Optimization considerations for the purification of alpha1-antitrypsin using silica-based ion-exchange adsorbents in packed and expanded beds.

Abstract

The influences of the fluid superficial velocity, sample concentration, loading volume, and wash cycle on the recovery and corresponding purification factors for alpha1-antitrypsin [syn. alpha1-proteinase inhibitor (alpha1-PI)] from crude mixtures of human plasma proteins were investigated using packed and expanded beds of DEAE-Spherodex LS. As part of this study, the effect of fluid superficial velocity on the bed dispersion number (Dv) and dispersion coefficient (D) for this adsorbent in expanded beds was determined with feedstocks containing human serum albumin (HSA), the most abundant of the contaminating proteins in human plasma protein preparations used for the isolation of alpha1-PI. When multicomponent protein feedstocks prepared from human plasma were examined with DEAE-Spherodex LS, reduced chromatographic productivity was observed for alpha1-PI as the extent of column utilization and the superficial velocity were increased, yet the opposite trend was evident for HSA. In particular, higher adsorption capacities and recoveries were obtained for alpha1-PI at lower fluid superficial velocities with both packed and expanded bed conditions. These findings indicate that for process scale purifications of alpha1-PI from multicomponent feedstocks with expanded beds containing this silica-based ion-exchange adsorbent, the optimal range of superficial velocities to achieve the highest bed productivity will not be synonymous with maximally fluidized modes of operation. Rather, the results confirm that the adsorbent has an optimum operational performance when fluidization procedures corresponding to plug flow expansion are employed for the capture of alpha1-PI. These findings also indicate that advantage can be taken of displacement effects between closely related protein species with packed and expanded bed systems containing the DEAE-Spherodex LS type of ion-exchange porous silicas.