Development of a new aerosol delivery system for systemic pulmonary delivery in anaesthetized and orotracheal intubated rats

Intratracheal Bleomycin Aerosolization: The Best Route of Administration for a Scalable and Homogeneous Pulmonary Fibrosis Rat Model?

Idiopathic pulmonary fibrosis (IPF) is a chronic disease with a poor prognosis and is characterized by the accumulation of fibrotic tissue in lungs resulting from a dysfunction in the healing process. In humans, the pathological process is patchy and temporally heterogeneous and the exact mechanisms remain poorly understood. Different animal models were thus developed. Among these, intratracheal administration of bleomycin (BML) is one of the most frequently used methods to induce lung fibrosis in rodents. In the present study, we first characterized histologically the time-course of lung alteration in rats submitted to BLM instillation. Heterogeneous damages were observed among lungs, consisting in an inflammatory phase at early time-points. It was followed by a transition to a fibrotic state characterized by an increased myofibroblast number and collagen accumulation. We then compared instillation and aerosolization routes of BLM administration. The fibrotic process was studied in each pulmonary lobe using a modified Ashcroft scale. The two quantification methods were confronted and the interobserver variability evaluated. Both methods induced fibrosis development as demonstrated by a similar progression of the highest modified Ashcroft score. However, we highlighted that aerosolization allows a more homogeneous distribution of lesions among lungs, with a persistence of higher grade damages upon time.

AEROSOL DELIVERY DURING MECHANICAL VENTILATION TO THE RAT

The authors have adjusted a jet nebulizer to a mechanical ventilator (Servo Ventilator, Siemens) to deliver an aerosol to rats. They aimed to clarify whether a modified jet nebulizer generating particles with a mass median aerodynamic diameter of 2 microm would be effective and safe in intubated ventilated rats. Fluorescent microspheres (diameter: 1.0 microm) were aerosolized to verify qualitatively and quantitatively intrapulmonary deposition. Particle deposition fraction was 3.8% (1.3%) of the delivered dose (median [interquartile range]). There was no evidence for any adverse event as assessed from heart rate, mean arterial pressure, PaO2 and PaCO2 before, during, and after nebulization. No pulmonary tissue trauma was detected histologically.

In vivo, in vitro and ex vivo models to assess pulmonary absorption and disposition of inhaled therapeutics for systemic delivery

Despite the interest in systemic delivery of therapeutic molecules including macromolecular proteins and peptides via the lung, the accurate assessment of their pulmonary biopharmaceutics is a challenging experimental task. This article reviews in vivo, in vitro and ex vivo models currently available for studying lung absorption and disposition for inhaled therapeutic molecules. The general methodologies are discussed with recent advances, current challenges and perspectives, especially in the context of their use in systemic pulmonary delivery research. In vivo approaches in small rodents continue to be the mainstay of assessment by virtue of the acquisition of direct pharmacokinetic data, more meaningful when attention is given to reproducible dosing and control of lung-regional distribution through use of more sophisticated lung-dosing methods, such as forced instillation, microspray, nebulization and aerosol puff. A variety of in vitro lung epithelial cell lines models and primary cultured alveolar epithelial (AE) cells when grown to monolayer status offer new opportunity to clarify the more detailed kinetics and mechanisms of transepithelial drug transport. While continuous cell lines, Calu-3 and 16HBE14o-, show potential, primary cultured AE cell models from rat and human origins may be of greater use, by virtue of their universally tight intercellular junctions that discriminate the transport kinetics of different therapeutic entities. Nevertheless, the relevance of using these reconstructed barriers to represent complex disposition of intact lung may still be debatable. Meanwhile, the intermediate ex vivo model of the isolated perfused lung (IPL) appears to resolve deficiencies of these in vivo and in vitro models. While controlling lung-regional distributions, the preparation alongside a novel kinetic modeling analysis enables separate determinations of kinetic descriptors for lung absorption and non-absorptive clearances, i.e., mucociliary clearance, phagocytosis and/or metabolism. This ex vivo model has been shown to be kinetically predictive of in vivo, with respect to macromolecular disposition, despite limitations concerning short viable periods of 2-3 h and likely absence of tracheobronchial circulation. Given the advantages and disadvantages of each model, scientists must make appropriate selection and timely exploitation of the best model at each stage of the research and development program, affording efficient progress toward clinical trials for future inhaled therapeutic entities for systemic delivery.