Are pigs more human than mice?

Pseudomonas aeruginosa: Infections, Animal Modeling, and Therapeutics

Pseudomonas aeruginosa is an important Gram-negative opportunistic pathogen which causes many severe acute and chronic infections with high morbidity, and mortality rates as high as 40%. What makes P. aeruginosa a particularly challenging pathogen is its high intrinsic and acquired resistance to many of the available antibiotics. In this review, we review the important acute and chronic infections caused by this pathogen. We next discuss various animal models which have been developed to evaluate P. aeruginosa pathogenesis and assess therapeutics against this pathogen. Next, we review current treatments (antibiotics and vaccines) and provide an overview of their efficacies and their limitations. Finally, we highlight exciting literature on novel antibiotic-free strategies to control P. aeruginosa infections.

Establishment and Characterization of Immortalized Miniature Pig Pancreatic Cell Lines Expressing Oncogenic K-RasG12D

In recent decades, many studies on the treatment and prevention of pancreatic cancer have been conducted. However, pancreatic cancer remains incurable, with a high mortality rate. Although mouse models have been widely used for preclinical pancreatic cancer research, these models have many differences from humans. Therefore, large animals may be more useful for the investigation of pancreatic cancer. Pigs have recently emerged as a new model of pancreatic cancer due to their similarities to humans, but no pig pancreatic cancer cell lines have been established for use in drug screening or analysis of tumor biology. Here, we established and characterized an immortalized miniature pig pancreatic cell line derived from primary pancreatic cells and pancreatic cancer-like cells expressing K-ras^G12D regulated by the human PTF1A promoter. Using this immortalized cell line, we analyzed the gene expression and phenotypes associated with cancer cell characteristics. Notably, we found that acinar-to-ductal transition was caused by K-ras^G12D in the cell line constructed from acinar cells. This may constitute a good research model for the analysis of acinar-to-ductal metaplasia in human pancreatic cancer.

The Pig: A Relevant Model for Evaluating the Neutrophil Serine Protease Activities during Acute Pseudomonas aeruginosa Lung Infection

The main features of lung infection and inflammation are a massive recruitment of neutrophils and the subsequent release of neutrophil serine proteases (NSPs). Anti-infectious and/or anti-inflammatory treatments must be tested on a suitable animal model. Mice models do not replicate several aspects of human lung disease. This is particularly true for cystic fibrosis (CF), which has led the scientific community to a search for new animal models. We have shown that mice are not appropriate for characterizing drugs targeting neutrophil-dependent inflammation and that pig neutrophils and their NSPs are similar to their human homologues. We induced acute neutrophilic inflammatory responses in pig lungs using Pseudomonas aeruginosa, an opportunistic respiratory pathogen. Blood samples, nasal swabs and bronchoalveolar lavage fluids (BALFs) were collected at 0, 3, 6 and 24 h post-insfection (p.i.) and biochemical parameters, serum and BAL cytokines, bacterial cultures and neutrophil activity were evaluated. The release of proinflammatory mediators, biochemical and hematological blood parameters, cell recruitment and bronchial reactivity, peaked at 6h p.i.. We also used synthetic substrates specific for human neutrophil proteases to show that the activity of pig NSPs in BALFs increased. These proteases were also detected at the surface of lung neutrophils using anti-human NSP antibodies. Pseudomonas aeruginosa-induced lung infection in pigs results in a neutrophilic response similar to that described for cystic fibrosis and ventilator-associated pneumonia in humans. Altogether, this indicates that the pig is an appropriate model for testing anti-infectious and/or anti-inflammatory drugs to combat adverse proteolytic effects of neutrophil in human lung diseases.

The bovine lung in biomedical research: visually guided bronchoscopy, intrabronchial inoculation and in vivo sampling techniques

There is an ongoing search for alternative animal models in research of respiratory medicine. Depending on the goal of the research, large animals as models of pulmonary disease often resemble the situation of the human lung much better than mice do. Working with large animals also offers the opportunity to sample the same animal repeatedly over a certain course of time, which allows long-term studies without sacrificing the animals.

The aim was to establish in vivo sampling methods for the use in a bovine model of a respiratory Chlamydia psittaci infection. Sampling should be performed at various time points in each animal during the study, and the samples should be suitable to study the host response, as well as the pathogen under experimental conditions.

Bronchoscopy is a valuable diagnostic tool in human and veterinary medicine. It is a safe and minimally invasive procedure. This article describes the intrabronchial inoculation of calves as well as sampling methods for the lower respiratory tract. Videoendoscopic, intrabronchial inoculation leads to very consistent clinical and pathological findings in all inoculated animals and is, therefore, well-suited for use in models of infectious lung disease. The sampling methods described are bronchoalveolar lavage, bronchial brushing and transbronchial lung biopsy. All of these are valuable diagnostic tools in human medicine and could be adapted for experimental purposes to calves aged 6-8 weeks. The samples obtained were suitable for both pathogen detection and characterization of the severity of lung inflammation in the host.

The pig as a model for investigating the role of neutrophil serine proteases in human inflammatory lung diseases

The serine proteases released by activated polymorphonuclear neutrophils [NSPs (neutrophil serine proteases)] contribute to a variety of inflammatory lung diseases, including CF (cystic fibrosis). They are therefore key targets for the development of efficient inhibitors. Although rodent models have contributed to our understanding of several diseases, we have previously shown that they are not appropriate for testing anti-NSP therapeutic strategies [Kalupov, Brillard-Bourdet, Dade, Serrano, Wartelle, Guyot, Juliano, Moreau, Belaaouaj and Gauthier (2009) J. Biol. Chem. 284, 34084–34091). Thus NSPs must be characterized in an animal model that is much more likely to predict how therapies will act in humans in order to develop protease inhibitors as drugs. The recently developed CFTR^−/− (CFTR is CF transmembrane conductance regulator) pig model is a promising alternative to the mouse model of CF [Rogers, Stoltz, Meyerholz, Ostedgaard, Rokhlina, Taft, Rogan, Pezzulo, Karp, Itani et al. (2008) Science 321, 1837–1841]. We have isolated blood neutrophils from healthy pigs and determined their responses to the bacterial pathogens Pseudomonas aeruginosa and Staphylococcus aureus, and the biochemical properties of their NSPs. We used confocal microscopy and antibodies directed against their human homologues to show that the three NSPs (elastase, protease 3 and cathepsin G) are enzymatically active and present on the surface of triggered neutrophils and NETs (neutrophil extracellular traps). All of the porcine NSPs are effectively inhibited by human NSP inhibitors. We conclude that there is a close functional resemblance between porcine and human NSPs. The pig is therefore a suitable animal model for testing new NSP inhibitors as anti-inflammatory agents in neutrophil-associated diseases such as CF.

A bovine model of respiratory Chlamydia psittaci infection: challenge dose titration

This study aimed to establish and evaluate a bovine respiratory model of experimentally induced acute C. psittaci infection. Calves are natural hosts and pathogenesis may resemble the situation in humans. Intrabronchial inoculation of C. psittaci strain DC15 was performed in calves aged 2–3 months via bronchoscope at four different challenge doses from 10⁶ to 10⁹ inclusion-forming units (ifu) per animal. Control groups received either UV-inactivated C. psittaci or cell culture medium. While 10⁶ ifu/calf resulted in a mild respiratory infection only, the doses of 10⁷ and 10⁸ induced fever, tachypnea, dry cough, and tachycardia that became apparent 2–3 days post inoculation (dpi) and lasted for about one week. In calves exposed to 10⁹ ifu C. psittaci, the respiratory disease was accompanied by severe systemic illness (apathy, tremor, markedly reduced appetite). At the time point of most pronounced clinical signs (3 dpi) the extent of lung lesions was below 10% of pulmonary tissue in calves inoculated with 10⁶ and 10⁷ ifu, about 15% in calves inoculated with 10⁸ and more than 30% in calves inoculated with 10⁹ ifu C. psittaci. Beside clinical signs and pathologic lesions, the bacterial load of lung tissue and markers of pulmonary inflammation (i.e., cell counts, concentration of proteins and eicosanoids in broncho-alveolar lavage fluid) were positively associated with ifu of viable C. psittaci. While any effect of endotoxin has been ruled out, all effects could be attributed to infection by the replicating bacteria. In conclusion, the calf represents a suitable model of respiratory chlamydial infection. Dose titration revealed that both clinically latent and clinically manifest infection can be reproduced experimentally by either 10⁶ or 10⁸ ifu/calf of C. psittaci DC15 while doses above 10⁸ ifu C. psittaci cannot be recommended for further studies for ethical reasons. This defined model of different clinical expressions of chlamydial infection allows studying host-pathogen interactions.

Tissue and cellular expression patterns of porcine CFTR: similarities to and differences from human CFTR

Emerging porcine models of cystic fibrosis (CF) are expected to mimic the human disease more closely than current mouse models do. However, little is known of the tissue and cellular expression patterns of the porcine CF transmembrane conductance regulator (pCFTR) and possible differences from human CFTR (hCFTR). Here, the expression pattern of pCFTR was systematically established on the mRNA and protein levels. Using specific anti-pCFTR antibodies, the majority of the protein was immunohistochemically detected on paraffin-embedded sections and on cryostate sections in the apical cytosol of intestinal crypt epithelial cells, nasal, tracheal, and bronchial epithelial cells, and other select, mostly glandular epithelial cells. Confocal laser scanning microscopy with co-localization of the Golgi marker 58K localized the protein in the cytosol between the Golgi apparatus and the apical cell membrane with occasional punctate or diffuse staining of the apical membrane. The tissue and cellular distribution patterns were confirmed by RT-PCR from whole tissue lysates or select cells after laser capture microdissection. Thus, expression of pCFTR was found to largely resemble that of hCFTR except for the kidney, brain, and cutaneous glands, which lack expression in pigs. Species-specific differences between pCFTR and hCFTR may become relevant for future interpretations of the CF phenotype in pig models.