LOSS OF GSH, OXIDATIVE STRESS, AND DECREASE OF INTRACELLULAR PH AS SEQUENTIAL STEPS IN VIRAL-INFECTION

Madin-Darby canine kidney cells infected with Sendai virus rapidly los e GSH without increase in the oxidized products. The reduced tripeptid e was quantitatively recovered in the culture medium of the cells. Sin ce the GSH loss in infected cells was not blocked by methionine, a kno wn inhibitor of hepatocyte GSH transport, a nonspecific leakage throug h the plasma membrane is proposed. UV-irradiated Sendai virus gave the same results, confirming that the major loss of GSH was due to membra ne perturbation upon virus fusion. Consequent to the loss of the tripe ptide, an intracellular pH decrease occurred, which was due to a rever sible impairment of the Na+/H+ antiporter, the main system responsible for maintaining unaltered pH(i) in those cells. At the end of the inf ection period, a rise in both pH, value and GSH content was observed, with a complete recovery in the activity of the antiporter. However, a secondary set up of oxidative stress was observed after 24 h from inf ection, which is the time necessary for virus budding from cells. In t his case, the GSH decrease was partly due to preferential incorporatio n of the cysteine residue in the viral proteins and partly engaged in mixed disulfides with intracellular proteins. In conclusion, under our conditions of viral infection, oxidative stress is imposed by GSH dep letion, occurring in two steps and following direct virus challenge of the cell membrane without the intervention of reactive oxygen species . These results provide a rationale for the reported, and often contra dictory, mutual effects of GSH and viral infection.