Enhanced oral bioavailability of insulin-loaded solid lipid nanoparticles: pharmacokinetic bioavailability of insulin-loaded solid lipid nanoparticles in diabetic rats

Objective: Insulin is a hormone used in the treatment of diabetes mellitus. Multiple injections of insulin every day may causes pain, allergic reactions at injection site, which lead to low patient compliance. The aim of this work was to develop and evaluate an efficient solid lipid nanoparticle (SLN) carrier for oral delivery of insulin. Methods: SLNs were prepared by double emulsion solvent evaporation (w/o/w) technique, employing glyceryltrimyristate (Dynasan 114) as lipid phase and soy lecithin and polyvinyl alcohol as primary and secondary emulsifier, respectively, and evaluated in vitro for particle size, polydispersity index (PDI) and drug entrapment. Results: Among the eight different developed formulae (F1–F8), F7 showed an average particle size (99 nm), PDI (0.021), high entrapment of drug (56.5%). The optimized formulation (F7) was further evaluated by FT-IR, DSC, XRD, in vitro release, permeation, stability, bioavailability and pharmacological studies. Insulin-loaded SLNs showed better protection from gastrointestinal environment as evident from the relative bioavailability, which was enhanced five times as compared to the insulin solution. A significant enhancement of relative bioavailability of insulin was observed, i.e. approximately five times of pure insulin solution when loaded in SLN (8.26% versus 1.7% only).