Contribution of bradykinin to the cardioprotective action of angiotensin converting enzyme inhibition in hypertension and after myocardial infarction

Bradykinin-(1-9) mitigates autophagy through upregulating PI3K/Akt in rats with myocardial infarction

The cardioprotective mechanisms of bradykinin-(1-9) in myocardial infarction were unclear. We investigated the effect of bradykinin-(1-9) on cardiac function, fibrosis, and autophagy induced by myocardial infarction and identified the mechanisms involved. To investigate the cardioprotective effect of bradykinin-(1-9), various doses of bradykinin-(1-9), its B2 receptor blocker HOE140, or their combination were administered to rats via subcutaneous osmotic minipump implantation before myocardial infarction. After 2 days, myocardial infarction was induced by ligation of the left anterior descending coronary artery. After 2 weeks, echocardiographic measurements and euthanasia were performed. Bradykinin-(1-9) treatment attenuated left ventricular dysfunction, fibrosis, and autophagy in rats with myocardial infarction, which was partially reversed by HOE140 administration. Moreover, the downregulatory effect of bradykinin-(1-9) on autophagy was partially reversed by combination with the PI3K inhibitor LY294002. Thus, bradykinin-(1-9) inhibits myocardial infarction-induced cardiomyocyte autophagy by upregulating the PI3K/Akt pathway.

Reduced blood pressure in sickle cell disease is associated with decreased angiotensin converting enzyme (ACE) activity and is not modulated by ACE inhibition

Background

Sickle cell disease (SCD) incurs vaso-occlusive episodes and organ damage, including nephropathy. Despite displaying characteristics of vascular dysfunction, SCD patients tend to present relatively lower systemic blood pressure (BP), via an unknown mechanism. We investigated associations between BP and renin-angiotensin-system (RAS) components in SCD and determined whether an inhibitor of angiotensin converting enzyme (ACE; often used to slow SCD glomerulopathy) further modulates BP and RAS components in a murine model of SCD.

Methods

BP was compared in human subjects and mice with/without SCD. Plasma angiotensin II, ACE and renin were measured by immunoassay. BP was reevaluated after treating mice with enalapril (25 mg/kg, 5x/week) for 5 weeks; plasma and organs were stored for angiotensin II and ACE activity measurement, and quantitative real-time PCR.

Results

Diastolic BP and systolic BP were significantly lower in patients and mice with SCD, respectively, compared to controls. Reduced BP was associated with increased plasma renin and markers of kidney damage (mice) in SCD, as well as significantly decreased plasma ACE concentrations and ACE enzyme activity. As expected, enalapril administration lowered BP, plasma angiotensin II and organ ACE activity in control mice. In contrast, enalapril did not further reduce BP or organ ACE activity in SCD mice; however, plasma angiotensin II and renin levels were found to be significantly higher in enalapril-treated SCD mice than those of treated control mice.

Conclusion

Relative hypotension was confirmed in a murine model of SCD, in association with decreased ACE concentrations in both human and murine disease. Given that ACE inhibition has an accepted role in decreasing BP, further studies should investigate mechanisms by which ACE depletion, via both Ang II-dependent and alternative pathways, could contribute to reduce BP in SCD and understand how ACE inhibition confers Ang II-independent benefits on kidney function in SCD.

Effect of oxymatrine, the active component from Radix Sophorae flavescentis (Kushen), on ventricular remodeling in spontaneously hypertensive rats

PURPOSE

To examine the effects of oxymatrine (OMT) on ventricular remodeling in spontaneous hypertension rat (SHR) and the underlying mechanism.

METHODS

SHRs were divided into four groups: SHR control, SHR+40 mg/kg captopril, SHR+30 mg/kg OMT and SHR+60 mg/kg OMT. Normotensive age-matched WKY rats were assigned to two groups: WKY control, WKY+30 mg/kg OMT. The rats were orally administered with the corresponding drugs or drinking water for 21 weeks. Mean arterial blood pressure (MAP) and heart rate (HR) were measured. The left ventricular weight index (LVWI) and heart weight index (HWI) were determined. Myocardium tissue was stained with picric acid/Sirius red for measurement of collagen content measurements. The concentrations of serum norepinephrine and angiotensin II (Ang II) in myocardium were determined. Real-time RT-PCR was used to detect the mRNA expressions of transforming growth factor-β1 (TGF-β1), collagen types I, III and angiotensin converting enzyme (ACE). Western blots were performed to determine bioactivities of extracellular signal regulated kinase (ERK1/2), c-Jun N-terminal kinase (JNK/SAPK), p38 mitogen-activated protein kinases (p38 MAPK) and phospho-specific protein kinase C (PKC).

RESULTS

In the SHR, hypertension, myocardium hypertrophy, more cardiac fibrosis, higher concentrations of serum norepinephrine and myocardium Ang II were observed. OMT treatment lowered the blood pressure, reduced the concentrations of serum norepinephrine and myocardium Ang II, favorably decreased the measured gravimetric parameters, decreased the interstitial and perivascular collagen deposition, attenuated the collagen of type I and III accumulation, downregulated the mRNA expression of ACE and TGF-β1, and suppressed the phosphorylation of ERK 1/2, JNK and p38 MAPK in SHRs.

CONCLUSION

OMT prevents ventricular remodeling in SHR. The mechanisms may be related to inhibiting the gene overexpression of ACE and TGF-β1, suppressing the activation of signaling pathways of ERK 1/2, JNK and p38 MAPK.

Liver regeneration and tumour stimulation: implications of the renin-angiotensin system

Liver resection is the most effective treatment for primary liver tumours and metastasis to the liver, and remains the only potentially long-term curative therapy for patients with colorectal cancer (CRC) liver metastases. Nevertheless, there is a significant incidence of tumour recurrence following liver resection. Cellular and molecular changes resulting from resection and the subsequent liver regeneration process may influence the kinetics of tumour growth, contributing to recurrence. Although commonly associated with the systemic homeostasis of blood pressure, fluid and electrolyte, the renin-angiotensin system (RAS) has recently been shown to play a role in regulating cell proliferation, apoptosis and angiogenesis in local organs as well as in malignancies. An electronic search of the English literature on the role of the RAS in liver regeneration and tumourigenesis was performed using PubMed, with additional relevant articles sourced from reference lists. Studies have shown that the blockade of the RAS pathway stimulates liver regeneration and inhibits tumour progression. An understanding of the role of RAS in liver regeneration and tumourigenesis may enable alternative strategies to improve patient outcome and survival after liver resection. This review will discuss the role of the RAS in liver regeneration and in tumour recurrence post-liver resection. The potential of the RAS as a novel therapeutic target for CRC liver metastases patients undergoing liver resection will be outlined.

Effect of antihypertensive agents on stellate cells during liver regeneration in rats

BACKGROUND: Although most studies have focused on the hepatocytes, all the hepatic cells participate in the regenerative process, among them the stellate cells. The stellate cells are mesenchymal cells involved in local neurotransmission and paracrine regulation of several liver functions. Acute hepatic tissue loss promotes the proliferation and activation of stellate cells from a quiescent state to myofibroblast-like cells. AIM: Investigate the effects of antihypertensive agents on the stellate cell population during the liver regenerative phenomenon in rats. METHODS: Adult male Wistar rats received lisinopril, losartan, bradykinin, or saline solution in a proportional volume, intraperitoneally, before and after 70% partial hepatectomy. Animals from the experimental and saline groups were sacrificed at 36 hours after partial hepatectomy. The alpha-smooth muscle actin labelled stellate cells population was counted in the periportal and pericentral zones of the liver specimen. RESULTS: The labelled stellate cells were more numerous in the control group both in the periportal and pericentral zones at 36 hours after partial hepatectomy than at the other times. The population of stellate cells was significantly lower in the losartan group and higher in the bradykinin and lisinopril groups than in the control group. CONCLUSIONS: These results suggest that losartan can inhibit and bradykinin and lisinopril can stimulate the stellate cell population during liver regeneration in rats. These cells synthesize several substances to stimulate liver regeneration.

Bradykinin inhibits development of myocardial infarction through B2 receptor signalling by increment of regional blood flow around the ischaemic lesions in rats

1 To identify the roles of endogenous kinins in prevention of myocardial infarction (MI), we performed the permanent ligation of coronary artery in rats. 2 The size of MI 12, 24, and 48 h after coronary ligation in kininogen-deficient Brown Norway Katholiek (BN-Ka) rats was significantly larger (49.7+/-0.2%, 49.6+/-2%, and 51.1+/-1%, respectively) than that of kinin-replete Brown Norway Kitasato (BN-Ki) rats (42+/-2%, 38.5+/-4%, and 41.5+/-1%). 3 Hoe140, a bradykinin (BK) B(2) receptor antagonist injected (1.0 mg kg(-1), i.v.) half an hour before, and every 8 h after, coronary ligation, significantly increased the size of MI in Sprague-Dawley rats. Aprotinin, a kallikrein inhibitor, which was infused intravenously (10,000 Units kg(-1) h(-1)) with an osmotic mini-pump, significantly increased the size of an MI 24 h after ligation. 4 When evaluated using microspheres, the regional myocardial blood flow around the necrotic lesion in BN-Ka rats 6 h after ligation was reduced more than that in BN-Ki rats with MI by 41-46%. The same was true in Hoe140-treated BN-Ki rats. 5 FR190997, a nonpeptide B(2) agonist, which was infused (10 microg kg(-1) h(-1)) into the vena cava of BN-Ka rats for 24 h with an osmotic mini-pump, caused significant reduction in the size of MI (38+/-3%), in comparison with the size in vehicle solution-treated rats (51+/-3%). The size of MI in FR190997-treated BN-Ka rats was the same as in BN-Ki rats. 6 These results suggested that endogenous kinin has the capacity to reduce the size of MI via B(2) receptor signalling because of the increase in regional myocardial blood flow around the ischaemic lesion.

Bradykinin for the treatment of cardiovascular disease

Bradykinin is a vasoactive kinin known to be involved in many biologic processes. Levels of bradykinin have been shown to be elevated in a number of cardiac diseases. It is thought that these elevated levels play a protective role in cardiovascular diseases. Preliminary studies have demonstrated that bradykinin may have beneficial effects on a wide spectrum of cardiovascular disorders. Though much study is still required, bradykinin augmentation represents an exciting new target for the treatment of cardiovascular disease.

Expression and activity of ectopeptidases in fibrillating human atria

Recent studies have demonstrated that atrial fibrillation (AF) occurs in the presence of degenerative changes of atrial tissue. In contrast, bradykinin (BK) appears to have cardioprotective effects diminishing myocardial hypertrophy and fibrosis. It is unknown, however, whether AF has direct effects on BK metabolism. Therefore, the purpose of this study was to determine the atrial expression of the membrane-bound peptidases, also referred to as ectopeptidases, carboxypeptidase M (CPM), dipeptidyl peptidase IV (DPIV), and alanyl-aminopeptidase (APN) in patients with and without AF. Atrial tissue samples of 35 patients undergoing open heart surgery were examined. Seventeen patients had chronic persistent AF (> or = 6 months; CAF), the remaining 18 patients (controls) had no history of AF. Peptidase expression was analyzed at the mRNA (quantitative RT-PCR) level and apparent changes were confirmed at the protein level. In case of unaltered mRNA levels, enzyme activity was determined. Reduced amounts of CPM-mRNA were found in patients with CAF (41.3+/-9.7 U nu controls: 86.1+/-17.5 U P<0.05). CPM protein was decreased to 47.5% in patients with CAF compared with controls (P<0.01). DPIV and APN mRNA amounts were similar in both groups. DPIV activity, however, was increased during CAF (219.6+/-30 pkat/mg protein v controls: 195.8+/-21.8 pkat/mg P<0.05). APN activity was unchanged. In conclusion, atrial bradykinin metabolizing activities are significantly altered during AF in humans. The observed alterations in ectopeptidase expression/activity may play a role in the structural remodeling of fibrillating atria.

Angiotensin-converting enzyme inhibition by lisinopril enhances liver regeneration in rats

Bradykinin has been reported to act as a growth factor for fibroblasts, mesangial cells and keratinocytes. Recently, we reported that bradykinin augments liver regeneration after partial hepatectomy in rats. Angiotensin-converting enzyme (ACE) is also a powerful bradykinin-degrading enzyme. We have investigated the effect of ACE inhibition by lisinopril on liver regeneration after partial hepatectomy. Adult male Wistar rats underwent 70% partial hepatectomy (PH). The animals received lisinopril at a dose of 1 mg kg body weight(-1) day(-1), or saline solution, intraperitoneally, for 5 days before hepatectomy, and daily after surgery. Four to six animals from the lisinopril and saline groups were sacrificed at 12, 24, 36, 48, 72, and 120 h after PH. Liver regeneration was evaluated by immunohistochemical staining for proliferating cell nuclear antigen using the PC-10 monoclonal antibody. The value for the lisinopril-treated group was three-fold above the corresponding control at 12 h after PH (P<0.001), remaining elevated at approximately two-fold above control values at 24, 36, 48 (P<0.001), and at 72 h (P<0.01) after PH, but values did not reach statistical difference at 120 h after PH. Plasma ACE activity measured by radioenzymatic assay was significantly higher in the saline group than in the lisinopril-treated group (P<0.001), with 81% ACE inhibition. The present study shows that plasma ACE inhibition enhances liver regeneration after PH in rats. Since it was reported that bradykinin also augments liver regeneration after PH, this may explain the liver growth stimulating effect of ACE inhibitors.

Bradykinin degradation and relation to myocyte contractility

BACKGROUND

Past studies have demonstrated that exogenous bradykinin (BK) causes vasodilation and increases coronary blood flow, effects that may be beneficial in the setting of cardiac disease states. An important pathway for BK degradation is through angiotensin-converting enzyme (ACE), which results in the formation of a degradative peptide, BK((1-7)). The goal of this study was to examine the effects of BK, BK((1-7)), and the potential modulation of BK by ACE inhibition on myocyte contractility.

METHODS AND RESULTS

Contractile function was examined in isolated adult porcine (n = 15) left ventricular (LV) myocyte preparations in the presence or absence of BK (10(-8) mol/L), BK((1-7)) (10(-8) mol/L), and with pretreatment by ACE inhibition (benazaprilat). Myocyte velocity of shortening fell by over 15% in the presence of BK and by 8% with BK((1-7)) (P <.05 vs basal). ACE inhibition blunted the negative effect of BK on myocyte velocity of shortening by over 60% (P <.05). Furthermore, robust ACE activity coupled with significant BK degradation was demonstrated in LV-isolated myocyte preparations, and BK proteolysis was influenced by ACE inhibition.

CONCLUSION

These results suggest that BK has a direct effect on LV myocyte contractility, and that this effect may be mediated by proteolysis of BK at the level of the LV myocyte sarcolemma.

Angiotensin-converting enzyme gene and diabetes mellitus

AIMS

The association of the insertion/deletion polymorphism in the angiotensin-converting enzyme (ACE) gene with cardiovascular disease and diabetic nephropathy remains a controversial issue. This review aims to give an overview of the research to date assessing the impact of the ACE polymorphism in Type 1 and Type 2 diabetes mellitus (DM).

METHODS

A systematic review of the literature was performed in the databases of MEDLINE, PubMed and EMBASE for the key words 'diabetes mellitus', 'diabetic nephropathy', 'ACE polymorphism' and 'genotype' and relevant articles were considered.

RESULTS

A meta-analysis assessing the influence of the ACE polymorphism on disease susceptibility demonstrated significant odds ratios in individuals with the DD genotype for coronary heart disease, myocardial infarction and both diabetic and nondiabetic renal disease. No association was found for left ventricular hypertrophy or hypertension in nondiabetic subjects.

CONCLUSIONS

The ACE polymorphism appears to have a significant impact on the progression of diabetic nephropathy and may have therapeutic implications for identifying those individuals resistant to the effects of ACE inhibitors. It also appears to be indicative of an increased vascular risk in diabetic patients; however, larger prospective studies are required to clarify this situation.

Identification of kallidin degrading enzymes in the isolated perfused rat heart

Kallidin (KD) is an important vasoactive kinin whose physiological effects are strongly dependent on its degradation through local kininases. In the present study, we examined the spectrum of these enzymes and their contribution to KD degradation in isolated perfused rat hearts. By inhibiting angiotensin-converting enzyme (ACE), aminopeptidase M (APM) and neutral endopeptidase (NEP) with ramiprilat (0.25 microM), amastatin (40 microM) and phosphoramidon (1 microM), respectively, relative kininase activities were obtained. APM (44%) and ACE (35%) are the main KD degrading enzymes in rat heart; NEP (7%) plays a minor role. A participation of carboxypeptidase N (CPN) could not be found.