Asymmetrical flow field-flow fractionation method for the analysis of submicron protein aggregates.

For the analysis of protein aggregates in the submicron size range, there is still a need for reliable, quantitative methods that can assist the development of therapeutic protein formulations. The aim of our study was to develop an asymmetrical flow field-flow fractionation (AF4) method for the analysis of protein aggregates in the size range of up to approximately 1000 nm. Method development was performed with polystyrene standard beads (60, 200, and 1000 nm) and a heat-stressed IgG formulation containing a substantial amount of submicron aggregates. By AF4, the analysis of these heterodisperse submicron IgG aggregates, as well as the monomer, could be achieved by a stepwise reduction of the cross-flow. The suitability of the developed AF4 method for aggregate analysis in general was demonstrated by analyzing several other stressed therapeutic protein samples (another IgG and etanercept). In each case, a clearly better separation and a more reproducible (although in some cases incomplete) recovery was achieved with AF4 as compared with high-performance size-exclusion chromatography. In conclusion, AF4 proved to be a valuable method for the characterization and quantification of submicron protein aggregates.