Physical Training Leads to Improved Fitness in CKD Despite no Change in Circulating Bioactive IGF-I

Abstract

Chronic kidney disease (CKD) is characterized by abnormalities in the insulin-like growth factor (IGF) system. The measurement of bioactive IGF-I in response to physical activity may provide further insight into the therapeutic potential of exercise training in CKD patients. PURPOSE: The purpose of the present study was to assess changes in the IGF system, including bioactive IGF-I,in CKD patients following a training program. METHODS: Patients (N = 21) with CKD (stage 2-4) were randomized into matched treatment and control groups. The treatment group participated in 48 weeks of progressive exercise training and dietary counseling. The control group received only usual care. Fitness measurements and blood samples for analyses of immunoreactive IGF-I, IGF-II, IGFBP-1 and -2, and bioactive IGF-I were taken at baseline, 24 weeks, and 48 weeks. Bioactive IGF-1 was assessed using the kinase receptor activation assay (KIRA). RESULTS: There were no significant differences in any of the components of the IGF system (all p- values >.05). Immunoreactive IGF-I levels correlated significantly with bioactive IGF-I at baseline (r =.50, p =.02) and at 48 weeks (r =.64, p =.01). Both VO2peak (p =.03) and total treadmill time (TT) (p =.00) increased over 48 weeks in the treatment group. CONCLUSIONS: Despite improvements in physical performance in this CKD patient population, a 48-week training program did not affect either immunoreactive or bioactive circulating IGF-I. These data suggest that if the IGF-I system is involved or mediating these positive exercise-induced adaptations in CKD patients; changes are not reflected by blood/serum measurements. Funded by the Baystate Medical Center Incubator Fund.Table