## 3 Results
### In Vivo Studies
Administration of SP and NESP to the I/R group increased the renal SOD activity (9.0 \(\pm\) 0.04 and 10.33 \(\pm\) 0.08 U/mg, respectively) compared to the I/R group (7.1 \(\pm\) 0.23 U/mg) (_p_ < 0.01 and \(p\) < 0.001, respectively). However, NESP administration to I/R group could completely normalize the altered SOD activity (_p_ = 0.31). Furthermore, NESP administered I/R rats showed greater increase in renal SOD activity (10.33 \(\pm\) 0.08 U/mg) compared to SP-treated I/R rats (9.0 \(\pm\) 0.04 U/mg) (_p_ < 0.05) as shown in the left panel of Figure 4.  
In the I/R group, there was a significant decrease in the renal CAT activity (2.9 \(\pm\) 0.5 U/mg) compared to the control rats (6.4 \(\pm\) 0.2 U/mg) (_p_ < 0.01) (right panel of Figure 4). There were no significant difference in CAT activity between SP and NESP groups (5.9 \(\pm\) 0.19 and 7.0 \(\pm\) 0.36 U/mg, respectively) compared to control rats (6.4 \(\pm\) 0.2 U/mg) (_p_ = 0.65, \(p\) = 0.89, respectively). Although administration of SP in the I/R group increased renal CAT activity (4.57 \(\pm\) 0.12 U/mg) compared to I/R group (2.9 \(\pm\) 0.5 U/mg), there was still a significant difference compared to the control rats (6.4 \(\pm\) 0.2 U/mg) (_p_ < 0.01). The oral administration of NESP to the I/R group increased renal CAT activity significantly (6.18 \(\pm\) 0.15 U/mg) compared to the I/R group (2.9 \(\pm\) 0.5 U/mg) (_p_ < 0.001) and, in this regard, there was no significant difference compared to control animals (_p_ = 1.0). Furthermore, there was a significant difference in the renal CAT activity between SP and NESP-administered I/R groups (6.18 \(\pm\) 0.15 and 4.57 \(\pm\) 0.12 U/mg, respectively) (_p_ < 0.05). Figure 5A demonstrates normal histology of kidney in control rats. The kidneys of the rats subjected to I/R exhibited pathological alterations such as tubular dilation, glomerular atrophy, tubular cast formation and hemorrhage, as shown in the Figure 5B. Although SP treatment tried to minimize most of the abnormal renal features, there were still some signs of injury including tubular dilation, glomerular atrophy and hemorrhage (Figure 5C). However, in rats undergoing renal ischemia, treatment by NESP alleviated all the abnormal renal histological features and restored the normal histological structure, as displayed in Figure 5D. Sections from SP and NESP groups presented normal kidney architecture  
Figure 4: Renal superoxide dismutase (SOD) and catalase (CAT) activities in different animal groups (_n_ = 8) at the end of interventions: Control, ischemic/reperfusion (I/R), spironolactone (SP), nano-encapsulated spironolactone (NESP), spironolactone-treated I/R (SP + I/R) and NESP-treated I/R (NESP + I/R) groups. The data are represented as mean \(\pm\) SD (Left panel: \({}^{**}\)_p_ < 0.01 and \({}^{***}\)_p_ < 0.001 compared to control group, \({\#}\)_p_ < 0.01 and \({\#}\)_p_ < 0.001 compared to I/R group, \({\#}\)_p_ < 0.05: difference between SP-treated I/R group and NESP-treated I/R group). (Right panel: \({}^{**}\)_p_ < 0.01 compared to control group; \({\#}\)_p_ < 0.05, \({\#}\)_p_ < 0.01 and \({\#}\)_p_ < 0.001 compared to I/R group; \({\#}\)_p_ < 0.05: difference between SP-treated I/R group and NESP-treated I/R group). without tubular dilation, glomerular atrophy, cast formation and hemorrhage, as depicted in Figure 5E,F. We also evaluated the effects of SP and NESP on the renal biomarkers. The difference in the renal functional biomarkers in the different rat groups have been depicted in Table 1. Induction of I/R induced significant increase in the serum levels of urea and creatinine (\(p<0.001\)). There were no significant differences in the levels of urea in free SP and NESP-treated rats compared to the control animals (\(p=1.0\), \(p=0.99\), respectively). The levels of creatinine also had no significant changes in free SP- and NESP-treated rats compared to the control rats (\(p=0.83\), \(p=0.92\), respectively).