Does hepatic metabolism of melatonin affect the endogenous serum melatonin level in man?

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.

Regulation effects of melatonin on bone marrow mesenchymal stem cell differentiation

Melatonin's therapeutic potential has been highly underestimated because its biological functional roles are diverse and relevant mechanisms are complicated. Among the numerous biological activities of melatonin, its regulatory effects on pluripotent mesenchymal stem cells (MSCs), which are found in bone marrow stem cells (BMSCs) and adipose tissue (AD-MSC), have been recently proposed, which has received increasingly more attention in recent studies. Moreover, receptor-dependent and receptor-independent responses to melatonin are identified to occur in these cells by regulating signaling pathways, which drive the commitment and differentiation of MSCs into osteogenic, chondrogenic, or adipogenic lineages. Therefore, the aim of our current review is to summarize the evidence related to the utility of melatonin as a regulatory agent by focusing on its relationship with the differentiation of MSCs. In particular, we aimed to review its roles in promoting osteogenic and chondrogenic differentiation and the relevant signaling cascades involved. Also, the roles that melatonin and, particularly, its receptors play in these processes are highlighted.

Inhibition of melatonin metabolism in humans induced by chemical components from herbs and effective prediction of this risk using a computational model

BACKGROUND AND PURPOSE

Herbs which are widely used as food and medicine, are involved in many physiopathological processes. Melatonin is a human hormone, synthesized and secreted by the pineal gland, with a range of biological functions. Here, we have evaluated the potential influences of components extracted from common herbs on melatonin metabolism in humans.

EXPERIMENTAL APPROACH

An in vivo pharmacokinetic study involving 12 healthy subjects, in vitro incubations with human liver microsomes (HLMs) and recombinant human cytochrome P (CYP) isoenzymes and an in silico quantitative structure-activity relationship (QSAR) model analysis using comparative molecular field analysis and comparative molecular similarity indices analysis methods were employed to explore these interactions.

KEY RESULTS

After systematic screening of 66 common herbs, Angelica dahurica exhibited the most potent inhibition of melatonin metabolism in vitro. The in vivo pharmacokinetic study indicated inhibition of melatonin metabolism, with approximately 12- and 4-fold increases in the AUC and C_max of melatonin in human subjects. Coumarins from A. dahurica, including imperatorin, isoimperatorin, phellopterin, 5-methoxypsoralen and 8-methoxypsoralen, markedly inhibited melatonin metabolism with K_i values of 14.5 nM, 38.8 nM, 6.34 nM, 5.34 nM and 18 nM respectively, through inhibition of CYP 1A2, 1A1 and 1B1 in HLMs. A QSAR model was established and satisfactorily predicted the potential risk of coumarins for inhibition of melatonin metabolism in vivo.

CONCLUSION AND IMPLICATIONS

Coumarins from A. dahurica inhibited melatonin metabolism in vivo and in vitro. Our findings provide vital guidance for the clinical use of melatonin.

Melatonin Therapy in Patients with Alzheimer's Disease

Alzheimer's disease (AD) is a major health problem and a growing recognition exists that efforts to prevent it must be undertaken by both governmental and non-governmental organizations. In this context, the pineal product, melatonin, has a promising significance because of its chronobiotic/cytoprotective properties potentially useful for a number of aspects of AD. One of the features of advancing age is the gradual decrease in circulating melatonin levels. A limited number of therapeutic trials have indicated that melatonin has a therapeutic value as a neuroprotective drug in the treatment of AD and minimal cognitive impairment (which may evolve to AD). Both in vitro and in vivo, melatonin prevented the neurodegeneration seen in experimental models of AD. For these effects to occur, doses of melatonin about two orders of magnitude higher than those required to affect sleep and circadian rhythmicity are needed. More recently, attention has been focused on the development of potent melatonin analogs with prolonged effects, which were employed in clinical trials in sleep-disturbed or depressed patients in doses considerably higher than those employed for melatonin. In view that the relative potencies of the analogs are higher than that of the natural compound, clinical trials employing melatonin in the range of 50-100 mg/day are urgently needed to assess its therapeutic validity in neurodegenerative disorders such as AD.

CYP1A2 polymorphisms in slow melatonin metabolisers: a possible relationship with autism spectrum disorder?

BACKGROUND

In some of our patients with intellectual disabilities (ID) and sleep problems, the initial good response to melatonin disappeared within a few weeks after starting treatment. In these patients melatonin levels at noon were extremely high (>50 pg/ml). We hypothesise that the disappearing effectiveness is associated with slow metabolisation of melatonin because of a single nucleotide polymorphism (SNP) of CYP1A2.

METHOD

In this pilot study we analysed DNA extracted from saliva samples of 15 consecutive patients with disappearing effectiveness of melatonin. Saliva was collected at noon and 4 pm for measuring melatonin levels.

RESULTS

In all patients' salivary melatonin levels at noon were >50 or melatonin half time was > 5 h. A SNP was found in eight of 15 patients. The allele 1C was found in two patients and in six patients the 1F allele was found.

CONCLUSIONS

Of 15 patients with disappearing effectiveness of melatonin, seven were diagnosed with autism spectrum disorder, and in four of them a SNP was found. The other eight patients were known with a genetic syndrome. In six of them behaviour was considered to be autistic-type and in three of them a SNP was found. This finding may give a new direction for research into the genetic background of autism.

Melatonin: comprehensive profile

This chapter includes the aspects of melatonin. The drug is synthesized in the pineal gland starting from tryptophane or synthetically by using indole as starting material. Melatonin has been used as an adjunct to interleukin-2 therapy for malignant neoplasms, as contraceptive, in the management of various forms of insomnia, to alleviate jet lag following long flights, and finally as free radical scavenger and hence as an antioxidant and an anti-inflammatory. The chapter discusses the drug metabolism and pharmacokinetics and presents various method of analysis of this drug such as biological analysis, spectroscopic analysis, and chromatographic techniques of separation. It also discusses its physical properties such as solubility characteristics, X-ray powder diffraction pattern, and thermal methods of analysis. The chapter is concluded with a discussion on its biological properties such as activity, toxicity, and safety.

Variation in CYP1A2 activity and its clinical implications: influence of environmental factors and genetic polymorphisms

CYP1A2 is involved in the metabolism of several widely used drugs and endogenous compounds, and in the activation of procarcinogens. Both genetic and environmental factors influence the activity of this enzyme. The current knowledge regarding factors influencing the activity of CYP1A2 is summarized in this review. Substrates, inhibitors and inducers of CYP1A2 activity, as well as phenotyping probes, are discussed. The functional significance and clinical importance of CYP1A2 gene polymorphisms are reviewed and interethnic differences in the distribution of CYP1A2 variant alleles and haplotypes are summarized. Finally, future perspectives for the possible clinical applications of CYP1A2 genotyping are discussed.

Melatonin increases survival and inhibits oxidative and amyloid pathology in a transgenic model of Alzheimer's disease

Increased levels of a 40-42 amino-acid peptide called the amyloid beta protein (A beta) and evidence of oxidative damage are early neuropathological markers of Alzheimer's disease (AD). Previous investigations have demonstrated that melatonin is decreased during the aging process and that patients with AD have more profound reductions of this hormone. It has also been recently shown that melatonin protects neuronal cells from A beta-mediated oxidative damage and inhibits the formation of amyloid fibrils in vitro. However, a direct relationship between melatonin and the biochemical pathology of AD had not been demonstrated. We used a transgenic mouse model of Alzheimer's amyloidosis and monitored over time the effects of administering melatonin on brain levels of A beta, abnormal protein nitration, and survival of the mice. We report here that administration of melatonin partially inhibited the expected time-dependent elevation of beta-amyloid, reduced abnormal nitration of proteins, and increased survival in the treated transgenic mice. These findings may bear relevance to the pathogenesis and therapy of AD.