Melatonin Receptor Agonist Piromelatine Ameliorates Impaired Glucose Metabolism in Chronically Stressed Rats Fed a High-Fat Diet

The Role of Piromelatine on Peripheral and Hippocampal Insulin Resistance in Rat Offspring Exposed to Chronic Maternal Stress

Prenatal stress (PNS), which alters the hypothalamic-pituitary-adrenal axis function in the offspring, predisposes to insulin resistance (IR) in later life and is associated with numerous disorders, including cognitive and memory impairments. At present, our main goal is to assess the effects of chronic piromelatine (Pir) administration, a melatonin analogue, on PNS-provoked IR in the periphery and the hippocampus in male and female offspring. Pregnant Sprague-Dawley rats were exposed to chronic stress (one short-term stressor on a daily basis and one long-term stressor on a nightly basis) from the first gestation week until birth. Vehicle or Pir 20 mg/kg were administered intraperitoneally for 21 days. Plasma glucose, serum insulin levels, and the homeostasis model assessment of insulin resistance (HOMA-IR) were determined as markers of peripheral IR. For the hippocampal IR assessment, insulin receptors (IRs) and glucose transporter 4 (GLUT4) were examined. Prenatally stressed offspring of both sexes indicated enhanced plasma glucose and serum insulin concentrations, increased HOMA-IR, and decreased hippocampal GLUT4 only in male rats. The PNS-induced changes were corrected by chronic treatment with Pir. The present results suggest that the melatoninergic compound Pir exerts beneficial effects on altered glucose/insulin homeostasis in PNS-exposed offspring.

Industrial and academic approaches to the search for alternative melatonin receptor ligands: An historical survey

The search for melatonin receptor agonists formed the main part of melatonin medicinal chemistry programs for the last three decades. In this short review, we summarize the two main aspects of these programs: the development of all the necessary tools to characterize the newly synthesized ligands at the two melatonin receptors MT1 and MT2, and the medicinal chemist's approaches to find chemically diverse ligands at these receptors. Both strategies are described. It turns out that the main source of tools were industrial laboratories, while the medicinal chemistry was mainly carried out in academia. Such complete accounts are interesting, as they delineate the spirits in which the teams were working demonstrating their strength and innovative character. Most of the programs were focused on nonselective agonists and few of them reached the market. In contrast, discovery of MT1-selective agonists and melatonergic antagonists with proven in vivo activity and MT1 or MT2-selectivity is still in its infancy, despite the considerable interest that subtype selective compounds may bring in the domain, as the physiological respective roles of the two subtypes of melatonin receptors, is still poorly understood. Poly-pharmacology applications and multitarget ligands have also been considered.

Chronic Piromelatine Treatment Alleviates Anxiety, Depressive Responses and Abnormal Hypothalamic-Pituitary-Adrenal Axis Activity in Prenatally Stressed Male and Female Rats

The prenatal stress (PNS) model in rodents can induce different abnormal responses that replicate the pathophysiology of depression. We applied this model to evaluate the efficacy of piromelatine (Pir), a novel melatonin analog developed for the treatment of insomnia, in male and female offspring. Adult PNS rats from both sexes showed comparable disturbance associated with high levels of anxiety and depressive responses. Both males and females with PNS demonstrated impaired feedback inhibition of the hypothalamic-pituitary-adrenal (HPA) axis compared to the intact offspring and increased glucocorticoid receptors in the hippocampus. However, opposite to female offspring, the male PNS rats showed an increased expression of mineralocorticoid receptors in the hippocampus. Piromelatine (20 mg/kg, i.p., for 21 days injected from postnatal day 60) attenuated the high anxiety level tested in the open field, elevated plus-maze and light-dark test, and depressive-like behavior in the sucrose preference and the forced swimming tests in a sex-specific manner. The drug reversed to control level stress-induced increase of plasma corticosterone 120 min later in both sexes. Piromelatine also corrected to control level the PNS-induced alterations of corticosteroid receptors only in male offspring. Our findings suggest that the piromelatine treatment exerts beneficial effects on impaired behavioral responses and dysregulated HPA axis in both sexes, while it corrects the PNS-induced changes in the hippocampal corticosteroid receptors only in male offspring.

The extent of involvement of ouabain, hippocampal expression of Na+/K+-ATPase, and corticosterone/melatonin receptors ratio in modifying stress-induced behavior differs according to the stressor in context

The aim of this study was to assess the effect of two types of stressors, regarding the extent of involvement of ouabain (OUA), hippocampal sodium/potassium ATPase (NKA) expression, and the hippocampal corticosterone receptors (CR)/melatonin receptors (MR) expression ratio, on the behavioral and cardiovascular responses and on the hippocampal cornu ammonis zone 3 (CA3) and dentate gyrus (DG). Thirty adult male Wistar albino rats aged 7-8 months were exposed to either chronic immobilization or a disturbed dark/light cycle and treated with either ouabain or vehicle. In the immobilized group, in the absence of hippocampal corticosterone (CORT) changes, rats were non-responsive to stress, despite experiencing increased pulse rate, downregulated hippocampal sodium/potassium pump, and enhanced hippocampal CR/MR expression ratio. Prolonged darkness precipitated a reduced upright attack posture, with elevated CORT against hippocampal MR downregulation. Both immobilization and, to a lesser extent, prolonged darkness stress resulted in histopathological and ultrastructural neurodegenerative changes in the hippocampus. OUA administration did not change the behavioral resilience in restrained rats, despite persistence of the underlying biochemical derangements, added to decreased CORT. On the contrary, with exposure to short photoperiods, OUA reverted the behavior towards a combative reduction of inactivity, with unvaried CR/MR and CORT, while ameliorating hippocampal neuro-regeneration, with co-existing NKA and MR repressions. Therefore, the extent of OUA, hippocampal NKA expression, and CR/MR expression, and subsequent behavioral and cardiac responses and hippocampal histopathology, differ according to the type of stressor, whether immobilization or prolonged darkness.

Melatonin Supplementation and Anthropometric Indices: A Randomized Double-Blind Controlled Clinical Trial

Obesity, as the most common metabolic disorder in the world, is characterized by excess body fat. This study is aimed at determining the effects of melatonin supplementation on body weight, nody mass index (BMI), waist circumference (WC), and body fat mass percentage (BFMP) in people with overweight or obesity. Thirty eight overweight or class-I obese adult individuals were recruited in the study (8 men and 30 women). Participants prescribed a weight-loss diet and then randomly were allocated to melatonin or placebo groups. Participants received either a 3-milligram melatonin or placebo tablet per day for 12 weeks. In order to assess differences at the significance level of 0.05, repeated measure ANOVA and paired t-test were used. According to the results, a significant reduction was found in participants' body weight, WC, and BMI in both groups (p = 0.001). However, for the last six weeks, significant reductions of these parameters were observed only in the melatonin group (p = 0.01). The BFMP of participants in the melatonin group showed a significant reduction at the end of the study compared to the initial measurements (p = 0.008). Nevertheless, the results of the present study alone are not sufficient to conclude on the effects of melatonin consumption on anthropometric indices, and it seems that further studies are required in this regard.

Hypothalamus-pituitary-adrenal Axis in Glucolipid metabolic disorders

With the change of life style, glucolipid metabolic disorders (GLMD) has become one of the major chronic disorders causing public health and clinical problems worldwide. Previous studies on GLMD pay more attention to peripheral tissues. In fact, the central nervous system (CNS) plays an important role in controlling the overall metabolic balance. With the development of technology and the in-depth understanding of the CNS, the relationship between neuro-endocrine-immunoregulatory (NEI) network and metabolism had been gradually illustrated. As the hub of NEI network, hypothalamus-pituitary-adrenal (HPA) axis is important for maintaining the balance of internal environment in the body. The relationship between HPA axis and GLMD needs to be further studied. This review focuses on the role of HPA axis in GLMD and reviews the research progress on drugs for GLMD, with the hope to provide the direction for exploring new drugs to treat GLMD by taking the HPA axis as the target and improve the level of prevention and control of GLMD.

Melatonin prevents early pituitary dysfunction induced by sucrose-rich diets

While physiological levels of glucocorticoids are required to ensure proper functions of the body, consistently high levels may engender several deleterious consequences. We have previously shown an increase in the activity of the hypothalamic-pituitary-adrenal (HPA) axis in rats fed sucrose-rich diets (SRD). The main goal of this study was to analyze the processes involved in the modulation of the pituitary production of ACTH by SRD, and to test melatonin as a possible therapeutic agent for the prevention of the HPA axis dysfunction. Male Wistar rats were fed standard chow and either SRD (30% sucrose in the drinking water) or plain water for three weeks. Melatonin was administered as subcutaneous pellets. Results showed that SRD treatment induced an increase in systemic ACTH and corticosterone levels and a decrease in melatonin levels. In the pituitary gland, we also detected an increase in the expression levels of proopiomelanocortin (POMC) that was accompanied by increased levels of: lipoperoxides, nitro-tyrosine modified proteins, catalase, heme oxygenase-1, interleukin-1β mRNA, and by an increase in the tissue number of inflammatory cells (F4/80 and Iba-1 positive cells). Melatonin treatment prevented all these systemic and pituitary changes as well as the increase in POMC expression induced by incubation of AtT-20 corticotrophs with conditioned media obtained from stimulated macrophages. In conclusion, stimulation of POMC/ACTH production in rats fed a SRD could involve the generation of oxidative stress and inflammation in the pituitary gland. Melatonin treatment prevented these effects and normalized the activity of the HPA axis.

The multiple protective roles and molecular mechanisms of melatonin and its precursor N-acetylserotonin in targeting brain injury and liver damage and in maintaining bone health

Melatonin is a neurohormone associated with sleep and wakefulness and is mainly produced by the pineal gland. Numerous physiological functions of melatonin have been demonstrated including anti-inflammation, suppressing neoplastic growth, circadian and endocrine rhythm regulation, and its potent antioxidant activity as well as its role in regeneration of various tissues including the nervous system, liver, bone, kidney, bladder, skin, and muscle, among others. In this review, we summarize the recent advances related to the multiple protective roles of melatonin receptor agonists, melatonin and N-acetylserotonin (NAS), in brain injury, liver damage, and bone health. Brain injury, including traumatic brain injury, ischemic stroke, intracerebral hemorrhage, subarachnoid hemorrhage, and newborn perinatal hypoxia-ischemia encephalopathy, is a major cause of mortality and disability. Liver disease causes serious public health problems and various factors including alcohol, chemical pollutants, and drugs induce hepatic damage. Osteoporosis is the most common bone disease in humans. Due in part to an aging population, both the cost of care of fracture patients and the annual fracture rate have increased steadily. Despite the discrepancy in the pathophysiological processes of these disorders, time frames and severity, they may share several common molecular mechanisms. Oxidative stress is considered to be a critical factor in these pathogeneses. We update the current state of knowledge related to the molecular processes, mainly including anti-oxidative stress, anti-apoptosis, autophagy dysfunction, and anti-inflammation as well as other properties of melatonin and NAS. Particularly, the abilities of melatonin and NAS to directly scavenge oxygen-centered radicals and toxic reactive oxygen species, and indirectly act through antioxidant enzymes are disscussed. In this review, we summarize the similarities and differences in the protection provided by melatonin and/or NAS in brain, liver and bone damage. We analyze the involvement of melatonin receptor 1A (MT1), melatonin receptor 1B (MT2), and melatonin receptor 1C (MT3) in the protection of melatonin and/or NAS. Additionally, we evaluate their potential clinical applications. The multiple mechanisms of action and multiple organ-targeted properties of melatonin and NAS may contribute to development of promising therapies for clinical trials.