Elevated Serum GGT Concentrations Predict Reduced Insulin Sensitivity and Increased Intrahepatic Lipids (original) (raw)

Horm Metab Res 2005; 37(4): 246-251
DOI: 10.1055/s-2005-861411

Original Clinical

© Georg Thieme Verlag KG Stuttgart · New York

C. Thamer1 , O. Tschritter1 , M. Haap1 , F. Shirkavand1 , J. Machann2 , A. Fritsche1 , F. Schick2 , H. Häring1 , M. Stumvoll1, 3

Further Information

Publication History

Received 21 June 2004

Accepted after revision 4 October 2004

Publication Date:
13 June 2005 (online)

Abstract

Elevated serum gamma-glutamyltransferase (GGT) concentrations have been related to features of the metabolic syndrome as well as increased risk of cardiovascular and liver disease. More recently, elevated GGT levels were shown to predict development of type 2 diabetes in a longitudinal study from Korea. The aim of the present study was to test the hypothesis that serum GGT is associated with glucose tolerance, insulin sensitivity and beta-cell function in a healthy, non-diabetic Caucasian population from the Tübingen family study. Insulin sensitivity was estimated by oGTT (n = 850) or measured by hyperinsulinemic euglycemic clamp (n = 245), respectively. A subgroup (n = 70) underwent additional determination of intrahepatic lipid content using 1H magnetic resonance spectroscopy. Serum GGT was positively correlated with two-hour glucose during oGTT (r = 0.15, p < 0.0001) and negatively correlated with insulin sensitivity from oGTT (r = - 0.31, p < 0.0001) and clamp (r = - 0.27, p < 0.0001). The relationship between GGT and insulin sensitivity remained significant after adjusting for sex, age, BMI, and AST using multivariate regression analysis. Inclusion of serum triglyceride levels as a parameter of lipid metabolism kept the relationship significant in the oGTT group (p < 0.0001), but not in the smaller clamp group (p = 0.11). Additionally, serum GGT was positively correlated with hepatic lipid content (r = 0.49, p < 0.001) independent of sex, age, BMI, AST or serum triglycerides. There was no significant correlation between GGT and the index for beta-cell function after adjusting for age, sex, BMI and insulin sensitivity (p = 0.74). In conclusion, elevated serum GGT levels predict glucose intolerance probably via insulin resistance rather than beta-cell dysfunction. This may be primarily related to hepatic insulin resistance and increased intrahepatic lipids. The association observed between elevated hepatic lipids and reduced insulin sensitivity might explain the increased diabetes risk observed in subjects with elevated serum GGT concentrations. In the absence of overt liver disease, elevated serum GGT concentrations may point the clinician to incipient disturbances in the glucose metabolism.

Key words

Intrahepatic lipids - Type 2 diabetes - Insulin resistance - Obesity - Gamma-glutamyltransferase

References

C. Thamer, M. D.

Medizinische Universitätsklinik

Otfried-Müller-Straße 10 · 72076 Tübingen · Germany

Phone: +49 (7071) 298 03 88

Fax: +49 (7071) 29 57 12

Email: claus.thamer@med.uni-tuebingen.de