Phthalocyanine-photosensitized inactivation of a pathogenic protozoan, Acanthamoeba palestinensis

Abstract

Incubation of Acanthamoeba palestinensis cells with a tetracationic phthalocyanine (RLP068) at concentrations ranging between 0.2 and 1.0 µM, caused a ready uptake of the photosensitizer with recoveries of the order of 0.5–2.5 nmol per mg of cell protein. The amount of cell-bound phthalocyanine did not appreciably change with incubation times ranging between 0.5 and 3 h. Fluorescence microscopic investigations showed an obvious accumulation of the phthalocyanine at the level of the vacuolar membranes. A nearly complete photoinduced cell death occurred upon irradiating A. palestinensis cells with 600–700 nm light with a total energy of 15–30 J cm⁻² using 1.0 µM RLP068 in the incubation medium. DAPI staining of the photosensitized cells indicates significant damage of the nucleus. On the other hand, photosensitization of the protozoan cells does not directly involve the mitochondria as shown by the lack of photoinduced decrease in the activity of typical mitochondrial enzymes, such as NADH dehydrogenase and citrate synthase.