The short-term effects of repetitiveE. coli-derived rhBMP-2 administration through intravenous injection in rats

Escherichia coli-derived recombinant human (rh)BMP-2 (E.BMP-2) can be used as a bone graft substitute because to its high osteoinductivity, but its toxicity is not well understood. Thus, we report on the toxicity of E.BMP-2 in Sprague-Dawley rats under the condition of repetitive injection for 2 weeks. Randomly selected 10 male and female rats were administered with E.BMP-2 at a dose of 0.05, 0.18 or 0.5 mg/kg as an experimental group. A control group with another 10 rats was given E.BMP-2 carrier. Both E.BMP-2 and E.BMP-2 carrier were administered through intravenous injection for 2 weeks. For toxicokinetics study, 3 male and female rats were randomly selected from each group. During the observation period, general symptom, weight and food intakes were monitored, and ophthalmic and urine tests were performed as well. After the observation period, all animals were subjected to blood test, biochemical analysis and organ-weight measurement. During autopsy, visual inspections and histopathological examinations were done. Toxicokinetics study confirmed systemic exposure of the test material. No death or abnormal clinical sign was found during the injection period. Toxicity changes induced by the injection were not detected in autopsy or the tests for weight, food intakes, ophthalmology, hematology and serum biochemistry. The female groups administered with 0.18 and 0.5 mg/kg (the female 0.18-mg/kg group and the female 0.5-mg/kg group) showed absolute and relative weight loss in ovaries and reduced corpora lutea. It was the expected pharmacologic activity, rather than toxicity. The histopathological test revealed cartilage formation and increased fibroblast around the tail vein, but these were thought to be the result of osteoinductivity of the test material. In the male group with 0.5 mg/kg of E.BMP-2 (the male 0.5-mg/kg group), local appearance of multinucleated cells in lung parenchyma was observed, but it was considered as the natural reaction to remove E.BMP-2, which is a recombinant protein. In toxicokinetics study, systemic exposure (area under the serum concentration-time curve and maximum observed serum concentration) increased as the injection dose was increased in both male and female rats, and no clear difference was noticed between the sexes. Blood drug content did not change during the injection period, but the half-life was shortened as the injection dose was increased. Under the condition of this study, the no observed adverse effects level of E.BMP-2 was over 0.5 mg/kg in both male and female rats.