Inhalation delivery of proteins from ethanol suspensions

To circumvent inherent problems associated with pulmonary administration of aqueous-solution and dry-powder protein drugs, inhalation delivery of prot eins from their suspensions in absolute ethanol was explored both in vitro and in vivo. Protein suspensions in ethanol of up to 9% (wt/vol) were readi ly aerosolized with a commercial compressor nebulizer. Experiments with enz ymic proteins revealed that nebulization caused no detectable loss of catal ytic activity; furthermore, enzyme suspensions in anhydrous ethanol retaine d their full catalytic activity for at least 3 weeks at room temperature. W ith the use of Zn2+-insulin, conditions were elaborated that produced submi cron protein particles in ethanol suspensions. The latter (insulin/EtOH) af forded respirable-size aerosol particles after nebulization. A 40-min expos ure of laboratory rats to 10 mg/ml insulin/EtOH aerosols resulted in a 2-fo ld drop in the blood glucose level and a marked rise in the serum insulin l evel. The bioavailability based on estimated deposited lung dose of insulin delivered by inhalation of ethanol suspension aerosols was 33% (relative t o an equivalent s.c. injection), i.e., comparable to those observed in rats after inhalation administration of dry powder and aqueous solutions of ins ulin. Inhalation of ethanol in a relevant amount/time frame resulted in no detectable acute toxic effects on rat lungs or airways, as reflected by the absence of statistically significant inflammatory or allergic responses, d amage to the alveolar/capillary barrier, and lysed and/or damaged cells.