Melatonin scavenges hydroxyl radical and protects isolated rat hearts from ischemic reperfusion injury

Protective role of melatonin and spirulina in aortic occlusion-reperfusion model in rats

The aim of this experiment was to investigate the role of melatonin and spirulina on multiorgan damage induced by ischemia/reperfusion injury (IR) in a rat model. A total of 32 male rats weighing 200-220 g were allocated into 4 groups (n = 8/group) (Sham, Control-IR [CIR], Melatonin-IR [MIR], and Spirulina-IR [SIR]). Sham group underwent midline laparotomy and dissection of the aorta without injury. In other groups, an IR model was established by clamping (ischemia) and releasing (reperfusion) the abdominal aorta at the supraceliac level for 20 min. All rats were given 3 ml/kg of distilled water by gavage for 14 days before and 7 days after the experiment. The treatment groups received either melatonin (50 mg/kg) or spirulina (50 mg/kg) by the same route. On the 21st day of the experiment, the rats were sacrificed. We found that melatonin and spirulina ameliorated the effects of IR at different levels of significance (ranging from p = .01 to p < .001), increasing total antioxidant capacity (TAC) and superoxide dismutase levels, and decreasing total oxidant status, oxidative stress index (OSI), myeloperoxidase, tumor necrosis factor-alfa and malondialdehyde levels. When compared MIR and SIR groups, only TAC and OSI levels did differ in favor of melatonin between the groups (p < .05). Histopathological and immunohistochemical examinations showed that melatonin and spirulina similarly reduced IR-related tissue damage and apoptosis. We concluded that melatonin and spirulina may have a protective role against oxidative tissue damage and apoptosis in the abdominal aortic IR animal model. PRACTICAL APPLICATIONS: Coarctation of aorta (CoA) and interrupted aortic arch (IAA) are serious cardiac defects with high morbidity and mortality if not diagnosed and treated early in life. Restoration of blood flow in CoA or IAA through prostaglandin E1 infusion, angioplasty or surgery can cause ischemia/reperfusion (IR) injury. This reperfusion period may be complicated IR injury at remote organs. It may be beneficial to increase antioxidant capacity in preventing stress-induced tissue damage. Melatonin and spirulina are agents with strong antioxidant properties. In this animal research, protective role of these products on multiorgan damage induced by IR was investigated for the first time. We found that both melatonin and spirulina ameliorate the effects of IR to varying degrees. This study provides evidence that melatonin and spirulina may have preventive effects on oxidative tissue damage and apoptosis in the abdominal aortic IR animal model.

Role of the Antioxidant Activity of Melatonin in Myocardial Ischemia-Reperfusion Injury

Ischemia-reperfusion injury is a common problem in the age of interventional cardiology; it is primarily mediated by oxidative stress and reactive agents. Melatonin has antioxidative properties that make its use promising for treating ischemia-reperfusion injury. Multiple experimental studies in murine and porcine models have been performed with good results. Clinical trials have also been conducted but given their heterogeneity, no conclusive results can be made. Melatonin pharmacokinetic properties are not ideal; therefore, many analogs have been proposed with improved characteristics, and some studies have evaluated their efficacy in animal models, but clinical trials are needed to recommend their use. In this review, we expose the results of the most impactful studies regarding melatonin use in ischemia-reperfusion injury.

Melatonin's neuroprotective role in mitochondria and its potential as a biomarker in aging, cognition and psychiatric disorders

Melatonin is an ancient molecule that is evident in high concentrations in various tissues throughout the body. It can be separated into two pools; one of which is synthesized by the pineal and can be found in blood, and the second by various tissues and is present in these tissues. Pineal melatonin levels display a circadian rhythm while tissue melatonin does not. For decades now, melatonin has been implicated in promoting and maintaining sleep. More recently, evidence indicates that it also plays an important role in neuroprotection. The beginning of our review will summarize this literature. As an amphiphilic, pleiotropic indoleamine, melatonin has both direct actions and receptor-mediated effects. For example, melatonin has established effects as an antioxidant and free radical scavenger both in vitro and in animal models. This is also evident in melatonin's prominent role in mitochondria, which is reviewed in the next section. Melatonin is synthesized in, taken up by, and concentrated in mitochondria, the powerhouse of the cell. Mitochondria are also the major source of reactive oxygen species as a byproduct of mitochondrial oxidative metabolism. The final section of our review summarizes melatonin's potential role in aging and psychiatric disorders. Pineal and tissue melatonin levels both decline with age. Pineal melatonin declines in individuals suffering from psychiatric disorders. Melatonin's ability to act as a neuroprotectant opens new avenues of exploration for the molecule as it may be a potential treatment for cases with neurodegenerative disease.

Melatonin to Rescue the Aged Heart: Antiarrhythmic and Antioxidant Benefits

Aging comes with gradual loss of functions that increase the vulnerability to disease, senescence, and death. The mechanisms underlying these processes are linked to a prolonged imbalance between damage and repair. Damaging mechanisms include oxidative stress, mitochondrial dysfunction, chronodisruption, inflammation, and telomere attrition, as well as genetic and epigenetic alterations. Several endogenous tissue repairing mechanisms also decrease. These alterations associated with aging affect the entire organism. The most devastating manifestations involve the cardiovascular system and may lead to lethal cardiac arrhythmias. Together with structural remodeling, electrophysiological and intercellular communication alterations during aging predispose to arrhythmic events. Despite the knowledge on repairing mechanisms in the cardiovascular system, effective antiaging strategies able to reduce the risk of arrhythmias are still missing. Melatonin is a promising therapeutic candidate due to its pleiotropic actions. This indoleamine regulates chronobiology and endocrine physiology. Of relevance, melatonin is an antiaging, antioxidant, antiapoptotic, antiarrhythmic, immunomodulatory, and antiproliferative molecule. This review focuses on the protective effects of melatonin on age-induced cardiac functional and structural alterations, potentially becoming a new fountain of youth for the heart.

Association Between Antiarrhythmic, Electrophysiological, and Antioxidative Effects of Melatonin in Ischemia/Reperfusion

Melatonin is assumed to confer cardioprotective action via antioxidative properties. We evaluated the association between ventricular tachycardia and/or ventricular fibrillation (VT/VF) incidence, oxidative stress, and myocardial electrophysiological parameters in experimental ischemia/reperfusion under melatonin treatment. Melatonin was given to 28 rats (10 mg/kg/day, orally, for 7 days) and 13 animals received placebo. In the anesthetized animals, coronary occlusion was induced for 5 min followed by reperfusion with recording of unipolar electrograms from ventricular epicardium with a 64-lead array. Effects of melatonin on transmembrane potentials were studied in ventricular preparations of 7 rats in normal and “ischemic” conditions. Melatonin treatment was associated with lower VT/VF incidence at reperfusion, shorter baseline activation times (ATs), and activation-repolarization intervals and more complete recovery of repolarization times (RTs) at reperfusion (less baseline-reperfusion difference, ΔRT) (p < 0.05). Superoxide dismutase (SOD) activity was higher in the treated animals and associated with ΔRT (p = 0.001), whereas VT/VF incidence was associated with baseline ATs (p = 0.020). In vitro, melatonin led to a more complete restoration of action potential durations and resting membrane potentials at reoxygenation (p < 0.05). Thus, the antioxidative properties of melatonin were associated with its influence on repolarization duration, whereas the melatonin-related antiarrhythmic effect was associated with its oxidative stress-independent action on ventricular activation.

Protection of cardiac cell-to-cell coupling attenuate myocardial remodeling and proarrhythmia induced by hypertension

Gap junction connexin channels are important determinants of myocardial conduction and synchronization that is crucial for coordinated heart function. One of the main risk factors for cardiovascular events that results in heart attack, congestive heart failure, stroke as well as sudden arrhythmic death is hypertension. Mislocalization and/or dysfunction of specific connexin-43 channels due to hypertension-induced myocardial remodeling have been implicated in the occurrence of life-threatening arrhythmias and heart failure in both, humans as well as experimental animals. Recent studies suggest that down-regulation of myocardial connexin-43, its abnormal distribution and/or phosphorylation might be implicated in this process. On the other hand, treatment of hypertensive animals with cardioprotective drugs (e.g. statins) or supplementation with non-pharmacological compounds, such as melatonin, omega-3 fatty acids and red palm oil protects from lethal arrhythmias. The antiarrhythmic effects are attributed to the attenuation of myocardial connexin-43 abnormalities associated with preservation of myocardial architecture and improvement of cardiac conduction. Findings uncover novel mechanisms of cardioprotective (antihypertensive and antiarrhythmic) effects of compounds that are used in clinical settings. Well-designed trials are needed to explore the antiarrhythmic potential of these compounds in patients suffering from hypertension.

Melatonin promotes cardiomyogenesis of embryonic stem cells via inhibition of HIF-1α stabilization

Melatonin, a molecule involved in the regulation of circadian rhythms, has protective effects against myocardial injuries. However, its capability to regulate the maturation of cardiac progenitor cells is unclear. Recently, several studies have shown that melatonin inhibits the stabilization of hypoxia-inducible factors (HIFs), important signaling molecules with cardioprotective effects. In this study, by employing differentiating mouse embryonic stem cells, we report that melatonin significantly upregulated the expression of cardiac cell-specific markers (myosin heavy chains six and seven) as well as the percentage of myosin heavy chain-positive cells. Importantly, melatonin decreased HIF-1α stabilization and transcriptional activity and, in contrast, induced HIF-2α stabilization. Interestingly, the deletion of HIF-1α completely inhibited the pro-cardiomyogenic effect of melatonin as well as the melatonin-mediated HIF-2α stabilization. Moreover, melatonin increased Sirt-1 levels in a HIF-1α-dependent manner. Taken together, we provide new evidence of a time-specific inhibition of HIF-1α stabilization as an essential feature of melatonin-induced cardiomyogenesis and unexpected different roles of HIF-1α stabilization during various stages of cardiac development. These results uncover new mechanisms underlying the maturation of cardiac progenitor cells and can help in the development of novel strategies for using melatonin in cardiac regeneration therapy.

Melatonin: A Potential Anti-Oxidant Therapeutic Agent for Mitochondrial Dysfunctions and Related Disorders

Mitochondria play a central role in cellular physiology. Besides their classic function of energy metabolism, mitochondria are involved in multiple cell functions, including energy distribution through the cell, energy/heat modulation, regulation of reactive oxygen species (ROS), calcium homeostasis, and control of apoptosis. Simultaneously, mitochondria are the main producer and target of ROS with the result that multiple mitochondrial diseases are related to ROS-induced mitochondrial injuries. Increased free radical generation, enhanced mitochondrial inducible nitric oxide synthase (iNOS) activity, enhanced nitric oxide (NO) production, decreased respiratory complex activity, impaired electron transport system, and opening of mitochondrial permeability transition pores have all been suggested as factors responsible for impaired mitochondrial function. Because of these, neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), Huntington's disease (HD), and aging, are caused by ROS-induced mitochondrial dysfunctions. Melatonin, the major hormone of the pineal gland, also acts as an anti-oxidant and as a regulator of mitochondrial bioenergetic function. Melatonin is selectively taken up by mitochondrial membranes, a function not shared by other anti-oxidants, and thus has emerged as a major potential therapeutic tool for treating neurodegenerative disorders. Multiple in vitro and in vivo experiments have shown the protective role of melatonin for preventing oxidative stress-induced mitochondrial dysfunction seen in experimental models of PD, AD, and HD. With these functions in mind, this article reviews the protective role of melatonin with mechanistic insights against mitochondrial diseases and suggests new avenues for safe and effective treatment modalities against these devastating neurodegenerative diseases. Future insights are also discussed.

Antioxidative and cardioprotective effects of total flavonoids extracted from Dracocephalum moldavica L. against acute ischemia/reperfusion-induced myocardial injury in isolated rat heart

This study evaluates antioxidative and cardioprotective effects of total flavonoids extracted from Dracocephalum moldavica L. (DML). The total flavonoids showed remarkable scavenging effects against 1,1-diphenyl-2-picrylhydrazyl, hydroxyl and superoxide anion radicals in vitro. Compared with the ischemia/reperfusion (I/R) group as demonstrated by the use of improved Langendorff retrograde perfusion technology, the total flavonoids (5 μg/mL) pretreatment improved the heart rate and coronary flow, rised left ventricular developed pressure and decreased creatine kinase, lactate dehydrogenase levels in coronary flow. The infarct size/ischemic area at risk of DML-treated hearts was smaller than that of I/R group; the superoxide dismutase activity and glutathione/glutathione disulfide ratio increased and malondialdehyde content reduced obviously (P < 0.01) in total flavonoids treatment groups. In conclusion, the total flavonoids possess obvious protective effects on myocardial I/R injury, which may be related to the improvement of myocardial oxidative stress states.

mtDNA T8993G mutation-induced F1F0-ATP synthase defect augments mitochondrial dysfunction associated with hypoxia/reoxygenation: the protective role of melatonin

Background

F1F0-ATP synthase (F1F0-ATPase) plays important roles in regulating mitochondrial function during hypoxia, but the effect of F1F0-ATPase defect on hypoxia/reoxygenation (H/RO) is unknown. The aim of this study was to investigate how mtDNA T8993G mutation (NARP)-induced inhibition of F1F0-ATPase modulates the H/RO–induced mitochondrial dysfunction. In addition, the potential for melatonin, a potent antioxidant with multiple mitochondrial protective properties, to protect NARP cells exposed to H/RO was assessed.

Methods And Findings

NARP cybrids harboring 98% of mtDNA T8993G genes were established as an in vitro model for cells with F1F0-ATPase defect; their parental osteosarcoma 143B cells were studied for comparison. Treating the cells with H/RO using a hypoxic chamber resembles ischemia/reperfusion in vivo. NARP significantly enhanced apoptotic death upon H/RO detected by MTT assay and the trypan blue exclusion test of cell viability. Based on fluorescence probe-coupled laser scanning imaging microscopy, NARP significantly enhanced mitochondrial reactive oxygen species (mROS) formation and mitochondrial Ca²⁺ (mCa²⁺) accumulation in response to H/RO, which augmented the depletion of cardiolipin, resulting in the retardation of mitochondrial movement. With stronger H/RO stress (either with longer reoxygenation duration, longer hypoxia duration, or administrating secondary oxidative stress following H/RO), NARP augmented H/RO-induced mROS formation to significantly depolarize mitochondrial membrane potential (ΔΨm), and enhance mCa²⁺ accumulation and nitric oxide formation. Also, NARP augmented H/RO-induced mROS oxidized and depleted cardiolipin, thereby promoting permanent mitochondrial permeability transition, retarded mitochondrial movement, and enhanced apoptosis. Melatonin markedly reduced NARP-augmented H/RO-induced mROS formation and therefore significantly reduced mROS-mediated depolarization of ΔΨm and accumulation of mCa²⁺, stabilized cardiolipin, and then improved mitochondrial movement and cell survival.

Conclusion

NARP-induced inhibition of F1F0-ATPase enhances mROS formation upon H/RO, which augments the depletion of cardiolipin and retardation of mitochondrial movement. Melatonin may have the potential to rescue patients with ischemia/reperfusion insults, even those associated with NARP symptoms.

Melatonin attenuates hypertension-related proarrhythmic myocardial maladaptation of connexin-43 and propensity of the heart to lethal arrhythmias

We hypothesized that the pineal hormone melatonin, which exhibits cardioprotective effects, might affect myocardial expression of cell-to-cell electrical coupling protein connexin-43 (Cx43) and protein kinase C (PKC) signaling, and hence, the propensity of the heart to lethal ventricular fibrillation (VF). Spontaneously hypertensive (SHR) and normotensive Wistar rats fed a standard rat chow received melatonin (40 μg/mL in drinking water during the night) for 5 weeks, and were compared with untreated rats. Melatonin significantly reduced blood pressure and normalized triglycerides in SHR, whereas it decreased body mass and adiposity in Wistar rats. Compared with healthy rats, the threshold to induce sustained VF was significantly lower in SHR (18.3 ± 2.6 compared with 29.2 ± 5 mA; p < 0.05) and increased in melatonin-treated SHR and Wistar rats to 33.0 ± 4 and 32.5 ± 4 mA. Melatonin attenuated abnormal myocardial Cx43 distribution in SHR, and upregulated Cx43 mRNA, total Cx43 protein, and its functional phosphorylated forms in SHR, and to a lesser extent, in Wistar rat hearts. Moreover, melatonin suppressed myocardial proapoptotic PKCδ expression and increased cardioprotective PKCε expression in both SHR and Wistar rats. Our findings indicate that melatonin protects against lethal arrhythmias at least in part via upregulation of myocardial Cx43 and modulation of PKC-related cardioprotective signaling.

Melatonin protects against isoproterenol-induced alterations in cardiac mitochondrial energy-metabolizing enzymes, apoptotic proteins, and assists in complete recovery from myocardial injury in rats

The present study was undertaken to explore the protective effect of melatonin against isoproterenol bitartrate (ISO)-induced rat myocardial injury and to test whether melatonin has a role in preventing myocardial injury and recovery when the ISO-induced stress is withdrawn. Treatment for rats with ISO altered the activities of some of the key mitochondrial enzymes related to energy metabolism, the levels of some stress proteins, and the proteins related to apoptosis. These changes were found to be ameliorated when the animals were pretreated with melatonin at a dose of 10 mg/kg BW, i.p. In addition to its ability to reduce ISO-induced mitochondrial dysfunction, we also studied the role of melatonin in the recovery of the cardiac tissue after ISO-induced damage. Continuation of melatonin treatment in rats after the withdrawal of ISO treatment was found to reduce the activities of cardiac injury biomarkers including serum glutamate oxaloacetate transaminase (SGOT), lactate dehydrogenase (LDH), and cardio-specific LDH1 to control levels. The levels of tissue lipid peroxidation and reduced glutathione were also brought back to that seen in control animals by continued melatonin treatment. Continuation of melatonin treatment in post-ISO treatment period was also found to improve cardiac tissue morphology and heart function. Thus, the findings indicate melatonin’s ability to provide cardio protection at a low pharmacological dose and its role in the recovery process. Melatonin, a molecule with very low or no toxicity may be considered as a therapeutic for the treatment for ischemic heart disease.

Cytoprotective effect of benzyl N'-(5-chloro-indol-3-yl-methylidene)-hydrazinecarbodithioate against ethanol-induced gastric mucosal injury in rats

Indolic compounds have attracted a lot of attention due to their interesting biological properties. The present study was performed to evaluate the subacute toxicity and anti-ulcer activity of BClHC against ethanol-induced gastric ulcers. Experimental animal groups were orally pre-treated with different doses of BClHC (50, 100, 200 and 400 mg/kg) in 10% Tween 20 solution (vehicle). Blank and ulcer control groups were pre-treated with vehicle. The positive group was orally pretreated with 20 mg/kg omeprazole. After one hour, all groups received absolute ethanol (5 mL/kg) to generate gastric mucosal injury except the blank control group which was administered the vehicle solution. After an additional hour, all rats were sacrificed, and the ulcer areas of the gastric walls determined. Grossly, the ulcer control group exhibited severe mucosal injury, whereas pre-treatment with either derivative or omeprazole resulted in significant protection of gastric mucosal injury. Flattening of gastric mucosal folds was also observed in rats pretreated with BClHC. Histological studies of the gastric wall of ulcer control group revealed severe damage of gastric mucosa, along with edema and leucocytes infiltration of the submucosal layer compared to rats pre-treated with either BClHC or omeprazole where there were marked gastric protection along with reduction or absence of edema and leucocytes infiltration of the submucosal layer. Subacute toxicity study with a higher dose of derivative (5 g/kg) did not manifest any toxicological signs in rats. In conclusions, the present finding suggests that benzyl N'-(5-chloroindol-3-ylmethylidene)hydrazinecarbodithioate promotes ulcer protection as ascertained by the comparative decreases in ulcer areas, reduction of edema and leucocytes infiltration of the submucosal layer.

Radiation protection following nuclear power accidents: a survey of putative mechanisms involved in the radioprotective actions of taurine during and after radiation exposure

There are several animal experiments showing that high doses of ionizing radiation lead to strongly enhanced leakage of taurine from damaged cells into the extracellular fluid, followed by enhanced urinary excretion. This radiation-induced taurine depletion can itself have various harmful effects (as will also be the case when taurine depletion is due to other causes, such as alcohol abuse or cancer therapy with cytotoxic drugs), but taurine supplementation has been shown to have radioprotective effects apparently going beyond what might be expected just as a consequence of correcting the harmful consequences of taurine deficiency per se. The mechanisms accounting for the radioprotective effects of taurine are, however, very incompletely understood. In this article an attempt is made to survey various mechanisms that potentially might be involved as parts of the explanation for the overall beneficial effect of high levels of taurine that has been found in experiments with animals or isolated cells exposed to high doses of ionizing radiation. It is proposed that taurine may have radioprotective effects by a combination of several mechanisms: (1) during the exposure to ionizing radiation by functioning as an antioxidant, but perhaps more because it counteracts the prooxidant catalytic effect of iron rather than functioning as an important scavenger of harmful molecules itself, (2) after the ionizing radiation exposure by helping to reduce the intensity of the post-traumatic inflammatory response, and thus reducing the extent of tissue damage that develops because of severe inflammation rather than as a direct effect of the ionizing radiation per se, (3) by functioning as a growth factor helping to enhance the growth rate of leukocytes and leukocyte progenitor cells and perhaps also of other rapidly proliferating cell types, such as enterocyte progenitor cells, which may be important for immunological recovery and perhaps also for rapid repair of various damaged tissues, especially in the intestines, and (4) by functioning as an antifibrogenic agent. A detailed discussion is given of possible mechanisms involved both in the antioxidant effects of taurine, in its anti-inflammatory effects and in its role as a growth factor for leukocytes and nerve cells, which might be closely related to its role as an osmolyte important for cellular volume regulation because of the close connection between cell volume regulation and the regulation of protein synthesis as well as cellular protein degradation. While taurine supplementation alone would be expected to exert a therapeutic effect far better than negligible in patients that have been exposed to high doses of ionizing radiation, it may on theoretical grounds be expected that much better results may be obtained by using taurine as part of a multifactorial treatment strategy, where it may interact synergistically with several other nutrients, hormones or other drugs for optimizing antioxidant protection and minimizing harmful posttraumatic inflammatory reactions, while using other nutrients to optimize DNA and tissue repair processes, and using a combination of good diet, immunostimulatory hormones and perhaps other nontoxic immunostimulants (such as beta-glucans) for optimizing the recovery of antiviral and antibacterial immune functions. Similar multifactorial treatment strategies may presumably be helpful in several other disease situations (including severe infectious diseases and severe asthma) as well as for treatment of acute intoxications or acute injuries (both mechanical ones and severe burns) where severely enhanced oxidative and/or nitrative stress and/or too much secretion of vasodilatory neuropeptides from C-fibres are important parts of the pathogenetic mechanisms that may lead to the death of the patient. Some case histories (with discussion of some of those mechanisms that may have been responsible for the observed therapeutic outcome) are given for illustration of the likely validity of these concepts and their relevance both for treatment of severe infections and non-infectious inflammatory diseases such as asthma and rheumatoid arthritis.

Melatonin in mitochondrial dysfunction and related disorders

Mitochondrial dysfunction is considered one of the major causative factors in the aging process, ischemia/reperfusion (I/R), septic shock, and neurodegenerative disorders like Parkinson's disease (PD), Alzheimer's disease (AD), and Huntington's disease (HD). Increased free radical generation, enhanced mitochondrial inducible nitric oxide (NO) synthase activity, enhanced NO production, decreased respiratory complex activity, impaired electron transport system, and opening of mitochondrial permeability transition pore all have been suggested as factors responsible for impaired mitochondrial function. Melatonin, the major hormone of the pineal gland, also acts as an antioxidant and as a regulator of mitochondrial bioenergetic function. Both in vitro and in vivo, melatonin was effective for preventing oxidative stress/nitrosative stress-induced mitochondrial dysfunction seen in experimental models of PD, AD, and HD. In addition, melatonin is known to retard aging and to inhibit the lethal effects of septic shock or I/R lesions by maintaining respiratory complex activities, electron transport chain, and ATP production in mitochondria. Melatonin is selectively taken up by mitochondrial membranes, a function not shared by other antioxidants. Melatonin has thus emerged as a major potential therapeutic tool for treating neurodegenerative disorders such as PD or AD, and for preventing the lethal effects of septic shock or I/R.

Is red wine a SAFE sip away from cardioprotection? Mechanisms involved in resveratrol- and melatonin-induced cardioprotection

Epidemiological studies suggest that regular moderate consumption of red wine confers cardioprotection but the mechanisms involved in this effect remain unclear. Recent studies demonstrate the presence of melatonin in wine. We propose that melatonin, at a concentration found in red wine, confers cardioprotection against ischemia-reperfusion injury. Furthermore, we investigated whether both melatonin and resveratrol protect via the activation of the newly discovered survivor activating factor enhancement (SAFE) prosurvival signaling pathway that involves the activation of tumor necrosis factor alpha (TNFα) and the signal transducer and activator of transcription 3 (STAT3). Isolated perfused male mouse (wild type, TNFα receptor 2 knockout mice, and cardiomyocyte-specific STAT3-deficient mice) or rat hearts (Wistars) were subjected to ischemia-reperfusion. Resveratrol (2.3 mg/L) or melatonin (75 ng/L) was perfused for 15 min with a 10-min washout period prior to an ischemia-reperfusion insult. Infarct size was measured at the end of the protocol, and Western blot analysis was performed to evaluate STAT3 activation prior to the ischemic insult. Both resveratrol and melatonin, at concentrations found in red wine, significantly reduced infarct size compared with control hearts in wild-type mouse hearts (25 ± 3% and 25 ± 3% respectively versus control 69 ± 3%, P < 0.001) but failed to protect in TNF receptor 2 knockout or STAT3-deficient mice. Furthermore, perfusion with either melatonin or resveratrol increased STAT3 phosphorylation prior to ischemia by 79% and 50%, respectively (P < 0.001 versus control). Our data demonstrate that both melatonin and resveratrol, as found in red wine, protect the heart in an experimental model of myocardial infarction via the SAFE pathway.

Melatonin protects against isoproterenol-induced myocardial injury in the rat: antioxidative mechanisms

The present study was undertaken to explore the protective effect of melatonin against isoproterenol bitartrate (ISO)-induced myocardial injury in rat. Treatment of rats with ISO increased the level of lipid peroxidation products and decreased the reduced glutathione levels in cardiac tissue indicating that this synthetic catecholamine induces oxidative damage following oxidative stress. Pretreatment of ISO-injected rats with melatonin at a dose of 10 mg/kg body weight, i.p. prevented these changes. Additionally, melatonin also restored the activities and the levels of antioxidant enzymes which were found to be altered by ISO treatment. Treatment of rats with ISO resulted into an increased generation of hydroxyl radicals with melatonin pretreatment significantly reducing their production. Finally, treatment of rats with ISO caused a lowering of systolic pressure with reduced cardiac output and diastolic dysfunction whereas melatonin pretreatment significantly restored many of these parameters to normal. The findings document melatonin's ability to provide cardio protection at a low pharmacological dose. Melatonin has virtually no toxicity which raises the possibility of this indole being a therapeutic treatment for ischemic heart disease.

Sickle cell disease and stroke

Twenty-four percent of sickle cell disease (SCD) patients have a stroke by the age of 45 years. Blood transfusions decrease stroke risk in patients deemed high risk by transcranial Doppler. However, transcranial Doppler has poor specificity, and transfusions are limited by alloimmunization and iron overload. Transfusion withdrawal may be associated with an increased rebound stroke risk. Extended blood typing decreases alloimmunization in SCD but is not universally adopted. Transfusions for thalassemia begun in early childhood are associated with lower rates of alloimmunization than are seen in SCD, suggesting immune tolerance. Optimal oxygen transport efficiency occurs at a relatively low hematocrit for SCD patients because of hyperviscosity. Consequently, exchange rather than simple transfusions are more effective in improving oxygen transport efficiency, but the former are technically more demanding and require more blood units. Although viscosity is of importance in the noncerebral manifestations of SCD, inflammation may play a larger role than viscosity in the development of large-vessel stroke. The future of SCD stroke management lies in the avoidance of transfusion. Hydroxyurea and anti-inflammatory measures may reduce the need for transfusion. Recent genome-wide association studies may provide methods for modulating fetal hemoglobin production enough to attenuate stroke risk and other complications of SCD.

Reducing oxidative/nitrosative stress: a newly-discovered genre for melatonin

The discovery of melatonin and its derivatives as antioxidants has stimulated a very large number of studies which have, virtually uniformly, documented the ability of these molecules to detoxify harmful reactants and reduce molecular damage. These observations have clear clinical implications given that numerous age-related diseases in humans have an important free radical component. Moreover, a major theory to explain the processes of aging invokes radicals and their derivatives as causative agents. These conditions, coupled with the loss of melatonin as organisms age, suggest that some diseases and some aspects of aging may be aggravated by the diminished melatonin levels in advanced age. Another corollary of this is that the administration of melatonin, which has an uncommonly low toxicity profile, could theoretically defer the progression of some diseases and possibly forestall signs of aging. Certainly, research in the next decade will help to define the role of melatonin in age-related diseases and in determining successful aging. While increasing life span will not necessarily be a goal of these investigative efforts, improving health and the quality of life in the aged should be an aim of this research.

Melatonin protects against heart ischemia-reperfusion injury by inhibiting mitochondrial permeability transition pore opening

Melatonin, a well-known antioxidant, has been shown to protect against ischemia-reperfusion myocardial damage. Mitochondrial permeability transition pore (MPTP) opening is an important event in cardiomyocyte cell death occurring during ischemia-reperfusion and therefore a possible target for cardioprotection. In the present study, we tested the hypothesis that melatonin could protect heart against ischemia-reperfusion injury by inhibiting MPTP opening. Isolated perfused rat hearts were subjected to global ischemia and reperfusion in the presence or absence of melatonin in a Langerdoff apparatus. Melatonin treatment significantly improves the functional recovery of Langerdoff hearts on reperfusion, reduces the infarct size, and decreases necrotic damage as shown by the reduced release of lactate dehydrogenase. Mitochondria isolated from melatonin-treated hearts are less sensitive than mitochondria from reperfused hearts to MPTP opening as demonstrated by their higher resistance to Ca(2+). Similar results were obtained following treatment of ischemic-reperfused rat heart with cyclosporine A, a known inhibitor of MPTP opening. In addition, melatonin prevents mitochondrial NAD(+) release and mitochondrial cytochrome c release and, as previously shown, cardiolipin oxidation associated with ischemia-reperfusion. Together, these results demonstrate that melatonin protects heart from reperfusion injury by inhibiting MPTP opening, probably via prevention of cardiolipin peroxidation.

A novel electrophysiologic effect of melatonin on ischemia/reperfusion-induced arrhythmias in isolated rat hearts

Reperfusion after a short period of cardiac ischemia triggers ventricular arrhythmias attributable to ionic imbalance and oxidative stress. Melatonin offers some degree of protection, but its effects on the cardiac action potentials are unknown. We evaluated the effects of 5, 10, 20 and 50 microM melatonin in isolated perfused rat hearts subjected to 10 min of regional ischemia. ECG and membrane potentials were synchronously displayed. After 15 min of reperfusion, total antioxidant capacity (TAC) was determined. Melatonin did not change the ischemic depolarization nor the action potential amplitude depression, but at the end of ischemia the action potential duration (APD) decreased in control and 5 microM melatonin-treated hearts. By contrast, it returned to preischemic levels in hearts given 20 and 50 microM melatonin. Melatonin reduced the incidence of reperfusion arrhythmias from 100% in control to 50% in 5 and 10 microM, to 40% in 20 microM and 30% in 50 microM hearts. TAC values were higher at all melatonin concentrations. We conclude that melatonin reduced the incidence of reperfusion arrhythmias because of its antioxidant effects. In addition, at 20 and 50 microM lengthened APD and promoted an improved protection. This latter effect should be considered when in vivo applications of melatonin are considered.

Adenosine receptors: therapeutic aspects for inflammatory and immune diseases

Adenosine is a key endogenous molecule that regulates tissue function by activating four G-protein-coupled adenosine receptors: A1, A2A, A2B and A3. Cells of the immune system express these receptors and are responsive to the modulatory effects of adenosine in an inflammatory environment. Animal models of asthma, ischaemia, arthritis, sepsis, inflammatory bowel disease and wound healing have helped to elucidate the regulatory roles of the various adenosine receptors in dictating the development and progression of disease. This recent heightened awareness of the role of adenosine in the control of immune and inflammatory systems has generated excitement regarding the potential use of adenosine-receptor-based therapies in the treatment of infection, autoimmunity, ischaemia and degenerative diseases.

Melatonin receptor-mediated protection against myocardial ischaemia/reperfusion injury: role of its anti-adrenergic actions

Melatonin has potent cardioprotective properties. These actions have been attributed to its free radical scavenging and anti-oxidant actions, but may also be receptor mediated. Melatonin also exerts powerful anti-adrenergic actions based on its effects on contractility of isolated papillary muscles. The aims of this study were to determine whether melatonin also has anti-adrenergic effects on the isolated perfused rat heart, to determine the mechanism thereof and to establish whether these actions contribute to protection of the heart during ischaemia/reperfusion. The results showed that melatonin (50 microM) caused a significant reduction in both isoproterenol (10(-7) M) and forskolin (10(-6) M) induced cAMP production and that both these responses were melatonin receptor dependent, since the blocker, luzindole (5 x 10(-6) M) abolished this effect. Nitric oxide (NO), as well as guanylyl cyclase are involved, as L-NAME (50 microM), an NO synthase inhibitor and ODQ (20 microM), a guanylyl cyclase inhibitor, significantly counteracted the effects of melatonin. Protein kinase C (PKC), as indicated by the use of the inhibitor bisindolylmaleimide (50 microM), also play a role in melatonin's anti-adrenergic actions. These actions of melatonin are involved in its cardioprotection: simultaneous administration of L-NAME or ODQ with melatonin, before and after 35 min regional ischaemia, completely abolished its cardioprotection. PKC, on the other hand, had no effect on the melatonin-induced reduction in infarct size. Cardioprotection by melatonin was associated with a significant activation of PKB/Akt and attenuated activation of the pro-apoptotic kinase, p38MAPK during early reperfusion. In summary, the results show that melatonin-induced cardioprotection may be receptor dependent, and that its anti-adrenergic actions, mediated by NOS and guanylyl cyclase activation, are important contributors.

The effect of high dose melatonin on cardiac ischemia- reperfusion Injury

PURPOSE

Melatonin, the most potent scavenger of toxic free radicals, has been found to be effective in protecting against pathological states due to the release of reactive oxygen species. This study was performed to establish the effect of high dose melatonin on protection against ischemia- reperfusion (I/R) injury in rat hearts.

MATERIALS AND METHODS

Forty male Sprague-Dawley rats were used in this study. They were separated into four groups of ten rats each. A left coronary artery occlusion was induced in the rats by ligating the artery for 20 minutes and then releasing the ligation (reperfusion) afterwards. The control group was Group A. Group B was subjected to myocardial ischemia-reperfusion without any treatment, while Group C underwent myocardial ischemia-reperfusion with a melatonin treatment before the ischemia. Group D was subjected to myocardial ischemia-reperfusion with a melatonin treatment before the reperfusion. After 20 minutes of reperfusion, blood samples were obtained from each group for biochemical studies, and the animals were sacrificed for histological and, immunohistochemical examinations of the myocardial tissue.

RESULTS

We found that the cardiac troponin T(cTn-T) levels were significantly increased in Group B when all groups were compared. In the Group C rats treated with melatonin, the cTn-T values were significantly lower than those in Groups B and D. In addition, malondialdehyde (MDA) and antioxidant enzymes including, superoxide dismutase (SOD) and myeloperoxidase (MPO) were lower than those in Group B in the melatonin treated groups. The differences were statistically significant (p < 0.05). Histopathologic and immunohistopathologic studies also supported the effectiveness of melatonin.

CONCLUSION

Our study suggests that high dose melatonin, appears to offer protection against cardiac ischemia-reperfusion injuries in rats by scavenging the free radicals and could have a potential clinical use in the management of myocardial ischemia.

Long-term postinfarction melatonin administration alters the expression of DHPR, RyR2, SERCA2, and MT2 and elevates the ANP level in the rat left ventricle

We investigated the effect of 2 wk continuous postinfarction subcutaneous melatonin supply on the expression of the rat left ventricular (LV) dihydropyridine receptor (DHPR), ryanodine receptor (RyR(2)), and sarco-endoplasmic reticulum Ca(2+)-ATPase2 (SERCA2), as they are fundamental proteins in cardiac contractility. The levels of plasma and LV atrial (ANP) and brain natriuretic peptide and melatonin were also measured, as was the expression of LV MT(1) and MT(2) receptors and pineal arylalkylamine N-acetyltransferase. Myocardial infarction (MI) was induced by ligation of the left anterior descending coronary artery and vehicle or melatonin (4.5 mg/kg per day) was administered by subcutaneous osmotic pumps. Echocardiography, real-time quantitative reverse transcription-polymerase chain reaction, and western blotting were used to analyze the samples. Echocardiography revealed that MI induced serious systolic LV dysfunction. The expression of DHPR, RyR(2), and SERCA2 mRNAs was significantly lower in the LVs of melatonin-treated MI rats compared with vehicle-treated rats (P < 0.01 for DHPR and P < 0.05 for RyR(2) and SERCA2). Melatonin also elevated the amount of LV MT(2) receptors to 1.9-fold (P < 0.05) and the concentration of LV ANP to over fivefold (P < 0.05) compared with vehicle rats after MI. Therefore, the results suggest that melatonin may influence the cardiac contractility after MI by regulating the expression of DHPR, RyR(2), and SERCA2, and melatonin receptors, particularly MT(2)s, might contribute to the postinfarction cardioprotective actions of melatonin. Furthermore, the finding of the relationship between melatonin and ANP suggests a novel mechanism for melatonin in protecting the heart after MI.

Cardiovascular diseases: protective effects of melatonin

This brief review considers some of the cardiac diseases and conditions where free radicals and related reactants are believed to be causative. The report also describes the beneficial actions of melatonin against oxidative cardiovascular disorders. Based on the data available, melatonin seems to have cardioprotective properties via its direct free radical scavenger and its indirect antioxidant activity. Melatonin efficiently interacts with various reactive oxygen and reactive nitrogen species (receptor independent actions) and it also upregulates antioxidant enzymes and downregulates pro-oxidant enzymes (receptor-dependent actions). Moreover, melatonin enters all cells and subcellular compartments and crosses morphophysiologic barriers. These findings have implications for the protective effects of melatonin against cardiac diseases induced by oxidative stress. Melatonin attenuates molecular and cellular damages resulting from cardiac ischemia/reperfusion in which destructive free radicals are involved. Anti-inflammatory and antioxidative properties of melatonin are also involved in the protection against a chronic vascular disease, atherosclerosis. The administration of melatonin, as a result of its antioxidant features, has been reported to reduce hypertension and cardiotoxicity induced by clinically used drugs. The results described herein help to clarify the beneficial effects of melatonin against these conditions and define the potential clinical applicability of melatonin in cardiovascular diseases.

Melatonin inhibits free radical-mediated mitochondrial-dependent hepatocyte apoptosis and liver damage induced during malarial infection

We showed earlier that malarial infection significantly induces liver apoptosis mediated by oxidative stress mechanisms. Thus, a nontoxic antioxidant-antiapoptotic molecule may be beneficial for hepatoprotection. Melatonin remarkably prevents hepatocyte apoptosis in mice induced during malaria as indicated by caspase 3 and TUNEL assays as well as transmission electron microscopy (TEM) of the liver tissue. The mitochondrial apoptotic pathway, which plays a critical role in liver cell death during malarial infection, was almost completely suppressed by melatonin as it corrects both the overexpression of Bax and down-regulation of bcl-2 as revealed by semiquantitative RT-PCR. Fluorometric studies using JC-1 documented that melatonin also restores mitochondrial transmembrane potential (DeltaPsim) in malaria-infected mice liver. The antiapoptotic effect of melatonin is associated with its antioxidant role because melatonin protects liver from oxidative stress induced during malaria by scavenging the hydroxyl radicals, preventing the depletion of reduced glutathione, inhibiting lipid peroxidation and protein carbonyl formation. The effective antioxidant dose of melatonin to protect liver from oxidative stress during malaria is 20 times lower than that of known antioxidants, vitamin C and vitamin E. Apoptosis of hepatocytes during malarial infection is well correlated with dysfunction of the liver while melatonin offers hepatoprotective effects as indicated by different liver function tests. Thus, melatonin may well be effective in combating oxidative stress-induced apoptosis and liver damage during malaria infection.

Remote organ injury induced by myocardial ischemia and reperfusion on reproductive organs, and protective effect of melatonin in male rats

OBJECTIVE

Myocardial ischemia and reperfusion (MI-R) leads to remote organ injury associated with oxidative stress. Melatonin is a well-known antioxidant and free-radical scavenger. This study was conducted to examine whether MI-R causes damage in the testes and sperm quality, and to investigate the possible protective effect of exogenous melatonin on these parameters in an in vivo rat model.

DESIGN

Experimental study.

SETTING

Experimental Research Center, Firat University Medical School, Elaziğ, Turkey.

PATIENT(S)

Eight-week-old male Wistar rats (n = 18).

INTERVENTION(S)

To produce MI-R, a branch of the descending left coronary artery was occluded for 30 minutes, followed by 120-minute reperfusion. Melatonin (10 mg/kg) or vehicle was given 10 minutes before ischemia via the jugular vein.

MAIN OUTCOME MEASURE(S)

Reproductive organ weights and epididymal sperm concentration, sperm motility, abnormal sperm rate, and testicular-tissue malondialdehyde (MDA) and glutathione (GSH) levels were examined after reperfusion.

RESULT(S)

MI-R significantly decreased epididymal sperm motility, and increased the testes-tissue level of MDA, compared to the control group. Administration of melatonin reversed the harmful effects of MI-R significantly. However, MI-R did not change sperm concentration, GSH levels, and reproductive organ weights.

CONCLUSION(S)

These findings indicate that MI-R leads to damage of testis tissue and sperm motility, and melatonin protects against MI-R-induced reproductive-organ injury. These results may also encourage the use of antioxidants to reduce remote organ injury in the testis after MI-R.

The effect of myocardial infarction on the synthesis, concentration and receptor expression of endogenous melatonin

We examined the time course of changes in the synthesis and levels of endogenous melatonin and in the expression of MT(1) and MT(2) melatonin receptors 1 day, 2 and 4 wk after myocardial infarction (MI) in rats. MI was produced by ligation of the left anterior descending coronary artery. Transthoracic echocardiography was performed to characterize structural and functional changes after MI. mRNA levels were measured by real-time quantitative reverse transcription-polymerase chain reaction and proteins by Western blotting. One day after infarction, MI rats had 4.3 times (P < 0.001) higher pineal melatonin synthesis, than sham-operated animals, which was associated with the increased concentration of melatonin in plasma (P < 0.001) and left ventricle (LV) (P = 0.01). The amount of MT(1) receptor protein decreased significantly in MI LVs compared with control LVs 1 day after infarction (P < 0.01), followed by recovery during the next 2 wk. Furthermore, the expression of MT(1) receptor mRNA of the MI LVs was elevated 2 wk after infarction (P < 0.01) compared with control LVs. The amount of MT(2) receptor proteins in MI LVs was higher than in sham-operated LVs 1 day (P < 0.05) and 4 wk (P < 0.01) after MI. In conclusion, melatonin synthesis in the pineal gland increased rapidly in response to the MI, supporting an important role for endogenous melatonin in protecting the heart after MI. The observed changes in the expression of MT(1) and MT(2) receptors suggest that melatonin receptors may be involved in mediating, at least, in part, the protective effects of melatonin in the heart after infarction.

Melatonin reduces ventricular arrhythmias and preserves capillary perfusion during ischemia-reperfusion events in cardiomyopathic hamsters

Earlier studies showed that melatonin has powerful antioxidative effects on ischemia-reperfusion (I/R) injury in healthy hamsters. In the present study, the possible protective effects of melatonin in 10-month-old cardiomyopathic (CM) hamsters were evaluated in a model of I/R in the cheek pouches observed by intravital microscopy. In CM (BIO 14.6) hamsters diameter, red blood cell (RBC) velocity and flow in arterioles as well as lipid peroxide and nitrite/nitrate concentrations in the systemic blood, perfused capillary length, vascular permeability, and leukocyte adhesion were measured after melatonin injection (6 mg/kg intraperitoneally daily for 3 weeks), and after I/R. The influence of melatonin on the incidence of postischemic-reperfusion-induced ventricular tachycardia (VT) and ventricular fibrillation (VF) were also measured. Changes in the arteriolar response to NG-monomethyl-L-arginine (L-NMMA), a nitric oxide inhibitor, norepinephrine (NE), and angiotensin II (ANG II) were studied before and after melatonin injection (10 mg/kg intravenously). In CM hamsters, melatonin restored normal arteriolar responses to L-NMMA, NE, and ANG II. I/R elevated lipid peroxide and nitrate/nitrite levels, and vascular permeability while arteriolar diameter, RBC velocity, flow and capillary perfusion were reduced. These effects were more marked in CM versus healthy hamsters. During I/R melatonin reduced oxidative and nitrosative stress, vasoconstriction, leukocyte adhesion, and vascular permeability and increased capillary perfusion. Melatonin reduced the incidence of VT while VF during reperfusion disappeared totally. In conclusion, melatonin prevents both microvascular injury and ventricular arrhythmias during postischemic reperfusion by modulating the lipid peroxide overproduction and nitrative stress which are involved in the development of cardiomyopathy.

Glycogen synthase kinase-3β activity plays very important roles in determining the fate of oxidative stress-inflicted neuronal cells

Glycogen synthase kinase-3, especially the beta form (GSK-3beta), plays key roles in oxidative stress-induced neuronal cell death, an important pathogenic mechanism of various neurodegenerative diseases. Although the neuroprotective effects of GSK-3beta inhibitors have been described, the optimal level of GSK-3beta inhibition for neuronal cell survival has not yet been determined. We investigated the effect of varying GSK-3beta activity on the viability of oxidative stress-injured neuronally differentiated PC12 (nPC12) cells and intracellular signals related with the GSK-3beta and caspase-3 pathways. Compared to the nPC12 control cells treated with only 100 microM H(2)O(2), treatment of 50-200 nM GSK-3beta inhibitor II or 25-500 nM GSK-3beta inhibitor VIII reduced the increased enzyme activity by about 50% and protected the cells against H(2)O(2)-induced oxidative stress. The optimal concentration of GSK-3beta inhibitor II enhanced heat shock transcription factor-1 levels, decreased levels of phosphorylated tau (Ser202) and cytosolic cytochrome c, activated caspase-3, and cleaved poly (ADP-ribose) polymerase. In contrast, higher concentrations of GSK-3beta inhibitor II (more than 500 nM) induced neuronal cell death and showed opposite effects relative to the above described intracellular signals. These results suggest that optimized inhibitor levels for modulating GSK-3beta activity may prevent apoptosis induced by oxidative stress associated with neurodegenerative diseases.

2,3-Butanedione monoxime does not protect cardiomyocytes under oxidative stress

Heart muscle ischemia-reperfusion provokes a pronounced cardiomyocyte oxidative stress. In the present study, we examined a possible protective effect of the cardioprotective drug, 2,3-butanedione monoxime (BDM), on the cultured neonatal cardiac myocytes exposed to oxidative stress induced by hypochlorous acid (HOCl), that may be formed by activated polymorphonuclear neutrophils in myocardium ischemic-reperfusion areas, and a useful model oxidant, tert-butyl hydroperoxide (tBHP). Using isolated rat cardiomyocytes substantial cytotoxicity of HOCl and tBHP was demonstrated: The concentrations of HOCl and tBHP causing a 50% decrease of cardiomyocyte cell viability were estimated to be 55 +/- 5 microM and 36 +/- 6 microM, respectively. The cell viability measured immediately after the tBHP oxidative treatment was significantly higher than that measured after 22 h of cell post-incubation in a fresh culture medium. This showed delayed cell death after removing tBHP. Hypochlorous acid treatment of cardiomyocytes did not change cellular viability during the cellular post-incubation in a fresh medium. Even a long-term (22 h) incubation of oxidatively damaged cardiomyocytes with BDM (5 mM) added after the HOCl removal did not recover the viability of the HOCl-exposed cells. In the presence of BDM, the cytotoxicity of HOCl significantly increased probably due to a direct reaction of both compounds and toxic chlorinated derivative formation. 2,3-Butanedione monoxime (5 mM) did not reduce cytotoxicity of tBHP, either. Such well-known antioxidative agents as melatonin or glutathione considerably prevented oxidant-induced cell death in a concentration-dependent manner.

Melatonin reduces ischemia/reperfusion-induced superoxide generation in arterial wall and cell death in skeletal muscle

The purpose of this study was to determine the effect of melatonin on superoxide generation in arterial wall at an early phase of reperfusion and on endothelial dysfunction of microvasculature and cell viability of cremaster muscle at late phase of reperfusion (24 hr) after prolonged ischemia. Bilateral vascular pedicles which supply blood flow to the cremaster muscle were exposed. After surgical preparation, microvascular clamps were applied on the right iliac, femoral and spermatic arteries to create 4 hr of ischemia in both feeding vessels and the unexposed cremaster muscle. The vascular clamping was omitted on the left iliac, femoral and spermatic arteries and served as an internal control. Melatonin or Vehicle was via by intravenous injection at 10 min prior to reperfusion and 10 min after reperfusion. In the first experiment, the vascular pedicle was harvested after reperfusion to measure superoxide generation in real time by lucigenin-derived chemiluminescence. In the second experiment, endothelial-dependent and -independent vasodilatation was examined in the terminal arteriole of cremaster muscle which was then harvested to examine cell viability by WST-1 assay on day 2. Superoxide generation in arterial wall peaked at first 5-min of reperfusion and declined to near baseline after 60 min of reperfusion. Melatonin treatment significantly reduced superoxide generation in arterial walls and improved cell viability in cremaster muscles. Melatonin treatment also significantly reduced microvascular endothelial dysfunction which was still observable in the microcirculation of cremaster muscle after 24 hr of reperfusion. Melatonin reduces superoxide generation in the early phase of reperfusion resulting in attenuating endothelial dysfunction and muscle cell death in the late phase of reperfusion.

C-phycocyanin protects against ischemia-reperfusion injury of heart through involvement of p38 MAPK and ERK signaling

We previously showed that C-phycocyanin (PC), an antioxidant biliprotein pigment of Spirulina platensis (a blue-green alga), effectively inhibited doxorubicin-induced oxidative stress and apoptosis in cardiomyocytes. Here we investigated the cardioprotective effect of PC against ischemia-reperfusion (I/R)-induced myocardial injury in an isolated perfused Langendorff heart model. Rat hearts were subjected to 30 min of global ischemia at 37°C followed by 45 min of reperfusion. Hearts were perfused with PC (10 μM) or Spirulina preparation (SP, 50 mg/l) for 15 min before the onset of ischemia and throughout reperfusion. After 45 min of reperfusion, untreated (control) hearts showed a significant decrease in recovery of coronary flow (44%), left ventricular developed pressure (21%), and rate-pressure product (24%), an increase in release of lactate dehydrogenase and creatine kinase in coronary effluent, significant myocardial infarction (44% of risk area), and TdT-mediated dUTP nick end label-positive apoptotic cells compared with the preischemic state. PC or SP significantly enhanced recovery of heart function and decreased infarct size, attenuated lactate dehydrogenase and creatine kinase release, and suppressed I/R-induced free radical generation. PC reversed I/R-induced activation of p38 MAPK, Bax, and caspase-3, suppression of Bcl-2, and increase in TdT-mediated dUTP nick end label-positive apoptotic cells. However, I/R also induced activation of ERK1/2, which was enhanced by PC treatment. Overall, these results for the first time showed that PC attenuated I/R-induced cardiac dysfunction through its antioxidant and antiapoptotic actions and modulation of p38 MAPK and ERK1/2.

Protective effect of melatonin against mitochondrial dysfunction associated with cardiac ischemiareperfusion: role of cardiolipin

Reactive oxygen species (ROS) are considered an important factor in ischemia/reperfusion injury to cardiac myocytes. Mitochondrial respiration, mainly at the level of complex I and III, is an important source of ROS generation and hence a potential contributor of cardiac reperfusion injury. Appropriate antioxidant strategies could be particularly useful to limit this ROS generation and associated mitochondrial dysfunction. Melatonin has been shown to effectively protect against ischemic-reperfusion myocardial damage. The mechanism by which melatonin exerts this cardioprotective effect is not well established. In the present study we examined the effects of melatonin on various parameters of mitochondrial bioenergetics in a Langerdoff isolated perfused rat heart model. After isolation of mitochondria from control, ischemic-reperfused and melatonin-treated ischemic-reperfused rat heart, various bioenergetic parameters were evaluated such as rates of mitochondrial oxygen consumption, complex I and complex III activity, H2O2 production as well as the degree of lipid peroxidation, cardiolipin content, and cardiolipin oxidation. We found that reperfusion significantly altered all these mitochondrial parameters, while melatonin treatment had strong protective effect attenuating these alterations. This effect appears to be due, at least in part, to the preservation, by ROS attack, of the content and integrity of cardiolipin molecules which play a pivotal role in mitochondrial bioenergetics. Protection of mitochondrial dysfunction was associated with an improvement of post-ischemic hemodynamic function of the heart. Melatonin had also strong protective effect against oxidative alterations to complex I and III as well as to cardiolipin in isolated mitochondria.

Short- and long-term effects of melatonin on myocardial post-ischemic recovery

Melatonin, the chief secretory product of the pineal gland, has been shown to protect the heart against ischemia-reperfusion injury. This was attributed to its free radical scavenging and broad-spectrum antioxidant properties. The possibility that melatonin may act via its receptor and intracellular signaling, has not yet been addressed in this regard. In all previous studies, only the acute effects of melatonin on the heart, were evaluated. The aims of the present study were to: (i) compare the acute and long-term effects of melatonin on infarct size and functional recovery of the ischemic heart, and (ii) evaluate the role of the melatonin receptor in cardioprotection. For evaluation of the short-term effects of melatonin on contractile recovery and infarct size, the isolated perfused working rat heart was subjected to 20 min global ischemia or 35 min regional ischemia respectively, and melatonin (25-50 microm) administered either before and during reperfusion, or before ischemia or during reperfusion after ischemia. The melatonin receptor was manipulated using luzindole and N-acetyltryptamine. The long-term effects of melatonin were evaluated 24 hr after melatonin administration (2.5 or 5.0 mg/kg, i.p.) or after oral administration for 7 days (20 or 40 microg/mL). Infarct size and mechanical recovery during reperfusion of the working heart were used as endpoints. Melatonin (50 microm), when administered either before and during reperfusion after ischemia or during reperfusion only, significantly improved cardiac output and work performance and reduced infarct size compared with untreated controls. Luzindole (5 microm), a melatonin receptor antagonist, abolished these cardioprotective effects. Long-term administration of melatonin (i.p. or orally for 7 days) caused a significant reduction in infarct size of hearts subjected to 35 min regional ischemia. The cardioprotection persisted for 2-4 days after discontinuation of treatment. In summary, the results obtained suggest that melatonin induces short- as well as long-term protection and that the melatonin receptor is also involved in its cardioprotective actions.

15-Deoxy-delta12,14-prostaglandin J2, a neuroprotectant or a neurotoxicant?

15-Deoxy-delta12,14-prostaglandin J2 (15d-PGJ2) is a potent ligand for peroxisome proliferators-activated receptor gamma (PPARgamma). However, its various effects independent of PPARgamma have recently been observed. The effect of 15d-PGJ2 on neuronal cells is still controversial. We investigated its effect on neuronal cells (N18D3 cells). When N18D3 cells were treated with 15d-PGJ2, the viability was not changed up to 8 microM, but decreased at higher than 8 microM. The expressions of survival signals, such as p85a phosphatidylinositol 3-kinase, phospho-Akt, and phospho-glycogen synthase kinase-3 beta (Ser-9), slightly increased up to 8 microM, however, decreased at higher than 8 microM. The levels of free radicals and membrane lipid peroxidation and the expression of c-Jun N-terminal Kinase increased in a dose-dependent manner, especially at higher than 8 microM. However, the expressions of death signals, such as cytosolic cytochrome c, activated caspase-3, and cleaved poly(ADP-ribose) polymerase, decreased up to 8 microM, however, increased at higher than 8 microM. In the study to evaluate whether low dose of 15d-PGJ2, up to 8 microM, had protective effect on oxidative stress-injured N18D3 cells, compared to the cells treated with only 100 microM H2O2, the pretreatment with 8 microM 15d-PGJ2 increased the viability and the expressions of the survival signals, but decreased them of the death signals. These results indicate that 15d-PGJ2 could be a neuroprotectant or a neurotoxicant, depending on its concentration. Therefore, some specific optimum dose of 15d-PGJ2 may be a new potential therapeutic candidate for oxidative stress-injury model of neurodegenerative diseases.

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.

Differential effects of diallyl disulfide on neuronal cells depend on its concentration

Diallyl disulfide (DADS) is one of the organosulfur compounds of garlic. The effects of DADS on neuronal cells have not clearly been established. We investigated its effects on the viability of neuronal cells (N18D3 cells), the levels of free radical and membrane lipid peroxidation, and the cell signals, such as phosphatidylinositol 3-kinase (PI3K)/Akt and glycogen synthase kinase-3 (GSK-3). When N18D3 cells were treated with several concentrations of DADS, the viability was not affected up to 25 microM, however, decreased at higher than 25 microM. The levels of free radicals and membrane lipid peroxidation were increased in a dose-dependent manner, especially at higher than 25 microM. The treatment of N18D3 cells with 25 microM DADS slightly increased the expressions of p85a PI3K, phosphorylated Akt and phosphorylated GSK-3, but the treatment with 100 microM significantly reduced them. To evaluate whether low concentration of DADS, up to 25 microM, had protective effect on oxidative stress-injured N18D3 cells, the viability of N18D3 cells (pretreated with DADS for 2h versus not pretreated) was evaluated 24h after their exposure to 100 microM H(2)O(2) for 30 min. Compared to the cells treated with only 100 microM H(2)O(2), the pretreatment with 25 microM DADS increased the viability, and the expressions of p85a PI3K, phosphorylated Akt and phosphorylated GSK-3. These results indicate that low concentration of DADS has protective effects on N18D3 cells, whereas high concentration is rather cytotoxic. Therefore, some specific optimum concentration of DADS may be a new potential therapeutic strategy for oxidative stress-injury in vitro model of neurodegenerative diseases.

The expression of MT1 and MT2 melatonin receptor mRNA in several rat tissues

The mechanisms that mediate the various effects of melatonin in mammalian tissues are not always known. Therefore, the aim of this study was to investigate whether MT(1) and MT(2) melatonin receptors are expressed in certain tissues of the rat. The expression of MT(1) and MT(2) melatonin receptor mRNA was determined using a real-time quantitative RT-PCR method. In addition, we examined whether mRNA for either subtype of receptor shows any difference in the expression between midnight and noon, similar to the changes in melatonin concentrations in plasma and tissue samples. MT(1) and MT(2) melatonin receptor mRNAs were found in the rat hypothalamus, retina and small intestine. We also showed a low expression of MT(2) mRNA in the rat liver and heart SA node. In the heart apex and the Harderian gland, no appearance of either of the receptor mRNAs was detectable. A significant difference in the expression of MT(1) mRNA between day and night was found in the hypothalamus. In conclusion, our findings suggest that at least some effects of melatonin are mediated through membrane MT(1) and MT(2) receptors in the hypothalamus, the retina and the small intestine. Down-regulation of receptors might be one reason for the difference in the hypothalamic MT(1) melatonin receptor mRNA expression between midnight and noon. In the liver and the heart SA node, the physiological significance of possible MT(2) receptors remains unclear. According to our negative midnight and noon results in the Harderian gland and heart apex melatonin may exert its effect on these tissues by a non-receptor mechanism.

Protective effect of diallyl disulfide on oxidative stress-injured neuronally differentiated PC12 cells

The effects of diallyl disulfide (DADS), a garlic-derived compound, on the viability of neuronal cells and cell signals, including phosphatidylinositol 3-kinase (PI3K)/Akt, glycogen synthase kinase-3 (GSK-3), cytochrome c, caspase-3, and poly(ADP-ribose) polymerase (PARP), were investigated in PC12 cells neuronally differentiated by nerve growth factor. To evaluate the toxicity of DADS itself, nPC12 cells were treated with several concentrations of DADS, and 3,(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and trypan blue stain revealed that the viability was not affected by low concentration of DADS, up to 20 microM, but it was decreased at higher than this concentration. The levels of free radicals and membrane lipid peroxidation were significantly increased in nPC12 cells when treated with more than 50 microM DADS, and treatment of PC12 cells with 100 microM DADS killed the cells by inhibiting PI3K/Akt and by promoting activation of GSK-3 and caspase-3, release of cytochrome c, and cleavage of PARP. To evaluate the protective effects of low concentration of DADS on oxidative stress-injured nPC12 cells, the viability of the cells (pretreated with DADS for 2 h vs. not pretreated) was evaluated 24 h after exposure to 100 microM H2O2 for 30 min. Compared to the cells treated with 100 microM H2O2 only, pretreatment of the cells with 20 microM DADS before exposure to 100 microM H2O2 increased the viability and induced activation of PI3K and Akt, inactivation of GSK-3, and inhibition of cytochrome c release, caspase-3 activation, and PARP cleavage. These results indicate that low concentration of DADS has neuroprotective effects by activating PI3K/Akt and by inhibiting GSK-3 activation, cytochrome c release, caspase-3 activation, and PARP cleavage, whereas high concentration is rather cytotoxic. Therefore, some specific optimum concentration of DADS may be a new potential therapeutic strategy for oxidative stress injured in vitro model of neurodegenerative diseases.

Protective effect of melatonin on liver ischemia reperfusion injury in rats

AIM: To investigate the effect of melatonin (Mel) on liver ischemia reperfusion (I/R) injury in rats.

METHODS: 150 male Wistar rats (190-210 g, 6-7weeks age) were divided into three groups at random: Mel exposure group, alcohol solvent control group and saline control group. The left branches of portal vein, hepatic artery, hepatic duct were blocked up for 60 min and then opened to establish liver I/R I models in rats. In each group, samples were collected in 0.5, 1, 6, 12, and 24 h after reperfusion respectively. 20 mg/kg of Mel was injected peritoneally in rats 30 min before experimentation in Mel exposure group. The duplicate concentration of alcohol and the same volume of saline were injected in control group as a substitution. Serum alanine aminotransferase (ALT) by auto biochemical analyzer, and superoxide dismutase (SOD) and terminal productions of lipid peroxidationin (MDA) in liver tissue were measured. Pathological changes in liver and immunohistochemical straining of ICAM-1 were determined with optical microscope.

RESULTS: The level of ALT measured in various time after reperfusion in Mel group was totally significantly lower than that in alcohol and saline control groups (P < 0.05). The level of MDA measured in 6 h, 12 h, and 24 h after reperfusion in Mel group was significantly lower than that in alcohol and saline control groups (P < 0.05). The level of SOD measured in 12, 24 h after reperfusion in Mel group was significantly higher than that in alcohol and saline control groups (P < 0.05). The expression level of ICAM-1 (%) measured in various time after reperfusion in Mel group was significantly lower than that in alcohol and saline control groups (P < 0.05).

CONCLUSION: Exotic Mel inhibits the activities of ALT, increases activities of superoxide dismutase (SOD), and decreases the cumulation of MDA in liver reperfusion tissue and expression of ICAM-1 in liver reperfusion tissue. Therefore, it can improve the hepatic function after reperfusion and plays a definitely protective role in liver I/R.

Cardioprotective effects of melatonin on recovery of rat donor hearts after 12-hour preservation

The cardioprotective effects of melatonin on recovery of rat donor hearts after 12 h of preservation were investigated. Wistar rats weighing 200 to 250 g (n=24) were randomly divided into 3 groups. In the non-storage group (n=8), donor hearts were not stored. In the melatonin group (n=8), donor hearts were stored in 4 degrees C St. Thomas solution with melatonin (0.1 mmol/L). In the control group (n=8), donor hearts were stored in 4 degrees C St. Thomas solution only. The coronary flow (CF), cardiac function, coronary vasodilatory response, creatine kinase (CK) and high energy phosphate levels were measured after the hearts had been preserved for 12 h. Transmission electron microscopy was used to examine the microstructural changes after 12 h of preservation. The recovery of cardiac function and coronary vasodilatory response were significantly improved in the melatonin group (P<0.01). CK release decreased greatly in the melatonin group (P<0.01). High energy phosphate levels were significantly better preserved in the melatonin group (P<0.01). Histological findings were much better in the melatonin group than in the control group. These results suggest that melatonin has cardioprotective effects on the recovery of rat donor hearts after 12 h of preservation.

Protective effect of melatonin on myocardial infarction

The dose- and time dependence of melatonin and the effective window of melatonin administration were determined in a mouse model of myocardial infarction. When mouse hearts were subjected to 60 min of occlusion of the left anterior descending artery (LAD) followed by 4 h of reperfusion, melatonin pretreatment for 30 min significantly reduced the infarct size/risk area. The most effective dose was found to be 150 microg/kg intraperitoneally, and the effective period of protection lasted up to 2 h after melatonin administration. Melatonin administration 45 min after LAD ligation or right before reperfusion was as effective as administration 30 min before ligation; however, melatonin administered after the release of occlusion was not protective. Melatonin's effect was still present in mice deficient for the Mel1a melatonin receptor. 8-Methoxy-2-propionamidotetralin, a melatonin receptor agonist with no antioxidant activity, offered no protection, suggesting a lack of involvement of melatonin receptors. Finally, the effects of melatonin were similar in rats and mice. Our results demonstrate that melatonin is an effective cardioprotective agent when administered either before or during coronary occlusion at a very low dose.