Pulmonary delivery of drugs has been used extensively in the treatment of respiratory diseases such as asthma, chronic obstructive pulmonary disease (COPD), and cystic fibrosis for many years. 1,2) Recently it is also studied widely for a optional administration route of large molecules drugs because the lung has large surface area, good permeability and high blood flow.3) Several drug delivery carriers have been used in the pulmonary administration of peptides and proteins including insulin. These can be liquid, solid or gaseous excipients, as has been reviewed by Courrier et al. 4) Compared with other carriers, dry powders offer more advantages, including enhanced drug stability, greater accuracy in dosing, breath-actuated delivery, improved patient compliance, and preferred delivery systems for protein and peptide drugs that are susceptible to degradation upon extended storage in aqueous solution.5) However, under normal circumstances, the alveolar-capillary barrier prevents fast absorption of macromolecules into the blood and thus the bioavailability is not high enough to promise effective systemic therapy.6,7) So, efficient pulmonary delivery requires drug powders with some additives (e.g. absorption enhancers), which can increase the amount of macromolecules reaching the blood flow. Various protease inhibitors, surfactants, lipids, polymers and other agents have been tested to improve the systemic availability of macromolecular drugs by pulmonary administration, but most of them were unsatisfactory for effectiveness or safety reasons.
8)Pulmonary surfactant (PS), a complex mixture of 78-90% phospholipids, 5-10% proteins and 4-10% neutral lipids, is synthesized and released by type II alveolar epithelial cells mainly to reduce surface tension at the gas-liquid interface of the lung. Jing et al. 9) proved that artificial pulmonary surfactant had the potential to improve the bioavailability of intratracheally instilled insulin. Our previous studies revealed that PS could enhance the absorption of insulin by lung in normal rats and it might be a possible absorption enhancer.10) However, the development of PS as absorption enhancer is difficult because of its limited content and perishable composition. Meanwhile, previous works in our laboratory showed that phospholipid hexadecanol tyloxapol (PHT), the analogical composition of PS, had similar capacity to promote the absorption of pulmonarily administered recombinant human insulin (rh-insulin) in normal rats (data not published yet). Then, it was speculated that PHT could be a promising absorption enhancer which could be applied to facilitate the pulmonary absorption of insulin.The objective of the present study was to evaluate the in vivo pharmacological activity of PS-or PHT-loaded dry powders for pulmonary delivery of rh-insulin in diabetic rats. Meanwhile, the toxicity of PS and PHT was estimated through a BAL (Bronchoalveolar Lavage) method.
ExperimentalMaterials Streptozotocin (STZ) was obtained from Sigma-Aldrich (St. Louis, U.S.A.). Recombinant human ...