Biomedical Engineering Reference
In-Depth Information
chronic.clinical.forms.of.the.disease.(Figure 20.2)..Current.trypanocidal.therapy.based.on.
the. irst-line. benznidazole. (BNZ). fails. to. eliminate. the. amastigote. forms,. contributing. to.
the. perpetuation. of. the. infection.
156
. In. 2005,. our. research. group. in. Argentina. employed.
pH-sensitive. liposomes. (DOPE/CHEMS,. 6:4,. ~400. nm). to. deliver. the. hypoxic. cell. radio-
sensitizer.2-nitroimidazole.etanidazole.(ETZ).to.an.acute.murine.model.of.Chagas.disease..
The. pH-sensitive. liposomes. should. increase. the. eficiency. of. treatment. by. allowing. the.
delivery.of.trypanocidal.drugs.to.the.cytoplasm..BNZ,.a.2-nitroimidazol.that.dissolves.in.
liposomal. bilayers,. was. replaced. by. the. hydrophilic. ETZ,. which. allows. its. dissolution. in.
the.inner.aqueous.space.of.liposomes..It.was.previously.determined.that.ETZ.is.not.a.suit-
able.trypanocidal.agent,.as.judged.by.its.LD
50
.on.trypomastigotes.and
.
IC
50
.on.intracellular.
amastigotes. upon. 48. h. incubation:. ETZ. was. 8.2-fold. less. active. on. RA. trypomastigotes,.
and. 23.5-fold. (amastigote-infected. Vero. cells). and. 15-fold. (amastigote-infected. J774. cells).
less. active. than. BNZ.
157
. However,. when. incorporated. in. DOPE/CHEMS. liposomes,. both.
in.vitro.and.in.vivo.trypanocidal.activities.of.ETZ.dramatically.increased.above.those.of.
free. ETZ. and. BNZ.. While. free. ETZ. (200. µg/ml). lacks. antiamastigote. activity. (aa). when.
loaded. in. pH-sensitive. liposomes,. the. aa. is. increased. to. 72%. on. amastigote-infected. J774.
cells. after. only. 2 h. incubation.. ETZ. pH-sensitive. liposomal. treatment. (i.v.. administration.
of.0.56.mg.of.ETZ/kg,.starting.5.days.postinfection.(p.i.),.3.days.a.week.over.3.weeks).sig-
niicantly.decreased.the.parasitemia.on.days.12,.19,.21,.and.23.of.Balb/c.mice.infected.with.
50.trypomastigotes.of.the.RA.strain..A.one.hundred.eighty-fold.higher.dose.of.free.ETZ.
does.not.decrease.parasitemia.
158
.Moreover,.ETZ.pH-sensitive.liposomal.treatment.(3.2.mg.
of.ETZ.(293.μg.of.liposomal.lipid)/mouse).leads.to.the.complete.elimination.of.parasitemia.
of.mice.infected.with.10
2
.trypomastigotes.of.the.Tulahuen.strain..The.same.dose.of.empty.
liposomes.or.free.ETZ.had.no.effect.on.parasitemia.(unpublished.results)..ETZ.pH-sensitive.
liposomal.therapy.remains.to.be.tested.against.higher-infecting.inoculums.from.different.
T. cruzi
.strains,.in.both.the.acute.and.the.indeterminate.and.chronic.stages.of.the.disease.
20.8.2 Systemic Cryptococcosis
Cryptococcosis. is. a. serious. and. potentially. fatal. fungal. disease. caused. by. the. opportu-
nistic.fungal.pathogen.
Cryptococcus neoformans
..
C. neoformans
.is.found.almost.exclusively.
in.macrophages.of.hosts.with.chronic.or.latent.infection..Upon.
C. neoformans
.being.taken.
up. by. macrophages,. phagolysosomal. fusion. occurs.. The. phagolysosomal. membrane.
becomes.leaky.and.its.inner.pH.is.alkalinized..Cells.containing.
C. neoformans
-illed.pha-
gosomes. retain. phagocytic. capacity. and. motility.. Phagosomes. of. infected. cells. became.
distended,.and.illed.with.yeast.cells.and.polysaccharides.that.inally.kill.the.macrophage.
(Figure 20.2).
159
The.polyene.antifungal.nystatin.(Nys).is.a.hydrophobic.macrolide.that.shares.a.chemical.
structure.with.amphotericin.B.(AMB),.employed.in.the.treatment.of.systemic.cryptococ-
cosis..Similar.to.AMB,.the.slight.hydrosolubility.of.Nys.at.neutral.pH.is.increased.as.the.
pH.is.reduced.
The.group.of.Owais.in.India.empoyed.pH-sensitive.liposomes.(DOPE/CHEMS,.6:4).to.
deliver.Nys.against.systemic.murine.cryptococcosis.
160
.Balb/C.mice.were.challenged.sys-
temically. with. 7.10
5
. spores. of.
C. neoformans
and. received. intraperitoneal. (i.p.). treatment.
on. days. 1,. 2,. and. 3. postinfection.. Nys. pH-sensitive. liposomal. treatments. (5. mg. of. Nys/
kg).presented.80%.survival.at.day.40.postinfection,.while.treatments.with.Nys.pH-insen-
sitive.(eggPC/Chol,.49:21).liposomes.or.free.Nys.resulted.in.50.and.10%.survival,.respec-
tively..At.lower.doses.(3.mg.of.Nys/kg),.the.survival.of.mice.treated.with.Nys.pH-sensitive.
liposomes.was.50%,.whereas.treatments.with.Nys.pH-insensitive.liposomes.or.free.Nys.
