Submitted on January 3, 2008
Accepted on May 14, 2008
Hepatic uptake and metabolism of galactose can be quantified in vivo by 2-[18F]Fluoro-2-deoxy-galactose Positron Emission Tomography
Michael Sorensen1*, Ole Lajord Munk2, Frank Viborg Mortensen3, Aage Kristian Olsen2, Dirk Bender2, Ludvik Bass4, and Susanne Keiding5
1 PET Center, Aarhus University Hospital, Aarhus, Denmark; Dept. of Medicine V, Aarhus University Hospital, Aarhus, Denmark
2 PET Center, Aarhus University Hospital, Aarhus, Denmark
3 Dept. of Surgery L, Aarhus University Hospital, Aarhus, Denmark
4 Dept. of Mathematics, University of Queensland, Brisbane, Queensland, Australia
5 PET Center, Aarhus University Hospital, Aarhus, Denmark; Dept. of Medicine V, Aarhus University Hospital, Denmark
* To whom correspondence should be addressed. E-mail: michael{at}pet.auh.dk.
Metabolism of galactose is a specialized liver function. The purpose of this PET study was to use the galactose analog 2-[18F]fluoro-2-deoxy-galactose, FDGal, to investigate hepatic uptake and metabolism of galactose in vivo.
FDGal kinetics was studied in 10 anaesthetized pigs at blood concentrations of non-radioactive galactose yielding approx. first-order kinetics (tracer only; n=4), intermediate kinetics (0.5 - 0.6 mmol galactose/L blood; n=2), and near-saturation kinetics (>3 mmol galactose/L blood; n=4). All animals underwent liver C15O PET (blood volume) and FDGal PET (galactose kinetics) with arterial and portal venous blood sampling. Flow rates in the hepatic artery and the portal vein were measured by ultrasound transit-time flow-meters. The hepatic uptake and net metabolic clearance of FDGal were quantified by non-linear and linear regression analyses.
The initial extraction fraction of FDGal from blood-to-hepatocyte was unity in all pigs. Hepatic net metabolic clearance of FDGal, KFDGal, was 332 - 455 mL blood/min/L tissue in experiments with approx. first-order kinetics and 15.2 - 21.8 mL blood/min/L tissue in experiments with near-saturation kinetics. Maximal hepatic removal rates of galactose was on average 600 µmol/min/L tissue (range 412 - 702) which was in agreement with other studies. There was no significant difference between KFDGal calculated using the dual tracer input or using the single arterial input.
In conclusion, hepatic galactose kinetics can be quantified with the galactose analog FDGal. At near-saturated kinetics, the maximal hepatic removal rate of galactose can be calculated from the net metabolic clearance of FDGal and the arterial blood concentration of galactose.
