The viral safety of blood products has been significantly enhanced as a consequence of improvements in donor screening. However, there are still measurable risks of viral transmission through blood products.1,2) Therefore, processes for the removal and/or inactivation of viruses may represent an additional level of safety for these biological materials.Hemoglobin derived from human red blood cells is being used to develop a variety of artificial oxygen carriers. [3][4][5] Out-dated red cells for transfusion are an important source of human hemoglobin for the development of artificial oxygen carriers. The usual techniques for virus removal or inactivation, respectively, in stroma-free hemoglobin (SFH) are filtration and heat-treatment. [6][7][8] However, a combination of at least two techniques, which have different mechanisms of action, is important for complete elimination. This is the approach that has been adopted for the sterilization of a variety of pooled plasma derivatives and could have implications for a pooled hemoglobin product.Photosensitizers have been utillized for virus inactivation of blood products.9,10) We have previously reported on virus photoinactivation in SFH by 1,9-dimethylmethylene blue (DMMB).11) Vesicular stomatitis virus (VSV) was inactivatedϾ6 log 10 by DMMB without Met-Hb formation using 1 mM DMMB and red (655 nm) LED light.11) These conditions favor activation of monomer DMMB, which has an absorption peak of ca. 650 nm. In other experiments, the requirement of oxygen for virus photoinactivation by DMMB was demonstrated by the failure to achieve inactivation in samples bubbled with nitrogen.12)The absorption spectrum of DMMB in aqueous solutions has two peaks, which represent light absorption from the monomer and dimer forms.12) Activation of the dimer (max 590 nm), in contrast to monomer, resulted in virus photoinactivation with photooxidation of hemoglobin to methemoglobin (Met-Hb).11) It was speculated that compared with the dimer, the monomer of DMMB has high affinity to nucleic acids and so inactivates virus without inducing Met-Hb formation. However, why Met-Hb forms on exposure to activated dimer but not monomer may also be explained by a difference in the reactive oxygen species (ROS) involved in the four events (virus inactivation by monomer DMMB, virus inactivation by dimer DMMB, Met-Hb formation by monomer DMMB and Met-Hb formation by dimer DMMB). Methylene blue (MB) is known to produce not only singlet oxygen but also other ROS. 13,14) Therefore, DMMB, which is a derivative of MB, may also produce ROS other than singlet oxygen. In order to clarify which ROS are involved in virus inactivation and Met-Hb formation by activated monomer or dimer DMMB, the extent of the inactivation and formation in the presence or absence of ROS scavengers, quenchers or enhancer was evaluated.
MATERIALS AND METHODSVirus Assays Bacteriophage R17 and its host, Escherichia coli Hfr C, were obtained from David Cook (Cerus Corporation, Concord, CA, U.S.A.). The plaque assay for bacteriophage R17 ...