Biomedical Engineering Reference
In-Depth Information
O
N +
Cl -
O
O
H
O
N
O
O
DODMA
DOTAP
O
O
O
O
P
O
P
O -
O
O
O
O
O
NH +
N +
O -
O
H
O
H
O
O
Egg PC
DOPE
O
O
O
P
O
H
O
O
H
(OCH 2 CH 2 ) 45 OCH 3
O -
O
H
NH +
H
H
HO
O
Cholesterol
mPEG-DSPE
Figure 24.3
Chemical.structures.of.commonly.used.lipids.
siRNA.(Koynova.and.Tenchov.2010,.Dominska.and.Dykxhoorn.2010,.Huang.and.Liu.2011)..
According.to.the.head.group,.cationic.lipids.can.be.divided.into.two.classes:.conditionally.
ionizable.and.permanently.ionized.cationic.lipids,.which.are.based.on.tertiary.and.quater-
nary.amines,.respectively.(Heyes.et.al..2005,.Semple.et.al..2010).
Generally.speaking,.simple.electrostatic.complexes.of.siRNA.and.cationic.lipid.are.not.
suitable.for.systemic.administration.because.of.their.poor.serum.stability.and.cytotoxicity..
Therefore,.sophisticated.formulation.strategies.need.to.be.developed..Typically,.a.lipophilic.
derivative.of.polyethylene.glycol.(PEG).is.used.to.sterically.stabilize.LNPs..Neutral.lipids,.
including.egg.phosphatidylcholine.(Egg.PC),.cholesterol,.and.dioleoyl-phosphatidyletha-
nolamine.(DOPE),.are.used.to.improve.the.stability.of.the.LNPs.or,.in.the.case.of.DOPE,.to.
promote.endosomal.escape..Some.commonly.used.lipids.are.shown.in.Figure.24.3.
24.5 Synthesis of siRNA-LNPs
Lipid. nanoparticles. are. formed. via. electrostatic. interactions. between. the. cationic. lipids.
and.the.anionic.siRNA..Due.to.similarities.between.AS-ODN.and.siRNA,.the.approaches.
designed.for.synthesis.of.ODN.loaded.LNPs.can.be.adapted.to.synthesis.of.siRNA-LNPs..
Several. techniques. have. been. reported. for. synthesis. of. ODN-based. LNPs,. including.
detergent.dialysis.(Wu.and.McMillan.2009),.ethanol.dilution/dialysis.(Maurer.et.al..2001),.
freeze-thaw.(Yamada.et.al..2005),.and.thin-ilm.hydration.(Podesta.and.Kostarelos.2009)..
Typically,.lipids.and.ODNs.spontaneously.assemble.into.heterogeneous.nanostructures.in.
the.bulk.phase..Sometimes.the.complex.formation.is.carried.out.in.40%.ethanol.to.facilitate.
particle.formation.followed.by.dilution.or.removal.of.the.ethanol.by.dialysis..Post-processing,.
such.as.sonication.or.extrusion,.which.reduces.particle.size.and.size.distribution.is.often.
required.. Consequently,. novel. one-step. engineering. approaches. capable. of. achieving.
controlled.mixing.are.desirable..Recently,.our.lab.developed.a.microluidic.hydrodynamic.
focusing.(MHF).technology.to.synthesize.ODN.LNPs.(Koh.et.al..2010)..The.MHF.synthesis.
 
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