Chitosan/heparin polyelectrolyte complexes as ion-paring approach to encapsulate heparin in orally administrable SLN: In vitro evaluation

Enhancing oral bioavailability of hydrophilic drugs by encapsulation in lipid-based nanocarriers, including Solid Lipid Nanoparticles (SLN), has been well documented. In this work, high molecular weight heparin was “insolubilized” by an “ion-paring” approach, forming Chitosan/Heparin Polyelectrolyte Complexes (PEC) to promote its encapsulation in SLN. Hybrid PEC-SLN, heparin-loaded SLN (H-SLN) as well as naked PEC were prepared and characterized regarding size, Z potential, morphology, drug loading and drug release. Physicochemical characterization of the nanoparticles was also performed by differential scanning calorimetry (DSC), and Fourier Transform Infra-Red (FTIR) analysis. FITC-labeled naked PEC along with Nile Red labeled PEC-SLN were assessed on CaCo-2 cells to study cytotoxicity as well as cell internalization ability by cytometric and confocal analysis. Transepithelial electrical resistance (TEER) was measured on NCM460 cell monolayers to evaluate whether chitosan may induce a modification of tight junctions’ integrity at epithelial level. Results showed that the minimum size of PEC (around 170 nm) was at pH 5.5 with a positive surface charge and after encapsulation in SLN produced hybrid PEC-SLN with a size of about 370 nm and a negative zeta potential. In comparison to both H-SLN and naked PEC, PEC-SLN were able to achieve a pH-controlled drug release and showed on CaCo-2 cells low toxicity and rapid internalization. Finally, TEER measurements highlighted that the hybrid nanocarriers were internalized without interference in the membrane resistance. Therefore, PEC-SLN could be considered valuable candidate for further in vivo investigations about the systemic bioavailability of oral heparin.