Low Concentration Of AgNPs Research Articles

Silver nanoparticles alter learning and memory formation in an aquatic organism, Lymnaea stagnalis

We tested the effect of silver nanoparticles (AgNPs) on the ability of the pond snail, Lymnaea stagnalis, to learn and form long-term memory (LTM) following operant conditioning of aerial respiration. We hypothesized that the AgNPs would act as a stressor and prevent learning and LTM formation. We tested snails exposed for either 72 h or only during training and testing for memory (i.e. 0.5 h) and found no difference between those treatments. We found that at a low concentration of AgNPs (5 μg/L) neither learning and nor memory formation were altered. When we increased the concentration of AgNPs (10 μg/L) we found that memory formation was enhanced. Finally, at a higher concentration (50 μg/L) memory formation was blocked. To determine if the disassociation of Ag+ from the AgNPs caused the effects on memory we performed similar experiments with AgNO3 and found similar concentration-dependent results. Finally, we found that snails perceive the AgNPs differently from Ag+ as there was context specific memory. That is, snails trained in AgNPs did not show memory when tested in Ag+ and vice-versa. We believe that changes in memory formation may be a more sensitive determination of AgNPs on aquatic organisms than the determination of a LC50.

Evaluation of vascular tone and cardiac contractility in response to silver nanoparticles, using Langendorff rat heart preparation

Silver nanoparticles (AgNPs) have been widely used because of their antimicrobial properties. However, several reports suggest that AgNPs exposure promote cardiac effects that involve nitric oxide (NO) and oxidative stress (OS). Nevertheless, there are no studies related to AgNPs-induced effects in cardiac physiology. The aim of this study was to evaluate the AgNPs direct actions on coronary vascular tone and cardiac contractility using Langendorff rat heart preparation. Low concentrations of AgNPs (0.1 and 1 μg/mL) increased NO derived from inducible NO-synthase (iNOS), without modifying cardiac parameters. Meanwhile, high concentrations (10 and 100 μg/mL) promoted a sustained vasoconstriction and increased cardiac contractility related to OS, leading to rhabdomyolysis. Furthermore, AgNPs were internalized in the cardiac muscle, hindering classic actions induced by phenylephrine (Phe) and acetylcholine (ACh). These data suggest that AgNPs affect cardiac physiology in function of the concentration and in part of the NO generation, NOS expression and OS.

Anticancer effects of silver nanoparticles encapsulated by Taxus baccata extracts

Cancer is one of the main causes of human fatality and finding effective anticancer drugs is a high priority. Modified anticancer medicines have advantages compared to traditional drugs including; better delivery and lower doses. In the present study, the anticancer activity of silver nanoparticles (Ag NPs) synthesized using Taxus baccata extracts was studied on Caov-4 and HeLa cancer cell lines as well as normal human fibroblast cells. Microscopic studies showed significant morphological changes of cancer cells following the exposure to the Ag NPs while MTT assay revealed dose, time and cell line dependent cytotoxicity. The toxic effect of Ag NPs on Caov-4 cells was considerably higher than HeLa cells as >98% mortality obtained after 72h incubation of Caov-4 cells with 5 and 20μg/mL Ag NPs encapsulated by aqueous and ethanolic extract, respectively. Interestingly, aqueous extract encapsulated Ag NPs had no significant toxicity on normal fibroblast cells suggesting potent and selective anticancer activity on cancer cell lines. Flow cytometric analysis revealed a combination of apoptosis and necrosis following the exposure of Ag NPs to cancer cells. Apoptosis was determined as main mechanism of cell death in low concentration of Ag NPs while considerable necrosis (up to 41%) was observed by increasing the Ag NPs dose (up to 10μg/mL) and incubation time (up to 72h). The significant DNA damage and change in expression level of caspase 8, caspase 9, bcl-2 and c-Abl genes indicated the induction of mitochondrial death pathway following cell exposure to Ag NPs. It can be concluded that the preparation method and stabilizing agents may have major effects on the biological activity of nanoparticles as well as their physicochemical properties.

Toxicological interactions of silver nanoparticles and organochlorine pesticides in mouse peritoneal macrophages

Nanotechnology occupies a prominent space in economy and science due to the beneficial properties of nanomaterials. However, nanoparticles may pose risks to living organisms due to their adsorption and pro-oxidative properties. The aim of the current study was to investigate the effects of polymer-coated silver nanoparticles (AgNPs) and organochlorine pesticides (OCPs), as well as their combined effects on mouse peritoneal macrophages. Macrophages were isolated and exposed to three concentrations of AgNPs (groups: N1 = 30, N2 = 300 and N3 = 3000 ng.ml−1), two concentrations of OCPs (groups: P1 = 30 and P2 = 300 ng.ml−1) and the six possible combinations of these two contaminants for 24 h. AgNPs had irregular shape, Feret diameter of 8.7 ± 7.5 nm and zeta potential of −28.7 ± 3.9 mV in water and −10.7 ± 1.04 mV in culture medium. OCP mixtures and the lower concentrations of AgNPs had no detectable effects on cell parameters, but the highest AgNPs concentration showed high toxicity (trypan blue and MTT assays) resulting in morphological changes, increase of nitric oxide levels and phagocytic index. Foremost, the association of N3 and P2 led to distinct effects from those observed under single exposure.

Prolonged Effects of Silver Nanoparticles on p53/p21 Pathway-Mediated Proliferation, DNA Damage Response, and Methylation Parameters in HT22 Hippocampal Neuronal Cells

It is widely accepted that silver nanoparticles (AgNPs) are toxic to biological systems. However, little is known about their actions at molecular level and the cytophysiological effects after AgNP removal. As nanoparticles are suggested a promising tool to transport drugs to the brain for use in neurological conditions, we used HT22 mouse hippocampal neuronal cells as a model to study AgNP-mediated effects after their removal from the cell culture medium. We selected a relatively low concentration of AgNPs, 5 μg/ml, treated the cells for 48 h, and evaluated AgNP-induced cytophysiological effects after 96 h of AgNP removal. AgNP removal did not result in cytotoxicity. In contrast, AgNPs modulated HT22 cell cycle and proliferation and induced oxidative stress and 53BP1 recruitment, which were accompanied by elevated levels of p53 and p21. AgNP-associated diminution in lamin B1 pools did not significantly affect the structure of the nucleus. No disruption in F-actin dynamics was observed upon AgNP treatment. Moreover, we showed for the first time that AgNPs stimulated changes in DNA methylation: the augmentation in 5-methylcytosine (5-mC) and DNMT1, DNMT2, DNMT3a, and DNMT3b levels were observed. The upregulation of DNMT2 may be a part of cellular stress response to AgNP treatment. Taken together, AgNP removal resulted in p53/p21-mediated inhibition of cell proliferation, oxidant-based DNA damage response, and changes in DNA methylation patterns, which suggests that more attention should be paid to the possible outcomes in individuals exposed to nano-sized biomaterials.

Fluorescence quenching N,N-bis(2,6-dimethylphenyl)-3,4:9,10-perylenetetracarboxylic diimide (BDPD) laser dye by colloidal silver nanoparticles.

The fluorescence quenching N,N-bis(2,6-dimethylphenyl)-3,4:9,10-perylenetetra-carboxylic diimide (BDPD) by colloidal silver nanoparticles (AgNPs) was studied in methanol and ethylene glycol by steady state fluorescence measurements. The Stern-Volmer quenching rate constant (Ksv) was calculated as 8.1 × 10(8) and 8.22 × 10(8) M(-1) in methanol and ethylene glycol respectively. Taking the fluorescence lifetime of BDPD in the absence of silver nanoparticles as 3.2 ns, the values of the fluorescence quenching rate constants (kq = Ksv/τ) are calculated as 2.54 × 10(17) and 2.56 × 10(17) M(-1) s(-1) in methanol and ethylene glycol respectively. From the data, fluorescence resonance energy transfer and / or electron transfer processes play a major role in the fluorescence quenching of BDPD by AgNPs in methanol and low concentrations of Ag NPs in ethylene glycol. The static quenching rate constant in ethylene glycol was calculated by modified Stern-Volmer equation as V = 8.86 × 10(9) M(-1). For dynamic quenching, the radius of quenching sphere volume r values were found to be 68.3 and 70.6 nm in ethanol and ethylene glycol, respectively. For static quenching in ethylene glycol the effective radius of quenching sphere action (kinetic radius) was calculated as r = 152 nm.

Chronic sublethal exposure to silver nanoparticles disrupts thyroid hormone signaling during Xenopus laevis metamorphosis

Nanoparticles (NPs) are engineered in the nanoscale (<100nm) to have unique physico-chemical properties from their bulk counterparts. Nanosilver particles (AgNPs) are the most prevalent NPs in consumer products due to their strong antimicrobial action. While AgNP toxicity at high concentrations has been thoroughly investigated, the sublethal effects at or below regulatory guidelines are relatively unknown. Amphibian metamorphosis is mediated by thyroid hormone (TH), and initial studies with bullfrogs (Rana catesbeiana) indicate that low concentrations of AgNPs disrupt TH-dependent responses in premetamorphic tadpole tailfin tissue. The present study examined the effects of low, non-lethal, environmentally-relevant AgNP concentrations (0.018, 0.18 or 1.8μg/L Ag; ∼10nm particle size) on naturally metamorphosing Xenopus laevis tadpoles in two-28 day chronic exposures beginning with either pre- or prometamorphic developmental stages. Asymmetric flow field flow fractionation with online inductively coupled plasma mass spectrometry and nanoparticle tracking analysis indicated a mixture of single AgNPs with homo-agglomerates in the exposure water with a significant portion (∼30–40%) found as dissolved Ag. Tadpoles bioaccumulated AgNPs and displayed transient alterations in snout/vent and hindlimb length with AgNP exposure. Using MAGEX microarray and quantitative real time polymerase chain reaction transcript analyses, AgNP-induced disruption of five TH-responsive targets was observed. The increased mRNA abundance of two peroxidase genes by AgNP exposure suggests the presence of reactive oxygen species even at low, environmentally-relevant concentrations. Furthermore, differential responsiveness to AgNPs was observed at each developmental stage. Therefore, low concentrations of AgNPs had developmental stage-specific endocrine disrupting effects during TH-dependent metamorphosis.

Laser-induced chemical transformation of PATP adsorbed on Ag nanoparticles by surface-enhanced Raman spectroscopy—A study of the effects from surface morphology of substrate and surface coverage of PATP

The laser induced transformation of p-aminothiophenol (PATP) to p,p′-dimercaptoazobenzene (DMAB) has attracted intensive interest recently, in which localized surface plasmon resonance (LSPR) assisted photocatalysis has been demonstrated to play an important role. In this paper, we systematically investigate the factors that influence the reaction for further understanding the mechanism using surface-enhanced Raman spectroscopy. The laser-induced formation of DMAB was found to depend on the surface coverage of PATP, the aggregation state of NPs, and the laser power. The disappearance of DMAB Raman signal at very low concentration of Ag NPs reveals that DMAB may only be formed between the neighboring NPs that can provide a suitable distance for the interaction between adsorbed PATP molecules.

Green Synthesis and Characterization of Silver Nanoparticles for Antimicrobial Activity Against Burn Wounds Contaminating Bacteria

Silver nanoparticles ( AgNPs ) were prepared from the plant extract of N. arbor-tristis under atmospheric conditions through green synthesis and characterized by various physicochemical techniques like UV-Visible spectroscopy, IR Spectra, energy dispersive X-ray spectrometry (EDS), X-ray diffraction and transmission electron microscopy (TEM) and the results confirmed the synthesis of homogeneous and stable AgNPs by the plant extracts. The antimicrobial activity of AgNPs was investigated against most common bacteria found in burn wound Staphylococcus epidermidis and Pseudomonas aeruginosa. In these tests, Mueller Hinton agar plates were used with AgNPs of various concentrations, supplemented in liquid systems. P. aeruginosa was inhibited at the low concentration of AgNPs , whereas the growth-inhibitory effect on S. epidermidis was mild. These results suggest that AgNPs can be used as effective growth inhibitors of various microorganisms, making them applicable to diverse medical devices and antimicrobial control systems.

Toxic effects of silver nanoparticles and nanowires on erythrocyte rheology

Rapid developments in the food applications of silver nanomaterials (Ag-NMs) have resulted in concerns related to the risk of overexposure of human blood. We investigated the effect of size and aspect ratio of Ag-NMs on rheological characteristics of human erythrocytes, including hemolysis, deformability, aggregation, and morphological changes. Red blood cells (RBCs) were exposed to two different sizes of spherical particles (d∼30nm or 100nm) or nanowires (d∼40nm, l–2μm in length) at a range of concentrations and incubation times. The concentrations of Ag-NMs were carefully chosen to avoid any hemorheological alteration due to hemolysis. Rheological properties were measured using microfluidic-laser diffractometry and aggregometry. RBC deformability apparently decreased after treatment with a low concentration of Ag-NPs for a short exposure time. However, RBC aggregation was significantly altered after treatment with a low concentration of either Ag-NWs or large Ag-NPs compared to small Ag-NPs. Additional experiments with Ag ions confirmed that the observed rheological changes were mainly caused by the Ag-NMs rather than the Ag ions. These hemorheological findings provide a better understanding of the interaction between RBCs and Ag-NMs and will help in assessing the risk of nanomaterial toxicity in blood.

Preparation of silver core-chitosan shell nanoparticles using catechol-functionalized chitosan and antibacterial studies

In this paper, we report the preparation and stabilization of colloidal silver nanoparticle solution, with the assistance of chitosan dihydroxyphenyl acetamide (CDHPA), or oligochitosan dihydroxyphenyl acetamide (OCDHPA). The structure of the chitosan derivatives were characterized by nuclear magnetic resonance (1H NMR) spectroscopy. The morphology of the synthesized silver core-chitosan shell nanoparticles were observed by transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques, and showed a well-defined core-shell structure of polymer-coated silver nanoparticles (AgNPs). The core-shell NPs exhibited a strong antibacterial activity against E. coli and S. aureus, at a very low concentration of AgNPs (2.5 ppm). Our studies offer a new method for the preparation and protection of silver nanoparticles for antibacterial applications. Open image in new window

Induction of Apoptosis in Cancer Cells at Low Silver Nanoparticle Concentrations using Chitosan Nanocarrier

We report the development of a chitosan nanocarrier (NC)-based delivery of silver nanoparticles (Ag NPs) to mammalian cells for induction of apoptosis at very low concentrations of the NPs. The cytotoxic efficacy of the Ag NP-nanocarrier (Ag-CS NC) system in human colon cancer cells (HT 29) was examined by morphological analyses and biochemical assays. Cell viability assay demonstrated that the concentration of Ag NPs required to reduce the viability of HT 29 cells by 50% was 0.33 μg mL(-1), much less than in previously reported data. The efficient induction of apoptosis by Ag-CS NCs was confirmed by flow cytometry. Additionally, the characteristic nuclear and morphological changes during apoptotic cell death were investigated by fluorescence and scanning electron microscopy (SEM), respectively. The involvement of mitochondrial pathway of cell death in the Ag-CS NCs induced apoptosis was evident from the depolarization of mitochondrial membrane potential (ΔΨ(m)). Real time quantitative RT-PCR analysis demonstrated the up-regulation of caspase 3 expression which was further reflected in the formation of oligo-nucleosomal DNA "ladders" in Ag-CS NCs treated cells, indicating the important role of caspases in the present apoptotic process. The increased production of intracellular ROS due to Ag-CS NCs treatment indicated that the oxidative stress could augment the induction of apoptosis in HT 29 cells in addition to classical caspase signaling pathway. The use of significantly low concentration of Ag NPs impregnated in chitosan nanocarrier is a much superior approach in comparison to the use of free Ag NPs in cancer therapy.

Biokinetic Uptake and Efflux of Silver Nanoparticles in Daphnia magna

Silver nanoparticles (AgNP) are widely used as antibacterial products, and there are increasing concerns for their potential environmental risks in aquatic ecosystems. The biokinetics of AgNP in aquatic organisms has not yet been determined. In the present study, we employed a radiotracer methodology to quantify the biokinetics of AgNP in a freshwater cladoceran Daphnia magna, including the uptake from water, dietary assimilation, and elimination of AgNP. We found that the uptake of AgNP was concentration dependent and governed by two phases. The uptake rate constant (k(u)) was 0.060 L/g/h at low AgNP concentrations (2, 10, and 40 μg/L), which was 4.3 times lower than that of the Ag free ion. At a higher AgNP concentration (160 and 500 μg/L), the uptake rate increased disproportionately, likely as a result of direct ingestion of these nanoparticles by the daphnids. When the AgNP were associated with the algal food, their dietary assimilation efficiency (AE) was in the range of 22-45%, which was much higher than the dietary assimilation of Ag quantified under the same food conditions. The efflux rate constants of AgNP in daphnids were also much lower than those of the Ag, again suggesting the difficulty of eliminating AgNP by the daphnids. Water excretion was the main elimination route for both AgNP and Ag, but a higher percentage of AgNP was lost through fecal production. Finally, we used a kinetic equation to compare the importance of aqueous and dietary uptake of AgNP using the quantified kinetic parameters. The biokinetic model showed that more than 70% of AgNP accumulated in the daphnids was through ingestion of algae, highlighting the importance of AgNP transport along the food chain. Our present study showed the unique characteristic of AgNP biokinetics and suggested that more attention should be paid to the dietborne AgNP toxicity in aquatic ecosystems.