Alkaline phosphatase activity in cultured cells of human healthy and hyperplastic gingivae: a preliminary study

The present study compared the alkaline phosphatase (ALP) expression in cultured cells derived from different types of gingival hyperplasia. Tissue biopsies were obtained from patients with clinically non-inflamed, enlarged gingivae of idiopathic gingivofibromatosis (IGF) and phenytoin-induced hyperplasia (PHG). Fibroblasts obtained from the gingivae or periodontal ligaments (PDL) of the same or different healthy subjects were used as controls. Fibroblasts were plated and the ALP activity and total amount of DNA per well were studied in each isolated cell type at 4, 7 and 9 days of culture. The results revealed that fibroblasts derived from IGF tissue synthesized a large amount of ALP by day 7 and day 9 of culture. The amount of ALP activity was cell density-dependent and the strongest expression of enzyme activity was noted after cell confluence. In contrast, only very low ALP activity was detected in cells derived from normal gingivae and PHG. Cytochemical examination of these cells revealed similar observations. The fact that fibroblasts derived from PHG tissue did not exhibit ALP in vitro suggests that there was a shift of cell phenotype in this tissue. The increased expression of ALP in IGF cells may imply a developmental trend toward osteoblastic phenotypes.