Myocardial extraction of a new type of technetium-labeled fatty acids

Introduction: Newly developed technetium-labeled fatty acid analogues are promising agents for myocardial metabolism imaging. We tested the myocardial extraction of ^99mTc analogues of rhenium model complexes synthesized according to the '4+1' mixed-ligand approach (see presentation M. Walther et al.) in a guinea pig heart LANGENDORFF model

Materials and Methods: Firstly 30 min of steady state perfusion with 10 ml/min of normotherm Krebs-Henseleit-Buffer enriched with 0,1 % albumin was performed. Isolated guinea pig heart were then perfused with fatty acid tracers for 180 seconds in a 1:100 ratio. The venous effluate was collected in intervals of 15 s for 225 s following the start of tracer infusion. Perfusion was stopped, the heart was dissected into atria and ventricle compartments and γ-activity was measured. Eight new (C₁₁, C₁₂, C₁₅, C₁₀S, C₁₁S, C₁₂S, C₁₄S, C₁₆S) and for known control substances (¹²³I-IPPA, ¹²³I-BMIPP, ^99mTc-MIBI, ^99mTc-DTPA) were tested in this model (n=3-5).

Results: All eight substances showed acceptable extractions rates. Especially experiments with the C₁₁ (39.8 %), but also C₁₂ (14.8 %)and C₁₁S (17.1 %) fatty acid analogues showed excellent results.

Conclusion: When compared with extraction rates for IPPA determined with the same set-up, extraction for the C₁₁ and ₁₁S compounds is 3 fold and 1.3 fold, respectively. These results confirm our hypothesis that the "4+1" Tc(III) chelate unit is promising tool for the Tc-labelling of fatty acids. Further experiments with different species are planned to elucidate exact myocardial uptake mechanisms.