Endogenous and 2-propanol-supported respiration of intact trophozoites of Entamoeba histolytica (stain HM-1:IMSS) were inhibited by bithionol, an effective chemotherapeutic agent for some trematode and cestode infections in humans. Dichlorophene and hexachlorophene also inhibited 2-propanol-supported respiration of the parasite. In contrast, ethanol formation by E. histolytica extract in the presence of N2 was scarcely inhibited by bithionol. The compound also inhibited in vitro growth of axenic (HM-1 strain) and polyxenic (strain HJ-1:KEIO) amoebae in culture. It took less than 24 hr to kill and disrupt virtually all amoebae of either strain with 0.28 mM bithionol. Omission of bovine serum from BI-S-33 medium resulted in considerably less disruption of HM-1 strain amoebae by the compound. However, organisms that looked undisrupted were stained with trypan blue. Moreover, the number of amoebae incubated for 10 min in the serum-free BI-S-33 medium containing 0.14 mM bithionol did not increase, even after incubation for 24 hr following replacement of the experimental culture fluid with fresh complete BI-S-33 medium free of the compound. These findings suggest that, although serum appears to diminish the antiamoebic action, some halogenated bisphenols (in particular bithionol) may be useful for treatment of amoebiasis.
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