Gamma irradiation of human bone allografts alters medullary lipids and releases toxic compounds for osteoblast-like cells

The uncertainties about the transmission of prion proteins from xenogenic grafts prepared from bovine bone has led to the reconsideration of allogenic bone as a grafting material. Allografting is a complementary technique to autografting nowadays when large bone volumes are necessary. Several preparation techniques have been proposed. Fresh-frozen, freeze-dried and gamma irradiation are the most common. However, a large amount of lipids is present in the medullary spaces (near 70% in weight for a human femoral head). They are known to strongly influence the biocompatibility of the bone graft. The exact changes of lipids upon the sterilization and storage processes are poorly known. The aims of the present study were to appreciate the effects of gamma irradiation on medullary lipids and to identify the cytotoxicity of gamma-irradiated bank bone with/without lipid on cultures of osteoblast-like cells. Bone cores from 8 femoral heads retrieved during prosthesis surgery for arthritis were prepared with a drilling trephine. Cores were either sterilized by gamma radiations (25000 gray) or kept frozen until lipid extraction and lipofuschine-like dosage by Folch's method and fluorometric study. Peroxidated lipids appeared 2 to 3-fold higher in the gamma-irradiated cores than in frozen ones. Slices were prepared from bone cores and were transferred on confluent osteoblast-like cell layers (Saos-2). The raw slices (containing lipids) did not induce cell death. On the other hand, cell death was dramatically increased around the gamma-irradiated slices. Defatted slices which had been sterilized by gamma radiations or UV did not induce cell death. Defatting procedures should be added when preparing bone allografts in human bone banks.