Article pubs.acs.org/cm
Glucose-Responsive Nanosystem Mimicking the Physiological Insulin Secretion via an Enzyme−Polymer Layer-by-Layer Coating Strategy Chun Xu,†,§ Chang Lei,† Lili Huang,‡ Jun Zhang,† Hongwei Zhang,† Hao Song,† Meihua Yu,† Yeda Wu,‡ Chen Chen,*,‡ and Chengzhong Yu*,† †
Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, Queensland 4072, Australia School of Biomedical Sciences, The University of Queensland, Brisbane, Queensland 4072, Australia § School of Dentistry, The University of Queensland, Brisbane, Queensland 4066, Australia ‡
S Supporting Information *
ABSTRACT: Insulin administration mimicking physiological insulin secretion behavior remains a challenge for the treatment of patients with type I diabetes. Herein, we report a novel glucose-responsive insulin-release nanosystem through an enzyme−polymer layer-by-layer coating strategy on silica vesicles loaded with insulin. With a choice of polyethylenimine with prioritized proton binding capability and glucose specific enzymes in the coating layer, the insulin-release threshold can be adjusted in a desired glucose concentration range 5−20 mM for the first time. In vitro tests show that the insulin release is switched “ON” in response to hyperglycemia (10, 20 mM) and “OFF” to normal glucose level (5 mM) repeatedly. Moreover, in vivo experiments in type I diabetes mice demonstrate that our nanosystem enables a fast glucose response insulin release and regulates the glycemia levels in a normal range up to 84 h with a single administration. In addition, when applied to healthy mice, the nanosystem maintains the blood glucose concentration in the normal range without causing hypoglycemia. Our nanosystem which mimics the physiological insulin secretion has the potential to be developed as a convenient and safe insulin delivery carrier for diabetes treatment.
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INTRODUCTION The management of diabetes is a worldwide public health challenge.1,2 For diabetics, especially those with type I diabetes characterized by deficient insulin production, daily multiple insulin administration is essential. This is uncomfortable for the patients3,4 and may cause hypoglycemia that can result in unconsciousness or even death, owing to the difficulty of administrating correct doses.5,6 A closed-loop insulin pump provides another option for glycemic control, whereby a mechanical insulin pump is connected to a continuous glucose sensor and administers insulin through a subcutaneous cannula. This large and complex device is expensive and inconvenient and carries an increased risk of infections.7 To avoid these problems and improve patients' satisfaction and compliance, development of a novel system that senses glucose level changes and supply insulin accordingly is of great significance in treating diabetes. Blood glucose levels fluctuated within a narrow range 3.9− 6.1 mM in fasting conditions and elevated up to 11.1 mM after meals in healthy humans (Figure 1A, black dashed curve).8 Small changes in circulating glucose concentrations are detected and responded by releasing insulin in a dosedependent manner: the insulin-release rate is slow and not © 2017 American Chemical Society
affected by glucose concentrations below 5 mM, but increases progressively between 5 and 15 mM.9 In diabetes, however, blood glucose levels go beyond 7 mM during fasting or 11.1 mM 2 h postprandially (Figure 1A, black solid curve).10 An ideal insulin supply system for diabetes should release insulin spontaneously in a way that mimics the physiological insulin secretion behavior: the release is switched on when the blood glucose level is above the critical normal/diabetes threshold (commonly at 7 mM when fasting or 11.1 mM postprandially)8,9 and switched off when the level drops back into the normal region of 5 mM in a repeatable “ON−OFF” manner (red solid line, Figure 1A). Recently, glucose-responsive insulin-release systems combining an insulin-loaded matrix and glucose-dependent release techniques have attracted much attention.5,11−20 For example, glucose specific enzymes such as glucose oxidase (GOD)17−20 have high specificity and reactivity to convert glucose into gluconic acid and H2O2 (Figure 1B).5 In combination with various pH-sensitive16−24 or H2O2-sensitive21 structures, the Received: May 10, 2017 Revised: August 11, 2017 Published: August 14, 2017 7725
DOI: 10.1021/acs.chemmater.7b01804 Chem. Mater. 2017, 29, 7725−7732
Article
Chemistry of Materials
Figure 1. (A) Ideal insulin-release behavior under different blood glucose levels. The black dashed and solid curves correspond to the blood glucose level fluctuation in 1 day in healthy nondiabetic and diabetic humans, respectively. (B) The mechanism of glucose-responsive insulin release in the enzyme system (up, blue area) and enzyme−PEI system (bottom, pink area). (C) Comparison between (I) traditional glucose-responsive insulinrelease systems where insulin would be released under normal glucose levels and (II) physiological glucose-responsive system which releases insulin only under “diabetic” glucose levels.
prioritized protonation on PEI buffers the pH variation36,37and reduces the permeability change in the enzyme layer, thus increasing the insulin-release threshold compared to previous designs.13−15,22,23,25,26,38 By adjusting the PEI amount, the insulin-release threshold can be tuned in desired glucose levels (5−20 mM). The insulin release is switched “ON” in response to hyperglycemia (10, 20 mM) and “OFF” to the normal glucose level (5 mM) repeatedly. The physiological insulin secretion mimicking concept is further confirmed in both type I diabetes mouse models and normal control mice, showing the efficacy and safety of our nanosystem in diabetes treatment.
glucose-responsive release can be achieved. With the GOD/ catalase (CAT, which converts H2O2 to O2)22,23 system as an example, the enzymes are cross-linked forming a Schiff base (pKb of 7)24 which can be protonated by the created gluconic acid (Figure 1B). Cross-linked enzyme layers act as a barrier to stop the release of insulin loaded in a matrix (Figure 1CI), while protonated enzyme layers are “loosened” with increased permeability responding to glucose to allow insulin release. However, most reported glucose-responsive systems released more than half of the loaded insulin at a glucose concentration below the diabetic condition (
