Cystic fibrosis sputum - A barrier to the transport of nanospheres

Cystic fibrosis (CF) is characterized by the presence of a viscoelastic muc us layer in the upper airways and bronchi. The underlying problem is a muta tion in the gene encoding the cystic fibrosis transmembrane conductance reg ulator protein. Clinical studies of gene transfer for CF are ongoing. For g ene delivery to the airways of CF patients to be effective, the mucus cover ing the target cells must be overcome. We therefore examined the extent to which CF sputum presents a physical barrier to the transport of nanospheres of a size comparable to that of lipoplexes and other transfection systems currently being clinically evaluated for CF gene therapy. We observed that an extremely low percentage of nanospheres (< 0.3%) moved through a 220-<mu >m-thick CF sputum layer after 150 min. The largest nanospheres studied (56 0 nm) were almost completely blocked by the sputum, whereas the smaller nan ospheres (124 nm) were retarded only by a factor of 1.3 as compared with bu ffer. Surprisingly, the nanospheres diffused significantly more easily thro ugh the more viscoelastic sputum samples. We hypothesize that the structure of the network in sputum becomes more macroporous when the sputum becomes more viscoelastic. Sputum from a patient with chronic obstructive pulmonary disease retarded the transport of nanospheres to the same extent as did CF sputum. When directly mixed with CF sputum, recombinant human deoxyribonuc lease I moderately facilitated the transport of nanospheres through CF sput um.