Xanthine oxidase inhibition alleviates the cardiac complications of insulin resistance: effect on low grade inflammation and the angiotensin system

Abstract

Background: We have previously shown that hyperuricemia plays an important role in the vascular complications of insulin resistance (IR). Here we investigated the effect of xanthine oxidase (XO) inhibition on the cardiac complications of IR.

Methods: IR was induced in rats by a high fructose high fat diet for 12 weeks. Allopurinol, a standard XO inhibitor, was administered in the last 4 weeks before cardiac hemodynamics and electrocardiography, serum glucose, insulin, tumor necrosis factor alpha (TNFα), 8-isoprostane, uric acid, lactate dehydrogenase (LDH) and XO activity were measured. Expression of cardiac angiotensin II (AngII) and angiotensin receptor 1 (AT1) were assessed by immunofluorescence.

Results: IR animals had significant hyperuricemia which was inhibited by allopurinol administration. IR was associated with impaired ventricular relaxation (reflected by a decreased diastolic pressure increment and prolonged diastolic duration) and XO inhibition greatly attenuated impaired relaxation. IR was accompanied by cardiac ischemia (reflected by increased QTc and T peak trend intervals) while XO inhibition alleviated the ECG abnormalities. When subjected to isoproterenol-induced ischemia, IR hearts were less resistant (reflected by larger ST height depression and higher LDH level) while XO inhibition alleviated the accompanying ischemia. In addition, XO inhibition prevented the elevation of serum 8-isoprostane and TNFα, and blocked elevated AngII and AT1 receptor expression in the heart tissue of IR animals. However, XO inhibition did not affect the developed hyperinsulinemia or dyslipidemia.

Conclusions: XO inhibition alleviates cardiac ischemia and impaired relaxation in IR through the inhibition of low grade inflammation and the angiotensin system.

Figure 1

Effect of allopurinol (Allo) administration (20 mg.kg ⁻¹ .day ⁻¹ ) in the last 4 weeks on serum levels of uric acid (a) and xanthine oxidase activity (b) in rats with high fructose high fat (for 12 weeks) -induced insulin resistance (IR). Data are presented as mean ± standard error of 8 animals in each group. ^*P < 0.05, compared with the corresponding control group values; ^#P < 0.05, ^##P < 0.01, compared with the corresponding IR group values; by one way ANOVA and Newman Keuls’ post hoc test.

Figure 2

Effect of xanthine oxidase inhibition by daily oral administration of allopurinol (20 mg.kg ⁻¹ , last 4 weeks) on the slope of cardiac diastolic pressure decrement (a), diastolic duration (b) and end diastolic pressure (c) in rats with high fructose high fat (for 12 weeks) -induced insulin resistance (IR). Data are presented as mean ± standard error of 8 animals in each group. ^*P < 0.05, compared with the corresponding control group values; ^#P < 0.05 compared with the corresponding IR group values; by one way ANOVA and Newman Keuls’ post hoc test.

Figure 3

Effect of xanthine oxidase inhibition by daily oral administration of allopurinol (20 mg.kg ⁻¹ , last 4 weeks) on the slope of electrocardiograph QT (a), JT (b) and T peak trend (c) intervals in rats with high fructose high fat (for 12 weeks) induced insulin resistance (IR). Data are presented as mean ± standard error of 8 animals in each group. ^*P < 0.05, compared with the corresponding control group values; ^#P < 0.05compared with the corresponding IR group values; by one way ANOVA and Newman Keuls’ post hoc test.

Figure 4

Effect of xanthine oxidase inhibition by daily oral administration of allopurinol (20 mg.kg ⁻¹ , last 4 weeks) on the ST height depression (a) and serum lactate dehydrogenase level (b) following isoproterenol-induced acute cardiac ischemia in rats with high fructose high fat (for 12 weeks) induced insulin resistance (IR). Data are presented as mean ± standard error of 8 animals in each group. ^*P < 0.05, ^**P < 0.01, compared with the corresponding control group values; ^#P < 0.05 compared with the corresponding IR group values; by one way ANOVA and Newman Keuls’ post hoc test.

Figure 5

Effect of xanthine oxidase inhibition by daily oral administration of allopurinol (20 mg.kg ⁻¹ , last 4 weeks) on serum levels of TNFα (a), 8-isoprostane (b) and adiponectin (c) in rats with high fructose high fat (for 12 weeks) induced insulin resistance (IR). Data are presented as mean ± standard error of 8 animals in each group. ^*P < 0.05, compared with the corresponding control group values; ^#P < 0.05 compared with the corresponding IR group values; by one way ANOVA and Newman Keuls’ post hoc test.

Figure 6

Effect of xanthine oxidase inhibition by daily oral administration of allopurinol (20 mg.kg ⁻¹ , last 4 weeks) on 4-hydroxy-2-noneal Michael Adducts (4HNE), angiotensin II (AngII) and angiotensin receptor type 1 (AT ₁ ) immunofluorescence in heart (a, c and e respectively) and coronary artery (b, d and f respectively) sections from rats with high fructose high fat (for 12 weeks) induced insulin resistance (IR). Data are presented as mean ± standard error of 8 animals in each group. ^*P < 0.05, compared with the corresponding control group values; ^#P < 0.05 compared with the corresponding IR group values; by one way ANOVA and Newman Keuls’ post hoc test. Micrographs at the top are representative fluorescence images of heart and coronary artery cross sections immunofluorescence stained by 4HNE, AngII or AT₁ antibodies followed by Alexa fluor conjugated secondary antibodies.