Endocrine Abstracts

We previously have reported that short-term treatment of mice with recombinant hGH leads to significant increases in bodyweight (BW), lean body mass (LBM) and liver weight, but – unlike in humans – does not robustly increase circulating levels of IGF1. We now tested the hypothesis that formation of neutralizing antibodies in mice treated with rhGH could explain the lack of IGF1 response. Therefore, we intentionally induced antibody formation against hGH in female FVB mice by repeated immunization (6×) using rhGH and adjuvans (Titermax Gold, Sigma). Subsequently, the 8 months old mice were treated with daily doses of rhGH (Nordiflex, Novo Nordisk, 0.5 mg/d i.p.) for 2-weeks. Age matched control mice were sham immunized using adjuvans only prior to daily rhGH treatment. Before start of rhGH treatment, BW was not significantly different between groups, but rhGH immunized mice showed significantly higher anti-hGH antibody titers (P<0.01). After 2-weeks of treatment, control mice had significantly higher BW (control: 30.2±2.5 g, immunized: 26±2.4 g; P<0.05), LBM (control: 11.3±0.8 g, immunized: 9.5±0.9 g; P<0.05) and liver weights (control: 1.77±0.15 g, immunized: 1.41±0.23 g; P<0.05) when compared to hGH immunized mice. In contrast, serum IGF1 levels were not significantly different between controls and immunized animals (controls: 444±81 ng/ml, immunized: 356±53 ng/ml, P>0.1). The IGF1 concentrations were in the range we had seen in previous experiments in young mice treated daily with either the same dose of rhGH or equal volumes of 0.9% NaCl for 2-weeks (rhGH-group: 481±88 ng/ml NaCl-group: 450±94 ng/ml). In conclusion, 2-weeks of daily rhGH treatment in mice do not lead to significant formation of neutralizing antibodies against rhGH. Intentionally induced anti-rhGH antibodies are capable to block hGH effects on BW, LBM and liver weight, but have no effect on IGF1 levels obtained after rhGH treatment. These data suggest that formation of neutralizing antibodies does not explain the lack of IGF1 response after rhGH treatment in mice.