Untargeted and targeted metabolomics reveal that adenosine nucleotides released in Actinobacillus pleuropneumoniae supernatant inhibit porcine reproductive and respiratory syndrome virus replication.

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most devastating viruses in the swine industry and causes major economic losses. To date, there has not been an effective antiviral treatment for the disease. We have shown in previous studies that culture supernatant of Actinobacillus pleuropneumoniae (App), the causative agent of porcine pleuropneumonia, possesses antiviral activity in vitro against PRRSV, and we have clearly established that the antiviral activity was mediated by small molecular weight (i.e., <1 kDa), heat resistant metabolites present in the App supernatant ultrafiltrates. However, the identity of those metabolites remains unknown. The objective of the current study was to identify the active metabolites using untargeted and targeted mass spectrometry-based metabolomics and test their respective antiviral activity against PRRSV in the Jude Porcine Lung Epithelial Cell Line (SJPL). The results presented reveal very significant antiviral activity of App supernatant ultrafiltrates against PRRSV in SJPL cells. Consequently, we identified and quantified several adenosine nucleotide metabolites present in App supernatant ultrafiltrates using mass spectrometry-based metabolomics, and the concentrations detected were very high. SJPL cells infected with PRRSV and treated with 2'-adenosine monophosphate (2-AMP), 3'-adenosine monophosphate (3-AMP) or 5'-adenosine monophosphate (5-AMP) significantly reduced PRRSV infection. Interestingly, many antiviral drugs or prodrugs are adenosine analogs, and the mechanism of action was previously elucidated. Currently marketed nucleoside analog drugs could potentially be used to treat PRRSV infection.

Virus role during intraepidemic increase in dengue disease severity.

Dengue epidemics in Cuba have repeatedly demonstrated a month-to-month increase in clinical severity during secondary infections. The dengue 2 outbreak that occurred in Santiago de Cuba in 1997 was accompanied by the most severe intraepidemic increase in disease severity reported to date. It was initially proposed that the appearance of neutralization escape mutants during the course of the epidemic might explain this phenomenon. Recent studies have revealed that during the course of this epidemic, nucleotide substitutions appeared only in nonstructural (NS) genes, most of which were silent, except for one change in the NS1 gene. To study whether or not variation in the NS1 gene might be associated with increased disease severity during the epidemic, this gene was partially sequenced from 15 isolates obtained at different times during the 1997 epidemic. Early epidemic isolates differed from those obtained later by replacement only of threonine with serine at position 164 in the NS1 protein, an amino acid rarely found in any genotype of dengue 2 virus. All viruses isolated from patients located in Health Districts, where dengue 2 transmissions occurred late in the epidemic, contained Serine at position 164, indicating that this change was fixed within a few months. Here we argue that this single mutation contributes to viral survival or replication efficiency, resulting in enhanced infection in the presence of enhancing antibodies, a phenomenon that we term increased virus "fitness" in contrast to "virulence," an intrinsic property of the virus.