Tamás Radovits

BACKGROUND: The sodium-glucose cotransporter-2 (SGLT2) inhibitor canagliflozin has been shown to reduce major cardiovascular events in type 2 diabetic patients, with a pronounced decrease in hospitalization for heart failure (HF) especially in those with HF at baseline. These might indicate a potent direct cardioprotective effect, which is currently incompletely understood. We sought to characterize the cardiovascular effects of acute canagliflozin treatment in healthy and infarcted rat hearts. METHODS: Non-diabetic male rats were subjected to sham operation or coronary artery occlusion for 30 min, followed by 120 min reperfusion in vivo. Vehicle or canagliflozin (3 µg/kg bodyweight) was administered as an intravenous bolus 5 min after the onset of ischemia. Rats underwent either infarct size determination with serum troponin-T measurement, or functional assessment using left ventricular (LV) pressure-volume analysis. Protein, mRNA expressions, and 4-hydroxynonenal (HNE) content of myocardial samples from sham-operated and infarcted rats were investigated. In vitro organ bath experiments with aortic rings from healthy rats were performed to characterize a possible effect of canagliflozin on vascular function. RESULTS: Acute treatment with canagliflozin significantly reduced myocardial infarct size compared to vehicle (42.5 ± 2.9% vs. 59.3 ± 4.2%, P = 0.006), as well as serum troponin-T levels. Canagliflozin therapy alleviated LV systolic and diastolic dysfunction following myocardial ischemia-reperfusion injury (IRI), and preserved LV mechanoenergetics. Western blot analysis revealed an increased phosphorylation of adenosine monophosphate-activated protein kinase (AMPK) and endothelial nitric-oxide synthase (eNOS), which were not disease-specific effects. Canagliflozin elevated the phosphorylation of Akt only in infarcted hearts. Furthermore, canagliflozin reduced the expression of apoptotic markers (Bax/Bcl-2 ratio) and that of genes related to myocardial nitro-oxidative stress. In addition, treated hearts showed significantly lower HNE positivity. Organ bath experiments with aortic rings revealed that preincubation with canagliflozin significantly enhanced endothelium-dependent vasodilation in vitro, which might explain the slight LV afterload reducing effect of canagliflozin in healthy rats in vivo. CONCLUSIONS: Acute intravenous administration of canagliflozin after the onset of ischemia protects against myocardial IRI. The medication enhances endothelium dependent vasodilation independently of antidiabetic action. These findings might further contribute to our understanding of the cardiovascular protective effects of canagliflozin reported in clinical trials.

Although incidence and prevalence of prediabetes are increasing, little is known about its cardiac effects. Therefore, our aim was to investigate the effect of prediabetes on cardiac function and to characterize parameters and pathways associated with deteriorated cardiac performance. Long-Evans rats were fed with either control or high-fat chow for 21 wk and treated with a single low dose (20 mg/kg) of streptozotocin at week 4. High-fat and streptozotocin treatment induced prediabetes as characterized by slightly elevated fasting blood glucose, impaired glucose and insulin tolerance, increased visceral adipose tissue and plasma leptin levels, as well as sensory neuropathy. In prediabetic animals, a mild diastolic dysfunction was observed, the number of myocardial lipid droplets increased, and left ventricular mass and wall thickness were elevated; however, no molecular sign of fibrosis or cardiac hypertrophy was shown. In prediabetes, production of reactive oxygen species was elevated in subsarcolemmal mitochondria. Expression of mitofusin-2 was increased, while the phosphorylation of phospholamban and expression of Bcl-2/adenovirus E1B 19-kDa protein-interacting protein 3 (BNIP3, a marker of mitophagy) decreased. However, expression of other markers of cardiac auto- and mitophagy, mitochondrial dynamics, inflammation, heat shock proteins, Ca 2+ /calmodulin-dependent protein kinase II, mammalian target of rapamycin, or apoptotic pathways were unchanged in prediabetes. This is the first comprehensive analysis of cardiac effects of prediabetes indicating that mild diastolic dysfunction and cardiac hypertrophy are multifactorial phenomena that are associated with early changes in mitophagy, cardiac lipid accumulation, and elevated oxidative stress and that prediabetes-induced oxidative stress originates from the subsarcolemmal mitochondria. Listen to this article's corresponding podcast http://ajpheart.podbean.com/e/myocardial-dysfunction-in-prediabetes/ .

BACKGROUND: The role of the nitric oxide/cGMP/cGMP-dependent protein kinase G pathway in myocardial protection and preconditioning has been the object of intensive investigations. The novel soluble guanylate cyclase activator cinaciguat has been reported to elevate intracellular [cGMP] and activate the nitric oxide/cGMP/cGMP-dependent protein kinase G pathway in vivo. We investigated the effects of cinaciguat on myocardial infarction induced by isoproterenol in rats. METHODS AND RESULTS: Rats were treated orally twice a day for 4 days with vehicle or cinaciguat (10 mg/kg). Isoproterenol (85 mg/kg) was injected subcutaneously 2 days after the first treatment at an interval of 24 hours for 2 days to produce myocardial infarction. After 17 hours, histopathological observations and left ventricular pressure-volume analysis to assess cardiac function with a Millar microtip pressure-volume conductance catheter were performed, and levels of biochemicals of the heart tissues were measured. Gene expression analysis was performed by quantitative real-time polymerase chain reaction. Isolated canine coronary arterial rings exposed to peroxynitrite were investigated for vasomotor function, and immunohistochemistry was performed for cGMP and nitrotyrosine. The present results show that cinaciguat treatment improves histopathological lesions, improves cardiac performance, improves impaired cardiac relaxation, reduces oxidative stress, ameliorates intracellular enzyme release, and decreases cyclooxygenase 2, transforming growth factor-beta, and beta-actin mRNA expression in experimentally induced myocardial infarction in rats. In vitro exposure of coronary arteries to peroxynitrite resulted in an impairment of endothelium-dependent vasorelaxation, increased nitro-oxidative stress, and reduced intracellular cGMP levels, which were all improved by cinaciguat. A cardioprotective effect of postischemic cinaciguat treatment was shown in a canine model of global ischemia/reperfusion. CONCLUSIONS: Pharmacological soluble guanylate cyclase activation could be a novel approach for the prevention and treatment of ischemic heart disease.