Duck hepatitis B virus inactivation and 8-methoxypsoralen photoadduct formation in human platelet concentrates.

Photochemical inactivation (PCI) of virus and bacteria in platelet concentrates (PC) has been demonstrated using 8-methoxypsoralen (8-MOP) and long-wavelength UV light (UVA). To study inactivation of blood-borne virus, we have employed duck hepatitis B virus (DHBV), a model for human hepatitis B virus. A specific hepatocyte culture infectivity assay, with PCR detection, could measure 5-6 log10 virus kill. The DHBV inactivation in PC was dependent on UVA dose, was enhanced when plasma was reduced from 100% to 20% and was limited by 8-MOP solubility in the reduced-plasma medium. Optimum conditions for PCI were 100 micrograms/mL 8-MOP in 20% plasma and 80% synthetic platelet storage medium. A radiolabeling assay for 8-MOP photoadducts in hepatocytes seeded into PC confirmed that DHBV inactivation reflected DNA modification and indicated that adduct formation was insensitive to minor variations in conditions. Kinetic modeling indicated that optimum adduct formation was a compromise between 8-MOP dark binding and optical transmittance and that plasma proteins competed for 8-MOP binding. The PCI results in various media correlated with corresponding DNA modification densities and were compared to statistical models incorporating DHBV characteristics and predictions of 8-MOP crosslink formation between DNA strands. Behavior was consistent with one or a small number of lethal modifications per DNA strand, including monoadducts, but probably not crosslinks alone. A minor subpopulation of DHBV was found to be somewhat more difficult to inactivate, consistent with three-fold lower modification, due possibly to single-stranded DNA character or host repair of photoadducts.