A. Carpentieri

New perspectives in melatonin uses

This review summarizes the metabolism, secretion, regulation and sites of action of melatonin. An updated description of the melatonin receptors, including their signal transduction mechanisms, distribution and characterization of receptor genes, is given. Special emphasis is focused on the clinical aspects and potential uses of melatonin in the sleep-wake rhythms, in the immune function, in cancer therapy, in neuroprotection against oxidative damage and antioxidant activities in different tissues. Finally, combined effects of melatonin with other drugs are discussed.

Retinal Ganglion Cells Are Autonomous Circadian Oscillators Synthesizing N-Acetylserotonin during the Day

Retinal ganglion cells send visual and circadian information to the brain regarding the environmental light-dark cycles. We investigated the capability of retinal ganglion cells of synthesizing melatonin, a highly reliable circadian marker that regulates retinal physiology, as well as the capacity of these cells to function as autonomous circadian oscillators. Chick retinal ganglion cells presented higher levels of melatonin assessed by radioimmunoassay during both the subjective day in constant darkness and the light phase of a light-dark cycle. Similar changes were observed in mRNA levels and activity of arylalkylamine N-acetyltransferase, a key enzyme in melatonin biosynthesis, with the highest levels of both parameters during the subjective day. These daily variations were preceded by the elevation of cyclic-AMP content, the second messenger involved in the regulation of melatonin biosynthesis. Moreover, cultures of immunopurified retinal ganglion cells at embryonic day 8 synchronized by medium exchange synthesized a [3H]melatonin-like indole from [3H]tryptophan. This [3H]indole was rapidly released to the culture medium and exhibited a daily variation, with levels peaking 8 h after synchronization, which declined a few hours later. Cultures of embryonic retinal ganglion cells also showed self-sustained daily rhythms in arylalkylamine N-acetyltransferase mRNA expression during at least three cycles with a period near 24 h. These rhythms were also observed after the application of glutamate. The results demonstrate that chick retinal ganglion cells may function as autonomous circadian oscillators synthesizing a melatonin-like indole during the day.

Synthesis of retinal ganglion cell phospholipids is under control of an endogenous circadian clock: Daily variations in phospholipid‐synthesizing enzyme activities

Retinal ganglion cells (RGCs) are major components of the vertebrate circadian system. They send information to the brain, synchronizing the entire organism to the light‐dark cycles. We recently reported that chicken RGCs display daily variations in the biosynthesis of glycerophospholipids in constant darkness (DD). It was unclear whether this rhythmicity was driven by this population itself or by other retinal cells. Here we show that RGCs present circadian oscillations in the labeling of [32P]phospholipids both in vivo in constant light (LL) and in cultures of immunopurified embryonic cells. In vivo, there was greater [32P]orthophosphate incorporation into total phospholipids during the subjective day. Phosphatidylinositol (PI) was the most 32P‐labeled lipid at all times examined, displaying maximal levels during the subjective day and dusk. In addition, a significant daily variation was found in the activity of distinct enzymes of the pathway of phospholipid biosynthesis and degradation, such as lysophospholipid acyltransferases (AT II), phosphatidate phosphohydrolase (PAP), and diacylglycerol lipase (DGL) in cell preparations obtained in DD, exhibiting differential but coordinated temporal profiles. Furthermore, cultures of immunopurified RGCs synchronized by medium exchange displayed a circadian fluctuation in the phospholipid labeling. The results demonstrate that chicken RGCs contain circadian oscillators capable of generating metabolic oscillations in the biosynthesis of phospholipids autonomously.

Circadian Phototransduction and the Regulation of Biological Rhythms

The vertebrate circadian system that controls most biological rhythms is composed of multiple oscillators with varied hierarchies and complex levels of organization and interaction. The retina plays a key role in the regulation of daily rhythms and light is the main synchronizer of the circadian system. To date, the identity of photoreceptors/photopigments responsible for the entrainment of biological rhythms is still uncertain; however, it is known that phototransduction must occur in the eye because light entrainment is lost with eye removal. The retina is also rhythmic in physiological and metabolic activities as well as in gene expression. Retinal oscillators may act like clocks to induce changes in the visual system according to the phase of the day by predicting environmental changes. These oscillatory and photoreceptive capacities are likely to converge all together on selected retinal cells. The aim of this overview is to present the current knowledge of retinal physiology in relation to the circadian timing system.

Melatonin and periodontal tissues: Molecular and clinical perspectives

&NA; Periodontal disease is a frequent chronic inflammatory pathology that implies the destruction of the tissues supporting the teeth, which represents a high sanitary cost. It usually appears associated with other systemic conditions such as diabetes, metabolic syndrome, depression and Alzheimer disease among others. The presence of melatonin and its receptors in the oral cavity supports the hypothesis that this hormone could play a role in homeostasis of periodontal tissues. In the present review we will discuss the potential role of melatonin, a circadian synchronizing hormone, with proved antiinflammatory and antioxidant profile, in the pathogenesis and treatment of periodontitis. Particular emphasis will be placed on the role of the indolamine in the treatment of periodontal disease when this oral condition is comorbid with other pathologies that would also benefit from the therapeutic potential of melatonin and its analogs through diverse mechanisms. Graphical abstract Melatonin actions in periodontitis associated to diabetes. MEL could improve periodontal status in diabetic patients, due its antiinflammatory properties. Figure. No caption available.

Melatonin not only restores but also prevents the inhibition of the intestinal Ca2 + absorption caused by glutathione depleting drugs

We have previously demonstrated that melatonin (MEL) blocks the inhibition of the intestinal Ca(2+) absorption caused by menadione (MEN). The purpose of this study were to determine whether MEL not only restores but also prevents the intestinal Ca(2+) absorption inhibited either by MEN or BSO, two drugs that deplete glutathione (GSH) in different ways, and to analyze the mechanisms by which MEN and MEL alter the movement of Ca(2+) across the duodenum. To know this, chicks were divided into four groups: 1) controls, 2) MEN treated, 3) MEL treated, and 4) treated sequentially with MEN and MEL or with MEN and MEL at the same time. In a set of experiments, chicks treated with BSO or sequentially with BSO and MEL or with BSO and MEL at the same time were used. MEL not only restored but also prevented the inhibition of the chick intestinal Ca(2+) absorption produced by either MEN or BSO. MEN altered the protein expression of molecules involved in the transcellular as well as in the paracellular pathway of the intestinal Ca(2+) absorption. MEL restored partially both pathways through normalization of the O2(-) levels. The nitrergic system was not altered by any treatment. In conclusion, MEL prevents or restores the inhibition of the intestinal Ca(2+) absorption caused by different GSH depleting drugs. It might become one drug for the treatment of intestinal Ca(2+) absorption under oxidant conditions having the advantage of low or null side effects.

Past, Present, and Future of Melatonin’s Clinical Uses

Melatonin (MEL) is a pleiotropic hormone which exerts its action through different mechanisms, either by binding to its receptors or by acting as an antioxidant molecule and ROS scavenger. Its mechanisms of action together with the wide distribution of MT1 and MT2 receptors have provoked an ever-increasing number of clinical trials in the last two decades. These studies have evaluated the exogenous administration of MEL in different doses and formulations to prevent or to treat many health disorders. The predominant field of research has been the treatment of insomnia and other circadian rhythm disorders due to the confirmed resynchronizing properties of this indolamine. However, in the last decade, a profound interest has arisen concerning its potential therapeutic value in different conditions such as cancer, cardiovascular diseases, gastrointestinal problems, and inflammatory states, among others. The relatively low toxicity of MEL over a wide range of doses has made the research even more promising. However, new multicenter clinical trials could shed light on different aspects of MEL’s clinical uses contributing thus to clarify the conditions in which MEL might be considered as a first-line therapeutical strategy and to identify when the combination of MEL with other drugs is necessary. In this chapter, we revise the milestones in the field of MEL research from its discovery to the present time and analyze the future perspectives of its clinical uses.

Melatonin: Basic and Clinical Aspects

Melatonin (MEL), the “hormone of darkness,” is an indolamine mainly secreted at night by the pineal gland. It is also synthesized by other tissues, being the enterochromaffin cells the most important extrapineal sites. The ubiquity, pleiotropy, and complexity are the three terms that summarize the properties and actions of MEL. Two well-characterized enzymes participate in its synthesis: N-acetyltransferase, the first-rate limiting enzyme in MEL production, which converts serotonin to N-acetylserotonin (NAS), and hydroxyindole-O-methyltransferase, which converts NAS to MEL. Most of the MEL’s actions are mediated by membrane (MT1 and MT2) and nuclear (ROR/RZR) receptors. However, some MEL effects seem to be independent of the involvement of receptors or related to Ca2+-binding proteins. The signal transduction pathways triggered by MEL involve the AC/cAMP/PKA/CREB, phospholipase C (PLC)-β and PLC-η, and Rafs/MEK1/2/ERK1/2 cascades. MEL participates in the circadian rhythms, the modulation of season changes, in reproduction, as well as an antioxidant, antiapoptotic, anti-inflammatory, oncostatic, and anticonvulsant drug. Exogenous MEL is employed in a number of physiopathological conditions, mainly for the treatment of sleep disorders and jet lag. The antioxidant properties of MEL have been proven to be beneficial to patients with rheumatoid arthritis, females with infertility, elderly patients with primary essential hypertension, and multiple sclerosis patients. The spectrum of the uses of MEL seems to be wide, although more investigation is needed in order to know better the molecular mechanisms and the possible side effects.

Clinical and molecular studies related to bone metabolism in patients with congenital adrenal hyperplasia

Abstract Patients with congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency need glucocorticoid (GC) therapy, which alters bone mineral metabolism. We analyze clinical and biochemical parameters and different polymorphisms of candidate genes associated with bone mineral density (BMD) in CAH patients. The CAH patients treated with GC and healthy controls were studied. Anthropometric parameters, biochemical markers of bone turnover, and BMD were evaluated. Polymerase chain reaction technique was used to genotype different candidate genes. The 192-192 genotype frequency (IGF-I) was lower in poorly controlled patients than that from controls. In CAH patients, FF genotype (vitamin D receptor, VDR) correlated with lower lumbar spine BMD and there was a significant association between the 0-0 genotype (IGF-I) and high values of β-CrossLaps and a low total BMD. This study contributes to understanding of the association of genetic determinants of BMD with the variable response to GC treatment in CAH patients and demonstrates the usefulness of these genetic polymorphisms.

Melatonin: A protective hormone of intestinal calcium absorption?

Introduction: Osteogenesis distraction (DO) is a surgical technique that allows distraction of the fracture callus. It has been used extensively in endochondral long bones but not in the craniofacial skeleton of endomembranous origin. Mandibular alveolar bone of endomembranous origin contains teeth sockets; it is a functional bone that undergoes bone turnover at a higher rate than other bone tissues. The aim of our work was to present the development of an experimental model of DO in rat mandibular alveolar bone including all stages, i.e. animal procedures, laboratory determinations, histological procedures and histomorphometric measurements. Methods: 8 Wistar rats, 80 g bw, underwent extraction of all mandibular molars. At 400 g bw, right hemimandibular osteotomy was performed and the device was placed. After 6 days (latency) it was activated (0.175 mm/d once a day/ 6 days) and then left in place 28 days (consolidation phase). Rats were sacrificed and hemimandibles were resected. The technique was standardized to perform radiographs and hemimandible orientation was adjusted to allow obtaining comparable histologic sections. A method to record and compare these measurements was designed. H&E stained mesiodistally oriented hemimandible sections were obtained. Screw loosening and loss of the device during the consolidation phase were initial problems (SAIO, 2008). The original design was perfected to avoid mobility. Results: The new, improved device remained in place throughout the experiment. Comparable mesiodistally oriented sections were obtained. Conclusion: This experimental model of mandibular DO will allow studying the cellular and molecular events that take place during DO under different experimental conditions. This article is part of a Special Issue entitled AAOMM 2010 Abstracts.