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Biological and Medical Applications of Materials and Interfaces
A nanozymatic antioxidant system based on MoS2 nanosheets Tongming Chen, Hang Zou, Xiaoju Wu, Chunchen Liu, Bo Situ, Lei Zheng, and Guowei Yang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 29 Mar 2018 Downloaded from http://pubs.acs.org on March 29, 2018
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ACS Applied Materials & Interfaces
A Nanozymatic Antioxidant System Based on MoS2 Nanosheets
Tongming Chen1 †, Hang Zou2 †, Xiaoju Wu1, Chunchen Liu2, Bo Situ2, Lei Zheng2*, and Guowei Yang1* 1
State Key Laboratory of Optoelectronic Materials and Technologies,
Nanotechnology Research Center, School of Materials Science & Engineering, School of Physics, Sun Yat-sen University, Guangzhou 510275, Guangdong, P. R. China 2
Department of Laboratory Medicine, Nanfang Hospital, Southern Medical
University/The First School of Clinical Medicine, Southern Medical University, Guangzhou 510515, Guangdong, P. R. China †
These authors contributed equally to this work.
* Corresponding authors:
[email protected],
[email protected] 1
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Abstract The enzymatic antioxidant system (EAS) protects aerobic cells from oxidative stress. However, it is brittle and susceptible of inactivation of reactive oxygen species (ROS) immoderate production. Here, we demonstrated that MoS2 nanosheets (few-layer MoS2), as a multifunctional nanozyme, possess intrinsic activity of mimicking enzymes of superoxide dismutases (SOD), catalases (CAT), and peroxidases (POD) under physiological conditions (pH 7.4, 25 oC). Further, MoS2 nanosheets showed POD-like activity by transferring electrons instead of generating ROS. Similar to EAS, a defense termed nanozymatic antioxidant system (NAS) was developed by MoS2 nanosheets, for regulation of oxidative stress. Surprisingly, this NAS can effectively scavenge other free radicals including hydroxyl radicals (•OH), nitrogen-centered free radicals (•DPPH), and nitric oxide (•NO). To evaluate these unique properties of MoS2-based NAS in vivo, Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), and A549 cell models were established, respectively. These results showed MoS2 nanosheets superiorly protect bacteria and cell against oxidative injury caused by H2O2. This work makes MoS2 nanosheets promising antioxidants in the pathological processes and expands their application in biocatalysis and nano-biomadicine.
Keywords. MoS2 nanosheets, multienzyme-like activities, nanozymatic antioxidant system, reactive oxygen species, free radicals.
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1. Introduction In normal metabolic process, reactive oxygen species (ROS) are constantly generated in living organisms and scavenged by antioxidant defenses1. ROS are highly reactive molecules, including oxygen ions: superoxide radicals (O2•-) and hydroxyl radicals (•OH), for example, and peroxides, such as hydrogen peroxide (H2O2)2. Excess production or reduced consumption of ROS, a situation termed cellular oxidative stress, may lead to oxidation of diverse sensitive compounds, interference in normal redox state of cells, and eventually cell death. For cellular ROS homeostasis regulation, aerobic organisms are equipped with an integrated antioxidant system, which includes antioxidant molecules, such as uric acid, ascorbic acid, and carotenes, and enzymatic antioxidant system (EAS). In aerobes, EAS are mainly constituted by antioxidant enzymes of superoxide dismutases (SOD), peroxidases (POD), and catalases (CAT)3. Nevertheless, in disease conditions, the antioxidant system can be affected strongly, since EAS is vulnerable to the attack of ultrahigh levels of ROS4. As we know, oxidative stress contributes to varieties of diseases, for instance, neurodegeneration, diabetes, osteoarthritis, and angiocardiopathy. Hence, appropriate control of ROS has a vital impact on human healthy5. MoS2 nanosheets (few-layer MoS2), one of the typical two-dimensional (2D) transition metal dichalcogenide materials, exhibit the individual mechanical, optical, electrical and chemical capabilities correlated with its ultrathin atomic layer structure6. Recently, MoS2 nanosheets have been widely applied in biomedical field, such as
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blood glucose detection, DNA biosensors, antibacterial, near-infrared photothermal agent, and drug delivery, which shows their low toxicity and excellent biocompatibility in living organisms7-13. In this contribution, we demonstrated that MoS2 nanosheets possess intrinsic multienzyme-like activity including SOD, CAT, and POD activity under physiological conditions. From a biochemical point of view, these findings are hardly unexpected, as enzymes containing molybdenum in their active sites is universally distributed in most living organisms, catalyzing redox and oxygen-transfer reactions14. In this case, the molecular mechanism of the POD-like activity was established that the MoS2 nanosheets accelerate the electron transferring between TMB and H2O2 rather than generating •OH. Moreover, we assumed that the source of the activity involves the Mo4+/Mo6+ switch on the surface of MoS2 nanosheets. Like EAS for regulating the ROS homeostasis, MoS2 nanosheets with antioxidant-enzyme mimetic activity can efficiently remove several kinds of ROS including O2•- and H2O2. We coined the term “nanozymatic antioxidant system” (NAS) to describe such defensive system built by MoS2 nanosheets. Besides, we found out that NAS can scavenge other free radicals including hydroxyl radicals (•OH), nitrogen-centered free radicals (•DPPH), and nitric oxide radicals (•NO), making it more widely used as antioxidant. To clarify the unique properties of MoS2-based NAS in vivo, several ROS disturbance models were established using Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), and A549 cells treated by H2O2, respectively. Interestingly, our results showed the excellent biocompatibility and protective effect of MoS2 nanosheets-based NAS
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against oxidative injure in bacteria and cell induced by H2O2. The cells preprocessed by MoS2 nanosheets show lower intracellular ROS level and higher viability in the presence of oxidative stress. Therefore, this study makes MoS2 nanosheets promising antioxidants for disease caused by oxidative stress and expand their application in biocatalysis and nano-biomadicine. 2. Experimental section 2.1. Chemicals and Reagents MoS2 powders (
