Report of the 'mechanisms of lung injury and immunomodulator interventions in influenza' workshop, 21 March 2010, Ventura, California, USA

Human mesenchymal stromal cells reduce influenza A H5N1-associated acute lung injury in vitro and in vivo

Influenza can cause acute lung injury. Because immune responses often play a role, antivirals may not ensure a successful outcome. To identify pathogenic mechanisms and potential adjunctive therapeutic options, we compared the extent to which avian influenza A/H5N1 virus and seasonal influenza A/H1N1 virus impair alveolar fluid clearance and protein permeability in an in vitro model of acute lung injury, defined the role of virus-induced soluble mediators in these injury effects, and demonstrated that the effects are prevented or reduced by bone marrow-derived multipotent mesenchymal stromal cells. We verified the in vivo relevance of these findings in mice experimentally infected with influenza A/H5N1. We found that, in vitro, the alveolar epithelium's protein permeability and fluid clearance were dysregulated by soluble immune mediators released upon infection with avian (A/Hong Kong/483/97, H5N1) but not seasonal (A/Hong Kong/54/98, H1N1) influenza virus. The reduced alveolar fluid transport associated with down-regulation of sodium and chloride transporters was prevented or reduced by coculture with mesenchymal stromal cells. In vivo, treatment of aged H5N1-infected mice with mesenchymal stromal cells increased their likelihood of survival. We conclude that mesenchymal stromal cells significantly reduce the impairment of alveolar fluid clearance induced by A/H5N1 infection in vitro and prevent or reduce A/H5N1-associated acute lung injury in vivo. This potential adjunctive therapy for severe influenza-induced lung disease warrants rapid clinical investigation.

Reduction of influenza virus-induced lung inflammation and mortality in animals treated with a phosophodisestrase-4 inhibitor and a selective serotonin reuptake inhibitor

Inflammatory responses contribute to the morbidity and mortality of severe influenza. Current antiviral therapy offers limited success in treating severe influenza infection with both H1N1 and H5N1 viruses. We evaluated the effect of a neuraminidase inhibitor in combination with immunomodulatory drugs in vitro and in a mouse model of influenza A H1N1 infection by determining survival rate, lung inflammation markers and histopathology. Sertraline and rolipram significantly improved survival in mice infected with a lethal dose of influenza A H1N1 virus. Prophylactic treatment resulted in survival rates of 40% (rolipram), 30% (oseltamivir), 0% (sertraline), 100% (rolipram/oseltamivir) and 70% (sertraline/oseltamivir). Treatment in a therapeutic setting (24 h post-infection) resulted in 80% (rolipram/oseltamivir) and 40% (sertraline/oseltamivir) survival. Sertraline and rolipram had no effect on virus replication in vitro and in vivo, but significantly reduced lung inflammation. A significant reduction in cellular infiltration (10-fold) along with inflammatory cytokines monocyte chemotactic protein-1 (10-fold), interleukin-6 (5-fold) and regulated on activation normal T cell expressed and secreted (5-fold) was observed in the animals treated with the combination compared to oseltamivir alone. Lung histopathology of mice treated with combinations revealed significantly reduced consolidation, infiltration and alveolitis compared to oseltamivir alone. Rolipram and sertraline reduced H1N1 virus-induced lung inflammation and mortality. These data support further development of immunomodulatory agents for severe influenza.

Influenza A induced cellular signal transduction pathways

Influenza A is a negative sense single stranded RNA virus that belongs to the Orthomyxoviridae Family. This enveloped virus contains 8 segments of viral RNA which encodes 11 viral proteins. Influenza A infects humans and is the causative agent of the flu. Annually it infects approximately 5% to 15% of the population world wide and results in an estimated 250,000 to 500,000 deaths a year. The nature of influenza A replication results in a high mutation rate which results in the need for seasonal vaccinations. In addition the zoonotic nature of the influenza virus allows for recombination of viral segments from different strains creating new variants that have not been encountered before. This type of mutation is the method by which pandemic strains of the flu arises. Infection with influenza results in a respiratory illness that for most individuals is self limiting. However in susceptible populations which include individuals with pre-existing pulmonary or cardiac conditions, the very young and the elderly fatal complications may arise. The most serious of these is the development of viral pneumonia which may be accompanied by secondary bacterial infections. Progression of pneumonia leads to the development of acute respiratory distress syndrome (ARDS), acute lung injury (ALI) and potentially respiratory failure. This progression is a combined effect of the host immune system response to influenza infection and the viral infection itself. This review will focus on molecular aspects of viral replication in alveolar cells and their response to infection. The response of select innate immune cells and their contribution to viral clearance and lung epithelial damage will also be discussed. Molecular aspects of antiviral response in the cells in particular the protein kinase RNA dependent response, and the oligoadenylate synthetase RNAse L system in relation to influenza infection.

Peptide targeting and imaging of damaged lung tissue in influenza-infected mice

AIM

In this study, we investigate whether pH (low) insertion peptide (pHLIP) can target regions of lung injury associated with influenza infection.

MATERIALS & METHODS

Fluorophore-conjugated pHLIP was injected intraperitoneally into mice infected with a sublethal dose of H1N1 influenza and visualized histologically.

RESULTS

pHLIP specifically targeted inflamed lung tissues of infected mice in the later stages of disease and at sites where alveolar type I and type II cells were depleted. Regions of pHLIP-targeted lung tissue were devoid of peroxiredoxin 6, the lung-abundant antioxidant enzyme, and were deficient in pneumocytes. Interestingly, a pHLIP variant possessing mutations that render it insensitive to pH changes was also able to target damaged lung tissue.

CONCLUSION

pHLIP holds potential for delivering therapeutics for lung injury during influenza infection. Furthermore, there may be more than one mechanism that enables pHLIP variants to target inflamed lung tissue.

The controversy over H5N1 transmissibility research: an opportunity to define a practical response to a global threat

Since December 2011, influenza virologists and biosecurity experts have been engaged in a controversial debate over research on the transmissibility of H5N1 influenza viruses. Influenza virologists disagreed with the NSABB's recommendation not to publish experimental details of their findings, whereas biosecurity experts wanted the details to be withheld and future research restricted. The virologists initially declared a voluntary moratorium on their work, but later the NSABB allowed their articles to be published, and soon transmissibility research will resume. Throughout the debate, both sides have had understandable views, but both have overlooked the more important question of whether anything could be done if one of these experimentally derived viruses or a naturally occurring and highly virulent influenza virus should emerge and cause a global pandemic. This is a crucial question, because during the 2009 H1N1 influenza pandemic, more than 90% of the world's people had no access to timely supplies of affordable vaccines and antiviral agents. Observational studies suggest that inpatient statin treatment reduces mortality in patients with laboratory-confirmed seasonal influenza. Other immunomodulatory agents (glitazones, fibrates and AMPK agonists) improve survival in mice infected with influenza viruses. These agents are produced as inexpensive generics in developing countries. If they were shown to be effective, they could be used immediately to treat patients in any country with a basic health care system. For this reason alone, influenza virologists and biosecurity experts need to join with public health officials to develop an agenda for laboratory and clinical research on these agents. This is the only approach that could yield practical measures for a global response to the next influenza pandemic.

Newer influenza antivirals, biotherapeutics and combinations

This summary provides an overview of investigational antiviral agents for influenza and of future directions for development of influenza therapeutics. While progress in developing clinically useful antiviral agents for influenza has been generally slow, especially with respect to seriously ill and high-risk patients, important clinical studies of intravenous neuraminidase inhibitors, antibodies and drug combinations are currently in progress. The current decade offers the promise of developing small molecular weight inhibitors with novel mechanisms of action, including host-directed therapies, new biotherapeutics and drug combinations, that should provide more effective antiviral therapies and help mitigate the problem of antiviral resistance. Immunomodulatory interventions also offer promise but need to be based on better understanding of influenza pathogenesis, particularly in seriously ill patients. The development of combination interventions, immunomodulators and host-directed therapies presents unique clinical trial design and regulatory hurdles that remain to be addressed.