Prophylactic use of melatonin protects against focal cerebral ischemia in mice: role of endothelin converting enzyme-1

Preclinical evaluation of pharmacokinetics and safety of melatonin in propylene glycol for intravenous administration

Melatonin is a highly effective treatment in different animal models of excitotoxicity or ischemia/reperfusion injury. Due to a lack of patentability, commercial sponsors are not interested in funding clinical evaluations of melatonin. Investigators may initiate small-scale clinical evaluation, and intravenous (i.v.) administration is appropriate in acute stroke patients. Institutional Review Boards may require proper preclinical evaluation of the preparation. In this pharmacokinetic and safety study, melatonin in propylene glycol was evaluated in adult male Sprague-Dawley rats. Following a single i.v. injection at 5 or 15 mg/kg, plasma concentrations of melatonin increased to 39 and 199 million pg/mL at 2 min and 128,000 and 772,000 pg/mL at 120 min. Within 60 min of injection, the blood pressure, heart rate and body temperature remained unaffected. Melatonin at 5 mg/kg did not influence the complete blood counts at 60 min, but melatonin at 15 mg/kg had some effects on the differential white cell and platelet counts. Melatonin at 5 or 15 mg/kg slightly elevated some liver enzymes at 60 min of injection, and melatonin at higher dose also elevated plasma creatinine and lactate dehydrogenase levels. At 24 hr after completion of six daily injections of melatonin, there was a 5.5% reduction in body weight. Gross postmortem examination and histological examination of the brain, kidney, liver and spleen did not reveal any evidence of toxicity. In conclusion, melatonin in propylene glycol markedly elevates plasma levels of melatonin with no serious toxicity. This preparation should be further evaluated in human patients.

Melatonin reduces infarction volume in a photothrombotic stroke model in the wild-type but not cyclooxygenase-1-gene knockout mice

Cyclooxygenase (COX)-2 plays a harmful role in cerebral ischemic/reperfusion injury, but the role of COX-1 is uncertain. In the present study, cerebral infarct was induced by photothrombosis. Intraperitoneal injections of melatonin at 15 g/kg or its vehicle were made at 0.5 hr before stroke and 24 and 48 hr after stroke. Cerebral blood flow (CBF) in the penumbra was monitored during stroke using a laser Doppler flowmeter. Sensorimotor behavior was evaluated using the turning in an alley and falling from a pole tests at 1 hr before stroke and 24 and 48 hr after stroke. Infarct volume was determined from the T2-weighted magnetic resonance images at 72 hr after stroke. During the first 15 min of stroke, CBF decreased in the penumbra in both homozygous COX-1-gene knockout and wild-type mice. Melatonin treatment improved the penumbral CBF in the wild-type mice. Mild poststroke impairment in sensorimotor behavior was detected by the turning in an alley test in which the COX-1-gene knockout mice performed better. Melatonin treatment did not affect the poststroke sensorimotor behavior. The relative infarct volume at 72 hr after stroke was 8.1% and 8.4% in the COX-1-gene knockout and wild-type mice, respectively. Melatonin treatment reduced the relative infarct volume to 6.3% in the latter but not in the former (8.2%). Thus, COX-1-gene knockout does not affect the brain's susceptibility to photothrombotic stroke. Melatonin treatment reduces infarct size in the wild-type mice following photothrombotic stroke partly via maintenance of penumbral CBF in which the COX-1-gene may play a role.

Melatonin reduces apoptosis and necrosis induced by ischemia/reperfusion injury of the pancreas

The pancreas is highly susceptible to the oxidative stress induced by ischemia/reperfusion (IR) injury leading to the generation of acute pancreatitis. Melatonin has been shown to be useful in the prevention of the damage by ischemia-reperfusion in liver, brain, myocardium, gut and kidney. The aim of the study was to evaluate the cytoprotective properties of melatonin against injury induced by IR in pancreas. The obstruction of gastro-duodenal and inferior splenic arteries induced pancreatic IR in male Wistar rats. Melatonin was intraperitoneally administered before or/and after IR injury. The animals were killed at 24 and 48 hr after reperfusion and there were evaluated parameters of oxidative stress (lipoperoxides, superoxide dismutase, catalase, glutathione peroxidase and reduced glutathione), glandular endocrine and exocrine function (lipase, amylase, insulin) and cell injury (apoptosis and necrosis). The IR induced a marked enhancement of oxidative stress and impaired pancreatic function. The histological analysis showed that IR induced acute pancreatitis with the accumulation of inflammatory infiltrate, disruption of tissue structure, cell necrosis and hemorrhage. Melatonin administration before or after pancreatic IR prevented all tissue markers of oxidative stress, biochemical and histological signs of apoptosis and necrosis, and restored glandular function. No histological signs of pancreatitis were observed 48 hr after reperfusion in 80% of the animals treated with melatonin, with only a mild edematous pancreatitis being observed in the remaining rats. Preventive or therapeutic administration of melatonin protected against the induction of oxidative stress and tissue injury, and restored cell function in experimental pancreatic IR in rats.

Protective effects of melatonin in experimental free radical-related ocular diseases

Melatonin (N-acetyl-5-methoxytryptamine) is an indoleamine with a range of antioxidative properties. Melatonin is endogenously produced in the eye and in other organs. Current evidence suggests that melatonin may act as a protective agent in ocular conditions such as photo-keratitis, cataract, glaucoma, retinopathy of prematurity and ischemia/reperfusion injury. These diseases are sight-threatening and they currently remain, for the most part, untreatable. The pathogenesis of these conditions is not entirely clear but oxidative stress has been proposed as one of the causative factors. Elevated levels of various reactive oxygen and nitrogen species have been identified in diseased ocular structures. These reactants damage the structure and deplete the eye of natural defense systems, such as the antioxidant, reduced glutathione, and the antioxidant enzyme superoxide dismutase. Oxidative damage in the eye leads to apoptotic degeneration of retinal neurons and fluid accumulation. Retinal degeneration decreases visual sensitivity and even a small change in the fluid content of the cornea and crystalline lens is sufficient to disrupt ocular transparency. In the eye, melatonin is produced in the retina and in the ciliary body. Continuous regeneration of melatonin in the eye offers a frontier antioxidative defense for both the anterior and posterior eye. However, melatonin production is minimal in newborns and its production gradually wanes in aging individuals as indicated by the large drop in circulating blood concentrations of the indoleamine. These individuals are possibly at risk of contracting degenerative eye diseases that are free radical-based. Supplementation with melatonin, a potent antioxidant, in especially the aged population should be considered as a prophylaxis to preserve visual functions. It may benefit many individuals worldwide, especially in countries where access to medical facilities is limited.

Preventive effect of melatonin on bleomycin-induced lung fibrosis in rats

Oxidative stress has an important role in the pathogenesis of idiopathic pulmonary fibrosis. Melatonin has direct and indirect free radical-detoxifying activity. The present study investigated whether melatonin treatment attenuates bleomycin-induced lung fibrosis in rats. A group of rats was given one dose of bleomycin while the control animals were given saline. The first dose of melatonin (4 mg/kg/day) was given 2 days before the bleomycin injection. At day 14, fibrotic changes were evaluated using Aschoft's criteria and lung hydroxyproline content. Bleomycin produced a 2.7-fold rise in the fibrosis score that was decreased 65% by melatonin (P < 0.05) and a 1.4-fold increase in hydroxyproline content which was completely prevented by melatonin. Protein carbonyl and thiobarbituric acid reactive substances levels, which were significantly elevated in the bleomycin treated rats, were significantly attenuated by melatonin. Bleomycin administration significantly reduced the activities of catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) in lung tissue. The reduction in CAT activity was prevented by melatonin but SOD and GSH-Px were not influenced. These results revealed that melatonin may prevent the development of bleomycin-induced lung fibrosis via the repression of protein and lipid peroxidation.

Neonatal pinealectomy induces Purkinje cell loss in the cerebellum of the chick: A stereological study

Melatonin plays an important role in certain physiological functions and morphological features of various structures. In the current study, the effects of pinealectomy on Purkinje cell number and morphological features of developing cerebellum in the chick were investigated using stereological methods. Fifteen Hybro Broiler newly hatched chicks were divided into three groups: a pinealectomized group (n = 5), sham-operated group (n = 5) and a non-pinealectomized control group (n = 5). Surgical pinealectomy was performed in 3-day-old chicks. In the 8th week, all animals were sacrificed for histopathological evaluation and subsequent stereological analysis. Each layer volume of molecular (+Purkinje cell), granular and white matter in the cerebellum was estimated in all animals. It was found that there was no significant difference for the volume of whole cerebellum and also molecular (+Purkinje cell) layer in these groups (P > 0.05). Nevertheless, the values of granular layer and white matter of sham-operated group were significantly different from those of control and pinealectomized animals (P < 0.01). It was also observed that pinealectomy significantly reduces the Purkinje cell number in cerebellar cortex (P < 0.01). The present study is the first stereological study to demonstrate the histomorphological effects of pinealectomy on the cerebellum in the chick. Our results suggest that pineal gland/melatonin might play an important role in morphological features of the developing cerebellum in the chick.

Melatonin reduces oxidative stress and increases gene expression in the cerebral cortex and cerebellum of aluminum-exposed rats

The pro-oxidant activity of aluminum (Al), the protective role of exogenous melatonin, as well as the mRNA levels of some antioxidant enzymes, were determined in cortex and cerebellum of rats following exposure to Al and/or melatonin. Two groups of male rats received intraperitoneal injections of Al lactate or melatonin at doses of 7 mg Al/kg/day and 10 mg/kg/day, respectively, for 11 wk. A third group of animals received concurrently Al lactate (7 mg Al/kg/day) plus melatonin (10 mg/kg/day) during the same period. A fourth group of rats was used as control. At the end of the treatment, the cerebral cortex and cerebellum were removed and processed to examine the following oxidative stress markers: glutathione transferase (GST), reduced glutathione (GSH), oxidized glutathione (GSSG), superoxide dismutase (SOD), glutathione reductase, glutathione peroxidase (GPx), catalase (CAT), thiobarbituric acid reactive substances (TBARS), as well as protein content. Moreover, gene expression of Cu-ZnSOD, MnSOD, GPx and CAT was evaluated by real-time RT-PCR. On the other hand, Al, Fe, Mn, Cu and Zn concentrations were determined in cortex and cerebellum of rats. Oxidative stress was promoted in both neural regions following Al administration, resulting from the pro-oxidant activity related with an increase in tissue Al concentrations. In contrast, melatonin exerted an antioxidant action which was related with an increase in the mRNA levels of the antioxidant enzymes evaluated. The results of the present investigation emphasize the potential use of melatonin as a supplement in the therapy of neurological disorders in which oxidative stress is involved.

Antioxidant strategies in the treatment of stroke

Excessive production of free radicals is known to lead to cell injury in a variety of diseases, such as cerebral ischemia. In this review, we describe some of the numerous studies that have examined this oxidative stress and the efficiency of antioxidant strategies in focal cerebral ischemia. Besides using genetically modified mice, these strategies can be divided into three groups: (1) inhibition of free radical production, (2) scavenging of free radicals, and (3) increase of free radical degradation by using agents mimicking the enzymatic activity of endogenous antioxidants. Finally, the clinical trials that have tested or are currently testing the efficiency of antioxidants in patients suffering from stroke are reviewed. The results presented here lead us to consider that antioxidants are very promising drugs for the treatment of ischemic stroke.

Microcirculatory effects of melatonin in rat skeletal muscle after prolonged ischemia

The purpose of this study was to determine microcirculatory effects and response of nitric oxide synthase (NOS) to melatonin in skeletal muscle after prolonged ischemia. A vascular pedicle isolated rat cremaster muscle model was used. Each muscle underwent 4 hr of zero-flow warm ischemia followed by 2 hr of reperfusion. Melatonin (10 mg/kg) or saline as a vehicle was given by intraperitoneal injection at 30 min prior to reperfusion and the same dose was given immediately after reperfusion. After reperfusion, microcirculation measurements including arteriole diameter, capillary perfusion and endothelial-dependent and -independent vasodilatation were performed. The cremaster muscle was then harvested to measure endothelial NOS (eNOS) and inducible NOS (iNOS) gene expression and enzyme activity. Three groups of rats were used: sham-ischemia/reperfusion (I/R), vehicle + I/R and melatonin + I/R. As compared with vehicle + I/R group, administration of melatonin significantly enhanced arteriole diameter, improved capillary perfusion, and attenuated endothelial dysfunction in the microcirculation of skeletal muscle after 4 hr warm ischemia. Prolonged warm ischemia followed by reperfusion significantly depressed eNOS gene expression and constitutive NOS activity and enhanced iNOS gene expression. Administration of melatonin did not significantly alter NOS gene expression or activity in skeletal muscle after prolonged ischemia and reperfusion. Melatonin provided a significant microvascular protection from reperfusion injury in skeletal muscle. This protection is probably attributable to the free radical scavenging effect of melatonin, but not to its anti-inflammatory effect.