Biosynthetic gas vesicles as a novel ultrasound contrast agent for diagnosing and treating myocardial infarction.

Rationale: Myocardial contrast echocardiography (MCE) plays an important role in diagnosis of myocardial infarction (MI). However, its accuracy is limited by image quality because microbubble-based MCE produces negative contrast enhancement in the infarcted myocardial tissue. This study aimed to develop nanoscale gas vesicles (GVs) from Halobacteria NRC-1 (hGVs) and GV-expressing genetically engineered E. coli (eGVs) and compare their imaging performance with commercial Sonovue in MI rats.

Methods

We developed nanoscale gas vesicles (GVs) from Halobacteria NRC-1 (hGVs) and GV-expressing genetically engineered E. coli (eGVs) and compared their imaging performance with Sonovue in MI rats. Unlike SF₆-filled Sonovue, GVs are air-filled protein nanobubbles with unique shapes. We used immunofluorescence and TEM to examine GVs' distribution in myocardial tissue and analyzed the mechanisms of their penetration into infarcted areas. Additionally, we evaluated the potential of oxygen delivery to ischemic myocardium using ultrasound-targeted bubble destruction.

Results

hGVs produced significantly positive contrast enhancement and could last for a longer time in the infarcted area. Immunofluorescence and TEM examination confirmed that hGVs penetrated out the blood vessels into the ischemic myocardium and eGVs primarily retained around endothelial cells, while Sonovue could not pass through the damaged vessels. Mechanistic analysis revealed that inflammatory cytokines results in leaky blood vessels, facilitating the penetration of nanoscale GVs into the infarcted myocardial tissue. Moreover, hGVs exhibited excellent imaging performance across different pathological stages, especially during the inflammatory phase. More importantly, oxygen delivery into the ischemic myocardium through ultrasound-targeted bubble destruction technology greatly promoted the functional recovery of the ischemic myocardium.

Conclusions

hGVs demonstrated superior imaging performance and penetration capabilities specifically at the myocardial infarction sites in rats.Their ability to provide positive contrast and deliver oxygen via ultrasound-targeted bubble destruction enables improved diagnosis and treatment of MI.