Bactericidal effects and accelerated wound healing using Tb4O7 nanoparticles with intrinsic oxidase-like activity

Abstract

Background: Nanomaterials that exhibit intrinsic enzyme-like characteristics have shown great promise as potential antibacterial agents. However, many of them exhibit inefficient antibacterial activity and biosafety problems that limit their usefulness. The development of new nanomaterials with good biocompatibility and rapid bactericidal effects is therefore highly desirable. Here, we show a new type of terbium oxide nanoparticles (Tb₄O₇ NPs) with intrinsic oxidase-like activity for in vitro and in vivo antibacterial application.

Results: We find that Tb₄O₇ NPs can quickly oxidize a series of organic substrates in the absence of hydrogen peroxide. The oxidase-like capacity of Tb₄O₇ NPs allows these NPs to consume antioxidant biomolecules and generate reactive oxygen species to disable bacteria in vitro. Moreover, the in vivo experiments showed that Tb₄O₇ NPs are efficacious in wound-healing and are protective of normal tissues.

Conclusions: Our results reveal that Tb₄O₇ NPs have intrinsic oxidase-like activity and show effective antibacterial ability both in vitro and in vivo. These findings demonstrate that Tb₄O₇ NPs are effective antibacterial agents and may have a potential application in wound healing.

Keywords: Antibacterial; Oxidase; Reactive oxygen species; Tb4O7 nanoparticles; Wound healing.

Fig. 1

Oxidase-like activity of Tb₄O₇ NPs. a A photograph showing the capability of the Tb₄O₇ NPs in catalyzing the oxidations of TMB, ABTS, and OPD that produce colored products. b Time-dependent absorption spectra of TMB catalyzed by Tb₄O₇ NPs. c Absorbance at 652 nm measured from samples containing TMB and different concentrations of Tb₄O₇ NPs. d The specific activities of Tb₄O₇ NPs. Steady-state kinetic assays of Tb₄O₇ NPs (e, f). e TMB concentration dependence of initial reaction velocity. f Double-reciprocal plot generated from (d)

Fig. 2

a Oxidation of AA by Tb₄O₇ NPs. b ESR spectra of BMPO/·OH generated from a sample solution containing 25 mM BMPO, 1 mM H₂O₂ in the absence (control) and presence of different concentrations of Tb₄O₇ NPs

Fig. 3

The effect of Tb₄O₇ NPs on survival rates of bacteria a CFUs of S. aureus following incubation with Tb₄O₇ NPs; b CFUs of E. coli following incubation with Tb₄O₇ NPs; c Representative fluorescence and SEM images of S. aureus after Tb₄O₇ NPs treatments. Bacterial cells were treated with 1) PBS as control, 2) 25 μg/mL Tb₄O₇ NPs, 3) 50 μg/mL Tb₄O₇ NPs or 4) 100 μg/mL Tb₄O₇ NPs; d Representative fluorescence and SEM images of E. coli after Tb₄O₇ NPs treatments. Bacterial cells were treated with 1) PBS as control, 2) 10 μg/mL Tb₄O₇ NPs, 3) 25 μg/mL Tb₄O₇ NPs or 4) 50 μg/mL Tb₄O₇ NPs. **p < 0.01 and ***p < 0.001 vs control

Fig. 4

a Fluorescence images of bacterial cells. b Analysis of the ROS levels by microplate reader. ***p < 0.001 vs control

Fig. 5

a Photographs of wounds on the backs of mice in control (PBS) and Tb₄O₇ NPs treatment groups (n = 5). Scale bar: 5 mm. b Related wound size in each treatment group. c Bacterial number of infected wounds on the 7th day. ***p < 0.001 vs control

Fig. 6

a The hemolysis ratio of red blood cells. The insert images of tubes containing red blood cells solution show the direct observation of hemolysis. Tube 1: PBS buffer; Tube 2–5: 25, 50, 100, and 200 μg/mL Tb₄O₇ NPs; Tube 6: ultrapure water. b MTT assays determined cell viability of HUVECs after Tb₄O₇ NPs treatment

Fig. 7

In vivo toxicity of Tb₄O₇ NPs. a The blood biochemistry data of the mice treated with Tb₄O₇ NPs after 7 d (n = 5). b Histological data (H&E staining images) are obtained from the major organs of mice treated with Tb₄O₇ NPs after 7 d. Scale bar = 100 μm