Thiazole orange, a DNA-binding photosensitizer with flexible structure, can inactivate pathogens in red blood cell...

Development of a robust pathogen reduction system for red cells (RBCs) utilizing photosensitive dyes has been constrained by hemolysis, usually mediated by reactive oxygen species emanating from dye free in solution as well as dye bound to the RBC membrane. The RBC binding properties of thiazole orange (TO), a flexible nucleic acid intercalating cyanine dye that predominantly acts as a photosensitizer only when bound, were assessed along with its virucidal, bactericidal, and light-induced hemolytic activities.

Leukodepleted 20% hematocrit RBCs suspended in Erythrosol (RAS-2) were oxygenated, inoculated with test organisms, incubated with TO, and illuminated. Control and treated samples were analyzed by appropriate assay. Identically prepared, but uncontaminated samples were phototreated, concentrated to 45% hematocrit, and assayed for potassium leakage, hemolysis, and ATP during storage.

Approximately 21 percent TO bound to RBCs. Phototreatment inactivated from 5.4 to 7.1 log(10) of 5 tested viruses and from 2.3 to greater than 7.0 log(10) of 8 tested bacteria. Phototreated RBCs exhibited only slightly increased hemolysis, moderately elevated potassium efflux, and similar levels of ATP compared to controls.

TO can photoinactivate several model viruses and pathogens in RBCs under conditions that produce limited hemolysis without the addition of quenchers or competitive inhibitors.