Probing Different Lengths of the Tertiary Amine Head Group on Triglyceride-Mimetic Ionizable Lipid-Mediated siRNA Delivery

Lipid nanoparticles (LNPs) have been utilized to deliver small interfering RNA (siRNA) to treat acute liver injury. However, LNPs exhibit suboptimal lysosomal escape capabilities and biodegradability. To address these limitations, we have designed triglyceride-mimetic ionizable lipids by conjugating <i>N</i>,<i>N</i>-dimethyl tertiary amine head groups to the sn-2 position of triglyceride (TG) through ester bonds. These ionizable lipids were abbreviated as 2C-TG, 3C-TG, and 4C-TG, with <i>N</i>,<i>N</i>-dimethyl tertiary amine head groups located in the β-, γ-, and δ-positions of the ester linkage bond, respectively. The uniform-size LNPs were prepared by using the ethanol dilution method. Notably, the position of the tertiary amine head group within the carbon chain of triglyceride-mimetic ionizable lipids is found to significantly influence critical parameters, including the encapsulation rate, p<i>K</i>_a, cellular uptake, lysosomal escape, lipase release, and gene silencing efficiency. Our findings hold promise for improving the efficacy and safety of LNP-based siRNA therapeutics.