Lack of physiological suppression of circulating IGFBP-1 in puberty in patients with insulin-dependent diabetes mellitus

Department of Pediatrics, Oulu University Hospital, Oulu, Finland.

OBJECTIVE: To evaluate the interaction between serum free insulin, insulin-like binding protein (IGFBP)-1 and leptin concentrations during puberty in insulin-dependent diabetes mellitus (IDDM). DESIGN: Adolescent patients with IDDM (n=101, age >9 years, duration >2 years) from the Outpatient Clinic of the Department of Pediatrics at Oulu University Hospital, and non-diabetic controls, were recruited to the study. Free insulin, IGFBP-1, leptin and insulin antibody concentrations were measured from a fasting serum sample. RESULTS: Free insulin concentrations were lower in the patients than in the controls (4.3+/-2.3 mU/l compared with 6.5+/-3.1 mU/l, P<0.001), and there was an inverse correlation between free insulin and fasting blood glucose in the boys with diabetes (r=-0.53, P<0.001), whereas a positive correlation was observed between free insulin and leptin concentrations in the girls with diabetes (r=0.30, P=0.020). The IGFBP-1 concentrations were greater in the patients than in the controls (16.5+/-10.6 microg/l compared with 4.0+/-3.3, P<0.001), and they correlated significantly with blood glucose (r=0.63, P<0.001) and free insulin (r=-0.35, P<0.001). No significant difference was observed in the leptin concentrations between the patients and controls overall, despite greater total body fat in the girls with diabetes compared with the control girls. CONCLUSIONS: Adolescents with IDDM are characterised by morning hypoinsulinaemia and high circulating IGFBP-1 concentrations, which may contribute to insulin resistance and impaired metabolic control during puberty. The mechanism behind the increased total body fat in the postpubertal female patients remains to be determined.