Treatment of established left ventricular hypertrophy with fibroblast growth factor receptor blockade in an animal model of CKD

Abstract

Background: Activation of fibroblast growth factor receptor (FGFR)-dependent signalling by FGF23 may contribute to the complex pathogenesis of left ventricular hypertrophy (LVH) in chronic kidney disease (CKD). Pan FGFR blockade by PD173074 prevented development of LVH in the 5/6 nephrectomy rat model of CKD, but its ability to treat and reverse established LVH is unknown.

Methods: CKD was induced in rats by 5/6 nephrectomy. Two weeks later, rats began treatment with vehicle (0.9% NaCl) or PD173074, 1 mg/kg once-daily for 3 weeks. Renal function was determined by urine and blood analyses. Left ventricular (LV) structure and function were determined by echocardiography, histopathology, staining for myocardial fibrosis (Sirius-Red) and investigating cardiac gene expression profiles by real-time PCR.

Results: Two weeks after inducing CKD by 5/6 nephrectomy, rats manifested higher (mean ± SEM) systolic blood pressure (208 ± 4 versus 139 ± 3 mmHg; P < 0.01), serum FGF23 levels (1023 ± 225 versus 199 ± 9 pg/mL; P < 0.01) and LV mass (292 ± 9 versus 220 ± 3 mg; P < 0.01) when compared with sham-operated animals. Thereafter, 3 weeks of treatment with PD173074 compared with vehicle did not significantly change blood pressure, kidney function or metabolic parameters, but significantly reduced LV mass (230 ± 14 versus 341 ± 33 mg; P < 0.01), myocardial fibrosis (2.5 ± 0.7 versus 5.4 ± 0.95% staining/field; P < 0.01) and cardiac expression of genes associated with pathological LVH, while significantly increasing ejection fraction (18 versus 2.5% post-treatment increase; P < 0.05).

Conclusions: FGFR blockade improved cardiac structure and function in 5/6 nephrectomy rats with previously established LVH. These data support FGFR activation as a potentially modifiable, blood pressure-independent molecular mechanism of LVH in CKD.

Keywords: CKD; FGF receptor; FGF23; echocardiography; left ventricular hypertrophy.

FIGURE 1:

FGFR blockade reverses LVH in an animal model of CKD. (A) Experiment outline. CKD was induced by 5/6 nephrectomy (Nx). After 2 weeks (pre-treatment), LV dimensions and function were determined by echocardiography. Rats were then treated for 3 weeks with vehicle (NaCl 0.9%) or PD173074, 1 mg/kg once-daily. A second echocardiography was repeated at the end of the experiment (3 weeks post-treatment). (B) Echocardiographic measurements of LV mass pre- and post-treatment. (C) At the end of the experiment, LVH was determined as the ratio of heart weight to tibia length. (D) Quantitative analysis of cardiomyocyte cross-sectional area. (E) Expression profile of adult cardiac genes (αMHC), fetal genes (βMHC) and markers of cardiac stress and remodelling (ANP, BNP). Relative gene expression was determined by real-time PCR using gapdh as housekeeping gene. Sham-operated rats were set as control. (F) Representative images of interstitial cardiac fibrosis of 5/6 nephrectomy rats treated with vehicle (left panel) or PD173074 (right panel) for 3 weeks. Staining was performed with Sirius-Red (dark red) (original magnification, ×20; scale bar: 50 µm). The bottom graphic represents quantification of the extent of cardiac fibrosis after 3 weeks of treatment. (G) Echocardiographic measurements of LV ejection fraction pre- and post-treatment. All data are mean ± SEM, n = 8 for Sham–Vehicle, 4 for Sham–PD173074, n = 8 for 5/6 nephrectomy rats receiving vehicle (Nx–Vehicle) and n = 7 for PD173074 (Nx–PD173074). ^†P < 0.05 for NaCl- and PD173074-treated rats in comparison with Sham–NaCl pre-treatment, ^§P < 0.05 for PD173074-treated rats in comparison with pre-treatment, ^&P < 0.05 for NaCl-treated rats in comparison with PD173074 post-treatment, *P < 0.05 in comparison with Sham–NaCl, **P < 0.05 in comparison with Sham–NaCl and Sham–PD173074; and ^#P < 0.05 in comparison with 5/6 nephrectomy rats receiving NaCl (vehicle).

FIGURE 2:

Histological effects of FGFR blockade on the hearts and kidneys of CKD animals. CKD was induced by 5/6 nephrectomy (Nx). Representative histological sections of the myocardium (upper panels) and kidneys (lower panels) from 5/6 nephrectomy rats treated for 3 weeks with vehicle (NaCl 0.9%) or PD173074 (1 mg/kg/day). Tissues show no evidence of mineralization by H&E or von Kossa staining, suggesting no adverse, toxic effects associated with the use of PD173074 at the dose used for up to 3 weeks. Magnification, ×20; scale bar: 100 µm. Interstitial fibrosis (arrows); tubular proteinaceous casts (asterisks).