One molecule, many derivatives: a never-ending interaction of melatonin with reactive oxygen and nitrogen species?

Melatonin treatment improves the antioxidant status and decreases lipid content in brain and liver of rats

This study examines the effect of a daily administration of melatonin for 45 days at two doses (0.5 and 1.0 mg/kg body wt.) on antioxidant status, lipid peroxidation and lipid profile in the brain and liver in rats. Both doses of melatonin caused a significant decrease in lipid peroxidation and the levels of cholesterol, phospholipids, triglycerides and free fatty acids in the examined tissues. Concomitantly, the treatment with melatonin augmented the activity of the brain and liver antioxidant enzymes superoxide dismutase, catalase and glutathione peroxidase as well as increased glutathione levels. These results offer a support to the hypothesis that melatonin in pharmacological amounts effectively reduces oxidative stress and acts as an antihyperlipidemic agent.

Melatonin attenuates metabolic disorders due to streptozotocin-induced diabetes in rats

Enhanced oxidative stress and impairments in nitric oxide synthesis and bioavailability are of considerable importance in the pathogenesis of diabetic vascular diseases. The aim of the present work was to evaluate the metabolic effects of pharmacological doses of the melatonin, a known antioxidant, on streptozotocin-induced diabetic damage in rats. We investigated the indolamine's influence on the cellular redox-balance, nitric oxide (NO) level, and the activities of antioxidative defence enzymes, as well as the activities of enzymes involved in phase II detoxication and NADPH-generating pentose phosphate pathway. Blood glucose, glycated hemoglobin, bilirubin, as well as plasma alanine aminotransferase activities increased and body weight was reduced in rats with streptozotocin-induced (60 mg/kg, i.p.) diabetes (25 days). The NO level was markedly increased in diabetic plasma (by 50%) and aortic tissue (by 30%). The hyperglycemia resulted in reduced activities of glutathione peroxidase (by 25%), catalase (by 20%), glucose-6-phosphate dehydrogenase (by 55%) and transketolase (by 40%) in liver tissue of diabetic animals. Melatonin treatment (10 mg/kg, 18 days) did not influence the level of hyperglycemia or glycated hemoglobin and it had little effect on the activities of antioxidative enzymes. However, melatonin markedly reversed the activities of glucose-6-phosphate dehydrogenase and transketolase in liver tissue of diabetic rats. The most pronounced effect of the melatonin administration was the prevention of an increase in nitric oxide levels in blood plasma and aortic tissue during diabetes. In in vitro experiments, nitrosomelatonin formation in the presence of nitrosodonors was observed. This implies that melatonin might operate as an NO scavenger and carrier. Thus, melatonin treatment may have some beneficial effects in controlling diabetic vascular complications.

Melatonin, environmental light, and breast cancer

Although many factors have been suggested as causes for breast cancer, the increased incidence of the disease seen in women working in night shifts led to the hypothesis that the suppression of melatonin by light or melatonin deficiency plays a major role in cancer development. Studies on the 7,12-dimethylbenz[a]anthracene and N-methyl-N-nitrosourea experimental models of human breast cancer indicate that melatonin is effective in reducing cancer development. In vitro studies in MCF-7 human breast cancer cell line have shown that melatonin exerts its anticarcinogenic actions through a variety of mechanisms, and that it is most effective in estrogen receptor (ER) alpha-positive breast cancer cells. Melatonin suppresses ER gene, modulates several estrogen dependent regulatory proteins and pro-oncogenes, inhibits cell proliferation, and impairs the metastatic capacity of MCF-7 human breast cancer cells. The anticarcinogenic action on MCF-7 cells has been demonstrated at the physiological concentrations of melatonin attained at night, suggesting thereby that melatonin acts like an endogenous antiestrogen. Melatonin also decreases the formation of estrogens from androgens via aromatase inhibition. Circulating melatonin levels are abnormally low in ER-positive breast cancer patients thereby supporting the melatonin hypothesis for breast cancer in shift working women. It has been postulated that enhanced endogenous melatonin secretion is responsible for the beneficial effects of meditation as a form of psychosocial intervention that helps breast cancer patients.

Effect of chronic treatments with GH, melatonin, estrogens, and phytoestrogens on oxidative stress parameters in liver from aged female rats

The aging theory postulates that this process may be due to the accumulation of oxidative damage in cells and molecules. The present study has investigated the effect of castration in old female rats on various parameters related to the antioxidant properties of several cellular fractions obtained from the liver, and the influence of several chronic treatments on it, both in intact and castrated animals. Sixty-one 22-month-old Wistar female rats, were used. About 21 intact animals were divided into three groups and treated for 10 weeks with GH, melatonin or saline, and 40 ovariectomized (at 12 months of age) animals were divided into five groups and treated for the same time with GH, melatonin, estrogens (Eos), phytoestrogens (Phyt) or saline. All animals were sacrificed at 24 months of age by decapitation. The activity of glutathione peroxidase (GPx) in cytosolic fraction, glutathione-S-transferase (GST) in cytosol and microsomal fractions, and the levels of nitric oxide (NO) and cytochrome C in mitochondrial and cytosol fractions of liver were determined. A decrease in GST activity was detected in cytosol and in the microsomal fraction in ovariectomized animals as compared to intact rats. The activity of GPx was also decreased in ovariectomized as compared with the intact group. NO level was increased and cytochrome C decreased in the mitochondrial fraction of the liver in ovariectomized females as compared with the intact group, respectively. No significant changes after melatonin or GH treatments were found in GPx, GST activity and NO level in mitochondrial fraction in the intact group. Administration of GH, melatonin, Eos and Phyt in the ovariectomized groups significantly increased the GPx, and GST activity in the cytosol and microsomal fraction and decreased the level of NO in the mitochondrial fraction as compared with the untreated rats. A significant increase in the level of cytochrome C in the mitochondrial fraction and a decrease in the cytosol fraction were also found with all treatments. The administration of GH, melatonin, Eos and Phyt to castrated females seem to reduce oxidative changes in the liver from old ovariectomized rats.

Melatonin prevents the estrogenic effects of sub-chronic administration of cadmium on mice mammary glands and uterus

Cadmium (Cd) is a heavy metal classified as a human carcinogen. Occupational exposure, dietary consumption and cigarette smoking are sources of Cd contamination. Cd-induced carcinogenicity depends on its oxidative and estrogenic actions. A possible role of Cd in breast cancer etiology has been recently suggested. Melatonin, because of its antioxidant and antiestrogenic properties could counteract the toxic effects of this metalloestrogen. Our aim was both to determine the effects of relevant doses of Cd on mice mammary glands and uterus and to test whether melatonin would counteract its effects. Female mice of different ages and estrogenic status (prepuberal, adult intact, adult ovariectomized) were treated with CdCl(2) (2-3 mg/kg, i.p.), melatonin (10 microg/mL in drinking water), CdCl(2) + melatonin, or diluents. Whereas in prepuberal animals Cd disturbs mammary ductal growth and reduces the number of terminal end buds, in adults, regardless of the steroidal milieu, Cd exerts estrogenic effects on mammary glands, increasing lobuloalveolar development and ductal branching. Uterine weight also increased as a result of Cd treatment. The effects of Cd are partially inhibited by melatonin. In adult ovariectomized mice, Cd concentration in blood of animals treated with CdCl(2) + melatonin was lower than in mice receiving only Cd; the opposite effects were found in non-castrated animals. As Cd mimics the effect of estrogens, the high incidence of breast cancer in tobacco smokers and women working in industries related with Cd could be explained because of the properties of this metal. The effects of melatonin point to a possible role of this indoleamine as a preventive agent for environmental or occupational Cd contamination.

NO-donor melatonin derivatives: synthesis and in vitro pharmacological characterization

Numerous studies document that melatonin possesses a broad-spectrum antioxidant activity. It traps a number of reactive oxygen species (ROS) such as hydroxyl and peroxyl radicals, singlet oxygen and hypochlorous acid. It also inhibits peroxynitrite-induced reactions. It is known that atherosclerosis progression involves ROS-induced oxidation of low-density lipoproteins in sub-endothelial space and the depletion of nitric oxide (NO) in blood vessels, as well as a decreased sensitivity of the vessels to the actions of NO. Considering this, a series of new NO-donor antioxidants were designed and synthesized by joining melatonin with NO-donor nitrooxy and furoxan moieties as polyvalent agents potentially useful for the treatment of cardiovascular diseases involving atherosclerotic vascular changes. The in vitro antioxidant properties of the resulting products were assessed in the thiobarbituric acid reactive substances assay (TBARS), the ABTS(+.) as well as in the alkaline phosphatase (ALP) assay. The antioxidant capacities of NO-donor melatonins to inhibit lipoperoxidation (TBARS-IC(50)) was predominantly dependent on their lipophilicity, and therefore on their partitioning process into membranes. On the other hand, their comparable capacity to inhibit protein oxidation (ALP-IC(50)) was independent of their lipophilicity and was consistent with their similar ability to participate in electron transfer reactions. All the NO-donor melatonins were also evaluated for their ability to relax rat aorta strips precontracted with 1 microM phenylephrine. Finally, binding affinities and intrinsic activity studies, carried out at MT(1) and MT(2) receptor subtypes, showed a rather complex picture in need of further investigation.

AFMK, a melatonin metabolite, attenuates X-ray-induced oxidative damage to DNA, proteins and lipids in mice

Antioxidant function of melatonin is well established. However, N(1)-acetyl-N(2)-formyl-5-methoxykynuramine (AFMK), a melatonin metabolite is a sparingly investigated biogenic amine, especially in relation to its in vivo antioxidant function. We have evaluated the oxidative damage to biomolecules (DNA, protein and lipid) induced by X-irradiation in C57BL mice and the prophylactic action of AFMK. The extent of DNA damage was analyzed by single-cell gel electrophoresis in cerebral cortex and serum 8-hydroxydeoxyguanosine (8-OHdG) levels by enzyme-linked immunosorbent assay. Oxidative modification of protein and lipid was measured in the terms of carbonyl content and 4-HAE + MDA (4-hydroxyalkenal + malondialdehyde) status of brain cortex. Radiation exposure dramatically augmented the level of 8-OHdG in serum as well as DNA migration in the comet tail. AFMK pretreatment significantly inhibited DNA damage. In addition, radiation-induced augmentation of protein carbonyl content and HAE + MDA was ameliorated by AFMK pretreatment. Whole-body exposure of mice to X-irradiation also reduced the level of brain sulfhydryl contents (protein-bound sulfhydryl, total sulfhydryl, and nonprotein sulfhydryl) which were significantly protected by AFMK. Radiation-induced decline in the total antioxidant capacity of plasma was significantly reversed in AFMK pretreated mice. Moreover, AFMK showed a very high level of in vitro hydroxyl radical scavenging potential which was measured by an electron spin resonance (ESR) study of the 2-hydroxy-5,5-dimethyl-1-pyrrolineN-oxide (DMPO-OH) adduct. IC(50) values resulting from ESR analysis was 338.08 nm. The present study indicate that AFMK is a potent antioxidant in both in vivo and in vitro systems.

Melatonin as a potential antihypertensive treatment

The number of patients with well-controlled hypertension is alarmingly low worldwide and new approaches to treatment of increased blood pressure (BP) are being sought. Melatonin has a role in blood pressure regulation. The nighttime production of melatonin is found to be reduced in hypertensive individuals. Administration of melatonin decreased BP in several animal models of hypertension, in healthy men and women, and in patients with arterial hypertension. Most promising results were achieved in patients with non-dipping nighttime pressure, in which the circadian rhythm of BP variation is disturbed. Several potential mechanisms of BP reduction are considered. Melatonin can, via its scavenging and antioxidant nature, improve endothelial function with increased availability of nitric oxide exerting vasodilatory and hypotensive effects. Melatonin seems to interfere with peripheral and central autonomic system, with a subsequent decrease in the tone of the adrenergic system and an increase of the cholinergic system. Melatonin may act on BP also via specific melatonin receptors localized in peripheral vessels or in parts of central nervous system participating in BP control. With a large clinical trial using melatonin in hypertension treatment, many important questions could be answered, such as the dose of melatonin and regimen of its application, the choice of patients with greatest possible benefit from melatonin treatment, the potential of anti-remodeling effect of melatonin and the interaction of melatonin with other antihypertensive drugs.

Novel rhythms of N1-acetyl-N2-formyl-5-methoxykynuramine and its precursor melatonin in water hyacinth: importance for phytoremediation

N1-acetyl-N2-formyl-5-methoxykynuramine (AMFK) is a major metabolite of melatonin in mammals. To investigate whether AFMK exists in plants, an aquatic plant, water hyacinth, was used. To achieve this, LC/MS/MS with a deuterated standard was employed. AFMK was identified in any plant for the first time. Both it and its precursor, melatonin, were rhythmic with peaks during the late light phase. These novel rhythms indicate that these molecules do not serve as the chemical signal of darkness as in animals but may relate to processes of photosynthesis or photoprotection. These possibilities are supported by higher production of melatonin and AFMK in plants grown in sunlight (10,000-15,000 microW/cm2) compared to those grown under artificial light (400-450 microW/cm2). Melatonin and AFMK, as potent free radical scavengers, may assist plants in coping with harsh environmental insults, including soil and water pollutants. High levels of melatonin and AFMK in water hyacinth may explain why this plant more easily tolerates environmental pollutants, including toxic chemicals and heavy metals and is successfully used in phytoremediation. These novel findings could lead to improvements in the phytoremediative capacity of plants by either stimulating endogenous melatonin synthesis or by adding melatonin to water/soil in which they are grown.

The immune-pineal axis: a shuttle between endocrine and paracrine melatonin sources

The time course of the innate immunological response involves a pro-inflammatory phase followed by an anti-inflammatory phase. Pro-inflammatory responses serve as a defense against several stressor conditions, and sequential processes that shut down these responses are necessary to avoid exacerbation or the development of chronic diseases. In the present review, we put together recent data that show that the pineal gland is a player in bidirectional control of the inflammatory response. Healthy organisms stay in standby mode, ready to react. The nocturnal melatonin surge impairs the rolling and adherence of leukocytes to endothelial layers, limiting cell migration, and stimulates nocturnal production of IL-2 by T helper lymphocytes, exerting an immunostimulatory effect. Otherwise, the release of TNF-alpha from activated macrophages suppresses the nocturnal melatonin surge, allowing a full cell migration and inhibiting IL-2 production. In sequence, activated mononuclear and polymorphonuclear cells produce melatonin in a paracrine manner at the site of injury, which scavenges free radicals and collaborates to resolve the inflammatory response. The sequential diminution of TNF-alpha production is followed by the recovery of the nocturnal melatonin surge and IL-2 production. In summary, the immune-pineal axis, implicated in the sequential involvement of the melatonin produced by the pineal gland and immune-competent cells, is an integral participant of the innate immune response.