Melatonin Pathway Research Articles

The flavonoid myricetin reduces nocturnal melatonin levels in the blood through the inhibition of serotonin N-acetyltransferase

Melatonin is secreted during the hours of darkness and is thought to influence the circadian and seasonal timing of a variety of physiological processes. AANAT, which is expressed in the pineal gland, retina, and various other tissues, catalyzes the conversion of serotonin to N-acetylserotonin and is the rate-limiting enzyme in the biosynthetic pathway of melatonin. The compounds that modulate the activity of AANAT can be used to treat patients with circadian rhythm disorders that are associated with specific circadian rhythm alterations, such as shift work disorder. In the present study, we screened modulators of AANAT activity from the water extracts of medicinal plants. Among the 267 tested medicinal plant extracts, Myricae Cortex (Myrica rubra), Perillae Herba (Perilla sikokiana), and Eriobotryae Folium (Eriobotrya japonica) showed potent inhibition of AANAT activity. Myricetin (5,7,3′,4′,5′-pentahydroxyflavonol), a main component of the Myricae Cortex, strongly inhibited the activity of AANAT and probably block the access to the substrate by docking to the catalytic residues that are important for AANAT activity. Myricetin significantly decreased the nocturnal serum melatonin levels in rats. In addition, the locomotor activity of rats treated with myricetin decreased during the nighttime and slightly increased throughout the day. These results suggest that myricetin could be used as a therapy to increase nighttime alertness by changing the circadian rhythm of serum melatonin and locomotor activity.

The Expression of Inflammatory Cytokines on the Aorta Endothelia Are Up-regulated in Pinealectomized Rats

This study was designed to investigate the effect of melatonin on the expression of aortic inflammatory cytokines and its underlying mechanisms in rats. Melatonin deficiency rats (Px, N = 16) were created by pinealectomy and were fed with normal diet for 16 weeks after the surgery, and compared with sham-operated rats (Con, N = 14). Serum lipid profile, glucose metabolism parameters, serum oxidative stress and inflammatory biomarkers were evaluated. The expression of inflammatory cytokines in the aorta endothelia was analyzed. To evaluate the signal transduction pathways of melatonin on the expression of cytokines, rat aortic endothelial cell lines (RAECs) were treated with melatonin, and their protein expressions of inflammatory cytokines and phosphorylation levels of relevant signal pathways were detected. At the 16th week after surgery in Px rats, their serum triglyceride, very low density lipoprotein cholesterol, free fatty acid and glucose levels were prominently elevated (all P < 0.05); serum oxidative stress biomarker malondialdehyde, serum inflammatory biomarkers oxidized low-density lipoprotein, tumor necrosis factor-α, interleukin-6 and C reactive protein were also significantly increased. Meanwhile, the expression of inflammatory cytokines: monocyte chemotactic protein-1 (MCP-1), vascular adhesion molecule 1 (VCAM-1) and matrix metalloproteinase-9 (MMP-9) of the aorta endothelia in Px rats were significantly up-regulated (all P < 0.05). In vitro, melatonin significantly decreased the expression of MCP-1, VCAM-1 and MMP-9 proteins, along with the suppression of phosphorylation levels of nuclear factor κB (NF-κB)/P65 and p38 mitogen-activated protein kinase (P38-MAPK) in RAECs. Melatonin deficiency elevates the serum inflammatory biomarkers and increases aortic inflammatory responses. Melatonin regulates these inflammatory responses by NF-κB and P38-MAPK involved pathways.

A novel enzyme‐dependent melatonin metabolite in humans

Exogenous melatonin is widely used in humans for multiple pharmacologic purposes. The metabolic pathways of melatonin reflect the fate and functions of melatonin in vivo. This study was designed to re-profile melatonin metabolism in humans using a metabolomic approach. In the urine of healthy subjects treated with 10 mg melatonin, sulfate- or glucuronide-conjugated metabolites of melatonin were detected, including 6-hydroxymelatonin sulfate, 6-hydroxymelatonin glucuronide, N-acetylserotonin glucuronide, N-acetylserotonin sulfate, and an unknown sulfated metabolite (X). The molecular weight of metabolite X was 14 Da smaller than 6-hydroxymelatonin sulfate, but 16 Da larger than N-acetylserotonin sulfate. Further studies suggest that metabolite X was produced via O-demethylation, 6-hydroxylation, and sulfation. The antioxidant products of melatonin, N(1)-acetyl-N(2)-formyl-5-methoxykynuramine and N(1)-acetyl-5-methoxy-kynuramine, were not detected in human urine. In summary, this study provided a global view of melatonin metabolism in humans and extended our knowledge of enzyme-dependent pathways of melatonin metabolism.

Effects of RFRP-3 on reproductive function and energy balance in mammals

The hypothalamo-pituitary-gonadal (HPG) axis integrates internal and external cues via a balance of stimulatory and inhibitory neurochemical systems to regulate reproductive function in mammals. However, RFRP-3 is a unique inhibitor of HPG axis at the hypothalamuic level in mammals to date. A large number of previous studies have confirmed that RFamide-related peptide (RFRP-3) suppresses gonadotropin-releasing hormone (GnRH) system and luteinizing hormone (LH) secretion, thereby affecting the reproduction. However, whether the inhibition of LH secretion by RFRP-3 occurs at the pituitary level or the hypothalamus level is not clear. It is interesting that RFRP-3 is also related to signal pathway of melatonin modulating mammal seasonal reproduction, but little is known about the effects of melatonin on the RFRP-3 neuron up to now. In addition, RFRP-3 also plays an important role in the regulation of energy balance and behavior. The regulatory mechanism of RFRP-3 in HPG axis and role of RFRP-3 in modulating mammalian energy balance, as well as behavior, are systematically elaborated and the remaining unsolved problems are also discussed in this paper.

Melatonin pathway genes are associated with progressive subtypes and disability status in multiple sclerosis among Finnish patients

In this study we investigated the relationship between melatonin pathway and multiple sclerosis (MS) in a high-risk Finnish population by studying the single nucleotide polymorphisms (SNPs) in the genes coding for critical enzymes and receptors involved in the melatonin pathway. A total of 590 subjects (193 MS patients and 397 healthy controls) were genotyped for seven SNPs in four genes including tryptophan hydroxylases (TPH)1 and 2, arylalkylamine N-acetyltransferase (AANAT) and melatonin receptor 1B (MTNR1B). An overrepresentation of T allele carriers of a functional polymorphism (G-703T, rs4570625) in the promoter region of TPH2 gene was observed in the progressive MS subtypes. The haplotype rs4570625-rs10506645TT of TPH2 gene was associated with the risk of severe disability in primary progressive MS (PPMS), while haplotype rs4570625-rs10506645TC appeared to be protective against disability in secondary progressive MS (SPMS). In the MTNR1B gene, the haplotype rs10830963-rs4753426GC was associated with the risk of SPMS, whereas another haplotype rs10830963-rs4753426GT showed an association with the risk of PPMS. These data showing the association of polymorphisms in the TPH2 and MTNR1B genes with the progressive subtypes of MS and disability suggest dysregulation in melatonin pathway. Melatonin pathway seems to be involved in disease progression, and therefore its potential effects in overcoming MS-related neurodegeneration may be worth evaluating in future clinical trials.

Biomechanical stress and estrogen impact on human osteoblasts

Biomechanical stress and estrogen impact on human osteoblasts

Melatonin pathway genes and breast cancer risk among Chinese women

Previous studies suggest that melatonin may act on cancer growth through a variety of mechanisms, most notably by direct anti-proliferative effects on breast cancer cells and via interactions with the estrogen pathway. Three genes are largely responsible for mediating the downstream effects of melatonin: melatonin receptors 1a and 1b (MTNR1a and MTNR1b), and arylalkylamine N-acetyltransferase (AANAT). It is hypothesized that genetic variation in these genes may lead to altered protein production or function. To address this question, we conducted a comprehensive evaluation of the association between common single nucleotide polymorphisms (SNPs) in the MTNR1a, MTNR1b, and AANAT genes and breast cancer risk among 2,073 cases and 2,083 controls, using a two-stage analysis of genome-wide association data among women of the Shanghai Breast Cancer Study. Results demonstrate two SNPs were consistently associated with breast cancer risk across both study stages. Compared with MTNR1b rs10765576 major allele carriers (GG or GA), a decreased risk of breast cancer was associated with the AA genotype (OR = 0.78, 95% CI = 0.62-0.97, P = 0.0281). Although no overall association was seen in the combined analysis, the effect of MTNR1a rs7665392 was found to vary by menopausal status (P-value for interaction = 0.001). Premenopausal women with the GG genotype were at increased risk for breast cancer compared with major allele carriers (TT or TG) (OR = 1.57, 95% CI = 1.07-2.31, P = 0.020), while postmenopausal women were at decreased risk (OR = 0.58, 95% 0.36-0.95, P = 0.030). No significant breast cancer associations were found for variants in the AANAT gene. These results suggest that common genetic variation in the MTNR1a and 1b genes may contribute to breast cancer susceptibility, and that associations may vary by menopausal status. Given that multiple variants in high linkage disequilibrium with MTNR1b rs76653292 have been associated with altered function or expression of insulin and glucose family members, further research may focus on clarifying this relationship.

Evidence for RGS4 Modulation of Melatonin and Thyrotrophin Signalling Pathways in the Pars Tuberalis

In mammals, the pineal hormone melatonin is secreted nocturnally and acts in the pars tuberalis (PT) of the anterior pituitary to control seasonal neuroendocrine function. Melatonin signals through the type 1 Gi-protein coupled melatonin receptor (MT1), inhibiting adenylate cyclase (AC) activity and thereby reducing intracellular concentrations of the second messenger, cAMP. Because melatonin action ceases by the end of the night, this allows a daily rise in cAMP levels, which plays a key part in the photoperiodic response mechanism in the PT. In addition, melatonin receptor desensitisation and sensitisation of AC by melatonin itself appear to fine-tune this process. Opposing the actions of melatonin, thyroid-stimulating hormone (TSH), produced by PT cells, signals through its cognate Gs-protein coupled receptor (TSH-R), leading to increased cAMP production. This effect may contribute to increased TSH production by the PT during spring and summer, and is of considerable interest because TSH plays a pivotal role in seasonal neuroendocrine function. Because cAMP stands at the crossroads between melatonin and TSH signalling pathways, any protein modulating cAMP production has the potential to impact on photoperiodic readout. In the present study, we show that the regulator of G-protein signalling RGS4 is a melatonin-responsive gene, whose expression in the PT increases some 2.5-fold after melatonin treatment. Correspondingly, RGS4 expression is acutely sensitive to changing day length. In sheep acclimated to short days (SP, 8 h light/day), RGS4 expression increases sharply following dark onset, peaking in the middle of the night before declining to basal levels by dawn. Extending the day length to 16 h (LP) by an acute 8-h delay in lights off causes a corresponding delay in the evening rise of RGS4 expression, and the return to basal levels is delayed some 4 h into the next morning. To test the hypothesis that RGS4 expression modulates interactions between melatonin- and TSH-dependent cAMP signalling pathways, we used transient transfections of MT1, TSH-R and RGS4 in COS7 cells along with a cAMP-response element luciferase reporter (CRE-luc). RGS4 attenuated MT1-mediated inhibition of TSH-stimulated CRE-luc activation. We propose that RGS4 contributes to photoperiodic sensitivity in the morning induction of cAMP-dependent gene expression in the PT.

Genetic variations of the melatonin pathway in patients with attention-deficit and hyperactivity disorders

Melatonin is a powerful antioxidant and a synchronizer of many physiological processes. Alteration in melatonin signaling has been reported in a broad range of diseases, but little is known about the genetic variability of this pathway in humans. Here, we sequenced all the genes of the melatonin pathway -AA-NAT, ASMT, MTNR1A, MTNR1B and GPR50 - in 321 individuals from Sweden including 101 patients with attention-deficit/hyperactivity disorder (ADHD) and 220 controls from the general population. We could find several damaging mutations in patients with ADHD, but no significant enrichment compared with the general population. Among these variations, we found a splice site mutation in ASMT (IVS5+2T>C) and one stop mutation in MTNR1A (Y170X) - detected exclusively in patients with ADHD - for which biochemical analyses indicated that they abolish the activity of ASMT and MTNR1A. These genetic and functional results represent the first comprehensive ascertainment of melatonin signaling deficiency in ADHD.

Mutation screening of ASMT, the last enzyme of the melatonin pathway, in a large sample of patients with Intellectual Disability

BackgroundIntellectual disability (ID) is frequently associated with sleep disorders. Treatment with melatonin demonstrated efficacy, suggesting that, at least in a subgroup of patients, the endogenous melatonin level may not be sufficient to adequately set the sleep-wake cycles. Mutations in ASMT gene, coding the last enzyme of the melatonin pathway have been reported as a risk factor for autism spectrum disorders (ASD), which are often comorbid with ID. Thus the aim of the study was to ascertain the genetic variability of ASMT in a large cohort of patients with ID and controls.MethodsHere, we sequenced all exons of ASMT in a sample of 361 patients with ID and 440 controls. We then measured the ASMT activity in B lymphoblastoid cell lines (BLCL) of patients with ID carrying an ASMT variant and compared it to controls.ResultsWe could identify eleven variations modifying the protein sequence of ASMT (ID only: N13H, N17K, V171M, E288D; controls only: E61Q, D210G, K219R, P243L, C273S, R291Q; ID and controls: L298F) and two deleterious splice site mutations (IVS5+2T>C and IVS7+1G>T) only observed in patients with ID. We then ascertained ASMT activity in B lymphoblastoid cell lines from patients carrying the mutations and showed significantly lower enzyme activity in patients carrying mutations compared to controls (p = 0.004).ConclusionsWe could identify patients with deleterious ASMT mutations as well as decreased ASMT activity. However, this study does not support ASMT as a causative gene for ID since we observed no significant enrichment in the frequency of ASMT variants in ID compared to controls. Nevertheless, given the impact of sleep difficulties in patients with ID, melatonin supplementation might be of great benefit for a subgroup of patients with low melatonin synthesis.

Genetic Variants in Melatonin Synthesis and Signaling Pathway are not Associated with Adolescent Idiopathic Scoliosis

Genetic association study investigating the association of genetic markers of melatonin signaling and biosynthesis with adolescent idiopathic scoliosis (AIS). To determine whether gene polymorphisms related to the melatonin signaling or biosynthesis pathways are associated with AIS. Data have been published on the potential role of gene polymorphisms for melatonin receptor (MTNR) 1B in predicting AIS. Other genes in the melatonin pathways have been tested for association with AIS. The following genes involved in melatonin synthesis were evaluated herein: tryptophan 5-hyroxylase 1 (TPH1), serotonin N-acetyltransferase (SNAT), and hydroxyindoleo-methyltransferase (HIOMT). In addition, proteins involved in melatonin signaling were also included in this study: MTNR1A, MTNR1B, and protein kinase C delta (PKCd). High throughput microarray-based single nucleotide polymorphism (SNP) genotyping was performed for these seven genes using DNA samples from 589 AIS subjects and 1533 ethnically matched controls. Chi-square analyses of allele frequency between AIS cases and controls were performed and odds ratios were calculated for all SNP markers. Three SNPs were tested for both MTNR1A and HIOMT, 4 for TPH1 and SNAT, 12 for PKCd, and 7 for MTNR1B. The minor allele frequencies were not significantly different between AIS cases and controls. No association was thus found between AIS and the investigated SNPs. Genetic polymorphisms associated with either melatonin synthesis or its signaling pathway are unlikely to be commonly associated with AIS.

Identification of Pathway-Biased and Deleterious Melatonin Receptor Mutants in Autism Spectrum Disorders and in the General Population

Melatonin is a powerful antioxidant and a synchronizer of many physiological processes. Alteration of the melatonin pathway has been reported in circadian disorders, diabetes and autism spectrum disorders (ASD). However, very little is known about the genetic variability of melatonin receptors in humans. Here, we sequenced the melatonin receptor MTNR1A and MTNR1B, genes coding for MT1 and MT2 receptors, respectively, in a large panel of 941 individuals including 295 patients with ASD, 362 controls and 284 individuals from different ethnic backgrounds. We also sequenced GPR50, coding for the orphan melatonin-related receptor GPR50 in patients and controls. We identified six non-synonymous mutations for MTNR1A and ten for MTNR1B. The majority of these variations altered receptor function. Particularly interesting mutants are MT1-I49N, which is devoid of any melatonin binding and cell surface expression, and MT1-G166E and MT1-I212T, which showed severely impaired cell surface expression. Of note, several mutants possessed pathway-selective signaling properties, some preferentially inhibiting the adenylyl cyclase pathway, others preferentially activating the MAPK pathway. The prevalence of these deleterious mutations in cases and controls indicates that they do not represent major risk factor for ASD (MTNR1A case 3.6% vs controls 4.4%; MTNR1B case 4.7% vs 3% controls). Concerning GPR50, we detected a significant association between ASD and two variations, Δ502–505 and T532A, in affected males, but it did not hold up after Bonferonni correction for multiple testing. Our results represent the first functional ascertainment of melatonin receptors in humans and constitute a basis for future structure-function studies and for interpreting genetic data on the melatonin pathway in patients.

Melatonin Sensitizes Human Myometrial Cells to Oxytocin in a Protein Kinase Cα/Extracellularly Regulated Kinase-Dependent Manner

abstract Context: Studies have shown that labor occurs primarily in the night/morning hours. Recently, we identified the human myometrium as a target for melatonin (MEL), the neuroendocrine output signal coding for circadian night. Objective: The purpose of this study was to determine the signaling pathway underlying the effects of MEL on contractility and the contractile machinery in immortalized human myometrial cells. Design: To ascertain the signaling pathway of MEL leading to its effects on myometrial contractility in vitro, we performed gel retraction assays with cells exposed to iodo-MEL (I-MEL) with or without oxytocin and the Rho kinase inhibitor Y27632. I-MEL effects on inositol trisphosphate (IP3)/diacylglycerol (DAG)/protein kinase C (PKC) signaling were also investigated. Additionally, we assayed for caldesmon phosphorylation and ERK1/2 activation. Results: I-MEL was found to activate PKCα via the phospholipase C/IP3/DAG signaling pathway, which was confirmed by PKC enzyme assay. I-MEL did not affect myosin light chain phosphatase activity, and its effects on contractility were insensitive to Rho kinase inhibition. I-MEL did increase phosphorylation of ERK1/2 and caldesmon, which was inhibited by the MAPK kinase inhibitor PD98059 or the PKC inhibitor C1. Conclusions: MEL sensitizes myometrial cells to subsequent procontractile signals in vitro through activation of the phospholipase C/IP3/DAG signaling pathway, resulting in specific activation of PKCα and ERK1/2, thereby phosphorylating caldesmon, which increases actin availability for myosin binding and cross-bridging. In vivo, this sensitization would provide a mechanism for the increased nocturnal uterine contractility and labor that has been observed in late-term human pregnancy.

Abstract LB-431: Randomized trial of oral melatonin supplementation in breast cancer survivors

Abstract Background: Night shift work has been classified by the International Agency for Research and Cancer and the World Health Organization as a probable carcinogen, presumably due to its effect on the melatonin pathway. Extensive laboratory and some human data also support that melatonin may influence breast cancer risk, although the mechanism is not clear. Both pharmacologic and physiologic doses of melatonin inhibit the growth of malignant cells of the breast in vitro and in animal models. Study Design: 95 postmenopausal women with a prior history of Stage 0-III breast cancer who had completed active cancer treatment (including hormonal therapy) were recruited to a double-blind randomized trial of 4 months of 3 mg melatonin daily compared to placebo. Endpoints included changes in breast cancer biomarkers, sleep, hot flashes, and mood. Results: 5 subjects on melatonin and 4 on placebo withdrew from the study or did not complete the 4 month assessment leaving 86 women (43 on placebo and 43 on melatonin) with evaluable data. Melatonin was well-tolerated without any grade 3/4 toxicity. At baseline, there was no statistical difference between the two arms for any of the endpoints or standard demographic characteristics. Mean age was 59 years (range 38-71) with mean 8 years since diagnosis. At 4 months, there were no statistically significant differences between the two groups for the biomarker endpoints (estradiol, IGF-1, IGFBP-3, or IGF-1/IGFBP-3 ratios), depressive symptoms, or hot flashes. However, subjects taking melatonin had significantly improved sleep quality, sleep duration, and total sleep scores compared with subjects taking placebo. Conclusions: Among postmenopausal women with a prior history of breast cancer, a 4 month course of 3 mg melatonin daily did not influence IGF-1, IGFBP-3 or estradiol levels. Effects of longer courses of melatonin and among premenopausal women are unknown. However, melatonin was effective in improving sleep quality among breast cancer survivors without any significant adverse effects. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-431.

Mutation screening of melatonin-related genes in patients with autism spectrum disorders

BackgroundOne consistent finding in autism spectrum disorders (ASD) is a decreased level of the pineal gland hormone melatonin and it has recently been demonstrated that this decrease to a large extent is due to low activity of the acetylserotonin O-methyltransferase (ASMT), the last enzyme in the melatonin synthesis pathway. Moreover, mutations in the ASMT gene have been identified, including a splice site mutation, that were associated with low ASMT activity and melatonin secretion, suggesting that the low ASMT activity observed in autism is, at least partly, due to variation within the ASMT gene.MethodsIn the present study, we have investigated all the genes involved in the melatonin pathway by mutation screening of AA-NAT (arylalkylamine N-acetyltransferase), ASMT, MTNR1A, MTNR1B (melatonin receptor 1A and 1B) and GPR50 (G protein-coupled receptor 50), encoding both synthesis enzymes and the three main receptors of melatonin, in 109 patients with autism spectrum disorders (ASD). A cohort of 188 subjects from the general population was used as a comparison group and was genotyped for the variants identified in the patient sample.ResultsSeveral rare variants were identified in patients with ASD, including the previously reported splice site mutation in ASMT (IVS5+2T>C). Of the variants affecting protein sequence, only the V124I in the MTNR1B gene was absent in our comparison group. However, mutations were found in upstream regulatory regions in three of the genes investigated, ASMT, MTNR1A, and MTNR1B.ConclusionsOur report of another ASD patient carrying the splice site mutation IVS5+2T>C, in ASMT further supports an involvement of this gene in autism. Moreover, our results also suggest that other melatonin related genes might be interesting candidates for further investigation in the search for genes involved in autism spectrum disorders and related neurobehavioral phenotypes. However, further studies of the novel variants identified in this study are warranted to shed light on their potential role in the pathophysiology of these disorders.

Resequencing and association analysis of arylalkylamine N-acetyltransferase (AANAT) gene and its contribution to major depression susceptibility

Circadian rhythms disruptions, including abnormalities of circadian phase position and melatonin secretion, have been described in major depression (MD). Arylalkylamine N-acetyltransferase (AANAT) is a key enzyme of the melatonin pathway involved in circadian oscillations of melatonin levels. We assessed the contribution of AANAT gene variability to susceptibility to MD considering common and rare genetic variations through a sequential sequencing and single nucleotide polymorphism (SNP)-based genotyping approach in a sample of 445 unrelated patients with MD (257 unipolar MD, 188 bipolar depression) and 440 community-based screened control subjects. We identified 17 sequence changes, thirteen of which represented novel sequence variations. We did not observe an over-representation of patients carrying rare variants compared with the healthy controls. Common variants (MAF > 2%) were included in a case-control association analysis that showed significant association after multiple testing correction of two SNPs located in the promoter region of AANAT with MD: rs3760138 (P = 0.00006) and rs4238989 (P = 0.005). Multimarker analysis found significant associations between two three-marker protective haplotypes and a susceptibility three-marker haplotype containing the rare alleles of rs3760138-rs4238989-rs8150 and MD. We present evidence of the association of genetic variability in the AANAT gene with susceptibility to MD. Our results support the hypothesis that the melatonin-signaling pathway and circadian clock mechanisms may contribute to the pathophysiology of MD.

Melatonin protects the cytochrome P450 system through a novel antioxidant mechanism

Melatonin, an endogenous hormone, is used as an antioxidant drug in doses quite higher than the endogenous circulating levels of this hormone. Hepatic endoplasmic reticulum contains the cytochrome P450 (CYP450) system, which catalyzes one biotransformation pathway of melatonin; this organelle is also one of the main sources of reactive oxygen species in cells. Therefore, we proposed that the antioxidant activity of this hormone may have a biological relevance in the organelle where it is biotransformed. To evaluate this postulate, we used Fe(3+)/ascorbate, an oxygen free radical generating system that leads to lipid peroxidation, loss of protein-thiol content, and activation of UDP-glucuronyltransferase in rat liver microsomes. We found that mM concentrations of melatonin prevented all these oxidative phenomena. We also found that Fe(3+)/ascorbate leads to structural alterations in the CYP450 monooxygenase, the enzyme that binds the substrate in the CYP450 system catalytic cycle, probably through direct oxidation of the protein, and also inhibited p-nitroanisole O-demethylation, a reaction catalyzed by the CYP450 system. Notably, melatonin prevented both phenomena at microM concentrations. We provide evidence suggesting that melatonin may be oxidized by oxygen free radicals. Thus, we postulate that melatonin may be acting as an oxygen free radical scavenger, and Fe(3+)/ascorbate-modified melatonin would be directly protecting the CYP450 system through an additional specific mechanism. Pharmacological relevance of this phenomenon is discussed.

Melatonin ameliorates cerulein‐induced pancreatitis by the modulation of nuclear erythroid 2‐related factor 2 and nuclear factor‐kappaB in rats

Melatonin exhibits a wide variety of biological effects, including antioxidant and anti-inflammatory functions. Its antioxidant role impedes the etiopathogenesis of pancreatitis, but little is known about the signaling pathway of melatonin in the induction of antioxidant enzymes in acute pancreatitis (AP). The aim of this study was to determine whether melatonin could prevent cerulein-induced AP through nuclear factor erythroid 2-related factor 2 (Nrf2) and curtail inflammation by inhibition of NF-kappaB. AP was induced by two intraperitoneal (i.p.) injections of cerulein at 2 h intervals (50 microg/kg) in Sprague-Dawley rats. Melatonin (10 or 50 mg/kg/daily, i.p.) was administered 24 h before each injection of cerulein. The rats were killed 12 h after the last injection. Acinar cell degeneration, pancreatic edema, and inflammatory infiltration were significantly different in cerulein- and melatonin-treated rats. Melatonin significantly reduced amylase, lipase, MPO, and MDA levels, and increased antioxidant enzyme activities including SOD and GPx, which were decreased in AP (P < 0.05). Melatonin increased the expression of NQO1, HO-1, and SOD2 when compared with the cerulein-induced AP group (P < 0.05). In addition, melatonin increased Nrf2 expression, and reduced expressions of tumor necrosis factor-alpha, IL-1beta, IL-6, IL-8, and iNOS. The elevated nuclear binding of NF-kappaB in the cerulein-induced pancreatitis group was inhibited by melatonin. These results show that melatonin increases antioxidant enzymes and Nrf2 expression, and limits inflammatory mediators in cerulein-induced AP. It is proposed that melatonin may play an important role in oxidative stress via the Nrf2 pathway in parallel with reduction of inflammation by NF-kappaB inhibition.

The effects of red and blue light on alertness and mood at night

This study was designed to explore the roles that long- and short-wavelength lights have on momentary mood and alertness at night. Twenty-two subjects participated in a mixed-design experiment, where we measured the impact of two levels of long- and short-wavelength lights on brain activity and on self-assessments of alertness, sleepiness and mood. Measurements were obtained 60 minutes prior to, during and after light exposure. Results showed that the red and the blue lights increased electroencephalographic beta power (12—30 Hz), reduced sleepiness, and increased positive affect relative to the previous dim-light period indicating that alertness and mood can be affected by light without necessarily stimulating the melatonin pathway. The impact of light was modest, however, compared to the increase in fatigue over the course of the night.

Association of disease-predisposition polymorphisms of the melatonin receptors and sunshine duration in the global human populations

Melatonin is predominantly involved in signaling circadian and seasonal rhythms, and its synthesis is regulated by the environmental light/dark cycle. The selection pressure by geographically different environmental light/dark cycles, which is predominantly determined by sunshine duration, on the global distribution of genetic polymorphisms in the melatonin pathway is not well understood. Recent genetic association studies identified various disease-predisposition polymorphisms in this pathway. We investigated the correlations between the prevalence of these clinically important single nucleotide polymorphisms (SNPs) and sunshine duration among worldwide human populations from twelve regions in the CEPH-HGDP database rs4753426, a recently reported predisposition SNP for type 2 diabetes in the promoter of the MT(2) melatonin receptor gene (MTNR1B), which was not included in the CEPH-HGDP genotyping array, was additionally genotyped. This SNP showed a marginally significant correlation in 760 CEPH-HGDP DNA samples (r = -0.5346, P = 0.0733), and it showed the most prominent association among the candidate melatonin pathway SNPs examined. To control for population structure, which may lead to a false positive correlation, we genotyped this SNP in a replication set of 1792 subjects from China. The correlation was confirmed among Chinese populations (r = -0.8694, P = 0.0002), and was also statistically significant after correction of other climatic and geographical covariants in multiple regression analysis (beta = -0.907, P = 1.94 x 10(-5)). Taken together, it suggests that the human melatonin signaling pathway, particularly MT(2) melatonin receptor may have undergone a selective pressure in response to global variation in sunshine duration.