Ifetroban reduces coronary artery dysfunction in a mouse model of Duchenne muscular dystrophy

Dilated cardiomyopathy contributes to morbidity and mortality in Duchenne muscular dystrophy (DMD), an inheritable muscle-wasting disease caused by a mutation in the dystrophin gene. Preclinical studies in mouse models of muscular dystrophy have demonstrated reduced cardiomyopathy and improved cardiac function following oral treatment with the potent and selective thromboxane A₂/prostanoid receptor (TPr) antagonist ifetroban. Furthermore, a phase 2 clinical trial (NCT03340675, Cumberland Pharmaceuticals) is currently recruiting subjects to determine whether ifetroban can improve cardiac function in patients with DMD. Although TPr is a promising therapeutic target for the treatment of dilated cardiomyopathy in DMD, little is known about TPr function in coronary arteries that perfuse blood through the cardiac tissue. In the current study, isolated coronary arteries from young (∼3-5 mo) and aged (∼9-12 mo) mdx mice, a widely used mouse model of DMD, and age-matched controls were examined using wire myography. Vasoconstriction to increasing concentrations of TPr agonist U-46619 (U4) was enhanced in young mdx mice versus controls. In addition, young mdx mice displayed a significant attenuation in endothelial cell-mediated vasodilation to increasing concentrations of the muscarinic agonist acetylcholine (ACh). Since TPr activation was enhanced in young mdx mice, U4-mediated vasoconstriction was measured in the absence and the presence of ifetroban. Ifetroban reduced U4-mediated vasoconstriction in young mdx mice and both aged mdx and control mice. Overall, our data demonstrate enhanced coronary arterial vasoconstriction to TPr activation in young mdx mice, a phenotype that could be reversed with ifetroban. These data could have important therapeutic implications for improving cardiovascular function in DMD.NEW & NOTEWORTHY This investigation revealed 1) impaired acetylcholine-mediated vasodilation, 2) increased U-46619-mediated vasoconstriction, and 3) reversal of the increase in U-46619-mediated vasoconstriction by the thromboxane A₂/prostanoid receptor (TPr) antagonist ifetroban in left anterior descending coronary arteries isolated from young mdx mice, a model of Duchenne muscular dystrophy (DMD). Ifetroban has been used in preclinical studies to demonstrate improved cardiac function in mouse models of muscular dystrophy and is currently being investigated in a phase 2 clinical trial in patients with DMD. The current study supports the role of ifetroban in improving coronary artery function in preclinical DMD models, which may contribute to improved cardiovascular health.

TRPM4 inhibitor 9-phenanthrol activates endothelial cell intermediate conductance calcium-activated potassium channels in rat isolated mesenteric artery

BACKGROUND AND PURPOSE

Smooth muscle transient receptor potential melastatin 4 (TRPM4) channels play a fundamental role in the development of the myogenic arterial constriction that is necessary for blood flow autoregulation. As TRPM4 channels are present throughout the vasculature, we investigated their potential role in non-myogenic resistance arteries using the TRPM4 inhibitor 9-phenanthrol.

EXPERIMENTAL APPROACH

Pressure and wire myography were used to assess the reactivity of rat arteries, the latter in combination with measurements of smooth muscle membrane potential. Immunohistochemistry (IHC) and endothelial cell (EC) calcium changes were assessed in pressurized vessels and patch clamp measurements made in isolated ECs.

KEY RESULTS

The TRPM4 inhibitor 9-phenanthrol reversibly hyperpolarized mesenteric arteries to circa EK and blocked α1 -adrenoceptor-mediated vasoconstriction. Hyperpolarization was abolished and vasoconstriction re-established by damaging the endothelium. In mesenteric and cerebral artery smooth muscle, 9-phenanthrol hyperpolarization was effectively blocked by the KCa 3.1 inhibitor TRAM-34. 9-Phenanthrol did not increase mesenteric EC [Ca(2+)]i , and Na(+) substitution with N-methyl-D-glucamine only increased the muscle resting potential by 10 mV. Immunolabelling for TRPM4 was restricted to the endothelium and perivascular tissue.

CONCLUSIONS AND IMPLICATIONS

These data reveal a previously unrecognized action of the TRPM4 inhibitor 9-phenanthrol - the ability to act as an activator of EC KCa 3.1 channels. They do not indicate a functionally important role for TRPM4 channels in the reactivity of non-myogenic mesenteric arteries.

Regulation of blood flow in the microcirculation: role of conducted vasodilation

This review is concerned with understanding how vasodilation initiated from local sites in the tissue can spread to encompass multiple branches of the resistance vasculature. Within tissues, arteriolar networks control the distribution and magnitude of capillary perfusion. Vasodilation arising from the microcirculation can 'ascend' into feed arteries that control blood flow into arteriolar networks. Thus distal segments of the resistance network signal proximal segments to dilate and thereby increase total oxygen supply to parenchymal cells. August Krogh proposed that innervation of capillaries provided the mechanism for a spreading vasodilatory response. With greater understanding of the ultrastructural organization of resistance networks, an alternative explanation has emerged: Electrical signalling from cell to cell along the vessel wall through gap junctions. Hyperpolarization originates from ion channel activation at the site of stimulation with the endothelium serving as the predominant cellular pathway for signal conduction along the vessel wall. As hyperpolarization travels, it is transmitted into surrounding smooth muscle cells through myoendothelial coupling to promote relaxation. Conducted vasodilation (CVD) encompasses greater distances than can be explained by passive decay and understanding such behaviour is the focus of current research efforts. In the context of athletic performance, the ability of vasodilation to ascend into feed arteries is essential to achieving peak levels of muscle blood flow. CVD is tempered by sympathetic neuroeffector signalling when governing muscle blood flow at rest and during exercise. Impairment of conduction during ageing and in diseased states can limit physical work capacity by restricting muscle blood flow.