Agonists of melatonin receptors strongly promote the functional recovery from the neuroparalysis induced by neurotoxic snakes.

Snake envenoming is a major, but neglected, tropical disease. Among venomous snakes, those inducing neurotoxicity such as kraits (Bungarus genus) cause a potentially lethal peripheral neuroparalysis with respiratory deficit in a large number of people each year. In order to prevent the development of a deadly respiratory paralysis, hospitalization with pulmonary ventilation and use of antivenoms are the primary therapies currently employed. However, hospitals are frequently out of reach for envenomated patients and there is a general consensus that additional, non-expensive treatments, deliverable even long after the snake bite, are needed. Traumatic or toxic degenerations of peripheral motor neurons cause a neuroparalysis that activates a pro-regenerative intercellular signaling program taking place at the neuromuscular junction (NMJ). We recently reported that the intercellular signaling axis melatonin-melatonin receptor 1 (MT1) plays a major role in the recovery of function of the NMJs after degeneration of motor axon terminals caused by massive Ca2+ influx. Here we show that the small chemical MT1 agonists: Ramelteon and Agomelatine, already licensed for the treatment of insomnia and depression, respectively, are strong promoters of the neuroregeneration after paralysis induced by krait venoms in mice, which is also Ca2+ mediated. The venom from a Bungarus species representative of the large class of neurotoxic snakes (including taipans, coral snakes, some Alpine vipers in addition to other kraits) was chosen. The functional recovery of the NMJ was demonstrated using electrophysiological, imaging and lung ventilation detection methods. According to the present results, we propose that Ramelteon and Agomelatine should be tested in human patients bitten by neurotoxic snakes acting presynaptically to promote their recovery of health. Noticeably, these drugs are commercially available, safe, non-expensive, have a long bench life and can be administered long after a snakebite even in places far away from health facilities.

Apparent resolution of hypersomnia episodes in two patients with Kleine-Levin syndrome following treatment with the melatonin receptor agonist ramelteon.

Kleine-Levin syndrome (KLS) is a rare disorder characterized by episodic bouts of severe hypersomnia associated with cognitive and behavioral abnormalities and normal alertness and functioning in between episodes. The pathophysiology is unclear but may involve neurotransmitter abnormalities, hypothalamic/thalamic dysfunction, viral/autoimmune etiology, or circadian abnormalities. No single treatment has been shown to be reliably efficacious; lithium has demonstrated the most consistent efficacy, although many do not respond and its use is limited by side effects. Due to the evidence of circadian involvement, we hypothesized that strengthening circadian signals may ameliorate symptoms. Ramelteon is a potent melatonin receptor agonist. In this report, two patients with KLS are described with apparent resolution of hypersomnia episodes following ramelteon initiation. CITATION: Dominguez D, Rudock R, Tomko S, Pathak S, Mignot E, Licis A. Apparent resolution of hypersomnia episodes in two patients with Kleine-Levin syndrome following treatment with the melatonin receptor agonist ramelteon. J Clin Sleep Med. 2024;20(4):657-662.

Efficacy and moderators of prevention and treatment of delirium with melatonin receptor agonists: A systematic review and meta-analysis of randomized controlled trials.

OBJECTIVE: Delirium is a complex and heterogeneous condition that significantly affects patient outcome. This study aimed to conduct a systematic review and meta-analysis to investigate the effects of melatonin and melatonin receptor agonists (MRAs) on delirium prevention and treatment. METHOD: Randomized controlled studies, using MRAs as an intervention and placebo as a control were included. We conducted meta-analyses with random-effects model and trial sequential analysis. RESULTS: A total of 33 studies involving 4850 participants were included. The meta-analysis revealed a significant preventive effect of MRAs on delirium (risk ratio = 0.65, p < 0.01), while no significant therapeutic effect was observed. Additionally, MRAs were associated with a significant reduction in mortality rate (risk ratio = 0.90, p = 0.02) in delirium prevention studies. Furthermore, subgroup analyses revealed that assessment scales and the frequency of delirium detection may be significant moderators of the delirium-preventive efficacy of MRAs. CONCLUSION: This study provides evidence of the potential effects of MRAs in preventing delirium and reducing mortality. Further research is required to elucidate the therapeutic potential of MRAs for delirium and identify specific patient populations that may benefit from this agent.

Melatonin alleviates PTSD-like behaviors and restores serum GABA and cortisol levels in mice.

RATIONALE: Melatonin is an endogenous hormone which modulates sleep-wake cycles. Previous studies have found a close correlation between melatonin and post-traumatic stress disorder (PTSD), a trauma- and stress-related psychiatric disorder with symptoms of sleep disturbance. However, it is still unclear if melatonin can have a therapeutic effect on PTSD. OBJECTIVE: This study aimed to investigate the effects of melatonin on foot shocks induced PTSD-like behaviors and abnormal neuroendocrine levels in mice. RESULTS: As compared to no-shock controls, PTSD-like mice spent significantly more time freezing and displayed less rearing in a contextual fear test, spent significantly less time in and had fewer entries into open arms in an elevated maze test, and spent significantly less time in and had fewer entries into a light box in a light-dark transition task. In addition, serum GABA and cortisol levels were both found to be significantly decreased, whereas epinephrine levels were significantly increased in the PTSD-like mice. Our results showed that intraperitoneal injections of melatonin (2 mM, but not 0.2 nor 20 mM, 0.1 ml/day for two consecutive weeks) alleviated PTSD-like behaviors and restored serum GABA and cortisol levels. Further, it was found that melatonin receptor 1/2 antagonist luzindole significantly blocked the beneficial effects of melatonin for PTSD-like behaviors and serum GABA and cortisol levels, whereas melatonin receptor 2 antagonist 4-P-PDOT slightly blocked these effects. CONCLUSIONS: These results indicate that melatonin has a potential therapeutic effect on PTSD-like symptoms in mice, and melatonin receptor 1 mediated the effect.

Agomelatine improves streptozotocin-induced diabetic nephropathy through melatonin receptors/SIRT1 signaling pathway.

INTRODUCTION: Diabetic nephropathy (DN) is a major cause of end-stage renal disease (ESRD). Agomelatine, a melatonin receptor agonist, has a potent anti-inflammatory activity. The current study aimed to determine the ameliorative anti-inflammatory effect of agomelatine against DN. METHODS: We used 10 % fructose with streptozotocin (STZ) to induce DN in male Wistar rats. Diabetic rats were treated with agomelatine in presence or absence of melatonin receptor antagonist (luzindole) or Sirtuin1 (SIRT1) inhibitor (EX527). SIRT1 expression was measured by qRT-PCR and immunohistochemical analysis. The expression of nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB), 5'adenosine monophosphate-activated protein kinase (AMPK), intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion protein-1 (VCAM-1), and monocyte chemoattractant protein-1 (MCP-1) were measured using ELISA. Histological assessment was performed using hematoxylin and eosin-stained renal sections. RESULTS: Fructose and STZ treatment induced diabetes, insulin resistance, and renal damage accompanied by reduced SIRT1 expression, increased NFκB activation, and decreased AMPK phosphorylation in the kidney. Agomelatine treatment improved kidney histology and function and upregulated SIRT1 expression (2-fold). Inhibition of melatonin receptors and SIRT1 activity increased NFκB phosphorylation (2.13 and 1.98-folds, respectively), reduced AMPK activation (0.51 and 0.53-folds, respectively), increased inflammatory markers ICAM-1 (2.16 and 2.23-folds, respectively), VCAM-1 (2.19 and 2.26-folds, respectively), and MCP-1(2.84 and 3.12-folds, respectively), and inhibited the ameliorative effect of agomelatine on kidney structure and function. CONCLUSION: Our findings reveal the ameliorative anti-inflammatory activity of agomelatine against STZ-induced DN and this effect is SIRT1- and melatonin receptor-dependent. Therefore, agomelatine may be beneficial to prevent the development of ESRD from diabetes mellitus.

Melatonin in Endometriosis: Mechanistic Understanding and Clinical Insight.

Endometriosis is defined as the development of endometrial glands and stroma outside the uterine cavity. Pathophysiology of this disease includes abnormal hormone profiles, cell survival, migration, invasion, angiogenesis, oxidative stress, immunology, and inflammation. Melatonin is a neuroendocrine hormone that is synthesized and released primarily at night from the mammalian pineal gland. Increasing evidence has revealed that melatonin can be synthesized and secreted from multiple extra-pineal tissues where it regulates immune response, inflammation, and angiogenesis locally. Melatonin receptors are expressed in the uterus, and the therapeutic effects of melatonin on endometriosis and other reproductive disorders have been reported. In this review, key information related to the metabolism of melatonin and its biological effects is summarized. Furthermore, the latest in vitro and in vivo findings are highlighted to evaluate the pleiotropic functions of melatonin, as well as to summarize its physiological and pathological effects and treatment potential in endometriosis. Moreover, the pharmacological and therapeutic benefits derived from the administration of exogenous melatonin on reproductive system-related disease are discussed to support the potential of melatonin supplements toward the development of endometriosis. More clinical trials are needed to confirm its therapeutic effects and safety.

The role of melatonin in pregnancies complicated by placental insufficiency: A systematic review.

Placental insufficiency affects about 10% of pregnancies and can lead to pre-eclampsia, fetal growth restriction, and preterm birth. Despite significant advances in early prediction and prevention of preterm pre-eclampsia with aspirin, the effects of prophylaxis on fetal growth restriction are less certain, and the rates of late-onset pre-eclampsia are not influenced by aspirin treatment. Pregnancies complicated by placental insufficiency are characterized by increased oxidative stress, and recent studies suggest that melatonin has antioxidant properties and contributes to maintaining placental homeostasis. We aimed to systematically review the available literature about melatonin in pregnancies complicated by placental insufficiency, specifically preeclampsia and fetal growth restriction, exploring three different aspects: 1) maternal melatonin levels; 2) expression and activity of melatonin placental receptors; 3) effects of maternal melatonin administration. PubMed (Medline) and Scopus were searched until December 2020. Identified studies were screened and assessed independently by two authors. Data were extracted and compiled in qualitative evidence synthesis. The circadian pattern of melatonin secretion seems to be altered in pregnancies complicated by placental insufficiency reflected by lower production of melatonin, with consequent lower systemic and placental concentrations and lower expression of melatonin receptors, thus reducing the local release of the indole and its autocrine function. Small intervention studies also suggest that treatment is safe and may lead to prolongation of pregnancy and better outcomes, but double-blind, randomized placebo-controlled trials are lacking.

Melatonin Attenuates Methamphetamine-Induced Alteration of Amyloid ß Precursor Protein Cleaving Enzyme Expressions via Melatonin Receptor in Human Neuroblastoma Cells.

Alzheimer's disease (AD) is the most prominent neurodegenerative disease represented by the loss of memory and cognitive impairment symptoms and is one of the major health imperilments among the elderly. Amyloid (Aß) deposit inside the neuron is one of the characteristic pathological hallmarks of this disease, leading to neuronal cell death. In the amyloidogenic processing, the amyloid precursor protein (APP) is cleaved by beta-secretase and γ-secretase to generate Aß. Methamphetamine (METH) is a psychostimulant drug that causes neurodegeneration and detrimental cognitive deficits. The analogy between the neurotoxic and neurodegenerative profile of METH and AD pathology necessitates an exploration of the underlying molecular mechanisms. In the present study, we found that METH ineluctably affects APP processing, which might contribute to the marked production of Aß in human neuroblastoma cells. Melatonin, an indolamine produced and released by the pineal gland as well as other extrapineal, has been protective against METH-induced neurodegenerative processes, thus rescuing neuronal cell death. However, the precise action of melatonin on METH has yet to be determined. We further propose to investigate the protective properties of melatonin on METH-induced APP-cleaving secretases. Pretreatment with melatonin significantly reversed METH-induced APP-cleaving secretases and Aß production. In addition, pretreatment with luzindole, a melatonin receptor antagonist, significantly prevented the protective effect of melatonin, suggesting that the attenuation of the toxic effect on METH-induced APP processing by melatonin was mediated via melatonin receptor. The present results suggested that melatonin has a beneficial role in preventing Aß generation in a cellular model of METH-induced AD.

Agomelatine: An Astounding Sui-generis Antidepressant?

Major depressive disorder (MDD) is one of the foremost causes of disability and premature death worldwide. Although the available antidepressants are effective and well tolerated, they also have many limitations. Therapeutic advances in developing a new drug's ultimate relation between MDD and chronobiology, which targets the circadian rhythm, led to a renewed focus on psychiatric disorders. In order to provide a critical analysis about antidepressant properties of agomelatine, a detailed PubMed (Medline), Scopus (Embase), Web of Science (Web of Knowledge), Cochrane Library, Google Scholar, and PsycInfo search was performed using the following keywords: melatonin analog, agomelatine, safety, efficacy, adverse effects, pharmacokinetics, pharmacodynamics, circadian rhythm, sleep disorders, neuroplasticity, MDD, bipolar disorder, anhedonia, anxiety, generalized anxiety disorder (GAD), and mood disorders. Agomelatine is a unique melatonin analog with antidepressant properties and a large therapeutic index that improves clinical safety. Published articles revealed that agomelatine is a melatonin receptors (MT1 and MT2) agonist and 5HT2C receptor antagonist. The effects receptors' on melatonin receptors enable the resynchronization of irregular circadian rhythms with beneficial effects on sleep architectures. In this way, agomelatine is accredited for its unique mode of action, which helps to exert antidepressant effects and resynchronize the sleep-wake cycle. To sum up, an agomelatine has not only antidepressant properties but also has anxiolytic effects.

Tasimelteon for treating non-24-h sleep-wake rhythm disorder.

INTRODUCTION: Non-24-h sleep-wake rhythm disorder (non-24) is observed in approximately half of totally blind individuals, a condition caused by their circadian pacemaker in the suprachiasmatic nucleus not being entrained to 24 h due to a lack of light perceptions. These subjects have a progressively delayed circadian cycle each day, non-24 periodically inducing nighttime insomnia and daytime sleepiness. Tasimelteon is a dual melatonin receptor agonist with high affinity for the melatonin 2 receptor, and it entrains endogenous melatonin rhythms and sleep-wake cycles in individuals with non-24. Areas covered: Herein, the authors review the treatment of non-24 with tasimelteon. The authors further compare tasimelteon with other melatonin receptor agonists. Expert opinion: The treatment strategies for non-24 aim to resynchronize the free-running rhythm with the 24 h light-dark cycle. Tasimelteon entrains circadian rhythms and improves the sleep-wake functions of individuals with non-24. Furthermore, the RESET study demonstrated that 20% of patients that discontinued tasimelteon maintained circadian entrainment whereas 90% of those who continued it maintained circadian entrainment. Long-term administration of tasimelteon is safe and well tolerated, and it is the only pharmacological therapy approved by the US Food and Drug Administration and the European Medicines Agency for non-24.