Aging and ectopic bone formation induced by partially purified bone morphogenetic protein

Abstract

Amixture of heparin-Sepharose-purified bovine bone morphogenetic protein (BMP) and type I atellocollagen as the carrier were implanted in the subcutaneous tissues of 4-week, 10-month and 18-month old rats. The effect of rat age on ectopic bone formation was evaluated on the explants after H & E staining, alkaline phosphatase (ALP) activity and calcium content determination. On day 14, bones were observed in 4-week old and 10-month old rats, however, calcium content of the later was approximately 66% of that of the former. On day 21, 10-month old rats had a calcium content 63% of 4-week old rats. In 18-month old rats, bone was first found in very limited regions of the explants on day 21 with a calcium content 14% of the 4-week old rats. The increase in ALP activity was consistent with the start of bone formation in all three groups, and at all periods ALP activity was higher in younger rats. The findings in the present study indicate that the rate and quantity of ectopic bone formation were reduced in aged rats but bone was induced even in 18-month old rats.