Background: Bone morphogenetic proteins (BMPs) play important roles in the
migration of osteoblast progenitor cells, the proliferation of mesenchymal
cells, and their differentiation into chondrogenic and osteogenic cells. Ho
wever, the optimum procedure to deliver BMPs remains unknown. To examine th
e effectiveness of a gene transfer procedure for the delivery of BMP-2, we
constructed a human BMP-2-expressing replication-deficient adenoviral vecto
r, AxCAOBMP-2, and evaluated its osteoinductive activity in vitro and in vi
vo.
Methods: C2C12 myoblasts were infected in vitro with this viral vector or a
n Escherichia coil LacZ gene-expressing control adenovirus vector (AxCALacZ
). Twenty-four hours after the infection, indirect immunofluorescence was p
erformed. On day 5 after the infection, alkaline phosphatase (ALP) in the c
ells and osteocalcin in the culture medium were measured. Furthermore, to e
xamine the effectiveness of gene transfer of BMP-2 in vivo, we evaluated os
teoinduction by AxCAOBMP-2, under transient immunosuppression with cyclopho
sphamide, given at a dose of 125 mg/kg intraperitoneally the day before inj
ection of the adenoviral vector. Twenty-five microliters of AxCAOBMP-2 (8.7
5 x 10(8) plaque-forming units [pfu], Group I) and AxCALacZ (1.75 x 10(8) p
fu, control group) and 5 yl of AxCAOBMP-2 (1.75 X 10(8) pfu, Group II) were
injected into a right calf muscle of Wistar rats. On day 21, bone formatio
n in each group was investigated radiologically and histologically.
Results: Abundant BMP-2 expression in C2C12 cells infected with this viral
vector was confirmed by immunofluorescence. C2C12 cells transferred with th
e BMP-2 gene by this vector produced ALP in the cells and also produced and
secreted osteocalcin in the culture medium. Osteoinduction was found only
in the AxCAOBMP-2 treated groups with immunosuppression. Osteoinduction act
ivity was higher in Group I than in Group II.
Conclusion: This study demonstrated the osteoinductive activity in vitro an
d in vivo by an adenoviral vector carrying the BMP-2 gene.
Clinical Relevance: Gene therapy with AxCAOBMP-2 under transient immunosupp
ression may be useful for bone reconstruction.