The identification of the UV degradants of melatonin and their ability to scavenge free radicals

Ultraviolet (UV) light is known to induce the generation of free radicals in biological tissues such as skin. Of these free radicals, the O2-. and particularly the.OH radical can induce cellular damage including lipid peroxidation. Thus, the use of antioxidants to prevent such damage induced by UV irradiation has received much attention recently. One such antioxidant, which has the potential to be incorporated into sunscreens, is the pineal secretory product melatonin. One of the concerns of using melatonin in sunscreens is its photostability. In the present study, we investigated the photostability of melatonin subjected to UV irradiation. In addition, we used liquid chromatography mass spectrometry (LC-MS) to identify the degradants and we also assessed the ability of the degradants to inhibit O2-. generation as well as lipid peroxidation in rat brain homogenate. The results show that UV irradiation of melatonin (0.1 mg/mL) using a 400-W lamp for 2 hr caused a significant decline of melatonin to 18% of its original concentration after 20 min, with the decline continuing until the melatonin concentration reaches zero at 120 min. The LC-MS results show that the degradants of melatonin are 6-hydroxymelatonin and N1-acetyl-N2-formyl-5-methoxykynurenamine (AFMK). These degradants were able to provide equipotent activity against potassium cyanide (KCN)-induced superoxide generation compared to non-irradiated melatonin. Thus, the study shows that although melatonin is rapidly degraded by UV irradiation, the degradants retain antioxidant activity, making melatonin a likely candidate for inclusion in sunscreens.     

Melatonin and 5-methoxytryptophol (5-ML) in nervous and/or neurosensory structures of a gastropod mollusc (Helix aspersa maxima): synthesis and diurnal rhythms

Daily patterns of melatonin and 5-methoxytryptophol (5-ML) concentrations and of aryl alkylamine N-acetyltransferase (AA-NAT) and hydroxyindole-O-methyltransferase (HIOMT) activities have been measured in the cerebroid ganglions, visceral ganglions, and ocular tentacles of the gastropod mollusc Helix aspersa maxima. Melatonin concentrations are very low in all the studied structures, except a small peak at the end of the night in the cerebroid ganglions. 5-ML, which is quite undetectable in the cerebroid and visceral ganglions, shows clear daily variations in the ocular tentacles with low values in the middle of the light period and high values during the night. These results are opposite to what is known on daily variations of 5-ML in vertebrates. AA-NAT activity was not detected, while the presence of an HIOMT-like activity supports the hypothesis that 5-ML is synthesized in the ocular tentacles. The temporal relationships existing between the 5-ML rhythm in the ocular tentacles and the hemolymph suggest that 5-ML could be released in the general circulation. These preliminary results suggest that 5-ML could be an informative molecule involved in adaptative processes in the snail and they reinforce the hypothesis that the different 5-methoxyindoles could be implicated in the integration of environmental information.     

Use of melatonin in the treatment of paediatric sleep disorders

Abstract: A group of Vancouver health professionals, including the authors, have studied the use of oral melatonin in the treatment of chronic sleep disorders in children with disabilities since the Fall of 1991. This review article is based on the first 100 patients, half of whom were visually impaired or blind. Children with neurological, neuropsychiatric, and developmental disabilities are predisposed to chronic sleep-wake cycle disturbances. Disorders such as blindness, deafblindness, mental retardation, autism, and central nervous system diseases, among others, diminish the ability of these individuals to perceive and interpret the multitude of cues for synchronizing their sleep with the environment. Melatonin, which benefitted slightly over 80% of our patients, appears to be a safe, inexpensive, and a very effective treatment of sleep-wake cycle disorders. The oral dose of fast release melatonin taken at bed-time ranged from 2.5 mg to 10 mg. Side effects or the development of tolerance have not been observed. Since the causes of sleep difficulties are extremely variable, not all children are candidates for treatment. For successful melatonin treatment, clinical experience is required, and the influences of other health problems and medications need to be considered. Further clinical and laboratory research in this field is imperative because melatonin treatment offers enormous health, emotional, social, and economic benefits to society, especially since multidisabled children with chronic sleep difficulties do not respond well to current therapeutic regimes.     

The Effect of Melatonin in Patients with Fibromyalgia: A Pilot Study

The aim of the study was to determine the possible effect of melatonin treatment on disturbed sleep, fatigue and pain symptoms observed in fibromyalgia (FM) patients. Twenty-one consecutive patients with FM were included in an open 4-week-duration pilot study. Before and after treatment with melatonin 3 mg at bedtime, patients were evaluated using tender point count by palpation of 18 classic anatomical regions, pain score in four predesignated areas, pain severity on a 10 cm visual analogue scale (VAS), sleep disturbances, fatigue, depression, anxiety, and patient and physician global assessments, also by a VAS. Urine 6-sulphatoxymelatonin levels (aMT-6S) were measured in the patients and 20 age- and sex-matched controls. Nineteen patients completed the study. One patient withdrew because of migraine and another was lost to follow-up. At day 30, median values for the tender point count and severity of pain at selected points, patient and physician global assessments and VAS for sleep significantly improved with melatonin treatment. Other variables improved but did not reach statistical significance. Adverse events were mild and transient. Lower levels of aMT-6S were found in FM patients compared with normal median controls (±SD, 9.16 ± 7.9 μg/24 h vs 16.8 ± 12.8 μg/24 h) (p= 0.06). Although this is an open study, our preliminary results suggest that melatonin can be an alternative and safe treatment for patients with FM. Double-blind placebo controlled studies are needed. Received: 14 September 1998 / Accepted: 14 May 1999     

The involvement of TRPV4 on the hypoxia-induced oxidative neurotoxicity and apoptosis in a neuronal cell line: Protective role of melatonin

The hypoxia (HYPX)-mediated excessive generation of mitochondrial free reactive oxygen species (mROS) and the overload Ca²⁺ influx via the inhibition of TRPV4 are controlled by the treatment of antioxidants. However, the molecular mechanisms underlying melatonin (MLT)'s neuroprotection remains elusive. We investigated the role of MLT via modulation of TRPV4 on oxidative neurodegeneration and death in SH-SY5Y neuronal cells. The SH-SY5Y cells were divided into five groups as follows: control, MLT (1 mM for 2 h), HYPX (200 μM CoCl₂ for 24 h), HYPX + MLT, and HYPX + TRPV4 blockers (ruthenium red-1 μM for 30 min). The HYPX caused to the increase of TRPV4 current density and overload Ca²⁺ influx with an increase of mitochondrial membrane potential and mROS generation. The changes were not observed in the absence of TRPV4. When HYPX exposure and TRPV4 agonist (GSK1016790A)-induced TRPV4 activity were inhibited by the treatment of ruthenium red or MLT, the increase of mROS, lipid peroxidation, apoptosis, Zn²⁺ concentrations, TRPV4, caspase -3, caspase -9, Bax, and Bcl-2 expressions were restored via upregulation of reduced glutathione, glutathione peroxidase, and total antioxidant status. The levels of apoptosis and cell death in the cells were enriched with increases of caspase -3 and -9 activations, although they were decreased by MLT treatment. In conclusion, the treatment of MLT modulates HYPX-mediated mROS, apoptosis, and TRPV4-mediated overload Ca²⁺ influx and may provide an avenue for protecting HYPX-mediated neurological diseases associated with the increase of mROS, Ca²⁺, and Zn²⁺ concentration.     

褪黑激素对体外培养神经元七氟醚损害的保护作用

目的 探讨褪黑激素（MLT）对体外培养神经元七氟醚（SEV）损伤的保护作用及其机制。方法 取SD大鼠乳鼠全脑皮层组织,分离皮质神经元进行体外培养;MLT预处理24 h后,4% SEV作用神经元;采用CCK-8法检测神经元存活率,流式细胞术检测神经元凋亡率,qPCR检测神经元miR-130a-3p和ROCK2 mRNA水平;免疫印迹法检测凋亡相关蛋白表达;应用在线预测软件TargetScan分析预测miR-130a-3p与ROCK2靶向关系并验证。结果 SEV明显降低神经元存活率以及miR-130a-3p和ROCK2 mRNA水平（P<0.05）,明显增加神经元凋亡率及凋亡相关蛋白cle-caspase3和cle-caspase9表达水平（P<0.05）;MLT明显抑制SEV的作用（P<0.05）。软件TargetScan分析显示,miR-130a-3p与ROCK2的3’非编码区第846~852碱基处存在结合位点,PCR和免疫印迹法检测显示,miR-130a-3p与ROCK2存在靶向关系。ROCK2过表达明显逆转MLT预处理的效果（P<0.05）。结论 MLT预处理明显改善SEV对体外培养的大鼠乳鼠皮质神经元的损害,机制可能是上调miR-130a,进而靶向抑制ROCK2表达。     

miR-6858 plays a key role in the process of melatonin inhibition of the malignant biological behavior of glioma

MicroRNAs (miRNAs), small non-coding RNA molecules with a length of 18–25 nucleotides, have been shown to be involved in mediating various malignant properties of GBM, including growth, invasion and angiogenesis. Here, we investigated whether miRNAs might be involved in mediating the suppression of malignant properties of GBM by melatonin (MEL), an amine hormone secreted by the pineal gland. Sequencing was performed to screen specifically for miRNAs induced by MEL in U87 and an orthotopically xenografted primary GBM cell line, GBM#P3. MiR-6858-5p was the most significantly up-regulated miR in GBM cell lines in response to MEL (~5 × ). Transfection of a mimic of miR-6858-5p into both cell lines led to a decrease in viability of ~ 50% at 72 h, confirming a suppressive role for miR-6858-5p in GBM. In contrast, an inhibitor of miR-6858-5p rescued GBM cells from MEL suppression of proliferation, migration and invasion. Analysis using Targetscan yielded candidate mRNAs targeted by miR-6858-5p, some of which are involved in the SIRT/AKT signaling pathway. In cells transfected with a mimic or an inhibitor of miR-6858-5p, levels of SIRT3 and downstream components of the AKT signaling pathway were suppressed or up-regulated, respectively, both in vitro and in an in vivo orthotopic xenograft model. Our results elucidated a novel molecular mechanism underlying MEL suppression of GBM, highlighting a role for miRNAs, and provide a potential therapeutic strategy for GBM.     

Sleep interventions and glucose metabolism: systematic review and meta-analysis

ObjectiveSleep disturbances (insufficient or poor sleep quality) have been linked to abnormal glucose metabolism. This systematic review and meta-analysis aimed to explore the effects of behavioral and pharmacological sleep interventions on glucose metabolism.MethodsMedline and Embase were used for systematic search. Studies reporting behavioral or pharmacological interventions in population with sleep disturbances, with measured outcomes of glucose metabolism and sleep parameters were selected.ResultsTwenty two studies were eligible for review (eight were conducted in people with type 2 diabetes). Studies were grouped into three types of intervention: sleep extension (n = 6), sleep education or cognitive behavioral therapy for insomnia (CBT-I, n = 6) and pharmacological interventions (n = 10). CBT-I and sleep education resulted in significantly improved self-reported sleep quality (Pittsburgh Sleep Quality Index, mean difference, MD, −1.31, 95% confidence interval (CI) −1.83, −0.80), non-significant reduction in hemoglobin A1c level (MD -0.35%, 95% CI -0.84, 0.13), and non-significant reduction in fasting glucose levels (MD -4.76 mg/dL, 95% CI -14.19, 4.67). Other studies were not eligible for meta-analysis due to heterogeneity of interventions or outcomes. Sleep extension was able to increase sleep duration by varying degrees in short sleepers, and five of six studies demonstrated relationships between the intervention and measures of insulin resistance. A majority of pharmacological intervention studies showed improved sleep but the effects on glucose metabolism were mixed.ConclusionsAvailable sleep interventions were effective in improving sleep but the effects on glucose metabolism were inconclusive. Larger randomized studies with consistent outcome measurements are needed to demonstrate this potential causal relationship.     

Effects of Organic Light-Emitting Diodes on Circadian Rhythm and Sleep

ObjectiveOrganic light-emitting diodes (OLEDs) emit less blue light than traditional light-emitting diodes (LEDs), and we previously found that early-night OLED light exposure (LE) delays the melatonin phase by less than LED at a color temperature of 4,000 K. As a follow-up study, we investigated the effects of OLED and LED at a different color temperature (3,000 K) on melatonin profile, sleep, and vigilance. Methods24 healthy subjects (27.5±5.1 years) were exposed to three light conditions [OLED, LED, and dim light (DL)] from 17:30 to 24:00, in a random order and with a 1-week interval. Saliva samples for melatonin were taken every hour from 18:00 to 24:00. Polysomnography (PSG) and a psychomotor vigilance test (PVT) were performed. ResultsMelatonin onset time was significantly delayed under OLED and LED compared with DL, with no significant difference between OLED and LED. The mean melatonin level at 24:00 under LED was lower than that under DL, but there was no significant difference between OLED LE and DL. The percentage of slow wave sleep (N3) in LED was significantly lower than in OLED. ConclusionExposure to light in the evening can suppress melatonin secretion late at night and disturb deep sleep, and those effects are slightly worse under LED than OLED.