Melatonin protects against apoptotic and autophagic cell death in C2C12 murine myoblast cells

Biomimetic multilayer polycaprolactone/sodium alginate hydrogel scaffolds loaded with melatonin facilitate tendon regeneration

Tendon injury is one of the most common musculoskeletal diseases in the world, severely challenging the public health care system. Electrospinning technique using polymer materials (i.e. polycaprolactone (PCL)) and hydrogels (i.e. sodium alginate (ALG)) contribute to the development and application of smart composite scaffolds in the tendon tissue engineering by advantageously integrating mechanical properties and biocompatibility. As a potential natural antioxidant, melatonin (MLT) represents the potential to promote tendon repair. Here, we develop an MLT-loaded PCL/ALG composite scaffold that effectively promotes tendon injury repair in vivo and in vitro via a controlled release of MLT, possibly mechanically relying on an antioxidant stress pathway. This biomimetic composite scaffold will be of great significance in the tendon tissue engineering.

Melatonin regulates chicken granulosa cell proliferation and apoptosis by activating the mTOR signaling pathway via its receptors

Melatonin is a key regulator of follicle granular cell maturation and ovulation. The mammalian target of rapamycin (mTOR) pathway plays an important role in cell growth regulation. Therefore, our aim was to investigate whether the mTOR signaling pathway is involved in the regulation of melatonin-mediated proliferation and apoptotic mechanisms in granulosa cells. Chicken follicle granular cells were cultured with melatonin (0, 2, 20, or 200 μmol/L) for 48 h. The results showed that melatonin treatment enhanced proliferation and suppressed apoptosis in granular cells at 20 μmol/L and 200 μmol/L (P < 0.05) by upregulation of cyclin D1 (P < 0.01) and Bcl-2 (P < 0.01) and downregulation of P21, caspase-3, Beclin1, and LC3-II (P < 0.01). The effects resulted in the activation of the mTOR signaling pathway by increasing the expression of avTOR, PKC, 4E-BP1, S6K (P < 0.05), p-mTOR, and p-S6K. We added an mTOR activator and inhibitor to the cells and identified the optimal dose (10 μmol/L MHY1485 and 100 nmol/L rapamycin) for subsequent experiments. The combination of 20 μmol/L melatonin and 10 μmol/L MHY1485 significantly enhanced granulosa cell proliferation (P < 0.05), while 100 nmol/L rapamycin significantly inhibited proliferation and enhanced apoptosis (P < 0.05), but this action was reversed in the 20-μmol/L melatonin and 100-nmol/L rapamycin cotreatment groups (P < 0.05). This was confirmed by mRNA and protein expression that was associated with proliferation, apoptosis, and autophagy (P < 0.05). The combination of 20 μmol/L melatonin and 10 μmol/L MHY1485 also activated the mTOR pathway upstream genes PI3K, AKT1, and AKT2 and downstream genes PKC, 4E-BP1, and S6K (P < 0.05), as well as protein expression of p-mTOR and p-S6K. Rapamycin significantly inhibited the mTOR pathway-related genes mRNA levels (P < 0.05). In addition, activation of the mTOR pathway increased melatonin receptor mRNA levels (P < 0.05). In conclusion, these findings demonstrate that melatonin regulates chicken granulosa cell proliferation and apoptosis by activating the mTOR signaling pathway via its receptor.

Sulfated glycolipid PG545 induces endoplasmic reticulum stress and augments autophagic flux by enhancing anticancer chemotherapy efficacy in endometrial cancer

The sulfated glycolipid PG545 shows promising antitumor activity in various cancers. This study was conducted to explore the effects and the mechanism of PG545 action in endometrial cancer (EC). PG545 exhibited strong synergy as assessed by the Chou-Talalay-Method in vitro when combined with cisplatin, or paclitaxel in both type I (Hec1B) and type II (ARK2) EC cell lines. While PG545 showed antitumor activity as monotherapy, a combination of PG545 with paclitaxel and cisplatin was highly effective in reducing the tumor burden and significantly prolonged survival of both Hec1B and ARK2 xenograft bearing mice. Mechanistically, PG545 elicits ER stress as an early response with resultant induction of autophagy. Our data demonstrated an increase in pERK, Bip/Grp78, IRE1α, Calnexin and CHOP/GADD153 within 6-24 hrs of PG545 treatment in EC cells. In parallel, PG545 also blocked FGF2 and HB-EGF mediated signaling in EC cells. Moreover, melatonin-mediated ER stress inhibition reduced PG545-mediated autophagy and PG545 in combination with cisplatin further heightened this stress response. Collectively these data indicate that PG545 exhibits strong synergistic effects with chemotherapeutics in vitro and showed promising antitumor activity in vivo. Our preclinical data indicates that in future studies PG545 can be a useful adjunct to chemotherapy in endometrial cancer.

Myomaker, and Myomixer-Myomerger-Minion modulate the efficiency of skeletal muscle development with melatonin supplementation through Wnt/β-catenin pathway

Melatonin, a pleiotropic hormone secreted from the pineal gland, has been shown to exert beneficial effects in muscle regeneration and repair due to its functional diversity, including anti-inflammation, anti-apoptosis, and anti-oxidative activity. However, little is known about the negative role of melatonin in myogenesis. Here, using skeletal muscle cells, we found that melatonin promoted C2C12 cells proliferation and inhibits differentiation both in C2C12 cells and primary myoblasts in mice. Melatonin administration significantly down-regulated differentiation and fusion related genes and inhibited myotube formation both in C2C12 cells and primary myoblasts in mice. RNA-seq showed that melatonin down-regulated essential fusion pore components Myomaker and Myomixer-Myomerger-Minion. Moreover, melatonin suppressed Wnt/β-catenin signaling. Inhibition of GSK3β by LiCl rescued the influence of melatonin on differentiation efficiency, Myomaker, but not Myomxier in C2C12 cells. In conclusion, melatonin inhibits myogenic differentiation, Myomaker, and Myomixer through reducing Wnt/β-catenin signaling. These data establish a link between melatonin and fusogenic membrane proteins Myomaker and Myomixer, and suggest the new perspective of melatonin in treatment or preventment of muscular diseases.

Dietary melatonin attenuates chromium-induced lung injury via activating the Sirt1/Pgc-1α/Nrf2 pathway

Exposure to chromium (Cr) causes a number of respiratory diseases, including lung cancer and pulmonary fibrosis. However, there is currently no safe treatment for Cr-induced lung damage. Here, we used in vivo and in vitro approaches to examine the protective effects of melatonin (MEL) on Cr-induced lung injury and to identify the underlying molecular mechanisms. We found that treatment of rats or a mouse lung epithelial cell MLE-12 with MEL attenuated K₂Cr₂O₇-induced lung injury by reducing the production of oxidative stress and inflammatory mediators and inhibiting cell apoptosis. MEL treatment upregulated the expression of silent information regulator 1 (Sirt1), which deacetylated the transcriptional coactivator peroxisome proliferator-activated receptor-γ coactivator-1α (Pgc-1α). In turn, this increased the expression of the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) and key anti-oxidant target genes. These results suggest that melatonin attenuates chromium-induced lung injury via activating the Sirt1/Pgc-1α/Nrf2 pathway. Dietary MEL supplement may be a potential new strategy for the treatment of Cr poisoning.

Melatonin Increases the Sensitivity of Hepatocellular Carcinoma to Sorafenib through the PERK-ATF4-Beclin1 Pathway

The mechanisms of resistance to the targeted drug sorafenib in the treatment of hepatocellular carcinoma (HCC) are poorly understood. The purpose of this study was to investigate the mechanism of sorafenib resistance and to elucidate the role of melatonin in overcoming sorafenib resistance. We first observed that sorafenib induced endoplasmic reticulum (ER) stress and activated autophagy in HCC, and the inhibition of ER stress and autophagy by specific inhibitors (PBA, TUDC and 3-MA) increased sorafenib-induced apoptosis, indicating that cells resist apoptosis by inducing ER stress and autophagy in the presence of sorafenib. Furthermore, specimens from patients with HCC revealed a close relationship between ER stress and autophagy, as demonstrated by the high correlation between expression of the autophagy-associated protein Beclin1 and expression of unfolded protein response (UPR) pathway proteins, especially PKR-like ER stress kinase (PERK); moreover, patients with combined expression of PERK and Beclin1 had more advanced disease (higher clinical stage) and a shorter overall survival time. ER stress inhibitors significantly blocked sorafenib-induced autophagy, selective knockdown of PERK and activating transcription factor 4 (ATF4) expression reduced sorafenib-induced autophagy activity compared with knockdown of the other two UPR pathways, and silencing ATF4 inhibited the expression of Beclin1. These results suggest that autophagy is downstream of ER stress and that the PERK-ATF4-Beclin1 pathway plays a role in ER stress-related autophagy. Interestingly, a low concentration of melatonin increased the sensitivity of HCC to sorafenib by inhibiting autophagy through the PERK-ATF4-Beclin1 pathway. Taken together, our findings suggest that cotreatment with sorafenib and melatonin is a potential therapy for HCC. Furthermore, ER stress-related autophagy plays key roles in apoptosis resistance. Therefore, targeting the PERK-ATF4-Beclin1 pathway may prove instrumental in HCC therapy.

Combined Fluid Shear Stress and Melatonin Enhances the ERK/Akt/mTOR Signal in Cilia-Less MC3T3-E1 Preosteoblast Cells

We investigated whether combined fluid shear stress (FSS) and melatonin stimulated signal transduction in cilia-less MC3T3-E1 preosteoblast cells. MC3T3-E1 cells were treated with chloral hydrate or nocodazole, and mechanotransduction sensor primary cilia were removed. p-extracellular signal–regulated kinase (ERK) and p-Akt with/without melatonin increased with nocodazole treatment and decreased with chloral hydrate treatment, whereas p-ERK and p-Akt in FSS with/without melatonin increased in cilia-less groups compared to cilia groups. Furthermore, p-mammalian target of rapamycin (mTOR) with FSS-plus melatonin increased in cilia-less groups compared to only melatonin treatments in cilia groups. Expressions of Bcl-2, Cu/Zn-superoxide dismutase (SOD), and catalase proteins were higher in FSS with/without melatonin with cilia-less groups than only melatonin treatments in cilia groups. Bax protein expression was high in FSS-plus melatonin with chloral hydrate treatment. In chloral hydrate treatment with/without FSS, expressions of Cu/Zn-SOD, Mn-SOD, and catalase proteins were high compared to only-melatonin treatments. In nocodazole treatment, Mn-SOD protein expression without FSS was high, and catalase protein level with FSS was low, compared to only melatonin treatments. These data show that the combination with FSS and melatonin enhances ERK/Akt/mTOR signal in cilia-less MC3T3-E1, and the enhanced signaling in cilia-less MC3T3-E1 osteoblast cells may activate the anabolic effect for the preservation of cell structure and function.

Melatonin Rescues Mesenchymal Stem Cells from Senescence Induced by the Uremic Toxin p-Cresol via Inhibiting mTOR-Dependent Autophagy

p-Cresol, found at high concentrations in the serum of chronic kidney failure patients, is known to cause cell senescence and other complications in different parts of the body. p-Cresol is thought to mediate cytotoxic effects through the induction of autophagy response. However, toxic effects of p-cresol on mesenchymal stem cells have not been elucidated. Thus, we aimed to investigate whether p-cresol induces senescence of mesenchymal stem cells, and whether melatonin can ameliorate abnormal autophagy response caused by p-cresol. We found that p-cresol concentration-dependently reduced proliferation of mesenchymal stem cells. Pretreatment with melatonin prevented pro-senescence effects of p-cresol on mesenchymal stem cells. We found that by inducing phosphorylation of Akt and activating the Akt signaling pathway, melatonin enhanced catalase activity and thereby inhibited the accumulation of reactive oxygen species induced by p-cresol in mesenchymal stem cells, ultimately preventing abnormal activation of autophagy. Furthermore, preincubation with melatonin counteracted other pro-senescence changes caused by p-cresol, such as the increase in total 5′-AMP-activated protein kinase expression and decrease in the level of phosphorylated mechanistic target of rapamycin. Ultimately, we discovered that melatonin restored the expression of senescence marker protein 30, which is normally suppressed because of the induction of the autophagy pathway in chronic kidney failure patients by p-cresol. Our findings suggest that stem cell senescence in patients with chronic kidney failure could be potentially rescued by the administration of melatonin, which grants this hormone a novel therapeutic role.

Melatonin prevents mitochondrial dysfunctions and death in differentiated skeletal muscle cells

Oxidative stress increase induces cellular damage and apoptosis activation, a mechanism believed to represent a final common pathway correlated to sarcopenia and many skeletal muscle disorders. The goal of this study is to evaluate if melatonin, a ROS scavenger molecule, is able to counteract or modulate myotube death. Here, differentiated C2C12 skeletal muscle cells have been treated with melatonin before chemicals known to induce apoptotic death and oxidative stress, and its effect has been investigated by means of morpho-functional analyses. Ultrastructural observations show melatonin protection against triggers by the reducing of membrane blebbing, chromatin condensation, myonuclei loss and in situ DNA cleavage. Moreover, melatonin is able to prevent mitochondrial dysfunctions which occur in myotubes exposed to the trigger alone. These findings demonstrate melatonin ability in preventing apoptotic cell death in skeletal muscle fibers in vitro, suggesting for this molecule a potential therapeutic role in the treatment of various muscle disorders.

Exosomes from Melatonin Treated Hepatocellularcarcinoma Cells Alter the Immunosupression Status through STAT3 Pathway in Macrophages

Immunosuppression is a significant factor in the progression of tumor invasion and metastasis. Melatonin, a well-known hormone, has certain cytotoxic and immune regulatory effects to inhibit tumor function. Exosomes are small membrane vesicles released by many kinds of cells, which contain different macromolecules, such as mRNAs and microRNAs (miRNAs), and proteins that can mediate communications between cells. Tumor-derived exosomes may cause immunosuppression, however, it is unknown whether melatonin can attenuate an immunosuppressive status by altering the function of tumor-derived exosomes. In the present study, we evaluated the effects of hepatocellularcarcinoma-derived exosomes (Exo-con) and exosomes derived from hepatocellularcarcinoma cells treated with 0.1 mM melatonin (Exo-MT), on the expression of inflammatory factors and programmed death ligand 1(PD-L1) by co-culturing Exo-con and Exo-MT, respectively, with macrophages differentiated from THP-1 cells or RAW264.7 cells. Our in vitro results indicate that Exo-MT can downregulate the expression of PD-L1 on macrophages while Exo-con can upregulate the expression of PD-L1 through flow cytometry and immunofluorescence analysis. In addition, Exo-con upregulates the secretion of cytokines, such as IL-6, IL-10, IL-1β, and TNF-α in macrophages. Accordingly, Exo-MT could attenuate the high expression of these inflammatory cytokines. Furthermore, in vivo experiments confirmed the results found in vitro. PD-L1 expression and cytokine secretion were lower in the Exo-MT group compared with those in the Exo-con group. Working to identify a specific mechanism, our research shows that Exo-MT decreases STAT3 activation compared to the Exo-con group. In summary, we found exosomes from melatonin treated hepatocellularcarcinoma cells alters the immunosupression status through STAT3 pathway in macrophages. Our study may provide a new avenue to investigate the mechanisms of melatonin in regulating an immunosuppressive status.

Melatonin synergizes the chemotherapeutic effect of 5-fluorouracil in colon cancer by suppressing PI3K/AKT and NF-κB/iNOS signaling pathways

5-Fluorouracil (5-FU) is one of the most commonly used chemotherapeutic agents in colon cancer treatment, but has a narrow therapeutic index limited by its toxicity. Melatonin exerts antitumor activity in various cancers, but it has never been combined with 5-FU as an anticolon cancer treatment to improve the chemotherapeutic effect of 5-FU. In this study, we assessed such combinational use in colon cancer and investigated whether melatonin could synergize the antitumor effect of 5-FU. We found that melatonin significantly enhanced the 5-FU-mediated inhibition of cell proliferation, colony formation, cell migration and invasion in colon cancer cells. We also found that melatonin synergized with 5-FU to promote the activation of the caspase/PARP-dependent apoptosis pathway and induce cell cycle arrest. Further mechanism study demonstrated that melatonin synergized the antitumor effect of 5-FU by targeting the PI3K/AKT and NF-κB/inducible nitric oxide synthase (iNOS) signaling. Melatonin in combination with 5-FU markedly suppressed the phosphorylation of PI3K, AKT, IKKα, IκBα, and p65 proteins, promoted the translocation of NF-κB p50/p65 from the nuclei to cytoplasm, abrogated their binding to the iNOS promoter, and thereby enhanced the inhibition of iNOS signaling. In addition, pretreatment with a PI3K- or iNOS-specific inhibitor synergized the antitumor effects of 5-FU and melatonin. Finally, we verified in a xenograft mouse model that melatonin and 5-FU exerted synergistic antitumor effect by inhibiting the AKT and iNOS signaling pathways. Collectively, our study demonstrated that melatonin synergized the chemotherapeutic effect of 5-FU in colon cancer through simultaneous suppression of multiple signaling pathways.

Melatonin alleviates postinfarction cardiac remodeling and dysfunction by inhibiting Mst1

Melatonin reportedly protects against several cardiovascular diseases including ischemia/reperfusion (I/R), atherosclerosis, and hypertension. The present study investigated the effects and mechanisms of melatonin on cardiomyocyte autophagy, apoptosis, and mitochondrial injury in the context of myocardial infarction (MI). We demonstrated that melatonin significantly alleviated cardiac dysfunction after MI. Four weeks after MI, echocardiography and Masson staining indicated that melatonin notably mitigated adverse left ventricle remodeling. The mechanism may be associated with increased autophagy, reduced apoptosis, and alleviated mitochondrial dysfunction. Furthermore, melatonin significantly inhibited Mst1 phosphorylation while promoting Sirt1 expression after MI, which indicates that Mst1/Sirt1 signaling may serve as the downstream target of melatonin. We thus constructed a MI model using Mst1 transgenic (Mst1 Tg) and Mst1 knockout (Mst1^-/- ) mice. The absence of Mst1 abolished the favorable effects of melatonin on cardiac injury after MI. Consistently, melatonin administration did not further increase autophagy, decrease apoptosis, or alleviate mitochondrial integrity and biogenesis in Mst1 knockout mice subjected to MI injury. These results suggest that melatonin alleviates postinfarction cardiac remodeling and dysfunction by upregulating autophagy, decreasing apoptosis, and modulating mitochondrial integrity and biogenesis. The attributed mechanism involved, at least in part, Mst1/Sirt1 signaling.

Melatonin Suppresses Autophagy Induced by Clinostat in Preosteoblast MC3T3-E1 Cells

Microgravity exposure can cause cardiovascular and immune disorders, muscle atrophy, osteoporosis, and loss of blood and plasma volume. A clinostat device is an effective ground-based tool for simulating microgravity. This study investigated how melatonin suppresses autophagy caused by simulated microgravity in preosteoblast MC3T3-E1 cells. In preosteoblast MC3T3-E1 cells, clinostat rotation induced a significant time-dependent increase in the levels of the autophagosomal marker microtubule-associated protein light chain (LC3), suggesting that autophagy is induced by clinostat rotation in these cells. Melatonin treatment (100, 200 nM) significantly attenuated the clinostat-induced increases in LC3 II protein, and immunofluorescence staining revealed decreased levels of both LC3 and lysosomal-associated membrane protein 2 (Lamp2), indicating a decrease in autophagosomes. The levels of phosphorylation of mammalian target of rapamycin (p-mTOR) (Ser2448), phosphorylation of extracellular signal-regulated kinase (p-ERK), and phosphorylation of serine-threonine protein kinase (p-Akt) (Ser473) were significantly reduced by clinostat rotation. However, their expression levels were significantly recovered by melatonin treatment. Also, expression of the Bcl-2, truncated Bid, Cu/Zn- superoxide dismutase (SOD), and Mn-SOD proteins were significantly increased by melatonin treatment, whereas levels of Bax and catalase were decreased. The endoplasmic reticulum (ER) stress marker GRP78/BiP, IRE1α, and p-PERK proteins were significantly reduced by melatonin treatment. Treatment with the competitive melatonin receptor antagonist luzindole blocked melatonin-induced decreases in LC3 II levels. These results demonstrate that melatonin suppresses clinostat-induced autophagy through increasing the phosphorylation of the ERK/Akt/mTOR proteins. Consequently, melatonin appears to be a potential therapeutic agent for regulating microgravity-related bone loss or osteoporosis.

Reduced fat mass and increased lean mass in response to 1 year of melatonin treatment in postmenopausal women: A randomized placebo-controlled trial

OBJECTIVE

Apart from regulating the circadian rhythm, melatonin exerts a variety of actions in the living organism. Among these functions, melatonin is believed to have a positive effect on body weight and energy metabolism. So far, the evidence for this relies mainly on animal models. In this study, we aimed to determine the effects of melatonin on body composition, lipid and glucose metabolism in humans.

DESIGN/METHODS

In a double-blind, placebo-controlled study, we randomized 81 postmenopausal women to 1 year of treatment with melatonin (1 or 3 mg nightly) or placebo. Body composition was measured by DXA. Measures were obtained at baseline and after 1 year of treatment along with leptin, adiponectin and insulin. Markers of glucose homeostasis were measured at the end of the study.

RESULTS

In response to treatment, fat mass decreased in the melatonin group by 6·9% (95% CI: 1·4%; 12·4%, P = 0·02) compared to placebo. A borderline significant increase in lean mass of 5·2% was found in the melatonin group compared to placebo (3·3%, (IQR:-1·7; 6·2) vs -1·9%, (IQR: -5·7; 5·8), P = 0·08). After adjusting for BMI, lean mass increased by 2·6% (95% CI: 0·1; 5·0, P = 0·04) in the melatonin group. Changes in body weight and BMI did not differ between groups. Adiponectin increased borderline significantly by 21% in the melatonin group compared to placebo (P = 0·08). No significant changes were observed for leptin, insulin or markers of glucose homeostasis.

CONCLUSION

Our results suggest a possibly beneficial effect of melatonin on body composition and lipid metabolism as 1 year of treatment reduces fat mass, increases lean mass and is associated with a trend towards an increase in adiponectin.

Rescue of proinflammatory cytokine-inhibited chondrogenesis by the antiarthritic effect of melatonin in synovium mesenchymal stem cells via suppression of reactive oxygen species and matrix metalloproteinases

Cartilage repair by mesenchymal stem cells (MSCs) often occurs in diseased joints in which the inflamed microenvironment impairs chondrogenic maturation and causes neocartilage degradation. In this environment, melatonin exerts an antioxidant effect by scavenging free radicals. This study aimed to investigate the anti-inflammatory and chondroprotective effects of melatonin on human MSCs in a proinflammatory cytokine-induced arthritic environment. MSCs were induced toward chondrogenesis in the presence of interleukin-1β (IL-1β) or tumor necrosis factor α (TNF-α) with or without melatonin. Levels of intracellular reactive oxygen species (ROS), hydrogen peroxide, antioxidant enzymes, and cell viability were then assessed. Deposition of glycosaminoglycans and collagens was also determined by histological analysis. Gene expression of chondrogenic markers and matrix metalloproteinases (MMPs) was assessed by real-time polymerase chain reaction. In addition, the involvement of the melatonin receptor and superoxide dismutase (SOD) in chondrogenesis was investigated using pharmacologic inhibitors. The results showed that melatonin significantly reduced ROS accumulation and increased SOD expression. Both IL-1β and TNF-α had an inhibitory effect on the chondrogenesis of MSCs, but melatonin successfully restored the low expression of cartilage matrix and chondrogenic genes. Melatonin prevented cartilage degradation by downregulating MMPs. The addition of luzindole and SOD inhibitors abrogated the protective effect of melatonin associated with increased levels of ROS and MMPs. These results demonstrated that proinflammatory cytokines impair the chondrogenesis of MSCs, which was rescued by melatonin treatment. This chondroprotective effect was potentially correlated to decreased ROS, preserved SOD, and suppressed levels of MMPs. Thus, melatonin provides a new strategy for promoting cell-based cartilage regeneration in diseased or injured joints.

Melatonin administration decreases adipogenesis in the liver of ob/ob mice through autophagy modulation

Despite efforts to curb the incidence of obesity and its comorbidities, this condition remains the fifth leading cause of death worldwide. To identify ways to reduce this global effect, we investigated the actions of daily melatonin administration on oxidative stress parameters and autophagic processes as a possible treatment of obesity in ob/ob mice. The involvement of melatonin in many physiological functions, such as the regulation of seasonal body weight variation, glucose uptake, or adiposity, and the role of this indoleamine as an essential antioxidant, has become the focus of numerous anti-obesity studies. Here, we examined the oxidative status in the livers of obese melatonin-treated and untreated mice, observing a decrease in the oxidative stress levels through elevated catalase activity. ROS-mediated autophagy was downregulated in the liver of melatonin-treated animals and was accompanied by significant accumulation of p62. Autophagy is closely associated with adipogenesis; in this study, we report that melatonin-treated obese mice also showed reduced adiposity, as demonstrated by diminished body weight and reduced peroxisome proliferator-activated receptor gamma expression. Based on these factors, it is reasonable to assume that oxidative stress and autophagy play important roles in obesity, and therefore, melatonin could be an interesting target molecule for the development of a potential therapeutic agent to curb body weight.

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.

Protective effect of melatonin on TNF-α-induced muscle atrophy in L6 myotubes

Muscle atrophy, characterized by decreased cell number and size, is a serious concern for patients afflicted with inflammatory diseases. Mounting evidence indicates that tumor necrosis factor alpha (TNF-α) plays a critical role in muscle atrophy in a number of clinical settings. We hypothesize that reactive oxygen species (ROS) mediate TNF-α-induced muscle cell death and hypotrophy. Recently, melatonin has attracted attention because of its free-radical scavenging and antioxidant properties. The aim of the current study was to evaluate the possible protective role of melatonin in TNF-α-induced muscle cell death and hypotrophy in rat L6 myotubes. To examine this possible role, L6 myotubes were exposed to various concentrations of recombinant TNF-α for 24 hr. We found that TNF-α at a concentration of 100 ng/mL induced ROS generation and decreased cell viability. Further analysis revealed that apoptosis, but not autophagy, may be important for TNF-α-induced cell death. Melatonin significantly attenuated TNF-α-induced ROS generation and apoptosis. In addition, decreased muscle fiber diameter and increased muscle cell proteolysis by TNF-α was highly attenuated by treatment with melatonin. The effects of melatonin were mediated neither through its plasmalemmal receptors nor by modulating the nuclear factor kappa B pathway activated by TNF-α. Taken together, these results suggest that TNF-α may mediate ROS-induced muscle cell death and hypotrophy and that melatonin may be a useful tool for protecting against muscle atrophy stemming from inflammatory diseases.

Melatonin modulates TLR4-mediated inflammatory genes through MyD88- and TRIF-dependent signaling pathways in lipopolysaccharide-stimulated RAW264.7 cells

Increasing evidence demonstrates that melatonin has an anti-inflammatory effect. Nevertheless, the molecular mechanisms remain obscure. In this study, we investigated the effect of melatonin on toll-like receptor 4 (TLR4)-mediated molecule myeloid differentiation factor 88 (MyD88)-dependent and TRIF-dependent signaling pathways in lipopolysaccharide (LPS)-stimulated macrophages. RAW264.7 cells were incubated with LPS (2.0 μg/mL) in the absence or presence of melatonin (10, 100, 1000 μm). As expected, melatonin inhibited TLR4-mediated tumor necrosis factor alpha (TNF-α), interleukin (IL)-1β, IL-6, IL-8, and IL-10 in LPS-stimulated macrophages. In addition, melatonin significantly attenuated LPS-induced upregulation of cyclooxygenase (COX)-2 and inducible nitric oxide synthase (iNOS) in macrophages. Further analysis showed that melatonin inhibited the expression of MyD88 in LPS-stimulated macrophages. Although it had no effect on TLR4-mediated phosphorylation of c-Jun N-terminal kinase (JNK), p38, and extracellular regulated protein kinase (ERK), melatonin significantly attenuated the activation of nuclear factor kappa B (NF-κB) in LPS-stimulated macrophages. In addition, melatonin inhibited TLR4-mediated Akt phosphorylation in LPS-stimulated macrophages. Moreover, melatonin significantly attenuated the elevation of interferon (IFN)-regulated factor-3 (IRF3), which was involved in TLR4-mediated TRIF-dependent signaling pathway, in LPS-stimulated macrophages. Correspondingly, melatonin significantly alleviated LPS-induced IFN-β in macrophages. In conclusion, melatonin modulates TLR4-mediated inflammatory genes through MyD88-dependent and TRIF-dependent signaling pathways.

Melatonin-induced autophagy is associated with degradation of MyoD protein in C2C12 myoblast cells

MyoD is a muscle-specific transcriptional factor that acts as a master switch for skeletal muscle differentiation. This protein regulates myoblast proliferation and myogenic differentiation and is also a short-lived regulatory protein that is degraded by the ubiquitin system. However, the lysosomal pathway of MyoD protein degradation remains unknown. In this study, we sought to determine whether melatonin (1, 2mm)-induced autophagy causes the degradation of MyoD protein in C2C12 myoblast cells. Melatonin induced a significant increase in expression of the microtubule-associated protein 1 light chain 3 (LC3)-II and Beclin-1 proteins in a dose-dependent manner. Melatonin treatment also significantly increased p-ERK, Ras, and p-Akt expressions in a dose-dependent manner. However, Bax expression was high compared with the absence of melatonin treatment, and Bcl-2 expression was high in the 0.1-0.5mm melatonin treatments and low in the 1 and 2mm melatonin treatments. Under the same conditions, cytosolic MyoD protein was significantly decreased in a dose-dependent manner and completely eliminated by 36hr. This decrease in MyoD protein involved ubiquitin-mediated proteasomal activity with proteasome inhibitor MG132 or autophagy-dependent lysosomal degradation with lysosomal inhibitor bafilomycin A1 (Baf-A1). In the same condition, phosphorylation of the mammalian target of rapamycin, p-mTOR, and p-S6K expression with Baf-A1 or Baf-A1-plus melatonin treatment were significantly decreased compared with the levels after treatment with melatonin only. Together, these results suggest that melatonin (1, 2mm)-induced autophagy results in partial lysosomal degradation of MyoD protein in C2C12 myoblast cells.

Role of melatonin in the regulation of autophagy and mitophagy: a review

Oxidative stress plays an essential role in triggering many cellular processes including programmed cell death. Proving a relationship between apoptosis and reactive oxygen species has been the goal of numerous studies. Accumulating data point to an essential role for oxidative stress in the activation of autophagy. The term autophagy encompasses several processes including not only survival or death mechanisms, but also pexophagy, mitophagy, ER-phagy or ribophagy, depending of which organelles are targeted for specific autophagic degradation. However, whether the outcome of autophagy is survival or death and whether the initiating conditions are starvation, pathogens or death receptors, reactive oxygen species are invariably involved. The role of antioxidants in the regulation of these processes, however, has been sparingly investigated. Among the known antioxidants, melatonin has high efficacy and, in both experimental and clinical situations, its protective actions against oxidative stress are well documented. Beneficial effects against mitochondrial dysfunction have also been described for melatonin; thus, this indoleamine seems to be linked to mitophagy. The present review focuses on data and the most recent advances related to the role of melatonin in health and disease, on autophagy activation in general, and on mitophagy in particular.

Melatonin potentiates chemotherapy-induced cytotoxicity and apoptosis in rat pancreatic tumor cells

Melatonin has antitumor activity via several mechanisms including its antiproliferative and proapoptotic effects in addition to its potent antioxidant action. Thus, melatonin has proven useful in the treatment of tumors in association with chemotherapeutic drugs. This study was performed to evaluate the effect of melatonin on the cytotoxicity and apoptosis induced by three different chemotherapeutic agents, namely 5-fluorouracil (5-FU), cisplatin, and doxorubicin in the rat pancreatic tumor cell line AR42J. We found that both melatonin and the three chemotherapeutic drugs induce a time-dependent decrease in AR42J cell viability, reaching the highest cytotoxic effect after 48 hr of incubation. Furthermore, melatonin significantly augmented the cytotoxicity of the chemotherapeutic agents. Consistently, cotreatment of AR42J cells with each of the chemotherapeutic agents in the presence of melatonin increased the population of apoptotic cells, elevated mitochondrial membrane depolarization, and augmented intracellular reactive oxygen species (ROS) production compared to treatment with each chemotherapeutic agent alone. These results provide evidence that in vitro melatonin enhances chemotherapy-induced cytotoxicity and apoptosis in rat pancreatic tumor AR42J cells and, therefore, melatonin may be potentially applied to pancreatic tumor treatment as a powerful synergistic agent in combination with chemotherapeutic drugs.

Melatonin enhances endogenous heme oxygenase-1 and represses immune responses to ameliorate experimental murine membranous nephropathy

Idiopathic membranous nephropathy (MN), an autoimmune-mediated glomerulonephritis, is one of the most common causes of nephrotic syndrome in adults. Therapeutic agents for MN remain ill defined. We assessed the efficacy of melatonin therapy for MN. Experimental murine MN was induced with cationic bovine serum albumin, and the mice were immediately administered 20 mg/kg melatonin or phosphate-buffered saline subcutaneously once a day. Disease severity was verified by examining serum and urine metabolic profiles and renal histopathology. The expression of cytokines and oxidative stress markers, cell apoptosis, and the associated mechanisms were also determined. Mice treated with melatonin displayed a significant reduction in proteinuria and a marked amelioration of glomerular lesions, with attenuated immunocomplex deposition. The subpopulations of T cells were not altered, but the CD19(+) B-cell subpopulation was significantly reduced in the MN mice treated with melatonin. The expression of cytokine mRNAs in splenocytes indicated that melatonin reduced the expression of proinflammatory cytokines and increased the expression of anti-inflammatory cytokines (interleukin 10). The production of reactive oxygen species and TUNEL-positive apoptotic cells in the kidney were also significantly reduced in the melatonin-treated MN mice. Melatonin also upregulated heme oxygenase 1 (HO1) and ameliorated MN. The blockade of HO1 expression with SnPP, a HO1 inhibitor, attenuated HO1 induction by melatonin and thus mitigated its renoprotective effects during MN. Our results suggest that melatonin treatment ameliorates experimental MN via multiple pathways, including by its antioxidative, antiapoptotic, and immunomodulatory effects. Melatonin should be considered a potential therapeutic intervention for MN in the future.

Beneficial actions of melatonin in the management of viral infections: a new use for this "molecular handyman"?

Melatonin (N‐acetyl‐5‐methoxytryptamine) is a multifunctional signaling molecule that has a variety of important functions. Numerous clinical trials have examined the therapeutic usefulness of melatonin in different fields of medicine. Clinical trials have shown that melatonin is efficient in preventing cell damage under acute (sepsis, asphyxia in newborns) and chronic states (metabolic and neurodegenerative diseases, cancer, inflammation, aging). The beneficial effects of melatonin can be explained by its properties as a potent antioxidant and antioxidant enzyme inducer, a regulator of apoptosis and a stimulator of immune functions. These effects support the use of melatonin in viral infections, which are often associated with inflammatory injury and increases in oxidative stress. In fact, melatonin has been used recently to treat several viral infections, which are summarized in this review. The role of melatonin in infections is also discussed herein. Copyright © 2012 John Wiley & Sons, Ltd.

Melatonin suppresses acrolein-induced IL-8 production in human pulmonary fibroblasts

Cigarette smoke (CS) causes harmful alterations in the lungs and airway structures and functions that characterize chronic obstructive pulmonary disease (COPD). In addition to COPD, active cigarette smoking causes other respiratory diseases and diminishes health status. Furthermore, recent studies show that, α, β-unsaturated aldehyde acrolein in CS induces the production of interleukin (IL)-8, which is known to be related to bronchitis, rhinitis, pulmonary fibrosis, and asthma. In addition, lung and pulmonary fibroblasts secrete IL-8, which has a chemotactic effect on leukocytes, and which in turn, play a critical role in lung inflammation. On the other hand, melatonin regulates circadian rhythm homeostasis in humans and has many other effects, which include antioxidant and anti-inflammatory effects, as demonstrated by the reduced expressions of iNOS, IL-1β, and IL-6 and increased glutathione (GSH) and superoxide dismutase activities. In this study, we investigated whether melatonin suppresses acrolein-induced IL-8 secretion in human pulmonary fibroblasts (HPFs). It was found that acrolein-induced IL-8 production was accompanied by increased levels of phosphorylation of Akt and extracellular signal-regulated kinases (ERK1/2) in HPFs, and that melatonin suppressed IL-8 production in HPFs. These results suggest that melatonin suppresses acrolein-induced IL-8 production via ERK1/2 and phosphatidylinositol 3-kinase (PI3K)/Akt signal inhibition in HPFs.

Exercise and melatonin in humans: reciprocal benefits

The aim of this review is to update the reader as to the association between physical exercise and melatonin, and to clarify how the melatonin rhythm may be affected by different types of exercise. Exercise may act as a zeitgeber, although the effects of exercise on the human circadian system are only now being explored. Depending on the time of the day, on the intensity of light, and on the proximity of the exercise to the onset or decline of the circadian production of melatonin, the consequence of exercise on the melatonin rhythm varies. Moreover, especially strenuous exercise per se induces an increased oxidative stress that in turn may affect melatonin levels in the peripheral circulation because indole is rapidly used to combat free radical damage. On the other hand, melatonin also may influence physical performance, and thus, there are mutually interactions between exercise and melatonin production which may be beneficial.

Melatonin protects against rotenone-induced cell injury via inhibition of Omi and Bax-mediated autophagy in Hela cells

Parkinson's disease is the second most common neurodegenerative disease, and environmental toxins such as rotenone play an important role in causing degeneration of dopaminergic neurons. Melatonin, a major secretory product of pineal, is recently reported to protect against rotenone-induced cell death in animal models. Yet, the mechanism involved in this protection needs to be elucidated. Here, we report that rotenone treatment (0-100 μM) decreased cell survival of Hela cells in a dose-dependent manner. At concentrations ranging from 0.1 to 100 μM, rotenone induced a dose-dependent increase in the expression of microtubule-associated protein 1 light chain 3 (LC3)-II, a protein associated with the autophagosomal membrane. Knockdown of Bax or Omi using shRNA inhibited 1 μM rotenone-induced autophagy. To determine whether melatonin would protect cells against rotenone-induced cell death and autophagy, we pretreated Hela cells with 250 μM melatonin for 24 hr in the presence of rotenone. Melatonin inhibited Bax expression and the release of the omi/HtrA2 into the cytoplasm induced by 1 μM rotenone. Melatonin 250 μM treatment also suppressed cell death induced by 0.1-100 μM rotenone and protected against the formation of LC3-II in cells exposed to 1 μM rotenone. This work demonstrates a novel role for melatonin as a neuroprotective agent against rotenone.