Introduction

Withania somnifera (L) Dunal, commonly known as Ashwagandha, is a perennial medicinal herb belonging to the order Solanaceae and, from ancient times, widely used in Ayurvedic medicine as a tonic to rejuvenate the body and prevent diseases (Kumar et al. 2011; Sharma et al. 2011). The biologically active chemical constituents of W. somnifera are alkaloids (isopellertierine, anferine), steroidal lactones (withanolides, withaferins), saponins (sitoindoside VII and VIII), withanolides (sitonidoside XI and X), and iron (Budhiraja et al. 1987; Niyaz and Siddiqui 2014). W. somnifera has extensive pharmacological activities in the field of traditional medicinal system and used as anti-tumor (Oberpichler et al. 1990), anti-inflammatory (Nittala and Lavie 1988), immunity stimulator (Kandil et al. 1994), anti-depressant (Abou-Douh 2002), anti-aging (Wagner et al. 1994), and anti-oxidant activities (Singh et al. 2003; Bhattacharya et al. 2001; Dhalla et al. 1961). In other reports, W. somnifera has also shown anti-osteoarthritic (Kulkarni et al. 1991) and anti-stroke activities (Chaudhary et al. 2003). Its two compounds, sitoindosides VII–X and withaferin A (glycowithanolides), have been studied for anti-oxidant activities which act with the help of free radical scavenging enzymes, superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX) (Panda and Kar 1997). Therefore, in the present study, W. somnifera was used to evaluate the change in the toxicity created by silver nanoparticles into the liver and kidney tissues.

There are several reports stating that silver nanoparticles (Ag NPs) have wide application for human uses. Hence, the toxicity studies of Ag NPs become a topic of important research. Researchers are focused on procedures used for the production of size and shaped-controlled of Ag NPs due to their distinct properties and potential use in various fields such as anti-microbial, optical, electromagnetic, catalytic properties, and other biological characteristics in comparisons of bulk silver (Wagner et al. 1994; Alarco et al. 2012; Choi et al. 2009). The anti-microbial properties of Ag NPs are being evaluated for their use in daily household products like washing machines; water purification; toothpaste; shampoos; and disinfecting bedding, nipples, nursing bottles, fabrics, deodorants, filters, kitchen utensils, toys, and humidifiers etc. (Anwar et al. 2013; Cheng et al. 2004; Lankveld et al. 2010; Ahamed et al. 2010). Ag NPs also have been found application in surgical instruments as well for in wound dressings and contraceptive devices (Muangman et al. 2006; Cohen et al. 2007; Lansdown 2006; Zhang and Sun 2007; Lu et al. 2010). The differences in shape and size of Ag NPs are being controlled with the help of reducing agent, stabilizer, and various methods (He et al. 2004; Wang et al. 2005).

Ag NPs have toxicity due to their size, structure, shape, and chemical–physical environment (Carlson et al. 2008; Park et al. 2011; Huiliang et al. 2011; Nel et al. 2012). As utilization of Ag NPs is continuously expanding, the risks regarding the health implications due to lack of information on the basic toxicity of size and shape dependence of Ag NPs are enormous (Yong et al. 2010). Therefore, the objective of this study was designed to investigate the acute toxicity effects associated with various sizes and shape of Ag NPs and its toxicity modulation by W. somnifera. Considering the applications of W. somnifera, it was used as herbal remedy to reduce the toxic effect of various Ag NPs in vivo model on Wistar rats. Before conducting in vivo study, we evaluate the adverse effect of Ag NPs against murin macrophages using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay.

Materials and methods

Materials

Aerosol OT (AOT; sodium, bis(2-ethylhexyl) sulfosuccinate), hexane, silver nitrate (AgNO3), tri-sodium citrate, sodium borohydride (NaBH4), ascorbic acid, and aqueous solution of hydrazine were purchased from Sigma-Aldrich, USA. Roswell Park Memorial Institute (RPMI) 1640 and MTT were purchased from Merck, India. Glutamate oxaloacetate transaminase (GOT), glutamate pyruvate transaminase (GPT), alkaline phosphatase (ALP), creatinine, and blood urea nitrogen (BUN) assay kits were purchased from Span Diagnostic Pvt. Ltd., Surat, India. W. somnifera was procured from Green Earth Products Pvt Ltd, India.

Methodology

Synthesis of spherical-shaped silver nanoparticles by microemulsion method

Reverse micelles of AOT were prepared by dissolving 0.444 g AOT in 10 ml hexane and adding precise volumes of water containing metal precursor or hydrazine. The amount of solubilized water is usually expressed as a molar ratio of water to AOT, i.e., W 0 = [H2O] / [AOT]. For preparation of Ag NPs, 75 μl of 0.1, 1.5, and 0.2-M aqueous solution of silver nitrate was added to 5 ml 0.1-M AOT solution. The resulting solution was stirred for 6 h on magnetic stirrer to form microemulsion (A). In another set of reaction, 75 μl (0.3 M), 75 μl (0.45 M), and 75 μl (0.6 M) of hydrazine hydrate solution were added drop wise to 5-ml AOT (0.1 M) solution. Similarly, this solution was also stirred for 6 h on magnetic stirrer to form microemulsion, named B. The molar ratio of hydrazine hydrate and silver nitrate was held constant for all experiment at a value of 3. In order to reduce the silver ions, microemulsion (B) containing hydrazine hydrate was added slowly into microemulsion (A) containing silver nitrate drop by drop and was subjected to continuous stirring for 6 h. Subsequently, the color of the microemulsion changed from colorless to a yellowish brown color, indicating the formation of spherical-shaped Ag NPs.

Synthesis of rod-shaped silver nanoparticles by aqueous-phase method

Aqueous solution of 2 × 10−4 M silver nitrate and anhydrous solution of 1 × 10−3 M sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in hexane were prepared. In 100 ml of round bottom flask, 50 ml of silver nitrate solution and 35 μl of anhydrous AOT solution were mixed by stirring for 1 h. Six hundred-microliter aqueous solution of 1 × 10−2 M tri-sodium citrate was added to the above solution and was refluxed at 100 °C with constant stirring for 70 min. After refluxing, reaction mixture becomes turbid and turns yellow-green. The final reaction mixture contained both spherical as well as rod-shaped Ag NPs. The silver nanorods were separated from the spherical particles by centrifuging the sample at 2,000 rpm for 30 min at 25 °C. The silver nanorod settled at the bottom of their container after centrifugation. The AOT and spherical-shaped Ag NPs were removed using a pipette. This separation procedure was repeated several times until the supernatant becomes colorless.

Characterization of Ag nanoparticles

UV–vis spectroscopy

UV–vis absorption spectra (UV-1601 Shimadzu, Japan) were use to find characteristic plasma band of the Ag nanoparticles.

Dynamic light scattering

Dynamic light scattering was used to determine the size distribution profile of small particles in suspension solution (Malvern Zetasizer ver. 6.01) at 25 °C with light scattering at 90° in the aqueous and nonaqueous medium.

High-resolution transmission electron microscopy

Field-emission transmission electron microscope (FE-TEM) [JEOL, JEM-2100, and 200 kV] was used for analysis. Samples were prepared by placing small drops of aqueous dispersions lyophilized Ag NPs on carbon-coated copper grids and allowing the solvent to slowly evaporate at room temperature.

3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay

Macrophages were collected by peritoneal lavage from sodium thioglycolate-stimulated mice. The peritoneal cells were collected in RPMI 1640 medium (incomplete), centrifuged at 1,400×g for 10 min at 4 °C, washed twice, and finally resuspended in complete medium. Macrophages at a density of 1 × 106 cells ml─1 were seeded in 96-well tissue culture plates (0.1 ml per well) and exposed to various sizes of Ag NPs (20, 50, and 100 nm spherical shape and 100 nm rod shape) at a concentration of 5, 15, 25, and 35 μg/ml for 12 h in a CO2 incubator (5 % CO2, 37 °C) to calculate the median lethal dose (LD50). Cell viability was evaluated using a modified MTT assay, where the conversion of MTT to formazan by mitochondrial enzymes served as an indicator of cell viability and amount of dye produced is directly proportional to the number of metabolically active cells (24) Accordingly, absorbance at 492 nm represented the number of live cells. LD50 value was calculated from the dose–response curve and used as a measure for drug resistance, and the mean percentage viability was calculated as follows:

$$ \frac{\mathrm{Mean}\;\mathrm{specific}\;\mathrm{absorbance}\;\mathrm{of}\;\mathrm{treated}\;\mathrm{macrophages}}{\mathrm{Mean}\;\mathrm{specific}\;\mathrm{absorbance}\;\mathrm{of}\;\mathrm{untreated}\;\mathrm{macrophages}}\times 100 $$

Cellular uptake of Ag NPs

Cellular uptakes of Ag NPs (20, 50, and 100 nm spherical shape and 100 nm rod shape) after 4-h incubation in microphages obtained from peritoneal lavage were visualized in TCS-SPE confocal laser scanning microscopy, equipped with an DMI4000 microscope (Leica Microsystems CMS GmbH, Germany) with a ×40 objective and 532-nm wavelength of laser radiation class 3B at scanning speed 800 Hz. LAS-AF software (Leica Microsystems) was used for data acquisition and processing.

In vivo study

Animals

Forty-five healthy Wistar albino rats of 7 to 8 weeks age, each weighing 250–350 g, were obtained and maintained in the Animal House of the Jamia Hamdard, New Delhi. They were kept under 12-h light–dark cycle at a temperature 24 ± 1 °C and relative humidity 55 ± 10 % and were acclimatized for 1 week prior to the experiment with animal feed (Hindustan Pvt. Ltd., India) and water supplied ad libitum. All animal experiments were performed according to the procedures established by the Ethical Committee of Jamia Hamdard, New Delhi, India (CPCSEA/173).

Preparation of the W. somnifera root extract

Approximately, 1 g of dried powder of W. somnifera root is poured into a 500-ml Erlenmeyer flask with 100 ml triple-distilled water, and the solution was kept overnight; then, the mixture was boiled up to one fourth of its volume. The solution is cooled at room temperature and finally filtered with Whatman filter paper to obtain a light-brown-colored aqueous extract of the W. somnifera root.

The obtained extract was further concentrated under vacuum to dry form. The residue obtained was then redissolved in water to the desired final concentration of 50 mg/kg body weight of W. somnifera.

Acute toxicity and treatment with W. somnifera

The acute toxicity of Ag nanoparticles on rats was examined following the protocol of Yong et al. 2010. Forty-five healthy rats were divided randomly into nine groups designated as groups 1–9, with each group comprising five rats. Rats in group 1 were given saline orally for 23 days daily and used as a control. Groups 2, 3, and 4 were administered 20, 50, and 100-nm spherical-shaped Ag NPs, respectively, whereas group 5 was given 100-nm rod-shaped Ag NPs. Fixed concentration of 35 mg/kg doses was given orally to groups 2–5 to evaluate acute toxicity in rats. Groups 6–9 were administered 35 mg/kg doses of Ag NPs (20, 50, and 100 nm spherical shape, and 100 nm rod shape, respectively) with W. somnifera (35 mg/kg BW) for 23 days to examine modulated toxicity.

Biochemical analysis

Blood samples were collected from cardiac puncture of rats into clean dry bottles containing ethylenediaminetetracetic acid (EDTA). Plasma was separated by centrifugation at 3,000 rpm for 5 min and stored at −20 °C until analysis for biochemical parameters. GOT, GPT (Reitman and Frankel 1957), and ALP (King and King 1954) activities were determined in plasma at 570, 340, and 405 nm, respectively, by UV–vis spectrophotometer according to the method described by Kind and King’s. Creatinine and urea concentrations were determined at 490 and 340 nm following the Husdan and Rapoport method (Husdan and Rapoport 1968), and urease and Berthlot method (Allain et al. 1978), respectively.

Histopathological examination

Ag NP-treated groups were compared with control group to observe liver and kidney tissue histopathology. On the last day of experiment, rats were anesthetized with ether and were perfuse transcardinally with saline. Samples of the liver and kidney were removed, postfixed in 10 % neutral buffered formalin for 24 h and processed for histopathological examinations (Wang et al. 2005). After fixation, 3–4-mm slices of tissues were dehydrated and embedded in paraffin. Cross sections of 5-μm thickness were cut washed with xylene, and tissues were mounted with DPX. Hematoxylin and eosin (H and E) stains were used to visualize and differentiate between normal tissue and Ag NP-treated tissues, and microphotographs were taken using an Olympus BX50 microscope (Olympus, Japan).

Statistical analysis

Cytotoxicity data was fitted in a parameter nonlinear logistic model from add-on options in Microsoft Excel, to calculate the lethal dose of Ag NPs that caused a 50 % inhibition in comparison with untreated controls. All LD50 values were calculated using the average cytotoxicity data of the three independent experimental results along with their associated errors, and the values are reported in ±95 % confidence intervals (±95 % CI) for the triplicate set of each experimental condition. Data are represented as mean ± standard deviation (SD), and statistical analysis were carried out to know the variance of results using ANOVA analysis followed by Dunnett’s test.

Results

Characterization of Ag nanoparticles

Dynamic light scattering analysis

Dynamic light scattering is a technique in physics which can be used to determine the size distribution profile of small particles in suspension. The hydrodynamic diameters (d) of Ag NPs were calculated by using the Stokes–Einstein equation d = k B T / 3πηD, where k B is the Boltzmann constant, T is the absolute temperature, η is the solvent viscosity, and D is the diffusion coefficient. CONTIN algorithms were used in the Laplace inversion of the autocorrelation function to obtain the size distribution (Wilhelm et al. 1991). The number average mean hydrodynamic sizes of Ag NPs at W 0 corresponding to 10, 12.5, and 15 were 20.21, 50.21, and 100 nm (Supporting Information Fig. S1a–c), respectively, with a narrow polydispersity index (0.22–0.29).

UV–vis spectrophotometer analysis

The UV–vis spectra of the synthesized spherical-shaped and rod-shaped Ag NPs are given in Supporting Information Fig. S2. The spectra illustrate that with increasing water contents in microemulsion, core size microemulsion increased and formed bigger nanoparticles than that with lower water contents, and accordingly, a red shift in plasma band of Ag NPs was observed. The absorption spectra were recorded at 407, 423, and 429 nm for Ag NPs synthesized at water content W 0 10, 12.5, and 15, respectively. The silver nanorods showed two plasma bands in absorption spectrum at 584 nm due to transverse plasmon band and the other at 435 nm due to longitudinal plasmon band. This confirmed that we were able to synthesize rod-shaped Ag nanomaterials from second synthetic route.

High-resolution transmission electron microscope analysis

The average sizes of Ag NPs synthesized by microemulsion synthesis route were calculated from HR-TEM image as 20, 50, and 100 nm at 10, 12.5, and 15 W 0 (Fig. 1a–c), all having spherical shape. The second route generated rod-shaped nanoparticles as seen from TEM image (Fig. 1d) which were in correlation with data from both dynamic light scattering (DLS) and UV–vis spectra.

Fig. 1
figure 1

HR-TEM micrograph of a 20 nm at 75 μl silver salt, b 50 nm at 100 μl silver salt, and c 100 nm at 150 μl silver salt with spherical shape synthesized through AOT microemulsion and d HR-TEM micrograph of 100-nm rod-shaped silver nanoparticles

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Toxicity analysis

MTT assay

A dose-dependent response was observed in MTT assay for calculating LD50 values, and cytotoxicity data for Ag NPs and macrophages is presented in Fig. 2a–d. LD50 values for 20-nm Ag NPs were the most sensitive among all nanoparticles (Fig. 2a) in macrophages. One hundred-nanometer rod-shaped Ag NPs (Fig. 2d) were found to be least sensitive in macrophages, while 100-nm spherical-shaped Ag NPs were found to be more toxic. Cell viability was found to decrease with the decreasing size of Ag NPs and exposure time in macrophages. However, viability was always above than 80 % for treated groups with W. somnifera (23 days) and various sizes and shapes of Ag NPs (Fig. 2).

Fig. 2
figure 2

Plots of cell viability MTT assay studied for Ag NPs after 12-h incubation period at different doses (5, 15, 25, and 35 μg/ml). a 20-nm spherical-shaped Ag NPs treated showing more toxic. b 50-nm spherical-shaped Ag NPs treated. c 100-nm spherical-shaped Ag NPs treated. d 100-nm rod-shaped Ag NPs treated

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LD50 values of 20-nm Ag NPs are much lower than those of 100-nm spherical Ag NPs at all exposure time points which has slightly higher values as compared to 100-nm rod-shaped Ag NPs after 12 h of exposure time. The LD50 values were 0.25 mg/ml (confidence interval ±2.97), 0.35 mg/ml (confidence interval ±1.09), 0.35 mg/ml (confidence interval ±1.09), and 0.35 mg/ml (confidence interval ±1.09) for 20, 50, and 100-nm spherical-shaped Ag NPs and 100-nm rod-shaped Ag NPs, respectively. This shows that the small-sized Ag NPs have much cytotoxicity in comparison with 100-nm Ag NPs, and 100-nm rod-shaped Ag NPs have least toxicity in comparison with spherical-shaped Ag NPs.

Cellular uptake of Ag NPs

Confocal laser scanning microphotographs of cell containing Ag NPs were taken, and the diameter of diffraction-limited spot corresponds to d B = 1.22*ë / NA, with ë representing the excitation wavelength and NA numerical aperture of the objective used with illuminations of specimens that are focused on the smallest possible spot. After 4-h exposure, 20, 50, and 100-nm spherical-shaped and 100-nm rod-shaped Ag NPs were visualized together with control without nanoparticles (Fig. 3a–e). These analyses showed that high cellular uptake in macrophages was obtained from murin peritoneal lavage after 4-h incubation at 37 °C. With decreasing size of Ag NPs, there had been rapid penetration in the cells that were dying out of the population (Liu et al. 2013).

Fig. 3
figure 3

Cellular uptake of Ag NPs in macrophages obtained from murin peritoneal lavage after 4-h incubation at 37 °C. Cellular uptake was determined by confocal microscopy. a 100-nm spherical-shaped Ag NPs, b 50-nm spherical-shaped Ag NPs, c 20-nm spherical-shaped Ag NPs, d 100-nm rod-shaped Ag NPs, and e control without nanoparticles

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Biochemical analysis

Results of biochemical assay showed that serum glutamic oxaloacetic transaminase (SGOT), serum glutamic pyruvic transaminase (SGPT), and ALP levels increased with 20, 50, and 100-nm Ag spherical NP-treated Wistar rats in comparison with control group. On the other hand, 100-nm rod Ag NP-treated rats had slightly increased SGOT levels, and no changes in SGPT and ALP levels were observed. Wistar rats treated with Ag NPs along with W. somnifera significantly reduced SGOT, SGPT, and ALP levels in control group (Fig. 4a–c). Creatinine values were increased only for 20-nm Ag NPs while no changes were observed for 50 or 100 nm (spherical) and rod 100-nm Ag NPs alone and with W. somnifera-treated groups (Fig. 5a). Spherical-shaped 20, 50, and 100-nm Ag NPs increased the BUN level. In rats treated with Ag NPs, along with W. somnifera, the BUN level reduced to normal level as in control group (Fig. 5b).

Fig. 4
figure 4

a–c Shows increased level of SGOT, SGPT, and ALP, respectively, for 20, 50, and 100-nm spherical Ag NPs, while for 100-nm rod Ag NPs, there is a slightly change in SGOT level. When rats are treated with AgNPs and W. somnifera, together it reduced significantly the SGOT, SGPT, and ALP levels

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Fig. 5
figure 5

a Graph showing that only 20-nm Ag NPs slightly increased the creatinine, while 50/100-nm (spherical) and 100-nm Ag NPs (rod) and Ag NPs with W. somnifera-treated groups have no effect on creatinine concentration. b Graph showing that 20, 50, and 100-nm Ag NPs (spherical) increased the BUN level while Ag NPs (rod 100 nm) slightly changed the BUN level. When rats are treated with Ag NPs and W. somnifera, together it reduced the BUN level

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Histopathological examination

Photomicrographs of liver and kidney tissues showed histopathological changes in liver tissue on treatment with Ag NPs and are illustrated in Fig. 6. Control group showed normal liver architecture, portal triad (PT), and central vein (CV) whereas 20-nm Ag NP-treated animal showed vacuolation of hepatocytes, focal necrosis in the centrizonal area, inflammation, and dilated CV. Animals treated with 50-nm Ag NPs have moderate sinusoidal dilatation in the centrizonal area and no necrosis, and hepatocytic vacuolation has been seen in portal triad (Fig. 6c). One hundred-nanometer spherical and 100-nm rod Ag NPs showed sinusoidal dilatation in the centrizonal area, dilated CV, and moderate sinusoidal dilatation in the centrizonal area, and normal PT and CV, respectively (Fig. 6d, e). W. somnifera resulted in reduced toxicity of 20, 50, and 100-nm Ag NPs as depicted with mild vacuolation in centrizonal area and dilated CV and PT, large vacuolation of hepatocytes in centrizonal area, inflammation with intact CV, mild vacuolation, and normal PT and CV, respectively (Fig. 6f–h). Rod-shaped 100-nm Ag NPs with W. somnifera showed normal liver architecture with PT and CV (Fig. 6i).

Fig. 6
figure 6

Photomicrographs showing histopathological changes in liver tissue. a Control group (×40) showing normal liver architecture, portal triad (PT), and central vein (CV). b Treated group (20-nm Ag NPs) (×40) showing vacuolation of hepatocytes and focal necrosis in the centrizonal area and inflammation and dilated CV. c Treated group (50-nm Ag NPs) (×40) showing moderate sinusoidal dilatation in the centrizonal area and no necrosis, and hepatocytic vacuolation is seen PT. d Treated group (100-nm Ag NPs) (×40) showing sinusoidal dilatation in the centrizonal area and dilated CV. e Treated group (rod 100-nm Ag NPs) (×40) showing moderate sinusoidal dilatation in the centrizonal area and normal PT and CV. f Treated group (20-nm Ag NPs with W. somnifera) (×40) showing mild vacuolation in the centrizonal area and dilated CV and PT. g Treated group (50-nm Ag NPs with W. somnifera) (×40) showing large vacuolation of hepatocytes in centrizonal area and inflammation with intact CV. h Treated group (Ag NPs 100 nm with W. somnifera) (×40) showing mild vacuolation and normal PT and CV. i Treated group (rod 100-nm Ag NPs with W. somnifera) (×40) showing normal liver architecture with PT and CV

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Histopathological changes in kidney tissue were also examined; control group showed normal kidney architecture with glomerula and normal cells, and treated groups by 20-nm Ag NPs showed nuclear loss, karyolysis, hyalinization, glomerular destruction, and necrosis and by 50-nm Ag NPs, mild hyalinization, eosinophilia, and mild glomerular destruction (Fig. 7a–c.) Spherical 100 nm and rod-shaped 100-nm Ag NPs showed normal glomerula and mild hyalinization (Fig. 7d, e). W. somnifera significantly normalized the changes with 20-nm Ag NPs and 50-nm Ag NPs, resulting in mild to negligible hyalinization, eosinophilia, glomerular destruction, and necrosis for both (Fig. 7f, g). W. somnifera with 100-nm spherical-shaped and 100-nm rod-shaped Ag NPs showed normal kidney architecture, glomerula, and cells (Fig. 7h, i).

Fig. 7
figure 7

Photomicrographs showing histopathological changes in kidney tissue. a Control group (×40) showing normal kidney architecture with glomerula and normal cells. b Treated group (20-nm Ag NPs) (×40) showing nuclear loss, karyolysis, hyalinization, glomerular destruction, and necrosis. c Treated group (50-nm Ag NPs) (×40) showing mild hyalinization, eosinophilia, and mild glomerular destruction. d Treated group (100-nm Ag NPs) (×40) showing normal glomerula and mild hyalinization. e Treated group (rod 100-nm Ag NPs) (×40) showing normal glomerula and mild hyalinization. f Treated group (20-nm Ag NPs with W. somnifera) (×40) showing hyalinization, eosinophilia, mild glomerular destruction, and no necrosis. g Treated group (50-nm Ag NPs with W. somnifera) (×40) showing mild hyalinization, no glomerular destruction, and no necrosis. h Treated group (Ag NPs 100 nm with W. somnifera) (×40) showing normal kidney architecture and glomerula. i Treated group (rod 100-nm Ag NPs with W. somnifera) (×40) showing normal kidney architecture and glomerula

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Discussion

Ag NPs have been used in health implications as anti-microbial agents and disinfectants for a very long time (Choi et al. 2009). As information presented in the literature, different sizes and shapes of Ag NPs have different toxic effects (Edwards-Jones 2009; Nel et al. 2006). In the present study, a comparison was done between different sizes and shapes of Ag NPs for their acute oral toxicity (Park and Bae 2010) for their potential application as anti-microbial agents, and acute toxicity modulation by W. somnifera was observed. In a previous study, bare Ag NPs (42 nm) in distilled water with doses of 0.25, 0.5, and 1 mg/kg induce hepatotoxicity by repeated oral administration (Kim et al. 2009; Oberdorster et al. 2005). Particle morphology plays a significant role in the toxicology of various kinds of nanoparticles (Larissa et al. 2011; Sharma 2010).

The absorbance spectroscopy data of Ag NP solution was explored, and a comparison between various sizes and shapes of Ag NPs investigated single peaks for 20, 50, and 100 nm spherical-shaped Ag NPs at different wavelengths and two peaks for 100-nm rod-shaped Ag NPs due to the distribution of radii and orientation of the particles in the solution, respectively.

The different sizes and shapes of nanoparticles can produce different biological responses and severe toxicity to tissue causing cell injury (Lam et al. 2004). Many studies suggested that crystalline small particles can induce more toxic to cells as well as being more persistent in the tissues (Linda et al. 2011). In this study, various sizes and shapes of Ag NPs produce different cell viability in macrophages. From the results obtained, it appears that 100-nm spherical- and rod-shaped Ag NPs caused no significant change, while at 20- and 50-nm spherical shapes of Ag NPs, there is a significant increase in plasma SGOT, SGPT, and ALP activities. The elevated levels of SGOT, SGPT, and ALP indicated a diseased level. SGPT and SGOT both are the liver-specific enzymes and used to diagnose liver diseases (Yong et al. 2010; Yadav et al. 2013; Shayestech et al. 2014). The studies showed that silver disrupts the activity of mitochondria, and this causes a rise in plasma transaminase (GOT, GPT) activity which is a sensitive indicator of damage to cytoplasmic and/or mitochondrial membranes (Oberdorster et al. 2005; Fabian et al. 2013). Slight effect of BUN and creatinine concentration was measured. Acute oral toxicity was also confirmed by histopathological changes in liver and kidney tissues that revealed marked mononuclear cell infiltration, nuclear degeneration, architectural disarray, glomerular destruction, and necrosis. On the other hand, the associated anatomy of these structures causes the damage of a part leading to disruption of the other parts (Yadav et al. 2013; Fabian et al. 2013; Singh et al. 2001).

Spherical-shaped Ag NPs increased glomerular destruction, and central vein and portal triad destruction causes severe hepatorenal toxicity. Hepatorenal and renal toxicity of Ag NPs was reduced significantly when the rats were treated with W. somnifera in the present case which indicated that W. somnifera has free radical scavenging enzymes that worked as anti-oxidant and normalizes all enzymatic activities and improves BUN and creatinine concentration. W. somnifera should be used and worked further as a toxicity modulator.

Conclusion

It is demonstrated that Ag NPs show toxicity in macrophages and Wistar rats. The toxicity of spherical-shaped Ag NPs is inversely proportional to their size which is due to deeper and higher penetration of small-sized nanoparticles; 100-nm rod-shaped Ag NPs showed negligible toxicity in comparison to 100-nm spherical-shaped nanoparticles in macrophages under in vitro conditions and in Wistar rats. When Ag NPs of different shapes and sizes were treated with extracts of W. somnifera administered to rats, the toxic effects were found to be reduced to a significant extent. This study indicates the potential use of W. somnifera extract as an anti-oxidant and anti-inflammatory against the toxic effects of different shapes and sizes of Ag NPs. The prospective applications W. somnifera will necessitate significant consideration by scientific community in the future.