Hyperlipidemia is Associated with Altered Levels of Insulin-Like Growth Factor-I

Previous studies revealed altered levels of the circulating insulin-like growth factor-I (IGF-I) and of its binding protein-3 (IGFBP-3) in subjects with coronary atherosclerosis, metabolic syndrome and premature atherosclerosis. Hyperlipidemia is a powerful risk factor of atherosclerosis. We expected IGF-I and IGFBP-3 alterations in subjects with moderate/severe hyperlipidemia but without any clinical manifestation of atherosclerosis. Total IGF-I and IGFBP-3 were assessed in 56 patients with mixed hyperlipidemia (MHL; cholesterol >6.0 mmol/l, triglycerides >2.0 mmol/l), in 33 patients with isolated hypercholesterolemia (IHC; cholesterol >6.0 mmol/l, triglycerides <2.0 mmol/l), and in 29 healthy controls (cholesterol <6.0 mmol/l, triglycerides <2.0 mmol/l). The molar ratio of IGF-I/IGFBP-3 was used as a measure of free IGF-I. IHC subjects differed from controls by lower total IGF-I (164 +/- 60 vs. 209 +/- 73 ng/ml, p=0.01) and IGF-I/IGFBP-3 ratio (0.14 +/- 0.05 vs. 0.17 +/- 0.04, p=0.04). Compared to controls, MHL subjects had lower total IGF-I (153 +/- 54 ng/ml, p=0.0002) and IGFBP-3 (2.8 +/- 0.6 mg/ml, p<0.0001), but higher IGF-I/IGFBP-3 ratio (0.25 +/- 0.06, p<0.0001). Differences remained significant after the adjustment for clinical and biochemical covariates, except for triglycerides. Patients with both IHC and MHL have lower total IGF-I compared to controls. The mechanism is presumably different in IHC and MHL. Because of prominent reduction of IGFBP-3 in patients with MHL, they have reduced total IGF-I despite the actual elevation IGF-I/IGFBP-3 ratio as a surrogate of free IGF-I.