A novel vitamin B12-nanosphere conjugate carrier system for peroral delivery of insulin

In spite of great potential, effective oral delivery of many vitamin B12-peptide/protein drug conjugates does not occur due to the limited uptake capacity of the VB12 transport system, loss of bioactivity of native protein and/or intrinsic factor affinity of VB12 and liability to GI degradation. In order to overcome these shortcomings in a two pronged way, we have endeavoured to develop a VB12-Nanoparticles (NPs) system to enhance the uptake capacity of both NPs and VB12 transport to deliver orally effective insulin. NPs were prepared using different molecular weight dextrans and epichlorohydrin as cross-linker by an emulsion method. NPs surface was modified with succinic anhydride, and conjugated with amino VB12 derivatives of carbamate linkage. VB12 attachment was confirmed by IR, XPS analysis, and was quantified by HPLC (4.0 to 4.4% w/w of NPs). The pre-formed NPs conjugates (Zave=160–250 nm; polydisperse) were loaded with 2, 3 and 4% w/w of insulin, and the entrapment was found to be 45–70%. NPs conjugates were found to protect 65–83% of entrapped insulin against in vitro gut proteases. In vitro release studies exhibit an initial burst followed by diffusion controlled first order kinetics with 75–95% release within 48 h. After oral administration of these carriers (20 IU/kg), a nadir of 70–75% reduction in plasma glucose was found in 5 h, reached basal levels in 8–10 h, and a prolonged second phase was found until 54 h. The % pharmacological availability (PA) of 70 K NPs conjugate containing 2, 3 and 4% w/w insulin was 1.1, 1.9 and 2.6 fold higher, respectively compared to NPs without VB12; consistent with the hypothesis that uptake was mediated by the vitamin B12 transport. NPs of 70 K dextran showed 1.4 fold PA compared to 10 K while negligible action was observed with 200 K. The potential utilities of VB12-NPs carrier as an oral delivery platform of proteins, especially insulin via dextran-coated particles necessities further elaborate investigations.