Activation of bradykinin B1 receptor by ACE inhibitors

Association between angiotensin-converting enzyme inhibitors or angiotensin receptor blockers and community-acquired pneumonia: A nationwide population propensity-score matching study

BACKGROUND

Few large-scale cohort studies have investigated the association between community-acquired pneumonia and the use of angiotensin-converting enzyme inhibitors (ACEIs) or angiotensin II receptor blockers (ARBs). We aimed to study whether using ACEIs or ARBs had protective effects for community-acquired pneumonia.

METHODS

This database cohort study was conducted retrospectively in Taiwan. The hypertensive patients were the target population of this study. Patients with ARB use were defined as our first study cohort. The second study cohort comprised patients who used ACEI. Propensity-score matching at 1:1 was used between ARB users and non-ARB users. We recruited 67 944 participants for the ARB study and 58 062 participants for the ACEI study. The same matching was also performed between ACEI users and non-ACEI users. Cox proportional hazard regression was used to analyse the risk of the outcome of viral pneumonia.

RESULTS

The hazard ratio of community-acquired pneumonia for ARB users relative to non-ARB users was 0.33. The hazard ratio of community-acquired pneumonia was 0.71 times in ACEI users compared with ACEI nonusers. In stratification analysis, both ARB and ACEI both exhibited a protective effect for community-acquired pneumonia in each age and sex group. In the analysis of the effects of therapy duration, patients using ARB for fewer than 100 days exhibited a greater reduction in the risk of community-acquired pneumonia (adjusted HR = 0.58) compared with the non-ARB cohort. For the ACEI study, patients who used ACEI for 121-450 days were more likely to exhibit reduced risks of community-acquired pneumonia (adjusted HR = 0.5).

CONCLUSION

Both ACEI and ARB uses were associated with decreased risk of community-acquired pneumonia infection.

Blinded, Multicenter Evaluation of Drug-induced Changes in Contractility Using Human-induced Pluripotent Stem Cell-derived Cardiomyocytes

Animal models are 78% accurate in determining whether drugs will alter contractility of the human heart. To evaluate the suitability of human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) for predictive safety pharmacology, we quantified changes in contractility, voltage, and/or Ca²⁺ handling in 2D monolayers or 3D engineered heart tissues (EHTs). Protocols were unified via a drug training set, allowing subsequent blinded multicenter evaluation of drugs with known positive, negative, or neutral inotropic effects. Accuracy ranged from 44% to 85% across the platform-cell configurations, indicating the need to refine test conditions. This was achieved by adopting approaches to reduce signal-to-noise ratio, reduce spontaneous beat rate to ≤ 1 Hz or enable chronic testing, improving accuracy to 85% for monolayers and 93% for EHTs. Contraction amplitude was a good predictor of negative inotropes across all the platform-cell configurations and of positive inotropes in the 3D EHTs. Although contraction- and relaxation-time provided confirmatory readouts forpositive inotropes in 3D EHTs, these parameters typically served as the primary source of predictivity in 2D. The reliance of these “secondary” parameters to inotropy in the 2D systems was not automatically intuitive and may be a quirk of hiPSC-CMs, hence require adaptations in interpreting the data from this model system. Of the platform-cell configurations, responses in EHTs aligned most closely to the free therapeutic plasma concentration. This study adds to the notion that hiPSC-CMs could add value to drug safety evaluation.

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).

Renin-angiotensin inhibitors reprogram tumor immune microenvironment: A comprehensive view of the influences on anti-tumor immunity

Renin-angiotensin system inhibitors (RASi) have shown potential anti-tumor effects that may have a significant impact in cancer therapy. The components of the renin-angiotensin system (RAS) including both, conventional and alternative axis, appear to have contradictory effects on tumor biology. The mechanisms by which RASi impair tumor growth extend beyond their function of modulating tumor vasculature. The major focus of this review is to analyze other mechanisms by which RASi reprogram the tumor immune microenvironment. These involve impairing hypoxia and acidosis within the tumor stroma, regulating inflammatory signaling pathways and oxidative stress, modulating the function of the non-cellular components and immune cells, and regulating the cross-talk between kalli krein kinin system and RAS.

The Biased G-Protein-Coupled Receptor Agonism Bridges the Gap between the Insulin Receptor and the Metabolic Syndrome

Insulin signaling, as mediated through the insulin receptor (IR), plays a critical role in metabolism. Aberrations in this signaling cascade lead to several pathologies, the majority of which are classified under the umbrella term "metabolic syndrome". Although many of these pathologies are associated with insulin resistance, the exact mechanisms are not well understood. One area of current interest is the possibility of G-protein-coupled receptors (GPCRs) influencing or regulating IR signaling. This concept is particularly significant, because GPCRs have been shown to participate in cross-talk with the IR. More importantly, GPCR signaling has also been shown to preferentially regulate specific downstream signaling targets through GPCR agonist bias. A novel study recently demonstrated that this GPCR-biased agonism influences the activity of the IR without the presence of insulin. Although GPCR-IR cross-talk has previously been established, the notion that GPCRs can regulate the activation of the IR is particularly significant in relation to metabolic syndrome and other pathologies that develop as a result of alterations in IR signaling. As such, we aim to provide an overview of the physiological and pathophysiological roles of the IR within metabolic syndrome and its related pathologies, including cardiovascular health, gut microflora composition, gastrointestinal tract functioning, polycystic ovarian syndrome, pancreatic cancer, and neurodegenerative disorders. Furthermore, we propose that the GPCR-biased agonism may perhaps mediate some of the downstream signaling effects that further exacerbate these diseases for which the mechanisms are currently not well understood.

First Report of Eurycoma longifolia Jack Root Extract Causing Relaxation of Aortic Rings in Rats

Although Eurycoma longifolia has been studied for erectile function, the blood pressure- (BP-) lowering effect has yet to be verified. Hence, this study aims at investigating the BP-lowering properties of the plant with a view to develop an antihypertensive agent that could also preserve erectile function. Ethanolic root extract was partitioned by hexane, dichloromethane (DCM), ethyl acetate, butanol, and water. The DCM fraction, found to be potent in relaxing phenylephrine- (PE-) precontracted rat aortic rings, was further purified by column chromatography. Subfraction DCM-II, being the most active in relaxing aortae, was studied for effects on the renin-angiotensin and kallikrein-kinin systems in aortic rings. The effect of DCM-II on angiotensin-converting enzyme (ACE) activity was also evaluated in vitro. Results showed that DCM-II reduced (p < 0.05) the contractions evoked by angiotensin I and angiotensin II (Ang II). In PE-precontracted rings treated with DCM-II, the Ang II-induced contraction was attenuated (p < 0.05) while bradykinin- (BK-) induced relaxation enhanced (p < 0.001). In vitro, DCM-II inhibited (p < 0.001) the activity of ACE. These data demonstrate that the vasodilatory effect of DCM-II appears to be mediated via inhibition of Ang II type 1 receptor and ACE as well as enhancement of Ang II type 2 receptor activation and BK activity.

Roles of kinins in the nervous system

The kallikrein-kinin system (KKS) is an endogenous pathway involved in many biological processes. Although primarily related to blood pressure control and inflammation, its activation goes beyond these effects. Neurogenesis and neuroprotection might be stimulated by bradykinin being of great interest for clinical applications following brain injury. This peptide is also an important player in spinal cord injury pathophysiology and recovery, in which bradykinin receptor blockers represent substantial therapeutic potential. Here, we highlight the participation of kinin receptors and especially bradykinin in mediating ischemia pathophysiology in the central and peripheral nervous systems. Moreover, we explore the recent advances on mechanistic and therapeutic targets for biological, pathological, and neural repair processes involving kinins.

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.

Gynura procumbens causes vasodilation by inhibiting angiotensin II and enhancing bradykinin actions

Previous studies showed that Gynura procumbens reduced blood pressure by blocking calcium channels and inhibiting the angiotensin-converting enzyme activity. The present experiments were to further explore the effects and mechanisms of a purer aqueous fraction (FA-I) of G. procumbens on angiotensin I (Ang I)-induced and angiotensin II (Ang II)-induced contraction of aortic rings and also on the bradykinin (BK) effect on cardiovascular system. Rat aortic rings suspended in organ chambers were used to investigate the vascular reactivity of FA-I. Effect of FA-I on BK was studied by in vitro and in vivo methods. Results show that FA-I significantly (P < 0.05) decreased the contraction evoked by Ang I and Ang II. In the presence of indomethacin (10 µM) or N-nitro-L-arginine methyl ester (0.1 µM), the inhibitory effect of FA-I on Ang II-induced contraction of aortic rings was reduced. Besides, FA-I potentiated the vasorelaxant effect and enhanced the blood pressure-lowering effect of BK. In conclusion, FA-I reduced the contraction evoked by Ang II probably via the endothelium-dependent pathways, which involve activation of the release of nitric oxide and prostaglandins. The inhibition of angiotensin-converting enzyme activity by FA-I may contribute to the potentiation of the effects of BK on cardiovascular system.

Angiotensin-converting enzyme and the tumor microenvironment: mechanisms beyond angiogenesis

The renin angiotensin system (RAS) is a network of enzymes and peptides that coalesce primarily on the angiotensin II type 1 receptor (AT1R) to induce cell proliferation, angiogenesis, fibrosis, and blood pressure control. Angiotensin-converting enzyme (ACE), the key peptidase of the RAS, is promiscuous in that it cleaves other substrates such as substance P and bradykinin. Accumulating evidence implicates ACE in the pathophysiology of carcinogenesis. While the role of ACE and its peptide network in modulating angiogenesis via the AT1R is well documented, its involvement in shaping other aspects of the tumor microenvironment remains largely unknown. Here, we review the role of ACE in modulating the immune compartment of the tumor microenvironment, which encompasses the immunosuppressive, cancer-promoting myeloid-derived suppressor cells, alternatively activated tumor-associated macrophages, and T regulatory cells. We also discuss the potential roles of peptides that accumulate in the setting of chronic ACE inhibitor use, such as bradykinin, substance P, and N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP), and how they may undercut the gains of anti-angiogenesis from ACE inhibition. These emerging mechanisms may harmonize the often-conflicting results on the role of ACE inhibitors and ACE polymorphisms in various cancers and call for further investigations into the potential benefit of ACE inhibitors in some neoplasms.

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.

Renin-Angiotensin system suppression mitigates experimental radiation pneumonitis

PURPOSE

To find the mitigators of pneumonitis induced by moderate doses of thoracic radiation (10-15 Gy).

METHODS AND MATERIALS

Unanesthetized WAG/RijCmcr female rats received a single dose of X-irradiation (10, 12, or 15 Gy at 1.615 Gy/min) to the thorax. Captopril (an angiotensin-converting enzyme inhibitor) or losartan (an angiotensin receptor blocker) was administered in the drinking water after irradiation. Pulmonary structure and function were assessed after 8 weeks in randomly selected rats by evaluating the breathing rate, ex vivo vascular reactivity, and histopathologic findings. Survival analysis was undertaken on all animals, except those scheduled for death.

RESULTS

Survival after a dose of 10 Gy to the thorax was not different from that of unirradiated rats for <or=1 year. Survival decreased to <50% by 45 weeks after 12 Gy and by 8-9 weeks after 15 Gy. Captopril (17-56 mg/kg/d) improved survival and reduced radiation-induced increases in breathing rate, changes in vascular reactivity, and histopathologic evidence of injury. Radiation-induced increases in the breathing rate were prevented even if captopril was started 1 week after irradiation or if it was discontinued after 5 weeks. Losartan, although effective in reducing mortality, was not as efficacious as captopril in mitigating radiation-induced increases in the breathing rate or altered vasoreactivity.

CONCLUSION

In rats, a moderate thoracic radiation dose induced pneumonitis and morbidity. These injuries were mitigated by captopril even when it was begun 1 week after radiation or if discontinued 5 weeks after exposure. Losartan was less effective in protecting against radiation-induced changes in vascular reactivity or tachypnea.

Reinventing the ACE inhibitors: some old and new implications of ACE inhibition

Since their inception, angiotensin-converting enzyme (ACE) inhibitors have been used as first-line therapy for the treatment of cardiovascular and renal diseases. They restore the balance between the vasoconstrictive salt-retentive and hypertrophy-causing peptide angiotensin II (Ang II) and bradykinin, a vasodilatory and natriuretic peptide. As ACE is a promiscuous enzyme, ACE inhibitors alter the metabolism of a number of other vasoactive substances. ACE inhibitors decrease systemic vascular resistance without increasing heart rate and promote natriuresis. They have been proven effective in the treatment of hypertension, and reduce mortality in congestive heart failure and left ventricular dysfunction after myocardial infarction. They inhibit ischemic events and stabilize plaques. Furthermore, they delay the progression of diabetic nephropathy and neuropathy and act as antioxidants. Ongoing studies have elucidated protective roles for them in both memory-related disorders and cancer. Lastly, N- and C-domain selective ACE inhibitors have led to new uses for ACE inhibitors.

The kinin B1 receptor contributes to the cardioprotective effect of angiotensin-converting enzyme inhibitors and angiotensin receptor blockers in mice

Recent studies have shown that inhibition of angiotensin-converting enzyme (ACE) or angiotensin II receptors causes upregulation of the B(1) receptor (B(1)R). Here we tested the hypothesis that activation of the B(1)R partly contributes to the cardiac beneficial effect of ACE inhibitor (ACEi) and angiotensin II receptor blockers (ARB). B(1)R knockout mice (B(1)R(-/-)) and C57Bl/6J (wild-type control animals, WT) were subjected to myocardial infarction (MI) by ligating the left anterior descending coronary artery. Three weeks after MI, each strain of mice was treated with vehicle, ACEi (ramipril, 2.5 mg kg(-1) day(-1) in drinking water) or ARB (valsartan, 40 mg kg(-1) day(-1) in drinking water) for 5 weeks. We found that: (1) compared with WT mice, B(1)R(-/-) mice that underwent sham surgery had slightly but significantly increased left ventricular (LV) diastolic dimension, LV mass and myocyte size, whereas systolic blood pressure, cardiac function and collagen deposition did not differ between strains; (2) MI leads to LV hypertrophy, chamber dilatation and dysfunction similarly in both WT and B(1)R(-/-) mice; and (3) ACEi and ARB improved cardiac function and remodelling in both strains; however, these benefits were significantly diminished in B(1)R(-/-) mice. Our data suggest that kinins, acting via the B(1)R, participate in the cardioprotective effects of ACEi and ARB.

Attenuation of left ventricular dysfunction by an ACE inhibitor after myocardial infarction in a kininogen-deficient rat model

Bradykinin (BK) coronary outflow and left ventricular (LV) performance of kininogen-deficient Brown Norway Katholiek (BNK) rats and Brown Norway Hannover (BNH) controls were investigated. We analyzed whether the angiotensin-converting enzyme (ACE) inhibitor ramipril is able to attenuate LV dysfunction after induction of myocardial infarction (MI) in this animal model. Ex vivo, the basal BK content in the coronary outflow of buffer-perfused, isolated hearts was measured by specific radioimmunoassay. In vivo, left ventricular pressure (LVP), the maximal rate of LVP increase, LV end-diastolic pressure, the maximal rate of LVP decrease and heart rate were determined using a tip catheter 3 weeks after induction of MI. Compared to BNK rats, basal BK outflow was increased 30-fold in controls (p<0.01). In vivo, we found no significant differences between sham-ligated BNK and BNH rats in basal LV function. After MI, the impairment of LV function was significantly worse in BNK rats when compared to BNH rats. ACE inhibition significantly attenuated this LV dysfunction in both groups, when compared to untreated animals. Reduced basal BK level resulting from kininogen deficiency has no effect on basal LV function, but remains to be a risk factor for the ischemic heart. However, ACE inhibition is sufficient to improve LV function despite kininogen deficiency.

ACE activity is modulated by kinin B2 receptor

Angiotensin-converting enzyme (ACE) is an ectoprotein able to modulate the activity of a plethora of compounds, among them angiotensin I and bradykinin. Despite several decades of research, new aspects of the mechanism of action of ACE have been elucidated, expanding our understanding of its role not only in cardiovascular regulation but also in different areas. Recent findings have ascribed an important role for ACE/kinin B(2) receptor heterodimerization in the pharmacological properties of the receptor. In this work, we tested the hypothesis that this interaction also affects ACE enzymatic activity. ACE catalytic activity was analyzed in Chinese hamster ovary cell monolayers coexpressing the somatic form of the enzyme and the receptor coding region using as substrate the fluorescence resonance energy transfer peptide Abz-FRK(Dnp)P-OH. Results show that the coexpression of the kinin B(2) receptor leads to an augmentation in ACE activity. In addition, this effect could be blocked by the B(2) receptor antagonist icatibant. The hypothesis was also tested in endothelial cells, a more physiological system, where both proteins are naturally expressed. Endothelial cells from genetically ablated kinin B(2) receptor mice showed a decreased ACE activity when compared with wild-type mice cells. In summary, this is the first report showing that the ACE/kinin B(2) receptor interaction modulates ACE activity. Taking into account the interplay among ACE, ACE inhibitors, and kinin receptors, we believe that these results will shed new light into the arena of the controversial search for the mechanism controlling these interactions.

Expression of angiotensin I-converting enzymes and bradykinin B2 receptors in mouse inner medullary-collecting duct cells

We described in mouse inner medullary-collecting duct cells (mIMCD-3) the somatic and the N-domain ACE synthesis and its interaction with the kallikrein-kinin system co-localized in the same cells. We purified two ACE forms from culture medium, M1 (130 kDa) and M2 (N-domain, 60 kDa), and cellular lysate, C1 (130 kDa) and C2 (N-domain, 60 kDa). Captopril and enalaprilat inhibited the purified enzymes. The immunofluorescence studies indicated that ACE is present in the membrane, cytoplasm and in the cell nucleus. Kinin B1 and B2 receptors were detected by immunofluorescence and showed to be activated by BK and DesR9 BK, increasing the acidification rate which was enhanced in the presence of enalaprilat. The presence of secreted and intracellular ACE in mIMCD-3 confirmed the hypothesis previously proposed by our group for a new site of ACE secretion in the collecting duct.

The role of the renal kallikrein-kinin system in diabetic nephropathy

PURPOSE OF REVIEW

Diabetic nephropathy is one of the most common complications in diabetes mellitus. Multiple pathogenic mechanisms are now believed to contribute to this disease, including inflammatory cytokines, autacoids and oxidative stress. Numerous studies have shown that the kallikrein-kinin system may be involved in these mechanisms. This review focuses on recent research advance on the potential role of the kallikrein-kinin system in the development of diabetic nephropathy, and its clinical relevance.

RECENT FINDINGS

A collection of recent studies has shown that angiotensin-converting enzyme inhibitors, which inhibit angiotensin II formation and degradation of bradykinin, and vasopeptidase inhibitors attenuated the development of diabetic nephropathy in experimental animals and clinical settings. The role of the kallikrein-kinin system in diabetes is further supported by findings that diabetic nephropathy is worsened in diabetic mice lacking bradykinin B2 receptors. Although long-acting bradykinin B2 receptor agonists have been shown to have renal protective effects, their therapeutic benefits have not been well studied.

SUMMARY

Current experimental investigations demonstrated that pharmacological intervention of the kallikrein-kinin system improved renal conditions in diabetes mellitus. These findings suggest that the kallikrein-kinin system may be a therapeutic target in preventing and treating diabetic nephropathy.

ACE phenotyping as a first step toward personalized medicine for ACE inhibitors. Why does ACE genotyping not predict the therapeutic efficacy of ACE inhibition?

Angiotensin (Ang)-converting enzyme (ACE) inhibitors are widely used for the treatment of cardiovascular diseases. Not all patients respond to ACE inhibitors, and it has been suggested that genetic variation might be a useful marker to predict the therapeutic efficacy of these drugs. In particular, the ACE insertion (I)/deletion (D) polymorphism has been investigated in this regard. Despite a decade of intensive research involving the genotyping of thousands of patients, we still do not know whether ACE genotyping helps in predicting the success of ACE inhibition. This review critically addresses the concept that predictive information on therapeutic efficacy of ACE inhibitors might be obtained based on ACE genotyping. It answers the following questions: Do higher ACE levels really result in higher Ang II levels? Is ACE the only converting enzyme in humans? Does ACE inhibition affect ACE expression? Why does ACE have 2 catalytically active domains? What is the relevance of ACE inhibitor-induced signaling through membrane-bound ACE? The review ends with the proposal that ACE phenotyping may prove to be a better first step toward personalized medicine for ACE inhibitors than ACE genotyping.

Blockade of renin-angiotensin system reduces QT dispersion and improves intracellular Ca/Mg status in hemodialysis patients

BACKGROUND

Electrolyte impairments are common in hemodialysis (HD) patients. Consequently, QT dispersion (QTd) is prolonged, correlating with high intracellular magnesium. In patients with cardiac disorders, renin-angiotensin system (RAS) inhibition reduces QTd.

AIM

To compare the effects of ACE inhibition or AT-1 blockade on QTd duration and intracellular magnesium (Mg)/calcium (Ca) in peripheral blood mononuclear cells (PBMC) from chronic HD patients.

METHODS

24 HD patients received cilazapril for 8 weeks and, following a 2-week withdrawal, were switched to valsartan for additional 8 weeks. QTd measurements and PBMC isolation were performed at the beginning and the end of each period. Total intracellular Ca and Mg were assessed by atomic spectrometer, and cytosolic free Ca2+ by fluorocytometer.

RESULTS

Both treatments significantly decreased QTd, demonstrating similar reduction magnitudes. In both groups, PBMC exhibited basally low cytosolic Ca2+ and undisturbed high transmembrane Ca2+ influx following phytohemagglutinin stimulation. Total intracellular Ca was increased, while Mg was reduced, following either treatment. The total intracellular Ca/Mg ratio inversely correlated with QTd duration.

CONCLUSIONS

(1) RAS inhibition reduces prolonged QTd in HD patients. (2) In PBMC from ordinarily Ca-depleted HD patients, RAS suppression brings about elevation of total intracellular Ca. (3) RAS blockade decreases high intracellular Mg in PBMC from HD patients. Consequently, the Ca/Mg ratio increases, inversely correlating with QTd reduction.

High glucose increases B1-kinin receptor expression and signaling in endothelial cells

The loss of endothelial function is the initiating factor in the development of diabetic vascular disease. Kinins control endothelial function by the activation of two receptors: the B2 which is constitutively expressed, and the B1 which is highly induced in pathological conditions. In the present study, we observed that the levels of B1-receptor mRNA and protein are induced in endothelial cells incubated in high glucose. An increase in B1-receptor was also observed in the endothelial layer of aortas, from 4-week diabetic rats. When cells were grown in high glucose, the B1 agonist des-Arg9-BK increased nitrite levels, whereas in normal glucose nitrite levels were unchanged. Nitrite increase was blocked by L-NAME and 1400W indicating the participation of the inducible Nitric Oxide Synthase (iNOS). iNOS protein levels were also increased in high glucose. These results demonstrate the participation of the B1 receptor in the signaling pathways mediated by kinins in high glucose.

Hypothesized and found mechanisms for potentiation of bradykinin actions

Potentiation of hormone actions can occur by different mechanisms, including inhibition of degrading enzymes, interaction with the hormone receptor leading to stabilization of bioactive conformation or leading to receptor homo- and hetero-oligomerization, receptor phosphorylation and dephosphorylation or can occur by directly influencing the signal transduction and ion channels. In this review the potentiation of bradykinin actions in different systems by certain compounds will be reviewed. Despite many long years of experimental research and investigation the mechanisms of potentiating action remain not fully understood. One of the most contradictory findings are the distinct differences between the inhibition of the angiotensin I-converting enzyme and the potentiation of the bradykinin induced smooth muscle reaction. Contradictory findings and hypothesized mechanisms in the literature are discussed in this review and in some cases compared to own results. Investigation of potentiating actions was extended from hypotension, smooth muscle reaction and cellular actions to activation of immunocompetent cells. In our opinion the potentiation of bradykinin action can occur by different mechanisms, depending on the system and the applied potentiating factor used.

B2-receptor modulation of the reactivity to phenylephrine and angiotensin II in the carotid artery of normotensive rats after trandolapril treatment

This study was designed to study the effects of angiotensin converting enzyme inhibitors (ACEI) following treatment with trandolapril (0.3 mg kg(-1) day(-1)) on carotid arterial responsiveness in normotensive Wistar rats. Carotid arteries were obtained from control or trandolapril-treated animals and mounted in an isolated organ bath. Reactivity to angiotensin II (Ang II), phenylephrine (Phe) and KCl was studied. Agonist concentration-response curves were constructed in either the absence or presence of the endothelium or after incubation with L-NAME (10(-6) M), HOE140 (10(-7) M) or indomethacin (10(-5) M). Trandolapril treatment decreased the Ang II and Phe potencies in carotid arteries, but did not affect the maximal response. The KCl responses (potency and Emax) were similar in both control and trandolapril-treated arteries. The absence of endothelium increased the response to both agonists in control and trandolapril-treated arteries; however, the inhibitory component from the endothelial layer of the Phe response was greater in trandolapril-treated animals than in control animals. The presence of L-NAME or HOE140 abolished the changes in the potency values of trandolapril-treated animals. The presence of indomethacin did not change the effect of trandolapril on the potency values of both agonists. We conclude that trandolapril treatment decreased the carotid arterial reactivity in normotensive rats and that this effect is endothelium-dependent. Furthermore, the involvement of B(2)-receptors and NO production, but not of prostaglandins, is suggested in this mechanism.

Kinin- and angiotensin-converting enzyme (ACE) inhibitor-mediated nitric oxide production in endothelial cells

Carboxypeptidase cleavage of the C-terminal Arg of kinins generates specific agonists of the B1 receptor. Activation of B1 receptors produces nitric oxide via eNOS in bovine endothelial cells and iNOS in cytokine-stimulated human endothelial cells. Angiotensin-converting enzyme (ACE) inhibitors are direct agonists of B1 receptors in endothelial cells, although they release NO via a different signaling pathway than peptide ligands in bovine cells. This brief review discusses carboxypeptidase M as a required processing enzyme for generating B1 agonists, how ACE inhibitors and peptide ligands stimulate NO production and the evidence for, as well as some consequences of, the direct activation of B1 receptors by ACE inhibitors.

Potentiation of bradykinin actions by analogues of the bradykinin potentiating nonapeptide BPP9alpha

Synthetic analogues of the bradykinin potentiating nonapeptide BPP9alpha indicate significantly different structural requirements for potentiation of the bradykinin (BK)-induced smooth muscle contraction (GPI) and the inhibition of isolated somatic angiotensin I-converting enzyme (ACE). The results disprove the ACE inhibition as the only single mechanism and also the direct interaction of potentiating peptides with the bradykinin receptors in transfected COS-7 cells as molecular mechanism of potentiation. Our results indicate a stimulation of inositol phosphates (IPn) formation independently from the B2 receptor. Furthermore, the results with La3+ support the role of extracellular Ca2+ and its influx through corresponding channels. The missing effect of calyculin on the GPI disproves the role of phosphatases in the potentiating action. These experimental studies should not only contribute to a better understanding of the potentiating mechanisms but also incorporate a shift in the research towards the immune system, in particular towards the immunocompetent polymorphonuclear leukocytes. The chemotaxis of these cells can be potentiated most likely by exclusive inhibition of the enzymatic degradation of bradykinin. Thus the obtained results give evidence that the potentiation of the bradykinin action can occur by different mechanisms, depending on the system and on the applied potentiating factor.

Putative roles of kinin receptors in the therapeutic effects of angiotensin 1-converting enzyme inhibitors in diabetes mellitus

The role of endogenous kinins and their receptors in diabetes mellitus is being confirmed with the recent developments of molecular and genetic animal models. Compelling evidence suggests that the kinin B(2) receptor is organ-protective and partakes to the therapeutic effects of angiotensin 1-converting enzyme inhibitors (ACEI) and angiotensin AT(1) receptor antagonists. Benefits derive primarily from vasodilatory, antihypertensive, antiproliferative, antihypertrophic, antifibrotic, antithrombotic and antioxidant properties of kinin B(2) receptor activation. Mechanisms include the formation of nitric oxide and prostacyclin and the inhibition of NAD(P)H oxidase activity involving classical and novel signalling pathways. Kinin B(2) receptor also ameliorates insulin resistance by increasing glucose uptake and supply, and by inducing glucose transporter-4 translocation either directly or through phosphorylation of insulin receptor. The kinin B(1) receptor, which is induced by the cytokine network, growth factors and hyperglycaemia, mediates hyperalgesia, vascular hyperpermeability and leukocytes infiltration in diabetic animals. However, emerging data highlight reno- and cardio-protective effects mediated by kinin B(1) receptor under chronic ACEI therapy in diabetes mellitus. Thus, the Janus-faced of kinin receptors needs to be taken into account in future drug development. For instance, locally acting kinin B(1)/B(2) receptor agonists if used in a safe therapeutic window may represent a more rationale strategy in the prevention and management of diabetic complications. Because kinin B(2) receptor antagonists may further increase insulin resistance, the persisting dogma that restricts the development of kinin receptor analogues to antagonists (that is still relevant to abrogate pain and inflammation) needs to be revisited.

Potentiation of des-Arg9-Kallidin-Induced Vasoconstrictor Responses by Metallopeptidase Inhibition in Isolated Human Umbilical Artery

Several metallopeptidases have been reported to be involved in bradykinin (BK) B(1) receptor agonist metabolism. Our goal was to evaluate in vitro roles of metallopeptidases [e.g., neutral endopeptidase (NEP), aminopeptidase M (APM), and angiotensin-converting enzyme (ACE)] as functional inactivators of the selective BKB(1) receptor agonist Lys-des-Arg(9)-BK (DAKD) in isolated human umbilical artery (HUA) rings. Concentration-response curves (CRCs) to DAKD were performed after a 5-h incubation period. Treatment with 10 microM phosphoramidon (NEP inhibitor) or 10 microM amastatin (APM inhibitor) potentiated DAKD-elicited responses, whereas 1 microM captopril (ACE inhibitor) had no significant effects. However, when the three enzymes were simultaneously inhibited, a significant potentiation over responses obtained under concurrent NEP and aminopeptidase M inhibition was observed. In contrast, responses induced by the peptidase resistant BKB(1) receptor agonist Sar-D-Phe(8)-des-Arg(9)-BK were not modified by triple peptidase inhibition. In addition, endothelial denudation failed to alter DAKD-induced responses in HUA. Finally, in the presence of NEP, ACE, and APM inhibition, Lys-des-Arg(9)-[Leu(8)]-BK, the potent BKB(1) receptor antagonist, produced a parallel, concentration-dependent, rightward shift of DAKD CRCs. The obtained pK(B) (8.57) and the Schild slope not different from unity are in agreement with an interaction at a single homogeneous BKB(1) receptor population. In summary, this work constitutes the first pharmacological evidence that metallopeptidases NEP, APM, and ACE represent a relevant inactivation mechanism of the endogenous BKB(1) receptor agonist DAKD in isolated HUA.

Role of the B1 kinin receptor in the regulation of cardiac function and remodeling after myocardial infarction

Kinins exert cardioprotective effects via 2 G-protein-coupled receptors, B1 and B2. Using B1 kinin receptor gene knockout mice (B1-/-), we tested the hypotheses that the B1 receptor plays an important role in preservation of cardiac function, whereas lack of B1 may accelerate cardiac remodeling and dysfunction after myocardial infarction, and that B2 receptors may compensate for lack of B1, whereas blockade of B2 receptors in B1-/- mice may cause further deterioration of cardiac function and remodeling. Female B1-/- mice and wild-type controls (C57BL/6J, B1+/+) underwent sham surgery or myocardial infarction and were treated with either vehicle or B2-antagonist (icatibant, 500 microg/kg per day, subcutaneous) for 8 weeks. We found that in sham myocardial infarction, B1-/- mice had a larger left ventricular diastolic chamber dimension both initially and at 4 to 8 weeks compared with B1+/+. Left ventricular mass and myocyte size were also larger in B1-/- with sham operation than in B1+/+, although cardiac function did not differ between strains. After myocardial infarction, cardiac remodeling and function were similar in both strains, although B1-/- mice tended to have lower blood pressure. Blockade of B2 receptors tended to worsen cardiac remodeling and dysfunction in B1-/- but not in B1+/+. These results may suggest that B2 receptors play an important role in compensating for lack of B1 receptors in mice with myocardial infarction. Dual blockade of both B1 and B2 eliminates this compensation, leading to further deterioration of cardiac dysfunction and remodeling after myocardial infarction.

Hypertension: a review for clinicians

Despite the existence of a variety of consistent hypertension guidelines,the issue of inadequate management of the condition persists. The challenge for health care professionals is not only to understand and adopt the guidelines but also to take a holistic approach to patient care. In addition, clinicians need to encourage adherence to medication protocols, which will hopefully lead to an overall reduction in morbidity and mortality associated with hypertension. It is the clinician's professional responsibility to be cognizant of the emerging research on vasoactive substances as new drugs are being developed that will effect endothelial receptors. It is important that clinicians are trained appropriately in blood pressure measurement and risk factor identification and intervention.

Synergistic interaction between enalapril, L-arginine and tetrahydrobiopterin in smooth muscle cell apoptosis and aortic remodeling induction in SHR

Smooth muscle cell (SMC) apoptosis occurs at the onset of enalapril-induced regression of aortic hypertrophy in SHR. A potential mechanism is the correction of endothelial dysfunction (ED) leading to reduced production of reactive oxygen species and enhanced bioavailability of nitric oxide (NO), a potent apoptosis inducer. Stimulants of NO include the precursor L-arginine and the NO synthase cofactor tetrahydrobiopterin (BH(4)), which correct ED in several models. The objective was to examine the relationships between ED and the cell growth/death balance during vascular remodeling induced by enalapril in SHR. SHR, 10-week-old, received enalapril (ENA: 30 mg x kg(-1) x day(-1) p.o.) for 1 or 2 weeks, or a co-treatment of L-arginine (2.0 g x kg(-1) x day(-1) p.o.) and BH(4) (5.4 mg x kg(-1) x day(-1) i.p. twice daily) administered alone (group: LB) or in combination with enalapril (ENA+LB) for 1 week. Controls received vehicle. After 1 week, ED was completely corrected with LB but not affected significantly by ENA, whereas both treatments failed to induce SMC apoptosis or aortic remodeling. The correction of ED and the induction of SMC apoptosis (3.3-fold increase in TUNEL labeling) required 2 weeks of ENA treatment. The combination of LB with ENA for 1 week, however, was additive for the reduction of SMC proliferation, and synergistic for the induction of apoptosis and regression of vascular hypertrophy. These interactions were independent of blood pressure regulation. Our results suggest that the correction of ED is not sufficient to induce SMC apoptosis and vascular remodeling, although it facilitates these responses during enalapril treatment.

Role of angiotensin II type 2 receptors and kinins in the cardioprotective effect of angiotensin II type 1 receptor antagonists in rats with heart failure

OBJECTIVES

We studied the role of angiotensin II type 2 (AT(2)) receptors and kinins in the cardioprotective effect of angiotensin II type 1 antagonists (AT(1)-ant) in rats with heart failure (HF) after myocardial infarction.

BACKGROUND

The AT(1)-ant is as effective as angiotensin-converting enzyme inhibitors in treating HF, but the mechanisms whereby AT(1)-ant exert their benefits on HF in vivo are more complex than previously understood.

METHODS

Brown Norway Katholiek rats (BNK), which are deficient in kinins because of a mutation in the kininogen gene, and their wild-type control (Brown Norway [BN]) underwent myocardial infarction. Two months later, they were treated for two months with: 1) vehicle; 2) AT(1)-ant (L158809, Merck, Rahway, New Jersey); 3) AT(1)-ant + AT(2)-ant (PD-123319, Parke Davis, Ann Arbor, Michigan); or 4) AT(1)-ant + kinin B(2) receptor antagonist (B(2)-ant) (icatibant) (only BN). We measured left ventricular weight (LVW) gravimetrically, myocyte cross-sectional area (MCSA) and interstitial collagen fraction (ICF) histologically, and ejection fraction by ventriculography.

RESULTS

Development of HF was comparable in BN and BNK rats. The AT(1)-ant reduced LVW and MCSA and the AT(2)-ant blocked these effects in BN rats, but the B(2)-ant did not. The AT(1)-ant reduced LVW and MCSA in BNK rats, and this effect was reversed by the AT(2)-ant. In BN rats, ICF was reduced and LVEF increased by AT(1)-ant, and both AT(2)-ant and B(2)-ant reversed these effects. In BNK rats, the AT(1)-ant failed to reduce ICF, and its therapeutic effect on LVEF was significantly blunted.

CONCLUSIONS

In HF, the AT(2) receptor plays an important role in the therapeutic effects of AT(1)-ant, and this effect may be mediated partly through kinins; however, kinins appear to play a lesser role in the antihypertrophic effect of AT(1)-ant.

Role of bradykinin in angiotensin-converting enzyme knockout mice

Angiotensin-converting enzyme (ACE) plays a central role in the renin-angiotensin system. Whereas ACE is responsible for the production of angiotensin II, it is also important in the elimination of bradykinin. Constitutively, the biological function of bradykinin is mediated through the bradykinin B(2) receptor. ACE knockout mice have a complicated phenotype including very low blood pressure. To investigate the role of bradykinin in the expression of the ACE knockout phenotype, we bred B(2) receptor knockout mice with ACE knockout mice, thus generating a line of mice deficient in both the B(2) receptor and ACE. Surprisingly, these mice did not differ from ACE knockout mice in blood pressure, urine concentrating ability, renal pathology, and hematocrit. Thus abnormalities of bradykinin accumulation do not play an important role in the ACE knockout phenotype. Rather, this phenotype appears due to the defective production of angiotensin II.