Quantitative association between a newly identified molecular variant in the endothelin-2 gene and human essential hypertension

Dissecting genetic factors affecting phenylephrine infusion rates during anesthesia: a genome-wide association study employing EHR data

BACKGROUND

The alpha-adrenergic agonist phenylephrine is often used to treat hypotension during anesthesia. In clinical situations, low blood pressure may require prompt intervention by intravenous bolus or infusion. Differences in responsiveness to phenylephrine treatment are commonly observed in clinical practice. Candidate gene studies indicate genetic variants may contribute to this variable response.

METHODS

Pharmacological and physiological data were retrospectively extracted from routine clinical anesthetic records. Response to phenylephrine boluses could not be reliably assessed, so infusion rates were used for analysis. Unsupervised k-means clustering was conducted on clean data containing 4130 patients based on phenylephrine infusion rate and blood pressure parameters, to identify potential phenotypic subtypes. Genome-wide association studies (GWAS) were performed against average infusion rates in two cohorts: phase I (n = 1205) and phase II (n = 329). Top genetic variants identified from the meta-analysis were further examined to see if they could differentiate subgroups identified by k-means clustering.

RESULTS

Three subgroups of patients with different response to phenylephrine were clustered and characterized: resistant (high infusion rate yet low mean systolic blood pressure (SBP)), intermediate (low infusion rate and low SBP), and sensitive (low infusion rate with high SBP). Differences among clusters were tabulated to assess for possible confounding influences. Comorbidity hierarchical clustering showed the resistant group had a higher prevalence of confounding factors than the intermediate and sensitive groups although overall prevalence is below 6%. Three loci with P < 1 × 10^-6 were associated with phenylephrine infusion rate. Only rs11572377 with P = 6.09 × 10^-7, a 3'UTR variant of EDN2, encoding a secretory vasoconstricting peptide, could significantly differentiate resistant from sensitive groups (P = 0.015 and 0.018 for phase I and phase II) or resistant from pooled sensitive and intermediate groups (P = 0.047 and 0.018).

CONCLUSIONS

Retrospective analysis of electronic anesthetic records data coupled with the genetic data identified genetic variants contributing to variable sensitivity to phenylephrine infusion during anesthesia. Although the identified top gene, EDN2, has robust biological relevance to vasoconstriction by binding to endothelin type A (ET_A) receptors on arterial smooth muscle cells, further functional as well as replication studies are necessary to confirm this association.

Endothelin-2, the forgotten isoform: emerging role in the cardiovascular system, ovarian development, immunology and cancer

Endothelin-2 [ET-2; also known as vasoactive intestinal contractor (VIC), in rodents] differs from endothelin-1 (ET-1) by only two amino acids, and unlike the third isoform, endothelin-3 (ET-3), it has the same affinity as ET-1 for both ET(A) and ET(B) receptors. It is often assumed that ET-2 would mimic the actions of the more abundant ET-1 and current pharmacological interventions used to inhibit the ET system would also block the actions of ET-2. These assumptions have focused research on ET-1 with ET-2 studied in much less detail. Recent research suggests that our understanding of the ET family requires re-evaluation. Although ET-2 is very similar in structure as well as pharmacology to ET-1, and may co-exist in the same tissue compartments, there is converging evidence for an important and distinct ET-2 pathway. Specifically is has been demonstrated that ET-2 has a key role in ovarian physiology, with ET-2-mediated contraction proposed as a final signal facilitating ovulation. Furthermore, ET-2 may also have a pathophysiological role in heart failure, immunology and cancer. Comparison of ET-2 versus ET-1 mRNA expression suggests this may be accomplished at the level of gene expression but differences may also exist in peptide synthesis by enzymes such as endothelin converting enzymes (ECEs) and chymase, which may allow the two pathways to be distinguished pharmacologically and become separate drug targets. LINKED ARTICLES This article is part of a themed section on Endothelin. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.168.issue-1.

Endothelin Type A Receptor Genotype is a Determinant of Quantitative Traits of Metabolic Syndrome in Asian Hypertensive Families: A SAPPHIRe Study

Co-heritability of hypertension and insulin resistance (IR) within families not only implies genetic susceptibility may be responsible for these complex traits but also suggests a rational that biological candidate genes for hypertension may serve as markers for features of the metabolic syndrome (MetS). Thus we determined whether the T323C polymorphism (rs5333) of endothelin type A (ETA) receptor, a predominant receptor evoking potent vasoconstrictive action of endothelin-1, contributes to susceptibility to IR-associated hypertension in 1694 subjects of Chinese and Japanese origins. Blood pressures (BPs) and biochemistries were measured. Fasting insulin level, insulin-resistance homeostasis model assessment (HOMAIR) score, and area under curve of insulin concentration (AUCINS) were selected for assessing insulin sensitivity. Genotypes were obtained by methods of polymerase chain reaction-restriction fragment length polymorphism. Foremost findings were that minor allele frequency of the T323C polymorphism was noticeable lower in our overall Asian subjects compared to multi-national population reported in gene database; moreover both the genotypic and allelic frequencies of the polymorphism were significantly different between the two ethnic groups we studied. The genotype distributions at TT/TC/CC were 65, 31, 4% in Chinese and 51, 41, 8% in Japanese, respectively (p < 0.0001). Additionally, carriers of the C homozygote revealed characteristics of IR, namely significantly higher levels of fasting insulin, HOMAIR score, and AUCINS at 29.3, 35.3, and 39.3%, respectively, when compared to their counterparts with TT/TC genotypes in Chinese. Meanwhile, the CC genotype was associated with a higher level of high density lipoprotein cholesterol in Japanese. No association of the polymorphism with BP was observed. This study demonstrated for the first time that T323C polymorphism of ETA receptor gene was associated with an adverse insulin response in Chinese and a favorite atherogenic index in Japanese.

Haplotype-based case-control study on human apurinic/apyrimidinic endonuclease 1/redox effector factor-1 gene and essential hypertension

BACKGROUND

Oxidative DNA damage is involved in the pathophysiology of essential hypertension (EH), which is a multifactorial disorder. Apurinic/apyrimidinic endonuclease 1/redox effector factor-1 (APE1/REF-1) is an essential endonuclease in the base excision repair pathway of oxidatively damaged DNA, in addition to having reducing properties that promote the binding of redox-sensitive transcription factors. Blood pressure in APE1/REF-1-knockout mice is reported to be significantly higher than in wild-type mice. The aim of this study was to investigate the relationship between EH and the human APE1/REF-1 gene through a haplotype-based case-control study using single-nucleotide polymorphisms (SNPs).

METHODS

We selected five SNPs in the human APE1/REF-1 gene (rs1760944, rs3136814, rs17111967, rs3136817, and rs1130409), and performed case-control studies in 265 EH patients and 266 age-matched normotensive (NT) subjects.

RESULTS

rs17111967 was found to show nonheterogeneity among Japanese subjects. There were no significant differences in the overall distribution of genotypes or alleles for each SNP between EH and NT groups. In the overall distribution of the haplotype-based case-control study constructed based on rs1760944, rs3136817, and rs1130409, the frequency of the G-T-T haplotype was significantly higher in the EH group than in the NT group (2.1% vs. 0.0%, P = 0.001). Multiple logistic regression analysis also revealed significant differences for the G-T-T haplotype, even after adjustment for confounding factors (OR = 8.600, 95% CI: 1.073-68.951, P = 0.043).

CONCLUSIONS

Based on the present results, the G-T-T haplotype appears to be a genetic marker of EH, and the APE1/REF-1 gene appears to be a susceptibility gene for EH.

Heritability and linkage study on heart rates in a Mongolian population

Elevated heart rate has been proposed as an independent risk factor for cardiovascular diseases, but their interrelationships are not well understood. In this study, we performed a genome-wide linkage scan in 1,026 individuals (mean age 30.6 years, 54.5% women) from 73 extended families of Mongolia and determined quantitative trait loci that influence heart rate. The DNA samples were genotyped using deCODE 1,039 microsatellite markers for 3 cM density genome-wide linkage scan. Correlation analysis was carried out to evaluate the correlation of the covariates and the heart rate. T-tests of the heart rate were also performed on sex, smoking and alcohol intake. Consequently, this model was used in a nonparametric genome-wide linkage analysis using variance component model to create a multipoint logarithm of odds (LOD) score and a corresponding P value. In the adjusted model, the heritability of heart rate was estimated as 0.32 (P<.0001) and a maximum multipoint LOD score of 2.03 was observed in 77 cM region at chromosome 18. The second largest LOD score of 1.52 was seen on chromosome 5 at 216 cM. Genes located on the specified locations in chromosomes 5 and 18 may be involved in the regulation of heart rate.

Relevance of Genetics and Genomics for Prevention and Treatment of Cardiovascular Disease

Atherosclerotic cardiovascular disease (CVD) is a major health problem in the United States and around the world. Evidence accumulated over decades convincingly demonstrates that family history in a parent or a sibling is associated with atherosclerotic CVD, manifested as coronary heart disease, stroke, and/or peripheral arterial disease. Although there are several mendelian disorders that contribute to CVD, most common forms of CVD are believed to be multifactorial and to result from many genes, each with a relatively small effect working alone or in combination with modifier genes and/or environmental factors. The identification and the characterization of these genes and their modifiers would enhance prediction of CVD risk and improve prevention, treatment, and quality of care. This scientific statement describes the approaches researchers are using to advance understanding of the genetic basis of CVD and details the current state of knowledge regarding the genetics of myocardial infarction, atherosclerotic CVD, hypercholesterolemia, and hypertension. Current areas of interest and investigation--including gene-environment interaction, pharmacogenetics, and genetic counseling--are also discussed. The statement concludes with a list of specific recommendations intended to help incorporate usable knowledge into current clinical and public health practice, foster and guide future research, and prepare both researchers and practitioners for the changes likely to occur as molecular genetics moves from the laboratory to clinic.

The Future of Antihypertensive Treatment

Despite progress in recent years in the prevention, detection, and treatment of high blood pressure (BP), hypertension remains an important public health challenge. Hypertension affects approximately 1 billion individuals worldwide. High BP is associated with an increased risk of mortality and morbidity from stroke, coronary heart disease, congestive heart failure, and end-stage renal disease; it also has a negative impact on the quality of life. Hypertension cannot be eliminated because there are no vaccines to prevent the development of hypertension, but, its incidence can be decreased by reducing the risk factors for its development, which include obesity, high dietary intake of fat and sodium and low intake of potassium, physical inactivity, smoking, and excessive alcohol intake. For established hypertension, efforts are to be directed to control BP by lifestyle modification (LSM). However, if BP cannot be adequately controlled with LSM, then pharmacotherapy can be instituted along with LSM. Normalization of BP reduces cardiovascular risk (for cardiovascular death, myocardial infarction, and cardiac arrest), provides renoprotection (prevention of the onset or slowing of proteinuria and progression of renal dysfunction to end-stage renal disease in patients with hypertension, diabetes mellitus types 1 and 2, and chronic renal disease), and decreases the risk of cerebrovascular events (stroke and cognition impairment), as has been amply demonstrated by a large number of randomized clinical trials. In spite of the availability of more than 75 antihypertensive agents in 9 classes, BP control in the general population is at best inadequate. Therefore, antihypertensive therapy in the future or near future should be directed toward improving BP control in treated hypertensive patients with the available drugs by using the right combinations at optimum doses, individually tailored gene-polymorphism directed therapy, or development of new modalities such as gene therapy and vaccines. Several studies have shown that BP can be reduced by lifestyle/behavior modification. Although, the reductions appear to be trivial, even small reductions in systolic BP (for example, 3-5 mm Hg) produce dramatic reduction in adverse cardiac events and stroke. On the basis of the results of clinical and clinical/observational studies, it has been recommended that more emphasis be placed on lifestyle/behavior modification (obesity, high dietary intake of fat and sodium, physical inactivity, smoking, excessive alcohol intake, low dietary potassium intake) to control BP and also to improve the efficacy of pharmacologic treatment of high BP. New classes of antihypertensive drugs and new compounds in the established drug classes are likely to widen the armamentarium available to combat hypertension. These include the aldosterone receptor blockers, vasodilator beta-blockers, renin inhibitors, endothelin receptor antagonists, and dual endopeptidase inhibitors. The use of fixed-dose combination drug therapy is likely to increase. There is a conceptual possibility that gene therapy may yield long-lasting antihypertensive effects by influencing the genes associated with hypertension. But, the treatment of human essential hypertension requires sustained over-expression of genes. Some of the challenging tasks for successful gene therapy that need to be mastered include identification of target genes, ideal gene transfer vector, precise delivery of genes into the required site (target), efficient transfer of genes into the cells of the target, and prompt assessment of gene expression over time. Targeting the RAS by antisense gene therapy appears to be a viable strategy for the long-term control of hypertension. Several problems that are encountered in the delivery of gene therapy include 1) low efficiency for gene transfer into vascular cells; 2) a lack of selectivity; 3) problem in determining how to prolong and control transgene expression or antisense inhibition; and 4) difficulty in minimizing the adverse effects of viral or nonviral vectors. In spite of the hurdles that face gene therapy administration in humans, studies in animals indicate that gene therapy may be feasible in treating human hypertension, albeit not in the near future. DNA testing for genetic polymorphism and determining the genotype of a patient may predict response to a certain class of antihypertensive agent and thus optimize therapy in individual patients. In this regard, there are some studies that report the effectiveness of antihypertensive therapy based upon the genotype of selected patients. Treatment of human hypertension with vaccines is feasible but is not likely to be available in the near future.

The vascular endothelium in hypertension

The vascular endothelium plays a fundamental role in the basal and dynamic regulation of the circulation. Thus, it has a crucial role in the pathogenesis of hypertension. A spectrum of vasoactive substances is synthesised in the endothelium; of these, nitric oxide (NO), prostacyclin (PGI2) and endothelin (ET)-1 are the most important. There is a continuous basal release of NO determining the tone of peripheral blood vessels. Systemic inhibition of NO synthesis or scavenging of NO through oxidative stress causes an increase in arterial blood pressure. Also, the renin-angiotensin-aldosterone system has a major role in hypertension as it has a direct vasoconstrictor effect and important interactions with oxygen free radicals and NO. Prostacyclin, in contrast to NO, does not contribute to the maintenance of basal vascular tone of conduit arteries, but its effect on platelets is most important. ET acts as the natural counterpart to endothelium-derived NO and has an arterial blood pressure-raising effect in man. Anti-hypertensive therapy lowers blood pressure and may influence these different mediators, thus influencing endothelial function. In summary, due to its position between the blood pressure and smooth muscle cells responsible for peripheral resistance, the endothelium is thought to be both victim and offender in arterial hypertension. The delicate balance of endothelium-derived factors is disturbed in hypertension. Specific anti-hypertensive and anti-oxidant treatment is able to restore this balance.

Fifteen polymorphisms in endothelin-1, endothelin-2 and endothelin-receptor-A genotyped by four duplex assays and seven simple assays on a LightCycler using hybridization probes

Endothelins (EDNs) are peptides, produced by various tissues, with potent vasoactive and mitogenic properties. Endothelin actions are mediated via specific G protein-coupled receptors of two subtypes, endothelin-receptor-A (EDNRA) and endothelin-receptor-B (EDNRB). Some polymorphisms of the EDN1, EDN2 and EDNRA genes may influence susceptibility to vascular diseases. Thus, genotyping for polymorphisms of these genes may represent a tool for predicting individual susceptibility to vascular diseases. Here, we report 11 fluorescence resonance energy transfer (FRET) assays for the detection of 15 polymorphisms, because the assays used in previous studies (allele-specific PCR and restriction fragment-length polymorphism assays) for some of these polymorphisms are laborious and time-consuming. The newly developed assays are fast and work without expensive ready-to-use mixtures.

A systematic analysis of disease-associated variants in the 3' regulatory regions of human protein-coding genes II: the importance of mRNA secondary structure in assessing the functionality of 3' UTR variants

In an attempt both to catalogue 3' regulatory region (3' RR)-mediated disease and to improve our understanding of the structure and function of the 3' RR, we have performed a systematic analysis of disease-associated variants in the 3' RRs of human protein-coding genes. We have previously analysed the variants that have occurred in two specific domains/motifs of the 3' untranslated region (3' UTR) as well as in the 3' flanking region. Here we have focused upon 83 known variants within the upstream sequence (USS; between the translational termination codon and the upstream core polyadenylation signal sequence) of the 3' UTR. To place these variants in their proper context, we first performed a comprehensive survey of known cis-regulatory elements within the USS and the mechanisms by which they effect post-transcriptional gene regulation. Although this survey supports the view that RNA regulatory elements function within the context of specific secondary structures, there are no general rules governing how secondary structure might exert its influence. We have therefore addressed this question by systematically evaluating both functional and non-functional (based upon in vitro reporter gene and/or electrophoretic mobility shift assay data) USS variant-containing sequences against known cis-regulatory motifs within the context of predicted RNA secondary structures. This has allowed us not only to establish a reliable and objective means to perform secondary structure prediction but also to identify consistent patterns of secondary structural change that could potentiate the discrimination of functional USS variants from their non-functional counterparts. The resulting rules were then used to infer potential functionality in the case of some of the remaining functionally uncharacterized USS variants, from their predicted secondary structures. This not only led us to identify further patterns of secondary structural change but also several potential novel cis-regulatory motifs within the 3' UTRs studied.

Genetic determinants of blood pressure regulation

Hypertension is a multifactorial disorder that probably results from the inheritance of a number of susceptibility genes and involves multiple environmental determinants. Existing evidence suggests that the genetic contribution to blood pressure variation is about 30-50%. Although a number of candidate genes have been studied in different ethnic populations, results from genetic analysis are still inconsistent and specific causes of hypertension remain unclear. Furthermore, the abundance of data in the literature makes it difficult to piece together the puzzle of hypertension and to define candidate genes involved in the dynamic of blood pressure regulation. In this review, we attempt to highlight the genetic basis of hypertension pathogenesis, focusing on the most important existing genetic variations of candidate genes and their potential role in the development of this disease. Our objective is to review current knowledge and discuss limitations to clinical applications of genotypic information in the diagnosis, evaluation and treatment of hypertension. Finally, some principles of pharmacogenomics are presented here along with future perspectives of hypertension.

Animal models of hypertension: an overview

Hypertension is a multifactorial disease involving complex interactions between genetic and environmental factors. Development of experimental models of hypertension allowed dissection and isolation of various factors associated with regulation of blood pressure, inheritance of hypertensive traits, and cellular responses to injury. The phenotype-driven approach is taking advantage of selective breeding of animals (primarily rats) that exhibit a desired phenotype, like the useful SHR. Genotype-driven models include transgenic techniques, in which mice are the most successful for selective deletion or overexpression of target genes. Notably, a combination of comparative genomics strategies and phenotypic correlates enhances the utility of hypertension models and their clinical relevance. Indeed, experimental models enabled development of targeted interventions aimed at decreasing not only blood pressure but also target organ injury. Continued utilization of experimental models simulating human hypertension, particularly those that combine other clinically relevant comorbidities like obesity or hypercholesterolemia, may afford development of effective strategies to address this common disease. Nevertheless, a cautious approach is mandatory when experimental findings in these models are extrapolated to human hypertension.

Genome-wide linkage scan for the metabolic syndrome in the HERITAGE Family Study

The metabolic syndrome involves multiple and interactive effects of genes and environmental factors. To identify chromosomal regions encoding genes possibly predisposing to the metabolic syndrome, we performed a genome-wide scan with 456 white and 217 black participants from 204 nuclear families of the HERITAGE Family Study, using regression-based, single- and multipoint linkage analyses on 509 markers. A principal component analysis was performed on 7 metabolic syndrome-related phenotypes. Two principal components, PC1 and PC2 (55% of the variance), were used as metabolic syndrome phenotypes. ANOVA was used to quantify the familial aggregation of PC1 and PC2. Family membership contributed significantly (P < 0.0023) to the variance in PC1 (r(2) = 0.38 in whites; r(2) = 0.55 in blacks) and PC2 (r(2) = 0.51; r(2) = 0.48). In whites, promising evidence for linkage (P < 0.0023) was found for PC1 (2 markers on 10p11.2) and PC2 (a marker on 19q13.4). Suggestive evidence of linkage (0.01 > P > 0.0023) appeared for PC1 (1q41 and 9p13.1) and PC2 (2p22.3). In blacks, promising linkage was found for PC2 on 1p34.1, and suggestive linkage was found on 7q31.3 and 9q21.1. The genome-wide scan revealed evidence for quantitative trait loci on chromosomal regions that have been previously linked with individual cardiovascular disease and type 2 diabetes risk factors. Some of these chromosomal regions harbor promising potential candidate genes.

Endothelin antagonism with bosentan: current status and future perspectives

Endothelin receptor antagonists have been proposed for the treatment of a variety of disorders in which the endothelins may act as pathogenic mediators, such as hypertension, congestive heart failure, and cerebral vasospasm. Bosentan is a nonpeptide competitive antagonist, which can be a good tool for studying the endothelin system. It is specific for the endothelin system and blocks the actions of endothelin at both mammalian receptors (A and B). Bosentan has recently moved into Phase III clinical trial. This review will attempt to overview the experimental and clinical effects of bosentan.

Epithelial sodium channel and the control of sodium balance: interaction between genetic and environmental factors

The epithelial sodium channel (ENaC) expressed in aldosterone-responsive epithelial cells of the kidney and colon plays a critical role in the control of sodium balance, blood volume, and blood pressure. In lung, ENaC has a distinct role in controlling the ionic composition of the air-liquid interface and thus the rate of mucociliary transport. Loss-of-function mutations in ENaC cause a severe salt-wasting syndrome in human pseudohypoaldosteronism type 1 (PHA-1). Gain-of-function mutations in ENaC beta and gamma subunits cause pseudoaldosteronism (Liddle's syndrome), a severe form of salt-sensitive hypertension. This review discusses genetically defined forms of a salt sensitivity and salt resistance in human monogenic diseases and in animal models mimicking PHA-1 or Liddle's syndrome. The complex interaction between genetic factors (ENaC mutations) and the risk factor (salt intake) can now be studied experimentally. The role of single-nucleotide polymorphisms (SNPs) in determining salt sensitivity or salt resistance in general populations is one of the main challenges of the post-genomic era.

Endothelin A receptor antagonists in congestive heart failure: blocking the beast while leaving the beauty untouched?

Congestive heart failure (CHF) is a disease process characterized by impaired left ventricular function, increased peripheral and pulmonary vascular resistance and reduced exercise tolerance and dyspnea. Thus, mediators involved in the control of myocardial function and vascular tone may be involved in its pathophysiology. The family of endothelins (ET) consists of four closely related peptides, ET-1, ET-2, ET-3, and ET-4, which cause vasoconstriction, cell proliferation, and myocardial effects through activation of ET(A) receptors. In contrast, endothelial ET(B) receptors mediate vasodilation via release of nitric oxide and prostacyclin. In addition, ET(B) receptors in the lung are a major pathway for the clearance of ET-1 from plasma. Thus, infusion of an ET(A) receptor antagonist into the brachial artery in healthy humans leads to vasodilation whereas infusion of an ET(B) receptor antagonist causes vasoconstriction. ET-1 plasma levels are elevated in CHF and correlate both with the hemodynamic severity and with symptoms. Plasma levels of ET-1 and its precursor, big ET-1, are strong independent predictors of death in patients after myocardial infarction and with CHF. ET-1 contributes to increased systemic and pulmonary vascular resistance, vascular dysfunction, myocardial ischemia, and renal impairment in CHF. Selective ET(A) as well as combined ET(A/B) receptor antagonists have been studied in patients with CHF showing impressive hemodynamic improvements (i.e. reduced peripheral vascular and pulmonary resistance as well as increased cardiac output). These results indicate that ET receptor antagonists indeed have a potential to improve hemodynamics, symptoms, and potentially prognosis of CHF which still carries a high mortality.

Endothelin receptor antagonists in congestive heart failure: a new therapeutic principle for the future?

Congestive heart failure (CHF) is characterized by impaired left ventricular function, increased peripheral and pulmonary vascular resistance and reduced exercise tolerance and dyspnea. Thus, mediators involved in the control of myocardial function and vascular tone may be involved in its pathophysiology. The family of endothelins (ET) consists of four closely related peptides, ET-1, ET-2, ET-3 and ET-4, which cause vasoconstriction, cell proliferation and myocardial effects through activation of ETA receptors. In contrast, endothelial ETB receptors mediate vasodilation via release of nitric oxide and prostacyclin. In addition, ETB receptors in the lung are a major pathway for the clearance of ET-1 from plasma. Thus, infusion of an ETA-receptor antagonist into the brachial artery in healthy humans leads to vasodilation, whereas infusion of an ETB-receptor antagonist causes vasoconstriction. Endothelin-1 plasma levels are elevated in CHF and correlate both with hemodynamic severity and symptoms. Plasma levels of ET-1 and its precursor, big ET-1, are strong independent predictors of death after myocardial infarction as well as in CHF. Endothelin-1 contributes to increased systemic and pulmonary vascular resistance, vascular dysfunction, myocardial ischemia and renal impairment in CHF. Selective ETA, as well as combined ETA/B-receptor antagonists, have been studied in patients with CHF, and their use has shown impressive hemodynamic improvement (i.e., reduced peripheral vascular and pulmonary resistance as well as increased cardiac output). These results indicate that ET-receptor antagonists, indeed, have a potential to improve hemodynamics, symptoms and, potentially, prognosis in patients with CHF, which still carries a high mortality.

Vascular protective effects of angiotensin converting enzyme inhibitors and their relation to clinical events

Endothelial cells are a rich source of a variety of vasoactive substances, which either cause vasodilation or vasoconstriction. Important endothelium-derived vasodilators are prostacyclin, bradykinin, nitric oxide and endothelium-derived hyperpolarizing factor. In particular, nitric oxide inhibits cellular growth and migration. In concert with prostacyclin. nitric oxide exerts potent anti-atherogenic and thromboresistant properties by preventing platelet aggregation and cell adhesion. Endothelium-derived contracting factors include the 21 amino acid peptide endothelin (ET). vasoconstrictor prostanoids such as thromboxane A2 and prostaglandin H2, as well as free radicals and components of the renin angiotensin system. In hypertension, elevated blood pressure transmits into cardiovascular disease by causing endothelial dysfunction. Hence, modem therapeutic strategies in human hypertension focus on preserving or restoring endothelial integrity. Angiotensin converting enzyme (ACE) inhibitors are a primary candidate for that concept as they inhibit the circulating and local renin angiotensin system. Angiotensin converting enzyme is an endothelial enzyme which converts angiotensin-I (A-I) into angiotensin-II (A-II). This effect of the ACE inhibitor prevents direct effects of angiotensin-II such as vasoconstriction and proliferation in the vessel wall but also prevents activation of the ET system and of plasminogen activator inhibitor. Furthermore, inhibition of ACE prolongs the half-life of bradykinin and stabilizes bradykinin receptors linked to the formation of nitric oxide and prostacyclin. In isolated arteries ACE inhibitors prevent the contractions induced by angiotensin II and enhance relaxation induced by bradykinin. Chronic treatment of experimental hypertension with ACE inhibitors normalizes endothelium-dependent relaxation to acetylcholine and other agonists. In addition, the dilator effects of exogenous nitric oxide donors are enhanced, at least in certain models of hypertension. In humans with essential hypertension ACE inhibitors augment endothelium-dependent relaxation to bradykinin, while those to acetylcholine remain unaffected, at least in the time frame of the published studies, i.e. 3-6 months. In patients with coronary artery disease, however, paradoxical vasoconstriction to acetylcholine is markedly reduced after 6 months of ACE inhibition. After myocardial infarction ACE inhibitors reduce the development of overt heart failure, the occurrence of reinfarction and cardiovascular death in hypertensive patients. These effects have also been demonstrated in a subgroup analysis of the SOLVD (Studies of Left Ventricular Dysfunction) trial. Thus, in summary, ACE inhibitors are an important class of drugs providing cardiovascular protection in patients with increased cardiovascular risk.

Association between diastolic blood pressure and variants of the endothelin-1 and endothelin-2 genes

The genes for endothelin (ET) and their receptors are candidates for essential hypertension. Those for ET-1, ET-2 and the ET(A) receptor were selected for mutation scanning, and associated studies comparing untreated hypertensive patients and matched controls. A number of silent polymorphisms were found, resulting from a single nucleotide insertion or a single nucleotide substitution. There were no significant differences in the frequency of any one of these between the two groups. However, for ET-1 and ET-2 there were significant differences in the quantitative measurements of blood pressure and the number of variant alleles. The variants which we have found are likely to be in linkage disequilibrium with so far undiscovered variants in the regulatory regions of the genes.

Therapeutic potential for endothelin receptor antagonists in cardiovascular disorders

The endothelins are synthesized in vascular endothelial and smooth muscle cells, as well as in neural, renal, pulmonal, and inflammatory cells. These peptides are converted by endothelin-converting enzymes (ECE-1 and -2) from 'big endothelins' originating from large preproendothelin peptides cleaved by endopeptidases. Endothelin (ET)-1 has major influence on the function and structure of the vasculature as it favors vasoconstriction and cell proliferation through activation of specific ET(A) and ET(B) receptors on vascular smooth muscle cells. In contrast, ET(B )receptors on endothelial cells cause vasodilation via release of nitric oxide (NO) and prostacyclin. Additionally, ET(B) receptors in the lung are a major pathway for the clearance of ET-1 from plasma. Indeed, ET-1 contributes to the pathogenesis of important disorders as arterial hypertension, atherosclerosis, and heart failure. In patients with atherosclerotic vascular disease (as well as in many other disease states), ET-1 levels are elevated and correlate with the number of involved sites. In patients with acute myocardial infarction, they correlate with 1-year prognosis. ET receptor antagonists have been widely studied in experimental models of cardiovascular disease. In arterial hypertension, they prevent vascular and myocardial hypertrophy. Experimentally, ET receptor blockade also prevents endothelial dysfunction and structural vascular changes in atherosclerosis due to hypercholesterolemia. In experimental myocardial ischemia, treatment with an ET receptor antagonist reduced infarct size and prevented left ventricular remodeling after myocardial infarction. Most impressively, treatment with the selective ET(A) receptor antagonist BQ123 significantly improved survival in an experimental model of heart failure. In many clinical conditions, such as congestive heart failure, both mixed ET(A/B )as well as selective ET(A) receptor antagonism ameliorates the clinical status of patients, i.e. symptoms and hemodynamics. A randomized clinical trial showed that a mixed ET(A/B) receptor antagonist effectively lowered arterial blood pressure in patients with arterial hypertension. In patients with primary pulmonary hypertension or pulmonary hypertension related to scleroderma, treatment with a mixed ET(A/B) receptor antagonist resulted in an improvement in exercise capacity. ET receptor blockers thus hold the potential to improve the outcome in patients with various cardiovascular disorders. Randomized clinical trials are under way to evaluate the effects of ET receptor antagonism on morbidity and mortality.