Potential enhancement of metformin hydrochloride in solidified reverse micellar solution-based PEGylated lipid nanoparticles targeting therapeutic efficacy in diabetes treatment

Metformin hydrochloride (MH) is a widely used oral biguanide antihyperglycemic (antidiabetic) drug with poor bioavailability which necessitates the development of novel drug delivery systems such as PEGylated solid lipid nanoparticles for improving its therapeutic activity. The aim of this study was to formulate, characterize and evaluate in vitro and in vivo pharmacodynamic properties of metformin-loaded PEGylated solid lipid nanoparticles (PEG-SLN) for improved delivery of MH. The lipid matrices (non-PEGylated lipid matrix and PEGylated lipid matrices) used in the formulation of both non-PEGylated (J0) and PEGylated SLNs (J10, J20, J40) were prepared by fusion using beeswax and Phospholipon ® 90H at 7:3 ratio with or without polyethylene glycol (PEG) 4000 (0, 10, 20 and 40% w/w), respectively. Representative lipid matrices (LM and PEG-LM) were loaded with MH by fusion and then characterized by differential scanning calorimetry (DSC) and Fourier transform infrared (FT-IR) spectroscopy. The PEG-SLNs were prepared by high shear hot homogenization using the lipid matrices (5% w/w), drug (MH) (1.0% w/w), sorbitol (4% w/w) (cryoprotectant), Tween ® 80 (2% w/w) (surfactant) and distilled water (q.s to 100% w/w) (vehicle). The non-PEGylated and PEGylated SLNs (J0, J10, J20, J40)) were characterized with respect to encapsulation efficiency (EE%), loading capacity (LC), morphology by scanning electron microscopy (SEM), mean particle size (Zav) and polydispersity indices (PDI) by photon correlation spectroscopy (PCS), compatibility by FT-IR spectroscopy and in vitro drug release in biorelevant medium. Thereafter, in vivo antidiabetic study was carried out in alloxanized rats' model and compared with controls (pure sample of MH and commercial MH- Glucophage®)). Solid state characterizations indicated the amorphous nature of MH in the drug loaded-lipid matrices. The PEG-SLNs were mostly smooth and spherical nanoformulations with Zav and PDI of 350.00 nm and 0.54, respectively, for non-PEGylated SLNs, and in the range of 386.80-783.10 nm and 0.592 to 0.752, respectively, for PEGylated SLNs. The highest EE% and LC were noted in batch J20 and were 99.28% and 16.57, respectively. There was no strong chemical interaction between the drug and excipients used in the preparation of the formulations. The PEGylated SLN (batch J40) exhibited the highest percentage drug released (60%) at 8 h. The PEGylated SLNs showed greater hyperglycemic control than the marketed formulation (Glucophage ®) after 24 h. This study has shown that metformin-loaded PEGylated solid lipid nanoparticles could be employed as a potential approach to improve the delivery of MH in oral diabetic management, thus encouraging further development of the formulations.