Effect of PEGylation on performance of protein microbubbles and its comparison with lipid microbubbles

Aqueous suspensions of microbubbles are being used in various biomedical applications such as contrast imaging, targeted drug and gene delivery, delivery of drugs through blood brain barrier (BBB) and IV O<inf>2</inf> delivery etc. Major microbubble formulations use either proteins or lipids as their shell material. Protein microbubble formulations mainly consist of serum albumin, lysozyme etc., while lipid microbubble formulations consist of phospholipids like 1,2-Distearoyl-sn-glycero-3-phosphocholine (DSPC), 1,2-dipalmitoyl-sn-glycero-3 phosphocholine (DPPC), etc. This work focuses on comparing performance of protein and lipid microbubbles in terms of their shelf life and in vitro performance. Protein microbubbles were produced using Bovine serum albumin (BSA) as main ingredient and N-acetyl-dl-tryptophan (Tryp) as an additive. Lipid microbubbles were produced using a mixture of DSPC as main ingredient and PEG40S (90:10 molar ratio) as emulsifier. A narrow sized range (3–5 μm) microbubble suspension was produced using sonication method followed by size isolation using centrifugation. These microbubbles were stored in a (PGO) solution containing 10% 1,2 propanediol (P), 10% glycerol (G) and 80% original solution used to make microbubbles (O) and were studied for their shelf stability, in vitro stability, immunogenicity and ability to produce contrast. For a 4 weeks of observation period, a least reduction in concentration of around 18% was observed for PEGylated BSA microbubbles whereas highest reduction of 38% was observed for DSPC-PEG40S microbubbles. In-vitro persistence performance for PEGylated BSA microbubbles was found to be better than non-PEGylated BSA microbubbles as well as DSPC-PEG40S microbubbles. Non-PEGylated BSA microbubbles were found to be immunogenic whereas PEGylated BSA and DSPC-PEG40S microbubles were found to be non-immunogenic.