In the field mouse Mus booduga melatonin phase response curves (PRCs) have a different time course and wave form relative to light PRC

The phase shifting effects of the pineal hormone melatonin on the circadian locomotor activity rhythm of the field mouse. Mus booduga was examined at various phases of the circadian cycle using single melatonin injections of two concentrations (10 mg/kg, high dose; and 1 mg/kg, low dose) and two phase response curves (PRCs) were constructed. A single dose of melatonin administered during the early subjective day evoked maximum phase delays, and during the late subjective night evoked phase advances in the locomotor activity rhythm. Other phases of the circadian cycle also responded to melatonin. The interval between circadian time 19 (CT19) and CT2 of the high dose melatonin PRC is marked by significant phase advances, whereas the interval between CT2 and 19 is marked by significant phase delays. A single dose of melatonin of strength 10 mg/kg was found to evoke phase shifts that were of comparable magnitude to those of the phase shifts evoked by natural daylight pulses. Control animals, treated with 50% dimethyl sulfoxide (DMSO), did not respond with phase shifts significantly greater than zero. Significant differences between the shapes of the two melatonin PRCs exist. Further melatonin PRCs appear to have a different time course and wave form relative to light-induced PRC.     

Low urinary 6-sulphatoxymelatonin levels in patients with coronary artery disease

A decrease in nocturnal serum melatonin levels was reported in patients with clinically uncharacterized coronary artery disease. To assess whether there was a correlation between melatonin production and disease stage, we measured the nocturnal urinary excretion of 6-sulphatoxymelatonin (an index of blood melatonin concentration) in patients with chronic stable or unstable coronary disease and in a group of age-matched controls. Three groups of individuals were studied: a) 24 healthy subjects (mean age: 63 +/- 13 yr); b) 32 patients with chronic, stable, coronary disease (62 +/- 11 yr); and c) 27 patients with unstable angina (62 +/- 12 yr). For 6-sulphatoxymelatonin measurement, urine was collected from 18:00 to 06:00 hr, within 48 hr of hospitalization in the case of unstable angina. 6-Sulphatoxymelatonin was measured by a specific radioimmunoassay. Urinary 6-sulphatoxymelatonin excretion was significantly lower in unstable angina patients than in healthy subjects or in patients with stable angina. 6-Sulphatoxymelatonin correlated negatively with age in healthy subjects, but not in coronary patients. 6-Sulphatoxymelatonin excretion in patients treated with beta-adrenoceptor blockers did not differ significantly from coronary patients not receiving beta-blockers. The results indicate that patients with coronary disease have a low melatonin production rate, with greater decreases in those with higher risk of cardiac infarction and/or death.     

The role of granulocyte-macrophage-colony stimulating factor, cortisol, and melatonin in the regulation of the circadian rhythms of peripheral blood cells in healthy volunteers and patients with breast cancer

The circulating blood cells show highly reproducible circadian rhythms. However, the factors that regulate these rhythms are not well understood. In the current study, we examined the diurnal variations of peripheral blood cells (white blood cells, neutrophils, lymphocytes), granulocyte-macrophage-colony stimulating factor (GM-CSF), and melatonin levels, and considered the role of melatonin on these rhythms in healthy volunteers and in patients with early breast cancer. Fourteen premenopausal patients with early stage breast cancer (T2, N1 tumors) and 10 premenopausal healthy volunteers were included in the study. Blood samples were taken every 4 hr for a period of 24 hr. Peripheral blood cells were counted by automated analyser and also from peripheral blood films. GM-CSF levels were measured by ELISA and melatonin levels by radioimmunoassay (RIA). Serum melatonin, cortisol, and GM-CSF levels, and peripheral blood cell counts showed significant circadian rhythms in healthy volunteers. Except for GM-CSF, these circadian rhythms were found not to be suppressed in early breast cancer patients. While there were significant correlations of serum GM-CSF and cortisol levels with peripheral blood cell counts in healthy volunteers, only lymphocyte counts were found to be significantly correlated with serum GM-CSF and cortisol levels in patients with breast cancer. Serum melatonin levels were found to be significantly correlated with lymphocyte counts in both groups. Our results suggest that peripheral blood cells show significant circadian rhythms in both healthy volunteers and in patients with stage II (T2, N1) breast cancer, and GM-CSF, cortisol, and melatonin may have a role in the regulation of peripheral blood cell counts.     

N-acetyltransferase is not the rate-limiting enzyme of melatonin synthesis at night

Abstract:  Circadian melatonin production in the pineal gland and retina is under the control of serotonin N-acetyltransferase (NAT) and hydroxyindole-O-methyltransferase. Because NAT activity varies diurnally, it has been considered both the melatonin rhythm-generating enzyme and the rate-limiting enzyme of melatonin synthesis. In rats with dramatically reduced NAT activity due to a H28Y mutation in NAT, melatonin levels remained the same as in wildtype controls, suggesting that NAT does not determine the rate of melatonin production at night. Using a combination of molecular approaches with a sensitive in vivo measurement of pineal diurnal melatonin production, we demonstrate that (i) N-acetylserotonin (NAS), the enzymatic product of NAT, is present in vast excess in the night pineals compared with melatonin; (ii) the continuous increase in NAT protein levels at late night does not produce a proportional increase in melatonin; and (iii) an increase in NAS in the same animal over several circadian cycles do not result in corresponding increase in melatonin output. These results strongly suggest that NAT is not the rate-limiting enzyme of melatonin formation at night.     

Melatonin, mitochondria, and cellular bioenergetics

Aerobic cells use oxygen for the production of 90-95% of the total amount of ATP that they use. This amounts to about 40 kg ATP/day in an adult human. The synthesis of ATP via the mitochondrial respiratory chain is the result of electron transport across the electron transport chain coupled to oxidative phosphorylation. Although ideally all the oxygen should be reduced to water by a four-electron reduction reaction driven by the cytochrome oxidase, under normal conditions a small percentage of oxygen may be reduced by one, two, or three electrons only, yielding superoxide anion, hydrogen peroxide, and the hydroxyl radical, respectively. The main radical produced by mitochondria is superoxide anion and the intramitochondrial antioxidant systems should scavenge this radical to avoid oxidative damage, which leads to impaired ATP production. During aging and some neurodegenerative diseases, oxidatively damaged mitochondria are unable to maintain the energy demands of the cell leading to an increased production of free radicals. Both processes, i.e., defective ATP production and increased oxygen radicals, may induce mitochondrial-dependent apoptotic cell death. Melatonin has been reported to exert neuroprotective effects in several experimental and clinical situations involving neurotoxicity and/or excitotoxicity. Additionally, in a series of pathologies in which high production of free radicals is the primary cause of the disease, melatonin is also protective. A common feature in these diseases is the existence of mitochondrial damage due to oxidative stress. The discoveries of new actions of melatonin in mitochondria support a novel mechanism, which explains some of the protective effects of the indoleamine on cell survival.     

Protective effects of chronic melatonin treatment against renal injury in streptozotocin-induced diabetic rats

The aim of this study was to investigate the effects of melatonin as an antioxidant, on prevention and treatment of streptozotocin (STZ)-induced diabetic renal injury in rats. Male Wistar rats were divided into four groups: (1) untreated, (2) melatonin-treated, (3) untreated diabetic (UD), (4) melatonin-treated diabetic (MD). Experimental diabetes was induced by single dose (60 mg/kg, i.p.) STZ injection. For 3 days prior to administration of STZ, melatonin was injected (200 microg/kg/day, i.p.); these injections were continued until the end of the study (4 weeks). Malondialdehyde (MDA) levels as a marker of lipid peroxidation were significantly increased in the renal homogenates of UD animals and decreased after melatonin administration. The activity of the antioxidative enzyme glutathione peroxidase (GSH-Px) was significantly reduced in UD rats. Melatonin treatment reversed STZ-induced reduction of GSH-Px activity without having an effect on blood glucose. Upon histopathological examination, it was observed that the melatonin treatment prevented the renal morphological damage caused by diabetes. Upon immunohistochemical investigation, glomerular anti-laminin beta1 staining decreased in MD rats. Additionally, no tubular anti-IGF-1 staining was observed in melatonin-treated rats. In conclusion, chronically administered melatonin reduced renal injury in STZ-induced diabetic rats and thus it may provide a useful therapeutic option in humans to reduce oxidative stress and the associated renal injury in patients with diabetes mellitus.     

Melatonin promotes survival of nonvascularized fat grafts and enhances the viability and migration of human adipose‐derived stem cells via down‐regulation of acute inflammatory cytokines

Nonvascularized fat grafting is a valuable technique for soft tissue reconstruction but poor survival of fat in the host environment remains a problem. A process known as cell‐assisted transfer is used to enhance fat graft retention by adding stromal vascular fraction, an adipose‐derived stem cell (ASC) rich content to lipoaspirate. We have recently shown that the use of melatonin, a reactive oxygen species scavenger, protects human ASCs from hydrogen peroxide‐induced oxidative stress and cell death in vitro but its role as a pharmacological adjunct in clinical fat grafting has not been studied. Herein, the effect of melatonin was examined on human ASCs in vitro using survival and functional assays including the MTT assay, CellTox Green assay, monolayer scratch assay as well as a human cytokine chemoluminescence, and tumour necrosis factor‐α assay. Further, the effect of melatonin‐treated fat grafts was tested in vivo with a murine model. Haematoxylin and eosin staining, perilipin and CD31 immunostaining were performed with morphometric analysis of adipose tissue. The results demonstrate that, in vitro, the addition of melatonin to ASCs significantly improved their cell‐viability, promoted cell migration and preserved membrane integrity as compared to controls. In addition, it induced a potent anti‐inflammatory response by downregulating acute inflammatory cytokines particularly tumour necrosis factor‐α. For the first time, it is demonstrated in vivo that melatonin enhances fat graft volume retention by reducing inflammation and increasing the percentage of adipose volume within fat grafts with comparable volumes to that of cell‐assisted lipotransfer. Based on these novel findings, melatonin may be a useful pharmacological adjunct in clinical fat grafting.     

骨髓间充质干细胞向神经元样细胞分化中褪黑素受体和多效蛋白的表达

目的体外诱导成人骨髓间充质干细胞（MSCs）向神经元样细胞分化,并探讨分化过程中多效蛋白（PTN）和褪黑素（Mel）受体亚型MT1、MT2 mRNA的表达,以探索MSCs向神经元样细胞分化的特性和机制。方法密度梯度离心加贴壁培养法分离成人MSCs,原代和传代培养。取第6代MSCs设对照和实验组进行诱导,诱导后30min至3d,观察细胞形态并计数。免疫细胞化学法和RT—PCR法测定分化后细胞神经细胞特异性表面标志神经元特异性烯醇化酶（NSE）、微管相关蛋白-2（MAP-2）、神经胶质纤维酸性蛋白（GFAP）和诱导前、诱导后12hPTN和MT1、MT2 mRNA的表达。结果接种24h后MSCs开始贴壁,呈圆形或椭圆形。3d后可见梭状细胞呈集落状生长,10d～14d融合。第5代～第6代时呈现较均一的成纤维细胞样形态。诱导后胞体向胞核收缩;出现双极及多极细胞。12h变形细胞增多,细长突起相互连接。24h后变形细胞增多不明显。诱导后12h大部分细胞表达NSE、MAP-2,未检测到GFAP的表达。实验组诱导后12h细胞有PTN和MT1 mRNA的表达。结论PTN和Me1信号传导可能参与调控了MSCs向神经元样细胞的分化。