Free leptin is increased in normal pregnancy and further increased in preeclampsia

We measured bound and free leptin levels in preeclamptic and matched normal pregnant and never-pregnant women to determine whether the free component of leptin is increased during pregnancy and further increased in preeclampsia. Two milliliters of serum was obtained from 18 normal and 18 preeclamptic patients matched by pre-pregnancy body mass index (BMI), and from 18 never-pregnant women matched by BMI with the pregnant groups. The sample was subjected to gel filtration using Sephadex G-100. Radioimmunoassay (RIA) was performed on all fractions, and the proportions of bound and free leptin were determined by analyzing the areas under the curve of the chromatographic profile. The total maternal serum leptin concentration was significantly higher in normal pregnancy compared with the nonpregnant state and was further increased in preeclampsia (33.8 +/- 4.1 v 15.2 +/- 1.8 ng/mL, P = .002, and 48.1 +/- 5.6 ng/mL, P = .02, respectively). Free leptin was increased in normal pregnant compared with never-pregnant women (25.9 +/- 4.1 v 11.0 +/- 2.0 ng/mL, respectively, P = .01), while the increase of total leptin in preeclampsia was exclusively in the free fraction that was significantly higher versus the normal pregnant group (41.8 +/- 5.6 v25.9 +/- 4.1 ng/mL, respectively, P = .01). The bound leptin fraction, by contrast, was significantly increased in the normal pregnant group compared with the preeclamptic group and the never-pregnant group (7.9 +/- 0.56 v 6.2 +/- 0.36 and 4.1 +/- 0.36 ng/mL, respectively, P = .009 and P = <.0001). In conclusion, the free leptin concentration increases in normal pregnancy and is further increased in preeclampsia. This supports the hypothesis that biologically active leptin is elevated in normal pregnancy and is increased more in women with preeclampsia.