Use of plethysmography in assessing the efficacy of antivirals in a mouse model of pandemic influenza A virus

Development of a respiratory disease model for enterovirus D68 in 4-week-old mice for evaluation of antiviral therapies

Enterovirus D68 (EV-D68) is a non-polio enterovirus that affects the respiratory system and can cause serious complications, especially in children and older people with weakened immune systems. As an emerging virus, there are no current antiviral therapies or vaccines available. Our goal was to develop a mouse model of human EV-D68 infection that mimicked the disease observed in humans and could be used for evaluation of experimental therapeutics. This is the first report of a respiratory disease model for EV-D68 infection in mice. We adapted the virus by 30 serial passages in AG129 mice, which are deficient in IFN- α/β and -γ receptors. Despite a lack of weight loss or mortality in mice, lung function measured by plethysmography, showed an increase in enhanced pause (Penh) on days 6 and 7 post-infection. In addition, as virus adapted to mice, virus titer in the lungs increased 50-fold, and the pro-inflammatory cytokines MCP-1 and RANTES increased 15-fold and 2-fold in the lung, respectively. In addition, a time course of mouse-adapted EV-D68 infection was determined in lung, blood, liver, kidney, spleen, leg muscle, spinal cord and brain. Virus in the lung replicated rapidly after intranasal inoculation of adapted virus, 10⁶ CCID₅₀/mL by 4 h and 10^8.3 CCID₅₀/mL by 24 h. Virus then spread to the blood and other tissues, including spinal cord and brain. This mouse model for EV-D68 infection includes enhanced pause (Penh) as an indicator of morbidity, and viremia, virus titers and proinflammatory cytokines in the lung, and lung histopathology as indicators of disease. Our mouse-adapted virus has a similar antiviral profile to the original isolate as well as another respiratory picornavirus, rhinovirus-14. This model will be valuable in evaluating experimental therapies in the future.

Re-understanding anti-influenza strategy: attach equal importance to antiviral and anti-inflammatory therapies

The direct replication of influenza virus is not the only cause of harm to human health; influenza infection leading to a hyper-inflammatory immune response can also result in serious conditions. So, the treatment strategy for influenza needs to keep balance between antivirus and anti-inflammation. Herein, we review the treatment strategies of anti-influenza drugs and traditional Chinese medicines.

Targeting Metabolic Reprogramming by Influenza Infection for Therapeutic Intervention

Influenza is a worldwide health and financial burden posing a significant risk to the immune-compromised, obese, diabetic, elderly, and pediatric populations. We identified increases in glucose metabolism in the lungs of pediatric patients infected with respiratory pathogens. Using quantitative mass spectrometry, we found metabolic changes occurring after influenza infection in primary human respiratory cells and validated infection-associated increases in c-Myc, glycolysis, and glutaminolysis. We confirmed these findings with a metabolic drug screen that identified the PI3K/mTOR inhibitor BEZ235 as a regulator of infectious virus production. BEZ235 treatment ablated the transient induction of c-Myc, restored PI3K/mTOR pathway homeostasis measured by 4E-BP1 and p85 phosphorylation, and reversed infection-induced changes in metabolism. Importantly, BEZ235 reduced infectious progeny but had no effect on the early stages of viral replication. BEZ235 significantly increased survival in mice, while reducing viral titer. We show metabolic reprogramming of host cells by influenza virus exposes targets for therapeutic intervention.

Serum amyloid A (SAA) is an early biomarker of influenza virus disease in BALB/c, C57BL/2, Swiss-Webster, and DBA.2 mice

Assessment of influenza virus disease progression and efficacy of antiviral therapy in the widely used mouse models relies mostly on body weight loss and lung virus titers as markers of disease. However, both parameters have their shortcomings. Therefore, the aim of our study was to find non-invasive markers in the murine model of severe influenza that could detect disease early and predict disease outcome. BALB/c mice were lethally infected with influenza A(H1N1)pdm09 virus and serum samples were collected at various time points. Enzyme-linked immunosorbent assays were performed to quantify amounts of serum amyloid A (SAA), C-reactive protein, complement 3, transferrin, corticosterone, prostaglandin E2, H2O2, and alpha-2,6-sialyltransferase. We found that SAA was the most promising candidate with levels acutely and temporarily elevated by several hundred-fold 3 days post virus inoculation. Upon treatment with oseltamivir phosphate, levels of SAA were significantly decreased. High levels of SAA were associated with poor disease prognosis, whereas body weight loss was not as a reliable predictor of disease outcome. SAA levels were also transiently increased in BALB/c mice infected with influenza A(H3N2) and influenza B virus, as well as in C57BL/2, Swiss-Webster, and DBA.2 mice infected with influenza A(H1N1)pdm09 virus. High levels of SAA often, but not always, were associated with disease outcome in these other influenza virus mouse models. Therefore, SAA represents a valid biomarker for influenza disease detection in all tested mouse strains but its prognostic value is limited to BALB/c mice infected with influenza A(H1N1)pdm09 virus.

Influenza lung injury: mechanisms and therapeutic opportunities

In this Perspectives, we discuss some recent developments in the pathogenesis of acute lung injury following influenza infection, with an emphasis on promising therapeutic leads. Damage to the alveolar-capillary barrier has been quantified in mice, and agents have been identified that can help to preserve barrier integrity, such as vasculotide, angiopoietin-like 4 neutralization, and sphingosine 1-phosphate mimics. Results from studies using mesenchymal stem cells have been disappointing, despite promising data in other types of lung injury. The roles of fatty acid binding protein 5, prostaglandin E2, and the interplay between IFN-γ and STAT1 in epithelial signaling during infection have been addressed in vitro. Finally, we discuss the role of autophagy in inflammatory cytokine production and the viral life cycle and the opportunities this presents for intervention.

Novel Ranking System for Identifying Efficacious Anti-Influenza Virus PB2 Inhibitors

Through antigenic drift and shifts, influenza virus infections continue to be an annual cause of morbidity in healthy populations and of death among elderly and at-risk patients. The emergence of highly pathogenic avian influenza viruses such as H5N1 and H7N9 and the rapid spread of the swine-origin H1N1 influenza virus in 2009 demonstrate the continued need for effective therapeutic agents for influenza. While several neuraminidase inhibitors have been developed for the treatment of influenza virus infections, these have shown a limited window for treatment initiation, and resistant variants have been noted in the population. In addition, an older class of antiviral drugs for influenza, the adamantanes, are no longer recommended for treatment due to widespread resistance. There remains a need for new influenza therapeutic agents with improved efficacy as well as an expanded window for the initiation of treatment. Azaindole compounds targeting the influenza A virus PB2 protein and demonstrating excellent in vitro and in vivo properties have been identified. To evaluate the in vivo efficacy of these PB2 inhibitors, we utilized a mouse influenza A virus infection model. In addition to traditional endpoints, i.e., death, morbidity, and body weight loss, we measured lung function using whole-body plethysmography, and we used these data to develop a composite efficacy score that takes compound exposure into account. This model allowed the rapid identification and ranking of molecules relative to each other and to oseltamivir. The ability to identify compounds with enhanced preclinical properties provides an opportunity to develop more-effective treatments for influenza in patients.

The use of plethysmography in determining the severity of lung pathology in a mouse model of minimally lethal influenza virus infection

To characterize the impact on lung function, we assessed plethysmography parameters in a course of infection with mouse-adapted A/Pennsylvania/14/2010 (H3N2) influenza virus. Several parameters, represented by enhanced pause (penh) and ratio of inspiratory/expiratory time (Ti/Te), were observed that had early (1-7dpi) and robust changes regardless of virus challenge dose. Other parameters, characterized by tidal volume (TV), breathing frequency (freq) and end inspiratory pause (EIP), changed later (7-15dpi) during the course of infection and had a virus challenge dose effect. A third category of lung function parameters, such as peak inspiratory flow, had early, virus challenge-independent changes followed by later changes that were challenge dependent. These parameters changed in a similar manner after infection with a non-mouse adapted virus, although the time-course of many parameters was delayed somewhat when compared with mouse-adapted virus. Histopathological assessment of lung samples corresponded with changes in lung function parameters. This study demonstrates the utility of plethysmography in assessing disease in a mouse model of mild influenza virus infection.

Bugs in the system

Immunity to respiratory virus infection is governed by complex biological networks that influence disease progression and pathogenesis. Systems biology provides an opportunity to explore and understand these multifaceted interactions based on integration and modeling of multiple biological parameters. In this review, we describe new and refined systems‐based approaches used to model, identify, and validate novel targets within complex networks following influenza and coronavirus infection. In addition, we propose avenues for extension and expansion that can revolutionize our understanding of infectious disease processes. Together, we hope to provide a window into the unique and expansive opportunity presented by systems biology to understand complex disease processes within the context of infectious diseases.

Intranasal influenza infection of mice and methods to evaluate progression and outcome

In vivo influenza infection models are critical for understanding viral dynamics and host responses during infection. Mouse models are extremely useful for infection studies requiring a high number of test animals. The vast array of gene knockout mice available is particularly helpful in investigating a particular gene's contributions to infection. Thus, more in vivo scientific experimentation of influenza has been done on mice than any other animal model. Here, we describe the technique of intranasal inoculation of mice and methods for assessing the severity of disease and humane endpoints, and discuss data acquired from infection of female C57BL/6J mice.

Moving H5N1 studies into the era of systems biology

The dynamics of H5N1 influenza virus pathogenesis are multifaceted and can be seen as an emergent property that cannot be comprehended without looking at the system as a whole. In past years, most of the high-throughput studies on H5N1-host interactions have focused on the host transcriptomic response, at the cellular or the lung tissue level. These studies pointed out that the dynamics and magnitude of the innate immune response and immune cell infiltration is critical to H5N1 pathogenesis. However, viral-host interactions are multidimensional and advances in technologies are creating new possibilities to systematically measure additional levels of 'omic data (e.g. proteomic, metabolomic, and RNA profiling) at each temporal and spatial scale (from the single cell to the organism) of the host response. Natural host genetic variation represents another dimension of the host response that determines pathogenesis. Systems biology models of H5N1 disease aim at understanding and predicting pathogenesis through integration of these different dimensions by using intensive computational modeling. In this review, we describe the importance of 'omic studies for providing a more comprehensive view of infection and mathematical models that are being developed to integrate these data. This review provides a roadmap for what needs to be done in the future and what computational strategies should be used to build a global model of H5N1 pathogenesis. It is time for systems biology of H5N1 pathogenesis to take center stage as the field moves toward a more comprehensive view of virus-host interactions.

Compromised respiratory function in lethal influenza infection is characterized by the depletion of type I alveolar epithelial cells beyond threshold levels

During influenza virus infection, it is unclear how much alveolar cell loss can be tolerated before the host succumbs to the disease. We sought to define relevant correlates of disease severity in the mouse influenza model, hypothesizing that a susceptibility threshold exists for alveolar epithelial cell loss. We compared lung pathology, virus spread, alveolar epithelial cell depletion, arterial blood oxygenation, physiological responses measured by unrestrained plethysmography, and oxygen consumption and carbon dioxide production by gas analysis in mice at intervals after infection with virus strains and doses that cause mild (x31) or severe (PR/8) influenza. Both mild and severe infections showed similar degrees of lung damage and virus dissemination until day 6 after inoculation but diverged in survival outcomes from day 9. Day 6 PR/8-infected mice had normal respiratory and gas exchange functions with 10% type I cell loss. However, day 10 PR/8-infected mice had 40% type I cell loss with a concomitant drastic decreases in tidal and minute volumes, Vo(2), Vco(2), and arterial blood oxygenation, compared with a maximum 3% type I cell loss for x31 on day 10 when they recovered body weight and respiratory functions. Alterations in breaths per minute, expiratory time, and metabolic rate were observed in both infections. A threshold for maintenance of proper respiratory function appears to be crossed once 10% of alveolar type I cells are lost. These data indicate that lethality in influenza virus infection is a matter of degree rather than quality.

Methods for evaluation of antiviral efficacy against influenza virus infections in animal models

Compounds undergoing preclinical development for anti-influenza virus activity require evaluation in small animal models. Laboratory mice are most commonly used for initial studies because of size, cost, and availability. Cotton rats, guinea pigs, and ferrets (particularly) have been used for more advanced studies. Each animal infection model has certain limitations relative to human influenza infections. For example, the fever response that is evident in humans only occurs with consistency in ferrets. Mice infected with mouse-adapted viruses and ferrets infected with highly pathogenic avian influenza viruses suffer severe disease, whereas cotton rats and guinea pigs manifest few symptoms. Thus, for each animal model there is a certain set of disease parameters that can be measured. Here we describe methods for assessing the efficacy of anti-influenza virus compounds in each of these animal species.