Serum retinol binding protein 4 is negatively related to estrogen in Chinese women with obesity: a cross-sectional study

Background: The association between serum Retinol Binding Protein 4 (RBP4) and obesity is still controversial. Serum RBP4 levels varies by gender, and estradiol may play a role in the difference. To investigate the participation of sex hormones in the association of RBP4 and obesity in humans, we measured serum RBP4, BMI, and sex hormones in 87 women from the outpatient. Methods: Eighty-seven subjects of Chinese women origin from the outpatient (aged 40.22 +/- 15.54 years) were enrolled. Subjects with diseases affecting the metabolic state or not suitable to participate in this study were excluded. Anthropometrics and laboratory tests, including lipid profile, luteinizing hormone (LH), follicle stimulating hormone (FSH), prolactin (PRL), estradiol (E2), progesterone (PROG), testosterone (TESTO), and dehydroepiandrosterone (DHEA) were conducted. Serum RBP4 was detected by an enzyme immunoassay kit and validated by quantitative Western blotting. Results: Circulating RBP4 levels were positively associated with BMI, waist circumference, waist-to-hip ratio (WHR), systolic and diastolic (SBP), diastolic blood pressure (DBP), triglycerides (TG), low high-density lipoprotein cholesterol(LDL-c), and testosterone (TESTO) in the total group. While only in obese individuals, serum RBP4 levels were negatively associated with E2. The highest value was in the subjects with both obesity and the low estrogen level. Multiple linear regression analysis revealed that RBP4 correlated independently with TG, TC and insulin in all subjects, TC in non-obese individuals. However, E2 were significantly associated with serum RBP4 only in obese individuals. Conclusions: RBP4 could be a marker of obesity-related factors; estrogen was negatively related to RBP4 and might be one of the influential factors.