Formulated muco-regulatory agents in the airways of patients with cystic fibrosis
Project: Research › R: Studentship
PhD Studentship: IBBS funded.<br /><br />Cystic fibrosis (CF) is a lethal hereditary disorder characterised by the unregulated production of viscoelastic mucus, which poses a barrier to the effective delivery of drugs to the CF lung. The barrier properties of CF sputum are thought to be due to the high DNA and actin content that together with mucins form a tangled network, held together by electrostatic charges, hydrogen bonds and van der Waals forces. CF sputum affects the deposition pattern of aerosols on the epithelial surface of the upper respiratory tract and thereby, preventing drug diffusion. To improve drug delivery in CF it is vital to reduce or remove this barrier. Recent studies have suggested that negatively charged species such as unfractionated heparin (UFH), a member of the glycosaminoglycan family, may possess mucoactive properties and shows promise as a potential therapy for treating patients with chronic obstructive pulmonary disease (COPD) and CF. This study investigates the potential mucoactive properties of UFH, and describes the development of dry powder inhaler (DPI) formulations of UFH that can be administered to CF patients to treat airway obstruction. <br /><br />In this study, a novel barrier function assay was employed to investigate the diffusion of the corticosteroid dexamethasone through CF sputum and calf-thymus DNA. In addition, atomic force microscopy (AFM) and confocal laser scanning microscopy (CLSM) were used to investigate the ultrastructure of both whole CF sputum and calf-thymus DNA. The effect of charged oligosaccharides and glycosaminoglycans, as potential mucoactive agents, on the barrier and structural properties of CF sputum were also investigated. The feasibility of producing dry powders of UFH, which are suitable for inhalation from DPIs, using spray drying, was investigated. The effect of these powders on CF sputum rheology was also studied. <br /><br />Studies investigating the barrier properties of CF sputum, showed that sputum significantly (p<0.05) reduced the diffusion of dexamethasone by 90 % in comparison to diffusion through buffer. Following treatment with 1.0 and 10 mg/ml UFH, the diffusion of dexamethasone through CF sputum was significantly (p<0.05) increased. CLSM analysis of untreated CF sputum showed the presence of highly polymerised fibrous bundles of DNA, which were observed to be interacting with F-actin present in the sputum. The fibrous bundles of DNA present in CF sputum were dissipated following treatment with UFH. Therefore, it was hypothesised that UFH may be exerting its mucoactive properties by targeting the interactions between DNA and other components present in CF sputum. Results suggest that the DNA component of CF sputum may also be responsible for the barrier properties of CF sputum. Indeed, it was observed that calf-thymus DNA (5 mg/ml) significantly (p<0.05) reduced the diffusion of dexamethasone. Treatment of calf-thymus DNA (5 mg/ml) with 10 mg/ml UFH, significantly (p<0.05) increased the diffusion of dexamethasone. AFM analysis of calf-thymus DNA showed the presence of DNA networks that exhibited pore sizes of 0.38 ± 0.03 µm. Treatment of DNA (5 mg/ml) with 0.01 mg/ml UFH significantly (p<0.05) increased the pore size of the DNA network to 0.78 0.07 µm. Hence, these data suggest that UFH may possess mucoactive properties. <br /><br />Spray drying was successfully used to produce spherical micronised UFH particles, which were suitable for inhalation. The material, however, was cohesive (forming agglomerates) and hygroscopic, which compromised its physical stability. These properties may render a UFH DPI drug delivery system ineffective, as insufficient fine material would be liberated that would penetrate the deep lung. Co-spray drying UFH with L-leucine significantly reduced the cohesive properties of UFH and improved its physical stability characteristics. Rapid formulation screening studies using a conventional DPI suggested that co-spray dried UFH/leucine formulations are easily dispersed from the inhaler, with the liberation of a large proportion of fine material. In addition, both spray-dried UFH and co-spray dried UFH/leucine significantly (p<0.05) reduced the viscoelasticity of CF sputum.<br /><br />This work suggests that UFH possess mucoactive properties, and that the use of L-leucine may aid the development of dry powder inhaler formulations of UFH, which can be administered to CF patients to treat airway obstruction.
|Effective start/end date||1/09/02 → 31/08/06|