PROTEIN NEBULIZATION .2. STABILIZATION OF G-CSF TO AIR-JET NEBULIZATION AND THE ROLE OF PROTECTANTS

Air-jet nebulization induces aggregation and degradation of granulocyt e-colony stimulating factor (G-CSF). The air-water interface as a site for destabilization of G-CSF is investigated and possible mechanisms of stabilization by polyethylene glycol (PEG) and Tween 80 are propose d. Equilibrium surface tension measurements show that G-CSF is highly surface-active, but dynamic surface tension measurements made using a maximum bubble pressure surface tensionometer show that G-CSF and surf actants have little surface activity in the interval between formation and destruction of aerosol generated within a nebulizer. Bubbling of air through solutions of 4 mg/ml G-CSF for up to 1 h resulted in appro ximate to 10% aggregation of total protein suggesting that destabiliza tion at the air-water interface occurs. Polyethylene glycol (PEG) and Tween 80 are effective in reducing aggregation and degradation of G-CS F but their respective modes of protection differ. Protection is impro ved by increasing the PEG molecular weight and concentration indicatin g that PEG may influence stability through steric effects. In contrast , the protective effects of Tween 80 appear to relate tp the micellar properties and not to the surface activity of the surfactant.