Dependence of Intestinal Absorption Profile of Insulin on Carrier Morphology Composed of ß-Cyclodextrin-Grafted Chitosan.

The effect of carrier morphology on the intestinal absorption of insulin was investigated using a morphology-tunable polymeric carrier, ß-cyclodextrin-grafted chitosan (BCC). The insulin-BCC complexes were prepared in either acetate or citrate buffer solutions, followed by dilution with phosphate buffer for the administration. The complex had a molecular network structure in the acetate buffer, whereas nanoparticles formed in the citrate buffer. The network structure in the acetate buffer was maintained even after dilution with a phosphate buffer, but the nanoparticles in the citrate buffer caused aggregation after dilution. Both complexes enhanced the intestinal absorption of insulin. Interestingly, their absorption profiles were totally different; prompt absorption was observed for the complex prepared in acetate buffer, whereas sustained absorption was observed for the complex prepared in citrate buffer. The difference in the absorption patterns was attributed to the difference in the complex morphology. Next, penetratin, a cell-penetrating peptide, was grafted to BCC to find further improvement in the absorption behavior. A simple mixture of penetratin and BCC was also effective. An oral administration study was also conducted in mice to observe effective suppression of glucose levels, which was further enhanced by coadministration of penetratin. Thus, BCC was proven to be an effective carrier for enhancing oral absorption of peptide drugs, and it is suggested that the carrier morphology is also an important factor that influences the absorption profile.

Reaction mediated artificial cell termination: control of vesicle viability using Rh(I)-catalyzed hydrogenation.

Methods for artificial cell control by applying catalytic processes are receiving increasing attention as a basis for artificial control of cellular functions. Here we have developed a Rh(I)-based catalytic hydrogenation reaction of unsaturated bonds of lipids that make up vesicles contained in aqueous media. The reduction reaction was applied to vesicles revealing that oleate vesicles collapse following catalytic reduction with H2 and a Rh(I) catalyst, while the distribution of EggPC liposomes was increased following the reaction. Proliferation and size of the vesicles could thus be controlled by catalysis based on variations in fluidity of the vesicle membrane. This process is applicable for use in artificial cells and/or even living cellular systems.

Media-dependent morphology of supramolecular aggregates of ß-cyclodextrin-grafted chitosan and insulin through multivalent interactions.

A supramolecular protein-binding system based on multivalent interactions was investigated using ß-cyclodextrin-grafted chitosan (BCC) and insulin. 1H NMR and fluorescence analyses revealed that BCC binds to insulin through electrostatic and host-guest interactions. The binding constant KBCC for the host-guest interaction between cyclodextrin (CyD) residues in BCC and Tyr and Phe residues in insulin was 478.7 M-1 in acetate buffer at pH 3.6, which was ca. 3-fold greater than the Kchi attributed to electrostatic interactions between chitosan and the Tyr residues of insulin. Furthermore, KBCC was ∼10 times greater than that of ß-CyD (KCyD), suggesting that multivalent interactions composed of electrostatic and host-guest interactions strongly enhance the host-guest interaction, similar to enzymes and antibodies in living systems. Enhanced host-guest interactions resulted in effective insulin binding over a wide pH range (3.6-7.4) as well as stabilization against digestive enzymes. BCC and insulin formed supramolecular aggregates with significantly different morphologies depending on the buffer species used: a network structure in acetate buffer, nanoparticles in citrate buffer, and large aggregates in phosphate buffer. The network structure formed in acetate buffer was maintained even after dilution with phosphate buffer, a situation that mimics the environment after oral administration. In addition, the structure was fragmented easily after application of a mild force, which could be an important property for achieving absorption of protein-peptide drugs from the gastrointestinal tract. This study provides new insights for the development of CyD-based nanoarchitectures suitable for application as protein-peptide carriers for oral drug delivery.