Research ArticleHEALTH AND MEDICINE

Synthetic “smart gel” provides glucose-responsive insulin delivery in diabetic mice

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Science Advances  22 Nov 2017:
Vol. 3, no. 11, eaaq0723
DOI: 10.1126/sciadv.aaq0723
  • Fig. 1 Structure and principle of the boronate gel–based insulin delivery system.

    (A) Glucose-dependent equilibria of PBA derivatives. (B) Chemical structure of glucose-responsive gel. Monomers and their polymerized (cross-linked) chemical structures are shown with their optimized molar fraction (l:m:n = 87.5:7.5:5) to yield the glucose sensitivity under physiological conditions (pH 7.4 and 37°C) accompanied by a threshold concentration of glucose at normoglycemic (100 mg/dl) (above which the gel delivers insulin). DMSO, dimethyl sulfoxide. (C) Schematic illustration of “pancreas-like” self-regulated insulin delivery function of the gel.

  • Fig. 2 Characterization of the glucose-responsive gel in vitro.

    (A) Images of a smart gel formed in a macroscopic slab shape equilibrated under hyperglycemic (1000 mg/dl) (left) and no-glucose (right) conditions. (B) Release experiment. Top: Temporal patterns of glucose fluctuation challenged through a HPLC setup under physiological conditions (pH 7.4; 37°C; 155 mM NaCl). Bottom: Time course change in fluorescence intensity of fluorescein isothiocyanate (FITC)–labeled bovine insulin released from the gel. The break in the x axis indicates an overnight interval between two experiments during which the gel was kept under constant flow (1 ml/min) of phosphate-buffered saline (PBS) containing glucose (100 mg/dl). a.u., arbitrary units. (C) Protocol for in vitro glucose-uptake assessment using differentiated 3T3-L1 adipocytes. (D) Insulin-dependent glucose uptake by the adipocytes. N.S., not significant. (E) Amount of cumulative insulin release in the culture. *P < 0.05. n = 4.

  • Fig. 3 Fabrication of catheter-combined device.

    (A and B) SEM images of 4-French (1.2 mm in diameter) silicone catheter bearing penetrating (perpendicular to the long axis) openings on the wall made by laser irradiation. (C to E) Overview (C), side view (D), and cross-sectional transmittance images (E) of the gel-modified catheter (the gel was stained by red-colored ink). (F and G) Overview of the ready-to-use device installed with the upstream (long tail) reservoir filled with insulin and its appearance on subcutaneous implantation. PEG, poly(ethyleneglycol).

  • Fig. 4 Working principle and behavior of catheter-combined device.

    (A) Schematic illustration of skin layer–driven glucose-dependent diffusion control of insulin accomplished by the catheter-combined device. (B) Release experiment under physiological conditions using a HPLC setup. Top: Temporal patterns of glucose. Bottom: Time course change in fluorescence intensity of FITC-labeled bovine insulin released from the gel. The break in the x axis indicates an overnight interval between two experiments during which the device was kept under constant flow (1 ml/min) of PBS containing glucose (100 mg/dl).

  • Fig. 5 Evaluation of glucose-responsive insulin release in vivo.

    (A) Protocol of the experimental design using healthy mice. (B) Glucose tolerance test (GTT). Glucose (3 g/kg body weight) was injected intraperitoneally 2 and 7 days after the implantation of the devices. **P < 0.01 and *P < 0.05 versus PBS group. ##P < 0.01 and #P < 0.05 versus 0 min. n = 8 to 12. (B) GTT with different dosage of glucose (1, 2, and 3 g/kg body weight). *P < 0.05. n = 10. (C) The fructose tolerance test (FTT) (fructose, 0.5 g/kg body weight) and the aspartame tolerance test (ATT) (aspartame, 0.1 g/kg body weight). **P < 0.01 and *P < 0.05. n = 8.

  • Fig. 6 Therapeutic efficacy for type 1 diabetes in mice.

    (A) Protocol of the experimental design. Type 1 diabetic models were induced by the intraperitoneal (i.p.) injection of STZ (125 mg/kg body weight) for 3 consecutive days. (B) Amount of drinking during the last 3 days of the experimental period and body weight, blood glucose concentrations, and tissue weights of the liver and epididymal fat at day 7. (C) Blood glucose concentrations and serum human insulin concentrations in the GTT (glucose, 1.5 g/kg body weight). (D) mRNA expression of glucose-6-phosphatase (G6Pase), phosphoenolpyruvate carboxykinase (PEPCK), fatty acid synthase (FAS), and sterol regulatory element–binding protein-1c (SREBP-1c) in the liver. **P < 0.01 and *P < 0.05 versus PBS group. ##P < 0.01 versus 0 min. n = 6 to 12. (E) Blood glucose concentrations under ad lib–fed conditions after implantation of the device. *P < 0.05. n = 6 to 12. (F) Time course of HbA1c. Type 1 diabetic mice were implanted with the device containing PBS and human insulin. *P < 0.05. n = 4.

  • Fig. 7 Therapeutic efficacy for type 2 diabetes in mice.

    (A) Protocol of the experimental design. HFD, high-fat diet. (B) Body weight when the GTT was conducted. SD, standard diet. (C) Blood glucose and serum mouse C-peptide concentrations in the GTT. (D) Body weight, blood glucose concentrations, and tissue weights of epididymal fat, liver, and muscle at the end of the experiment. **P < 0.01 and *P < 0.05 versus high-fat diet/PBS group. n = 8.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/11/eaaq0723/DC1

    fig. S1. Phase diagram of the gel.

    fig. S2. Assessment of skin layer formation.

    fig. S3. Optical images of the device sections.

    fig. S4. SEM images of the device sections without poly(ethyleneglycol) coating.

    fig. S5. SEM images of the device sections with poly(ethyleneglycol) coating.

    fig. S6. SEM images of the poly(ethyleneglycol)-coated device sections after 1 week in vivo implantation.

    fig. S7. Optical images of the device after 1 week in vivo implantation.

    fig. S8. Investigation of biosafety of the device in vitro and in vivo.

    fig. S9. Evaluation of long-term efficacy of the device in vivo.

    fig. S10. Diagram of the HPLC setup used for release experiments.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Phase diagram of the gel.
    • fig. S2. Assessment of skin layer formation.
    • fig. S3. Optical images of the device sections.
    • fig. S4. SEM images of the device sections without poly(ethyleneglycol) coating.
    • fig. S5. SEM images of the device sections with poly(ethyleneglycol) coating.
    • fig. S6. SEM images of the poly(ethyleneglycol)-coated device sections after 1 week in vivo implantation.
    • fig. S7. Optical images of the device after 1 week in vivo implantation.
    • fig. S8. Investigation of biosafety of the device in vitro and in vivo.
    • fig. S9. Evaluation of long-term efficacy of the device in vivo.
    • fig. S10. Diagram of the HPLC setup used for release experiments.

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