Recombinant human insulin-like growth factor (IGF)-binding protein-1 inhibits somatic growth stimulated by IGF-I and growth hormone in hypophysectomized rats.

We have examined the effects of exogenously administered recombinant human insulin-like growth factor-binding protein-1 (rhIGFBP-1) alone and in combination with recombinant human insulin-like growth factor-I (rhIGF-I) or human GH on weight gain and tibial epiphysis enlargement in hypophysectomized rats. rhIGF-I, given twice daily by sc injection, increased both growth parameters in a dose-dependent manner. Coadministration of increasing amounts of rhIGFBP-1 with a constant amount of rhIGF-I (80 micrograms/injection, given twice daily) resulted in a dose-dependent inhibition of the growth-promoting effects of rhIGF-I. A rhIGFBP-1 dose of 9.8 micrograms/injection (an IGFBP-1/IGF-I molar ratio of 0.04:1) caused no significant effect on rhIGF-I-stimulated growth parameters, whereas a rhIGFBP-1 dose of 1200 micrograms/injection (IGFBP-1/IGF-I molar ratio of 5:1) resulted in 78% or greater inhibition of rhIGF-I-stimulated growth (P < 0.05). rhIGFBP-1 doses of 48 and 240 micrograms/injection (IGFBP-1/IGF-I molar ratios of 0.2:1 and 1:1, respectively) had intermediate inhibitory effects. None of the rhIGFBP-1 doses potentiated the growth-promoting effects of rhIGF-I. Rats treated with rhIGFBP-1 alone (twice daily injections of 9.8, 48, 240, or 1200 micrograms) showed no significant differences in growth parameters compared to rats treated with vehicle. Coadministration of rhIGFBP-1 (1200 micrograms/injection, given twice daily) with GH (15 mU/injection, given twice daily) inhibited weight gain and tibial epiphysis enlargement stimulated by GH by at least 50% in each of two experiments (P < 0.05). These studies demonstrate that nonphosphorylated rhIGFBP-1 can inhibit the growth-promoting effects of rhIGF-I and GH in vivo. The results suggest that in addition to its proposed role in glucose homeostasis, IGFBP-1 may play a role in inhibiting somatic growth and other physiological functions stimulated by IGF-I and GH.

Multifunctional regulation of the biological effects of TNF-alpha by the soluble type I and type II TNF receptors.

Two soluble receptors of tumour necrosis factor were evaluated for development as potential therapeutic agents for inflammatory disease. The recombinant human soluble Type I and Type II TNF receptors, rsTNF-RI and rsTNF-RII, were expressed at high levels in E. coli, refolded, and chromatographically purified to homogeneity. The potencies of both recombinant soluble receptors were similar to their naturally occurring soluble receptors. In in vitro cytotoxicity and competitive binding assays, both recombinant soluble receptors functioned to inhibit the biological effects of rhTNF-alpha although rsTNF-RI was a 5 to 30 fold more potent inhibitor of rhTNF-alpha than was rsTNF-RII or a truncated form of the soluble receptor, TNF-RII delta. In in vivo experiments in mice, rsTNF-RI was a better inhibitor than rsTNF-RII delta of rhTNF-alpha-stimulated changes in the percentages of circulating lymphocytes and neutrophils, influx of neutrophils into the peritoneal cavity, and serum IL-6 induction. At molar ratios of 0.1:1 and 0.01:1 (rsTNF-R:rhTNF-alpha), using the rsTNF-I or rsTNF-II delta, there was a trend towards enhancement of the induction of IL-6. However, higher ratios of either rsTNF-RI or rsTNF-RII delta significantly inhibited the rhTNF-alpha-stimulated increase in serum IL-6 levels. In a murine model of cytokine-induced shock, either rsTNF-RI or rsTNF-RII delta provided protection against the lethality of shock induced by a synergistic combination of rhTNF-alpha and rhIL-1 beta. Based on the results of these experiments, the rsTNF-RI was chosen as the better candidate for development as an anti-inflammatory agent.