Photosensitized inactivation of Plasmodium falciparum- and Babesia divergens-infected erythrocytes in whole blood by lipophilic pheophorbide derivatives

Background and objectives: Blood transfusions can transmit parasitic infections, such as those caused by Plasmodium (malaria), Trypanosoma cruzi (Chagas' disease), and Babesia (babesiosis), A higher degree of blood transfusion safety would be reached if methods were available for inactivating such parasites. Materials and methods: We evaluated the effectiveness of photosensitization using lipophilic pheophorbide and red light illumination to eradicate red blood cells infected with Plasmodium falciparum, and with Babesia divergens, in whole blood. Fluorescence microscopy and conventional fluorometry showed the specific accumulation of pheophorbide derivatives in the RBC infected with either parasite, compared with uninfected RBC. The effectiveness of different derivatives in eradicating infected RBC was first estimated in parasite cultures. Results: The best photosensitizer was the N-(4-butanol) phrophorbide derivative (Ph4-OH) at 0.2 mu M concentration and 5-min illumination. In whole blood, the eradication of RBC infected with B. divergens and P. falciparum was obtained with 2 mu M Ph4-OH and 10 and 20 min illumination, respectively. Under these conditions of photosensitization, low levels of RBC hemolysis were noted even after 2 weeks of storage at 4 degrees C and a subsequent 48-hour incubation at 37 degrees C. No reduction of negative charges on treated RBC was noted and no increase in methemoglobin content. Conclusion: In plasma, Ph4-OH is mainly transported by high-density lipoproteins (HDL). This high affinity for HDL may explain the selective accumulation of lipophilic pheophorbide derivatives in the intracellular parasites. Photosensitization with pheophorbide derivatives may be a promising approach to inactivation of transfusion-transmissible parasites and viruses in blood bank units.