Reactive oxygen species mitigate perturbations in coronary microvascular tone in exercising swine with multiple risk factors

Abstract

Abstract Background Multiple cardiovascular risk factors, such as diabetes mellitus (DM), chronic kidney disease (CKD) and dyslipidemia are known to induce inflammation and microvascular dysfunction contributing to impaired myocardial perfusion. We previously observed that a combination of DM, high fat diet (HFD) and CKD produced an increase in coronary microvascular tone in awake swine, resulting in perturbations in myocardial O2 balance. The increased microvascular tone was mediated by an impaired NO bioavailability and was accompanied by increased myocardial levels of reactive oxygen species (ROS) and increased circulating levels of endothelin (ET). Hypothesis: In the present study in swine, we tested the hypothesis that ROS scavenging and ET receptor blockade reduce coronary microvascular tone, improving myocardial O2 delivery and O2 balance in swine with DM+HFD+CKD. Methods DM (streptozotocin), HFD and CKD (renal artery embolization) were induced in 13 female swine (DM+HFD+CKD), while 11 healthy female swine on normal pig chow served as controls (Normal). After 6 months, the effects of ROS scavenging and ET receptor blockade on coronary microvascular tone were studied at rest and during graded treadmill exercise. Results 6 months of sustained hyperglycemia (18.1±1.0 in DM+HFD+CKD vs 8.5±0.6 mmol/l in Normal), hypercholesterolemia (12.3±2.0 vs 1.7±0.1 mmol/l) and renal dysfunction (plasma creatinine: 165±7 vs 119±3 µmol/l) were accompanied by systemic inflammation (TNF 52±5 vs 25±6 pg/ml), elevated ET plasma levels, (36±2 vs 29±2 pg/ml), and oxidative stress (myocardial PGF2a 12.9±0.8 vs 10.2±0.5 pg/mg protein, all P<0.05 by t-test). Surprisingly, in vivo ROS scavenging (TEMPOL+MPG) reduced myocardial O2 delivery (forcing an increased myocardial O2 extraction) in DM+HFD+CKD swine, indicative of a coronary microvascular constrictor response to ROS scavenging, implying a ROS-mediated vasodilator influence (Fig. A, B). In vitro experiments, using catalase in coronary small arteries, suggested a vasodilator role for hydrogen peroxide (H2O2) in DM+HFD+CKD but not in Normal swine. A switch from NO towards to H2O2 in the regulation of coronary microvascular tone was further supported by an increase in ceramide production (138±34 vs 45±4 nmol/ml, P<0.05) and increased activity of catalase in the myocardium (44±3 vs 31±4 nmol/min/mg, P<0.05) of DM+HFD+CKD vs Normal swine. Despite elevated ET plasma levels in DM+HFD+CKD swine, combined ETA/ETB receptor blockade with tezosentan did not affect myocardial O2 balance in either Normal or DM+HFD+CKD swine (Fig C, D). Conclusion In swine, 6 months exposure to multiple risk factors resulted in increased oxidative stress that paradoxically acted to mitigate perturbations in coronary microvascular tone via an H2O2-mediated coronary vasodilator influence. Despite an increase in circulating ET levels, we found no evidence for an increased ET-1 mediated coronary vasoconstrictor influence.