Increase in the activity of alkaline phosphatase by L-ascorbic acid 2-phosphate in a human osteoblast cell line, HuO-3N1.

The activity of alkaline phosphatase (ALPase) was significantly enhanced in a human osteoblast cell line, HuO-3N1, when it was cultured in the presence of L-ascorbic acid 2-phosphate (AsA-P; a stable ascorbic acid derivative). With AsA-P in the culture, the level of ALPase activity increased approximately 3-fold without any effect on either the morphology or growth rate. This increase was dependent on the AsA-P concentration in the range of 0.2-2 mM and required at least 48 h incubation with AsA-P. The ALPase mRNA level, however, remained rather constant irrespective of the enzyme activity. Removal of AsA-P from the precultured medium decreased the stimulatory effect of ascorbic acid on the ALPase activity, indicating that the effect was reversible. Dexamethasone, an inducer for osteoblastic differentiation, enhanced the level of ALPase activity irreversibly, in parallel with the increase in the level of its mRNA. The enhancement of the ALPase activity by ascorbic acid in this cell line appeared to be independent of cell differentiation.