Leptin plays an important role in the regulation of body weight and is known to circulate in both free and bound forms. One of the leptin receptor isoforms exists in a circulating soluble form that can bind leptin. Clinical studies have shown that soluble leptin receptor (sOB-R) levels are lower in obese individuals. In the present study, we measured the serum sOB-R level in 419 healthy Japanese subjects (198 men and 221 women, aged 30 to 65 years, body mass index [BMI] 21.7 ± 2.6 [SD] kg/m2) and in 150 type 2 diabetic patients (96 men and 54 women, BMI 24.3 ± 3.8 kg/m2). We investigated the relationships between serum sOB-R level and BMI, blood pressure, homeostasis model assessment-insulin resistance index (HOMA-IR), serum leptin and adiponectin levels, lipid profile, and leptin receptor (LEPR) gene Lys109Arg and Gln223Arg polymorphisms. Serum leptin and sOB-R levels were measured by radioimmunoassay (RIA) and enzyme-linked immunosorbent assay (ELISA), respectively. The serum sOB-R level in men was significantly higher than that in women. The serum sOB-R level was negatively correlated with BMI, fasting insulin, HOMA-IR, and serum leptin level and positively correlated with high-density lipoprotein (HDL)-cholesterol and serum adiponectin levels. The correlations between serum sOB-R level and fasting insulin, HOMA-IR, serum leptin, adiponectin, and HDL-cholesterol levels were significant even after adjustment for age, sex, and BMI in healthy subjects. There was no association between serum sOB-R level and the LEPR polymorphisms examined. These findings suggest that the serum sOB-R level is negatively correlated with HOMA-IR and serum leptin level and positively correlated with HDL-cholesterol level and serum adiponectin level, independent of age, sex, and BMI, in the Japanese population.
ASJC Scopus subject areas
- Endocrinology, Diabetes and Metabolism