99mTc-Hynic-annexin V imaging to evaluate inflammation and apoptosis in rats with autoimmune myocarditis

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Abstract
Inflammation and cell death are two important components of myocarditis. We evaluated the distribution of inflammation and apoptotic cell death in rats with autoimmune myocarditis using two radiotracers – technetium-99m Hynic-annexin V (99mTc-annexin) as a marker of apoptotic cell death and carbon-14 deoxyglucose (14C-DG) as a marker of inflammation – in comparison with histologic findings. Three, 7 and 14 weeks after immunization with porcine cardiac myosin (acute, subacute, and chronic phases, respectively) 99mTc-annexin and 14C-DG were injected. The uptake in the total heart was determined as the percentage of injected dose per gram (% ID/g) by tissue counting. Dual-tracer autoradiography with 99mTc-annexin and 14C-DG was performed. The distribution of each of these agents was compared with the results of hematoxylin and eosin staining to identify areas of inflammation, and TUNEL staining to identify areas of apoptosis. Total cardiac uptake of 99mTc-annexin in the acute phase of myocarditis was significantly higher than that in normal rats (1.28%±0.30% vs 0.46%±0.01%; PP=NS). Total cardiac uptake of 14C-DG in the acute phase of myocarditis was significantly higher than that in normal rats (2.78%±0.95% vs 1.02%±0.25%; PP14C-DG uptake; some also corresponded to areas of high 99mTc-annexin uptake in the acute phase of myocarditis. 99mTc-annexin localization was strongly correlated with the number of TUNEL-positive cells (Pr=0.83), but the uptake of 14C-DG showed no relationship with it. There is a marked difference in the distribution of inflammation and apoptotic cell death in the myocardium of animals with immune myocarditis. These changes are mirrored by the localization of 14C-DG and 99mTc-annexin. Sites of inflammation and zones of apoptotic cell death change over the course of immune myocarditis.

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