Renal Cortical Glucose Uptake Is Decreased in Insulin Resistance and Correlates Inversely With Serum Free-fatty Acids

Studies on human renal metabolism are scanty. Nowadays, functional imaging allows the characterization of renal metabolism in a non-invasive manner. We have recently demonstrated that [18F]FDG-PET can be used to analyze renal glucose uptake rates (GU), and that the renal cortex is an insulin sensitive tissue.To confirm that renal GU is decreased in people with obesity, and to test whether circulating metabolites are related to renal GU.18 people with obesity and 18 non-obese controls were studied with [18F]FDG-PET during insulin clamp. Renal scans were obtained ∼60 min after [18F]FDG injection. Renal GU was measured using fractional uptake rate and after correcting for residual intratubular [18F]FDG. Circulating metabolites were measured using high-throughput proton NMR metabolomics.Cortical GU was higher in healthy non-obese controls compared to people with obesity (4.7 [3.4-5.6] vs 3.1 [2.2-4.3], p = 0.004, respectively), and it associated positively with the degree of insulin sensitivity (M value) (r = 0.42, p = 0.01). Moreover, cortical GU was inversely associated with circulating β-OH-butyrate (r = -0.58, p = 0.009), acetoacetate (r = -0.48, p = 0.008), citrate (r = -0.44, p = 0.01) and free fatty acids (FFA) (r = -0.68, p < 0.0001), even when accounting for the M value. On the contrary, medullary GU was not associated with any clinical parameters.These data confirm differences in renal cortical GU between people with obesity and healthy non-obese controls. Moreover, the negative correlations between renal cortex GU and FFA, ketone bodies and citrate are suggestive of substrate competition in the renal cortex.