Biomedical Engineering Reference
In-Depth Information
Early endosome pH 6-5.9
Late endosome pH 6-5
Recycling endosome pH 6-4
4
Phagosome
3
?
2
Lysosome pH 5.5-5
1
Phagolysosomal
target:
Cryptococcosis
Cytoplasmic targets:
Amastigotes (Chagas disease)/Apoptotic factors
Pathway to the nucleus/ L. monocytogenes /
recombinant S . typhimurium
5
Nucleus
ER
Caveosome pH 7
Golgi
: pH sensitive liposome
: clathrin dependent endocytic pathway (degradative). Numbers indicate
the sequence from uptake (1) to cytoplasmic delivery (5). 1,2,3,5
sequence means early endosomal escape.
: phagocytic pathway (degradative)
: caveolin dependent endocytic pathway (non-degradative)
: cytoplasmic acid-triggered release of liposomal aqueous content
FIGURE 20.2
Cell.uptake.mechanisms.
20.2 DOPE-ContainingLiposomes:AcidTriggering
theL α H II PhaseTransition
The.phase.behavior.of.lipids.depends.on.their.molecular.shape. 35,36 .Cylindric.lipids.self-
assemble.into.bilayers.(lamellar.phase.Lα),.and.those.with.a.cone.shape.(transversal.area.of.
the.headgroup.higher.than.the.transversal.area.of.acyl.chains).self-assemble.into.micelles..
In. particular,. the. unsaturated. dioleoylphosphatidylethanolamine. (DOPE). is. an. inverted.
cone.(small.and.poorly.hydrated.headgroup,.with.a.minor.transversal.area.compared.to.
that.of.acyl.chains).(Figure 20.3)..The.inverted.cone.shape.favors.the.formation.of.hydro-
gen.bonds.between.headgroups.of.DOPE.(amino.group.and.phosphate.group.of.adjacent.
DOPE).that.diminish.interfacial.hydration.and.favor.its.assemblage.into.an.inverted.hex-
agonal.phase.(H II )..At.physiological.pH.DOPE.molecules.do.not.form.bilayers,.and.above.
the.phase.transition.temperature.(T H .=.10°C),.they.adopt.the.H II. phase. 35,37
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