Impaired Insulin Clearance as the Initial Regulator of Obesity-Associated Hyperinsulinemia: Novel Insight Into the Underlying Mechanism Based on Serum Bile Acid Profiles
To investigate the roles of insulin clearance and insulin secretion in the development of hyperinsulinemia in obese subjects and to reveal the association between insulin clearance and bile acids (BAs).
RESEARCH DESIGN AND METHODS
In cohort 1, insulin secretion, sensitivity and endogenous insulin clearance were evaluated with an oral glucose tolerance test (OGTT) in 460 recruited participants. In cohort 2, 81 participants underwent an intravenous glucose tolerance test (IVGTT) and a hyperinsulinemic-euglycemic clamp to assess insulin secretion, endogenous and exogenous insulin clearance, and insulin sensitivity. Based on insulin resistance levels ranging from mild to severe, nondiabetic obese participants were further divided into 10 quantiles in cohort 1 and into tertiles in cohort 2. Forty serum BAs were measured in cohort 2 to examine the association between BAs and insulin clearance.
All obese participants had impaired insulin clearance, and it worsened with additional insulin resistance in nondiabetic obese subjects. However, insulin secretion was unchanged from quantile 1 to 3 in cohort 1, and no difference was found in cohort 2. After adjustments for all confounding factors, serum conjugated BAs, especially glycodeoxycholic acid (GDCA, β=-0.335, P=0.004) and taurodeoxycholic acid (TDCA, β=-0.333, P=0.003), were negatively correlated with insulin clearance. The ratio of unconjugated to conjugated BAs (UnconBA/ConBA, β=0.335, P=0.002) was positively correlated with insulin clearance.
Hyperinsulinemia in obese subjects might be primarily induced by decreased insulin clearance rather than increased insulin secretion. Changes in circulating conjugated BAs, especially GDCA and TDCA, might play an important role in regulating insulin clearance.