Biopharmaceutical characterisation of insulin and recombinant human growth hormone loaded lipid submicron particles produced by supercritical gas micro-atomisation

Homogeneous dispersions of insulin and recombinant human growth hormone (rh-GH) in tristearin/phosphatidylcholine/PEG mixtures (1.3:1.3:0.25:0.15 w/w ratio) were processed by supercritical carbon dioxide gas micro-atomisation to produce protein-loaded lipid particles. The process yielded spherical particles, with a 197 +/- 94 nm mean diameter, and the insulin and rh-GH recovery in the final product was 57 +/- 8% and 48 +/- 5%, respectively. In vitro, the proteins were slowly released for about 70-80 h according to a diffusive mechanism. In vivo, the insulin and glucose profiles in plasma obtained by subcutaneous administration of a dose of particles containing 2 mu g insulin to diabetic mice overlapped that obtained with 2 mu g of insulin in solution. Administration of a dose of particles containing 5 mu g insulin resulted in faster and longer glycaemia reduction. Oral administration of 20 and 50 mu g insulin equivalent particles produced a significant hypoglycaemic effect. The glucose levels decreased since 2 h after administration, reaching about 50% and 70% glucose reduction in 1-2 h with the lower and higher dose, respectively. As compared to subcutaneous administration, the relative pharmacological bioavailability obtained with 20 and 50 mu g equivalent insulin particles was 7.7% and 6.7%, respectively. Daily subcutaneous administration of 40 mu g of rh-GH-loaded particles to hypophysectornised rats induced similar body weight increase as 40 mu g rh-GH in solution. The daily oral administration of 400 mu g rh-GH equivalent particles elicited a slight body weight increase, which corresponded to a relative pharmacological bioavailability, of 3.4% compared to subcutaneous administration. (C) 2009 Elsevier B.V. All rights reserved.