Keywords

3.1 Introduction

3.1.1 Nanoparticles Used in Antioxidant Activity

Nanotechnology is one of the most recent areas to be explored for its applications related to engineering, medicine and various other sciences. Nanoparticles are particles in the size range of 1–100 nm and have the most applications in nanotechnology. Nanoparticles in different forms play vital roles in biomedical applications. The different types or forms of nanoparticles include metal nanoparticles (gold, silver, zinc, copper, selenium, etc.), metal oxide nanoparticles (silver oxide, zinc oxide, copper oxide, cadmium oxide and zirconium oxide), polymer nanoparticles (chitosan, silica, polyethylene glycol, cellulose, polyvinyl alcohol and polyvinyl pyrrolidine), carbon nanotubes, magnetic nanoparticles, nanohydrogels, aerogels, graphene nanostructures, nanocomposites, nanoshells, nanohybrids and biomolecules (curcumin, beta cyclodextrins, etc.).

Previously, nanoparticles were synthesized using physical and chemical techniques such as chemical vapour deposition, microwave irradiation, sol–gel techniques, plasma synthesis techniques, mechanical milling, ultrasound techniques, the hydrothermal method, the solvothermal method, the electrodeposition process, electroexplosion and laser techniques. Because of the high cost and environmental factors, researchers have recently been exploring use of green materials for the synthesis of nanoparticles, using microorganisms such as Bacillus subtilis, Klebsiella planticola, Klebsiella pneumoniae and Aspergillus niger; plant extracts from Coleus aromaticus, Pongamia pinnata, etc.; and algal extracts of Turbinaria conoides, Padina tetrastromatica, etc. [1,2,3,4,5,6]. Synthesis of nanoparticles using biological methods is very simple and cost effective. The prepared nanoparticles have been characterized using various techniques such as scanning electron microscopy, atomic force microscopy, ultraviolet–visible light (UV-vis) spectroscopy, dynamic light scattering, transmission electron microscopy, Fourier transform infrared spectroscopy, gas chromatography with mass spectroscopy, zeta potential analysis, thermogravimetric analysis, elemental dispersive analysis and x-ray diffraction assays [7,8,9]. Figure 3.1 shows green synthesis of nanoparticles and their characterization.

Fig. 3.1
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Biosynthesis and characterization of nanoparticles

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These nanoparticles are used in diverse applications such as anticancer activity.

Different types of nanoparticles are used for antioxidant activity in vitro and in vivo. Among these nanoparticles, metal and metal oxide nanoparticles are majorly involved in the activity in different experimental procedures. Figure 3.2 shows the different types of nanoparticles involved in antioxidant activity.

Fig. 3.2
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Different nanoparticles (NPs) used in antioxidant activity

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3.1.1.1 Silver Nanoparticles

Silver nanoparticles are the major metal nanoparticles in use and are intensively used in antimicrobial applications for their antibacterial and antifungal activities. In addition, silver nanoparticle have achieved very good results in anticancer and antioxidant activities [10,11,12,13]. Table 3.1 provides information on green synthesis of silver nanoparticles characterized using various techniques and antioxidant activities.

Table 3.1 Synthesis, characterization and antioxidant activity of silver nanoparticles (AgNPs)
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3.1.1.2 Gold Nanoparticles

Gold nanoparticles are widely used for delivery of drugs, proteins and genes in biomedical applications because of their surface plasmon resonance. These advanced metal nanoparticles also have applications in photothermal therapy, cancer imaging, identification of pathogens using immune chromatographic techniques, tissue imaging, anti-inflammatory activities and anticancer activities [39,40,41]. Table 3.2 provides information on gold nanoparticles and their antioxidant activities in various biochemical assays.

Table 3.2 Antioxidant activity of gold nanoparticles (AuNPs)
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3.1.1.3 Zinc Oxide Nanoparticles

Zinc oxide nanoparticles have unique properties with many applications in many fields such as photocatalytic activity; antibacterial and antifungal activity against clinical, animal and plant pathogens; dye degradation and heavy metal degradation activity; and UV-filtering properties [10, 50,51,52]. Zinc oxide nanoparticles are one of the important types of semiconductor nanoparticles used in multitasking applications, including antioxidant activity, as shown in Table 3.3.

Table 3.3 Antioxidant activity of zinc oxide nanoparticles (ZnONPs)
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3.1.1.4 Antioxidant Activity of Other Nanoparticles

Apart from silver, gold and zinc nanoparticles, other nanoparticles such as chitosan, titanium dioxide, cerium oxide, selenium, magnetic nanoparticles, silicon dioxide and nickel oxide nanoparticles also show very good antioxidant activity in different assays. Figure 3.3 shows different antioxidant assays used for free radical–scavenging nanoparticles.

Fig. 3.3
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In vitro antioxidant activity of nanoparticles using various assays. ABTS 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid), DPPH 2,2-diphenyl-1-picryl-hydrazyl-hydrate

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3.1.1.5 Antioxidant Activity of Polymer, Magnetic and Oxide Nanoparticles

Chitosan is an important bioactive product, obtained from crab shells and prawn shells. It shows good antimicrobial activity against Escherichia coli and Staphylococcus aureus and antifungal activity against Candida albicans, and it has shown good scavenging activity of 76% in a 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH) assay [72]. Super-para iron oxide nanoparticles synthesized using Stevia leaf extract had a spherical shape and were 25 nm in size on high-resolution transmission electron microscopy (TEM) analysis. They showed good antioxidant activity in a DPPH assay and a half-maximal inhibitory concentration (IC50) of 65 μg/mL [73]. Manganese oxide nanoparticles prepared using mature seeds of Atropa belladonna L. showed a crystalline structure (on x-ray diffraction (XRD)) and a spherical shape with a size of 30 nm, confirmed by TEM. The free radical–scavenging activity of MnO2 nanoparticles, investigated using a DPPH assay with plantlets at 200 mg/L with an IC50 of 134.6 μg/mL and Fe2+-chelating activity, also showed the same tendency [74].

Selenium nanoparticles synthesized using pectin showed DPPH radical–scavenging activity of 92%, a Trolox-equivalent antioxidant capacity assay value of 222.18 μmol Trolox per gram of the sample and a ferric-reducing ability of plasma (FRAP) assay value of 127.51 μmol Fe2+ per gram of the sample [75]. A hyperbranched polysaccharide from Lignosus rhinocerotis also showed good activity in a DPPH assay (24.29%, 23.28%, 44.84%, 52.31% and 43.22%) and in an ABTS radical–scavenging assay (83.18% and 81.54%) [76].

Pisonia alba leaf extract–mediated cerium oxide nanoparticles with the characteristics of a cubic fluorite crystal structure (on XRD), UV-vis spectroscopy values of 258 and 317 nm, and a 12 nm size on TEM showed good antifungal activity and moderate antioxidant activity in a DPPH assay and FRAP assay [77].

3.1.1.6 Antioxidant Activity of Nanoparticles In Vivo

In a recent research article, Qin et al. showed that layered double hydroxide (LDH) nanoparticles possessed a DPPH-scavenging effect, a hydroxyl radical (OH)–scavenging effect and a pro-oxidative Cu2+-chelating effect. This was mainly due to folic acid coupling with the LDH nanoparticles; moreover, folic acid–LDH was successful in increasing glycogen levels in muscle and hepatic glycogen. It was suggested that a folic acid–LDH antioxidant could have indications for use as a novel antioxidant or an antifatigue nutritional supplement [78].

An in vivo study by Zhang et al. revealed that nano-gold loaded with resveratrol (Res-GNPs) showed a better antitumour effect than resveratrol alone. This was due to the fact that the gold nanoparticles could transport more resveratrol to cells and to mitochondria; thus, the gold nanoparticles coupled with resveratrol reduced the cancer effect both in vitro and in vivo [79].

The above studies clearly indicate that nanoparticles, when coupled with antioxidants, provide more protection for healthy cells and provide anticancer effects.

In in vitro studies on sulphoraphane-modified selenium nanoparticles, Krug et al. showed anticancer action in several cancer cell cultures. They also showed that this high antitumour activity and selectivity with regard to diseased and healthy cells is an extremely promising treatment for cancer cells [80]. The different parameters analysed to determine the in vivo antioxidant activity of the nanoparticles are shown in Fig. 3.4.

Fig. 3.4
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In vivo antioxidant activity of nanoparticles. LDL low-density lipoprotein

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Khan et al. studied the effects of cobalt-doped tin oxide (Co-doped SnO2) nanoparticles and revealed that in breast carcinoma cells, green-synthesized Co-doped SnO2 nanoparticles showed potential antioxidant activity in a DPPH assay and also showed significant anticancer and antitumour activity in both in vitro and in vivo conditions. The multipurpose properties of synthesized nanoparticles demonstrated in this study showed that they could be useful for pharmaceutical and nanomedicine applications [81].

A research study by Tang et al. demonstrated the characterization of epigallocatechin-3-gallate (EGCG)–functionalized chitin (CH) derivative nanoparticles (CE-HKNPs) and compared their antitumour activity with that of free Honokiol (HK). The result showed that the CE-HKNPs were effective, inhibiting the cell proliferation of HepG2 cells and decreasing the mitochondrial membrane potential. Moreover, in both in vitro and in vivo conditions they did not elicit any side effects in the cells. It was suggested that CE-HKNPs are an effective delivery system against liver cancer cells [82]

A recent article by Shanmugasundaram et al. described a Sprague Dawley (SD) rat model in which hepatoprotective experiments were conducted against diethyl nitrosamine (DEN)–stimulated liver cancer cells using biocompatible nanoparticles of silver (AgNPs), gold (AuNPs) and their alloy (Ag/AuNPs), synthesized from microbes. The animals treated with nanoparticles showed significant tumour reduction in in vivo studies, and this was also confirmed by other studies. The results showed anticancer activity only in DEN-stimulated liver cells, due to the synthesized AgNPs, AuNPs and Ag/AuNPs. In nanodrug development, microbial biocompatible nanoparticles have been shown to have potential as an effective drug [83].

Sulaiman et al. described an experiment, using an Oleo europaea leaf extract, in which copper oxide (CuO) nanoparticles (CuNPs) were synthesized. Because of the stability of the antioxidant effect, the free radical–scavenging activity of the CuNPs against 2,2-diphenyl-1-picryl-hydrazyl was assured. In mice, immune responses were observed in both the thymus and the spleen. After CuNP treatment the thymus, spleen and serum showed reductions in the adenosine deaminase (ADA) enzyme. In a dose-dependent manner, application of CuNPs against AMJ-13 and SKOV-3 cancer cells induced cell death by apoptosis. Normal dermal fibroblast cells showed less significant cytotoxic effects. Thus, CuNPs have the ability to act as an anticancer agent [84].

In contrast, Nemmer et al. found that exposure to cerium oxide nanoparticles (CeO2NPs) induced lung toxicity. In their study, a noticeable increase in neutrophils in the bronchoalveolar lavage fluid, along with an increase in tumour necrosis factor (TNF) and a drop in the activity of the antioxidant catalase, were stimulated by CeO2NPs. Increased plasma levels of C-reactive protein and TNF were also noted [85]. In this in vivo study it was found that thrombosis was due to acute pulmonary oxidative damage and systemic inflammation.

Qiao et al. studied andrographolide (ADG), a diterpenoid separated from Andrographis paniculata with a range of pharmacological activities including antitumour, anti-inflammatory, anticancer and hepatoprotective effects. They showed that a freeze-dried ADG nanosuspension (ADG-NS) could remain highly stable [86].

Pramanik et al. performed in vitro and in vivo studies on biotin-enriched gold nanoparticles targeted for delivering an anticancer active copper complex, copper (II) diacetyl-bis (N 4-methylthiosemicarbozane), tethered to 20 nm gold nanoparticles (AuNPs) and additionally decorated with biotin for target achievement. They revealed very good anticancer activity against HeLa cells derived from cervical cancer cells; less activity was observed against HaCaT cells. In an in vivo comparison with a nanoparticle conjugate without biotin, using a HeLa cell xenograft tumour model, the biotin-enriched nanoparticle conjugate showed a greater reduction in tumour volume than the control (without biotin), suggesting significant targeting [87].

3.2 Mechanisms of Action

Different metal nanoparticles, polymer nanoparticles, metal-coated polymer nanoparticles and bioactive compound–coated/decorated nanoparticles act as nanoantioxidants. The major mechanisms of action of these nanoparticles mimic the behaviour of catalase (CAT), glutathione peroxidase (GPX), superoxide dismutase (SOD) and chain-breaking activity. Examples of these nanoparticles and their mechanisms of action in different assays are cerium oxide nanoparticles, which show catalase-like behaviour in hydrogen peroxide disappearance on spectrophotometric analysis [88], polyvinyl pyrrolidone–coated gold nanoparticles, which decrease H2O2 in spectrometric analysis and show catalase-like behaviour [89], and gold nanorods, gold with platinum nanorods, core shells and gold with palladium nanorods, which shows catalase-like behaviour in H2O2 assays, spectrophotometric analysis and O2 evaluation using dark electrodes [90].

Nanoparticles such as manganese oxide nanoflowers and grapheme oxide–supported selenium nanoparticles have shown glutathione peroxidase–like behaviour in a glutathione reductase–coupled assay using spectrophotometric analysis [91, 92].

The chain-breaking mechanism is the major action in various antioxidants (also called radical-trapping antioxidants) such as flavonoids, vitamin C, vitamin E and many synthetic alternatives.

A chain-breaking or slowdown mechanism of action was found in some nanoparticles, such as oleic acid–coated cerium oxide nanoparticles, when an AAPH-derived radical-scavenging (oxygen radical absorbance capacity (ORAC)) assay was performed [93]. Polyacrylic acid–protected platinum nanoparticles were analysed using a DPPH assay with spectrophotometric analysis. Inhibition of linoleic acid peroxidation was observed with electron paramagnetic resonance (EPR) detection of AAPH-derived radical–scavenging activity [94]. Zirconium oxide nanoparticles and polyethylene glycol–coated melanin nanoparticles have also shown chain-breaking activity, confirmed by a DPPH assay [95, 96].

Superoxide dismutase–like behaviour is the major mechanism in many antioxidant nanomaterials and xanthine/xanthine oxidase and cytochrome C analysed by spectrophotometric analysis, potassium oxide reaction, EPR study of reactions with potassium oxide with 5-diethoxyphosphoryl 5-methyl-1-pyrroline-n-oxide (DEPMPO) and oxide evaluation. The nanomaterials involved in these actions are fullerene, multiwalled carbon nanotubes, trismalanyl C-60, dimercaptosuccinic acid–coated Co3O4 nanoparticles, polyvinyl pyrrolidone–coated gold nanoparticles, glycine-coated copper nanoparticles, polyethylene glycol–coated manganese and carbon nanoclusters, palladium nanoparticles, platinum nanopowder and Mn3O4 nanoflowers [89, 91, 97,98,99,100,101,102,103,104,105].