Sildenafil attenuates renal injury in an experimental model of rat cisplatin-induced nephrotoxicity

Abstract

Sildenafil is the first commercially available selective inhibitor of phosphodiesterase-5 (PDE5) and is widely used for the treatment of erectile dysfunction. In recent years, investigations of the role of sildenafil in cardioprotection in animal models have received considerable interest. We evaluated whether sildenafil can attenuate cisplatin-induced nephrotoxicity in a rat experimental model. Male Sprague–Dawley rats were divided into five groups: control rats, sildenafil-control rats, cisplatin-injected rats (5 mg kg⁻¹ IP, single dose), sildenafil-treated cisplatin-injected rats (0.4 mg kg⁻¹, daily), and sildenafil + NG-nitro-l-arginine methyl ester hydrochloride (l-NAME)-treated rats. The molecular, functional, and structural parameters of the kidney were measured. At 96 h after cisplatin injection, serum levels of creatinine were lower in rats treated with both sildenafil + cisplatin compared with rats treated with cisplatin alone, and renal iNOS and eNOS expression was significantly higher in sildenafil + cisplatin-treated rats compared with rats treated with cisplatin alone (all P < 0.05). Renal Bax gene and protein expression was significantly higher in cisplatin-treated rats compared with control rats, and sildenafil treatment significantly reduced the levels of Bax and increased the renal Bax/Bcl-2 ratio (P < 0.05). Sildenafil treatment also reduced renal caspase-3 activation and TUNEL-positive apoptotic cells. These data suggest that sildenafil attenuates experimental cisplatin-induced nephrotoxicity by preventing apoptosis.

Introduction

Although cisplatin is a highly effective anti-neoplastic agent, its nephrotoxicity is a major clinical problem. Nephrotoxicity by cisplatin occurs in a dose-dependent manner, is cumulative, and occurs to varying degrees in 25–35% of patients receiving a single dose of cisplatin (Ries and Klastersky, 1986, Saleh and El-Demerdash, 2005). Cisplatin-induced nephrotoxicity can result in severe renal tubular injury leading to acute renal failure (Kang et al., 2004). Cisplatin causes tubular injury through multiple mechanisms, including hypoxia, the generation of free radicals, inflammation, and apoptosis. Cisplatin-induced nephrotoxicity was shown to be associated with an increase in the pro-apoptotic protein Bax and a decrease in the anti-apoptotic protein Bcl-2 (Tsuruya et al., 2003). Additionally, significant interactions among these various pathways may occur in cisplatin injury (Engineer et al., 1989, Yao et al., 2007). In particular, nitric oxide (NO) has been suggested to play an important role in cisplatin-induced nephrotoxicity. l-Arginine, the precursor of NO in the body, attenuates cisplatin-induced nephrotoxicity, and a competitive inhibitor of NO synthase, NG-nitro-l-arginine methyl ester hydrochloride (l-NAME), exacerbates cisplatin-induced nephrotoxicity (Palmer et al., 1988, Saleh and El-Demerdash, 2005).

Sildenafil is a selective inhibitor of phosphodiesterase-5 (PDE5), which degrades cyclic guanosine monophosphate (cGMP), a downstream product in the NO–soluble guanylate cyclase cascade, in endothelial cells. NO is synthesized by three isoforms of NO synthase (NOS), i.e., neuronal NOS (nNOS), inducible NOS (iNOS), and endothelial NOS (eNOS), all of which can be expressed in the kidney (Kone, 2004). Interestingly, sildenafil can induce iNOS and eNOS, and sildenafil-induced increases in NO have been associated with attenuation of doxorubicin-induced cardiotoxicity (Ockaili et al., 2002). Recently, several studies have shown that, in addition to treating erectile dysfunction, sildenafil can prevent or decrease tissue injury. In vivo and in vitro, early treatment with sildenafil ameliorated the progression of renal damage in the “5/6 nephrectomy” model (Rodriguez-Iturbe et al., 2005), and sildenafil has been reported to provide cardioprotection against ischemic injury when infused at the onset of reperfusion in rabbits (Das et al., 2004). In addition, sildenafil was found to reduce the hypertrophic response to isoprenaline in rat hearts (Fisher et al., 2005).

Owing to these effects of sildenafil, we hypothesized that sildenafil would attenuate cisplatin-induced nephrotoxicity. Here, we report that sildenafil decreases cisplatin-induced nephrotoxicity and present potential mechanism(s) involved in sildenafil-mediated protection.