of Melatonin in the Treatment of Ocular Disorders-A Systematic Review

Melatonin's cytoprotective properties may have therapeutic implications in treating ocular diseases like glaucoma and age-related macular degeneration. Literature data suggest that melatonin could potentially protect ocular tissues by decreasing the production of free radicals and pro-inflammatory mediators. This study aims to summarize the screened articles on melatonin's clinical, pharmacological, and formulation evaluation in treating ocular disorders. The identification of relevant studies on the topic in focus was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA 2020) guidelines. The studies were searched in the following databases and web search engines: Pubmed, Scopus, Science Direct, Web of Science, Reaxys, Google Scholar, Google Patents, Espacenet, and Patentscope. The search time interval was 2013-2023, with the following keywords: melatonin AND ocular OR ophthalmic AND formulation OR insert AND disease. Our key conclusion was that using melatonin-loaded nano-delivery systems enabled the improved permeation of the molecule into intraocular tissues and assured controlled release profiles. Although preclinical studies have demonstrated the efficacy of developed formulations, a considerable gap has been observed in the clinical translation of the results. To overcome this failure, revising the preclinical experimental phase might be useful by selecting endpoints close to clinical ones.

Lighting the way: Exploring diurnal physical performance differences in school-aged visually impaired children and adolescents

Circadian rhythms play a pivotal role in governing various physiological processes, including physical performance. However, in individuals deprived of light perception, such as the blind, these circadian rhythms face disruption. This study aimed to explore the influence of disturbed circadian rhythms on short-term maximal physical performance in children and adolescents with visual impairment. Forty-five volunteers participated in this study, comprising 17 blind, 13 visually impaired, and 15 sighted participants. The participants underwent a series of tests assessing maximal isometric strength performance across two days. To mitigate the influence of morning session fatigue on the evening results, each participant group performed in two separate testing sessions (i.e. in the morning (7:00 h) and in the evening (17:00 h)) on non-consecutive days in a randomized and counterbalanced setting, with approximately 36 h of recovery time between sessions. To mitigate the impact of inter-individual differences on mean values and to account for the influence of age and sex on the studied variables, data were normalized. The outcomes revealed a significant diurnal variation in maximal isometric strength performance among sighted individuals, with peak performance observed in the evening. This pattern aligns with their well-entrained circadian rhythm. In contrast, blind and visually impaired individuals did not display significant diurnal variation, signaling disrupted circadian rhythms due to the absence of light perception. These findings emphasize the crucial consideration of circadian rhythms in assessments of physical performance, especially among participants with visual impairments.

[Primary open angle glaucoma and sleep apnea syndrome: A review of the literature]

The relationship between glaucoma and Obstructive Sleep Apnea Syndrome (OSAS) has long been discussed, with conflicting study findings. OSAS appears in the most recent studies to be more of an aggravating factor than an independent risk factor for glaucoma. Patients with OSAS may develop a more rapid progression of primary open-angle glaucoma (POAG). OSAS may damage the optic nerve not only by increasing the intraocular pressure (IOP) but also by altering the blood supply to the optic nerve as shown by more recent work with OCT-Angiography. Although the systemic benefits of Continuous Positive Airway Pressure (CPAP) have been demonstrated, few studies have evaluated its effect on the optic nerve. CPAP might act on glaucomatous neuropathy by improving the blood supply to the optic nerve. The study of this mechanism of action might provide new insights into the relationship between OSAS and glaucoma.

Melatonin prevents EAAC1 deletion-induced retinal ganglion cell degeneration by inhibiting apoptosis and senescence

Normal tension glaucoma (NTG) is referred to as a progressive degenerative disorder of the retinal ganglion cells (RGCs), resulting in nonreversible visual defects, despite intraocular pressure levels within the statistically normal range. Current therapeutic strategies for NTG yield limited benefits. Excitatory amino acid carrier 1 (EAAC1) knockout (EAAC1-/- ) in mice has been shown to induce RGC degeneration without elevating intraocular pressure, mimicking pathological characteristics of NTG. In this study, we explored whether daily oral administration of melatonin could block RGCs loss and prevent retinal morphology and function defects associated with EAAC1 deletion. We also explored the molecular mechanisms underlying EAAC1 deletion-induced RGC degeneration and the neuroprotective effects of melatonin. Our RNA sequencing and in vivo data indicated EAAC1 deletion caused elevated oxidative stress, activation of apoptosis and cellular senescence pathways, and neuroinflammation in RGCs. However, melatonin administration efficiently prevented these detrimental effects. Furthermore, we investigated the potential role of apoptosis- and senescence-related redox-sensitive factors in EAAC1 deletion-induced RGCs degeneration and the neuroprotective effects of melatonin administration. We observed remarkable upregulation of p53, whereas NRF2 and Sirt1 expression were significantly decreased in EAAC1-/- mice, which were prevented by melatonin treatment, suggesting that melatonin exerted its neuroprotective effects possibly through modulating NRF2/p53/Sirt1 redox-sensitive signaling pathways. Overall, our study provided a solid foundation for the application of melatonin in the management of NTG.

Blue Light and Temperature Actigraphy Measures Predicting Metabolic Health Are Linked to Melatonin Receptor Polymorphism

This study explores the relationship between the light features of the Arctic spring equinox and circadian rhythms, sleep and metabolic health. Residents (N = 62) provided week-long actigraphy measures, including light exposure, which were related to body mass index (BMI), leptin and cortisol. Lower wrist temperature (wT) and higher evening blue light exposure (BLE), expressed as a novel index, the nocturnal excess index (NEIbl), were the most sensitive actigraphy measures associated with BMI. A higher BMI was linked to nocturnal BLE within distinct time windows. These associations were present specifically in carriers of the MTNR1B rs10830963 G-allele. A larger wake-after-sleep onset (WASO), smaller 24 h amplitude and earlier phase of the activity rhythm were associated with higher leptin. Higher cortisol was associated with an earlier M10 onset of BLE and with our other novel index, the Daylight Deficit Index of blue light, DDIbl. We also found sex-, age- and population-dependent differences in the parametric and non-parametric indices of BLE, wT and physical activity, while there were no differences in any sleep characteristics. Overall, this study determined sensitive actigraphy markers of light exposure and wT predictive of metabolic health and showed that these markers are linked to melatonin receptor polymorphism.

Melatonin-mediated mitophagy protects against long-term impairments after repeated neonatal sevoflurane exposures

BACKGROUND

Melatonin is known to have protective effects in aging, neurodegenerative disorders and mitochondria-related diseases, while there is a poor understanding of the effects of melatonin treatment on mitophagy in neonatal cognitive dysfunction after repeated sevoflurane exposures. This study explores the protective effects of melatonin on mitophagy and cognition in developing rats exposed to sevoflurane.

METHODS

Postnatal day six (P6) neonatal rats were exposed to 3 % sevoflurane for 2 h daily from P6 to P8. In the intervention groups, rats received 3-Methyladenine (3-MA) intracerebroventricularly from P6 to P8 and melatonin intraperitoneally from P6 to P8 following water drinking once daily from P21 to P41, respectively. Behavioral tests, including open field (OF), novel object recognition (NOR), and fear conditioning (FC) tests, were performed to assess cognitive function during young adulthood. In another experiment, rat brains were harvested for biochemical, histopathological, and electron microscopy studies.

RESULTS

Rats exposed to sevoflurane showed disordered mitophagy and mitochondrial dysfunction as revealed by increased mitophagy marker proteins (microtubule-associated protein 1 light chain 3 (LC3) II/I, and parkin), decreased autophagy marker protein (sequestosome 1 (P62/SQSTM1)), electron transport chain (ETC) proteins and ATP levels. Immunofluorescent staining of LC3 was co-localized mostly with a neuronal marker and microglial marker but was not co-localized with a marker for astrocytes in rats exposed to sevoflurane. These rats had poorer performance in the NOR and FC tests than control rats during young adulthood. Melatonin treatment reversed the abnormal expression of mitophagy proteins, mitochondrial energy metabolism, the activity of microglia, and impaired cognition. These ameliorations were blocked by an autophagy inhibitor, 3-MA, except for the activation of microglia.

CONCLUSION

We have demonstrated that melatonin inhibits microglial activation by enhancing mitophagy and finally significantly reduces sevoflurane-induced deficits in cognition in neonatal rats. These results suggest that melatonin might be beneficial if considered when the anesthesia must be administered at a very young age.

Melatonin protects retinal tissue damage in streptozotocin-induced aged rats

OBJECTIVES

The aim of this study was to investigate how melatonin administration affects retinal oxidative damage and retinal SIRT1 gene activation in diabetic elderly female rat model.

METHODS

16-months-old female rats were used in the study. A total of 24 rats were divided into 4 groups in equal numbers: Group 1. Control, Group 2. Control + Melatonin, Group 3. Diabetes, Group 4. Diabetes + Melatonin. In group 3 and 4 rats, diabetes was induced by intraperitoneal (IP) injection of streptozotocin. Groups 2 and 4 were given ip melatonin for 4 weeks. SIRT-1 gene expression was determined by PCR method and GSH and MDA levels by ELISA in retinal tissue samples taken from animals sacrificed under general anesthesia.

RESULTS

In our study, the highest retinal SIRT1 expression values were obtained in the diabetes + melatonin (G4) group. The retinal SIRT1 expression values of the diabetes group (G3) were lower than group 4 and higher than the general control (G1) and control + melatonin (G2) groups. Again in our study, the highest retinal MDA values were obtained in the diabetes group (G3). The highest retinal GSH values were obtained in the Diabetes + melatonin group (G4).

CONCLUSION

The results of our study showed that melatonin supplementation has a protective effect on retinal tissue in a diabetic elderly female rat model. This protective effect of melatonin supplementation occurs by increasing both retinal antioxidant activity and retinal SIRT1 gene expression.

Illuminating the way: the role of bright light therapy in the treatment of depression

INTRODUCTION

Despite the growing number of different therapeutic options, treatment of depression is still a challenge. A broader perspective reveals the benefits of bright light therapy (BLT). It stimulates intrinsically photosensitive retinal ganglion cells, which induces a complex cascade of events, including alterations in melatonergic, neurotrophic, GABAergic, glutamatergic, noradrenergic, serotonergic systems, and HPA axis, suggesting that BLT effects expand beyond the circadian pacemaker.

AREAS COVERED

In this review, the authors present and discuss recent data of BLT in major depressive disorder, non-seasonal depression, bipolar depression or depressive phase of bipolar disorder, and seasonal affective disorder, as well as in treatment-resistant depression (TRD). The authors further highlight BLT effects in various depressive disorders compared to placebo and report data from several studies suggesting a response to BLT in TRD. Also, the authors report data showing that BLT can be used both as a monotherapy or in combination with other pharmacological treatments.

EXPERT OPINION

BLT is an easy-to-use and low-budget therapy with good tolerability. Future studies should focus on clinical and biological predictors of response to BLT, on defining specific populations which may benefit from BLT and establishing treatment protocols regarding timing, frequency, and duration of BLT.

Melatonin regulates microglial polarization to M2 cell via RhoA/ROCK signaling pathway in epilepsy

BACKGROUND

Melatonin (MEL), an endogenous hormone, has been widely investigated in neurological diseases. Microglia (MG), a resident immunocyte localizing in central nervous system is reported to play important functions in the animal model of temporal lobe epilepsy (TLE). Some evidence showed that MEL influenced activation of MG, but the detailed model of action that MEL plays in remains uncertain.

METHODS

In this study, we established a model of TLE in mice by stereotactic injection of kainic acid (KA). We treated the mice with MEL. Lipopolysaccharide, ROCK2-knockdown (ROCK-KD) and -overexpression (ROCK-OE) of lentivirus-treated cells were used in cell experiments to simulate an in vitro inflammatory model.

RESULTS

The results of electrophysiological tests showed that MEL reduced frequency and severity of seizure. The results of behavioral tests indicated MEL improved cognition, learning, and memory ability. Histological evidences demonstrated a significant reduction of neuronal death in the hippocampus. In vivo study showed that MEL changed the polarization status of MG from a proinflammatory M1 phenotype to an anti-inflammatory M2 phenotype by inversely regulating the RhoA/ROCK signaling pathway. In cytological study, we found that MEL had a significant protective effect in LPS-treated BV-2 cells and ROCK-KD cells, while the protective effect of MEL was significantly attenuated in ROCK-OE cells.

CONCLUSION

MEL played an antiepileptic role in the KA-induced TLE modeling mice both in behavioral and histological levels, and changed MG polarization status by regulating the RhoA/ROCK signaling pathway.

Contact Lens Sensor with Anti-jamming Capability and High Sensitivity for Intraocular Pressure Monitoring

Contact lens sensors provide a noninvasive approach for intraocular pressure (IOP) monitoring in patients with glaucoma. Accurate measurement of this imperceptible pressure variation requires highly sensitive sensors in the absence of simultaneously amplifying IOP signal and blinking-induced noise. However, current noise-reduction methods rely on external filter circuits, which thicken contact lenses and reduce signal quality. Here, we introduce a contact lens strain sensor with an anti-jamming ability by utilizing a self-lubricating layer to reduce the coefficient of friction (COF) to remove the interference from the tangential force. The sensor achieves exceptionally high sensitivity due to the strain concentration layout and the confined occurrence of sympatric microcracks. The animal tests prove our lens can accurately detect IOP safely and reliably.

Melatonin protects against NMDA-induced retinal ganglion cell injury by regulating the microglia-TNFα-RGC p38 MAPK pathway

Glaucoma, one of the most common ocular neurodegenerative diseases worldwide, is characterized by retinal ganglion cell (RGC) loss. There is a large body of literature that describes the neuroprotective role of melatonin against neurodegenerative diseases by regulating neuroinflammation, although the exact mechanism through which melatonin acts on RGC is still uncertain. This study assessed the protective effects of melatonin using a NMDA-induced RGC injury model, and studied the possible mechanisms involved in this process. Melatonin promoted RGC survival, improved retinal function, and inhibited the apoptosis and necrosis of retinal cells. To understand the mechanism of the neuroprotective effects of melatonin on RGC, microglia and inflammation-related pathways were assessed after melatonin administration and microglia ablation. Melatonin promoted RGC survival by suppressing microglia-derived proinflammatory cytokines, in particular TNFα, which in turn inhibited the activation of p38 MAPK pathway. Inhibiting TNFα or manipulating p38 MAPK pathway protected damaged RGC. Our results suggest that melatonin protects against NMDA-induced RGC injury by inhibiting the microglial TNFα-RGC p38 MAPK pathway. It should be considered a candidate neuroprotective therapy against retinal neurodegenerative diseases.

Circadian clock organization in the retina: From clock components to rod and cone pathways and visual function

Circadian (24-h) clocks are cell-autonomous biological oscillators that orchestrate many aspects of our physiology on a daily basis. Numerous circadian rhythms in mammalian and non-mammalian retinas have been observed and the presence of an endogenous circadian clock has been demonstrated. However, how the clock and associated rhythms assemble into pathways that support and control retina function remains largely unknown. Our goal here is to review the current status of our knowledge and evaluate recent advances. We describe many previously-observed retinal rhythms, including circadian rhythms of morphology, biochemistry, physiology, and gene expression. We evaluate evidence concerning the location and molecular machinery of the retinal circadian clock, as well as consider findings that suggest the presence of multiple clocks. Our primary focus though is to describe in depth circadian rhythms in the light responses of retinal neurons with an emphasis on clock control of rod and cone pathways. We examine evidence that specific biochemical mechanisms produce these daily light response changes. We also discuss evidence for the presence of multiple circadian retinal pathways involving rhythms in neurotransmitter activity, transmitter receptors, metabolism, and pH. We focus on distinct actions of two dopamine receptor systems in the outer retina, a dopamine D4 receptor system that mediates circadian control of rod/cone gap junction coupling and a dopamine D1 receptor system that mediates non-circadian, light/dark adaptive regulation of gap junction coupling between horizontal cells. Finally, we evaluate the role of circadian rhythmicity in retinal degeneration and suggest future directions for the field of retinal circadian biology.

Formulation and Characterization of Electrospun Nanofibers for Melatonin Ocular Delivery

The poor ocular bioavailability of melatonin (MEL) limits the therapeutic action the molecule could exert in the treatment of ocular diseases. To date, no study has explored the use of nanofiber-based inserts to prolong ocular surface contact time and improve MEL delivery. Here, the electrospinning technique was proposed to prepare poly (vinyl alcohol) (PVA) and poly (lactic acid) (PLA) nanofiber inserts. Both nanofibers were produced with different concentrations of MEL and with or without the addition of Tween^® 80. Nanofibers morphology was evaluated by scanning electron microscopy. Thermal and spectroscopic analyses were performed to characterize the state of MEL in the scaffolds. MEL release profiles were observed under simulated physiological conditions (pH 7.4, 37 °C). The swelling behavior was evaluated by a gravimetric method. The results confirmed that submicron-sized nanofibrous structures were obtained with MEL in the amorphous state. Different MEL release rates were achieved depending on the nature of the polymer. Fast (20 min) and complete release was observed for the PVA-based samples, unlike the PLA polymer, which provided slow and controlled MEL release. The addition of Tween^® 80 affected the swelling properties of the fibrous structures. Overall, the results suggest that membranes could be an attractive vehicle as a potential alternative to liquid formulations for ocular administration of MEL.

Depression scores are associated with retinal ganglion cells loss

BACKGROUND

Light is a known factor affecting mood and the circadian system. Light deficit is linked to deteriorated transduction of photic information to the brain, and reduced amplitude of the perceived circadian light signaling. Retinal ganglion cells (RGCs) loss due to advanced glaucoma can be a factor compromising light perception, with consequences for circadian rhythms, sleep and mood. This study aimed to estimate associations of RGCs loss with a depression score by multiple regression, accounting for other features of glaucoma.

METHODS

One hundred and fifteen patients diagnosed with primary open-angle glaucoma completed the Beck Depression Inventory II questionnaire. The damage to their RGCs was assessed by high-definition optical coherence tomography (HD-OCT) and their function by pattern electroretinogram (PERG). On fifteen of these patients, 24-h salivary melatonin patterns were determined under light-controlled laboratory conditions, and analysis of eight clock related gene polymorphisms was performed.

RESULTS

Backward stepwise multiple regression revealed that the BDI score was the strongest factor that was most closely associated with the HD-OCT-based percentage of global RGCs loss (standardized coefficient, b* = 0.784, p < 0.001), surpassing other related factors, including age, intraocular pressure, visual field loss, and PERG amplitude. A high BDI score was associated with the GNβ3 825C > T polymorphism (dbSNP rs5443).

LIMITATIONS

This study did not specifically address damage to intrinsically photoreceptive RGCs. The gene study is based on a limited number of volunteers.

CONCLUSIONS

Depression scores are strongly associated with RGCs loss, increasing abruptly above a threshold of 15 %, supporting the hypothesis that RGCs loss in advanced glaucoma may affect non-visual photic transduction and lead to mood disturbances.

Regulation of Aqueous Humor Secretion by Melatonin in Porcine Ciliary Epithelium

Secretion of melatonin, a natural hormone whose receptors are present in the ciliary epithelium, displays diurnal variation in the aqueous humor (AH), potentially contributing to the regulation of intraocular pressure. This study aimed to determine the effects of melatonin on AH secretion in porcine ciliary epithelium. The addition of 100 µM melatonin to both sides of the epithelium significantly increased the short-circuit current (Isc) by ~40%. Stromal administration alone had no effect on the Isc, but aqueous application triggered a 40% increase in Isc, similar to that of bilateral application without additive effect. Pre-treatment with niflumic acid abolished melatonin-induced Isc stimulation. More importantly, melatonin stimulated the fluid secretion across the intact ciliary epithelium by ~80% and elicited a sustained increase (~50-60%) in gap junctional permeability between pigmented ciliary epithelial (PE) cells and non-pigmented ciliary epithelial (NPE) cells. The expression of MT3 receptor was found to be >10-fold higher than that of MT1 and MT2 in porcine ciliary epithelium. Aqueous pre-treatment with MT1/MT2 antagonist luzindole failed to inhibit the melatonin-induced Isc response, while MT3 antagonist prazosin pre-treatment abolished the Isc stimulation. We conclude that melatonin facilitates Cl- and fluid movement from PE to NPE cells, thereby stimulating AH secretion via NPE-cell MT3 receptors.

MTNR1A and MTNR1B Gene Variants of the Melatonin Receptor and Arterial Stiffness in Persons without Arterial Hypertension

A comparative analysis of vascular stiffness indices and the results of blood test was carried out in 85 healthy donors aged 19-64 years, carriers of polymorphic variants of type 1 and type 2 melatonin receptor genes. The associations of polymorphic markers of type 1 MTNR1A (rs34532313) and type 2 MTNR1B (rs10830963) melatonin receptor genes with parameters of vascular stiffness and blood parameters in healthy patients were studied. Genotyping was performed using allele-specific PCR. In all patients, 24-h BP monitoring with assessment of arterial stiffness was performed. Allele C homozygotes of MTNR1A differed significantly from carriers of the major T allele by elevated triglyceride, LDL, and fibrinogen levels. The major allele C of the rs10830963 polymorphic variant of the MTNR1B gene is associated with elevated LDL and triglycerides, as well as with individual differences in the elastic properties of the vascular wall in the examined subjects.

Role of Melatonin in Daily Variations of Plasma Insulin Level and Pancreatic Clock Gene Expression in Chick Exposed to Monochromatic Light

To clarify the effect of monochromatic light on circadian rhythms of plasma insulin level and pancreatic clock gene expression and its mechanism, 216 newly hatched chicks were divided into three groups (intact, sham operation and pinealectomy) and were raised under white (WL), red (RL), green (GL) or blue (BL) light for 21 days. Their plasma and pancreas were sampled at six four-hour intervals. For circadian rhythm analysis, measurements of plasma melatonin, insulin, and clock gene expression (cClock, cBmal1, cBmal2, cCry1, cCry2, cPer2, and cPer3) were made. Plasma melatonin, insulin, and the pancreatic clock gene all expressed rhythmically in the presence of monochromatic light. Red light reduced the mesor and amplitude of plasma melatonin in comparison to green light. The mesor and amplitude of the pancreatic clock gene in chickens exposed to red light were dramatically reduced, which is consistent with the drop in plasma melatonin levels. Red light, on the other hand, clearly raised the level of plasma insulin via raising the expression of cVamp2, but not cInsulin. After the pineal gland was removed, the circadian expressions of plasma melatonin and pancreatic clock gene were significantly reduced, but the plasma insulin level and the pancreatic cVamp2 expression were obviously increased, resulting in the disappearance of differences in insulin level and cVamp2 expression in the monochromatic light groups. Therefore, we hypothesize that melatonin may be crucial in the effect of monochromatic light on the circadian rhythm of plasma insulin level by influencing the expression of clock gene in chicken pancreas.

Daily Patterns of Accelerometer-Measured Movement Behaviors in Glaucoma Patients: Insights From UK Biobank Participants

PURPOSE

The purpose of this study is to compare daily patterns of accelerometer-measured movement behaviors between glaucoma patients and those without glaucoma.

METHODS

From 2013 to 2015, 106,053 UK Biobank participants took part in a 7-day accelerometer test. Based on established algorithms, continuous accelerometer data were classified into 4 movement behaviors: moderate to vigorous physical activity (MVPA), light physical activity, sedentary behaviors, and sleep. Glaucoma and other covariates were defined according to baseline assessments and inpatient diagnosis records. Negative binomial regression models were used to compare daily patterns of movement behaviors between glaucoma patients and those without glaucoma.

RESULTS

Accelerometer data from 1262 glaucoma patients and 81,551 participants without glaucoma were included. Compared with participants without glaucoma, glaucoma patients spent 4.7% less time on MVPA in multivariable models [mean=28.3 vs 31.4 min/d; incidence-rate ratio (IRR) 0.953, 95% confidence interval (CI): 0.910-0.998; P=0.044], which was mainly attributed to the decreased MVPA time during 18:00-23:59 (IRR=0.863, Bonferroni-corrected 95% CI: 0.768-0.970; P=0.002). Subgroup analyses indicated that compared with those with normal body mass index, the decreased MVPA time was more pronounced in participants with overweight and obesity (IRR=0.912, Bonferroni-corrected 95% CI: 0.851-0.978; P for interaction=0.007). No significant association was found between glaucoma and time spent on other movement behaviors including light physical activity, sedentary behaviors, and sleep.

CONCLUSIONS

Daily patterns of movement behaviors were significantly changed in glaucoma patients. Compared with those without glaucoma, glaucoma patients spent less time on MVPA, especially in the evening.

Association of sleep behaviour and pattern with the risk of glaucoma: a prospective cohort study in the UK Biobank

OBJECTIVES

Given the role of intraocular pressure in glaucoma, the patient's sleeping pattern might contribute to the development and progression of glaucoma. We performed a study to understand the association between sleep behaviours and glaucoma.

DESIGN

Our study was a prospective cohort study.

SETTING

This was a prospective cohort study in the UK Biobank. Self-reported data on five sleep behaviours were collected using a questionnaire at baseline. We identified four sleep patterns based on a cluster analysis of the sleep behaviours.

PARTICIPANTS

In the UK Biobank, 409 053 participants were recruited between 2006 and 2010 and followed for a diagnosis of glaucoma. We identified glaucoma as any hospital admission with a diagnosis of glaucoma, based on UK Biobank inpatient hospital data. Individuals who withdrew from the UK Biobank, or were diagnosed with glaucoma before recruitment, or had self-reported surgery or laser treatment for glaucoma, or had no information on sleep behaviors were excluded.

PRIMARY AND SECONDARY OUTCOME MEASURES

We estimated hazard ratios (HRs) with 95% confidence intervals (CI) using Cox proportional hazards models to estimate the associations of different sleep behaviors, as well as identified sleep patterns, with the risk of glaucoma, adjusting for multiple confounders.

RESULTS

Compared with individuals who had a healthy sleep pattern, an excess risk of any glaucoma was observed among individuals with snoring and daytime sleepiness (HR 1.11, 95% CI 1.03 to 1.19) or insomnia and short/long sleep duration (HR 1.13, 95% CI 1.06 to 1.20), but not late chronotype sleep pattern (HR 0.98, 95% CI 0.93 to 1.03).

CONCLUSION

Snoring, daytime sleepiness, insomnia, and short/long duration, individually or jointly, were all associated with the risk of glaucoma. These findings underscore the need for sleep intervention for individuals at high risk of glaucoma as well as potential ophthalmologic screening among individuals with chronic sleep problems for glaucoma prevention.

Dietary supplements in retinal diseases, glaucoma, and other ocular conditions

Environmental pollution, inadequate eating habits and unhealthy lifestyles have led to a tremendous increase in ocular diseases worldwide. Given the costly treatments that are currently available for the most common and threatening eye diseases (such as cataract, dry eye disorder, or diabetic retinopathy), curing these diseases or preventing refractive errors by taking nutraceuticals and natural compounds that are present in our daily diet is a very valuable intervention. The eyes are the most important part of our visual system and require micronutrients such as vitamins, carotenoids, trace metals, and omega-3 fatty acids in order to function properly and to protect themselves against light-induced and age-mediated degenerative disorders. The Mediterranean Diet (MedDiet) has been in the limelight since the 1980s because of the several health benefits it provides, including eye health. MedDiet is characterized by the consumption of small amounts of red meat, while emphasizing the intake of fish, eggs, nuts, legumes, citrus fruits, green vegetables, olives and their derivatives, especially olive oil, and dairy products in a proportionate manner, in order to achieve the maximum health benefits. The antioxidant, anti-inflammatory, and neuroprotective properties of these foods - both when used as an ingredient in the dietary regime or as a source of nutritional supplements - have shown promising results in the management of chronic degenerative ocular diseases, both in animal models and in human subjects. In this chapter, we will focus on the importance of MedDiet and natural compounds for the visual system and its role in slowing down age-related ocular degeneration.

An Overview of the Circadian Clock in the Frame of Chronotherapy: From Bench to Bedside

Most living organisms in both the plant and animal kingdoms have evolved processes to stay in tune with the alternation of day and night, and to optimize their physiology as a function of light supply. In mammals, a circadian clock relying on feedback loops between key transcription factors will thus control the temporally regulated pattern of expression of most genes. Modern ways of life have highly altered the synchronization of human activities with their circadian clocks. This review discusses the links between an altered circadian clock and the rise of pathologies. We then sum up the proofs of concept advocating for the integration of circadian clock considerations in chronotherapy for health care, medicine, and pharmacotherapy. Finally, we discuss the current challenges that circadian biology must face and the tools to address them.

Daytime Lipid Metabolism Modulated by CLOCK Gene Is Linked to Retinal Ganglion Cells Damage in Glaucoma

Lipid metabolism is intimately linked to circadian mechanisms and light signaling. Deteriorated photic transduction because of retinal ganglion cell (RGC) loss occurring with glaucoma progression reduces perceived light amplitude, causing circadian disruption. To investigate associations with RGCs, total cholesterol (TC), its low-density (LDL-C) and high-density (HDL-C) fractions, and triglycerides (TG) were measured, under a controlled meal regimen, during daytime hours in 114 patients diagnosed with primary open-angle glaucoma (POAG). RGC damage was assessed by high-definition optical coherence tomography (HD-OCT). Analysis of eight clock, clock-related, and melatonin receptor gene polymorphisms was performed on 19 patients. RGC loss was associated with changes in lipid metabolism in a time-dependent manner. Morning (08:00) values of HDL-C (r = 0.613, p < 0.0001) and TG (r = 0.568, p < 0.0001) correlated positively with RGC global loss, while LDL-C at 08:00 had a weak correlation (r = 0.235; p = 0.012) but showed a strong correlation in the evening (20:00) (r = 0.533, p < 0.0001). The morning–evening gradients (MEGs, changes at 20:00 versus 08:00) in TC and LDL-C changed sign from a negative to a positive association in patients exceeding the 15% two-eye mean GLV threshold. MEG (LDL-C higher in the evening than in the morning) was positive only in POAG patients with the CLOCK_3111 TT genotype.

The Relationship Between Circadian Typology and Dry Eye Symptoms in Chinese College Students

PURPOSE

To explore the relationship between symptomatic dry eye and circadian typology in college students.

METHODS

This study included 269 students from 3 Chinese universities. All participants completed the ocular surface disease index (OSDI) questionnaire, the morningness-eveningness questionnaire (MEQ), and the Pittsburgh sleep quality index (PSQI) questionnaire. Participants were grouped into 3 types by the reduced MEQ (rMEQ) score:E-Type, N-Type, and M-Type. All these parameters were then analyzed for the effect on the severity of dry eye.

RESULTS

The occurrence rates of poor sleep quality (PSQI>5) and symptomatic dry eye (OSDI > 13) in the college students were 53.2% and 40.2%, respectively. The distribution of the circadian typology differed significantly among the college students with different dry eye severities (χ ² = 59.44, P = 0. 000), and E-type was associated with the most severe dry eye symptoms. The OSDI and PSQI scores were both significantly different among college students with different chronotypes (F = 22.14, P = 0.000; F = 15.21, P = 0.000; respectively). For both scores, the E-type scored the highest, followed by N-type, and M-type was the lowest. The circadian typology was an independent factor for dry eye. The risk of E-Type was 6.99 times higher than that of M-Type (P = 0.000), and the risk of N-types was 3.23 times higher than that of M-Type (P = 0.000). Sleep quality was also an independent risk factor for dry eye (P = 0.000). Gender and awareness of dry eye were not risk factors for dry eye.

CONCLUSION

The severity of dry eye symptoms and sleep quality were associated with different circadian typologies. The more the circadian preference tended to be E-type, the worse the sleep quality and the more serious dry eye symptoms would appear.

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

Glaucoma is the leading cause of irreversible blindness. The progressive degeneration of retinal ganglion cells (RGCs) is the major characteristic of glaucoma. Even though the control of intraocular pressure could delay the loss of RGCs, current clinical treatments cannot protect them directly. The overactivation of N-methyl-D-aspartic acid (NMDA) receptors by excess glutamate (Glu) is among the important mechanisms of RGC death in glaucoma progression. Melatonin (MT) is an indole neuroendocrine hormone mainly secreted by the pineal gland. This study aimed to investigate the therapeutic effect of MT on glutamate excitotoxicity of mouse RGCs and R28 cells. The Glu-induced R28 cell excitotoxicity model and NMDA-induced retinal injury model were established. MT was applied to R28 cells and the vitreous cavity of mice by intravitreal injection. Cell counting kit-8 assay and propidium iodide/Hoechst were performed to evaluate cell viability. Reactive oxygen species and glutathione synthesis assays were used to detect the oxidative stress state of R28 cells. Retina immunofluorescence and hematoxylin and eosin staining were applied to assess RGC counts and retinal structure. Flash visual-evoked potential was performed to evaluate visual function in mice. RNA sequencing of the retina was performed to explore the underlying mechanisms of MT protection. Our results found that MT treatment could successfully protect R28 cells from Glu excitotoxicity and decrease reactive oxygen species. Also, MT rescued RGCs from NMDA-induced injury and protected visual function in mice. This study enriches the indications of MT in the treatment of glaucoma, providing practical research ideas for its comprehensive prevention and treatment.

The connection of polymorphism and diurnal changes of the biological clock gene expression with the risk of progression of primary open-angle glaucoma

The purpose of this work is to study the connection betweengenetic factors (polymorphism and expression of key genes of the biological clock (KGBC), key genes controlled by KGBC, melatonin receptors) and the diurnal oscillation of melatonin in patients with stable and progressing primary open-angle glaucoma. Materials and methods. The study involved 115 patients aged 53–86 (averagely, 68.8 ± 7.9 years) with stable and progressive glaucoma. All patients underwent primary ophthalmological examination, tested for diurnal body temperature profile, intraocular pressure (IOP), melatonin (by the DLMO protocol) and were typed for key genes of the biological clock using the real-time polymerase chain reaction. We studied the sleep phase shift to later hours in carriers of the G-allele of the melatonin receptor gene during the progression of glaucoma. Results. The study of the clinical and genotypic features of the POAG course revealed phasal shifts of the circadian rhythms of body temperature, IOP, salivary melatonin levels and sleep phases which contributed to the progression of glaucomatous optic neuropathy. Certain polymorphic variants of genes contribute to individual frequent manifestations of desynchronosis. The clock rs1801260 and MTNR1B rs10830963 gene polymorphism was found to be related to disturbances in melatonin production and sleep phase. Conclusion. Complex manifestations of circadian desynchronization accompanying the progressive course of glaucoma are the late phase of rhythms and a decrease in sleep duration, body temperature, salivary melatonin and IOP, internal desynchronization between IOP and body temperature, IOP and sleep, evening dyslipidemia. The revealed patterns open up prospects for future studies of the relationship between polymorphism and daily changes of the expression of key genes in the biological clock with the risk of progression of primary open angle glaucoma.

Therapeutic Effects of Melatonin on Ocular Diseases: Knowledge Map and Perspective

Melatonin plays a critical role in the pathophysiological process including circadian rhythm, apoptosis, and oxidative stress. It can be synthesized in ocular tissues, and its receptors are also found in the eye, triggering more investigations concentrated on the role of melatonin in the eye. In the past decades, the protective and therapeutic potentials of melatonin for ocular diseases have been widely revealed in animal models. Herein, we construct a knowledge map of melatonin in treating ocular diseases through bibliometric analysis and review its current understanding and clinical evidence. The overall field could be divided into twelve topics through keywords co-occurrence analysis, in which the glaucoma, myopia, and retinal diseases were of greatest research interests according to the keywords burst detection. The existing clinical trials of melatonin in ocular diseases mainly focused on the glaucoma, and more research should be promoted, especially for various diseases and drug administration. We also discuss its bioavailability and further research topics including developing melatonin sensors for personalized medication, acting as stem cell therapy assistant drug, and consuming food-derived melatonin for facilitating its clinical transformation.

From Oxidative Stress to Inflammation in the Posterior Ocular Diseases: Diagnosis and Treatment

Most irreversible blindness observed with glaucoma and retina-related ocular diseases, including age-related macular degeneration and diabetic retinopathy, have their origin in the posterior segment of the eye, making their physiopathology both complex and interconnected. In addition to the age factor, these diseases share the same mechanism disorder based essentially on oxidative stress. In this context, the imbalance between the production of reactive oxygen species (ROS) mainly by mitochondria and their elimination by protective mechanisms leads to chronic inflammation. Oxidative stress and inflammation share a close pathophysiological process, appearing simultaneously and suggesting a relationship between both mechanisms. The biochemical end point of these two biological alarming systems is the release of different biomarkers that can be used in the diagnosis. Furthermore, oxidative stress, initiating in the vulnerable tissue of the posterior segment, is closely related to mitochondrial dysfunction, apoptosis, autophagy dysfunction, and inflammation, which are involved in each disease progression. In this review, we have analyzed (1) the oxidative stress and inflammatory processes in the back of the eye, (2) the importance of biomarkers, detected in systemic or ocular fluids, for the diagnosis of eye diseases based on recent studies, and (3) the treatment of posterior ocular diseases, based on long-term clinical studies.

Ocular Complications of Obstructive Sleep Apnea

Obstructive sleep apnea (OSA), the most common form of sleep-disordered breathing, is characterized by repetitive episodes of paused breathing during sleep, which in turn induces transient nocturnal hypoxia and hypercapnia. The high prevalence of OSA and its associated health consequences place a heavy burden on the healthcare system. In particular, the consequent episodic oxygenic desaturation/reoxygenation series and arousals from sleep in patients with OSA have the potential to trigger oxidative stress, elevated systemic inflammatory responses, and autonomic dysfunction with sympathetic activation. Given these adverse side-effects, OSA is highly correlated to many eye diseases that are common in everyday ophthalmic practices. Some of these ocular consequences are reversible, but they may permanently threaten a patient’s vision if not treated appropriately. Here, this article seeks to review the ocular consequences and potential pathophysiologic associations in patients with OSA. Understanding these OSA-related eye diseases may help clinicians provide comprehensive care to their patients.