Maternal autoantibodies from preeclamptic patients activate angiotensin receptors on human trophoblast cells

OBJECTIVES

Recent evidence indicates that preeclampsia is associated with the presence of autoantibodies capable of activating the angiotensin II receptor, AT1. We sought to evaluate the role of AT1 agonistic autoantibodies (AT1-AA) in two major features of preeclampsia-increased plasminogen activator inhibitor-1 (PAI-1) production and shallow trophoblast invasion.

METHODS

This study included 38 pregnant patients, 20 of whom had severe preeclampsia and 18 normotensive individuals. Immunoglobulin (Ig)G was purified from these individuals, and the presence of AT1-AA was determined based on its ability to stimulate an increase in the contraction rate of cultured rat neonatal cardiac myocytes. Immortalized human trophoblasts were chosen to study PAI-1 production and secretion after treatment with IgG from normotensive and preeclamptic women. An in vitro Matrigel invasion assay was used to test the effect of AT1-AA on the invasive properties of human trophoblasts. Losartan and cyclosporin A were used to determine whether the AT1-AA-induced stimulation of PAI-1 secretion is through the AT1 receptor and the calcineurin-nuclear factor of activated t-cells (NFAT)-dependent pathway.

RESULTS

The results show that IgG from 18 of 20 severely preeclamptic women stimulated increased cardiomyocyte contraction rates of 20-40 beats per minute. A significant stimulation of PAI-1 secretion from human trophoblasts was observed with IgG from the same 18 of 20 patients with severe preeclampsia. Of IgG obtained from 18 normotensive pregnant patients, only two showed a relatively low level of biologic activity in the cardiomyocyte contraction and PAI-1 secretion assays. Activation of AT1 receptors by AT1-AA was blocked by losartan (an AT1 receptor antagonist) and by a seven amino acid peptide corresponding to a sequence present on the second extracellular loop of the AT1 receptor. Activation of AT1 receptors by AT1-AA resulted in decreased trophoblast invasiveness as determined by the in vitro Matrigel invasion assay. Additional data indicate that AT1 receptor activation by AT1-AA is followed by the downstream activation of the calcium-dependent calcineurin-NFAT signaling pathway leading to increased PAI-1 gene expression.

CONCLUSION

Our findings suggest that maternal autoantibody with the ability to activate AT1 receptors may account for two features of preeclampsia, increased PAI-1 production and shallow trophoblast invasion.

Renoprotective mechanisms of angiotensin II antagonism in experimental chronic renal failure

AIMS

We investigated angiotensin II and nitric oxide-cGMP pathway in the development of hypertension and renal damage in chronic experimental nephritis.

METHODS

Rats with autoimmune nephritis were treated for 12 weeks with AT1 receptor antagonist L-158,809 and/or ACE inhibitor captopril given in drinking water. Blood pressure, urinary albumin, and urinary excretion of cGMP were measured. Renal density of ACE, AT1 and AT2 receptors was determined by quantitative in vitro autoradiography.

RESULTS

L-158,809, captopril, and their combination decreased blood pressure and normalised urinary albumin excretion rate in rats with nephritis. In L-158,809-treated rats, cGMP excretion was increased compared to the vehicle-treated nephritic group suggesting that the dysfunctional nitric oxide system may be activated by angiotensin antagonism. In nephritic rats, AT1 and AT2 receptor binding densities in renal medulla were decreased, cortical AT receptor expression remained unchanged. Following L-158,809 treatment, both AT1 and AT2 receptor binding was suppressed.

CONCLUSION

Long-term blockade of AT1 receptors in chronic nephritis has beneficial effects both on albuminuria and blood pressure being as effective as ACE inhibition or their combination. The stimulatory effect of AT1 receptor antagonism on cGMP production was not mediated by AT2 receptor-dependent mechanisms suggesting that AT1 receptor blockade per se favours activation of humoral pathways that stimulate cGMP production and potentially contribute to renal protection in chronic nephritis.

Role of K+ATP channels, endothelin A receptors, and effect of angiotensin II on blood flow in oral tissues

K+(ATP) channels are involved in CGRP-mediated vasodilation and in the vasoconstriction induced by endothelin or angiotensin II. In this study, we examined the effects of a K+(ATP) channel antagonist and an ET(A) receptor antagonist on resting blood flow in the pulp and gingiva, and observed their role in the vasodilation induced by tooth stimulation. We also investigated whether receptors for angiotensin II exist in the pulp and gingiva. Blood flow was measured with laser-Doppler flowmetry. Under control conditions, the K+(ATP) channel antagonist and angiotensin II caused a significant drop in blood flow in both target tissues. Blocking of ET(A) receptor did not change basal blood flow. The vasodilation observed after tooth stimulation remained unchanged following blockade of K+(ATP) channels and ET(A) receptors. Analysis of the data shows that open K+(ATP) channels exist during resting conditions in the pulp and gingiva, but that CGRP seems to induce vasodilation mainly via mechanisms other than K+(ATP) channels. ET(A) and AT(1) receptors are found in the pulp and gingiva, but ET(A) receptors are not involved in modulation of a basal vascular tone in these tissues or in the vasodilation observed after tooth stimulation.

Renoprotective effects of chronic candesartan treatment in uninephrectomized rat

The authors recently observed an age-dependent reduction in the diuretic and natriuretic responses to plasma volume expansion in uninephrectomized control and glucose-intolerant rats. To determine the involvement of angiotensin II AT receptors in this phenomenon, the authors tested the hypothesis that chronic candesartan treatment preserves renal excretory function in the uninephrectomized rat. Control and glucose-intolerant rats underwent right nephrectomy at 4 weeks of age. Two weeks later, the animals in each group were further subdivided and maintained on tap water containing either candesartan cilexetil (10 mg. kg(-1). day(-1) ) or vehicle. Renal excretory responses to acute extracellular fluid volume expansion (5% of body weight over 30 min) were determined in the 9-month-old conscious animal. Candesartan treatment markedly reduced the mean arterial pressure of controls and glucose-intolerant rats. Nonetheless, the baseline rates of fluid and electrolyte excretion, as well as the saline volume-induced diuretic, natriuretic, and kaliuretic responses, were greater in the candesartan-treated rats than in their vehicle-treated counterparts. The augmented baseline rates of fluid and sodium excretion in candesartan-treated rats were caused by a reduction in tubular reabsorption activity and an increase in glomerular filtration rate. However, the candesartan-mediated enhancement in saline volume-induced diuresis and natriuresis was caused by a reduction in tubular reabsorption activity. In addition to improving renal function, candesartan treatment reduced proteinuria in both groups. In conclusion, chronic blockade of the angiotensin II receptors exerts hypotensive and renoprotective effects in the aging uninephrectomized rat.

Cerivastatin: a cellular and molecular drug for the future?

The 'statin story' began in 1987 when the first-generation, fungal HMG-CoA reductase inhibitor lovastatin received FDA approval in the USA. Ten years later, the sixth compound of this class came onto the world market--the fully synthetic statin cerivastatin. A number of clinical studies had confirmed its high pharmacological efficacy, its excellent pharmacokinetic properties with fast and nearly complete absorption after oral uptake, a linear kinetic over a broad concentration range, and its favorable safety profile. The greatest advantages, of cerivastatin, however, are its lipophilicity, its high bioavailability of about 60% after oral application and its potency at 100-fold lower doses compared to other lipophilic statins. Nevertheless, the most exciting findings are certainly its non-lipid-related, pleiotropic effects at the cellular and molecular level. Statin therapy was also found to reduce mortality in cases where cholesterol levels or atherosclerotic plaque formation remained unaltered. However, cerivastatin improves endothelial dysfunction, possesses anti-inflammatory, antioxidant, anticoagulant, antithrombotic, antiproliferative, plaque-stabilizing, immunmodulatory, and angiogenic effects, and may even prevent tumor growth, Alzheimer's disease, and osteoporosis. Most of these effects seem to be based on the inhibition of isoprenoid synthesis. Although cerivastatin is no longer on the market because of some problematic side effects, it could be one of the most potent cellular and molecular drugs for the future.

Association of polymorphisms of the renin-angiotensin system and bradykinin B2 receptor with ACE-inhibitor-related cough

The use of angiotensin-converting enzyme (ACE) inhibitors to treat hypertension has recently increased. However, their use is associated with a persistent dry cough in a significant percentage of such patients. The present study was designed to assess the contribution of polymorphisms as a genetic marker of ACE-inhibitor-related cough in a Japanese hypertensive population. Genotyping was carried out in 190 patients, 70 with cough and 120 without cough, who had been treated with ACE inhibitors. Polymorphisms of ACE insertion/deletion (I/D), angiotensin II type 1 receptor (1166A/C), type 2 receptor (3123C/A), and bradykinin B2 receptor (-58T/C, exon 1, I/D), were analyzed in these subjects. The TT genotype and T allele of bradykinin B2 receptor (-58T/C) were identified at a significantly higher frequency in the cough (+) patients than in the cough (-) patients. This difference was even more pronounced in women. However, there was no significant relationship between polymorphisms of ACE, angiotensin II receptors, or bradykinin B2 receptor exon 1, and occurrence of ACE-inhibitor-related cough. The transcriptional activity of the bradykinin B2 receptor promoter is involved in the occurrence of cough, and this new marker may provide a valuable tool to detect patients at risk of developing this side effect of ACE inhibitors. In conclusion, Susceptibility to develop cough is associated with a genetic variant of the bradykinin B2 receptor promoter; thus, it may be possible to identify those patients who will develop this adverse reaction to ACE inhibitors in advance.

In vitro inhibition of [3H]-angiotensin II binding on the human AT1 receptor by proanthocyanidins from Guazuma ulmifolia bark

A bioassay-guided fractionation of the 70% acetone extract of the bark of Guazuma ulmifolia Lam. on the inhibition of angiotensin II binding to the AT 1 receptor led to the isolation and identification of bioactive oligomeric and polymeric proanthocyanidins consisting mainly of (-)-epicatechin units. The displacement of [3H]-angiotensin II binding was dose-dependent and correlated with the degree of polymerization of the different fractions containing proanthocyanidins. A strong displacement was seen for the residual fraction suggesting that the most active substances corresponding to the highly polymerized proanthocyanidins. Angiotensin II AT 1 receptor binding might be considered as a potentially interesting biological activity of proanthocyanidins contributing to the very broad spectrum of biological activities of the condensed tannins.

AVE 0991, a nonpeptide mimic of the effects of angiotensin-(1-7) on the endothelium

Recently, we demonstrated that the heptapeptide angiotensin-(1-7) (Ang-[1-7]) exhibits a favorable kinetic of nitric oxide (NO) release accompanied by extremely low superoxide (O2-) production. In this report we describe AVE 0991, a novel nonpeptide compound that evoked effects similar to Ang-(1-7) on the endothelium. AVE 0991 and unlabeled Ang-(1-7) competed for high-affinity binding of [125I]-Ang-(1-7) to bovine aortic endothelial cell membranes with IC50 values of 21+/-35 and 220+/-280 nmol/L, respectively. Stimulated NO and O2- release from bovine aortic endothelial cells was directly and simultaneously measured on the cell surface by selective electrochemical nanosensors. Peak concentrations of NO and O2- release by AVE 0991 and Ang-(1-7) (both 10 micromol/L) were not significantly different (NO: 295+/-20 and 270+/-25 nmol/L; O2-: 18+/-2 and 20+/-4 nmol/L). However, the released amount of bioactive NO was approximately 5 times higher for AVE 0991 in comparison to Ang-(1-7). The selective Ang-(1-7) antagonist [D-Ala(7)]-Ang-(1-7) inhibited the AVE 0991-induced NO and O2- production by approximately 50%. A similar inhibition level was observed for the Ang II AT1 receptor antagonist EXP 3174. In contrast, the Ang II AT2 receptor antagonist PD 123,177 inhibited the AVE 0991-stimulated NO production by approximately 90% but without any inhibitory effect on O2- production. Both NO and O2- production were inhibited by NO synthase inhibition ( approximately 70%) and by bradykinin B2 receptor blockade (approximately 80%). AVE 0991 efficiently mimics the effects of Ang-(1-7) on the endothelium, most probably through stimulation of a specific, endothelial Ang-(1-7)-sensitive binding site causing kinin-mediated activation of endothelial NO synthase.

[The effect of angiotensin-converting enzyme inhibitors on the progression of chronic renal failure]

SEVERAL MECHANISMS: The progression in renal failure first implies hemodynamic mechanisms and among which angiotensin II has a central role, but also an increase in proteinuria and the induction of many inflammatory and mitogenic mediators that enhance fibrosis (TGF-beta), an effect stimulating the thrombotic mechanism. Among these factors of progression in renal failure, hypertension and proteinuria are the two major factors. Proteinuria is "nephrotoxic" and leads to glomerular and tubulo-interstitial lesions. THE ROLE OF ANGIOTENSIN-CONVERTING ENZYME INHIBITORS: Angiotensin-converting enzyme inhibitors (ACE) affect the different mechanisms that lead to glomerulosclerosis: antihypertensive effect, with the normalisation of blood pressure having demonstrated its determining role in the production of nephrosis in various epidemiological studies; hemodynamic effect with a decrease in glomerular capillary pressure, in the filtration fraction, and inhibition of the bradykinin deterioration; antiproteinuric effect superior to that of other anti-hypertensive drugs (excepting angiotensin II-receptor antagonists). Two indications ACE inhibitors have demonstrated their efficacy in slowing the progression of renal failure in two large pathological fields: diabetic nephropathy in which this effect is demonstrated in type I diabetes, although the results are not as obvious in type II diabetes in which the nephropathy is multi-factor. The recent French and American recommendations are that ACE inhibitors should be used in first intention in diabetic nephropathies and aimed at tight blood pressure control; non-diabetic nephropathies Two pivotal studies have demonstrated the efficacy of ACE inhibitors in nephropathies whatever their type. These data have led to propose ACE inhibitors in first intention in patients exhibiting chronic nephropathies, whether hypertensive or not THE COMBINATION WITH OTHER HYPERTENSIVE DRUGS: Calcium channel blockers have a beneficial trophic effect in renoprotection and can be combined with ACE inhibitors, particularly in the case of diabetic nephropathies. ACE inhibitors and angiotensin II-receptor antagonists have comparable effect on hemodynamics and glomerulosclerosis factors. Clinically, the decrease in proteinuria is identical. Endothelin antagonists have also been studied in renoprotection and appear to have a beneficial effect when combined with ACE inhibitors. GLOBALLY: ACE inhibitors remain the only treatment with demonstrated long-term efficacy in the progression of chronic renal failure. However, the concept of renoprotection needs to be widened to all the factors implied in the progression of chronic renal failure, and ACE inhibitors only represent one aspect of treatment. The role of angiotensin II-receptor antagonists, alone or combined, is clearly promising.

Biphasic regulation of Na+-HCO3- cotransporter by angiotensin II type 1A receptor

Although angiotensin (Ang) II is known to regulate renal proximal transport in a biphasic way, the receptor subtype(s) mediating these Ang II effects remained to be established. To clarify this issue, we compared the effects of Ang II in wild-type mice (WT) and Ang II type 1A receptor-deficient mice (AT(1A) KO). The Na+-HCO3- cotransporter (NBC) activity, analyzed in isolated nonperfused tubules with a fluorescent probe, was stimulated by 10(-10) mol/L Ang II but was inhibited by 10(-6) mol/L Ang II in WT. Although valsartan (AT1 antagonist) blocked both stimulation and inhibition by Ang II, PD 123,319 (AT2 antagonist) did not modify these effects of Ang II. In AT1A KO, in contrast, this biphasic regulation was lost, and only stimulation of NBC activity by 10(-6) mol/L Ang II was observed. This stimulation was blocked by valsartan but not by PD 123,319. More than 10(-8) mol/L Ang II induced a transient increase in cell Ca2+ concentrations in WT, which was again blocked by valsartan but not by PD 123,319. However, up to 10(-5) mol/L Ang II did not increase cell Ca2+ concentrations in AT1A KO. Finally, the addition of arachidonic acid inhibited the NBC activity similarly in WT and AT(1A) KO, suggesting that the inhibitory pathway involving P-450 metabolites is preserved in AT(1A) KO. These results indicate that AT(1A) mediates the biphasic regulation of NBC. Although low-level expression of AT(1B) could be responsible for the stimulation by 10(-6) mol/L Ang II in AT1A KO, no evidence was obtained for AT2 involvement.

Angiotensin-(1-7) inhibits angiotensin II-induced signal transduction

The inhibitory effects of angiotensin-(1-7) on angiotensin II-induced vasoconstriction, growth of vascular smooth muscle cells, stimulation of protein kinase C, extracellular signal-regulated kinases (ERK), and angiotensin subtype 1 receptor (AT1) and subtype 2 receptor (AT2) mRNA expression were investigated. The hemodynamic effects of angiotensin-(1-7) were measured in Wistar rats. Vasoconstriction was measured using aortic rings. DNA synthesis or protein synthesis was measured in cultured vascular smooth muscle cells using [3H] thymidine or [3H] leucine incorporation, respectively. Angiotensin II stimulated protein kinase C and ERK1/2 were measured by Western blot analysis using phosphospecific protein kinase C and ERK1/2 antibodies. AT1 and AT2 receptor mRNA expression was measured using reverse-transcription polymerase chain reaction. Infusion of angiotensin II significantly increased whereas infusion of angiotensin-(1-7) had no effects on mean arterial blood pressure in Wistar rats. Angiotensin-(1-7) dose-dependently showed partial antagonism on angiotensin II-induced contraction of aortic rings. Angiotensin-(1-7) showed partial antagonism on angiotensin II-induced DNA synthesis and protein synthesis. Angiotensin-(1-7) showed partial antagonism on angiotensin II-induced activation of protein kinase C and ERK1/2. The administration of angiotensin-(1-7) showed partial antagonism on angiotensin II-induced downregulation of AT1 receptor mRNA expression, whereas AT2 receptor mRNA expression was unchanged. Angiotensin-(1-7) showed partial antagonism on angiotensin II-induced intracellular signal transduction and may play a crucial role in the adaptation process of AT1 receptors to sustained stimulation of angiotensin II.

Antagonist interaction with endogenous AT(1) receptors in human cell lines

Using Chinese Hamster Ovary cells expressing human AT(1) receptors cells (CHO-hAT(1)), it was previously shown that insurmountable inhibition of the angiotensin II response by non-peptide antagonists is related to the duration of their receptor occupancy. In the present study it was shown that these antagonists displayed similar binding characteristics to endogenously expressed AT(1) receptors in human adrenal cortex cells (NCI-h295) and renal vascular smooth muscle cells (HVSMC). Competition binding studies with [(3)H]candesartan for NCI-h295 cells, with [(125)I]Sar(1)-Ile(8) angiotensin II for HVSMC and with both radioligands for CHO-hAT(1) cells displayed the same potency order for unlabelled antagonists: candesartan>EXP3174>irbesartan>losartan. The AT(2) receptor antagonist PD123319 displayed low potency in all instances. The apparent half-lives of the antagonist-AT(1) receptor complexes in NCI-h295 cells and HVSMC were comparable to those obtained under identical conditions with CHO-hAT(1) cells. Angiotensin II increased the inositol phosphate accumulation dose dependently with half-maximal response at 17.4+/-1.6nM for NCI-h295 cells and 4.5+/-0.8nM for HVSMC. Pre-incubation of the cells with losartan only produced concentration-dependent rightward shifts of the angiotensin II concentration-response curve. The maximal response was decreased by 85-92% with candesartan, 70-88% with EXP3174 and 60% with irbesartan. The similar binding and inhibitory properties of these antagonists among the investigated cell types validates the use of CHO-hAT(1) cells for investigating pharmacological properties of human AT(1) receptors.

Increased AT(2)R protein expression but not increased apoptosis during cardioprotection induced by AT(1)R blockade

BACKGROUND

The angiotensin II type 2 receptor (AT2R) is considered to be antigrowth and to mediate apoptosis in several cell types. Whether AT2R upregulation, associated with angiotensin II type 1 receptor (AT1R) blockade and cardioprotection after ischemia-reperfusion (IR), might not result in increased cardiomyocyte (CM) apoptosis has not been documented.

OBJECTIVES

To determine whether increased AT2R protein expression, during AT1R blockade after acute IR, is associated with no increase in CM apoptosis.

MATERIALS AND METHODS

The recovery of left ventricular (LV) mechanical function after acute IR (30 min of ischemia, 40 min of reperfusion) was measured in isolated Langendorff rat hearts following pretreatment with the AT1R antagonist candesartan (CN) (CN 10 nmol/L) for 40 min before ischemia. The authors established with an initial dose-response curve using escalating concentrations of CN that 10 nmol/L abrogated vasoconstriction induced by angiotensin II (0.1 mol/L). AT1R and AT2R protein expression (Western immunoblot), CM apoptosis (terminal deoxynucleotidyl transferase-mediated 2'-deoxyuridine 5'-triphosphate nick end-labelling assay and nuclear morphology) and apoptotic markers (Bax, Bcl-2, caspase-3, p53) were assessed in LV tissue.

RESULTS

Compared with IR controls, CN improved peak systolic pressure, LV developed pressure and positive dp/dt, and increased AT2R (not AT1R) protein, but did not change the level of apoptosis or the expression of Bax, Bcl-2, caspase-3 or p53. CN also increased AT2R protein after ischemia alone but did not change CM apoptosis or expression of the markers.

CONCLUSIONS

Increased AT2R protein expression during AT1R blockade after IR in the isolated Langendorff rat heart is associated with cardioprotection but no increase in CM apoptosis.

Angiotensin II's antiproliferative effects mediated through AT2-receptors depend on down-regulation of SM-20

Angiotensin II (ANG II) inhibits proliferation and induces differentiation through AT2 receptors. However, target genes involved in this process are not well characterized. We studied PC12 cells, a rat pheochromocytoma cell line exclusively expressing AT2 receptors. ANG II attenuated proliferation of PC12 cells without concomitant induction of apoptosis. To identify potential novel genes involved in the antimitogenic actions of ANG II, we performed differential display analysis of PC12 cells after challenge with 10(-7) M ANG II for 6 hours. One identified gene selected for further study that was down-regulated by ANG II in PC12 cells was SM-20. This gene has been previously isolated from vascular smooth muscle cells treated with mitogens by differential hybridization. Recent findings show a homology of SM-20 with enzymes involved in the regulation of hypoxia inducible factor 1. ANG II suppressed mRNA expression of SM-20 in PC12 cells after only 30 minutes, as detected by Northern blotting. This effect was antagonized by an AT2 receptor blocker, but not by losartan. A rabbit polyclonal antibody was generated against a peptide sequence of SM-20 and detected a major band of the predicted size of 40 kd and a second 33-kd band that likely represents a processed form present in mitochondria. Immunohistochemistry revealed a granular staining of the cytoplasm of PC12 cells compatible with a previously described mitochondrial localization of SM-20 protein. Western blots confirmed the down-regulation of SM-20 protein in PC12 cells subsequent to incubation with ANG II. SM-20 transcripts were also reduced by ANG II acting on AT2 receptors in rat glomerular endothelial cells that express both AT1 and AT2 receptors. SM-20 antisense, but not sense, phosphothioate-modified oligonucleotides reduced base-line proliferation of PC12 cells. In contrast, inducible overexpression of SM-20 using the ecdysone system prevented the antiproliferative effects of ANG II in PC12 cells. In summary, our study identified SM-20 as an essential component of ANG II's growth-suppressive effects mediated through AT2 receptors. This gene apparently plays an important role in the regulatory processes determining whether a cell should undergo differentiation, apoptosis, or proliferation.

Contemporary treatment of heart failure: is there adequate evidence to support a unique strategy for African-Americans? Pro position

Clinical trials provide average effects of interventions but are not powered to identify differences in subgroup responses. African-Americans have been under-represented in most previous trials in patients with heart failure. Furthermore, physiologic differences have been demonstrated between African-Americans and whites in the mechanisms and response to therapy in hypertension. Review of previous heart failure trials reveals that African-Americans exhibit less benefit than whites from ACE inhibitors, angiotensin receptor blockers, and at least one b-blocker. In contrast, black patients experienced a greater benefit than white patients from the combination of nitrate and hydralazine. These data emphasize the need for trials in black patients to identify effective therapy. The first such trial, African-American Heart Failure Trial, is currently underway.

Are clinical endpoint benefits of angiotensin converting enzyme inhibitors independent of their blood pressure effects?

Both basic and experimental data indicate that the renin-angiotensin system through angiotensin II mediates its classic hemodynamic role, but also has a significant deleterious role in a number of cardiac, vascular, and renal disorders. Indeed, evidence indicates that angiotensin II negatively impacts endothelial function, cardiac remodeling, vessel wall hypertrophy, atherosclerosis, and progressive renal disease. Newer data point to a significant role for angiotensin II in inflammation and in inducing plasminogen activator inhibitor. This widespread negative effect can be countered by newer antihypertensive drugs, angiotensin converting enzyme inhibitors, and angiotensin receptor blockers. Both small and large clinical trials suggest a large benefit of such drugs on not only organ-specific endpoints such as renal disease or proteinuria, but on global cardiovascular events. It does appear that when blood pressure is significantly elevated, lowering blood pressure does indeed provide protection for larger endpoints such as stroke. However, at lower blood pressure levels, a hemodynamically independent effect is likely to be contributing to the positive effects. We should embrace these effects and champion them for our patients.

Angiotensin II and cAMP regulate AT(1)-mRNA expression in rat cardiomyocytes by transcriptional mechanism

Mechanisms of angiotensin II and cAMP regulating the expression of angiotensin II type 1 (AT(1)) receptor mRNA were studied in neonatal rat cardiomyocytes. Angiotensin II induced a transient decrease of AT(1)-mRNA expression in time- and dose-dependent manner. Maximal decrease (49.2 +/- 9.5% of control) occurred at 6 h of angiotensin II (10 nmol/l) treatment. AT(1) receptor antagonists 4-ethyl-2-n-propyl-1-[2'-(1H-tetrazol-5-yl)biphenyl-4-yl)methyl]imidazole-5-carboxylic acid (DMP811) and losartan as well as 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7) reversed the down-regulation of AT(1)-mRNA expression. 6 h of phorbol 12-myristate 13-acetate (PMA) stimulation caused a decrease of AT(1)-mRNA level. Treatment by angiotensin II plus actinomycin D for 6 h produced the same effect as actinomycin D alone. These results suggest that angiotensin II down-regulates AT(1)-mRNA level of rat cardiomyocytes by inhibiting the transcription of AT(1) gene, which is mediated by AT(1) receptor and related to the activation of protein kinase C. Stimulation by forskolin plus 3-isobutyl-1-methyl-xanthine (IBMX) decreased the expression of AT(1)-mRNA to 68.1 +/- 21.5% of control at 6 h treatment; while increased to 207.9 +/- 27.1% of control at 48 h treatment. A series of 5'-upstream deletion mutants of AT(1A) promoter were produced and then were recombined with pGL(3) basic vector utilizing luciferase as reporter gene. Among all the constructors, p(-201/+ 74)Luc was of the highest luciferase activity (5.9 times higher than control) after stimulation by forskolin for 48 h. Further deletion from -201 to -61 resulted in a large decrease of activity. These results indicate that cAMP induces a time-dependent bi-directional regulation of AT(1)-mRNA expression. The cAMP responsible element (CRE) cis-element located in the region -201/-61 of rat AT(1A) promoter is forskolin inducible, which may mediate the up-regulation of AT(1)-mRNA expression induced by cAMP long-lasting stimulation.

Angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers synergistically increase coronary blood flow in canine ischemic myocardium: role of bradykinin

OBJECTIVES

We examined whether the combination of an angiotensin-converting enzyme (ACE) inhibitor and an angiotensin II receptor blocker (ARB) synergistically mediates coronary vasodilation and improves myocardial metabolic and contractile dysfunction in ischemic hearts.

BACKGROUND

Either an ACE inhibitor or ARB mediates coronary vasodilation in ischemic hearts.

METHODS

In dogs with myocardial ischemia, we infused an ACE inhibitor (temocaprilat, 10 microg/kg/min) or ARB (RNH-6270, 10 microg/kg/min) into the coronary artery.

RESULTS

Perfusion pressure of the left anterior descending coronary artery was reduced from 104 +/- 8 to 42 +/- 2 mm Hg, so that coronary blood flow (CBF) decreased to one-third of the baseline value. Ten minutes after starting the infusion of temocaprilat, the cardiac bradykinin level increased (from 32 +/- 6 to 98 +/- 5 pg/ml). Coronary blood flow (29 +/- 2 to 44 +/- 3 ml/100 g/min) and the cardiac level of nitric oxide (NO) (7.8 +/- 1.9 to 17.5 +/- 3.2 microm) also increased, with these changes being attenuated by either N(omega)-nitro-L-arginine methyl ester or HOE140. RNH-6270 alone caused a modest increase in CBF (34 +/- 3 ml/100 g/min), with no increase in the cardiac NO or bradykinin levels. Both temocaprilat and RNH-6270 caused a further increase in both CBF (51 +/- 4 ml/100 g/min) and cardiac NO levels, without increasing the bradykinin level, and these changes were inhibited by HOE140. In the nonischemic heart, RNH-6270 augmented bradykinin-induced increases in CBF.

CONCLUSIONS

The combination of an ACE inhibitor and ARB mediates greater increases in CBF and more potent cardioprotective effects through bradykinin-dependent mechanisms than either drug alone.

Use of lipid-lowering drugs and blood pressure control in patients with arterial hypertension

A large proportion of patients have both hypertension and hypercholesterolemia, two of the most important risk factors for cardiovascular diseases. Statins are the most widely used drugs for the treatment of plasma lipid abnormalities and have been reported to interact with elevated blood pressure. A reduction in blood pressure associated with the use of these agents has been reported in patients with untreated hypertension and in patients treated with antihypertensive drugs, particularly angiotensin-converting enzyme inhibitors and calcium channel blockers. This effect on blood pressure control has also been observed in diabetic patients. The mechanism responsible for the hypotensive effect seems to be largely independent of the effect of statins on plasma cholesterol, and probably is related to the interaction of the medications with endothelial function or angiotensin II receptors. The capacity of statins to improve blood pressure control may represent a useful tool for improvement in the prevention of cardiovascular diseases.

Differential PI 3-kinase dependence of early and late phases of recycling of the internalized AT1 angiotensin receptor

Agonist-induced endocytosis and processing of the G protein-coupled AT1 angiotensin II (Ang II) receptor (AT1R) was studied in HEK 293 cells expressing green fluorescent protein (GFP)- or hemagglutinin epitope-tagged forms of the receptor. After stimulation with Ang II, the receptor and its ligand colocalized with Rab5-GFP and Rab4-GFP in early endosomes, and subsequently with Rab11-GFP in pericentriolar recycling endosomes. Inhibition of phosphatidylinositol (PI) 3-kinase by wortmannin (WT) or LY294002 caused the formation of large endosomal vesicles of heterogeneous Rab composition, containing the ligand-receptor complex in their limiting membranes and in small associated vesicular structures. In contrast to Alexa(R)-transferrin, which was mainly found in small vesicles associated with the outside of large vesicles in WT-treated cells, rhodamine-Ang II was also segregated into small internal vesicles. In cells labeled with 125I-Ang II, WT treatment did not impair the rate of receptor endocytosis, but significantly reduced the initial phase of receptor recycling without affecting its slow component. Similarly, WT inhibited the early, but not the slow, component of the recovery of AT1R at the cell surface after termination of Ang II stimulation. These data indicate that internalized AT1 receptors are processed via vesicles that resemble multivesicular bodies, and recycle to the cell surface by a rapid PI 3-kinase-dependent recycling route, as well as by a slower pathway that is less sensitive to PI 3-kinase inhibitors.

Site-directed mutagenesis of the gerbil and human angiotensin II AT(1) receptors identifies amino acid residues attributable to the binding affinity for the nonpeptidic antagonist losartan

Gerbil angiotensin II AT(1) receptors have more than 90% amino acid sequence homology with human AT(1) receptors and similar affinity for the natural peptide agonist angiotensin II. However, their binding affinity for the biphenylimidazole AT(1) receptor antagonist losartan is greatly reduced compared with the hAT(1) receptor (400 times lower for the gAT(1A) receptor and 40 times lower for the gAT(1B) receptor cloned here). Gain- and loss-of-function site-directed mutagenesis revealed that in gerbil and human AT(1) receptors, the amino acid most important for losartan binding is located in position 108, followed by 107, both in transmembrane (TM) III. In both gerbil and human AT(1) receptors, the effect of G107S and I108V mutants is cumulative. Mutation L195M in TM V is very important, when combined with mutations G107S and I108V, for both gerbil and human AT(1) receptors. In the gerbil, less important amino acids are located in positions 150/151 (TM IV) and 177 in the extracellular loop 2. The study of gerbil natural mutants allowed us to advance our understanding of amino acids selectively involved in the determination of antagonist affinity for gerbil and, most importantly, for human angiotensin II AT(1) receptors.

Blockade of the renin-angiotensin system

The renin-angiotensin-aldosterone system plays a key role in the regulation of fluid and electrolyte balance. Angiotensin-converting enzyme inhibitors inhibit angiotensin-converting enzyme and have been shown to be effective in many cardiovascular diseases. They should be considered for the treatment of hypertension in patients with heart failure, previous myocardial infarction, diabetes, or proteinuria. There are a number of side-effects associated with angiotensin-converting enzyme inhibitors, especially persistent dry cough. Angiotensin II receptor antagonists (sartans) provide a more specific blockade of the renin-angiotensin-aldosterone system and are associated with fewer side-effects, including cough. Their long-term efficacy and tolerability in the treatment of patients with hypertension has, however, yet to be established. Periodic monitoring of renal function and electrolytes is required in patients treated with an angiotensin-converting enzyme inhibitor or a sartan.

Differences in AT2 -receptor stimulation between AT1 -receptor blockers valsartan and losartan quantified by renal interstitial fluid cGMP

OBJECTIVE

Angiotensin II-receptor blockers are an established class of antihypertensive agents, but the differences between individual members of the class are largely unknown. The present study employed an animal model to demonstrate angiotensin II-receptor blocker-specific effects and to quantify these differences by comparing two common agents, losartan and valsartan.

METHODS

We measured the effects on angiotensin II AT2-receptor-mediated renal cGMP by microdialysis in the outer renal cortex in conscious normotensive, sodium-depleted, 4-week-old Sprague-Dawley rats. Rats (n = 8) were given equimolar and equidepressor doses of losartan (0.02 mmol/kg) or valsartan (0.02 mmol/kg) either intravenously or orally. Time was allowed for the conversion of losartan into its active metabolite, EXP 3174.

RESULTS

Both drugs had equal effects on blood pressure. There were significantly greater increases in cGMP levels after administration of valsartan than of losartan with both routes of administration. Intravenous administration of valsartan led to a 69.1% increase in cGMP, versus a 10.3% increase with losartan. Five hours after oral administration of valsartan, a 48% increase in cGMP was observed versus a 10.9% increase with losartan. The increase after oral administration of valsartan was sustained 8 h after administration, whereas the effect of losartan was not sustained. The effects of losartan and valsartan on cGMP were completely inhibited by AT2-receptor blockade.

CONCLUSION

The results indicate that AT1-receptor blockade with valsartan influences AT2-receptor-mediated angiotensin II responses to a greater extent than with losartan, as quantified by renal interstitial fluid cGMP.