Insulin-like Growth Factor-binding Protein 1 (IGFBP-1)

Insulin-like growth factor-binding protein 1 is a member of the family of structurally homologous proteins that specifically binds and modulates the activities of IGF-1 and IGF-2.^1,2 IGFBP-1 is a 25 kilodalton protein that is produced predominantly by hepatocytes and decidualized ovarian endometrium.³ Serum levels of IGFBP-1 exhibit considerable diurnal variation with levels highest early in the morning and lowest in the evening. Serum IGFBP-1 levels are controlled by insulin with the postprandial increase in insulin levels producing a four- to fivefold decrease in IGFBP-1 levels relative to fasting levels.¹ IGFBP-1 levels have been shown to be elevated in type 1 diabetics and in patients with insulin resistance syndromes. Type 2 diabetics tend to have low serum IGFBP-1 levels. Patients with growth hormone deficiency tend to have elevated IGFBP-1 levels. Low levels are observed in acromegaly, Cushing disease, and polycystic ovary syndrome. IGFBP-1 is the predominant IGF-binding protein in amniotic fluid and in fetal and maternal circulation.^4,5 The levels are high in the fetus and newborn, but decline steadily until puberty. In a recent study of women in the second trimester of pregnancy, IGFBP-1 levels were higher in women who subsequently developed preëclampsia than in matched controls who did not develop the syndrome.⁶