Maurizio Degan

Increased Oxidative Stress and Platelet Activation in Patients With Hypertension and Renovascular Disease

Background—Hypertensive patients with renovascular disease (RVD) may be exposed to increased oxidative stress, possibly related to activation of the renin-angiotensin system. Methods and Results—We measured the urinary excretion of 8-iso-prostaglandin (PG) F2&agr; and 11-dehydro-thromboxane (TX) B2 as indexes of in vivo lipid peroxidation and platelet activation, respectively, in 25 patients with RVD, 25 patients with essential hypertension, and 25 healthy subjects. Plasma renin activity in peripheral and renal veins, angiotensin II in renal veins, cholesterol, glucose, triglycerides, homocysteine, and antioxidant vitamins A, C, and E were also determined. Patients were also studied 6 months after a technically successful angioplasty of the stenotic renal arteries. Urinary 8-iso-PGF2&agr; was significantly higher in patients with RVD (median, 305 pg/mg creatinine; range, 124 to 1224 pg/mg creatinine) than in patients with essential hypertension (median, 176 pg/mg creatinine; range, 48 to 384 pg/mg creatinine) or in healthy subjects (median, 123 pg/mg creatinine; range, 58 to 385 pg/mg creatinine). Urinary 11-dehydro-TXB2 was also significantly higher in RVD patients compared with healthy subjects. In RVD patients , urinary 8-iso-PGF2&agr; correlated with 11-dehydro-TXB2 (rs=0.48;P <0.05) and renal vein renin (rs=0.67;P <0.005) and angiotensin II (rs=0.65;P =0.005) ratios. A reduction in 8-iso-PGF2&agr; after angioplasty was observed in RVD patients with high baseline levels of lipid peroxidation. Changes in 8-iso-PGF2&agr; were related to baseline lipid peroxidation (rs=−0.73;P <0.001), renal vein angiotensin II (rs=−0.70;P <0.01) and renin (rs=−0.63;P <0.05) ratios. Conclusions—Lipid peroxidation is markedly enhanced in hypertensive patients with RVD and is related to activation of the renin-angiotensin system. Moreover, persistent platelet activation triggered or amplified by bioactive isoprostanes may contribute to the progression of cardiovascular and renal damage in this setting.

The F2-Isoprostane 8-epiprostaglandin F2α increases platelet adhesion and reduces the antiadhesive and antiaggregatory effects of NO

F2-isoprostanes are prostaglandin (PG) isomers produced in vivo through free radical-catalyzed peroxidation of arachidonic acid, which may affect platelet function. The current study investigated the effects of 8-epiprostaglandin F2alpha (8-epi-PGF2alpha) on critical events of platelet activation. A dose-dependent increase in platelet adhesion to fibrinogen- and plasma-coated microwells by 8-epi-PGF2alpha (1 to 1000 nmol/L) was observed when resting platelets (plasma from 1.3+/-0.2% to 5.5+/-0.2%, EC50 of 48 nmol/L; fibrinogen from 3.3+/-0.3% to 6.4+/-0.2%, EC50 of 35 nmol/L; mean+/-SEM, n=8, P<0.001) and thrombin-stimulated human platelets were used. The expression of the adhesion molecule glycoprotein IIb/IIIa was increased by 10 to 1000 nmol/L 8-epi-PGF2alpha in resting platelets (from 64.8+/-2.1% to 83.9+/-1.3%; n=5, P<0.01) and in stimulated platelets. The secretion of the glycoprotein GMP-140 increased only in the presence of both thrombin and 10 to 1000 nmol/L 8-epi-PGF2alpha (from 48.5+/-3.1% to 63.1+/-2.0%, P<0.05). The antiaggregatory effects of both the NO donor NOR-3 (basal, 21.4+/-4.6%; with 8-epi-PGF2alpha, 30.8+/-6.9%; n=14, P<0.05) and endothelial cells that release NO (basal, 18.5+/-4.6%; with 8-epi-PGF2alpha, 30.7+/-5.3%; n=15, P<0.001) were also reduced. All of these effects were prevented by the thromboxane receptor antagonist GR32191 but not affected by acetylsalicylic acid. An increase in free intracellular calcium concentration, measured with the use of fura 2, was observed with 8-epi-PGF2alpha. In conclusion, F2-isoprostanes may participate in oxidative injury by inducing platelet activation and by reducing the antiplatelet activity of NO: increased platelet adhesiveness and expression of the fibrinogen receptor are induced by nanomolar amounts of 8-epi-PG-F2alpha. Platelet secretion and aggregation can also be induced in the presence of platelet agonists.

Determinants of Platelet Activation in Human Essential Hypertension

Abstract—Experimental data suggest that oxidative stress might be enhanced in hypertension and contribute to platelet activation. We hypothesized that both oxidative stress and platelet activation could be related to the clinical characteristics of hypertensive patients. The urinary excretion of 11-dehydrothromboxane (TX) B2, reflecting in vivo platelet activation, was measured in 75 patients with mild to severe essential hypertension and 75 pair-matched, healthy controls. The urinary excretion of 8-iso-prostaglandin (PG) F2&agr; was determined as an index of in vivo lipid peroxidation. Urinary 11-dehydro-TXB2 was significantly higher in essential hypertensives compared with controls. Although no statistically significant difference in urinary 8-iso-PGF2&agr; was observed between patients and controls, plasma vitamin C was lower and plasma homocysteine higher in hypertensive patients than in controls. Both urinary 11-dehydro-TXB2 and 8-iso-PGF2&agr; were higher in patients with advanced hypertensive retinopathy compared with patients without retinopathy. Multivariate linear regression analysis identified urinary 8-iso-PGF2&agr;, plasma fibrinogen, homocysteine, and vitamin E as the only variables independently correlated with urinary 11-dehydro-TXB2. Logistic regression analysis showed that high urinary 8-iso-PGF2&agr;, plasma fibrinogen, and homocysteine, as well as low plasma vitamin E, advanced retinopathy, elevated diastolic blood pressure, and the absence of antihypertensive treatment, were predictors of high urinary 11-dehydro-TXB2. We demonstrated increased oxidative stress and persistent platelet activation in essential hypertensives with advanced vascular lesions. These findings might help identify hypertensive patients who are at increased risk of cardiovascular events and who might benefit from long-term antiplatelet therapy.

Endothelial progenitor cells in patients with essential hypertension.

Objective(s) The eventual role of blood pressure on the endothelial progenitor cell (EPC) has rarely been evaluated and data collected so far relate to patients with co-existing coronary heart disease. Methods We have studied the number and functional activity of EPC as well as the number of EPC endothelial colony-forming units (CFU) in a carefully selected group of 36 patients with essential hypertension and 24 normotensive control subjects. Results In patients with essential hypertension, the EPC number was not statistically different from that found in control subjects (mean ± SD, essential hypertension 58 ± 29, controls 53 ± 20; EPC/high power field). CFU per well were not statistically different in patients with essential hypertension compared with normotensive controls (mean ± SD, patients with essential hypertension 2.4 ± 2.6, normotensive controls 3 ± 3.3 CFU/well). In essential hypertension patients, the EPC number was inversely correlated with both total (R = 0.635, P < 0.0001) and low-density lipoprotein (LDL)-cholesterol (R = 0.486, P < 0.05). Neither the EPC number nor the EPC CFU were correlated with age, systolic blood pressure, diastolic blood pressure, body mass index, lipoprotein(a), high-sensitivity C-reactive protein or homocysteine. Conclusions The present study shows that essential hypertension is not characterized by the altered number or functional activity of EPC. Plasma total and LDL-cholesterol are independent predictors of reduced numbers of circulating EPC in essential hypertension patients. The absence of any correlation between the characteristics of EPC and several markers predictive of cardiovascular damage merits further investigation.

Effects of six months of vitamin D supplementation in patients with heart failure: A randomized double-blind controlled trial

BACKGROUND AND AIM Low plasma vitamin D levels have been associated with heart failure (HF). This research attempts to explain the role of vitamin D supplementation on myocardial function in elderly patients with HF. METHODS AND RESULTS Twenty-three chronic HF patients were randomized in a small parallel group, double-blind, placebo-controlled trial. All patients, with a mean age of 74 years and vitamin D levels <30 ng/mL, received 800,000 IU (4000 IU/daily) of cholecalciferol or placebo for 6 months. The outcomes measured at baseline and after 6 months were ejection fraction (EF) and other echocardiography parameters, carboxyterminal propeptide of procollagen type I (PIP), natriuretic peptides, lipid profile, renin, parathyroid hormone, blood pressure, and body mass index (BMI). In 13 patients under active treatment for 6 months, mean plasma 25-hydroxy vitamin D concentrations (15.51 vs. -1.40 ng/mL, p < 0.001) and plasma calcium (from 9.3 to 9.6 mmol/L, p < 0.05) increased significantly. However, other biomarkers of bone metabolism did not differ between the treatment and placebo groups. EF increased significantly in the intervention group (6.71 vs. -4.3%; p < 0.001), and the serum concentration of PIP increased only in the placebo group after 6 months (1140.98 vs. -145 mcg/L; p < 0.05). Systolic blood pressure was lower after 6 months of cholecalciferol treatment (from 129.6 to 122.7 mm Hg, p < 0.05). No significant variations were observed for other parameters. CONCLUSIONS Six months of vitamin D supplementation significantly improves EF in elderly patients with HF and vitamin D deficiency.

Intralymphocyte free magnesium in patients with primary aldosteronism: aldosterone and lymphocyte magnesium homeostasis.

It is known that hyperaldosteronism has been associated with magnesium deficiency, yet there are no data on the intracellular concentration of ionized magnesium ([Mg(2+)(i)]) in subjects with primary aldosteronism (PA). We measured intralymphocyte free magnesium ([Mg(2+)(i)]) and intralymphocyte free calcium ([Ca(2+)(i)]) in 16 patients with PA and 26 normotensive control subjects (NCs). [Mg(2+)(i)] and [Ca(2+)(i)] were also measured in blood lymphocytes incubated in vitro with aldosterone, according to a fluorimetric method. In subjects with PA, [Mg(2+)(i)] was significantly lower than that in NCs (mean+/-SD; PA 203+/-56 micromol/L, NCs 291+/-43 micromol/L, 95% confidence interval 57 to 119, P=0.001). In the patients, [Ca(2+)(i)] did not prove to be statistically different from that of NCs (mean+/-SD; PA 47.2+/-10.6 nmol/L, NCs 53.2+/-11 nmol/L). The lymphocytes exposed to the action of aldosterone showed a significant reduction in [Mg(2+)(i)] (n=15, NCs 271+/-28 micromol/L, aldosterone treatment 188+/-39 micromol/L, P=0.001, 95% confidence interval 57 to 108). The dose-effect curve of aldosterone on [Mg(2+)(i)] showed an EC(50) value of approximately 0.5 to 1 nmol/L aldosterone. The reduction in [Mg(2+)(i)] mediated by aldosterone is antagonized by the receptor inhibitor of aldosterone; it is inhibited by inhibitors of protein synthesis and is not measurable when the lymphocytes are incubated in an Na(+)-free medium. The data are consistent with the hypothesis that aldosterone affects the cellular homeostasis of magnesium, probably through modification of the activity of the Na(+)-Mg(2+) antiporter.

Rapid stimulation of tyrosine phosphorylation signals downstream of G-protein-coupled receptors for thromboxane A2 in human platelets

Signals ensuing from trimeric G-protein-coupled receptors synergize to induce platelet activation. At low doses, the thromboxane A2 analogue U46619 does not activate integrin alphaIIbbeta3 or trigger platelet aggregation, but it induces shape changes. In the present study, we addressed whether low doses of U46619 trigger tyrosine phosphorylation independently of integrin alphaIIbbeta3 activation and ADP secretion, and synergize with adrenaline (epinephrine) to induce aggregation in acetylsalicylic acid (aspirin)-treated platelets. Low doses of U46619 triggered tyrosine phosphorylation of different proteins, including FAK (focal adhesion kinase), Src and Syk, independently of signals ensuing from integrin alphaIIbbeta3 or ADP receptors engaged by secreted ADP. The G(12/13)-mediated Rho/Rho-kinase pathway was also increased by low doses of U46619; however, this pathway was not upstream of tyrosine phosphorylation, because this occurred in the presence of the Rho-kinase inhibitor Y-27632. Although low doses of U46619 or adrenaline alone were unable to trigger platelet aggregation and integrin alphaIIbbeta3 activation, the combination of the two stimuli effectively induced these responses. PP2, a tyrosine kinase inhibitor, and Y-27632 inhibited platelet activation induced by low doses of U46619 plus adrenaline and, when used in combination, totally suppressed this platelet response. In addition, the two inhibitors selectively blocked tyrosine kinases and the Rho/Rho-kinase pathway respectively. These findings suggest that both tyrosine phosphorylation and the Rho/Rho-kinase pathway are required to activate platelet aggregation via G(12/13) plus G(z) signalling.

NCX4016 (NO-Aspirin) has multiple inhibitory effects in LPS-stimulated human monocytes.

NCX4016 (2 acetoxy‐benzoate 2‐(2‐nitroxymethyl)‐phenyl ester, NicOx S.A., France) is an anti‐thrombotic agent, chemically related to acetylsalicylic acid (ASA) and able to release NO. We tested the effects of NCX4016 and ASA on the release of the thromboxane (TX) A2 metabolite TXB2, tumour necrosis factor‐α (TNF‐α), interleukin‐6 (IL‐6), expression and activity of tissue factor (TF) in stimulated, adherent human monocytes. Both ASA and NCX4016 1 – 1000 μmol l−1 dose‐dependently reduced TXB2 concentration, measured by RIA in the supernatant of 10 μg ml−1 LPS‐stimulated cells. NCX4016 activity was comparable to that of equimolar ASA when incubation lasted 6 h (NCX4016 30 μmol l−1: −86.0±10.1%, NCX4016 300 μmol l−1: −92.2±9.0%, ASA 30 μmol l−1: −92.3±7.5%, ASA 300 μmol l−1: −97.3±1.0%, n=6, M±s.d.). Most of the activity of NCX4016 up to 100 μmol l−1 was prevented by 10 μmol l−1 ODQ, inhibitor of cyclic GMP. NCX4016 100 – 300 μmol l−1 reduced TNF‐α (NCX4016 300 μmol l−1=−77.2±19.9%, n=6) and IL‐6 (NCX4016 300 μmol l−1: −61.9±15.2%, n=6) in LPS stimulated monocytes while ASA had no significant effects. TF activity (NCX4016 300 μmol l−1: 53.7±39.9%, n=4) and immunoreactive TF (NCX4016 300 μmol l−1: −93.9±7.9%, n=7), measured in the supernatant of stimulated cells, were also dose‐dependently inhibited by NCX4016 but not by ASA. The present results indicate that NCX4016 inhibits TXA2 generation as well as cytokine release and TF in human monocytes partly via NO‐dependent mechanisms. NCX4016 may have a favourable profile of activities in the clinical setting of athero‐thrombosis.

Altered excretion of prostaglandin and thromboxane metabolites in pregnancy-induced hypertension.

The renal and systemic metabolites (the latter as 2,3-dinor derivatives) of prostacyclin and thromboxane A2 were measured, along with renal prostaglandin E2 and kallikrein, in the urine of 15 patients with pregnancy-induced hypertension, 15 normotensive pregnant women matched for both age and gestational age, and 15 normotensive nonpregnant control women. Urinary excretion of all prostaglandin and thromboxane metabolites studied proved significantly higher in normotensive pregnant women than in controls. Prostaglandin E2, 6-keto-prostaglandin F1 alpha, and 2,3-dinor-6-keto-prostaglandin F1 alpha were significantly lower in pregnancy-induced hypertensive women than in normotensive pregnant women, whereas thromboxane B2 and 2,3-dinor-thromboxane B2 showed no significant differences in the two groups. A significant negative correlation (r = -0.636, p less than 0.01) was found between urinary 2,3-dinor-6-keto-prostaglandin F1 alpha and mean blood pressure in the two groups of pregnant women taken as a whole. These data indicate that, in pregnancy-induced hypertension, there is an imbalance between vasodilator and vasoconstrictor factors, not only in the kidneys, but also at the systemic vascular level. This imbalance, which may in itself produce vasoconstriction, may also potentiate the hypertensive effect of catecholamines and angiotensin II.

Increased protein nitration in mitochondrial diseases: evidence for vessel wall involvement.

Mitochondrial diseases (MD) are heterogeneous disorders because of impairment of respiratory chain function leading to oxidative stress. We hypothesized that in MD the vascular endothelium may be affected by increased oxidative/nitrative stress causing a reduction of nitric oxide availability. We therefore, investigated the pathobiology of vasculature in MD patients by assaying the presence of 3-nitrotyrosine in muscle biopsies followed by the proteomic identification of proteins which undergo tyrosine nitration. We then measured the flow-mediated vasodilatation as a proof of altered nitric oxide generation/bioactivity. Here, we show that 3-nitrotyrosine staining is specifically located in the small vessels of muscle tissue and that the reaction is stronger and more evident in a significant percentage of vessels from MD patients as compared with controls. Eleven specific proteins which are nitrated under pathological conditions were identified; most of them are involved in energy metabolism and are located mainly in mitochondria. In MD patients the flow-mediated vasodilatation was reduced whereas baseline arterial diameters, blood flow velocity and endothelium-independent vasodilatation were similar to controls. The present results provide evidence that in MD the vessel wall is a target of increased oxidative/nitrative stress.