Detection of inflammation induced by myocardial ischemia-reperfusion using a dual-domain cytokine radioligand via TNF and IL-1 pathways

Objectives TNFR2-Fc-IL-1ra, a dual-domain fusion protein, contains soluble tumor necrosis factor receptor-2 (TNFR2) and interleukin-1 receptor antagonist (IL-1ra), and it binds to inflammatory sites via TNF and IL-1 pathways. This study was designed to assess the capability of ^99mTc-labeled TNFR2-Fc-IL-1ra (TFcI) for detection of inflammation in ischemic-reperfused rat hearts compared to the two individual cytokine radioligands, ^99mTc-TNFR2-Fc (TFc) and ^99mTc-IL-1ra-Fc (IFc).

Methods The fusion proteins were conjugated with NHS-HYNIC and specifically labeled with ^99mTc. Using a rat heart model with 45-min ischemia and 2-hr reperfusion (IR) (n=4), TFcI and ¹¹¹In-labeled polymorphonuclear neutrophils (¹¹¹In-PMN) isolated from donor rats were injected i.v. to assess the correlation between TFcI uptake and leukocyte infiltration. Dynamic cardiac images of TFcI, TFc, and IFc were acquired using a small-animal SPECT imager in rats with IR (n=5 per group). Inflammatory response in the hearts was determined by histologic assay.

Results A significant correlation of TFcI vs. PMN distribution was observed in the ischemic-reperfused hearts (P<0.001). SPECT images with each radioligand exhibited distinct focal radioactive accumulations in the hearts. TFcI showed more potent affinity with enhanced uptake in the ischemic-reperfused sites. The radioactivity ratios of infarcted myocardium to remote viable myocardium were 13.11±1.72 for TFcI, 7.44±1.42 for IFc, and 9.64±0.39 for TFc (both P<0.05 vs. TFcI).

Conclusions Targeting proinflammatory sites with TFcI may provide a specific approach for noninvasive detection of inflammation in hearts with ischemia-reperfusion injury.