Uric acid promotes left ventricular diastolic dysfunction in mice fed a Western diet

Abstract

The rising obesity rates parallel increased consumption of a Western diet, high in fat and fructose, which is associated with increased uric acid. Population-based data support that elevated serum uric acids are associated with left ventricular hypertrophy and diastolic dysfunction. However, the mechanism by which excess uric acid promotes these maladaptive cardiac effects has not been explored. In assessing the role of Western diet-induced increases in uric acid, we hypothesized that reductions in uric acid would prevent Western diet-induced development of cardiomyocyte hypertrophy, cardiac stiffness, and impaired diastolic relaxation by reducing growth and profibrotic signaling pathways. Four-weeks-old C57BL6/J male mice were fed excess fat (46%) and fructose (17.5%) with or without allopurinol (125 mg/L), a xanthine oxidase inhibitor, for 16 weeks. The Western diet-induced increases in serum uric acid along with increases in cardiac tissue xanthine oxidase activity temporally related to increases in body weight, fat mass, and insulin resistance without changes in blood pressure. The Western diet induced cardiomyocte hypertrophy, myocardial oxidative stress, interstitial fibrosis, and impaired diastolic relaxation. Further, the Western diet enhanced activation of the S6 kinase-1 growth pathway and the profibrotic transforming growth factor-β1/Smad2/3 signaling pathway and macrophage proinflammatory polarization. All results improved with allopurinol treatment, which lowered cardiac xanthine oxidase as well as serum uric acid levels. These findings support the notion that increased production of uric acid with intake of a Western diet promotes cardiomyocyte hypertrophy, inflammation, and oxidative stress that lead to myocardial fibrosis and associated impaired diastolic relaxation.

Conflict of interest statement

Disclosures: No potential conflicts of interest relevant to this article were report.

© 2014 American Heart Association, Inc.

Figures

Fig. 1. Western Diet (WD) induced cardiac diastolic dysfunction is prevented with xanthine oxidase inhibition

(A) Representative mid-ventricle short-axis cine-MRI images that correspond to end-diastole, end-systole, and early diastole phases of cardiac cycle from WD fed mouse (WD, middle row), and WD fed mouse treated with allopurinol (WD + Allo, lower row) compared to the control diet (CD) fed mouse (upper row). (B) Left ventricular diastolic relaxation time and (C) Left ventricular initial filling rate derived from in vivo cine-MRI. *P<0.01 compared with CD; † P<0.05 compared with WD.

Fig. 2. Western Diet (WD) induced cardiac hypertrophy is prevented by xanthine oxidase inhibition

(A) Representative images of myocardial immunostaining for hypertrophy with quantitative analysis of the cardiomyocyte sizes below (B) Phosphorylation (p) of S6K in left ventricular tissues using western-blot with representative analysis below or the ratio of (p) S6K to total. *P<0.05 compared with control diet (CD); † P<0.05 compared with WD.

Fig. 3. Western Diet (WD) induced cardiac fibrosis is prevented by xanthine oxidase inhibition

(A) Representative images of left ventricular immunostaining for interstitial fibrosis using picrosirius red with quantification of interstitial collagen deposition by average gray scale intensities below. (B) Representative images immunostaining for Collagen-I with corresponding measures of average gray scale intensities below. Scale bar = 50 μm. (C) Representative blots of TGF-β and phosphorylation of Smad 2/3 in left ventricle tissues by using western-blot with corresponding quantitative analysis to the right. (D) Gelatin zymography analysis of expression of MMP-9 expression in LV tissue *P<0.05 compared with control diet (CD); † P<0.05 compared with WD.

Fig. 4. Western Diet (WD) induced myocardial oxidative stress and M1 macrophage expression are ameliorated by xanthine oxidase inhibition

(A) Representative images of left ventricular sections stained for 3-nitrotyrosine (NT), a marker of oxidant stress from accumulation of oxidant peroxynitrite (ONOO−). (B) PCR expression of M1 macrophage CD11b expression. Allopurinol induced M2 macrophage marker IL10 and CD206 mRNA expression in WD fed mice by using real-time PCR. *P<0.05 compared with control diet (CD); † P<0.05 compared with WD.

Fig. 5. Ultrastructural observations of the myocardium utilizing transmission electron microscopy (TEM)

Note the excessive mitochondrial accumulation in the intermyofibrillar regions and the disorganization and thinning of sarcomeres in western diet (WD) as compared to the control diet (CD) and allopurinol treated controls (CD-Allo). Also, note the loss of lipid droplets (encircled) in the WD as compared to the CD and CD-Allo, which were restored with allopurinol treatment. Additionally, note that allopurinol treatment did not completely restore intermyofibrillar mitochondria to that of CD; however, allopurinol did partially restore sarcomeric disorganization and thinning. Magnification, ×800; scale bar, 2 μm.