Proinflammatory cytokines lower ^99mTc sestamibi retention and enhance the washout in isolated cardiomyocytes

Purpose: ^99mTc-Sestamibi is a myocardial perfusion tracer with prolonged myocardial retention due to mitochondrial binding. Inflammmation can affect mitochondrial function, which may in turn alter the kinetics of ^99mTc-sestamibi. We investigated the effects of pro-inflammatory cytokines on uptake and retention of ^99mTc-sestamibi in isolated cardiomyocytes and fibroblasts.

Methods: Neonatal rat cardiomyocytes (NRCM) and fibroblasts (NRFB) were isolated and maintained in optimal culture medium. After equilibration, cells were stimulated by increasing concentrations of interferon-γ (5, 10 or 25 ng/mL) or vehicle for 24 or 48 hours. ^99mTc-Sestamibi was added to the medium and incubated for 30min. Supernatant activity was measured at 30min, 90min, and 240min to determine tracer washout. Total retention was measured at 240min in cell lysate. All counts were normalized to protein content. Cell viability after treatment was assessed using ¹⁸F-deoxyglucose uptake.

Results: Control NRCM showed a normalized 99mTc-sestamibi retention of 1.7±0.5% injected dose (ID) at 30min and 0.6%ID at 240min. Stimulation with IFN-γ over 24h resulted in modestly decreased tracer uptake at 30min (25ng/ml, 1.3±0.5%ID, p=0.06) and significantly lower retention at 90min compared to control NRCM (%ID, 0.8±0.4 vs 1.1±0.4, p=0.04). Consistently, washout was accelerated compared to control (%, 90min: 38±10 vs 32±6, p=0.06; 240min 72±5 vs 68±5, p=0.04). Longer pro-inflammatory stimulation resulted in modest NRCM hypertrophy. ^99mTc-Sestamibi uptake was further decreased compared to matched control NRCM (%ID, 30min: 1.4±0.1 vs 1.7±0.2, p= 0.08; 90min: 0.6±0.1 vs 0.9±0.3, p=0.003; 240min: 0.2±0.1 vs 0.4±0.3, p=0.001), while washout rate was higher (%, 90min: 57±5 vs 45±7, p=0.003; 240min: 86±3 vs 75±12, p=0.026). Decreased retention and elevated washout were also observed with low and intermediate doses of IFN-γ. By contrast, inflammatory cytokines affected neither retention nor washout in NRFB. ¹⁸F-Deoxyglucose displayed similar uptake between IFN-γ stimulated and control cells, supporting maintained viability. Conclusion: Cardiomyocyte stress induced by inflammatory cytokines lowers retention and enhances washout of ^99mTc-sestamibi in culture, likely reflecting mitochondrial dysfunction. These findings suggest that kinetics of ^99mTc-sestamibi may be sensitive to inflammation, and should be considered when interpreting myocardial perfusion images.