Changes in protein turnover, IGF-I and IGF binding proteins in children with cancer

Changes in insulin-like growth factor-I (IGF-I) and insulin-like growth factor binding proteins (IGFBPs) were correlated with protein synthesis and breakdown using [1- ¹³C]leucine before chemotherapy and during subsequent febrile neutropenia (FN) in eight children with cancer, aged 6.3–17.5 y. IGF-I levels were similar to age-matched controls before chemotherapy (mean ±SEM: 250 ±28 and 228 ±22 μg l^-1, respectively). During FN, IGF-I fell to 156 ±22 /ng l ^-1(p= 0:02), and rose to 276 ±27 μ g l ^-1 with recovery at 6 months (p = 0:004). Similarly, IGFBP-3 decreased from 4.0 ±0.2mgl^-1 before chemotherapy to 3.0 ±0.3 mgl^-1 during FN (p= 0:01), and returned to 4.1 ±0.2mgl ^-1 at 6 months (p= 0:01). IGF-I correlated with IGFBP-3 (r=+0:7, p <0:001). Scanning densitometry showed a decrease in IGFBP-3 from 94 to 54% during FN, when the presence of IGFBP-3 protease activity was observed. Compared with normal human serum, IGFBP-2 was elevated throughout the study. IGFBP-1 increased from 14.6 ±3.5 to 30.6 ±2.8/ngl^-1 (p = 0:004), whereas serum insulin decreased from 26.5 ±6.8 to 7.8 ±0.8 mUl^-1 (p= 0:03) before and during FN, respectively. Whilst IGF-I and IGFBP-3 fell, daytime growth hormone increased from 3.3 ±0.6 to 6.7±0.8mUl ^-1 (p= 0:01), and cortisol from 197 ±48 to 594±98nmoll ^-1 (p = 0:005). Albumin decreased from 47 ±2 to 38 ±2gl^-1 (p= 0:004) and improved to 47 ±2gl^-1 with recovery (p= 0:003). Protein synthesis increased from 4.5 ±0.4 to 5.0 ±0.6gkg^-1 d^-1 before chemotherapy and during FN, while protein breakdown rose from 5.4 ±0.4 to 6.3 ±0.4kg^-1d^-1. Increasing protein breakdown was related to falling IGF-I and IGFBP-3 levels. Modification of IGFBP-3 by circulating proteolytic activity may alter IGF bioavailability, allowing protein synthesis to increase during periods of severe catabolic stress.