Protective role of testosterone in ischemia-reperfusion-induced acute kidney injury

Abstract

Men are at greater risk for renal injury and dysfunction after acute ischemia-reperfusion (I/R) than are women. Studies in animals suggest that the reason for the sex difference in renal injury and dysfunction after I/R is the protective effect of estrogens in females. However, a reduction in testosterone in men is thought to play an important role in mediating cardiovascular and renal disease, in general. In the present study, we tested the hypothesis that I/R of the kidney reduces serum testosterone, and that contributes to renal dysfunction and injury. Male rats that were subjected to renal ischemia of 40 min followed by reperfusion had a 90% reduction in serum testosterone by 3 h after reperfusion that remained at 24 h. Acute infusion of testosterone 3 h after reperfusion attenuated the increase in plasma creatinine and urinary kidney injury molecule-1 (KIM-1) at 24 h, prevented the reduction in outer medullary blood flow, and attenuated the increase in intrarenal TNF-α and the decrease in intrarenal VEGF at 48 h. Castration of males caused greater increases in plasma creatinine and KIM-1 at 24 h than in intact males with renal I/R, and treatment with anastrozole, an aromatase inhibitor, plus testosterone almost normalized plasma creatinine and KIM-1 in rats with renal I/R. These data show that renal I/R is associated with sustained reductions in testosterone, that testosterone repletion protects the kidney, whereas castration promotes renal dysfunction and injury, and that the testosterone-mediated protection is not conferred by conversion to estradiol.

Keywords: androgens; kidney injury molecule-1; sex; vascular endothelial growth factor.

Fig. 1.

Testosterone supplementation attenuates plasma creatinine (A), KIM-1 (B), and proteinuria (C) 24 h after ischemia-reperfusion (I/R)-induced acute kidney injury (AKI) in male rats. Testosterone supplementation (TST) was given 3 h after reperfusion (or sham surgery) in males subjected to 40 min of ischemia. Data are expressed as milligrams creatinine per deciliter plasma (A), KIM-1 excretion per 24 h (B), and urinary protein excretion per 24 h (C). *P < 0.05 compared with sham. #P < 0.05 compared with I/R-AKI.

Fig. 2.

Serum testosterone levels measured serially every 3 h for 24 h following reperfusion after renal ischemia for 45 min in I/R or sham rats with or without testosterone supplementation. A: percentage change in serum testosterone levels at 3, 6, 12, and 24 h in sham (surgery only) and rats subjected to I/R (no testosterone supplements). Serum testosterone levels in sham and I/R rats are compared with age-matched untreated controls (serum testosterone = 387.72 ± 93.27 ng/dl). *P < 0.05 compared with I/R treated or untreated sham. B: numerical changes in serum testosterone levels in sham or I/R-treated rats with and without testosterone supplements given 3 h after reperfusion. Data are expressed as nanograms testosterone/deciliter serum. **P < 0.05 for all samples compared with untreated controls (387.72 ± 93.27 ng/dl); αP < 0.05 compared with sham; βP < 0.05 compared with sham+testosterone; γP < 0.05 compared with I/R; *P < 0.05 compared with previous time point for the same animal group.

Fig. 3.

Testosterone supplementation improved outer medullary blood flow (OMBF) by 48 h in the same male rats subjected to I/R-induced AKI as in Figs. 1 and 2. Data are expressed as arbitrary tissue perfusion units (TPU) *P < 0.05 compared with sham. #P < 0.05 compared with I/R-AKI.

Fig. 4.

Testosterone supplementation reduces renal TNF-α (A) and VEGF (B) by 48 h in male rats subjected to I/R-induced AKI. Data are expressed as picogram of TNF-α/μg kidney tissue (A) and picogram of VEGF/μg kidney tissue (B). *P < 0.05 compared with sham. #P < 0.05 compared with I/R-AKI.

Fig. 5.

I/R-induced AKI in castration increased plasma creatinine (A) and urinary excretion of KIM-1 (B) compared with intact males with I/R, and testosterone supplements in castrated rats attenuated the increase in both. Int, intact males; cast, castrated males. Data are expressed as milligrams of creatinine per deciliter plasma (A) and KIM-1 excretion per 24 h (B). *P < 0.05 compared with intact sham. #P < 0.05 compared with intact with I/R-AKI. §P < 0.05 compared with untreated castrated rats with I/R-AKI.

Fig. 6.

I/R-induced AKI significantly reduced plasma testosterone in intact males, and testosterone was further reduced in castrated rats, but it was slightly improved with testosterone supplements. Data are expressed as nanograms of testosterone/deciliter plasma. *P < 0.05 compared with intact sham. #P < 0.05 compared with intact with I/R-AKI. §P < 0.05 compared with untreated castrated rats with I/R-AKI.

Fig. 7.

Chronic anastrozole (ANT), an aromatase inhibitor, attenuated plasma creatinine (A), KIM-1 excretion (B), and proteinuria (C) in intact male rats subjected to I/R-induced AKI. Testosterone supplementation with anastrazole further reduced plasma creatinine (A), KIM-1 excretion (B), but not proteinuria (C). Data are expressed as milligrams of creatinine per deciliter plasma (A), KIM-1 excretion per 24 h (B), and protein excretion per 24 h (C). *P < 0.05 compared with intact sham. #P < 0.05 compared with intact with I/R-AKI. §P < 0.05 compared with anastrozole-treated rats with I/R-AKI.

Fig. 8.

Effect of chronic anastrozole on plasma (PL) testosterone levels measured 24 h after reperfusion in control and testosterone-supplemented rats subjected to I/R-AKI. Data are expressed as nanograms of testosterone/deciliter plasma. *P < 0.05 compared with intact sham. #P < 0.05 compared with intact with I/R-AKI. §P < 0.05 compared with anastrozole-treated rats with I/R-AKI.

Fig. 9.

Chronic anastrazole reduced renal expression of TNF-α and the combination of anastrazole+testosterone further reduced renal TNF-α in male rats subjected to I/R-induced AKI. Data are expressed as picograms of TNF-α/μg kidney tissue. *P < 0.05 compared with intact sham. #P < 0.05 compared with intact with I/R-AKI. §P < 0.05 compared with anastrozole-treated rats with I/R-AKI.