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Background
Respiratory diseases, both chronic and acute, account for millions of deaths every year. In 2012 about 68% of global deaths were caused by noncommunicable diseases (NCD), with chronic lung disease being one of the four main reasons [1]. The very fact that of the approximately 38 million annual deaths attributed to NCD about 10.5% are accounted for by chronic respiratory diseases (CRD) [2], emphasizes the urgent need for improved respiratory therapies.
In this context of understanding physiological lung behavior in-vitro , it is essential to develop new therapeutic substances. In recent years, the technique of precision-cut lung slices (PCLS) has expanded the tools available for respiratory research with a link between human based in-vitro models and complex cellular anatomy [3]. PCLS, as a 3D organotypic tissue model, reflects the natural and relevant microanatomy of the respiratory tract, as well as its functional responses to specific stimuli [4-7]. Especially with regard to the three Rs principle, PCLS represents an alternative to in-vivo models and can help to reduce the number of animal studies [3].
Since the description of human agarose-filled lung slices in 1994 [8], optimizations have been made to reproducibly prepare very thin tissue slices of defined thickness. These improvements have led to the wide application of the PCLS technique [7, 9-11]. Ever since, PCLS from different species have been used for the assessment of pharmacological and toxicological compounds [7, 9, 10], as well as to model airway constriction [6]. Additionally, the use of PCLS as a model has expanded into the fields of nanotechnology [12, 13] and virology [14]. However, most of these studies using PCLS were conducted under short-term culturing conditions (?72 h) [9, 13, 15], which limits their value to certain questions investigating rapid and acute effects. Accordingly, slowly metabolized therapeutics or chemicals, as well as repeated applications, which might be important to investigate basic mechanisms and treatments of CRD, have not been addressed with cultured PCLS. Even though some effort has been made prior to 2000 to establish long-term cultivation of agarose-embedded tracheal and lung tissue [16-18], these studies only focused on limited endpoints to evaluate the feasibility of long-term cultivation of lung tissue.
The maintenance of structural and cellular integrity of long-term cultivated murine or porcine lungs has primarily...