High-dose enalapril treatment reverses myocardial fibrosis in experimental uremic cardiomyopathy

Abstract

Aims: Patients with renal failure develop cardiovascular alterations which contribute to the higher rate of cardiac death. Blockade of the renin angiotensin system ameliorates the development of such changes. It is unclear, however, to what extent ACE-inhibitors can also reverse existing cardiovascular alterations. Therefore, we investigated the effect of high dose enalapril treatment on these alterations.

Methods: Male Sprague Dawley rats underwent subtotal nephrectomy (SNX, n = 34) or sham operation (sham, n = 39). Eight weeks after surgery, rats were sacrificed or allocated to treatment with either high-dose enalapril, combination of furosemide/dihydralazine or solvent for 4 weeks. Heart and aorta were evaluated using morphometry, stereological techniques and TaqMan PCR.

Results: After 8 and 12 weeks systolic blood pressure, albumin excretion, and left ventricular weight were significantly higher in untreated SNX compared to sham. Twelve weeks after SNX a significantly higher volume density of cardiac interstitial tissue (2.57±0.43% in SNX vs 1.50±0.43% in sham, p<0.05) and a significantly lower capillary length density (4532±355 mm/mm(3) in SNX vs 5023±624 mm/mm(3) in sham, p<0.05) were found. Treatment of SNX with enalapril from week 8-12 significantly improved myocardial fibrosis (1.63±0.25%, p<0.05), but not capillary reduction (3908±486 mm/mm(3)) or increased intercapillary distance. In contrast, alternative antihypertensive treatment showed no such effect. Significantly increased media thickness together with decreased vascular smooth muscles cell number and a disarray of elastic fibres were found in the aorta of SNX animals compared to sham. Both antihypertensive treatments failed to cause complete regression of these alterations.

Conclusions: The study indicates that high dose ACE-I treatment causes partial, but not complete, reversal of cardiovascular changes in SNX.

Figure 1. Experimental protocol (A) and left ventricular weight (B).

A. Experimental protocol. B. Effect of treatment with the ACE-I enalapril or furosemide/dihydralazine on left ventricular weight (g). The increase in left ventricular weight (g) in untreated SNX at week 12 is completely prevented by enalapril, not by furosemide/dihydralazine treatment.

Figure 2. Effect of treatment with the ACE-I enalapril or furosemide/dihydralazine on systolic blood pressure (A) and myocardial interstitial fibrosis (B).

A. Enalapril (E) and furosemide/dihydralazine (F/D) treatment lowered systolic blood pressure (bp) in sham and SNX to the same extent. Two weeks after SNX systolic bp was not significantly different between the groups. From week 5 onward bp was significantly higher (p<0.01) in untreated SNX than in untreated sham. At week 7 bp was highest in the SNX+F/D group. Treatment with E and F/D significantly and comparably lowered bp in SNX and sham compared to untreated animals. Mean of systolic blood pressure measurements at weeks 2, 5, 7, 9 and 11 using tail plethysmography in conscious rats that were acquainted to the measuring conditions. *: p<0.01 compared to all other groups. +: p<0.05 compared to all other groups. B. The increase in myocardial interstitial tissue (%) in untreated SNX at week 12 is completely prevented by enalapril, but not by furosemide/dihydralazine treatment. *: p<0.05 vs SNX 12 weeks. +: p<0.05 vs corresponding sham.

Figure 3. Myocardial fibrosis in untreated sham operated animals (A), sham+enalapril (B), untreated SNX 12 weeks (C) and SNX + enalapril (D).

Note increased myocardial fibrous tissue content (depicted in red) in untreated SNX at 12 weeks (C) compared to untreated and treated sham (A,B). Complete regression of interstitial fibrosis is seen at 12 weeks after 4 weeks treatment with enalapril (D).Sirius red stain, magnification x 400.

Figure 4. Effect of treatment with the ACE-I enalapril or furosemide/dihydralazine on cardiac mRNA expression of TGF-β (A), TIMP-1 (B) and TIMP-2 (B).

Increased TGF-β mRNA expression in untreated SNX was lowered by both antihypertensive treatments. Cardiac TIMP-1 gene expression was also significantly higher in untreated SNX 12 weeks than in sham and SNX 8 weeks; RAS blockade by ACE-I and alternative antihypertensive treatment both lowered cardiac TIMP-1 gene expression in SNX animals. The same tendency was seen for TIMP-2 mRNA expression. The data are provided as box plots of the ΔCT analysis. ° indicate outlyers.

Figure 5. Effect of treatment with the ACE-I enalapril (E) on aortic wall thickness and aortic remodelling in sham (A,B) and SNX rats (C,D).

The increase in aortic wall thickness in untreated SNX (C) compared to untreated and E-treated sham (A,B) reversed by antihypertensive treatment with enalapril (D).