Clinical and experimental studies have confirmed the reno-protective effects of klotho(18) and allopurinol(19) in renal dysfunction induced by renal ischemia–reperfusion. Allopurinol, as a xanthine oxidase inhibitor, plays an important role in reducing oxidative stress in ischemic reperfusion(20). On the other hand, klotho, as an endogenous factor, protects the organs against ischemic and reperfusion injury through its antioxidative action (21). Therefore, in this study, we investigated the cross-talk between the allopurinol and soluble klotho. Our study demonstrated that administration of allopurinol increased the plasma klotho level after bilateral renal ischemic-reperfusion.
Xanthine oxidase (X.O.) is a main source of ROS by disruption in uric acid formation from hypoxanthine and xanthine during ischemic and reperfusion time (22). The superoxide anion (.O2−), hydroxyl radical (O.H.), and hydrogen peroxide (H2O2), as reactive oxygen species (ROS), are dangerous mediators for cell metabolism, and extreme production can lead to cell death (23). Oxidative stress induced by oxygen-derived free radicals plays a critical role in the progression of renal ischemia–reperfusion injury(24).
There are studies (25) consistent with our data that indicated plasma activity of X.O. significantly increased at 24 h of reperfusion. X.O., as a source for ROS generation, induced oxidative stress in the plasma and target organs (26). Similar to our previous study(3), in this study, total oxidative stress (TOS) level and OSI ratio increased, and total antioxidative capacity (TAC) decreased in the plasma and kidney tissues on day one after renal ischemia. X.O., as a critical source of ROS, has a key effect on the pathogenesis of renal ischemic/reperfusion(I/R) injury(27). Therefore, the use of allopurinol as a xanthine oxidase inhibitor could be a therapeutic target for I/R injury. In clinical medicine, allopurinol has been administrated as an antioxidant drug to inhibit kidney damage produced by renal I/R injury (28). We revealed that allopurinol decreased the plasma X.O. activity. There was a negative correlation between X.O. activity and oxidative index. Allopurinol administration suppresses the content of TOS and elevates the TAC level in the post-ischemic plasma and kidney samples.
Klotho is a single-pass transmembrane protein that exists in transmembrane, intracellular, and secreted forms. Epigenetic and non-epigenetic factors are involved in the regulation of Klotho expression in various kidney diseases. Reactive oxygen species, as a non-epigenetic mediator, regulate endogenous Klotho expression (29). This study was designed to investigate the influence of allopurinol on the systemic level of klotho protein in rats subjected to bilateral renal ischemia-reperfusion. In the same line with the study of Ming-Chang et al. (15), the present study indicated that the α-soluble level of klotho decreased in the plasma 24h after reperfusion. When Klotho proteins has the antioxidant effect(21), oxidative stress can supress Klotho expression through a range of mechanisms(30). First, our result demonstrated that pretreatment of the rats with allopurinol resulted in a significant increase in the circulating form of klotho.
Based on our results, renal dysfunction in response to bilateral renal I/R injury was confirmed by the increase in the plasma concentration of creatinine and BUN and the decrease in glomerular filtration rat(GFR), obviously along with a changed renal morphology. In the present study, allopurinol attenuated the tubular and vascular damages induced by renal I/R injury. Structural improvement significantly increased the urine flow rat and GFR and decreased the plasma creatinine and BUN levels.