Ultrasound-targeted sirolimus-loaded microbubbles improves acute rejection of heart transplantation in rats by inhibiting TGF-β1-Smad signaling pathway, promoting autophagy and reducing inflammation.

Acute rejection (AR) remains a pivotal complication and leading cause of mortality within the first year following heart transplantation (HT). In this study, we assessed the impact of ultrasound-targeted microbubbles loaded with sirolimus (SIR-MBs) on AR in a rat HT model and delved into the underlying mechanisms. We established a rat abdominal ectopic HT model, which was stratified into three groups receiveing the PBS, SIR-MBs + ultrasound-targeted microbubble destruction (UTMD), and sirolimus, respectively. The protective effects of each treatments on survival rate, inflammatory response, autophagy and TGF-β1-Smad signaling pathway-related proteins were evaluted. Additionally, rescue experiment was performed adding the autophagy inhibitor or TGF-β1 agonist in combination therapy. UTMD combined SIR-MBs mediated 15-fold higher local drug concentration compared to direct sirolimus administration. The infiltration of inflammatory cells in the transplanted hearts indicated that SIR-MBs combined with UTMD were effective in mitigating the inflammatory response, achieving levels significantly lower than those observed in the sirolimus group. Furthermore, after SIR-MBs combined with UTMD treatment, the expression levels of TGF-β1-Smad signaling pathway-related proteins in heart tissues also showed a significant decrease compared to the model control group. Conversely, the expressions of autophagy proteins LC3-II, Beclin-1 and β-arrestin showed an up-regulated trend. Rescue experiments also revealed that the enhancement in survival trends was markedly suppressed following the administration of CsA or SRI-011381, respectively. Collectively, our findings suggest that SIR-MBs combined with UTMD augment the local treatment efficacy for AR in rat HT models by inhibiting the TGF-β1-Smad signaling pathway, promoting autophagy, and alleviating inflammation.