Ventricular arrhythmias remain the leading cause of death in patients suffering myocardial ischemia. Myeloperoxidase, a heme enzyme released by polymorphonuclear neutrophils, accumulates within ...ischemic myocardium and has been linked to adverse left ventricular remodeling.
To reveal the role of myeloperoxidase for the development of ventricular arrhythmias.
In different murine models of myocardial ischemia, myeloperoxidase deficiency profoundly decreased vulnerability for ventricular tachycardia on programmed right ventricular and burst stimulation and spontaneously as assessed by ECG telemetry after isoproterenol injection. Experiments using CD11b/CD18 integrin-deficient (CD11b
) mice and intravenous myeloperoxidase infusion revealed that neutrophil infiltration is a prerequisite for myocardial myeloperoxidase accumulation. Ventricles from myeloperoxidase-deficient (Mpo
) mice showed less pronounced slowing and decreased heterogeneity of electric conduction in the peri-infarct zone than wild-type mice. Expression of the redox-sensitive gap junctional protein Cx43 (Connexin 43) was reduced in the peri-infarct area of wild-type compared with Mpo
mice. In isolated wild-type cardiomyocytes, Cx43 protein content decreased on myeloperoxidase/H
O
incubation. Mapping of induced pluripotent stem cell-derived cardiomyocyte networks and in vivo investigations linked Cx43 breakdown to myeloperoxidase-dependent activation of matrix metalloproteinase 7. Moreover, Mpo
mice showed decreased ventricular postischemic fibrosis reflecting reduced accumulation of myofibroblasts. Ex vivo, myeloperoxidase was demonstrated to induce fibroblast-to-myofibroblast transdifferentiation by activation of p38 mitogen-activated protein kinases resulting in upregulated collagen generation. In support of our experimental findings, baseline myeloperoxidase plasma levels were independently associated with a history of ventricular arrhythmias, sudden cardiac death, or implantable cardioverter-defibrillator implantation in a cohort of 2622 stable patients with an ejection fraction >35% undergoing elective diagnostic cardiac evaluation.
Myeloperoxidase emerges as a crucial mediator of postischemic myocardial remodeling and may evolve as a novel pharmacological target for secondary disease prevention after myocardial ischemia.
Recent observational clinical and ex-vivo studies suggest that inflammation and in particular leukocyte activation predisposes to atrial fibrillation (AF). However, whether local binding and ...extravasation of leukocytes into atrial myocardium is an essential prerequisite for the initiation and propagation of AF remains elusive. Here we investigated the role of atrial CD11b/CD18 mediated infiltration of polymorphonuclear neutrophils (PMN) for the susceptibility to AF.
C57bl/6J wildtype (WT) and CD11b/CD18 knock-out (CD11b(-/-)) mice were treated for 14 days with subcutaneous infusion of angiotensin II (Ang II), a known stimulus for PMN activation. Atria of Ang II-treated WT mice were characterized by increased PMN infiltration assessed in immunohistochemically stained sections. In contrast, atrial sections of CD11b(-/-) mice lacked a significant increase in PMN infiltration upon Ang II infusion. PMN infiltration was accompanied by profoundly enhanced atrial fibrosis in Ang II treated WT as compared to CD11b(-/-) mice. Upon in-vivo electrophysiological investigation, Ang II treatment significantly elevated the susceptibility for AF in WT mice if compared to vehicle treated animals given an increased number and increased duration of AF episodes. In contrast, animals deficient of CD11b/CD18 were entirely protected from AF induction. Likewise, epicardial activation mapping revealed decreased electrical conduction velocity in atria of Ang II treated WT mice, which was preserved in CD11b(-/-) mice. In addition, atrial PMN infiltration was enhanced in atrial appendage sections of patients with persistent AF as compared to patients without AF.
The current data critically link CD11b-integrin mediated atrial PMN infiltration to the formation of fibrosis, which promotes the initiation and propagation of AF. These findings not only reveal a mechanistic role of leukocytes in AF but also point towards a potential novel avenue of treatment in AF.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The role of polymorphonuclear neutrophils (PMN) in myocardial ischemia and reperfusion (I/R) is controversially discussed. The PMN surface protein CD11b/CD18 plays a critical role for PMN activation ...and adhesion. Using CD11b/CD18 deficient (CD11b-/-) mice we herein sought to further elucidate the effects of infiltrating PMN on ventricular remodeling and arrhythmogenesis in the context of myocardial I/R.
Wildtype (WT) and CD11b-deficient (CD11b-/-) mice of C57BL/6J background were subjected to 40 minutes of myocardial ischemia by ligation of the left anterior descending artery following 6- or 48 hours of reperfusion (I/R). CD11b-/- resulted in significantly less myocardial myeloperoxidase release (MPO+ cells / field of view: WT: 308.4 ± 22.2 vs. CD11b-/-: 178.3 ± 13.1, p < 0.05) and tyrosin chlorination (fluorescence intensity / AU: WT: 0.5 ± 0.07 vs. CD11b-/-: 0.18 ± 0.04, p < 0.01) after ischemia following 6 hours of reperfusion. Immunohistochemical Ly6g staining revealed a significant decrease in PMN infiltration in CD11b-/- hearts after 48 hours of reperfusion (Ly6g+ cells / field of view: WT: 84.07±2.74 vs. CD11b-/-: 64.72 ± 2.53, p < 0.03). Infarct size, as analysed by Triphenyl-tetrazolium chloride / Evans-Blue dye staining of myocardial sections was markedly reduced in CD11b-/- compared to WT mice (infarct area / area at risk: WT: 37.26 ± 7.72% vs. CD11b-/-: 21.8 ± 6.73%; p < 0.001). Standardized right ventricular stimulation in vivo indicated a significantly reduced susceptibility of CD11b-/- animals to ventricular tachycardias (VT) (WT: 8.11±2.85 vs. CD11b-/-: 4.75±1.5, p = 0.009) and a reduced VT length (WT: 8.11±2.85 vs. CD11b-/-: 4.75±1.5, p = 0.009) as compared to WT mice after ischemia followed by 2 days of reperfusion (WT: 8.11±2.85 vs. CD11b-/-: 4.75±1.5, p < 0.01).
Decreased myocardial PMN infiltration and oxidative protein modifactions caused by the absence of CD11b/CD18 suggests a clear role of PMN infiltration for maldadaptive left ventricular remodelling and arrhythmogenesis following myocardial I/R.
Nitro-fatty acids are electrophilic anti-inflammatory mediators which are generated during myocardial ischemic injury. Whether these species exert anti-arrhythmic effects in the acute phase of ...myocardial ischemia has not been investigated so far. Herein, we demonstrate that pretreatment of mice with 9- and 10-nitro-octadec-9-enoic acid (nitro-oleic acid, NO
-OA) significantly reduced the susceptibility to develop acute ventricular tachycardia (VT). Accordingly, epicardial mapping revealed a markedly enhanced homogeneity in ventricular conduction. NO
-OA treatment of isolated cardiomyocytes lowered the number of spontaneous contractions upon adrenergic isoproterenol stimulation and nearly abolished ryanodine receptor type 2 (RyR2)-dependent sarcoplasmic Ca
leak. NO
-OA also significantly reduced RyR2-phosphorylation by inhibition of increased CaMKII activity. Thus, NO
-OA might be a novel pharmacological option for the prevention of VT development.
Pulmonary arterial hypertension (PAH) remains a disease with limited therapeutic options and dismal prognosis. Despite its etiologic heterogeneity, the underlying unifying pathophysiology is ...characterized by increased vascular tone and adverse remodeling of the pulmonary circulation. Myeloperoxidase (MPO), an enzyme abundantly expressed in neutrophils, has potent vasoconstrictive and profibrotic properties, thus qualifying as a potential contributor to this disease. Here, we sought to investigate whether MPO is causally linked to the pathophysiology of PAH. Investigation of 2 independent clinical cohorts revealed that MPO plasma levels were elevated in subjects with PAH and predicted adverse outcome. Experimental analyses showed that, upon hypoxia, right ventricular pressure was less increased in Mpo-/- than in WT mice. The hypoxia-induced activation of the Rho-kinase pathway, a critical subcellular signaling pathway yielding vasoconstriction and structural vascular remodeling, was blunted in Mpo-/- mice. Mice subjected to i.v. infusion of MPO revealed activation of Rho-kinase and increased right ventricular pressure, which was prevented by coinfusion of the Rho-kinase inhibitor Y-27632. In the Sugen5416/hypoxia rat model, PAH was attenuated by the MPO inhibitor AZM198. The current data demonstrate a tight mechanistic link between MPO, the activation of Rho-kinase, and adverse pulmonary vascular function, thus pointing toward a potentially novel avenue of treatment.
Background Recent observational clinical and ex-vivo studies suggest that inflammation and in particular leukocyte activation predisposes to atrial fibrillation (AF). However, whether local binding ...and extravasation of leukocytes into atrial myocardium is an essential prerequisite for the initiation and propagation of AF remains elusive. Here we investigated the role of atrial CD11b/CD18 mediated infiltration of polymorphonuclear neutrophils (PMN) for the susceptibility to AF. Methods and Results C57bl/6J wildtype (WT) and CD11b/CD18 knock-out (CD11b-/-) mice were treated for 14 days with subcutaneous infusion of angiotensin I delta (Ang II), a known stimulus for PMN activation. Atria of Ang II-treated WT mice were characterized by increased PMN infiltration assessed in immunohistochemically stained sections. In contrast, atrial sections of CD11b-/- mice lacked a significant increase in PMN infiltration upon Ang I delta infusion. PMN infiltration was accompanied by profoundly enhanced atrial fibrosis in Ang I delta treated WT as compared to CD11b-/- mice. Upon in-vivo electrophysiological investigation, Ang I delta treatment significantly elevated the susceptibility for AF in WT mice if compared to vehicle treated animals given an increased number and increased duration of AF episodes. In contrast, animals deficient of CD11b/CD18 were entirely protected from AF induction. Likewise, epicardial activation mapping revealed decreased electrical conduction velocity in atria of Ang I delta treated WT mice, which was preserved in CD11b-/- mice. In addition, atrial PMN infiltration was enhanced in atrial appendage sections of patients with persistent AF as compared to patients without AF. Conclusions The current data critically link CD11b-integrin mediated atrial PMN infiltration to the formation of fibrosis, which promotes the initiation and propagation of AF. These findings not only reveal a mechanistic role of leukocytes in AF but also point towards a potential novel avenue of treatment in AF.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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