Validation of (99m)Tc-labeled "4+1" fatty acids for myocardial metabolism and flow imaging: Part 2. Subcellular distribution.
BACKGROUND
Our group has synthesized technetium-labeled fatty acids (FA) that are extracted into the myocardium and sequestered due to heart-type fatty acid binding protein (H-FABP) binding. In this article, we further address the detailed subcellular distribution and potential myocardial metabolism of [(99m)Tc]"4+1" FA.


METHODS
Experiments were conducted using isolated hearts of Wistar rats, as well as of wild-type and H-FABP(-/-) mice. Myocardium samples underwent subcellular fractionation [subsarcolemmal mitochondria (SM), intermyofibrillar mitochondria (IM), cytosol with microsomes, and nuclei and crude membranes] and analysis by thin-layer chromatography and high-performance liquid chromatography.


RESULTS
The largest fraction of tissue radioactivity was associated with cytosol [79.69+/-8.88% of infused dose]. About 9.07+/-0.95% and 3.43+/-1.38% of the infused dose were associated with SM and IM fractions, respectively. In the rat heart, etomoxir, an inhibitor of carnitin-palmitoyl transferase I, did not significantly decrease radioactivity associated with mitochondrial fractions, whereas myocardial extraction of [(123)I]-labeled 15-(p-iodophenyl)-pentadecanoic acid (13.26% vs. 49.49% in controls) and the radioactivity associated with the SM and IM fractions were blunted. The percentage of the infused dose in the mitochondrial and crude fractions increased with the number of NH-amide groups of the FA derivative. Absence of H-FABP significantly decreased radioactivity count in the cytosolic fraction (P<.001). No metabolic product of [(99m)Tc]"4+1" FA could be detected in any isolated heart.


CONCLUSIONS
Myocardial [(99m)Tc]"4+1" FA extraction reflects binding to H-FABP and membrane structures (including the mitochondrial membrane). However, the compounds do not undergo mitochondrial metabolism because they do not reach the mitochondrial matrix.
Mirtschink
Peter
P
Institute of Physiology, Medical Faculty Carl Gustav Carus, Technical University Dresden, 01307 Dresden, Germany. peter_mirtschink@web.de
Stehr
Sebastian N
SN
Walther
Martin
M
Pietzsch
Jens
J
Bergmann
Ralf
R
Pietzsch
Hans-Jürgen
HJ
Weichsel
Johannes
J
Pexa
Annette
A
Dieterich
Peter
P
Wunderlich
Gerd
G
Binas
Bert
B
Kropp
Joachim
J
Deussen
Andreas
A
D000577:Amides / Q000737:chemistry; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002334:Carnitine O-Palmitoyltransferase / Q000037:antagonists & inhibitors / Q000378:metabolism; D002417:Cattle; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004852:Epoxy Compounds / Q000494:pharmacology; D000074026:Fatty Acid Binding Protein 3; D050556:Fatty Acid-Binding Proteins / Q000378:metabolism; D005227:Fatty Acids / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism*; D005260:Female; D006321:Heart / Q000000981:diagnostic imaging / Q000187:drug effects; D066298:In Vitro Techniques; D042541:Intracellular Space / Q000187:drug effects / Q000378:metabolism*; D007553:Isotope Labeling; D008297:Male; D051379:Mice; D008928:Mitochondria / Q000378:metabolism; D055414:Myocardial Perfusion Imaging; D009206:Myocardium / Q000166:cytology* / Q000378:metabolism*; D015609:Organotechnetium Compounds / Q000737:chemistry*; D051381:Rats; D015203:Reproducibility of Results
D000577:Amides; D004791:Enzyme Inhibitors; D004852:Epoxy Compounds; C493409:Fabp3 protein, mouse; D000074026:Fatty Acid Binding Protein 3; D050556:Fatty Acid-Binding Proteins; D005227:Fatty Acids; D015609:Organotechnetium Compounds; D002334:Carnitine O-Palmitoyltransferase; C054207:etomoxir