Melatonin is known to regulate a variety of physiological processes including control of circadian rhythms, regulation of seasonal reproductive function, regulation of body temperature, and so forth. Accumulating evidence from in vitro and in vivo experiments using rodent and chicken has also suggested that melatonin may have an influence on skeletal growth and bone formation. However, little is known about the effects of melatonin on human osteoblasts, which thus remains to be elucidated. This study was performed to determine whether melatonin could affect the proliferation and differentiation of human osteoblasts in vitro and to demonstrate the possibility that melatonin could be applied as a pharmaceutical agent to shorten the treatment period of bone fracture, various osteotomies, and bone distraction. Reverse transcription-polymerase chain reaction and Western blot analysis showed that human osteoblasts expressed melatonin 1a receptor and that its expression levels decreased gradually with the age of the hosts. Melatonin stimulated the proliferation and alkaline phosphatase activity of human osteoblasts in a dose-dependent manner at the pharmacological concentrations. Melatonin also promotes gene expression of type I collagen, osteopontin, bone sialoprotein, and osteocalcin in a dose-dependent manner, and stimulated the mineralized matrix formation in vitro. Moreover, intraperitoneal administration of melatonin to mice increased the volume of newly formed cortical bone of femora. These results demonstrated that melatonin directly accelerated the differentiation of osteoblasts of human as well as rodent and chicken and also suggested that melatonin could be applied as a pharmaceutical agent to promote bone regeneration.

IL-1 receptor antagonist (IL-1ra) is a cytokine that competitively binds the IL-1 receptor to antagonize IL-1 activity without any agonist function. Previous experiments indicated that the ratio of IL-1ra to IL-1alpha in the normal stratum corneum (SC) was much higher in the sun-exposed face than in the sun-protected area, upper arms. It was also reported by another laboratory that IL-1ra is increased in the lesional skin of psoriatic patients. This study was designed to measure the contents of IL-1alpha and IL-1ra in non-lesional and pathological SC obtained from inflammatory skin diseases including psoriasis and non-psoriatic dermatoses such as atopic dermatitis. The SC materials were obtained with a non-invasive tape-stripping method. Their soluble fractions were prepared and assayed for IL-1alpha and IL-1ra by enzyme-linked immunosorbent assays. As a result we confirmed the previous findings that the ratio of IL-1ra to IL-1alpha in the normal SC was much higher in the face than in the sun-protected sites, the trunk as well as extremities. Next, we found that IL-1alpha contents were significantly reduced in the SC samples obtained from inflammatory skin regardless of whether their IL-1ra contents increased or unchanged. Moreover, we noted that an increased ratio of IL-1ra to IL-1alpha in the SC was not specific to psoriasis, but was also found in other inflammatory skin diseases including atopic dermatitis. This ratio was found to become lower after successful treatment of these skin lesions with topical glucocorticoids. We conclude from these observations that the increased ratio of IL-1ra to IL-1alpha in the SC is a non-specific phenomenon that can occur in any inflammatory skin diseases regardless of the inflammatory pattern, probably reflecting a skin regulation process against various kinds of inflammation.

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Multidrug resistance (MDR) caused by the overexpression of ATPbinding cassette (ABC) transporters in cancer cells is a major obstacle in cancer chemotherapy. Previous studies have shown that curcumin, a natural product and a dietary constituent of turmeric, inhibits the function of MDR-related ABC transporters, including ABCB1, ABCC1, and especially ABCG2. However, the limited bioavailability of curcumin prevents its use for modulation of the function of these transporters in the clinical setting. In this study, we investigated the effects of 24 synthetic curcumin analogs with increased bioavailability on the transport function of ABCG2. The screening of the 24 synthetic analogs by means of flow cytometry revealed that four of the curcumin analogs (GO-Y030, GO-Y078, GO-Y168, and GO-Y172) significantly inhibited the efflux of the ABCG2 substrates, mitoxantrone and pheophorbide A, from ABCG2-overexpressing K562/breast cancer resistance protein (BCRP) cells. Biochemical analyses showed that GO-Y030, GO-Y078, and GO-Y172 stimulated the ATPase activity of ABCG2 at nanomolar concentrations and inhibited the photolabeling of ABCG2 with iodoarylazidoprazosin, suggesting that these analogs interact with the substrate-binding sites of ABCG2. In addition, when used in cytotoxicity assays, GO-Y030 and GO-Y078 were found to improve the sensitivity of the anticancer drug, SN-38, in K562/BCRP cells. Taken together, these results suggest that nontoxic synthetic curcumin analogs with increased bioavailability, especially GO-Y030 and GO-Y078, inhibit the function of ABCG2 by directly interacting at the substrate-binding site. These synthetic curcumin analogs could therefore be developed as potent modulators to overcome ABCG2-mediated MDR in cancer cells.