Pharmacological Activities of AgNPs

Pharmacological Activities of AgNPs: History

Please note this is an old version of this entry, which may differ significantly from the current revision.

Subjects: Microbiology

Contributor: Tze Yan Lee , Uzma Ramzan , Waqar Majeed , Abdul Ahad Hussain , Fasiha Qurashi , Safi Ur Rehman Qamar , Muhammad Naeem , Jalal Uddin , Ajmal Khan , Ahmed Al-Harrasi , Saiful Izwan Abd Razak

Silver nanoparticles (AgNPs) are commonly used in numerous consumer products, including textiles, cosmetics, and health care items.

AgNPs
pharmacological activities
antimicrobial
microbiology
toxicity

1. Antimicrobial Activities of AgNPs

AgNPs possess excellent pharmacological activities against bacteria, fungi, and yeasts in aquatic groups of organisms. A study conducted by Moustafa et al. [124] investigated the antibacterial potential of AgNPs in marine organisms. They reported that these NPs showed excellent antibacterial properties against S. agalactiae and V. alginolyticu [124]. Another study conducted by Ghetas et al. [125] investigated that AgNPs possess antibacterial action against S. agalactiae, A. hydrophila, V. alginolyticus, and antifungal action against F. moniliform, and C. albicans [125]. AgNPs also possess antiviral activities in some aquatic organisms. White spot syndrome and hepatopancreatic parvoviruses are common viruses in aquatic organisms. A study conducted by Quinonez et al. [126] showed that a 1000 ng dose significantly reduced mortality by up to 50% and thus a potential role in controlling the White spot syndrome in striped harlequin, bumblebee red cherry shrimps. AgNPs also showed interaction with the envelope of hepatopancreatic parvoviruses and inhibited their viral replication in A. japonicus and L. vannamei [127].

Some recent studies have been reported about the antibacterial action of AgNPs in aquatic organisms. The larger surface area of AgNPs shows strong interaction with the biological membranes of microorganisms [128]. Therefore, these particles attach to the bacterial surface and enter the cell membrane due to their small size. It is also described as highly poisonous to bacterial species. Their antibacterial potency can be improved [129]. Free radical production mainly targets the membrane lipids in the living organism, occurs with dissociation and disruption, and ultimately inhibits microorganism growth [130]. The same mass of silver ions and AgNPs show an equivalent inhibition of bacteria, Staphylococcus aureus, and Escherichia coli [131]. The silver ions are infused through the cell wall into bacteria; due to this cell wall breakdown, the cells’ protein is denatured, and the organisms die [132,133]. The silver ions are small and positively charged and freely communicate negatively charged biomolecules in the bacterial cell wall [134,135].

Silver ions discharged from AgNPs and entered across the bacterial cell-like protein and peptidoglycan constituents, preventing them from additional replication [136]. Discharge of silver ions occurs through oxidizing agents, which oxidize the elemental silver and convert them into toxic forms. Organic groups such as protein and carbonyl inside bacteria’s cell walls are donors of electrons instead of electrons acceptors. The silver atom cannot generate silver ions. Therefore, the production of silver ions approves oxidizing agents [137]. Rai et al. [138] have noted how AgNPs correlated with the E. coli cell wall, which interfered with all membrane sides, dissolved with the release of silver ions into the cell, and affected the transcriptional response. They also illustrated a new dimension of the target microorganism species’ significance, as the antibacterial behavior of NPs often relies on the target microorganism species. Antibacterial activity is explained stepwise in the later section: (1) NPs attract electrostatically [139], (2) generation of the free radicals, permeability changes, respiration disturbance, intracellular contents linkage [140], (3) modulation of protein phosphotyrosine profiles, activated in the development of the cell cycle and the synthesis of capsular polysaccharides [141], (4) associations with SH-groups; synthesis of protein and its function inhibited [142], and (5) interact with DNA-phosphorus that contain phosphorus [143,144].

2. Chronic and Acute Toxicity Effects of AgNPs

AgNPs influence the cellular processes in living organisms and increase the production of reactive species in aquatic organisms in both in vitro and in vivo. These reactive species disrupted mitochondrial DNA activity and lipid peroxidation, stopping embryonic development and reproduction [146]. When AgNPs are exposed at high concentrations by two folds, even with a slow time of exposure, the survival of organisms is reduced abruptly [147,148]. The generally established explanation for this phenomenon leads to silver ion blockage of the Na⁺, K⁺-ATPase and inhibits the incorporation of Na ions via the gill membranes. It triggers the failure of ion regulation and eventually leads to the organism’s death [149]. The acute toxicity of AgNP exposure has both a direct and indirect effect. ROS generation, protein denaturation, membrane deformation, and DNA disruption are all direct effects of AgNP free radicals. In contrast, the indirect effect includes the discharge of Ag ions from the AgNP suspension [150].

Chronic toxicity tests utilizing minimal doses of exposure (ppb) and spanning the whole life cycle are required to accurately determine the toxicity of AgNPs in the aquatic environment. The chronic toxicity of AgNPs involves lipid peroxidation and oxidative stress caused by these NPs as free radicals [151]. The supply of food and the hurdles of purifying these NPs form the gut lines of the aquatic organisms [152]. In the chronic toxicity experiments, the waterborne AgNPs substantially reduce the proliferation of daphnids at a low concentration, i.e., 5 mg/L, suggesting that AgNPs provoke chronic toxicity in animals. Daphnid replication significantly decreased under the borne AgNP exposure when the algae were loaded with 0.1 mg/L AgNPs, far lower than the existing freshwater requirements [153]. AgNPs are affecting the organism’s life in the aquatic ecosystem, as some of them are described in Table 3.

Table 3. AgNPs toxicity and effects on different aquatic life.

Groups	Role of AgNPs in Toxicity/Malfunctioning of Cells/Organ/Organisms	Example	Reference
Protozoa	Ag ions destroy the sporozoites by entering the oocyst and ultimately break the oocyst wall	Cryptosporidium parvum	[154]
Protozoa	The effects of protein-coated AgNPs (14.6 nm, Collargol) have shown in the viability, oxidative stress, and gene expression levels of ciliates species	Tetrahymena thermophila	[155]
Monera	AgNPs are highly toxic to bacteria, often associated with ion release and induction of oxidative stress. AgNPs serve as an antibacterial against bacterial tension and thus avoids its horrendous impact	Bacteria	[156,157]
	Inhibition of bacterial growth increased permeability due to the formation of “pits”	Escherichia coli	[134]
	The interaction of the bacterial cell with AgNPs causes Proton Motive Force dissipation leading to the death of the cell	Staphylococcus aureus	[158]
	Generation of ROS	Autotrophic nitrifying bacteria	[147]
	AgNPs caused toxicity in the membrane when they attached with less than ten nm-sized NPs	Salmonella typhi, Pseudomonas aeruginosa and Vibrio cholera	[159]
Fungi	AgNPs show antifungal activity, which suppresses the growth of fungal cells	Aspergillus sp., Rhizoctonia solani, Sclerotinia sclerotiorum, S. minor	[160]
Plant	AgNPs changed/inhibited seed’s germination, the surface area of leaf, morphology, biomass, and growth potential	Spirodela polyrhiza	[161]
	Metabolic disorders arise, foliar proline accumulation is caused by a decrease in the contents of sugar. Total protein and chlorophyll, elongation of shoots and roots become reduced	Lupinus termis	[162]
	Repressed down-regulated induction of auxin receptor-related genetics, gravitropism of root, and reduction in root tips accumulation of auxins	Arabidopsis thaliana	[163]
	DNA damages when cytotoxicity enhances at lethal concentration; LC₅₀, i.e., up to 10 mg/L	Allium cepa	[164]
Animals	Apoptosis occurs when AgNPs directly contact the intestinal epithelium. In specific, typhlosole wherein the apoptosis impaired chloragogenous cells have a role like that of the liver invertebrate species or tissue in molluscs and arthropods	Oligochaetes, vertebrates, molluscs, arthropoda	[165]
	Acute toxicity/cause immobilization	Daphnia magna	[152]
Algae	AgNPs increase toxicity and disrupts the Photosynthetic system, cell metabolism, and cell membrane. The percentage of overall NPs absorbed by algae cells was 21% and 31%, respectively, for both species	Chlorella vulgaris, Raphidocelis subcapitata	[166]
Algae	AgNPs cause inhibitory effects on algae species	Chlorella vulgaris Dunaliella tertiolecta	[79]
	Chronic toxicity/Growth inhibition	Euglena gracilis	[167]
	Chronic toxicity/Growth inhibition	Chlamydomonas reinhardtii	[167]
Fishes	AgNPs induce changes in haematology parameters such as the mean corpuscular haemoglobin (MCH) and mean corpuscular volume (MCV) become decreased. In contrast, red blood cells (RBCs) and white blood cells (WBCs) become increased as the concentration (Conc.) of AgNPs increased	Rainbow trout (Oncorhynchus mykiss)	[154]
Fishes	AgNPs decreased the concentration of albumin (Al), globulin (Gl), and total proteins (Tp). In contrast, the concentration of alkaline phosphatase (ALP), Aspartic aminotransferase (AST), Glucose (Glu), Alanine aminotransferase (ALT), and total lipids (Tl) increases. At tissue and cell levels, pyknotic nuclei, proliferation of hepatocytes, cytoplasmic vacuolation, hepatic necrosis, central vein wall rupture, infiltrations of inflammatory cells, melanoma-macrophages aggregation, and apoptotic cells occurs in the liver of AgNPs-exposed fish	Clarias gariepinus	[168]
	Acute toxicity/Abnormality	Oryzias latipes	[167]
	Recent findings revealed that AgNPs had influenced the fish behaviour at the highest concentration (0.09 mg/L). The bioaccumulation AgNPs was found high in the liver, intestine, gills, and muscles. Moreover, the results revealed that at the highest concentration (0.09 mg/L), the bioaccumulation of AgNPs led to histopathological alterations, including gill damage leading to necrosis	Cyprinus carpio	[169]
	Acute toxicity/Abnormality in different functions	Danio rerio	[167]
Amphibians	The influence of AgNPs on stress and thyroid hormones is being studied with tadpole caudal fin cultures in vitro	Lithobates catesbeianus, Rana catesbeiana	[170,171]

Many microorganisms, including bacteria, fungi, algae, and protozoa, are used as bioremediation to reduce the toxicity of inorganic and heavy metals like cobalt (Co), lead (Pb), copper (Cu), chromium (Cr), nickel (Ni), and zinc (Zn), which contaminate the aquatic ecosystem. Bacterial species of Cellulosi microbium, Pseudomonas, Staphylococcus, and Enterobacter cloacae [172] and fungal species like Aspergillus niger, Aspergillus vesicolor, Phanerochaete chrysosporium, Sphaerotilus natans, Saccharomyces cerevisiae, and Gloeophyllum sepiarium are used to minimize the toxicity effect [173,174]. Similarly, many species of algae; Chlorella vulgaris [175], Spirogyra, Spirulina, Nostoc sp., [176] and protozoa; Tetrahymena rostrata are also reported to detoxify the heavy metal concentration in the aquatic ecosystem [177]. The toxicity of silver particles is a severe threat to all living organisms in the aquatic ecosystem. There is also a need for urgent attention to establishing the biological control and bioremediation of AgNPs to reduce the silver toxicity through microorganisms (bacteria, fungi, protozoa) and algae to save the ecosystem’s living aquatic life. However, from literature databases, we found a minimal number of studies published providing little detail on overcoming excessive bioaccumulation in an aquatic ecosystem. Chromobacterium violaceum is used for bioremediation purposes. They found that bacteria efficiently absorbed AgNPs released during cloth washing [178]. The morphological changes were observed in bacteria upon uptake of AgNPs. However, after subsequent culture, the original shape was restored to it.

This entry is adapted from the peer-reviewed paper 10.3390/w14142192

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