Journal of pineal research
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Review
Analgesic effects of melatonin: a review of current evidence from experimental and clinical studies.
Melatonin is an endogenous indoleamine, produced mainly by the pineal gland. Melatonin has been proven to have chronobiotic, antioxidant, antihypertensive, anxiolytic and sedative properties. There are also experimental and clinical data supporting an analgesic role of melatonin. ⋯ The effects may be linked to G(i) -coupled melatonin receptors, to G(i) -coupled opioid μ-receptors or GABA-B receptors with unknown downstream changes with a consequential reduction in anxiety and pain. Also, the repeated administration of melatonin improves sleep and thereby may reduce anxiety, which leads to lower levels of pain. In this paper, we review the current evidence regarding the analgesic properties of melatonin in animals and humans with chronic pain.
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Melatonin is a potent scavenger of reactive oxygen species and a strong antioxidant. Melatonin exerts protective effects against damage by the enhancing the Akt signal pathway, thus regulating apoptotic cell death. Akt phosphorylates pro-apoptotic proteins such as Bad and FoxO1 and inhibits the pro-apoptotic functions of these proteins. ⋯ However, melatonin prevented hepatic I/R injury-induced decreases in these proteins levels. Moreover, the interaction levels between phospho-Bad and 14-3-3 and between phospho-FoxO1 and 14-3-3 are reduced in vehicle-treated animals, and melatonin attenuated decreases in the binding levels of these proteins. 14-3-3 exerts an anti-apoptotic function by sequestration of Bad and FoxO1. These findings suggest that melatonin exerts protective effects in case of hepatic I/R damage by maintaining the binding of phospho-Bad and 14-3-3 and the binding of phospho-FoxO1 and 14-3-3, thus preventing activation of apoptotic cell death.
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Melatonin reportedly exerts beneficial effects to attenuate multiple organ dysfunction syndrome (MODS) in septic shock. Heatstroke resembles septic shock in many aspects. ⋯ We evaluated the effect of melatonin, a versatile molecule synthesized in the pineal gland and in many organs, in heatstroke rats and showed that melatonin (0.2-5.0 mg/kg of body weight, i.v., immediately after the start of heat stress) significantly (i) attenuated hyperthermia, hypotension and hypothalamic ischemia and hypoxia, (ii) reduced plasma index of the toxic oxidizing radicals like nitric oxide metabolites and hydroxyl radicals, (iii) diminished plasma index of hepatic and renal dysfunction like creatinine, blood urea nitrogen, alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, and lactate dehydrogenase, (iv) attenuated plasma systemic inflammation response molecules like soluble intercellular and lesion molecule-1, E-selectin, tumor necrosis factor-alpha, interleukin (IL)-1β, and IL-6, (v) promoted plasma levels of an anti-inflammatory cytokine IL-10, (vi) reduced an index of infiltration of polymorphonuclear neutrophils in the lung like myeloperoxidase activity, and (vii) promoted the survival time to fourfold compared with the heatstroke alone group. Thus, melatonin could be a novel agent for the treatment of heatstroke animals or patients in the early stage.
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Randomized Controlled Trial
Adjuvant use of melatonin for treatment of fibromyalgia.
Fibromyalgia syndrome (FMS) is a chronic musculoskeletal disorder characterized by generalized muscular pain accompanied by fatigue and tenderness at specific anatomic sites called tender points. Although preliminary evidence indicates that melatonin may be effective in treating the pain associated with FMS, no definitive evidence supports this claim. This study was designed to evaluate the significance of using different doses of melatonin, alone or in combination with fluoxetine for the management of FMS. ⋯ Each patient was clinically evaluated through direct interview with the patients using the Fibromyalgia Impact Questionnaire (FIQ) at zero time and after 8 wk. Using melatonin (3 mg or 5 mg/day) in combination with 20 mg/day fluoxetine resulted in significant reduction in both total and different components of FIQ score compared to the pretreatment values. In conclusion, administration of melatonin, alone or in a combination with fluoxetine, was effective in the treatment of patients with FMS.
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Melatonin (5-15 mg/kg) protects male animals against ischemic stroke. We explored the potential interactions and synergistic neuroprotection of melatonin and estrogen using a panel of lipid peroxidation and radical-scavenging assays, primary neuronal cultures subjected to oxygen-glucose deprivation (OGD), and lipopolysaccharide (LPS)-stimulated RAW 264.7 cells. Neuroprotective efficacy of melatonin was also evaluated in both reproductively active and ovariectomized female rats subjected to transient focal cerebral ischemia. ⋯ Relative to vehicle-injected controls, melatonin given intravenously at 1-5 mg/kg, but not 0.1 or 15 mg/kg, significantly reduced brain infarction and improved neurobehavioral outcomes (P<0.05, respectively) in reproductively active female rats. In ovariectomized stroke rats, melatonin was only effective at a large dosage (15-50 mg/kg). These results demonstrate complex interactions and synergistic antioxidant, radical-scavenging, and anti-inflammatory actions between estradiol and melatonin, and highlight the potential need to rectify the melatonin's hormetic dose-response by the level of circulating estradiol in the treatment of female stroke patients.