Serum γ-glutamyl transpeptidase is a determinant of insulin resistance independently of adiposity in Pima Indian children

Abstract

Context: Elevated activities of serum enzymes, including alanine aminotransferase (ALT), aspartate aminotransferase (AST), and γ-glutamyltransferase (GGT), have been associated with obesity and insulin resistance (IR). ALT is an independent predictor of type 2 diabetes mellitus (T2DM) in adult Pima Indians, and GGT predicts T2DM in other adult populations. Objective: Our aim was to establish whether independent relationships exist between either adiposity or IR and hepatic enzymes in a group of Pima Indian children. Subjects and Methods: In a cross-sectional study, 44 children (22 males and 22 females; 7-11 yr old) were measured for weight (WT), height, percent body fat, and serum activities of ALT, AST, and GGT. Body mass index (kilograms per meter squared) was calculated. IR was calculated from fasting plasma concentrations of glucose and insulin using the homeostasis model assessment (HOMA-IR). Results: Hepatic enzymes were positively associated with obesity measures, fasting insulin, and HOMA-IR. GGT was additionally associated with serum lipids and white blood cell count. GGT, but not AST or ALT, was a significant determinant of HOMA-IR independently of age, sex, and WT, body mass index, or percent body fat. The model that accounted for the largest portion of the variance in HOMA-IR included WT (β = 0.004; P = 0.008) and GGT (β = 0.20; P = 0.004; total R 2 = 0.62; P < 0.0001). Conclusion: Significant relationships between adiposity and hepatic enzyme activities exist during childhood in Pima Indians. Whether serum GGT activity predicts the development of T2DM in these children remains to be determined in follow-up studies. Copyright © 2006 by The Endocrine Society.