Melatonin Ameliorates Cerebral Vasospasm After Experimental Subarachnoidal Haemorrhage Correcting Imbalance of Nitric Oxide Levels in Rats

Glucose-6-phosphate dehydrogenase and 8-iso-prostaglandin F2α as potential predictors of delayed cerebral ischemia after aneurysmal subarachnoid hemorrhage

OBJECTIVE

Delayed cerebral ischemia (DCI) is a serious complication of aneurysmal subarachnoid hemorrhage (aSAH), which is responsible for significant death and disability. The dynamic balance between the production and elimination of reactive oxygen species (ROS) in patients with DCI is suspected be shifted to favor ROS formation. The authors assessed the relationship between F2-isoprostanes (F2-IsoPs), oxidative stress biomarkers, and glucose-6-phosphate dehydrogenase (G6PD), which are responsible for nicotinamide adenine dinucleotide phosphate (NADPH) production for glutathione system function, with post-aSAH DCI.

METHODS

The authors assessed 45 aSAH patients for F2-IsoP and G6PD concentration using commercial ELISA on days 2, 4, and 6 after aSAH. The authors examined the correlation between plasma F2-IsoP and G6PD concentrations and clinical factors with DCI occurrence and aSAH outcome.

RESULTS

Expectedly, the most important clinical predictors of DCI were Hunt and Hess grade and modified Fisher (mFisher) grade. Plasma F2-IsoP and G6PD concentrations were greater in aSAH patients than the control group (p < 0.01). F2-IsoP concentrations were greater and G6PD concentrations were lower in patients with DCI than those without (p < 0.01). Plasma F2-IsoP and G6PD concentrations on day 2 were correlated with DCI occurrence (p < 0.01). Plasma F2-IsoP concentrations on days 2 and 6 were correlated with outcome at 1 and 12 months (p < 0.01).

CONCLUSIONS

Decreased G6PD indirectly informs the reduced antioxidant response, especially for the glutathione system. G6PD concentration was lower in patients with DCI than those without, which may explain the increased F2-IsoP concentrations. mFisher grade, plasma F2-IsoP concentration, and G6PD concentration on day 2 after aSAH, in combination, may serve as predictors of DCI. Further research is necessary to investigate the therapeutic utility of F2-IsoPs and antioxidants in clinical practice.

Melatonin as a Potential Neuroprotectant: Mechanisms in Subarachnoid Hemorrhage-Induced Early Brain Injury

Subarachnoid hemorrhage (SAH) is a common cerebrovascular disease with high mortality and disability rates. Despite progressive advances in drugs and surgical techniques, neurological dysfunction in surviving SAH patients have not improved significantly. Traditionally, vasospasm has been considered the main cause of death and disability following SAH, but anti-vasospasm therapy has not benefited clinical prognosis. Many studies have proposed that early brain injury (EBI) may be the primary factor influencing the prognosis of SAH. Melatonin is an indole hormone and is the main hormone secreted by the pineal gland, with low daytime secretion levels and high nighttime secretion levels. Melatonin produces a wide range of biological effects through the neuroimmune endocrine network, and participates in various physiological activities in the central nervous system, reproductive system, immune system, and digestive system. Numerous studies have reported that melatonin has extensive physiological and pharmacological effects such as anti-oxidative stress, anti-inflammation, maintaining circadian rhythm, and regulating cellular and humoral immunity. In recent years, more and more studies have been conducted to explore the molecular mechanism underlying melatonin-induced neuroprotection. The studies suggest beneficial effects in the recovery of intracerebral hemorrhage, cerebral ischemia-reperfusion injury, spinal cord injury, Alzheimer’s disease, Parkinson’s disease and meningitis through anti-inflammatory, antioxidant and anti-apoptotic mechanisms. This review summarizes the recent studies on the application and mechanism of melatonin in SAH.

Melatonin and risk of mortality in subjects with aneurysmal subarachnoid hemorrhage

BACKGROUND

Delayed cerebral ischemia (DCI) is a cause of morbidity associated with aneurysmal subarachnoid hemorrhage (aSAH). Neuroinflammation contributes to the development of DCI. Melatonin is a sleep-promoting hormone known to have cerebral anti-inflammatory properties. We hypothesized that synthetic melatonin (or the selective melatonin receptor agonist ramelteon) incidentally prescribed to improve sleep may lower the incidence of DCI among hospitalized aSAH patients.

METHODS

Subjects with a Hunt and Hess Grade I-III were identified from a data registry involving all aSAH patients admitted to our hospital between January 2015 and September 1, 2018. A cohort of patients who received either melatonin or ramelteon during their hospitalization was compared to a matched cohort that did not receive these drugs. The primary endpoint was incidence of DCI. Secondary outcomes included modified Rankin score (mRS) at discharge, discharge destination, and mortality at 6 weeks from discharge. The two groups were compared using univariate analysis. P < 0.05 was considered significant.

RESULTS

There was no significant difference in the incidence of DCI (15.8% vs. 16.9%, p = 1), discharge mRS (mRS 0-3: 51.3% vs. 45.1%, p = 0.59), discharge disposition (Home: 43.6% vs. 44.4, p = 0.47), or mortality (0% vs. 9.2%; p = 0.074) between the melatonin/ramelteon and non-melatonin groups.

CONCLUSION

The use melatonin had no effect on DCI but may improve mortality in aSAH subjects. Prospective studies using a larger cohort are warranted to validate these findings.

The relationship between staying up late and risk of intracranial aneurysm rupture: A single-center study

OBJECTIVE

To evaluate the impact of staying up late (SUL) on the risk of intracranial aneurysm (IA) rupture.

METHODS

This case-control study included 452 patients diagnosed with IA. They were divided into ruptured and unruptured groups. Staying up late was categorized in three levels (11-12 o'clock, 12-1 o'clock, after 1 o'clock) according to the time of falling asleep. To explore the relationship between staying up late and risk of IA rupture, univariate and multivariate logistic regression analyses were performed.

RESULTS

Multivariate analysis found a significant difference in the percentage of patients falling asleep at 12-1 o'clock (OR, 2.25; 95% CI, 1.10-4.59) or after 1 o'clock (OR, 4.68; 95% CI, 1.74-12.55) between the ruptured and unruptured groups. The following risk factors differed significantly between the two groups: hypertension (OR, 2.05; 95% CI, 1.33-3.17), current smoking (OR, 1.72; 95% CI, 1.09-2.71), irregular IA (OR, 1.85; 95% CI, 1.15-3.00), IA size ≥8mm (OR, 1.92; 95% CI, 1.22-3.02), MCA location (OR, 2.45; 95% CI, 1.19-5.02), and aspect ratio (OR, 1.33; 95% CI, 1.02-1.73).

CONCLUSION

Patients who fell asleep later than 12 midnight on average showed higher risk of IA rupture. The reasons for this are not very clear. A review of the literature suggests that this association may be related to a series of physiological, pathophysiological, endocrine and metabolic changes.

Pharmacological agents under investigation in the treatment of coronavirus disease 2019 and the importance of melatonin

Coronavirus disease 2019 (COVID-19) is a life-threatening infectious respiratory disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). COVID-19 pandemic causing morbidities and even deaths worldwide revealed that there is urgent need to find pharmacological agents or vaccines. Although there are a lot of agents under investigation, there is no approved agent for the prevention or treatment of the COVID-19 yet. Treatment of patients remains mainly supportive as well as compassionate use of the agents under investigation. It is well established that excessive inflammatory and immune response and oxidative injury play a critical role in the pathogenesis of COVID-19. In this review, we aimed to update knowledge about pathogenesis, clinical features, and pharmacological treatment of COVID-19 and review the potential beneficial effects of ancient antioxidant, anti-inflammatory, and immunomodulatory molecule melatonin for prevention and treatment of COVID-19.

Melatonin Prevents Mice Cortical Astrocytes From Hemin-Induced Toxicity Through Activating PKCα/Nrf2/HO-1 Signaling in vitro

Secondary injuries mediated by oxidative stress lead to deterioration of neurological functions after intracerebral hemorrhage (ICH). Cortical astrocytes are among the most important cells in the central nervous system (CNS), and play key roles in maintaining redox homeostasis by providing oxidative stress defense. Hemin is a product of hemoglobin degradation, which has strong toxicity and can induce reactive oxygen species (ROS). Melatonin (Mel) and its metabolites are well tolerated without toxicity, prevent tissue damage as well as effectively assist in scavenging free radicals. We evaluated the hemin neurotoxicity to astrocytes and the resistance of Mel-treated astrocytes to hemin neurotoxicity. And we found Mel induced PKCα phosphorylation (p-PKC), nuclear translocation of Nrf2 in astrocytes, and upregulation of HO-1, which contributed to the reduction of ROS accumulation and cell apoptosis. Nrf2 and HO1 protein expression upregulated by Mel were decreased after administration of PKC inhibitor, Ro 31-8220 (Ro 31). Luzindole (Luz), a melatonin receptor inhibitor, suppressed p-PKCα, HO-1, and Nrf2 expression upregulated by Mel and increased cell apoptosis rate. The upregulation of HO-1 induced by Mel was depressed by knocking down Nrf2 expression by siRNA, which also decreased the resistance of astrocytes to toxicity of hemin. Mel activates astrocytes through PKCα/Nrf2/HO-1 signaling pathway to acquire resistance to toxicity of hemin and resist from oxidative stress and apoptosis. The positive effect of Mel on PKCα/Nrf2/HO-1 signaling pathway may become a new target for neuroprotection after intracerebral hemorrhage.

Antioxidant Melatonin: Potential Functions in Improving Cerebral Autoregulation After Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) is a subtype of stroke with high mortality and morbidity. Impaired cerebral autoregulation following SAH has been reported owing to effects on sympathetic control, endothelial function, myogenic response, and cerebral metabolism. Impaired cerebral autoregulation is associated with early brain injury, cerebral vasospasm/delayed cerebral ischemia, and SAH prognosis. However, few drugs have been reported to improve cerebral autoregulation after SAH. Melatonin is a powerful antioxidant that is effective (easily crosses the blood brain barrier) and safe (tolerated in large doses without toxicity). Theoretically, melatonin may impact the control mechanisms of cerebral autoregulation via antioxidative effects, protection of endothelial cell integrity, suppression of sympathetic nerve activity, increase in nitric oxide bioavailability, mediation of the myogenic response, and amelioration of hypoxemia. Furthermore, melatonin may have a comprehensive effect on cerebral autoregulation. This review discusses the potential effects of melatonin on cerebral autoregulation following SAH, in terms of the association between pharmacological activities and the mechanisms of cerebral autoregulation.

Effectiveness of arginase inhibitors against experimentally induced stroke

Stroke is a lethal disease, but it disables more than it kills. Stroke is the second leading cause of death and the most frequent cause of permanent disability in adults worldwide, with 90% of survivors having residual deficits. The pathophysiology of stroke is complex and involves a strong inflammatory response associated with oxidative stress and activation of several proteolytic enzymes. The current study was designed to investigate the effect of arginase inhibitors (L-citruline and L-ornithine) against ischemic stroke induced in rats by middle cerebral artery occlusion (MCAO). MCAO resulted in alteration in rat behavior, brain infarct, and edema associated with disruption of the blood-brain barrier (BBB). This was mediated through overexpression of arginase I and II, inducible NOS (iNOS), malondialdehyde (MDA), advanced glycation end products (AGEs), TNF-α, and IL-1β and downregulation of endothelial nitric oxide synthase (eNOS). Treatment with L-citruline and L-ornithine and the standard neuroprotective drug cerebrolysin ameliorated all the deleterious effects of stroke. These results indicate the possible use of arginase inhibitors in the treatment of stroke after suitable clinical trials are done.

Ischemic brain injury: New insights on the protective role of melatonin

Stroke represents one of the most common causes of brain's vulnerability for many millions of people worldwide. The plethora of physiopathological events associated with brain ischemia are regulate through multiple signaling pathways leading to the activation of oxidative stress process, Ca²⁺ dyshomeostasis, mitochondrial dysfunction, proinflammatory mediators, excitotoxicity and/or programmed neuronal cell death. Understanding this cascade of molecular events is mandatory in order to develop new therapeutic strategies for stroke. In this review article, we have highlighted the pleiotropic effects of melatonin to counteract the multiple processes of the ischemic cascade. Additionally, experimental evidence supports its actions to ameliorate ischemic long-term behavioural and neuronal deficits, preserving the functional integrity of the blood-brain barrier, inducing neurogenesis and cell proliferation through receptor-dependent mechanism, as well as improving synaptic transmission. Consequently, the synthesis of melatonin derivatives designed as new multitarget-directed products has focused a great interest in this area. This latter has been reinforced by the low cost of melatonin and its reduced toxicity. Furthermore, its spectrum of usages seems to be wide and with the potential for improving human health. Nevertheless, the molecular and cellular mechanisms underlying melatonin´s actions need to be further exploration and accordingly, new clinical studies should be conducted in human patients with ischemic brain pathologies.

Effects of melatonin in the treatment of asthenia in aneurysmal subarachnoid hemorrhage

BACKGROUND AND OBJECTIVES

Survivors of aneurysmal subarachnoid hemorrhage (aSAH) commonly experience sleep disorders resulting in asthenia. The objective of this prospective study was to determine, in a cohort of patients with treated ruptured intracranial aneurysm (IA), the proportion of asthenia at 2months, in a cohort of patients treated with melatonin and in a control cohort.

PATIENTS AND METHODS

Twenty consecutive patients admitted for the treatment of ruptured IA and able to answer a standardized questionnaire were included in the study. After evaluation for fatigue at discharge, we divided our population into 2 cohorts of 10 patients: the first cohort was treated with melatonin for a period of 2months; the second cohort had no specific treatment for fatigue. The primary endpoint was the proportion of asthenia at 2months in both groups. Confounding factors, such as depression, autonomy and apathy were evaluated at the same time.

RESULTS

At discharge, there was no significant difference observed between both groups in terms of mean age and initial clinical status (WFNS, Rankin Scale and Fatigue Severity Scale). At 2months, the mean FSS score in the control group was of 4.7±1.0 versus 3.8±0.9 in the melatonin group (P=0.03). The mean MADRS score in the control group was of 1.1±1.45 versus 2.7±2.5 in the melatonin group (P=0.10). The mean LARS score in the control group was of -32.5±1.7 versus -31.7±1.9 in the melatonin group (P=0.24).

DISCUSSION

In a prospective evaluation of post-aSAH fatigue, we suggest that melatonin could decrease fatigue. There is no significant impact on depression and apathy. Further studies would be necessary to improve our comprehension of fatigue physiopathology in a context of aSAH.

Melatonin protects against oxygen and glucose deprivation by decreasing extracellular glutamate and Nox-derived ROS in rat hippocampal slices

Therapeutic interventions on pathological processes involved in the ischemic cascade, such as oxidative stress, neuroinflammation, excitotoxicity and/or apoptosis, are of urgent need for stroke treatment. Melatonin regulates a large number of physiological actions and its beneficial properties have been reported. The aim of this study was to investigate whether melatonin mediates neuroprotection in rat hippocampal slices subjected to oxygen-glucose-deprivation (OGD) and glutamate excitotoxicity. Thus, we describe here that melatonin significantly reduced the amount of lactate dehydrogenase released in the OGD-treated slices, reverted neuronal injury caused by OGD-reoxygenation in CA1 and CA3 hippocampal regions, restored the reduction of GSH content of the hippocampal slices induced by OGD, and diminished the oxidative stress produced in the reoxygenation period. Furthermore, melatonin afforded maximum protection against glutamate-induced toxicity and reversed the glutamate released almost basal levels, at 10 and 30μM concentration, respectively. Consequently, we propose that melatonin might strongly and positively influence the outcome of brain ischemia/reperfusion.

Expression signatures of long non-coding RNAs in early brain injury following experimental subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) is an important cause of mortality in stroke patients. Long non-coding RNAs (LncRNAs) have important functions in brain disease, however their expression profiles in SAH remain to be elucidated. The present study aimed to investigate the expression signatures of LncRNAs and mRNAs in early brain injury (EBI) following SAH in a rat model. Male Wistar rats were randomly divided into an SAH group and a sham operation group. The expression signatures of the LncRNAs and mRNAs in the temporal lobe cortex were investigated using a rat LncRNAs array following experimental SAH. The results revealed that there were 144 downregulated and 64 upregulated LncRNAs and 181 downregulated and 221 upregulated mRNAs following SAH. Additionally, two upregulated (BC092207, MRuc008hvl) and three downregulated (XR_006756, MRAK038897, MRAK017168) LncRNAs were confirmed using reverse transcription quantitative polymerase chain reaction. The differentially expressed mRNAs were further analyzed using the Gene Ontology and the Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. The pathway analysis results provided by the KEGG database indicated that eight pathways associated with inflammation were involved in EBI following SAH. In conclusion, these results demonstrated that the expression profiles of the LncRNAs and mRNAs were significantly different between the SAH-induced EBI group and the sham operation group. These differently expressed LncRNAs may be important in EBI following SAH.

The comparative effects of recombinant human erythropoietin and darbepoetin-alpha on cerebral vasospasm following experimental subarachnoid hemorrhage in the rabbit

BACKGROUND

Darbepoetin alpha is a hypersialylated analogue of erythropoietin effective for activating erythropoietin-receptors. This study investigated the vasodilator and neuroprotective effects of darbepoetin alpha on an experimental subarachnoid hemorrhage model and compared it with erythropoietin.

METHODS

Forty adult male New Zealand white rabbits were randomly divided into four groups of ten rabbits each: group 1 (control), group 2 (subarachnoid hemorrhage), group 3 (erythropoietin), and group 4 (darbepoetin alpha). Recombinant human erythropoietin was administered at a dose of 1,000 U/kg intraperitoneally after the induction of subarachnoid hemorrhage and continued every 8 h up to 72 h. Darbepoetin alpha was administered at a single intraperitoneal dose of 30 μg/kg. Animals were killed 72 h after subarachnoid hemorrhage. Basilar artery cross-sectional areas, arterial wall thicknesses, hippocampal degeneration scores and biochemical analyses were measured in all groups.

RESULTS

Both erythropoietin and darbepoetin alpha treatments were found to attenuate cerebral vasospasm and provide neuroprotection after subarachnoid hemorrhage in rabbits. Darbepoetin alpha revealed better morphometric and histopathological results than erythropoietin among experimental subarachnoid hemorrhage-induced vasospasm.

CONCLUSIONS

Our findings, for the first time, showed that darbepoetin alpha can prevent vasospasm and provides neuroprotection following experimental subarachnoid hemorrhage. Moreover, darbepoetin alpha showed better results when compared with erythropoietin.

Estradiol reduces ferrous citrate complex-induced NOS2 up-regulation in cerebral endothelial cells by interfering the nuclear factor kappa B transactivation through an estrogen receptor β-mediated pathway

Hemorrhagic stroke caused leakage of red blood cells which converts to hemoglobin, heme, and iron accumulated at the lesions. High concentration of ferrous iron from subarachnoid hemorrhage (SAH) induced cerebral vasospasm. Using the two-hemorrhage SAH model in rats, we previously demonstrated that estradiol (E2) significantly attenuated the SAH-induced vasospasm by inhibiting the NOS2 expression. Adding ferrous citrate (FC) complexes to the primary cultured mouse cerebral endothelial cells (CEC) to mimic the SAH conditions, we also showed that FC up-regulates NOS2 through nuclear translocation of NFκB induced by free radicals generation. Here, we further studied the molecular mechanism underlying E2-mediated reduction of the FC-induced up-regulation of NOS2. Treatment with E2 (100 nM) reduced the FC (100 µM)-induced increases of free radical generation and the levels of NOS2 mRNA and protein in the CEC. Moreover, E2 also prevented the FC-induced increases of IκBα phosphorylation, NFκB nuclear translocation, NFκB binding onto the NOS2 promoter, and the NOS2 promoter luciferase activity. However, knock-down the estrogen receptor β (ERβ), but not ERα, abolished the E2-mediated prevention on the FC-induced increases of NOS2 mRNA and protein. The data from the present study suggest that E2 inhibited NOS2 gene expression by interfering with NFκB nuclear translocation and NFκB binding onto the NOS2 through an ERβ-mediated pathway. Our results provide the molecular basis for designing the applicable therapeutic or preventive strategies in the treatment SAH patients.

Ferrous citrate up-regulates the NOS2 through nuclear translocation of NFκB induced by free radicals generation in mouse cerebral endothelial cells

Previous studies indicate that the inducible nitric oxide synthase 2 (NOS2) of the brain vascular tissue in experimental subarachnoid hemorrhage (SAH) rats is a critical factor for inducing cerebral vasospasm. However, the underlying molecular mechanisms remain to be elucidated. Here, we applied ferrous citrate (FC) complexes to the primary cultured mouse cerebral endothelial cell (CEC) to mimic the SAH conditions and to address the issue how SAH-induced NOS2 up-regulation. Using immunocytochemical staining technique, we demonstrated that NOS2 was expressed in the cultured CEC. Treatment of the CEC with FC induced increases of the intracellular level of ROS, nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) nuclear translocation as well as NFκB binding onto the NOS promoter, and the levels of NOS2 mRNA and protein. These effects were abolished by pre-treatment of the cell with N-Acetyl-Cysteine (NAC), a reactive oxygen species (ROS) scavenger. In the present study, two previously predicted NFκB binding sites were confirmed in the NOS2 promoter within the range of −1529 bp to −1516 bp and −1224 bp to −1210 bp. Interestingly, both NFκB binding sites are involved in the FC-activated NOS2 transcriptional activity; the binding site located at −1529 bp to −1516 bp played a greater role than the other binding site located at −1224 bp to −1210 bp in the mouse CEC. These findings highlight the molecular mechanism underlying FC-induced up-regulation of NOS2 in the mouse CEC.

Melatonin treatment following stroke induction modulates L-arginine metabolism

The efficacy of melatonin treatment in experimental stroke has been established. Some of the neuroprotective properties have been attributed to its anti-oxidant and anti-inflammatory effects. Nitric oxide synthases (NOS) and cyclooxygenases (COX) are considered to have a significant role in the inflammatory milieu occurring in acute stroke. While previous reports have shown that pretreatment with melatonin in a stroke model can modulate NOS isoforms, the effect of post-treatment with melatonin on l-arginine metabolism has not been investigated. This study initially examined the effect of melatonin (1 nm-1 mm) on l-arginine metabolism pathways in human fibrosarcoma fibroblasts (HT-1080) fibroblasts. Evidence of neuroprotection with melatonin was evaluated in rats subjected to middle cerebral artery occlusion (MCAO). Animals were treated with three daily doses of 5 mg/kg i.p., starting 1 hr after the onset of ischemia. Constitutive NOS activity but not expression was significantly increased by in vitro exposure (72 hr) to melatonin. In addition, melatonin treatment increased arginase activity by increasing arginase II expression. In vivo studies showed that melatonin treatment after MCAO significantly inhibited inducible NOS activity and attenuated expression of the inducible isoform, resulting in decreased total NOS activity and tissue nitrite levels. COX activity was significantly reduced with melatonin treatment. The neuroprotective anti-inflammatory effects of melatonin were consistent with the substantial reduction in infarct volume throughout the cortex and striatum and recovery of mitochondrial enzyme activities. The evidence presented here suggests that modulation of l-arginine metabolism by melatonin make it a valuable neuroprotective therapy for stroke.

Melatonin signaling and cell protection function

Besides its well-known regulatory role on circadian rhythm, the pineal gland hormone melatonin has other biological functions and a distinct metabolism in various cell types and peripheral tissues. In different tissues and organs, melatonin has been described to act as a paracrine and also as an intracrine and autocrine agent with overall homeostatic functions and pleiotropic effects that include cell protection and prosurvival factor. These latter effects, documented in a number of in vitro and in vivo studies, are sustained through both receptor-dependent and -independent mechanisms that control detoxification and stress response genes, thus conferring protection against a number of xenobiotics and endobiotics produced by acute and chronic noxious stimuli. Redox-sensitive components are included in the cell protection signaling of melatonin and in the resulting transcriptional response that involves the control of NF-κB, AP-1, and Nrf2. By these pathways, melatonin stimulates the expression of antioxidant and detoxification genes, acting in turn as a glutathione system enhancer. A further and converging mechanism of cell protection by this indoleamine described in different models seems to lie in the control of damage and signaling function of mitochondria that involves decreased production of reactive oxygen species and activation of the antiapoptotic and redox-sensitive element Bcl2. Recent evidence suggests that upstream components in this mitochondrial route include the calmodulin pathway with its central role in melatonin signaling and the survival-promoting component of MAPKs, ERK1/2. In this review article, we will discuss these and other molecular aspects of melatonin signaling relevant to cell protection and survival mechanisms.