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Background and Objective: The unique properties of carbon nanotubes have been used for medical, biological and industrial applications, but it simultaneously exposure to humans and organisms poses a potential for toxic effects on human health and the environment. This study was done to evaluate the effect of multi-wall carbon nanotubes toxicity on kidney function and tissue in rats.
Methods: In this experimental study, 50 mature female Wistar rats were allocated into five groups including: control and experimental groups with dosage of 2.5, 5, 10, 20 mg/kg/bw, respectively. Animals in control group were received physiological saline and Tween.Animals in treatment groups were received 2.5, 5, 10, 20 mg/kg/bw of multi-wall carbon nanotubes functionalized with carboxylic group with diameter less than 8 nm and length 30 micrometers in 8 steps in one day intraperitoneally. Blood samples were conducted in two phases: one day after the last injection and 20 days after the last injection. Urea, uric acid, creatinine and malondialdehyde levels were measured in blood serum. Tissue samples were provided by preparing histological sections of kidney in each group and stain with hematoxylin-eosin. The tissue structure of the kidney was examined by optical microscopy.
Results: In the first stage (one day after the last injection), only the amount of uric acid at concentrations of 2.5 and 5 mg/kg significantly reduced in comparison with controls and other treated groups, respectively (P<0.05). There were no significant changes in the level of other biochemical factors in compared to the control. However, 20 days after the last injection, significant reduction in the level of uric acid and urea was observed in 2.5, 5, 10, 20 mg/kg/bw of multi-wall carbon nanotubes in compared to the control group, although significant reduction in creatinine was seen in dosages of 5 and 10 mg/kg/bw of multi-wall carbon nanotubes in compared to controls (P<0.05). Histological studies showed altrations in trated groups including  accumulation of hyaline-like substances derived from the activity of eosinophils and accumulation of inflammatory cells (basophils and neutrophils) in the cortical and medula of the kidney, glomerular degeneration, Bowman capsule dilatation and degeneration of  proximal tube wall in the renal cortex which  these alterations  were dose-dependent.
Conclusion: Multi-wall carbon nanotubes functionalized with carboxyl groups even in low dosage (2.5 mg/kg) and after 20 days of injection cause toxicity in tissue structure and kidney function.