Bioimaging of botulinum toxin and hyaluronate hydrogels using zwitterionic near-infrared fluorophores

Abstract

Background: The injection of botulinum toxin (BTX) to reduce facial wrinkles is one of the most frequently performed plastic surgery procedures. The biocompatible hydrogels are injected with BTX for effective tissue augmentation. However, it is difficult to determine the interval of injection for effective tissue augmentation.

Method: BTX and hyaluronate (HA) hydrogels were labeled with zwitterionic (ZW) near-infrared (NIR) fluorophores and visualized for 3 weeks after injection to BALB/c nude mice.

Results: BTX-ZW conjugates and diaminohexane (DAH)-HA-ZW hydrogels were successfully prepared by the conventional EDC/NHS chemistry. Using the NIR fluorescence imaging, we confirmed that approximately 10% of BTX-ZW conjugates and 50% of DAH-HA-ZW hydrogels remained 3 weeks post-injection.

Conclusion: This bioimaging technique using invisible NIR fluorescence light can be exploited for various biomedical applications.

Keywords: Bioimaging; Botulinum toxin; Hyaluronate; Tissue augmentation; Zwitterionic fluorophore.

Fig. 1

Schematic diagrams for the synthesis of (a) BTX-ZW conjugates and (b) DAH-HA-ZW hydrogel, and for the illustrated structure of (c) DAH-HA hydrogel

Fig. 2

a The gel-permeation chromatogram of BTX, HA, and the mixture of HA and BTX. b NMR spectrum of DAH-HA conjugates

Fig. 3

NIR fluorescence images of ZW700–1 with subcutaneous (s.c.) injection, ZW800–1 with intramuscular (i.m.) injection, DAH-HA-ZW hydrogel with s.c. injection, and BTX-ZW conjugates with i.m. injection, in order from top to bottom

Fig. 4

Quantification of fluorescence intensity after i.m injections of ZW800–1 and BTX-ZW conjugates, s.c. injections of ZW700–1 and DAH-HA-ZW hydrogel