Lipid nanoparticles (LNPs) are currently in the spotlight as delivery systems for mRNA therapeutics and have been used in the Pfizer/BioNTech and Moderna COVID-19 vaccines. mRNA-LNP formulations have been indicated to require strict control, including maintenance at fairly low temperatures during their transport and storage. Since it is a new pharmaceutical modality, there is a lack of information on the systematic investigation of how storage and handling conditions affect the physicochemical properties of mRNA-LNPs and their protein expression ability. In this study, using the mRNA-LNPs with standard composition, we evaluated the effects of temperature, cryoprotectants, vibration, light exposure, and syringe aspiration from the vials on the physicochemical properties of nanoparticles in relation to their in vitro/in vivo protein expression ability. Among these factors, storage at −80 °C without a cryoprotectant caused a decrease in protein expression, which may be attributed to particle aggregation. Exposure to vibration and light also caused similar changes under certain conditions. Exposure to these factors can occur during laboratory and hospital handling. It is essential to have sufficient knowledge of the stability of mRNA-LNPs in terms of their physical properties and protein expression ability at an early stage to ensure reproducible research and development and medical care.

Delivery of messenger RNA (mRNA) using lipid nanoparticles (LNPs) is expected to be applied to various diseases following the successful clinical use of the mRNA COVID-19 vaccines. This study aimed to evaluate the effect of the cholesterol molar percentage of mRNA-LNPs on protein expression in hepatocellular carcinoma-derived cells and in the liver after intramuscular or subcutaneous administration of mRNA-LNPs in mice. For mRNA-LNPs with cholesterol molar percentages reduced to 10 mol% and 20 mol%, we formulated neutral charge particles with a diameter of approximately 100 nm and polydispersity index (PDI) <0.25. After the intramuscular or subcutaneous administration of mRNA-LNPs with different cholesterol molar percentages in mice, protein expression in the liver decreased as the cholesterol molar percentage in mRNA-LNPs decreased from 40 mol% to 20 mol% and 10 mol%, suggesting that reducing the cholesterol molar percentage in mRNA-LNPs decreases protein expression in the liver. Furthermore, in HepG2 cells, protein expression decreased as cholesterol in mRNA-LNPs was reduced by 40 mol%, 20 mol%, and 10 mol%. These results suggest that the downregulated expression of mRNA-LNPs with low cholesterol content in the liver involves degradation in systemic circulating blood and decreased protein expression after hepatocyte distribution.

Intratracheal (i.t.) administration, which takes advantage of the specific structure of the respiratory system, can effectively deliver nanoparticles to the lung. Much remains unknown about the i.t. administration of messenger RNA (mRNA)-lipid nanoparticles (LNPs) and the effect of lipid composition. In this study, we administered minute amounts of mRNA-LNP solutions into mice intratracheally and investigated the effect of lipid composition on protein expression in the lungs. We first validated higher protein expression with mRNA-LNP compared to that with mRNA-PEI complex and naked mRNA. Then, we evaluated the influence of lipid composition of LNPs on the protein expression and found that: 1) decreasing the PEG molarity from 1.5% to 0.5% could significantly increase the protein expression; 2) replacing DMG-PEG with DSG-PEG could slightly increase the protein expression; 3) using DOPE instead of DSPC could increase protein expression by an order of magnitude. We successfully prepared an mRNA-LNP with optimal lipid compositions that led to robust protein expression following i.t. administration, thus providing meaningful insights into advanced development of mRNA-LNPs for therapeutic i.t. administration.