The potential renal toxicity of silver nanoparticles after repeated oral exposure and its underlying mechanisms

Abstract

Background: Silver nanoparticles (AgNPs) can accumulate in various organs after oral exposure. The main objective of the current study is to evaluate the renal toxicity induced by AgNPs after repeated oral exposure and to determine the relevant molecular mechanisms.

Methods: In this study, 40 male Wistar rats were treated with solutions containing 30, 125, 300, and 700 mg/kg of AgNPs. After 28 days of exposure, histopathological changes were assessed using hematoxylin-eosin (H&E), Masson's trichrome, and periodic acid-Schiff (PAS) staining. Apoptosis was quantified by TUNEL and immunohistochemistry of caspase-3, and the level of expression of the mRNAs of growth factors was determined using RT-PCR.

Results: Histopathologic examination revealed degenerative changes in the glomeruli, loss of tubular architecture, loss of brush border, and interrupted tubular basal laminae. These changes were more noticeable in groups treated with 30 and 125 mg/kg. The collagen intensity increased in the group treated with 30 mg/kg in both the cortex and the medulla. Apoptosis was much more evident in middle-dose groups (i.e., 125 and 300 mg/kg). The results of RT-PCR indicated that Bcl-2 and Bax mRNAs upregulated in the treated groups (p < 0.05). Moreover, the data related to EGF, TNF-α, and TGF-β1 revealed that AgNPs induced significant changes in gene expression in the groups treated with 30 and 700 mg/kg compared to the control group.

Conclusion: Our observations showed that AgNPs played a critical role in in vivo renal toxicity.

Keywords: Apoptosis; Kidney; Silver nanoparticles; Toxicity.

Fig. 1

TEM micrograph and particle size distribution of AgNPs

Fig. 2

Light micrographs of rat kidney sections (H&E stain, ×400). The renal cortex shows a normal architecture in the control group. Groups treated with 30, 125, and 300 mg/kg show marked degenerative changes in the glomeruli, showing necrosis with loss of glomerular tufts and wide Bowman’s space. The group treated with 700 mg/kg shows swelled renal glomerulus. Hyaline casts in renal tubule are observed in the group treated with 125 mg/kg. Congestion of the capillary loops, infiltration of inflammatory cells, and disorganization of the tubules are seen in the groups treated with AgNPs. The effects of various concentrations of AgNPs on the diameter of the glomeruli are presented and compared to the control group. #P < 0.001

Fig. 3

Periodic acid-Schiff (PAS) staining of kidney sections after 28 days of oral exposure to AgNPs (original magnification ×400). The disruption of the brush border (arrows) and the basement membrane integrity (arrowheads) were observed in the renal tubules of the groups treated with 30 and 125 mg/kg of AgNPs

Fig. 4

Masson’s trichrome staining (original magnification ×400). Collagen depositions were quantified by counting the number of blue pixels in the medulla and the cortex using the ImageJ software. * indicates a significant difference with the control group (P < 0.05)

Fig. 5

Cell apoptosis (arrowheads) detected by TUNEL in the renal tubule epithelial cells (original magnification × 400). ** indicates a significant difference with the control group (P < 0.01)

Fig. 6

Cell apoptosis detected by caspase-3 immunostaining (arrowheads) in the renal tubule epithelial cells (original magnification ×400). **P < 0.01 and #P < 0.001 compared to the control group

Fig. 7

Bax and Bcl-2 genes expression and the ratio of Bax to Bcl-2 changes in the kidney of the rats treated with AgNPs. *P < 0.05, **P < 0.01, and #P < 0.001 compared to the control group

Fig. 8

Gene expression of EGF, TNF-α, and TGF-β1. *P < 0.05 and **P < 0.01 compared to the control group