The role of mitochondrial complex III in melatonin-induced ROS production in cultured mesangial cells

Melatonin-Loaded Nanoparticles Augment Mitophagy to Retard Parkinson's Disease

The molecular pathways that melatonin follows as a Parkinson's disease (PD) antagonist remain poorly elucidated, despite it being a safe and a potential neurotherapeutic drug with a few limitations such as less bioavailability, premature oxidation, brain delivery, etc. Here, we used a biocompatible protein (HSA) nanocarrier for the delivery of melatonin to the brain. This nanomelatonin showed better antioxidative and neuroprotective properties, and it not only improves mitophagy to remove unhealthy mitochondria but also improves mitochondrial biogenesis to counteract rotenone-induced toxicity in an in vitro PD model. We also showed BMI1, a member of the PRC1 complex that regulates mitophagy, whose protein expression was enhanced after nanomelatonin dosage. These effects were translated to a rodent model, where nanomelatonin improves the TH+ve neuron population in SNPC and protects against rotenone-mediated toxicity. Our findings highlight the significantly better in vitro and in vivo neuroprotective effect of nanomelatonin as well as the molecular/cellular dynamics it influences to regulate mitophagy as a measure of the potential therapeutic candidate for PD.

Unveiling the Protective Role of Melatonin in Osteosarcoma: Current Knowledge and Limitations

Melatonin, an endogenous neurohormone produced by the pineal gland, has received increased interest due to its potential anti-cancer properties. Apart from its well-known role in the sleep-wake cycle, extensive scientific evidence has shown its role in various physiological and pathological processes, such as inflammation. Additionally, melatonin has demonstrated promising potential as an anti-cancer agent as its function includes inhibition of tumorigenesis, induction of apoptosis, and regulation of anti-tumor immune response. Although a precise pathophysiological mechanism is yet to be established, several pathways related to the regulation of cell cycle progression, DNA repair mechanisms, and antioxidant activity have been implicated in the anti-neoplastic potential of melatonin. In the current manuscript, we focus on the potential anti-cancer properties of melatonin and its use in treating and managing pediatric osteosarcoma. This aggressive bone tumor primarily affects children and adolescents and is treated mainly by surgical and radio-oncological interventions, which has improved survival rates among affected individuals. Significant disadvantages to these interventions include disease recurrence, therapy-related toxicity, and severe/debilitating side effects that the patients have to endure, significantly affecting their quality of life. Melatonin has therapeutic effects when used for treating osteosarcoma, attributed to its ability to halt cancer cell proliferation and trigger apoptotic cell death, thereby enhancing chemotherapeutic efficacy. Furthermore, the antioxidative function of melatonin alleviates harmful side effects of chemotherapy-induced oxidative damage, aiding in decreasing therapeutic toxicities. The review concisely explains the many mechanisms by which melatonin targets osteosarcoma, as evidenced by significant results from several in vitro and animal models. Nevertheless, if further explored, human trials remain a challenge that could shed light and support its utility as an adjunctive therapeutic modality for treating osteosarcoma.

Effect of neonatal melatonin administration on behavioral and brain electrophysiological and redox imbalance in rats

Introduction

Melatonin (MLT) reportedly has beneficial effects in neurological disorders involving brain excitability (e.g., Epilepsy and Migraine) and behavioral patterns (e.g., Anxiety and Depression). This study was performed to investigate, in the developing rat brain, the effect of early-in-life administration of two different doses of exogenous MLT on behavioral (anxiety and memory) and electrophysiological (CSD analysis) aspects of brain function. Additionally, brain levels of malondialdehyde (MDA) and superoxide dismutase (SOD), both cellular indicators of redox balance status, were evaluated. We hypothesize that MLT differentially affects the behavioral and CSD parameters as a function of the MLT dose.

Materials and methods

Male Wistar rats received, from the 7th to the 27th postnatal day (PND), on alternate days, vehicle solution, or 10 mg/kg/or 40 mg/kg MLT (MLT-10 and MLT-40 groups), or no treatment (intact group). To perform behavioral and cognition analysis, from PND30 to PND32, they were tested in the open field apparatus, first for anxiety (PND30) and then for object recognition memory tasks: spatial position recognition (PND31) and shape recognition (PND32). On PND34, they were tested in the elevated plus maze. From PND36 to 42, the excitability-related phenomenon known as cortical spreading depression (CSD) was recorded, and its features were analyzed.

Results

Treatment with MLT did not change the animals' body weight or blood glucose levels. The MLT-10 treatment, but not the MLT-40 treatment, was associated with behaviors that suggest less anxiety and improved memory. MLT-10 and MLT-40 treatments, respectively, decelerated and accelerated CSD propagation (speed of 2.86 ± 0.14 mm/min and 3.96 ± 0.16 mm/min), compared with the control groups (3.3 ± 0.10 mm/min and 3.25 ± 0.11 mm/min, for the intact and vehicle groups, respectively; p < 0.01). Cerebral cortex levels of malondialdehyde and superoxide dismutase were, respectively, lower and higher in the MLT-10 group but not in the MLT40 group.

Conclusion

Our findings suggest that MLT intraperitoneal administration during brain development may differentially act as an antioxidant agent when administered at a low dose but not at a high dose, according to behavioral, electrophysiological, and biochemical parameters.

Protective effect of natural products in the metabolic-associated kidney diseases via regulating mitochondrial dysfunction

Metabolic syndrome (MS) is a complex group of metabolic disorders syndrome with hypertension, hyperuricemia and disorders of glucose or lipid metabolism. As an important organ involved in metabolism, the kidney is inevitably attacked by various metabolic disorders, leading to abnormalities in kidney structure and function. Recently, an increasing number of studies have shown that mitochondrial dysfunction is actively involved in the development of metabolic-associated kidney diseases. Mitochondrial dysfunction can be used as a potential therapeutic strategy for the treatment of metabolic-associated kidney diseases. Many natural products have been widely used to improve the treatment of metabolic-associated kidney diseases by inhibiting mitochondrial dysfunction. In this paper, by searching several authoritative databases such as PubMed, Web of Science, Wiley Online Library, and Springer Link. We summarize the Natural Products Protect Against Metabolic-Associated Kidney Diseases by Regulating Mitochondrial Dysfunction. In this review, we sought to provide an overview of the mechanisms by which mitochondrial dysfunction impaired metabolic-associated kidney diseases, with particular attention to the role of mitochondrial dysfunction in diabetic nephropathy, gouty nephropathy, hypertensive kidney disease, and obesity-related nephropathy, and then the protective role of natural products in the kidney through inhibition of mitochondrial disorders, thus providing a systematic understanding of the targets of mitochondrial dysfunction in metabolic-associated kidney diseases, and finally a review of promising therapeutic targets and herbal candidates for metabolic-associated kidney diseases through inhibition of mitochondrial dysfunction.

Understanding the Mechanism of Action of Melatonin, Which Induces ROS Production in Cancer Cells

Reactive oxygen species (ROS) constitute a group of highly reactive molecules that have evolved as regulators of important signaling pathways. In this context, tumor cells have an altered redox balance compared to normal cells, which can be targeted as an antitumoral therapy by ROS levels and by decreasing the capacity of the antioxidant system, leading to programmed cell death. Melatonin is of particular importance in the development of innovative cancer treatments due to its oncostatic impact and lack of adverse effects. Despite being widely recognized as a pro-oxidant molecule in tumor cells, the mechanism of action of melatonin remains unclear, which has hindered its use in clinical treatments. The current review aims to describe and clarify the proposed mechanism of action of melatonin inducing ROS production in cancer cells in order to propose future anti-neoplastic clinical applications.

Melatonin and Phytomelatonin: Chemistry, Biosynthesis, Metabolism, Distribution and Bioactivity in Plants and Animals-An Overview

Melatonin is a ubiquitous indolamine, largely investigated for its key role in the regulation of several physiological processes in both animals and plants. In the last century, it was reported that this molecule may be produced in high concentrations by several species belonging to the plant kingdom and stored in specialized tissues. In this review, the main information related to the chemistry of melatonin and its metabolism has been summarized. Furthermore, the biosynthetic pathway characteristics of animal and plant cells have been compared, and the main differences between the two systems highlighted. Additionally, in order to investigate the distribution of this indolamine in the plant kingdom, distribution cluster analysis was performed using a database composed by 47 previously published articles reporting the content of melatonin in different plant families, species and tissues. Finally, the potential pharmacological and biostimulant benefits derived from the administration of exogenous melatonin on animals or plants via the intake of dietary supplements or the application of biostimulant formulation have been largely discussed.

Melatonin as a promising modulator of aging related neurodegenerative disorders: Role of microRNAs

One of the host risk factors involved in aging-related diseases is coupled with the reduction of endogenous melatonin (MLT) synthesis in the pineal gland. MLT is considered a well-known pleiotropic regulatory hormone to modulate a multitude of biological processes such as the regulation of circadian rhythm attended by potent anti-oxidant, anti-inflammatory, and anti-cancer properties. It has also been established that the microRNAs family, as non-coding mRNAs regulating post-transcriptional processes, also serve a crucial role to promote MLT-related advantageous effects in both experimental and clinical settings. Moreover, the anti-aging impact of MLT and miRNAs participation jointly are of particular interest, recently. In this review, we aimed to scrutinize recent advances concerning the therapeutic implications of MLT, particularly in the brain tissue in the face of aging. We also assessed the possible interplay between microRNAs and MLT, which could be considered a therapeutic strategy to slow down the aging process in the nervous system.

Suppression of oxidative phosphorylation and IDH2 sensitizes colorectal cancer to a naphthalimide derivative and mitoxantrone

Colorectal cancer (CRC) is one of the most prevalent cancers worldwide. Oxidative phosphorylation (OXPHOS) has attracted a considerable attention in CRC. It is of great interest to explore novel therapies that inhibit OXPHOS for CRC treatment. Compound 6c is a novel naphthalimide derivative. However, the effects of 6c on CRC and the underlying mechanism are unclear. In this study, 6c suppressed CRC tumor growth and metastasis. RNA-seq data showed that 6c triggered the inhibition of OXPHOS and tricarboxylic acid cycle. 6c specifically inhibited mitochondrial complex III activity and the expression of isocitrate dehydrogenase 2 (IDH2), resulting in oxidative stress. Antioxidants reversed 6c-induced cell death, senescence, and autophagosomes formation. 6c inhibited autophagy flux; however, pretreatment with autophagy inhibitors resulted in the reduction of 6c-induced cytoplasmic vacuolization and proliferation inhibition. Moreover, combinatory treatment of 6c and mitoxantrone (MIT) showed stronger inhibitory effects on CRC compared with the single agent. Downregulation of IDH2 induced reactive oxygen species production, leading to MIT accumulation and autophagic cell death after co-treatment with 6c and MIT. In summary, our findings indicated 6c as a promising candidate for CRC treatment.

Utilization of redox modulating small molecules that selectively act as pro-oxidants in cancer cells to open a therapeutic window for improving cancer therapy

There is a rapidly growing body of literature supporting the notion that differential oxidative metabolism in cancer versus normal cells represents a metabolic frailty that can be exploited to open a therapeutic window into cancer therapy. These cancer cell-specific metabolic frailties may be amenable to manipulation with non-toxic small molecule redox active compounds traditionally thought to be antioxidants. In this review we describe the potential mechanisms and clinical applicability in cancer therapy of four small molecule redox active agents: melatonin, vitamin E, selenium, and vitamin C. Each has shown the potential to have pro-oxidant effects in cancer cells while retaining antioxidant activity in normal cells. This dichotomy can be exploited to improve responses to radiation and chemotherapy by opening a therapeutic window based on a testable biochemical rationale amenable to confirmation with biomarker studies during clinical trials. Thus, the unique pro-oxidant/antioxidant properties of melatonin, vitamin E, selenium, and vitamin C have the potential to act as effective adjuvants to traditional cancer therapies, thereby improving cancer patient outcomes.

Melatonin Modulates the Antioxidant Defenses and the Expression of Proinflammatory Mediators in Pancreatic Stellate Cells Subjected to Hypoxia

Pancreatic stellate cells (PSC) play a major role in the formation of fibrotic tissue in pancreatic tumors. On its side, melatonin is a putative therapeutic agent for pancreatic cancer and inflammation. In this work, the actions of melatonin on PSC subjected to hypoxia were evaluated. Reactive oxygen species (ROS) generation reduced (GSH) and oxidized (GSSG) levels of glutathione, and protein and lipid oxidation were analyzed. The phosphorylation of nuclear factor erythroid 2-related factor (Nrf2), nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB), and the regulatory protein nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor-alpha (IκBα) was studied. The expression of Nrf2-regulated antioxidant enzymes, superoxide dismutase (SOD) enzymes, cyclooxygenase 2 (COX-2), interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) were also studied. Total antioxidant capacity (TAC) was assayed. Finally, cell viability was studied. Under hypoxia and in the presence of melatonin generation of ROS was observed. No increases in the oxidation of proteins or lipids were detected. The phosphorylation of Nrf2 and the expression of the antioxidant enzymes catalytic subunit of glutamate-cysteine ligase, catalase, NAD(P)H-quinone oxidoreductase 1, heme oxygenase-1, SOD1, and of SOD2 were augmented. The TAC was increased. Protein kinase C was involved in the effects of melatonin. Melatonin decreased the GSH/GSSG ratio at the highest concentration tested. Cell viability dropped in the presence of melatonin. Finally, melatonin diminished the phosphorylation of NF-kB and the expression of COX-2, IL-6, and TNF-α. Our results indicate that melatonin, at pharmacological concentrations, modulates the red-ox state, viability, and the expression of proinflammatory mediators in PSC subjected to hypoxia.

The screening of albumin as a key serum component in preventing release of neutrophil extracellular traps by selectively inhibiting mitochondrial ROS generation

Neutrophil extracellular traps (NETs) are extracellular DNA webs released from neutrophils to mediate the host antimicrobial defense. As NETs could also induce thrombosis and cause organ injury, their release should be strictly controlled; however, the intrinsic mechanisms that prevent unfavorable NETs are not well understood. Herein, an accidental finding of NET release from human peripheral neutrophils was first described in a serum-free culture, which was later determined to be a conserved NET prevention effect of serum. In contrast to canonical NETs induced by phorbol-12-myristate-13-acetate (PMA), NET formation by serum-free culture was rapid and without prevalent NETosis. Next, albumin was screened out as a key serum component that mediated the suppression of NETs. Moreover, NETs induced upon serum or albumin deficiency were independent of the canonical pathway that involves NADPH oxidase 2 (NOX2) activation and cytosol reactive oxygen species (ROS) production. Instead, the generation of mitochondrial ROS (mtROS) was upregulated to promote NET release. Albumin exhibited mtROS scavenging activity and thus inhibited NETs. Serum-free culture also induced the release of NET-bound oxidized mtDNA, which stimulated interferon-β (IFN-β) production. Overall, our research provides new evidence that characterizes the NET production in serum-free culture and determines the mechanisms by which serum albumin inhibits NETs.

Transcriptomic Insights into the Effect of Melatonin in Saccharomyces cerevisiae in the Presence and Absence of Oxidative Stress

Melatonin is a ubiquitous indolamine that plays important roles in various aspects of biological processes in mammals. In Saccharomyces cerevisiae, melatonin has been reported to exhibit antioxidant properties and to modulate the expression of some genes involved in endogenous defense systems. The aim of this study was to elucidate the role of supplemented melatonin at the transcriptional level in S. cerevisiae in the presence and absence of oxidative stress. This was achieved by exposing yeast cells pretreated with different melatonin concentrations to hydrogen peroxide and assessing the entry of melatonin into the cell and the yeast response at the transcriptional level (by microarray and qPCR analyses) and the physiological level (by analyzing changes in the lipid composition and mitochondrial activity). We found that exogenous melatonin crossed cellular membranes at nanomolar concentrations and modulated the expression of many genes, mainly downregulating the expression of mitochondrial genes in the absence of oxidative stress, triggering a hypoxia-like response, and upregulating them under stress, mainly the cytochrome complex and electron transport chain. Other categories that were enriched by the effect of melatonin were related to transport, antioxidant activity, signaling, and carbohydrate and lipid metabolism. The overall results suggest that melatonin is able to reprogram the cellular machinery to achieve tolerance to oxidative stress.

Melatonin restores neutrophil functions and prevents apoptosis amid dysfunctional glutathione redox system

Melatonin is a chronobiotic hormone, which can regulate human diseases like cancer, atherosclerosis, respiratory disorders, and microbial infections by regulating redox system. Melatonin exhibits innate immunomodulation by communicating with immune system and influencing neutrophils to fight infections and inflammation. However, sustaining redox homeostasis and reactive oxygen species (ROS) generation in neutrophils are critical during chemotaxis, oxidative burst, phagocytosis, and neutrophil extracellular trap (NET) formation. Therefore, endogenous antioxidant glutathione (GSH) redox cycle is highly vital in regulating neutrophil functions. Reduced intracellular GSH levels and glutathione reductase (GR) activity in the neutrophils during clinical conditions like autoimmune disorders, neurological disorders, diabetes, and microbial infections lead to dysfunctional neutrophils. Therefore, we hypothesized that redox modulators like melatonin can protect neutrophil health and functions under GSH and GR activity-deficient conditions. We demonstrate the dual role of melatonin, wherein it protects neutrophils from oxidative stress-induced apoptosis by reducing ROS generation; in contrast, it restores neutrophil functions like phagocytosis, degranulation, and NETosis in GSH and GR activity-deficient neutrophils by regulating ROS levels both in vitro and in vivo. Melatonin mitigates LPS-induced neutrophil dysfunctions by rejuvenating GSH redox system, specifically GR activity by acting as a parallel redox system. Our results indicate that melatonin could be a potential auxiliary therapy to treat immune dysfunction and microbial infections, including virus, under chronic disease conditions by restoring neutrophil functions. Further, melatonin could be a promising immune system booster to fight unprecedented pandemics like the current COVID-19. However, further studies are indispensable to address the clinical usage of melatonin.

Ethionine Suppresses Mitochondria Autophagy and Induces Apoptosis via Activation of Reactive Oxygen Species in Neural Tube Defects

Abnormal development of central nervous system (CNS) caused by neural tube defects (NTDs) is not only remained the major contributor in the prevalence of stillbirths and neonatal deaths, but also represents a significant cause of lifelong physical disability in the surviving infants. Ethionine is a non-proteinogenic amino acid and antagonist of methionine. Methionine cycle is essential for the elimination of reactive oxygen species (ROS), while lysosomes are involved in the initiation of autophagy. However, its role in ethionine-induced cell death in neural tube defects, still need to be explored. In this study, we investigated the effect of ethionine on NTDs as well as the underlying mechanism involved in this process. Following the establishment of NTDs model using ethionine-induced C57BL/6 mice, ethionine was intraperitoneally injected at a dose of 500 mg/kg in E7.5. Our study revealed that ethionine has induced mitochondrial apoptosis in NTDs by reducing mitochondrial autophagy both in vivo and in vitro. These results provided a possible molecular mechanism for redox regulation of autophagic process.

Melatonin ameliorates the drug induced nephrotoxicity: Molecular insights

BACKGROUND

Drug-induced nephrotoxicity is a frequent adverse event that can lead to acute or chronic kidney disease and increase the healthcare expenditure. It has high morbidity and mortality incidence in 40-70% of renal injuries and accounts for 66% cases of renal failure in elderly population.

OBJECTIVE

Amelioration of drug-induced nephrotoxicity has been long soughed to improve the effectiveness of therapeutic drugs. This study was conducted to review the melatonin potential to prevent the pathogenesis of nephrotoxicity induced by important nephrotoxic drugs.

METHODS

We analyzed the relevant studies indexed in Pubmed, Medline, Scielo and Web of science to explain the molecular improvements following melatonin co-administration with special attention to oxidative stress, inflammation and apoptosis as key players of drug-induced nephrotoxicity.

RESULTS

A robust consensus among researchers of these studies suggested that melatonin efficiently eradicate the chain reaction of free radical production and induced the endogenous antioxidant enzymes which attenuate the lipid peroxidation of cellular membranes and subcellular oxidative stress in drug-induced nephrotoxicity. This agreement was further supported by the melatonin role in disintegration of inflammatory process through inhibition of principle pro-inflammatory or apoptotic cytokines such as TNF-α and NF-κB. These studies highlighted that alleviation of drug-induced renal toxicity is a function of melatonin potential to down regulate the cellular inflammatory and oxidative injury process and to stimulate the cellular repair or defensive mechanisms.

CONCLUSION

The comprehensive nephroprotection and safer profile suggests the melatonin to be a useful adjunct to improve the safety of nephrotoxic drugs.

Inhibition of SGK1 confers vulnerability to redox dysregulation in cervical cancer

Cervical cancer has poor prognosis and patients are often diagnosed at advanced stages of the disease with limited treatment options. There is thus an urgent need for the discovery of new therapeutic strategies in cervical cancer. The activation of SGK1 has been linked to the development of various cancer types but little is known about the role of SGK1 in cervical cancer and its potential as a therapeutic target. Here we report that SGK1 is an antioxidative factor that promotes survival of cervical cancer cells. Gene set enrichment analysis of RNA-Seq data reveals a strong inverse association between SGK1 and oxidative phosphorylation. Consistently, inhibition of SGK1 via siRNA or pharmacological inhibitor GSK650394 induces ROS and cytotoxicity upon H₂O₂ stress. Further analysis of clinical data associates SGK1 with gene expression signatures regulated by the antioxidant transcription factor NRF2 in cervical cancer. Mechanistically, SGK1 activation exerts antioxidant effect through induction of c-JUN-dependent NRF2 expression and activity. Importantly, we find that inhibition of SGK1 confers vulnerability to melatonin as a pro-oxidant, resulting in ROS over-accumulation and consequently enhanced cell cytotoxicity. We further demonstrate that combined use of GSK650394 and melatonin yields substantial regression of cervical tumors in vivo. This work opens new perspectives on the potential of SGK1 inhibitors as sensitizing agents to enable the design of therapeutically redox-modulating strategies against cervical cancer.

Dose-dependent proliferative and cytotoxic effects of melatonin on human epidermoid carcinoma and normal skin fibroblast cells

New in vitro studies have demonstrated that N-acetyl-5-methoxytryptamine (Melatonin) has cytotoxic and apoptotic effects on various cell types although most of the previous investigations document that it is a potent antioxidant. However, the precise molecular mechanism(s) of its effects are not fully elucidated. In this study, we examined dose-dependent cytotoxic, genotoxic, apoptotic and reactive oxygen species (ROS) generating effects of melatonin in human epidermoid carcinoma cells (A-431) and human normal skin fibroblastic cells (CCD-1079Sk). The cells were incubated with different doses of melatonin (0.031-5 mM) for 24 h. Cell viability was assessed based on luminometric ATP cell viability assay. Intracellular ROS was detected using 2,7-dichlorodihydrofluorescein-diacetate (H₂DCF-DA) fluorescent probes. Genotoxicity was evaluated by alkaline single cell gel electrophoresis assay (Comet Assay). Apoptosis was evaluated by western blotting, DAPI staining, acridine orange/ethidium bromide and Annexin V-FITC/propidium iodide double staining methods Mitochondrial membrane potentials were measured by flow cytometry. Although lower doses of melatonin (0.031-0.06 mM) increased cell proliferation and decreased ROS generation, higher doses (0.125-5 mM) markedly inhibited the cell viability, induced DNA damage, apoptosis and ROS generation. Cytotoxic, genotoxic, apoptotic and ROS generating effects were significantly higher in cancer cells than those observed in normal cells. Melatonin-induced cell death, and ROS generating activity were effectively inhibited by N-acetyl-l-cysteine (NAC) In conclusion, at low doses, melatonin has proliferative effects on both cancer and normal cells, whereas high concentrations have cytotoxic effects. Cytotoxic, genotoxic and apoptotic effects at higher doses of melatonin may be due to its ROS production capacity.

Melatonin, mitochondria, and the cancer cell

The long-recognized fact that oxidative stress within mitochondria is a hallmark of mitochondrial dysfunction has stimulated the development of mitochondria-targeted antioxidant therapies. Melatonin should be included among the pharmacological agents able to modulate mitochondrial functions in cancer, given that a number of relevant melatonin-dependent effects are triggered by targeting mitochondrial functions. Indeed, melatonin may modulate the mitochondrial respiratory chain, thus antagonizing the cancer highly glycolytic bioenergetic pathway of cancer cells. Modulation of the mitochondrial respiratory chain, together with Ca2+ release and mitochondrial apoptotic effectors, may enhance the spontaneous or drug-induced apoptotic processes. Given that melatonin may efficiently counteract the Warburg effect while stimulating mitochondrial differentiation and mitochondrial-based apoptosis, it is argued that the pineal neurohormone could represent a promising new perspective in cancer treatment strategy.

The melatonin immunomodulatory actions in radiotherapy

Radiotherapy has a key role in cancer treatment in more than half of patients with cancer. The management of severe side effects of this treatment modality is a limiting factor to appropriate treatment. Immune system responses play a pivotal role in many of the early and late side effects of radiation. Moreover, immune cells have a significant role in tumor response to radiotherapy, such as angiogenesis and tumor growth. Melatonin as a potent antioxidant has shown appropriate immune regulatory properties that may ameliorate toxicity induced by radiation in various organs. These effects are mediated through various modulatory effects of melatonin in different levels of tissue reaction to ionizing radiation. The effects on the DNA repair system, antioxidant enzymes, immune cells, cytokines secretion, transcription factors, and protein kinases are most important. Moreover, anti-cancer properties of melatonin may increase the therapeutic ratio of radiotherapy. Clinical applications of this agent for the management of malignancies such as breast cancer have shown promising results. It seems anti-proliferative, anti-angiogenesis, and stimulation or suppression of some immune cell responses are the main anti-tumor effects of melatonin that may help to improve response of the tumor to radiotherapy. In this review, the effects of melatonin on the modulation of immune responses in both normal and tumor tissues will be discussed.

Melatonin antiproliferative effects require active mitochondrial function in embryonal carcinoma cells

Although melatonin oncostatic and cytotoxic effects have been described in different types of cancer cells, the specific mechanisms leading to its antitumoral effects and their metabolic context specificity are still not completely understood. Here, we evaluated the effects of melatonin in P19 embryonal carcinoma stem cells (CSCs) and in their differentiated counterparts, cultured in either high glucose medium or in a galactose (glucose-free) medium which leads to glycolytic suppression and increased mitochondrial metabolism. We found that highly glycolytic P19 CSCs were less susceptible to melatonin antitumoral effects while cell populations relying on oxidative metabolism for ATP production were more affected. The observed antiproliferative action of melatonin was associated with an arrest at S-phase, decreased oxygen consumption, down-regulation of BCL-2 expression and an increase in oxidative stress culminating with caspase-3-independent cell death. Interestingly, the combined treatment of melatonin and dichloroacetate had a synergistic effect in cells grown in the galactose medium and resulted in an inhibitory effect in the highly resistant P19 CSCs. Melatonin appears to exert its antiproliferative activity in P19 carcinoma cells through a mitochondrially-mediated action which in turn allows the amplification of the effects of dichloroacetate, even in cells with a more glycolytic phenotype.

Oncostatic-Cytoprotective Effect of Melatonin and Other Bioactive Molecules: A Common Target in Mitochondrial Respiration

For several years, oncostatic and antiproliferative properties, as well as thoses of cell death induction through 5-methoxy-N-acetiltryptamine or melatonin treatment, have been known. Paradoxically, its remarkable scavenger, cytoprotective and anti-apoptotic characteristics in neurodegeneration models, such as Alzheimer’s disease and Parkinson’s disease are known too. Analogous results have been confirmed by a large literature to be associated to the use of many other bioactive molecules such as resveratrol, tocopherol derivatives or vitamin E and others. It is interesting to note that the two opposite situations, namely the neoplastic pathology and the neurodegeneration, are characterized by deep alterations of the metabolome, of mitochondrial function and of oxygen consumption, so that the oncostatic and cytoprotective action can find a potential rationalization because of the different metabolic and mitochondrial situations, and in the effect that these molecules exercise on the mitochondrial function. In this review we discuss historical and general aspects of melatonin, relations between cancers and the metabolome and between neurodegeneration and the metabolome, and the possible effects of melatonin and of other bioactive molecules on metabolic and mitochondrial dynamics. Finally, we suggest a common general mechanism as responsible for the oncostatic/cytoprotective effect of melatonin and of other molecules examined.

Glutathione-dependent induction of local and systemic defense against oxidative stress by exogenous melatonin in cucumber (Cucumis sativus L.)

Melatonin is involved in defending against oxidative stress caused by various environmental stresses in plants. In this study, the roles of exogenous melatonin in regulating local and systemic defense against photooxidative stress in cucumber (Cucumis sativus) and the involvement of redox signaling were examined. Foliar or rhizospheric treatment with melatonin enhanced tolerance to photooxidative stress in both melatonin-treated leaves and untreated systemic leaves. Increased melatonin levels are capable of increasing glutathione (reduced glutathione [GSH]) redox status. Application of H2 O2 and GSH also induced tolerance to photooxidative stress, while inhibition of H2 O2 accumulation and GSH synthesis compromised melatonin-induced local and systemic tolerance to photooxidative stress. H2 O2 treatment increased the GSH/oxidized glutathione (GSSG) ratio, while inhibition of H2 O2 accumulation prevented a melatonin-induced increase in the GSH/GSSG ratio. Additionally, inhibition of GSH synthesis blocked H2 O2 -induced photooxidative stress tolerance, whereas scavenging or inhibition of H2 O2 production attenuated but did not abolish GSH-induced tolerance to photooxidative stress. These results strongly suggest that exogenous melatonin is capable of inducing both local and systemic defense against photooxidative stress and melatonin-enhanced GSH/GSSG ratio in a H2 O2 -dependent manner is critical in the induction of tolerance.

Melatonin enhances photo-oxidation of 2',7'-dichlorodihydrofluorescein by an antioxidant reaction that renders N1-acetyl-N2-formyl-5-methoxykynuramine (AFMK)

The indolamine melatonin (MEL) is described as an antioxidant and a free radical scavenger. However occasionally, the indoleamine has been reported to increase free radicals with insufficient mechanistic explanation. In an attempt to find a reason for those controversial results, a potential mechanism that explains MEL prooxidant activity is investigated. The current controversy about redox detection methods has prompted us to search a possible interaction between MEL and dichlorodihydrofluorescein (DCFH₂), perhaps the most widely fluorescence probe employed for free radicals detection in cellular models. Here, it is demonstrated that melatonin potentiates the photooxidation of DCFH₂ in a cell-free system, increasing the production of its fluorescent metabolite. Indeed, MEL works as an antioxidant scavenging hydroxyl radicals in this system. Thus, this reaction between MEL and DCFH₂ produces N1-acetyl-N2-formyl-5-methoxykynuramine (AFMK), a biogenic amine with antioxidant properties too. This reaction is O₂ and light dependent and it is prevented by antioxidants such as N-acetylcysteine or ascorbic acid. Furthermore, when DCFH₂ has been employed to evaluate antioxidant or prooxidant activities of MEL in cellular models it is confirmed that it works as an antioxidant but these results can be modulated by light misleading to a prooxidant conclusion. In conclusion, here is demonstrated that DCFH₂, light and melatonin interact and results obtained using these fluorescence probes in studies with melatonin have to be carefully interpreted.

Melatonin: a well-documented antioxidant with conditional pro-oxidant actions

Melatonin (N-acetyl-5-methoxytryptamine), an indoleamine produced in many organs including the pineal gland, was initially characterized as a hormone primarily involved in circadian regulation of physiological and neuroendocrine function. Subsequent studies found that melatonin and its metabolic derivatives possess strong free radical scavenging properties. These metabolites are potent antioxidants against both ROS (reactive oxygen species) and RNS (reactive nitrogen species). The mechanisms by which melatonin and its metabolites protect against free radicals and oxidative stress include direct scavenging of radicals and radical products, induction of the expression of antioxidant enzymes, reduction of the activation of pro-oxidant enzymes, and maintenance of mitochondrial homeostasis. In both in vitro and in vivo studies, melatonin has been shown to reduce oxidative damage to lipids, proteins and DNA under a very wide set of conditions where toxic derivatives of oxygen are known to be produced. Although the vast majority of studies proved the antioxidant capacity of melatonin and its derivatives, a few studies using cultured cells found that melatonin promoted the generation of ROS at pharmacological concentrations (μm to mm range) in several tumor and nontumor cells; thus, melatonin functioned as a conditional pro-oxidant. Mechanistically, melatonin may stimulate ROS production through its interaction with calmodulin. Also, melatonin may interact with mitochondrial complex III or mitochondrial transition pore to promote ROS production. Whether melatonin functions as a pro-oxidant under in vivo conditions is not well documented; thus, whether the reported in vitro pro-oxidant actions come into play in live organisms remains to be established.

A melatonin-based fluorescence method for the measurement of mitochondrial complex III function in intact cells

Mitochondrial complex III (MC-3) plays a pivotal role in electron transfer and oxidative phosphorylation. Impaired MC-3 functions may contribute to a variety of diseases by interrupting normal bioenergetics and increasing reactive oxygen production and oxidative stress. Currently, MC-3 function is assessed by measuring the cytochrome c reductase activity spectrophotometrically in isolated mitochondria or MC-3. The cytoplasmic microenvironment critical for mitochondrial complex functions may be depleted during these isolation processes. The development of a reliable method to measure MC-3 activities in intact cells or tissues is highly desirable. This report describes a novel fluorescence-based method to assess MC-3 functions, i.e., Qi site electron transfer, in the intact cells. Human mesangial and teratocarcinoma NT2 cells were used to demonstrate that melatonin-induced oxidation of 2',7'-dichlorodihydrofluorescein (H2 DCF) was inhibited by antimycin A, the MC-3 Qi site-specific inhibitor, but not by myxothiazol, the MC-3 Qo site-specific inhibitor, nor rotenone, the mitochondrial complex I inhibitor. These results indicate that melatonin-induced oxidation of H2 DCF is reflecting MC-3 Qi site electron transfer activities. Modifying structures of the side groups at the R3 and R5 positions of the indole ring of melatonin diminished its efficacy for inducing H2 DCF oxidation, suggesting a specific interaction of melatonin with the MC-3 Qi site. These results suggest that the fluorogenic property of melatonin-induced H2 DCF oxidation provides a MC-3 Qi site electron transfer-specific measurement in intact cells. Interestingly, using this method, the Qi site electron transfer activity in transformed or immortalized cells was found to be significantly higher than the nontransformed cells.

Melatonin and the theories of aging: a critical appraisal of melatonin's role in antiaging mechanisms

The classic theories of aging such as the free radical theory, including its mitochondria-related versions, have largely focused on a few specific processes of senescence. Meanwhile, numerous interconnections have become apparent between age-dependent changes previously thought to proceed more or less independently. Increased damage by free radicals is not only linked to impairments of mitochondrial function, but also to inflammaging as it occurs during immune remodeling and by release of proinflammatory cytokines from mitotically arrested, DNA-damaged cells that exhibit the senescence-associated secretory phenotype (SASP). Among other effects, SASP can cause mutations in stem cells that reduce the capacity for tissue regeneration or, in worst case, lead to cancer stem cells. Oxidative stress has also been shown to promote telomere attrition. Moreover, damage by free radicals is connected to impaired circadian rhythmicity. Another nexus exists between cellular oscillators and metabolic sensing, in particular to the aging-suppressor SIRT1, which acts as an accessory clock protein. Melatonin, being a highly pleiotropic regulator molecule, interacts directly or indirectly with all the processes mentioned. These influences are critically reviewed, with emphasis on data from aged organisms and senescence-accelerated animals. The sometimes-controversial findings obtained either in a nongerontological context or in comparisons of tumor with nontumor cells are discussed in light of evidence obtained in senescent organisms. Although, in mammals, lifetime extension by melatonin has been rarely documented in a fully conclusive way, a support of healthy aging has been observed in rodents and is highly likely in humans.

Melatonin induces apoptosis through a caspase-dependent but reactive oxygen species-independent mechanism in human leukemia Molt-3 cells

Melatonin is a naturally occurring indoleamine synthesized in the pineal gland that exhibits an extensive repertoire of biological activities. An increasing number of studies indicate that melatonin protects normal cells, while it reducing cancer cell proliferation. In this study, we investigated the effect of melatonin on the growth of the human leukemia cells and found that it efficiently reduced the number of cells in a concentration- and time-dependent manner. Thus, incubation with the indoleamine increased the percentage of cells with a hypodiploid DNA content, augmented the number of annexin V-positive cells, and also provoked ultrastructural changes that are features of apoptotic cell death. Evaluation of caspases revealed that caspase-3, caspase-6, caspase-7, and caspase-9, but not caspase-8 and caspase-2, were quickly activated (3-6 hr). The increase in the activity of these proteases was associated with up-regulation of the pro-apoptotic factor Bax and also with the release of cytochrome c from mitochondria. Pretreatment of the cells with the general caspase inhibitor z-VAD-fmk, reduced melatonin-induced apoptosis, but it did not block cell death suggesting that melatonin activates an alternative cell death modality in the absence of caspase activity. Thus, the activation of caspases was preceded by a fast (<30 min) increase in reactive oxygen species (ROS). Rotenone and antimycin A reduced the levels of ROS stimulated by melatonin, indicating that the complex I and the complex III of the mitochondrial electron transport chain are important sources of these chemical species. However, the role of ROS in melatonin-induced cell death remains elusive because anti-oxidants that were shown to decrease ROS levels (glutathione, N-acetyl-l-cysteine and Trolox) were unable to abrogate melatonin-induced cell death.

Rotenone-induced oxidative stress and apoptosis in human liver HepG2 cells

Rotenone, a commonly used pesticide, is well documented to induce selective degeneration in dopaminergic neurons and motor dysfunction. Such rotenone-induced neurodegenration has been primarily suggested through mitochondria-mediated apoptosis and reactive oxygen species (ROS) generation. But the status of rotenone induced changes in liver, the major metabolic site is poorly investigated. Thus, the present investigation was aimed to study the oxidative stress-induced cytotoxicity and apoptotic cell death in human liver cells-HepG2 receiving experimental exposure of rotenone (12.5-250 μM) for 24 h. Rotenone depicted a dose-dependent cytotoxic response in HepG2 cells. These cytotoxic responses were in concurrence with the markers associated with oxidative stress such as an increase in ROS generation and lipid peroxidation as well as a decrease in the glutathione, catalase, and superoxide dismutase levels. The decrease in mitochondrial membrane potential also confirms the impaired mitochondrial activity. The events of cytotoxicity and oxidative stress were found to be associated with up-regulation in the expressions (mRNA and protein) of pro-apoptotic markers viz., p53, Bax, and caspase-3, and down-regulation of anti-apoptotic marker Bcl-2. The data obtain in this study indicate that rotenone-induced cytotoxicity in HepG2 cells via ROS-induced oxidative stress and mitochondria-mediated apoptosis involving p53, Bax/Bcl-2, and caspase-3.

Mitochondria and chloroplasts as the original sites of melatonin synthesis: a hypothesis related to melatonin's primary function and evolution in eukaryotes

Mitochondria and chloroplasts are major sources of free radical generation in living organisms. Because of this, these organelles require strong protection from free radicals and associated oxidative stress. Melatonin is a potent free radical scavenger and antioxidant. It meets the criteria as a mitochondrial and chloroplast antioxidant. Evidence has emerged to show that both mitochondria and chloroplasts may have the capacity to synthesize and metabolize melatonin. The activity of arylalkylamine N-acetyltransferase (AANAT), the reported rate-limiting enzyme in melatonin synthesis, has been identified in mitochondria, and high levels of melatonin have also been found in this organelle. From an evolutionary point of view, the precursor of mitochondria probably is the purple nonsulfur bacterium, particularly, Rhodospirillum rubrum, and chloroplasts are probably the descendents of cyanobacteria. These bacterial species were endosymbionts of host proto-eukaryotes and gradually transformed into cellular organelles, that is, mitochondria and chloroplasts, respectively, thereby giving rise to eukaryotic cells. Of special importance, both purple nonsulfur bacteria (R. rubrum) and cyanobacteria synthesize melatonin. The enzyme activities required for melatonin synthesis have also been detected in these primitive species. It is our hypothesis that mitochondria and chloroplasts are the original sites of melatonin synthesis in the early stage of endosymbiotic organisms; this synthetic capacity was carried into host eukaryotes by the above-mentioned bacteria. Moreover, their melatonin biosynthetic capacities have been preserved during evolution. In most, if not in all cells, mitochondria and chloroplasts may continue to be the primary sites of melatonin generation. Melatonin production in other cellular compartments may have derived from mitochondria and chloroplasts. On the basis of this hypothesis, it is also possible to explain why plants typically have higher melatonin levels than do animals. In plants, both chloroplasts and mitochondria likely synthesize melatonin, while animal cells contain only mitochondria. The high levels of melatonin produced by mitochondria and chloroplasts are used to protect these important cellular organelles against oxidative stress and preserve their physiological functions. The superior beneficial effects of melatonin in both mitochondria and chloroplasts have been frequently reported.

A Comparison of B16 Melanoma Cells and 3T3 Fibroblasts Concerning Cell Viability and ROS Production in the Presence of Melatonin, Tested Over a Wide Range of Concentrations

Melatonin is a pleiotropic molecule with many cellular and systemic actions, including chronobiotic effects. Beneficial effects are widely documented concerning the treatment of neoplastic diseases in vivo as well as reductions in viability of cultured cells from melanoma, one of the most aggressive cancers in humans. However, studies of its effects on non-tumor cells in vitro have not focused on viability, except for experiments aiming to protect against oxidotoxicity or other toxicological insults. Furthermore, there is no agreement on the range of effective melatonin concentrations in vitro, and the mechanisms that reduce cell viability have remained unclear. Tumor cell-specific increases in the production of reactive oxygen and nitrogen species (ROS/RNS) may provide a possible explanation. Our aim was to analyze the potential inhibition of tumor (B16 melanoma 4A5) and non-tumor cell (3T3 Swiss albino) viability using a wide range of melatonin concentrations (10⁻¹¹–10⁻² M), and to determine whether intracellular ROS enhancement was involved in this process. In the absence of fetal bovine serum (FBS), low melatonin concentrations (10⁻⁹–10⁻⁵ M) reduced the proliferation of melanoma cells with no effect in fibroblasts, whereas, in the presence of FBS, they had no effect or even increased the proliferation of both fibroblast and melanoma cells. Melatonin concentrations in the upper millimolar range increased ROS levels and reduced the viability of both cell types, but more markedly so in non-tumor cells. Thus, low melatonin concentrations reduce proliferation in this specific melanoma cell line, whereas high concentrations affect the viability of both tumor (B16 4A5 melanoma) and non-tumor (3T3 fibroblasts) cells. Increased ROS levels in both lines indicate a role for ROS production in the reduction of cell viability at high—but not low—melatonin concentrations, although the mechanism of action still remains to be elucidated.

Astrocyte activation: a key step in rotenone induced cytotoxicity and DNA damage

Astrocytes are the most abundant glial cells, which provide metabolic support for neurons. Rotenone is a botanical pesticide of natural origin, known to exhibit neurotoxic potential via inhibition of mitochondrial complex-I. This study was carried out to explore the effect of rotenone on C6 cells. The cell line C6 derived from rat glioma cells represents astrocyte-like cell. C6 cells were treated with rotenone (0.1, 1 and 10 μM) for 4 h. The effect of rotenone was studied on cell survival (MTT reduction and PI uptake); free radicals (ROS and RNS) and DNA damage (comet assay and Hoechst staining). The glial cell activation and apoptotic cell death was evaluated by expression of Glial fibrillary acidic protein (GFAP) and caspase-3 respectively. The treatment with rotenone resulted in decreased cell survival and increased free radical generation. Altered nuclear morphology and DNA damage were evident following rotenone treatment in Hoechst staining and Comet assay. Rotenone elevated expression of GFAP and caspase-3 that indicates glial cell activation and apoptosis, respectively. We further studied the effect of melatonin, an antioxidant, on the observed toxic effects. Co-incubation of antioxidant, melatonin (300 μM), significantly suppressed rotenone induced above-mentioned effects in C6 cells. Inhibitory effects of melatonin suggest that free radicals play a major role in rotenone induced astrocyte activation and cellular toxicity leading to apoptosis of astroglial cells.

Rotenone-induced apoptosis and role of calcium: a study on Neuro-2a cells

Rotenone causes cytotoxicity in astrocytic cell culture by glial activation, which is linked to free radical generation. The present study is an investigation to explore whether rotenone could also cause cellular toxicity in mouse neuroblastoma cells (Neuro-2a) under treatment similar to astroglial cells. The effect of rotenone (0.1, 1, and 10 μM) on mitochondrial dehydrogenase enzyme activity by MTT reduction assay, PI uptake, total reactive oxygen species (ROS)/superoxide levels, nitrite levels, extent of DNA damage (by comet assay), and nuclear morphological alteration by Hoechst staining was studied. Caspase-3 and Ca⁺²/calmodulin-dependent protein kinase II (CaMKIIα) gene expression was determined to evaluate the apoptotic cell death and calcium kinase, respectively. Calcium level was estimated fluorometrically using fura-2A stain. Rotenone decreased mitochondrial dehydrogenase enzyme activity and generated ROS, superoxide, and nitrite. Rotenone treatment impaired cell intactness and nuclear morphology as depicted by PI uptake and chromosomal condensation of Neuro-2a cells, respectively. In addition, rotenone resulted in increased intracellular Ca⁺² level, caspase-3, and CaMKIIα expression. Furthermore, co-exposure of melatonin (300 μM), an antioxidant to cell culture, significantly suppressed the rotenone-induced decreased mitochondrial dehydrogenase enzyme activity, elevated ROS and RNS. However, melatonin was found ineffective to counteract rotenone-induced increased PI uptake, altered morphological changes, DNA damage, elevated Ca⁺², and increased expression of caspase-3 and CaMKIIα. The study indicates that intracellular calcium rather than oxidative stress is a major factor for rotenone-induced apoptosis in neuronal cells.

Geldanamycin derivative ameliorates high fat diet-induced renal failure in diabetes

Diabetic nephropathy is a serious complication of longstanding diabetes and its pathogenesis remains unclear. Oxidative stress may play a critical role in the pathogenesis and progression of diabetic nephropathy. Our previous studies have demonstrated that polyunsaturated fatty acids (PUFA) induce peroxynitrite generation in primary human kidney mesangial cells and heat shock protein 90β1 (hsp90β1) is indispensable for the PUFA action. Here we investigated the effects of high fat diet (HFD) on kidney function and structure of db/db mice, a widely used rodent model of type 2 diabetes. Our results indicated that HFD dramatically increased the 24 h-urine output and worsened albuminuria in db/db mice. Discontinuation of HFD reversed the exacerbated albuminuria but not the increased urine output. Prolonged HFD feeding resulted in early death of db/db mice, which was associated with oliguria and anuria. Treatment with the geldanamycin derivative, 17-(dimethylaminoehtylamino)-17-demethoxygeldanamycin (17-DMAG), an hsp90 inhibitor, preserved kidney function, and ameliorated glomerular and tubular damage by HFD. 17-DMAG also significantly extended survival of the animals and protected them from the high mortality associated with renal failure. The benefit effect of 17-DMAG on renal function and structure was associated with a decreased level of kidney nitrotyrosine and a diminished kidney mitochondrial Ca²⁺ efflux in HFD-fed db/db mice. These results suggest that hsp90β1 is a potential target for the treatment of nephropathy and renal failure in diabetes.

Impaired mitochondrial complex III and melatonin responsive reactive oxygen species generation in kidney mitochondria of db/db mice

We have previously demonstrated that melatonin, at pharmacological concentrations, causes rapid reactive oxygen species (ROS) generation at the antimycin-A sensitive site of mitochondrial complex III (MC-3). In the current work, we used this melatonin response to investigate the role of mitochondrial dysfunction in the development of diabetic nephropathy. We find that the development of diabetic nephropathy, as indicated by hyperfiltration and histopathological lesions in the kidney of db/db mice, is associated with diminished melatonin-induced ROS generation and MC-3 activity, indicating impaired MC-3 at the antimycin-A site. The MC-3 protein level in the renal mitochondria was equivalent in db/db and the nondiabetic db/m mice, whereas mitochondrial complex I (MC-1) protein was dramatically upregulated in the db/db mice. This differential regulation in mitochondrial complexes may alter the equilibrium of the electron transport in renal mitochondria and contribute to ROS overproduction. The study provides one mechanism of enhanced oxidative stress that may be involved in the pathogenesis of diabetic nephropathy in db/db mice.

Interactions of melatonin with mammalian mitochondria. Reducer of energy capacity and amplifier of permeability transition

Melatonin, a metabolic product of the amino acid tryptophan, induces a dose-dependent energy drop correlated with a decrease in the oxidative phosphorylation process in isolated rat liver mitochondria. This effect involves a gradual decrease in the respiratory control index and significant alterations in the state 4/state 3 transition of membrane potential (ΔΨ). Melatonin, alone, does not affect the insulating properties of the inner membrane but, in the presence of supraphysiological Ca2+, induces a ΔΨ drop and colloid-osmotic mitochondrial swelling. These events are sensitive to cyclosporin A and the inhibitors of Ca2+ transport, indicative of the induction or amplification of the mitochondrial permeability transition. This phenomenon is triggered by oxidative stress induced by melatonin and Ca2+, with the generation of hydrogen peroxide and the consequent oxidation of sulfydryl groups, glutathione and pyridine nucleotides. In addition, melatonin, again in the presence of Ca2+, can also induce substantial release of cytochrome C and AIF (apoptosis-inducing factor), thus revealing its potential as a pro-apoptotic agent.