Prevention of structural perturbations and aggregation upon encapsulation of bovine serum albumin into poly(lactide-co-glycolide) microspheres using the solid-in-oil-in-water technique

Bovine serum albumin (BSA) was encapsulated into poly(lactide-co-glycolide) (PLG) microspheres by a solid-in-oil-in-water (s/o/w) technique. We tested whether perturbations in BSA secondary structure could be minimized during encapsulation by using trehalose and how this would influence BSA aggregat ion and release. BSA secondary structure was monitored noninvasively by Fou rier-transform infrared spectroscopy. When BSA was co-lyophilized with treh alose, lyophilization-induced structural perturbations were significantly r educed. The formulation obtained (BSA-Tre) was encapsulated into PLG micros pheres and, by optimizing critical encapsulation parameters, a loading effi ciency of 85 % was achieved. However, due to the loss of the excipient in t he o/w emulsion step, the structure of BSA-Tre was more perturbed than befo re encapsulation. Excipient-loss and encapsulation-induced structural pertu rbations could be prevented by saturating the aqueous phase in the o/w step with trehalose and by using the organic solvent chloroform. This in turn r educed the formation of soluble BSA aggregates. BSA was released from PLG m icrospheres using the improved formulations with an initial release in 24 h of not more than 22 %, followed by a sustained release over at least 2 wee ks. In summary, optimization of the encapsulation conditions in the s/o/w p rocedure resulted in the encapsulation of BSA without procedure-induced str uctural perturbations and minimized the release of aggregated protein. This demonstrates that the s/o/w technique is an excellent alternative to the m ost common encapsulation procedure, namely the water-in-oil-in-water techni que.