In Vivo Imaging of Human ^sup 11^C-Metformin in Peripheral Organs: Dosimetry, Biodistribution, and Kinetic Analyses

• Published in: The Journal of nuclear medicine (1978) Vol. 57; no. 12; p. 1920
• Main Authors: Gormsen, Lars C, Sundelin, Elias Immanuel, Jensen, Jonas Brorson, Vendelbo, Mikkel Holm, Jakobsen, Steen, Munk, Ole Lajord, Christensen, Mette Marie Hougaard, Brøsen, Kim, Frøkiaer, Jørgen, Jessen, Niels
• Format: Journal Article
• Language: English
• Published: New York Society of Nuclear Medicine 01.12.2016
• Subjects: Dosimetry; Medical imaging; Prescription drugs; Reaction kinetics; Tissues; Tomography
• ISSN: 0161-5505

Metformin is the most widely prescribed oral antiglycemic drug, with few adverse effects. However, surprisingly little is known about its human biodistribution and target tissue metabolism. In animal experiments, we have shown that metformin can be labeled by ^sup 11^C and that ^sup 11^C-metformin PET can be used to measure renal function. Here, we extend these preclinical findings by a first-in-human ^sup 11^C-metformin PET dosimetry, biodistribution, and tissue kinetics study. Methods: Nine subjects (3 women and 6 men) participated in 2 studies: in the first study, human radiation dosimetry and biodistribution of ^sup 11^C-metformin were estimated in 4 subjects (2 women and 2 men) by whole-body PET. In the second study, 11C-metformin tissue kinetics were measured in response to both intravenous and oral radiotracer administration. A dynamic PET scan with a field of view covering target tissues of metformin (liver, kidneys, intestines, and skeletal muscle) was obtained for 90 (intravenous) and 120 (oral) min. Results: Radiation dosimetry was acceptable, with effective doses of 9.5 μSv/MBq (intravenous administration) and 18.1 μSv/MBq (oral administration). Whole-body PET revealed that ^sup 11^C-metformin was primarily taken up by the kidneys, urinary bladder, and liver but also to a lesser extent in salivary glands, skeletal muscle, and intestines. Reversible 2-tissue-compartment kinetics was observed in the liver, and volume of distribution was calculated to be 2.45 mL/mL (arterial input) or 2.66 mL/mL (portal and arterial input). In the kidneys, compartmental models did not adequately fit the experimental data, and volume of distribution was therefore estimated by a linear approach to be 6.83 mL/mL. Skeletal muscle and intestinal tissue kinetics were best described by 2-tissue-compartment kinetics and showed only discrete tracer uptake. Liver ^sup 11^C-metformin uptake was pronounced after oral administration of the tracer, with tissue-to-blood ratio double what was observed after intravenous administration. Only slow accumulation of ^sup 11^C-metformin was observed in muscle. There was no elimination of ^sup 11^C-metformin through the bile both during the intravenous and during the oral part of the study. Conclusion: ^sup 11^C-metformin is suitable for imaging metformin uptake in target tissues and may prove a valuable tool to assess the impact of metformin treatment in patients with varying metformin transport capacity.