THE EFFECT OF AGING ON BONE-FORMATION IN POROUS HYDROXYAPATITE - BIOCHEMICAL AND HISTOLOGICAL ANALYSIS

The effect of aging on osteoblastic differentiation of marrow stromal stem cells was examined. Porous hydroxyapatite (HA) disks: were soaked in cells suspensions of bone marrow cells from young (8 weeks) and ol d rats (60 weeks) and then implanted subcutaneously in syngeneic young and old rats. The bone marrow/HA composites were harvested 8 weeks la ter, and the contents of bone Gla protein (BGP) and alkaline phosphata se (ALP) activity in them were determined. Histologically, bone format ion could be detected in all the composites in young recipient rats; h owever, some old bone marrow/HA composites in old recipients did not s how bone formation and the bone volume in the young bone marrow/HA com posites was greater than in the old bone marrow/HA composites. The rat ios of ALP activities of young bone marrow/HA composites to old bone m arrow/HA composites in young and old recipients were about five times and four times, respectively. The ratios of BGP contents of young bone marrow/HA to old bone marrow/HA composite in young and old recipients were about nine and eight times, respectively. The results suggest th at the decreased bone formation observed in old bone marrow cells was due to a smaller population of stromal cells and/or decreased capacity of differentiation of stromal stem cells into osteogenic cells.