ACE activity is modulated by kinin B2 receptor

Physiological and pharmacological perspectives of melatonin

The pineal gland is a interface between light-dark cycle and shows neuro-endocrine functions. Melatonin is the primary hormone of pineal gland, secreted at night. The night-time melatonin peak regulates the physiological functions at dark. Melatonin has several unique features as it synchronises internal rhythm with daily and seasonal variations, regulates circadian rhythm and sleep-wake cycle. Physiologically melatonin involves in detoxification of free radicals, immune functions, neuro-protection, oncostatic effects, cardiovascular functions, reproduction, and foetal development. The precise functions of melatonin are exhibited by specific receptors. In relation to pathophysiology, impaired melatonin secretion promotes sleep disorder, cancer progression, type-2 diabetes, and neurodegenerative diseases. Several reports have highlighted the therapeutic benefits of melatonin specially related to cancer protection, sleep disorder, psychiatric disorders, and jet lag problems. This review will touch the most of the area of melatonin-oriented health impacts and its therapeutic aspects.

Role of Kinins in Hypertension and Heart Failure

The kallikrein-kinin system (KKS) is proposed to act as a counter regulatory system against the vasopressor hormonal systems such as the renin-angiotensin system (RAS), aldosterone, and catecholamines. Evidence exists that supports the idea that the KKS is not only critical to blood pressure but may also oppose target organ damage. Kinins are generated from kininogens by tissue and plasma kallikreins. The putative role of kinins in the pathogenesis of hypertension is discussed based on human mutation cases on the KKS or rats with spontaneous mutation in the kininogen gene sequence and mouse models in which the gene expressing only one of the components of the KKS has been deleted or over-expressed. Some of the effects of kinins are mediated via activation of the B2 and/or B1 receptor and downstream signaling such as eicosanoids, nitric oxide (NO), endothelium-derived hyperpolarizing factor (EDHF) and/or tissue plasminogen activator (T-PA). The role of kinins in blood pressure regulation at normal or under hypertension conditions remains debatable due to contradictory reports from various laboratories. Nevertheless, published reports are consistent on the protective and mediating roles of kinins against ischemia and cardiac preconditioning; reports also demonstrate the roles of kinins in the cardiovascular protective effects of the angiotensin-converting enzyme (ACE) and angiotensin type 1 receptor blockers (ARBs).

Kinins and nitric oxide in patients with chronic chagas disease and systemic arterial hypertension

BACKGROUND

Chronic Chagas disease (CCHD) associated with Systemic Arterial Hypertension (SAH) is frequently found in areas where the disease is endemic. The pathogenesis of patients with both pathologies (CCHD-SAH) is unsettled. Nitric Oxide (NO) and Kinins are important players in the myocardial inflammation process in experimental CCHD. No previous study has addressed this question in patients with CCHD, particularly in those with CCHD-SAH. Accordingly, this study was undertaken in an attempt to contribute to the understanding of the pathogenesis of patients with CCHD-SAH.

METHODS

Thirty-seven patients with a positive serology for Chagas disease were enrolled; 15 had CCHD alone, 22 had CCHD-SAH (abnormal ECG/Doppler echocardiogram plus a systolic blood pressure > 140 mmHg or diastolic blood pressure > 90 mmHg on admission), and 11 had SAH alone. Thirty healthy individuals matched by age and sex served as controls. Plasma High-molecular (Hkg) and low-molecular weight (LKg) kininogens, plasma kallikrein levels (Pkal and Tcal), Kininase II, and plasma NO were measured.

RESULTS

HKg and LKg were lower in CCHD-SAH patients in comparison with other groups (P < .0001). Pkal and Tcal were higher in CCHD-SAH patients in comparison with the other groups (P< .0001). Kininase II levels were similar in SAH, CCHD, and CCHD-SAH patients, but lower in comparison with controls (P< .0001). NO levels were similar in CCHD and CCHD-SAH patients, but higher in comparison with SAH patients and controls (P > .0001).

CONCLUSION

Such findings suggest increased Kinin and NO activity in patients with CCHD-SAH, thus contributing to the understanding of the pathogenesis of this condition.

Investigation into the Mechanism of Homo- and Heterodimerization of Angiotensin-Converting Enzyme

Angiotensin-converting enzyme (ACE) plays a central role in the renin-angiotensin system (RAS), which is primarily responsible for blood pressure homeostasis. Studies have shown that ACE inhibitors yield cardiovascular benefits that cannot be entirely attributed to the inhibition of ACE catalytic activity. It is possible that these benefits are due to interactions between ACE and RAS receptors that mediate the protective arm of the RAS, such as angiotensin II receptor type 2 (AT2R) and the receptor MAS. Therefore, in this study, we investigated the molecular interactions of ACE, including ACE homodimerization and heterodimerization with AT2R and MAS, respectively. Molecular interactions were assessed by fluorescence resonance energy transfer and bimolecular fluorescence complementation in human embryonic kidney 293 cells and Chinese hamster ovary-K1 cells transfected with vectors encoding fluorophore-tagged proteins. The specificity of dimerization was verified by competition experiments using untagged proteins. These techniques were used to study several potential requirements for the germinal isoform of angiotensin-converting enzyme expressed in the testes (tACE) dimerization as well as the effect of ACE inhibitors on both somatic isoforms of angiotensin-converting enzyme expressed in the testes (sACE) and tACE dimerization. We demonstrated constitutive homodimerization of sACE and of both of its domains separately, as well as heterodimerization of both sACE and tACE with AT2R, but not MAS. In addition, we investigated both soluble sACE and the sACE N domain using size-exclusion chromatography-coupled small-angle X-ray scattering and we observed dimers in solution for both forms of the enzyme. Our results suggest that ACE homo- and heterodimerization does occur under physiologic conditions.

Beneficial effects of kinin B1 receptor antagonism on plasma fatty acid alterations and obesity in Zucker diabetic fatty rats

Kinins are the endogenous ligands of the constitutive B2 receptor (B2R) and the inducible B1 receptor (B1R). Whereas B2R prevents insulin resistance, B1R is involved in insulin resistance and metabolic syndrome. However, the contribution of B1R in type 2 diabetes associated with obesity remains uncertain. The aim of the present study was to examine the impact of 1-week treatment with a selective B1R antagonist (SSR240612, 10 mg/kg per day, by gavage) on hyperglycemia, hyperinsulinemia, leptinemia, body mass gain, and abnormal plasma fatty acids in obese Zucker diabetic fatty (ZDF) rats. Treatment with SSR240612 abolished the body mass gain and reduced polyphagia, polydipsia, and plasma fatty acid alterations in ZDF rats without affecting hyperglycemia, hyperinsulinemia, and hyperleptinemia. The present study suggests that the upregulated B1R plays a role in body mass gain and circulating fatty acid alterations in ZDF rats. However, mechanisms other than B1R induction would be implicated in glucose metabolism disorder in ZDF rats, based on the finding that SSR240612 did not reverse hyperglycemia and hyperinsulinemia.

Control of ENaC-mediated sodium reabsorption in the distal nephron by Bradykinin

Kinins, such as Bradykinin (BK), are peptide hormones of the kallikrein-kinin system. Apart from being a vasodilator, BK also increases urinary sodium excretion to reduce systemic blood pressure. It is becoming appreciated that BK modulates function of the epithelial Na(+) channel in the distal part of the renal nephron to affect tubular sodium reabsorption. In this chapter, we outline the molecular details, as well as discuss the physiological relevance of this regulation for the whole organism sodium homeostasis and setting chronic blood pressure.

Downregulation of kinin B1 receptor function by B2 receptor heterodimerization and signaling

Signaling through the G protein-coupled kinin receptors B1 (kB1R) and B2 (kB2R) plays a critical role in inflammatory responses mediated by activation of the kallikrein-kinin system. The kB2R is constitutively expressed and rapidly desensitized in response to agonist whereas kB1R expression is upregulated by inflammatory stimuli and it is resistant to internalization and desensitization. Here we show that the kB1R heterodimerizes with kB2Rs in co-transfected HEK293 cells and natively expressing endothelial cells, resulting in significant internalization and desensitization of the kB1R response in cells pre-treated with kB2R agonist. However, pre-treatment of cells with kB1R agonist did not affect subsequent kB2R responses. Agonists of other G protein-coupled receptors (thrombin, lysophosphatidic acid) had no effect on a subsequent kB1R response. The loss of kB1R response after pretreatment with kB2R agonist was partially reversed with kB2R mutant Y129S, which blocks kB2R signaling without affecting endocytosis, or T342A, which signals like wild type but is not endocytosed. Co-endocytosis of the kB1R with kB2R was dependent on β-arrestin and clathrin-coated pits but not caveolae. The sorting pathway of kB1R and kB2R after endocytosis differed as recycling of kB1R to the cell surface was much slower than that of kB2R. In cytokine-treated human lung microvascular endothelial cells, pre-treatment with kB2R agonist inhibited kB1R-mediated increase in transendothelial electrical resistance (TER) caused by kB1R stimulation (to generate nitric oxide) and blocked the profound drop in TER caused by kB1R activation in the presence of pyrogallol (a superoxide generator). Thus, kB1R function can be downregulated by kB2R co-endocytosis and signaling, suggesting new approaches to control kB1R signaling in pathological conditions.

Direct regulation of ENaC by bradykinin in the distal nephron. Implications for renal sodium handling

PURPOSE OF REVIEW

Locally produced peptide hormones kinins, such as bradykinin, are thought to oppose many of the prohypertensive actions of the renin-angiotensin-aldosterone system. In the kidney, bradykinin, via stimulation of B2 receptors (B2R), favors natriuresis mostly due to the inhibition of tubular Na reabsorption. Recent experimental evidence identifies the epithelial Na channel (ENaC) as a key end effector of bradykinin actions in the distal tubular segments. The focus of this review is the physiological relevance and molecular details of the bradykinin signal to ENaC.

RECENT FINDINGS

The recent epidemiological GenSalt study demonstrated that genetic variants of the gene encoding B2R show significant associations with the salt sensitivity of blood pressure. Bradykinin was shown to have an inhibitory effect on the distal nephron sodium transport via stimulation of B2 receptor-phospholipase C (B2R-PLC) cascade to decrease ENaC open probability. Genetic ablation of bradykinin receptors in mice led to an augmented ENaC function, particularly during elevated sodium intake, likely contributing to the salt-sensitive hypertensive phenotype. Furthermore, augmentation of bradykinin signaling in the distal nephron was demonstrated to be an important component of the natriuretic and antihypertensive effects of angiotensin converting enzyme inhibition.

SUMMARY

Salt-sensitive inhibition of ENaC activity by bradykinin greatly advances our understanding of the molecular mechanisms that are responsible for shutting down distal tubule sodium reabsorption during volume expanded conditions to avoid salt-sensitive hypertension.

The kallikrein-kinin system as a regulator of cardiovascular and renal function

Autocrine, paracrine, endocrine, and neuroendocrine hormonal systems help regulate cardio-vascular and renal function. Any change in the balance among these systems may result in hypertension and target organ damage, whether the cause is genetic, environmental or a combination of the two. Endocrine and neuroendocrine vasopressor hormones such as the renin-angiotensin system (RAS), aldosterone, and catecholamines are important for regulation of blood pressure and pathogenesis of hypertension and target organ damage. While the role of vasodepressor autacoids such as kinins is not as well defined, there is increasing evidence that they are not only critical to blood pressure and renal function but may also oppose remodeling of the cardiovascular system. Here we will primarily be concerned with kinins, which are oligopeptides containing the aminoacid sequence of bradykinin. They are generated from precursors known as kininogens by enzymes such as tissue (glandular) and plasma kallikrein. Some of the effects of kinins are mediated via autacoids such as eicosanoids, nitric oxide (NO), endothelium-derived hyperpolarizing factor (EDHF), and/or tissue plasminogen activator (tPA). Kinins help protect against cardiac ischemia and play an important part in preconditioning as well as the cardiovascular and renal protective effects of angiotensin-converting enzyme (ACE) and angiotensin type 1 receptor blockers (ARB). But the role of kinins in the pathogenesis of hypertension remains controversial. A study of Utah families revealed that a dominant kallikrein gene expressed as high urinary kallikrein excretion was associated with a decreased risk of essential hypertension. Moreover, researchers have identified a restriction fragment length polymorphism (RFLP) that distinguishes the kallikrein gene family found in one strain of spontaneously hypertensive rats (SHR) from a homologous gene in normotensive Brown Norway rats, and in recombinant inbred substrains derived from these SHR and Brown Norway rats this RFLP cosegregated with an increase in blood pressure. However, humans, rats and mice with a deficiency in one or more components of the kallikrein-kinin-system (KKS) or chronic KKS blockade do not have hypertension. In the kidney, kinins are essential for proper regulation of papillary blood flow and water and sodium excretion. B2-KO mice appear to be more sensitive to the hypertensinogenic effect of salt. Kinins are involved in the acute antihypertensive effects of ACE inhibitors but not their chronic effects (save for mineralocorticoid-salt-induced hypertension). Kinins appear to play a role in the pathogenesis of inflammatory diseases such as arthritis and skin inflammation; they act on innate immunity as mediators of inflammation by promoting maturation of dendritic cells, which activate the body's adaptive immune system and thereby stimulate mechanisms that promote inflammation. On the other hand, kinins acting via NO contribute to the vascular protective effect of ACE inhibitors during neointima formation. In myocardial infarction produced by ischemia/reperfusion, kinins help reduce infarct size following preconditioning or treatment with ACE inhibitors. In heart failure secondary to infarction, the therapeutic effects of ACE inhibitors are partially mediated by kinins via release of NO, while drugs that activate the angiotensin type 2 receptor act in part via kinins and NO. Thus kinins play an important role in regulation of cardiovascular and renal function as well as many of the beneficial effects of ACE inhibitors and ARBs on target organ damage in hypertension.

Vascular reactivity and ACE activity response to exercise training are modulated by the +9/−9 bradykinin B2 receptor gene functional polymorphism

The bradykinin receptor B2 ( BDKRB 2) gene +9/−9 polymorphism has been associated with higher gene transcriptional activity, and characteristics of cardiovascular phenotypes and physical performance. We hypothesized that vasodilation and ACE activity response to exercise training is modulated by BDKRB 2 gene. We genotyped 71 healthy volunteers were genotyped for the BDKRB 2 gene polymorphism. Heart rate (HR), mean blood pressure (MBP), and forearm blood flow (FBF) were evaluated. Angiotensin-I converting enzyme (ACE) activity was measured by fluorescence. Aerobic training was performed for 16 wk. All variables were reassessed after completion of the training period. In pretraining period, HR, MBP, FBF, and forearm vascular conductance (FVC) were similar among all genotypes. After physical training, the FBF and the FVC response during handgrip exercise such as area under the curve were higher in −9/−9 carriers than the other two groups. However, there were no changes in HR and MBP for all three groups. In addition, in posttraining period the decrease in ACE activity was higher in the −9/−9 group than the other two groups. These results suggest that reflex muscle vasodilation and ACE activity in response to exercise training are modulated by BDKRB 2 gene +9/−9 polymorphism in healthy individuals.

Evidence that kinin B2 receptor expression is upregulated by endothelial overexpression of B1 receptors

Bradykinin (BK) and des-Arg(9)-bradykinin (DBK) of kallikrein-kinin system exert its effects mediated by the B2 (B2R) and B1 (B1R) receptors, respectively. It was already shown that the deletion of kinin B1R or of B2R induces upregulation of the remaining receptor subtype. However studies on overexpression of B1R or B2R in transgenic animals have supported the importance of the overexpressed receptor but the expression of another receptor subtype has not been determined. Previous study described a marked vasodilatation and increased susceptibility to endotoxic shock which was associated with increased mortality in response to DBK in thoracic aorta from transgenic rat overexpressing the kinin B1R (TGR(Tie2B1)) exclusively in the endothelium. In another study, mice overexpressing B1R in multiple tissues were shown to present high susceptibility to inflammation and to lipopolysaccharide-induced endotoxic shock. Therefore the role of B2R was investigated in the thoracic aorta isolated from TGR(Tie2B1) rats overexpressing the B1R exclusively in the vascular endothelium. Our findings provided evidence for highly increased expression level of the B2R in the transgenic rats. It was reported that under endotoxic shock, these rats exhibited exaggerated hypotension, bradycardia and mortality. It can be suggested that the high mortality during the pathogenesis of endotoxic shock provoked in the transgenic TGR(Tie2B1) rats could be due to the enhanced expression of B2R associated with the overexpression of the B1R.

Salt-dependent inhibition of epithelial Na+ channel-mediated sodium reabsorption in the aldosterone-sensitive distal nephron by bradykinin

We have documented recently that bradykinin (BK) directly inhibits activity of the epithelial Na(+) channel (ENaC) via the bradykinin B2 receptor (B2R)-G(q/11)-phospholipase C pathway. In this study, we took advantage of mice genetically engineered to lack bradykinin receptors (B1R, B2R(-/-)) to probe a physiological role of BK cascade in regulation of ENaC in native tissue, aldosterone-sensitive distal nephron. Under normal sodium intake (0.32% Na(+)), ENaC open probability (P(o)) was modestly elevated in B1R, B2R(-/-) mice compared with wild-type mice. This difference is augmented during elevated Na(+) intake (2.00% Na(+)) and negated during Na(+) restriction (<0.01% Na(+)). Saturation of systemic mineralocorticoid status with deoxycorticosterone acetate similarly increased ENaC activity in both mouse strains, suggesting that the effect of BK on ENaC is independent of aldosterone. It is accepted that angiotensin-converting enzyme represents the major pathway of BK degradation. Systemic inhibition of angiotensin-converting enzyme with captopril (30 mg/kg of body weight for 7 days) significantly decreases ENaC activity and P(o) in wild-type mice, but this effect is diminished in B1R, B2R(-/-) mice. At the cellular level, acute captopril (100 μmol/L) treatment sensitized BK signaling cascade and greatly potentiated the inhibitory effect of 100 nmol/L of BK on ENaC. We concluded that BK cascade has its own specific role in blunting ENaC activity, particularly under conditions of elevated sodium intake. Augmentation of BK signaling in the aldosterone-sensitive distal nephron inhibits ENaC-mediated Na(+) reabsorption, contributing to the natriuretic and antihypertensive effects of angiotensin-converting enzyme inhibition.

Distribution of the activity of the angiotensin-converting enzyme in the rat aorta and changes in the activity with aging and by the action of L-NAME

The activity of the angiotensin-converting enzyme (ACE) of the inner surface (the endothelium surface) of rat aorta sections has been studied depending on their distance from the aortic arch, age of rats, and the duration of treatment of rats with the NO synthase inhibitor, N (ω)-nitro-L-arginine (L-NAME). The activity of ACE of aorta sections was determined by measuring the hydrolysis of hippuryl-L-histidyl-L-leucine and was expressed as picomoles of Hip-His-Leu hydrolyzed per minute per square millimeter of the endothelium surface. It was found that the ACE activity considerably varies along the aorta of young rats. This variability decreases with increasing age of rats and by the action of L-NAME. The average ACE activity in the aorta increases with the age of rats and with increasing time of L-NAME treatment. Enalapril normalizes the distribution of the ACE activity along the aorta and decreases the average ACE activity. The changes in the distribution of the ACE activity along the aorta and in the average ACE activity in the aorta with increasing age of the rat and by the action of L-NAME may play a role in the development of atherosclerosis of vessels on aging and the inhibition of formation of nitric oxide.

Bradykinin B2 receptor-dependent enhancement of enalapril-evoked hypotension in ethanol-fed female rats

Our previous studies showed that chronic ethanol feeding attenuates centrally (clonidine) evoked and potentiates peripherally (hydralazine) evoked hypotension in female rats. In this study, we investigated whether chronic ethanol (8 weeks, 5% wt/vol) alters hemodynamic responses elicited by angiotensin-converting enzyme (ACE) inhibition (enalapril) in telemetered female rats. Given the intimate interaction between ACE and bradykinin, studies were extended to investigate the role of bradykinin receptor (B2R) in ethanol-enalapril interaction. Compared with pair-fed controls, ethanol-fed female rats exhibited (1) higher renal expressions of ACE and B2R proteins and angiotensin II levels and (2) lower blood pressure. Pharmacological inhibition of ACE and B2R supports functional role for the higher levels of these 2 proteins in ethanol-fed rats because enalapril (10 mg/kg, intraperitoneally) caused significantly greater hypotensive response in ethanol-fed rats than in control rats. Further, blockade of B2R with bradyzide (2 mg/kg, intraperitoneally) abrogated the enhanced hypotensive effect of enalapril in ethanol-fed rats but had no effect on enalapril-evoked hypotension in control rats. Finally, enalapril enhancement of spontaneous baroreflex sensitivity (BRS) in control was absent in ethanol-fed rats. These findings demonstrate that chronic ethanol produces B2R-dependent enhancement of the hypotensive response elicited by enalapril and abrogates enalapril-evoked enhancement of spontaneous baroreflex response in female rats.

Ace inhibitors - activators of kinin receptors

Angiotensin converting enzyme (ACE) inhibitors are widely used for treatment of cardiovascular diseases. The effects of ACE inhibitors on the human bradykinin receptors were investigated. The mode of action of ACE inhibitors is considered. There is evidence that ACE inhibitors exert effects on the vascular system that cannot be attributed simply to the inhibition of ACE activity and accumulation of locally produced bradykinin. ACE inhibitors augment bradykinin effects on receptors indirectly by inducing cross-talk between ACE and the B2 receptor when enzyme and receptor molecules are sterically close, possibly forming a heterodimer. ACE inhibitors activate B1 receptors directly and independently of ACE via the zink-binding consensus sequence HEXXH, which is present in B1, but not in B2 receptor. Particular structure of B2 and B1 are represented, as well as receptor amino acids coupled with the G-proteins. Activation of kinin receptors by ACE inhibitors leads to clinically beneficial effects of ACE inhibitors.

Leptin regulates ACE activity in mice

Leptin is a hormone related to metabolism. It also influences blood pressure, but the mechanisms triggered in this process are not yet elucidated. Angiotensin-I converting enzyme (ACE) regulates cardiovascular functions and recently has been associated with metabolism control and obesity. Here, we used ob/ob mice, a model lacking leptin, to answer the question whether ACE and leptin could interact to influence blood pressure, thereby linking the renin-angiotensin system and obesity. These mice are obese and diabetic but have normal 24 h mean arterial pressure. Our results show that plasma and lung ACE activities as well as ACE mRNA expression were significantly decreased in ob/ob mice. In agreement with these findings, the hypotensive effect produced by enalapril administration was attenuated in the obese mice. Plasma renin, angiotensinogen, angiotensin I, bradykinin, and angiotensin 1-7 were increased, whereas plasma angiotensin II concentration was unchanged in obese mice. Chronic infusion of leptin increased renin activity and angiotensin II concentration in both groups and increased ACE activity in ob/ob mice. Acute leptin infusion restored ACE activity in leptin-deficient mice. Moreover, the effect of an ACE inhibitor on blood pressure was not changed in ob/+ mice during leptin treatment but increased four times in obese mice. In summary, our findings show that the renin-angiotensin system is altered in ob/ob mice, with markedly reduced ACE activity, which suggests a possible connection between the renin-angiotensin system and leptin. These results point to an important interplay between the angiotensinergic and the leptinergic systems, which may play a role in the pathogenesis of obesity, hypertension, and metabolic syndrome.

Differential regulation of inducible and endothelial nitric oxide synthase by kinin B1 and B2 receptors

Kinins are vasoactive peptides that play important roles in cardiovascular homeostasis, pain and inflammation. After release from their precursor kininogens, kinins or their C-terminal des-Arg metabolites activate two distinct G protein-coupled receptors (GPCR), called B2 (B2R) or B1 (B1R). The B2R is expressed constitutively with a wide tissue distribution. In contrast, the B1R is not expressed under normal conditions but is upregulated by tissue insult or inflammatory mediators. The B2R is considered to mediate many of the acute effects of kinins while the B1R is more responsible for chronic responses in inflammation. Both receptors can couple to Galphai and Galphaq families of G proteins to release mediators such as nitric oxide (NO), arachidonic acid, prostaglandins, leukotrienes and endothelium-derived hyperpolarizing factor and can induce the release of other inflammatory agents. The focus of this review is on the different transduction events that take place upon B2R and B1R activation in human endothelial cells that leads to generation of NO via activation of different NOS isoforms. Importantly, B2R-mediated eNOS activation leads to a transient ( approximately 5min) output of NO in control endothelial cells whereas in cytokine-treated endothelial cells, B1R activation leads to very high and prolonged ( approximately 90min) NO production that is mediated by a novel signal transduction pathway leading to post-translational activation of iNOS.

Angiotensin I-converting enzyme inhibitors are allosteric enhancers of kinin B1 and B2 receptor function

The beneficial effects of angiotensin I-converting enzyme (ACE) inhibitors go beyond the inhibition of ACE to decrease angiotensin (Ang) II or increase kinin levels. ACE inhibitors also affect kinin B1 and B2 receptor (B1R and B2R) signaling, which may underlie some of their therapeutic usefulness. They can indirectly potentiate the actions of bradykinin (BK) and ACE-resistant BK analogs on B2Rs to elevate arachidonic acid and NO release in laboratory experiments. Studies indicate that ACE inhibitors and some Ang metabolites increase B2R functions as allosteric enhancers by inducing a conformational change in ACE. This is transmitted to B2Rs via heterodimerization with ACE on the plasma membrane of cells. ACE inhibitors are also agonists of the B1R, at a Zn-binding sequence on the second extracellular loop that differs from the orthosteric binding site of the des-Arg-kinin peptide ligands. Thus, ACE inhibitors act as direct allosteric B1R agonists. When ACE inhibitors enhance B2R and B1R signaling, they augment NO production. Enhancement of B2R signaling activates endothelial NO synthase, yielding a short burst of NO; activation of B1Rs results in a prolonged high output of NO by inducible NO synthase. These actions, outside inhibiting peptide hydrolysis, may contribute to the pleiotropic therapeutic effects of ACE inhibitors in various cardiovascular disorders.

Predisposition to atherosclerosis and aortic aneurysms in mice deficient in kinin B1 receptor and apolipoprotein E

Kinin B1 receptor is involved in chronic inflammation and expressed in human atherosclerotic lesions. However, its significance for lesion development is unknown. Therefore, we investigated the effect of kinin B1 receptor deletion on the development of atherosclerosis and aortic aneurysms in apolipoprotein E-deficient (ApoE(-/-)) mice. Mice deficient both in ApoE and in kinin B1 receptor (ApoE(-/-)-B(1)(-/-)) were generated and analyzed for their susceptibility to atherosclerosis and aneurysm development under cholesterol rich-diet (western diet) and angiotensin II infusion. Kinin B1 receptor messenger RNA (mRNA) expression was significantly increased in ApoE(-/-) mice after Western-type diet. Although no difference in serum cholesterol was found between ApoE(-/-)-B(1)(-/-) and ApoE(-/-) mice under Western-type diet, aortic lesion incidence was significantly higher in ApoE(-/-)-B(1)(-/-) after this treatment. In accordance, we observed increased endothelial dysfunction in these mice. The mRNA expression of cyclic guanosine monophosphate-dependent protein kinase I, CD-11, F4/80, macrophage colony-stimulating factor, and tumor necrosis factor-alpha were increased in the aorta of double-deficient mice following Western-type diet, whereas the levels of peroxisome proliferator-activated receptor gamma protein and the activity of matrix metalloproteinase-9 activity were decreased. In addition to the increased atherosclerotic lesions, the lack of kinin B(1) receptor also increased the incidence of abdominal aortic aneurysms after angiotensin II infusion. In conclusion, our results show that kinin B(1) receptor deficiency aggravates atherosclerosis and aortic aneurysms under cholesterolemic conditions, supporting an antiatherogenic role for the kinin B(1) receptor.