Photosensitized inactivation of Plasmodium falciparum in human red cells by phthalocyanines

Background: Photodynamic treatment of red cell concentrate with phthalocyanines and red light inactivates lipid-enveloped viruses such as vesicular stomatitis virus and human immunodeficiency virus. This procedure is evaluated for its ability to enhance the viral safety of red cell concentrate for transfusion. It is of interest to study whether photodynamic treatment could also inactivate parasites in blood (e.g., Plasmodium falciparum). Study Design and Methods: Red cells parasitized by P. falciparum were treated with phthalocyanines and red light and then cultured in vitro for 48 hours. The percentage of parasitemia was then estimated by microscopic examination of the red cells. Results: Of the phthalocyanines studied, the one that proved to be the most effective was HOSiPcOSi(CH3)(2)(CH2)(3)N(CH3)(2) (Pc 4). The extent of parasite inactivation increased with light dose and decreased with an increase in hematocrit. At a hematocrit of 60 percent and 2 mu M Pc 4, greater than or equal to 3 log(10) kill occurred at a light dose of 60 J per cm(2). This is a lower dose than is required for greater than or equal to 6 log(10) of vesicular stomatitis virus inactivation (90 J/cm(2)). Conclusion: Photodynamic treatment with Pc 4 could make red cell concentrate not only virally safe for transfusion but also safe with respect to transmitting malaria.