Hydroxyapatite fiber material with BMP-2 gene induces ectopic bone formation.

Collagen containing bone morphogenetic protein-2 (BMP-2) expression vector, which is called "gene-activated matrix," promotes bone regeneration when transplanted to the bone defect. We speculated that hydroxyapatite fiber (HF) would be an ideal matrix for "gene-activated matrix" especially for bone regeneration, because it is oseteoconductive and has high affinity to DNA. The purpose of this study is to clarify whether HF containing BMP-2 expression vector induces ectopic bone formation. We prepared HF containing 0, 10, 50, and 100 microg BMP-2 expression vector. Wistar male rats (8 weeks) were used and each rat received two HF implants in the left and right dorsal muscle. The rats were sacrificed 4, 8, and 12 weeks after the operation, and implants were analyzed radiographically by softex, dual-energy X-ray absorptiometry, and they were histologically examined. At 4 weeks, HF containing 50 or 100 microg BMP-2 expression vector showed high bone mineral contents and large radiopaque volume compared to the other implants. At 8 and 12 weeks, HF containing 50 microg BMP-2 expression vector exerted the highest values in the radiographic analyses. Bonelike tissue was histologically observed in HF containing 50 and 100 microg BMP-2 expression vector groups but not detected in the other implants. The present results suggest that HF is potential as a matrix for "gene-activated matrix" for bone tissue engineering.