The role of melatonin in glaucoma: implications concerning pathophysiological relevance and therapeutic potential

The Therapeutic Trip of Melatonin Eye Drops: From the Ocular Surface to the Retina

Melatonin is a ubiquitous molecule found in living organisms, ranging from bacteria to plants and mammals. It possesses various properties, partly due to its robust antioxidant nature and partly owed to its specific interaction with melatonin receptors present in almost all tissues. Melatonin regulates different physiological functions and contributes to the homeostasis of the entire organism. In the human eye, a small amount of melatonin is also present, produced by cells in the anterior segment and the posterior pole, including the retina. In the eye, melatonin may provide antioxidant protection along with regulating physiological functions of ocular tissues, including intraocular pressure (IOP). Therefore, it is conceivable that the exogenous topical administration of sufficiently high amounts of melatonin to the eye could be beneficial in several instances: for the treatment of eye pathologies like glaucoma, due to the IOP-lowering and neuroprotection effects of melatonin; for the prevention of other dysfunctions, such as dry eye and refractive defects (cataract and myopia) mainly due to its antioxidant properties; for diabetic retinopathy due to its metabolic influence and neuroprotective effects; for macular degeneration due to the antioxidant and neuroprotective properties; and for uveitis, mostly owing to anti-inflammatory and immunomodulatory properties. This paper reviews the scientific evidence supporting the use of melatonin in different ocular districts. Moreover, it provides data suggesting that the topical administration of melatonin as eye drops is a real possibility, utilizing nanotechnological formulations that could improve its solubility and permeation through the eye. This way, its distribution and concentration in different ocular tissues may support its pleiotropic therapeutic effects.

The rational design of novel 5-amino-2-oxindole derivatives with antiglaucomic activity

Compounds with a 2-oxindole scaffold play an important role in organic synthesis and especially in the synthesis of bioactive organic compounds, therefore, the development of new methods for modifying this scaffold is a very interesting and urgent task. In the framework of this study, we have created a rational approach to the synthesis of 5-amino-substituted derivatives of 2-oxindole. The approach is characterized by good total yield and a small number of steps. One-stage modification of obtained 5-amino-2-oxindoles leads to compounds with promising antiglaucomic activity. The most active compound 7a reduce intraocular pressure by 24% in normotensive rabbits (18% for reference drug timolol).

Structural Basis for Agonistic Activity and Selectivity toward Melatonin Receptors hMT1 and hMT2

Glaucoma, a major ocular neuropathy originating from a progressive degeneration of retinal ganglion cells, is often associated with increased intraocular pressure (IOP). Daily IOP fluctuations are physiologically influenced by the antioxidant and signaling activities of melatonin. This endogenous modulator has limited employment in treating altered IOP disorders due to its low stability and bioavailability. The search for low-toxic compounds as potential melatonin agonists with higher stability and bioavailability than melatonin itself could start only from knowing the molecular basis of melatonergic activity. Thus, using a computational approach, we studied the melatonin binding toward its natural macromolecular targets, namely melatonin receptors 1 (MT1) and 2 (MT2), both involved in IOP signaling regulation. Besides, agomelatine, a melatonin-derivative agonist and, at the same time, an atypical antidepressant, was also included in the study due to its powerful IOP-lowering effects. For both ligands, we evaluated both stability and ligand positioning inside the orthosteric site of MTs, mapping the main molecular interactions responsible for receptor activation. Affinity values in terms of free binding energy (ΔG_bind) were calculated for the selected poses of the chosen compounds after stabilization through a dynamic molecular docking protocol. The results were compared with experimental in vivo effects, showing a higher potency and more durable effect for agomelatine with respect to melatonin, which could be ascribed both to its higher affinity for hMT2 and to its additional activity as an antagonist for the serotonin receptor 5-HT2c, in agreement with the in silico results.

Association of Glaucoma with Poor Quality of Sleep in an Ethiopian Glaucoma Population – A Comparative Cross-Sectional Study

Background

Glaucoma is a group of ocular disorders characterized by progressive optic nerve damage resulting in irreversible visual field defects. Poor quality of sleep in glaucoma patients could be explained by the reduction of the light input to the circadian system as a result of damage to photosensitive retinal ganglion cells in the retina. Information is limited on the association of poor quality of sleep with glaucoma in general and the Ethiopian glaucoma population in particular.

Objective

The study aimed to explore the association between poor quality of sleep and glaucoma at a Tertiary Eye Care Center in Ethiopia.

Methods

An institutional-based comparative cross-sectional study was conducted among 200 glaucoma and 201 non-glaucoma participants recruited by systematic random sampling. Each group was administered with a Pittsburgh Sleep Quality Index (PSQI) questionnaire. Stata-14 was employed for data analysis; an independent t-test was used to show the statistical difference in the global mean PSQI score for the two groups. A binary logistic regression model was applied to identify factors associated with poor quality of sleep. Statistical significance was declared at a 95% confidence interval and a p-value of <0.05.

Results

The prevalence of poor quality of sleep was 82.5% among the glaucoma population, which statistically differed (p<0.001) from the non-glaucomatous population (55.7%). Poor quality of sleep in glaucoma was associated with older age (adjusted odds ratio (AOR)=4.4, 95% confidence interval (CI): 1.5–5.4), depression (AOR=2.9, 95% CI: 1.1–7.3), visual impairment (AOR=3.9, 95% CI: 1.3–12.3) and severe glaucoma (AOR=2.5, 95% CI: 1.1–5.9).

Conclusion and Recommendation

Poor quality of sleep was significantly higher in the glaucoma population compared to their non-glaucoma control. It was associated with older age, depression, visual impairment and advanced glaucoma. Incorporating psychiatric counseling into the existing glaucoma follow-up was recommended.

Anti-PANoptosis is involved in neuroprotective effects of melatonin in acute ocular hypertension model

Acute ocular hypertension (AOH) is the most important characteristic of acute glaucoma, which can lead to retinal ganglion cell (RGC) death and permanent vision loss. So far, approved effective therapy is still lacking in acute glaucoma. PANoptosis (pyroptosis, apoptosis, and necroptosis), which consists of three key modes of programmed cell death-apoptosis, necroptosis, and pyroptosis-may contribute to AOH-induced RGC death. Previous studies have demonstrated that melatonin (N-acetyl-5-methoxytryptamine) exerts a neuroprotective effect in many retinal degenerative diseases. However, whether melatonin is anti-PANoptotic and neuroprotective in the progression of acute glaucoma remains unclear. Thus, this study aimed to explore the role of melatonin in AOH retinas and its underlying mechanisms. The results showed that melatonin treatment attenuated the loss of ganglion cell complex thickness, retinal nerve fiber layer thickness, and RGC after AOH injury, and improved the amplitudes of a-wave, b-wave, and oscillatory potentials in the electroretinogram. Additionally, the number of terminal deoxynucleotidyl transferase dUTP nick-end labeling-positive cells was decreased, and the upregulation of cleaved caspase-8, cleaved caspase-3, Bax, and Bad and downregulation of Bcl-2 and p-Bad were inhibited after melatonin administration. Meanwhile, both the expression and activation of MLKL, RIP1, and RIP3, along with the number of PI-positive cells, were reduced in melatonin-treated mice, and p-RIP3 was in both RGC and microglia/macrophage after AOH injury. Furthermore, melatonin reduced the expression of NLRP3, ASC, cleaved caspase-1, gasdermin D (GSDMD), and cleaved GSDMD, and decreased the number of Iba1/interleukin-1β-positive cells. In conclusion, melatonin ameliorated retinal structure, prevented retinal dysfunction after AOH, and exerted a neuroprotective effect via inhibition of PANoptosis in AOH retinas.

Essential Oils and Melatonin as Functional Ingredients in Dogs

Simple Summary

Phytogenics are plant-based compounds with beneficial actions in feed technology and/or animal health. These so-called plant secondary metabolites are very diverse and with wide possible applications in humans and animals. Among them, essential oils (EOs) are the most used in feed for livestock and pets. Lately, melatonin has acquired new and interesting applications in dogs. Recent studies using EOs and/or melatonin in dog feeding and their involvement in health aspects are presented.

Abstract

The use of nutraceuticals or functional ingredients is increasingly widespread in human food; their use is also widespread in animal feed. These natural compounds generally come from plant materials and comprise a wide range of substances of a very diverse chemical nature. In animals, these compounds, so-called phytogenics, are used to obtain improvements in feed production/stability and also as functional components with repercussions on animal health. Along with polyphenols, isoprenoid compounds represent a family of substances with wide applications in therapy and pet nutrition. Essential oils (EOs) are a group of complex substances with fat-soluble nature that are widely used. Melatonin is an indolic amine present in all living with amphiphilic nature. In this work, we present a review of the most relevant phytogenics (polyphenol, isoprenoid, and alkaloid compounds), their characteristics, and possible uses as nutraceuticals in dogs, with special emphasis on EOs and their regulatory aspects, applied in foods and topically. Additionally, a presentation of the importance of the use of melatonin in dogs is developed, giving physiological and practical aspects about its use in dog feeding and also in topical application, with examples and future projections. This review points to the combination of EOs and melatonin in food supplements and in the topical application as an innovative product and shows excellent perspectives aimed at addressing dysfunctions in pets, such as the treatment of stress and anxiety, sleep disorders, alopecia, and hair growth problems, among others.

Validation of a Rapid and Easy-to-Apply Method to Simultaneously Quantify Co-Loaded Dexamethasone and Melatonin PLGA Microspheres by HPLC-UV: Encapsulation Efficiency and In Vitro Release

This paper discusses the development and validation of a rapid method for the reversed phase HPLC-UV quantification of biodegradable poly(D,L-lactic-co-glycolic) acid (PLGA) microspheres co-loaded with two neuroprotective agents (dexamethasone and melatonin) (DX-MEL-MSs) to be intravitreally administered as a promising glaucoma treatment. The study was performed to validate two procedures that quantify the content of the two active substances entrapped into the polymer matrix during an encapsulation efficiency assay and the amount of drugs liberated over time during the in vitro release assay. The reversed-phase method allowed for the simultaneous determination of dexamethasone and melatonin, which were respectively detected at 240.5 and 222.7 nm. Chromatographic separation was performed using an Ascentis^® C18 HPLC Column (25 cm × 4.6 mm, 5 µm) with an isocratic mobile phase composed of methanol-water (70:30, v/v) with 1.0 mL min⁻¹ flow rate. The two procedures were validated analytically in terms of system suitability testing, specificity, linearity, precision, accuracy, sensitivity, and robustness. Both the validated procedures were applied to characterize DX-MEL-MSs and were found appropriate to quantify the drug quantities encapsulated and estimate their release profile over 10 days. The validation study designed in this work can be helpful for planning any other protocols that refer to the quantification of PLGA based drug delivery systems.

Effects of long-term oral administration of melatonin on tear production, intraocular pressure, and tear and serum melatonin concentrations in healthy dogs

OBJECTIVE

To evaluate the effects of long-term (30-day) oral administration of melatonin on tear production, intraocular pressure (IOP), and concentration of melatonin in the tears and serum of healthy dogs.

ANIMALS

20 healthy sexually intact adult male dogs.

PROCEDURES

10 dogs were given melatonin (0.3 mg/kg, PO, q 24 h, administered in food at 9 am), and 10 dogs were given a placebo. Tear and serum melatonin concentrations, IOP, and tear production (determined with a Schirmer tear test) were recorded before (baseline) and 30 minutes, 3 hours, and 5 hours after administration of melatonin or the placebo on day 1 and 30 minutes after administration of melatonin or the placebo on days 8, 15, and 30.

RESULTS

Data collection time had significant effects on tear production, IOP, and tear melatonin concentration but not on serum melatonin concentration. Treatment (melatonin vs placebo) had a significant effect on tear melatonin concentration, but not on tear production, IOP, or serum melatonin concentration; however, tear melatonin concentration was significantly different between groups only 30 minutes after administration on day 1 and not at other times.

CLINICAL RELEVANCE

In healthy dogs, long-term administration of melatonin at a dosage of 0.3 mg/kg, PO, every 24 hours did not have any clinically important effects on tear production, IOP, or serum or tear melatonin concentrations.

Potentiating the Benefits of Melatonin through Chemical Functionalization: Possible Impact on Multifactorial Neurodegenerative Disorders

Although melatonin is an astonishing molecule, it is possible that chemistry will help in the discovery of new compounds derived from it that may exceed our expectations regarding antioxidant protection and perhaps even neuroprotection. This review briefly summarizes the significant amount of data gathered to date regarding the multiple health benefits of melatonin and related compounds. This review also highlights some of the most recent directions in the discovery of multifunctional pharmaceuticals intended to act as one-molecule multiple-target drugs with potential use in multifactorial diseases, including neurodegenerative disorders. Herein, we discuss the beneficial activities of melatonin derivatives reported to date, in addition to computational strategies to rationally design new derivatives by functionalization of the melatonin molecular framework. It is hoped that this review will promote more investigations on the subject from both experimental and theoretical perspectives.

Prevalence of common mental disorders and associated factors among adults with Glaucoma attending University of Gondar comprehensive specialized hospital tertiary eye care and training center, Northwest, Ethiopia 2020

PURPOSE

This study aimed to assess the prevalence of common mental disorders and associated factors among adults with glaucoma at Gondar university comprehensive specialized hospital tertiary eye care and training center. Glaucoma predisposes patients to common mental problems and leads to wasteful, costly and inefficient use of medical services and complications of the diagnoses. So, determining the level and factors associated with common mental disorders among glaucoma patient would help to improve and integrate comprehensive ophthalmic services which address common mental disorder in a follow-up visit.

METHODS

An institution-based cross-sectional study was conducted on 495 glaucoma patients selected by using systematic random sampling. Data were collected through face-to-face interview and chart review. Self-reported questionnaire (SRQ-20) was used to assess the presence of common mental disorders. Binary logistic regression analysis was done to identify factors associated with common mental disorders. Variables with P<0.05 were considered as factors significantly associated with common mental disorders.

RESULT

Four hundred sixty-eight patients were included in this study with a response rate of 94.54%. The mean age of the participant was 58 ± 14.11 years. The prevalence of common mental disorders was found to be 29.5% (95% CI 25.4-33.3). Female sex (AOR = 3.79, 95% CI: 1.66-8.62) (p-value = 0.001), average monthly income of less than 1200 birr (AOR = 6.05 95% CI: 2.26-16.22) (p-value = 0.001), poor level of social support (AOR = 17.39 95% CI: 7.79-38.82) (p-value = 0.001), moderate and high risk of alcohol use (AOR = 10.42 95%CI: 2.74-39.54) (p-value = 0.001), presence of chronic medical illness (AOR = 3.85 95% CI: 2.07-7.16) (p-value = 0.001), receiving both drug and surgical treatment (AOR = 2.50, 95%CI: 1.30-4.83) (p-value = 0.006) and presence of systemic carbonic anhydrase inhibitors use (AOR = 3.16, 95%CI: 1.65-6.06) (p-value = 0.001) were significantly associated with increased level of common mental disorders.

CONCLUSION

Significant numbers of glaucoma patients have CMD and found significantly associated with socio-economic, ocular and systemic clinical factors. Therefore, the integration of psychosocial care into the current treatment of patients with glaucoma would have a significant advantage to help these patients.

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

Glaucoma is a progressive optic neuropathy associated with damage to retinal ganglion cells (RGCs) and disrupted circadian rhythms. Melatonin is a promising substance to ameliorate glaucoma-associated compromised circadian rhythms, sleep, mood, and retinal cells function. However, studies estimating melatonin effects in glaucoma are currently lacking. Therefore, In this study, we investigated the effect of long-term (daily at 10:30 pm for 90 days) oral melatonin administration on systemic (Tb) and local to the organ of vision (IOP) circadian rhythms, pattern electroretinogram (PERG), sleep, and mood, depending on glaucoma stage in patients diagnosed with stable or advanced primary open-angle glaucoma. In a laboratory study in 15 of them, 24-hour records of salivary melatonin were obtained and MTNR1B receptor gene polymorphism was assessed. Melatonin increased the stability of the Tb circadian rhythm by improving its phase alignment and alignment with IOP. Melatonin time-dependently decreased IOP and IOP standard deviation (SD). IOP 24-hour mean and IOP SD decreases were more pronounced in individuals with the higher initial 24-hour IOP mean. Melatonin improved RGCs function in advanced glaucoma; N95 amplitude increase correlated positively with RGCs loss. The beneficial effects of melatonin on sleep and mood were greater in advanced glaucoma. Finally, delayed salivary melatonin and Tb phases were observed in MTNR1B G-allele carriers with advanced glaucoma. Combined, these results provide evidence for melatonin efficiency in restoring disrupted circadian rhythms in glaucoma with different effects of melatonin on systemic vs. local circadian rhythms, indicating that a personalized strategy of melatonin administration may further refine its treatment benefits.

Depression in glaucoma patients: A review of the literature

Purpose: The purpose of this review was to evaluate the association between glaucoma and depression and to identify possible risk factors for depressive symptoms in glaucoma patients.Methods: A total of 587 abstracts were screened and 32 studies were deemed eligible for inclusion in this review.Results: An association of glaucoma and depression was found, while advanced disease stage, older age, female sex and faster visual loss progression were recognized as potential risk factors for depression in patients with glaucoma.Conclusions: Our findings may have important clinical significance, such as alerting ophthalmologists to implement a multidisciplinary approach in patients with glaucoma. Further research is needed to examine this association in different types of glaucoma and try to investigate the underlying pathophysiological mechanisms to establish a causal inference between glaucoma and depression.

Effects of primary glaucoma on sleep quality and daytime sleepiness of patients residing at an equatorial latitude

AIM

To investigate the impact of primary glaucoma on sleep quality and daytime sleepiness of patients.

METHODS

Prospective cross-sectional study with consecutive sampling in South-East Asian population was performed. Validated questionnaires: the Pittsburg Sleep Quality Index (PSQI) and Epworth Sleepiness Scale (ESS) were administered prospectively. Subjects with non-glaucomatous optic neuropathy or concomitant retinal pathology were excluded. Glaucoma severity was based on HVF 24-2 perimetry. Binocular single vision was represented based on the better eye. Frequency of and predictive factors for poor sleep quality and excessive daytime sleepiness were compared.

RESULTS

A total of 79 primary open angle glaucoma (POAG), 27 primary angle-closure glaucoma (PACG) patients, and 89 controls were recruited. PACG patients had higher median PSQI scores (P=0.004) and poorer sleep quality (P<0.001). Compared to controls, PACG patients were 3.34 times more likely to have poor sleep quality (P=0.008), which remained significant after adjustment for demographics (P=0.016) and predictive variables (P=0.013). PACG patients have poorer sleep quality when visual acuity (VA) was 6/15 or worse (P=0.009). Univariate and multivariate analysis of predictive variables for poor sleep quality and daytime sleepiness did not find statistical significance.

CONCLUSION

PACG patients have poorer sleep quality but not daytime sleepiness. This is important in South-East Asian population with heavy disease burden. Evaluations on sleep disturbances can be considered to provide more holistic care.

Contact Lenses as Drug Delivery System for Glaucoma: A Review

Glaucoma is an optical neuropathy associated to a progressive degeneration of retinal ganglion cells with visual field loss and is the main cause of irreversible blindness in the world. The treatment has the aim to reduce intraocular pressure. The first therapy option is to instill drugs on the ocular surface. The main limitation of this is the reduced time of the drug staying on the cornea. This means that high doses are required to ensure its therapeutic effect. A drug-loaded contact lens can diffuse into the post lens tear film in a constant and prolonged flow, resulting in an increased retention of the drug on the surface of the cornea for up to 30 min and thus providing a higher drug bioavailability, increasing the therapeutic efficacy, reducing the amount of administered drug, and thereby provoking fewer adverse events. Several different systems of drug delivery have been studied in recent decades; ranging from more simple methods of impregnating the lenses, such as soaking, to more complex ones, such as molecular imprinting have been proposed. Moreover, different drugs, from those already commercially available to new substances such as melatonin have been studied to improve the glaucoma treatment efficacy. This review describes the role of contact lenses as an innovative drug delivery system to treat glaucoma.

Effect of orally administered melatonin on intraocular pressure of ophthalmologically normal dogs

OBJECTIVE

To determine the effect of orally administered melatonin on the intraocular pressure (IOP) of ophthalmologically normal dogs.

ANIMALS

20 ophthalmologically normal dogs (40 eyes).

PROCEDURES

In a randomized crossover study, each dog received a 7-day regimen of melatonin (0.1 to 0.2 mg/kg, PO, q 12 h) and a placebo (150 mg of lactose powder in a capsule, PO, q 12 h), with a 7-day washout period between treatment regimens. Rebound tonometry was used to measure the IOP in both eyes of each dog 5 times at 2-hour intervals on days 0 (before administration of the first dose), 2, 4, and 7 (after administration of the last dose) of each treatment period. Repeated-measures ANOVA was used to evaluate the effects of treatment, day, and IOP measurement time within day on IOP.

RESULTS

Intraocular pressure was not significantly associated with treatment but was associated with day and the interaction between day and IOP measurement time within day. The mean ± SD IOP was 14.26 ± 2.95 and 14.34 ± 2.69 mm Hg for the melatonin and placebo regimens, respectively. Within each treatment period, the mean IOP tended to decrease from day 0 to 7 as well as within each day, which was attributed to the dogs becoming acclimated to the study protocol and natural diurnal variations in IOP.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that oral administration of melatonin (0.1 to 0.2 mg/kg, q 12 h for 7 d) did not significantly affect the IOP of ophthalmologically normal dogs.

Progressive retinal ganglion cell loss in primary open-angle glaucoma is associated with temperature circadian rhythm phase delay and compromised sleep

Advanced primary open-angle glaucoma (POAG) is characterized by progressive retinal ganglion cell complex (RGCC) damage that may cause subsequent disruption of the circadian rhythms. Therefore, we evaluated circadian body temperature (BT) rhythm and sleep characteristics of 115 individuals (38 men and 77 women) diagnosed with POAG. GLV (global loss volume; %), a measure of RGCC damage, was estimated by high-definition optical coherence tomography, and RGC functional ability was assessed by pattern electroretinogram amplitude (PERGA). Depending on dynamics of POAG progression criteria, two groups were formed that were distinctively different in GLV: Stable POAG group (S-POAG; GLV = 5.95 ± 1.84, n = 65) and Progressive POAG group (P-POAG; GLV = 24.27 ± 5.09, n = 50). S-POAG and P-POAG groups were not different in mean age (67.61 ± 7.56 versus 69.98 ± 8.15) or body mass index (24.66 ± 3.03 versus 24.77 ± 2.90). All subjects performed 21 around-the-clock BT self-measurements during a 72-h period and kept activity/sleep diaries. Results showed pronounced disruption of circadian physiology in POAG and its progression with increasing severity of the disease. The daily mean of BT was unusually low, compared to age-matched controls. Moreover, our results revealed distinctive features of BT circadian rhythm alterations in POAG development and POAG progression. S-POAG is associated with lowered BT circadian rhythm robustness and inter-daily phase stability compared to controls. In the P-POAG group, the mean phase of the circadian BT rhythm was delayed by about 5 h and phases were highly scattered among individual patients, which led to reduced group mean amplitude. Circadian amplitudes of individuals were not different between the groups. Altogether, these results suggest that the body clock still works in POAG patients, but its entrainment to the 24-h environment is compromised. Probably because of the internal desynchronization, bedtime is delayed, and sleep duration is accordingly shortened by about 55 min in P-POAG compared to S-POAG patients. In the entire POAG cohort (both groups), later sleep phase and shorter mean sleep duration correlate with the delayed BT phase (r = 0.215; p = 0.021 and r = 0.322; p = 0.0004, respectively). An RGCC GLV of 15% apparently constitutes a threshold above which a delay of the circadian BT rhythm and a shortening of sleep duration occur.

Protective stabilization of mitochondrial permeability transition and mitochondrial oxidation during mitochondrial Ca2+ stress by melatonin's cascade metabolites C3-OHM and AFMK in RBA1 astrocytes

Cyclic 3-hydroxymelatonin (C3-OHM) and N1-acetyl-N2-formyl-5-methoxykynuramine (AFMK) are two major cascade metabolites of melatonin. We previously showed melatonin provides multiple levels of mitochondria-targeted protection beyond as a mitochondrial antioxidant during ionomycin-induced mitochondrial Ca²⁺ (mCa²⁺ ) stress in RBA1 astrocytes. Using noninvasive laser scanning fluorescence coupled time-lapse digital imaging microscopy, this study investigated whether C3-OHM and AFMK also provide mitochondrial levels of protection during ionomycin-induced mCa²⁺ stress in RBA1 astrocytes. Interestingly, precise temporal and spatial dynamic live mitochondrial images revealed that C3-OHM and AFMK prevented specifically mCa²⁺ -mediated mitochondrial reactive oxygen species (mROS) formation and hence mROS-mediated depolarization of mitochondrial membrane potential (△Ψ_m ) and permanent lethal opening of the MPT (p-MPT). The antioxidative effects of AFMK, however, were less potent than that of C3-OHM. Whether C3-OHM and AFMK targeted directly the MPT was investigated under a condition of "oxidation free-Ca²⁺ stress" using a classic antioxidant vitamin E to remove mCa²⁺ -mediated mROS stress and the potential antioxidative effects of C3-OHM and AFMK. Intriguingly, two compounds still effectively postponed "oxidation free-Ca²⁺ stress"-mediated depolarization of △Ψ_m and p-MPT. Measurements using a MPT pore-specific indicator Calcein further identified that C3-OHM and AFMK, rather than inhibiting, stabilized the MPT in its transient protective opening mode (t-MPT), a critical mechanism to reduce overloaded mROS and mCa²⁺ . These multiple layers of mitochondrial protection provided by C3-OHM and AFMK thus crucially allow melatonin to extend its metabolic cascades of mitochondrial protection during mROS- and mCa²⁺ -mediated MPT-associated apoptotic stresses and may provide therapeutic benefits against astrocyte-mediated neurodegeneration in the CNS.

Melatonin concentrations in serum of primary glaucoma patients

AIM

To determine whether glaucoma patients exhibit an abnormal melatonin concentration in serum and the effects of psychiatric disorders caused by glaucoma in melatonin secretion.

METHODS

A sample of 80 primary angle-closure glaucoma (PACG) patients, 120 primary open angle glaucoma (POAG) patients, and 120 normal controls were enrolled in this study. All the participants were asked to complete the following questionnaires: Pittsburgh sleep quality index (PSQI), self-rating anxiety scale (SAS), and self-rating depression scale (SDS). Variance analysis was used to compare the subscores between the groups. After that, we chose 58 patients with primary glaucoma and 20 non-glaucoma control patients to collect their serum samples at 7-10 a.m. Serum melatonin levels were measured using enzyme linked immunosorbent assay (ELISA).

RESULTS

Of all participants, the scores of PSQI, SAS, and SDS in PACG and POAG group were 9.38±0.40, 46.08±8.99, 51.11±10.72 and 7.43±0.35, 45.42±9.87, 49.04±12.24 respectively, significantly higher than those in control group (4.16±0.28, 35.49±9.18, 40.31±13.08). The serum melatonin levels in PACG (37.29±2.99 pg/mL) and POAG (35.97±3.64 pg/mL) were significantly higher than the controls (29.96±3.94 pg/mL) (P<0.001). But no difference was found between the PACG and POAG (P=0.216). Glaucoma patients with sleep disorders, anxiety and depression were more likely resulting in the increase of melatonin levels.

CONCLUSION

There is a significant increase in serum melatonin levels in glaucoma patients compared to the controls especially in glaucoma patients with psychiatric disorders such as sleep disorders, anxiety and depression.

Melatonin and its metabolites vs oxidative stress: From individual actions to collective protection

Oxidative stress (OS) represents a threat to the chemical integrity of biomolecules including lipids, proteins, and DNA. The associated molecular damage frequently results in serious health issues, which justifies our concern about this phenomenon. In addition to enzymatic defense mechanisms, there are compounds (usually referred to as antioxidants) that offer chemical protection against oxidative events. Among them, melatonin and its metabolites constitute a particularly efficient chemical family. They offer protection against OS as individual chemical entities through a wide variety of mechanisms including electron transfer, hydrogen transfer, radical adduct formation, and metal chelation, and by repairing biological targets. In fact, many of them including melatonin can be classified as multipurpose antioxidants. However, what seems to be unique to the melatonin's family is their collective effects. Because the members of this family are metabolically related, most of them are expected to be present in living organisms wherever melatonin is produced. Therefore, the protection exerted by melatonin against OS may be viewed as a result of the combined antioxidant effects of the parent molecule and its metabolites. Melatonin's family is rather exceptional in this regard, offering versatile and collective antioxidant protection against OS. It certainly seems that melatonin is one of the best nature's defenses against oxidative damage.

Melatonin attenuated retinal neovascularization and neuroglial dysfunction by inhibition of HIF-1α-VEGF pathway in oxygen-induced retinopathy mice

Retinopathy of prematurity (ROP) is a retinopathy characterized by retinal neovascularization (RNV) occurring in preterm infants treated with high concentrations of oxygen and may lead to blindness in severe cases. Currently, anti-VEGF therapy is a major treatment for ROP, but it is costly and may cause serious complications. The previous study has demonstrated that melatonin exerted neuroprotective effect against retinal ganglion cell death induced by hypoxia in neonatal rats. However, whether melatonin is anti-angiogenic and neuroglial protective in the progression of ROP remains unknown. Thus, this study was to investigate the effect of melatonin on RNV and neuroglia in the retina of oxygen-induced retinopathy (OIR) mice. The results showed a reduction in retinal vascular leakage in OIR mice after melatonin treatment. Besides, the size of retinal neovascular and avascular areas, the number of preretinal neovascular cell nuclei, and the number of proliferative vascular endothelial cells within the neovascular area were significantly decreased in mice treated with melatonin. After oxygen-induced injury, the density of astrocytes was decreased, accompanied by morphologic and functional changes of astrocytes. Besides, retinal microglia were also activated. Meanwhile, the levels of inflammatory factors were elevated. However, these pathologic processes were all hindered by melatonin treatment. Furthermore, HIF-1α-VEGF pathway was activated in the retina of OIR mice, yet was suppressed in melatonin-treated OIR mice retinas. In conclusion, melatonin prevented pathologic neovascularization, protected neuroglial cells, and exerts anti-inflammation effect via inhibition of HIF-1α-VEGF pathway in OIR retinas, suggesting that melatonin could be a promising therapeutic agent for ROP.

Regulatory mechanism of melatonin on the retinal ganglion cell photoreaction in mice

The study aimed to analyze the regulatory mechanism of melatonin (MLT) on the retinal ganglion cell photoreaction in mice. Forty-eight, 3-week-old healthy ICR mice, regardless of gender, were randomly divided into 4 groups. Group A was exposed to an illumination/dark time of 0 h/24 h, 6 h/18 h in group B, 12 h/12 h in group C and 18 h/6 h in group D, for up to 6 weeks. Four mice in each group were sacrificed at week 1, 3 and 6, respectively, for harvesting of retinal ganglion cells. ELISA was used to detect nocturnal plasma MLT levels at midnight. Immunohistochemistry was used to detect the expression of the retinal MLT receptor and the expression levels of inducible nitric oxide synthase (iNOS) and c-fos protein. The plasma MLT levels, MLT receptor levels and c-fos protein expression levels of group C, after 1, 3 and 6 weeks of light application, were the highest, followed by groups B and D, while group A had the lowest levels. For each illumination time, the iNOS levels of group C were the lowest and group A was the highest. Differences were all statistically significant (P<0.05). In conclusion, appropriate illumination regimens can increase c-fos protein, decrease iNOS activity and regulate the physiological activities of the retinal ganglion cells by regulating the expressions of MLT and its receptor.

TRPV4 Stimulation Induced Melatonin Secretion by Increasing Arylalkymine N-acetyltransferase (AANAT) Protein Level

Melatonin is a molecule which has gained a great deal of interest in many areas of science; its synthesis was classically known to be in the pineal gland. However, many organs synthesize melatonin, such as several ocular structures. Melatonin is known to participate in many functions apart from its main action regulating the circadian rhythm. It is synthesized from serotonin in two steps, with a rate-limiting step carried out by arylalkymine N-acetyltransferase (AANAT). In this report, the role of TRPV4 channel present in human ciliary body epithelial cells in AANAT production was studied. Several experiments were undertaken to verify the adequate time to reach the maximal effect by using the TRPV4 agonist GSK1016790A, together with a dose-response study. An increase of 2.4 folds in AANAT was seen after 18 h of incubation with 10 nM of GSK1016790A (p < 0.001, n = 6). This increment was verified by antagonist assays. In summary, AANAT levels and therefore melatonin synthesis change after TRPV4 channel stimulation. Using this cell model together with human ciliary body tissue it is possible to suggest that AANAT plays an important role in pathologies related to intraocular pressure.

Associations of sleep duration with open angle glaucoma in the Korea national health and nutrition examination survey

The aim of this study is to investigate the relationship between sleep duration and glaucoma, stratified by obesity status.This study was conducted using data from the Korean National Health and Nutrition Examination Survey V 2010 to 2012. Open-angle glaucoma was diagnosed according to the International Society of Geographical and Epidemiological Ophthalmology criteria. Subjects were divided into subgroups based on those who were overweight (body mass index ≥25 kg/m or <25 kg/m) or with abdominal obesity (based on waist circumference). Multiple logistic regression analysis was done to estimate the magnitude of the association between sleep duration (<7 h, 7-<9, or ≥9 hours) and prevalence of glaucoma in the total population and in the subgroups.Individuals who slept <5 hours per night had the highest prevalence of glaucoma (5.55 ± 1.09%), followed by those who slept ≥9 hours per night (4.56 ± 0.10%), and then by those who slept 5 to <6 hours per night (4.15 ± 0.68%), which revealed a U-shaped pattern (P for trend = 0.072). Among overweight individuals, subjects who slept <7 hours and those who slept ≥9 hours were significantly more likely to have glaucoma compared with subjects who slept 7 to <9 hours after adjusting for survey year, age, sex, smoking, drinking, exercise, education level, household income, hypertension, intraocular pressure, stress, and depression (odds ratio, 2.41; 95% confidence interval, 1.14-5.03). Unlike for overweight individuals, sleep duration in nonoverweight individuals was not statistically significantly associated with glaucoma.Our results reveal a U-shaped association between sleep duration and the prevalence of glaucoma. An effect of sleep duration on glaucoma was present in the subgroup of overweight patients.

Seasonal changes of 24-hour intraocular pressure rhythm in healthy Shanghai population

The aim of the present study was to investigate and compare the 24-hour intraocular pressure (IOP) rhythms in winter and summer in the healthy population of Shanghai, China.This is a cross-sectional study in which 24-hour IOP measurements were taken for all eligible healthy volunteers in winter and summer, respectively, and the temperature, hours of sunlight (sunlight time), and circulatory parameters, including heart rate, systolic blood pressure, and diastolic blood pressure, were also recorded. The 24-hour IOP curves and IOP parameters (mean, peak, trough, and fluctuation of IOP together with the diurnal-to-nocturnal IOP change) in winter and summer were obtained and compared. The magnitude of IOP changes from summer to winter was also calculated.A total of 29 participants (58 eyes), 14 (48.28%) male and 15 (51.72%) female, aged 43.66 ± 12.20 (19-61) years, were considered eligible for this study. Generally, IOP decreased progressively before noon, increased notably in the nocturnal period, and peaked at 12:00 AM in winter and at 2:00 AM in summer. The pattern of 24-hour IOP in winter and summer was significantly different (P = 0.002). The average IOPs from 4:00 PM to 8:00 AM, except for 6:00 AM, were significantly higher in winter (P < 0.05). However, no significant differences were shown after adjusting for temperature and/or sunlight time. From summer to winter, the extent of IOP increase was mostly around 0 to 3 mm Hg, and the IOPs increased more significantly in the nocturnal period than in the diurnal period (P = 0.05).The 24-hour IOP rhythms were different in winter and summer, with higher IOP level in winter. Temperature and sunlight time, which are independent of heart rate and blood pressure, affected the 24-hour IOP rhythms in healthy people in Shanghai, China. Further investigations are expected for the rhythm of some endogenous substance secretion and the inner mechanism of regulation of IOP.

Increased melatonin levels in aqueous humor of patients with proliferative retinopathy in type 2 diabetes mellitus

AIM

To report the association between melatonin levels in aqueous humor and serum, and diabetic retinopathy (DR) grade in type 2 diabetic patients.

METHODS

Aqueous humor and plasma samples from 26 patients with DR (in nonproliferative and proliferative stages) and 14 control subjects were collected during cataract surgery after 6 p.m. Melatonin concentrations were determined using an enzyme-linked immunosorbent assay (ELISA).

RESULTS

Melatonin levels were significantly higher in the aqueous humor of patients with proliferative diabetic retinopathy (PDR) [18.57±2.67 pg/mL (range 15.20-23.06) vs 13.63±2.71 pg/mL (range 10.20-20.20), P=0.0001], but not in those with nonproliferative retinopathy (NPDR) [13.79±2.56 pg/mL (range 9.80-20.10) vs 13.63±2.71 pg/mL (range 10.20-20.20), P=0.961] compared to controls. There was decrement in the plasma melatonin level of patients with PDR, but no significant differences between the plasma melatonin levels of the study groups [5.37±1.74 pg/mL (range 2.85-8.65) vs 6.11±1.90 pg/mL (range 3.13-9.41), P=0.293], or between control and DR groups [NPDR 6.11±1.90 pg/mL (range 3.13-9.41) vs control 6.15±1.91 pg/mL (range 2.18-9.86); PDR (5.37±1.74 pg/mL (range 2.85-8.65) vs control 6.15±1.91 pg/mL (range 2.18-9.86), P=0.808, P=0.264].

CONCLUSION

Elevated melatonin levels in aqueous humor in PDR may indicate the level to be associated with DR severity.

Evaluation of cationic nanosystems with melatonin using an eye-related bioavailability prediction model

In this study, two types of nanosystems, namely lecithin/chitosan nanoparticles and Pluronic® F127/chitosan micelles, have been prepared and evaluated for their potential for the ocular delivery of melatonin, which is known to exert an ocular hypotensive effect. The melatonin content, particle size, zeta potential and in vitro drug release properties were studied as a function of the presence of chitosan in the nanosystem. Lecithin/chitosan nanoparticles were evaluated in terms of the mucoadhesive properties by a newly established method based on HCE-T cells, also used in in vitro biocompatibility and permeability studies. Lecithin/chitosan nanoparticles were significantly larger than the corresponding F127/chitosan micelles (mean diameter of 241.8 vs. 20.7nm, respectively) and characterised by a higher surface charge (22.7 vs. 4.3mV, respectively). The HCE-T cell viability assay did not show significant toxic effects of nanosystems investigated at the (relevant) chitosan concentration tested. The permeability study results confirmed the permeation enhancing effect of F127, which was hindered in the presence of chitosan. Lecithin/chitosan nanoparticles were characterised by prominent mucoadhesive properties and prolonged melatonin release, which was shown to control melatonin permeation across an in vitro corneal epithelial model. Such properties demonstrate the potential for nanoparticles to provide an extended pre-corneal residence time of melatonin, ensuring higher eye-related bioavailability and extended intraocular pressure reduction compared to melatonin in both aqueous and micelle solutions.

Cationic solid lipid nanoparticles enhance ocular hypotensive effect of melatonin in rabbit

The study was aimed at evaluating whether the ocular hypotensive effect of melatonin (MEL) was enhanced by its encapsulation in cationic solid lipid nanoparticles (cSLN), as well as at determining the tolerability of these formulations on the ocular surface. MEL was loaded in cSLN that had already been shown to be suitable for ophthalmic use. The formulations were prepared using Softisan(®) 100 as the main lipid matrix, with the presence of either stearic (SA) or palmitic acid (PA) as lipid modifiers. A fixed positive charge was provided by the addition of a cationic lipid (didecyldimethylammonium bromide). The ocular hypotensive effect was evaluated by measuring the intraocular pressure (IOP) during 24h in albino rabbits. MEL elicited a significant (p<0.01) IOP reduction in rabbit eye. All the formulations tested in vivo demonstrated a good tolerability. The nanocarrier containing SA was the most effective in terms of IOP reduction (maximum IOP reduction: -7 mmHg), and its effect lasted approximately 24h. The experimental data indicate that the new formulations based on cSLN loaded with MEL represent a potent anti-glaucoma treatment with a safe profile, warranting further clinical evaluation of the proposed nanotechnological strategy.

Is the melatonin receptor type 1 involved in the pathogenesis of glaucoma?

Melatonin in the mammalian eye is synthesized by the photoreceptors and its levels show a clear daily pattern with high levels at night and lower levels during the day. It is synthesized in the ciliary body and secreted into the aqueous humor with a pattern similar to what has been reported for the retina. It acts by interacting with a family of G-protein coupled receptors that are negatively coupled with adenylate cyclase. Melatonin receptor subtypes MT1 and MT2 have been identified in the retina. Both are found in the inner nuclear layer (horizontal and amacrine cells), in the inner plexiform layer, ganglion cells (RGC) and retinal pigmented epithelium. They are also present in the ciliary body. Several studies implicate melatonin in the rhythmic regulation of intraocular pressure. MT1 and MT2 melatonin receptors are expressed in many parts of the eye. Melatonin receptors are expressed in the iris and ciliary body. Recent studies showed that mice lacking MT1 receptors have elevated intraocular pressure during the night and show a significantly reduced number of RGCs. These new studies suggest that dysfunctional melatonin signaling may be considered a possible risk factor in the pathogenesis of glaucoma and that mice deficient in MT1 receptors may be an animal model of glaucoma.

Changes in the circadian rhythm in patients with primary glaucoma

Purpose

The current study was undertaken to investigate whether glaucoma affects the sleep quality and whether there is any difference between patients with primary glaucoma (primary open angle glaucoma, POAG and primary angle-closure glaucoma, PACG) and healthy subjects, using a validated self-rated questionnaire, the Pittsburgh Sleep Quality Index (PSQI).

Methods

The sleep quality of patients with POAG and PACG was tested against normal controls. Subjects were divided into three sub-groups according to age. Differences in the frequency of sleep disturbances (PSQI score >7) were assessed. The differences of sleep quality within the three groups and within the POAG group depending on the patients’ intraocular pressure (IOP) and impairment of visual field (VF) were also studied.

Results

92 POAG patients, 48 PACG patients and 199 controls were included. Sleep quality declined with age in control and POAG group (tendency chi-square, P<0.05). The prevalence of sleep disturbances was higher in POAG and PACG group than in the control group, the differences were statistically significant. The prevalence of sleep disturbances was higher in patients with PACG, compared to POAG patients in the age interval of 61–80. In POAG group, the ratio of patients with sleep disorders increased with augmented impairment of VF, but the differences were not statistically significant (χ²-test, P>0.05). No significant differences were found in POAG group between patients with a highest IOP in daytime and at nighttime (χ²-test, P>0.05).

Conclusions

The prevalence of sleep disorders was higher in patients with POAG and PACG than in controls. PACG patients seemed to have a more serious problem of sleep disorders than POAG patients between 61 to 80 years old. No correlation was found between the prevalence of sleep disorders and impairment of VF or the time when POAG patients showed a highest IOP.

Melatonin and its analog 5-methoxycarbonylamino-N-acetyltryptamine potentiate adrenergic receptor-mediated ocular hypotensive effects in rabbits: significance for combination therapy in glaucoma

Melatonin is currently considered a promising drug for glaucoma treatment because of its ocular hypotensive and neuroprotective effects. We have investigated the effect of melatonin and its analog 5-methoxycarbonylamino-N-acetyltryptamine, 5-MCA-NAT, on β₂/α(2A)-adrenergic receptor mRNA as well as protein expression in cultured rabbit nonpigmented ciliary epithelial cells. Quantitative polymerase chain reaction and immunocytochemical assays revealed a significant β₂-adrenergic receptor downregulation as well as α(2A)-adrenergic receptor up-regulation of treated cells (P < 0.001, maximal significant effect). In addition, we have studied the effect of these drugs upon the ocular hypotensive action of a nonselective β-adrenergic receptor (timolol) and a selective α₂-adrenergic receptor agonist (brimonidine) in normotensive rabbits. Intraocular pressure (IOP) experiments showed that the administration of timolol in rabbits pretreated with melatonin or 5-MCA-NAT evoked an additional IOP reduction of 14.02% ± 5.8% or 16.75% ± 5.48% (P < 0.01) in comparison with rabbits treated with timolol alone for 24 hours. Concerning brimonidine hypotensive action, an additional IOP reduction of 29.26% ± 5.21% or 39.07% ± 5.81% (P < 0.001) was observed in rabbits pretreated with melatonin or 5-MCA-NAT when compared with animals treated with brimonidine alone for 24 hours. Additionally, a sustained potentiating effect of a single dose of 5-MCA-NAT was seen in rabbits treated with brimonidine once daily for up 4 days (extra IOP decrease of 15.57% ± 5.15%, P < 0.05, compared with brimonidine alone). These data confirm the indirect action of melatoninergic compounds on adrenergic receptors and their remarkable effect upon the ocular hypotensive action mainly of α₂-adrenergic receptor agonists but also of β-adrenergic antagonists.

On the free radical scavenging activities of melatonin's metabolites, AFMK and AMK

The reactions of N(1) -acetyl-N(2) -formyl-5-methoxykynuramine (AFMK) and N(1) -acetyl-5-methoxykynuramine (AMK) with (•) OH, (•) OOH, and •OOCCl3 radicals have been studied using the density functional theory. Three mechanisms of reaction have been considered: radical adduct formation (RAF), hydrogen transfer (HT), and single electron transfer (SET). Their relative importance for the free radical scavenging activity of AFMK and AMK has been assessed. It was found that AFMK and AMK react with •OH at diffusion-limited rates, regardless of the polarity of the environment, which supports their excellent •OH radical scavenging activity. Both compounds were found to be also very efficient for scavenging •OOCCl3 , but rather ineffective for scavenging •OOH. Regarding their relative activity, it was found that AFMK systematically is a poorer scavenger than AMK and melatonin. In aqueous solution, AMK was found to react faster than melatonin with all the studied free radicals, while in nonpolar environments, the relative efficiency of AMK and melatonin as free radical scavengers depends on the radical with which they are reacting. Under such conditions, melatonin is predicted to be a better •OOH and •OOCCl3 scavenger than AMK, while AMK is predicted to be slightly better than melatonin for scavenging •OH. Accordingly it seems that melatonin and its metabolite AMK constitute an efficient team of scavengers able of deactivating a wide variety of reactive oxygen species, under different conditions. Thus, the presented results support the continuous protection exerted by melatonin, through the free radical scavenging cascade.

Oxidative stress and potential applications of free radical scavengers in glaucoma

Glaucoma is the leading cause of irreversible blindness in industrialized countries and comprises a group of diseases characterized by progressive optic nerve degeneration. Glaucoma is commonly associated with elevated intraocular pressure due to impaired outflow of aqueous humor resulting from abnormalities within the drainage system of the anterior chamber angle (open-angle glaucoma) or impaired access of aqueous humor to the drainage system (angle-closure glaucoma). Oxidative injury and altered antioxidant defense mechanisms in glaucoma appear to play a role in the pathophysiology of glaucomatous neurodegeneration that is characterized by death of retinal ganglion cells. Oxidative protein modifications occurring in glaucoma serve as immunostimulatory signals and alter neurosupportive and immunoregulatory functions of glial cells. Initiation of the apoptotic cascade observed in glaucomatous retinopathy can involve oxidant mechanisms and different agents have been shown to be neuroprotective. This review focuses on the molecular mechanisms of oxidant injury and summarizes studies that have investigated novel free radical scavengers in the treatment of glaucomatous neurodegeneration.

Polymeric nanoparticles augment the ocular hypotensive effect of melatonin in rabbits

Melatonin, a neurohormone secreted by the pineal gland, is able to modulate intraocular pressure (IOP). The aim of this study was to generate nanoparticle (NPs) sustained release formulations that allow to extend the pre-corneal residence time of melatonin, thus prolonging its pharmacological effects. Poly(D,L-lactide-co-glycolide) (PLGA) and PLGA-poly(ethylenglycole) (PEG) nanoparticles (NPs) were used to prepare the new melatonin formulations. Mean particle diameter and zeta potential, determined after freeze-drying in the presence of glucose as a cryoprotectant, ranged between 100 and 400 nm and -32.2/-8.2 mV, respectively for PLGA and PLGA-PEG NPs. Melatonin loading ranged between 44% and 80%. DSC analysis showed a homogeneous molecular dispersion of the drug in the NPs matrix. The hypotensive effect was evaluated by measuring IOP during 24h after instillation in the rabbit eye, in comparison with a melatonin aqueous solution at the same concentration (0.08%, w/v). The tested NPs showed good ocular tolerability in rabbit eye using biomicroscopy. Melatonin-loaded PLGA-PEG NPs were the most effective in reducing IOP up to 8h (maximum IOP reduction: 5 mmHg).

Production of melatonin by Saccharomyces strains under growth and fermentation conditions

Melatonin is a bioactive compound that is present in wine because it is contained in vinification grapes and synthesized by yeast during alcoholic fermentation. The purpose of this study was to determine the capacity of various Saccharomyces strains to form melatonin during its growth and alcoholic fermentation. A selection of yeasts including six S. cerevisiae (Lalvin CLOS, Lalvin ICV-D254, Enoferm QA23 Viniferm ARM, Viniferm RVA, and Viniferm TTA), one S. uvarum (Lalvin S6U) and one S. cerevisiae var. bayanus (Uvaferm BC) were tested to determine whether they produce melatonin in yeast extract peptose dextrose and synthetic must media in a variety of conditions. Two S. cerevisiae strains (ARM, and QA23), the S. uvarum and the S. cerevisiae var. bayanus, synthesized melatonin. The conditions in which they did so, however, were different: the QA23 strain produced melatonin best in a medium with a low concentration of reducing sugars and Lalvin S6U and Uvaferm BC required a synthetic must under fermentation conditions. Melatonin synthesis largely depended on the growth phase of the yeasts and the concentration of tryptophan, reducing sugars and the growth medium. These results indicate that melatonin may have a role as a yeast growth signal molecule.

The effect of melatonin on retinal ganglion cell survival in ischemic retina

Our objective was to determine whether melatonin increases retinal ganglion cell (RGC) survival in ischemic mouse retina. Transient retinal ischemia was induced by an acute elevation of intraocular pressure in C57BL/6 mice. To evaluate the effect of melatonin on retinal ischemia, an equal amount of either melatonin or vehicle was intraperitoneally injected into the mice 1 hour before ischemia, at the time of ischemia, and 1 hour after ischemia. Hypoxia inducible factor 1α (HIF-1α) and glial fibrillary acidic protein (GFAP) expression were assessed 6, 12, and 24 hours after ischemia-reperfusion by Western blot. RGC survival was measured 2 weeks after ischemia-reperfusion. The expression of HIF-1α and GFAP peaked 24 hours after ischemia-reperfusion in ischemic retina. The treatment of ischemic retina with melatonin resulted in the inhibition of increased expression of HIF-1α and GFAP. RGC survival was greater in retinas treated with melatonin than in retinas treated with vehicle 2 weeks after ischemia-reperfusion. On the basis of our results, we suggest that melatonin treatment increased RGC survival in ischemic mouse retina. The neuroprotective effect of melatonin is mediated by the inhibition of HIF-1α stabilization and reduced activity of glial cells in ischemic mouse retina.

Ocular disorders and the utility of animal models in the discovery of melatoninergic drugs with therapeutic potential

INTRODUCTION

  The pineal indole-derived hormone melatonin is a modulator of circadian and seasonal rhythms with an important role in ocular health and disease. This could be due to specific melatonin receptors that have been identified in structures such as cornea, lens, ciliary body, retina, choroid and sclera. In addition, a local synthesis of melatonin occurs in several of these ocular tissues.

AREAS COVERED

The authors review existing literature on the most common animal models where ocular melatonin actions have been tested. The therapeutic potential of melatonin in diabetic keratopathy and retinopathy, keratitis, cataracts, glaucoma, uveitis, age-related macular degeneration and retinitis pigmentosa is discussed. Furthermore, the authors comment on the usefulness of different animal models for the development of melatoninergic drugs with therapeutic potential.

EXPERT OPINION

The use of animals for the study of ocular diseases and the potentiality of melatonin and its analogs, as future therapeutic drugs, should be performed on the basis of a rationale study. It is important to note that melatonin receptors seem to be widespread all over the eye. This strongly suggests that, in order to modify the physiology and biochemistry of malfunctioning ocular tissue, the melatonin receptors which are present in that tissue must be first identified. Second there is the need to confirm that those receptors targeted perform the desirable responses, and as a third measure, to use selective agonists (or antagonists) instead of melatonin. However, although some animals mimic ocular pathologies relatively well, and these can be used in melatonin studies, there is still a long way to go till some of the results obtained in animal models could be used for human therapy.

Melatonin, the circadian multioscillator system and health: the need for detailed analyses of peripheral melatonin signaling

Evidence is accumulating regarding the importance of circadian core oscillators, several associated factors, and melatonin signaling in the maintenance of health. Dysfunction of endogenous clocks, melatonin receptor polymorphisms, age- and disease-associated declines of melatonin likely contribute to numerous diseases including cancer, metabolic syndrome, diabetes type 2, hypertension, and several mood and cognitive disorders. Consequences of gene silencing, overexpression, gene polymorphisms, and deviant expression levels in diseases are summarized. The circadian system is a complex network of central and peripheral oscillators, some of them being relatively independent of the pacemaker, the suprachiasmatic nucleus. Actions of melatonin on peripheral oscillators are poorly understood. Various lines of evidence indicate that these clocks are also influenced or phase-reset by melatonin. This includes phase differences of core oscillator gene expression under impaired melatonin signaling, effects of melatonin and melatonin receptor knockouts on oscillator mRNAs or proteins. Cross-connections between melatonin signaling pathways and oscillator proteins, including associated factors, are discussed in this review. The high complexity of the multioscillator system comprises alternate or parallel oscillators based on orthologs and paralogs of the core components and a high number of associated factors with varying tissue-specific importance, which offers numerous possibilities for interactions with melatonin. It is an aim of this review to stimulate research on melatonin signaling in peripheral tissues. This should not be restricted to primary signal molecules but rather include various secondarily connected pathways and discriminate between direct effects of the pineal indoleamine at the target organ and others mediated by modulation of oscillators.

Light-emitting diodes (LED) for domestic lighting: any risks for the eye?

Light-emitting diodes (LEDs) are taking an increasing place in the market of domestic lighting because they produce light with low energy consumption. In the EU, by 2016, no traditional incandescent light sources will be available and LEDs may become the major domestic light sources. Due to specific spectral and energetic characteristics of white LEDs as compared to other domestic light sources, some concerns have been raised regarding their safety for human health and particularly potential harmful risks for the eye. To conduct a health risk assessment on systems using LEDs, the French Agency for Food, Environmental and Occupational Health & Safety (ANSES), a public body reporting to the French Ministers for ecology, for health and for employment, has organized a task group. This group consisted physicists, lighting and metrology specialists, retinal biologist and ophthalmologist who have worked together for a year. Part of this work has comprised the evaluation of group risks of different white LEDs commercialized on the French market, according to the standards and found that some of these lights belonged to the group risk 1 or 2. This paper gives a comprehensive analysis of the potential risks of white LEDs, taking into account pre-clinical knowledge as well as epidemiologic studies and reports the French Agency's recommendations to avoid potential retinal hazards.