Melatonin induces cell cycle arrest and apoptosis in hepatocarcinoma HepG2 cell line

Melatonin and (-)-Epigallocatechin-3-Gallate: Partners in Fighting Cancer

We have demonstrated previously that melatonin attenuates hepatotoxicity triggered by high doses of (−)-epigallocatechin-3-gallate (EGCG) in mice. The current work investigated the influence of melatonin on the oncostatic activity of EGCG in two cancer cell lines, wherein melatonin induced an opposite response of p21. In human tongue cancer TCA8113 cells, melatonin-induced p21 and EGCG-mediated formation of quinoproteins were positively associated with the oncostatic effects of melatonin and EGCG. Melatonin-stimulated an increase in p21 which was correlated with a pronounced nuclear translocation of thioredoxin 1 and thioredoxin reductase 1, both of which are known to induce p21 via promoting p53 trans-activation. Melatonin did not influence the EGCG-mediated increase of quinoprotein formation nor did EGCG impair melatonin-induced p21 up-regulation. Co-treatment with both agents enhanced the cell-killing effect as well as the inhibitory activities against cell migration and colony formation. It is known that p21 also plays a powerful anti-apoptotic role in some cancer cells and confers these cells with a survival advantage, making it a target for therapeutic suppression. In human hepatocellular carcinoma HepG2 cells, melatonin suppressed p21 along with the induction of pro-survival proteins, PI3K and COX-2. However, EGCG prevented against melatonin-induced PI3K and COX-2, and melatonin probably sensitized HepG2 cells to EGCG cytotoxicity via down-regulating p21, Moreover, COX-2 and HO-1 were significantly reduced only by the co-treatment, and melatonin aided EGCG to achieve an increased inhibition on Bcl2 and NFκB. These events occurring in the co-treatment collectively resulted in an enhanced cytotoxicity. In addition, the co-treatment also enhanced the inhibitory activities against cell migration and colony formation. Overall, the results gathered from these two cancer cell lines with a divergent p21 response to melatonin show that the various oncostatic activities of melatonin and EGCG together are more robust than each agent alone, suggesting that they may be useful partners in fighting cancer.

Immunoregulatory role of melatonin in cancer

Melatonin is a ubiquitous indole amine that plays a fundamental role in the regulation of the biological rhythm. Disrupted circadian rhythm alters the expression of clock genes and deregulates oncogenes, which finally promote tumor development and progression. An evidence supporting this notion is the higher risk of developing malignancies among night shift workers. Circadian secretion of the pineal hormone also synchronizes the immune system via a reciprocal association that exists between the immune system and melatonin. Immune cells are capable of melatonin biosynthesis in addition to the expression of its receptors. Melatonin induces big changes in different immune cell proportions, enhances their viability and improves immune cell metabolism in the tumor microenvironment. These effects might be directly mediated by melatonin receptors or indirectly through alterations in hormonal and cytokine release. Moreover, melatonin induces apoptosis in tumor cells via the intrinsic and extrinsic pathways of apoptosis, while it protectsthe immune cells. In general, melatonin has a profound impact on immune cell trafficking, cytokine production and apoptosis induction in malignant cells. On such a basis, using melatonin and resynchronization of sleep cycle may have potential implications in immune function enhancement against malignancies, which will be the focus of the present paper.

Binding of Pb-Melatonin and Pb-(Melatonin-metabolites) complexes with DMT1 and ZIP8: implications for lead detoxification

We have applied the docking methodology to characterize the binding modes of the divalent metal transporter 1 (DMT1) and the zinc transporter 8 (ZIP8) protein channels with: melatonin, some melatonin metabolites, and a few lead complexes of melatonin and its metabolites, in three different coordination modes (mono-coordinated, bi-coordinated and tri-coordinated). Our results show that bi-coordinated and tri-coordinated lead complexes prefer to bind inside the central region of ZIP8. Moreover, the interaction strength is larger compared with that of the free melatonin and melatonin metabolites. On the other hand, the binding modes with DMT1 of such complexes display lower binding energies, compared with the free melatonin and melatonin metabolites. Our results suggest that ZIP8 plays a major role in the translocation of Pb, bi or tri coordinated, when melatonin metabolites are present. Finally, we have characterized the binding modes responsible for the ZIP8 large affinities, found in bi-coordinated and tri-coordinated lead complexes. Our results show that such interactions are greater, because of an increase of the number of hydrogen bonds, the number and intensity of electrostatic interactions, and the interaction overlay degree in each binding mode. Our results give insight into the importance of the ZIP8 channel on lead transport and a possible elimination mechanism in lead detoxification processes. Graphical abstract .

Melatonin maximizes the therapeutic potential of non-preconditioned MSCs in a DEN-induced rat model of HCC

Pretreatment of mesenchymal stem cells (MSCs) with melatonin (Mel) improves their potential therapeutic effect on chronic diseases and cancers. However, this preconditioning strategy may direct the effect of Mel toward MSCs alone and deprive cancer cells of the oncostatic effect of Mel. Herein, we hypothesized that Mel given before transplantation of non-preconditioned MSCs may maximize the therapeutic outcome via the oncostatic effect of Mel by preparing a suitable tumor microenvironment for MSCs. Female rats (n = 60) were equally divided into 6 groups; normal control, diethylnitrosamine (DEN), DEN + Mel, DEN + MSCs, DEN + MSCs preconditioned with Mel, and DEN + MSCs + Mel. The obtained data revealed that administration of Mel before MSCs treatment without preconditioning yielded a better ameliorative effect against DEN-induced hepatocellular carcinoma (HCC) as evidenced by: 1) reduced serum levels of alpha fetoprotein and gamma-glutamyl transferase; 2) decreased number and area of glutathione S-transferase placental positive foci; 3) induced apoptosis (as indicated by increased cleaved caspase-3 activity, upregulated expression of proapoptotic genes Bax and caspase 3 and downregulated expression of anti-apoptotic genes Bcl2, survivin); 4) decreased malondialdehyde level and increased activities of superoxide dismutase, catalase, and glutathione peroxidase enzymes; and 5) reduced inflammation, angiogenesis and metastasis as indicated by downregulated expression of interleukin 1 beta, nuclear factor kappa B, vascular endothelial growth factor, and matrix metallopeptidase 9 genes and upregulated expression of metalloproteinase inhibitor 1 gene. Thus, administration of Mel before MSCs (without preconditioning) fostered the survival and therapeutic potential of MSCs in HCC, possibly through induction of apoptosis and inhibition of inflammation and oxidative stress. This new strategy showed better therapeutic outcomes and may improve MSC-based therapies for HCC.

Melatonin suppresses lung cancer metastasis by inhibition of epithelial–mesenchymal transition through targeting to Twist

The epithelial–mesenchymal transition (EMT) phenotype, whereby mature epithelial cells undergo phenotype transition and differentiate into motile, invasive cells, has been indicated in tumor metastasis. The melatonin hormone secreted by the pineal gland has an antioxidant effect and protects cells against carcinogenic substances that reduce tumor progression. However, the effects of melatonin in EMT and lung cancer metastasis are largely unknown. We found that melatonin down-regulated EMT by inhibiting Twist/Twist1 (twist family bHLH transcription factor 1) expression. This effect was mediated by MT1 receptor, PLC, p38/ERK and β-catenin signaling cascades. Twist expression was positively correlated with tumor stage and negatively correlated with MT1 expression in lung cancer specimens. Furthermore, melatonin inhibited EMT marker expression and lung cancer metastasis to liver in vivo. Finally, melatonin shows promise in the treatment of lung cancer metastasis and deserves further study.

Promising Antineoplastic Actions of Melatonin

Melatonin is an endogenous indoleamine with an incredible variety of properties and activities. In recent years, an increasing number of studies have investigated this indoleamine’s interaction with cancerous cells. In particular, it seems that melatonin not only has the ability to improve the efficacy of many drugs used in chemotherapy but also has a direct inhibitory action on neoplastic cells. Many publications underlined the ability of melatonin to suppress the proliferation of various cancer cells or to modulate the expression of membrane receptors on these cells, thereby reducing tumor aggressiveness to metastasize. In addition, while melatonin has antiapoptotic actions in normal cells, in many cancer cells it has proapoptotic effects; these dichotomous actions have gained the interest of researchers. The increasing focus on melatonin in the field of oncology and the growing number of studies on this topic require a deep understanding of what we already know about the antineoplastic actions of melatonin. This information would be of value for potential use of melatonin against neoplastic diseases.

Melatonin modulates dysregulated circadian clocks in mice with diethylnitrosamine-induced hepatocellular carcinoma

Disruption of circadian rhythms, which are regulated by the circadian clock machinery, plays an important role in different long-term diseases including hepatocellular carcinoma (HCC). Melatonin has been reported to alleviate promotion and progression of HCC, but the potential contribution of circadian clock modulation is unknown. We investigated the effects of melatonin in mice which received diethylnitrosamine (DEN) (35 mg/kg body weight ip) once a week for 8 weeks. Melatonin was given at 5 or 10 mg kg-1 d-1 ip beginning 4 weeks after the onset of DEN administration and ending at the sacrifice time (10, 20, 30, or 40 weeks). Liver expression of Bmal1, Clock, Npas2, Rorα, and Sirt1 increased, whereas Cry1, Per1, Per2, Per3, CK1ε, Rev-erbα, and Rev-erbβ decreased following DEN administration. Melatonin treatment prevented changes in the expression of clock genes, and this effect was accompanied by an upregulation of the MT1 receptor and reduced levels of the hypoxia-inducible factors Hif-1α and Hif-2α. An increased expression of p21, p53, and PARP1/2, a higher Bax/Bcl-2 ratio, and a lower expression of Cyclin D1, CDK6, HSP70, HSP90, and GRP78 proteins were also observed in melatonin-treated mice. Melatonin significantly potentiated the suppression of proliferation and cell cycle arrest induced by the synthetic REV-ERB agonist SR9009 in human Hep3B cells, and BMAL1 knocking down attenuated the pro-apoptotic and antiproliferative effect of melatonin. Results support a contribution of changes in the circadian clock components to the beneficial effects of melatonin in HCC and highlight the usefulness of strategies modulating the circadian machinery in hepatocarcinogenesis.

Melatonin inhibits epithelial‑to‑mesenchymal transition in gastric cancer cells via attenuation of IL‑1β/NF‑κB/MMP2/MMP9 signaling

Although melatonin has been shown to exert marked antitumor effects against a variety of cancers, the underlying mechanisms remain to be fully elucidated. It has been hypothesized that the anticancer properties of melatonin are associated with its ability to suppress epithelial‑to‑mesenchymal transition (EMT) of cancer cells. In the present study, melatonin effectively suppressed interleukin (IL)‑1β‑induced EMT in human gastric adenocarcinoma (GA) cells. Sequential treatment of GA cells with melatonin after IL‑1β challenge markedly reversed the IL‑1β‑induced morphological changes, reduced cell invasion and migration, increased β‑catenin and E‑cadherin expression, and downregulated fibronectin, vimentin, Snail, matrix metalloproteinase (MMP)2 and MMP9 expression. Moreover, IL‑1β‑induced activation of NF‑κB was attenuated following treatment with melatonin. Knockdown of NF‑κB significantly reduced the IL‑1β‑induced EMT in GA cells. Taken together, these findings indicate that melatonin may act by suppressing EMT and tumor progression by inhibiting NF‑κB activity.

Melatonin Synergizes the Chemotherapeutic Effect of Cisplatin in Ovarian Cancer Cells Independently of MT1 Melatonin Receptors

BACKGROUND/AIM

Melatonin (MLT), through the interaction with membrane melatonin receptors MT1, can improve the effectiveness of cytostatic agents, including cisplatin (CP). The aim of this study was to examine the synergistic effect of MLT and CP in three cell lines: IOSE 364, SK-OV-3 and OVCAR-3, as well as to assess the role of MT1 receptors in this mechanism.

MATERIALS AND METHODS

Using the SRB assay we investigated the effect of different concentrations of CP and MLT on cell viability. Tests, using luzindole - MT1 inhibitor, allowed us to assess the potential involvement of MT1 in the mechanism of MLT action.

RESULTS

MLT at certain concentrations demonstrated a synergistic effect in combination with CP. The addition of luzindole did not affect the action of MLT in combination with CP.

CONCLUSION

In summary, the synergistic effect of MLT with CP seems to be independent of membrane MT1 receptors.

Melatonin enhances sorafenib actions in human hepatocarcinoma cells by inhibiting mTORC1/p70S6K/HIF-1α and hypoxia-mediated mitophagy

The antiangiogenic effects of sustained sorafenib treatment in hepatocellular carcinoma (HCC) lead to the occurrence of hypoxia-mediated drug resistance resulting in low therapy efficiency and negative outcomes. Combined treatments with coadjuvant compounds to target the hypoxia-inducible factor-1α (HIF-1α) represent a promising therapeutic approach through which sorafenib efficiency may be improved. Melatonin is a well-documented oncostatic agent against different cancer types. Here, we evaluated whether melatonin could enhance sorafenib cytotoxicity and overcome the hypoxia-mediated resistance mechanisms in HCC. The pharmacological melatonin concentration (2 mM) potentiated the oncostatic effects of sorafenib (5 μM) on Hep3B cells even under hypoxia. Melatonin downregulated the HIF-1α protein synthesis through the inhibition of the mammalian target of rapamycin complex 1 (mTORC1)/ribosomal protein S6 kinase beta-1 (p70S6K)/ribosomal protein S6 (RP-S6) pathway, although the indole enhanced Akt phosphorylation by the mTORC1/C2 negative feedback. Furthermore, melatonin and sorafenib coadministration reduced the HIF-1α-mitophagy targets expression, impaired autophagosome formation and subsequent mitochondria and lysosomes colocalization. Together, our results indicate that melatonin improves the Hep3B sensitivity to sorafenib, preventing HIF-1α synthesis to block the cytoprotective mitophagy induced by the hypoxic microenvironment, an important element of the multifactorial mechanisms responsible for the chemotherapy failure.

Melatonin as a potential inhibitory agent in head and neck cancer

Melatonin is a molecule secreted by the pineal gland; it is an important regulator of sleep and circadian rhythms. Through multiple interrelated mechanisms, melatonin exhibits various inhibitory properties at different stages of tumor progression. Many studies have explored the oncostatic effects of melatonin on hormone-dependent tumors. In this review, we highlight recent advances in understanding the effects of melatonin on the development of head and neck cancers, including molecular mechanisms identified through experimental and clinical observations. Because melatonin exerts a wide range of effects, melatonin may influence many mechanisms that influence the development of cancer. These include cell proliferation, apoptosis, angiogenesis, extracellular matrix remodeling through matrix metalloproteinases, and genetic polymorphism. Thus, the evidence discussed in this article will serve as a basis for basic and clinical research to promote the use of melatonin for understanding and controlling the development of head and neck cancers.

Melatonin: A pleiotropic molecule that modulates DNA damage response and repair pathways

DNA repair is responsible for maintaining the integrity of the genome. Perturbations in the DNA repair pathways have been identified in several human cancers. Thus, compounds targeting DNA damage response (DDR) hold great promise in cancer therapy. A great deal of effort, in pursuit of new anticancer drugs, has been devoted to understanding the basic mechanisms and functions of the cellular DNA repair machinery. Melatonin, a widely produced indoleamine in all organisms, is associated with a reduced risk of cancer and has multiple regulatory roles on the different aspects of the DDR and DNA repair. Herein, we have mainly discussed how defective components in different DNA repair machineries, including homologous recombination (HR), nonhomologous end-joining (NHEJ), base excision repair (BER), nucleotide excision repair (NER), and finally DNA mismatch repair (MMR), can contribute to the risk of cancer. Melatonin biosynthesis, mode of action, and antioxidant effects are reviewed along with the means by which the indoleamine regulates DDR at the transduction, mediation, and functional levels. Finally, we summarize recent studies that illustrate how melatonin can be combined with DNA-damaging agents to improve their efficacy in cancer therapy.

Melatonin suppresses hepatocellular carcinoma progression via lncRNA-CPS1-IT-mediated HIF-1α inactivation

Melatonin is the primary pineal hormone that relays light/dark cycle information to the circadian system. It was recently reported to exert intrinsic antitumor activity in various cancers. However, the regulatory mechanisms underlying the antitumor activity of melatonin are poorly understood. Moreover, a limited number of studies have addressed the role of melatonin in hepatocellular carcinoma (HCC), a major life-threatening malignancy in both sexes in Taiwan. In this study, we investigated the antitumor effects of melatonin in HCC and explored the regulatory mechanisms underlying these effects. We observed that melatonin significantly inhibited the proliferation, migration, and invasion of HCC cells and significantly induced the expression of the transcription factor FOXA2 in HCC cells. This increase in FOXA2 expression resulted in upregulation of lncRNA-CPS1 intronic transcript 1 (CPS1-IT1), which reduced HIF-1α activity and consequently resulted in the suppression of epithelial-mesenchymal transition (EMT) progression and HCC metastasis. Furthermore, the results of the in vivo experiments confirmed that melatonin exerts tumor suppressive effects by reducing tumor growth. In conclusion, our findings suggested that melatonin inhibited HCC progression by reducing lncRNA-CPS1-IT1-mediated EMT suppression and indicated that melatonin could be a promising treatment for HCC.

Amelioration of Dalton's lymphoma-induced angiogenesis by melatonin

For tumor to grow beyond 1-2 mm³ size, tumor recruits new blood vessels referred as angiogenesis; therefore, targeting angiogenesis can be a promising strategy to suppress cancer progression. In this study, in order to develop a good angiogenesis model, we investigated effect of Dalton's lymphoma on angiogenesis and further monitored the role of melatonin on regulation of angiogenesis. To evaluate angiogenesis, endothelial cells were isolated from main thoracic aorta and cultured in vitro in the presence or absence of Dalton's lymphoma supplemented with or without melatonin to monitor their role on its proliferation and migration, a hallmark of angiogenesis. Chick chorioallantoic membrane as well as mice mesentery which allows in vivo studies of tumor angiogenesis and testing of anti-angiogenic molecules was used to validate the in vitro analysis. To further extend our understanding about the regulation of the angiogenesis, we evaluated expression of tissue inhibitor of metalloproteinases 3, vascular endothelial growth factor, vascular endothelial growth factor receptor, and fibroblast growth factor in Dalton's lymphoma cells and mesentery by semiquantitative and quantitative reverse transcription polymerase chain reaction analysis. Dalton's lymphoma ascites induced significant increase in endothelial cell proliferation, migration, and sprouting of the tertiary branching in chorioallantoic membrane and mesentery of Dalton's lymphoma-bearing mice, whereas melatonin treatment led to their inhibition in a dose-dependent manner. Semiquantitative and quantitative reverse transcription polymerase chain reaction analysis of melatonin-treated Dalton's lymphoma cells and mesentery tissue clearly demonstrated restoration of angiogenesis-related genes tissue inhibitor of metalloproteinases 3 and reduction of vascular endothelial growth factor, vascular endothelial growth factor receptor, and fibroblast growth factor messenger RNA expression. Taken together, our results strongly demonstrate that Dalton's lymphoma provides pro-angiogenic environment leading to significant increase in angiogenesis, and further melatonin treatment reduced the Dalton's lymphoma ascites-induced angiogenesis implying that Dalton's lymphoma can serve as a very good model to study angiogenesis as well as for screening of drugs that can target angiogenesis.

Melatonin and Fertoprotective Adjuvants: Prevention against Premature Ovarian Failure during Chemotherapy

Premature ovarian failure is one of the side effects of chemotherapy in pre-menopausal cancer patients. Preservation of fertility has become increasingly important in improving the quality of life of completely recovered cancer patients. Among the possible strategies for preserving fertility such as ovarian tissue cryopreservation, co-treatment with a pharmacological adjuvant is highly effective and poses less of a burden on the human body. Melatonin is generally produced in various tissues and acts as a universally acting antioxidant in cells. Melatonin is now more widely used in various biological processes including treating insomnia and an adjuvant during chemotherapy. In this review, we summarize the information indicating that melatonin may be useful for reducing and preventing premature ovarian failure in chemotherapy-treated female patients. We also mention that many adjuvants other than melatonin are developed and used to inhibit chemotherapy-induced infertility. This information will give us novel insights on the clinical use of melatonin and other agents as fertoprotective adjuvants for female cancer patients.

Athyrium multidentatum (Doll.) Ching extract induce apoptosis via mitochondrial dysfunction and oxidative stress in HepG2 cells

Athyrium multidentatum (Doll.) Ching (AMC), a unique and nutritious potherb widely distributed in china, has been extensively used in traditional Chinese medicine. Previous studies indicated that AMC extract exhibited antioxidant and antitumor properties. However, the chemical composition of AMC and molecular mechanism of AMC toxicity to HepG2 cells have not yet been elucidated. Hence, this study aimed to investigate the chemical compositions and the underlying mechanisms of the antiproliferative and apoptotic effects of AMC on HepG2. HPLC-MS analysis showed that AMC contain five compounds with chlorogenic acid accounting for 43 percent. Also, AMC strongly inhibited the cell growth and induced apoptosis and cell cycle arrest in HepG2 cells by significantly upregulating the protein expressions of Fas, Fas-L, Bax/Bcl-2, cyto-c, cleaved caspase-3, and PARP in a dose-dependent manner, which indicates AMC induces apoptosis in HepG2 cells through both intrinsic and extrinsic pathways. Moreover, AMC provoked the production of ROS, H₂O₂, and NO, modulating the PI3K/Akt, MAPK, NFκB and Nrf2 pathways and their downstream transcriptional cascades, ultimately evoked oxidative stress and apoptosis in HpeG2 cells. Further in vivo experiments demonstrated that AMC significantly suppressed the tumor growth, suggesting that AMC may be a novel promising agent for hepatocellular carcinoma treatment.

Human transporters, PEPT1/2, facilitate melatonin transportation into mitochondria of cancer cells: An implication of the therapeutic potential

Melatonin is present in virtually all organisms from bacteria to mammals, and it exhibits a broad spectrum of biological functions, including synchronization of circadian rhythms and oncostatic activity. Several functions of melatonin are mediated by its membrane receptors, but others are receptor-independent. For the latter, melatonin is required to penetrate membrane and enters intracellular compartments. However, the mechanism by which melatonin enters cells remains debatable. In this study, it was identified that melatonin and its sulfation metabolites were the substrates of oligopeptide transporter (PEPT) 1/2 and organic anion transporter (OAT) 3, respectively. The docking analysis showed that the binding of melatonin to PEPT1/2 was attributed to their low binding energy and suitable binding conformation in which melatonin was embedded in the active site of PEPT1/2 and fitted well with the cavity in three-dimensional space. PEPT1/2 transporters play a pivotal role in melatonin uptake in cells. Melatonin's membrane transportation via PEPT1/2 renders its oncostatic effect in malignant cells. For the first time, PEPT1/2 were identified to localize in the mitochondrial membrane of human cancer cell lines of PC3 and U118. PEPT1/2 facilitated the transportation of melatonin into mitochondria. Melatonin accumulation in mitochondria induced apoptosis of PC3 and U118 cells. Thus, PEPT1/2 can potentially be used as a cancer cell-targeted melatonin delivery system to improve the therapeutic effects of melatonin in cancer treatment.

Melatonin promotes sorafenib-induced apoptosis through synergistic activation of JNK/c-jun pathway in human hepatocellular carcinoma

Melatonin has been shown to exert anticancer activity on hepatocellular carcinoma (HCC) through its antiproliferative and pro-apoptotic effect in both experimental and clinical studies, and sorafenib is the only approved drug for the systemic treatment of HCC. Thus, this study was designed to investigate the combined effect of melatonin and sorafenib on proliferation, apoptosis, and its possible mechanism in human HCC. Here, we found that both melatonin and sorafenib resulted in a dose-dependent growth inhibition of HuH-7 cells after 48 hours treatment, and the combination of them enhanced the growth inhibition in a synergistic manner. Colony formation assay indicated that co-treatment of HuH-7 cells with melatonin and sorafenib significantly decreased the clonogenicity compared to the treatment with single agent. Furthermore, FACS and TUNEL assay confirmed that melatonin synergistically augmented the sorafenib-induced apoptosis after 48 hours incubation, which was in accordance with the activation of caspase-3 and the JNK/c-jun pathway. Inhibition of JNK/c-jun pathway with its inhibitor SP600125 reversed the phosphorylation of c-jun and the activation of caspase-3 induced by co-treatment of HuH-7 cells with melatonin and sorafenib in a dose-dependent manner. Furthermore, SP600125 exhibited protective effect against apoptosis induced by the combination of melatonin and sorafenib. This study demonstrates that melatonin in combination with sorafenib synergistically inhibits proliferation and induces apoptosis in human HCC cells; therefore, supplementation of sorafenib with melatonin may serve as a potential therapeutic choice for advanced HCC.

Effects of Melatonin on Liver Injuries and Diseases

Liver injuries and diseases are serious health problems worldwide. Various factors, such as chemical pollutants, drugs, and alcohol, could induce liver injuries. Liver diseases involve a wide range of liver pathologies, including hepatic steatosis, fatty liver, hepatitis, fibrosis, cirrhosis, and hepatocarcinoma. Despite all the studies performed up to now, therapy choices for liver injuries and diseases are very few. Therefore, the search for a new treatment that could safely and effectively block or reverse liver injuries and diseases remains a priority. Melatonin is a well-known natural antioxidant, and has many bioactivities. There are numerous studies investigating the effects of melatonin on liver injuries and diseases, and melatonin could regulate various molecular pathways, such as inflammation, proliferation, apoptosis, metastasis, and autophagy in different pathophysiological situations. Melatonin could be used for preventing and treating liver injuries and diseases. Herein, we conduct a review summarizing the potential roles of melatonin in liver injuries and diseases, paying special attention to the mechanisms of action.

Melatonin treatment induces apoptosis through regulating the nuclear factor-κB and mitogen-activated protein kinase signaling pathways in human gastric cancer SGC7901 cells

Melatonin, which is synthesized by the pineal gland and released into the blood, exhibits antitumor properties. However, the mechanisms underlying these effects, particularly in stomach cancer, remain unknown. In the present study, the effect of melatonin on the nuclear factor (NF)-κB signaling pathway and the mitogen-activated protein kinase signaling pathway, involving p38 and c-Jun-N-terminal kinase (JNK), were investigated in SGC7901 gastric cancer cells. In addition, the effect of melatonin on the survival, migration and apoptosis of these cells was investigated in vitro in order to evaluate the use of melatonin for the treatment of gastric cancer. The results of the present study revealed that melatonin decreased the viability and migration of SGC7901 cells. Furthermore, melatonin induced apoptosis. Melatonin was identified to elevate the expression levels of phosphorylated (p)-p38 and p-JNK protein, and decrease the expression level of nucleic p-p65. These results suggest that the protein levels of p65, p38 and JNK are associated with the survival of SGC7901 cells following treatment with melatonin. The optimal concentration of melatonin was demonstrated to be 2 mM, which significantly induced apoptosis following a 24 h treatment period. These findings suggest that conflicting growth signals in cells may inhibit the efficacy of melatonin in the treatment of gastric cancer. Therefore, adjunct therapy would be required to improve the efficacy of melatonin in the treatment of cancer.

Melatonin prevents deregulation of the sphingosine kinase/sphingosine 1-phosphate signaling pathway in a mouse model of diethylnitrosamine-induced hepatocellular carcinoma

The sphingosine kinase (SphK)/sphingosine 1-phosphate (S1P) pathway is involved in multiple biological processes, including carcinogenesis. Melatonin shows beneficial effects in cell and animal models of hepatocellular carcinoma, but it is unknown if they are associated with the modulation of the SphK/S1P system, along with different downstream signaling pathways modified in cancer. We investigated the effects of melatonin in mice which received diethylnitrosamine (DEN) (35 mg/kg body weight i.p) once a week for 8 weeks. Melatonin was given at 5 or 10 mg/kg/day i.p. beginning 4 weeks after the onset of DEN administration and ending at the sacrifice time (10, 20, 30, or 40 weeks). Melatonin alleviated the distortion of normal hepatic architecture, lowered the incidence of preneoplastic/neoplastic lesions, and inhibited the expression of proliferative/cell cycle regulatory proteins (Ki67, PCNA, cyclin D1, cyclin E, CDK4, and CDK6). S1P levels and expression of SphK1, SphK2, and S1P receptors (S1PR1/S1PR3) were significantly elevated in DEN-treated mice. However, there was a decreased expression of S1P lyase. These effects were significantly abrogated in a time- and dose-dependent manner by melatonin, which also increased S1PR2 expression. Following DEN treatment, mice exhibited increased phosphorylation of PI3K, AKT, mTOR, STAT3, ERK, and p38, and a higher expression of NF-κB p50 and p65 subunits. Melatonin administration significantly inhibited those changes. Data obtained suggest a contribution of the SphK/S1P system and related signaling pathways to the protective effects of melatonin in hepatocarcinogenesis.

Melatonin Immunoreactivity in Malignant Small Intestinal Neuroendocrine Tumours

BACKGROUND/AIMS

Small intestinal neuroendocrine tumours (SI-NETs) are derived from enterochromaffin cells. After demonstrating melatonin in enterochromaffin cells, we hypothesized that SI-NETs may express and secrete melatonin, which may have an impact on clinical factors and treatment response.

METHODS

Tumour tissue from 26 patients with SI-NETs, representing paired sections of primary tumour and metastasis, were immunohistochemically stained for melatonin and its receptors, MT1 and MT2. Plasma melatonin and immunoreactivity (IR) for melatonin, MT1 and MT2 in tumour cells were compared to other tumour markers and clinical parameters. Melatonin was measured at two time points in fasting morning plasma from 43 patients with SI-NETs.

RESULTS

Melatonin IR was found in all SI-NETS. Melatonin IR intensity in primary tumours correlated inversely to proliferation index (p = 0.022) and patients reported less diarrhoea when melatonin IR was high (p = 0.012). MT1 IR was low or absent in tumours. MT2 expression was medium to high in primary tumours and generally reduced in metastases (p = 0.007). Plasma-melatonin ranged from 4.5 to 220.0 pg/L. Higher levels were associated with nausea at both time points (p = 0.027 and p = 0.006) and flush at the second sampling. In cases with disease stabilization or remission (n = 34), circulating melatonin levels were reduced in the second sample (p = 0.038).

CONCLUSION

Immunoreactive melatonin is present in SI-NETs. Circulating levels of melatonin in patients with SI-NETs are reduced after treatment. Our results are congruent with recent understanding of melatonin's endocrine and paracrine functions and SI-NETs may provide a model for further studies of melatonin function.

Melatonin-induced increase in sensitivity of human hepatocellular carcinoma cells to sorafenib is associated with reactive oxygen species production and mitophagy

Effects of sorafenib in hepatocellular carcinoma (HCC) are frequently transient due to tumor-acquired resistance, a phenotype that could be targeted by other molecules to reduce this adaptive response. Because melatonin is known to exert antitumor effects in HCC cells, this study investigated whether and how melatonin reduces resistance to sorafenib. Susceptibility to sorafenib (10 nmol/L to 50 μmol/L) in the presence of melatonin (1 and 2 mmol/L) was assessed in HCC cell lines HepG2, HuH7, and Hep3B. Cell viability was reduced by sorafenib from 1 μmol/L in HepG2 or HuH7 cells, and 2.5 μmol/L in Hep3B cells. Co-administration of melatonin and sorafenib exhibited a synergistic cytotoxic effect on HepG2 and HuH7 cells, while Hep3B cells displayed susceptibility to doses of sorafenib that had no effect when administrated alone. Co-administration of 2.5 μmol/L sorafenib and 1 mmol/L melatonin induced apoptosis in Hep3B cells, increasing PARP hydrolysis and BAX expression. We also observed an early colocalization of mitochondria with lysosomes, correlating with the expression of mitophagy markers PINK1 and Parkin and a reduction of mitofusin-2 and mtDNA compared with sorafenib administration alone. Moreover, increased reactive oxygen species production and mitochondrial membrane depolarization were elicited by drug combination, suggesting their contribution to mitophagy induction. Interestingly, Parkin silencing by siRNA to impair mitophagy significantly reduced cell killing, PARP cleavage, and BAX expression. These results demonstrate that the pro-oxidant capacity of melatonin and its impact on mitochondria stability and turnover via mitophagy increase sensitivity to the cytotoxic effect of sorafenib.

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.

A novel all-trans retinoic acid derivative 4-amino‑2‑trifluoromethyl-phenyl retinate inhibits the proliferation of human hepatocellular carcinoma HepG2 cells by inducing G0/G1 cell cycle arrest and apoptosis via upregulation of p53 and ASPP1 and downregulation of iASPP

4-Amino-2-trifluoromethyl-phenyl retinate (ATPR), a novel all-trans retinoic acid (ATRA) derivative, was reported to function as a tumor inhibitor in various types of cancer cells in vitro. However, little is known concerning its antitumor effect on human hepatocellular carcinoma (HCC) HepG2 cells. The aims of the present study were to investigate the effects of ATPR on the proliferation of HepG2 cells and to explore the probable mechanisms. A series of experiments were performed following the treatment of HepG2 cells with ATRA and ATPR. MTT and plate colony formation assays were used to measure the cell viability. To confirm the influence on proliferation, flow cytometry was used to detect the distribution of the cell cycle. Apoptosis was observed by Hoechst staining and flow cytometry. In addition, to characterize the underlying molecular mechanisms, immunofluorescence was applied to observe the distribution of p53. The transcription and translation levels of p53 were analyzed by real-time quantitative RT-PCR (qRT-PCR) and western blotting. The expression levels of murine double minute 2 (MDM2), apoptosis stimulating proteins of p53 (ASPP), cell cycle- and apoptosis-associated proteins were detected by western blotting. After HepG2 cells were incubated with ATRA and ATPR, the viability of the HepG2 cells was inhibited in a dose- and time-dependent manner. As well, ATPR significantly suppressed HepG2 cell colony formation and arrested cells at the G0/G1 phase, while ATRA had no obvious effects. Both Hoechst staining and flow cytometry unveiled the apoptosis of HepG2 cells. Moreover, the fluorescent density of p53 was higher in the nuclei after exposure to ATPR than that in the ATRA group. HepG2 cells treated with ATPR showed elevated mRNA and protein levels of p53 when compared with these levels in the ATRA-treated cells. Western blotting showed that ATPR increased ASPP1, p21 and Bax expression and decreased MDM2, iASPP, cyclin D and E, cyclin-dependent kinase 6 (CDK6) and Bcl-2 expression, while CDK4 and ASPP2 expression were scarcely altered. Consequently, ATPR exerted a better inhibitory effect on the proliferation of HepG2 cells than ATRA through increased expression of p53 and ASPP1 and downregulation of iASPP, thereby resulting in G0/G1 cell cycle arrest and apoptosis.

Sustained release of melatonin: A novel approach in elevating efficacy of tamoxifen in breast cancer treatment

BACKGROUND

Finding advanced anti-cancer agents with selective toxicity in tumor tissues is the goal of anticancer delivery systems. This study investigated potential application of nanostructured lipid carriers (NLCs) in increasing melatonin induced cytotoxicity and apoptosis in MCF-7 breast cancer cells.

METHODS

Melatonin-loaded NLCs were characterized for particle size, zeta potential, Fourier transforms infrared spectroscopy, differential scanning calorimetry, cellular uptake, and scanning electron microscope (SEM). Anti-proliferative and apoptotic effects of new formulation were evaluated by MTT and flow cytometric assays, respectively. Gene expression of apoptotic markers including survivin, Bcl-2 and Bid were examined by Real time quantitative PCR.

RESULTS

The optimized formulation of NLCs revealed mean particle size of 71±5nm with nearly narrow size distribution. The formulation exhibited an acceptable stability during four months in terms of size and lack of drug release. The IC50 values for melatonin and tamoxifen were 1.3±0.4mM and 30.7±5.2μM, respectively. Melatonin loaded NLCs decreased percentage of cell proliferation from 55±7.2% to 40±4.1% (p<0.05). Co-treatment of the cells with melatonin loaded nanoparticles and tamoxifen caused two fold increase in the percentage of apoptosis (p<0.05). Evaluation of gene expression profile demonstrated a marked decrease in anti-apoptotic survivin with increase in pro-apoptotic Bid mRNA levels.

CONCLUSION

Taken together, our results suggest NLC technology as a promising delivery system, which elevates the efficacy of chemotherapeutics in breast cancer cells.

Melatonin action in tumor skeletal muscle cells: an ultrastructural study

Melatonin (Mel), or N-acetyl-5-methoxytryptamine, is a circadian hormone that can diffuse through all the biological membranes thanks to its amphiphilic structure, also overcoming the blood-brain barrier and placenta. Although Mel has been reported to exhibit strong antioxidant properties in healthy tissues, studies carried out on tumor cultures gave a different picture of its action, often describing Mel as effective to trigger the cell death of tumor cells by enhancing oxidative stress. Based on this premise, here Mel effect was investigated using a tumor cell line representative of the human alveolar rhabdomyosarcoma (ARMS), the most frequent soft tissue sarcoma affecting childhood. For this purpose, Mel was given either dissolved in ethanol (EtOH) or dimethyl sulfoxide (DMSO) at different concentrations and time exposures. Cell viability assays and ultrastructural observations demonstrated that Mel was able to induce a dose- and time-dependent cell death independently on the dissolution solvent. Microscopy analyses highlighted the presence of various apoptotic and necrotic patterns correlating with the increasing Mel dose and time of exposure. These findings suggest that Mel, triggering apoptosis in ARMS cells, could be considered as a promising drug for future multitargeted therapies.

Apoptosis is triggered by melatonin in an in vivo model of ovarian carcinoma

Apoptosis plays an important role in the treatment of cancer, and targeting apoptosis-related molecules in ovarian cancer (OC) is of great therapeutic value. Melatonin (Mel) is an indoleamine displaying several anti-cancer properties and has been reported to modulate apoptosis signaling in multiple tumor subtypes. We investigated OC and the role of Mel therapy on the pro-apoptotic (p53, BAX, caspase-3, and cleaved caspase-3) and anti-apoptotic (Bcl-2 and survivin) proteins in an ethanol (EtOH)-preferring rat model. To induce OC, the left ovary was injected directly with a single dose of 100 μg 7,12-dimethylbenz(a)anthracene dissolved in 10 μl of sesame oil under the bursa. Right ovaries were used as sham-surgery controls. After developing OC, half of the animals received i.p. injections of Mel (200 μg/100 g BW per day) for 60 days. Body weight gain, EtOH consumption, and energy intake were unaffected by the treatments. Interestingly, absolute and relative OC masses showed a significant reduction after Mel therapy, regardless of EtOH consumption. To accomplish OC-related apoptosis, we first observed that p53, BAX, caspase-3, and cleaved caspase-3 were downregulated in OC tissue while Bcl-2 and survivin were overexpressed. Notably, Mel therapy and EtOH intake promoted apoptosis along with the upregulation of p53, BAX, and cleaved caspase-3. Fragmentation of DNA observed by TUNEL-positive nuclei was also enhanced following Mel treatment. In addition, Bcl-2 was downregulated by the EtOH intake and lower survivin levels were observed after Mel therapy. Taken together, these results suggest that Mel induce apoptosis in OC cells of EtOH-preferring animals.

Melatonin Suppresses the Growth of Ovarian Cancer Cell Lines (OVCAR-429 and PA-1) and Potentiates the Effect of G1 Arrest by Targeting CDKs

Melatonin is found in animals as well as plants. In animals, it is a hormone that anticipates the daily onset of darkness and regulates physiological functions, such as sleep timing, blood pressure, and reproduction. Melatonin has also been found to have anti-tumor properties. Malignant cancers are the most common cause of death, and the mortality rate of ovarian tumor is the highest among gynecological diseases. This study investigated the anti-tumor effects of melatonin on the ovarian cancer lines, OVCAR-429 and PA-1. We observed the accumulation of melatonin-treated cells in the G₁ phase due to the down-regulation of CDK 2 and 4. Our results suggest that in addition to the known effects on prevention, melatonin may also provide anti-tumor activity in established ovarian cancer.

Melatonin Activates Endoplasmic Reticulum Stress and Apoptosis in Rats with Diethylnitrosamine-Induced Hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is one of the most lethal human cancers worldwide because of its high incidence, its metastatic potential and the low efficacy of conventional treatment. Inactivation of apoptosis is implicated in tumour progression and chemotherapy resistance, and has been linked to the presence of endoplasmic reticulum stress. Melatonin, the main product of the pineal gland, exerts anti-proliferative, pro-apoptotic and anti-angiogenic effects in HCC cells, but these effects still need to be confirmed in animal models. Male Wistar rats in treatment groups received diethylnitrosamine (DEN) 50 mg/kg intraperitoneally twice/once a week for 18 weeks. Melatonin was given in drinking water at 1 mg/kg/d, beginning 5 or 12 weeks after the start of DEN administration. Melatonin improved survival rates and successfully attenuated liver injury, as shown by histopathology, decreased levels of serum transaminases and reduced expression of placental glutathione S-transferase. Furthermore, melatonin treatment resulted in a significant increase of caspase 3, 8 and 9 activities, polyadenosine diphosphate (ADP) ribose polymerase (PARP) cleavage, and Bcl-associated X protein (Bax)/Bcl-2 ratio. Cytochrome c, p53 and Fas-L protein concentration were also significantly enhanced by melatonin. Melatonin induced an increased expression of activating transcription factor 6 (ATF6), C/EBP-homologous protein (CHOP) and immunoglobulin heavy chain-binding protein (BiP), while cyclooxygenase (COX)-2 expression decreased. Data obtained suggest that induction of apoptosis and ER stress contribute to the beneficial effects of melatonin in rats with DEN-induced HCC.

Breast cancer cells: Modulation by melatonin and the ubiquitin-proteasome system--a review

Melatonin inhibits human breast cancer cells stimulated with estrogen. This antiproliferative action depends on the presence of the estrogen receptor alpha (ERα) in the human MCF-7 cell line and is strictly dose-dependent. Since researchers concerned with melatonin and breast cancer have not considered the relevance of the ubiquitin-proteasome system to this research in this review we do so. The fact that the first breast cancer susceptibility gene to be identified, Brca1, functions as a ubiquitin ligase indicates that the ubiquitin-proteasome system has a role in regulating susceptibility to breast cancer. While mutations of this gene increase the incidence of breast cancer, the wild type gene suppresses estrogen-dependent transcriptional events relying on the estrogen receptor ERα. Three other ubiquitin ligases, SCF(Skp2), E6AP and APC, interact directly with ERα at the ERE and AP-1 promoters of ERα target genes. Melatonin, like proteasome inhibitors, decreases estrogen-induced gene transcription. Indeed, it has been reported that melatonin specifically inhibits estrogen-induced transcription mediated by ERα at the ERE and AP1 gene promoters. Herein, we present a model in which the inhibitory action of melatonin on MCF-7 cells is mediated, directly or indirectly, by the ubiquitin-proteasome system. In this model ERα, apoptotic proteins, and cell cycle proteins, all influenced by melatonin, are substrates of key ubiquitin ligases including SCF(Skp2), E6AP, and SCF(B-TrCP). Since dysfunction of the ubiquitin-proteasome system is a risk factor for breast cancer, this model provides a context in which to test the clinical potential, and limitations, of melatonin and proteasome inhibitors.

Melatonin and endoplasmic reticulum stress: relation to autophagy and apoptosis

Endoplasmic reticulum (ER) is a dynamic organelle that participates in a number of cellular functions by controlling lipid metabolism, calcium stores, and proteostasis. Under stressful situations, the ER environment is compromised, and protein maturation is impaired; this causes misfolded proteins to accumulate and a characteristic stress response named unfolded protein response (UPR). UPR protects cells from stress and contributes to cellular homeostasis re-establishment; however, during prolonged ER stress, UPR activation promotes cell death. ER stressors can modulate autophagy which in turn, depending of the situation, induces cell survival or death. Interactions of different autophagy- and apoptosis-related proteins and also common signaling pathways have been found, suggesting an interplay between these cellular processes, although their dynamic features are still unknown. A number of pathologies including metabolic, neurodegenerative and cardiovascular diseases, cancer, inflammation, and viral infections are associated with ER stress, leading to a growing interest in targeting components of the UPR as a therapeutic strategy. Melatonin has a variety of antioxidant, anti-inflammatory, and antitumor effects. As such, it modulates apoptosis and autophagy in cancer cells, neurodegeneration and the development of liver diseases as well as other pathologies. Here, we review the effects of melatonin on the main ER stress mechanisms, focusing on its ability to regulate the autophagic and apoptotic processes. As the number of studies that have analyzed ER stress modulation by this indole remains limited, further research is necessary for a better understanding of the crosstalk between ER stress, autophagy, and apoptosis and to clearly delineate the mechanisms by which melatonin modulates these responses.

Ceramide metabolism regulates autophagy and apoptotic cell death induced by melatonin in liver cancer cells

Autophagy is a process that maintains homeostasis during stress, although it also contributes to cell death under specific contexts. Ceramides have emerged as important effectors in the regulation of autophagy, mediating the crosstalk with apoptosis. Melatonin induces apoptosis of cancer cells; however, its role in autophagy and ceramide metabolism has yet to be clearly elucidated. This study was aimed to evaluate the effect of melatonin administration on autophagy and ceramide metabolism and its possible link with melatonin-induced apoptotic cell death in hepatocarcinoma (HCC) cells. Melatonin (2 mm) transiently induced autophagy in HepG2 cells through JNK phosphorylation, characterized by increased Beclin-1 expression, p62 degradation, and LC3II and LAMP-2 colocalization, which translated in decreased cell viability. Moreover, ATG5 silencing sensitized HepG2 cells to melatonin-induced apoptosis, suggesting a dual role of autophagy in cell death. Melatonin enhanced ceramide levels through both de novo synthesis and acid sphingomyelinase (ASMase) stimulation. Serine palmitoyltransferase (SPT) inhibition with myriocin prevented melatonin-induced autophagy and ASMase inhibition with imipramine-impaired autophagy flux. However, ASMase inhibition partially protected HepG2 cells against melatonin, while SPT inhibition significantly enhanced cell death. Findings suggest a crosstalk between SPT-mediated ceramide generation and autophagy in protecting against melatonin, while specific ASMase-induced ceramide production participates in melatonin-mediated cell death. Thus, dual blocking of SPT and autophagy emerges as a potential strategy to potentiate the apoptotic effects of melatonin in liver cancer cells.

The potential physiological crosstalk and interrelationship between two sovereign endogenous amines, melatonin and homocysteine

The antioxidant melatonin and the non-proteinogenic excitotoxic amino acid homocysteine (Hcy) are very distinct but related reciprocally to each other in their mode of action. The elevated Hcy level has been implicated in several disease pathologies ranging from cardio- and cerebro-vascular diseases to neurodegeneration owing largely to its free radical generating potency. Interestingly, melatonin administration potentially normalizes the elevated Hcy level, thereby protecting the cells from the undesired Hcy-induced excitotoxicity and cell death. However, the exact mechanism and between them remain obscure. Through literature survey we have found an indistinct but a vital link between melatonin and Hcy i.e., the existence of reciprocal regulation between them, and this aspect has been thoroughly described herein. In this review, we focus on all the possibilities of co-regulation of melatonin and Hcy at the level of their production and metabolism both in basal and in pathological conditions, and appraised the potential of melatonin in ameliorating homocysteinemia-induced cellular stresses. Also, we have summarized the differential mode of action of melatonin and Hcy on health and disease states.

Developmental changes of melatonin receptor expression in the spleen of the chicken, Gallus domesticus

Melatonin plays an essential role in development and immunoregulation of the avian spleen through its receptors; however, the variations in the expression of the melatonin receptor subtypes in the developing avian spleen are still unclear. The objective of the present study was not only to investigate the distribution patterns and development changes of the expression of the melatonin receptor subtypes (Mel1a, Mel1b and Mel1c) in the chicken spleen but also to identify the correlation between the plasma melatonin concentration and the expression of the melatonin receptor subtypes. The immunohistochemical results indicated that Mel1a was mainly distributed in the red pulp and capillaries, Mel1b was predominantly distributed in the periarterial lymphatic sheath (PALS) and splenic nodule, and Mel1c was widely located in the red pulp, PALS and splenic nodule. From P0 to P21, the mRNA and protein expressions of Mel1a, Mel1b and Mel1c in the spleen were increased (P<0.05); however, a slight increase in the expression of the three melatonin receptor subtypes was observed after P21 (P>0.05). Furthermore, the mRNA levels of Mel1b and Mel1c between P0 and P14 raised more quickly than Mel1a. The plasma melatonin concentration increased in an age-dependent manner in the chicken from P0 to P42 (P<0.05), and this increasing change was linear after P14 (P<0.05). The melatonin level in the plasma is strongly correlated with the protein expressions of Mel1a (r=0.938, P=0.005), Mel1b (r=0.912, P=0.011), and Mel1c (r=0.906, P=0.012) in the chicken spleen. These results suggest the existence of age-related and region-specific changes in the expression of the melatonin receptor subtypes within the spleen of the chicken, and this characteristic pattern may be involved in the development and functional maturation of the avian spleen.

Melatonin induces apoptosis of colorectal cancer cells through HDAC4 nuclear import mediated by CaMKII inactivation

Melatonin induces apoptosis in many different cancer cell lines, including colorectal cancer. However, the precise mechanisms involved remain largely unresolved. In this study, we provide evidence to reveal a new mechanism by which melatonin induces apoptosis of colorectal cancer LoVo cells. Melatonin at pharmacological concentrations significantly suppressed cell proliferation and induced apoptosis in a dose-dependent manner. The observed apoptosis was accompanied by the melatonin-induced dephosphorylation and nuclear import of histone deacetylase 4 (HDAC4). Pretreatment with a HDAC4-specific siRNA effectively attenuated the melatonin-induced apoptosis, indicating that nuclear localization of HDAC4 is required for melatonin-induced apoptosis. Moreover, constitutively active Ca(2+) /calmodulin-dependent protein kinase II alpha (CaMKIIα) abrogated the melatonin-induced HDAC4 nuclear import and apoptosis of LoVo cells. Furthermore, melatonin decreased H3 acetylation on bcl-2 promoter, leading to a reduction of bcl-2 expression, whereas constitutively active CaMKIIα(T286D) or HDAC4-specific siRNA abrogated the effect of melatonin. In conclusion, the present study provides evidence that melatonin-induced apoptosis in colorectal cancer LoVo cells largely depends on the nuclear import of HDAC4 and subsequent H3 deacetylation via the inactivation of CaMKIIα.

Effects of ghrelin, leptin and melatonin on the levels of reactive oxygen species, antioxidant enzyme activity and viability of the HCT 116 human colorectal carcinoma cell line

Obesity is associated with an increased risk of certain types of cancer, including colon cancer. Adipose tissue is an endocrine organ that produces biologically active substances, such as leptin and ghrelin. Recent research has suggested that adipose-derived hormones may be associated with mechanisms linked to tumorigenesis and cancer progression. Furthermore, previous studies have demonstrated that pineal gland-derived melatonin possesses important oncostatic and antioxidant properties. The present study aimed to determine the effects of the adipokines ghrelin and leptin, and the melatonin on intracellular levels of reactive oxygen species (ROS) and the activity of selected antioxidant enzymes, such as superoxide dismutase, catalase (CAT) and glutathione peroxidase. The effects of these compounds were also determined on the viability of HCT 116 human colorectal carcinoma cells in vitro. The pro-oxidant and growth inhibitory effects of melatonin resulted in an accumulation of ROS and decreased antioxidant capacity in melatonin-treated cells. Ghrelin administration alone caused a significant decrease in the levels of ROS, due to an increased activity of CAT in the HCT 116 cells. In addition, the present study observed increased lipid peroxidation following melatonin treatment, and decreased levels of malondialdehyde following ghrelin or leptin treatment. In conclusion, ghrelin, leptin and melatonin have various influences on the antioxidant capacity of HCT 116 cells. Compared with the adipokines, treatment with melatonin increased ROS levels and decreased cellular viability.

Human gastroenteropancreatic expression of melatonin and its receptors MT1 and MT2

Background and Aim

The largest source of melatonin, according to animal studies, is the gastrointestinal (GI) tract but this is not yet thoroughly characterized in humans. This study aims to map the expression of melatonin and its two receptors in human GI tract and pancreas using microarray analysis and immunohistochemistry.

Method

Gene expression data from normal intestine and pancreas and inflamed colon tissue due to ulcerative colitis were analyzed for expression of enzymes relevant for serotonin and melatonin production and their receptors. Sections from paraffin-embedded normal tissue from 42 individuals, representing the different parts of the GI tract (n=39) and pancreas (n=3) were studied with immunohistochemistry using antibodies with specificity for melatonin, MT₁ and MT₂ receptors and serotonin.

Results

Enzymes needed for production of melatonin are expressed in both GI tract and pancreas tissue. Strong melatonin immunoreactivity (IR) was seen in enterochromaffin (EC) cells partially co-localized with serotonin IR. Melatonin IR was also seen in pancreas islets. MT₁ and MT₂ IR were both found in the intestinal epithelium, in the submucosal and myenteric plexus, and in vessels in the GI tract as well as in pancreatic islets. MT₁ and MT₂ IR was strongest in the epithelium of the large intestine. In the other cell types, both MT₂ gene expression and IR were generally elevated compared to MT₁. Strong MT₂, IR was noted in EC cells but not MT₁ IR. Changes in gene expression that may result in reduced levels of melatonin were seen in relation to inflammation.

Conclusion

Widespread gastroenteropancreatic expression of melatonin and its receptors in the GI tract and pancreas is in agreement with the multiple roles ascribed to melatonin, which include regulation of gastrointestinal motility, epithelial permeability as well as enteropancreatic cross-talk with plausible impact on metabolic control.

Melatonin potentiates cisplatin-induced apoptosis and cell cycle arrest in human lung adenocarcinoma cells

OBJECTIVES

Melatonin produces anti-cancer effects via several mechanisms, including by induction of apoptosis. In this way, it has been shown to be of use, in combination with chemotherapeutic drugs, for cancer treatment. The study described here has evaluated effects of melatonin on cytotoxicity, apoptosis and cell cycle arrest induced with the chemotherapeutic agent cisplatin, in human lung adenocarcinoma cisplatin-sensitive cell line (SK-LU-1), which previously had only limit data.

MATERIALS AND METHODS

Cells of the SK-LU-1 line were treated with melatonin alone at 1-5 mM concentration or cisplatin alone 10-200 μM, for 48 h in culture. Cytotoxicity was measured by MTT reduction assay. Apoptosis induction was detected by annexin V/PI staining using flow cytometric analysis and DAPI nuclear staining. Change in mitochondrial membrane potential (ΔΨm) was quantified using DiOC6(3) reagent and activities of caspases-3/7 were also investigated. DNA fractions were measured using propidium iodide (PI) staining.

RESULTS

Melatonin or cisplatin alone had 50% (IC50 ) cytotoxicity at 5 mM or 34 μM concentrations respectively. Combination of 1 or 2 mM melatonin and cisplatin significantly augmented cytotoxicity of cisplatin by reducing its IC50 to 11 and 4 μM, respectively. Consistently, combined treatment increased population of apoptotic cells by elevating mitochondrial membrane depolarization, activating caspases-3/7 and inducing cell cycle arrest in the S phase, compared to treatment with cisplatin alone.

CONCLUSION

These data demonstrate that melatonin enhanced cisplatin-induced cytotoxicity and apoptosis in SK-LU-1 lung cancer cells. SK-LU-1 cell population growth inhibition was mediated by cell cycle arrest in the S phase. These findings suggest that melatonin has the potential to be used for NSCLC treatment in combination with a chemotherapeutic agent such as cisplatin.

Melatonin reduces lead levels in blood, brain and bone and increases lead excretion in rats subjected to subacute lead treatment

Melatonin, a hormone known for its effects on free radical scavenging and antioxidant activity, can reduce lead toxicity in vivo and in vitro.We examined the effects of melatonin on lead bio-distribution. Rats were intraperitoneally injected with lead acetate (10, 15 or 20mg/kg/day) with or without melatonin (10mg/kg/day) daily for 10 days. In rats intoxicated with the highest lead doses, those treated with melatonin had lower lead levels in blood and higher levels in urine and feces than those treated with lead alone, suggesting that melatonin increases lead excretion. To explore the mechanism underlying this effect, we first assessed whether lead/melatonin complexes were formed directly. Electronic density functional (DFT) calculations showed that a lead/melatonin complex is energetically feasible; however, UV spectroscopy and NMR analysis showed no evidence of such complexes. Next, we examined the liver mRNA levels of metallothioneins (MT) 1 and 2. Melatonin cotreatment increased the MT2 mRNA expression in the liver of rats that received the highest doses of lead. The potential effects of MTs on the tissue distribution and excretion of lead are not well understood. This is the first report to suggest that melatonin directly affects lead levels in organisms exposed to subacute lead intoxication.

Melatonin induces apoptosis in cholangiocarcinoma cell lines by activating the reactive oxygen species-mediated mitochondrial pathway

We previously demonstrated that melatonin could be used as a chemopreventive agent for inhibiting cholangiocarcinoma (CCA) development in a hamster model. However, the cytotoxic activity of melatonin in cancer remains unclear. In the present study, we investigated the effect of melatonin on CCA cell lines. Human CCA cell lines (KKU-M055 and KKU-M214) were treated with melatonin at concentrations of 0.5, 1 and 2 mM for 48 h. Melatonin treatment exerted a cytotoxic effect on CCA cells by inhibiting CCA cell viability in a concentration-dependent manner. Treatment with melatonin, especially at 2 mM, increased intracellular reactive oxygen species (ROS) production and in turn led to increased oxidative DNA damage and 8-oxodG formation. Moreover, melatonin treatment enhanced the production of cytochrome c leading to apoptosis in a concentration-dependent manner, as indicated by increased expression of apoptosis-related proteins caspase-3 and caspase-7. In conclusion, melatonin acts as a pro-oxidant by activating ROS-dependent DNA damage and thus leading to the apoptosis of CCA cells.