Carbon tetrachloride (CCl4) induces hepatocellular damage, resulting in liver cirrhosis by generating reactive oxygen species (ROS). At the stage of decompensated liver cirrhosis, many patients suffer from the abnormal regulation of sodium and water balance such as ascites. Also, the kidney can be directly damaged by CCl4-induced ROS generation. The aquaporin (AQP) is an important transmembrane protein located in the kidney to reabsorb water, and it may be affected by the ROS to alter water balance. ROS is related with the development of hypertension and alteration of antioxidant enzymes.
This study was undertaken to investigate the effects of CCl4 on the expression of AQPs (AQP1 and AQP2) and superoxide dismutase (SOD) in the kidney of spontaneously hypertensive rat (SHR) and normotensive Wistar- Kyoto rat (WKY). The SOD is known as a scavenger of ROS, and we hypothesized that oxidative stress in the aged kidneys may be increased by hypertension.
Male WKY and SHR were randomly divided into control and CCl4-treated groups at 8, 16 and 24 weeks of age, respectively. The experimental group received olive oil-dissolved CCl4 (1.6 mL/kg) on its back subcutaneous tissue twice a week for 4 weeks, and control animals received olive oil only. After 24 hours following the last injection, blood samples and kidneys were obtained under anesthesia. Renal histopathology was examined by H&E stain, and the expression of AQP1, AQP2, CuZn-SOD and Mn-SOD were evaluated by immunohistochemical methods and Western blot analysis.
CCl4 treatment induced the tubular swelling, tubular epithelial atrophy or detachment in both WKY and SHR, and interstitial edema, tubular cast and infiltration of leukocyte in SHR.
The BUN levels in both WKY and SHR were increased by CCl4 treatment at 16 weeks of age. The expression of AQP1 were increased by CCl4 treatment at 8 and 24 weeks of age SHR. The expressions of AQP2 in 24 weekold control SHR was decreased compared to 8 week-old control SHR. CCl4 treatment increased the expressions of AQP2 at 8 week-old and 24 week-old SHR, and the increasing of AQP2 was more remakable in advanced age.
The expressions of CuZnSOD and MnSOD were increased at 24 week-old control SHR compared to same aged WKY. Whereas the expression of CuZnSOD was increased by CCl4 treatment in 8 week-old SHR, the expression of both CuZnSOD and MnSOD were decreased by CCl4 treatment in 24 week-old SHR.
In summary, CCl4-treated SHR showed an increase in AQP expression and a decrease in SODs at the advanced age. These results suggest that CCl4-induced oxidative stress in the aged hypertensive rats may alter water balance via upregulation of AQPs and accelerate renal damage via downregulation of SODs.