Atherosclerosis – also known as the “hardening of arteries” – is a major cause of stroke and ischemic heart disease. While there is no cure for the condition, existing treatments are either invasive, inefficient, or serve only to delay it from progressing. Although gene regulation is an emerging therapeutic approach, the delivery of therapeutic gene cargoes to atherosclerotic plaque sites still needs to be optimised.

A team led by Professor Jonathan Choi Chung-hang, Associate Professor in the Faculty of Engineering’s Department of Biomedical Engineering at The Chinese University of Hong Kong (CUHK), developed a novel RNA nanoparticle to offer a potentially safe, effective treatment for atherosclerosis. Based on the research conducted in collaboration with Professor Tian Xiao-yu, Assistant Professor in the Faculty of Medicine’s School of Biomedical Sciences, the RNA nanoparticle can modulate genes related to atherogenesis, reducing and stabilising plaque without inducing severe toxicity. As a trailblazing project paving the way forward for the use of nucleic acid nanotechnology in the treatment of cardiovascular diseases, the research was recently published in The Proceedings of the National Academy of Sciences (PNAS).

Limitations of existing treatments

According to the World Health Organisation (WHO), stroke and ischemic heart disease accounted respectively for 11% and 16% of global mortality rates in 2020. In Hong Kong alone, heart disease has been the third-leading cause of death since the 1960s. A form of chronic inflammation, atherosclerosis is mainly induced by high levels of blood lipids. It results from the formation of atherosclerotic plaque, caused by the build-up of fats, cholesterol, and immune cells on the arterial wall. Such plaques can either narrow blood vessels to restrict blood flow or burst to form blood clots that block thinner arteries in the brain or heart, leading to stroke or ischemic heart disease.

Although surgical procedures such as balloon angioplasty and endarterectomy can be key in treating patients with atherosclerosis, they are invasive and inefficient in reducing multiple plaque sites. Lipid-lowering drugs such as statins can also be prescribed for lowering cholesterol, but they merely delay the condition from deteriorating.

Bypassing the bottleneck for gene delivery with nucleic acid nanotechnology

For the gene regulation approach to be successful in atherosclerosis treatment, there is the issue of inefficient gene delivery to consider. While current nanomedicines mostly employ cationic carriers to complex gene cargoes through electrostatic interactions, they are often bulky (larger than 100nm), which means they can be rapidly filtered by the liver and spleen following an intravenous injection before they reach the plaque – potentially inducing cytotoxicity.

To bypass this bottleneck, Professor Choi’s team applied nucleic acid nanotechnology to develop a smaller spherical nanoparticle (about 70nm) that includes a biocompatible iron oxide nanoparticle core and about 300 therapeutic microRNA-146a strands attached to the core’s surface. Experiments showed that besides naturally entering plaque cells without the aid of cationic transfection agents to facilitate the intracellular delivery of microRNA-146a, the novel RNA nanoparticle could also target class A scavenger receptors on macrophages and endothelial cells inside the plaque to achieve robust cellular entry.

According to Dr Shirley Bai Qian-qian, first author of the publication and PhD graduate in the Faculty of Engineering’s Department of Biomedical Engineering, “The unique receptor-targeting property of the RNA nanoparticles contributes to their elevated plaque accumulation of up to 1.2% of the injected dose – one of the highest in the field of nanomedicine.”

Alleviating atherosclerosis with intravenous injections of RNA nanostructures

In further experiments, repeated intravenous injections of the RNA nanoparticle into atherosclerotic plaque-bearing mice were found to not only regress and stabilise the plaques itself, but also downregulate genes related to immune response and vascular inflammation. After four weeks of treatment, there was no pronounced accumulation of RNA nanoparticles inside the major internal organs of mice, nor did it induce severe toxicity.

Professor Tian said, “The findings suggest that this RNA nanoparticle is a safe, effective agent to treat atherosclerosis, and it is now possible to design nucleic acid nanomedicines that are dual plaque targeting and therapeutic agents.”

Professor Choi added, “This study highlights the promise of nucleic acid nanotechnology to treat cardiovascular diseases. We hope to continue our collaboration with the CUHK Faculty of Medicine by validating the safety and efficacy of this RNA nanostructure in large animals. Ultimately, we hope to offer a safe, effective nanomedicine for patients.”

The project was supported by the Research Grants Council of Hong Kong, the CUHK Vice-Chancellor Discretionary Fund, the CUHK Chow Yuk Ho Technology Centre for Innovative Medicine, the National Nature Science Foundation of China, and the Croucher Innovation Award from the Croucher Foundation.

The research paper can be found at https://www.pnas.org/doi/10.1073/pnas.2201443119.