Validation of [18F]fluorodeoxyglucose and positron emission tomography (PET) for the measurement of intestinal metabolism in pigs, and evidence of intestinal insulin resistance in patients with morbid obesity.

AIMS/HYPOTHESIS: The role of the intestine in the pathogenesis of metabolic diseases is gaining much attention. We therefore sought to validate, using an animal model, the use of positron emission tomography (PET) in the estimation of intestinal glucose uptake (GU), and thereafter to test whether intestinal insulin-stimulated GU is altered in morbidly obese compared with healthy human participants. METHODS: In the validation study, pigs were imaged using [(18)F]fluorodeoxyglucose ([(18)F]FDG) and the image-derived data were compared with corresponding ex vivo measurements in tissue samples and with arterial-venous differences in glucose and [(18)F]FDG levels. In the clinical study, GU was measured in different regions of the intestine in lean (n = 8) and morbidly obese (n = 8) humans at baseline and during euglycaemic hyperinsulinaemia. RESULTS: PET- and ex vivo-derived intestinal values were strongly correlated and most of the fluorine-18-derived radioactivity was accumulated in the mucosal layer of the gut wall. In the gut wall of pigs, insulin promoted GU as determined by PET, the arterial-venous balance or autoradiography. In lean human participants, insulin increased GU from the circulation in the duodenum (from 1.3 ± 0.6 to 3.1 ± 1.1 µmol [100 g](-1) min(-1), p < 0.05) and in the jejunum (from 1.1 ± 0.7 to 3.0 ± 1.5 µmol [100 g](-1) min(-1), p < 0.05). Obese participants failed to show any increase in insulin-stimulated GU compared with fasting values (NS). CONCLUSIONS/INTERPRETATION: Intestinal GU can be quantified in vivo by [(18)F]FDG PET. Intestinal insulin resistance occurs in obesity before the deterioration of systemic glucose tolerance.

Proteinuria modifies the effects of physical activity on total and cardiovascular disease mortality rates in patients with type 2 diabetes.

AIMS/HYPOTHESIS: Physical activity reduces cardiovascular disease (CVD) and total mortality rates in patients with type 2 diabetes. However, it is not known whether or not the effects of physical activity on mortality rates depend on the presence of proteinuria in type 2 diabetic patients. METHODS: We prospectively followed up 577 patients with type 2 diabetes who were aged 45 to 64 years and were free of CVD at baseline. Participants were stratified according to the presence of proteinuria (300 mg/l) and the degree of physical activity (0-4 metabolic equivalent tasks [MET] or >4 MET). The Cox proportional hazards model was used to estimate the association of physical activity and proteinuria with risk of mortality. RESULTS: During the 18-year follow-up, 356 patients died, of whom 217 died from CVD. Physically more active patients had significantly reduced total, CVD and CHD mortality rates if they did not have proteinuria. In contrast, physically active proteinuric patients had significantly increased total and CVD mortality rates (HR 1.83, 95% CI 1.00-3.36, p=0.049) in univariate analyses, with HR 2.43 (95% CI 1.09-5.40, p=0.030) in multivariate analyses. CONCLUSIONS/INTERPRETATION: Physical activity reduces total and CVD mortality rates in type 2 diabetic patients without proteinuria. However, in proteinuric patients, no protective effect was observed. Larger studies are needed to confirm the latter finding and to define which exercise intensity leads to possible harmful effects.