Short-Term Regulation of Lipocalin-2 but not RBP-4 During Oral Lipid Tolerance Test and Oral Glucose Tolerance Test

The postprandial regulation of lipocalin-2 and retinol binding protein-4 (RBP-4) by oral uptake of lipids and carbohydrates in healthy individuals has not yet been investigated. The regulation of lipocalin-2 and RBP-4 in 2 large cohorts of healthy volunteers during oral lipid tolerance test (OLTT; n=100) and oral glucose tolerance test (OGTT; n=100) was analyzed. One hundred healthy volunteers underwent OLTT and OGTT in an outpatient setting. Venous blood was drawn after 0, 2, 4, and 6 h in OLTT and after 0, 1, and 2 h in OGTT. In order to dissect carbohydrate-induced from lipid-induced effects, a novel OLTT solution completely free of carbohydrates and protein was applied. Subjects were characterized by anthropometric and laboratory parameters. Serum concentrations of lipocalin-2 and RBP-4 were measured by enzyme-linked immunosorbent assay (ELISA). Whereas RBP-4 levels remained unchanged during OGTT, lipocalin-2 concentrations significantly decreased during OGTT. During OLTT, RBP-4 levels were not influenced, whereas lipocalin-2 levels decreased significantly and stepwise. Fasting concentrations of RBP-4 were negatively correlated with BMI and waist-hip ratio, whereas lipocalin-2 levels were positively associated with BMI and waist-hip ratio. Female users of hormonal contraception had higher RBP-4 levels than females not on contraceptives. There is no significant short-term regulation of RBP-4 by orally ingested lipids or carbohydrates. Lipocalin-2 is downregulated after lipid and carbohydrate ingestion and this kind of regulation was not predicted by age, sex, triglycerides, glucose, or insulin levels.