JB3, an IGF-I Receptor Antagonist, Inhibits Early Renal Growth in Diabetic and Uninephrectomized Rats JOHN HAYLOR,* HELEN HICKLING,* EMAN EL ETER,* ARTHUR MOIR, ‡ SIMON OLDROYD,* COLIN HARDISTY, ² and A. MEGUID EL NAHAS* *Sheffield Kidney Institute, ² Diabetic Centre, Northern General Hospital Trust, and ‡ Krebs Institute, University of Sheffield, Sheffield, United Kingdom. Abstract. Biochemical evidence suggests that insulin-like growth factor I (IGF-I) may play an important role as a mediator of kidney growth. In the present study, an IGF-I receptor antagonist (JB3) was synthesized, and its effect on the renal growth that follows the induction of diabetes or unilateral nephrectomy (UNx) was examined. JB3 was generated by solid phase peptide synthesis. Its activity as an IGF-I antago- nist was confirmed in an opossum kidney cell line from its inhibitory effect on the increase in thymidine incorporation into DNA induced by recombinant human IGF-I. Male Wistar rats were anesthetized with halothane and subjected to either the induction of diabetes by streptozotocin (intravenous 60 mg/kg) for 4 d (control animals received citrate buffer) or UNx for 11 d (control animals were sham operated). JB3 was delivered by subcutaneous infusion using an osmotic minipump implanted 3 d before the induction of diabetes or UNx. Kidney wet weight, DNA, and protein all were signifi- cantly higher 4 d after the induction of diabetes (24%) or 11 d after UNx (55%). Dose-response studies (1 to 30 g/kg per day) showed JB3 administration to inhibit the increase in kidney growth in both diabetic and UNx rats. The increase in kidney wet weight, DNA, and protein was significantly lower in UNx rats that were treated with JB3 10 g/kg per day (P  0.05) than in saline vehicle controls but was abolished in diabetic rats that were treated with JB3 3 g/kg per day (P  0.01). Increasing the dose of JB3 to 30 g/kg per day was associated with a decrease in its inhibitory effect, resulting in bell-shaped dose-response curves. JB3 administration had no effect on the blood glucose concentration or food consumption by either diabetic or nondiabetic animals. The results support the concept of IGF-I as an important mediator of the early renal growth that follows the induction of diabetes or UNx in the rat. Insulin-like growth factor I (IGF-I) is a potent mitogen pro- posed to play an important role in the regulation of cell proliferation, apoptosis, and tumorigenicity (1). Kidney growth is enhanced after the systemic administration of exogenous recombinant human IGF-I to the rat (2), and glomerular hy- pertrophy is a feature of the overproduction of IGF-I in trans- genic mice (3). The renal growth that follows either the induc- tion of diabetes or unilateral nephrectomy (UNx) has previously been attributed to an increase in the kidney content of IGF-I protein (4), located principally in the collecting duct and ascending limb, suggested to precede the growth response (5,6). Diabetes is associated with a sustained fall in hepatic IGF-I mRNA (7), and even though serum IGF-I declines (8), the systemic circulation has been proposed to be the source of IGF-I protein that accumulates in the kidney (9). Upregulation of kidney IGF-I receptor mRNA and receptor protein have also been observed (10,11), and opposing regional changes in in- sulin-like growth factor-binding protein I (IGFBP-I) and IG- FBP-5 between the renal medulla and cortex have been de- scribed (12). Time course studies suggest the increase in renal IGF-I protein to be paralleled by an increase in renal IGFBP-1 rather than by an increase in the IGF receptor protein (12). In contrast, after UNx, the increased renal accumulation of IGF-I is not associated with a change in the serum IGF-I concentra- tion (13), and both serum IGFBP (1– 4) and kidney tissue IGFBP (1– 4) were reported to remain unchanged (14). Con- vincing evidence for an increase in renal IGF-I mRNA and IGF-I receptor mRNA has been obtained in the immature rat only in the 48-h period after UNx (15), whereas 7 d after UNx in weanling rats, an increase in mRNA for IGFBP 3, 4, and 5 has recently been detected (16). In the adult rat, compensatory renal hypertrophy was suggested to be dependent on growth hormone (GH) (17). However, a role for GH as a mediator of compensatory renal growth is not supported by studies using the Lewis dwarf rat, which is GH deficient (18,19). The precise role of IGF-I in kidney growth may be difficult to define solely from the complex pattern of changes in renal IGF-I biochemistry that follow the induction of diabetes or a reduction in renal mass. Slow progress in establishing a precise role for IGF-I in kidney growth has previously been attributed to a lack of available IGF-I receptor antagonists (20). However, the three-dimensional modeling of the human IGF-I protein has allowed the synthesis of selective antagonists of the IGF type 1 receptor designed to mimic the D-domain of the IGF-I Received October 4, 1999. Accepted March 13, 2000. Correspondence to Dr. John L. Haylor, Sheffield Kidney Institute, Floor G, Northern General Hospital Trust, Herries Road, Sheffield S5 7AU, United Kingdom. Phone: +44-0-114-271-4563; Fax: +44-0-114-256-2514; E-mail: J.L.Haylor@sheffield.ac.uk 1046-6673/1110-2027 Journal of the American Society of Nephrology Copyright © 2000 by the American Society of Nephrology J Am Soc Nephrol 11: 2027–2035, 2000