Demidchik, V. V.

Przhevalskaya, D. A.

Svistunenko, D. A.

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Silver nanoparticles do not catalyse haber-weiss cycle but they oxidise ascorbate both in vitro and in vivo

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Тезисы докладов Стендовой сессии / Poster Session Abstracts                                   June 25-26,2015 
 
 
44 
SILVER NANOPARTICLES DO NOT CATALYSE HABER-WEISS 
CYCLE BUT THEY OXIDISE ASCORBATE BOTH IN VITRO  
AND IN VIVO 
Demidchik V.V.1, Przhevalskaya D.A.1, Svistunenko D.A.2 
1Department of Plant Cell Biology and Bioengineering, Biological Faculty,  
Belarusian State University, Minsk, Belarus 
2School of Biological Sciences, University of Essex, Colchester, United Kingdom 
Silver nanoparticles (Ag NPs) have gained particular attention from in-
dustrialists due to their relatively low cost of production and tremendously en-
hanced physical/chemical characteristics. Since the 19th century, the unique 
antimicrobial and fungicidal properties have been encouraging very wide utili-
zation of Ag NPs in medical products, fabrics, antiseptics, food containers, 
cosmetics, paints, and even plush toys. As a result, Ag NPs have been the 
most widely used nanotechnology products in the world over the last century. 
Nowadays, nearly 25% of all nanotechnology consumer products include Ag 
NPs (according to Inventory of Nanotechnology Consumer Products). The 
dramatic increase in industrial use of Ag NPs has raised considerable concern 
about their potential release and effects on flora and ecosystems, as well as the 
possibility of it entering human food chain through plants. Silver does not 
have any established function in plants or animals and has been acknowledged 
as a trace element. Only few reports have dealt with investigation of the ef-
fects of Ag+ and engineered Ag NPs on living systems at the molecular and 
cellular level. Ag NPs were shown to promote long-term redox imbalance and 
oxidative stress in a number of organisms however the mechanism of this tox-
ic effect remains largely unclear. It was recently shown that, under very alka-
line pHs, Ag NPs react with H2O2, forming Ag+ and •O2-, and further with •O2- 
to give “negatively charged Ag NPs” and O2. Negatively charged Ag NPs can 
interact with ionic silver (Ag+) by reducing it to metallic Ag0, promoting for-
mation of new Ag NPs. Thus Ag NPs can potentially behave as a transition 
metal ions (such as copper or iron). This has raised a question about possible 
production of hydroxyl radicals through transition metal catalysed Haber-
Weiss cycle involving H2O2 and ascorbate, which are both are present in liv-
ing cells. Here, this hypothesis was tested using Electron Paramagnetic Reso-
nance (EPR) spectroscopy. Another possibility is that Ag NPs affect cell anti-
oxidants, such as L-ascorbic acid, thus decreasing the reducing power and 
causing accumulation of oxidizing and oxidized species. This question was al-
so addressed in the present study. To examine the capacity of inducing hy-
droxyl radical generation by Ag NPs, 5,5-dimethyl-pyrroline N-oxide 
(DMPO) was applied with Fenton-like mixture with Ag NPs or bulk used in-
Тезисы докладов Стендовой сессии / Poster Session Abstracts                                   June 25-26,2015 
 
 
45 
stead of the transition metal (30-15000 mg L-1 Ag NPs or bulk were tested). In 
contrast to the standard mixture (containing 1 mM CuCl2 instead Ag NPs), the 
NP-containing mixture was ineffective in the producing characteristic four-
peak spectrum of hydroxyl radical DMPO adducts. However, Ag NPs caused 
the appearance of an ascorbyl radical-specific signal which showed the classi-
cal two-peak shape spectrum. Ascorbyl radicals are the products of ascorbate 
oxidation, relatively long-living and having distinct characteristic spectrum. 
An addition of natural plant radical scavenger mannitol (1 mM) or key antiox-
idant glutathione (1 mM) resulted in the disappearance of the ascorbyl radical 
signal, suggesting that these substances are capable of protecting ascorbate 
from Ag-NP mediated oxidation. Interestingly, Ag NPs did not induce genera-
tion of mannitol or glutathione radicals. Thiourea, caused an effect, which was 
similar to that of glutathione while bulk or supernatant did not induce ascorbyl 
radical signal. Application of Ag NPs (3000 and 15000 mg L-1) to intact roots 
(sterile seedlings of Arabidopsis thaliana L. plants) resulted in characteristic 
ascorbyl radical peaks, which was sensitive to a number of free radical scav-
engers. High concentrations of H2O2, which are known to cause the oxidation 
of L-ascorbic acid, also induced the formation of the ascorbyl radicals (used as 
a positive control). Addition of bulk particles or supernatant did not result in 
the formation of ascorbyl radicals in intact roots. Overall, these results showed 
that Ag NPs can promote redox imbalance and oxidative stress through affect-
ing cell ascorbate pool but not via production of hydroxyl radicals. 
REACTION OF CHOOSEN COMPOUNDS FOUNDED IN EEP  
WITH FREE RADICALS 
Seget S., Drozdz M., Czuba Z.P., Krol W. 
School of Medicine with the Division of Dentistry in Zabrze, Medical University of Silesia 
in Katowice, Chair and Department of Microbiology and Immunology, Zabrze, Poland 
Antioxidant activity of ethanolic extract of Polish propolis (EEP) de-
pends on its chemical composition. Our previous study allowed to identify 
main phenolic compounds, flavonoids and their derivatives in our EEP. In this 
study we tested selected compounds (the highest concentration in sample of 
EEP): caffeic acid, p-coumaric acid, ferulic acid and chrisin using three below 
methods: 
1. DPPH radical scavenging activity. 
To 0.04 ml test sample was added 0.120 ml methanol. Then the sample 
was mixed with 0.04 ml DPPH in methanol about (A524nm = 0.900 ± 0.020). 


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Silver nanoparticles do not catalyse haber-weiss cycle but they oxidise ascorbate both in vitro and in vivo

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