The relative importance of type I and type II mechanisms in the photodynamic treatment of red blood cell concentrations (RBCC) to inactivate viruses was studied using
aluminum phthalocyanine tetrasulfonate (
AlPcS4), visible light and quenching or enhancing agents of reactive forms of
oxygen. Treatment of a human RBCC with 10-13 microM
AlPcS4 and 25-26 mW/cm2 visible light resulted in the rapid and complete inactivation of added
vesicular stomatitis virus (VSV). The addition of
mannitol,
glycerol,
reduced glutathione (GSH), or
superoxide dismutase (SOD), known quenching agents of type I mechanisms, had little to no effect on the rate of inactivation of VSV. Significant inhibition of VSV kill was observed on addition of
tryptophan or
sodium azide, known quenchers of type II mechanisms. Additionally, the rate of VSV kill was enhanced in the presence of D2O. Taken together, these results indicate a predominant role of
singlet oxygen in the inactivation of VSV on photodynamic treatment of RBCC. The relative importance of type I and type II mechanisms on cellular toxicity was also evaluated. Little, if any
hemoglobin release was observed on treatment of human or rabbit RBCC with 10 microM
AlPcS4 and 44 J/cm2 of visible light in the presence or absence of the above mentioned quenchers. The effect of the addition of quenchers on the recovery and circulatory survival of treated, autologous rabbit RBCC, labeled with 51Cr, was also assessed.(ABSTRACT TRUNCATED AT 250 WORDS)