Histone Deacetylase Inhibitors Enhance the Amoebicidal Effect of Low Concentration of Polyhexamethylene Biguanide by Inducing Apoptosis.

Purpose: The aim of this study was to reduce the cytotoxicity and improve the amoebicidal effect of polyhexamethylene biguanide (PHMB) at low concentrations by combining it with histone deacetylase (HDAC) inhibitors.

Methods: To reduce the cytotoxic effect on human corneal epithelial (HCE) cells, the concentration of PHMB was reduced to 0.0002%. To enhance the amoebicidal effect of PHMB, HDAC inhibitors such as suberoylanilide hydroxamic acid, MS275, or MC1568 were combined with it. Acanthamoeba and HCE cells were treated with 3 combinations to evaluate the amoebicidal and cytotoxic effects. Microscopy and fluorescence-activated cell sorting analysis were performed to investigate the apoptotic cell death of Acanthamoeba by these combinatorial treatments.

Results: The low concentration of PHMB (0.0002%) alone demonstrated no cytopathic effects (CPEs) on HCE cells. Three combinatorial treatments using 0.0002% PHMB with 10 μM suberoylanilide hydroxamic acid, 10 μM MS275, or 10 μM MC1568 showed higher amoebicidal effects on A. castellanii trophozoites than PHMB alone. Fluorescence-activated cell sorting analysis confirmed that HDAC inhibitors increased the apoptotic cell death of Acanthamoeba. Mild CPEs were observed from HCE cells cotreated with PHMB and the HDAC inhibitors after 24 hours of exposure.

Conclusions: Combinatorial treatments showed high amoebicidal effects on Acanthamoeba and low CPEs on HCE cells, which suggests their potential application for Acanthamoeba keratitis treatment.