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Kathy McClellan, Kevin Howard, Jerry Y. Niederkorn, Hassan Alizadeh; Effect of Steroids on Acanthamoeba Cysts and Trophozoites. Invest. Ophthalmol. Vis. Sci. 2001;42(12):2885-2893.
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purpose. Topical steroids are frequently used to control corneal inflammation
and uveitis or is administered after surgery, to prevent corneal graft
rejection. This study was undertaken to determine whether steroids
could affect the pathogenicity of Acanthamoeba
methods. The effect of dexamethasone phosphate on excystment, proliferation, and
encystment of trophozoites and cysts of A. castellanii was examined in vitro. Cytolysis capacity of steroid-treated Acanthamoeba was quantified by a spectrophotometric
assay, and plasminogen activators were measured by a fibrinolysis
assay. The influence of steroid treatment on corneal infection in a
Chinese hamster model of Acanthamoeba keratitis was
examined in vivo.
results. Treatment of Acanthamoeba cysts with dexamethasone
induced 4- to 10-fold increases in the number of trophozoites compared
with untreated control cultures. Acceleration of trophozoite
proliferation was observed when trophozoites were treated with
dexamethasone. However, dexamethasone treatment did not affect
encystment of Acanthamoeba trophozoites.
Dexamethasone-treated trophozoites or cysts induced a significant
cytopathic effect on corneal epithelial cells compared with untreated
organisms. Supernatants collected from either dexamethasone-treated or
untreated organisms failed to lyse corneal epithelial cells. Treatment
of organisms with dexamethasone had no effect on production of
plasminogen activators by Acanthamoeba trophozoites.
Intramuscular injection of dexamethasone had a profound effect on the
incidence, severity, and chronicity of keratitis. Keratitis in
dexamethasone–treated hamsters was significantly more severe at
all time points than in untreated animals (P <
conclusions. These findings indicate that exposure of Acanthamoeba trophozoites and cysts to dexamethasone increases the pathogenicity of
the organisms. The results emphasize the importance of maintaining
adequate amebicidal therapy if a topical steroid is used in the
management of Acanthamoeba keratitis.
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