Comparison of methylene blue and methylene violet for photoinactivation of intracellular and extracellular virus in red cell suspensions.

Previous studies with methylene blue (MB) in red cell suspensions have demonstrated that extracellular, but not intracellular, virus can be readily photoinactivated. To test if the resistance of intracellular virus to inactivation is related to the permanent positive charge of the phenothiazine, a series of uncharged phenothiazine dyes, methylene violet (MV), monodemethylated MV and didemethylated MV, were studied. Values of the sensitivity of intracellular relative to extracellular vesicular stomatitis virus (VSV) inactivation for the three dyes (D10 extracellular/D10 intracellular) in buffer were 1.0, 0.60 and 0.33, respectively. In contrast, intracellular virus was resistant to inactivation with MB, with a D10 extracellular/D10 intracellular of 0.05 in buffer. Because virucidal activity of MV was inhibited by the presence of plasma, the red cells (30% hematocrit) were repeatedly washed prior to photoinactivation and storage. Under conditions where MB and MV inactivated approximately 5 log10 of extracellular VSV, intracellular VSV was inactivated by more than 4 log10 with MV compared to 0.88 log10 with MB. These phototreatment conditions did not significantly affect red cell morphology, extracellular pH, ATP or 2,3-diphosphoglycerol levels during 42 days of 1-6 degrees C storage. There was enhanced potassium efflux and hemolysis over values obtained from untreated control; the extent of change from controls was comparable for each phototreatment. These results indicate that the uncharged phenothiazine dye, MV, can inactivate both intracellular and extracellular virus yet exhibit similar in vitro red cell storage properties as MB phototreatment.