Pascal Laurant

T Regulatory Lymphocytes Prevent Angiotensin II–Induced Hypertension and Vascular Injury

Angiotensin (Ang) II induces hypertension by mechanisms mediated in part by adaptive immunity and T effector lymphocytes. T regulatory lymphocytes (Tregs) suppress T effector lymphocytes. We questioned whether Treg adoptive transfer would blunt Ang II–induced hypertension and vascular injury. Ten- to 12-week–old male C57BL/6 mice were injected IV with 3×105 Treg (CD4+CD25+) or T effector (CD4+CD25−) cells, 3 times at 2-week intervals, and then infused or not with Ang II (1 &mgr;g/kg per minute, SC) for 14 days. Ang II increased systolic blood pressure by 43 mm Hg (P<0.05), NADPH oxidase activity 1.5-fold in aorta and 1.8-fold in the heart (P<0.05), impaired acetylcholine vasodilatory responses by 70% compared with control (P<0.05), and increased vascular stiffness (P<0.001), mesenteric artery vascular cell adhesion molecule expression (2-fold; P<0.05), and aortic macrophage and T-cell infiltration (P<0.001). All of the above were prevented by Treg but not T effector adoptive transfer. Ang II caused a 43% decrease in Foxp3+ cells in the renal cortex, whereas Treg adoptive transfer increased Foxp3+ cells 2-fold compared with control. Thus, Tregs suppress Ang II–mediated vascular injury in part through anti-inflammatory actions. Immune mechanisms modulate Ang II–induced blood pressure elevation, vascular oxidative stress, inflammation, and endothelial dysfunction.

Physiological and pathophysiological role of magnesium in the cardiovascular system: implications in hypertension

Attention is growing for a potential role of magnesium in the pathoetiology of cardiovascular disease. Magnesium modulates mechanical, electrical and structural functions of cardiac and vascular cells, and small changes in extracellular magnesium levels and/or intracellular free magnesium concentration may have significant effects on cardiac excitability and on vascular tone, contractility and reactivity. Thus, magnesium may be important in the physiological regulation of blood pressure whereas alterations in cellular magnesium metabolism could contribute to the pathogenesis of blood pressure elevation. Although most epidemiological and experimental studies support a pathological role for magnesium in the etiology and development of hypertension, data from clinical studies have been less convincing. Furthermore, the therapeutic value of magnesium in the management of essential hypertension is unclear. The present review discusses the molecular, biochemical, physiological and pharmacological roles of magnesium in the regulation of vascular function and blood pressure and introduces novel concepts relating to magnesium as a second messenger in intracellular signaling in cardiovascular cells. In addition, alterations in magnesium regulation in experimental and clinical hypertension and the potential antihypertensive therapeutic effects of magnesium are addressed.

T Regulatory Lymphocytes Prevent Aldosterone-Induced Vascular Injury

Aldosterone mediates actions of the renin-angiotensin-aldosterone system inducing hypertension, oxidative stress, and vascular inflammation. Recently, we showed that angiotensin II–induced hypertension and vascular damage are mediated at least in part by macrophages and T-helper effector lymphocytes. Adoptive transfer of suppressor T-regulatory lymphocytes (Tregs) prevented angiotensin II action. We hypothesized that Treg adoptive transfer would blunt aldosterone-induced hypertension and vascular damage. Thirteen to 15-week–old male C57BL/6 mice were injected intravenously at 1-week intervals with 3×105 CD4+CD25+ cells (representing Treg) or control CD4+CD25− cells and then infused or not for 14 days with aldosterone (600 &mgr;g/kg per day, SC) while receiving 1% saline to drink. Aldosterone induced a small but sustained increase in blood pressure (P<0.001), decreased vasodilatory responses to acetylcholine by 66% (P<0.001), increased both media:lumen ratio (P<0.001) and media cross-sectional area of resistance arteries by 60% (P<0.05), and increased NADPH oxidase activity 2-fold in aorta (P<0.001), kidney and heart (P<0.05), and aortic superoxide production. As well, aldosterone enhanced aortic and renal cortex macrophage infiltration and aortic T-cell infiltration (all P<0.05), and tended to decrease Treg in the renal cortex. Treg adoptive transfer prevented all of the vascular and renal effects induced by aldosterone. Adoptive transfer of CD4+CD25− cells exacerbated aldosterone effects except endothelial dysfunction and increases in media:lumen ratio of resistance arteries. Thus, Tregs suppress aldosterone-mediated vascular injury, in part through effects on innate and adaptive immunity, suggesting that aldosterone-induced vascular damage could be prevented by an immunomodulatory approach.

Treatment with the arginase inhibitor Nω-hydroxy-nor-L-arginine improves vascular function and lowers blood pressure in adult spontaneously hypertensive rat

Objective High vascular arginase activity and subsequent reduction in vascular nitric oxide production were recently reported in animal models of hypertension. The present study investigated the effects of in-vivo arginase inhibition on blood pressure and vascular function in adult spontaneously hypertensive rats. Methods Ten-week-old spontaneously hypertensive rats and normotensive age-matched Wistar–Kyoto rats were treated with or without the selective arginase inhibitor Nω-hydroxy-nor-L-arginine for 3 weeks (10 or 40 mg/kg per day, intraperitoneally). Systolic blood pressure and cardiac rate were measured before and during treatment. Flow and pressure-dependent reactivity as well as remodeling of mesenteric arteries, acetylcholine-dependent vasodilation of aortic rings, cardiac hypertrophy, arginase activity and nitric oxide production were investigated in 13-week-old spontaneously hypertensive rats. Results In spontaneously hypertensive rats, Nω-hydroxy-nor-L-arginine treatment decreased arginase activity (30–40%), reduced blood pressure (∼35 mmHg) and improved the reactivity of mesenteric vessels. However, vascular and cardiac remodeling was not different between treated and untreated spontaneously hypertensive rats. In Wistar–Kyoto rats, Nω-hydroxy-nor-L-arginine did not affect blood pressure. Finally, arginase inhibition was associated with increased nitric oxide production. Consistent with this, the response of aortic rings to acetylcholine was fully restored by Nω-hydroxy-nor-L-arginine, and the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester significantly reduced the effect of Nω-hydroxy-nor-L-arginine on flow-dependent vasodilation. Conclusion Pharmacological inhibition of arginase in adult spontaneously hypertensive rats decreases blood pressure and improves the reactivity of resistance vessels. These data represent in-vivo argument in favor of selective arginase inhibition as a new therapeutic strategy against hypertension.

Effect of Pressurization on Mechanical Properties of Mesenteric Small Arteries from Spontaneously Hypertensive Rats

The mechanical properties of the wall of isolated perfused arterial segments of mesenteric small arteries from 17-week-old spontaneously hypertensive rats (SHR) and age-matched Wistar Kyoto rats (WKY) were investigated. Third-order branches of mesenteric arteries were mounted in a pressure myograph chamber and pressurized from 1 to 140 mm Hg. Under isobaric conditions, the outer diameter and the lumen of small arteries studied were smaller in SHR than in WKY, whereas media width, media cross-sectional area and media-lumen ratio were greater in SHR. Under passive conditions, the total change in internal and external diameter in response to increasing intravascular pressure was smaller in arteries from SHR. Incremental distensibility was significantly lower in arteries of SHR at intravascular pressures between 1 and 40 mm Hg, but was significantly greater between pressures of 40-100 mm Hg. Wall stress generated by intravascular pressure was significantly smaller in arteries from SHR. As a function of wall strain (under isometric conditions), stress and incremental elastic modulus were shifted to the left in SHR vessels. Under isobaric conditions or in relation to wall stress, the slope of elastic modulus was smaller in SHR. This decrease in elastic modulus may confer additional elasticity to the vascular wall of resistance arteries from SHR. The presence of a greater distensibility at physiological levels of intravascular pressure and decreased incremental elastic modulus indicates that the changes in the structure of small mesenteric arteries in SHR can be defined as the result of a combination of eutrophic and hypertrophic remodeling.

Exercise reverses metabolic syndrome in high-fat diet-induced obese rats.

PURPOSE Chronic consumption of a high-fat diet induces obesity. We investigated whether exercise would reverse the cardiometabolic disorders associated with obesity without it being necessary to change from a high- to normal-fat diet. METHODS Sprague-Dawley rats were placed on a high-fat (HFD) or control diet (CD) for 12 wk. HFD rats were then divided into four groups: sedentary HFD (HFD-S), exercise trained (motor treadmill for 12 wk) HFD (HFD-Ex), modified diet (HFD to CD; HF/CD-S), and exercise trained with modified diet (HF/CD-Ex). Cardiovascular risk parameters associated with metabolic syndrome were measured, and contents of aortic Akt, phospho-Akt at Ser (473), total endothelial nitric oxide synthase (eNOS), and phospho-eNOS at Ser (1177) were determined by Western blotting. RESULTS Chronic consumption of HFD induced a metabolic syndrome. Exercise and dietary modifications reduced adiposity, improved glucose and insulin levels and plasma lipid profile, and exerted an antihypertensive effect. Exercise was more effective than dietary modification in improving plasma levels of thiobarbituric acid-reacting substance and in correcting the endothelium-dependent relaxation to acetylcholine and insulin. Furthermore, independent of the diet used, exercise increased Akt and eNOS phosphorylation. CONCLUSIONS Metabolic syndrome induced by HFD is reversed by exercise and diet modification. It is demonstrated that exercise training induces these beneficial effects without the requirement for dietary modification, and these beneficial effects may be mediated by shear stress-induced Akt/eNOS pathway activation. Thus, exercise may be an effective strategy to reverse almost all the atherosclerotic risk factors linked to obesity, particularly in the vasculature.

Endothelin‐1‐induced contraction in isolated aortae from normotensive and DOCA‐salt hypertensive rats: effect of magnesium

1 The contractile responses to endothelin‐1 and the effect on these of various magnesium concentrations, were studied in isolated aortic rings from normotensive Sprague‐Dawley rats and deoxycorticosterone acetate‐salt (DOCA‐salt) hypertensive rats. 2 Contractions induced by endothelin‐1 were smaller in endothelium‐denuded aortae from DOCA‐salt hypertensive rats than in those from normotensive rats. The absence of calcium in the medium attenuated endothelin‐1‐induced contractions of aortae from both normotensive and DOCA‐salt rats, but the contraction was greater in aortae from DOCA‐salt hypertensive rats. Ryanodine (which inhibits the release of intracellular calcium) inhibited endothelin‐1‐induced contractions in aortae from DOCA‐salt hypertensive rats to a greater extent than in aortae from normotensive rats. 3 A high extracellular magnesium concentration (4.8 mM) attenuated endothelin‐1‐induced contractions in tissues from DOCA‐salt hypertensive rats but not in tissues from normotensive rats. In the absence of calcium, a high concentration of magnesium attenuated endothelin‐1‐induced contraction in aortae from both normotensive and hypertensive rats. In the presence of ryanodine, a high concentration of magnesium did not modify the contraction in preparations from either strain. 4 Absence of magnesium attenuated endothelin‐1‐induced contractions in aortae from both normotensive and DOCA‐salt hypertensive rats. In the absence of calcium, removal of magnesium totally inhibited endothelin‐1‐induced contraction in tissues from normotensive rats but had no effect in those from hypertensive rats. In the presence of ryanodine, the lack of magnesium inhibited endothelin‐1‐induced contractions in aortae from DOCA‐salt hypertensive rats but increased the sensitivity to endothelin‐1 of aortae from normotensive rats. 5 The presence of endothelium did not modify the effect of high magnesium on endothelin‐1‐induced contractions in aortae from normotensive and DOCA‐salt hypertensive rats. Conversely, the attenuating effect of magnesium removal on endothelin‐1‐induced contractions did not occur when endothelium was present. 6 In conclusion, endothelin‐1‐induced contraction was blunted in aortae from DOCA‐salt hypertensive rats. The blunted response was related to altered calcium utilization during contraction. Changes in extracellular magnesium concentration differentially alter endothelin‐1‐induced contraction in aortae from normotensive and hypertensive rats, possibly by interfering with calcium utilization during contraction. Magnesium may be required for the contractile response to endothelin‐1 and increasing magnesium may limit the vascular effects of endothelin‐1 in blood vessels from DOCA‐salt hypertensive rats.

Long-term exercise stabilizes atherosclerotic plaque in ApoE knockout mice.

PURPOSE Exercise is known to reduce cardiovascular mortality. However, the precise mechanisms are still unknown. Because atherosclerotic plaque destabilization and rupture leads to dramatic cardiovascular events, stabilization of plaque might be regarded as an important goal of an exercise preventive therapy. The present study examined the plaque-stabilizing effect of long-term exercise in experimental atherosclerosis using apolipoprotein E-deficient mice (ApoE(-/-)). METHODS ApoE(-/-) mice were subjected to 6 months of swimming exercise. A group of sedentary animals were used as controls. Morphometry and characteristics of atherosclerotic plaque stability were assessed in aortic sinus by immunohistochemistry. Aortic levels of total protein kinase Akt (protein kinase B), phosphorylated Akt at Ser(473) (p-Akt), total endothelial nitric oxide synthase (eNOS), and phosphorylated eNOS at Ser(1177) (p-eNOS) were assessed by Western blotting. RESULTS Exercised mice developed a more stable plaque phenotype as shown by decreased macrophage and increased smooth muscle cell content. Protein expressions of Akt, p-Akt, eNOS, and p-eNOS were not modulated by exercise. CONCLUSIONS Long-term exercise promotes plaque stability in ApoE(-/-) mice. The Akt-mediated eNOS phosphorylation pathway seems not to be the primary molecular mechanism.

Swimming Prevents Vulnerable Atherosclerotic Plaque Development in Hypertensive 2-Kidney, 1-Clip Mice by Modulating Angiotensin II Type 1 Receptor Expression Independently From Hemodynamic Changes

Exercise is known to reduce cardiovascular risk. However, its role on atherosclerotic plaque stabilization is unknown. Apolipoprotein E−/− mice with vulnerable (2-kidney, 1-clip: angiotensin [Ang] II–dependent hypertension model) or stable atherosclerotic plaques (1-kidney, 1-clip: Ang II–independent hypertension model and normotensive shams) were used for experiments. Mice swam regularly for 5 weeks and were compared with sedentary controls. Exercised 2-kidney, 1-clip mice developed significantly more stable plaques (thinner fibrous cap, decreased media degeneration, layering, macrophage content, and increased smooth muscle cells) than sedentary controls. Exercise did not affect blood pressure. Conversely, swimming significantly reduced aortic Ang II type 1 receptor mRNA levels, whereas Ang II type 2 receptor expression remained unaffected. Sympathetic tone also significantly diminished in exercised 2-kidney, 1-clip mice compared with sedentary ones; renin and aldosterone levels tended to increase. Ang II type 1 downregulation was not accompanied by improved endothelial function, and no difference in balance among T-helper 1, T-helper 2, and T regulatory cells was observed between sedentary and exercised mice. These results show for the first time, in a mouse model of Ang II–mediated vulnerable plaques, that swimming prevents atherosclerosis progression and plaque vulnerability. This benefit is likely mediated by downregulating aortic Ang II type 1 receptor expression independent from any hemodynamic change. Ang II type 1 downregulation may protect the vessel wall from the Ang II proatherogenic effects. Moreover, data presented herein further emphasize the pivotal and blood pressure–independent role of Ang II in atherogenesis.

Effect of Magnesium Deficiency on Blood Pressure and Mechanical Properties of Rat Carotid Artery

The purpose of this study was to determine the effect of dietary Mg deficiency (80 mg/kg versus control diet: 960 mg/kg) on blood pressure and mechanical properties of the rat common carotid artery. The internal diameter and intra-arterial pressure of carotid artery were measured continuously with an echo-tracking device. At 19 weeks, systolic, diastolic, and mean blood pressures were higher in Mg-deficient rats. Histological examination showed an increase in cross-sectional area, intima-media thickness, and media-to-lumen ratio in carotid artery of Mg-deficient rats. Mg deficiency did not modify the arterial distensibility-blood pressure curve. At mean blood pressure, arterial distensibility was significantly less in 19-week-old rats than in 5-week-old rats of both control and Mg-deficient groups. A significant interaction between age and Mg-deficient diet on arterial distensibility (P<0.04) indicates an accelerated age-dependent decreased arterial distensibility with Mg deficiency. At 19 weeks, the artery was stiffer in hypertensive Mg-deficient rats, as illustrated by a shift to higher levels of the incremental elastic modulus-stress curve. In conclusion, the increased blood pressure and the vascular morphological alterations observed in Mg-deficient rats may contribute to an accelerated alteration of the wall material, which in turn leads to a stiffening of the carotid artery.