THE IGF-I IGFBP SYSTEM IN CONGENITAL PARTIAL LIPODYSTROPHY/

BACKGROUND AND OBJECTIVES Insulin and IGF-I interact at many levels. L ittle is known about the insulin-like growth factor-I/insulin-Iike gro wth factor binding proteins (IGF-I/IGFBP) system in congenital partial lipodystrophy, a syndrome characterized by insulin resistance, hyperi nsulinaemia and absence of truncal and limb fat. Some cases have acrom egaloid features with thick skin and large hands and feet in associati on with normal levels of circulating growth hormone. METHODS In four f emales known with congenital partial lipodystrophy, hyperinsulinaemia with acromegaloid features, the number and affinity of the IGF-I recep tors on peripheral blood mononuclear cells (PBMCs), and the concentrat ion of circulating insulin, total and free IGF-I, IGFBP-1 and IGFBP-3 levels were measured in the fasting and the fed state. Cultures of PBM Cs of the patients with lipodystrophy were also used to study the effe ct of IGF-I stimulation on thymidine uptake in vitro. MEASUREMENTS In the subjects with lipodystrophy the affinity and the number of the IGF -I receptors on peripheral mononuclear cells (PBMCs) and erythrocytes did not differ significantly from controls in the fasting state. Insul in levels were significantly higher in subjects with lipodystrophy bot h in the fasting as well in the fed state. Total IGF-I, free IGF-I and IGFBP-3 levels did not differ but serum IGFBP-1 levels were lower in lipodystrophy subjects than in healthy controls. The free IGF-I/IGFBP- 1 ratio was increased in lipodystrophy subjects both in the fasting an d the fed states. The effects of IGF-I stimulation on thymidine uptake by PBMCs of lipodystrophy subjects in the absence of IGFBP-1 were not different from healthy controls cultures in vitro. When a combination of IGFBP-1 tin a concentration comparable to the fasting serum IGFBP- 1 levels in lipodystrophy patients found in our study) and IGF-I was a dded to PBMC cultures from lipodystrophy patients no decrease in thymi dine uptake by PBMCs was found. CONCLUSIONS In the four subjects with lipodystrophy hyperinsulinaemia, lowered free IGF-I and IGFBP-1 levels , but increased free IGF-I/IGBP-1 ratios were observed. Low IGFBP-1 co ncentrations in culture media did not reduce the stimulating IGF-I eff ect on thymidine uptake by PBMCs from lipodystrophy patients. Our data suggest that the observed increased IGF-I/IGFBP-1 ratio in lipodystro phy patients contributes to an unopposed biological effect of IGF-I on IGF-I receptors, thereby inducing the development of acromegaloid fea tures, acanthosis nigricans and polycystic ovaries in some patients wi th congenital partial lipodystrophy.