Angiotensin-converting enzyme 2 deficiency is associated with impaired gestational weight gain and fetal growth restriction.

Angiotensin-converting enzyme 2 (ACE2) is a key enzyme of the renin-angiotensin system that influences the relative expression of angiotensin II (Ang II) and Ang-(1-7). Although ACE2 expression increases in normal pregnancy, the impact of ACE2 deficiency in pregnancy has not been elucidated. We determined the influence of ACE2 deficiency on circulating and tissue renin-angiotensin system components, fetal and maternal growth characteristics, and maternal hemodynamics (mean blood pressure and cardiac output) at day 18 of gestation. Gestational body weight gain was lower in the ACE2 knockout (KO) versus C57BL/6 (wild-type) mice (30.3±4.7 versus 38.2±1.0 g; P<0.001). Fetal weight (0.94±0.1 versus 1.24±0.01 g; P<0.01) and length (19.6±0.2 versus 22.2±0.2 mm; P<0.001) were less in KO. Mean blood pressure was significantly reduced in C57BL/6 with pregnancy; it was elevated (P<0.05) in the KO virgin and pregnant mice, and this was associated with an increased cardiac output in both C57BL/6 and KO pregnant mice (P<0.05). Plasma Ang-(1-7) was reduced in pregnant KO mice (P<0.05). Placenta Ang II levels were higher in KO mice (52.9±6.0 versus 22.0±3.3 fmol/mg of protein; P<0.001). Renal Ang II levels were greater in KO virgin mice (30.0±1.7 versus 23.7±1.1 fmol/mg of protein; P<0.001). There was no change in the Ang-(1-7) levels in the KO placenta and virgin kidney. These results suggest that ACE2 deficiency and associated elevated placenta Ang II levels impact pregnancy by impairing gestational weight gain and restricting fetal growth.

Angiotensin II AT1 receptor blockade normalizes CD11b+ monocyte production in bone marrow of hypercholesterolemic monkeys.

The enhanced production of monocytes expressing pro-inflammatory markers such as the integrin CD11b in patients with hypercholesterolemia may promote vascular inflammation and exacerbate atherogenesis. The objective of the present study was to determine whether hypercholesterolemia stimulates the production of CD11b(+) monocytes in bone marrow, and whether the renin-angiotensin system participates in this process and thus provides a target for therapeutic intervention. The dietary induction of hypercholesterolemia in adult male cynomolgus monkeys was accompanied by increased bone marrow cellularity and elevated peripheral blood and bone marrow monocyte CD11b expression. Isolated bone marrow CD34(+) hematopoietic stem cells (HSCs) evaluated by in vitro functional assays exhibited enhanced myeloproliferative capacity and differentiation into CD11b(+) monocytes. Treatment of hypercholesterolemic monkeys with the angiotensin II AT(1) receptor blocker losartan for 15 weeks reduced bone marrow cellularity, suppressed peripheral blood and bone marrow monocyte CD11b expression, and normalized CD34(+) cell function assays. All variables returned to pretreatment levels 6 weeks after discontinuation of losartan treatment. Hypercholesterolemia was associated with increased CD34(+) cell AT(1) receptor expression and an exaggerated in vitro myeloproliferative response to angiotensin II stimulation that positively correlated to plasma LDL concentrations. In vitro exposure to native low-density lipoproteins (LDL) also increased CD34(+) cell AT(1) receptor expression and the myeloproliferative response to angiotensin II stimulation in a dose-dependent and receptor-mediated manner. Our data provide support for a positive regulatory role of plasma LDL on AT(1) receptor-mediated HSC differentiation and the production of pro-atherogenic monocytes. LDL-regulated HSC function may explain in part hypercholesterolemia-induced inflammation as well as the anti-inflammatory and anti-atherosclerotic effects of AT(1) receptor blockers.

Role of the renin-angiotensin-aldosterone system and proinflammatory mediators in cardiovascular disease.

Inflammation is a key mechanism in the initiation, progression, and clinical sequelae of cardiovascular diseases (CVDs), including atherosclerosis, nephropathy, and cardiomyopathy. Angiotensin II, the major effector peptide of the renin-angiotensin-aldosterone system (RAAS), plays a significant role in the advent and perpetuation of these inflammatory diseases, most notably in atherogenesis. Consequently, suppression of the influence of angiotensin II by angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers may reduce or potentially reverse atherosclerosis and other inflammation-associated CVDs. Angiotensin II receptor blockers and angiotensin-converting enzyme inhibitors exert anti-inflammatory actions and prevent or reduce the development of atherosclerosis in animal models. Clinically, RAAS suppression reduces common carotid and femoral artery intima-media thickness, thus indicating moderation of the vascular disease process. These clinical benefits likely involve restraint of the deleterious effects of angiotensin II in addition to, or independent of, lowering blood pressure. Increasing evidence that the detection and monitoring of vascular inflammation are important tools in the management of atherosclerosis also implicates the RAAS in this pathogenic process. Inflammatory molecules such as intercellular adhesion molecule-1, vascular cell adhesion molecule-1, monocyte chemoattractant protein-1, tumor necrosis factor-alpha, and C-reactive protein have potential diagnostic and prognostic values in CVD and are modified by angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers. Monitoring these markers may be crucial for determining which agents, or combinations of agents, will result in the most clinically beneficial outcomes for patients. Large-scale trials are still required to determine the effects of the long-term suppression of inflammation on CVDs through the use of RAAS modulating agents, as well as to determine how closely markers of inflammatory activity may correlate with CVD outcomes.

Angiotensin II AT1 receptors regulate ACE2 and angiotensin-(1-7) expression in the aorta of spontaneously hypertensive rats.

When increased in vascular tissues, angiotensin-converting enzyme 2 (ACE2), a carboxypeptidase that hydrolyzes angiotensin II to angiotensin-(1-7), may augment the growth inhibitory and vasodilatory effects of the heptapeptide. We investigated the regulation of ACE2 and angiotensin-(1-7) expression in aortas and carotid arteries of 12-wk-old male spontaneously hypertensive rats (SHR) by determining the effect of sustained angiotensin type 1 (AT(1)) receptor blockade with olmesartan (10 mg.kg(-1).day(-1), n = 13) compared with those that received atenolol (30 mg.kg(-1).day(-1), n = 13), hydralazine (10 mg.kg(-1).day(-1), n = 13), or vehicle (n = 21). Systolic blood pressures were approximately 30% lower (P < 0.05) in rats treated for 2 wk with olmesartan compared with vehicle-treated rats. Both atenolol and hydralazine produced similar decreases in systolic blood pressure. ACE2 mRNA in the thoracic aorta of olmesartan-treated rats (n = 8) was fivefold greater (P < 0.05) than that in vehicle-treated rats (n = 16), whereas atenolol (n = 8) or hydralazine (n = 8) had no effect. Immunostaining intensities in rats treated with olmesartan (n = 5) were also associated with increased (P < 0.05) ACE2 and angiotensin-(1-7) in thoracic aorta media compared with vehicle-treated rats. In contrast, immunostaining intensities for both ACE2 and angiotensin-(1-7) were not different from vehicle (n = 5) in carotid arteries of SHR medicated with either atenolol (n = 5) or hydralazine (n = 5). A comparison of vessel wall dimensions showed that olmesartan selectively reduced the thoracic aorta media-to-lumen ratio (P < 0.05) and media thickness (P < 0.05) without an effect on carotid artery morphometry. Compared with vehicle-treated SHR, vascular hypertrophy determined from media and lumen measurements was not changed in SHR given either atenolol or hydralazine. These data represent the first report of ACE2 and angiotensin-(1-7) expression in the aorta and carotid arteries of SHR. Increased ACE2 and angiotensin-(1-7) in association with altered dimensions of the thoracic aorta but not carotid arteries in response to olmesartan treatment provides evidence that this pathway is regulated by AT(1) receptors and may be important in mediating the pressure-independent vascular remodeling effects of angiotensin peptides.

Renin-angiotensin system expression in rat bone marrow haematopoietic and stromal cells.

The existence of a bone marrow renin-angiotensin system (RAS) is evidenced by the association of renin, angiotensin converting enzyme (ACE), and angiotensin (Ang) II and its AT(1) and AT(2) receptors with both normal and disturbed haematopoiesis. The expression of RAS components by rat unfractionated bone marrow cells (BMC), haematopoietic-lineage BMC and cultured marrow stromal cells (MSC) was investigated to determine which specific cell types may contribute to a local bone marrow RAS. The mRNAs for angiotensinogen, renin, ACE, and AT(1a) and AT(2) receptors were present in BMC and in cultured MSC; ACE2 mRNA was detected only in BMC. Two-colour flow fluorocytometry analysis showed immunodetectable angiotensinogen, ACE, AT(1) and AT(2) receptors, and Ang II, as well as binding of Ang II to AT(1) and AT(2) receptors, in CD4(+), CD11b/c(+), CD45R(+) and CD90(+) BMC and cultured MSC; renin was found in all cell types with the exception of CD4(+) BMC. Furthermore, Ang II was detected by radioimmunoassay in MSC homogenates as well as conditioned culture medium. The presence of Ang II receptors in both haematopoietic-lineage BMC and MSC, and the de novo synthesis of Ang II by MSC suggest a potential autocrine-paracrine mechanism for local RAS-mediated regulation of haematopoiesis.

Renin-angiotensin system as a therapeutic target in managing atherosclerosis.

Clinical and experimental evidence suggests that the pathways by which hypertension and dyslipidemia lead to vascular disease may overlap and that angiotensin II (Ang II) is involved in restructuring of the arterial wall in both atherosclerosis and hypertension. Ang II represents a potent proinflammatory agent promoting recruitment of monocytes into the vascular intima. Ang II also indirectly facilitates transformation of macrophages and smooth muscle cells into foam cells by promoting superoxide radical formation (via NADP/NADPH oxidase stimulation). The oxidative stress produced by Ang II leads to enhanced low-density lipoprotein oxidation and degradation of nitric oxide, an important vascular protective molecule capable of retarding atherosclerosis progression. The importance of the renin-angiotensin system (RAS) in atherogenesis is highlighted by studies in animal models as well as human beings indicating that inhibition of angiotensin-converting enzyme or blockade of type 1 Ang II receptors retards the development of atherosclerotic lesions. In light of a causal and central role of Ang II in atherogenesis, blockade of the RAS represents an important therapeutic consideration in the prevention and treatment of atherosclerotic disease.

Angiotensin II stimulates arachidonic acid release from bone marrow stromal cells.

INTRODUCTION: Angiotensin II (Ang II) is recognised as a regulator of haematopoiesis, but its actions within the bone marrow are not fully understood. Support of haematopoiesis by bone marrow stromal cells (MSC) is dependent on factors that include arachidonic acid and macrophage colony stimulating factor (MCSF), both of which are increased by Ang II stimulation in other tissues. To further elucidate the mechanisms of Ang II-regulated haematopoiesis, we determined whether Ang II-stimulation alters arachidonic acid release and MCSF secretion from MSC. METHODS: Cynomolgus monkey MSC isolated from bone marrow aspirates and the human HS-5 stromal cell line were studied for Ang II-mediated arachidonic acid (AA) release, while secretion of MCSF in response to Ang II was studied in HS-5 cells. Cells were labelled overnight with 3H-AA and the release of 3H-AA was measured in culture medium following 20 minutes stimulation with Ang II, alone or in combination with the AT1- or AT2-receptor antagonists, losartan and PD 123319, respectively. MCSF secretion into culture medium was measured using an enzyme immunoassay following 24 hours of treatment with Ang II alone or in combination with losartan or PD 123319. Phorbol-myristate-acetate, known to stimulate release of AA and MCSF, was used as a positive control in both experiments. RESULTS: In response to Ang II, release of 3H-AA from monkey and human MSC was increased (p<0.05) to 147+/-4% and 124+/-3% of control, respectively. The AT1- and AT2-receptor antagonists, losartan and PD 123319, individually reduced Ang II-stimulated 3H-AA release. In contrast, Ang II had no effect on secretion of MCSF from HS-5 cells. CONCLUSIONS: These results provide mechanistic evidence for Ang II-mediated haematopoiesis through AA release that may, in part, explain Ang II-facilitated recovery of haematopoiesis in experimental myelosuppression and the anaemias associated with Ang II receptor blockade.

Mechanisms linking angiotensin II and atherogenesis.

PURPOSE OF REVIEW: The concept that angiotensin II plays a central role in early atherogenesis, progression to atherosclerotic plaque, and the most serious clinical sequelae of coronary artery disease is the subject of considerable current interest. Results from recent large clinical trials confirm that blunting of the renin-angiotensin system through either angiotensin converting enzyme inhibition or angiotensin II type 1 receptor blockade incurs significant beneficial outcomes in patients with coronary artery disease. The exact mechanisms for these effects are not yet clear, but are suggested by studies demonstrating that suppression of the renin-angiotensin system is associated with muted vascular oxidative stress. RECENT FINDINGS: As most of the biological effects of the renin-angiotensin system occur through stimulation of the angiotensin II type 1 receptor, the focus of this review is on changes in the vascular wall mediated by this receptor and primarily related to endothelial and vascular smooth muscle cells, monocyte/macrophages and platelets. The interactions between angiotensin II and nitric oxide exert particular demands on the vascular capacity to adapt to dyslipidemia, hypertension, estrogen deficiency and diabetes mellitus that appear to exacerbate atherogenesis. Associated with each of these conditions is angiotensin II-mediated stimulation of macrophages, platelet aggregation, plasminogen activator inhibitor 1, endothelial dysfunction, vascular smooth muscle cell proliferation and migration, apoptosis, leukocyte recruitment, fibrogenesis and thrombosis. SUMMARY: Inhibition of the actions of angiotensin II serves a dual purpose: indirectly through reduction of mechanical stress on the vascular wall, and directly by diminished stimulation for vascular restructuring and remodeling. Collectively, data from studies published over the last year confirm and extend the notion that angiotensin II is a true cytokine prevalent at all stages of atherogenesis.

[Pathophysiological and clinical implications of AT(1) and AT(2) angiotensin II receptors in metabolic disorders: hypercholesterolaemia and diabetes]. / Implications physiopathologiques et cliniques des récepteurs AT(1)/AT(2) de l'angiotensine II dans les pathologies métaboliques: hypercholestérolémie et diabète.

The coexistence of hypercholesterolaemia and diabetes dramatically and synergistically increases the risk of microvascular and macrovascular complications in patients. A single unifying mechanism of increased production of reactive oxygen species (ROS) by angiotensin II (Ang II) may serve as a causal link between hyperglycaemia and hypercholesterolaemia and many of the major pathways responsible for atherogenic and diabetic disorders. Several lines of evidence suggest a crucial role for Ang II-mediated oxidative stress in the pathogenesis of hyperglycaemia- and hypercholesterolemia-associated endothelial dysfunction. Endothelial dysfunction in these scenarios may be due to impaired nitric oxide (NO) synthesis and/or inactivation of endothelium-derived NO by ROS. That Ang II plays an important role in the development of atherosclerosis and glomerulosclerosis is supported by numerous studies indicating that angiotensin receptor blockers (ARBs) retard the progression of these diseases in both experimental animal models and humans. Evidence indicates that Ang II contributes to atherogenesis at both transcriptional and translational levels by upregulating adhesion molecule mRNA and protein synthesis. The recent demonstration of Ang II AT(2) receptors in the adult kidney and their potential to oppose the vasoconstrictive, antinatriuretic, and profibrotic properties of AT(1) receptors suggests that the balance of intrarenal AT(1) and AT(2) receptors may be important in determining the cellular responses to Ang II in diabetic nephropathy. Results of these studies suggest that hypercholesterolaemia and hyperglycaemia can induce a pro-inflammatory response within coronary arteries and the kidney glomerulus. This response involves production of well described macrophage chemotactic and adhesion molecules, which results in macrophage recruitment and the development of acute and chronic injury. Glomerular macrophage recruitment in experimental diabetes occurs via Ang II-stimulated monocyte chemoattractant protein (MCP)-1 expression, suggesting that the renin-angiotensin system is an important regulator of local MCP-1 expression, and strongly implicating macrophage recruitment and activation in the pathogenesis of early diabetic glomerular injury. Diabetes-associated vascular complications may also involve an activation of the nuclear factor (NF)-kappaB by hyperglycaemia. NF-kappaB activation is related to AT(1) receptor-mediated pathways, and is believed to be dependent on activation of the Rho proteins belonging to the superfamily of low molecular weight guanosine triphosphatases (GTPases) that regulate intracellular signalling. Preincubation of vascular smooth muscle cells with insulin doubled NF-kappaB transactivation stimulated by Ang II and hyperglycaemia, suggesting a potential mechanism for crosstalk between the renin-angiotensin system and hyperglycaemia. Taken together, these data suggest that activation of the renin-angiotensin system is a mechanism for the initiation and progression of inflammatory cell infiltration found in early changes common to both hypercholesterolaemia and hyperglycaemia. While the base of information regarding ARBs in high-risk patients with diabetes and hypercholesterolemia is lacking, preclinical and pilot trial data suggest that the ARBs are reno- and vasculoprotective in these patients. Therapeutic blockade of Ang II AT(1) receptors in diabetic and hypercholesterolaemic humans by ARBs, with concomitant elevation in plasma and tissue Ang II levels, may provide vascular and renal protection not only by reducing AT(1) receptor-mediated pro-oxidative effects, but also by unopposed AT(2) receptor stimulation.