Noninvasive Whole-Body Imaging of Phosphatidylethanolamine as a Cell Death Marker Using 99mTc-Duramycin During TNF-Induced SIRS

Systemic inflammatory response syndrome (SIRS) is an inflammatory state affecting the whole body. It is associated with the presence of pro- and antiinflammatory cytokines in serum, including tumor necrosis factor (TNF). TNF has multiple effects and leads to cytokine production, leukocyte infiltration, and blood pressure reduction and coagulation, thereby contributing to tissue damage and organ failure. A sterile mouse model of sepsis, TNF-induced SIRS, was used to visualize the temporal and spatial distribution of damage in susceptible tissues during SIRS. For this, a radiopharmaceutical agent, Tc-99m-duramycin, that binds to exposed phosphatidylethanolamine on dying cells was longitudinally visualized using SPECT/CT imaging. Methods: C57BL/6J mice were challenged with intravenous injections of murine TNF or vehicle, and necrostatin-1 was used to interfere with cell death. Two hours after vehicle or TNF treatment, mice received Tc-99m-duramycin intravenously (35.44 +/- 3.80 MBq). Static whole-body Tc-99m-duramycin SPECT/CT imaging was performed 2, 4, and 6 h after tracer injection. Tracer uptake in different organs was quantified by volume-of-interest analysis using PMOD software and expressed as SUVmean. After the last scan, ex vivo biodistribution was performed to validate the SPECT imaging data. Lastly, terminal deoxynucleotidyl-transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL) staining was performed to correlate the obtained results to cell death. Results: An increased Tc-99m-duramycin uptake was detected in mice injected with TNF, when compared with control mice, in lungs (0.55 +/- 0.1 vs. 0.34 +/- 0.05), intestine (0.75 +/- 0.13 vs. 0.56 +/- 0.1), and liver (1.03 +/- 0.14 vs. 0.64 +/- 0.04) 4 h after TNF and remained significantly elevated until 8 h after TNF. The imaging results were consistent with ex vivo gamma-counting results. Significantly increased levels of tissue damage were detected via TUNEL staining in the lungs and intestine of mice injected with TNF. Interestingly, necrostatin-1 pretreatment conferred protection against lethal SIRS and reduced the Tc-99m-duramycin uptake in the lungs 8 h after TNF (SUV, 0.32 +/- 0.1 vs. 0.51 +/- 0.15). Conclusion: This study demonstrated that noninvasive Tc-99m-duramycin SPECT imaging can be used to characterize temporal and spatial kinetics of injury and cell death in susceptible tissues during TNF-induced SIRS, making it useful for global, whole-body assessment of tissue damage during diseases associated with inflammation and injury.