Monofluorophosphate is hydrolyzed by alkaline phosphatase and mimics the actions of NaF on skeletal tissues, In Vitro

These studies were intended to assess the osteogenic activity of monofluorophosphate (MFP)in vitro, and to identify the enzyme(s) responsible for MFP hydrolysis-alkaline phosphatase (ALP) and/or acid phosphatase (AcP). ALP and AcP activities were determined by hydrolysis of p-nitrophenylphosphate (PNPP) at pH>8 and pH 5.5, respectively, and MFP hydrolysis was determined, between pH 5.5 and pH 9.0, from measurements of [fluoride ion], using an ion-specific electrode. We found (1) that MFP was an alternative substrate for purified ALP, but not for AcP; (2) that MFPase activity in the embryonic chick resembled ALP, but not AcP, with respect to pH-dependent hydrolysis, sensitivity to effectors (r=0.98, P<.001), and tissue distribution (r=0.96, P <.001); and (3) that intestinal MFPase activity in the embryonic chick co-purified with ALP activity (r=0.93, P<.01) and resembled ALP, but not AcP, in its distribution along the small intestine, being highest in the duodenum and lowest in the distal ileum (r=0.96, P<.001). We also found that in vitro exposure to MFP increased (1) the proliferation rate of embryonic chick calvarial cells in serum-free monolayer cultures (i.e.,³[H]-thymidine incorporation into DNA, P<.001); (2) ALP activity in calvarial cells (P<.005) and in intact calvaria (P<.05); and (3) collagen production by intact calvaria (i.e.,³[H]-proline incorporation as³[H]-hydroxyproline, P<.05). Together these data indicate that ALP, and not AcP, is responsible for MFP hydrolysis, and that MFP can mimic the osteogenic actions of NaF, in vitro.