Sugar-Responsive Layer-by-Layer Film Composed of Phenylboronic Acid-Appended Insulin and Poly(vinyl alcohol)

Abstract

Previous studies have shown that reversible chemical bond formation between phenylboronic acid (PBA) and 1,3-diol can be utilized as the driving force for the preparation of layer-by-layer (LbL) films. The LbL films composed of a PBA-appended polymer and poly(vinyl alcohol) (PVA) disintegrated in the presence of sugar. This type of LbL films has been recognized as a promising approach for sugar-responsive drug release systems, but an issue preventing the practical application of LbL films is combining them with insulin. In this report, we have proposed a solution for this issue by using PBA-appended insulin as a component of the LbL film. We prepared two kinds of PBA-appended insulin derivatives and confirmed that they retained their hypoglycemic activity. The LbL films composed of PBA-appended insulin and PVA were successfully prepared through reversible chemical bond formation between the boronic acid moiety and the 1,3-diol of PVA. The LbL film disintegrated upon treatment with sugars. Based on the results presented herein, we discuss the suitability of the PBA moiety with respect to hypoglycemic activity, binding ability, and selectivity for D-glucose.Key words layer-by-layer; phenylboronic acid; insulin; sugar response; smart materialThe layer-by-layer (LbL) deposition technique has attracted considerable interest for the preparation of nano-sized multilayer films on solid surfaces.1,2) The LbL deposition technique usually leverages the electrostatic interactions between oppositely charged molecules. This type of LbL films is stable on the solid support unless the pH of the surrounding solution is changed, which is advantageous for the construction of thin stable films. However, the good stability of the films, which need to be disintegrated for drug release, causes an issue for drug delivery applications.An LbL film that disintegrates upon exposure to specific stimuli is desirable for drug delivery systems, but requires a reversible driving force for LbL film.3) To meet this demand, the incorporation of phenylboronic acid (PBA) is a promising approach. [4][5][6][7][8][9][10] PBA derivatives show binding ability for the 1,2-diol, and 1,3-diol of sugars, which can result in the formation of a cyclic ester even in aqueous solution. 11,12) The cyclic ester formation is a reversible reaction, which is suitable for stimuli-responsive LbL films. For example, Anzai's group has prepared LbL films composed of a PBA-modified amine dendrimer and poly(vinyl alcohol) (PVA) through interaction between PBA and the 1,3-diol of PVA with great success. 7-9)This LbL film disintegrated when the film was immersed in sugar solutions, which is driven by the displacement of PVA by sugar on the PBA moiety.

Cell Adhesive Character of Phenylboronic Acid-Modified Insulin and Its Potential as Long-Acting Insulin

“…PBA-Ins was prepared in accordance with the previous method, and the modification number of PBA was evaluated with the TNBS method [25]. The results show that two PBA moieties were introduced into one insulin molecule.…”

“…In a report by Burnett et al, published in 1980, it was reported that PBA-dimer induced RBC agglutination [26]. In this study, we evaluated the PBA modification ratio by counting the remaining amino groups with the TNBS method [25]. The results showed that, on average, one PBA-Ins molecule has two PBA moieties.…”

“…In accordance with our previous report [25], PBA-Ins was prepared by condensing amino groups of insulin and 4-carboxyphenylboronic acid, using isobutyl chloroformate as a condensing agent. PBA-Ins was purified by dialysis and lyophilized.…”

“…PBA-Ins was purified by dialysis and lyophilized. The modification ratio was evaluated with a method using TNBS [25].…”

Preparation of Microparticles Capable of Glucose-Induced Insulin Release under Physiological Conditions

“…Glucose-sensitive insulin release has attracted particular attention, since the development of insulin delivery systems for the self-regulation of blood glucose levels would be helpful for diabetes mellitus patients. Glucose-sensitive materials such as lectins [6], glucose oxidase [7,8] and phenyl boronic acid (PBA) [9,10,11] have been employed for this purpose. Because the glucose-sensitive release of insulin could mimic the function of the pancreas, this technology might eliminate repetitive insulin injections.…”