Background Exosomes -– nano-sized, lipidvesicles released by cells into the blood – can protect the myocardium against ischaemia/reperfusion (IR) injury.¹ This cardioprotection is mediated by heat shock protein 70 (HSP70) on the exosome surface interacting with Toll-like receptor 4 (TLR-4) on cardiomyocytes and activating intracellular protective signalling kinases.¹ Polymersomes are synthetic nanovesicles with a structural similarity to exosomes, and the capacity to function as drug delivery vehicles.

Aim The aim of this project was to develop polymersomes functionalized with HSP70 peptides as “synthetic exosomes” with a potential therapeutic application against IR injury.

Methods POEGMA-PDPA polymersomes were synthesised from hydrophilic poly[oligo (ethylene glycol) methacrylate] and poly[2-(diisopropylamino)ethyl methacrylate] blocks, and covalently functionalized with either KSTGKANKITITNDKGRLSK (“KST”) or TKDNNLLGRFELSG (“TKD”) peptides from HSP70. They were analysed using Nanosight LM10-HS nanoparticle tracking analysis (NTA) and dynamic light scattering (DLS). Adult rat ventricular cardiomyocytes were pre-treated with polymersomes, then subjected to simulated IR. Percentage cell death was assessed using a vital dye and fluorescent microscopy.

Results In line with previously published data, pre-incubation with recombinant HSP70 protected cardiomyocytes from simulated IR injury, significantly reducing cell death from 74+-4% to 44+-1% (P < 0.001) with maximal protection observed at 1 ng/ml HSP70 equivalent to molar concentration of 14.3 pM. Cytoprotection was blocked in the presence of TAK-242, an inhibitor of TLR4 (83+-3%). The average size of polymersomes was ~70 nm (DLS) or 80–90 nm (NTA), and they expressed ~145 peptides per polymersome. Pre-incubation with KST- or TKD- functionalized polymersomes reduced death of cardiomyocytes exposed to simulated IR from 62+-3% to 38+-4% or 42+-4% respectively (P < 0.001). Significant protection was observed even at 10⁸ particles /ml, representing a concentration of 0.17 pM particles, or 0.025 pM of HSP70 peptide. No protection was recorded with non-functionalized polymersomes.

Conclusion Polymersomes with HSP70-derived peptide sequences are non-toxic to cardiomyocytes and powerfully cardioprotective in a cell model of acute IR injury. Future ex vivo and in vivo experiments are required for pre-clinical assessment of these novel nanoparticles, before potential translational application.

Reference

1. Vicencio et al. Plasma exosomes protect the myocardium from ischemia-reperfusion injury, J Am Coll Cardiol. 2015;65(2015):1525–36