N-acetylpenicillamine inhibits the replication of porcine reproductive and respiratory syndrome virus in vitro

Nitric oxide (NO) was proposed to be an important molecule against some microorganisms. In this study, we investigated the inhibitory effect of NO on the infection by porcine reproductive and respiratory syndrome virus (PRRSV) in vitro and the role of NO in the defense against PRRSV. Our results indicated that exogenous NO did not inhibit PRRSV infection. Unexpectedly, N-acetylpenicillamine (NAP), a commonly used compound as negative control for NO-producing reagents, inhibited PRRSV replication. Thus, the inhibition effect of NAP on PRRSV replication was further explored. We found that the maximal inhibition effect of NAP on PRRSV replication was achieved upon treatment 1 h after virus infection and the virus yield was reduced by approximately 50 fold in the presence of 400 mu M NAP. An obvious inhibitory effect on viral RNA and protein synthesis was also observed. However, the inhibitory effect was only achieved at early phase of virus infection. The normal virus yield could be restored upon the removal of NAP treatment. The inhibitory effect might be caused by sulfhydryl-reducing capacity and metal chelating properties of NAP. These studies suggested that (i) NO production or NO synthase (NOS) expression profiling may not be a reliable index for the immune response to PRRSV; (ii) NAP could inhibit the replication of PRRSV.