Influence of angiotensin II type 1 receptor polymorphism on aortic stiffness in never-treated hypertensive patients

Molecular Mechanisms in Genetic Aortopathy-Signaling Pathways and Potential Interventions

Thoracic aortic disease affects people of all ages and the majority of those aged <60 years have an underlying genetic cause. There is presently no effective medical therapy for thoracic aneurysm and surgery remains the principal intervention. Unlike abdominal aortic aneurysm, for which the inflammatory/atherosclerotic pathogenesis is well established, the mechanism of thoracic aneurysm is less understood. This paper examines the key cell signaling systems responsible for the growth and development of the aorta, homeostasis of endothelial and vascular smooth muscle cells and interactions between pathways. The evidence supporting a role for individual signaling pathways in pathogenesis of thoracic aortic aneurysm is examined and potential novel therapeutic approaches are reviewed. Several key signaling pathways, notably TGF-β, WNT, NOTCH, PI3K/AKT and ANGII contribute to growth, proliferation, cell phenotype and survival for both vascular smooth muscle and endothelial cells. There is crosstalk between pathways, and between vascular smooth muscle and endothelial cells, with both synergistic and antagonistic interactions. A common feature of the activation of each is response to injury or abnormal cell stress. Considerable experimental evidence supports a contribution of each of these pathways to aneurysm formation. Although human information is less, there is sufficient data to implicate each pathway in the pathogenesis of human thoracic aneurysm. As some pathways i.e., WNT and NOTCH, play key roles in tissue growth and organogenesis in early life, it is possible that dysregulation of these pathways results in an abnormal aortic architecture even in infancy, thereby setting the stage for aneurysm development in later life. Given the fine tuning of these signaling systems, functional polymorphisms in key signaling elements may set up a future risk of thoracic aneurysm. Multiple novel therapeutic agents have been developed, targeting cell signaling pathways, predominantly in cancer medicine. Future investigations addressing cell specific targeting, reduced toxicity and also less intense treatment effects may hold promise for effective new medical treatments of thoracic aortic aneurysm.

A Review of Vascular Traits and Assessment Techniques, and Their Heritability

Various tools are available to assess atherosclerosis, arterial stiffening, and endothelial function. They offer utility in the assessment of hypertensive phenotypes, in cardiovascular risk prediction, and as surrogate endpoints in clinical trials. We explore the relative influence of participant genetics, with reference to large-scale genomic studies, population-based cohorts, and candidate gene studies. We find heritability estimates highest for carotid intima-media thickness (CIMT 35–65%), followed by pulse wave velocity as a measure of arterial stiffness (26–43%), and flow mediated dilatation as a surrogate for endothelial function (14–39%); data were lacking for peripheral artery tonometry. We furthermore examine genes and polymorphisms relevant to each technique. We conclude that CIMT and pulse wave velocity dominate the existing evidence base, with fewer published genomic linkages for measures of endothelial function. We finally make recommendations regarding planning and reporting of data relating to vascular assessment techniques, particularly when genomic data are also available, to facilitate integration of these tools into cardiovascular disease research.

Aortic Stiffness: Epidemiology, Risk Factors, and Relevant Biomarkers

Aortic stiffness (AoS) is a maladaptive response to hemodynamic stress and both modifiable and non-modifiable risk factors, and elevated AoS increases afterload for the heart. AoS is a non-invasive marker of cardiovascular health and metabolic dysfunction. Implementing AoS as a diagnostic tool is challenging as it increases with age and varies amongst races. AoS is associated with lifestyle factors such as alcohol and smoking, as well as hypertension and comorbid conditions including metabolic syndrome and its components. Multiple studies have investigated various biomarkers associated with increased AoS, and this area is of particular interest given that these markers can highlight pathophysiologic pathways and specific therapeutic targets in the future. These biomarkers include those involved in the inflammatory cascade, anti-aging genes, and the renin-angiotensin aldosterone system. In the future, targeting AoS rather than blood pressure itself may be the key to improving vascular health and outcomes. In this review, we will discuss the current understanding of AoS, measurement of AoS and the challenges in interpretation, associated biomarkers, and possible therapeutic avenues for modulation of AoS.

COVID's Razor: RAS Imbalance, the Common Denominator Across Disparate, Unexpected Aspects of COVID-19

A modern iteration of Occam's Razor posits that "the simplest explanation is usually correct." Coronavirus Disease 2019 involves widespread organ damage and uneven mortality demographics, deemed unexpected from what was originally thought to be "a straightforward respiratory virus." The simplest explanation is that both the expected and unexpected aspects of COVID-19 share a common mechanism. Silent hypoxia, atypical acute respiratory distress syndrome (ARDS), stroke, olfactory loss, myocarditis, and increased mortality rates in the elderly, in men, in African-Americans, and in patients with obesity, diabetes, and cancer-all bear the fingerprints of the renin-angiotensin system (RAS) imbalance, suggesting that RAS is the common culprit. This article examines what RAS is and how it works, then from that baseline, the article presents the evidence suggesting RAS involvement in the disparate manifestations of COVID-19. Understanding the deeper workings of RAS helps one make sense of severe COVID-19. In addition, recognizing the role of RAS imbalance suggests potential routes to mitigate COVID-19 severity.

Therapeutic modification of arterial stiffness: An update and comprehensive review

Arterial stiffness has been recognized as a marker of cardiovascular disease and associated with long-term worse clinical outcomes in several populations. Age, hypertension, smoking, and dyslipidemia, known as traditional vascular risk factors, as well as diabetes, obesity, and systemic inflammation lead to both atherosclerosis and arterial stiffness. Targeting multiple modifiable risk factors has become the main therapeutic strategy to improve arterial stiffness in patients at high cardiovascular risk. Additionally to life style modifications, long-term ω-3 fatty acids (fish oil) supplementation in diet may improve arterial stiffness in the population with hypertension or metabolic syndrome. Pharmacological treatment such as renin-angiotensin-aldosterone system antagonists, metformin, and 3-hydroxy-3-methyl-glutaryl-CoA reductase inhibitors were useful in individuals with hypertension and diabetes. In obese population with obstructive sleep apnea, weight reduction, aerobic exercise, and continuous positive airway pressure treatment may also improve arterial stiffness. In the populations with chronic inflammatory disease such as rheumatoid arthritis, a use of antibodies against tumor necrosis factor-alpha could work effectively. Other therapeutic options such as renal sympathetic nerve denervation for patients with resistant hypertension are investigated in many ongoing clinical trials. Therefore our comprehensive review provides knowledge in detail regarding many aspects of pathogenesis, measurement, and management of arterial stiffness in several populations, which would be helpful for physicians to make clinical decision.

International Union of Basic and Clinical Pharmacology. XCIX. Angiotensin Receptors: Interpreters of Pathophysiological Angiotensinergic Stimuli [corrected]

The renin angiotensin system (RAS) produced hormone peptides regulate many vital body functions. Dysfunctional signaling by receptors for RAS peptides leads to pathologic states. Nearly half of humanity today would likely benefit from modern drugs targeting these receptors. The receptors for RAS peptides consist of three G-protein-coupled receptors—the angiotensin II type 1 receptor (AT1 receptor), the angiotensin II type 2 receptor (AT2 receptor), the MAS receptor—and a type II trans-membrane zinc protein—the candidate angiotensin IV receptor (AngIV binding site). The prorenin receptor is a relatively new contender for consideration, but is not included here because the role of prorenin receptor as an independent endocrine mediator is presently unclear. The full spectrum of biologic characteristics of these receptors is still evolving, but there is evidence establishing unique roles of each receptor in cardiovascular, hemodynamic, neurologic, renal, and endothelial functions, as well as in cell proliferation, survival, matrix-cell interaction, and inflammation. Therapeutic agents targeted to these receptors are either in active use in clinical intervention of major common diseases or under evaluation for repurposing in many other disorders. Broad-spectrum influence these receptors produce in complex pathophysiological context in our body highlights their role as precise interpreters of distinctive angiotensinergic peptide cues. This review article summarizes findings published in the last 15 years on the structure, pharmacology, signaling, physiology, and disease states related to angiotensin receptors. We also discuss the challenges the pharmacologist presently faces in formally accepting newer members as established angiotensin receptors and emphasize necessary future developments.

Angiotensin II type 1 receptor (AT1) gene A1166C is associated with the risk of hypertension

AIM

This study was performed on primary hypertension patients in a Turkish population to determine the frequency of the A1166C polymorphism in the angiotensin II type 1 receptor (AT1) gene and to examine the role of this polymorphism in hypertension development.

MATERIALS AND METHODS

In this study, 250 genomic DNA samples were collected (from 142 hypertension patients and 108 healthy subjects), randomized, and analyzed. Genomic DNA was prepared from peripheral blood using the salt extraction method. The presence of the A1166C polymorphism in the AT1 gene was determined using the polymerase chain reaction (PCR)-restriction fragment length polymorphism method. PCR products were separated by 2% agarose gel electrophoresis and visualized by a charge-coupled device camera.

RESULTS

Genotype distribution and allele frequency A1166C genotype frequency was determined as AA 96.3% and AC 3.7% for controls and as AA 86.6% and AC 13.4% for patients. A statistically significant difference was found between the control group and patients in terms of genotype and allele frequency.

CONCLUSION

Our results suggest that an interaction exists between the AT1 gene polymorphism and hypertension in the Turkish population.

Genetic determinants of arterial stiffness

Stiffness of large arteries (called arteriosclerosis) is an independent predictor of cardiovascular morbidity and mortality. Although previous studies have shown that arterial stiffness is moderately heritable, genetic factors contributing to arterial stiffness are largely unknown. In this paper, we reviewed the available literature on genetic variants that are potentially related to arterial stiffness. Most variants have shown mixed depictions of their association with arterial stiffness across multiple studies. Various methods to measure arterial stiffness at different arterial sites can contribute to these inconsistent results. In addition, studies in patient populations with hypertension or atherosclerosis may overestimate the impact of genetic variants on arterial stiffness. Future studies are recommended to standardize current measures of arterial stiffness in different age groups. Studies conducted in normal healthy subjects may also provide better opportunities to find novel genetic variants of arterial stiffness.

Effect of high-fat diet upon inflammatory markers and aortic stiffening in mice

Changes in lifestyle such as increase in high-fat food consumption are an important cause for vascular diseases. The present study aimed to investigate the involvement of ACE and TGF-β in the aorta stiffness induced by high-fat diet. C57BL/6 male mice were divided in two groups according to their diet for 8 weeks: standard diet (ST) and high-fat diet (HF). At the end of the protocol, body weight gain, adipose tissue content, serum lipids and glucose levels, and aorta morphometric and biochemical measurements were performed. Analysis of collagen fibers by picrosirius staining of aorta slices showed that HF diet promoted increase of thin (55%) and thick (100%) collagen fibers deposition and concomitant disorganization of these fibers orientations in the aorta vascular wall (50%). To unravel the mechanism involved, myeloperoxidase (MPO) and angiotensin I converting enzyme (ACE) were evaluated by protein expression and enzyme activity. HF diet increased MPO (90%) and ACE (28%) activities, as well as protein expression of ACE. TGF-β was also increased in aorta tissue of HF diet mice after 8 weeks. Altogether, we have observed that the HF diet-induced aortic stiffening may be associated with increased oxidative stress damage and activation of the RAS in vascular tissue.

The A(1166)C polymorphism of the AT1R gene is associated with an early onset of hypertension and high waist circumference in Jordanian males attending the Jordan University Hospital

There is no agreement on the involvement of angiotensin II type 1 receptor (AT1R) gene A(1166)C variant and essential hypertension. The purpose of this study was to investigate the association between angiotensin II type 1 receptor (AT1R) gene A(1166)C variants with essential hypertension and some related parameters in a sample of Jordanian hypertensive patients. DNA samples from 108 hypertensive individuals and 102 age- and gender-matched non-hypertensive controls of the Jordanian population were analyzed by polymerase chain reaction followed by restriction fragment length polymorphism assay (PCR-RFLP) methods to determine the frequency of A(1166)C variants alleles. No statistically significant differences were found in the distribution of alleles and genotypes between hypertensive and non-hypertensive individuals, not even after gender segregation. The frequency of the variant allele (C(1166)) was significantly higher in the early-onset compared to the late-onset group of hypertensive males, in subjects with positive family history of hypertension, and in subjects with high waist circumference. In conclusion, the A(1166)C polymorphism is not associated with essential hypertension in Jordanian hypertensive individuals. However, it was associated with an early onset of hypertension in males, with positive family history of hypertension, and with high waist circumference irrespective of blood pressure status.

Common genetic variation in the 3'-BCL11B gene desert is associated with carotid-femoral pulse wave velocity and excess cardiovascular disease risk: the AortaGen Consortium

BACKGROUND

Carotid-femoral pulse wave velocity (CFPWV) is a heritable measure of aortic stiffness that is strongly associated with increased risk for major cardiovascular disease events.

METHODS AND RESULTS

We conducted a meta-analysis of genome-wide association data in 9 community-based European ancestry cohorts consisting of 20 634 participants. Results were replicated in 2 additional European ancestry cohorts involving 5306 participants. Based on a preliminary analysis of 6 cohorts, we identified a locus on chromosome 14 in the 3'-BCL11B gene desert that is associated with CFPWV (rs7152623, minor allele frequency=0.42, β=-0.075±0.012 SD/allele, P=2.8×10(-10); replication β=-0.086±0.020 SD/allele, P=1.4×10(-6)). Combined results for rs7152623 from 11 cohorts gave β=-0.076±0.010 SD/allele, P=3.1×10(-15). The association persisted when adjusted for mean arterial pressure (β=-0.060±0.009 SD/allele, P=1.0×10(-11)). Results were consistent in younger (<55 years, 6 cohorts, n=13 914, β=-0.081±0.014 SD/allele, P=2.3×10(-9)) and older (9 cohorts, n=12 026, β=-0.061±0.014 SD/allele, P=9.4×10(-6)) participants. In separate meta-analyses, the locus was associated with increased risk for coronary artery disease (hazard ratio=1.05; confidence interval=1.02-1.08; P=0.0013) and heart failure (hazard ratio=1.10, CI=1.03-1.16, P=0.004).

CONCLUSIONS

Common genetic variation in a locus in the BCL11B gene desert that is thought to harbor 1 or more gene enhancers is associated with higher CFPWV and increased risk for cardiovascular disease. Elucidation of the role this novel locus plays in aortic stiffness may facilitate development of therapeutic interventions that limit aortic stiffening and related cardiovascular disease events.

The effects of angiotensin II on the coupled microstructural and biomechanical response of C57BL/6 mouse aorta

RATIONALE

Abdominal aortic aneurysm (AAA) is a complex disease that leads to a localized dilation of the infrarenal aorta, the rupture of which is associated with significant morbidity and mortality. Animal models of AAA can be used to study how changes in the microstructural and biomechanical behavior of aortic tissues develop as disease progresses in these animals. We chose here to investigate the effect of angiotensin II (AngII) in C57BL/6 mice as a first step towards understanding how such changes occur in the established ApoE(-/-) AngII infused mouse model of AAA.

OBJECTIVE

The objective of this study was to utilize a recently developed device in our laboratory to determine how the microstructural and biomechanical properties of AngII-infused C57BL/6 wildtype mouse aorta change following 14 days of AngII infusion.

METHODS

C57BL/6 wildtype mice were infused with either saline or AngII for 14 day. Aortas were excised and tested using a device capable of simultaneously characterizing the biaxial mechanical response and load-dependent (unfixed, unfrozen) extracellular matrix organization of mouse aorta (using multiphoton microscopy). Peak strains and stiffness values were compared across experimental groups, and both datasets were fit to a Fung-type constitutive model. The mean mode and full width at half maximum (FWHM) of fiber histograms from two photon microscopy were quantified in order to assess the preferred fiber distribution and degree of fiber splay, respectively.

RESULTS

The axial stiffness of all mouse aorta was found to be an order of magnitude larger than the circumferential stiffness. The aortic diameter was found to be significantly increased for the AngII infused mice as compared to saline infused control (p=0.026). Aneurysm, defined as a percent increase in maximum diameter of 30% (defined with respect to saline control), was found in 3 of the 6 AngII infused mice. These three mice displayed adventitial collagen that lacked characteristic fiber crimp. The biomechanical response in the AngII infused mice showed significantly reduced circumferential compliance. We also noticed that the ability of the adventitial collagen fibers in AngII infused mice to disperse in reaction to circumferential loading was suppressed.

CONCLUSIONS

Collagen remodeling is present following 14 days of AngII infusion in C57BL/6 mice. Aneurysmal development occurred in 50% of our AngII infused mice, and these dilatations were accompanied with adventitial collagen remodeling and decreased circumferential compliance.

Stiffness of the large arteries in individuals with and without Down syndrome

BACKGROUND

Down syndrome is known to cause premature aging in several organ systems. However, it remains unclear whether this aging effect also affects the structure and function of the large arterial trunks. In this controlled study, the possibility of changes in the large arteries due to aging was evaluated in patients with Down syndrome.

METHODS

Eighty-two subjects of both genders were selected. The Down syndrome group had 41 active subjects consisting of 19 males and 22 females (mean age 21 ± 1, range 13-42 years) without cardiovascular complications and who did not use vasoactive drugs. The control group consisted of 41 healthy individuals without trisomy 21 of the same gender and age as the Down syndrome group and who did not use vasoactive medication. Carotid-femoral pulse wave velocity was obtained as an index of aortic stiffness using an automatic noninvasive method.

RESULTS

Individuals with Down syndrome had significantly lower blood pressure than those in the control group. Systolic blood pressure for the Down syndrome group and control group was 106 ± 2 mmHg vs 117 ± 2 mmHg (P < 0.001), respectively; diastolic blood pressure was 66 ± 2 mmHg vs 77 ± 2 mmHg (P < 0.001); and mean arterial pressure was 80 ± 1 mmHg vs 90 ± 1 mmHg (P < 0.001). Only age and systolic blood pressure were shown to correlate significantly with pulse wave velocity, but the slopes of the linear regression curves of these two variables showed no significant difference between the two study groups. Pulse wave velocity, which was initially significantly lower in the Down syndrome group (7.51 ± 0.14 m/s vs 7.84 ± 0.12 m/s; P <0.05), was similar between the groups after systolic blood pressure adjustment (7.62 ± 0.13 m/s vs 7.73 ± 0.13 m/s).

CONCLUSION

Despite evidence in the literature that patients with Down syndrome undergo early aging, this process does not seem to affect the large arterial trunks, given that values of carotid-femoral pulse wave velocity were similar in individuals with or without trisomy 21. Considering that Down syndrome presents with chronic hypotension, it is reasonable to propose that the prolonged reduction of arterial distending pressure may contribute to functional preservation of the arteries in patients with Down syndrome.

ACE and AGTR1 polymorphisms and left ventricular hypertrophy in endurance athletes

OBJECTIVE

This study aimed to evaluate the role of angiotensin type 1 receptor gene (AGTR1) polymorphism (A1166C) in left ventricular hypertrophy (LVH) mediated by the angiotensin-converting enzyme (ACE) in endurance athletes.

METHODS

A group of 74 white, healthy male endurance athletes, aged between 25 and 40 yr, were enrolled in this study. All of them participated primarily in isotonic sports, training for at least >10 h x wk(-1), for at least 5 yr. The ACE genotype (insertion [I] or deletion [D] alleles) was ascertained by polymerase chain reaction (DD in 35, ID in 36, and II in 3). Group II was excluded from the analysis because of its small size. No difference was found between the two groups as regards age, blood pressure, HR, and echocardiographic data.

RESULTS

The left ventricular mass index (LVMI) was significantly higher in group DD rather than in group ID (P = 0.029). The group DD showed a slightly higher prevalence of subjects with LVH (LVMI > 131 g x m(-2); 62.9%) than group ID (44.4%, P = 0.120). No association was found between ACE-DD and LVH (odds ratio (OR) = 2.12, 95% confidence interval = 0.82-5.46). Concerning the role of AGTR1 polymorphism, the highest LVMI was found in 15 athletes with ACE-DD and AGTR1-AC/CC genotypes (150 +/- 23 g x m(-2)); the lowest value of LVMI was found in the case of ACE-ID and AGTR1-AA (127 g x m(-2) +/- 18 g x m(-2)), whereas LVMI in subjects with ACE-DD + AGTR1-AA was similar to that in the ACE-ID + AGTR1-AC/CC group (134 +/- 18 g x m(-2) vs 133 +/- 20 g x m(-2), P = 0.880). The presence of ACE-DD + AGTR1 + AC/CC was strongly associated with LVH (OR = 4.6, P = 0.029). Moreover, subjects with LVH showed longer left ventricular isovolumetric relaxation time and higher end-systolic wall stress. The latter was strongly correlated to LVMI (r = 0.588), especially in the presence of ACE-DD + AGTR1 + AC/CC (r = 0.728).

CONCLUSIONS

LVMI may be greater in the presence of ACE- DD and AGTR1-AC/CC polymorphisms.

Genetic variation in the renin-angiotensin system and arterial stiffness. The Rotterdam Study

We studied the associations of three renin-angiotensin system polymorphisms, angiotensin-converting enzyme (ACE) I/D, angiotensinogen 235 M/T, and angiotensin II receptor type I 573 C/T, with arterial stiffness. The study was embedded in the Rotterdam Study, a population-based study older adults. The association of the polymorphisms with pulse wave velocity, the carotid distensibility, and pulse pressure was investigated in 3706 subjects. We found no association of the ACE I/D polymorphism with pulse wave velocity, but the D-allele was associated with a lower distensibility coefficient (p = 0.05) and higher pulse pressure (p = 0.01). For the angiotensinogen 235 M/T polymorphism, no significant associations with either pulse wave velocity (p = 0.71), the distensibility coefficient (p = 0.16) or pulse pressure (p = 0.34) were found. Also, we found no significant associations of pulse wave velocity (PWV) (p = 0.32), the distensibility coefficient (p = 0.08), and pulse pressure (p = 0.09) with the angiotensin II receptor type 1 573 C/T polymorphism. No epistatic effects were observed between the three renin-angiotensin system (RAS) genes with arterial stiffness. Our findings suggest that genetic variation in the renin-angiotensin system may play a role in determining carotid distensibility and pulse pressure.

Association between angiotensin II type 1 receptor polymorphisms and the occurrence of nonalcoholic fatty liver disease

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is one of the most common causes of chronic liver injury in many countries. Genetic factors are important for the development of NAFLD, as well as environmental factors. Recently an angiotensin II type 1 receptor (AGTR1) has been recognized as important in the aetiology of fibrosis in the liver.

OBJECTIVE

In this study we investigated the association between angiotensin II type 1 receptor gene polymorphism (ATGR1) and NAFLD.

METHODS

One hundred and sixty-seven NAFLD patients [106 with nonalcoholic steatohepatitis (NASH) and 61 with simple steatosis] with a positive diagnosis by liver biopsy and 435 healthy control subjects were recruited in this study.

RESULTS

We investigated 12 single nucleotide polymorphisms (SNPs) of the ATGR1 gene, among which rs3772622 showed the lowest P-value of allele frequency model (P=0.0000012) with an odds ratio (95% confidence interval) of 1.95 (1.49-2.55). Five SNPs (rs3772622, rs3772633, rs2276736, rs3772630 and rs3772627) were significantly associated with NAFLD, even when the most conservative Bonferroni's correction was applied. Linkage disequilibrium analysis revealed that SNP rs3772622 and another four SNPs (rs3772633, rs2276736, rs3772630 and rs3772627) were in the same block. We investigated the association between rs3772622 genotypes and the fibrosis index. The results of the analysis revealed an additive increase of the fibrosis index in the patients with the A allele of rs3772622.

CONCLUSIONS

This is the first report to demonstrate the genetic variations in ATGR1 that may influence the risk of NAFLD and liver fibrosis in NAFLD.

Assessment of arterial stiffness, a translational medicine biomarker system for evaluation of vascular risk

AIMS

Stiffening of the large arteries is a common feature of aging and is exacerbated by a number of disorders such as hypertension, diabetes, and renal disease. Arterial stiffening is recognized as an important and independent risk factor for cardiovascular events. This article will provide a comprehensive review of the recent advance on assessment of arterial stiffness as a translational medicine biomarker for cardiovascular risk.

DISCUSSIONS

The key topics related to the mechanisms of arterial stiffness, the methodologies commonly used to measure arterial stiffness, and the potential therapeutic strategies are discussed. A number of factors are associated with arterial stiffness and may even contribute to it, including endothelial dysfunction, altered vascular smooth muscle cell (SMC) function, vascular inflammation, and genetic determinants, which overlap in a large degree with atherosclerosis. Arterial stiffness is represented by biomarkers that can be measured noninvasively in large populations. The most commonly used methodologies include pulse wave velocity (PWV), relating change in vessel diameter (or area) to distending pressure, arterial pulse waveform analysis, and ambulatory arterial stiffness index (AASI). The advantages and limitations of these key methodologies for monitoring arterial stiffness are reviewed in this article. In addition, the potential utility of arterial stiffness as a translational medicine surrogate biomarker for evaluation of new potentially vascular protective drugs is evaluated.

CONCLUSIONS

Assessment of arterial stiffness is a sensitive and useful biomarker of cardiovascular risk because of its underlying pathophysiological mechanisms. PWV is an emerging biomarker useful for reflecting risk stratification of patients and for assessing pharmacodynamic effects and efficacy in clinical studies.

Genetics and pathophysiology of arterial stiffness

Arterial stiffness is a cardiovascular risk factor that is independent of arterial pressure. Clinically, carotid-femoral pulse wave velocity (PWV) is the gold-standard parameter of arterial stiffness. Recent genetic studies have revealed specific genes that contribute to arterial stiffening. Here we review the recent findings on genome-wide linkage analyses and candidate gene polymorphism association studies. We also focus on the latest advances in the identification of gene variants affecting PWV using high density array single nucleotide polymorphism technology in a recent genome-wide association (GWA) study. Linkage and polymorphism studies revealed a first group of genes affecting the renin-angiotensin-aldosterone system, elastic fibre structural components, metalloproteinases, and the NO pathway. A second group of genes, identified by polymorphism association studies and possibly involved in the pathophysiology of arterial stiffness, includes beta-adrenergic receptors, endothelin receptors, and inflammatory molecules. The last group of genes, identified by GWA studies and unrelated to currently suspected mechanisms of arterial stiffness, may target transcriptional pathways controlling gene expression, differentiation of vascular smooth muscle cells, apoptosis of endothelial cells, or the immune response within the vascular wall.

Angiotensin II type 1 receptor 1166C polymorphism is associated with abdominal aortic aneurysm in three independent cohorts

OBJECTIVE

Although polymorphic variations in genes of the RAS system have previously been associated with susceptibility to AAA, such studies have been significantly limited by small sample sizes. This study was undertaken, using the largest case series yet reported, to determine whether common genetic variants of the RAS are associated with either susceptibility or severity of AAA.

METHODS AND RESULTS

The frequencies of 4 common genetic variants of genes related to the renin-angiotensin system were investigated in 3 geographically distinct, but ethnically similar, case-control cohorts, resulting in comparison of 1226 AAA cases with 1723 controls. In all 3 the AGTR1 1166C allele was significantly more common in AAA patients than controls (overall adjusted OR 1.60, 95% CI 1.32 to 1.93, P=1.1x10(-6)). Overall, the ACE ID genotype was associated with AAA (OR 1.33, 95% CI 1.06 to 1.67, P<0.02). The AGT 268T allele appeared to have an epistatic effect on large aneurysm size.

CONCLUSIONS

This study has identified a strong and repeated association between the AGTR1 1166C allele and susceptibility to AAA, and a weaker effect associated with the ACE deletion allele, in 3 geographically distinct, but ethnically similar, case-control cohorts. This study highlights the key role of the RAS in AAA and emphasizes the need for replication and validation of results in suitable independent cohorts.

Synergistic effect of angiotensin II type 1 receptor and endothelial nitric oxide synthase gene polymorphisms on arterial stiffness

Angiotensin II and nitric oxide belong to important factors in the functional and structural changes of vessel wall, leading to its increased stiffness. We investigated, whether common mutations of angiotensin II type 1 receptor (AGTR(1)) and endothelial nitric oxide synthase (eNOS) are associated with increased arterial stiffness. Two polymorphisms, A(1166)C of AGTR(1) and T(786)C of Enos, were estimated in a random, general population-based sample of 250 subjects. Arterial stiffness was measured using Sphygmocor as aortic (carotid-femoral) and peripheral (femoral-tibial) pulse wave velocities (PWV). Carriers of 3-4 mutant alleles from both polymorphisms, that is, homozygous for both mutations or homozygous for one and heterozygous for the second one, showed significantly higher peripheral PWV (17.92+/-2.40) than those with none or only 1-2 mutant alleles (12.37+/-0.51; P<0.003). Carriers of 3-4 mutant alleles had three times higher risk of having increased peripheral PWV (>or= 13.63 m s(-1), that is, in the top quartile) and this association remained significant after adjustment for potential confounders. No association was found between estimated genotypes and aortic PWV. In conclusion, combination of A(1166)C of AGTR(1) and T(786)C of eNOS mutations increased stiffness of muscular-type arteries.

HEREDITARY AND ENVIRONMENTAL INFLUENCES ON ARTERIAL FUNCTION

1. With the ageing population and increasing heart failure, arterial function has been shown to contribute to cardiovascular risk because of its adverse effects on ventriculovascular coupling. Population studies have confirmed independent prognostic information of arterial stiffening on cardiovascular survival. 2. The term 'arterial function' encompasses a range of phenotypes, including measures of arterial structure/remodelling, measures of arterial wall mechanics, surrogate measures of stiffness and of wave reflection. There exists significant interaction between these measures and none is truly independent of the others. Added to this complexity is the recognition that, although arterial function has a strong genetic component, quantification requires a range of techniques from twin to family and population studies. 3. The contribution of heritability is often derived from statistical models with input from genomic scanning and candidate gene studies. Studies to date confirm a significant heritable component for the majority of phenotypes examined. However, it has also been recognized that the factors involved in blood pressure maintenance are likely to be separate to those in arterial structural degeneration with ageing. Candidate genes for arterial function go beyond those of the sympathetic and renin-angiotensin systems and include genes involved in signalling pathways and extracellular matrix modulation. 4. The present review examines the evidence for heritability of the major arterial function phenotypes with environmental and ageing modulation. A brief overview of the impact of atherosclerotic risk factors on arterial function is included.

GENETIC INFLUENCES ON THE ARTERIAL WALL

1. Arterial stiffness, which has independent predictive value for cardiovascular events, seems to have a genetic component, largely independent of the influence of blood pressure and other cardiovascular risk factors. 2. In animal models of essential hypertension (stroke-prone spontaneously hypertensive rats and spontaneously hypertensive rats), structural modifications of the arterial wall include an increase in the number of elastin-smooth muscle cell connections and smaller fenestrations of the internal elastic lamina, possibility leading to redistribution of the mechanical load towards elastic materials. These modifications may give rise to mechanisms explaining why changes in arterial wall material accompanying wall hypertrophy in these animals are not associated with an increase in arterial stiffness. 3. In monogenic connective tissue diseases (Marfan, Williams and Ehlers-Danlos syndromes) and the corresponding animal models, precise characterization of the arterial phenotype makes it possible to determine the influence of abnormal, genetically determined, wall components on arterial stiffness. 4. Such studies have highlighted the role of extracellular matrix signalling in the vascular wall and have shown that elastin and collagen not only display elasticity or rigidity, but are also involved in the control of smooth muscle cell function. 5. These data provide strong evidence that arterial stiffness is affected by the amount and density of stiff wall material and the spatial organization of that material.

Long-term trandolapril treatment is associated with reduced aortic stiffness: the prevention of events with angiotensin-converting enzyme inhibition hemodynamic substudy

The Prevention of Events with Angiotensin Converting Enzyme inhibition (PEACE) trial evaluated angiotensin-converting enzyme inhibition with trandolapril versus placebo added to conventional therapy in patients with stable coronary disease and preserved left ventricular function. The PEACE hemodynamic substudy evaluated effects of trandolapril on pulsatile hemodynamics. Hemodynamic studies were performed in 300 participants from 5 PEACE centers a median of 52 months (range, 25 to 80 months) after random assignment to trandolapril at a target dose of 4 mg per day or placebo. Central pulsatile hemodynamics and carotid-femoral pulse wave velocity were assessed by using echocardiography, tonometry of the carotid and femoral arteries, and body surface transit distances. Patients randomly assigned to trandolapril tended to be older (mean+/-SD: 64.2+/-7.9 versus 62.9+/-7.7 years; P=0.14), with a higher body mass index (28.5+/-4.0 versus 27.8+/-3.9 kg/m(2); P=0.09) and lower ejection fraction (57.1+/-8.1% versus 58.7+/-8.4%; P<0.01). At the time of the hemodynamic substudy, the trandolapril group had lower mean arterial pressure (93.1+/-10.2 versus 96.3+/-11.3 mm Hg; P<0.01) and lower carotid-femoral pulse wave velocity (geometric mean [95% CI]: 10.4 m/s [10.0 to 10.9 m/s] versus 11.2 m/s [10.7 to 11.8 m/s]; P=0.02). The difference in carotid-femoral pulse wave velocity persisted (P<0.01) in an analysis that adjusted for baseline characteristics and follow-up mean pressure. In contrast, there was no difference in aortic compliance, characteristic impedance, augmentation index, or total arterial compliance. Angiotensin-converting enzyme inhibition with trandolapril produced a modest reduction in carotid-femoral pulse wave velocity, a measure of aortic wall stiffness, beyond what would be expected from blood pressure lowering or differences in baseline characteristics alone.

Effect of dietary supplementation with βcasein A1 or A2 on markers of disease development in individuals at high risk of cardiovascular disease

The present study is the first to examine the hypothesis that dietary supplementation with β-casein A1 promotes an increased risk relative to supplementation with β-casein A2 in patients traditionally at high risk of developing CVD. The study was conducted in fifteen asymptomatic participants (six male; nine female) at high risk of developing CVD. A double-blind cross-over study design was used with a total duration of 24 weeks. Dietary intervention was a daily supplementation (25g) of either casein A1 or A2 (for 12 weeks each). Surrogate measures of cardioprotection studied included the examination of vascular (endothelium and arterial) function, resting blood pressure, plasma lipids and biochemical markers of inflammation. Total plasma cholesterol levels were significantly lower following 12 weeks of both casein A1 and A2 interventions but the decrease was not different between intervention. Plasma insulin, homocysteine, C-reactive protein, fibrinogen, protein C and S and von Willebrand factor levels were not different between the two casein supplements. Endothelium function, measured as a vascular response using venous occlusion plethysmography to intra-aterial infusions of the endothelium-dependent agonist acetylcholine, were not different between the two casein interventions. Similarly, neither blood pressure nor measures of large artery stiffness were affected by differing the casein variant. We therefore conclude that there is no evidence from the present study that supplementation with casein A1 has any cardiovascular health disadvantage over consumption of casein A2.

Early sign of atherosclerosis in slow coronary flow and relationship with angiotensin-converting enzyme I/D polymorphism

Increase in carotid artery intima-media thickness (IMT) is an early sign of atherosclerosis. Slow coronary flow (SCF) is characterized by delay of opacification of coronary arteries in coronary angiography in the absence of any evident obstructive lesion, but its etiopathogenesis remains unclear. Genes that regulate the renin angiotensin system also play a role in developing cardiovascular system disorders. The presence of deletion (D) allele in angiotensin converting enzyme (ACE) gene polymorphism is associated with coronary artery disease. The aim of this study was to investigate the carotid artery IMT measurement, as an early sign of atherosclerosis, in patients with SCF and without SCF and also to assess the effect of the renin-angiotensin gene system on carotid IMT. Forty-four patients with angiographically proven SCF and 44 cases with normal coronary flow (NCF) pattern with similar risk profile were enrolled in the study. Coronary flow patterns of the cases were determined by thrombolysis in myocardial infarction (TIMI) frame count method. Intima-media thickness was measured by recording ultrasonographic images of both the left and right common carotid artery with a 12-MHz linear array transducer. ACE I/D polymorphism and Angiotensin II tip 1 receptor (AT1R) A/C gene polymorphism were determined by polymerase chain reaction (PCR) amplification. Demographic characteristics and coronary artery disease risk factors of SCF and NCF groups were similar. Mean TIMI frame count and carotid IMT (mm) were significantly higher in the SCF group than controls (45.9 +/- 12 vs 23.3 +/- 3.7, P = 0.0001; 0.75 +/- 0.08 vs 0.69 +/- 0.06, P = 0.0001, respectively). Mean TIMI frame count was positively correlated with IMT of carotid artery in correlation analysis (r = 0.45, P = 0.0001). When analyzed in regard to ACE genotype in all subjects, IMT values were statistically different (0.78 +/- 0.06 for DD genotype, 0.72 +/- 0.05 for ID genotype, and 0.64 +/- 0.06 for II genotype, P = 0.0001). This difference remained significant in subgroup analyses for each genotype. No association could be observed between the AT1R A/C(1166) polymorphism and IMT of carotid artery measurement (P > 0.05). Lack of association was still observed with analysis carried out when genotype effect was assumed to be inherited as additive (CC versus AA versus AC) or dominant (AA versus AC+CC). Increased IMT in patients with SCF shows that subclinical atherosclerosis may play role in this phenomenon. This increase was most marked in the presence of D allele of ACE genotype, which is associated with vascular hypertrophy.

Influence of the Angiotensin II Type I Receptor Gene 1166A > C Polymorphism on BP and Aortic Pulse Wave Velocity Among Malays

Angiotensin II type 1 receptor (AGT1R) gene 1166A > C polymorphism has been shown to be associated with essential hypertension and aortic stiffness as measured by carotid femoral pulse wave velocity (PWV). This study was carried out to investigate the association of the 1166A > C polymorphism with blood pressure (BP) and PWV among Malay hypertensive and normotensive subjects. Two hundred and one hypertensive subjects without evidence of cardiovascular (CV) complications and 201 age- and sex-matched normotensive subjects were studied in a cross-sectional design. Blood pressures (BP) and PWV were measured, and 1166A > C genotype was determined by polymerase chain reaction followed by restriction enzyme digestion. The 1166C allele frequency was 7.96% and 7.73% among Malay hypertensive and normotensive subjects, respectively. There was no association of the 1166A > C polymorphism with BP in the hypertensive, normotensive or overall Malay populations. PWV was significantly higher among 1166C allele carriers as compared to non-carriers (10.52 +/- 1.82 vs. 10.15 +/- 1.80, p = 0.040) in the overall population, but not in the hypertensive and normotensive populations separately. In conclusion, the frequency of 1166C polymorphism is similar among Malay hypertensive and normotensive subjects. This polymorphism has no association with BP but may have an influence on PWV in Malays, which needs further investigation.

Angiotensin II type 1 receptor 1166A/C polymorphism in association with blood pressure response to exogenous angiotensin II

BACKGROUND

The angiotensin II type 1 receptor (AT1R) 1166A/C polymorphism is reported to be implicated in cardiovascular diseases. The association between the 1166A/C polymorphism and diastolic blood pressure (DBP) changes in response to exogenous angiotensin II and valsartan was evaluated by pharmacokinetic and pharmacodynamic modeling.

METHODS

Thirteen normotensive, healthy adults (six with the 1166A/A polymorphism and seven with 1166A/C) were enrolled in this clinical study. Angiotensin II was infused continuously over a 2-min period at four different rates (from 5 ng/kg/min and increased by 5 ng/kg/min) at 0 (before valsartan dosing), 2, 4, 8, 12, and 24 h after a single oral dose of valsartan (40 mg). BP was measured serially before and at the end of each rate of angiotensin II infusion. Plasma concentration-time profiles of valsartan were established over a 24-h period. We analyzed data using NONMEM and studied the relationship between the AT1R 1166A/C genotypes and BP responses.

RESULTS

Plasma valsartan concentrations and DBP data best fitted into a two-compartment linear model and E(max) model (E(max) with baseline for angiotensin II and inhibitory E(max) for valsartan), respectively. The ED50 for angiotensin II in the subjects with 1166A/C [95% confidence interval (CI): 4.30 approximately 14.02 ng/kg/min] was significantly lower than in those with 1166A/A (95% CI: 14.23 approximately 28.77 ng/kg/min), while the E(max) for angiotensin II and EC50 for valsartan was similar in both genotype groups.

CONCLUSIONS

These results suggest that exogenous human angiotensin II increases the BP more potently in subjects with 1166A/C than in those with 1166A/A.

Angiotensin II cell signaling: physiological and pathological effects in the cardiovascular system

The renin-angiotensin system is a central component of the physiological and pathological responses of cardiovascular system. Its primary effector hormone, angiotensin II (ANG II), not only mediates immediate physiological effects of vasoconstriction and blood pressure regulation, but is also implicated in inflammation, endothelial dysfunction, atherosclerosis, hypertension, and congestive heart failure. The myriad effects of ANG II depend on time (acute vs. chronic) and on the cells/tissues upon which it acts. In addition to inducing G protein- and non-G protein-related signaling pathways, ANG II, via AT(1) receptors, carries out its functions via MAP kinases (ERK 1/2, JNK, p38MAPK), receptor tyrosine kinases [PDGF, EGFR, insulin receptor], and nonreceptor tyrosine kinases [Src, JAK/STAT, focal adhesion kinase (FAK)]. AT(1)R-mediated NAD(P)H oxidase activation leads to generation of reactive oxygen species, widely implicated in vascular inflammation and fibrosis. ANG II also promotes the association of scaffolding proteins, such as paxillin, talin, and p130Cas, leading to focal adhesion and extracellular matrix formation. These signaling cascades lead to contraction, smooth muscle cell growth, hypertrophy, and cell migration, events that contribute to normal vascular function, and to disease progression. This review focuses on the structure and function of AT(1) receptors and the major signaling mechanisms by which angiotensin influences cardiovascular physiology and pathology.

Estimation of an age-specific reference interval for pulse wave velocity: a meta-analysis

OBJECTIVE

To estimate an age-specific reference interval for carotid-femoral pulse wave velocity (PWV), an index of aortic stiffness, and to determine the predictive values of the reference range for detecting those at moderate and high risk of cardiovascular disease (CVD).

DESIGN AND METHODS

We searched MEDLINE using PubMed from 1995 to 2005 for all studies in which Carotid-Femoral PWV was measured using a Complior (Colson, Paris, France) apparatus in Caucasian non-pregnant adults. Twenty-five studies were included, covering 30 groups of subjects; these groups were classified a priori into low (normal), moderate, and high CVD risk categories, with 2008, 5979, and 180 (total 8167) subjects, respectively. Individual-level data were simulated for each group, and an age-specific reference interval was calculated by using fractional polynomial functions.

RESULTS

We plotted an age-adjusted normal curve for PWV with 2.5, 5, 50, 90, 95, and 97.5 centile limits. Applying this reference interval to the moderate- and high-risk groups using simulations yielded sensitivities of 34.3 [95% confidence interval (CI) 33.2-35.3] and 57.2 (95% CI 55.2-59.3), respectively, specificities of 95.3 (95% CI 94.8-95.8) and 95.3 (95% CI 94.4-96.2), respectively, and positive likelihood ratios of 7.3 and 12.2, respectively.

CONCLUSION

We constructed an age-adjusted reference curve for PWV. Using the 95th centile of this curve as a threshold (e.g. 10.94, 11.86, and 13.18 m/s for 20, 40, and 60 years old) shows construct validity, as it appears to identify medium and high CVD risk groups reasonably accurately. This reference range needs to be tested using other datasets.

Molecular genetics of human hypertension

EH (essential hypertension) is a major public health problem in many countries due to its high prevalence and its association with coronary heart disease, stroke, renal disease, peripheral vascular disease and other disorders. Epidemiological studies have demonstrated that EH is heritable. Owing to the fact that blood pressure is controlled by cardiac output and total peripheral resistance, many molecular pathways are believed to be involved in the disease. In this review, recent genetic studies investigating the molecular basis of EH, including different molecular pathways, will be highlighted.

Common carotid arterial stiffness and the risk of ischaemic stroke

In the present case-control study we aimed to investigate the association of common carotid arterial (CCA) stiffness with ischaemic stroke (IS) and to determine whether this relationship was independent of conventional risk factors including CCA intima-media thickness (CCA-IMT). CCA distensibility, defined as the change of CCA-diameter during the cardiac cycle, and CCA-IMT were evaluated by means of high-resolution B-mode carotid ultrasound examination in consecutive, first-ever IS patients (n=193) and in age- and sex-matched control subjects (n=106). The CCA distensibility (inverse of CCA stiffness) was significantly (P=0.007) lower in IS (0.353 mm, 95% CI: 0.326-0.379) than in control subjects (0.415 mm, 95% CI: 0.378-0.451) even after adjusting for blood pressure values, diastolic CCA-diameter and height. The multivariate logistic regression procedure selected CCA-IMT and CCA distensibility as the only independent predictor variables of IS. Each 1 SD increase in the CCA-IMT and each 1 SD decrease in the CCA distensibility independently increased the likelihood of IS by 167.0% (OR: 2.67, 95% CI: 1.80-3.96, P<0.001) and 59.0% (OR: 1.59, 95% CI: 1.22-2.07, P=0.001) respectively. Increased CCA stiffness is associated with IS independent of conventional risk factors and CCA-IMT. The causal interrelationship between the elastic properties of the CCA and the risk of stroke deserves further investigation by longitudinal studies.

Genetic contribution to the acute effects of angiotensin II type 1 receptor blockade

OBJECTIVE

Clinical observations point towards heterogeneity in patients' responses to antihypertensive drugs. As our earlier work showed that angiotensin II (AngII) sensitivity is associated with the A1166C polymorphism of the AngII type 1 receptor (AT1R) gene, we conducted the present study in which the responses to acute AT1R blockade were evaluated.

METHODS

After 7 days of low and high sodium diet, the hormonal as well as systemic and renal hemodynamic responses to acute AT1R blockade with EXP3174 (active metabolite of losartan) were studied in 15 AA and 14 CC essential hypertensive patients. By means of platelet-binding studies the baseline AT1R density (Bmax) and affinity (KD) was tested.

RESULTS

During low and high salt diet, baseline Bmax and KD were comparable between both genotype groups. At baseline, during low salt diet, CC patients had significantly lower glomerular filtration rate and a trend towards lower effective renal plasma flow (ERPF) compared to AA patients. Blood pressure responses to EXP3174 during high salt were significantly blunted in CC patients compared to AA patients (mean arterial pressure: 1.8 versus 7.5%; P < 0.05). During low salt the increase in ERPF (12.9 versus 16.1%; P = 0.08), as well as the decrease in filtration fraction (9.0 versus 14.0%; P = 0.05) and renal vascular resistance (7.5 versus 15.1%; P = 0.06) were blunted in CC patients compared to AA patients. Humoral effects did not differ between the groups.

CONCLUSION

This study shows that the systemic and renal hemodynamic responses to acute AT1R blockade are, at least in part, genetically determined.

Association between angiotensin II type 1 receptor gene polymorphism and essential hypertension: the Ohasama Study

Gene targeting approaches have suggested that the angiotensin II type 1 receptor (AT1R) is involved in blood pressure (BP) regulation and modulation of the effect of angiotensin II. The A1166C polymorphism of the AT1 receptor gene (AT1R/A1166C) is associated with hypertension in Caucasians, but not in Japanese. The goal of this study, the Ohasama Study, was to examine the association between AT1R/A1166C and hypertension, especially home BP, in the Japanese general population. The Ohasama Study was a cohort study based on Japanese rural residents of Ohasama Town in the northern part of Japan. Subjects who gave informed consent to the study protocol and genetic analysis were recruited. Home BP was measured twice in the morning within 1 h of waking up and in the evening just before going to bed. The TaqMan polimerase chain reaction (PCR) method clearly determined AT1R/A1166C genotypes (n =1,207). The genotype distribution of AT1R/A1166C was as follows: AA 84%; AC 15%; CC 1%. There was almost no difference in baseline characteristics among the AT1R genotypes (AA, AC, CC). In the subjects not receiving antihypertensive medication (n =817), both casual BP and home BP were not different among the AT1R genotypes after adjusting for confounding factors (age, sex, body mass index, current smoking habit and current alcohol consumption). The frequency of hypertension showed no difference among AT1R genotypes after adjusting for confounding factors, though the AC and CC genotypes were more frequent in hypertensives than in normotensives. Our data suggested that the AT1R/A1166C polymorphism is not a major genetic predisposing factor for hypertension in Japanese.

ACE DD Genotype: A Predisposing Factor for Abdominal Aortic Aneurysm

OBJECTIVE

To examine the role of polymorphisms in angiotensin converting enzyme (ACE, I/D) and angiotensin II receptor (AT1R, A1166C) in the development of abdominal aortic aneurysm (AAA).

MATERIALS AND METHODS

We investigated 250 consecutive patients, 217 males and 33 females (median age 72, range 50-83), undergone AAA elective repair and 250 healthy controls, comparable for sex and age. ACE and AT1R polymorphisms were studied by PCR-RFLP analysis. The genotype distribution was in Hardy-Weinberg equilibrium for all polymorphisms.

RESULTS

The genotype distribution and allele frequency of ACE I/D, but not AT1R A1166C polymorphism were significantly different between patients and controls (ACE I/D: p=0.0002 and p<0.0001, respectively, and AT1R A1166C: p=0.6 and p=0.4, respectively). An association between the ACE DD genotype and the predisposition to AAA was found (OR DD vs. ID+II=1.9 95% CI 1.3-2.9, p<0.0001). Multivariate analysis adjusted for age, sex, traditional vascular risk factors and other atherosclerotic localizations, showed ACE DD genotype to be independently related to the disease (OR DD vs. ID+II=2.4, 95% CI 1.3-4.2 p=0.003).

CONCLUSIONS

Our findings document that ACE DD genotype represents a susceptibility factor for AAA.

A1166C polymorphism of angiotensin II type 1 receptor, blood pressure and arterial stiffness in hypertension

OBJECTIVE

To study the association of the AC polymorphism of angiotensin II type 1 receptor gene (AGTR1) with blood pressure and central arterial stiffness in a population of hypertensive patients referred to hospital for further work-up.

METHODS

One hundred and eighty-five patients, referred to our department from April 1998 to February 2002, were included. Blood pressure was measured by conventional and 24-h ambulatory methods, and arterial stiffness by carotid-femoral pulse wave velocity (PWV) determination. Genotyping for the AGTR1 AC polymorphism was performed by polymerase chain reaction.

RESULTS

AGTR1 AC polymorphism was not associated with systolic or diastolic blood pressure, measured either by conventional (P=0.89 and P=0.67, respectively) or by 24-h ambulatory (P=0.57 and P=0.56, respectively) methods. Conversely, this polymorphism was significantly associated with PWV (P=0.006) and had a dose-allele effect, PWV increasing with the number of A alleles (10.6 +/- 2.4 m/s in CC, 11.9 +/- 2.5 m/s in AC and 12.7 +/- 2.7 m/s in AA patients, P=0.002). Multiple regression analysis showed that AC polymorphism was still independently associated with PWV (P=0.01) and was the third most important determinant of PWV after age (P <0.0001) and 24-h mean blood pressure (P <0.0001).

CONCLUSION

In our study population, central arterial stiffness assessed by PWV was significantly and independently associated with the AC polymorphism, increased PWV being associated with the presence of the A allele. Further investigations are required for identification of the underlying mechanisms.

Gene polymorphisms of the renin???angiotensin???aldosterone system and the risk of ischemic stroke

OBJECTIVE

The role of the renin-angiotensin-aldosterone system (RAAS) genes on predisposition to develop stroke, a multifactorial and polygenic cardiovascular trait, is still under investigation. In the present study we characterized the contributory role of RAAS genes in the susceptibility to develop ischemic stroke in humans.

METHODS

Allele and genotype frequencies of RAAS genes were characterized in a population of 215 cases (including only atherothrombotic and lacunar forms) and 236 controls selected in Sardinia, a large Mediterranean island with a well-known segregated population. Statistical analysis was performed in the whole population and, based on a significant interaction between angiotensin II receptor (AT1) genotype and hypertension, was also repeated in the hypertensive subgroup.

RESULTS

A significant association of the C1166/AT1 gene allelic variant with stroke was found when assuming a dominant model of transmission [unadjusted odds ratio (OR)=1.5, 95% confidence interval (CI) 1.1-2.2, P=0.024]. The strength of the association became more evident in the subgroup of hypertensive individuals (135 cases and 110 controls). In fact, in this cohort the independent OR for the AT1 gene was 2.1, 95% CI 1.2-3.7, P=0.006 in the dominant model and 2.0, 95% CI 1.3-3.2, P=0.002 in the additive model. No other RAAS gene was identified as a contributor to stroke.

CONCLUSIONS

Our findings support a predisposing role of an AT1 gene variant in the development of ischemic stroke. In particular, the AT1 gene variant exerted a major impact on ischemic stroke occurrence in the presence of hypertension.

Multiple Polymorphisms in the renin- angiotensin-aldosterone system (ACE, CYP11B2, AGTR1) and their contribution to hypertension in African Americans and Latinos in the multiethnic cohort

OBJECTIVE

When compared with other U.S. populations, African Americans have excess hypertension. Genetic variants in elements of the renin-angiotensin-aldosterone system (RAAS), namely the angiotensin-converting enzyme (ACE), aldosterone synthase (CYP11B2), and angiotensin II type 1 receptor (AGTR1) genes, have been associated with risk of hypertension in some populations.

METHODS

We genotyped the D/I polymorphism in the ACE gene, the C(-344)T polymorphism in the CYP11B2 gene, and the C(-535)T polymorphism in the AGTR1 gene among African American and Latino members of the Multiethnic Cohort Study (MEC) to determine their association with hypertension.

RESULTS

We observed no significant increase in the risk of hypertension for either African Americans or Latinos homozygous or heterozygous for the D allele of the ACE gene. Among African Americans we observed carriers of the (-344)T allele of CYP11B2 to be at increased risk of hypertension (versus CC genotype: TC genotype, OR = 1.66 [95% CI: 1.01-2.72]; TT genotype, OR = 1.74 [95% CI: 1.07-2.82]). There was also an increase in risk of hypertension associated with the AGTR1 T allele for African Americans (versus CC genotype: TC genotype, OR = 2.62 [95% CI: 1.46-4.72]; TT genotype, OR = 2.67 [95% CI: 1.51-4.74]). The associations observed with CYP11B2 and AGTR1 genotypes were not observed among Latinos.

CONCLUSION

These data suggest that the (-535)T allele of AGTR1 and (-344)T allele of CYP11B2 may increase hypertension risk among African Americans but not among Latinos. Characterization of the linkage disequilibrium and haplotype patterns in the RAAS pathway genes will be crucial to understanding differences in hypertension susceptibility in these ethnic populations.

Possible synergic effect of angiotensin-I converting enzyme gene insertion/deletion polymorphism and angiotensin-II type-1 receptor 1166A/C gene polymorphism on ischemic heart disease in patients with Kawasaki disease

ACE I/D and AT1R 1166A/C polymorphisms are considered to comprise individual risk factors for the development of coronary disease. We sought to demonstrate that the ACE I/D and AT1R 1166A/C polymorphisms affect coronary artery stenosis in patients with Kawasaki disease (KD). We examined 147 healthy controls and 281 Japanese children with KD. The patients were further divided into group N (n = 246, no ischemia) and group I (n = 35, severe coronary artery stenosis with myocardial ischemia), and we studied the genotype of ACE I/D and AT1R 1166A/C polymorphisms. We also examined ACE activity in patients with acute KD. We did not detect any prevalent genotypes of the ACE and AT1R polymorphisms between controls and KD patients. However, the prevalence of the D allele in the ACE polymorphism and of the C allele in the AT1R polymorphism tended to be higher in group I than in group N (odds ratios, 2.00 and 2.32, respectively). In addition, the presence of the D and/or C alleles significantly increased the relative risk of developing myocardial ischemia (odds ratio, 2.71; p = 0.038). During the convalescent phase of KD, ACE activity was increased despite significant attenuation during the acute phase. These results suggested that the renin-angiotensin system is associated with the formation of severe coronary artery stenosis and myocardial ischemia.

Arterial stiffness and the systolic hypertension syndrome

PURPOSE OF REVIEW

This review is intended to provide the background for a new comprehensive hemodynamic view of the syndrome of systolic or wide pulse pressure hypertension and its hallmark abnormality: increased central arterial stiffness.

RECENT FINDINGS

Studies of the pathogenesis of systolic hypertension have lagged. This review describes the systolic hypertension syndrome as a complex set of hemodynamic maladaptations that include stiff central arteries, normal peripheral arteries with variable pressure amplification characteristics, arteriolar constriction, microcirculatory rarefaction, metabolic abnormalities, cardiac hypertrophy, and increased blood pressure variability. Because the structural and functional properties of arteries of different caliber are highly heterogeneous and vary with aging and disease, simple measurements such as standard brachial artery blood pressure, brachial pulse pressure, or mean arterial pressure are inadequate to provide meaningful insight into the pathophysiology of the syndrome. Additional parameters developed to describe changes in arterial mechanics (arterial compliance or stiffness, elastic modulus, impedance, pulse wave velocity, augmentation index, and pulse pressure amplification) are intrinsically limited and are directly or indirectly pressure-dependent. Quantitation of central arterial stiffness provides a modest increment in cardiovascular and renal risk stratification.

SUMMARY

Better clinical management of systolic hypertension depends on greater insight into the syndrome as a whole, more critical analysis of existing techniques, and the development of new approaches.

Arterial stiffness and angiotensinogen gene in hypertensive patients and mutant mice

OBJECTIVE

To determine whether carotid artery stiffness was increased in patients with untreated essential hypertension who are homozygous for the T allele of the M235T polymorphism of the angiotensinogen (AGT) gene and in mutant mice carrying three copies of the angiotensinogen (Agt) gene.

METHODS

Using echotracking systems, we studied carotid mechanical properties in 98 never-treated hypertensive patients according to their AGT genotype, and in Agt mutant mice.

RESULTS

Patients homozygous for the T allele had a reduced carotid distensibility and an increased stiffness of the carotid wall material (Young's elastic modulus), independent of blood pressure, compared with patients homozygous for the M allele. In Agt1/2 mice, carotid distensibility was not significantly different from that of Agt1/1 (wild-type). Moreover, the stiffness of the arterial wall material was lower in Agt1/2 mice than in wild-type mice. In Agt1/2 mice, the greater blood pressure was not associated with arterial hypertrophy, resulting in a greater circumferential wall stress. The in-vivo and in-vitro pressor responses to angiotensin II were reduced in Agt1/2 mice, whereas the contractile response to phenylephrine was not significantly different between Agt1/1 and Agt1/2 mice, indicating the integrity of the contractile apparatus and suggesting a dysfunction of the angiotensin II type 1 receptor signalling pathways in Agt1/2 mice.

CONCLUSION

These data suggest that the angiotensinogen TT genotype at position 235 could be a genetic marker for arterial stiffness in patients with never-treated hypertension, whereas in Agt1/2 mice the dysfunction of the angiotensin II type 1 receptor signalling pathways could explain the lack of arterial wall hypertrophy and stiffness.

Genetic polymorphism of the renin???angiotensin???aldosterone system and arterial hypertension in the Italian population

OBJECTIVE

To detect the association of single polymorphisms of the renin-angiotensin-aldosterone system (RAAS), or different combinations thereof, with hypertension.

DESIGN AND METHODS

The GENIPER database is the result of a collaborative effort of 13 Italian research centres to collect genomic DNA in subjects well characterized in terms of blood pressure status. A total of 2461 subjects (normotensive = 611; hypertensive = 1850) were selected and genotyped for the angiotensin-converting enzyme insertion/deletion (ACE I/D), angiotensinogen (AGT) T/C704, angiotensin receptor type 1 (AT1) A/C1166 and aldosterone synthase (ALDO) T/C-344 genetic variants.

RESULTS

Allele frequencies were homogeneous over the Italian territory, with the relevant exception of the ACE I/D, the D allele being significantly less frequent in the northern region (61%) than in the rest of the country (67%; P < 0.0001). When comparing allele and genotype distributions in normotensives and hypertensives, the latter presented a small but statistically significant increase of the C allele of AGT T/C704, the A allele of AT1 A/C1166 and the T allele of ALDO T/C-344 polymorphisms (P = 0.018, P = 0.037 and P = 0.015, respectively), with similar trends all over the country. A step-wise logistic regression analysis confirmed these findings, by entering in the model as independent predictors of blood pressure status of AGT T/C704 (P = 0.013), ALDO T/C-344 (P = 0.032) and AT1 A/C1166 polymorphisms (P = 0.075), but not ACE I/D (P = 0.996). We also found some evidence of an additive effect of individual genetic variants of the RAAS, modulating at different levels the same functional pathway, on the risk of developing hypertension, but no synergistic interaction was observed.

CONCLUSIONS

Our results suggest that some allelic variants of RAAS genes carry a small but identifiable risk of developing arterial hypertension.

Aortic pulse wave velocity index and mortality in end-stage renal disease

BACKGROUND

Aortic pulse wave velocity (PWV) is a strong independent predictor of overall and cardiovascular mortality in patients with end-stage renal disease (ESRD). Nevertheless, because age, blood pressure, heart rate, and gender are strong determinants of both arterial stiffness and mortality, the individual relevance of PWV measurements remains controversial.

METHODS

A cohort of 242 patients with ESRD undergoing hemodialysis was studied for a mean (+/- SD) duration of 78 +/- 46 months. At entry, together with standard clinical and biochemical analyses, PWV was measured using Doppler ultrasonography. On the basis of a nomogram established on 469 nonuremic subjects, a theoretical value of PWV was determined in ESRD patients according to their age, blood pressure, gender, and heart period. The PWV index (measured PWV - theoretical PWV) was then calculated for each individual ESRD patient.

RESULTS

Based on Cox analysis, the PWV index, but neither pulse pressure nor cardiac mass, was a strong and independent predictor of both cardiovascular and overall mortality, together with age and time on dialysis before inclusion. Patients with positive (versus negative) PWV index had a twofold adjusted risk of mortality during the follow-up. Per each 1 meter/second PWV index increment, we observed a 34% (crude) and a 14% (adjusted) increase in both cardiovascular and overall mortality (P < 0.02 for all).

CONCLUSION

In ESRD patients, the calculation of a PWV index provides information about cardiovascular and overall mortality risk with high predictive power, showing that PWV measurements provide discriminatory prognostic power over and above conventional cardiovascular risk factors.