Ophthalmic Demulcents Associated with Acanthamoeba Encystment in Model Multi-Purpose Lens Care Solutions Do Not Cause Encystment in Model Hydrogen Peroxide Solutions

Abstract

Purpose: : Acanthamoebaare opportunistic protozoa that cause rare but serious Acanthamoeba Keratitis (AK) infections. Recent publications have suggested that the 2007 withdrawal of a multi-purpose solution (MPS) associated with AK was due to encystment promoting effects of a propylene glycol (PG) demulcent ingredient. The current study evaluated encystment effects of ophthalmic demulcents in MPS-based versus hydrogen peroxide-based contact lens disinfecting solutions.

Methods: : Test solutions were a series of phosphate buffered MPS-based (0.25 ppm poly-amino-propyl-biguanide [PAPB]) or 3% hydrogen peroxide-based samples that also contained dose responses of the ophthalmic demulcents PG or polyvinylpyrrolidone (PVP) which spanned FDA monograph concentration ranges. Acanthamoeba castellanii ATCC 50370 trophozoites were cultured in antibiotic-free AC6 medium, treated with test solutions for 20-24 hr in appropriate MPS or peroxide neutralizing lens cases, and assessed for encystment via fluorescent microscopy with Calcofluor White staining.

Results: : The MPS-based positive control solution containing 0.25 ppm PAPB and 0.5% PG consistently showed ≥ 70% encystment. Both PG and PVP showed dose-dependent encystment when present in model MPS-based solutions (PG up to 88% encystment; PVP up to 14% encystment). However, PG and PVP always showed ≤ 1% encystment when present at any concentration in hydrogen peroxide-based solutions, similar to the ≤ 1% encystment observed for MPS-based negative control solutions tested in parallel that did not contain any demulcent.

Conclusions: : The dose-dependent encystment effects observed in vitro for the ophthalmic demulcents PG and PVP only occurred in MPS-based model solutions containing 0.25 ppm PAPB as a single biocidal component. The absence of any PG or PVP mediated encystment effects when present in peroxide solutions in this study suggests that that these demulcents do not promote Acanthamoeba encystment in model one-step hydrogen peroxide-based disinfecting solutions.

Keywords: Acanthamoeba • keratitis • contact lens