Mechanistic insights into interactions between ionizable lipid nanodroplets and biomembranes

Delivery of RNA into cells using lipid nanoparticles (LNPs) has been a significant breakthrough in RNA-based medicine, with clinical applicability expanded through the use of ionizable lipids (ILs). These unique lipids can alter their charge state in response to pH changes, which is crucial for pH-triggered endosomal escape and effective lipid-mediated RNA delivery. In this study, we conducted a comprehensive set of molecular dynamics (MD) simulations to investigate interactions between IL-containing lipid nanodroplets (LNDs) and cell membrane models. Using an atomistic resolution model, we investigated the merging process of LNDs with cell membrane models under neutral conditions relevant to an intercellular environment and acidic pH conditions found in late endosomes. Our observations revealed that at neutral pH, LNDs merged with lipid membranes while preserving the bilayer structure. Under acidic conditions, the LNDs remained attached to the bilayer without fusing into the membranes. Importantly, the presence of ILs did not disrupt the original biomembrane structure during the simulation period. The MD simulations provided valuable atomistic insights into the mechanism of interaction between IL-containing nanodroplets and biomembranes, which could aid the rational design of ILs to develop more efficient LNPs for RNA therapies.

利用脂质纳米颗粒（lipid nanoparticles, LNPs）将RNA递送入细胞，是RNA药物研发领域的一项重大突破，而可电离脂质（ionizable lipids, ILs）的应用进一步拓展了其临床应用潜力。这类特殊脂质可随pH环境变化改变自身带电状态，这一特性对于pH触发的内涵体逃逸以及脂质介导的高效RNA递送至关重要。本研究开展了一系列全面的分子动力学（molecular dynamics, MD）模拟，以探究携带可电离脂质的脂质纳米液滴（lipid nanodroplets, LNDs）与细胞膜模型之间的相互作用机制。研究采用全原子分辨率模型（atomistic resolution model），分别模拟了与细胞间环境相符的中性pH条件，以及晚期内涵体中存在的酸性pH条件下，脂质纳米液滴与细胞膜模型的融合过程。观测结果表明：在中性pH环境中，脂质纳米液滴可与脂质双层膜发生融合，且完整保留双层膜结构；而在酸性条件下，脂质纳米液滴仅附着于双层膜表面，并未发生膜融合事件。值得注意的是，在整个模拟周期内，可电离脂质的存在并未破坏原始生物膜的结构。本项分子动力学模拟为揭示携带可电离脂质的纳米液滴与生物膜的相互作用机制提供了宝贵的全原子尺度的机制洞察，可为合理设计可电离脂质以开发更高效的RNA治疗用脂质纳米颗粒提供理论支撑。