Anthony Johns

Endothelin converting enzyme

The putative endothelin‐converting enzyme (ECE) has been the focus of intense research, both within academia and the pharmaceutical industry. Interest in ECE stems mainly from the hypothesis that development of inhibitors of ECE will provide an effective means of preventing production of endothelin in circumstances where it may play a pathogenic role. Both an aspartic and a metalloprotease have been identified that have characteristics of this putative enzyme. Evidence suggests that the metalloprotease, which is inhibited by phosphoramidon, may be the physiologically relevant converting enzyme. However, it remains to be demonstrated conclusively that any inhibitor of an ECE activity directly alters endogenous endothelin production and/or the pathogenesis of a disease condition in which endothelin is thought to play a primary role.— Opgenorth, T. J.; Wu‐Wong, J. R.; Shiosaki, K. Endothelin‐converting enzymes. FASEB J. 6: 2653‐2659; 1992.

Mechanoreception by the endothelium: mediators and mechanisms of pressure- and flow-induced vascular responses.

Mechanoreception, a widely distributed sensory modality, has been shown to be present in certain blood vessels. Changes in physical forces, like sudden increase of transmural pressure or flow velocity (shear stress), trigger changes in blood vessel diameter; the former reduces it while the latter increases vessel caliber. These changes in diameter, which are the result of contraction and relaxation of vascular smooth muscle in the blood vessel media, can serve the purpose of physiological regulation of blood flow (autoregulation) and protection of the intima against damages from high shear forces. The precise location of mechanosensor(s) and the mechanism of mechanoreception and signal transduction are poorly understood. Accumulating evidence suggests that the endothelium may be a site of mechanoreception and that changes in the synthesis/release of endothelium-derived relaxing (EDRF, EDHF, PGI2) and contracting factors (EDCF) result in altered vascular smooth muscle tone and vessel caliber. Increased shear stress stimulates the release of EDRF and PGI2 probably via activation of a K+ channel (inward rectifier) in endothelial cell membrane. Endothelium-dependent vascular contraction evoked by increased transmural pressure may be the result of (1) reduced release of EDRF (canine carotid artery) and (2) stimulation of the release of a still unidentified EDCF(s) (feline cerebral artery). Thus the endothelium can serve as pressure and flow sensor and is capable of transducing changes in mechanical forces into changes of vascular smooth muscle tone by modulating the release of endothelium-derived vasoactive factors. The physiological importance of the mechanoreception by endothelial cells in the intact circulation remains to be determined.

Effect of estrogen on endothelial function and angiogenesis

Animal studies evaluating gender difference, the effects of gonadectomy and estrogen replacement and clinical studies in post-menopausal women with and without estrogen replacement therapy (ERT) proved that estrogen exerts significant benefits on the cardiovascular system. Since effects on the plasma lipoprotein profile is responsible for only approximately 25-40% of the cardiovascular protection exerted by estrogens, it is postulated that direct effects of estrogen on the vascular wall must play an important role. Indeed, experimental and clinical evidence accumulated over the past decade, and reviewed briefly here, indicate that at least a part of cardiovascular benefits of 17 beta-estradiol can be attributed to the direct effect of the ovarian sex steroid hormone on vascular endothelial cells. Maintenance and upregulation of endothelial nitric oxide production and suppression of EDCF generation by 17 beta-estradiol may play an important role in preventing or reversing endothelial dysfunction, associated with atherosclerosis, hypertension and other cardiovascular diseases. Stimulation of angiogenesis (especially collateral vessel formation in ischemic tissues) by the ovarian steroid hormone could be beneficial in coronary artery disease, peripheral vascular disease, cerebral ischemia (stroke) and congestive heart failure. Despite these indisputable beneficial effects, several key questions remain to be answered in the future, including the better understanding of the apparently opposite effects of estrogen on prevention of cardiovascular disease vs. treatment of existing disease.

Role of estrogen receptors in the vascular system

Estrogens have been shown to exert significant benefits on the cardiovascular system both in animals and in postmenopausal women. However, the exact mechanism of these effects are, for the most part, still unknown. The goal of this paper is to evaluate the role of estrogen receptors (ER) in mediating some of the cardiovascular beneficial actions of 17 beta-estradiol (E2). This analysis was possible because of the availability of ER alpha (ER alpha KO) and ER beta-deficient (ER beta KO) mice, and access to a patient with ER alpha-deficiency. Experimental results obtained in our laboratory demonstrated that the ER alpha subtype mediates E2-induced increase in endothelial nitric oxide production and facilitation of fibroblast growth factor-elicited angiogenesis in vivo. Others have confirmed these findings. Experiments using a novel ER-antagonist and ApoExER alpha double-knockout mice proved that ER alpha mediates some of the antiatherosclerotic effects of E2 as well. In contrast, both the ER alpha and ER beta subtypes appear to mediate the beneficial effects of E2 on vascular smooth muscle proliferation after vessel injury. The young male patient with ER alpha-deficiency exhibited reduced endothelial nitric oxide production and premature coronary arteriosclerosis. These studies in mice and a male human subject suggest that absence of functional ER may represent a novel risk factor for cardiovascular diseases.

Endothelin-1 stimulates phosphatidylinositol hydrolysis and calcium uptake in isolated canine coronary arteries.

Summary The effects of synthetic endothelin-1 (ET-1) (10–103

A model of the acid sphingomyelinase phosphoesterase domain based on its remote structural homolog purple acid phosphatase

10–7 M) on isometric force, 45Ca2+ uptake, and Phosphatidylinositol (PI) hydrolysis were determined in isolated canine coronary artery rings. ET-1 caused contraction and stimulated 45Ca2+ uptake and PI hydrolysis (determined as inositol monophosphate accumulation) in a concentration-dependent manner with ECjo values of 6.3

A novel high-throughput screening format to identify inhibitors of secreted acid sphingomyelinase.

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