Inhibitory activities of plastoquinones and chromene derivative from a brown alga Sagassum micracanthum on bone resorption

We evaluated inhibitory effects of plastoquinones (1, 2) and chromene derivative (3) from the methanol extract of Sargassum micracanthum on the differentiation of osteoclast progenitors into osteoclast-like cells (OCLs), bone-resorbing activity and the survival of OCLs. When OCL formation was investigated using osteoclast progenitor cells obtained from macrophage-colony stimulating factor (M-CSF)-treated mouse bone marrow, 1-3 inhibited dose-dependently OCL formation at the concentrations of 3-10 mu M, the order of inhibitory potency being 1 > 3 > 2. In addition, they suppressed dose-dependently the pit formation induced by OCL on dentine slices, the order of inhibitory potency being 1 > 3 > 2. The survival of OCLs was inhibited by about 35, 45 and 60% in the presence of 6 mu M of 2, 3 and 1, respectively. These results suggest that the inhibitory effects of the three compounds on the differentiation, pit formation and the survival of OCLs might contribute to the suppression of bone resorption.