Melatonin attenuates TNF‐α and IL‐1β expression in synovial fibroblasts and diminishes cartilage degradation: Implications for the treatment of rheumatoid arthritis

The hormone melatonin has many properties, including antioxidant, anti‐inflammatory, and immunomodulatory effects. Melatonin has been demonstrated to be beneficial in several inflammatory autoimmune diseases, but its effects in rheumatoid arthritis (RA) remain controversial. We sought to determine how melatonin regulates inflammation in RA. We found that melatonin dose‐dependently inhibits tumor necrosis factor‐α (TNF‐α) and interleukin (IL)‐1β expression through the PI3K/AKT, ERK, and NF‐κB signaling pathways. We also identified that melatonin inhibits TNF‐α and IL‐1β production by upregulating miR‐3150a‐3p expression. Synovial tissue specimens from RA patients and culture of human rheumatoid fibroblast‐like synoviocytes confirmed that the MT1 receptor is needed for the anti‐inflammatory activities of melatonin. Importantly, melatonin also significantly reduced paw swelling, cartilage degradation, and bone erosion in the collagen‐induced arthritis mouse model. Our results indicate that melatonin ameliorates RA by inhibiting TNF‐α and IL‐1β production through downregulation of the PI3K/AKT, ERK, NF‐κB signaling pathways, as well as miR‐3150a‐3p overexpression. The role of melatonin as an adjuvant treatment in patients with RA deserves further clinical studies.     

Melatonin alleviates adipose inflammation through elevating α‐ketoglutarate and diverting adipose‐derived exosomes to macrophages in mice

Obesity is associated with macrophage infiltration and metabolic inflammation, both of which promote metabolic disease progression. Melatonin is reported to possess anti‐inflammatory properties by inhibiting inflammatory response of adipocytes and macrophages activation. However, the effects of melatonin on the communication between adipocytes and macrophages during adipose inflammation remain elusive. Here, we demonstrated melatonin alleviated inflammation and elevated α‐ketoglutarate (αKG) level in adipose tissue of obese mice. Mitochondrial isocitrate dehydrogenase 2 (Idh2) mRNA level was also elevated by melatonin in adipocytes leading to increase αKG level. Further analysis revealed αKG was the target for melatonin inhibition of adipose inflammation. Moreover, sirtuin 1 (Sirt1) physically interacted with IDH2 and formed a complex to increase the circadian amplitude of Idh2 and αKG content in melatonin‐inhibited adipose inflammation. Notably, melatonin promoted exosomes secretion from adipocyte and increased adipose‐derived exosomal αKG level. Our results also confirmed that melatonin alleviated adipocyte inflammation and increased ratio of M2 to M1 macrophages by transporting of exosomal αKG to macrophages and promoting TET‐mediated DNA demethylation. Furthermore, exosomal αKG attenuated signal transducers and activators of transduction‐3 (STAT3)/NF‐κB signal by its receptor oxoglutarate receptor 1 (OXGR1) in adipocytes. Melatonin also attenuated adipose inflammation and deceased macrophage number in chronic jet‐lag mice. In summary, our results demonstrate melatonin alleviates metabolic inflammation by increasing cellular and exosomal αKG level in adipose tissue. Our data reveal a novel function of melatonin on adipocytes and macrophages communication, suggesting a new potential therapy for melatonin to prevent and treat obesity caused systemic inflammatory disease.     

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 overcomes gemcitabine resistance in pancreatic ductal adenocarcinoma by abrogating nuclear factor‐κB activation

Constitutive activation and gemcitabine induction of nuclear factor‐κB (NF‐κB) contribute to the aggressive behavior and chemotherapeutic resistance of pancreatic ductal adenocarcinoma (PDAC). Thus, targeting the NF‐κB pathway has proven an insurmountable challenge for PDAC therapy. In this study, we investigated whether the inhibition of NF‐κB signaling pathway by melatonin might lead to tumor suppression and overcome gemcitabine resistance in pancreatic tumors. Our results showed that melatonin inhibited activities of NF‐κB by suppressing IκBα phosphorylation and decreased the expression of NF‐κB response genes in MiaPaCa‐2, AsPc‐1, Panc‐28 cells and gemcitabine resistance MiaPaCa‐2/GR cells. Moreover, melatonin not only inhibited cell proliferation and invasion in a receptor‐independent manner, but also enhanced gemcitabine cytotoxicity at pharmacologic concentrations in these PDAC cells. In vivo, the mice treated with both agents experienced a larger reduction in tumor burden than the single drug‐treated groups in an orthotopic xenograft mouse model. Taken together, these results indicate that melatonin inhibits proliferation and invasion of PDAC cells and overcomes gemcitabine resistance of pancreatic tumors through NF‐κB inhibition. Our findings therefore provide novel preclinical knowledge about melatonin inhibition of NF‐κB in PDAC and suggest that melatonin should be investigated clinically, alone or in combination with gemcitabine for PDAC treatment.     

Melatonin potentiates the antiproliferative and pro‐apoptotic effects of ursolic acid in colon cancer cells by modulating multiple signaling pathways

Ursolic acid (UA), a natural pentacyclic triterpenoid carboxylic acid, is largely distributed in medical herbs and edible plants. Melatonin is an indoleamine compound produced in the pineal gland and also a plant‐derived product. Both UA and melatonin have been shown to inhibit cancer cell growth in numerous studies, but they have never been combined altogether as an anticolon cancer treatment. In this study, we investigated whether the association between UA and melatonin leads to an enhanced antiproliferative and pro‐apoptotic activities in colon cancer SW480 and LoVo cells. We found that combined treatment with UA and melatonin significantly enhanced inhibition of cell viability and migration, promoted changes in cell morphology and spreading, and increased induction of apoptosis, thereby potentiating the effects of UA alone in colon cancer cells. Moreover, we found that the enhanced effects of UA and melatonin combination are mediated through simultaneous modulation of cytochrome c/caspase, MMP9/COX‐2, and p300/NF‐κB signaling pathways. Combined treatment with UA and melatonin triggered the release of cytochrome c from the mitochondrial intermembrane space into the cytosol, induced cleavage of caspase and PARP proteins, enhanced inhibition of MMP9 and COX‐2 expression, promoted p300 and NF‐κB translocation from cell nuclei to cytoplasm, and abrogated NF‐κB binding and p300 recruitment to COX‐2 promoter in colon cancer cells. These results, therefore, demonstrated that melatonin potentiated the antiproliferative and pro‐apoptotic effects of UA in colon cancer cells by modulating multiple signaling pathways and suggest that such a combinational treatment might potentially become an effective way in colon cancer therapy.     

Melatonin suppresses activation of hepatic stellate cells through RORα‐mediated inhibition of 5‐lipoxygenase

Liver fibrosis is scar tissue resulting from an uncontrolled wound‐healing process in response to chronic liver injury. Liver damage generates an inflammatory reaction that activates hepatic stellate cells (HSC) that transdifferentiate from quiescent cells that control retinol metabolism to proliferative and migratory myofibroblasts that produce excessive amounts of extracellular matrix proteins, in particular collagen 1a1 (COL1A1). Although liver fibrosis is reversible, no effective drug therapy is available to prevent or reverse HSC activation. Melatonin has potent hepatoprotective properties in a variety of acute and chronic liver injury models and suppresses liver fibrosis. However, it remains unclear whether melatonin acts indirectly or directly on HSC to prevent liver fibrosis. Here, we studied the effect of melatonin on culture‐activated rat HSC. Melatonin dose‐dependently suppressed the expression of HSC activation markers Col1a1 and alpha‐smooth muscle actin (αSMA, Acta2), as well as HSC proliferation and loss of lipid droplets. The nuclear melatonin sensor retinoic acid receptor‐related orphan receptor‐alpha (RORα/Nr1f1) was expressed in quiescent and activated HSC, while the membranous melatonin receptors (Mtrn1a and Mtrn1b) were not. The synthetic RORα agonist SR1078 more potently suppressed Col1a1 and αSma expression, HSC proliferation, and lipid droplet loss, while the RORα antagonist SR1001 blocked the antifibrotic features of melatonin. Melatonin and SR1078 inhibited the expression of Alox5, encoding 5‐lipoxygenase (5‐LO). The pharmacological 5‐LO inhibitor AA861 reduced Acta2 and Col1a1 expression in activated HSC. We conclude that melatonin directly suppresses HSC activation via RORα‐mediated inhibition of Alox5 expression, which provides novel drug targets to treat liver fibrosis.     

Melatonin ameliorates Aβ42‐induced alteration of βAPP‐processing secretases via the melatonin receptor through the Pin1/GSK3β/NF‐κB pathway in SH‐SY5Y cells

Melatonin is involved in the physiological regulation of the β‐amyloid precursor protein (βAPP)‐cleaving secretases which are responsible for generation of the neurotoxic amyloid beta (Aβ) peptide, one of the hallmarks of Alzheimer's disease (AD) pathology. In this study, we aimed to determine the underlying mechanisms of this regulation under pathological conditions. We establish that melatonin prevents Aβ₄₂‐induced downregulation of a disintegrin and metalloproteinase domain‐containing protein 10 (ADAM10) as well as upregulation of β‐site APP‐cleaving enzyme 1 (BACE1) and presenilin 1 (PS1) in SH‐SY5Y cell cultures. We also demonstrate that the intrinsic mechanisms of the observed effects occurred via regulation of nuclear factor kappa‐light‐chain‐enhancer of activated B cells (NF‐κB) and glycogen synthase kinase (GSK)‐3β as melatonin reversed Aβ₄₂‐induced upregulation and nuclear translocation of NF‐κBp65 as well as activation of GSK3β via its receptor activation. Furthermore, specific blocking of the NF‐κB and GSK3β pathways partially abrogated the Aβ₄₂‐induced reduction in the BACE1 and PS1 levels. In addition, GSK3β blockage affected α‐secretase cleavage and modulated nuclear translocation of NF‐κB. Importantly, our study for the first time shows that peptidyl‐prolyl cis‐trans isomerase NIMA‐interacting 1 (Pin1) is a crucial target of melatonin. The compromised levels and/or genetic variation of Pin1 are associated with age‐dependent tau and Aβ pathologies and neuronal degeneration. Interestingly, melatonin alleviated the Aβ₄₂‐induced reduction of nuclear Pin1 levels and preserved the functional integrity of this isomerase. Our findings illustrate that melatonin attenuates Aβ₄₂‐induced alterations of βAPP‐cleaving secretases possibly via the Pin1/GSK3β/NF‐κB pathway.     

Melatonin prevents Drp1‐mediated mitochondrial fission in diabetic hearts through SIRT1‐PGC1α pathway

Myocardial contractile dysfunction is associated with an increase in mitochondrial fission in patients with diabetes. However, whether mitochondrial fission directly promotes diabetes‐induced cardiac dysfunction is still unknown. Melatonin exerts a substantial influence on the regulation of mitochondrial fission/fusion. This study investigated whether melatonin protects against diabetes‐induced cardiac dysfunction via regulation of mitochondrial fission/fusion and explored its underlying mechanisms. Here, we show that melatonin prevented diabetes‐induced cardiac dysfunction by inhibiting dynamin‐related protein 1 (Drp1)‐mediated mitochondrial fission. Melatonin treatment decreased Drp1 expression, inhibited mitochondrial fragmentation, suppressed oxidative stress, reduced cardiomyocyte apoptosis, improved mitochondrial function and cardiac function in streptozotocin (STZ )‐induced diabetic mice, but not in SIRT 1^?/? diabetic mice. In high glucose‐exposed H9c2 cells, melatonin treatment increased the expression of SIRT 1 and PGC ‐1α and inhibited Drp1‐mediated mitochondrial fission and mitochondria‐derived superoxide production. In contrast, SIRT 1 or PGC ‐1α siRNA knockdown blunted the inhibitory effects of melatonin on Drp1 expression and mitochondrial fission. These data indicated that melatonin exerted its cardioprotective effects by reducing Drp1‐mediated mitochondrial fission in a SIRT 1/PGC ‐1α‐dependent manner. Moreover, chromatin immunoprecipitation analysis revealed that PGC ‐1α directly regulated the expression of Drp1 by binding to its promoter. Inhibition of mitochondrial fission with Drp1 inhibitor mdivi‐1 suppressed oxidative stress, alleviated mitochondrial dysfunction and cardiac dysfunction in diabetic mice. These findings show that melatonin attenuates the development of diabetes‐induced cardiac dysfunction by preventing mitochondrial fission through SIRT 1‐PGC 1α pathway, which negatively regulates the expression of Drp1 directly. Inhibition of mitochondrial fission may be a potential target for delaying cardiac complications in patients with diabetes.     

Melatonin influences somatostatin secretion from human pancreatic δ‐cells via MT1 and MT2 receptors

Melatonin is an effector of the diurnal clock on pancreatic islets. The membrane receptor‐transmitted inhibitory influence of melatonin on insulin secretion is well established and contrasts with the reported stimulation of glucagon release from α‐cells. Virtually, nothing is known concerning the melatonin‐mediated effects on islet δ‐cells. Analysis of a human pancreatic δ‐cell model, the cell line QGP‐1, and the use of a somatostatin‐specific radioimmunoassay showed that melatonin primarily has an inhibitory effect on somatostatin secretion in the physiological concentration range. In the pharmacological range, melatonin elicited slightly increased somatostatin release from δ‐cells. Cyclic adenosine monophosphate (cAMP) is the major second messenger dose‐dependently stimulating somatostatin secretion, in experiments employing the membrane‐permeable 8‐Br‐cAMP. 8‐Br‐cyclic guanosine monophosphate proved to be of only minor relevance to somatostatin release. As the inhibitory effect of 1 nm melatonin was reversed after incubation of QGP‐1 cells with the nonselective melatonin receptor antagonist luzindole, but not with the MT2‐selective antagonist 4‐P‐PDOT (4‐phenyl‐2‐propionamidotetraline), an involvement of the MT1 receptor can be assumed. Somatostatin release from the δ‐cells at low glucose concentrations was significantly inhibited during co‐incubation with 1 nm melatonin, an effect which was less pronounced at higher glucose levels. Transient expression experiments, overexpressing MT1, MT2, or a deletion variant as a control, indicated that the MT1 and not the MT2 receptor was the major transmitter of the inhibitory melatonin effect. These data point to a significant influence of melatonin on pancreatic δ‐cells and on somatostatin release.     

Evidence of the receptor‐mediated influence of melatonin on pancreatic glucagon secretion via the Gαq protein‐coupled and PI3K signaling pathways

Abstract: Melatonin has been shown to modulate glucose metabolism by influencing insulin secretion. Recent investigations have also indicated a regulatory function of melatonin on the pancreatic α‐cells. The present in vitro and in vivo studies evaluated whether melatonin mediates its effects via melatonin receptors and which signaling cascade is involved. Incubation experiments using the glucagon‐producing mouse pancreatic α‐cell line αTC1 clone 9 (αTC1.9) as well as isolated pancreatic islets of rats and mice revealed that melatonin increases glucagon secretion. Preincubation of αTC1.9 cells with the melatonin receptor antagonists luzindole and 4P‐PDOT abolished the glucagon‐stimulatory effect of melatonin. In addition, glucagon secretion was lower in the pancreatic islets of melatonin receptor knockout mice than in the islets of the wild‐type (WT) control animals. Investigations of melatonin receptor knockout mice revealed decreased plasma glucagon concentrations and elevated mRNA expression levels of the hepatic glucagon receptor when compared to WT mice. Furthermore, studies using pertussis toxin, as well as measurements of cAMP concentrations, ruled out the involvement of Gαi‐ and Gαs‐coupled signaling cascades in mediating the glucagon increase induced by melatonin. In contrast, inhibition of phospholipase C in αTC1.9 cells prevented the melatonin‐induced effect, indicating the physiological relevance of the Gαq‐coupled pathway. Our data point to the involvement of the phosphatidylinositol 3‐kinase signaling cascade in mediating melatonin effects in pancreatic α‐cells. In conclusion, these findings provide evidence that the glucagon‐stimulatory effect of melatonin in pancreatic α‐cells is melatonin receptor mediated, thus supporting the concept of melatonin‐modulated and diurnal glucagon release.     

Insulin and IGF1 enhance IL‐17‐induced chemokine expression through a GSK3B‐dependent mechanism: a new target for melatonin's anti‐inflammatory action

Obesity is a chronic inflammation with increased serum levels of insulin, insulin‐like growth factor 1 (IGF1), and interleukin‐17 (IL‐17). The objective of this study was to test a hypothesis that insulin and IGF1 enhance IL‐17‐induced expression of inflammatory chemokines/cytokines through a glycogen synthase kinase 3β (GSK3B)‐dependent mechanism, which can be inhibited by melatonin. We found that insulin/IGF1 and lithium chloride enhanced IL‐17‐induced expression of C‐X‐C motif ligand 1 (Cxcl1) and C‐C motif ligand 20 (Ccl20) in the Gsk3b^+/+, but not in Gsk3b^?/? mouse embryonic fibroblast (MEF) cells. IL‐17 induced higher levels of Cxcl1 and Ccl20 in the Gsk3b^?/? MEF cells, compared with the Gsk3b^+/+ MEF cells. Insulin and IGF1 activated Akt to phosphorylate GSK3B at serine 9, thus inhibiting GSK3B activity. Melatonin inhibited Akt activation, thus decreasing P‐GSK3B at serine 9 (i.e., increasing GSK3B activity) and subsequently inhibiting expression of Cxcl1 and Ccl20 that was induced either by IL‐17 alone or by a combination of insulin and IL‐17. Melatonin's inhibitory effects were only observed in the Gsk3b^+/+, but in not Gsk3b^?/? MEF cells. Melatonin also inhibited expression of Cxcl1, Ccl20, and Il‐6 that was induced by a combination of insulin and IL‐17 in the mouse prostatic tissues. Further, nighttime human blood, which contained high physiologic levels of melatonin, decreased expression of Cxcl1, Ccl20, and Il‐6 in the PC3 human prostate cancer xenograft tumors. Our data support our hypothesis and suggest that melatonin may be used to dampen IL‐17‐mediated inflammation that is enhanced by the increased levels of insulin and IGF1 in obesity.     

Melatonin reduces inflammatory response in human intestinal epithelial cells stimulated by interleukin‐1β

Melatonin is the main secretory product of the pineal gland, and it is involved in the regulation of periodic events. A melatonin production independent of the photoperiod is typical of the gut. However, the local physiological role of melatonin at the intestinal tract is poorly characterized. In this study, we evaluated the anti‐inflammatory activities of melatonin in an in vitro model of inflamed intestinal epithelium. To this purpose, we assessed different parameters usually associated with intestinal inflammation using IL‐1β‐stimulated Caco‐2 cells. Differentiated monolayers of Caco‐2 cells were preincubated with melatonin (1 nmol/L‐50 μmol/L) and then exposed to IL‐1β. After each treatment, different inflammatory mediators, DNA‐breakage, and global DNA methylation status were assayed. To evaluate the involvement of melatonin membrane receptors, we also exposed differentiated monolayers to melatonin in the presence of luzindole, a MT1 and MT2 antagonist. Our results showed that melatonin, at concentrations similar to those obtained in the lumen gut after ingestion of dietary supplements for the treatment of sleep disorders, was able to attenuate the inflammatory response induced by IL‐1β. Anti‐inflammatory effects were expressed as both a decrease of the levels of inflammatory mediators, including IL‐6, IL‐8, COX‐2, and NO, and a reduced increase in paracellular permeability. Moreover, the protection was associated with a reduced NF‐κB activation and a prevention of DNA demethylation. Conversely, luzindole did not reverse the melatonin inhibition of stimulated‐IL‐6 release. In conclusion, our findings suggest that melatonin, through a local action, can modulate inflammatory processes at the intestinal level, offering new opportunities for a multimodal management of IBD.