Dystrophic calcification and mineralization during bone induction: biochemical differences.

The calcification of implants of glutaraldehyde-cross linked collagenous tissues and collagen was studied in young and old rats and compared to bone induction by non-crosslinked osteogenically active demineralized bone matrix (DBM). Glutaraldehyde-crosslinked implants of DBM, tendon, and cartilage calcified in young but not in old animals and accumulated only trace amounts of BGP (Bone Gla protein, osteocalcin). Alkaline phosphatase activity and BGP was high in implants of DBM and undetectable in crosslinked implants. To try and understand why bone formation is so significantly reduced in older Fischer 344 rats, we developed a system which consists of cylinders of DBM sealed at the ends with a Millipore filter. Cells originating from 20 day old embryo donors were introduced into the chambers prior to subcutaneousmplantation. After 4 weeks of implantation in 26 month old rats, the cylinders containing embryonic calvaria or muscle cells were found to be full of bone and/or cartilage.