Armando Magagna

Vitamin C Improves Endothelium-Dependent Vasodilation by Restoring Nitric Oxide Activity in Essential Hypertension

BACKGROUND Essential hypertension is associated with impaired endothelium-dependent vasodilation. Inactivation of endothelium-derived nitric oxide by oxygen free radicals participates in endothelial dysfunction in experimental hypertension. To test this hypothesis in humans, we evaluated the effect of antioxidant vitamin C on endothelium-dependent responses in essential hypertensive patients. METHODS AND RESULTS In 14 healthy subjects (47.1+/-4.8 years; blood pressure, 120.6+/-4.5/80.9+/-3.5 mm Hg) and 14 essential hypertensive patients (47.3+/-5.1 years; blood pressure, 153.9+/-7.1/102.3+/-4.1 mm Hg), we studied forearm blood flow (strain-gauge plethysmography) modifications induced by intrabrachial acetylcholine (0.15, 0.45, 1.5, 4.5, and 15 microg x 100 mL(-1) x min(-1)) or sodium nitroprusside (1, 2, and 4 microg/100 mL forearm tissue per minute), an endothelium-dependent and -independent vasodilator, respectively, in basal conditions and during infusion of intrabrachial vitamin C (2.4 mg/100 mL forearm tissue per minute). In hypertensive patients but not in control subjects, vitamin C increased (P<0.01) the impaired vasodilation to acetylcholine, whereas the response to sodium nitroprusside was unaffected. Moreover, in another 14 hypertensive patients (47.1+/-5.2 years; blood pressure, 155.2+/-6.9/103.7+/-4.5 mm Hg), the facilitating effect of vitamin C on vasodilation to acetylcholine was reversed by N(G)-monomethyl-L-arginine (100 microg/100 mL forearm tissue per minute), a nitric oxide synthase inhibitor, suggesting that in essential hypertension superoxide anions impair endothelium-dependent vasodilation by nitric oxide breakdown. Finally, because in adjunctive 7 hypertensive patients (47.8+/-6.1 years; blood pressure, 155.3+/-6.8/103.5+/-4.3 mm Hg), indomethacin (50 microg/100 mL forearm tissue per minute), a cyclooxygenase inhibitor, prevented the potentiating effect of vitamin C on vasodilation to acetylcholine, it is possible that in essential hypertension a main source of superoxide anions could be the cyclooxygenase pathway. CONCLUSIONS In essential hypertensive patients, impaired endothelial vasodilation can be improved by the antioxidant vitamin C, an effect that can be reversed by the nitric oxide synthase inhibitor N(G)-monomethyl-L-arginine. These findings support the hypothesis that nitric oxide inactivation by oxygen free radicals contributes to endothelial dysfunction in essential hypertension.

Age-Related Reduction of NO Availability and Oxidative Stress in Humans

Abstract—Age-related endothelial dysfunction could be caused by an alteration in the l-arginine-NO system and the production of oxidative stress in both normotensive and hypertensive individuals. In 47 normotensive subjects and 49 patients with essential hypertension, we evaluated forearm blood flow (by strain-gauge plethysmography) modifications induced by intrabrachial sodium nitroprusside (1, 2, and 4 &mgr;g/100 mL per minute) and acetylcholine (0.15, 0.45, 1.5, 4.5, and 15 &mgr;g/100 mL per minute), an endothelium-independent vasodilator and an endothelium-dependent vasodilator, respectively. Acetylcholine was repeated in the presence of the NO synthase inhibitor NG-monomethyl-l-arginine (L-NMMA, 100 &mgr;g/100 mL per minute), the antioxidant vitamin C (8 mg/100 mL per minute), or both. Vasodilation to acetylcholine, but not to sodium nitroprusside, was lower (P <0.01) in hypertensive patients compared with control subjects. Moreover, in both groups, endothelium-dependent vasodilation declined with aging. In normotensive subjects, the inhibiting effect of L-NMMA on response to acetylcholine decreased in parallel with advancing age, whereas vitamin C increased vasodilation to acetylcholine in only the oldest group (age >60 years). In young hypertensive patients (age <30 years), vasodilation to acetylcholine was sensitive to L-NMMA, whereas in hypertensive patients age >30 years, vitamin C enhanced endothelium-dependent vasodilation and restored the inhibiting effect of L-NMMA on response to acetylcholine. In normotensive individuals, an earlier primary dysfunction of the NO system and a later production of oxidative stress cause age-related reduction in endothelium-dependent vasodilation. These alterations are similar but anticipated in hypertensive patients compared with normotensive subjects.

Different Effect of Antihypertensive Drugs on Conduit Artery Endothelial Function

Abstract— To compare the effect of antihypertensive drugs on endothelium‐dependent vasodilation in the peripheral conduit arteries of patients with essential hypertension, in a prospective, randomized, parallel group study, endothelial function was assessed in 168 hypertensive patients before and after 6‐month treatment with randomly assigned nifedipine GITS (30 to 60 mg, n=28), amlodipine (5 to 10 mg, n=28), atenolol (50 to 100 mg, n=29), nebivolol (5 to 10 mg, n=28), telmisartan (80 to 160 mg, n=29), and perindopril (2 to 4 mg, n=28). If necessary, hydrochlorothiazide (25 mg) was added to each compound. We evaluated brachial artery flow‐mediated, endothelium‐dependent dilation (high‐resolution ultrasound) compared with endothelium‐independent response to glyceryl trinitrate (25 &mgr;g/s). Brachial artery diameter was measured by automatic computerized analysis. Forty healthy subjects were evaluated as a control group. Oxidative stress production was evaluated by measuring plasma malondialdehyde and plasma lipoperoxides; plasma antioxidant capacity was assessed as ferric‐reducing antioxidant power. Hypertensive patients showed a significantly (P <0.01) lower flow‐mediated dilation (5.2±1.9%) as compared with healthy control subjects (7.1±2.6%). Response to glyceryl trinitrate was similar in control subjects and patients. At baseline, blood pressure, diameter, flow‐mediated dilation, and response to glyceryl trinitrate were similar in the different treatment groups. All treatments similarly reduced blood pressure, but only perindopril increased flow mediated dilation (from 5.1±2 to 6.4±2.4%;P <0.01) without modifying the response to glyceryl trinitrate. Perindopril but also telmisartan nifedipine and amlodipine reduced oxidative stress and increased plasma antioxidant capacity. In patients with essential hypertension, ACE inhibitors appear to be the only compounds able to improve conduit artery endothelium‐dependent vasodilation.

Cyclooxygenase Inhibition Restores Nitric Oxide Activity in Essential Hypertension

To evaluate whether cyclooxygenase constrictor substances can impair nitric oxide-mediated vasodilation in essential hypertension, in seven normotensive subjects (43.3 +/- 4.1 years; BP, 117 +/- 6/81 +/- 2 mm Hg) and seven essential hypertensive patients (47.1 +/- 5.2 years; BP, 151 +/- 8/98 +/- 4 mm Hg) we studied forearm blood flow (strain-gauge plethysmography) modifications induced by intrabrachial acetylcholine (0.15, 0.45, 1.5, 4.5, 15 micrograms.100 mL-1.min-1) in basal conditions, during infusion of NG-monomethyl-L-arginine (L-NMMA; 100 micrograms.100 mL-1.min-1), a nitirc oxide synthase inhibitor, or indomethacin (50 micrograms.100 mL-1.min-1), a cyclooxygenase inhibitor, or simultaneous indomethacin and L-NMMA. In normotensives, vasodilation to acetylcholine was blunted by L-NMMA (maximum flow increase: 671 +/- 64% and 386 +/- 42%, respectively; P < .01), and this effect was unchanged by indomethacin. In contrast, in hypertensive patients, vasodilation to acetylcholine (maximum flow increase: 458 +/- 33%) was unchanged by L-NMMA. Indomethacin significantly (P < .01) increased the response to acetylcholine (maximum flow increase: 635 +/- 53%) and restored the inhibitory effect of L-NMMA (maximum flow increase: 445 +/- 36%; P < .01 versus indomethacin alone). In an adjunctive seven normotensives (51.4 +/- 4.2 years; BP, 114 +/- 5/79 +/- 3 mm Hg) and seven essential hypertensives (53.2 +/- 7.6 years; BP, 153 +/- 9/100 +/- 3 mm Hg) we repeated the same protocol by replacing L-NMMA with L-arginine (200 micrograms.100 mL-1.min-1), the substrate for NO synthase. In normotensives, vasodilation to acetylcholine was increased by L-arginine (maximum flow increase: 539 +/- 48% and 806 +/- 61%, respectively) and this effect was unchanged by indomethacin. In hypertensive patients, vasodilation to acetylcholine (maximum flow increase: 339 +/- 32%) was unchanged by L-arginine but was significantly (P < .01) increased by indomethacin (maximum flow increase: 592 +/- 38%). Moreover, indomethacin restored the facilitatory effect of L-arginine (maximum flow increase: 804 +/- 56%; P < .01 versus indomethacin alone). Therefore, cyclooxygenase inhibition restores nitric oxide-mediated vasodilation in essential hypertension, suggesting that cyclooxygenase-dependent substances can impair nitric oxide production.

Effect of the Angiotensin II Type 1 Receptor Blocker Candesartan on Endothelial Function in Patients With Essential Hypertension

Patients with essential hypertension are characterized by impaired basal and agonist-evoked nitric oxide release and increased endogenous endothelin (ET)-1-induced vasoconstriction. To assess whether candesartan, an angiotensin II type 1 receptor blocker, can improve endothelial function, we studied the changes in forearm blood flow (FBF) induced in 15 hypertensive patients and in 15 control subjects by the intrabrachial infusion of N(G)-monomethyl-L-arginine (L-NMMA), norepinephrine, the ET A/B receptor antagonist TAK 044, sodium nitroprusside, and acetylcholine. In hypertensive patients, the FBF study was repeated 2 and 12 months after the start of treatment with candesartan cilexetil (8 to 16 mg daily). Compared with controls (maximal FBF decrease, -46+/-11%), hypertensive patients showed a reduced (P<0.001) vasoconstrictor response to L-NMMA (maximal FBF decrease, -28+/-7%); the response to norepinephrine was only slightly impaired, and the response to sodium nitroprusside was similar to that of controls. Finally, TAK-044 caused greater vasodilation in hypertensive patients (maximal FBF increase, 77+/-9%) than in controls (maximal FBF increase, 17+/-10%). In hypertensive patients, candesartan cilexetil significantly enhanced vasoconstriction to L-NMMA after 2 and 12 months (maximal FBF decrease, 37+/-2% [P<0.05] and 42+/-2% [P<0.001], respectively). The responses to norepinephrine, acetylcholine, and sodium nitroprusside were not modified after 2 months. After 12 months, the responses to acetylcholine and sodium nitroprusside were significantly (P<0.05) enhanced at the highest rates. Vasodilation to TAK-044 was abolished after treatment with candesartan cilexetil; this effect is associated with a reduced plasma ET-1 concentration. This study demonstrated that the angiotensin II receptor blocker candesartan improves tonic nitric oxide release and reduces vasoconstriction to endogenous ET-1 in the forearm of hypertensive patients.

Restoration of nitric oxide availability after calcium antagonist treatment in essential hypertension.

Essential hypertension is associated with impaired endothelium-dependent vasodilation caused by oxygen free radical–induced nitric oxide (NO) breakdown. Because calcium antagonists can improve endothelial function in patients with essential hypertension, in this study we tested the hypothesis that this beneficial effect could be related to restoration of NO availability by antioxidant properties. In 15 healthy subjects and 15 hypertensive patients, we studied forearm blood flow (strain-gauge plethysmography) modifications induced by intrabrachial acetylcholine (ACh; 0.15, 0.45, 1.5, 4.5, and 15 &mgr;g/100 mL per minute), an endothelium-dependent vasodilator in basal conditions, during infusion of NG-monomethyl-l-arginine (L-NMMA, 100 &mgr;g/100 mL forearm tissue per minute), an NO-synthase inhibitor, vitamin C (8 mg/100 mL forearm tissue per minute), and finally, simultaneous infusion of L-NMMA and vitamin C. The response to sodium nitroprusside (SNP; 1, 2, and 4 &mgr;g/100 mL forearm tissue per minute) was also evaluated. In control subjects, vasodilation to ACh was inhibited by L-NMMA and not changed by vitamin C. In hypertensive patients, vasodilation to ACh was blunted as compared with control subjects and resistant to L-NMMA. Vitamin C, which decreased plasma isoprostanes and increased plasma antioxidant capacity, increased the response to ACh and restored the inhibiting effect of L-NMMA. In hypertensive patients, the study was repeated after 3-month treatment with nifedipine gastrointestinal therapeutic system (30 to 60 mg/daily). Nifedipine treatment decreased circulating plasma lipoperoxides and isoprostanes and increased plasma antioxidant capacity. Moreover, nifedipine increased the vasodilation to ACh but not to SNP and restored the inhibiting effect of L-NMMA on ACh-induced vasodilation, whereas vitamin C no longer exerted its facilitating activity. These results indicate that nifedipine increases endothelium-dependent vasodilation by restoring NO availability, an effect probably determined by antioxidant activity.

Lacidipine Restores Endothelium-Dependent Vasodilation in Essential Hypertensive Patients

Essential hypertension is characterized by impaired endothelium-dependent vasodilation. The present study was designed to test whether antihypertensive treatment with the calcium antagonist lacidipine can improve endothelium-dependent vasodilation in essential hypertensive patients. In 12 normotensive subjects (mean age, 47.8+/-8.6 years; blood pressure, 118.6+/-4.2/76.7+/-3.9 mm Hg) and 19 hypertensive patients (mean age, 49.4+/-10.2 years; blood pressure; 153.5+/-13.3/101.3+/-6.4 mm Hg), we studied forearm blood flow modifications (strain-gauge plethysmography) induced by intrabrachial infusion of acetylcholine (0.15, 0.45, 1.5, 4.5, and 15 microg/100 mL per minute) and bradykinin (5, 15, and 50 ng/100 mL per minute), two endothelium-dependent vasodilators that act through different receptors and signal transduction pathways, and sodium nitroprusside (1, 2, and 4 microg/100 mL per minute), an endothelium-independent vasodilator. In essential hypertensive patients, vascular reactivity was repeated during prolonged (8 weeks of oral treatment at 6 mg/d) lacidipine administration and 2 weeks after withdrawal of chronic (32-week) treatment. Hypertensive patients showed significantly (P<.01) blunted vasodilation in response to acetylcholine (vascular resistance, 31.5+/-4.9 to 7.6+/-2.4 SU) and bradykinin (vascular resistance, 32.3+/-5.8 to 8.5+/-3.0 SU) compared with control subjects (vascular resistance: acetylcholine, 24.3+/-3.9 to 3.7+/-1.2 SU; bradykinin, 24.7+/-0.4 to 4.1+/-1.3 SU), whereas the response to sodium nitroprusside was similar. After either 8 or 32 weeks of lacidipine treatment, the vasodilation in response to acetylcholine (30.6+/-7.7 to 5.7+/-1.5 and 34.3+/-6.6 to 5.9+/-1.9 SU, respectively) and bradykinin (31.3+/-7.2 to 6.4+/-1.6 and 33.7+/-5.4 to 6.1+/-1.5 SU, respectively), but not to sodium nitroprusside, proved to be significantly (P<.05) increased compared with baseline. In essential hypertensive patients, oral treatment with lacidipine increased forearm vasodilation in response to acetylcholine and bradykinin, suggesting that this drug can improve endothelial function in patients with essential hypertension.

Effect of calcium antagonist or beta blockade treatment on nitric oxide-dependent vasodilation and oxidative stress in essential hypertensive patients

Objectives Essential hypertension is associated with impaired endothelium-dependent vasodilation caused by oxygen free radical-induced nitric oxide (NO) breakdown. Since calcium antagonists can improve endothelial function in hypertensive patients, we tested whether this beneficial effect could be related to restoration of NO availability by antioxidant activity. Methods In 10 healthy subjects and 20 essential hypertensive patients, we studied forearm blood flow (strain-gauge plethysmography) modifications induced by intrabrachial acetylcholine (from 0.15–15 μg/100 ml per min), bradykinin (0.005–0.05 μg/100 ml per min), two endothelium-dependent vasodilators, and sodium nitroprusside (1–4 μg/100 ml forearm tissue per min), an endothelium independent vasodilator, in the absence and presence of NG-monomethyl-l-arginine (l-NMMA) (100 μg/100 ml forearm tissue per min), an NO synthase inhibitor. Results In controls, vasodilation to acetylcholine and bradykinin was inhibited by l-NMMA. In hypertensive patients, vasodilation to acetylcholine and bradykinin, but not to sodium nitroprusside, was blunted and resistant to l-NMMA. Hypertensive patients were randomized to a 12-week treatment with lacidipine (4–6 mg/daily) or atenolol (50–100 mg/daily) (n = 10 each group). Lacidipine but not atenolol increased the vasodilation to acetylcholine and bradykinin and restored the inhibiting effect of l-NMMA on endothelium-dependent vasodilation, without affecting the response to sodium nitroprusside. Moreover, lacidipine reduced circulating markers of oxidative stress including plasma and low-density lipoprotein (LDL) hydroperoxides, the susceptibility of LDL to Cu2+-induced oxidation and the reactive oxygen species generated from human umbilical vein endothelial cells after incubation with LDL derived from plasma of the patients. Conclusions Lacidipine increases endothelium-dependent vasodilation by restoring NO availability, and this effect possibly is related to antioxidant activity.

Mechanisms responsible for endothelial dysfunction induced by fasting hyperhomocystinemia in normotensive subjects and patients with essential hypertension

OBJECTIVES We sought to evaluate whether fasting hyperhomocystinemia reduces endothelial function by oxidative stress in normotensive subjects and hypertensive patients. BACKGROUND Subjects with hyperhomocystinemia have endothelial dysfunction. METHODS In 23 normotensive subjects and 28 hypertensive patients, classified into normohomocystinemic and hyperhomocystinemic groups according to homocysteine plasma levels (< 8.7 and >14.6 micromol/l, respectively), we studied forearm blood flow changes (strain-gauge plethysmography) induced by intrabrachial administration of acetylcholine (0.15 to 15 microg/100 ml tissue per min) or sodium nitroprusside (1 to 4 microg/100 ml per min), an endothelium-dependent and -independent vasodilator, respectively. Acetylcholine was repeated with N(G)-monomethyl-L-arginine (L-NMMA; 100 microg/100 ml per min), vitamin C (8 mg/100 ml per min) and L-NMMA plus vitamin C. RESULTS Normotensive hyperhomocystinemic patients showed a blunted response to acetylcholine and a lower inhibiting effect of L-NMMA on acetylcholine, as compared with normohomocystinemic patients. Although vitamin C was ineffective in normohomocystinemic subjects, it increased the response to acetylcholine and restored the inhibiting effect of L-NMMA on acetylcholine in hyperhomocystinemic patients. Hypertensive hyperhomocystinemic patients showed a reduced response to acetylcholine, as compared with normohomocystinemic subjects. In both subgroups, L-NMMA failed to blunt the response to acetylcholine. The potentiating effect of vitamin C on acetylcholine was greater in hyperhomocystinemic patients than in normohomocystinemic subjects, although it restored the inhibitory effect of L-NMMA on acetylcholine-induced vasodilation to the same extent in both groups. Hyperhomocystinemia did not change the response to sodium nitroprusside. CONCLUSIONS In normotensive subjects and hypertensive patients, hyperhomocystinemia impairs endothelium-dependent vasodilation. It could be related to oxidant activity.

Effect of acute blood pressure reduction on endothelial function in the brachial artery of patients with essential hypertension.

Objectives To evaluate the effect of acute blood pressure reduction on endothelium-dependent vasodilation in the peripheral circulation of essential hypertensive patients. Design A parallel group study; endothelial function measured in 64 essential hypertensive patients before and after (2 h) treatment with nifedipine (20 mg, n = 32) or captopril (50 mg, n = 32), p.o., randomly assigned. Methods In hypertensive patients, we evaluated flow-mediated, endothelium-dependent dilation (FMD, high resolution ultrasound) of the brachial artery compared with endothelium-independent response to glyceryl trinitrate (GTN, 25 μg s.l.). Automatic computerized analysis was used to measure brachial artery diameter on end-diastolic frames acquired every second during the study. Sixty-six healthy normotensive subjects were also evaluated to assess the presence of endothelial dysfunction in hypertensive patients. Results Hypertensive patients showed a significantly (P < 0.01) lower FMD (5.9 ± 2.5%) as compared to healthy controls (7.7 ± 3.8%). The response to GTN was similar in normotensive subjects (7.5 ± 3.1%) and hypertensive patients (7.2 ± 6.5%). At baseline brachial artery diameter, FMD and response to GTN were similar in the nifedipine- and captopril-treated groups. Nifedipine and captopril similarly reduced blood pressure, but only nifedipine increased heart rate. Acute nifedipine, but not captopril, significantly (P < 0.01) increased brachial artery diameter, while FMD and response to GTN were not modified after nifedipine or captopril. Conclusions Endothelial dysfunction in the brachial artery of essential hypertensive patients is not improved by acute blood pressure reduction.