Selective protection of RBCs against photodynamic damage by the band 3 ligand dipyridamole.

BACKGROUND: All studied photosensitizers for virus inactivation impair RBCs. To reduce damage to the RBCs without affecting virucidal activity, selective protection of the RBCs is necessary. The ability of the band 3 ligand, dipyridamole, to react with singlet oxygen and to increase the selectivity of photosterilization was investigated. STUDY DESIGN AND METHODS: Solutions of dipyridamole were illuminated in the presence of tetrasulfonated aluminum phthalocyanine (AIPcS 4 ) and dimethylmethylene blue (DMMB). Solutions of amino acids, RBCs, and vesicular stomatitis virus (VSV) in RBC suspensions were photodynamically treated in the presence or absence of dipyridamole. RESULTS: Illumination of a solution of dipyridamole in the presence of AIPcS 4 or DMMB resulted in changes in the optical spectrum of dipyridamole. The photooxidation of dipyridamole was inhibited by azide and augmented by D 2 O, which suggests the involvement of singlet oxygen. Photooxidation of amino acids and photodamage to RBCs was strongly reduced in the presence of dipyridamole. In contrast, photoinactivation of VSV in RBC suspensions was only slightly affected by dipyridamole. CONCLUSION: Dipyridamole can improve the specificity of photodynamic sterilization of RBC concentrates, thereby increasing the practical applicability of this photodecontamination method.