The 3Rs on World Asthma Day

Asthma is a common chronic disease of the respiratory system that affects around 5.4 million people in the UK and more than 300 million globally. Many patients have symptoms that can’t be effectively controlled. Various animal species are currently used in asthma research, including mice, rats, guinea pigs, dogs and non-human primates. The limitations of the animal models have been well documented and of course by definition many are associated with suffering and distress because of the nature of the procedures involved. These factors have driven the asthma research community to seek new approaches and we have harnessed this to maximise the use of advances in tissue engineering and mathematical modelling as well as organisms such as the fruit fly that aren’t traditionally used by the respiratory biology community.

The NC3Rs strategy has been led by our head of technology development Dr Anthony Holmes and guided by an expert group with representatives from industry and academia and provides a template for applying the 3Rs (primarily replacement) to other disease areas. At the heart of the strategy has been the recognition that multi-disciplinary approaches are essential and much of our effort has been placed on fostering links between different research communities. Our approach has ranged from funding research to develop and test new approaches through to working with agencies such as the Human Tissue Authority to increase the availability of human tissue for asthma researchers. There is still some way to go before the “go-to” mouse models are replaced but important steps are being made to achieve this with significant buy-in from those who ultimately will be using the models to benefit patients.

One question we have asked is “Can you study asthma in organisms that don’t have lungs?” It is a pretty fundamental question and if you think the answer is “no”, you may be surprised! The potential of non-mammalian systems such as the nematode worm, fruit fly and zebrafish has not been fully investigated by the asthma research community and to address this in 2014 we funded four projects totalling around £0.5 million to test whether these organisms could be used as part of the asthma researchers’ “toolkit”. The outcomes of the awards are starting to emerge and the results are really interesting. For example, one of the awards was to Professor Donna Davies from the University of Southampton to use Drosophila to explore the function of asthma susceptibility genes. The team at Southampton has been studying two genes associated with the development of asthma. While population studies in humans had pinpointed the involvement of the genes in asthma, their function has remained unknown. By expressing the genes in the fly, they observed significant distortions in the structure of the fly’s airway, which affected its permeability. In people with asthma, similar effects might allow allergens and pollutants to move across the airway barrier. This has the potential to trigger an asthmatic reaction, and is now the focus of the team’s ongoing research, proving the value of using simple systems. Donna is very enthusiastic about this proof-of-concept work and says “I have been impressed by how quickly we have been able to understand how the two asthma genes affect the airways of the fly. Similar studies in vertebrate models would have taken many, many years. I hope we can continue to study the fruit fly model and test it as a rapid screening tool for potential novel therapies.”

In the same funding call, Professor Maggie Dallman from Imperial College London was awarded a grant to develop a zebrafish model for the study of respiratory inflammation. Maggie and colleagues have previously shown that the response of gill tissue to inflammatory stimuli such as cigarette smoke reflects some features of the responses observed in humans. With the recent NC3Rs funding, the team has developed a non-invasive approach to sampling from the gill which allows longitudinal studies in fish to examine basic mechanisms and pathway biology of severe asthma.

Commenting on the project, Maggie says: “Most people would think that fish gills are a poor model for human respiratory disease. But we reasoned that if the gills’ function and structure is similar to human lungs, then they could behave in a similar way and could be used as a model. It’s been an incredibly positive experience; we are hoping that the outcomes will convince even the sceptics that the zebrafish gill model is relevant for studying conditions like asthma and chronic obstructive pulmonary disease.”

The best models are likely to be dependent on the use of human cells and tissues. This is one of the many advantages that the tissue engineering revolution is delivering – the ability to combine human cells in dynamic systems that allow the complexity of multi-cellular architecture and function to be closely recapitulated, providing a realistic alternative to the use of traditional animal models. Donna Davies has also been at the forefront of this and illustrates the importance of combining different approaches. Donna has received nearly £1 million of funding from the NC3Rs for tissue engineering approaches. She has developed an integrated tissue engineered model of the human airway, with lung epithelial cells (the cells that line the airways and form a ‘barrier’ to the external environment) and endothelial cells (the cells that interface with the blood) on opposite sides of a porous membrane. The epithelial cells are exposed to air and the cells are supplied with nutrition via microfluidic flow of medium with nutrients (‘blood’) which allows long term studies and enables the introduction of immune cells. The platform can be used to look at the relationship between different cell types and measure the barrier properties of the airway epithelium in real time using impedance spectroscopy and time-lapse microscopy.

Donna says: “This work has allowed us to develop complex models using epithelial cells that have been collected from the airways of volunteers with asthma. With these models we can monitor how the integrity of the epithelial barrier changes in response to an environmental trigger and how this affects the recruitment of immune cells. What is really exciting is that our parellel work with the fruit fly has given us real insight into the underlying genetic causes of why and how the epithelial barrier is abnormal in asthma.  We are now in a position to move from the simple fly model to the human tissue-engineered model to test new ideas and develop novel therapies.”