Charge-switching ionizable lipids lower the toxicity of lipid nanoparticles

Lipid nanoparticles (LNPs) have great potential as nucleic acid delivery vehicles; however, they trigger the production of inflammatory cytokines, which limits their medical applications. Developing non-inflammatory LNPs is challenging because the LNP's ionizable lipid and the process of endosomal disruption are the major sources of LNP toxicity but are also essential for delivering nucleic acids. Here we demonstrate that ionizable lipids containing a carboxylic acid and an amine (termed S-lipid) switch their charged state between the pHs of 7.4 and 4.0, allowing them to generate LNPs (termed switchable nanoparticles) that efficiently encapsulate nucleic acid and trigger endosomal release without activation of the TLR4, complement, galectin-8 and platelet activating factor signalling pathways. Finally, we demonstrate that switchable nanoparticles are better at treating lipopolysaccharide-induced acute lung injury than traditional LNPs because they do not exacerbate pre-existing inflammation. Collectively, these results demonstrate that negatively charged ionizable lipids can mitigate the toxicity of LNPs.