Oxygen free radical involvement in acute lung injury induced by H5N1 virus in mice

Interpretation of the anti-influenza active ingredients and potential mechanisms of Ge Gen Decoction based on spectrum-effect relationships and network analysis

ETHNOPHARMACOLOGICAL RELEVANCE

Ge Gen Decoction (GGD) is a classic traditional Chinese medicine (TCM) prescription that originated in the ancient Chinese medical book "Treatise on Febrile Diseases". The prescription consists of 7 herbs: Pueraria lobata (Willd.) Ohwi, Ephedra sinica Stapf, Cinnamomum cassia (L.) J.Presl, Paeonia lactiflora Pall., Glycyrrhiza uralensis Fisch., Zingiber officinale Rosc., and Ziziphus jujuba Mill. It can alleviate high fever and soreness in the neck and shoulders caused by exogenous wind chill and is widely used in both China and Japan. Currently, GGD is primarily utilized for treating flu and the common cold. GGD has been reported to show significant anti-influenza A virus (IAV) activity both in vitro and in vivo. However, the active ingredients responsible for its anti-influenza properties have not been elucidated, and the mechanisms underlying its anti-influenza effects require further research.

AIM OF THE STUDY

This study aims to investigate the active ingredients and molecular mechanisms of GGD in treating influenza.

MATERIALS AND METHODS

HPLC chromatograms were established for GGD water and different polar extracts. The effect of different GGD extracts on pulmonary virus titers and TNFα expression was assessed through RT-PCR analysis. Spectrum-effect relationships between chromatographic peaks of GGD and its virus inhibition rate and TNFα inhibition rate were investigated using partial least squares regression (PLSR) analysis. HPLC-Q-TOF-MS was utilized to identify the constituents absorbed into the blood after oral administration of GGD. Network analysis of the absorbed forms of active ingredients was conducted to predict the potential mechanisms of GGD. Subsequently, total SOD activity, CAT and HO-1 expression and Nrf2 nuclear translocation were then analyzed. Finally, the impact of interfering with HO-1 expression on the anti-IAV activity of GGD was examined.

RESULTS

The study identified 11 anti-influenza active ingredients in GGD, which are daidzein, ononin, genistin, daidzin, 3'-methoxypuerarin, puerarin, pseudoephedrine, paeoniflorin, pormononetin-7-xylosyl-glucoside, penistein-7-O-apiosyl-glucoside, and ephedrine. Network analysis revealed various biological activities of GGD, including responses to ROS and oxidative stress. GGD also involves multiple antiviral pathways, such as hepatitis B, IAV, and Toll-like receptor pathways. Experimental assays demonstrated that GGD possesses independent antioxidant activity both in vitro and in vivo. In vitro, GGD inhibits the increase in intracellular ROS induced by IAV. In vivo, it reduces MDA levels and increases total pulmonary SOD activity. Applying siRNA and flow cytometry analysis revealed that GGD alleviates IAV-induced oxidative burst by promoting the expression of HO-1 and CAT. Western blot analysis revealed that GGD effectively promotes Nrf2 nuclear translocation and enhances Nrf2 expression. Furthermore, this study found that the enhancement of HO-1 expression by GGD contributed to its anti-IAV activity.

CONCLUSIONS

The study identified the active ingredients of GGD against influenza and demonstrated the beneficial role of GGD's antioxidant activity in treating flu. The antioxidant activity of GGD is associated with the promotion of Nrf2 nuclear translocation and the upregulation of antioxidant enzymes such as SOD, HO-1, and CAT. Overall, this study provides evidence supporting the use of GGD as an adjunctive or complementary therapy for influenza.

Anti-influenza drug screening and inhibition of apigetrin on influenza A virus replication via TLR4 and autophagy pathways

Activation of Toll-like receptor (TLR) 4 plays important roles in the influenzaA virus (IAV) infection. To explore TLR4 inhibitors, 161 traditional Chinese medicines (TCMs) were screened. Further, we screened out Ixeris sonchifolia Hance, and its active compound, Apigetrin (apigenin-7-O-glucoside). Antiviral activity of Apigetrin was determined by plaque assay. We also further investigated the influence of Apigetrin on immune signaling pathways including TLRs, MAPK, NF-κB and autophagy pathways. The in-vitro results showed that the extract and its several ingredients could significantly inhibit IAV replication. Apigetrin significantly improved IAV-induced oxidative stress, inhibited the IAV-induced cytokine storm by suppressing the excessive activation of TLR3/4/7, JNK/p38 MAPK and NF-κB. Apigetrin decreased autophagosome accumulation and promoted degradation of IAV protein. Interestingly, Apigetrin antiviral activity was reversed by using H2O2 and the agonists of TLR4, JNK/p38, NF-κB and autophagy. Most important, the in-vitro effective concentration is higher than the reported plasma concentration. The in-vivo test showed that Apigetrin significantly increased the average survival time, reduced the lung edema and IAV replication. In conclusion, we have found that Ixeris sonchifolia Hance and its several ingredients can inhibit IAV infection, and the mechanisms of action of Apigetrin against IAV is by regulating TLR4 and autophagy signaling pathways.

Glycerol Monolaurate Alleviates Oxidative Stress and Intestinal Flora Imbalance Caused by Salinity Changes for Juvenile Grouper

Groupers with an initial body weight of 9.10 ± 0.03 g were selected to investigate whether dietary addition of 0 (G0) and 1800 mg/kg glycerol monolaurate (GML, G1800) could alleviate the oxidative stress response and intestinal flora imbalance after 0, 6, 12, and 24 h of salinity change in grouper. Experimental results show that the dietary addition of GML significantly reduced the liver MDA content and increased the SOD activity of grouper. The gene expression of CAT and SOD increased and then decreased with time after adding 1800 mg/kg GML, and the highest values were significantly higher than those of the control group. Salinity change had a slight effect on the top four intestinal flora composition of grouper at 0, 12, and 24 h, with changes occurring only at 6 h when Cyanobacteria replaced Actinobacteria. The addition of dietary GML slowed down the intestinal flora disorder, inhibited the colonization of harmful bacterium Vibrio, and promoted the abundance of beneficial bacterium Bacillus. In conclusion, dietary GML significantly reduced the oxidative damage caused by sudden changes in salinity, improved the antioxidant capacity, and alleviated the intestinal flora imbalance in juvenile grouper.

Upregulation of oxidative stress gene markers during SARS-COV-2 viral infection

Severe viral infections, including SARS-COV-2, could trigger disruption of the balance between pro-oxidant and antioxidant mediators; the magnitude of which could reflect the severity of infection and lung injury. Using publicly available COVID-19 transcriptomic datasets, we conducted an in-silico analyses to evaluate the expression levels of 125 oxidative stress genes, including 37 pro-oxidant genes, 32 oxidative-responsive genes, and 56 antioxidant genes. Seven oxidative stress genes were found to be upregulated in whole blood and lung autopsies (MPO, S100A8, S100A9, SRXN1, GCLM, SESN2, and TXN); these genes were higher in severe versus non-severe COVID-19 leucocytes. Oxidative genes were upregulated in inflammatory cells comprising macrophages and CD8⁺ T cells isolated from bronchioalveolar fluid (BALF), and neutrophils isolated from peripheral blood. MPO, S100A8, and S100A9 were top most upregulated oxidative markers within COVID-19's lung autopsies, whole blood, leucocytes, BALF derived macrophages and circulating neutrophils. The calprotectin's, S100A8 and S100A9 were upregulated in SARS-COV-2 infected human lung epithelium. To validate our in-silico analysis, we conducted qRT-PCR to measure MPO and calprotectin's levels in blood and saliva samples. Relative to uninfected donor controls, MPO, S100A8 and S100A9 were significantly higher in blood and saliva of severe versus asymptomatic COVID-19 patients. Compared to other different viral respiratory infections, coronavirus infection showed a prominent upregulation in oxidative stress genes with MPO and calprotectin at the top of the list. In conclusion, SARS-COV-2 induce the expression of oxidative stress genes via both immune as well as lung structural cells. The observed correlation between oxidative stress genes dysregulation and COVID-19 disease severity deserve more attention. Mechanistical studies are required to confirm the correlation between oxidative stress gene dysregulation, COVID-19 severity, and the net oxidative stress balance.

Targeting TLR4 Signaling to Blunt Viral-Mediated Acute Lung Injury

Respiratory viral infections have been a long-standing global burden ranging from seasonal recurrences to the unexpected pandemics. The yearly hospitalizations from seasonal viruses such as influenza can fluctuate greatly depending on the circulating strain(s) and the congruency with the predicted strains used for the yearly vaccine formulation, which often are not predicted accurately. While antiviral agents are available against influenza, efficacy is limited due to a temporal disconnect between the time of infection and symptom development and viral resistance. Uncontrolled, influenza infections can lead to a severe inflammatory response initiated by pathogen-associated molecular patterns (PAMPs) or host-derived danger-associated molecular patterns (DAMPs) that ultimately signal through pattern recognition receptors (PRRs). Overall, these pathogen-host interactions result in a local cytokine storm leading to acute lung injury (ALI) or the more severe acute respiratory distress syndrome (ARDS) with concomitant systemic involvement and more severe, life threatening consequences. In addition to traditional antiviral treatments, blocking the host's innate immune response may provide a more viable approach to combat these infectious pathogens. The SARS-CoV-2 pandemic illustrates a critical need for novel treatments to counteract the ALI and ARDS that has caused the deaths of millions worldwide. This review will examine how antagonizing TLR4 signaling has been effective experimentally in ameliorating ALI and lethal infection in challenge models triggered not only by influenza, but also by other ALI-inducing viruses.

Redox control in the pathophysiology of influenza virus infection

Triggered in response to external and internal ligands in cells and animals, redox homeostasis is transmitted via signal molecules involved in defense redox mechanisms through networks of cell proliferation, differentiation, intracellular detoxification, bacterial infection, and immune reactions. Cellular oxidation is not necessarily harmful per se, but its effects depend on the balance between the peroxidation and antioxidation cascades, which can vary according to the stimulus and serve to maintain oxygen homeostasis. The reactive oxygen species (ROS) that are generated during influenza virus (IV) infection have critical effects on both the virus and host cells. In this review, we outline the link between viral infection and redox control using IV infection as an example. We discuss the current state of knowledge on the molecular relationship between cellular oxidation mediated by ROS accumulation and the diversity of IV infection. We also summarize the potential anti-IV agents available currently that act by targeting redox biology/pathophysiology.

Modeling the oxidative consumption of curcumin from controlled released poly(beta-amino ester) microparticles in the presence of a free radical generating system

Despite the promise of its therapeutic benefits, curcumin as a free molecule has failed to demonstrate significant clinical success. Arguably, its inherently poor stability and rapid clearance is a significant reason for these negative outcomes. The incorporation of curcumin into the backbone of a crosslinked hydrogel that utilizes poly(beta-amino ester) (PBAE) chemistry can provide a tunable protective network with the ability to release at a controlled rate while improving its therapeutic potential. Kinetics of curcumin conjugated PBAE microparticles controlled release delivery system in the presence of oxidative environments was studied for the first time, where consumption rates of active curcumin and release products were obtained. The constituent amount of curcumin present in solution was improved by incorporating the active into the network in comparison to curcumin as a free drug. Modeling curcumin conjugated PBAE microparticles will provide a design platform to improve translation and overall success in delivering a therapeutic agent that matches levels of oxidative stress.

Anti-Inflammatory and Anti-Oxidant Activity of Portulaca oleracea Extract on LPS-Induced Rat Lung Injury

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are classified as two lung complications arising from various conditions such as sepsis, trauma, and lung inflammation. Previous studies have shown that the extract of the leaves of Portulaca oleracea (PO) possesses anti-inflammatory and anti-oxidant activities. In the present study, the effects of PO (50–200 mg/kg) and dexamethasone (Dexa; 1.5 mg/kg) on lipopolysaccharide (LPS)-induced ALI were investigated. Subsequentially, the lung wet/dry ratio; white blood cells (WBC); levels of nitric oxide (NO); myeloperoxidase (MPO); malondialdehyde (MDA); thiol groups formation; super oxide dismutase (SOD) and catalase (CAT) activities; and levels of interleukin (IL)-1β, tumor necrosis factor (TNF)-α, IL-6, IL-10, prostaglandin E2 (PGE₂), and transforming growth factor (TGF)-β in the broncho alveolar lavage fluid (BALF) were evaluated in order to demonstrate the anti-oxidant and anti-inflammatory activity of PO. Our results show that PO suppresses lung inflammation by the reduction of IL-β, IL-6, TNF-α, PGE₂, and TGF-β, as well as by the increase of IL-10 levels. We also found that PO improves the level of WBC, MPO, and MDA, as well as thiol group formation and SOD and CAT activities, compared with the LPS group. The results of our investigation also show that PO significantly decreased the lung wet/dry ratio as an index of interstitial edema. Taken together, our findings reveal that PO extract dose-dependently displays anti-oxidant and anti-inflammatory activity against LPS-induced rat ALI, paving the way for rational use of PO as a protective agent against lung-related inflammatory disease.

Inhibition of curcumin on influenza A virus infection and influenzal pneumonia via oxidative stress, TLR2/4, p38/JNK MAPK and NF-κB pathways

Oxidative stress, Nrf2-HO-1 and TLR-MAPK/NF-κB signaling pathways have been proved to be involved in influenza A virus (IAV) replication and influenzal pneumonia. In the previous studies, we have performed several high-throughput drug screenings based on the TLR pathways. In the present study, through plaque inhibition test, luciferase reporter assay, TCID₅₀, qRT-PCR, western blotting, ELISA and siRNA assays, we investigated the effect and mechanism of action of curcumin against IAV infection in vitro and in vivo. The results showed that curcumin could directly inactivate IAV, blocked IAV adsorption and inhibited IAV proliferation. As for the underlying mechanisms, we found that curcumin could significantly inhibit IAV-induced oxidative stress, increased Nrf2, HO-1, NQO1, GSTA3 and IFN-β production, and suppressed IAV-induced activation of TLR2/4/7, Akt, p38/JNK MAPK and NF-κB pathways. Suppression of Nrf2 via siRNA significantly abolished the stimulatory effect of curcumin on HO-1, NQO1, GSTA3 and IFN-β production and meanwhile blocked the inhibitory effect of curcumin on IAV M2 production. Oxidant H₂O₂ and TLR2/4, p38/JNK and NF-κB agonists could significantly antagonize the anti-IAV activity of curcumin in vitro. Additionally, curcumin significantly increased the survival rate of mice, reduced lung index, inflammatory cytokines and lung IAV titer, and finally improved pulmonary histopathological changes after IAV infection. In conclusion, curcumin can directly inactivate IAV, inhibits IAV adsorption and replication; and its inhibition on IAV replication may be via activating Nrf2 signal and inhibiting IAV-induced activation of TLR2/4, p38/JNK MAPK and NF-κB pathways.

Emodin Inhibition of Influenza A Virus Replication and Influenza Viral Pneumonia via the Nrf2, TLR4, p38/JNK and NF-kappaB Pathways

Lasting activations of toll-like receptors (TLRs), MAPK and NF-κB pathways can support influenza A virus (IAV) infection and promote pneumonia. In this study, we have investigated the effect and mechanism of action of emodin on IAV infection using qRT-PCR, western blotting, ELISA, Nrf2 luciferase reporter, siRNA and plaque inhibition assays. The results showed that emodin could significantly inhibit IAV (ST169, H1N1) replication, reduce IAV-induced expressions of TLR2/3/4/7, MyD88 and TRAF6, decrease IAV-induced phosphorylations of p38/JNK MAPK and nuclear translocation of NF-κB p65. Emodin also activated the Nrf2 pathway, decreased ROS levels, increased GSH levelss and GSH/GSSG ratio, and upregulated the activities of SOD, GR, CAT and GSH-Px after IAV infection. Suppression of Nrf2 via siRNA markedly blocked the inhibitory effects of emodin on IAV-induced activations of TLR4, p38/JNK, and NF-κB pathways and on IAV-induced production of IL-1β, IL-6 and expression of IAV M2 protein. Emodin also dramatically increased the survival rate of mice, reduced lung edema, pulmonary viral titer and inflammatory cytokines, and improved lung histopathological changes. In conclusion, emodin can inhibit IAV replication and influenza viral pneumonia, at least in part, by activating Nrf2 signaling and inhibiting IAV-induced activations of the TLR4, p38/JNK MAPK and NF-κB pathways.

iTRAQ-based quantitative proteomics reveals important host factors involved in the high pathogenicity of the H5N1 avian influenza virus in mice

We previously reported a pair of H5N1 avian influenza viruses which are genetically similar but differ greatly in their virulence in mice. A/Chicken/Jiangsu/k0402/2010 (CK10) is highly lethal to mice, whereas A/Goose/Jiangsu/k0403/2010 (GS10) is avirulent. In this study, to investigate the host factors that account for their virulence discrepancy, we compared the pathology and host proteome of the CK10- or GS10-infected mouse lung. Moderate lung injury was observed from CK10-infected animals as early as the first day of infection, and the pathology steadily progressed at later time point. However, only mild lesions were observed in GS10-infected mouse lung at the late infection stage. Using the quantitative iTRAQ coupled LC-MS/MS method, we first found that more significantly differentially expressed (DE) proteins were stimulated by GS10 compared with CK10. However, bio-function analysis of the DE proteins suggested that CK10 induced much stronger inflammatory response-related functions than GS10. Canonical pathway analysis also demonstrated that CK10 highly activated the "Acute Phase Response Signaling," which results in a wide range of biological activities in response to viral infection, including many inflammatory processes. Further in-depth analysis showed that CK10 exacerbated acute lung injury-associated responses, including inflammatory response, cell death, reactive oxygen species production and complement response. In addition, some of these identified proteins that associated with the lung injury were further confirmed to be regulated in vitro. Therefore, our findings suggest that the early increased lung injury-associated host response induced by CK10 may contribute to the lung pathology and the high virulence of this virus in mice.

Erythropoietin Pretreatment Attenuates Seawater Aspiration-Induced Acute Lung Injury in Rats

Seawater drowning-induced acute lung injury (ALI) is a serious clinical condition characterized by increased alveolar-capillary permeability, excessive inflammatory responses, and refractory hypoxemia. However, current therapeutic options are largely supportive; thus, it is of great interest to search for alternative agents to treat seawater aspiration-induced ALI. Erythropoietin (EPO) is a multifunctional agent with antiinflammatory, antioxidative, and antiapoptotic properties. However, the effects of EPO on seawater aspiration-induced ALI remain unclear. In the present study, male rats were randomly assigned to the naive group, normal saline group, seawater group, or seawater + EPO group. EPO was administered intraperitoneally at 48 and 24 h before seawater aspiration. Arterial blood gas analysis was performed with a gas analyzer at baseline, 30 min, 1 h, 4 h, and 24 h after seawater aspiration, respectively. Histological scores, computed tomography scan, nuclear factor kappa B p65, inducible nitric oxide synthase, caspase-3, tumor necrosis factor-alpha, interleukin (IL)-1β, IL-6, IL-10, wet-to-dry weight ratio, myeloperoxidase activity, malondialdehyde, and superoxide dismutase in the lung were determined 30 min after seawater aspiration. Our results showed that EPO pretreatment alleviated seawater aspiration-induced ALI, as indicated by increased arterial partial oxygen tension and decreased lung histological scores. Furthermore, EPO pretreatment attenuated seawater aspiration-induced increase in the expressions of pulmonary nuclear factor kappa B p65, inducible nitric oxide synthase, caspase-3, tumor necrosis factor-alpha, IL-1β, myeloperoxidase activity, and malondialdehyde when compared with the seawater group. Collectively, our study suggested that EPO pretreatment attenuates seawater aspiration-induced ALI by down-regulation of pulmonary pro-inflammatory cytokines, oxidative stress, and apoptosis.

NEMO-Binding Domain Peptide Attenuates Lipopolysaccharide-Induced Acute Lung Injury by Inhibiting the NF-κB Signaling Pathway

The aim of the present study is to investigate the protective effects and relevant mechanisms exerted by NEMO-binding domain peptide (NBD) against lipopolysaccharide- (LPS-) induced acute lung injury (ALI) in mice. The ALI model was induced by intratracheally administered atomized LPS (5 mg/kg) to BABL/c mice. Half an hour before LPS administration, we treated the mice with increasing concentrations of intratracheally administered NBD or saline aerosol. Two hours after LPS administration, each group of mice was sacrificed. We observed that NBD pretreatment significantly attenuated LPS-induced lung histopathological injury in a dose-dependent manner. Western blotting established that NBD pretreatment obviously attenuated LPS-induced IκB-α and NF-κBp65 activation and NOX1, NOX2, and NOX4 overexpression. Furthermore, NBD pretreatment increased SOD and T-AOC activity and decreased MDA levels in lung tissue. In addition, NBD also inhibited TNF-α and IL-1β secretion in BALF after LPS challenge. In conclusion, NBD protects against LPS-induced ALI in mice.

PA-X-associated early alleviation of the acute lung injury contributes to the attenuation of a highly pathogenic H5N1 avian influenza virus in mice

PA-X is a novel discovered accessory protein encoded by the PA mRNA. Our previous study demonstrated that PA-X decreases the virulence of a highly pathogenic H5N1 strain A/Chicken/Jiangsu/k0402/2010 in mice. However, the underlying mechanism of virulence attenuation associated with PA-X is still unknown. In this study, we compared two PA-X-deficient mutant viruses and the parental virus in terms of induction of pathology and manipulation of host response in the mouse lung, stimulation of cell death and PA nuclear accumulation. We first found that down-regulated PA-X expression markedly aggravated the acute lung injury of the infected mice early on day 1 post-infection (p.i.). We then determined that loss of PA-X expression induced higher levels of cytokines, chemokines and complement-derived peptides (C3a and C5a) in the lung, especially at early time point’s p.i. In addition, in vitro assays showed that the PA-X-deficient viruses enhanced cell death and increased expression of reactive oxygen species (ROS) in mammalian cells. Moreover, we also found that PA nuclear accumulation of the PA-X-null viruses accelerated in MDCK cells. These results demonstrate that PA-X decreases the level of complement components, ROS, cell death and inflammatory response, which may together contribute to the alleviated lung injury and the attenuation of the virulence of H5N1 virus in mice.

Intracellular redox state as target for anti-influenza therapy: are antioxidants always effective?

Influenza virus infections represent a big issue for public health since effective treatments are still lacking. In particular, the emergence of strains resistant to drugs limits the effectiveness of anti-influenza agents. For this reason, many efforts have been dedicated to the identification of new therapeutic strategies aimed at targeting the virus-host cell interactions. Oxidative stress is a characteristic of some viral infections including influenza. Because antioxidants defend cells from damage caused by reactive oxygen species induced by different stimuli including pathogens, they represent interesting molecules to fight infectious diseases. However, most of the available studies have found that these would-be panaceas could actually exacerbate the diseases they claim to prevent, and have thus revealed "the dark side" of these molecules. This review article discusses the latest opportunities and drawbacks of the antioxidants used in anti-influenza therapy and new perspectives.

Carnosine markedly ameliorates H9N2 swine influenza virus-induced acute lung injury

Oxidative stress injury is an important pathogenesis of influenza virus in critically ill patients. The present study investigated the efficacy of carnosine, an antioxidant and free radical scavenger, on a model of acute lung injury (ALI) induced by H9N2 swine influenza virus. Female specific-pathogen-free BALB/c mice were randomized into four groups and treated as follows: (1) H9N2 group, (2) mock control group, (3) H9N2+carnosine group and (4) carnosine control group. The H9N2 group mice were inoculated intranasally with A/Swine/Hebei/012/2008/ (H9N2) virus (100 μl) in allantoic fluid (AF), whilst mock-infected animals were intranasally inoculated with non-infectious AF. Carnosine [10 mg (kg body mass)- 1] was administered orally (100 μl) for 7 days consecutively. The survival rate, lung water content, TNF-α and IL-1β levels, lung histopathology, myeloperoxidase (MPO) activity, and Toll-like receptor (TLR)-4 levels were determined at 2, 4, 6, 8 and 14 days after inoculation. Carnosine treatment effectively decreased the mortality (43 versus 75 %, P < 0.05), significantly ameliorated pathological lesions in lungs and decreased the lung wet/dry mass ratio (P < 0.05). It also inhibited MPO activity, suppressed TNF-α and IL-1β release, decreased the H9N2 viral titre, and markedly inhibited levels of TLR-4 mRNA and protein in the lungs of infected mice (P < 0.05), which supported the use of carnosine for managing severe influenza cases.

N-acetyl-l-cystine (NAC) protects against H9N2 swine influenza virus-induced acute lung injury

The antioxidant N-acetyl-l-cysteine (NAC) had been shown to inhibit replication of seasonal human influenza A viruses. Here, the effects of NAC on H9N2 swine influenza virus-induced acute lung injury (ALI) were investigated in mice. BALB/c mice were inoculated intranasally with 10⁷ 50% tissue culture infective doses (TCID₅₀) of A/swine/HeBei/012/2008/(H9N2) viruses with or without NAC treatments to induce ALI model. The result showed that pulmonary inflammation, pulmonary edema, MPO activity, total cells, neutrophils, macrophages, TNF-α, IL-6, IL-1β and CXCL-10 in BALF were attenuated by NAC. Moreover, our data showed that NAC significantly inhibited the levels of TLR4 protein and TLR4 mRNA in the lungs. Pharmacological inhibitors of TLR4 (E5564) exerted similar effects like those determined for NAC in H9N2 swine influenza virus-infected mice. These results suggest that antioxidants like NAC represent a potential additional treatment option that could be considered in the case of an influenza A virus pandemic.

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NAC protects against H9N2 swine influenza virus-induced acute lung injury (ALI).

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NAC protects against acute lung injury by inactivation of TLR4.

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Eritoran (E5564), a TLR4 antagonist, also protects against acute lung injury.

Oxygen free radical involvement in acute lung injury induced by H5N1 virus in mice

Background

Acute lung injury is an important cause of death in humans infected with H5N1. It has been found that oxygen free radicals (OFRs) are elevated in lung tissue during influenza virus infections. In this study, we used a mouse model to explore the role of OFRs in acute lung injury caused by H5N1 viral infection.

Methods

Four‐ to six‐week‐old male specific pathogen‐free BALB/c mice were inoculated intranasally with 10⁵ 50% tissue culture infective doses (TCID₅₀) of highly pathogenic A/Chicken/Hebei/108/2002 (H5N1) viruses and were then given 1000 IU of lauric acid modified superoxide dismutase (LA‐SOD) by intraperitoneal injection, starting 2 days post‐infection and continuing for 6 days.

Results

The extent of lung injury and the concentration of OFRs were higher, and the SOD activity was lower in H5N1 virus‐infected mice than that in uninfected control mice on days 3, 6, and 7 post‐inoculation. Weak amelioration of clinical signs, a minor decrease in the total mortality and the extent of lung injury, and the lower OFRs concentration were seen in the LA‐SOD treatment group, but a reduction in lung virus titers was not observed in the LA‐SOD treatment at all time points.

Conclusions

The LA‐SOD treatment has a mild inhibitory effect on H5N1 influenza virus infection in mice. OFRs, therefore, might play an important role in the pathogenesis of acute lung injury induced by H5N1 virus.