Altered frequency of a promoter polymorphism of the kinin B2 receptor gene in hypertensive African-Americans

Components of the kallikrein kinin system have been associated with the pathophysiology of hypertension in animal and human studies. In this study, we examined the distribution of four different polymorphisms of the kinin B₁ and B₂ receptor genes in a population of 120 normotensive and 77 hypertensive African-Americans. Allelic frequencies for three of the four polymorphisms were significantly different from those previously reported in Caucasian populations. Among the polymorphisms analyzed, a potentially functionally significant polymorphism in the core promoter of the kinin B₂ receptor (C⁻⁵⁸→T transition) displayed an increased prevalence of the C⁻⁵⁸ allele in the hypertensive patients as compared with the controls (0.75 v 0.62, P = .009). Thus, this B₂ receptor promoter polymorphism may represent a susceptibility marker for essential hypertension in African-Americans.     

原花青素B2对LPS诱导的心肌细胞损伤的保护作用及机制

目的 探讨原花青素B₂(PCB₂)对LPS诱导的心肌细胞损伤的保护作用及机制。方法 正常培养心肌细胞H9c2,用LPS诱导H9c2细胞建立细胞损伤模型,分别用6.25、12.5、25.0 μmol/L的PCB₂处理模型细胞,25.0 μmol/L的PCB₂处理模型细胞后加入核因子κB(NF-κB)信号通路抑制剂PDTC处理。采用MTT法检测细胞存活率;流式细胞术检测细胞凋亡率;酶联免疫吸附法(ELISA)检测细胞肿瘤坏死因子α(TNF-α)、白细胞介素1β(IL-1β)和白细胞介素6(IL-6)的水平;丙二醛(MDA)、超氧化物歧化酶(SOD)、谷胱甘肽过氧化物酶(GSH-Px)试剂盒分别检测MDA含量和SOD、GSH-Px活性;Westem blot检测细胞中NF-κB、IκB-α蛋白表达。结果 LPS组细胞存活率较对照组显著降低(P＜0.05),而PCB₂显著升高细胞存活率(P＜0.05)。LPS组细胞凋亡率较对照组显著升高(P＜0.05),而PCB₂显著降低LPS处理的细胞凋亡率(P＜0.05)。LPS组细胞TNF-α、IL-1β、IL-6水平较对照组显著升高(P＜0.05),而PCB₂显著降低LPS处理细胞TNF-α、IL-1β、IL-6水平(P＜0.05)。与对照组比较,LPS组细胞MDA含量显著升高,SOD、GSH-Px活性显著降低(P＜0.05);PCB₂显著降低LPS处理的细胞MDA含量,显著升高SOD、GSH-Px活性(P＜0.05)。与对照组比较,LPS组细胞NF-κB蛋白表达显著升高,IκB-α蛋白表达显著降低(P＜0.05);与LPS组比较,PCB₂显著降低细胞NF-κB蛋白表达,显著升高IκB-α蛋白表达(P＜0.05)。与LPS+PCB₂组相比,LPS+PCB₂₊PDTC能显著降低细胞凋亡率和TNF-α、IL-1β、IL-6、MDA含量,显著升高SOD、GSH-Px活性。结论 PCB₂降低LPS诱导的心肌细胞凋亡率、炎症水平和氧化应激,提高细胞存活率,这可能与抑制NF-κB信号通路的活化有关。     

多巴胺受体D2基因TaqI位点多态性与高血压病的关系

目的 探讨多巴胺受体D2基因TaqI位点多态性与原发性高血压病的相关性。方法 运用聚合酶链反应一限制性片段长度多态性法（PCR－RFLP）分析TaqI位点A1A1，A1A2，A2A2基因型在原发性高血压病组和对照组的分布情况。结果 等位基因A1，A2在原发性高血压病组和对照组的分布频率分别为0．34，0．66和0．43，0．57。基因频率分布符合Hardy-Weinberg平衡，样本具有群体代表性，两组人群的基因型和等位基因频率比较，差异有显著性（P＜0．05）。原发性高血压病组中A2等位基因舒张压明显高于A1等位基因舒张压（P＜0．05）。结论 在湖北省人群中，多巴胺受体D2基因TaqＩ位点多态性与原发性高血压病显著相关。     

The Cardiac Effects of Prolonged Vitamin B12 and Folate Deficiency in Rats

In the recent past, hyperhomocysteinemia (HHCY) has been linked to chronic heart failure. Folate and vitamin B12 deficiencies are the common causes of HHCY. The impact of these vitamins on cardiac function and morphology has scarcely been investigated. The aim of this study was to conduct an analysis of the cardiac effect of folate and vitamin B12 deficiency in vivo. Two groups of rats, a control (Co, n = 10) and a vitamin-deficient group (VitDef, n = 10), were fed for 12 weeks with a folate and vitamin B12-free diet or an equicaloric control diet. Plasma and tissue concentrations of HCY, S-adenosyl-homocysteine (SAH), S-adenosyl-methionine (SAM), and brain natriuretic peptide (BNP) were measured. Moreover, echocardiographic and histomorphometric analyses were performed. VitDef animals developed a significant HHCY (Co vs VitDef: 6.8 ± 2.7 vs 61.1 ± 12.8 μmol/l, P < 0.001). Fractional shortening, left ventricular dimension at end-diastole and end-systole, posterior wall thickness, perivascular collagen, mast cell number, and BNP tissue levels were comparable in VitDef and Co animals. Interstitial collagen (Co vs VitDef: 6.8 ± 3.0 vs 4.5 ± 2.1%, P < 0.05), plasma BNP (Co vs VitDef: 180 ± 80 vs 70 ± 60 ng/l, P < 0.05), and tissue HCY (Co vs VitDef: 0.13 ± 0.07 vs 0.07 ± 0.04 μmol/g protein, P < 0.05) were lower in VitDef animals. Folate and vitamin B₁₂ deficiency do not affect cardiac function and morphology.     

CB2 cannabinoid receptor activation is cardioprotective in a mouse model of ischemia/reperfusion

Preventive treatment with cannabinoid agonists has been reported to reduce the infarct size in a mouse model of myocardial ischemia/reperfusion. Here we investigated the possible cardioprotective effect of selective CB₂ cannabinoid receptor activation during ischemia. We performed left coronary artery ligature in C57Bl/6 mice for 30 min, followed by 24 h of reperfusion. Five minutes before reperfusion, mice received intraperitoneal injection of the CB₂ selective agonist JWH-133 (20 mg/kg) or vehicle. Infarct size was assessed histologically and by cardiac troponin I (cTnI) ELISA. Immunohistochemical analysis of leukocyte infiltration, oxidative stress in situ quantification, real-time RT-PCR analysis of inflammatory mediators as well as western blots for kinase phosphorylation was also performed. In addition, we studied chemotaxis and integrin expression of human neutrophils in vitro. JWH-133 significantly reduced the infarct size (I/area at risk: 19.27% ± 1.91) as compared to vehicle-treated mice (31.77% ± 2.7). This was associated with a reduction of oxidative stress and neutrophil infiltration in the infarcted myocardium, whereas activation of ERK 1/2 and STAT-3 was increased. Preinjection of PI3K inhibitor LY294002, MEK 1/2 inhibitor U0126 and JAK-2 inhibitor AG-490 partially abrogated the JWH-133 mediated infarct size reduction. No changes in cardiac CXCL1, CXCL2, CCL3, TNF-α, and ICAM-1 expression levels were found. Furthermore, JWH-133 inhibited the TNF-α induced chemotaxis and integrin CD18/CD11b (Mac-1) upregulation on human neutrophils. Our data suggest that JWH-133 administration during ischemia reduces the infarct size in a mouse model of myocardial ischemia/reperfusion through a direct cardioprotective activity on cardiomyocytes and neutrophils.     

The glycine allele of a glycine/arginine polymorphism in the beta2-adrenergic receptor gene is associated with essential hypertension in a population of Chinese origin.

BACKGROUND: Several studies implicate polymorphisms in the human beta-adrenergic receptor gene (ADRB2) in the susceptibility to hypertension. We sought to replicate these results in a population of Chinese origin primarily from Taiwan and the San Francisco Bay area. METHODS: We genotyped >800 hypertensive subjects and individuals with low-normal blood pressure that were derived largely from the same families as the hypertensive patients for three polymorphisms in the ADRB2 gene: a C/T transition at position 47 (C-47T) in the 5' leader cistron; another C/T transition that results in a glycine/ arginine substitution at codon 16 (Gly16Arg), and a G/C transversion that causes a glutamate/glutamine substitution at codon 27 (Glu27Gln). RESULTS: The Gly16Arg was significantly associated with hypertension (P < .03). Under a dominant model, for hypertension the relative risk for the Gly/Gly and Gly/Arg genotypes versus the Arg/Arg genotype was 1.35 (95% confidence limits [CL] 1.08, 1.70); for low-normal blood pressure the relative risk was 0.79 (95% CL 0.66, 0.94). This polymorphism explained approximately 1% of the variance in systolic and diastolic blood pressures in our study population. There was no evidence of association between the C-47T and Glu27Gln polymorphisms and hypertension in this population. CONCLUSIONS: The Glyl6 allele in the beta2-adrenergic receptor gene is a susceptibility allele for essential hypertension in a population of Chinese origin.     

Direct AT2 receptor stimulation is athero-protective and stabilizes plaque in Apolipoprotein E-deficient mice

Background

The angiotensin II type 2 receptor (AT₂R) has been suggested to have an athero-protective role, however no studies have investigated the effect of direct stimulation of this receptor in atherosclerosis. Thus this study aimed to determine the effect of direct AT₂R stimulation in setting of atherosclerosis, using the known AT₂R agonist, CGP42112.

Methods and results

Apolipoprotein E-deficient (ApoE^−/−) mice were fed a high fat (21%) diet for 16 weeks, with subcutaneous infusions of CGP42112 (1, 5 or 10 μg/kg/min) administered via osmotic mini-pumps in the final 4 weeks. CGP42112 treatment at all doses significantly improved endothelial function (p < 0.001) when compared to acetylcholine mediated-vasorelaxation in aorta taken from vehicle-treated ApoE^−/− mice. In aortic segments adjacent to those used for vascular reactivity studies, CGP42112 treatment at all doses concomitantly increased eNOS immunoreactivity and protein levels whilst superoxide (O₂⁻) production was significantly (p < 0.01) decreased compared to levels measured in aorta from vehicle-treated ApoE^−/− mice. Moreover, CGP42112 (1 μg/kg/min) treatment significantly attenuated (p < 0.05) atherosclerotic lesion progression (assessed as both lipid deposits and luminal encroachment in thoracic aorta and aortic arch) and significantly increased plaque stability in the brachiocephalic artery, a region normally prone to rupture. Both the vaso- and athero-protective effects of CGP42112 (1 μg/kg/min) were reversed with co-infusion of the AT₂R antagonist, PD123319, but not the MasR antagonist, A779.

Conclusion

For the first time we have shown that direct stimulation of the AT₂R improves endothelial function, reduces atherosclerotic lesion progression and mediates plaque stability with these effects at least partly due to restoration of nitric oxide bioavailability.     

CHADS2 versus CHA2DS2-VASc score in assessing the stroke and throm-boembolism risk stratification in patients with atrial fibrillation: a systematic review and meta-analysis

Objective To perform a systematic review and meta-analysis of the predictive abilities of CHADS2 and CHA2DS2-VASc in stroke and thromboembolism risk stratification of atrial fibrillation (AF) patients....     

Role of a functional polymorphism in the F2R gene promoter in sarcoidosis

Sarcoidosis is a multisystem granulomatous disease of unknown aetiology characterized by increased inflammation, and results from gene–environment interactions. Proteinase‐activated receptor‐1 mediates the interplay between coagulation and inflammation. The rs2227744G > A promoter single nucleotide polymorphism has been linked to inflammation, cardiovascular disease and chronic obstructive pulmonary disease exacerbations. Using a case‐control study (184 cases with sarcoidosis and 368 controls), we show that the rs2227744A allele significantly associates with protection from sarcoidosis (P = 0.003, OR = 0.68 (0.52–0.88)).     

Lack of association between the microsatellite polymorphism in intron 2 of human Toll-like receptor 2 gene and bronchiectasis among Koreans

BACKGROUND AND OBJECTIVE: The genetic factors for the development of bronchiectasis are not well understood in most patients. The aim of this study was to elucidate the possible association between bronchiectasis and guanine-thymine (GT) repeat polymorphism in intron 2 of the human Toll-like receptor 2 (TLR2), which has a crucial role in adaptive as well as innate immunity. METHODS: A total of 194 patients with bronchiectasis and the same number of age- and gender-matched healthy blood donors were prospectively enrolled. The numbers of GT repeats were determined by PCR and gene scans. For further analysis, the alleles were classified into three subclasses: 12-16 GT repeats, short alleles (S allele); 17-22 repeats, medium-length alleles (M allele); and 23-27 repeats, long alleles (L allele). RESULTS: The overall distribution of alleles was not different between patient and control groups (P = 0.71). In addition, the frequencies of genotypes including short alleles were not different between patient and control groups (P = 0.92). Extent of bronchiectasis (P = 0.92) and bacterial colonization (P = 0.48) were not associated with any subclass genotype. CONCLUSIONS: Alleles and genotype including the shorter GT repeats in intron 2 of the TLR2, were not associated with the development, extent and bacterial colonization of bronchiectasis in Koreans.     

胰岛素受体底物-2基因多态性与2型糖尿病的相关性研究

目的 研究北京地区汉族人群中胰岛素受体底物-2（IRS-2）基因密码子1057g/a多态性与2型糖尿病及其中间表型的相关性。方法 选取北京地区的中国汉族患者110例，对照组80例。用聚合酶链反应-限制性内切酶片段长度多态性（PCR-RFLP）的方法检测IRS-2基因密码了1057g/a多态性。结果 （1）IRS-2基因密码子1057g/a多态性的a等位基因频率在糖尿病组和对照组中分别为26.4%和36.3%。（2）糖尿病组aa基因型频率明显低于对照组，分别为5.5%和18.7%(P=0.016),Logistic相关分析表明：aa基因型为2型糖尿病的保护性因素，OR值为0.28(95%CI=0.09-0.91,P=0.03)。（3）不同基因型组间血压、血脂，胰岛素抵抗指数及胰岛β细胞功能指数等均差异无显著性。结论 中国北方地区汉族人群中IRS-2基因密码子1057g/a多态性的aa基因型在2型糖尿病中明显减少。但2型糖尿病各种中间表型自欺欺人持征在不同基因型间均无明显差异。上述结果有待于进一步扩大样本量来加以确认。     

From angiotensin IV binding site to AT4 receptor

One of the fragments of the cardiovascular hormone Angiotensin II incited the interest of several research groups. This 3–8 fragment, denoted as Angiotensin IV (Ang IV) causes a number of distinct biological effects (see Introduction), unlikely to be explained by its weak binding to AT₁ and/or AT₂ receptors. Moreover the discovery of high affinity [¹²⁵I]-Ang IV binding sites and their particular tissue distribution led to the concept of the AT₄ receptor. An important breakthrough was achieved by defining the AT₄ receptor as the membrane-bound insulin-regulated aminopeptidase (IRAP). Crucial for the definition as a receptor the binding of the endogenous ligand(s) should be linked to particular cellular and/or biochemical processes. With this respect, cultured cells offer the possibility to study the presence of binding sites in conjunction with ligand induced signaling. This link is discussed for the AT₄ receptor by providing an overview of the cellular effects by AT₄ ligands.     

The critical role of intracellular zinc in adenosine A2 receptor activation induced cardioprotection against reperfusion injury

Exogenous zinc can protect cardiac cells from reperfusion injury, but the exact roles of endogenous zinc in the pathogenesis of reperfusion injury and in adenosine A₂ receptor activation-induced cardioprotection against reperfusion injury remain unknown. Adenosine A₁/A₂ receptor agonist 5′-(N-ethylcarboxamido) adenosine (NECA) given at reperfusion reduced infarct size in isolated rat hearts subjected to 30 min ischemia followed by 2 h of reperfusion. This effect of NECA was partially but significantly blocked by the zinc chelator N,N,N′,N′-tetrakis-(2-pyridylmethyl) ethylenediamine (TPEN), and ZnCl₂ given at reperfusion mimicked the effect of NECA by reducing infarct size. Total tissue zinc concentrations measured with inductively coupled plasma optical emission spectroscopy (ICPOES) were decreased upon reperfusion in rat hearts and this was reversed by NECA. NECA increased intracellular free zinc during reperfusion in the heart. Confocal imaging study showed a rapid increase in intracellular free zinc in isolated rat cardiomyocytes treated with NECA. Further experiments revealed that NECA increased total zinc levels upon reperfusion in mitochondria isolated from isolated hearts. NECA attenuated mitochondrial swelling upon reperfusion in isolated hearts and this was inhibited by TPEN. Similarly, NECA prevented the loss of mitochondrial membrane potential (ΔΨm) caused by oxidant stress in cardiomyocytes. Finally, both NECA and ZnCl₂ inhibited the mitochondrial metabolic activity. NECA-induced cardioprotection against reperfusion injury is mediated by intracellular zinc. NECA prevents reperfusion-induced zinc loss and relocates zinc to mitochondria. The inhibitory effects of zinc on both the mPTP opening and the mitochondrial metabolic activity may account for the cardioprotective effect of NECA.     

Purinergic P2X7 receptors regulate secretion of interleukin-1 receptor antagonist and beta cell function and survival

Aims/hypothesis  In obesity, beta cells activate compensatory mechanisms to adapt to the higher insulin demand. Interleukin-1 receptor antagonist (IL-1Ra) prevents obesity-induced hyperglycaemia and is a potent target for the treatment of diabetes, but the mechanisms of its secretion and regulation in obesity are unknown. In the present study, we hypothesise the regulation of IL-1Ra secretion by purinergic P2X₇ receptors in islets. Methods  Production and regulation of P2X₇ were studied in pancreatic sections from lean and obese diabetic patients, non-diabetic controls and in isolated islets. IL-1Ra, IL-1β and insulin secretion, glucose tolerance and beta cell mass were studied in P2x7 (also known as P2Rx7)-knockout mice. Results  P2X₇ levels were elevated in beta cells of obese patients, but downregulated in patients with type 2 diabetes mellitus. Elevated glucose and non-esterified fatty acids rapidly activated P2X₇ and IL-1Ra secretion in human islets, and this was inhibited by P2X₇ blockade. In line with our results in vitro, P2x7-knockout mice had a lower capacity to secrete IL-1Ra. They exhibited severe and rapid hyperglycaemia, glucose intolerance and impaired beta cell function in response to a high-fat/high-sucrose diet, were unable to compensate by increasing their beta cell mass in response to the diet and showed increased beta cell apoptosis. Conclusions/interpretation  Our study shows a tight correlation of P2X₇ activation, IL-1Ra secretion and regulation of beta cell mass and function. The increase in P2X₇ production is one mechanism that may explain how beta cells compensate by adapting to the higher insulin demand. Disturbances within that system may result in the progression of diabetes. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorised users.     

Up-regulation of A 2B adenosine receptor in A 2A adenosine receptor knockout mouse coronary artery

In this study, we looked into possible compensatory changes of other adenosine receptors (ARs) in A_2A genetic knockout mice (A2AKO) as well as the functional role of nitric oxide (NO) in A_2A AR-mediated vasodilation. Gene expression of ARs from coronary arteries of A_2A AR wild type mice (A2AWT) and A2AKO was studied using real-time PCR. Functional studies were carried out in isolated heart and isolated coronary artery preparations. A_2B AR was found to be 4.5 fold higher in A2AKO than in A2AWT, while A_2A AR expression was absent in A2AKO. There was no difference in A₁ and A₃ ARs between WT and KO animals. The concentration-relaxation curve for adenosine-5′-N-ethylcarboxamide (NECA, non-selective AR agonist) in isolated coronary arterial rings in A2AKO was shifted to the left when compared to A2AWT. The concentration-response curve for A_2B selective agonist (BAY 60-6583) was also shifted to the left in A2AKO hearts. L-NAME, a non-specific NO synthase inhibitor, did not affect baseline coronary flow (CF) until the concentration reached 10 µM in A2AWT (76.32 ± 11.35% from baseline, n = 5). In A2AKO, the CF decreased significantly by L-NAME only at a higher concentration (100 µM, 93.32 ± 5.8% from baseline, n = 5). L-NMA (1 µM, n = 4), another non-specific NO synthase inhibitor, also demonstrated similar results in decreasing CF (59.66 ± 3.23% from baseline in A2AWT, while 81.76 ± 8.91% in A2AKO). It was further demonstrated that the increase in CF by 100 µM NECA was significantly blunted with 10 µM L-NAME (377.08 ± 25.23% to 305.41 ± 30.73%, n = 9) in A2AWT but not in A2AKO (153.66 ± 22.7% to 143.88 ± 36.65%, n = 5). Similar results were also found using 50 nM of CGS-21680 instead of NECA in A2AWT (346 ± 22.85 to 277 ± 31.39, n = 6). No change in CF to CGS-21680 was noted in A_2AAKO. Our data demonstrate, for the first time, that coronary A_2B AR was up-regulated in mice deficient in A_2A AR. We also provide direct evidence supporting a role for NO in A_2A AR-mediated coronary vasodilation. The data further support the role for A_2A AR in the regulation of basal coronary tone through the release of NO.     

Cytokine responses of intraepithelial lymphocytes are regulated by histamine H2 receptor

Backgrounds  Histamine participates in the immune regulation of several gastrointestinal diseases. However, the effect of histamine on intestinal intraepithelial lymphocytes (IELs), the front line of the intestinal mucosal immune system, is not well understood. We examined whether histamine has a direct effect on cytokine production by IELs and the involvement of histamine receptor subtypes. Methods  Murine IELs were activated by PMA plus ionomycin with/without histamine. Secreted cytokines were measured and compared with those of splenocytes. Intracellular cytokines were detected by flow cytometry. Expression of histamine receptor subtypes in IELs was examined by RT-PCR. Results  Histamine H₁ receptor (H₁R), H₂R, and H₄R, but not H₃R mRNA were expressed on IELs. Histamine significantly decreased Th1-cytokine (IFN-γ, TNF-α, and IL-2) and also IL-4 production in IELs as well as splenocytes. The selective H₂R antagonist famotidine, but not the H₁R antagonist pyrilamine nor the H₃R/H₄R antagonist thioperamide, competes with the inhibitory effect of histamine on these cytokine production in IELs. These suppressive effects of histamine were mimicked by a selective H₂R/H₄R agonist dimaprit. Further, these suppressive effects of histamine for Th1-cytokine and IL-4 did not accompany the enhancement of IL-10 production or IL-10 mRNA level in IELs. Intracellular cytokine analysis revealed that the number of IFN-γ-producing αβ T cells was significantly reduced by histamine in IELs. Conclusions  Histamine has a direct suppressive effect on IEL-derived cytokines via H₂R, which would have a crucial role in the suppression of local immunoregulation in the intestinal epithelium.     

Denufosol: A review of studies with inhaled P2Y2 agonists that led to Phase 3

Among the most promising of the new therapies being developed for the treatment of Cystic Fibrosis (CF) are those targeted at increasing mucosal hydration on the surface of the airways. One of these therapies, P2Y₂ receptor agonists, bypasses the defective CFTR chloride channel, and activates an alternative chloride channel. This activation results in an increase in airway surface epithelial hydration, and through these actions and effects on cilia beat frequency, increases mucociliary clearance. The pharmacology of P2Y₂ agonists has been confirmed in several preclinical and clinical studies. Denufosol tetrasodium is a novel second-generation, metabolically stable, selective P2Y₂ receptor agonist currently in Phase 3 clinical development. In radiolabelled deposition studies of P2Y₂ agonists in healthy non-smokers and smokers, approximately 7 mg of a 40-mg nebulizer (PARI LC Star) load was deposited in the lungs. In a pharmacokinetic study in healthy volunteers, very limited systemic exposure was observed when doses of 200 mg of denufosol were nebulized. Thus, it appears that high concentrations of denufosol can be achieved in the airways with very low systemic absorption. Denufosol has been generally well-tolerated in healthy volunteers and patients with CF. The most common adverse events were in the respiratory system, with cough having the highest frequency. Doses of 20–60 mg have been evaluated in Phase 2 trials of up to 28 days duration, and superiority relative to placebo on FEV1 has been observed in patients with relatively normal lung function (FEV1 greater than or equal to 75% of predicted). The first Phase 3 trial is a comparison of denufosol 60 mg and placebo in 350 patients with CF with FEV1 at study entry greater than or equal to 75% of predicted.     

Angiotensin-Converting Enzyme Inhibitors Potentiate Preconditioning Through Bradykinin B2 Receptor Activation in Human Heart

Objectives. This study was designed to determine whether angiotensin-converting enzyme (ACE) inhibitors play a role in cardioprotection in a human model of preconditioning.

Background. Recent studies have suggested that bradykinin may contribute to the protective effects of preconditioning in animal models. ACE inhibitors are known to inhibit the degradation of bradykinin and hence may be able to potentiate the effect of preconditioning.

Methods. We examined the effects of the ACE inhibitors captopril and lisinopril in combination with a subthreshold preconditioning stimulus (i.e., insufficient to have any protective effects alone). Human atrial trabeculae were superfused with Krebs buffer and paced at 1 Hz. They were subjected to a full or subthreshold preconditioning stimulus consisting of either 3 or 1.5 min of simulated ischemia and 7 min of reoxygenation. In each instance, this stimulus was followed by 90 min of simulated ischemia and 2 h of reoxygenation. In addition, the subthreshold preconditioned group had 20 min of previous ACE inhibitor treatment.

Results. Recovery of contractile function (percent of baseline) was 22 ± 1% (mean ± SEM) in the control group versus 61 ± 1% in the preconditioned group. The subthreshold preconditioned group and the ACE inhibitor-alone groups did not exhibit any protection; however, in combination, the protection was significant (71 ± 4% in the captopril group, 58 ± 8% in the lisinopril group, p < 0.005) compared with the control group. There was no significant difference between these values and recovery after the full preconditioning stimulus. Furthermore, Hoe 140, a specific bradykinin B₂ receptor antagonist, abolished the protection.

Conclusions. To our knowledge, these are the first results in human muscle to suggest that ACE inhibitors may augment ischemic preconditioning, possibly through B₂ receptor activation.

(J Am Coll Cardiol 1997;29:1599–606)