Assessment of Myocardial Inflammation Produced by Experimental Coronary Occlusion and Reperfusion With ^99m Tc-RP517, a New Leukotriene B4 Receptor Antagonist That Preferentially Labels Neutrophils In Vivo

Abstract

Background-99m Tc-RP517 is a new leukotriene B 4 (LTB4) receptor antagonist developed for imaging acute inflammation or infection. A unique property of 99m Tc-RP517 is its ability to label white blood cells in vivo after intravenous injection. The goals of this study were to determine relative 99m Tc-RP517 binding to human leukocyte subtypes and the 99m Tc-RP517 uptake pattern in canine myocardium where inflammation was induced by either coronary occlusion and reperfusion or tumor necrosis factor ␣ (TNF␣) injection. Methods and Results-Fluorescence-activated cell sorter analysis was performed on whole human blood (nϭ2) and isolated neutrophils (nϭ4) with a fluorescent analog of 99m Tc-RP517, [F]-RP517. In whole blood, [F]-RP517 (500 nmol/L) preferentially labeled neutrophils. On isolated neutrophils, [F]-RP517 (10 nmol/L) binding was inhibited by 44% when LTB4 (400 nmol/L) was added.99m Tc-RP517 was injected intravenously in anesthetized, open-chest dogs before coronary occlusion (90 minutes) and reperfusion (120 minutes) (nϭ9) or before intramyocardial TNF␣ injection (nϭ3). Ex vivo images of heart slices were acquired. The left ventricle was divided into 72 segments for flow and 99m Tc-RP517 uptake analysis. There was an inverse exponential relationship between 99m Tc-RP517 uptake and occlusion flow (rϭ0.73). In the same 15 segments, 99m Tc-RP517 uptake was highly correlated with the neutrophil enzyme myeloperoxidase (rϭ0.91). Ex vivo images revealed tracer uptake in the reperfused area (ischemic to normal count ratioϭ2.7Ϯ0.2). Conclusions-RP517 binds to the neutrophil LTB4 receptor after intravenous injection. After reperfusion, 99m Tc-RP517 uptake correlated with myeloperoxidase and was observed on ex vivo images, indicating that this tracer may have potential as an inflammation-imaging agent. (Circulation. 2002;106:592-598.)

Reduction of infarct size and postischemic inflammation from ATL-146e, a highly selective adenosine A2Areceptor agonist, in reperfused canine myocardium

“…The effect of ATL-146e (1-1,000 nM) and ATL-146e ϩ rolipram (300 nM, Cedar Knolls, NJ) on neutrophil oxidative burst was assessed as previously described (35). The in vitro samples containing mixed leukocytes were gated for neutrophils by forward and side scatter, and the fluorescence of 10,000 neutrophils was measured in the FL1 channel of a FACScan (Becton-Dickinson) flow cytometer.…”

“…Thirty-two fasted, adult mongrel dogs (mean 23.3 Ϯ 0.6 kg, range 17.3-29.5 kg) were anesthetized with pentobarbital sodium (30 mg/kg iv), tracheally intubated, and mechanically ventilated with room air (Harvard Apparatus). Open-chest surgery and instrumentation were performed as previously described (8,35).…”

“…A control group of seven dogs had no treatment. Myocardial inflammation was assessed with the neutrophil tracer 99m Tc-RP517 35 and by postmortem immunohistochemical techniques. Before euthanasia, the LAD was briefly reoccluded and 40 ml of monastral blue dye were rapidly injected into the left atrial catheter to delineate the anatomic risk area.…”

“…After excision, the hearts were sliced evenly into four rings from apex to base and placed directly on the collimator of a gamma camera (Siemens Orbiter) for quantitative ex vivo imaging of 99m Tc-RP517 activity, as previously described (35). Determination of regional myocardial blood flow and 99m Tc-RP517 myocardial activity.…”

Real-time detection of implant-associated neutrophil responses using a formyl peptide receptor-targeting NIR nanoprobe

“…19,20 A leukotriene B4 receptor antagonist, 99m technetium-RP517, has exhibited a neutrophil targeting ability and has been developed for imaging acute myocardium inflammation. 21 Recently, optical imaging systems have been developed to target neutrophils. Specifically, studies have shown that the peptide cinnamoyl-Phe-(D)Leu-Phe-(D)Leu-Phe (cFLFLF) has a high affinity to the formyl peptide receptor (FPR) of neutrophils, 22 and that near-infrared (NIR)-conjugated cFLFLF can be used to detect activated neutrophils in a mouse model of ear inflammation.…”