Industrial and academic approaches to the search for alternative melatonin receptor ligands: An historical survey.

The search for melatonin receptor agonists formed the main part of melatonin medicinal chemistry programs for the last three decades. In this short review, we summarize the two main aspects of these programs: the development of all the necessary tools to characterize the newly synthesized ligands at the two melatonin receptors MT1 and MT2, and the medicinal chemist's approaches to find chemically diverse ligands at these receptors. Both strategies are described. It turns out that the main source of tools were industrial laboratories, while the medicinal chemistry was mainly carried out in academia. Such complete accounts are interesting, as they delineate the spirits in which the teams were working demonstrating their strength and innovative character. Most of the programs were focused on nonselective agonists and few of them reached the market. In contrast, discovery of MT1-selective agonists and melatonergic antagonists with proven in vivo activity and MT1 or MT2-selectivity is still in its infancy, despite the considerable interest that subtype selective compounds may bring in the domain, as the physiological respective roles of the two subtypes of melatonin receptors, is still poorly understood. Poly-pharmacology applications and multitarget ligands have also been considered.

Anticonvulsant activity of melatonin and its success in ameliorating epileptic comorbidity-like symptoms in zebrafish.

Epilepsy is one of common neurological disorders, greatly distresses the well-being of the sufferers. Melatonin has been used in clinical anti-epileptic studies, but its effect on epileptic comorbidities is unknown, and the underlying mechanism needs further investigation. Herein, by generating PTZ-induced zebrafish seizure model, we carried out interdisciplinary research using neurobehavioral assays, bioelectrical detection, molecular biology, and network pharmacology to investigate the activity of melatonin as well as its pharmacological mechanisms. We found melatonin suppressed seizure-like behavior by using zebrafish regular locomotor assays. Zebrafish freezing and bursting activity assays revealed the ameliorative effect of melatonin on comorbidity-like symptoms. The preliminary screening results of neurobehavioral assays were further verified by the expression of key genes involved in neuronal activity, neurodevelopment, depression and anxiety, as well as electrical signal recording from the midbrain of zebrafish. Subsequently, network pharmacology was introduced to identify potential targets of melatonin and its pathways. Real-time qPCR and protein-protein interaction (PPI) were conducted to confirm the underlying mechanisms associated with glutathione metabolism. We also found that melatonin receptors were involved in this process, which were regulated in response to melatonin exposure before PTZ treatment. The antagonists of melatonin receptors affected anticonvulsant activity of melatonin. Overall, current study revealed the considerable ameliorative effects of melatonin on seizure and epileptic comorbidity-like symptoms and unveiled the underlying mechanism. This study provides an animal model for the clinical application of melatonin in the treatment of epilepsy and its comorbidities.

Changes in melatonin receptor expression in a murine model of glaucoma.

Purpose: The objective of this study was to evaluate the changes in the melatoninergic receptors of DBA/2J and C57BL/6J mice with the development of glaucoma. DBA/2J mice are widely used to study the physiopathology of glaucoma due to the similarities of their eyes to human eyes and the resulting similarity in the development of their pathology. In addition, melatoninergic receptors are known for their control of intraocular pressure (IOP), reducing the production of aqueous humor; however, little is known about their relationship with the development of this pathology. Methods: mRNA expression of MT1, MT2, and GPR50 melatoninergic receptors was performed with quantitative real-time PCR. In addition, receptor expression was performed with immunohistochemical techniques on the ciliary processes. To further investigate the effect of melatonin and its analog 5-methoxycarbonylamino-N-acetyltryptamine (5-MCA-NAT) on IOP, animals were instilled with these compounds and the corresponding melatoninergic antagonists to assess their effect on IOP. Results: All melatoninergic receptor expression decayed with the development of the glaucomatous pathology in the DBA/2J mice, and was especially visible for the MT2 receptor. However, receptor expression was consistent in the C57BL/6J control mice across all ages investigated. Furthermore, IOP blockage was stronger with 4PPDOT (MT2 antagonist) only in the DBA/2J mice which suggests a correlation of this receptor with the development of the glaucomatous pathology in DBA/2J animals. Conclusions: Melatonin receptor expression decays with the development of the glaucomatous pathology. This implies that the physiologic hypotensive effect of endogenous melatonin reducing IOP is not possible. A solution for such changes in receptor expression is the exogenous application of melatonin or any of its analogs that permit the activation of the remaining melatonin receptors.

Melatonin receptor ligands: A pharmaco-chemical perspective.

Melatonin MT1 and MT2 receptor ligands have been vigorously explored for the last 4 decades. Inspection of approximately 80 publications in the field revealed that most melatonergic ligands were structural analogues of melatonin combining three essential features of the parent compound: an aromatic ring bearing a methoxy group and an amide side chain in a relative arrangement similar to that present in melatonin. While several series of MT2 -selective agents-agonists, antagonists, or partial agonists-were reported, the field was lacking MT1 -selective agents. Herein, we describe various approaches toward the development of melatonergic ligands, keeping in mind that most of the molecules/pharmacophores obtained were essentially melatonin copies, even though diverse tri- or tetra-cyclic compounds were explored. In addition to lack of structural diversity, only few studies examined the activity of the reported melatonergic ligands in vivo. Moreover, an extensive pharmacological characterization including biopharmaceutical stability, pharmacokinetic properties, specificity toward other major receptors to name a few remained scarce. For example, many of the antagonists described were not stable in vivo, were not selective for the melatonin receptor subtype of interest, and were not fully characterized from a pharmacological standpoint. Indeed, virtual screening of large compound libraries has led to the recent discovery of potent and selective melatonin receptor agonists and partial agonists of new chemotypes. Having said this, the melatonergic field is still lacking subtype-selective melatonin receptor antagonists "active" in vivo, which are critical to our understanding of melatonin and melatonin receptors' role in basic physiology and disease.

Characterization of the various functional pathways elicited by synthetic agonists or antagonists at the melatonin MT1 and MT2 receptors.

Melatonin is a neurohormone that translates the circadian rhythm to the peripheral organs through a series of binding sites identified as G protein-coupled receptors MT1 and MT2. Due to minute amounts of receptor proteins in target organs, the main tool of studies of the melatoninergic system is recombinant expression of the receptors in cellular hosts. Although a number of studies exist on these receptors, studies of several signaling pathways using a large number of melatoninergic compounds are rather limited. We chose to fill this gap to better describe a panel of compounds that have been only partially characterized in terms of functionality. First, we characterized HEK cells expressing MT1 or MT2, and several signaling routes with melatonin itself to validate the approach: GTPγS, cAMP production, internalization, ß-arrestin recruitment, and cell morphology changes (CellKey ® ). Second, we chose 21 compounds from our large melatoninergic chemical library and characterized them using this panel of signaling pathways. Notably, antagonists were infrequent, and their functionality depended largely on the pathway studied. This will permit redefining the availability of molecular tools that can be used to better understand the in situ activity and roles of these receptors.

Fetal liver mesenchymal stem cells restore ovarian function in premature ovarian insufficiency by targeting MT1.

BACKGROUND: With the development of regenerative medicine and tissue engineering technology, almost all stem cell therapy is efficacious for the treatment of premature ovarian failure (POF) or premature ovarian insufficiency (POI) animal models, whereas little stem cell therapy has been practiced in clinical settings. The underlying molecular mechanism and safety of stem cell treatment in POI are not fully understood. In this study, we explored whether fetal mesenchymal stem cells (fMSCs) from the liver restore ovarian function and whether melatonin membrane receptor 1 (MT1) acts as a regulator for treating POI disease. METHODS: We designed an in vivo model (chemotherapy-induced ovary damage) and an in vitro model (human ovarian granulosa cells (hGCs)) to understand the efficacy and molecular cues of fMSC treatment of POI. Follicle development was observed by H&E staining. The concentration of sex hormones in serum (E2, AMH, and FSH) and the concentration of oxidative and antioxidative metabolites and the enzymes MDA, SOD, CAT, LDH, GR, and GPx were measured by ELISA. Flow cytometry (FACS) was employed to detect the percentages of ROS and proliferation rates. mRNA and protein expression of antiapoptotic genes (SURVIVIN and BCL2), apoptotic genes (CASPASE-3 and CASPASE-9), and MT1 and its downstream genes (JNK1, PCNA, AMPK) were tested by qPCR and western blotting. MT1 siRNA and related antagonists were used to assess the mechanism. RESULTS: fMSC treatment prevented cyclophosphamide (CTX)-induced follicle loss and recovered sex hormone levels. Additionally, fMSCs significantly decreased oxidative damage, increased oxidative protection, improved antiapoptotic effects, and inhibited apoptotic genes in vivo and in vitro. Furthermore, fMSCs also upregulated MT1, JNK1, PCNA, and AMPK at the mRNA and protein levels. With MT1 knockdown or antagonist treatment in normal hGCs, the protein expression of JNK1, PCNA, and AMPK and the percentage of proliferation were impaired. CONCLUSIONS: fMSCs might play a crucial role in mediating follicular development in the POI mouse model and stimulating the activity of POI hGCs by targeting MT1.

Melatonin MT1 and MT2 Receptors Exhibit Distinct Effects in the Modulation of Body Temperature across the Light/Dark Cycle.

Melatonin (MLT) is a neurohormone that regulates many physiological functions including sleep, pain, thermoregulation, and circadian rhythms. MLT acts mainly through two G-protein-coupled receptors named MT1 and MT2, but also through an MLT type-3 receptor (MT3). However, the role of MLT receptor subtypes in thermoregulation is still unknown. We have thus investigated the effects of selective and non-selective MLT receptor agonists/antagonists on body temperature (Tb) in rats across the 12/12-h light-dark cycle. Rectal temperature was measured every 15 min from 4:00 a.m. to 9:30 a.m. and from 4:00 p.m. to 9:30 p.m., following subcutaneous injection of each compound at either 5:00 a.m. or 5:00 p.m. MLT (40 mg/kg) had no effect when injected at 5 a.m., whereas it decreased Tb during the light phase only when injected at 5:00 p.m. This effect was blocked by the selective MT2 receptor antagonist 4P-PDOT and the non-selective MT1/MT2 receptor antagonist, luzindole, but not by the α1/MT3 receptors antagonist prazosin. However, unlike MLT, neither the selective MT1 receptor partial agonist UCM871 (14 mg/kg) nor the selective MT2 partial agonist UCM924 (40 mg/kg) altered Tb during the light phase. In contrast, UCM871 injected at 5:00 p.m. increased Tb at the beginning of the dark phase, whereas UCM924 injected at 5:00 a.m. decreased Tb at the end of the dark phase. These effects were blocked by luzindole and 4P-PDOT, respectively. The MT3 receptor agonist GR135531 (10 mg/kg) did not affect Tb. These data suggest that the simultaneous activation of both MT1 and MT2 receptors is necessary to regulate Tb during the light phase, whereas in a complex but yet unknown manner, they regulate Tb differently during the dark phase. Overall, MT1 and MT2 receptors display complementary but also distinct roles in modulating circadian fluctuations of Tb.

Melatonin protects rabbit spermatozoa from cryo-damage via decreasing oxidative stress.

Mammalian spermatozoa are highly susceptible to reactive oxygen species (ROS) stress. The aim of the present study was to investigate whether and how melatonin protects rabbit spermatozoa against ROS stress during cryopreservation. Semen was diluted with Tris-citrate-glucose extender in presence of different concentrations of melatonin. It was observed that addition of 0.1 mM melatonin significantly improved spermatozoa motility, membrane integrity, acrosome integrity, mitochondrial membrane potential as well as AMP-activated protein kinase (AMPK) phosphorylation. Meanwhile, the lipid peroxidation (LPO), ROS levels and apoptosis of post-thaw spermatozoa were reduced in presence of melatonin. Interestingly, when fresh spermatozoa were incubated with 100 µM H2O2, addition of 0.1 mM melatonin significantly decreased the oxidative damage compared to the H2O2 treatment, whereas addition of luzindole, an MT1 receptor inhibitor, decrease the effect of melatonin in spermatozoa. It was observed that the glutathione (GSH) content and activities of glutathione peroxidase (GPx), superoxide dismutase (SOD) and catalase (CAT) were significantly increased with addition of melatonin during cryopreservation. In conclusion, addition of melatonin to the freezing extender protects rabbit spermatozoa against ROS attack by enhancing AMPK phosphorylation for increasing the antioxidative defense.

Indole based antimalarial compounds targeting the melatonin pathway: Their design, synthesis and biological evaluation.

Malaria, one of the most severe global diseases, infects nearly 300 million people causing death of about a million population annually. Herein we have reported design, synthesis and biological evaluation of potent antimalarial compounds that target melatonin hormone as a potential pathway for the inhibition of the parasite proliferation. The molecular design is based on melatonin and indole based synthetic and natural antimalarial agents. The library of compounds was accessed via an iodine catalyzed one pot organocatalytic ring opening of 1-aryltetrahydro-ß-carbolines followed by in situ imination of the resulting C2-aroyl intermediates. Inhibition of parasite growth progression (3D7 and chloroquine resistant RKL9 strain) in the presence of the tested compounds indicated that few of the compounds substantially inhibited the parasite survival and the most potent compound 2j blocked the parasite growth at the trophozoite stage. Compound 2j also disrupted the melatonin induced synchronization of the parasite culture in vitro. The active compounds were screened against melatonin receptor MT1 to demonstrate substantial binding.

Sleep well. Untangling the role of melatonin MT1 and MT2 receptors in sleep.

The pharmacological potential of targeting selectively melatonin MT1 or MT2 receptors has not yet been exploited in medicine. Research using selective MT1/MT2 receptor ligands and MT1/MT2 receptor knockout mice has indicated that the activation of MT2 receptors selectively increases non-rapid eye movement (NREM) sleep whereas MT1 receptors seem mostly implicated in the regulation of REM sleep. Moreover, MT1 knockout mice show an increase in NREM sleep, while MT2 knockout a decrease, suggesting an opposite role of these two receptors. A recent paper in mice by Sharma et al (J Pineal Res, 2018, e12498) found that MT1 but not MT2 receptors are expressed on orexin neurons in the perifornical lateral hypothalamus (PFH). Moreover, after injecting melatonin or luzindole into the mouse PFH, the authors suggest that melatonin promotes NREM sleep because activates PFH MT1 receptors, which in turn inhibit orexin neurons that are important in promoting arousal and maintaining wakefulness. In this commentary, we have critically commented on some of these findings on the bases of previous literature. In addition, we highlighted the fact that no conclusions could be drawn on the melatonin receptor subtype mediating the effects of melatonin on sleep because the authors used the non-selective MT1/MT2 receptors antagonist luzindole. More solid research should further characterize the pharmacological function of these two melatonin receptors in sleep.

Docking studies for melatonin receptors.

INTRODUCTION: Melatonin is a neurohormone that controls many relevant physiological processes beyond the control of circadian rhythms. Melatonin's actions are carried out by two main types of melatonin receptors; MT1 and MT2. These receptors are important, and not just because of the biological actions of its natural agonist; but also, because melatonin analogues can improve or antagonize their biological effect. Area covered: The following article describes the importance of melatonin as a biologically relevant molecule. It also defines the receptors for this substance, as well as the second messengers coupled to these receptors. Lastly, the article describes the amino acid residues involved in the docking process in both MT1 and MT2 melatonin receptors. Expert opinion: The biological actions of melatonin and their interpretations are becoming more relevant and therefore require the development of new pharmacological tools. Understanding the second messenger mechanisms involved in melatonin actions, as well as the characteristics of the docking of this molecule to MT1 and MT2 melatonin receptors, will permit the development of more selective agonists and antagonists which will help us to better understand this molecule as well to develop new therapeutic compounds.

Melatonin reduces oxidative damage and upregulates heat shock protein 90 expression in cryopreserved human semen.

Sperm cells can be damaged during the semen cryopreservation process, decreasing their fertilizing ability. Physical damage and oxidative stress may occur during the freeze-thawing process. Antioxidants such as the native antioxidant melatonin can potentially improve cryopreservation outcomes. In this study, we added melatonin to cryoprotectant to examine its effect on frozen-thawed human sperm. We found that adding 0.1mM melatonin to cryoprotectant significantly increased sperm viability (24.80 ± 0.46% vs. 20.97 ± 1.27%, P < 0.05) and membrane integrity (P < 0.05), and decreased intracellular reactive oxygen species and lipid peroxidation damage. Furthermore, mRNA levels of the transcription factor NF-E2-related factor-2 and its downstream genes were significantly increased. Resistance to oxidative stress was enhanced and expression of the antiapoptotic gene Bcl-2 was increased by inclusion of 0.1mM melatonin in the cryoprotectant. Moreover, 0.1mM melatonin upregulated the expression of heat shock protein 90 (HSP90), which confers resistance to stressors in frozen-thawed sperm. Results obtained upon addition of inhibitors of melatonin receptors (luzindole and 4-P-PDOT) and an HSP90 inhibitor (geldanamycin) in the cryoprotectant demonstrated that melatonin promoted HSP90 translation via the melatonin receptor MT1 and increased adenosine triphosphate levels, thus increasing the viability of thawed sperm.

Melatonin Synergizes the Chemotherapeutic Effect of Cisplatin in Ovarian Cancer Cells Independently of MT1 Melatonin Receptors.

BACKGROUND/AIM: Melatonin (MLT), through the interaction with membrane melatonin receptors MT1, can improve the effectiveness of cytostatic agents, including cisplatin (CP). The aim of this study was to examine the synergistic effect of MLT and CP in three cell lines: IOSE 364, SK-OV-3 and OVCAR-3, as well as to assess the role of MT1 receptors in this mechanism. MATERIALS AND METHODS: Using the SRB assay we investigated the effect of different concentrations of CP and MLT on cell viability. Tests, using luzindole - MT1 inhibitor, allowed us to assess the potential involvement of MT1 in the mechanism of MLT action. RESULTS: MLT at certain concentrations demonstrated a synergistic effect in combination with CP. The addition of luzindole did not affect the action of MLT in combination with CP. CONCLUSION: In summary, the synergistic effect of MLT with CP seems to be independent of membrane MT1 receptors.

Melatonin protects against cisplatin-induced ovarian damage in mice via the MT1 receptor and antioxidant activity.

This study evaluated the receptor- and/or antioxidant stress-mediated mechanisms by which melatonin prevents the ovarian toxicity of cisplatin treatment. The expression of the MT1 receptor in mouse ovaries was investigated by immunohistochemistry. Pretreatment with melatonin (5, 10, or 20 mg/kg body weight, i.p.) before cisplatin (5 mg/kg body weight, i.p.) was administered to mice once daily for 3 days (phase I). The pharmacological modulation via melatonin type 1 and/or 2 receptors was analyzed by administration of receptor antagonists (luzindole: nonselective MT1/MT2 antagonist; 5 mg/kg body weight or 4-phenyl-2-propionamidotetralin: selective MT2 antagonist; 4 mg/kg body weight) once daily for 3 days, 15 min before the treatment with melatonin and cisplatin (phase II). Thereafter, the ovaries were harvested and used for histological (morphology and activation), immunohistochemical (PCNA, activated caspase-3 and bcl-2 expression), terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling, and fluorescence (reactive oxygen species [ROS], glutathione [GSH], and active mitochondria levels) analyses. The expression of the MT1 protein in mouse ovaries was documented. Pretreatment with 20 mg/kg melatonin before cisplatin administration preserved the normal follicular morphology and cell proliferation rate, reduced apoptosis, ROS production, mitochondrial damage and increased GSH expression, as compared to the cisplatin treatment alone. Additionally, administration of the nonselective MT1/MT2 receptor antagonist inhibited the melatonin ovarian protection from the cytotoxic effects of cisplatin. However, administration of a selective MT2 antagonist did not modify the protective effects observed at 20 mg/kg melatonin. In conclusion, pretreatment with 20 mg/kg melatonin effectively protected the ovaries against cisplatin-induced damage. Moreover, the MT1 receptor and melatonin antioxidant effects mediated this cytoprotective activity.

Activation of melatonin receptor (MT1/2) promotes P-gp transporter in methamphetamine-induced toxicity on primary rat brain microvascular endothelial cells.

Melatonin has been known as a neuroprotective agent for the central nervous system (CNS) and the blood-brain barrier (BBB), which is the primary structure that comes into contact with several neurotoxins including methamphetamine (METH). Previous studies have reported that the activation of melatonin receptors (MT1/2) by melatonin could protect against METH-induced toxicity in brain endothelial cells via several mechanisms. However, its effects on the P-glycoprotein (P-gp) transporter, the active efflux pump involved in cell homeostasis, are still unclear. Thus, this study investigated the role of melatonin and its receptors on the METH-impaired P-gp transporter in primary rat brain microvascular endothelial cells (BMVECs). The results showed that METH impaired the function of the P-gp transporter, significantly decreasing the efflux of Rho123 and P-gp expression, which caused a significant increase in the intracellular accumulation of Rho123, and these responses were reversed by the interaction of melatonin with its receptors. Blockade of the P-gp transporter by verapamil caused oxidative stress, apoptosis, and cell integrity impairment after METH treatment, and these effects could be reversed by melatonin. Our results, together with previous findings, suggest that the interaction of melatonin with its receptors protects against the effects of the METH-impaired P-gp transporter and that the protective role in METH-induced toxicity was at least partially mediated by the regulation of the P-gp transporter. Thus, melatonin and its receptors (MT1/2) are essential for protecting against BBB impairment caused by METH.

Exogenous melatonin reduced blood pressure in late-term ovine fetus via MT1/MT2 receptor pathways.

Melatonin is involved in the regulation of blood pressure through the receptor dependent or independent route. However, the effect of melatonin on fetal blood pressure is unknown. This study investigated the effect of melatonin on blood pressure of the late-term ovine fetus in utero. Melatonin and/or antagonists were intravenously administered into the fetuses. Mean arterial pressure and heart rate were recorded. Fetal blood samples were analyzed for biochemical parameters and hormones, including cortisol, angiotensin I, angiotensin II, aldosterone, atrial natriuretic peptide, corticotrophin-releasing hormone, adrenocorticotropic hormone, and endothelin. Fetal blood pressure was decreased following administration of melatonin, whereas it was increased following administration of luzindole, but not prazosin. Plasma level of endothelin was decreased by melatonin, which was blocked by luzindole. Our study suggested that melatonin reduced fetal blood pressure via MT1/MT2 receptors and possibly involving release of endothelin.

Melatonin receptors as therapeutic targets in the suprachiasmatic nucleus.

INTRODUCTION: Disorders of rhythmicity can cause a variety of pathologies and are known to impair processes involved in metabolism, as well as in cardiovascular disease and cancer. Developing strategies to treat or prevent such diseases is a new challenge for medicine. Rhythms depend on a complex multi-oscillatory circadian network which, in mammals, is hierarchically organized with the suprachiasmatic nuclei (SCN) as master clock. The SCN, thus form an ideal structure for target discovery in circadian pathologies. AREAS COVERED: The development of strategies to treat or prevent disorders of rhythmicity is a new challenge for medicine. Several pharmacological approaches have been suggested, but until now, it has been mostly melatonin (MTL) or MTL-agonists which have demonstrated usefulness in modulating clock activities in vivo. A great number of structurally different MTL receptor ligands have been developed, some of which are already approved and marketed as drugs. The MTL receptor involved in phase-shifting circadian rhythms (chronobiotic effect) is the MT1 subtype. EXPERT OPINION: As the two receptor subtypes for MTL may have divergent functions, the development of highly selective MT1 and MT2 agonists (and antagonists) is key for the discovery of novel therapeutic agents in specifically defined circadian pathologies. The identification of cells expressing the different MTL receptor subtypes should also permit a better understanding of MLT physiology/pharmacology.

Melatonin Upregulates the Activity of AMPK and Attenuates Lipid Accumulation in Alcohol-induced Rats.

AIMS: Melatonin is supposed to be an effective hepatoprotective agent. The effects and mechanisms of melatonin on alcoholic fatty liver (AFL) have not been well explored. The aim of this study was to investigate the preventive and therapeutic effects of melatonin on alcohol-induced fatty liver rats. METHODS: The AFL rats were induced by intragastric infusion of alcohol plus a high-fat diet for 6 weeks, and melatonin (10, 20, 40 mg/kg) was administered by gastric perfusion. We also established fatty acid overload cell model in HepG2 cells to investigate the effect of melatonin on AMP-activated protein kinase (AMPK) activity. RESULTS: The results showed that melatonin (20 and 40 mg/kg) administration significantly reduced alcohol-induced hepatic steatosis with lowering activities of serum alanine aminotransferase, aspartate aminotransferase and levels of serum and hepatic triglyceride. The activity of superoxide dismutase was increased and the content of malondialdehyde was decreased in liver homogenates of rats treated with melatonin. Melatonin increased the phosphorylation of AMPK in the liver tissues of alcohol-induced rats as well. Additionally, in vitro studies showed that melatonin increased the expression of melatonin1A receptor (MT1R), whereas luzindole, a receptor antagonist of melatonin, had no effect on its expression. In addition, melatonin reduced the levels of adenosine 3',5'-cyclic monophosphate (cAMP) and increased the phosphorylation of AMPK, and melatonin treatment could markedly reverse these effects. CONCLUSION: In conclusion, melatonin could protect against liver injury caused by alcohol gastric perfusion. The effect may be related to alleviating lipid peroxidation and upregulating the activity of AMPK mediated by MT1R signaling pathway.

[Luzindol accelerates the aging of estrous function of female rats].

In this paper, we investigated the dynamics of aging of the estrous function of female rats kept in the conditions of standard vivarium lighting and receiving luzindol - the blocker of melatonin receptors. Every three months, daily, for two weeks, vaginal smears were taken from the animals and cytological examination of the vaginal contents was conducted. Despite different mechanisms of the development of melatonin system failure (a decreased production of melatonin and a blockade of melatonin receptors), the effects of the influence on the ovulatory function are similar. In case of the blockade of melatonin receptors, the appearance of premature signs of aging of the reproductive function in rats was observed. It was manifested by an increased duration of ovulatory cycle; a decrease in the number of regular cycles; the emergence of irregular cycles; a decrease in the number of short estrous cycles and an increase of long cycles; the early development of persistent estrus.

[The use of agomelatine (valdoxan) in gambling therapy: a pilot study].

OBJECTIVE: To study the antidepressant agomelatine (M1/M2 agonist and 5-HT2C antagonist) in pathological gambling (PG) (ICD-10 item F63.0). MATERIAL AND METHODS: An open label 8-week trial was carried out in 22 outpatients (17 male and 5 female, mean age 38±7). PG severity was assessed by the Yale-Brown Obsessive-Compulsive Scale adapted for Pathological Gambling (PG-YBOCS). Anxiety and depression level was measured by the Hospital Anxiety Depression Scale (HADS). RESULTS: Agomelatine significantly decreased PG-YBOCS scores from the second week of the trial (12.6±3.0 compared to 24.2±2.1 at baseline, p<0.05). In the end of the trial, PG-YBOCS score decreased to 5.3. The total HADS score decreased significantly in the end of the study (from 23.6±2.9 to 11.4±1.9, p<0.05). There was an improvement in behavior as well. CONCLUSION: Thus, agomelatine has demonstrated efficacy in PG patients.