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Zwitterionic micelles efficiently deliver oral insulin without opening tight junctions

Abstract

Oral delivery of protein drugs is considered a life-changing solution for patients who require regular needle injections. However, clinical translation of oral protein formulations has been hampered by inefficient penetration of drugs through the intestinal mucus and epithelial cell layer, leading to low absorption and bioavailability, and safety concerns owing to tight junction openings. Here we report a zwitterionic micelle platform featuring a virus-mimetic zwitterionic surface, a betaine side chain and an ultralow critical micelle concentration, enabling drug penetration through the mucus and efficient transporter-mediated epithelial absorption without the need for tight junction opening. This micelle platform was used to fabricate a prototype oral insulin formulation by encapsulating a freeze-dried powder of zwitterionic micelle insulin into an enteric-coated capsule. The biocompatible oral insulin formulation shows a high oral bioavailability of >40%, offers the possibility to fine tune insulin acting profiles and provides long-term safety, enabling the oral delivery of protein drugs.

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Fig. 1: Schematic representation of DSPE-PCB micelles for oral delivery of insulin.
Fig. 2: Nanoparticles with virus-mimetic zwitterionic surface show the highest diffusive property in mucus compared with others including the PEG-based particles.
Fig. 3: Zwitterionic micelle/insulin formulation: characterization, high intestinal absorption efficacy and transporter-mediated absorptive mechanism.
Fig. 4: In vitro cellular uptake of zwitterionic micelle particles showed a transporter-mediated mechanism.
Fig. 5: Zwitterionic micelle/insulin treatment did not open intestinal tight junctions.
Fig. 6: Zwitterionic micelle/insulin aqueous formulation loses pharmacological activity through direct oral administration but shows stability to form dry powders for potentially oral capsule formulation.
Fig. 7: Pharmacological activity and bioavailability of an oral insulin capsule containing zwitterionic micelle/insulin, and the capability of adjusting the drug acting profile.
Fig. 8: DSPE-PCB micelles show no notable cytotoxicity or leaky gut-related endotoxin leakage and inflammation of repeated consecutive dosing.

Data availability

The authors declare that all data supporting the findings of this study are available within the paper and its Extended Data.

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Acknowledgements

This work was supported by the faculty start-up fund at Wayne State University, the National Science Foundation (grant nos. 1410853 and 1809229) and the National Institute of Diabetes and Digestive and Kidney Diseases of the National Institutes of Health (grant nos. DP2DK111910 and R01DK123293). This work made use of the JEOL 2010 transmission electron microscope supported by National Science Foundation Award No. 0216084. We thank A. Withrow at Michigan State University for supporting tissue sample processing and TEM study. We thank N. Peraino of the Lumigen Instrument Center Mass Spectrometry facilities for access to Shimadzu 8040 (LC–MS–MS). The microscopy and imaging are supported, in part, by NIH Center grant No. P30 CA22453 to the Karmanos Cancer Institute, Wayne State University, and the Perinatology Research Branch of the Nation Institutes of Child Health and Development.

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Contributions

Z.C., X.H., Y.L. and J.X. conceived and designed the experiments. X.H. conducted all the experiments except the nanogel transport and cell toxicity experiments. J.X. conducted the nanogel transport experiment and helped with characterization and animal experiments. Y.L. contributed to the mouse experiment. E.Z. performed the cell toxicity and live/dead experiment, and histological staining. B.S. helped with the synthesis of DSPE-PCB and the formulation. K.W. and Y.S. helped with the TEM imaging. E.Z., H.D. and H.Z. helped with the animal experiments. C.Y. contributed to the cell uptake flow cytometry experiment. All authors discussed the results and commented on the manuscript. Z.C., X.H., Y.L. and J.X. outlined and wrote the paper. E.Z. analysed the data and helped revise the paper. Z.C. developed the concept and supervised the study.

Corresponding author

Correspondence to Zhiqiang Cao.

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The authors declare no competing interests.

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Peer review information Nature Nanotechnology thanks Tim Heise and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 DSPE-PCB/insulin formulations with increasing zinc content showed increased retention of insulin release.

DSPE-PCB/insulin formulations were dialyzed (10 kDa MWCO) against pH 1.2 and 6.8 buffer with 5 mM bile salt at 37 °C. Formulation 1, 2, and 3 had an insulin/ZnCl2 feeding ratio of 50/1, 20/1, and 2.5/1 by weight during the encapsulation process, respectively. Their drug loading is 6.24%, 6.23% and 6.10%, while the corresponding particle sizes are 28.52, 26.36 and 25.96nm respectively. The cumulative released insulin was measured using the BCA assay (N=3 independent experiments, means connected).

Extended Data Fig. 2 Representative images of the tight junction protein ZO-1 of monolayer of Caco-2 cells after treated with different micelles.

The tight junction protein ZO-1 was stained with ZO-1 Monoclonal Antibody Alexa Fluor 488 (green) while the nucleus was stained with Hochest 33342 (blue). Scale bar =20μm. Experiments were repeated three times independently with similar results.

Extended Data Fig. 3 DSPE-PCB micelles did not increase intestinal monolayer permeability in vitro.

Sodium decanoate caused greater reductions in the TEER of Caco-2 monolayers than polysorbate 80. (N=3 biologically independent samples, means connected). Caco-2 cells were cultured for 96 hours to form monolayers and then treated with different micelles for 4 hours. The electrical resistance was measured at different time points.

Extended Data Fig. 4 Blood glucose profiles for various formulations of DSPE-PCB/insulin capsules on diabetic rats through oral gavage (N=6 biologically independent animals, means connected).

Formulation 0, 1, 2 and 3 had an insulin/ZnCl2 feeding ratio of 75/1, 50/1, 20/1, and 2.5/1 by weight during the encapsulation process, respectively. Their drug loading is 6.25%, 6.24%, 6.23% and 6.10%, while the corresponding particle hydrodynamic sizes are 28.56, 28.52, 26.36 and 25.96 nm respectively.

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Han, X., Lu, Y., Xie, J. et al. Zwitterionic micelles efficiently deliver oral insulin without opening tight junctions. Nat. Nanotechnol. 15, 605–614 (2020). https://doi.org/10.1038/s41565-020-0693-6

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