The gut microbial metabolite phenylacetylglycine protects against cardiac injury caused by ischemia/reperfusion through activating β2AR

Background: Myocardial ischemia/reperfusion (I/R) injury is closely related to cardiomyocyte Apoptosis. Stimulating β2 Adrenergic Receptor (β2AR) can effectively combat cardiomyocyte Apoptosis. Previous studies demonstrate that the gut microbial metabolite phenylacetylglycine (PAGly) can stimulate β2AR. However, the effect of PAGly on myocardial I/R injury remains unknown.

Methods: The hypoxia/reoxygenation (H/R) model was established using the neonatal mouse cardiomyocytes (NMCMs). Different doses of PAGly were used to treat NMCMs, and Apoptosis was detected by terminal deoxynucleotidyl transferase-mediated nick end labeling (TUNEL) staining. Additionally, the level of cyclic adenosine monophosphate (cAMP) was examined by using a cAMP detection kit. Mouse model of myocardial I/R injury was established in C57BL/6 mice, and different doses of phenylacetic acid were administrated intraperitoneally. Apoptosis of myocardial cells was detected by TUNEL and α-actin staining. The area at risk and the infarct areas were identified by 2,3,5-triphenyltetrazolium chloride (TTC) and Evans blue staining. Western blotting was used to measure the protein expression levels of phosphorylated phosphatidylinositol 3-kinase (p-PI3K), total Akt (t-Akt), phosphorylated Akt (p-AKT), Bcl-2-associated X protein (Bax), B-cell lymphoma-2 (Bcl-2), cleaved Caspase-3.

Results: PAGly significantly suppressed H/R injury-induced Apoptosis in NMCMs and inhibited Apoptosis in myocardial I/R injured mice in vivo. We verified that PAGly activated the anti-apoptotic Gαi/PI3K/Akt signaling cascade in NMCMs via stimulating β2AR signaling. Continuous administration of PAGly at an appropriate dose could inhibit Apoptosis and reduce the infarct size resulting from I/R injury in mice. However, high-dose PAGly treatment was associated with a higher mortality rate. Moreover, we demonstrated that Aspirin reduced the infarct size and the high mortality caused by high doses of PAGly in I/R injured mice.

Conclusions: These findings suggest that treatment with the gut microbial metabolite PAGly could suppress cardiomyocyte Apoptosis caused by myocardial I/R injury and reduce the infarct size, which provides a novel therapeutic strategy for patients with myocardial infarction.

Apoptosis; Myocardial ischemia/reperfusion (I/R); Phenylacetylglycine (PAGly); β2 adrenergic receptor (β2AR).