Stabilizing protein formulations during air-jet nebulization

Abstract

Whilst some proteins can be effectively administered to the lungs using a nebulizer, others, such as lactate dehydrogenase (LDH) are degraded during air-jet nebulization. In order to deliver LDH by nebulization a protective delivery system or carrier may therefore be appropriate. The aim of this study was to produce and characterize a formulation of LDH, which retains enzyme activity during nebulization. Chitosan, a biocompatible, biodegradable and bioadhesive polysaccharide polymer, was included in the formulations studied as a potential protective agent. Complexes of LDH with chitosan of different molecular weights and concentrations were assessed for size, zeta potential, aerosol droplet size and delivery from a jet nebulizer. The highest molecular weight chitosan had the greatest complex size and a net positive charge of +29.7 mV. Jet nebulization resulted in aerosol droplets with median size in the range 2.36–3.52 μm. Nebulization of LDH solution resulted in enzyme denaturation and reduced activity. The stability of LDH was greatly improved in formulations with chitosan; with greater than 50% total LDH available in a nebulizer delivered to the lower stage of a two-stage impinger, with up to 62% retained enzyme activity. The nonionic surfactant Tween 80 also improved the stability of LDH to nebulization and had an additive protective effect when included, with chitosan, in formulations. These findings suggest chitosan may be a useful excipient in the preparation of stable protein formulations for jet nebulization.