Macrophage-derived extracellular vesicles alter cardiac recovery and metabolism in a rat heart model of donation after circulatory death

Conditions to which the cardiac graft is exposed during transplantation with donation after circulatory death (DCD) can trigger the recruitment of macrophages that are either unpolarized (M0) or pro-inflammatory (M1) as well as the release of extracellular vesicles (EV). We aimed to characterize the effects of M0 and M1 macrophage-derived EV administration on post-ischaemic functional recovery and glucose metabolism using an isolated rat heart model of DCD. Isolated rat hearts were subjected to 20 min aerobic perfusion, followed by 27 min global, warm ischaemia or continued aerobic perfusion and 60 min reperfusion with or without intravascular administration of EV. Four experimental groups were compared: (1) no ischaemia, no EV; (2) ischaemia, no EV; (3) ischaemia with M0-macrophage-dervied EV; (4) ischaemia with M1-macrophage-derived EV. Post-ischaemic ventricular and metabolic recovery were evaluated. During reperfusion, ventricular function was decreased in untreated ischaemic and M1-EV hearts, but not in M0-EV hearts, compared to non-ischaemic hearts (p < 0.05). In parallel with the reduced functional recovery in M1-EV versus M0-EV ischaemic hearts, rates of glycolysis from exogenous glucose and oxidative metabolism tended to be lower, while rates of glycogenolysis and lactate release tended to be higher. EV from M0- and M1-macrophages differentially affect post-ischaemic cardiac recovery, potentially by altering glucose metabolism in a rat model of DCD. Targeted EV therapy may be a useful approach for modulating cardiac energy metabolism and optimizing graft quality in the setting of DCD.

Additional Heparin Preadministration Improves Cardiac Glucose Metabolism Suppression over Low-Carbohydrate Diet Alone in ¹⁸F-FDG PET Imaging

Adequate suppression of cardiac glucose metabolism increases the interpretability and diagnostic reliability of (18)F-FDG PET studies performed to detect cardiac inflammation and infection. There are no standardized guidelines, though prolonged fasting (>6 h), carbohydrate-restricted diets, fatty meals, and heparin loading all have been proposed. The aim of this study was to compare the 3 preparatory protocols used in our institution.

METHODS

(18)F-FDG PET scans were selected and grouped according to 3 preparatory protocols (50 consecutive scans per group): 6-h fast (group 1), low-carbohydrate diet plus 12-h fast (group 2), and low-carbohydrate diet plus 12-h fast plus intravenous heparin preadministration (50 IU/kg) (group 3). Consecutive scans were retrospectively included from time frames during which the particular protocol was used. Group 1 included oncologic indications, and groups 2 and 3 infection or inflammation detection. Cardiac segments for which inflammation or infection foci had been confirmed on other imaging modalities were excluded from the analysis. (18)F-FDG uptake in normal myocardium was scored according to a scale ranging from 0 (uptake less than that in left ventricle blood pool) to 4 (diffuse uptake greater than that in liver). Adequate suppression was defined as uptake less than that in liver and without any focus (scores 0-2).

RESULTS

Adequate suppression differed significantly between groups: 28% in group 1, 54% in group 2, and 88% in group 3 (P< 0.0001 for all comparisons).

CONCLUSION

Single-dose heparin administration before (18)F-FDG PET in addition to a low-carbohydrate diet significantly outperforms a low-carbohydrate diet alone in adequately suppressing cardiac glucose metabolism.