Rachida Essalihi

A new model of isolated systolic hypertension induced by chronic warfarin and vitamin K1 treatment

BACKGROUND Isolated systolic hypertension is the predominant form of hypertension in the elderly population. Reduction of arterial compliance appears to contribute to the elevation of pulse pressure (PP) and among potential mechanisms, gradual vascular calcification, fragmentation of elastic lamellae, and augmentation of rigid component like collagen could contribute to increase aortic stiffening. Few experimental models of the disease are currently available. METHODS To induce large artery calcification, rats were treated with warfarin and vitamin K(1) (WK) for 4 and 8 weeks, to inhibit the maturation of matrix Gla protein. The impact of chronic PP elevation was determined on large artery and cardiac remodeling and on aortic endothelial function. RESULTS The WK treatment led to aortic medial calcification and a proportional elevation of PP, attributable mainly to a selective elevation of systolic blood pressure. The chronic treatment also increased collagen, whereas elastin decreased in the aorta. Pulse wave velocity, an index of aortic stiffening, increased in rats treated with WK. However, indices of left ventricular and aortic hypertrophy and remodeling remained normal. In addition, the WK treatment did not modify the vasoconstriction to norepinephrine and endothelin-1, and the vasodilatory response to acetylcholine and sodium nitroprusside. CONCLUSIONS Chronic treatment with WK represents a new model of isolated systolic hypertension with several characteristics of the human disease. The relative ease to induce calcification in this model may help to foster more fundamental research, which is lacking in this type of hypertension.

Pharmacological prevention and regression of arterial remodeling in a rat model of isolated systolic hypertension.

Objectives and design Isolated systolic hypertension (ISH) is the predominant form of hypertension in the elderly population and drug treatment is unsatisfactory. We compared the efficacy of an endothelin-receptor antagonist (darusentan), an angiotensin-receptor blocker (irbesartan) and a thiazide diuretic (hydrochlorothiazide, HCTZ) to prevent and regress pulse pressure (PP) elevation and remodeling of large and small arteries, in a rat model of ISH obtained by the chronic administration of warfarin and vitamin K1 (WK). Methods and results Warfarin and vitamin K1 treatment for 4 or 8 weeks led to an elevation of PP, associated with increases in aortic calcium deposition and the ratio of collagen to elastin (C/E). Despite these changes in the composition of the aortic wall, the global structure of the aorta was unchanged. In contrast, an outward hypertrophic remodeling was observed in the middle cerebral artery. An early treatment with all drugs (darusentan, irbesartan, HCTZ) prevented PP elevation, changes of aortic media composition and the development of vascular remodeling. However, after 4 weeks of ISH, only darusentan and irbesartan reduced PP when administered from week 4 to 8. Darusentan was the most effective to regress existent aortic calcification, while only irbesartan reversed small artery hypertrophic remodeling. Conclusions During the development of ISH, drug treatment appears more beneficial when started early. Indeed, the three agents prevented PP elevation, aortic calcification and C/E increase in the aorta, and hypertrophy in small arteries. In contrast, once the disease is established, endothelin appears crucial in the maintenance of aortic calcification, while angiotensin II sustains small artery hypertrophy.

Regression of Medial Elastocalcinosis in Rat Aorta A New Vascular Function for Carbonic Anhydrase

Background—We sought to determine whether carbonic anhydrase (CA), which plays an important role in bone resorption, contributes to vascular mineral loss induced by an endothelin receptor antagonist. Methods and Results—Wistar rats were compared with rats receiving warfarin and vitamin K1 (WVK) for 8 weeks alone or in association with the endothelin receptor antagonist darusentan (30 mg/kg per day), the CA inhibitor acetazolamide (100 mg/kg per day), or both for the last 4 weeks. Rats were also treated with WVK for 5 or 6 weeks, and darusentan was added for the last week or last 2 weeks of treatment, respectively. Treatment with WVK produced medial elastocalcinosis in the aorta and carotid arteries. Immunohistochemistry revealed that CA II was already abundant in the adventitia and in calcified areas of aortic sections from WVK-treated rats. Darusentan did not significantly modify its abundance or distribution. In contrast, CA IV immunostaining, which was weak in WVK-treated rats, became apparent after 1 week of darusentan treatment and declined toward basal levels thereafter. These findings were confirmed by a parallel increase in CA IV protein abundance and activity in the aorta. The mineral loss induced by darusentan was blunted by acetazolamide treatment, confirming the functional relevance of the biochemical findings. Moreover, CA IV immunostaining was enhanced much later in the carotids, where darusentan did not cause regression of elastocalcinosis. Conclusions—Vascular mineral loss induced by the blockade of endothelin receptors seems dependent on the activation of membrane-bound CA IV, suggesting that mineral loss may proceed via local changes in pH similar to that seen in bone resorption.

Phenotypic modulation of vascular smooth muscle cells during medial arterial calcification: a role for endothelin?

We have previously shown that an endothelin receptor antagonist can regress medial arterial calcification in a rat model. The aim of this study was to characterize the phenotypic changes of vascular smooth muscle cells during calcification and mineral loss, in order to understand better the underlying mechanisms. Control Wistar rats were compared with rats treated only with warfarin/ vitamin K1 (15 mg/kg per day) for 8 weeks, or in combination with darusentan (30 mg/kg per day) for the final 4 weeks. Vascular smooth muscle cell, bone cell and macrophage phenotypes were evaluated by the local expression of α-actin, tartrate-resistant acid phosphatase and ED-1, respectively. Proteins involved in the modulation of bone resorption like osteopontin and osteoprotegerin were also evaluated by immunohistochemistry. The warfarin/vitamin K1 treatment increased medial arterial calcification ninefold (P < 0.05). At sites of calcification, there was a decrease in α-actin localization, and an appearance of osteopontin immunostaining. Histochemical and immunostaining for osteoclast and macrophage markers, as well as for osteoprotegerin, were negative. Although the extent of calcification foci was reduced by darusentan, protein localization in the calcified areas was not modified. Thus, the development of medial arterial calcification produces a phenotypic change in vascular smooth muscle cells that does not appear to be normalized in regions remaining calcified during mineral loss.

Distinct effects of amlodipine treatment on vascular elastocalcinosis and stiffness in a rat model of isolated systolic hypertension

Objective Medial elastocalcinosis (MEC) contributes to the development of large artery stiffness and isolated systolic hypertension. Since endothelin receptor antagonists can prevent and regress elastocalcinosis, our aim was to determine whether amlodipine, a calcium channel blocker that inhibits endothelin signaling, could likewise influence MEC, or reduce pressure mainly through its vasorelaxing properties. Methods Control male Wistar rats were compared with rats receiving warfarin (20 mg/kg per day) with vitamin K1 (15 mg/kg per day) alone (WVK) or in association with amlodipine (15 mg/kg per day) for 4 weeks or during the last week or last 4 weeks of an 8-week WVK treatment (two regression groups). Results Inactivation of matrix Gla protein by WVK for 4 or 8 weeks increased the calcium content 10-fold in the aorta, inducing a significant elevation of pulse wave velocity and pulse pressure by selective augmentation of systolic blood pressure. Amlodipine prevented aortic MEC, pulse wave velocity and pulse pressure elevation, but reversed only MEC and pulse pressure when administered for 4 weeks. One week of amlodipine administered after 7 weeks of WVK partially decreased pulse pressure without modifying aortic MEC. Amlodipine did not reduce the fibrosis associated with calcified areas in the WVK model during the regression protocols. Conclusion The clinical efficacy of amlodipine in improving hemodynamic variables and reducing cardiovascular events in isolated systolic hypertension could be explained by its beneficial effect on vascular calcification. Amlodipines lack of effect on pulse wave velocity and collagen deposition, however, suggests that it may reduce pulse pressure by means other than improving arterial stiffness.

Arterial Stiffness As A Therapeutic Target For Isolated Systolic Hypertension: Focus on Vascular Calcification and Fibrosis

Isolated systolic hypertension is the most common form of essential hypertension in patients over 65 years old and is not well controlled by current antihypertensive therapies. Current antihypertensive pharmacology is focused on reducing peripheral resistance and ventricular ejection. However, the increase of systolic blood pressure is mainly a consequence of large artery stiffening. This pathological process seems to be the result of medial arterial calcification (or elastocalcinosis), elastin degradation, extracellular matrix fibrosis and endothelial dysfunction. As a unifying hypothesis, we propose that initial extracellular calcification could promote extracellular matrix-cellular interactions by involving metalloproteinase matrix degradation, leading to the liberation of embedded transforming growth factor-β. This growth factor could promote a cascade of events involving vascular smooth muscle cells that adopt an osteogenic phenotype and express a different set of proteins, such as endothelin, that appear to play a central role in medial calcification and fibrosis. This review highlights the evidence supporting the hypothesis. It also presents the effects of current drugs on calcification and/or fibrosis in experimental model of isolated systolic hypertension to illustrate where we stand in our efforts to modify the process of arterial stiffening.