Melatonin Receptor Antagonist Research Articles

Luzindole attenuates LPS/d-galactosamine-induced acute hepatitis in mice.

Melatonin is a well-documented hormone that plays central roles in the regulation of sleep–wake cycles. There is cumulative evidence to suggest that melatonin is also a pleiotropic regulator of inflammation, and luzindole has been widely used as a melatonin receptor antagonist. This study investigated the potential effects of luzindole on LPS/d-galactosamine (d-GalN)-induced acute hepatitis. The results indicated that treatment with luzindole alleviated histological damage in the liver, reduced the level of transaminases in plasma and improved the survival of LPS/d-GalN-exposed mice. Treatment with luzindole also suppressed the production of the pro-inflammatory cytokines TNF-α and IL-6 in LPS/d-GalN-exposed mice. In addition, treatment with luzindole inhibited the activation of caspase-3, -8 and -9, and suppressed the cleavage of caspase-3 and poly(ADP-ribose) polymerase. Therefore, treatment with luzindole attenuates LPS/d-GalN-induced acute liver injury, suggesting that luzindole might have potential value for the intervention of inflammation-based hepatic disorders.

Melatonin Promotes Nerve Regeneration Following End-to-Side Neurorrhaphy by Accelerating Cytoskeletal Remodeling via the Melatonin Receptor-dependent Pathway

Acceleration of cytoskeletal remodeling in regenerated axons is crucial for a fully functional recovery following peripheral nerve injury (PNI). Melatonin plays important roles in cell differentiation and protection of cytoskeleton stability, thus, the present study aimed to investigate whether melatonin can enhance neurite outgrowth and promote cytoskeletal remodeling in a PNI animal model and in differentiated neurons.End-to-side neurorrhaphy (ESN) rat model was used for assessing cytoskeletal rearrangement in regenerated axon. Subject rats received 1 mg/kg/day melatonin injection for one month. The amplitude of compound muscle action potentials and the number of re-innervated motor end plates on target muscles were assessed to represent the functional recovery after ESN.Melatonin treatment enhanced functional recovery after ESN, compared to the saline treated group. Additionally, in spinal cord and peripheral nerve tissue, animals receiving melatonin displayed enhanced expression of GAP43 and β3-tubulin one month after ESN, and an increased number of re-innervated motor end plates on their target muscle. In vitro analysis revealed that melatonin treatment significantly promoted neurite outgrowth, and increased expression of melatonin receptors as well as β3-tubulin in mouse neuroblastoma Neuro-2a (N2a) cells. Treatment with a melatonin receptor antagonist, luzindole, significantly suppressed melatonin receptors and β3-tubulin expression.Importantly, we found that melatonin treatment suppressed activation of calmodulin-dependent protein kinase II (CaMKII) in vitro and in vivo, suggesting that the β3-tubulin remodeling may occur via CaMKII-mediated Ca2+ signaling. These results suggested that melatonin may promote functional recovery after PNI by accelerating cytoskeletal remodeling through the melatonin receptor-dependent pathway.

Constant darkness conditions modulate the effects of melatonin and luzindole on the antioxidant enzyme activities and levels of retinol and α-tocopherol in rats

This study was conducted to evaluate the effects of both exogenous melatonin and melatonin receptor antagonist luzindole on the activities of antioxidant enzymes (AOE) (superoxide dismutase, SOD; catalase, CAT) and the level of low-molecular antioxidant vitamins (retinol, α-tocopherol) in male Wistar rats kept in normal light conditions (LD 12:12) or constant darkness (DD). In LD, while melatonin had no influence on the studied antioxidants, luzindole caused an increase in retinol and a decrease in α-tocopherol contents in the liver compared to the control. In DD, with no influence on AOE activities, both drugs exerted similar effects on the liver retinol and kidney α-tocopherol contents, increasing them in comparison with control. Exposing the animals to DD induced an increase in kidney SOD activity and in liver retinol content. Moreover, DD-mel rats had higher SOD activity in the liver and kidney and a higher retinol level in the liver compared to LD-mel ones; DD-luz rats had a higher liver retinol content compared to LD-luz ones. Liver retinol level seems to be the most sensitive to influence of DD, melatonin and luzindole; the data are probably connected with the involvement of vitamin A in the regulation of circadian rhythms.

Biological effects of melatonin on human adipose‑derived mesenchymal stem cells.

Mesenchymal stem cells (MSCs) are capable of differentiating into other cell types and exhibit immunomodulatory effects. MSCs are affected by several intrinsic and extrinsic signaling modulators, including growth factors, cytokines, extracellular matrix and hormones. Melatonin, produced by the pineal gland, is a hormone that regulates sleep cycles. Recent studies have shown that melatonin improves the therapeutic effects of stem cells. The present study aimed to investigate whether melatonin enhances the biological activities of human adipose-derived MSCs. The results demonstrated that treatment with melatonin promoted cell proliferation by inducing SRY-box transcription factor 2 gene expression and preventing replicative senescence. In addition, melatonin exerted anti-adipogenic effects on MSCs. PCR analysis revealed that the expression of the CCAAT enhancer binding protein a gene, a key transcription factor in adipogenesis, was decreased following melatonin treatment, resulting in reduced adipogenic differentiation in an in vitro assay. The present study also examined the effect of melatonin on the immunomodulatory response using a co-culture system of human peripheral blood mononuclear cells and MSCs. Activated T cells were strongly inhibited following melatonin exposure compared with those in the control group. Finally, the favorable effects of melatonin on MSCs were confirmed using luzindole, a selective melatonin receptor antagonist. The proliferation-promoting, anti-inflammatory effects of melatonin suggested that melatonin-treated MSCs may be used for effective cell therapy.

Evaluation of the anticonvulsant effect of novel melatonin derivatives in the intravenous pentylenetetrazol seizure test in mice

The design of new pharmacologically active compounds with affinity to melatonin receptors has become an area of great interest during the last decade. Recently, we reported that newly synthesized melatonin derivatives, containing aroylhydrazone moiety in the indole scaffold, with the highest affinity to the elaborated pharmacophore model, possess an anticonvulsant activity in the maximal electroshock (MES) and 6Hz test in mice. We aimed further to explore the effect of these melatonin derivatives and the role of melatonin receptors on seizure threshold measured by the timed intravenous pentylenetetrazole (iv PTZ) infusion test in mice. Carbamazepine (CBZ) and melatonin were used as positive controls. Three out of six compounds, 3c, 3f, and 3e, respectively, dose-dependently increased the PTZ-induced seizure thresholds for myoclonic twitch, clonic, and tonic seizures comparable to the effect of CBZ and melatonin. The anticonvulsant effect of 3c, 3f, and 3e was blocked by the non-selective melatonin receptor antagonist luzindol suggesting the involvement of melatonin receptors in the activity of these compounds. Also docking study of 3c, 3f and 3e in the melatonin-binding site of melatonin receptor confirm the possible mechanism of action of these compounds involving melatonin receptors. Our previous and present results suggest that 3c, 3f, and 3e can be considered promising agents with anticonvulsant activity on melatonin receptors in the brain.

Role of Melatonin Receptors in Hyperthermia-Induced Acute Seizure Model of Rats.

Melatonin is a neurohormone that has anticonvulsant activity in different experimental seizure models including hyperthermic febrile seizure. However, the mechanisms of this effect are not clear at the receptor level. The aim of the study was to determine which melatonin receptors involve in the hyperthermic febrile seizure model. 22-30days Wistar male rats were used, and in children, it corresponds to 1.5-2years. Groups were performed as (1) control, (2) ethanol/saline, (3) DMSO, (4) melatonin (MT), (5) MT + luzindole (LUZ), (6) MT + K-185, (7) MT + prazosin (PRZ), (8) MT + LUZ + K-185, (9) MT + LUZ + PRZ, (10) MT + K-185 + PRZ, and (11) MT + LUZ + PRZ + K-185. The hyperthermic febrile seizure pattern was established by keeping the rats in 45°C hot water, and the latency, duration, and severity of seizures were determined in all groups. MT, LUZ, K-185, and PRZ were given 15, 45, 15, and 30min before the induction of seizure, respectively. It was observed that melatonin shortened the duration of seizure, reduced the severity, and did not affect latency and that these effects were not completely blocked by receptor antagonists when compared with control, ethanol/saline, and DMSO groups. In conclusion, the fact that the anticonvulsant effect of melatonin is not completely blocked by all melatonin receptor antagonists. We can conclude that a multimodal mechanism may be responsible for the effect of melatonin receptors alone on the anticonvulsant effect of melatonin. It will be useful to design new pharmacological studies to make the subject clear.

The melatonin receptor antagonist luzindole induces Ca2+ mobilization, reactive oxygen species generation and impairs trypsin secretion in mouse pancreatic acinar cells

BackgroundIn this work we studied the effects of the melatonin receptor-antagonist luzindole (1 μM–50 μM) on isolated mouse pancreatic acinar cells. MethodsChanges in intracellular free-Ca2+ concentration, reactive oxygen species production and trypsin secretion were analyzed. ResultsLuzindole induced increases in [Ca2+]i that diminished CCK-8 induced Ca2+ mobilization, compared with that observed when CCK-8 was applied alone. Treatment of cells with thapsigargin (1 μM), in the absence of Ca2+ in the extracellular medium, evoked a transient increase in [Ca2+]i. The additional incubation of cells with luzindole (10 μM) failed to induce further mobilization of Ca2+. In the presence of luzindole a concentration-dependent increase in ROS generation was observed that decreased in the absence of Ca2+ or by pretreatment of cells with melatonin (100 μM). Incubation of pancreatic acinar cells with luzindole (10 μM) impaired CCK-8-induced trypsin secretion. Melatonin was unable to revert the effect of luzindole on CCK-8-induced trypsin secretion. ConclusionThe melatonin receptor-inhibitor luzindole induces Ca2+-mediated pro-oxidative conditions and impairment of enzyme secretion, which creates a situation in pancreatic acinar cells that might compromise their function. General significanceThe effects of luzindole that we have observed, might be unspecific and could mislead the observations when it is used to study the actions of melatonin on the gland. Another possibility is that melatonin receptors exhibit a basal or agonist-independent activity in pancreatic acinar cells, which might be modulated by melatonin or luzindole.

Melatonin prevents lung injury by regulating apelin 13 to improve mitochondrial dysfunction

Pulmonary fibrosis is a progressive disease characterized by epithelial cell damage, fibroblast proliferation, excessive extracellular matrix (ECM) deposition, and lung tissue scarring. Melatonin, a hormone produced by the pineal gland, plays an important role in multiple physiological and pathological responses in organisms. However, the function of melatonin in the development of bleomycin-induced pulmonary injury is poorly understood. In the present study, we found that melatonin significantly decreased mortality and restored the function of the alveolar epithelium in bleomycin-treated mice. However, pulmonary function mainly depends on type II alveolar epithelial cells (AECIIs) and is linked to mitochondrial integrity. We also found that melatonin reduced the production of reactive oxygen species (ROS) and prevented apoptosis and senescence in AECIIs. Luzindole, a nonselective melatonin receptor antagonist, blocked the protective action of melatonin. Interestingly, we found that the expression of apelin 13 was significantly downregulated in vitro and in vivo and that this downregulation was reversed by melatonin. Furthermore, ML221, an apelin inhibitor, disrupted the beneficial effects of melatonin on alveolar epithelial cells. Taken together, these results suggest that melatonin alleviates lung injury through regulating apelin 13 to improve mitochondrial dysfunction in the process of bleomycin-induced pulmonary injury.

Melatonin alleviates asphyxial cardiac arrest-induced cerebellar Purkinje cell death by attenuation of oxidative stress

Although multiple reports using animal models have confirmed that melatonin appears to promote neuroprotective effects following ischemia/reperfusion-induced brain injury, the relationship between its protective effects and activation of autophagy in Purkinje cells following asphyxial cardiac arrest and cardiopulmonary resuscitation (CA/CPR) remains unclear. Rats used in this study were randomly assigned to 6 groups as follows; vehicle-treated sham operated group, vehicle-treated asphyxial CA/CPR operated group, melatonin-treated sham operated group, melatonin-treated asphyxial CA/CPR operated group, PDOT (a MT2 melatonin receptor antagonist) plus (+) melatonin-treated sham operated group and PDOT+melatonin-treated asphyxial CA/CPR operated group. Melatonin (20 mg/kg, i.p., 4 times before CA and 3 times after CA) treatment significantly improved survival rate and neurological deficit compared with the vehicle-treated asphyxial CA/CPR rats (survival rates ≥40% vs 10%), showing that melatonin treatment exhibited protective effect against asphyxial CA/CPR-induced Purkinje cell death. The protective effect of melatonin against CA/CPR-induced Purkinje cell death paralleled a remarkable attenuation of autophagy-like processes (Beclin-1, Atg7 and LC3), as well as a dramatic reduction in superoxide anion radical (O2·-), intense enhancements of CuZn superoxide dismutase (SOD1) and MnSOD (SOD2) expressions. Furthermore, the protective effect was notably reversed by treatment with PDOT, which is a selective MT2 antagonist. In brief, melatonin conferred neuroprotection against asphyxial CA/CPR-induced Purkinje cell death via inhibiting autophagic activation by reducing expressions of O2·- and increasing expressions of antioxidant enzymes, and suggests that MT2 is involved in neuroprotective effect of melatonin against Purkinje cell death caused by asphyxial CA/CPR.

Melatonin promotes proliferation of neural stem cells from adult mouse spinal cord via the PI3K/AKT signaling pathway.

In this study, we tested the effect of melatonin on proliferation and differentiation of neural stem/progenitor cells (NSPCs) obtained from adult mouse spinal cord. We found that melatonin increases neurosphere formation from adult spinal cord NSPCs but does not alter the differentiation of the cells. Western blot results show that adult spinal cord NSPCs express both MT1 and MT2 melatonin receptors. The melatonin receptor antagonist 4P-PDOT abrogates the melatonin-induced neurosphere formation. Melatonin increases the phosphorylation level of protein kinase B (AKT). Blockage of phosphatidylinositol 3-kinase (PI3K), a kinase upstream of AKT, abolishes the stimulatory effect of melatonin on spinal cord NSPCs. We conclude that melatonin promotes the proliferation of adult spinal cord NSPCs via the PI3K/AKT signaling pathway.

Melatonin supports alendronate in preserving bone matrix and prevents gastric inflammation in ovariectomized rats.

The anti-catabolic bisphosphonate alendronate is considered as the first-line medical treatment in post-menopausal osteoporosis; but several side effects, including gastric mucosal injury, are associated with its use. The aim was to elucidate whether combined treatment with melatonin plus alendronate would be more advantageous in the maintenance of bone and the prevention of gastric side effects. Under anaesthesia, female Sprague-Dawley rats underwent bilateral ovariectomy (OVX), while control group had sham surgery. Four weeks after the surgery, OVX rats were treated with saline, melatonin (25μg/mL/d), alendronate (70μg/kg/wk), melatonin+alendronate, melatonin+melatonin receptor antagonist (luzindole, 10μg/kg/d) or alendronate+melatonin+luzindole for 8weeks. Rats were euthanized at the end of 12th week. Runx2 expression, apoptotic cells, and trabecular thickness were evaluated in tibiae, while gastric tissues were analysed for oxidative injury parameters. In all OVX groups, Runx2 expression was depressed. Saline-treated OVX group presented an extreme decrease in calcified area in opposition to melatonin- or alendronate-treated groups, while the bones in alendronate+melatonin-treated group were similar to those of the sham-operated group. Concomitant with the improvements examined histologically in bone tissues, quantitative TUNEL (+) cells were similarly lower in alendronate- or melatonin-treated groups. Oxidative gastric damage was increased in saline- or alendronate-treated groups, which were depressed in the presence of melatonin. Although melatonin and alendronate exerted similar supportive effects on the maintenance of bone mass, melatonin may have a more advantageous impact by protecting against OVX-induced gastric injury, which was aggravated by alendronate use. HIGHLIGHTS: Our results demonstrate that alendronate and melatonin had similar supportive effects on the maintenance of bone mass, while melatonin prevented the gastric side effects of alendronate, making this combination an advisable therapeutic approach in the treatment of menopausal osteoporosis.

Melatonin receptor stimulation by agomelatine prevents Aβ-induced tau phosphorylation and oxidative damage in PC12 cells.

PurposeAs a novel antidepressant drug, agomelatine has good therapeutic effect on the mood disorder and insomnia in Alzheimer’s disease (AD). Recent studies have shown the neuroprotective function of agomelatine, including anti-oxidative and anti-apoptosis effect. However, it remains unclear whether agomelatine exerts neuroprotection in AD. Thus, the neuroprotective effect of agomelatine against amyloid beta 25–35 (Aβ25–35)-induced toxicity in PC12 cells was evaluated in this study.MethodsThe concentration of malondialdehyde (MDA), LDH, and ROS was investigated to evaluate oxidative damage. The expression of P-tau, tau, PTEN, P-Akt, Akt, P-GSK3β, and GSK3β proteins was assessed by Western blotting. Our results demonstrated that Aβ25–35 significantly increased the content of MDA, LDH, and ROS. Meanwhile, Aβ25–35 upregulated the expression of P-tau and PTEN as well as downregulated P-Akt and P-GSK3β expression. These effects could be blocked by agomelatine pretreatment. Furthermore, luzindole, the melatonin receptor (MT) antagonist, could reverse the neuroprotective effect of agomelatine.ConclusionThe results demonstrated that antidepressant agomelatine might prevent the tau protein phosphorylation and oxidative damage induced by Aβ25–35 in PC12 cells by activating MT-PTEN/Akt/GSK3β signaling. This study provided a novel therapeutic target for AD in the future.

AGE-RELATED CHANGES IN THE BEHAVIOR AND PHOBIC ANXIETY REACTIONS IN RATS UNDER EXPOSURE TO LIGHT DEPRIVATION AND LUZINDOLE

The effect of both long-term stay of rats under the specific extreme conditions of light deprivation, and the administration of a melatonin receptor antagonist luzindole on the agerelated pattern of behavioral reactions and psycho-emotional manifestations was studied. The level of the emotional and phobic anxiety state of the animals was assessed in an “Open field” installation in combination with the test “Dark chamber with holes”. We found that in the process of aging, rats kept in standard light conditions (LD) demonstrated a decline in motor activity along with an increase in phobic anxiety reactions. The effect of a prolonged exposure to light deprivation on the psycho-emotional state and motor activity of rats varied depending on the ontogenetic period during which the animals were placed in these specific conditions. At an advanced age, the anxiety level increased in rats kept in the dark since birth (LD/DD) to a greater degree than in the animals exposed to such conditions since prenatal development (DD/DD). The administration of a melatonin receptor antagonist luzindole to animals kept in constant darkness led to an age-related increase in phobic anxiety in the open space (as shown in the “Open Field” test), but had a normalizing effect on the psycho-emotional state of the rats in the “Dark chamber with holes” installation, imitating the animals’ natural shelter. It is concluded that the melatoninergic system, including the pineal gland, melatonin and its receptors, is directly involved in the regulation of the behavior and psycho-emotional state of rats under specific lighting conditions, which are often extreme and harmful for their health.

Agomelatine modulates calcium signaling through protein kinase C and phospholipase C-mediated mechanisms in rat sensory neurons.

Agomelatine, a novel antidepressant exerting its effects through melatonergic and serotonergic systems, implicated to be effective against pain including neuropathic pain but without any knowledge of mechanism of action. To explore the possible role of agomelatine on nociceptive transmission at the peripheral level, the effects of agomelatine on intracellular calcium ([Ca2+ ]i ) signaling in peripheral neurons were investigated in cultured rat dorsal root ganglion (DRG) neurons. Using the fura-2-based calcium imaging technique, the effects of agomelatine on [Ca2+ ]i and roles of the second messenger-mediated pathways were assessed. Agomelatine caused [Ca2+ ]i signaling in a dose-dependent manner when tested at 10 and 100 μM concentration. Luzindole, a selective melatonin receptor antagonist, almost completely blocked the agomelatine-induced calcium signals. The agomelatine-induced calcium transients were also nearly abolished following pretreatment with the 100 ng/ml pertussis toxin, a Gi/o protein inhibitor. The stimulatory effects of agomelatine on [Ca2+ ]i transients were significantly reduced by applications of phospholipase C (PLC) and protein kinase C (PKC) blockers, 10 μM U73122, and 10 μM chelerythrine chloride, respectively. The obtained results of agomelatine-induced [Ca2+ ]i signals indicates that peripheral mechanisms are involved in analgesic effects of agomelatine. These mechanisms seems to involve G-protein-coupled receptor activation and PLC and PKC mediated mechanisms.

Iodine‐Catalyzed Metal‐Free Oxidative Ring Opening of 1‐Aryltetrahydro‐β‐carbolines: Facile Synthesis of C‐2 Aroyl and Aryl Methanimino Indole Derivatives

Indole derivatives bearing C‐2 substituents have garnered a lot of attention due to their diverse biological activities. Various methods forthe synthesis of these compounds have been reported. Inspired by the hydrolysis of imines, an oxidative ring‐opening reaction of 1‐aryltetrahydro‐β‐carbolines with catalytic iodine in aqueous hydrogen peroxide, and also in the presence of appropriate amines, is described for the generation of 2‐aroyl and arylmethanimine indole derivatives. The reaction proceeds under mild reaction conditions with ethanol as the solvent or under solvent‐free conditions, respectively. This metal‐free strategy facilitates the formation of the desired substituted C‐2 indoles in moderate to excellent yields. The utility of this reaction is demonstrated by a facile multigram‐scale synthesis of Luzindole, a selective melatonin receptor antagonist and an investigational drug against depression and disruption of the circadian rhythm.

Melatonin Receptor Agonist Ramelteon Reduces Ischemia-Reperfusion Injury Through Activation of Mitochondrial Potassium Channels.

Activation of melatonin receptors induces cardioprotection. Mitochondrial potassium channels (mKCa and mKATP) are involved in the signaling cascade of preconditioning. The melatonin receptor agonist ramelteon is an approved oral medication for treatment of insomnia, but nothing is known about possible cardioprotective properties. We investigated whether (1) ramelteon induces cardioprotection mediated by the melatonin receptor; (2) this effect is concentration-dependent; and (3) mKCa and/or mKATP channels are critically involved in ramelteon-induced cardioprotection. Hearts of male Wistar rats were randomized and placed on a Langendorff system, perfused with Krebs-Henseleit buffer at a constant pressure of 80 mm Hg. All hearts were subjected to 33 minutes of global ischemia and 60 minutes of reperfusion. Before, ischemic hearts were perfused with different concentrations of ramelteon (0.01-5 μM) for determination of a concentration-effect curve. In subsequent experiments, the lowest protective concentration of ramelteon was administered together with paxilline (mKCa channel inhibitor) and 5-hydroxydecanoate (mKATP channel inhibitor). To determine whether the reduction of ischemia and reperfusion injury by ramelteon is mediated by melatonin receptor, we combined ramelteon with luzindole, a melatonin receptor antagonist. Infarct size was determined by triphenyltetrazolium chloride staining. In control animals, infarct size was 58% ± 6%. Ramelteon in a concentration of 0.03 µM reduced infarct size to 28% ± 4% (P < 0.0001 vs. Con). A lower concentration of ramelteon did not initiate cardioprotection, and higher concentrations did not further decrease infarct size. Paxilline, 5-hydroxydecanoate, and luzindole completely blocked the ramelteon-induced cardioprotection. This study shows for the first time that (1) ramelteon induces cardioprotection through melatonin receptor; (2) the effect is not concentration-dependent; and (3) activation of mKCa and mKATP channels is involved.

Aerobic exercise enhanced endothelium-dependent vasorelaxation in mesenteric arteries in spontaneously hypertensive rats: the role of melatonin.

Melatonin, a neuroendocrine hormone synthesized primarily by the pineal gland, provides various cardiovascular benefits. Regular physical activity is an effective non-pharmacological therapy for the prevention and control of hypertension. In the present study, we hypothesized that melatonin plays an important role in the aerobic exercise-induced increase of endothelium-dependent vasorelaxation in the mesenteric arteries (MAs) of spontaneously hypertensive rats (SHRs) in a melatonergic receptor-dependent manner. To test this hypothesis, we evaluated the vascular mechanical and functional properties in normotensive Wistar Kyoto (WKY), SHRs, and SHRs that were trained on a treadmill (SHR-EX) for 8 weeks. Exercise training produced a significant reduction in blood pressure and heart rate in SHR, which was significantly attenuated by the intraperitoneal administration of luzindole, a non-selective melatonin receptor (MT1/MT2) antagonist. Serum melatonin levels in the SHR group were significantly lower than those in the WKY group at 8:00-9:00 and 21:00-22:00, while exercise training reduced this difference. Endothelium-dependent vessel relaxation induced by acetylcholine was significantly blunted in SHR compared with age-matched WKY. Both exercise training and luzindole ameliorated this endothelium-dependent impairment of relaxation in hypertension. Immunohistochemistry and Western blotting showed that the protein expression of the MT2 receptor and eNOS, as well as their colocalization in the endothelial cell layer in SHRs, was significantly decreased; as exercise training suppressed this reduction. These results provide evidence that regular exercise has a beneficial effect on improving endothelium-dependent vasorelaxation in MAs, in which melatonin plays a critical role by acting on MT2 receptors to increase NO production and/or NO bioavailability.

Protective Efffects of Melatonin in Corpus Callosum Astrocytes during Ischemia in Transgenic Mice

Objective: Stroke is a leading cause of adult death and disability worldwide. Around 80% of all stroke cases are classed as ischemic stroke, which affects both gray and white matter brain regions. During ischemia, reactive oxygen species are generated and initiate multiple damaging processes such as lipid peroxidation, mitochondrial dysfunction, blood–brain barrier damage and brain edema. Melatonin is a potent antioxidant which can act as a direct oxygen species scavenger. Melatonin can also act at receptors (melatonin receptor 1 and 2), which are expressed in the nervous system cells including astrocytes.&#x0D; Methods: Using live cell imaging of transgenic mice, the viability of astrocytes in the corpus callosum of adult brain sections was monitored during a standard 60 minutes period of modeled ischemia (oxygen-glucose deprivation) and 30 minutes of reperfusion in 8 groups; Control, artificial cerebrospinal fluid + Melatonin, oxygen-glucose deprivation, oxygen-glucose deprivation + Melatonin, oxygen-glucose deprivation + Melatonin + Luzindole (a nonselective melatonin receptor antagonist), oxygen-glucose deprivation + Luzindole, oxygen-glucose deprivation + Melatonin + propionamidotetralin (a selective melatonin receptor 2 antagonist), and oxygen-glucose deprivation + propionamidotetralin.&#x0D; Results: Addition of melatonin significantly reduced the level of astrocyte death during oxygen-glucose deprivation from 71.94% ± 1.45 to 37.84% ± 1.9; p &lt; 0.0001. This protective effect was blocked by luzindole or propionamidotetralin. Following known scoring categories for glial injury, ultrastructural morphology confirmed the protective effect of melatonin against acute ischemic injury in the white matter glial cells.&#x0D; Conclusion: Melatonin is a promising neuroprotective agent during white matter ischemia.

Nickel-Catalyzed Regioselective C(2)-H Difluoroalkylation of Indoles with Difluoroalkyl Bromides.

Regioselective C(2)-H difluoroalkylation of C-3 unsubstituted indoles with commonly available fluoroalkyl bromides is successfully achieved employing a simple nickel catalyst system, (DME)NiCl2 /Xantphos. This methodology shows excellent regioselectivity and exhibits a broad substrate scope. Various functional groups, such as -OMe, -F, and -Br, are tolerated on the indole backbone to give the difluoroalkylated products in moderate to good yields. Preliminary mechanistic findings demonstrate that the reaction is homogeneous in nature and involves a radical manifold. Synthetic utility of this nickel-catalyzed method is demonstrated by synthesizing melatonin receptor antagonist Luzindole derivative.

Copper chelators promote nonamyloidogenic processing of AβPP via MT1/2 /CREB-dependent signaling pathways in AβPP/PS1 transgenic mice.

Copper is essential for the generation of reactive oxygen species (ROS), which are induced by amyloid-β (Aβ) aggregation; thus, the homeostasis of copper is believed to be a therapeutic target for Alzheimer's disease (AD). Although clinical trials of copper chelators show promise when applied in AD, the underlying mechanism is not fully understood. Here, we reported that copper chelators promoted nonamyloidogenic processing of AβPP through MT1/2 /CREB-dependent signaling pathways. First, we found that the formation of Aβ plaques in the cortex was significantly reduced, and learning deficits were significantly improved in AβPP/PS1 transgenic mice by copper chelator tetrathiomolybdate (TM) administration. Second, TM and another copper chelator, bathocuproine sulfonate (BCS), promoted nonamyloidogenic processing of AβPP via inducing the expression of ADAM10 and the secretion of sAβPPα. Third, the inducible ADAM10 production caused by copper chelators can be blocked by a melatonin receptor (MT1/2 ) antagonist (luzindole) and a MT2 inhibitor (4-P-PDOT), suggesting that the expression of ADAM10 depends on the activation of MT1/2 signaling pathways. Fourth, three of the MT1/2 -downstream signaling pathways, Gq/PLC/MEK/ERK/CREB, Gs/cAMP/PKA/ERK/CREB and Gs/cAMP/PKA/CREB, were responsible for copper chelator-induced ADAM10 production. Based on these results, we conclude that copper chelators regulate the balance between amyloidogenic and nonamyloidogenic processing of AβPP via promoting ADAM10 expression through MT1/2 /CREB-dependent signaling pathways.