Successful reprogramming of cellular protein production through mRNA delivered by functionalized lipid nanoparticles

Inside the core, the main part of the ionizable cationic lipid, cholesterol (dependent on its concentration), water and mRNA are present.

“Inside the core, the main part of the ionizable cationic lipid, cholesterol (dependent on its concentration), water and mRNA are present.”

The isotropic LNP core consists for 24% (volume fraction) of water.

“Interestingly, their research indicates that the isotropic LNP core consists for 24% (volume fraction) of water.”

The mRNA is -at least partly- exposed to water inside the LNPs, which likely contributes to its instability upon storage under non-frozen conditions.

“This would mean that the mRNA is –at least partly– exposed to water inside the LNPs, which likely contributes to its instability upon storage under non-frozen conditions (Arteta et al., 2018).”

A key aspect of LNPs is the presence of lipids in the core, although water is also present to some extent.

“A key aspect of LNPs and the characteristic that makes them different from liposomes (spherical vesicles with at least one lipid bilayer and an aqueous core) is the presence of lipids in the core, although data from several studies indicate that water is also present to some extent (Yanez Arteta et al., 2018, Kulkarni et al., 2018, Brader et al., 2021).”

Arteta et al. found that DSPC and PEG-lipid as well as part of the ionizable cationic lipid and cholesterol are located on the surface of the LNPs.

“They found that 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and PEG-lipid as well as part of the ionizable cationic lipid and cholesterol are located on the surface of the LNPs.”

In mRNA-LNP formulations, the fraction of accessible mRNA is very low and encapsulation efficiencies are typically > 90%.

“In mRNA-LNP formulations, such as those used in mRNA vaccines, the fraction of accessible mRNA is very low (Yanez Arteta et al., 2018, Patel et al., 2020) and thus, encapsulation efficiencies, derived from RiboGreen assays, are typically > 90%.”

The shell of Arteta et al.'s mRNA-LNPs is a monolayer.

“Another interesting finding by Arteta et al. is that the shell of their mRNA-LNPs is a monolayer (Yanez Arteta et al., 2018, Verbeke et al., 2019).”

mRNA LNPs with enriched DSPC content at the surface (approaching an almost pure monolayer of DSPC) exhibit weak transfection capacity.

“By contrast, mRNA LNPs with an enriched DSPC content at the surface (approaching an almost pure monolayer of DSPC) exhibited a weak transfection capacity.”

By adjusting the molar ratios of different lipids, mRNA LNPs with varying surface characteristics can be produced.

“Interestingly, by adjusting the molar ratios of the different lipids, the authors could produce mRNA LNPs with varying surface characteristics.”

The core of these LNPs is surrounded by a lipid monolayer containing mainly DSPC and DMPE-PEG2000, as well as a fraction of D-Lin-MC3-DMA and cholesterol.

“This core was surrounded by a lipid monolayer containing mainly the DSPC and DMPE-PEG2000 content, as well as a fraction of D-Lin-MC3-DMA and cholesterol [113].”

LNP compositions that favour partial segregation of D-Lin-MC3-DMA from the internal core to the outer surface correlate with increased transfection efficiency.

“They found that LNP compositions that favour a partial segregation of D-Lin-MC3-DMA lipids from the internal core to the outer surface, correlated with an increased transfection efficiency.”

mRNA LNPs based on D-Lin-MC3-DMA, DSPC, cholesterol and a PEG-lipid exhibit a disordered inverse hexagonal phase containing D-Lin-MC3-DMA, cholesterol, water and mRNA.

“In another study, Yanez Arteta et al. indicated that the structural arrangement of mRNA LNPs based on D-Lin-MC3-DMA, DSPC, cholesterol and a PEG-lipid exhibited a disordered inverse hexagonal phase containing D-Lin-MC3-DMA, cholesterol, water and mRNA.”