Scavenging of reactive oxygen and nitrogen species with nanomaterials

Abstract

Reactive oxygen and nitrogen species (RONS) are essential for normal physiological processes and play important roles in cell signaling, immunity, and tissue homeostasis. However, excess radical species are implicated in the development and augmented pathogenesis of various diseases. Several antioxidants may restore the chemical balance, but their use is limited by disappointing results of clinical trials. Nanoparticles are an attractive therapeutic alternative because they can change the biodistribution profile of antioxidants, and possess intrinsic ability to scavenge RONS. Herein, we review the types of RONS, how they are implicated in several diseases, and the types of nanoparticles with inherent antioxidant capability, their mechanisms of action, and their biological applications.

Keywords: ROS scavenging; antioxidant nanoparticles; mnanomaterials; reactive nitrogen species; reactive oxygen species (ROS).

Figure 1

Types of RONS produced in the cell (reproduced with permission from Ref. [4], © Springer eBook 2014).

Figure 2

Main routes of RONS generation; RH=organic molecule (reproduced with permission from Ref. [46], © Elsevier 2009).

Figure 3

A model of the reaction mechanism for oxidation of hydrogen peroxide by nanoceria and regeneration via reduction by superoxide. An oxygen vacancy site on nanoceria surface (1) presents a 2Ce⁴⁺ binding site for H₂O₂ (2). After the release of protons and two-electron transfer to the two cerium ions (3), oxygen is released from the now fully reduced oxygen vacancy site (4). Subsequently, superoxide can bind to this site (5); after the transfer of a single electron from one Ce³⁺, and uptake of two protons from the solution, H₂O₂ is formed (6) and can be released. After repeating this reaction with a second superoxide molecule (7), the oxygen vacancy site returns to the initial 2Ce⁴⁺ state (1). It is also possible that the third Ce³⁺ indicated, which generates the oxygen vacancy, can participate directly in the reaction mechanism. Reproduced with permission from Ref. [65], © Royal Society of Chemistry 2011.

Figure 4

TEM micrographs (a)–(c) of water-soluble nanoceria. All scale bars are 20 nm from (a) to (c). (a) Oleic acid-coated CeO₂ nanoparticles (3.8 ± 0.4 nm); (b) PEI-coated CeO₂ nanoparticles (5.4 ±1.0 nm); (c) PAAOA-coated CeO₂ nanoparticles (8.2 ± 1.7 nm). The size distribution histograms (d)–(f) are placed at the bottom of the corresponding images together with a schematic depiction of the coated nanomaterial. (g) The extent of H₂O₂ quenching capacity depends on the diameter and surface stabilizers of nanoceria. To compare the surface polymer-dependent H₂O₂ quenching efficiency of nanoceria, the extent of the band shift (Δλ) was measured at 0.30 absorbance after the injection of H₂O₂ from the control. For diameter-dependent H₂O₂ quenching, three CeO₂ suspensions with different diameters were utilized (d = 3.8, 5.4, and 8.2 nm; PAAOA-coated CeO₂). Surface coating-dependent H₂O₂ quenching was shown by 3.8-nm CeO₂ covered with four different polymers (PAAOA, oleic acid, PEI, and PMAO). (h) Schematic detailing of the proposed regenerative properties of nanoceria, and probable mechanism of free-radical scavenging and auto-catalytic behavior of cerium oxide nanoparticles. (a)–(g) are adapted with permission from Ref. [68], © American Chemical Society 2013. (h) is reproduced with permission from Ref. [71], © Elsevier 2007.

Figure 5

(a)–(c) Characterization of ceria nanoparticles. (a) TEM images reveal discrete and uniform 3 nm-sized ceria nanoparticles. Scale bar = 100 nm. (b) High-resolution TEM images reveal a cross-lattice pattern, demonstrating the highly crystalline nature of ceria nanoparticles. Scale bar = 5 nm. (c) The geometry of ceria nanoparticles after hydrophilic encapsulation with phospholipid-PEG (core diameter (d_c) = 3–4 nm; hydrodynamic diameter (d_h) = 17–18 nm). (d) and (e) Infarct volume and ischemic cell death in vivo. (d) Representative slices showing that 0.5 and 0.7 mg·kg⁻¹ of ceria nanoparticles can significantly reduce infarct volumes. (e) The number of TUNEL-positive cells are decreased in the ceriainjected group (*p < 0.05; n = 4 each). Adapted with permission from Ref. [80], © John Wiley and Sons 2012.

Figure 6

(a) Coronal brain sections (stained with triphenyltetrazolium chloride (TTC)) of sham-operated control and PBS- or a-SWNT-treated rats. Brain slices were arranged in sequence. White areas represent the infarcted region after MCAO. (b) Quantification of the ischemic lesions of brain sections in (a). (c) and (d) Bar graphs showing quantification of (c) GFAP- and (d) Iba-1-positive cells on the ipsilateral side. Data are the mean number of cells from five random fields. (e) Graph showing that pretreatment with a-SWNTs reduces neurological damage after ischemia. Neurological score was evaluated by the Rota-Rod treadmill test. (f) and (g) Effects of treatment with a-SWNTs on the production of proinflammatory cytokines IL-1b (f) and TNF-a (g). Cytokine levels, determined by ELISA, were normalized against the cortex of the contralateral hemisphere. Immunohistochemical analysis and ELISA were performed 7 days after MCAO. Data are expressed as means ± s.e.m. *p < 0.001. Adapted with permission from Ref. [92], © Springer Nature 2011.

Figure 7

(a) Diagram and TEM images of MnO₂ and A-MnO₂ NPs. Precursor MnO₂ NPs (~ 15 nm) are stabilized by positively charged PAH. In A-MnO₂ (~ 50 nm), several MnO₂ particles are entrapped in a poly(allylamine hydrochloride) (PHA)/BSA complex due to strong electrostatic interaction between the protein and polymer. (b) Representative optical images of EMT6 tumor-bearing mouse with i.t. injected near-infrared-labeled A-MnO₂ NPs; images were acquired at various times. (c) Quantification of tumor hypoxia after treatments, determined using classified images (not shown) (n = 3). Error bars represent standard errors of the mean. (*) Statistically significant difference (*p = 6.9 × 10⁻⁵) as compared to saline (control)-treated group. (d) Tumor volume measured over time after treatment. Adapted with permission from Ref. [101], © American Chemical Society 2014.

Figure 8

(a) Platinum nanoparticles [106]—the lipid peroxide content in mouse liver 6 h after hepatic ischemia/reperfusion. Lipid peroxides were detected by TBA method. Each of the Pt-NPs was administered at an equivalent platinum dose (50 mg of platinum per kg). The results are expressed as the mean ± S.D. of 3 to 7 mice. *p < 0.05, indicates significant difference from the saline-treated group. (b) and (c) Melanin nanoparticles [109]. (b) TEM image of PEG-MeNPs. (c) O₂ production in the KO₂ solution (100 µM) with or without PEG-MeNPs. The insert is the digital image of the PEG-MeNPs solution before and after the addition of KO₂. (d) Selenium nanoparticles [112]—comparison of the antioxidant capacities of CS-SeNPs in DPPH, ABTS, and lipid peroxidation systems. The different letter markers denote the significant mean difference at p < 0.05. (e) and (f) Selenium-doped carbon quantum dots [113]. (e) Synthesis of Se-CQDs with green fluorescence using hydrothermal treatment with selenocysteine. (f) Once the Se-CQDs are internalized in cells with elevated ROS levels, a portion of the ROS can be scavenged, protecting the cells from ROS-induced damage. (a) is reproduced with permission from Ref. [106], © Royal Society of Chemistry 2014. (b) and (c) are reproduced with permission from Ref. [109], © American Chemical Society 2017. (d) is reproduced with permission from Ref. [112] under the Creative Commons Attribution License, © Zhai et al. 2017. (e) and (f) are reproduced with permission from Ref. [113], © John Wiley and Sons 2017.

Figure 9

(a) Schematic representation of the ischemic stroke model. (b) Representative images of TTC-stained brain slices from different groups. The corresponding (c) infarct areas and (d) O₂^•− levels in brain tissues of the three groups (*p < 0.05 and **p < 0.01 vs. saline control). Adapted with permission from Ref. [109], © American Chemical Society 2017.

Figure 10

(a) and (b) Illustration, characterization, and ROS-scavenging activities of ceria NPs and CZNPs. (a) Illustration of the structure of CZNPs. (b) TEM image of CZNPs; scale bar: 5 nm. (c) Mortality-reducing effects of CZNPs in the in vivo mouse model of CLP-induced bacteremia. After induction of CLP, PBS or CZNPs (2 mg·kg⁻¹) were placed into the intraperitoneal space, and then the abdomen was sutured. Graph shows the survival curves in the CLP over 14 days; n = 18, *p < 0.05. (d) Representative histopathological images. Asterisk, ulcer detritus; arrow, mucosal disruption; arrowhead, mononuclear cell infiltration. Scale bars: 100 mm. (e) Representative in vivo near-infrared fluorescent optical images of the models 9 h after intravenous injection with Cy5.5-CZNPs. Colored signals denote Cy5.5 fluorescence (excitation = 620 nm, emission = 710 nm). Adapted with permission from Ref. [81], © John Wiley and Sons 2017.

Figure 11

(a) Design, synthesis, and characterization of TPP-CNPs as therapeutic mitochondrial antioxidants for the treatment of Alzheimer’s disease. Scheme of DSPE-PEG-TPP-coated ceria nanoparticles exhibiting ROS recyclable scavenging activity. (b) TPP-CNPs reduce reactive glial activation. Confocal fluorescence images (left) of gliosis in tissue sections co-labeled with GFAP (red) and Iba-1 (blue). Quantified levels of GFAP and Iba-1 in the images (n = 4 per group). Statistical analysis was performed using ANOVA. Error bars represent 95% CIs. **p < 0.01; ***p < 0.001; LT + sham: littermate mice; Tg + sham: 5XFAD mice. Scale bar = 30 µm. (c) Western blot analysis for oxidative stress markers in 5XFAD mice treated with TPP-CNPs (n = 3 per group). Data were normalized with respect to the signal of GAPDH. Statistical analysis was performed using ANOVA. Error bars represent 95% CIs. *p < 0.05; **p < 0.01; ***p < 0.001; LT + sham: littermate mice; Tg + sham: 5XFAD mice. Adapted with permission from Ref. [135], © American Chemical Society 2016.

Figure 12

(a)–(c) Effect of SeNPs and insulin on activities of the antioxidant enzymes ((a) superoxide dismutase: SOD and (b) catalase: CAT) in the testes of control and STZ-diabetic rats. (c) Impact of SeNPs and insulin on oxidative stress markers is shown by the levels of nitric oxide (NO) in the testes of control and STZ-diabetic rats. Values are mean ± SEM (n = 7). ^ap < 0.05, significant change with respect to Control group; ^bp < 0.05, significant change with respect to Diabetic group. (d) Impact of SeNPs and/or insulin on the morphology of the testes in diabetic rats. (1) control rats; showing typical testicular architecture; (2) SeNPs-treated rats; showing typical spermatogenic cells in the seminiferous tubules; (3) STZ-diabetic rats; showing severe testicular damage; (4) and (5) STZ-SeNPs-treated group, STZ-Ins-treated rats, and STZ-SeNPs-Ins-treated rats, respectively; SeNPs and/or insulin ameliorated the defects caused by diabetes in the spermatogenic cells of the seminiferous tubules. Tissues were stained with hematoxylin and eosin. Scale bar = 50 µm. Adapted with permission from Ref. [146] under the Creative Commons Attribution License, © Dkhil et al. 2016.

Figure 13

(a) Composition/structure of a photodriven NR; mechanisms of using NR for photosynthesis of H₂ gas in situ to reduce oxidative stress in a mouse model of LPS-induced inflamed paw. (b) Fluorescence image of Chla embedded in Lip membrane of NR. (c) TEM image of AuNPs encapsulated in NR. (d) Spectral changes of AA encapsulated in NR after various periods of laser irradiation. (e) Bright-field images of H₂ bubbles generated in an NR following laser irradiation. (f) IVIS images of ROS in LPS-induced inflamed paws after treatment with BS and NR without/with laser irradiation. Adapted with permission from Ref. [153], © American Chemical Society 2017.

Figure 14

High-resolution transmission electron micrographs show the presence of (a) loose agglomerates of 15–20 nm at low magnification and (b) individual 3–5 nm crystallites. The d spacing of 0.31 nm shows planes of ceria, while the selected area electron diffraction (SAED) pattern confirms the presence of fluorite lattice of cerium oxide. (c) Gross morphology of representative mouse with tumors at day 30 (n = 6). (d) Cumulative abdominal circumference measured at the end of the study. (e) Excised tumor weight from vehicle (PBS)-treated and NCe-treated mice (0.1 mg·kg⁻¹ bd wt; every third day). Results are shown as mean ± S.D. of six individual animals. **p < 0.01; NCe-treated groups were compared with untreated group using two-tailed Student’s t-test (Prism). (f) Enumeration of metastatic nodules found per lung in untreated and NCe-treated mice. Total of five lung sections were observed to obtain the average count. *p < 0.005; NCe-treated groups were compared with untreated group using two-tailed Student’s t-test (Prism). Adapted with permission from Ref. [164] under the terms of the Creative Commons Attribution License, © Giri et al. 2013.