The effect of sterilization on transforming growth factor beta isolated from demineralized human bone

Growth factors have been identified as the primary cause of osteoinduction in bone healing. Transforming growth factor beta (TGF-beta) has been shown to promote bone formation and is present in bone in high quantities. The aims of the present study were to isolate TGF-beta from human bone, demonstrate its biologic activity, and analyze the effects of conventional sterilization techniques on activity. Bone, obtained from femoral heads of five patients (mean age, 70 years) was ground, demineralized, and freeze-dried, and samples from each patient were divided into three groups: no treatment, sterilization with 1.60 to 1.94 Mrad of 60Co irradiation, and sterilization with ethylene oxide (ETO). Carrier-free recombinant TGF-beta control was also treated and was totally inactivated by ETO but not by irradiation (p < 0.01). TGF-beta activity in demineralized bone was not significantly diminished (p > 0.1) by either sterilization procedure, and substantial amounts of active TGF-beta were recovered in all bone samples: 1.04 +/- 0.77 ng per mg of protein in irradiated samples, 0.67 +/- 0.26 ng per mg in ETO-treated samples, and 1.04 +/- 0.33 in untreated samples, respectively (mean +/- SD). Although a recent report demonstrated that the osteoinductive activity of bone morphogenetic protein in bone powder is diminished considerably by ETO and by 2.5 Mrad of irradiation sterilization of bone powder, these data demonstrate that TGF-beta activity, with its osteoinductive properties, was not destroyed in more coarsely ground, demineralized bone by ETO or by lower doses of irradiation. These findings support the use of human bone allografts in clinical instances involving impaired bone formation.