FLUORIDE AND ALKALINE-PHOSPHATASE

Since serum alkaline phosphatase increases in fluoride therapy for ost eoporosis, it is generally accepted that fluoride stimulates bone form ation. However, histochemical studies have shown that alkaline phospha tase is also increased in resorbing osteocytes. Fluoride is toxic to m etabolically active bone cells, alkaline phosphatase is released, and serum alkaline phosphatase increases. We propose that the increased se rum alkaline phosphatase following fluoride therapy may reflect a toxi city of fluoride for both osteoblasts (bone forming cells) and resorbi ng osteocytes. When cells are injured their first response is to initi ate repair processes and a this repair fails the cell dies. An increas e of serum alkaline phosphatase and increased bone mass following fluo ride therapy represent a failed repair response involving an initial i ncrease in both bone formation and resorption. This repair response to cell injury results in pathological bone formation. Furthermore, as t he repair process fails there is a toxic death of resorbing osteocytes and a decrease in bone resorption. Osteoclasia of fluorotic bone may result in secondary toxic effects of fluoride on osteoclasts, and cont ribute to decreased bone resorption. The increased amount of trabecula r bone in fluoride therapy is claimed to be the morphologic expression for fluoride as a stimulus for bone formation. We propose that the in creased amount of trabecular bone results from pathological bone forma tion by injured osteoblasts and decreased bone resorption by resorbing osteocytes and osteoclasts. Both resorptive processes are required fa r the remodeling of trabecular bone into compact bone. Fluoride has on ly negative effects on bone cell metabolism. Fluoride should be avoide d, especially in osteoporosis.