Eplerenone inhibits aldosterone-induced renal expression of cyclooxygenase

Abstract

Introduction: The upregulation of cyclooxygenase (COX) expression by aldosterone (ALDO) or high salt diet intake is very interesting and complex in the light of what is known about the role of COX in renal function. Thus, in this study, we hypothesize that apocynin (APC) and/or eplerenone (EPL) inhibit ALDO/salt-induced kidney damage by preventing the production of prostaglandin E₂ (PGE₂).

Methods: Dahl salt-sensitive rats on either a low-salt or high-salt diet were treated with ALDO (0.2 mg pellet) in the presence of EPL (100 mg/kg/day) or APC (1.5 mM). Indirect blood pressure, prostaglandins and ALDO levels and histological changes were measured.

Results: Cyclooxygenase-2 (COX-2) levels were upregulated in the renal tubules and peritubular vessels after high-salt intake, and APC attenuated renal tubular COX-2 protein expression induced by ALDO. Plasma PGE₂ levels were significantly reduced by ALDO in the rats fed a low-salt diet when compared to rats fed a high-salt diet. PGE₂ was blocked by EPL but increased in the presence of APC.

Conclusions: The beneficial effects of EPL may be associated with an inhibition of PGE₂. The mechanism underlying the protective effects of EPL is clearly distinct from that of APC and suggests that these agents can have differential roles in cardiovascular disease.

Figure 1

Effect of eplerenone (EPL) and apocynin (APC) on systolic blood pressure in Dahl salt-sensitive rats on an aldosterone (ALDO)/salt diet for four weeks. (A) represents the rats that were fed a low-salt diet and (B) represents the rats fed a high-salt diet. Data are represented as mean±SEM for six animals per group. # denotes significant difference (p<0.05) from the basal (week=0) systolic blood pressure. ++ denotes significant difference (p<0.05) from control group (low-salt diet with no treatment). * denotes significant difference (p<0.05) from aldosterone treatment only. SEM, standard error of mean.

Figure 2

Effect of eplerenone (EPL) and apocynin (APC) on plasma prostacyclin (PGI₂) and PGE₂ (prostaglandin E₂) levels in Dahl salt-sensitive rats on an aldosterone (ALDO)/salt diet. (A) represents the plasma PGI₂ levels measured as 6-keto-PGF_1α and (B) represents plasma PGE₂ levels. Data are represented as mean ±SEM for six animals per group. # denotes a significant difference (p<0.05) from its control (on diet with no drug treatment) value. * denotes significant difference (p<0.05) from low-salt group. + denotes significant difference from ALDO group with no drug treatment.

Figure 3

(A) Representative western blots of aldosterone (ALDO)/salt-induced protein levels of cyclooxygenase-1 (COX-1) following treatment with eplerenone (EPL). (B) is a histogram reflecting the data in (A). HS: high salt; LS: low salt.

Figure 4

(A) Representative western blots of aldosterone (ALDO)/salt-induced protein levels of cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) and following treatment with apocynin (APC). (B) and (C) are histograms reflecting the data in (A). HS: high salt; LS: low salt.

Figure 5

Representative photomicrographs of cyclooxygenase-2 (COX-2) immunohistochemistry in rat kidneys from this study. Treatment protocol and COX-2 score are noted on each image. Most positive binding occurs in renal tubular epithelium in the cortex (arrows). 200× magnification for all. ALDO: aldosterone; HS: high salt; LS: low salt.