Intravenous administration of melatonin reduces the intracerebral cellular inflammatory response following transient focal cerebral ischemia in rats

Melatonin and ischemia-reperfusion injury of the brain

This review summarizes the reports that have documented the neuroprotective effects of melatonin against ischemia/reperfusion brain injury. The studies were carried out on several species, using models of acute focal or global cerebral ischemia under different treatment schedules. The neuroprotective actions of melatonin were observed during critical evolving periods for cell processes of immediate or delayed neuronal death and brain injury, early after the ischemia/reperfusion episode. Late neural phenomena accounting either for brain damage or neuronal repair, plasticity and functional recovery taking place after ischemia/reperfusion have been rarely examined for the protective actions of melatonin. Special attention has been paid to the advantageous characteristics of melatonin as a neuroprotective drug: bioavailability into brain cells and cellular organelles targeted by morpho-functional derangement; effectiveness in exerting several neuroprotective actions, which can be amplified and prolonged by its metabolites, through direct and indirect antioxidant activity; prevention and reversal of mitochondrial malfunction, reducing inflammation, derangement of cytoskeleton organization, and pro-apoptotic cell signaling; lack of interference with thrombolytic and neuroprotective actions of other drugs; and an adequate safety profile. Thus, the immediate results of melatonin actions in reducing infarct volume, necrotic and apoptotic neuronal death, neurologic deficits, and in increasing the number of surviving neurons, may improve brain tissue preservation. The potential use of melatonin as a neuroprotective drug in clinical trials aimed to improve the outcome of patients suffering acute focal or global cerebral ischemia should be seriously considered.

Utility of melatonin to treat surgical stress after major vascular surgery--a safety study

Surgery for abdominal aortic aneurysm is associated with elevated oxidative stress. As an antioxidant in animal and human studies, melatonin has the potential of ameliorating some of this oxidative stress, but melatonin has never been administered to adults during surgery for the purpose of reducing oxidative damage. The aim of this pilot study was to evaluate the safety of various doses of melatonin administered during or after surgery and to monitor the changes in biomarkers of oxidative stress and inflammation during the pre-, intra-, and postoperative period. Six patients undergoing aortic surgery received 10 (n = 2), 30 (n = 2) or 60 (n = 2) mg melatonin intravenously in the intraoperative phase and 10 mg orally for three nights after surgery. Patients were monitored for hemodynamic parameters during and after surgery. Any unexpected events during the hospitalization were registered. Blood samples were collected preoperatively and at 5 min, 6 hr and 24 hr after clamp removal or after re-circulation of the first leg and the samples were analyzed for malondialdehyde (MDA), ascorbic acid (AA), dehydroascorbic acid (DHA), and interleukin-6 (IL-6). Troponin I (TpI) and C-reactive protein (CRP) were also measured for 4 days after surgery. Melatonin administration did not change hemodynamic parameters (mean arterial pressure or pulse rate) during surgery (P = 0.499 and 0.149, respectively), but oxidative stress parameters (MDA and AA) decreased significantly (P = 0.014 and 0.001, respectively). There was a significant increase in the inflammatory parameters (IL-6 and CRP) (P = 0.001 and 0.001, respectively) and an increase in TpI (P = 0.009) as a consequence of surgery. These were not influenced by melatonin treatment. Treatment of patients undergoing major aortic surgery with melatonin intravenously up to 60 mg in the intraoperative phase was safe and without complications. Melatonin may decrease oxidative damage resulting from surgery, but randomized clinical trials are required before definitive conclusions can be drawn regarding the clinical benefit of melatonin in surgical situations.

Melatonin ameliorates hippocampal nitric oxide production and large conductance calcium-activated potassium channel activity in chronic intermittent hypoxia

Melatonin protects against hippocampal injury induced by intermittent hypoxia (IH). IH-induced oxidative stress is associated with decreases in constitutive production of nitric oxide (NO) and in the activity of large conductance calcium-activated potassium (BK) channels in hippocampal neurons. We tested the hypothesis that administration of melatonin alleviates the NO deficit and impaired BK channel activity in the hippocampus of IH rats. Sprague-Dawley rats were injected with melatonin (10 mg/kg, i.p.) or vehicle before daily IH exposure for 8 hr for 7 days. The NO and intracellular calcium ([Ca2+]i) levels in the CA1 region of hippocampal slices were measured by electrochemical microsenor and spectrofluorometry, respectively. The activity of BK channels was recorded by patch-clamping electrophysiology in dissociated CA1 neurons. Malondialdehyde levels were increased in the hippocampus of hypoxic rats and were lowered by the melatonin treatment. Levels of NO under resting and hypoxic conditions, and the protein expression of neuronal NO synthase (nNOS) were significantly reduced in the CA1 neurons of hypoxic animals compared with the normoxic controls. These deficits were mitigated in the melatonin-treated hypoxic rats with an improved [Ca2+]i response to acute hypoxia. The open probability of BK channels was decreased in the hypoxic rats and was partially restored in the melatonin-treated animals, without alterations in the expression of channel subunits and unitary conductance. Acute treatment of melatonin had no significant effects on the BK channel activity or on the [Ca2+]i response to hypoxia. Collectively, these results suggest that melatonin ameliorates the constitutive NO production and BK channel activity via an antioxidant mechanism against an IH-induced down-regulation of nNOS expression in hippocampal neurons.