Effect of antioxidants on apoptosis induced by influenza virus infection: inhibition of viral gene replication and transcription with pyrrolidine dithiocarbamate.

Influenza virus (IV) infection induced apoptotic DNA fragmentation and the moderate overproduction of reactive oxygen species (ROS) in primary cultured chorion cells prepared from human fetal membranes, and IV particles were released from the infected cells. The antioxidant pyrrolidine dithiocarbamate (PDTC) inhibited the induced DNA fragmentation, ROS overproduction and IV particle release. Although Trolox inhibited ROS overproduction, it did not inhibit DNA fragmentation or IV production. The inhibitory effect of PDTC on DNA fragmentation was manifested when added up to 3 h after infection or by exposing the infected cells to it for only 1 h after infection. PDTC inhibited IV hemagglutinin (HA) viral (vRNA) and complementary (cRNA and mRNA) RNAs synthesis until 6 h after infection and delayed and decreased HA protein synthesis. However, HA RNA synthesis resumed after 12 h even in the presence of PDTC. These results suggested that PDTC inhibited apoptosis by inhibiting viral macromolecule synthesis rather than through its antioxidant effect, because Trolox did not inhibit apoptosis or IV production, although ROS overproduction was inhibited. The synthesis of specific viral macromolecules at the early stage of infection may play a critical role in the mechanism of apoptosis induction and moderate ROS overproduction may not be involved in the mechanism.