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Melatonin possesses a number of important biologic activities including oncostatic, anti-oxidant, and immunostimulatory actions. This study was designed to assess the effects of melatonin on inflammation-related gene expression in lipopolysaccharide (LPS)-stimulated human peripheral blood mononuclear cells (PBMCs), using CombiMatrix 2K Human Inflammation chip. After pretreatment with melatonin (100 microm) for 4 hr, cells were incubated with LPS (1 microg/mL) for 24 hr. We compared gene expression profiles between LPS-treated, melatonin-treated, LSP/melatonin-treated, and control groups. LPS induced the upregulation of 95 genes, compared with controls. Melatonin pretreatment in LPS-stimulated PBMCs suppressed the expression of 23 genes more than twofold. Interestingly, melatonin showed a suppressive effect on the expression of CC chemokine subfamily genes, including CCL2/MCP1, CCL3/MIP1 alpha, CCL4/MIP1 beta, CCL5/RANTES, CCL8/MCP2, CCL20/MDC, and CCL22/MIP3 alpha, in LPS-stimulated PBMCs. This result was confirmed by reverse transcriptase polymerase chain reaction. Among the CC chemokine subfamily genes, particularly, the expression of CCL2 and CCL5 was markedly downregulated by melatonin in LPS-stimulated PBMCs. The secretion levels of CCL2 and CCL5 were measured using enzyme-linked immunosorbent assay. Stimulation of PBMCs by LPS induced the secretion of CCL2 (2334.3 +/- 161.4 pg/mL, mean +/- S.E.M.), whereas melatonin pretreatment (153.0 +/- 3.8 pg/mL) inhibited the LPS-induced secretion of CCL2. Melatonin pretreatment (2696.2 +/- 385.3 pg/mL) also inhibited the LPS-induced secretion of CCL5 (4679.6 +/- 107.5 pg/mL). Taken together, these results suggest that melatonin may have a suppressive effect on LPS-induced expression of CC chemokine genes, especially CCL2 and CCL5, which may explain its beneficial effects in the treatment of various inflammatory conditions.

The prevalence of diabetes has exponentially increased in recent decades due to environmental factors such as nocturnal lifestyle and aging, both of which influence the amount of melatonin produced in the pineal gland. The present study investigated the effect of melatonin on signaling pathways of glucose transport in C2C12 mouse skeletal muscle cells. Intriguingly, treatment of C2C12 cells with melatonin (1 nm) stimulated glucose uptake twofold increase. Melatonin-stimulated glucose transport was inhibited with co-treatment with the melatonin receptor antagonist luzindole. Furthermore, treatment of stably over-expressed melatonin receptor type 2B containing C2C12 myotubes with melatonin amplified glucose transport c. 13-fold. Melatonin also increased the phosphorylation level of insulin receptor substrate-1 (IRS-1) and the activity of phosphoinositide 3-kinase (PI-3-kinase). However, 3',5'-cyclic adenosine monophosphate-activated protein kinase (AMPK), another important glucose transport stimulatory mediator via an insulin-independent pathway, was not influenced by melatonin treatment. Activity of p38 mitogen-activated protein kinase (MAPK), a downstream mediator of AMPK, was also not changed by melatonin. In addition, melatonin increased the expression level of forkhead box A2, which was recently discovered to regulate fatty acid oxidation and to be inhibited by insulin. In summary, melatonin stimulates glucose transport to skeletal muscle cells via IRS-1/PI-3-kinase pathway, which implies, at the molecular level, its role in glucose homeostasis and possibly in diabetes. Additionally, exposure to light at night and aging, both of which lower endogenous melatonin levels may contribute to the incidence and/or development of diabetes.

The existence of specific melatonin-binding sites in lymphoid cells led to the discovery of signal transduction pathway for melatonin in human lymphocytes and immunomodulatory role of melatonin in immune cells. In recent years, transcriptional regulation of melatonin on various transcription factors has been demonstrated. Therefore, this study was designed to assess by cDNA microarray analysis the regulatory effects of melatonin on transcription factors in human peripheral blood mononuclear cells (PBMCs). Forty-six genes were upregulated and 23 were downregulated more than twofold in melatonin-treated PBMCs. Of the more than twofold upregulated transcription factor genes, homeo box A4 (HOXA4), forkhead box O1A (FOXO1A), transcription elongation factor B (SIII), polypeptide 3 (TCEB3), and peroxisome proliferative activated receptor delta (PPARD) were identified. Of the more than twofold downregulated genes, PHD finger protein 15 (PHF15) and zinc finger protein 33a (ZNF33A) were identified. In summary, identification of these genes by cDNA microarray analysis in response to melatonin administration may provide a foundation for further studies on the function of melatonin in human PBMCs.

Melatonin is reported to be an anti-inflammatory agent. No genetic study concerning the association between melatonin and inflammatory disease has yet been reported. Here we performed a polymorphism study on the melatonin receptor type 1B (MTNR1B) in Korean rheumatoid arthritis (RA) patients and controls. The polymorphism of MTNR1B located in 3¢- untranslated region (rs 1562444) was selected for its higher rate of heterozygosity among other single nucleotide polymorphisms (SNPs) in both MTNR1A and MTNR1B genes and investigated in RA patients (n ¼ 173) and healthy controls (n ¼ 195) by polymerase chain reaction-restriction fragment length polymorphism assay using NlaIII restriction enzyme. No statistically significant difference in either genotype distribution or allele frequency was observed between RA patients and controls. The genotype distributions and allele frequencies of rheumatoid factor negative (RF())) patients were similar to those of controls. However, statistical analysis of genotype revealed a significant association (v 2 ¼ 6.42, P ¼ 0.04) is present between RF(+) and MTNR1B SNP (rs 1562444). Although no statistically significant difference in allele frequency between RF(+) and controls was observed (v 2 ¼ 2.75, P ¼ 0.10), the results might suggest that MTNR1B SNP

The excessive proliferation and migration of synoviocytes are well-characterized phenomena that play key roles in the pathophysiology of rheumatoid arthritis (RA). Melatonin has been shown to have potent anti-proliferative effect in various cancer cells such as breast and prostate cancer cells. In this study, we examined the role of melatonin on synoviocyte proliferation in primary cultured human fibroblast-like synoviocytes (FLSs) by analyzing protein expression of P21(CIP1) (P21) and P27(KIP1) (P27), the cyclin-dependent kinase inhibitors that are important in cell cycle control, and the phosphorylation of mitogen-activated protein kinases (MAPKs). RA-FLS proliferation was determined by a [(3)H]-thymidine incorporation assay. Western blot analysis was applied to examine the underlying mechanisms of melatonin's effect. Melatonin inhibited RA-FLS proliferation in a dose-dependent manner. It reduced proliferation of passage 2 FLSs by 25% at 10 microm and by nearly 40% at 100 microm concentrations. The inhibitory effect of melatonin on RA-FLS proliferation was also observed in passages 4 and 6. Melatonin upregulated the expression levels of P21 and P27 dose-dependently (24 hr), induced the phosphorylation of extracellular signal-regulated protein kinase (ERK) time-dependently (10 microm), but did not affect phosphorylation of P38 in RA-FLSs. In addition, the expression of P21 and P27 triggered by melatonin was inhibited by the pretreatment of the ERK inhibitor, PD98059 (10 microm). The anti-proliferative action of melatonin in RA-FLSs was also blocked by PD98059. Taken together, these results suggest that melatonin exerts the inhibitory effect of the proliferation of RA-FLSs through the activation of P21 and P27 mediated by ERK. Hence we suggest that melatonin could be used as a therapeutic agent for the treatment of RA.

Melatonin is reported to be an anti-inflammatory agent. No genetic study concerning the association between melatonin and inflammatory disease has yet been reported. Here we performed a polymorphism study on the melatonin receptor type 1B (MTNR1B) in Korean rheumatoid arthritis (RA) patients and controls. The polymorphism of MTNR1B located in 3'-untranslated region (rs 1562444) was selected for its higher rate of heterozygosity among other single nucleotide polymorphisms (SNPs) in both MTNR1A and MTNR1B genes and investigated in RA patients (n = 173) and healthy controls (n = 195) by polymerase chain reaction-restriction fragment length polymorphism assay using NlaIII restriction enzyme. No statistically significant difference in either genotype distribution or allele frequency was observed between RA patients and controls. The genotype distributions and allele frequencies of rheumatoid factor negative [RF(-)] patients were similar to those of controls. However, statistical analysis of genotype revealed a significant association (chi2 = 6.42, P = 0.04) is present between RF(+) and MTNR1B SNP (rs 1562444). Although no statistically significant difference in allele frequency between RF(+) and controls was observed (chi2 = 2.75, P = 0.10), the results might suggest that MTNR1B SNP (rs 1562444) is associated with the presence of RF in RA. This is the first study, to our knowledge, to report a positive genetic relationship between melatonin and RA.