Assessment of inflammatory response in ischemic-reperfused rat hearts using a ^99mTc-labeled peptide targeting neutrophil formyl-peptide receptor

Objectives The intense inflammatory reaction following myocardial infarction and reperfusion has been implicated as a crucial factor in contractile dysfunction and infarct extension. Proinflammatory cytokines released by injured myocardium, such as tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β), mediate recruitment of neutrophils and mononuclear cells to induce a local myocardial inflammation. Neutrophils are the first leukocytes to appear at the injured site and release more cytokines in response to ischemia-reperfusion injury. This study was designed to assess neutrophil-mediated myocardial inflammation using cFLFLF-PEG3.4-HYNIC-^99mTc (cFP), a newly developed probe targeting neutrophil formyl-peptide receptor.

Methods In vitro neutrophil targeting specificity of cFP was studied using isolated rat polymorphonuclear leukocytes (PMN). Rat ischemic heart models were created by ligating the left coronary artery (LCA) for 45 min. cFP (3-4 mCi) was i.v. given to the rats at 2 hr (n=6) and 24 hr (n=4), after onset of LCA reflow. SPECT cardiac images were acquired 2 hr after tracer injection, followed by ex vivo assays to delineate radioactive uptake related to PMN infiltration and cytokine upregulation in the ischemic-reperfused area (IRA) and remote healthy myocardium (HM).

Results cFP in freshly isolated PMN yielded a mean Kd value of 23.4 nM. SPECT images with cFP showed distinct focal radioactive accumulations in the IRA. The results of histological and cytokine assays revealed that cFP distribution was significantly enhanced in the IRA with up-regulated PMN infiltration, IL-1β and TNF-α expression. The ratio of IRA to HM cFP uptake at 2 hr and 24 hr after reperfusion was 5.89±0.22 and 3.77±0.14 (P<0.05).

Conclusions This study supports cFP as a specific SPECT imaging agent for detecting neutrophil-mediated inflammation in injured myocardium and understanding myocardial ischemia-reperfusion injury related to IL-1β and TNF-α.

Research Support NIH grants NHLBI R01-HL090716 and NIBIB P41-EB002035