Reiko Tokuyama

Melatonin at pharmacological doses enhances human osteoblastic differentiation in vitro and promotes mouse cortical bone formation in vivo.

Abstract:  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.

High-dose-rate brachytherapy for patients with maxillary gingival carcinoma using a novel customized intraoral mold technique

OBJECTIVE The purpose of this study was to introduce a novel customized intraoral mold treatment for maxillary gingival carcinoma (UGC). STUDY DESIGN Two patients with UGC were treated as salvage therapy using this technique. The mold was designed to keep normal soft tissues adjacent to the tumor away from the radioactive source as much as possible, and it was shielded by lead. The radiation dose on the buccal mucosa and tongue was measured at the inner and outer surfaces of the intraoral mold before starting high-dose-rate brachytherapy by the remote afterloading system, and was reduced to almost one tenth. RESULTS The patient had no recurrence and no severe adverse effects on the normal soft tissue adjacent to the tumor until the end of the follow-up period. CONCLUSION High-dose-rate brachytherapy using the novel customized intraoral mold might be a treatment option of not only salvage therapy, but definitive therapy of UGC.

Maspin Is Involved in Bone Matrix Maturation by Enhancing the Accumulation of Latent TGF-ↇ

Maspin, a serine protease inhibitor, is expressed by formative osteoblasts. The repression of maspin expression in osteoblastic cells decreased the level of latent TGF‐β in the extracellular matrix, whereas the overexpression of maspin increased latent TGF‐β. These findings suggest that maspin plays an important role in bone matrix formation, particularly in the accumulation of latent TGF‐β.

Effect of Melatonin on Human Dental Papilla Cells

Melatonin regulates a variety of biological processes, which are the control of circadian rhythms, regulation of seasonal reproductive function and body temperature, free radical scavenging and so on. Our previous studies have shown that various cells exist in human and mouse tooth germs that express the melatonin 1a receptor (Mel1aR). However, little is known about the effects of melatonin on tooth development and growth. The present study was performed to examine the possibility that melatonin might exert its influence on tooth development. DP-805 cells, a human dental papilla cell line, were shown to express Mel1aR. Expression levels of mRNA for Mel1aR in DP-805 cells increased until 3 days after reaching confluence and decreased thereafter. Real-time reverse transcription-polymerase chain reaction showed that melatonin increased the expression of mRNAs for osteopontin (OPN), osteocalcin (OCN), bone sialoprotein (BSP), dentin matrix protein-1 (DMP-1) and dentin sialophosphoprotin (DSPP). Melatonin also enhanced the mineralized matrix formation in DP-805 cell cultures in a dose-dependent manner. These results strongly suggest that melatonin may play a physiological role in tooth development/growth by regulating the cellular function of odontogenic cells in tooth germs.

Possible Involvement of Leptin in the Elevated Osteoblastic Activity Observed in High Turnover Type Osteoporosis of Ovariectomized Mice

Postmenopausal osteoporosis is a high turnover type of osteoporosis induced by estrogen deficiency following menopause. In this type of osteoporosis, the osteoblastic activity is known to be elevated even though bone resorption by osteoclasts eventually exceeds bone formation by osteoblasts, resulting in the deterioration of the bone structure. Although the mechanisms underlying the progression of bone resorption in this disease are relatively well understood, the mechanisms underlying the elevated osteoblastic activity are yet to be elucidated. The purpose of this study is to investigate the possibility that leptin, a 16 kDa circulating hormone secreted mainly by white adipose tissue, is involved in the development and/or progression of the high turnover type of osteoporosis. Immunohistochemical analysis and ELISA were used to examine the expression of leptin in bones of ovariectomized mice. To investigate the effect of leptin on proliferation and osteoblastic differentiation of bone marrow stromal cells, cell proliferation assay and real-time RT-PCR analysis were performed using a mouse bone marrow stromal cell line, MMSC3. Immunohistochemistry and ELISA revealed enhanced expression of leptin in bone marrows of ovariectomized mice. A cell proliferation assay detected no significant effect of leptin on the proliferation of MMSC3 cells. In contrast, real-time RT-PCR revealed that leptin promoted the osteoblastic differentiation of this cell line. Estrogen depletion caused by ovariectomy induces the pregulation of leptin expression in the bone marrow cavity,which leads to the elevated osteoblastic activity observed in the early phase of high turnover type osteoporosis of ovariectomized mice.

Antibacterial and Antifungal Effect of 405 nm Monochromatic Laser on Endodontopathogenic Microorganisms

The purpose of this study is to evaluate the usefulness of 405 nm monochromatic laser irradiation as an alternative management for prevention and/or treatment of endodontic infections. A monochromatic laser-emitting device equipped with a 405-nm laser diode was developed. Using this device, the effect of 405 nm laser irradiation on the growth of Porphyromonas gingivalis, Prevotella intermedia, Enterococcus faecalis, and Candida albicans, which are microorganisms associated with persistent endodontic infections, was evaluated by viable colony counting. As a result, the irradiation with a 405 nm laser had a significant bactericidal/fungicidal effect on P. gingivalis, P. intermedia, and C. albicans, whereas the growth of E. faecalis was not affected by the irradiation. The inhibition rate in P. gingivalis and P. intermedia was ~60% and ~80%, respectively, following irradiation at 0.2 W for 300 sec. The inhibition rate in C. albicans was ~90% following irradiation at 0.2 W for 1200 sec. These results indicate that 405 nm monochromatic laser irradiation exerts a bactericidal/fungicidal effect on these microorganisms. The present study clearly demonstrates that 405 nm laser irradiation is a promising alternative management strategy for prevention and/or treatment of endodontic infections.