Supercritical Fluid Extraction of ¹¹C-Labeled Metabolites in Tissue Using Supercritical Ammonia

Abstract

Supercritical fluid extraction (SFE) of 11C-labeled tracer compounds and their metabolites from biological tissue was performed using supercritical ammonia in an attempt to develop a rapid extraction procedure that allowed subsequent analysis of the labeled metabolites. Metabolites were extracted from kidneys and brain in rats given in vivo injections of the radiotracers O-[2-11C]acetyl-L-carnitine and N-[11C]methylpiperidyl benzilate, respectively. Only a minimal sample pretreatment of the tissue was necessary, i.e., cutting into 10-20 pieces and mixing with the drying agent Hydromatrix, before it was loaded into the extraction vessel. Extraction efficiency was measured for SFE at temperatures over the range of 70-150 degrees C and a pressure of 400 bar. For O-[2-11C]acetyl-L-carnitine, 66% of the radioactivity was trapped in the collected fractions and 12% remained in the extraction vessel. For the more lipophilic N-[11C]methylpiperidyl benzilate, 93% of the activity was collected and less than 1% remained in the extraction vessel. Labeled metabolites were analyzed by LC and also, in the case, of O-[2-11C]acetyl-L-carnitine by LC/MS. The complete extraction procedure, from removal of the biological tissue until an extract was ready for analysis, was 25 min, corresponding to about one half-life of the radionuclide 11C.

Mass spectrometry in metabolome analysis

“…Supercritical fluid extraction (SFE) also presents a great potential to enhance the extraction of intracellular metabolites. SFE is increasingly being used for extraction of metabolites from plants (Reverchon, 1997;Sargenti & Lanças, 1997;Murga et al, 2000;Maraschin et al, 2001;Beek, 2002;Vaher & Koel, 2003), whereas there are only few examples of applying SFE to extract metabolites from animal tissues (Brooks & Uden, 1995;Jacobson et al, 1997;Stolker et al, 2002), filamentous fungi (Young & Games, 1993;Abdullah, Young, & Games, 1994), and microorganisms (Gharaibeh & Voorhees, 1996;Lim et al, 2002).…”

Supercritical fluids in medical radioisotope processing and chemistry, Part II: Applications – real and demonstrated

“…8 This application utilized supercritical ammonia in an attempt to develop a rapid extraction procedure that allowed subsequent analysis of the radioactive labeled metabolites after in vivo injection of O-[2-…”

Supercritical Fluid Chromatography and Extraction

“…Enhanced-fluidity liquid chromatography continues to be advanced by Olesik and co-workers ( − ). Miller and Hawthorne () and Smith and Burgess () used neat liquid water, pressurized and heated well above its normal boiling point, as mobile phase, finding it to easily transport alcohols, hydroxylbenzenes, amino acids, phenols, parabens, barbiturates, and other materials.…”

“…Huopalahti and Henion characterized anabolic steroids in bovine tissues (464). Jacobson et al used supercritical ammonia for the rapid characterization of radiolabeled metabolites in tissues (58,145).…”