P. Chowienczyk

Asymmetric Dimethylarginine and Reduced Nitric Oxide Bioavailability in Young Black African Men

Black Africans have a higher incidence of cardiovascular disease than white Europeans. We explored potential mechanisms of this excess risk by assessing endothelium function, inflammatory status (C-reactive protein), oxidative stress (isoprostane-F2&agr;), and plasma asymmetrical dimethyl arginine (ADMA; an endogenous competitive inhibitor of NO synthase) in each ethnic group. Thirty healthy black Africans and 28 well-matched white European male subjects were studied (mean age±SE: 32.2±0.9 and 29.2±1.2 years, respectively; P=0.07). High-resolution ultrasound was used to assess vascular function in the brachial artery by measuring flow mediated dilatation ([percentage of change]; endothelium-dependent function) and glyceryltrinitrate dilatation ([percentage of change]; endothelium-independent function). Blood pressure, fasting lipids, glucose, and estimated glomerular filtration rate levels were similar in both groups. There was no difference in C-reactive protein (black Africans: 0.8±0.1 mg/L; white Europeans: 0.6±0.1 mg/L; P=0.22), isoprostane-F2&agr; (black Africans: 42.9±1.5 pg/mL; white Europeans: 39.2±1.5 pg/mL; P=0.23), and leptin (black Africans: 64.1±10.2 ng/mL; white Europeans: 47.8±9.8 ng/mL; P=0.37) levels between the 2 ethnic groups. However, compared with white Europeans, plasma ADMA levels were significantly higher in black Africans (0.34±0.02 &mgr;mol/L and 0.25±0.03 &mgr;mol/L; P=0.03). There was no difference in the percentage of glyceryltrinitrate dilatation (P=0.7), but the percentage of flow-mediated dilatation was significantly lower in black Africans (black Africans: 5.2±0.3; white Europeans: 6.3±0.4; P=0.02). In a stepwise multiple regression model, ADMA level was the only independent determinant of flow-mediated dilatation (P=0.02). In turn, race was the only independent determinant of ADMA levels (P=0.03). Our findings indicate that circulating ADMA levels are significantly higher in healthy black African males than in white European males. This may contribute to the lower NO bioavailability and higher incidence of cardiovascular disease seen in black Africans.

Integrated multiomics approach identifies calcium and integrin-binding protein-2 as a novel gene for pulse wave velocity

Background: Carotid-femoral pulse wave velocity (PWV) is an important measure of arterial stiffness, which is an independent predictor of cardiovascular morbidity and mortality. In this study, we used an integrated genetic, epigenetic and transcriptomics approach to uncover novel molecular mechanisms contributing to PWV. Methods and results: We measured PWV in 1505 healthy twins of European descendent. A genomewide association analysis was performed using standardized residual of the inverse of PWV. We identified one single-nucleotide polymorphism (rs7164338) in the calcium and integrin-binding protein-2 (CIB2) gene on chromosome 15q25.1 associated with PWV [&bgr; = −0.359, standard error (SE) = 0.07, P = 4.8 × 10–8]. The same variant was also associated with increased CIB2 expression in leucocytes (&bgr; = 0.034, SE = 0.008, P = 4.95 × 10–5) and skin (&bgr; = 0.072, SE = 0.01, P = 2.35 × 10–9) and with hypomethylation of the gene promoter (&bgr; = −0.899, SE = 0.098, P = 3.63 × 10–20). Conclusion: Our data indicate that reduced methylation of the CIB2 promoter in individuals carrying rs7164338 may lead to increased CIB2 expression. Given that CIB2 is thought to regulate intracellular calcium levels, an increase in protein levels may prevent the accumulation of serum calcium and phosphate, ultimately slowing down the process of vascular calcification. This study shows the power of integrating multiple omics to discover novel cardiovascular mechanisms.

[PP.03.08] THE HAEMODYNAMIC MECHANISM OF THE AGE-RELATED INCREASE IN PULSE PRESSURE IN WOMEN

Objective: An age-related increase in pulse pressure is the major cause of morbidity and mortality in the ageing population and is more marked in women than in men. The haemodynamic determinants of increased pulse pressure remain incompletely understood. The aim of this study is was to examine the contribution of ventricular dynamics, large artery stiffness, and pressure wave reflection to central pulse pressure. Design and method: A total of 2162 women aged 18 to 91 years (mean ± SD, age 57 ± 13 years) from the Twins UK cohort were studied. Non-invasive aortic flow velocity and blood pressure were measured by Doppler sonography and carotid tonometry system respectively. Carotid-femoral PWV was measured using the SphygmoCor system. Reflection index (the ratio of the peak of the backward pressure wave over that of the forward pressure wave) was computed from the pressure and flow waves. Results: Central pulse pressure increased with age, from 29.5 ± 0.46 mmHg for those aged below 40 years to 52.6 ± 0.85 mmHg for those over 70 years (means ± SE, P < 0.001). PWV increased approximately 13.2% per decade. Maximum flow velocity tended to increase (from 1.11 ± 0.01 to 1.16 ± 0.01 m/s over the 5 decades, P < 0.01), and ejection volume at the time of peak pulse pressure increased from 63.3 ± 1.41 to 72.3 ± 1.92 ml (P < 0.001) but reflection index decreased from 0.28 ± 0.01 to 0.25 ± 0.01 (P < 0.001). Conclusions: These results suggest that the age-related increase in central pulse pressure is driven mainly by an increase in arterial stiffening and increased ventricular ejection.

[PP.33.02] FORWARD AND BACKWARD PRESSURE WAVEFORM MORPHOLOGY IN HYPERTENSIVE SUBJECTS

Objective: Beyond middle age hypertension results mainly from an increase in pulse pressure which may be attributed to a forward pressure wave generated by the interaction of the ventricle with the arterial tree and a backward wave due to “reflection” of the forward wave. We investigated whether increased pulse pressure in hypertension relates to a proportionally greater backward/forward wave or is driven by an increase in the forward wave. Design and method: Non-invasive central pressure and flow were obtained by carotid tonometry and Doppler sonography respectively in 158 hypertensive patients (mean ± SD age, 46 ± 17 years). Patients were divided into three groups by pulse pressure (group 1: 29.7 ± 5.3, group 2: 41.5 ± 2.6, group 3: 60.1 ± 12.5 mmHg). Forward and backward pressure waves were separated using wave intensity analysis. Dimensionless ratios were used to examine how characteristics of the backward wave: maximum amplitude, slope of upstroke, width at 80% maximum and area compared to the same characteristics of the forward wave. Results: All the dimensionless ratios were similar across the three groups, with no statistically significant difference in any ratio. However, the backward wave provided a slightly greater contribution to central pulse pressure in group 3 compared to group 1 (20.2 ± 1.3% vs. 16.3 ± 1.8%, means ± SE due to earlier time of arrival of the backward wave: 95 ± 2.8 vs. 107 ± 5.2 ms, P < 0.05). Conclusions: Increased pulsatile components of blood pressure in hypertension derive predominantly from the interaction of ventricular contraction with the impedance of the arterial tree. “Reflection” of the backward wave remains approximately the same across groups with a two-fold difference in pulse pressure. Earlier arrival of the backward wave contributes to a small proportion of the increase in pulse pressure.

5B.04: TIME TO PEAK SYSTOLIC MYOCARDIAL WALL STRESS IS INDEPENDENTLY ASSOCIATED WITH DIASTOLIC FUNCTION.

Objective: Diastolic dysfunction in hypertensive patients with preserved left ventricular (LV) ejection fraction (EF) (>40%) could be associated with prolonged systolic contraction and delayed systolic relaxation. We therefore examined whether time to peak systolic myocardial wall stress (MWS) relates to diastolic dysfunction. Design and method: We studied 178 subjects, evaluated for hypertension but otherwise free of clinically apparent cardiovascular disease aged 45.8 ± 16.3 (mean ± SD) years with mean systolic blood pressure (SBP) of 139 ± 23 mmHg and EF of 57.9 ± 7.5%. The E/E’ ratio was calculated from Doppler echocardiography mitral valve inflow and tissue Doppler of the basal lateral segment and used as a surrogate of diastolic function. MWS, a function of left ventricle (LV) pressure and geometry was obtained using carotid tonometry to estimate LV pressure during systole and 2D transthoracic echocardiographic wall tracking analysis (Tomtec) to derive cavity and myocardial wall volume. Subjects were divided into three groups (Group one (n = 64): SBP < 130mmHg and E/E’ < 10; Group two (n = 92): SBP >  = 130mmHg and E/E’ < 10; Group three (n = 22): SBP >  = 130mmHg and E/E’ >  = 10). Results: EF was preserved and not significantly different between groups (p = 0.44). Time to peak systolic MWS (Group one: 81.4 ± 3.9ms (mean ± SE), Group two 91.8 ± 4.2ms and Group three 116.4 ± 12.2ms) was significantly higher in group three with or without adjustment for age, body surface area (BSA) and HR compared to group one and two (p = 0.001). Across all groups, time to peak MWS was positively associated (standardized &bgr; = 0.24, p = 0.001) with E/E’ ratio. Conclusions: In hypertensive patients with preserved EF, impaired diastolic relaxation is associated with prolonged ventricular contraction independent of age, BSA and HR.