Abstract
Complement activation is a recognised mediator of myocardial ischaemia-reperfusion-injury (IRI) and cardiomyocytes are a known source of complement proteins including the central component C3, whose activation products can mediate tissue inflammation, cell death and profibrotic signalling. We investigated the potential to detect and quantify the stable covalently bound product C3d by external body imaging, as a marker of complement activation in heart muscle in a murine model of myocardial IRI. We used single-photon-emission-computed-tomography (SPECT) in conjunction with 99mTechnecium-labelled recombinant complement receptor 2 (99mTc-rCR2), which specifically detects C3d at the site of complement activation. Compared to control imaging with an inactive CR2 mutant (99mTc-K41E CR2) or an irrelevant protein (99mTc-PSMA) or using 99mTc-rCR2 in C3-deficient mice, the use of 99mTc-rCR2 in complement-intact mice gave specific uptake in the reperfused myocardium. The heart to skeletal muscle ratio of 99mTc-rCR2 was significantly higher than in the three control groups. Histological analysis confirmed specific uptake of 99mTc-rCR2. Following therapeutic inhibition of complement C3 activation, we found reduced myocardial uptake of 99mTc-rCR2. We conclude, therefore that 99mTc-rCR2 imaging can be used for non-invasive detection of activated complement and in future could be exploited to quantify the severity of myocardial damage due to complement activation.
Highlights
Complement activation is a recognised mediator of myocardial ischaemia-reperfusion-injury (IRI) and cardiomyocytes are a known source of complement proteins including the central component C3, whose activation products can mediate tissue inflammation, cell death and profibrotic signalling
It has been shown that myocardial reperfusion therapy in humans who suffer and subsequently die from acute myocardial infarction (AMI) is associated with significantly more complement deposition, suggesting that activation of complement in the ischaemic human myocardium may be enhanced by reperfusion[18]
Our results demonstrate the capability of SPECT imaging combined with radiolabelled Complement Receptor 2 (CR2) to detect in vivo complement C3 deposited the myocardium after the induction of cardiac IRI
Summary
99mTc-rCR2 SPCET/CT imaging detects C3d in hearts post IRI. To study the extent of complement activation in injured heart muscle, we used radiolabelled rCR2 to non-invasively image complement activation product after induction of IRI in a mouse model[24,25]. Results of SPECT/CT imaging starting at 1 hour after injection of Tc-labelled tracer injection and continuing for 45 minutes are shown in Fig. 1A and B and Supplementary Fig. 2a and b These show 99mTc-rCR2 uptake in the myocardium (position indicated by white arrows) of Group 1 mice, but not in control studies in Groups 2–5 mice. Group 1 hearts demonstrated significantly higher uptake (1.17 ± 0.11) as compared to Group 2, 99mTc-PSMA, (0.35 ± 0.03), Group 3, C3−/− (0.43 ± 0.05), or Group 4, Sham operated hearts (0.41 ± 0.05) (p < 0.0001) Both ex vivo biodistribution and non-invasive image quantification confirmed the data obtained by non-invasive SPECT-CT image analysis of the hearts (Fig. 1 and Supplementary Fig. 2).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
