Molecular cloning and sequencing of the gene encoding human angiotensin II type 1 receptor

Angiotensin Receptor Blockers Are Not Just for Hypertension Anymore

Beyond blood pressure control, angiotensin receptor blockers reduce common injury mechanisms, decreasing excessive inflammation and protecting endothelial and mitochondrial function, insulin sensitivity, the coagulation cascade, immune responses, cerebrovascular flow, and cognition, properties useful to treat inflammatory, age-related, neurodegenerative, and metabolic disorders of many organs including brain and lung.

Correlation between gene polymorphism in angiotensin II type 1 receptor and type 2 diabetes mellitus complicated by hypertension in a population of Inner Mongolia

Background

The role of angiotensin II type 1 receptor (AT1R) as a key player in type 2 diabetes mellitus (T2DM) complicated with hypertension remains controversial. The present case-control study systematically investigated the association between gene the correct variation type in the angiotensin II type 1 receptor (AT1R) gene and type 2 diabetes mellitus complicated with hypertension in the Han population from the Inner Mongolia region, China.

Method

Here, state which variants were analysis, including age, occupation, triglyceride, systolic, diastolic, sex, culture, marital status, smoking, alcohol, BMI (body mass index), SBP (systolic blood pressure), DBP (diastolic blood pressure), TG (triglyceride), TC (total cholesterol), HDL-C (high-density lipoprotein cholesterol), LDL-C (low-density lipoprotein cholesterol), FPG (fasting plasma glucose). Genomic DNA was extracted from samples from 202 type 2 diabetic patients with hypertension and 216 type 2 diabetic patients without hypertension.

Results

Non-conditional regression analysis showed that in comparison with the TT genotype, the presence of the CC genotype for the T573 site of the AT1R gene increased the risk for diabetes mellitus complicated with hypertension by 3.219-fold (OR = 3.219, 95% CI: 1.042–9.941, P = 0.042). The results from multivariate linear regression analysis suggested the rs5182 polymorphism in the AT1R gene to be associated with diastolic blood pressure (P = 0.032). No other associations were found between the incidence of disease and the correct variation type at other sites of the AT1R gene.

Conclusions

Our results suggest that the rs5182 polymorphism in the AT1R gene is associated with diabetes complicated by hypertension in the Han population of Inner Mongolia.

Characterisation of angiotensin II receptors in isolated human subcutaneous resistance arteries

Subcutaneous arteries have been used as a model for resistance arteries, which are potentially involved in enhanced blood pressure (BP) regulation in man. Angiotensin II (Ang II) is an important regulator of tone, acting via type 1 (AT1-) and type 2 (AT2-) receptor subtypes. The aim of this study was to characterise the Ang II receptors in isolated human subcutaneous arteries, using pharmacological and molecular methods.

Subcutaneous arteries were obtained from patients undergoing elective gut surgery and were carefully dissected from the abdominal wall. Cylindrical segments were mounted on two L-shaped metal prongs, one of which was connected to a force-displacement transducer for continuous recording of isometric tension. Concentration-response curves to Ang II were constructed in the presence and absence of various selective AT1-receptor antagonists, candesartan, EXP3174, irbesartan and losartan, and the AT2-receptor antagonist, PD 123319. Responses to Ang II were measured as increases in force (mN) and expressed as a percentage of the response to 60 mM of KCl. Ang II caused a concentration-dependent contraction (pEC50=9.45±0.48, Emax=120±13%). Candesartan and EXP3174 caused concentration-dependent depression of the Emax of Ang II without any major shift of pEC50. Losartan and irbesartan caused a significant, dose-dependent rightward shift of the Ang II contraction-response curve in human subcutaneous arteries. The results show that contractile responses of human subcutaneous arteries are mediated via the AT1-receptor. The AT1-receptor antagonists, candesartan and EXP3174, acted in an insurmountable manner, while losartan and irbesartan were surmountable AT1-receptor antagonists. The AT2-receptor antagonist, PD 123319, (10, 100 nM) had no effect on Ang II-induced contraction. This is supported by the positive identification of mRNA for the human AT 1-receptor by RT-PCR.

Polymorphisms within angiotensin II receptor type 1 gene associated with essential hypertension in Chinese Hani and Yi minorities

INTRODUCTION

Angiotensin II receptor type 1 mediates the major cardiovascular effects of angiotensin II to regulate blood pressure. Polymorphisms of angiotensin II receptor type 1 are associated with essential hypertension, but the results are inconsistent and conflicting. The aim of the present study is to assess the association between angiotensin II receptor type 1 polymorphisms and essential hypertension risk in Chinese Hani and Yi minorities.

METHODS

This study recruited 692 unrelated Chinese Hani subjects (case vs. control = 346:346) and 615 unrelated Chinese Yi subjects (case vs. control = 303:312). Twelve selected single nucleotide polymorphisms in the angiotensin II receptor type 1 gene were genotyped using a polymerase chain reaction-restriction fragment length polymorphism method.

RESULTS

Statistical analysis indicated that the GC+CC genotype of rs387967 was significantly associated with the decreased susceptibility to essential hypertension compared with GG in a Yi population (odds ratio = 0.58, 95% confidence intervals 0.41-0.83, P = 0.003). Allele C was a protective allele for essential hypertension (odds ratio = 0.78, 95% confidence intervals 0.61-0.99, P = 0.040). This association was confirmed respectively by comparing systolic blood pressure and diastolic blood pressure between different genotypes and between different alleles, which indicated that the genotype (GC+CC) had a tendency of lower systolic blood pressure and diastolic blood pressure than GG (PSBP = 3.716 × 10(-4), PDBP = 1.187 × 10(-3)); Carriers with C had lower systolic blood pressure and diastolic blood pressure (PSBP = 7.301 × 10(-3), PDBP = 9.142 × 10(-4)). Another single nucleotide polymorphism (rs2638360) was analysed in a Hani minority, then replicated in a Yi minority. The C allele showed a consistent risk trend for essential hypertension in two independent populations (Hani: odds ratio = 1.74, 95% confidence intervals 1.01-2.99, P = 0.046; Yi: odds ratio = 1.27, 95% confidence intervals 0.82-1.96, P = 0.277). Meta-analysis revealed that the C allele could significantly increase the risk of essential hypertension (odds ratio = 1.44, 95% confidence intervals 1.02-2.02, P = 0.037).

CONCLUSION

Our findings suggest that rs387967 is associated with the susceptibility to essential hypertension in a Yi population and the tendency was replicated in systolic blood pressure and diastolic blood pressure detection. Meta-analysis revealed that C allele of rs2638360 could significantly increase the risk of essential hypertension. The two single nucleotide polymorphisms maybe play a role in the pathology of essential hypertension.

Agonistic autoantibodies against the angiotensin AT1 receptor increase in unstable angina patients after stent implantation

OBJECTIVES

Agonistic AT1 receptor autoantibodies have been described in patients with hypertension and preeclampsia. These autoantibodies could stimulate proliferation of vascular smooth muscle cells (VSMCs), which are involved in angiotensin II-induced vascular injury in cardiovascular disease. Hence, in this study, we explored the existence of agonistic AT1 receptor autoantibodies in unstable angina (UA) patients and the possible effects of them on the in-stent restenosis of these patients.

METHODS

A total of 95 UA patients and 98 healthy volunteers were enrolled. The serum of each patient was analyzed for the presence of AT1 receptor autoantibodies by enzyme-linked immunosorbent assay. Their effects on VSMC proliferation and c-fos and c-jun expression were studied in vitro.

RESULTS

AT1 receptor autoantibodies were detected in 34/95 patients with UA. The incidence was 10.2% in the control group and rose to 47.37% after stent implantation. In vitro, this autoantibody had agonist-like activity, shown as stimulation of VSMC proliferation and upregulation of c-fos and c-jun expression. These effects were similar to that of angiotensin II and could be weakened partly by the AT1-receptor blocker valsartan.

CONCLUSION

Our findings show that the autoantibody from UA patients has similar agonistic activity to angiotensin II and might play a role in the pathogenesis of in-stent restenosis in these patients.

MAPK signaling pathway regulates cerebrovascular receptor expression in human cerebral arteries

BACKGROUND

Cerebral ischemia results in enhanced expression of contractile cerebrovascular receptors, such as endothelin type B (ET(B)), 5-hydroxytryptamine type 1B (5-HT(1B)), angiotensin II type 1 (AT(1)) and thromboxane (TP) receptors in the cerebral arteries within the ischemic area. The receptor upregulation occurs via activation of the mitogen-activated protein kinases (MAPK) pathway. Previous studies have shown that inhibitors of the MAPK pathway diminished the ischemic area and contractile cerebrovascular receptors after experimental cerebral ischemia. The aim of this study was to examine if the upregulation of contractile cerebrovascular receptors after 48 h of organ culture of human cerebral arteries involves MAPK pathways and if it can be prevented by a MEK1/2 inhibitor. Human cerebral arteries were obtained from patients undergoing intracranial tumor surgery. The vessels were divided into ring segments and incubated for 48 h in the presence or absence of the specific MEK1/2 inhibitor U0126. The vessels were then examined by using in vitro pharmacological methods and protein immunohistochemistry.

RESULTS

After organ culture of the cerebral arteries the contractile responses to endothelin (ET)-1, angiotensin (Ang) II and thromboxane (TP) were enhanced in comparison with fresh human arteries. However, 5-carboxamidotryptamine (5-CT) induced decreased contractile responses after organ culture as compared to fresh arteries. Incubation with U0126 diminished the maximum contraction elicited by application of ET-1, Ang II and U46619 in human cerebral arteries. In addition, the MEK1/2 inhibitor decreased the contractile response to 5-CT. Immunohistochemistry revealed that organ culture resulted in increased expression of endothelin ET(A), endothelin ET(B) angiotensin AT(2), 5-hydroxytryptamine 5-HT(1B) and thromboxane A2 receptors, and elevated levels of activated pERK1/2, all localized to the smooth muscle cells of the cerebral arteries. Co-incubation with U0126 normalized these proteins.

CONCLUSION

The study demonstrated that there is a clear association between human cerebrovascular receptor upregulation via transcription involving activation of the MAPK pathway after organ culture. Inhibition of the MAPK pathways attenuated the vasoconstriction mediated by ET, AT and TP receptors in human cerebral arteries and the enhanced expression of their receptors. The results indicate that MAPK inhibition might be a novel target for treatment of cerebrovascular disorders.

Contribution of deletion in angiotensin-converting enzyme but not A1166C angiotensin II type-1 receptor gene polymorphisms to clinical outcomes in atherothrombotic disease

BACKGROUND AND AIMS

Angiotensin-converting enzyme insertion/deletion (rs4340) and angiotensin II type 1 receptor A1166C (rs5186) gene polymorphisms may be involved in coronary heart disease (CHD). This study was designed to evaluate potential relationships between these polymorphisms and the risk of long-term all-cause mortality and major adverse cardiovascular events (MACE) in patients requiring revascularization for atherothrombotic disease (ATD) lesions.

METHOD

This prospective observational study concerned patients referred for supra-aortic vessel disease (SVD), CHD, peripheral artery occlusive disease (PAOD) or visceral artery disease (VAD). Collected data included ATD referral site, ATD symptoms, personal and familial medical histories, ATD extent, vascular risk factors, biological values, medication use and rs4340 and rs5186 polymorphisms. The primary end point was all-cause mortality. The secondary end point, MACE, included cardiovascular death, clinical ischemic event related to SVD, CHD, PAOD or VAD.

RESULTS

The cohort comprised 956 patients of whom 872 (91.2%) were genotyped and followed for 21.1 ± 9.9 months. Patients were referred for SVD (25.9%), CHD (42.3%), PAOD (35.2%) or VAD (1.6%). All-cause mortality and MACE rates were 7.6 and 27.2%, respectively. When comparing I/D + D/D vs. I/I genotypes, rs4340 polymorphism was associated with higher all-cause mortality rates according to uni- and multivariate analyses (p=0.008 and 0.011, respectively). Other differences were not significant (rs4340 polymorphism and MACE, rs5186 polymorphism and all-cause mortality and MACE). No interaction was found between the polymorphisms. Other independent predictors of all-cause mortality included PAOD history, SVD history, body mass index <25 kg/m(2), HbA(1c) ≥6.5%, absence of dyslipidemia and no use of aspirin.

CONCLUSION

rs4340 polymorphism is associated with long-term all-cause mortality in advanced ATD patients requiring revascularization, whereas rs5186 polymorphism does not.

Increased angiotensin II type 1 receptor expression in temporal arteries from patients with giant cell arteritis

PURPOSE

Currently, giant cell arteritis (GCA) is primarily treated with corticosteroids or immunomodulating agents, but there is interest in identifying other noncorticosteroid alternatives. Similarities exist in the injury pathways between GCA and atherosclerosis. Angiotensin II is a vasoactive peptide involved in vessel inflammation during atherosclerosis, and angiotensin II receptor inhibitors are effective in preventing atherosclerosis. The present study was performed to elucidate the role of angiotensin type 1 (AT(1)) and type 2 (AT(2)) receptors in GCA.

DESIGN

Experimental retrospective immunohistochemical study of temporal arteries using archival formalin-fixed, paraffin-embedded tissue.

PARTICIPANTS

Ten patients with GCA and 10 control patients, who were clinically suspected of having GCA but were diagnosed as not having GCA, were included.

METHODS

Immunohistochemistry, using anti-AT(1) and anti-AT(2) antibodies, was performed on formalin-fixed and paraffin-embedded temporal arteries.

MAIN OUTCOME MEASURES

AT(1) and AT(2) receptor immunostaining intensity was quantified.

RESULTS

Hematoxylin-eosin-stained sections of temporal arteries from patients with GCA showed intimal hyperplasia, internal elastic lamina degeneration, and band-shaped infiltrates of inflammatory cells, including lymphocytes, histocytes, and multinucleated giant cells. AT(1) receptor staining was primarily observed in the medial layer of the temporal arteries and was higher in the patients with GCA than in the control patients. This was a result of increased AT(1) receptor immunostaining of both vascular smooth muscle cells and infiltrating inflammatory cells. Only faint immunostaining was seen for AT(2) receptors, primarily in the endothelial cells, and to a lesser extent on the smooth muscle cells. Immunostaining with antibodies for the AT(2) receptor was similar in the patients with GCA and in controls.

CONCLUSIONS

These results suggest that AT(1) receptors play a role in the development of GCA. Inhibition of the angiotensin system may thus provide a noncorticosteroid alternative for the treatment of GCA.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Association between the angiotensin-converting enzyme (insertion/deletion) and angiotensin II type 1 receptor (A1166C) polymorphisms and breast cancer among Brazilian women

Introduction.We evaluated the association between components of the renin-angiotensin system and the development of breast cancer in a case-control study by means of angiotensin-converting enzyme (ACE) insertion/deletion (I/D) and angiotensin II type 1 (AT 1)-receptor A1166C polymorphisms.

Methods. Genotyping was performed by PCR-RFLP (restriction fragment length polymorphism) or PCR (polymerase chain reaction) using genomic DNA extracted from buccal cells of subjects with (101 cases) or without (307 controls) breast cancer.

Results.The frequencies of genotypes for ACE were: DD, ID and II (in %: cases: 60; 20; 20; controls: 46; 37; 17; p=0.019, χ2); and for AT1receptor were:AA,AC and CC (in %: cases: 65; 30; 5; controls: 51; 44; 5; p=0.114, χ 2).The results suggested that the A1166C polymorphism was not associated with breast cancer risk. On the other hand, for the ACE (I/D), there seemed to be different risks for cancer between cases and controls.

Conclusions.The ID genotype was less frequently associated with the disease than were the DD or II; that is, women with the ID genotype were 3.1 times less likely to develop breast cancer than those with the other genotypes.The ID genotype might be protective against breast cancer and the ACE (I/D) polymorphism a possible target for developing genetic markers for breast cancer.

Angiotensin II type 1 receptor polymorphisms and susceptibility to hypertension: a HuGE review

The angiotensin II type 1 receptor (AGTR1) plays an integral role in blood pressure control, and is implicated in the pathogenesis of hypertension. Polymorphisms within this gene have been extensively studied in association with hypertension; however, findings are conflicting. To clarify these data, we conducted a systematic review of association studies of AGTR1 polymorphisms and hypertension, and performed a meta-analysis of the rs5186 variant. Results show that the currently available literature is too heterogeneous to draw meaningful conclusions. The definition of hypertension and gender composition of individual studies helps to explain this heterogeneity. Although the structure and splicing pattern of AGTR1 would suggest a likely effect of polymorphisms within the promoter region on gene function, few studies have been conducted thus far. In conclusion, there is insufficient evidence that polymorphisms in the AGTR1 gene are risk factors for hypertension. However, most studies are inadequately powered, and larger well-designed studies of haplotypes are warranted.

Angiotensin II Signaling in Vascular Physiology and Pathophysiology

Initially recognized as a physiologic regulator of blood pressure and body fluid homeostasis, angiotensin (Ang) II has now been shown in innumerable experiments and clinical studies to contribute to the development and maintenance of cardiovascular disease. Dissection of its signaling mechanisms over the past decades has led to the discovery of several novel concepts, such as tissue-specific metabolism of Ang peptides. Identification and cloning of the various receptors through which Ang II acts on almost all tissues has led to the development of specific pharmacologic inhibitors with proven clinical benefit in patients with cardiovascular disorders. Work on the G-protein-coupled Ang II Type 1 receptor has demonstrated that different receptors interact through oligomerization, compartmentalization, and transactivation, and may explain how Ang II can activate G-protein-independent pathways. Unraveling the downstream effects of Ang II in specific cell types corroborates the importance of the cellular redox state on certain signaling pathways. Finally, the effects of Ang II on cell function and phenotype, such as the expression of inflammatory cytokines and receptors promoting the recruitment of inflammatory cells into vascular tissues, have indicated its role in local inflammation as a general pathogenetic basis of cardiovascular disease. The recognition of Ang II as a contributor to such fundamental pathophysiologic mechanisms, which are believed to be a common pathway for diverse cardiovascular risk factors like hypertension and diabetes, has greatly advanced our knowledge of pathologic signaling in vascular tissues and may help to eventually define novel targets for pharmacologic interventions.

Cerebrovascular ETB, 5-HT1B, and AT1 receptor upregulation correlates with reduction in regional CBF after subarachnoid hemorrhage

We hypothesize that cerebral ischemia leads to enhanced expression of endothelin (ET), 5-hydroxytryptamine (5-HT), and angiotensin II (ANG II) receptors in the vascular smooth muscle cells. Our aim is to correlate the upregulation of cerebrovascular receptors and the underlying molecular mechanisms with the reduction in regional and global cerebral blood flow (CBF) after subarachnoid hemorrhage (SAH). SAH was induced by injecting 250 microl blood into the prechiasmatic cistern in rats. The cerebral arteries were removed 0, 1, 3, 6, 12, 24, and 48 h after the SAH for functional and molecular studies. The contractile responses to ET-1, 5-carboxamidotryptamine (5-CT), and ANG II were investigated with myograph. The receptor mRNA and protein levels were analyzed by quantitative real-time PCR and immunohistochemistry, respectively. In addition, regional and global CBFs were measured by an autoradiographic method. As a result, SAH resulted in enhanced contractions to ET-1 and 5-CT. ANG II [via ANG II type 1 (AT(1)) receptors] induced increased contractile responses [in the presence of the ANG II type 2 (AT(2)) receptor antagonist PD-123319]. In parallel the ET(B), 5-HT(1B), and AT(1) receptor, mRNA and protein levels were elevated by time. The regional and global CBF showed a successive reduction with time after SAH. In conclusion, the results demonstrate for the first time that SAH induces the upregulation of ET(B), 5-HT(1B), and AT(1) receptors in a time-dependent manner both at functional, mRNA, and protein levels. These changes occur in parallel with a successive decrease in CBF. Thus there is a temporal correlation between the changes in receptor expression and CBF reduction, suggesting a linkage.

[Mutation screening in Angiotensin II receptors, AGTR1 and AGTR2, and evaluation of AGTR1 polymorphisms C573T and A1166C in patients with premature adrenarche]

Precocious pubarche is the appearance of pubic hair before the age of 8 years in girls and 9 years in boys. The most frequent etiology is idiopathic precocious adrenarche, suggested, after long-term follow-up, to be associated with metabolic syndrome. One of the factors involved in the genesis of precocious adrenarche is Angiotensin II (Ang II), which promotes cell proliferation and steroidogenesis through type 1 (AT1) and type 2 (AT2) receptors. In order to study Ang II receptors mutations, 50 children with idiopathic precocious adrenarche were evaluated and compared to a control group of normal individuals. Mutations were not detected in the AGTR1 and AGTR2 genes; however, two polymorphisms were identified in the AGTR1 gene: the C573T (exon 5) and the A1166C (3' untranslated region). The polymorphic allele T573 was found in 35% of the patients and 38% of controls. The polymorphic allele C1166 was present in 24% of the patients and 26% of controls. There was no statistical difference between groups. There was also no correlation between the polymorphisms and clinical and laboratory findings, as well as their family history of metabolic syndrome.

Tissue-specific renin-angiotensin system in pulmonary lymphangioleiomyomatosis

Lymphangioleiomyomatosis (LAM), a multisystem disease found in middle-aged women, is characterized by cystic lung destruction and abdominal tumors (e.g., angiomyolipomas, lymphangioleimyomas), resulting from proliferation of abnormal-appearing, smooth muscle-like cells (LAM cells). The LAM cells, in combination with other cells, form nodular structures within the lung interstitium and in the walls of the cysts. LAM cells contain mutations in the tuberous sclerosis complex TSC1 and/or TSC2 genes, which lead to dysregulation of the mammalian target of rapamycin, affecting cell growth and proliferation. Proliferation and migration of vascular smooth muscle cells and production of angiogenic factors are regulated, in part, by angiotensin II. To determine whether a LAM-specific renin-angiotensin system might play a role in the pathogenesis of LAM, we investigated the expression of genes and gene products of this system in LAM nodules. mRNA for angiotensinogen was present in RNA isolated by laser-captured microdissection from LAM nodules. Angiotensin I-converting enzyme and chymase-producing mast cells were present within the LAM nodules. We detected renin in LAM cells, as determined by the presence of mRNA and immunohistochemistry. Angiotensin II type 1 and type II receptors were identified in LAM cells by immunohistochemistry and immunoblotting of microdissected LAM nodules. Angiotensin II is localized in cells containing alpha-smooth muscle actin (LAM cells). A LAM-specific renin-angiotensin system appears to function within the LAM nodule as an autocrine system that could promote LAM cell proliferation and migration, and could represent a pharmacologic target.

Ischemic heart disease down-regulates angiotensin type 1 receptor mRNA in human coronary arteries

Angiotensin II is important in the development of cardiovascular disease. In the present study, angiotensin II receptor mRNA levels were quantified by real-time polymerase chain reaction (real-time PCR) in human coronary arteries from patients with ischemic heart disease and controls. Furthermore, the suitability of artery culture for studying angiotensin receptor changes was evaluated by in vitro pharmacology and real-time PCR. The angiotensin type 1 (AT1) receptor mRNA levels were down-regulated in human coronary arteries from patients with ischemic heart disease as compared to controls (P<0.05). Culture of coronary arteries for 48 h induced down-regulation of the angiotensin AT1 and AT2 receptor mRNA levels and also a less efficacious angiotensin II-induced vasoconstriction (Emax=103+/-2% before and 23+/-7% after artery culture, P<0.001). Artery culture may thus be a suitable method for studying angiotensin receptor regulation.

Angiotensin II Receptor mRNA Expression and Vasoconstriction in Human Coronary Arteries: Effects of Heart Failure and Age

Angiotensin II is a potent vasoconstrictor that is implicated in the pathogenesis of hypertension, heart failure and atherosclerosis. In the present study, angiotensin II receptor mRNA expression levels were quantified by real-time polymerase chain reaction and the vasocontractile responses to angiotensin II were characterised by in vitro pharmacology in endothelium-denuded human coronary arteries. Angiotensin II type 1 (AT(1)) and type 2 (AT(2)) receptor mRNA expression levels were significantly down-regulated in arteries from patients with heart failure as compared to controls. The angiotensin II-induced vasoconstriction diminished with increasing age in patients with heart failure (r(2)=0.31, P<0.05). Also, the AT(1) receptor mRNA expression levels decreased with increasing age in patients with heart failure (r(2)=0.74, P<0.05), while no such correlation could be shown in the control group (r(2)=0.04, P=n.s.). The AT(2) receptor mRNA expression levels did not correlate with age in patients with heart failure or controls. In conclusion, the diminished angiotensin II vasoconstriction with age in heart failure patients is most likely due to a lower density of AT(1) receptors and may result from a longer period of exposure to heart failure in older patients.

Exploring type I angiotensin (AT1) receptor functions through gene targeting

The renin-angiotensin system (RAS) modulates a diverse set of physiological processes including development, blood pressure, renal function and inflammation. The principal effector molecule of this system, angiotensin II, mediates most of these actions. The classically recognized functions of the RAS are triggered via the type 1 (AT(1)) class of angiotensin receptors. Pharmacological blockade of the AT(1) receptor lowers blood pressure and slows the progression of cardiovascular and renal diseases. Gene-targeting technology provides an experimental approach for precisely dissecting the physiological functions of the RAS. Here, we review how gene-targeting experiments have elucidated AT(1) receptor functions.

The angiotensin II receptor (Agtr1a): functional regulatory polymorphisms in a locus genetically linked to blood pressure variation in the mouse

Hypertension is a complex trait with multiple genetic determinants. A previous genome-wide linkage study of systolic blood pressure in a mouse genetic backcross implicated a region of chromosome 13 (LOD = 3.3 at 16.0 cM) as a determinant of blood pressure differences between a hereditary low blood pressure strain of Mus musculus (BPL/1) and Mus spretus (SPRET); at this locus, the unexpected effect of the BPL/1 allele was to increase blood pressure. A plausible candidate locus encoding angiotensin II receptor isoform 1a (Agtr1a) is also located at 16.0 cM on chromosome 13. We therefore investigated structural and functional differences at Agtr1a between BPL/1 and SPRET, as well as the BPH/2 strain. Resequencing Agtr1a in the three strains established the exon/intron and proximal promoter structure of the mouse gene. Coding exon 3 spanned 1,960 bp (with 26 SNPs), including the 1,077-bp/359-amino acid ORF (with 5 cSNPs, all of which were synonymous). Promoter sequences revealed a consensus TATA box, conserved G/C-rich regions, and a striking, lengthy simple sequence repeat region, composed of di-, tri-, tetra-, and penta-nucleotide repeats, whose overall length varied markedly among the strains. Twenty-five other SNPs and three single nucleotide deletions differentiated the strains' promoters, six of which were in likely functional promoter motifs. Agtr1a mRNA abundance in the adrenal gland in vivo was greater (P < 0.05) in BPL/1 than SPRET, consistent with the predicted effect of the BPL/1 allele to confer higher blood pressure. When Agtr1a promoters were subcloned into luciferase reporter plasmids and transfected into PC12 chromaffin cells, basal promoter expression was higher (P < 0.001) in BPL/1 than in SPRET, consistent with the endogenous mRNA results. In summary, Agtr1a on chromosome 13 is highly polymorphic between mouse strains, although the amino acid sequence specified by the ORF is invariant, even across mouse species. We conclude that polymorphisms in the Agtr1a promoter account for differences in gene expression in vivo between BPL/1 and SPRET, in a way consistent with the effects of alleles at this locus on chromosome 13 to affect blood pressure in the mouse genome-wide linkage study.

Differential expression of AT1 receptors in the pituitary and adrenal gland of SHR and WKY

The renin-angiotensin (ANG) system has been implicated in the development of hypertension in spontaneously hypertensive rats (SHR). Because SHR are more susceptible to stress than normotensive Wistar-Kyoto rats (WKY), we measured the mRNA expression of AT1A, AT1B, and AT2 receptors in the hypothalamo-pituitary-adrenal (stress) axis of male SHR in comparison to age-matched WKY at prehypertensive (3 to 4 weeks), developing (7 to 8 weeks), and established (12 to 13 weeks) stages of hypertension. AT1A receptor mRNA was mainly expressed in the hypothalamus and adrenal gland. AT1B receptor mRNA was detected in the pituitary and adrenal gland. AT2 receptor mRNA was prominent only in the adrenal gland. When compared with WKY, SHR showed increased AT1A receptor mRNA levels in the pituitary gland at all ages in contrast to reduced pituitary AT1B receptor mRNA levels. In the adrenal gland of SHR, AT1B receptor mRNA levels were decreased at the hypertensive stages when compared with WKY. The reduced expression of adrenal AT1B receptor mRNA was localized selectively in the zona glomerulosa by in situ hybridization. No differences were observed between WKY and SHR in the expression of hypothalamic ANG receptors. ANG significantly increased plasma levels of adrenocorticotropic hormone (ACTH) and corticosterone in dexamethasone-treated SHR but not in WKY. The aldosterone response to ANG was similar in SHR and WKY. Our results suggest a differential gene expression of AT1A and AT1B receptors in the hypothalamo-pituitary-adrenal axis of SHR and normotensive WKY and imply the participation of AT1 receptors in an exaggerated endocrine stress response of SHR to ANG.

Hybrid formation between the intracellular faces of the bradykinin B2 and angiotensin II AT1 receptors and signal transduction

Most frequently, the physiologic functions of the angiotensin II (Ang II) type 1 receptor (AT1R) and bradykinin B2 receptor (BKB2R) are antagonistic, particularly with respect to the regulation of vascular tone. Despite major differences in their physiologic actions, the receptors share sequence similarities. Both link to Galpha(i) and Galpha(q) and transduce very similar signal paths, not only those relating to the traditional G-protein associated second messengers, but also those involved in transactivation mechanisms involving receptor tyrosine kinases. With respect to these paths, some differences in signaling may be accounted for by cell type specificity. However, alternative signal cascades for these two receptors are becoming increasingly evident. One such is the recruitment of signaling molecules upon receptor translocation and internalization. The AT1R translocates into clathrin-coated pits and internalizes upon recruitment of beta-arrestin 2 which then recruits ASK1 and JNK3. The BKB2R translocates and internalizes mainly via caveolae. Another signaling divergence may be due to the direct activation of small G-proteins by both receptors. AT1R activates the RhoA, Rac1, Cdc42 while BKB2R couples only with Rac1 and Cdc42. Both receptors may serve as docking stations for intracellular proteins. One such example is the YIPP motif within the C-terminus of the ATIR which associates with the JAK/STAT pathway. Another potential alternative is the activation of tyrosine/serine kinase phosphatases by BK. This mechanism may directly oppose some of the protein tyrosine/ serine kinase paths activated by AT1R. These alternative mechanisms in sum are potentially responsible for the diversion in signal transduction between these two receptors. Regardless of the route of action, our results suggest that in Rat-1 fibroblasts stably transfected with BKB2R, BK slightly decreases connective tissue growth factor (CTGF) mRNA level while in ATIR transfected cells Ang II increases CTGF mRNA markedly. To determine whether mutant hybrids can be formed between these two receptors which encompass some of the function of the donor receptor but bind the ligand of the recipient receptor, a series of hybrids were formed with BKB2R the recipient and AT1R the donor receptor. Some of these hybrids show resistance to exchanges with the AT1R and form receptors which either do not bind (IC1 exchanges) or demonstrate poor function but normal internalization (proximal C-terminus exchanges). However, other hybrids have proven very functional. For example, the IC2, IC3 and distal C-terminus of the BKB2R IC face can be replaced simultaneously with the AT1R resulting in an hybrid which binds BK, continues to signal, is internalized and resensitized. Formation of this and other less extensive hybrids is discussed. Some of these hybrids possess the capacity to function as the AT1R as exemplified by their ability to upregulate CTGF expression as wild-type (WT) AT1R.

Comparison of the antagonistic effects of different angiotensin II receptor blockers in human coronary arteries

BACKGROUND

Angiotensin II (Ang II) is a potent vasoconstrictor and a deleterious factor in cardiovascular pathophysiology. Ang II receptor blockers (ARBs) have recently been introduced into clinical practice for treatment of hypertension and congestive heart failure.

AIMS

This study was undertaken to evaluate the inhibitory effects of ARBs on vasoconstriction in humans.

METHODS

Vasomotor tone was analyzed in endothelium denuded, human coronary artery (HCA) segments. Ang II type 1 (AT(1)) and type 2 (AT(2)) receptor mRNA expression was examined by reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULTS

Ang II was a potent vasoconstrictor (pEC(50) = 7.7). At 1 nM of the AT(1) receptor antagonists, candesartan and valsartan, the maximum contraction was depressed to 57 and 50% of Ang II, respectively, indicating insurmountability. Although generally considered surmountable, the presence of 100 nM losartan elicited a depression of the Ang II response to 32%. Its active metabolite, EXP 3174 (1 nM), abolished the Ang II contraction. The AT(1) receptor antagonists had the following order of blocking effect; EXP 3174 > candesartan = valsartan > losartan. The AT(2) receptor antagonist, PD 123319 (100 nM) significantly attenuated the Ang II contraction (E(max) = 62% of Ang II). RT-PCR of HCA smooth muscle cells demonstrated expression of both AT(1) and AT(2) receptor mRNA.

CONCLUSIONS

Ang II contraction in HCA is mediated mainly by AT(1) but also involves AT(2) receptors. The active metabolite of losartan, EXP 3174, is the most efficacious AT(1) receptor antagonist in HCA.

Angiotensin II type 1 receptor gene adenine/cytosine1166 polymorphism is not associated with mitral valve prolapse syndrome in Taiwan Chinese

The adenine/cytosine1166 (A/C1166) polymorphism of the angiotensin-II type 1 receptor (AGTR1) gene is presumed to be associated with mitral valve prolapse syndrome (MVPS) in Caucasians. To investigate whether a similar association exists among the Chinese population in Taiwan, 100 patients with MVP diagnosed by echocardiography and 100 normal subjects were studied by polymerase chain reaction-based restriction analysis. The difference in genotype (chi2=0.24; p=0.89) and allelic (Yates' chi2=0.06; p=0.81) frequencies between the groups were not significant. Further categorization of the MVP patients into mild and severe subgroups also revealed no statistical difference from the controls. It was concluded that A/C1166 polymorphism of the AGTR1 gene is not a suitable genetic marker of MVPS in Taiwan Chinese.

The angiotensin II type 1 receptor and receptor-associated proteins

The mechanisms of regulation, activation and signal transduction of the angiotensin II (Ang II) type 1 (AT1) receptor have been studied extensively in the decade after its cloning. The AT1 receptor is a major component of the renin-angiotensin system (RAS). It mediates the classical biological actions of Ang II. Among the structures required for regulation and activation of the receptor, its carboxyl-terminal region plays crucial roles in receptor internalization, desensitization and phosphorylation. The mechanisms involved in heterotrimeric G-protein coupling to the receptor, activation of the downstream signaling pathway by G proteins and the Ang II signal transduction pathways leading to specific cellular responses are discussed. In addition, recent work on the identification and characterization of novel proteins associated with carboxyl-terminus of the AT1 receptor is presented. These novel proteins will advance our understanding of how the receptor is internalized and recycled as they provide molecular mechanisms for the activation and regulation of G-protein-coupled receptors.

Influence of angiotensin II type 1 receptor polymorphism on hypertension in patients with hypercholesterolemia

Essential hypertension results from the combined influence of environmental and genetic factors. The relationship between angiotensin II type 1 receptor (AT(1)) A-C(1166) polymorphism and essential hypertension is controversial. Because it is accepted that high concentration of serum cholesterol is one of risk factors of atherosclerosis, we investigated the influence of the AT(1) A-C(1166) polymorphism on hypertension in patients with hypercholesterolemia. A total of 131 hypertensive, 97 borderline, and 175 normotensive subjects were enrolled in this study. We selected hypercholesterolemic subjects on the condition that their serum concentration of total cholesterol was >220 mg/dl, and obtained 55 hypertensive, 24 borderline, and 52 normotensive subjects with hypercholesterolemia. There were no significant differences in the genotype nor allele frequency between hypertensive and normotensive subjects in the overall population. However, the presence of the C allele of the AT(1) gene has a tendency to increase the value of systolic blood pressure not only in subjects with hypercholesterolemia but also in the overall population. Furthermore, we found a significant relationship between the AT(1) polymorphism and hypertension in subjects with hypercholesterolemia; i.e., the frequency of the C allele of the AT(1) gene was significantly higher in hypertensives than in normotensives (P<0.005). These results suggested that high concentration of total cholesterol was an important risk factor to the occurrence of essential hypertension for patients who carried the C allele of the AT(1) gene.

Inhibition of angiotensin II-induced inositol phosphate production by triacid nonpeptide antagonists in CHO cells expressing human AT1 receptors

PURPOSE

The aim of the present work is to describe the inhibitory properties of LY301875 and LY303336, two polysubstituted 4-aminoimidazole AT1 receptor antagonists, on CHO cells expressing human recombinant AT1 receptors.

METHODS

The binding of [3H]-angiotensin II to intact cells as well as to angiotensin II induced inositol phosphate accumulation is measured.

RESULTS

Both antagonists inhibit specific [3H]-angiotensin II binding to AT1 receptors in these cells, with IC50 values of 5.9 and 5.2 nM, respectively. Preincubation of the cells with LY301875 results in a decline of up to 80% of the maximal angiotensin II-stimulated inositol phosphate (IP) production. A near complete decline of the maximal response is observed for LY303336. This insurmountable inhibition is attenuated for both antagonists when losartan is included during the preincubation of the cells.

CONCLUSIONS

Functional recovery experiments, in which antagonist-preincubated cells are washed and exposed to fresh media, suggest that the insurmountable inhibition by LY301875 and LY303336 is related to their relatively slow dissociation from the AT1 receptors. As already described for losartan and the derived insurmountable AT1 antagonists candesartan. EXP3174, and irbesartan, coincubation experiments reveal that LY301875 and LY303336 interact with the AT1 receptor in a manner that is competitive with angiotensin II.

Angiotensin-(1-7): an update

The renin-angiotensin system is a major physiological regulator of arterial pressure and hydro-electrolyte balance. Evidence has now been accumulated that in addition to angiotensin (Ang) II other Ang peptides [Ang III, Ang IV and Ang-(1-7)], formed in the limited proteolysis processing of angiotensinogen, are importantly involved in mediating several actions of the RAS. In this article we will review our knowledge of the biological actions of Ang-(1-7) with focus on the puzzling aspects of the mediation of its effects and the interaction Ang-(1-7)-kinins. In addition, we will attempt to summarize the evidence that Ang-(1-7) takes an important part of the mechanisms aimed to counteract the vasoconstrictor and proliferative effects of Ang II.

The effects of monotherapy or combined therapy with an angiotensin converting enzyme inhibitor following initial treatment with calcium channel blockers on residual cardiovascular abnormalities

The effects of sequential therapy with angiotensin-converting enzyme inhibitor (cilazapril) on left ventricular (LV) mass, LV diastolic function, and carotid artery distensibility were evaluated in 90 hypertensive patients whose blood pressure controlled below 140/90 mmHg with a calcium channel blocker monotherapy. The possibility of predicting the efficacy of cilazapril based on evaluation of biochemical and genetic markers of the renin-angiotensin system was examined. Before cilazapril therapy, LV diastolic function and carotid artery distensibility were significantly impaired in 32 patients with residual LV hypertrophy compared with patients without LV hypertrophy. Cilazapril improved the LV mass in these patients with LV hypertrophy and improved LV diastolic function in a subset of 20 patients with elevated plasma renin activity. Patients with residual LV hypertrophy accompanied by cardiovascular functional abnormalities. Subsequent treatment with cilazapril significantly improved LV morphology and function in those with residual LV hypertrophy or elevated plasma renin activity.

The novel G-protein coupled receptor SALPR shares sequence similarity with somatostatin and angiotensin receptors

A cDNA encoding a novel G-protein coupled receptor (GPCR) was isolated from a human cerebral cortex cDNA library by low stringency hybridization screening. This putative seven-transmembrane domain receptor of 469 amino acids was designated SALPR (Somatostatin- and Angiotensin- Like Peptide Receptor). SALPR shares the highest amount of amino acid similarity with the somatostatin (35% with SSTR5) and angiotensin receptors (31% with AT1). Reverse transcription-polymerase chain reaction (RT-PCR) analysis revealed that the SALPR mRNA is predominantly expressed in human brain regions, particularly the substantia nigra and pituitary, although the mRNA can also be detected in the peripheral tissues, albeit at low levels. Chromosomal mapping by radiation hybrid analysis localized the human SALPR gene to the chromosome 5p15.1-5p14. Transient expression of SALPR in COS-1 cells did not produce any binding sites for somatostatin or angiotensin II, indicating the necessity for further study to discover its ligand and physiological significance.

Evaluation of three polymorphisms in the promoter region of the angiotensin II type I receptor gene

BACKGROUND

Angiotensin II induces vasoconstriction and growth via stimulation of the AT1 receptor. A genetic variant (+1166A/C) in the 3' untranslated region of this gene had been found to be associated with arterial hypertension, aortic stiffness and coronary artery disease.

OBJECTIVE

In order to evaluate further the potential implications of the genetic variability of the AT1 gene we explored three newly characterized single nucleotide polymorphisms (SNPs) in its promoter in a Caucasian population-based sample (n = 623). One of these (-2228G/A) is in complete linkage disequilibrium with six additional SNPs in the region such that, indirectly, potential functional implications of these sites were assessed as well. For comparison, we genotyped the previously described +1166A/C variant

RESULTS

The allele frequencies of the -2228G/A, -1424C/ G and -521 C/T SNPs were 0.82/0.18, 0.963/0.037 and 0.64/0.36, respectively. Statistical analysis by one-factor ANOVA revealed no significant relationship of any allele, genotype or haplotype with age, sex, body mass index, heart rate, systolic or diastolic blood pressure, hypertension, the intake of antihypertensive medication or left ventricular mass. Likewise, renin, angiotensinogen, angiotensin-converting enzyme, aldosterone or atrial natriuretic peptide levels were not found to be associated with any of these SNPs. Surprisingly, the -2228 A allele was found to be overrepresented in subjects with diabetes mellitus (n = 25, P = 0.006). However, this result could not be confirmed when additional individuals with diabetes mellitus (n = 45) were analysed. A weak linkage disequilibrium was observed between the -2228 A allele and the +1166 C allele (chi2 1 3.1; P = 0.010).

CONCLUSION

From the present data it is unlikely that any one of the nine newly characterized SNPs in the promoter region of AT1 gene is associated with arterial hypertension.

Angiotensin II type 1 receptor gene polymorphism and mitral valve prolapse syndrome

BACKGROUND

Mitral valve prolapse syndrome (MVPS), a term applied to patients who have a variety of symptoms, has been associated with autonomic or neuroendocrine dysfunction. Recent evidence suggests that effects of angiotensin II mediated by the angiotensin II type 1 (AT(1)) receptor are involved in modulation of cardiovascular autonomic control in human beings. Association of a genetic polymorphism (A-C(1166)) of the AT(1) gene with abnormal vasomotion and low blood pressure related to autonomic control has been reported recently. Because the role of this genetic variant in MVPS has not been studied, we performed a case-control study of the A-C(1166) variant in a group of 76 white subjects with MVPS.

METHODS AND RESULTS

All patients were genotyped by use of a mismatch polymerase chain reaction/Afl II restriction fragment length polymorphism analysis. Frequency of the C(1166) allele was 0.4 in patients with MVPS and 0.26 in control patients. The difference in genotype (chi square = 6.5; P <.05) and allele (chi square = 5.9; P =.02) frequencies between the groups was significant. The odds ratio in favor of carrying the C allele was 4 times greater for patients with MVP than for control patients (95% confidence interval 1.4 to 12.1).

CONCLUSIONS

The current results indicate that the A-C(1166) polymorphism of the angiotensin II type 1 receptor gene is associated with MVPS in the white population.

Angiotensin II type 1 receptor gene polymorphism predicts response to losartan and angiotensin II

Angiotensin II type 1 receptor gene polymorphism predicts response to losartan and angiotensin II.

BACKGROUND

Most of the known actions of angiotensin II (Ang II) are mediated by the Ang II type 1 receptor (AGT1R). A noncoding polymorphism of the AGT1R gene has been described in which there is either an adenine (A) or cytosine (C) base at position 1166. The functional significance of this polymorphism is unknown, prompting us to examine the relationship between this polymorphism and the systemic and renal responses to AGT1R blockade and subpressor Ang II infusion.

METHODS

Sixty-six healthy Caucasian men and women, genotyped for the AGT1R polymorphism by polymerase chain reaction, were chosen to form two homogeneous groups: AA and AC/CC. Renal hemodynamic function was assessed with inulin and para-aminohippurate clearance before and after AGT1R receptor blockade with losartan and Ang II infusion.

RESULTS

The mean values at baseline for glomerular filtration rate (GFR), renal plasma flow (ERPF), and renal blood flow (RBF) were significantly lower in the AC/CC group compared with the AA group. Losartan increased the GFR and decreased the mean arterial pressure (MAP) in the AC/CC group, but did not influence these parameters in the AA group. The aldosterone responses to losartan were blunted in the AA subgroup. During Ang II infusion, AC/CC subjects maintained GFR despite equivalent declines in RBF, suggesting an enhanced efferent arteriolar constrictive response.

CONCLUSIONS

Taken together, these results suggest that there is a relationship between the AGT1R A1166-->C polymorphism and the humoral and renal hemodynamic responses to AGT1R blockade and to Ang II infusion in the sodium-replete state, and that the C allele is associated with enhanced intrarenal and peripheral Ang II activity. Further studies are required to determine the genetic locus for this effect.

Emerging features of brain angiotensin receptors

In mammalian brain, angiotensin II AT1 and AT2 receptor subtypes are apparently expressed only in neurons and not in glia. AT1 and AT2 receptor subtypes are sometimes closely associated, but apparently expressed in different neurons. Brain AT1/AT2 interactions may occur in selective cases as inter-neuron cross talk. There are two AT1 isoforms in rodents. AT1A, which predominates, and AT1B. There are also important inter-species differences in receptor expression. Relative lack of amino acid conservation in the gerbil gAT1A receptor substantially decreases affinity for the AT1 antagonists. AT1 receptors are expressed in brain areas regulating autonomic and hormonal responses. AT1A receptors are heterogeneously regulated in a number of experimental conditions. In specific areas, AT1A receptors are not normally expressed, but are induced under influence of reproductive hormones in dopaminergic neurons. There are AT1 and AT2 receptors also in areas related to limbic, sensory and motor functions and their expression is developmentally regulated. A picture is emerging of widespread, neuronally localized, heterogeneously regulated, closely associated brain angiotensin receptor subtypes, modulating multiple functions including neuroendocrine and autonomic responses, stress, cerebrovascular flow, and perhaps brain maturation, neuronal plasticity, memory and behavior.

Spectrum of use for the angiotensin-receptor blocking drugs

The renin-angiotensin system (RAS) plays an important role in regulating blood pressure, and maintaining fluid and electrolyte balance. Angiotensin II is the principal mediator of the RAS and has been implicated in the development of hypertension as well as other forms of cardiovascular and renal disease. Angiotensin II-receptor antagonists are a new class of drugs that inhibit the RAS by selectively blocking the AT(1) receptor. These compounds therefore provide more specific and thorough blockade of the RAS by inhibiting the deleterious actions of angiotensin II at the receptor level, irrespective of how this peptide is formed. The increased specificity of action of angiotensin II-receptor antagonists may also circumvent unwanted side-effects normally associated with angiotensin-converting enzyme (ACE) inhibitors (eg, cough and angioedema) as these agents do not interfere with the metabolism of other peptides (eg, bradykinin, substance P, etc.). There is still some concern with angiotensin II-receptor antagonists and the long-term effects of hyper-stimulation of the unopposed AT(2) receptor that is caused by elevated levels of angiotensin II. However, it appears that stimulation of the AT(2) receptor may actually contribute to the beneficial effects of angiotensin II-receptor antagonists by counteracting the effects mediated by the AT(1) receptor. Angiotensin II-receptor antagonists display great therapeutic promise in the field of cardiovascular medicine and are currently being exploited as new antihypertensive agents. These drugs have demonstrated safety, efficacy, and tolerability; however, morbidity and mortality data are still lacking. Nonetheless, it is likely that angiotensin II-receptor antagonists will become part of the medical arsenal against cardiovascular and renal disease, thus consideration should be given to their future use as first-line antihypertensive agents.

1166 A/C polymorphism of the angiotensin II type 1 receptor gene and the response to short-term infusion of angiotensin II

BACKGROUND

Previous studies reported an association of the 1166 A/C polymorphism of the angiotensin II (Ang II) type 1 receptor gene with high blood pressure and cardiovascular disease. We tested the hypothesis that this polymorphism affects the blood-pressure, renal hemodynamic, and aldosterone response to infused Ang II.

METHODS AND RESULTS

Young, male, white volunteers (n = 116) with normal (n = 65) or mildly elevated (n = 51) blood pressure on a high salt intake were genotyped for the 1166 A/C polymorphism. Two doses of Ang II (0.5 and 3 ng x kg(-1) x min(-1) over 30 minutes each) increased blood pressure, plasma aldosterone, glomerular filtration rate, and filtration fraction and decreased renal blood flow. The blood-pressure, renal hemodynamic, and aldosterone responses were not significantly different between subjects homozygous for the A allele (n = 56) and heterozygous subjects (n = 47) or subjects homozygous for the C allele (n = 13). Comparison of A allele homozygotes with all C allele carriers pooled (n = 60) or restriction of the analysis to normotensive volunteers also revealed no significant differences between genotypes.

CONCLUSIONS

The 1166 C variant of the Ang II type 1 receptor does not lead to a greater blood-pressure, aldosterone, or renal vascular response to infused Ang II in young, male, white subjects. We conclude that the 1166 A/C polymorphism does not have a major effect on these actions of Ang II.

The frequency of occurrence of anti-cardiac receptor autoantibodies and their correlation with clinical manifestation in patients with hypertrophic cardiomyopathy

The purpose of this study was to investigate the frequency of occurrence of autoantibodies against G-protein coupled cardiovascular receptors and their relation to the clinical manifestation of hypertrophic cardiomyopathy (HCM). Autoantibodies against beta1-receptors, Muscarin-2-receptors, Angiotensin-II-receptor subtype 1 and alpha1-receptors were determined with ELISA in 52 patients with HCM (37 male, 15 female, mean age 55 +/- 15 years) and 40 healthy, age and sex matched controls. The clinical characterization of the HCM-patients included ECG, 24-h Holter, and echocardiography. The results showed that there is no significant difference in the frequency of a single autoantibody between HCM-patients and controls. However, if the number of patients who have autoantibodies against beta1-receptors and/or Muscarin-2-receptors were counted together, there are significantly more autoantibodies in HCM compared to controls (11 vs. 2, p = 0.035). Analysis of clinical data from this pooled group of patients showed that in patients with autoantibodies, heart rate variability (HRV), ultra low frequency (ULF) and very low frequency (VLF) were decreased (HRV by 20%, ULF by 50%, and VLF by 46%, p < 0.008) whereas the QTc-interval was increased by 8% (p < 0.02 each). The ratio of septal to posterior wall thickness was increased by 23% (p = 0.05), and the preejection period was prolonged by 46% in patients with autoantibodies (p < 0.001). These results suggest that the existence of these autoantibodies could be associated with an advanced stage or a severe manifestation of HCM.

Distinction between surmountable and insurmountable selective AT1 receptor antagonists by use of CHO-K1 cells expressing human angiotensin II AT1 receptors

1. CHO-K1 cells that were stably transfected with the gene for the human AT1 receptor (CHO-AT1 cells) were used for pharmacological studies of non-peptide AT1 receptor antagonists. 2. In the presence of 10 mM LiCl, angiotensin II caused a concentration-dependent and long-lasting increase of inositol phosphates accumulation with an EC50 of 3.4 nM. No angiotensin II responses are seen in wild-type CHO-K1 cells. 3. [3H]-Angiotensin II bound to cell surface AT1 receptors (dissociates under mild acidic conditions) and is subject to rapid internalization. 4. Non-peptide selective AT1 antagonists inhibited the angiotensin II (0.1 microM) induced IP accumulation and the binding of [3H]-angiotensin II (1 nM) with the potency order: candesartan > EXP3174 > irbesartan > losartan. Their potencies are lower in the presence of bovine serum albumin. 5. Preincubation with the insurmountable antagonist candesartan decreased the maximal angiotensin II induced inositol phosphate accumulation up to 94% and, concomitantly, decreased the maximal binding capacity of the cell surface receptors. These inhibitory effects were half-maximal for 0.6 nM candesartan and were attenuated by simultaneous preincubation with 1 microM losartan indicating a syntopic action of both antagonists. 6. Losartan caused a parallel rightward shift of the angiotensin II concentration-response curves and did not affect the maximal binding capacity. EXP3174 (the active metabolite of losartan) and irbesartan showed a mixed-type behavior in both functional and binding studies. 7. Reversal of the inhibitory effect was slower for candesartan as compared with EXP3174 and irbesartan and it was almost instantaneous for losartan, suggesting that the insurmountable nature of selective AT1 receptor antagonists in functional studies was related to their long-lasting inhibition.

Absence of effect of chronic angiotensin II type 1 receptor blockade on endogenous kinin concentrations-induced paw edema model in the rat

The effects of chronic treatment with losartan. an AT1 receptor antagonist, on the tissue content of bradykinin (BK) and des-Arg9-BK and on their pharmacological effects were examined in the carrageenan-induced paw edema model (0.5% solution, 50 microl/paw) in the rat. These effects were compared with those of angiotensin-converting enzyme inhibitors (ACEi). For this purpose, rats were chronically treated with losartan (3, 10 and 30 mg/kg/day) and enalapril or quinapril (1 mg/kg/day). Endogenous BK and des-Arg9-BK tissue contents at the site of local inflammation were measured by highly sensitive and specific enzyme immunoassays. Losartan 3 mg/kg/day for 7, 14 and 28 days had no significant effect on carrageenan-induced paw edema, but both losartan 10 and 30 mg/kg/day for 14 days significantly increased the hindpaw volume by 50% at 3 h and by 59% at 5 h. These effects, similar to those measured for ACEi, were inhibited by icatibant, a B2 kinin receptor antagonist (32.5 nmol/paw), that reduced carrageenan-induced paw edema to the level seen in vehicle-treated rats. In the same model, and contrary to ACEi, losartan 3, 10 and 30 mg/kg/day for 14 days had no significant effect on endogenous BK and des-Arg9-BK levels in the local inflammatory site or on circulating and tissue ACE activities. These results show, at least in that model, that the potentiating effects of losartan on carrageenan-induced paw edema are independent of the concentrations of endogenous kinins.

Drug discovery: past, present and future

New drug discovery from early on involved a trial-and-error approach on naturally derived materials and substances until the end of the nineteenth century. The first half of the twentieth century witnessed systematic pharmacological evaluations of both natural and synthetic compounds. However, most new drugs until the 1970s were discovered by serendipity. With the exponential development of molecular biology on one hand and computer technology on the other, it became possible from 1980 onwards to place drug discovery on a rational basis. Cloning of genes has led to the development of methodologies for specific receptor-directed and enzyme-directed drug discoveries. Advances in recombinant DNA and transgenic technologies have enabled the production of human hormonal and other endogenous biomolecules as new drugs. As we understand more about the co-ordinating and regulating powers of the cerebral cortex during the next century, especially of the frontal lobe, man may be able to use bio-feedback training to voluntarily regulate the release of neurotransmitters, hormones, and other molecules involved in the regulation of various physiological processes in health as well as in disease.

Highly sensitive detection of gene expression of an intronless gene: amplification of mRNA, but not genomic DNA by nucleic acid sequence based amplification (NASBA)

NASBA is an isothermal nucleic acid amplification reaction that amplifies mRNA in a dsDNA background. Although similar to the sensitive reverse transcription/polymerase chain reaction (RT-PCR) in mRNA detection, NASBA is not prone to give false positive results caused by genomic dsDNA. Therefore, NASBA is unique for sensitive detection of transcription of intronless genes, which preclude strategies such as intron spanning primer pairs to control false positive results in RT-PCR. Using NASBA, mRNA of the intronless human interferon-beta gene was demonstrated with a sensitivity of 10 copies, whereas 100 ng genomic DNA gave a negative result.

Characterization and distribution of angiotensin II receptor subtypes in the mouse brain

We localized and characterized angiotensin II receptor subtypes (AT1 and AT2) in the mouse brain, with the use of autoradiography after incubation with [l25I][Sar1]-angiotensin II or [125I]CGP 42112 and displacement with selective angiotensin AT1 (losartan and candesartan) or angiotensin AT2 (CGP 42112(1) and PD 123319(2)) receptor ligands. In the mouse, the receptor subtype affinity for the different ligands was similar to that of the rat. The receptor subtype distribution was also similar to that in the rat, with some notable exceptions, such as the presence of angiotensin AT1 but not AT2 receptors in the locus coeruleus, and the expression of angiotensin AT1 receptors in the caudate putamen. These results confirm that careful consideration of the specific distribution of receptor subtypes in different species, even those closely related such as the mouse and the rat, should be conducted before meaningful comparisons could be proposed. Our data also form the basis for future studies of mouse models such as those with angiotensin receptor gene deficiencies.

N- and C-terminal structure-activity study of angiotensin II on the angiotensin AT2 receptor

The predominant angiotensin II receptor expressed in the human myometrium is the angiotensin AT2 receptor. This preparation was used for a structure-activity relationship study on angiotensin II analogues modified in positions 1 and 8. The angiotensin AT2 receptor present on human myometrium membranes displayed a high affinity (pKd = 9.18) and was relatively abundant (53-253 fmol/mg of protein). The pharmacological profile was typical of an angiotensin AT2 receptor with the following order of affinities: (angiotensin III > or = angiotensin II > angiotensin I > PD123319 > angiotensin-(1-7) > angiotensin-(1-6) approximately angiotensin IV >> Losartan). Modifications of the N-terminal side chain and of the primary amine of angiotensin II were evaluated. Neutralisation of the methylcarboxylate (Asp) to a methylcarboxamide (Asn) or to a hydroxymethyl (Ser) or substitution for a methylsulfonate group (cysteic acid) improved the affinity. Extension from methylcarboxylate (Asp) to ethylcarboxylate (Glu) did not affect the affinity. Introduction of larger side chains such as the bulky p-benzoylphenylalanine (p-Bpa) or the positively charged Lys did not substantially affect the affinity. Complete removal of the side chain (angiotensin III), however, resulted in a significant affinity increase. Removal or acetylation of the primary amine of angiotensin II did not noticeably influence the affinity. Progressive alkylation of the primary amine significantly increased the affinity, betain structures being the most potent. It appears that quite important differences exist between the angiotensin AT1 and AT2 receptors concerning their pharmacological profile towards analogues of angiotensin II modified in position 1. On position 8 of angiotensin II, a structure-activity relationship on the angiotensin AT2 receptor was quite similar to that observed with angiotensin AT1 receptor. Bulky, hydrophobic aromatic residues displayed affinities similar to or even better than [Sarcosine1]angiotensin II. Aliphatic residues, especially those of reduced size, caused a significant decrease in affinity especially [Sarcosine1, Gly8]angiotensin II who showed a 30-fold decrease. Introduction of a positive charge (Lys) at position 8 reduced the affinity even further. Stereoisomers in position 8 (L-->D configuration) also induced lower affinities. The angiotensin AT2 receptor display a structure-activity relationship similar to that observed on the AT1 receptor for the C-terminal position of the peptide hormone. Position 1 structure-activity relationships are however fundamentally different between the angiotensin AT1 and AT2 receptor.

Association of angiotensin II type 1 receptor polymorphism with resistant essential hypertension

Angiotensin II type 1 receptor (AT1) mediates the vasoconstrictive and growth-promoting effect of angiotensin II in humans. It has been reported that a polymorphism of the AT1 gene (an A/C transversion at position 1166: A-C1166) occurs more frequently in resistant hypertensives taking two or more antihypertensive drugs. On the contrary, a recent study of the influence of the A-C1166 polymorphism on aortic stiffness demonstrated that the distribution of the genotypes did not differ between normotensive and hypertensive subjects. In addition, a recent population-based survey of Caucasian hypertensives reported lower blood pressure values in CC homozygotes than in heterozygotes and AA homozygotes. Because of these controversial results and the lack of a sufficient amount of data the present study was designed to assess the contribution of the AT, gene A-C1166 polymorphism to resistant essential hypertension. Forty-eight subjects with resistant essential hypertension (HT) and 48 normotensive (NT), age and sex-adjusted controls (from a population of 300 healthy blood donors) were selected. All subjects were genotyped for the A-C1166 polymorphism in the 3'-UTR of the AT1 gene using PCR-based techniques. The influence of genotype on blood pressure (BP) was investigated using ANOVA Randomized Complete Block (ANOVA RCB) design according to sex, age and BMI. There were no significant differences in allele or genotype frequencies between HT and NT subjects (X2 = 0.61; P = NS). In HT subjects higher values of systolic blood pressure were associated with the C allele of the AT1 gene only in older and overweight patients (P < 0.001 and P < 0.001, respectively). Also in HT patients an association between the presence of the C allele of the AT1 gene and higher values of diastolic blood pressure was present in overweight patients (P = 0.001). These results suggest that in resistant hypertensive subjects the AT1 A-C1166 polymorphism is potentially involved in the regulation of blood pressure. As the effects of genotypes on blood pressure are pronounced in older and overweight subjects this polymorphism may amplify the effects of age and BMI on resistant essential hypertension.

Up-regulated expression of angiotensin II type 1 receptor gene in human pathologic hearts

BACKGROUND

An accumulation of evidence suggests that the local renin-angiotensin system plays a role in the development of cardiac hypertrophy in vivo; however, it remains unknown how the expression of angiotensin II type 1 receptor (AT1), which mediates most of the cardiovascular effects of angiotensin II, is regulated in the left ventricles of human pathologic hearts.

METHODS AND RESULTS

Expression of AT1 gene in the left ventricle wall of 14 autopsied human hearts was examined by reverse transcription polymerase chain reaction. The levels of AT1 messenger RNA relative to those of beta-actin messenger RNA in the left ventricle wall were increased 3.8-fold in the hearts with dilated cardiomyopathy (n = 4, P < .05) and 6.2-fold in the noninfarcted areas of hearts with old myocardial infarction (n = 4, P < .05), compared with the control hearts without any cardiac disease (n = 6). The increases in the relative AT1 messenger RNA level showed a positive correlation with myocyte diameter in the adjacent tissue (r = .927, P < .001 for dilated cardiomyopathy and r = .934, P < .005 for old myocardial infarctions) and with the extent of fibrosis (r = .880, P < .005 for dilated cardiomyopathy and r = .690, P < .05 for old myocardial infarction).

CONCLUSIONS

Expression of AT1 in these human pathologic hearts was associated with myocardial cell hypertrophy and extent of fibrosis, a finding that further emphasizes the importance of the local renin-angiotensin system in the remodeling of human hearts with dilated cardiomyopathy and old myocardial infarction.