Sildenafil citrate for prophylaxis of nephropathy in an animal model of contrast-induced acute kidney injury

Abstract

Contrast-induced acute kidney injury (CIAKI) is one of the commonest complications associated with contrast media (CM). Although the exact etiology of CIAKI remains unclear, one hypothesis involves vasoconstriction of afferent arterioles resulting in renal ischemia. Increased renal blood flow, therefore, might represent an attractive target for the treatment of CIAKI. In this study we evaluated the protective effects of the phosphodiesterase type 5 (PDE5) inhibitor, sildenafil citrate, in a rabbit model of CIAKI. New Zealand white rabbits were used due to their susceptibility to CIAKI. To evaluate the effects of sildenafil, the drug was administered before CM infusion and repeatedly throughout the remainder of the experiment (6 mg/kg, p.o.). Animals were sacrificed after 48 hours and kidneys were prepared for histological evaluation. Intravenous administration of CM produced marked kidney injury. Serum creatinine concentrations were elevated within two hours of the infusion and remained elevated for the duration of the experiment. Histological evaluation of the kidneys revealed significant tubular necrosis. The effects of the CM were dose dependent. Treatment with sildenafil was associated with lesser degree of histological injury, attenuation in markers of acute kidney injury (48 hour creatinine 1.54±0.21 versus 4.42±1.31 mg/dl, p<0.05) and reduction in electrolyte derangement (percent change in serum K+ at 48 hours 2.55±3.80% versus 15.53±4.47%, p<0.05; serum Na+ at 48 hours -0.14±0.26% versus -1.97±1.29%, p = 0.20). The results suggest a possible role for PDE5 inhibitors in the treatment of CIAKI and warrant further evaluation to determine the exact mechanism of protection.

Figure 1. Kidney to body weight ratio analysis in rabbits subjected to CIAKI.

The kidney to body weight ratio was measured as the average weight of both kidneys per 100 g body weight. (a) Kidney to body weight ratio for animals treated with increasing doses of CM. (b) Kidney to body weight ratio for animals pretreated with sildenafil citrate (6.0 mg/kg; single dose or q8 h).

Figure 2. The effects of sildenafil citrate on CM-induced renal dysfunction.

Serum samples were prepared from whole blood collected at various time points. Creatinine concentrations were determined using a Luminex xMap assay. (A) Time course of serum creatinine concentration in animals treated with increasing concentrations of CM. (B) Time course of serum creatinine concentration in animals pretreated with sildenafil citrate (6.0 mg/kg; single dose or q8 h) prior to CM exposure (5.0 g I/kg). (C) Maximum serum creatinine concentration in animals treated with increasing concentrations of CM. (D) Maximum serum creatinine concentration in animals pretreated with sildenafil citrate (6.0 mg/kg; single dose or q8 h) prior to CM exposure (5.0 g I/kg). Values are presented as mean ± SEM; n = 3–5. * indicates p<0.05 vs. 2.5 g I/kg and † indicates p<0.05 versus 5.0 g I/kg by one-way ANOVA and Dunnett's multiple comparisons test.

Figure 3. Repeated treatment with sildenafil citrate prevents hyponatremia and hyperkalemia in animals exposed to CM.

(A) Percent change (t = 0 vs. 48 h) in plasma Na⁺ concentrations in animals administered intravenous ioxilan (5.0 g I/kg) with/without simultaneous sildenafil therapy. (B) Percent change (t = 0 vs. 48 h) in plasma K⁺ concentrations in animals administered intravenous ioxilan (5.0 g I/kg) with/without simultaneous sildenafil therapy. Values are presented as mean ± SEM; n = 3–5. † indicates p<0.05 versus 5.0 g I/kg by one-way ANOVA and Dunnett's multiple comparisons test.

Figure 4. Representative histological lesions in kidneys from rabbits subjected to CIAKI.

Renal cortex from rabbits treated with (A) 2.5 g I/kg CM, (B) 10.0 g I/kg CM, or (C) 5.0 g I/kg CM and sildenafil citrate (6.0 mg/kg, q8 h). In a rabbit treated with 2.5 g I/kg there were no histological alterations in the cortex. (A, summary pathology score  = 0) In a rabbit treated with 10.0 g I/kg there was severe tubular necrosis (arrows) affecting >50% of the cortical tubules. (B, summary pathology score  = 7). In a rabbit treated with 5.0 g I/kg CM and sildenafil citrate there was tubular necrosis affecting a much smaller percentage of cortical tubules (C, summary pathology score  = 3). Higher magnification of tubular necrosis from a rabbit in the 10.0 g I/kg group shows details of tubular necrosis, (arrows) evidenced by loss of cellular detail in the tubules, nuclear loss or condensation, and sloughing of necrotic cell debris into the tubule lumen. (D). A similar area in a rabbit treated with 2.5 g I/kg CM shows no alterations in the tubules (E). Hematoxylin and eosin stain. Original magnifications for A, B, C = ×200; bars  = 100 µm; for D, E  = ×600, bar  = 20 µm.

Figure 5. Representative histological lesions in kidneys from rabbits subjected to CIAKI.

Outer stripe of the renal medulla from rabbits treated with (A) 2.5 g I/kg CM, (B) 10.0 g I/kg CM, or (C) 5.0 g I/kg CM and sildenafil citrate (6.0 mg/kg, q8 h). Damage consisted of intraluminal pale eosinophilic (proteinaceous) exudate. Hematoxylin and eosin stain. Original magnification ×200; bars  = 100 µm.

Figure 6. Kidney pathology scores from rabbits subjected to CIAKI.

Summary pathology scores were calculated as outlined in the methods. (A) Pathology scores for animals treated with increasing doses of CM. (B) Pathology scores for animals pretreated with sildenafil citrate (6.0 mg/kg; single dose or q8 h) prior to CM exposure (5.0 g I/kg). Values are presented as mean ± SEM; n = 3–5. * indicates p<0.05 vs. 2.5 g I/kg.