Longitudinal effects of MRI-measured hepatic steatosis on biomarkers of glucose homeostasis and hepatic apoptosis in obese youth

OBJECTIVE - We used fast-gradient magnetic resonance imaging (MRI) to determine the longitudinal associations between the hepatic fat content (HFF), glucose homeostasis, and a biomarker of hepatocellular apoptosis in obese youth. RESEARCH DESIGN AND METHODS - Baseline and longitudinal liver and abdominal MRI were performed with an oral glucose tolerance test in 76 obese youth followed for an average of 1.9 years. Cytokeratin-18 (CK-18) was measured at baseline and follow-up as a biomarker of hepatic apoptosis. The relationship between baseline HFF and metabolic parameters and circulating levels of CK-18 at follow-up were assessed using a bivariate correlation. RESULTS - At baseline, 38% had hepatic steatosis based on %HFF ≥5.5% with alterations in indices of insulin sensitivity and secretion. At follow-up, BMI increased in both groups and baseline %HFF correlated strongly with the follow-up %HFF (r = 0.81, P < 0.001). Over time, markers of insulin sensitivity and 2-h glucose improved significantly in the group without fatty liver, in contrastwith the persistence of the insulin resistance and associated correlates in the fatty liver group. Baseline HFF correlated with 2-h glucose (r = 0.38, P = 0.001), whole-body insulin sensitivity (r = 2 0.405, P = 0.001), adiponectin (r = 20.44, P < 0.001), CK-18 levels, ( r = 0.63, P < 0.001), and disposition index (r = 20.272, P = 0.021) at follow-up. In a multivariate analysis, we showed that baseline HFF is an independent predictor of 2-h glucose and whole-body insulin sensitivity. CONCLUSIONS - In obese youth, the phenotype of MRI-measured hepatic steatosis is persistent. Baseline HFF stronglymodulates longitudinally 2-h blood glucose, biomarkers of insulin resistance, and hepatocellular apoptosis.