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      Liver Enzymes Are Associated With Hepatic Insulin Resistance, Insulin Secretion, and Glucagon Concentration in Healthy Men and Women

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          The pathophysiological mechanisms to explain the association between risk of type 2 diabetes and elevated concentrations of γ-glutamyltransferase (GGT) and alanineaminotransferase (ALT) remain poorly characterized. We explored the association of liver enzymes with peripheral and hepatic insulin resistance, insulin secretion, insulin clearance, and glucagon concentration.


          We studied 1,309 nondiabetic individuals from the Relationship between Insulin Sensitivity and Cardiovascular disease (RISC) study; all had a euglycemic-hyperinsulinemic clamp and an oral glucose tolerance test (OGTT) with assessment of insulin secretion and hepatic insulin extraction. The hepatic insulin resistance index was calculated in 393 individuals.


          In both men and women, plasma concentrations of GGT and ALT were inversely related with insulin sensitivity ( M/ I) (all P < 0.01). Likewise, the hepatic insulin resistance index was positively correlated with both GGT ( r = 0.37, P < 0.0001, men; r = 0.36, P < 0.0001, women) and ALT ( r = 0.25, P = 0.0005, men; r = 0.18, P = 0.01, women). These associations persisted in multivariable models. Increased GGT and ALT were significantly associated with higher insulin secretion rates and with both reduced endogenous clearance of insulin and hepatic insulin extraction during the OGTT ( P = 0.0005 in men; P = 0.003 in women). Plasma fasting glucagon levels increased over ALT quartiles (men, quartile 4 vs. quartile 1 11.2 ± 5.1 vs. 9.3 ± 3.8 pmol/L, respectively, P = 0.0002; women, 9.0 ± 4.3 vs. 7.6 ± 3.1, P = 0.001).


          In healthy individuals, increased GGT and ALT were biomarkers of both systemic and hepatic insulin resistance with concomitant increased insulin secretion and decreased hepatic insulin clearance. The novel finding of a positive correlation between ALT and fasting glucagon level concentrations warrants confirmation in type 2 diabetes.

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          Insulin sensitivity indices obtained from oral glucose tolerance testing: comparison with the euglycemic insulin clamp.

          Several methods have been proposed to evaluate insulin sensitivity from the data obtained from the oral glucose tolerance test (OGTT). However, the validity of these indices has not been rigorously evaluated by comparing them with the direct measurement of insulin sensitivity obtained with the euglycemic insulin clamp technique. In this study, we compare various insulin sensitivity indices derived from the OGTT with whole-body insulin sensitivity measured by the euglycemic insulin clamp technique. In this study, 153 subjects (66 men and 87 women, aged 18-71 years, BMI 20-65 kg/m2) with varying degrees of glucose tolerance (62 subjects with normal glucose tolerance, 31 subjects with impaired glucose tolerance, and 60 subjects with type 2 diabetes) were studied. After a 10-h overnight fast, all subjects underwent, in random order, a 75-g OGTT and a euglycemic insulin clamp, which was performed with the infusion of [3-3H]glucose. The indices of insulin sensitivity derived from OGTT data and the euglycemic insulin clamp were compared by correlation analysis. The mean plasma glucose concentration divided by the mean plasma insulin concentration during the OGTT displayed no correlation with the rate of whole-body glucose disposal during the euglycemic insulin clamp (r = -0.02, NS). From the OGTT, we developed an index of whole-body insulin sensitivity (10,000/square root of [fasting glucose x fasting insulin] x [mean glucose x mean insulin during OGTT]), which is highly correlated (r = 0.73, P < 0.0001) with the rate of whole-body glucose disposal during the euglycemic insulin clamp. Previous methods used to derive an index of insulin sensitivity from the OGTT have relied on the ratio of plasma glucose to insulin concentration during the OGTT. Our results demonstrate the limitations of such an approach. We have derived a novel estimate of insulin sensitivity that is simple to calculate and provides a reasonable approximation of whole-body insulin sensitivity from the OGTT.
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            Is serum gamma glutamyltransferase a marker of oxidative stress?

            The primary role of cellular gamma glutamyltransferase (GGT) is to metabolize extracellular reduced glutathione (GSH), allowing for precursor amino acids to be assimilated and reutilized for intracellular GSH synthesis. Paradoxically, recent experimental studies indicate that cellular GGT may also be involved in the generation of reactive oxygen species in the presence of iron or other transition metals. Although the relationship between cellular GGT and serum GGT is not known and serum GGT activity has been commonly used as a marker for excessive alcohol consumption or liver diseases, our series of epidemiological studies consistently suggest that serum GGT within its normal range might be an early and sensitive enzyme related to oxidative stress. For example, serum and dietary antioxidant vitamins had inverse, dose-response relations to serum GGT level within its normal range, whereas dietary heme iron was positively related to serum GGT level. More importantly, serum GGT level within its normal range positively predicted F2-isoprostanes, an oxidative damage product of arachidonic acid, and fibrinogen and C-reactive protein, markers of inflammation, which were measured 5 or 15 years later, in dose-response manners. These findings suggest that strong associations of serum GGT with many cardiovascular risk factors and/or events might be explained by a mechanism related to oxidative stress. Even though studies on serum and/or cellular GGT is at a beginning stage, our epidemiological findings suggest that serum GGT might be useful in studying oxidative stress-related issues in both epidemiological and clinical settings.
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              Alanine Aminotransferase, γ-Glutamyltransferase, and Incident Diabetes

              OBJECTIVE To estimate and compare associations of alanine aminotransferase (ALT) and γ-glutamyltransferase (GGT) with incident diabetes. RESEARCH DESIGN AND METHODS ALT and GGT were studied as determinants of diabetes in the British Women's Heart and Health Study, a cohort of 4,286 women 60–79 years old (median follow-up 7.3 years). A systematic review and a meta-analysis of 21 prospective, population-based studies of ultrasonography, which diagnosed nonalcoholic fatty liver disease (NAFLD), ALT, and GGT as determinants of diabetes, were conducted, and associations of ALT and GGT with diabetes were compared. RESULTS Ultrasonography-diagnosed NAFLD was associated with more than a doubling in the risk of incident diabetes (three studies). ALT and GGT both predicted diabetes. The fully adjusted hazard ratio (HR) for diabetes per increase in one unit of logged ALT was 1.83 (95% CI 1.57–2.14, I 2 = 8%) and for GGT was 1.92 (1.66–2.21, I 2 = 55%). To directly compare ALT and GGT as determinants of diabetes, the fully adjusted risk of diabetes in the top versus bottom fourth of the ALT and GGT distributions was estimated using data from studies that included results for both markers. For ALT, the HR was 2.02 (1.59–2.58, I 2 = 27%), and for GGT the HR was 2.94 (1.98–3.88, I 2 = 20%), suggesting that GGT may be a better predictor (P = 0.05). CONCLUSIONS Findings are consistent with the role of liver fat in diabetes pathogenesis. GGT may be a better diabetes predictor than ALT, but additional studies with directly determined liver fat content, ALT, and GGT are needed to confirm this finding.

                Author and article information

                American Diabetes Association
                June 2011
                21 May 2011
                : 60
                : 6
                : 1660-1667
                1Service Endocrinologie-Diabétologie, Centre Hospitalo-Universitaire (CHU) Rennes, University Rennes 1, INSERM UMR 991, Rennes, France
                2Service Endocrinologie-Diabétologie, CHU d'Angers, Angers, France
                3Cardiometabolic Risk Unit, Institute of Clinical Physiology, National Research Centre (CNR), Pisa, Italy
                4Centre de Recherche en Nutrition Humaine, CRNH Rhône-Alpes, INSERM U 870-INRA 1235, Lyon, France
                5Clinical Division of Endocrinology and Metabolism, Department of Internal Medicine III, Medical University of Vienna, Vienna, Austria
                6Institute for Metabolic Research, Academic Teaching Institute of the Medical Faculty of Johann Wolfgang Goethe, University Frankfurt am Main, Frankfurt am Main, Germany
                7Institute of Biomedical Engineering, Padua, Italy
                8INSERM U1018, Centre de recherche en Épidémiologie et Santé des Populations (CESP) Centre for Research in Epidemiology and Population Health, Epidemiology of Diabetes, Obesity and Chronic Kidney Disease Over the Lifecourse and Determinants of Early Nutrition, Villejuif, France
                9University Paris Sud 11, UMRS 1018, Villejuif, France
                Author notes
                Corresponding author: Fabrice Bonnet, fabrice.bonnet@ 123456chu-rennes.fr .
                © 2011 by the American Diabetes Association.

                Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered. See http://creativecommons.org/licenses/by-nc-nd/3.0/ for details.


                Endocrinology & Diabetes


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