Interaction Among PCV2Infection, Oxidative Stress And Selenium And Their Mechanism

Porcine circovirus diseases (PCVD) include porcine respiratory disease complex (PRDC), enteric disease, reproductive disease, and porcine dermatitis and nephropathy syndrome (PDNS). The most economically important PCVD is post-weaning multisystemic wasting syndrome (PMWS), characterized by wasting and growth retardation. PMWS primarily affects weanling piglets at the age of3to15weeks and has a high morbidity rate of up to60%. Several studies have linked PMWS expression to management measures, presence of concurrent viral infections, stimulation of the immune system, nutrition and oxidative stress, but the pathogenic mechanism of PCV2remains poorly understood. Selenium is an essential micronutrient for human and animals and its important biological functions have been attributed largely to its presence in selenoproteins as the21st amino acid, selenocysteine. The physiological roles of selenoproteins are closely related to selenium status. Low selenium status has been reported both to influence progression of some viral diseases while selenium supplementation has been found to affect the progression of some viral infections. However, further work is needed to provide insight into the role of selenium and specific selenoproteins in relation to viral diseases. In addition, precious studies have suggested that organic forms of Se (e.g., Se-enriched yeast, which mainly contains selenomethionine) are less toxic than inorganic forms of Se such as sodium selenite, and the bioavailability of organic Se is relatively high. The present study was conducted to investigate the interaction among PCV2infection, oxidative stress and selenium and their mechanism.Experiment1:Interaction of porcine circovirus type2replication with intracellular redox status in vitroRedox status influences replication of some viruses but its effect on porcine circovirus type2(PCV2), the primary causative agent of the emerging swine disease postweaning multisystemic wasting syndrome is not known. In this study we examined the interaction of PCV2replication with intracellular redox status in PK15cells. Both intracellular glutathione (GSH) and total superoxide dismutase activity (SOD) decreased significantly48h post-infection and subsequently returned to normal levels after72h, while malondialdehyde (MDA) concentration increased significantly at72h post-infection. Furthermore, PCV2replication in PK15cells was significantly impaired after the elevation of intracellular GSH through treatment with the antioxidant N-acetyl-1-cysteine (NAC), a precursor in glutathione synthesis. In contrast, PCV2replication in PK15cells was enhanced after reduction of GSH levels through H2O2-mediated oxidation. We conclude that PCV2infection induces oxidative stress and that intracellular redox status influences PCV2replication in PK15cells. This is the first demonstration of the interaction of PCV2replication with intracellular redox status.Experiment2:Reactive oxygen species regulate the replication of porcine circovirus type2via NF-κB pathwayIntracellular redox state has been suggested to have various effects on the replication of different viruses within host cells. The aim of the present study was to investigate the influence of reactive oxygen species (ROS) on replication of porcine circovirus type2(PCV2), in PK15cells. Following PCV2infection there was a time-dependent increase in ROS. Antioxidant N-acetyl-1-cysteine treatment of cells resulted lower ROS levels and lower PCV2replication. In contrast, treatment by buthionine sulfoximine (BSO), a GSH synthesis inhibitor, resulted in elevation of ROS levels and increased PCV2replication. Furthermore, inhibiting the activity of NF-κB, a redox-responsive transcription factor, suppressed BSO-mediated increase of PCV2replication, indicating that increased PCV2replication likely occurs via ROS activation of NF-κB. Taken together, our results indicate that the generation of ROS during PCV2infection is involved in its replication and this progression is associated with the alteration in NF-κB activity induced by ROS.Experiment3:Selenium blocks PCV2replication promotion induced by oxidative stress via improving GPxl expressionPorcine circovirus type2(PCV2) is recognized as a key infectious agent in post-weaning multisystemic wasting syndrome (PMWS), but not all pigs infected with PCV2will develop PMWS. The aim of this work was to explore the relationships between PCV2infection, oxidative stress and selenium in a PK-15cell culture model of PCV2infection. The results showed that oxidative stress induced by H2O2treatment increased PCV2replication as measured by PCV2DNA copies and the number of infected cells. Furthermore, PCV2replication was inhibited by selenomethionine (SeMet) at a high concentration (6μM) and the increase in PCV2replication by oxidative stress was blocked by SeMet at physiological concentrations (2or4μM). PCV2infection caused a decrease of glutathione peroxidase1(GPxl) activity but an increase of GPxl mRNA levels, suggesting that GPx1may represent an important defense mechanism during PCV2infection. SeMet did not significantly block the promotion of PCV2replication in GPxl-knockdown cells. This observation correlates with the observed influence of SeMet on GPxl mRNA and activity in GPxl-knockdown cells, indicating that GPxl plays a key role in blocking the promotion of PCV2replication. We conclude that differences in morbidity and severity of PMWS caused on different pig farms may be related to variations in oxidative stress and that selenium has a potential role in control of PCV2infection.Experiment4:Effects of selenium on growth performance, anti-oxidation, selenoprotein expression and PCV2infection of weaned piglets in a PCV2-infected pig farm.This trial was conducted to study the effect of selenium on growth performance, anti-oxidation, selenoprotein expression and PCV2infection of weaned piglets in a PCV2-infected pig farm.60Duroc X (Landrace X Largewhite) weaned piglets were allotted to five treatments with three replications per treatment and4weaned piglets per replication. The control group was given a basal diet and other four groups were given a basal diet supplemented with0.3or0.6mg/kg selenium (sodium selenite or selenium-riched yeast). The results showed that supplementation of sodium selenite or selenium-enriched yeast at various concentrations significantly improved the ADG and ADFI of weaned piglets, increased SOD and GSH-PX activity while significantly (P<0.05) reduced MDA content of serum. In addition, selenium supplmentaion increased the mRNA levels of GPx1, GPx4and TR1, and decreased the PCV2DNA copies in weaned piglets. Compared to sodium selenite, selenium-enriched yeast showed better effects on growth performance, anti-oxidation, selenoprotein expression and PCV2infection of weaned piglets.Experiment5:Effects of selenium on the immunity of weaned piglets in a PCV2-infected pig farmThis trial was conducted to study the effect of selenium on the immunity of weaned piglets in a PCV2-infected pig farm.60Duroc X (Landrace X Largewhite) weaned piglets were allotted to five treatments with three replications per treatment and4weaned piglets per replication. The control group was given a basal diet and other four groups were given a basal diet supplemented with0.3or0.6mg/kg selenium (sodium selenite or selenium-riched yeast). The results showed that sodium selenite or selenium-enriched yeast supplemented at various concentrations improved the immunity of weaned piglets, with a significantly increase in IL-2and TNF-a levels (P<0.05). In addition, sodium selenite or selenium-riched yeast supplemented at various concentrations significantly promoted the proliferation of peripheral blood lymphocyte (P<0.05). Compared to sodium selenite, selenium-enriched yeast showed better effects on the immunity of PCV2-infected piglets.