Alkaline Phosphatase and the Biosynthesis of Collagen in Human Fibroblast Cultures

Studies were initiated in tissue culture to determine whether activation of alkaline phosphatase is directly related to the biosynthesis of collagen in human diploid skin fibroblasts. Prednisolone 21-phosphate added to monolayer cultures every 3 days with medium change induced a linear increase in specific activity of alkaline phosphatase which began on the fourth day and reached 7 times the control level by the 13th day. Under the same experimental conditions, addition of ascorbate induced an increase in the specific activity of the enzyme to 2.5 times the control level. Prednisolone phosphate did not affect accumulation of collagen-hydroxyproline in cell monolayers when compared to control cultures. Addition of ascorbate, however, resulted in rapid accumulation of hydroxyproline. The addition of prednisolone and ascorbate together resulted in an increased rate of collagen biosynthesis on the fourth. When prednisolone and ascorbate were added in combination, the induction of alkaline phosphatase was 5 times the control level by the 13th day. The accumulation of hydroxyproline, however, was no greater in these cultures by the 13th day than in cultures to which ascorbate alone was added. These studies demonstrate that the activity of alkaline phosphatase induced by prednisolone phosphate is not directly related to the biosynthesis of collagen in human skin fibroblasts in tissue culture. (Author)