How does colloidal silver kill viruses

To assess the role of AgNPs in viral entry, we performed the luciferase based pseudovirus entry assay. PVP-AgNP 10 potently inhibited pseudoviral entry characterized by significant reduction of luciferase activity similar to that of the neutralizing antibody used as control Fig. NC - Negative control. Crystal violet staining reveals partial protection with visible plaques red arrowheads and complete protection with absence of plaques black arrowheads.

NC - Negative control, nAb - Neutralizing antibody. For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article. Ag is long known for its antimicrobial effect and the antiviral property of AgNPs is being extensively researched with renewed interest in the recent past [ 1 ]. The exact mechanism by which AgNPs exert its killing effect on viruses is still obscure.

However, it has been consistently observed that AgNPs interact with the structural proteins on the surface of extracellular viruses to inhibit infection in the early phase, by either preventing viral attachment or entry, or by damaging the surface proteins to affect the structural integrity of virions [ 11 , 12 ]. AgNPs have been shown to preferentially bind to viral surface proteins rich in sulfhydryl groups and cleave the disulfide bonds to destabilize the protein, thereby affecting viral infectivity [ 11 , 13 ].

Studies on HIV have shown that AgNPs associate to the disulfide bonds that are in close proximity to the CD4 binding domain of the gp surface protein [ 11 ]. Hati and Bhattacharyya have demonstrated the importance disulfide bonds in binding of SARS-CoV-2 spike protein with the angiotensin converting enzyme-2 ACE2 receptor and the disruption of which lead to impaired viral binding to the receptor [ 14 ].

AgNPs have also been claimed to possess intracellular antiviral action by interacting with viral nucleic acids [ 15 ]. While the reason for this effect is not known at present, it is possibly explained to be either due to the destruction of disulfide bridges on ACE2 receptor or due to a true intracellular mechanism there by inhibiting serial viral infection of newly produced virus from infected cells to uninfected cells.

Also, since Ag binds non-specifically to proteins, their use as antiviral agents might also cause some cellular dysfunction. Further studies are required to more precisely explain the holistic effect of Ag in vivo.

Several studies have reiterated the size dependent antiviral effect of AgNPs with particles around 10 nm diameter being most effective [ 1 ]. This has been attributed the higher stability of interaction to the viral protein achieved by 10 nm particles which is not capable by larger particles [ 11 ]. AgNPs can be generated by several methods and can contain reducing agents and capping agents along with the metal particles [ 16 ]. Coated or capped AgNPs are found to be more advantageous than plain AgNPs as coating increases stability, decreases agglomeration and reduces cytotoxicity of AgNPs [ 17 ].

It has been observed that PVP coating of AgNPs does not hinder their antiviral activity while other coating agents do [ 18 ]. Antiviral effect of AgNPs is also concentration dependent. Most studies have observed the antiviral efficacy of AgNPs at concentrations ranging between 10 and ppm [ 1 ]. However, 0.

In the current study, we observed naked AgNPs to inhibit SARS-CoV-2 at concentrations ranging between 1 and 10 ppm and become cytotoxic to mammalian cells from 20 ppm and above.

Mehrbod et al. Naked AgNPs with NaBH4 reducing agent were found to induce apoptosis in colon adenocarcinoma cells at 11 ppm, while Citrate-stabilized naked AgNPs have been observed to exhibit cytotoxicity at concentrations higher than 30 ppm [ 21 , 22 ]. In this regard, PVP coated AgNPs have been demonstrated to be the least cytotoxic with no demonstrable cytotoxicity even at 50 ppm in human alveolar basal epithelial cells [ 19 ].

Smaller particles have a higher toxic potential due to the greater surface area of interaction with the bound protein [ 23 ].

We observed this effect as AgNP 2 showed cytotoxicity even at 2 ppm while none of the bigger particles were cytotoxic at this concentration. Therefore, care should be exercised when Ag is used on biological surfaces. Various ingestible and inhalable formulations of Ag are being marketed as cure for COVID, which available to purchase over the counter.

The cytotoxic potential of these formulations should be considered before personal use. Also, Ag is a very broad spectrum microbicide. Illicit use of Ag might create an imbalance in the commensal microbiota leading to unforeseen consequences [ 24 ].

Ag coated masks have been found to be effective in inhibiting SARS-CoV-2 and could potentially be effective when applied on the air filters of air conditioners and medical devices [ 25 ]. Herodotus described water carts taken to war by the kings of Ancient Persia in which water from the Choaspes River was "ready boiled for use and stored in flagons of silver.

The surface of metallic silver will always harbour some silver oxide, a result of reaction with oxygen of the air. Small amounts of silver oxide dissolve in water and the silver ions in solution can indeed disrupt the metabolism of bacterial cells. Some water filters today contain small amounts of silver oxide to prevent bacterial contamination within the filter and silver nitrate is sometimes used in eye drops administered to new born babies to prevent conjunctivitis, an infection that can be acquired by passage through the birth canal.

But these applications are a long way from curing AIDS or cancer. There is no evidence that taking colloidal silver orally has the claimed beneficial effects. There is evidence that it can cause harm.

Before antibiotics, silver nitrate nose drops were commonly used in the battle against infection. But not for long. Journal of the German Society of Dermatology.

Dressings and topical agents for treating venous leg ulcers. Cochrane Database of Systematic Reviews. Journal of wound care. The silver-releasing foam dressing, Contreet Foam,promotes faster healing of critically colonised venous leg ulcers: a randomised, controlled trial.

International wound journal. Sustained silver-releasing dressing in the treatment of diabeticfoot ulcers British Journal of Nursing. Journal des Plaies et Cicatrisations. Clinical and microbiologicaleffectiveness of a hydropolymer alveolar dressing with ionic silver complex and silicone adhesive. Plos One. A Literature Review. Ostomy WoundManagement.

Adderley UJ. Managing wound exudate and promoting healing. British Journal of Community Nursing. In vitro evaluation of a silver foam dressing with and without silicone adhesive againstbiofilms and a broad range of microorganisms. Silver in health care: antimicrobial effects and safety in use. Current Problems in Dermatology. The antimicrobial efficacy of silver on antibiotic-resistant bacteria isolated fromburn wounds.

Poster, EWMA; For example, remdesivir, favipiravir, lopinavir and hydroxychloroquine at micromolar concentrations have been reported to inhibit SARS-CoV-2 based on the in vitro assays. Remdesivir is even recently applied in compassionate use for patients with severe COVID infection 5.

In contrast to the small molecules, we consider using metal nanoparticles as the prophylactic of COVID infection. Metal nanoparticles may interact with virus surface glycoproteins and thus interfere with viral attachment and entry into host cells 6. Metal nanoparticles may also exert antiviral activity by interaction with viral genomes 7. Silver nanoparticle Ag-NP , zinc oxide nanoparticle ZnO-NP and gold nanoparticle Au-NP are well-known antimicrobial agents against many kinds of bacteria, fungi and viruses 7 , 8 , 9 , Silver nanoparticles are antiviral agents against various types of viruses including hepatitis B virus HBV , herpes simplex virus type 1 HSV-1 , human immunodeficiency virus type 1 HIV-1 and influenza virus, in addition to the antimicrobial activity against both Gram-positive and Gram-negative bacteria such as Bacillus subtilis , Escherichia coli, Pseudomonas aeruginosa , Vibrio cholera and methicillin-resistant Staphylococcus aureus MRSA.

On exposure to UV-radiation, ZnO-NP further acts as a photocatalyst for generation of reactive oxygen species to damage viruses and bacteria Au-NP, generally used as a carrier in photodynamic therapy and biomedical applications, also shows potential use in suppressing HIV-1 and Mycobacterium tuberculosis 13 , In this study, we aimed to determine the antiviral activity of a metal nanoparticle composite, TPNT1, against SARS-CoV-2 and another respiratory pathogen, influenza virus, which also exhibit the potential to trigger a global outbreak in humans.

The individual metal nanoparticles were synthesized according to our patented method The physicochemical properties of the synthesized nanoparticles were fully characterized by ultraviolet—visible spectroscopy, infrared spectroscopy, inductively coupled plasma atomic emission spectroscopy, transmission electron microscopy TEM , dynamic light scattering DLS analysis and potentiometric titration Fig.

As shown in Fig. The virus isolates used were summarized in Table 1. Among the eight clinical isolates, three NTU3, 14, and 16 contains the DG mutation, which is circulating predominantly worldwide since March, , and has been reported to exhibit increased viral infectivity The viral titers in the culture supernatants was determined by plaque assay.

A significant inhibition of infectious virus titers in the culture supernatants was observed for all clinical isolates, including the DG variants, in the presence of TPNT1 by plaque assay Fig. At least three independent experiments were performed and one representative result was shown. The schematic illustration for experimental design was shown in Fig.

The culture supernatants and cell lysates were harvested for subsequent analysis. TPNT1 functioned at a stage before virus infection since the virus titers in the supernatants reduced significantly when TPNT1 was preincubated with virus before infection Fig.

Since syncytium formation is a step critical for virus entry after receptor binding, we also examined the ability of TPNT1 to inhibit syncytium formation. Although there are currently four FDA-approved influenza antiviral drugs, peramivir, zanamivir, oseltamivir phosphate, and baloxavir marboxil, drug-resistant viruses have emerged and new therapeutics targeting drug-resistant viruses are needed 18 , 19 , 20 , In addition, the threat from avian influenza A virus to cause pandemics in human population cannot be ignored Similar inhibitory effects against wild-type and oseltamivir-resistant influenza viruses were observed, although a slightly reduced inhibition against oseltamivir-resistant H1N1 viruses was noticed.

The antiviral activities of TPNT1 against influenza viruses in vitro. The person-to-person contact through respiratory droplets generated by sneezing and coughing, or contaminated fomites from the infected individuals has been shown to be the major transmission route for SARS-CoV Besides efficient use of protective personal equipment, such as masks, as well as keeping social distance, implementation of a more active prevention strategy is required to contain the SARS-CoV-2 pandemic.

In addition, the anti-influenza activity of TPNT1 was also examined because influenza virus, known to infect millions of people annually and causing severe diseases, especially in the elderly 23 , shares the similar transmission routes, clinical presentations and seasonal coincidence with SARS-CoV Receptor binding represents a critical step for viral entry and subsequent virus replication in host cells.

Interactions between the SARS-CoV-2 spike protein and the ACE2 receptor 24 , 25 , and the hemagglutinin HA of avian and human influenza viruses with the 2,3-linked or 2,6-linked Neu5Ac receptor on host cells 26 have been shown to be essential for virus infection.

Metal nanoparticles with large surface area can conjugate modifiers to attain multivalent effect on targeting viruses. For example, the Au-NPs conjugated with multivalent sialic-acid-terminated glycerol dendrons can tightly bind influenza hemagglutinin, and thus interfere with the attachment of virus to host cell However, preparation of organic modifiers and encapsulation of nanoparticles usually require tremendous synthetic effort.

The SARS-CoV-2 and influenza virions, having average diameters of 80— nm, are in the size range of nanoparticles 28 , As TPNT1 is most effective by pre-incubation with viruses, one possible mechanism for the antiviral activity of TPNT1 may be attributable to bindings of virus surface glycoproteins with the metal nanoparticles, and thus preventing the virions from attachment to host cells 27 , 30 , 31 , 32 , Indeed, our experiments Fig.

It has been suggested that nanoparticles can diminish virus entry by direct interaction with the sulfur-bearing residues on the viral surface Based on the sequence analysis, SARS-CoV-2 spike has 40 cysteine residues while influenza hemagglutinin has 15 cysteine residues.

Another study shows that the combination of single-wall carbon nanotubes and NaOCl or H 2 O 2 also displays a synergistic sporicidal effect We assume that the ClO 2 component in TPNT1 may render oxidative damage of virus surface, and thus provide enhanced effect for viral inhibition by the metal nanoparticles.

Although metal nanoparticles have been demonstrated to have a wide range of biomedical applications 38 , the toxicity is an issue of concern. Most metal nanoparticles have beneficial and adverse dual effects. The degree of toxicity varies by the type, shape, size, purity, concentration, administration method and exposure time of metal nanoparticles. The current available data from many research teams are insufficient, and some are even contradictory, to determine the adverse effects of metal nanoparticles on human health 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , Gold compounds have been used in medicine for decades and most studies on animal models support that AuNPs do not cause appreciable toxicity The previous studies showed that 0.

Considering its prophylactic application, inorganic metal nanoparticles-based TPNT1 will have a relatively lower tendency to induce resistant viruses compared with therapeutic organic drugs. All the reagents were reagent grade and used as purchase without further purification. Tetrachloroauric acid HAuCl 4 , 0. Silver nitrate AgNO 3 , 0. New Jersey, USA. Ultra-pure water was purchased from Hao Feng Biotech Co. Taipei, Taiwan. All cell culture reagents were obtained from Invitrogen Inc.

The transformations in the surface plasmonic resonance of Au-NP and Ag-NP were measured on an Agilent Technologies Cary60 ultraviolet—visible UV—vis spectrophotometer operating at a resolution of 2 nm. The content of metal ions was determined by inductively coupled plasma optical emission spectrometry ICP-OES on an Agilent instrument.

All the analyses were carried out with triplicate measurements for a single sample. Tetrachloroauric acid 2. The reduction reaction produced a composition containing gold nanoparticles and HCl gas. At the same time, HCl gas was guided through the recovery port attached to the flat-bottomed flask and was trapped with 10 mL water in an Erlenmeyer flask for collection.

Silver nitrate 15 mL of 0. The reduction reaction produced a composition containing silver nanoparticles and NO 2 gas. At the same time, NO 2 gas produced from the reduction reaction was guided through the recovery port attached to the flat-bottomed flask and was trapped with 10 mL water in an Erlenmeyer flask for collection.

Finally, an aqueous solution mL of citric acid mg, Zinc chloride 8 mL of 2 M aqueous solution, 16 mmol and citric acid mg, The reduction reaction produced a composition containing zinc nanoparticles and HCl gas. At the same time, HCl gas produced from the reduction reaction was guided through the recovery port attached to the flat-bottomed flask and was trapped with 10 mL water in an Erlenmeyer flask for collection. The above-prepared Au-NP 0. The human lung adenocarcinoma cell line H was generously provided by Prof.

The virus isolates used in the current study were summarized in Table 1. Jann-Tay Wang , and the informed consent was obtained from all subjects.