Biocompatible nanocarriers that respond to oxidative environments via interactions between chitosan and multiple metal ions

Abstract

Hydrogen peroxide (H₂O₂) functions as an early damage signal contributing to the oxidative stress response and can act as a trigger in smart oxidation-responsive drug delivery systems that are currently in development. Current H₂O₂-triggered oxidation-responsive polymeric systems are usually derived from chemical synthesis and rarely include natural polymers. Herein, we report two series of nanoparticle (NP) complexes prepared with the biopolymer chitosan (CS) and four different metal ions (Cu²⁺, Ca²⁺, Zn²⁺, and Fe³⁺), defined as CSNPs-metal complexes (Series 1) and CS-metal complexes NPs (Series 2), which responded to oxidation by dissolving upon H₂O₂ exposure. Experiments examining Nile red release and H₂O₂-triggered degradation confirmed that both series of complexes showed better sensitivity to oxidation than the CSNPs alone. Furthermore, preliminary cytotoxicity and histological observations indicated that the two series exhibited little or no cytotoxicity and generated a mild inflammatory response. Our work provides a novel and promising strategy for developing NPs for use as intelligent oxidation-responsive systems.

Keywords:

• oxidation-responsive system
• chitosan
• nanoparticles
• hydrogen peroxide
• metal complexes

Supplementary materials

Figure S1 Schematic representation of the two NP series (Series 1 and Series 2).

Abbreviations: NP, nanoparticle; CS, chitosan; CSNP, chitosan nanoparticle.

Figure S2 Calibration curve used for the determination of Nile red encapsulation efficiency.

Figure S3 Fluorescence intensity of Nile red (0.03 mg/mL) in acetone, with or without addition of various concentration gradients of H₂O₂.

Abbreviation: h, hours.

Figure S4 Changes in particle size distribution of CSNPs in 1,000 mM H₂O₂.

Abbreviation: CSNPs, chitosan nanoparticles.

Figure S5 Cytotoxicity tests.

Note: Flow cytometry cytotoxicity results in RAW264.7 cells treated with 1% HOAc and the NPs at 500 μg/mL.

Abbreviations: CSNPs, chitosan nanoparticles; CS, chitosan; NPs, nanoparticles.

Figure S6 Biocompatibility study.

Note: Sections of different organs stained with hematoxylin and eosin.

Abbreviations: CSNPs, chitosan nanoparticles; CS, chitosan; NPs, nanoparticles.

Table S1 FTIR analysis – IR bands of CS and CS-metal complexes of Series 2 (cm⁻¹)

Table S2 FTIR analysis – IR bands of CSNPs and Series 1 (cm⁻¹)

Table S3 TGA-DTA – T_max for the thermal degradation of CSNPs and Series 1 (°C)

Table S4 T_max for the thermal degradation of CS and CS-metal complexes of Series 2 (°C)

Table S5 Nile red encapsulation efficiency of CSNPs, Series 1 and Series 2

Table S6 Changes in particle size of CSNPs with varying levels of H₂O₂

Acknowledgments

This work was supported by the National Nature Science Foundation of China (grant number 81573618), the Pearl River S&T Nova Program of Guangzhou (grant number 2013J2200059), and the Cultivation Foundation for Distinguished Young Teachers in Higher Education of Guangdong (grant number Yq2013099).

Disclosure

The authors report no conflicts of interest in this work.