Neuroprotective effect of melatonin against kainic acid-induced oxidative injury in hippocampal slice culture of rats

The MT1 receptor as the target of ramelteon neuroprotection in ischemic stroke

Stroke is the leading cause of death and disability worldwide. Novel and effective therapies for ischemic stroke are urgently needed. Here, we report that melatonin receptor 1A (MT1) agonist ramelteon is a neuroprotective drug candidate as demonstrated by comprehensive experimental models of ischemic stroke, including a middle cerebral artery occlusion (MCAO) mouse model of cerebral ischemia in vivo, organotypic hippocampal slice cultures ex vivo, and cultured neurons in vitro; the neuroprotective effects of ramelteon are diminished in MT1-knockout (KO) mice and MT1-KO cultured neurons. For the first time, we report that the MT1 receptor is significantly depleted in the brain of MCAO mice, and ramelteon treatment significantly recovers the brain MT1 losses in MCAO mice, which is further explained by the Connectivity Map L1000 bioinformatic analysis that shows gene-expression signatures of MCAO mice are negatively connected to melatonin receptor agonist like Ramelteon. We demonstrate that ramelteon improves the cerebral blood flow signals in ischemic stroke that is potentially mediated, at least, partly by mechanisms of activating endothelial nitric oxide synthase. Our results also show that the neuroprotection of ramelteon counteracts reactive oxygen species-induced oxidative stress and activates the nuclear factor erythroid 2-related factor 2/heme oxygenase-1 pathway. Ramelteon inhibits the mitochondrial and autophagic death pathways in MCAO mice and cultured neurons, consistent with gene set enrichment analysis from a bioinformatics perspective angle. Our data suggest that Ramelteon is a potential neuroprotective drug candidate, and MT1 is the neuroprotective target for ischemic stroke, which provides new insights into stroke therapy. MT1-KO mice and cultured neurons may provide animal and cellular models of accelerated ischemic damage and neuronal cell death.

The protective effects of melatonin in high glucose environment by alleviating autophagy and apoptosis on primary cortical neurons

Cognitive dysfunction has been regarded as a complication of diabetes. Melatonin (MLT) shows a neuroprotective effect on various neurological diseases. However, its protective effect on cortical neurons in high glucose environment has not been reported. Our present study aims to observe the protective effect of melatonin on rat cortical neurons and its relationship with autophagy in high glucose environment. The rat primary cortical neurons injury model was induced by high glucose. The CCK-8, flow cytometry, Western blot and immunofluorescence methods were used to examine the cell viability, apoptosis rate and proteins expression. Our results showed that there were no differences in cell viability, apoptosis rate, and protein expression among the control, MLT and mannitol group. The cell viability of the glucose group was significantly lower than that of the control group, and the apoptosis rate of the glucose group was significantly higher than that of the control group. Compared with the glucose group, the glucose + melatonin group showed a significant increase in cell viability and a notable decrease in apoptosis rate. Melatonin concentration of 0.1-1 mmol/L can significantly alleviate the injury of cortical neurons caused by high glucose. Compared with the control group, the glucose group showed a significant reduction of B-cell lymphoma 2 (Bcl-2) protein expression, while remarkable elevations of Bcl2-associated X protein (Bax), cleaved Caspase-3, coiled-coil, myosin-like Bcl2-interacting protein (Beclin-1) and microtubule-associated protein 1 light chain-3B type II (LC3B-II) levels. The neurons pre-administered with melatonin obtained significantly reversed these changes induced by high glucose. The phosphorylation levels of protein kinase B (Akt), mechanistic target of rapamycin kinase (mTOR) and Unc-51 like autophagy activating kinase 1(ULK1) were decreased in the glucose group compared with the control group, whereas significant increase were observed in the glucose + MLT group, compared with the glucose group. These data indicated that melatonin has a neuroprotective effect on cortical neurons under high glucose environment, which may work by activating Akt/mTOR/ULK1 pathway and may be deeply associated with the downregulation of autophagy.

Effects of Melatonin Alone or Associated with Acyclovir on the Suppressive Treatment of Recurrent Genital Herpes: A Prospective, Randomized, and Double-Blind Study

Suppressive therapy of recurrent genital herpes is a challenge, and melatonin may be an alternative. Objective: To evaluate the action of melatonin, acyclovir, or the association of melatonin with acyclovir as a suppressive treatment in women with recurrent genital herpes. Design: The study was prospective, double-blind, and randomized, including 56 patients as follows: (a) The melatonin group received 180 placebo capsules in the ‘day’ container and 180 melatonin 3 mg capsules in the ‘night’ container (n = 19); (b) The acyclovir group received 360 capsules of 400 mg acyclovir twice a day (one capsule during the day and another during the night) (n = 15); (c) the melatonin group received 180 placebo capsules in the ‘day’ container and 180 melatonin 3 mg capsules in the ‘night’ container (n = 22). The length of treatment was six months. The follow-up after treatment was six months. Patients were evaluated before, during, and after treatment through clinical visits, laboratory tests, and the application of four questionnaires (QSF-36, Beck, Epworth, VAS, and LANNS). Results: No statistically significant difference was observed for the depression and sleepiness questionnaires. However, in the Lanns scale for pain, all groups decreased the mean and median values in time (p = 0.001), without differentiation among the groups (p = 0.188). The recurrence rates of genital herpes within 60 days after treatment were 15.8%, 33.3%, and 36.4% in the melatonin, acyclovir, and association of melatonin with acyclovir groups, respectively. Conclusion: Our data suggest that melatonin may be an option for the suppressive treatment of recurrent genital herpes.

Caveolin-1 suppresses hippocampal neuron apoptosis via the regulation of HIF1α in hypoxia in naked mole-rats

Naked mole-rats (NMRs) (Heterocephalus glaber) are highly social and subterranean rodents with large communal colonies in burrows containing low oxygen levels. The inhibition of severe hypoxic conditions is of particular interest to this study. To understand the mechanisms that facilitate neuronal preservation during hypoxia, we investigated the proteins regulating hypoxia tolerance in NMR hippocampal neurons. Caveolin-1 (Cav-1), a transmembrane scaffolding protein, confers prosurvival signalling in the central nervous system. The present study aimed to investigate the role of Cav-1 in hypoxia-induced neuronal injury. Western blotting analysis and immunocytochemistry showed that Cav-1 expression was significantly upregulated in NMR hippocampal neurons under 8% O₂ conditions for 8 h. Cav-1 alleviates apoptotic neuronal death from hypoxia. Downregulation of Cav-1 by lentiviral vectors suggested damage to NMR hippocampal neurons under hypoxic conditions in vitro and in vivo. Overexpression of Cav-1 by LV-Cav-1 enhanced hypoxic tolerance of NMR hippocampal neurons in vitro and in vivo. Mechanistically, the levels of hypoxia inducible factor-1α (HIF-1α) are also increased under hypoxic conditions. After inhibiting the binding of HIF-1α to hypoxia response elements in the DNA by echinomycin, Cav-1 levels were downregulated significantly. Furthermore, chromatin immunoprecipitation assays showed the direct role of HIF1α in regulating the expression levels of Cav-1 in NMR hippocampal neurons under hypoxic conditions. These findings suggest that Cav-1 plays a critical role in modulating the apoptosis of NMR hippocampal neurons and warrant further studies targeting Cav-1 to treat hypoxia-associated brain diseases.

Inhibiting Hv1 channel in peripheral sensory neurons attenuates chronic inflammatory pain and opioid side effects

Both opioids and nonsteroidal anti-inflammatory drugs (NSAIDS) produce deleterious side effects and fail to provide sustained relief in patients with chronic inflammatory pain. Peripheral neuroinflammation (PN) is critical for initiation and development of inflammatory pain. A better understanding of molecular mechanisms underlying PN would facilitate the discovery of new analgesic targets and the development of new therapeutics. Emerging evidence suggests that peripheral sensory neurons are not only responders to painful stimuli, but are also actively engaged in inflammation and immunity, whereas the intrinsic regulatory mechanism is poorly understood. Here we report the expression of proton-selective ion channel Hv1 in peripheral sensory neurons in rodents and humans, which was previously shown as selectively expressed in microglia in mammalian central nervous system. Neuronal Hv1 was up-regulated by PN or depolarizing stimulation, which in turn aggravates inflammation and nociception. Inhibiting neuronal Hv1 genetically or by a newly discovered selective inhibitor YHV98-4 reduced intracellular alkalization and ROS production in inflammatory pain, mitigated the imbalance in downstream SHP-1-pAKT signaling, and also diminished pro-inflammatory chemokine release to alleviate nociception and morphine-induced hyperalgesia and tolerance. Thus, our data reveal neuronal Hv1 as a novel target in analgesia strategy and managing opioids-related side effects.

CaMKIIγ regulates the viability and self-renewal of acute myeloid leukaemia stem-like cells by the Alox5/NF-κB pathway

Acute myeloid leukaemia (AML) is a frequently fatal malignant disease of haematopoietic stem and progenitor cells. The molecular and phenotypic characteristics of AML are highly heterogeneous. Our previous study concluded that CaMKIIγ was the trigger of chronic myeloid leukaemia progression from the chronic phase to blast crisis, but how CaMKIIγ influences AML stem-like cells remains elusive. In this study, we found that CaMKIIγ was overexpressed in AML patients and AML cell lines, as measured by qRT-PCR and Western blot assays. Moreover, CaMKIIγ decreased when the disease was in remission. Using an shRNA lentivirus expression system, we established CaMKIIγ stable-knockdown AML cell lines and found that knockdown of CaMKIIγ inhibited the viability and self-renewal of AML stem-like cell lines. Additionally, the ratio of CD₃₄ ⁺ AML cell lines decreased, and CaMKIIγ knockdown induced the downregulation of Alox5 levels. We further detected downstream molecules of the Alox5/NF-κB pathway and found that c-myc and p-IκBα decreased while total IκBα remained normal. In conclusion, our study describes a new role for CaMKIIγ as a stem-like cell marker that is highly regulated by the Alox5/NF-κB pathway in AML stem-like cells. CaMKIIγ can participate in the viability and self-renewal of AML stem-like cells by regulating the Alox5/NF-κB pathway.

The role of melatonin and its analogues in epilepsy

Extensive research has gone into proposing a promising link between melatonin administration and attenuation of epileptic activity, the majority of which suggest its propensity as an antiseizure with antioxidant and neuroprotective properties. In the past few years, a number of studies highlighting the association of the melatonergic ligands with epilepsy have also emerged. In this context, our review is based on discussing the recent studies and various mechanisms of action that the said category of drugs exhibit in the context of being therapeutically viable antiseizure drugs. Our search revealed several articles on the four major drugs i.e. melatonin, agomelatine, ramelteon and piromelatine along with other melatonergic agonists like tasimelteon and TIK-301. Our review is suggestive of antiseizure effects of both melatonin and its analogues; however, extensive research work is still required to study their implications in the treatment of persons with epilepsy. Further evaluation of melatonergic signaling pathways and mechanisms may prove to be helpful in the near future and might prove to be a significant advance in the field of epileptology.

Neuroprotection from Excitotoxic Injury by Local Administration of Lipid Emulsion into the Brain of Rats

Lipid emulsion was recently shown to attenuate cell death caused by excitotoxic conditions in the heart. There are key similarities between neurons and cardiomyocytes, such as excitability and conductibility, which yield vulnerability to excitotoxic conditions. However, systematic investigations on the protective effects of lipid emulsion in the central nervous system are still lacking. This study aimed to determine the neuroprotective effects of lipid emulsion in an in vivo rat model of kainic acid-induced excitotoxicity through intrahippocampal microinjections. Kainic acid and/or lipid emulsion-injected rats were subjected to the passive avoidance test and elevated plus maze for behavioral assessment. Rats were sacrificed at 24 h and 72 h after kainic acid injections for molecular study, including immunoblotting and qPCR. Brains were also cryosectioned for morphological analysis through cresyl violet staining and Fluorojade-C staining. Anxiety and memory functions were significantly preserved in 1% lipid emulsion-treated rats. Lipid emulsion was dose-dependent on the protein expression of β-catenin and the phosphorylation of GSK3-β and Akt. Wnt1 mRNA expression was elevated in lipid emulsion-treated rats compared to the vehicle. Neurodegeneration was significantly reduced mainly in the CA1 region with increased cell survival. Our results suggest that lipid emulsion has neuroprotective effects against excitotoxic conditions in the brain and may provide new insight into its potential therapeutic utility.

The Timing of Melatonin Administration Is Crucial for Its Antidepressant-Like Effect in Mice

Melatonin is synthesized by the pineal gland with a circadian rhythm in synchrony with the environmental light/dark cycle. A gradual increase in circulating levels of melatonin occur after lights off, reaching its maximum around the middle of the dark phase. Agonists of melatonin receptors have proved effectiveness as antidepressants in clinical trials. However, there is contradictory evidence about the potential antidepressant effect of melatonin itself. Herein we studied melatonin administration in mice at two zeitgeber times (ZT; ZT = 0 lights on; 12:12 L/D), one hour before the beginning (ZT11) and at the middle (ZT18) of the dark phase after either a single or a three-dose protocol. Behavioral despair was assessed through a forced-swimming test (FST) or a tail suspension test (TST), at ZT18.5. A single dose of 4 mg/kg melatonin at ZT11 was effective to reduce the immobility time in both tests. However, acute administration of melatonin at ZT18 was not effective in mice subjected to FST, and a higher dose (16 mg/kg) was required to reduce immobility time in the TST. A three-dose administration protocol of 16 mg/kg melatonin (ZT18, ZT11, and ZT18) significantly reduced immobility time in FST. Data indicate that the timely administration of melatonin could improve its antidepressant-like effect.

ALOX5 exhibits anti-tumor and drug-sensitizing effects in MLL-rearranged leukemia

MLL-rearranged acute myeloid leukemia (AML) remains a fatal disease with a high rate of relapse and therapeutic failure due to chemotherapy resistance. In analysis of our Affymetrix microarray profiling and chromatin immunoprecipitation (ChIP) assays, we found that ALOX5 is especially down-regulated in MLL-rearranged AML, via transcription repression mediated by Polycomb repressive complex 2 (PRC2). Colony forming/replating and bone marrow transplantation (BMT) assays showed that Alox5 exhibited a moderate anti-tumor effect both in vitro and in vivo. Strikingly, leukemic cells with Alox5 overexpression showed a significantly higher sensitivity to the standard chemotherapeutic agents, i.e., doxorubicin (DOX) and cytarabine (Ara-C). The drug-sensitizing role of Alox5 was further confirmed in human and murine MLL-rearranged AML cell models in vitro, as well as in the in vivo MLL-rearranged AML BMT model coupled with treatment of “5 + 3” (i.e. DOX plus Ara-C) regimen. Stat and K-Ras signaling pathways were negatively correlated with Alox5 overexpression in MLL-AF9-leukemic blast cells; inhibition of the above signaling pathways mimicked the drug-sensitizing effect of ALOX5 in AML cells. Collectively, our work shows that ALOX5 plays a moderate anti-tumor role and functions as a drug sensitizer, with a therapeutic potential, in MLL-rearranged AML.

Melatonin: an ancient molecule that makes oxygen metabolically tolerable

Melatonin is remarkably functionally diverse with actions as a free radical scavenger and antioxidant, circadian rhythm regulator, anti-inflammatory and immunoregulating molecule, and as an oncostatic agent. We hypothesize that the initial and primary function of melatonin in photosynthetic cyanobacteria, which appeared on Earth 3.5-3.2 billion years ago, was as an antioxidant. The evolution of melatonin as an antioxidant by this organism was necessary as photosynthesis is associated with the generation of toxic-free radicals. The other secondary functions of melatonin came about much later in evolution. We also surmise that mitochondria and chloroplasts may be primary sites of melatonin synthesis in all eukaryotic cells that possess these organelles. This prediction is made on the basis that mitochondria and chloroplasts of eukaryotes developed from purple nonsulfur bacteria (which also produce melatonin) and cyanobacteria when they were engulfed by early eukaryotes. Thus, we speculate that the melatonin-synthesizing actions of the engulfed bacteria were retained when these organelles became mitochondria and chloroplasts, respectively. That mitochondria are likely sites of melatonin formation is supported by the observation that this organelle contains high levels of melatonin that are not impacted by blood melatonin concentrations. Melatonin has a remarkable array of means by which it thwarts oxidative damage. It, as well as its metabolites, is differentially effective in scavenging a variety of reactive oxygen and reactive nitrogen species. Moreover, melatonin and its metabolites modulate a large number of antioxidative and pro-oxidative enzymes, leading to a reduction in oxidative damage. The actions of melatonin on radical metabolizing/producing enzymes may be mediated by the Keap1-Nrf2-ARE pathway. Beyond its direct free radical scavenging and indirect antioxidant effects, melatonin has a variety of physiological and metabolic advantages that may enhance its ability to limit oxidative stress.

Organotypic Hippocampal Slices as Models for Stroke and Traumatic Brain Injury

Organotypic hippocampal slice cultures (OHSCs) have been used as a powerful ex vivo model for decades. They have been used successfully in studies of neuronal death, microglial activation, mossy fiber regeneration, neurogenesis, and drug screening. As a pre-animal experimental phase for physiologic and pathologic brain research, OHSCs offer outcomes that are relatively closer to those of whole-animal studies than outcomes obtained from cell culture in vitro. At the same time, mechanisms can be studied more precisely in OHSCs than they can be in vivo. Here, we summarize stroke and traumatic brain injury research that has been carried out in OHSCs and review classic experimental applications of OHSCs and its limitations.

Endoplasmic Reticulum Stress Plays a Key Role in Rotenone-Induced Apoptotic Death of Neurons

Rotenone, a pesticide, causes neurotoxicity via the mitochondrial complex-I inhibition. The present study was conducted to evaluate the role of endoplasmic reticulum (ER) stress in rotenone-induced neuronal death. Cell viability, cytotoxicity, reactive oxygen species (ROS) generation, nitrite level, mitochondrial membrane potential (MMP), and DNA damage were assessed in rotenone-treated neuro-2A cells. Protein levels of ER stress markers glucose regulated protein 78 (GRP78), growth arrest- and DNA damage-inducible gene 153 (GADD153), and phosphorylation of eukaryotic translation initiation factor 2 subunit α (eIF2-α) were estimated to assess the ER stress. To confirm the apoptotic death of neurons, mRNA levels of caspase-9, caspase-12 and caspase-3 were estimated. Further, to confirm the involvement of ER stress, neuro-2A cells were pretreated with ER stress inhibitor salubrinal. Co-treatment of antioxidant melatonin was also given to assess the role of oxidative stress in rotenone-induced apoptosis. Rotenone (0.1, 0.5, and 1 μM) treatment to neurons caused significantly decreased cell viability, increased cytotoxicity, increased ROS generation, increased expression of GRP78 and GADD, DNA damage and activation of caspase-12 and caspase-3 which were significantly attenuated by pretreatment of salubrinal (25 μM). Rotenone-induced dephosphorylation of eIF2α was also inhibited with salubrinal treatment. However, pretreatment of salubrinal did not affect the rotenone-induced increased nitrite levels, decreased MMP and caspase-9 activation. Co-treatment of antioxidant melatonin (1 mM) did not offer attenuation against rotenone-induced increased expression of caspase-9, caspase-12 and caspase-3. In conclusion, results indicated that ER stress plays a key role in rotenone-induced neuronal death, rather than oxidative stress. Graphical Abstract Pictorial presentation showed the involvement of endoplasmic reticulum (ER) stress, increased reactive oxygen species (ROS), nitrite level, decreased mitochondrial membrane potential (MMP), caspase activation and DNA damage in neuronal cells after rotenone treatment. ER stress inhibitor-salubrinal showed significant attenuation against most of the rotenone-induced adverse effects reflecting its key involvement in rotenone-induced neuronal death.

Mechanism of the beneficial effect of melatonin in experimental Parkinson's disease

This study aimed to elucidate locomotor activity changes in 6-hydroxydopamine (6-OHDA) induced Parkinson's disease (PD) and investigate the possible beneficial effects of melatonin on altered levels of locomotor activity, cyclooxygenase (COX), prostaglandin E2 (PGE2), nuclear factor kappa-B (NF-κB), nitrate/nitrite and apoptosis. Male Wistar rats were divided into five groups: vehicle (V), melatonin-treated (M), 6-OHDA-injected (6-OHDA), 6-OHDA-injected + melatonin-treated (6-OHDA-Mel) and melatonin treated + 6-OHDA-injected (Mel-6-OHDA). Melatonin was administered intraperitoneally at a dose of 10 mg/kg/day for 30 days in M and Mel-6-OHDA groups, for 7 days in 6-OHDA-Mel group. Experimental PD was created stereotactically via unilateral infusion of 6-OHDA into the medial forebrain bundle (MFB). The 6-OHDA-Mel group started receiving melatonin when experimental PD was created and treatment was continued for 7 days (post-treatment). In the Mel-6-OHDA group, experimental PD was created on the 23rd day of melatonin treatment and continued for the remaining 7 days (pre- and post-treatment). Locomotor activity performance decreased in 6-OHDA group compared with vehicle; however melatonin treatment did not improve this impairment. Nuclear factor kappa Bp65 and Bcl-2 levels were significantly decreased while COX, PGE2 and caspase-3 activity were significantly increased in 6-OHDA group. Melatonin treatment significantly decreased COX, PGE2 and caspase-3 activity, increased Bcl-2 and had no effect on NF-κB levels in experimental PD. 6-Hydroxydopamine injection caused an obvious reduction in TH positive dopaminergic neuron viability as determined by immunohistochemistry. Melatonin supplementation decreased dopaminergic neuron death in 6-OHDA-Mel and Mel-6-OHDA groups compared with 6-OHDA group. Melatonin also protected against 6-OHDA-induced apoptosis, as identified by increment in Bcl-2 levels in dopaminergic neurons. The protective effect of melatonin was more prominent for most parameter following 30 days treatment (pre- and post-) than 7 days post-treatment. In summary, melatonin treatment decreased dopaminergic neuron death in experimental PD model by increasing Bcl-2 protein level and decreasing caspase-3 activity.