title: Alginate microspheres prepared by internal gelation: development and effect on insulin stability.
abstract: Recombinant human insulin was encapsulated within alginate microspheres by the emulsification/internal gelation technique with the objective of preserving protein stability during encapsulation procedure. The influence of process and formulation parameters was evaluated on the morphology and encapsulation efficiency of insulin. The in vitro release of insulin from microspheres was studied under simulated gastrointestinal conditions and the in vivo activity of protein after processing was assessed by subcutaneous administration of extracted insulin from microspheres to streptozotocin-induced diabetic rats. Microspheres mean diameter, ranging from 21 to 287 microm, decreased with the internal phase ratio, emulsifier concentration, mixer rotational speed and increased with alginate concentration. Insulin encapsulation efficiency, near 75%, was not affected by emulsifier concentration, mixer rotational speed and zinc/insulin hexamer molar ratio but decreased either by increasing internal phase ratio and calcium/alginate mass ratio or by decreasing acid/calcium molar ratio and alginate concentration. A high insulin release, above 75%, was obtained at pH 1.2 and under simulated intestinal pH a complete dissolution of microspheres occurred. Extracted insulin from microspheres decreased hyperglycemia of diabetic rats proving to be bioactive and showing that encapsulation in alginate microspheres using the emulsification/internal gelation is an appropriate method for protein encapsulation.
authors.affiliation: Laboratório de Tecnologia Farmacêutica, Faculdade de Farmácia, Universidade de Coimbra, Rua do Norte, 3000-295 Coimbra, Portugal. catarinasilva@ci.uc.pt
authors.forename: Catarina M
authors.initials: CM
authors.lastname: Silva
authors.forename: António J
authors.initials: AJ
authors.lastname: Ribeiro
authors.forename: Isabel Vitória
authors.initials: IV
authors.lastname: Figueiredo
authors.forename: Alexandra Rocha
authors.initials: AR
authors.lastname: Gonçalves
authors.forename: Francisco
authors.initials: F
authors.lastname: Veiga
mesh_terms: D000464:Alginates / Q000737:chemistry*; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D002626:Chemistry, Pharmaceutical; D003921:Diabetes Mellitus, Experimental / Q000097:blood; D004355:Drug Stability; D004655:Emulsions; D020723:Glucuronic Acid / Q000737:chemistry; D006603:Hexuronic Acids / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007004:Hypoglycemic Agents / Q000008:administration & dosage / Q000737:chemistry*; D007279:Injections, Subcutaneous; D007328:Insulin / Q000008:administration & dosage / Q000737:chemistry* / Q000235:genetics; D008297:Male; D008863:Microspheres; D010316:Particle Size; D011489:Protein Denaturation; D051381:Rats; D017208:Rats, Wistar; D011994:Recombinant Proteins / Q000008:administration & dosage / Q000737:chemistry; D012995:Solubility; D013311:Streptozocin; D013678:Technology, Pharmaceutical / Q000379:methods
chemical_list: D000464:Alginates; D001786:Blood Glucose; D004655:Emulsions; D006603:Hexuronic Acids; D007004:Hypoglycemic Agents; D007328:Insulin; D011994:Recombinant Proteins; D013311:Streptozocin; D020723:Glucuronic Acid