Reactive Oxygen Species Mitigate Perturbations in Coronary Microvascular Tone in Exercising Swine with Multiple Risk Factors

Abstract

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 O 2 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). In the present study in swine, we tested the hypothesis that ROS scavenging and ET receptor blockade reduce coronary microvascular tone, improving myocardial O 2 delivery and O 2 balance in swine with DM+HFD+CKD. 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. 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 PGF2α 12.9±0.8 vs 10.2±0.5 pg/mg protein, all P<0.05 by t-test). Surprisingly, i n vivo ROS scavenging (TEMPOL+MPG) reduced myocardial O 2 delivery (forcing an increased myocardial O 2 extraction) in DM+HFD+CKD swine, indicative of a coronary microvascular constrictor response to ROS scavenging, implying a ROS-mediated vasodilator influence. In vitro experiments, using catalase in coronary small arteries, suggested a vasodilator role for hydrogen peroxide (H 2 O 2 ) in DM+HFD+CKD but not in Normal swine. A switch from NO towards to H 2 O 2 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 ET A /ET B receptor blockade with tezosentan did not affect myocardial O 2 balance in either Normal or DM+HFD+CKD swine. 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 H 2 O 2 -mediated coronary vasodilator influence. Despite an increase in circulating ET levels, we found no evidence for an increased ET mediated coronary vasoconstrictor influence. Funding: Grants 2017B018 ARENA-PRIME and 2020B008 RECONNEXT This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.