Oxidative stress in cells infected with bovine viral diarrhoea virus: a crucial step in the induction of apoptosis.

Bovine viral diarrhoea virus (BVDV) belongs to the genus Pestivirus of the family Flaviviridae. Both a noncytopathic (ncp) and an antigenically related cytopathic (cp) BVDV can be isolated from persistently infected animals suffering from mucosal disease. In every case studied so far, the genomic changes leading to the cp biotype correlate with the production of the NS3 nonstructural protein, which, in the ncp biotype, is present in its uncleaved form, NS23. This report shows that, in contrast to ncp BVDV, the cp biotype induces apoptosis in cultured embryonic bovine turbinate cells. Early in the process of apoptosis, cells show a rise in the intracellular level of reactive oxygen species, which is indicative of oxidative stress. This precedes two hallmarks of apoptosis, caspase activation as shown by cleavage of the caspase substrate poly(ADP-ribose) polymerase, and DNA fragmentation. Cells were protected from apoptosis only by certain antioxidants (butylated hydroxyanisole and ebselen), whereas others (N-acetylcysteine, pyrrolidine dithiocarbamate, lipoic acid, dihydrolipoic acid and tiron) turned out to be ineffective. Antioxidants that protected cells from apoptosis prevented oxidative stress but failed to block virus growth. These observations suggest that oxidative stress, which occurs early in the interaction between cp BVDV and its host cell, may be a crucial event in the sequence leading to apoptotic cell death. Hence, apoptosis is not required for the multiplication of the cp biotype of BVDV.