Assessment of retinal and choroidal microvasculature in night shift medical workers by OCT angiography.

This study evaluated retinal and choroidal microvascular changes in night shift medical workers and its correlation with melatonin level. Night shift medical workers (group A, 25 workers) and non-night shift workers (group B, 25 workers) were recruited. The images of macula and optic nerve head were obtained by swept-source OCT-angiography. Vessel density of retina, choriocapillaris (CC), choriocapillaris flow deficit (CC FD), choroidal thickness (CT) and choroidal vascularity index (CVI) were measured. 6-sulfatoxymelatonin concentration was analyzed from the morning urine. CC FD and CVI were significantly decreased and CT was significantly increased in group A (all P < 0.05). 6-sulfatoxymelatonin concentration was significantly lower in group A (P < 0.05), which was significantly positively correlated with CC FD size (r = 0.318, P = 0.024) and CVI of the most regions (maximum r-value was 0.482, P < 0.001), and was significantly negatively associated with CT of all regions (maximum r-value was - 0.477, P < 0.001). In night shift medical workers, the reduction of melatonin was significantly correlated with CT thickening, CVI reduction and CC FD reduction, which suggested that they might have a higher risk of eye diseases. CC FD could be a sensitive and accurate indicator to reflect CC perfusion.

Rational modification of melatonin for broad-spectrum antifungal agents discovery.

Natural products, known for their environmental safety, are regarded as a significant basis for the modification and advancement of fungicides. Melatonin, as a low-cost natural indole, exhibits diverse biological functions, including antifungal activity. However, its potential as an antifungal agent has not been fully explored. In this study, a series of melatonin derivatives targeting the mitogen-activated protein kinase (Mps1) protein of fungal pathogens were synthesized based on properties of melatonin, among which the trifluoromethyl-substituted derivative Mt-23 exhibited antifungal activity against seven plant pathogenic fungi, and effectively reduced the severity of crop diseases, including rice blast, Fusarium head blight of wheat and gray mold of tomato. In particular, its EC50 (5.4 µM) against the rice blast fungus Magnaporthe oryzae is only one-fourth that of isoprothiolane (22 µM), a commercial fungicide. Comparative analyzes revealed that Mt-23 simultaneously targets the conserved protein kinase Mps1 and lipid protein Cap20. Surface plasmon resonance assays showed that Mt-23 directly binds to Mps1 and Cap20. In this study, we provide a strategy for developing antifungal agents by modifying melatonin, and the resultant melatonin derivative Mt-23 is a commercially valuable, eco-friendly and broad-spectrum antifungal agent to combat crop disease.

Melatonina en trastornos del sueño: comparación de distintos productos y revisión bibliográfica / Melatonin in sleep disorders. comparison of different products and literature review

Introducción: los trastornos del sueño en Pediatría son un problema creciente. La melatonina es el producto de elección y es común recibir publicidad de múltiples productos que la contienen. En este texto se lleva a cabo un análisis comparativo de los mismos, examinando la evidencia científica más reciente, con el fin de determinar si está justificado o no su uso. Métodos: se ha realizado un estudio descriptivo de los productos que contenían melatonina comercializados en España, de venta en farmacias y dirigidos a la población pediátrica. Posteriormente, se ha llevado a cabo una revisión de documentos sobre el uso de melatonina en niños y sobre cada componente extra presente en los productos recogidos. Resultados: se analizaron 53 productos. La forma de administración mayoritaria fue en gotas o mililitros. La dosis recomendada habitual de melatonina fue de 1 mg al día. El componente añadido más frecuente registrado fue la vitamina B6, y melisa y pasiflora fueron las plantas más utilizadas. Ninguno de los productos estaba catalogado como fármaco por la Agencia Española de Medicamentos y Productos Sanitarios (AEMPS) y tampoco se encontró en la publicidad de ninguno referencias bibliográficas. Conclusiones: aunque es conocida la eficacia de la melatonina en trastornos del sueño, actualmente no hay un consenso sobre su dosis eficaz en edad pediátrica. Las sustancias que más frecuentemente se asocian a melatonina cuentan con poca bibliografía que respalde sus resultados sobre el sueño, además de que para ellas tampoco existen, de momento, dosis estandarizadas para la población infantil. (AU)

Introduction: sleep disorders in paediatrics are a growing problem. Melatonin is the drug of choice and it is common to receive advertising for multiple products containing melatonin in primary care. In this paper, a comparative analysis of these products is carried out, examining the most recent scientific evidence, in order to determine whether their use is justified or not. Methods: a descriptive study was conducted on melatonin-containing products sold in pharmacies in Spain and aimed at the paediatric population. Subsequently, a systematic review of documents on the use of melatonin in children and on each extra component present in the products collected was carried out. Results: fifty-three products were analysed. The most common form of administration was drops or millilitres. The usual recommended dose of melatonin was 1 mg per day. The most frequently reported added component was vitamin B6, and lemon balm and passionflower were the most frequently used herbs. None of the products were specifically listed in the Spanish Agency for Medicines and Health Products, and no bibliographical references were found in the advertising of any of the products. Conclusions: although the efficacy of melatonin in sleep disorders is well known, there is currently no consensus on its effective dose in children. The substances most frequently associated with melatonin have little literature to support their results in sleep, and there are no standardised doses for them either, or doses lower than these are used due to a lack of studies in the paediatric population. (AU)

Measuring Urinary 6-Sulphatoxymelatonin in Humans.

The pineal melatonin rhythm provides a robust reference signal for the timing of the endogenous human circadian system. The rhythm in the major urinary metabolite of melatonin, 6-sulphatoxymelatonin (aMT6s), is highly correlated with plasma melatonin and provides a noninvasive method to measure circadian phase, particularly in field-based studies. In this chapter, we describe the protocol for collecting urinary aMT6s and the method used to calculate the acrophase, or peak, time as a circadian phase marker.

2-Arylmelatonin analogues: Probing the 2-phenyl binding pocket of melatonin MT1 and MT2 receptors.

In crystal structures of melatonin MT1 and MT2 receptors, a lipophilic subpocket has been characterized which accommodates the phenyl ring of the potent agonist 2-phenylmelatonin. This subpocket appears a key structural element to achieve high binding affinity and selectivity for the MT2 receptor. A series of 2-arylindole ligands was synthesized to probe the requirements for the optimal occupation and interaction with the 2-phenyl binding pocket. Thermodynamic integration simulations applied to MT1 and MT2 receptors in complex with the α-naphthyl derivative provided a rationale for the MT2-selectivity and investigation on the binding mode of a couple of atropisomers allowed to define the available space and arrangement of substituents inside the subpocket. Interestingly, more hydrophilic 2-aza-substituted compounds displayed high binding affinity and molecular dynamics simulations highlighted polar interaction with residues from the subpocket that could be responsible for their potency.

Sleep Problems and 6-Sulfatoxymelatonin as Possible Predictors of Symptom Severity, Adaptive and Maladaptive Behavior in Children with Autism Spectrum Disorder.

In children with autism spectrum disorder (ASD), sleep disturbances are a frequent comorbidity with an adverse effect on their behavior and functioning. It was suggested that melatonin deficit is at least partly responsible for the sleep problems. The study aimed to investigate, in a sample of 56 children with ASD aged 2.8-13.3 years, if the sleep problems and melatonin secretion can serve as predictors of adaptive functioning and severity of the ASD core symptoms. We demonstrated that, after adjustment for age, the Sleep score assessed by the Children's Sleep Habits Questionnaire predicts the Adaptive behavior composite score only in children younger than 6 years, and the preferred predictive model is for the domain Socialization. The age-adjusted Sleep score predicted Externalizing and Internalizing maladaptive behavior, with a near-zero contribution of age to the relationship between the Internalizing maladaptive behavior and Sleep score. After adjustment for age, the reduced night-time melatonin secretion predicted a higher severity of ASD symptoms in the domain Social affect and the Calibrated Severity Score, but not the sleep problems. Our results emphasize the importance of assessing sleep problems as a modifiable predictor of behavior in children with ASD and support the hypothesis about the role of melatonin in pathophysiology of ASD.

Interaction between Melatonin and NO: Action Mechanisms, Main Targets, and Putative Roles of the Emerging Molecule NOmela.

Melatonin (MEL), a ubiquitous indolamine molecule, has gained interest in the last few decades due to its regulatory role in plant metabolism. Likewise, nitric oxide (NO), a gasotransmitter, can also affect plant molecular pathways due to its function as a signaling molecule. Both MEL and NO can interact at multiple levels under abiotic stress, starting with their own biosynthetic pathways and inducing a particular signaling response in plants. Moreover, their interaction can result in the formation of NOmela, a very recently discovered nitrosated form of MEL with promising roles in plant physiology. This review summarizes the role of NO and MEL molecules during plant development and fruit ripening, as well as their interactions. Due to the impact of climate-change-related abiotic stresses on agriculture, this review also focuses on the role of these molecules in mediating abiotic stress tolerance and the main mechanisms by which they operate, from the upregulation of the entire antioxidant defense system to the post-translational modifications (PTMs) of important molecules. Their individual interaction and crosstalk with phytohormones and H2S are also discussed. Finally, we introduce and summarize the little information available about NOmela, an emerging and still very unknown molecule, but that seems to have a stronger potential than MEL and NO separately in mediating plant stress response.

Development and Validation of an LC-MS/MS-Based Method for Quantifying Urinary Endogenous 6-Hydroxymelatonin.

Evaluation of endogenous melatonin (MEL) secretion using its urinary metabolites is useful for the treatment of circadian rhythm sleep disorders. The primary melatonin metabolites excreted in the urine are 6-hydroxymelatonin (6-O-MEL) sulfate (S-O-MEL) and 6-O-MEL glucuronate, which result from sequential MEL metabolism by phases I and II drug metabolizing enzymes. To determine the accurate MEL secretion level, these urinary metabolites should be enzymatically deconjugated and converted into MEL. Furthermore, the use of LC-tandem mass spectrometry (LC-MS/MS) is preferable for the precision of this determination. Therefore, as part of our ongoing efforts to ultimately determine the level of MEL secretion, we herein aimed to develop an LC-MS/MS-based quantification method for 6-O-MEL and optimize deconjugation conditions. We determined the LC-MS/MS conditions of 6-O-MEL measurement and optimized the conditions of enzymatic reactions. The most efficient S-O-MEL deconjugation (102.1%) was achieved with Roche Glucuronidase/Arylsulfatase (from Helix pomatia) at 37 °C, pH-4.0 reaction buffer, and 60 min of reaction time. For human urine samples, the minimum amount of the enzyme required was 5944 units. Under these conditions, the accuracy and precision values of the 6-O-MEL determination (relative errors and standard deviation) were -3.60--0.47% and <6.80%, respectively. Finally, we analyzed the total amount of MEL metabolites excreted in 24-h urine samples; it was 6.70-11.28 µg in three subjects, which is comparable with the values reported till date. Thus, we have established a new method of measuring the total 6-O-MEL in human urine samples using an LC-MS/MS coupled with the prerequisite deconjugation reaction.

Reference intervals for 6-sulfatoxymelatonin in urine: A meta-analysis.

Despite the essential functions of melatonin in the human body, until now no norms of the amount of melatonin produced overnight have been established. Measuring the amount of the main urinary melatonin metabolite 6-sulfatoxymelatonin (aMT6s), corrected for creatinine, in the first morning void is the most simple as well as reliable method to evaluate the total amount of melatonin produced at night. We performed a meta-analysis to provide reference estimates and intervals by consolidating data from multiple studies. A total of 68 studies, representing 17,847 subjects, were retained for the analysis. No gender differences could be found in aMT6s values in this meta-review. aMT6s excretion is very high during the first 5 years of life, flattens out in adolescence with gradual decline continuing to 50-60 years, after which the decline stagnates and a limited increase occurs around about 60 years of age. This late increase may suggest the premature death of individuals with low aMT6s levels, as lower aMT6s levels are found in various disorders, such as cardiovascular diseases, cancer and neurodegenerative disorders. Our aMT6s values can be used to identify individuals with a possible melatonin deficiency.

Evaluation of CYP1A2 activity: Relationship between the endogenous urinary 6-hydroxymelatonin to melatonin ratio and paraxanthine to caffeine ratio in dried blood spots.

The suitability of the endogenous 6-hydroxymelatonin/melatonin urinary metabolic ratio as a surrogate for the paraxanthine/caffeine ratio to predict cytochrome P450 1A2 (CYP1A2) activity was assessed in this study. Twelve healthy volunteers completed four study sessions spread over 1 month (including overnight urine collection with first morning voids collected separately). Except for the third session, volunteers were asked to abstain from methylxanthine-containing beverages and foods at least 24 h before urine collection. At the end of urine collection, subjects were given a caffeinated beverage and capillary blood samples were collected 2 h after the drink administration. A significant linear relationship between the 6-hydroxymelatonin/melatonin ratios from 12-h urine samples and first morning voids was observed (R2  = 0.876, p < 0.0001). In contrast to the paraxanthine/caffeine ratio, consumption of methylxanthine-containing beverages during session three did not significantly influence the 6-hydroxymelatonin/melatonin ratios compared with the other sessions requiring abstinence from caffeine. A larger intra- and interindividual variability in the 6-hydroxymelatonin/melatonin ratios compared with the paraxanthine/caffeine ratio was also observed. A very weak correlation was observed between the paraxanthine/caffeine ratio and both of the endogenous 6-hydroxymelatonin/melatonin ratios (Pearson r < 0.35, p < 0.05). All these results question whether this endogenous metric could adequately reflect CYP1A2 activity or substitute for the probe caffeine. Additional studies with larger study samples are needed to examine this endogenous metric in more details.

Structural basis of the ligand binding and signaling mechanism of melatonin receptors.

Melatonin receptors (MT1 and MT2 in humans) are family A G protein-coupled receptors that respond to the neurohormone melatonin to regulate circadian rhythm and sleep. Numerous efforts have been made to develop drugs targeting melatonin receptors for the treatment of insomnia, circadian rhythm disorder, and cancer. However, designing subtype-selective melatonergic drugs remains challenging. Here, we report the cryo-EM structures of the MT1-Gi signaling complex with 2-iodomelatonin and ramelteon and the MT2-Gi signaling complex with ramelteon. These structures, together with the reported functional data, reveal that although MT1 and MT2 possess highly similar orthosteric ligand-binding pockets, they also display distinctive features that could be targeted to design subtype-selective drugs. The unique structural motifs in MT1 and MT2 mediate structural rearrangements with a particularly wide opening on the cytoplasmic side. Gi is engaged in the receptor core shared by MT1 and MT2 and presents a conformation deviating from those in other Gi complexes. Together, our results provide new clues for designing melatonergic drugs and further insights into understanding the G protein coupling mechanism.

Evaluation of multiple reaction monitoring cubed performed by a quadrupole-linear ion trap mass spectrometer for quantitative determination of 6-sulfatoxymelatonin in urine.

Liquid chromatography (LC) - mass spectrometry quantitative analysis of substances in biological samples is usually performed in the multiple reaction monitoring (MRM) variant. In complex biological matrices, strong interferences can be observed when using the LC-MRM method. Interference levels can be significantly reduced by using LC - multiple reaction monitoring cubed (MRM3). 6-sulfatoxymelatonin (6-SM) is a metabolite of melatonin, an important regulator of many biological processes. The quantitative analysis of 6-SM in urine allows monitoring of the melatonin level in the blood. The aim of the present work was to evaluate the LC-MRM3 method for the quantitative determination of 6-SM in urine. We found that for 6-SM in aqueous solutions, under some parameters of the MRM3 experiment, the effect of degradation of the MRM3 signal is observed. When analyzing 6-SM in urine, this signal degradation effect was significantly reduced. We have shown that optimization of such parameters of the MRM3 method as the linear ion trap fill time, the number of scans to sum, and the range of triple-stage scan allows obtaining the LC-MRM3 method, which is comparable to the LC-MRM in sensitivity and significantly exceeds it in selectivity.

Urinary 6-sulfatoxymelatonin Levels and Prostate Cancer Risk among Men in the Multiethnic Cohort.

BACKGROUND: The circadian hormone melatonin has anticancer properties, and prior studies suggest a positive association between low melatonin and prostate cancer risk. The purpose of this study was to examine urinary melatonin levels and prostate cancer in a racially/ethnically diverse cohort. METHODS: We conducted a nested case-control study, including 1,263 prostate cancer cases and 2,346 controls, sampled from participants in the Multiethnic Cohort Study with prediagnostic urine samples assayed for 6-sulfatoxymelatonin, the primary melatonin metabolite. Conditional logistic regression was used to examine the association between melatonin levels and the development of prostate cancer outcomes (all incident cases, advanced, lethal, high-grade, and aggressive), overall and by race/ethnicity. RESULTS: Among 1,263 cases, 135 were advanced stage, 101 were lethal cases, and 282 were high-grade disease. Median melatonin levels were similar in controls [17.12 ng/mL; interquartile range (IQR), 19.78] and cases (17.93 ng/mL; IQR, 19.76), and we found no significant association between urinary melatonin levels and prostate cancer risk overall or in any clinical or racial subgroup. CONCLUSIONS: In this diverse cohort, there was no significant association between melatonin and any prostate cancer outcome, nor were there any differences by racial/ethnic group. IMPACT: These results do not support a strong association between melatonin levels and risk of prostate cancer.

Simultaneous determination of melatonin and 6-hydroxymelatonin in human overnight urine by LC-MS/MS.

For the quantification of the pineal hormone melatonin and its metabolite, 6-hydroxymelatonin, in human overnight urine, a single accurate method by liquid chromatography-tandem mass spectrometry (LC-MS/MS) has been developed. Urine samples were deconjugated using ß-glucuronidase/arylsulfatase from Helix pomatia before solid phase extraction (SPE) purification. Chromatographic separation was performed using a reverse phase C18 column with a 7-minute gradient elution. Water was used as matrix to prepare the calibration standards, and deuterated analogues of melatonin and 6-hydroxymelatonin were used as internal standards. This newly developed method was validated in terms of linearity, accuracy, repeatability, intermediate precision, recovery, matrix effect, and stability according to the guidelines of the European Medicines Agency. The method was successfully applied to the analysis of overnight urine samples from 12 healthy volunteers, showing significant correlations of urinary melatonin and 6-hydroxymelatonin excretion rates with age. The urinary 6-hydroxymelatonin to melatonin ratio was also established and will be assessed in further studies as a potential endogenous metric of CYP1A2 activity.

Anti-Inflammatory Comparison of Melatonin and Its Bromobenzoylamide Derivatives in Lipopolysaccharide (LPS)-Induced RAW 264.7 Cells and Croton Oil-Induced Mice Ear Edema.

The pineal gland is a neuroendocrine organ that plays an important role in anti-inflammation through the hormone melatonin. The anti-inflammatory effects of melatonin and its derivatives have been reported in both in vitro and in vivo models. Our previous study reported the potent antioxidant and neuroprotective activities of bromobenzoylamide substituted melatonin. In silico analysis successfully predicted that melatonin bromobenzoylamid derivatives were protected from metabolism by CYP2A1, which is a key enzyme of the melatonin metabolism process. Therefore, the anti-inflammatory activities of melatonin and its bromobenzoylamide derivatives BBM and EBM were investigated in LPS-induced RAW 264.7 macrophages and croton oil-induced ear edema in mice. The experiments showed that BBM and EBM significantly reduced production of the inflammatory mediators interleukin-6 (IL-6), prostaglandin E2 (PGE2), and nitric oxide (NO) in a dose-dependent manner, but only slightly affected TNF-α in LPS-induced RAW 264.7 macrophages. This suggests that modifying melatonin at either the N1-position or the N-acetyl side chain affected production of NO, PGE2 and IL-6 in in vitro model. In the croton oil-induced mouse ear edema model, BBM, significantly decreased ear edema thickness at 2-4 h. It leads to conclude that bromobenzoylamide derivatives of melatonin may be one of the potential candidates for a new type of anti-inflammatory agent.

Metabolic responses to polychromatic LED and OLED light at night.

Light exposure at night has various implications for human health, but little is known about its effects on energy metabolism during subsequent sleep. We investigated the effects of polychromatic white light using conventional light-emitting diodes (LED) and an alternative light source, organic light-emitting diodes (OLED), producing reduced spectral content in the short wavelength of blue light (455 nm). Ten male participants were exposed to either LED, OLED (1000 lx), or dim (< 10 lx) light for 4 h before sleep in a metabolic chamber. Following OLED exposure, energy expenditure and core body temperature during sleep were significantly decreased (p < 0.001). Fat oxidation during sleep was significantly reduced (p = 0.001) after the exposure to LED compared with OLED. Following exposure to OLED, fat oxidation positively correlated with the 6-sulfatoxymelatonin levels, suggesting that the role of melatonin in lipolysis differs depending on the light. These findings advance our knowledge regarding the role of light in energy metabolism during sleep and provide a potential alternative to mitigate the negative consequences of light exposure at night.

Enhanced anti-angiogenic activity of novel melatonin-like agents.

Hypoxia-inducible factor-1 (HIF-1) plays an important role in cellular responses to hypoxia, including the transcriptional activation of several genes involved in tumor angiogenesis. Melatonin, also known as N-acetyl-5-methopxytryptamine, is produced naturally by the pineal gland and has anti-angiogenic effects in cancer through its ability to modulate HIF-1α activity. However, the use of melatonin as a therapeutic is limited by its low oral bioavailability and short half-life. Here, we synthesized melatonin-like molecules with enhanced HIF-1α targeting activity and less toxicity and investigated their effects on tumor growth and angiogenesis, as well as the underlying molecular mechanisms. Among melatonin derivatives, N-butyryl-5-methoxytryptamine (NB-5-MT) showed the most potent HIF-1α targeting activity. This molecule was able to (a) reduce the expression of HIF-1α at the protein level, (b) reduce the transcription of HIF-1α target genes, (c) reduce reactive oxygen species (ROS) generation, (d) decrease angiogenesis in vitro and in vivo, and (e) suppress tumor size and metastasis. In addition, NB-5-MT showed improved anti-angiogenic activity compared with melatonin due to its enhanced cellular uptake. NB-5-MT is thus a promising lead for the future development of anticancer compounds with HIF-1α targeting activity. Given that HIF-1α is overexpressed in the majority of human cancers, the melatonin derivative NB-5-MT could represent a novel potent therapeutic agent for cancer.

N-Nitrosomelatonin, an efficient nitric oxide donor and transporter in Arabidopsis seedlings.

Nitric oxide (NO) produced in plant cells has the unique ability to interact with various other biomolecules, thereby facilitating its own as well as their signaling and associated actions at their sites of biosynthesis and at other sites via transcellular long distance transport of the molecular complexes. Melatonin (Mel) is one such biomolecule produced in plant cells which has fascinated plant biologists with regard to its molecular crosstalk with other molecules to serve its roles as a growth regulator. Present work reports the synthesis of N-nitrosomelatonin (NOMela) and its preferential uptake by Arabidopsis seedlings roots and long distance transport to the leaves through vascular strands. Equimolar (250 µM) concentrations of NOMela and S-nitrosoglutathione (GSNO) in aqueous solutions bring about 52.8% more release of NO from NOMela than from GSNO. Following confocal laser scanning microscopic (CLSM) imaging, Pearson's correlation coefficient analysis of the Scatter gram of endogenously taken up NOMela demonstrates significant NO signal in roots emanating from mitochondria. NOMela (250 µM) taken up by Arabidopsis seedling roots also proved more efficient as a NO transporter from primary root to leaves than 250 µM of GSNO. These novel observations on NOMela thus hold promise to decipher its crucial role as a NO carrier and reservoir in plant cells, and also as a facilitator of melatonin action in plant development.

Presence of Peripheral Neuropathy Does Not Affect Urine 6-Sulfatoxymelatonin Levels in Type 2 Diabetics.

BACKGROUND: Oxidative stress plays a crucial role in the pathogenesis of diabetic peripheral neuropathy. Melatonin is one of the most powerful antioxidant substances and its role in the pathogenesis of diabetes has been the focus of much research. However, no data exist on melatonin levels in diabetic peripheral neuropathy. We investigated how levels of urinary 6-sulfatoxymelatonin, the main metabolite of melatonin, differed in diabetic peripheral neuropathy. METHODS: A total of 127 participants were enrolled into 3 groups: diabetic neuropathy (n=43), diabetes but no neuropathy (n=44), and controls (n=40). Neuropathy was diagnosed using the Michigan Neuropathy Screening Instrument. Melatonin level was evaluated by measuring 24-hour urine 6-sulfatoxymelatonin levels. RESULTS: We found significant differences in urinary 6-sulfatoxymelatonin levels between the 3 groups (p=0.023). The distribution of 6-sulfatoxymelatonin among all diabetic participants was significantly lower than in the control group (p=0.006). However, there was no difference in diabetics with and without neuropathy (p=0.792). 6-sulfatoxymelatonin levels were negatively and weakly correlated with plasma glucose(r = -0.211, p=0.017) and positively and weakly correlated with microalbuminuria (r= 0.209, p=0.023). Regression analysis was found a significant relationship between age (B = 0.826, 95% Cl=0.227 to 1.426), insulin use (B = 14.584, 95% CI= 3.857 to 25.311), glomerular filtration rate (B = 0.248, 95% CI= 0.018 to 0.478) and 6-sulfatoxymelatonin levels. 6-sulfatoxymelatonin levels in insulin users were significantly higher than they were in nonuser diabetics (p=0.001). CONCLUSION: Urinary 6-sulfatoxymelatonin levels were lower in diabetics but the presence of neuropathy did not affect 6-sulfatoxymelatonin levels. Insulin may improve melatonin levels in diabetics.

Exploratory assessment of pineal gland volume, composition, and urinary 6-sulfatoxymelatonin levels on prostate cancer risk.

INTRODUCTION: Melatonin levels are partially driven by the parenchyma volume of the pineal gland. Low urinary levels of 6-sulfatoxymelatonin have been associated with increased risk of advanced prostate cancer, but the relationship between pineal gland volume and composition and prostate cancer risk has not been examined. MATERIALS AND METHODS: We utilized data from 864 men from the AGES-Reykjavik Study with complete pineal gland volumes and urinary 6-sulfatoxymelatonin measurements. Pineal parenchyma, calcification, and cyst volumes were calculated from brain magnetic resonance imaging. Levels of 6-sulfatoxymelatonin were assayed from prediagnostic urine samples. We calculated Pearson correlation coefficients between parenchyma volume and urinary 6-sulfatoxymelatonin levels. We used Cox proportional hazards regression to calculate multivariable hazard ratios (HRs) and 95% confidence intervals (95% CIs) comparing prostate cancer risk across parenchyma volume tertiles and across categories factoring in parenchyma volume, gland composition, and urinary 6-sulfatoxymelatonin level. RESULTS: Parenchyma volume was moderately correlated with urinary 6-sulfatoxymelatonin level (r = .24; p < .01). There was no statistically significant association between parenchyma volume tertile and prostate cancer risk. Men with high parenchyma volume, pineal cysts and calcifications, and low urinary 6-sulfatoxymelatonin levels had almost twice the risk of total prostate cancer as men with low parenchyma volume, no pineal calcifications or cysts, and low urinary 6-sulfatoxymelatonin levels (HR: 1.98; 95% CI: 1.02, 3.84; p: .04). CONCLUSIONS: Although parenchyma volume is not associated with prostate cancer risk, pineal gland composition and other circadian dynamics may influence risk for prostate cancer. Additional studies are needed to examine the interplay of pineal gland volume, composition, and melatonin levels on prostate cancer risk.