Melatonin suppresses osteoclastic and osteoblastic activities in the scales of goldfish

The effects of melatonin on osteoclastic and osteoblastic cells were examined using a culture system of the goldfish scale. Tartrate-resistant acid phosphatase (TRACP) and alkaline phosphatase (ALP) were used as markers of osteoclastic and osteoblastic cells, respectively. In Earle's minimum essential medium containing melatonin (10(-9) to 10(-5) M, activities of both enzymes in scales were significantly suppressed at 6 hr after incubation (TRACP: 10(- 8), 10(-6), 10(-5) M ALP: 10(-7) to 10(-5) M, but at 18 hr only ALP activity was significantly lowered (10(-8), 10(-7) M. Estradiol-17beta (E-2) enhanced both activities, which were significantly inhibited and brought down to the level of the controls when co-incubated with E-2 and melatonin (TRACP at 6 hr: 10(-9) to 10(-5) M ALP at 6 hr: 10(-7) M ALP at 18 hr: 10(-8) M). Moreover, using reverse-transcription polymerase chain reaction, the mRNA expression of the estrogen receptor (ER) and insulin-like growth factor (IGF)-1, which are related to osteoblastic growth and differentiation, was decreased in the melatonin-treated scales. These results suggest that melatonin acts directly on the scale osteoclastic and osteoblastic cells where it suppresses the ALP activity via down-regulation of ER and IGF-1 mRNAs expression. This is the first report on the function of melatonin in osteoclasts and on the suppressive effect of melatonin in osteoblasts among vertebrates.