Volume 139, Issue 3, Pages 846-856.e6 (September 2010) Fatty Acid Metabolism in the Liver, Measured by Positron Emission Tomography, Is Increased in Obese Individuals  Patricia Iozzo, Marco Bucci, Anne Roivainen, Kjell Någren, Mikko J. Järvisalo, Jan Kiss, Letizia Guiducci, Barbara Fielding, Alexandru G. Naum, Ronald Borra, Kirsi Virtanen, Timo Savunen, Piero A. Salvadori, Ele Ferrannini, Juhani Knuuti, Pirjo Nuutila  Gastroenterology  Volume 139, Issue 3, Pages 846-856.e6 (September 2010) DOI: 10.1053/j.gastro.2010.05.039 Copyright © 2010 AGA Institute Terms and Conditions

Figure 1 (A) Configuration of the model used to derive the rate constants (K1–k5) describing the fractional inward/backward movement of FA from plasma into the tissue and between the cytoplasm, and the lipid and oxidative pool compartments. (B) A representative example of arterial and portal venous concentrations of 11C-palmitate over time showing that the curves converge after the first sampling minutes (expanded time scale on the right). (C) The model fit to the measured tissue 11C-palmitate time-activity curve shows that the mathematic derivation predicts the measured tracer kinetics with excellent approximation; the tracer radioactivity in each model compartment also is shown, as derived from the estimated rate constants in one study animal. Gastroenterology 2010 139, 846-856.e6DOI: (10.1053/j.gastro.2010.05.039) Copyright © 2010 AGA Institute Terms and Conditions

Figure 2 Comparison showing that the model predicted hepatic uptake and oxidative or nonoxidative metabolism of FA is similar to values obtained by direct measurement of arterial-portal vs hepatic venous substrate and products differences. Gastroenterology 2010 139, 846-856.e6DOI: (10.1053/j.gastro.2010.05.039) Copyright © 2010 AGA Institute Terms and Conditions

Figure 3 The effects of insulin on the hepatic FA model rate constants (top) document a direct suppression of the fractional release of labeled TG (magnified graph), whereas liver FA uptake and metabolic fluxes (bottom) are suppressed by indirect inhibition of circulating FA levels by insulin. Values are given as mean ± standard error of the mean. Gastroenterology 2010 139, 846-856.e6DOI: (10.1053/j.gastro.2010.05.039) Copyright © 2010 AGA Institute Terms and Conditions

Figure 4 (A) Representative 2-dimensional and 3-dimensional PET-CT images of hepatic 11C-palmitate distribution, allowing optimal visualization of the portal vein. (B) The arterial input function (left) is used to estimate a dual-input function with the approach shown in Supplementary Figure 2, and the estimated is compared with the measured curve on the right. (C) The comparison between FA flux rates (mean ± standard error of the mean) obtained with the original vs estimated dual- vs single-arterial input functions, showing good correspondence between the first 2, and an underestimation in the parameters derived from the third approach. Gastroenterology 2010 139, 846-856.e6DOI: (10.1053/j.gastro.2010.05.039) Copyright © 2010 AGA Institute Terms and Conditions

Figure 5 (A) Metabolic flux rates of FA in the liver in obese and control subjects (mean ± standard error of the mean), showing a 2-fold increase in hepatic FA oxidation in the former group, leading to the relative shift in favor of the oxidative vs esterification pathway, as shown in panel B, given as percentages on the right and rate constants on the left. (C) Lipolytic rates, as determined from 11C-palmitate arterial and portal venous plasma levels (left); the difference between the 2 measurements (right) represents the visceral contribution. Gastroenterology 2010 139, 846-856.e6DOI: (10.1053/j.gastro.2010.05.039) Copyright © 2010 AGA Institute Terms and Conditions

Figure 6 (A) Regression analyses in 15 human subjects show significant positive relationships between hepatic FA oxidative metabolism and indexes of insulin resistance, and (B) between hepatic FA esterification and extrahepatic lipolysis. (C) The visceral FA contribution to the liver appears dependent on the mass of the corresponding fat depot, and not on that of total body fat. Gastroenterology 2010 139, 846-856.e6DOI: (10.1053/j.gastro.2010.05.039) Copyright © 2010 AGA Institute Terms and Conditions

Supplementary Figure 1 Study design in the animal investigation. The imaging or sampling procedures are listed on the left, and the sampling times are specified on the right. The red thick line at top indicates frequent blood sampling for the determination of the arterial and portal venous input functions. Labeled products were determined in samples collected simultaneously from the carotid artery and portal and hepatic veins. TR indicates the PET transmission scan, followed by 11C-palmitate injection and dynamic emission scan. Gastroenterology 2010 139, 846-856.e6DOI: (10.1053/j.gastro.2010.05.039) Copyright © 2010 AGA Institute Terms and Conditions

Supplementary Figure 2 Flowchart representation of the sequence of operations and compartmental model used to estimate parameters describing the dual from the arterial input function in human beings (steps 1 and 2). These parameters subsequently were used to create new dual-input functions and to estimate liver FA metabolism (step 4), the results of which were compared with those from the originally measured image-derived, dual-input function. Gastroenterology 2010 139, 846-856.e6DOI: (10.1053/j.gastro.2010.05.039) Copyright © 2010 AGA Institute Terms and Conditions

Supplementary Figure 3 Regression analyses between the model-predicted hepatic oxidative or nonoxidative metabolism of FA and the related pools and processes. Gastroenterology 2010 139, 846-856.e6DOI: (10.1053/j.gastro.2010.05.039) Copyright © 2010 AGA Institute Terms and Conditions