Injectable gel may help revive 'broken' hearts

Scientists have found an injectable gel that may help regrow cardiac muscles after heart attack.
The gel slowly releases short gene sequences known as microRNAs into the heart muscle, according to researchers at the University of Pennsylvania in the US.
After a heart attack, there is a dramatic loss of these heart muscle cells and those that survive cannot effectively replicate.
With fewer of these contractile cells, known as cardiomyocytes, the heart pumps less blood with each beat, leading to the increased mortality associated with heart disease.
For the study, published in the journal Nature Biomedical Engineering, the researchers used mouse models to demonstrate a new approach to restart replication in existing cardiomyocytes.

Though the reasons cardiomyocytes do not regenerate are not fully understood, the researchers used microRNAs that target signalling pathways related to cell proliferation.

They were able to inhibit some of the inherent "stop" signals that keep cardiomyocytes from replicating. This resulted in cardiomyocytes reactivating their proliferative potential.
With more heart cells dividing and reproducing, mice treated with this gel after heart attack showed improved recovery in key clinically relevant categories.
"Biologic drugs turn over very fast. The microRNAs that we used last less than eight hours in the bloodstream, so having a high local concentration has strong advantages," said Edward Morrisey, from the University of Pennsylvania.

Their short lifespan means that if patients were treated systemically, they would need to be injected frequently with large doses to ensure that a sufficient amount of microRNAs reaches their target in the heart.
Since these microRNAs are designed to promote cell proliferation, there would be a risk of tumour-producing, off-target effects.
"The most important traits of this gel are that it is shear-thinning and self-healing. Shear-thinning means it has bonds that can be broken under mechanical stress, making it more fluid and allowing it to flow through a syringe or catheter," said Jason Burdick, from the University of Pennsylvania.

"Self-healing means that when that stress is removed, the gel's bonds re-form, allowing it to stay in place within the heart muscle," Burdick said.