Timo Speer

Inhibition of Nicotinamide Phosphoribosyltransferase Reduces Neutrophil-Mediated Injury in Myocardial Infarction

AIMSnNicotinamide phosphoribosyltransferase (Nampt) is a key enzyme for nicotinamide adenine dinucleotide (NAD(+)) biosynthesis, and recent evidence indicates its role in inflammatory processes. Here, we investigated the potential effects of pharmacological Nampt inhibition with FK866 in a mouse myocardial ischemia/reperfusion model. In vivo and ex vivo mouse myocardial ischemia/reperfusion procedures were performed.nnnRESULTSnTreatment with FK866 reduced myocardial infarct size, neutrophil infiltration, and reactive oxygen species (ROS) generation within infarcted hearts in vivo in a mouse model of ischemia and reperfusion. The benefit of FK866 was not shown in the Langendorff model (ex vivo model of working heart without circulating leukocytes), suggesting a direct involvement of these cells in cardiac injury. Sera from FK866-treated mice showed reduced circulating levels of the neutrophil chemoattractant CXCL2 and impaired capacity to prime migration of these cells in vitro. The release of CXCL8 (human homolog of murine chemokine CXCL2) by human peripheral blood mononuclear cells (PBMCs) and Jurkat cells was also reduced by FK866, as well as by sirtuin (SIRT) inhibitors and SIRT6 silencing, implying a pivotal role for this NAD(+)-dependent deacetylase in the production of this chemokine.nnnINNOVATIONnThe pharmacological inhibition of Nampt might represent an effective approach to reduce neutrophilic inflammation- and oxidative stress-mediated tissue damage in early phases of reperfusion after a myocardial infarction.nnnCONCLUSIONSnNampt inhibition appears as a new strategy to dampen CXCL2-induced neutrophil recruitment and thereby reduce neutrophil-mediated tissue injury in mice.

Total-to-ionized calcium ratio predicts mortality in continuous renal replacement therapy with citrate anticoagulation in critically ill patients.

IntroductionRegional citrate anticoagulation is safe, feasible and increasingly used in critically ill patients on continuous renal replacement therapy (CRRT). However, in patients with hepatic or multi-organ dysfunction, citrate accumulation may lead to an imbalance of calcium homeostasis. The study aimed at evaluating the incidence and prognostic relevance of an increased total to ionized calcium ratio (T/I Ca2+ ratio) and its association to hepatic dysfunction.MethodsWe performed a prospective observational study on n = 208 critically ill patients with acute kidney injury (AKI) and necessity for CRRT with regional citrate anticoagulation (CRRT-citrate) between September 2009 and September 2011. Critical illness was estimated by Simplified Acute Physiology Score II; hepatic function was measured with indocyanine green plasma disappearance rate. After achieving a steady state of calcium homeostasis patients were classified into tertiles according to the T/I Ca2+ ratio (<2.0 versus 2.0 - 2.39 versus ≥2.4).ResultsThe T/I Ca2+ ratio was determined as an independent predictor for 28-day mortality in critically ill patients with AKI on CRRT-citrate confirmed by receiver operating characteristics and multivariate analysis (Area under the curve 0.94 ± 0.02; p<0.001). A T/I Ca2+ ratio ≥2.4 independently predicted a 33.5-fold (p<0.001) increase in 28-day mortality-rate. There was a significant correlation between the T/I Ca2+ ratio and the hepatic clearance (p<0.001) and the severity of critical illness (p<0.001). The efficacy and safety of citrate anticoagulation, determined by blood urea nitrogen, mean filter patency and bleeding episodes, were not significantly different between the tertiles.ConclusionsIn patients on CRRT-citrate T/I Ca2+ ratio is closely related to the clinical outcome and emerged as an independent predictor of 28-day mortality. Larger studies are required to define the cut-off and predictive value for the T/I Ca2+ ratio. This ratio is associated with hepatic and/or multi-organ dysfunction and therefore an important therapeutic target.

Short-term inhibition of DPP-4 enhances endothelial regeneration after acute arterial injury via enhanced recruitment of circulating progenitor cells

BACKGROUNDnEndothelial injuries regularly occur in atherosclerosis and during interventional therapies of the arterial occlusive disease. Disturbances in the endothelial integrity can lead to insufficient blood supply and bear the risk of thrombus formation and acute vascular occlusion. At present, effective therapeutics to restore endothelial integrity are barely available. We analyzed the effect of pharmacological DPP-4-inhibition by Sitagliptin on endogenous progenitor cell-based endothelial regeneration via the SDF-1α/CXCR4-axis after acute endothelial damage in a mouse model of carotid injury.nnnMETHODS AND RESULTSnInduction of a defined endothelial injury was performed in the carotid artery of C57Bl/6 mice which led to a local upregulation of SDF-1α expression. Animals were treated with placebo, Sitagliptin or Sitagliptin+AMD3100. Using mass spectrometry we could prove that Sitagliptin prevented cleavage of the chemokine SDF-1α. Accordingly, increased SDF-1α concentrations enhanced recruitment of systemically applied and endogenous circulating CXCR4+ progenitor cells to the site of vascular injury followed by a significantly accelerated reendothelialization as compared to placebo-treated animals. Improved endothelial recovery, as well as recruitment of circulating CXCR4+ progenitor cells (CD133+, Flk1+), was reversed by CXCR4-antagonization through AMD3100. In addition, short-term Sitagliptin treatment did not significantly promote neointimal or medial hyperplasia.nnnCONCLUSIONnSitagliptin can accelerate endothelial regeneration after acute endothelial injury. DPP-4 inhibitors prevent degradation of the chemokine SDF-1α and thus improve the recruitment of regenerative circulating CXCR4+ progenitor cells which mediate local endothelial cell proliferation without adversely affecting vessel wall architecture.

Novel Insights Into the Critical Role of Bradykinin and the Kinin B2 Receptor for Vascular Recruitment of Circulating Endothelial Repair–Promoting Mononuclear Cell Subsets Alterations in Patients With Coronary Disease

Background— Endothelial injury is considered critical for progression of atherosclerosis and its complications in coronary artery disease (CAD). The endothelial-supportive effects of bradykinin have mainly been attributed to activation of the resident endothelium. Here we newly investigate the role of bradykinin and its B2 receptor for the recruitment and functional activation of circulating mononuclear cell subsets with endothelial-repair promoting capacity, such as CD34+CXCR4+cells, at sites of arterial injury. Methods and Results— Bradykinin-B2-receptor (B2R) blockade by icatibant substantially impaired recruitment of circulating CD34+CXCR4+ mononuclear cells (expressing high levels of B2R) to endothelial cells in vitro and to injured arterial wall in vivo, whereas recruitment of CD14hi monocytes (expressing low levels of B2R) was unchanged. Moreover, the capacity of genetically B2R-deficient bone marrow cells to promote endothelial repair in vivo was markedly impaired as compared with wild-type bone marrow cells. B2R expression was reduced on CD34+CXCR4+mononuclear cells and endothelial repair–promoting early outgrowth cells, but not on CD14himonocytes, from CAD patients as compared with healthy subjects. B2R stimulation induced CD18 activation in early outgrowth cells of healthy subjects, but not in early outgrowth cells of CAD patients. Adenoviral B2R overexpression enhanced in vivo vascular recruitment and rescued impaired endothelial repair capacity of early outgrowth cells from CAD patients. Conclusions— We newly report that bradykinin/B2R signaling may promote endothelial repair after arterial injury by selective recruitment and functional activation of B2R-expressing circulating mononuclear cell subsets. In CAD patients, B2R downregulation on endothelial repair–promoting circulating mononuclear cells substantially impairs the bradykinin-dependent endothelial repair, representing a novel mechanism promoting endothelial injury in CAD patients.

Novel Insights Into the Critical Role of Bradykinin and the Kinin B2 Receptor for Vascular Recruitment of Circulating Endothelial Repair–Promoting Mononuclear Cell SubsetsClinical Perspective

Background— Endothelial injury is considered critical for progression of atherosclerosis and its complications in coronary artery disease (CAD). The endothelial-supportive effects of bradykinin have mainly been attributed to activation of the resident endothelium. Here we newly investigate the role of bradykinin and its B2 receptor for the recruitment and functional activation of circulating mononuclear cell subsets with endothelial-repair promoting capacity, such as CD34+CXCR4+cells, at sites of arterial injury. Methods and Results— Bradykinin-B2-receptor (B2R) blockade by icatibant substantially impaired recruitment of circulating CD34+CXCR4+ mononuclear cells (expressing high levels of B2R) to endothelial cells in vitro and to injured arterial wall in vivo, whereas recruitment of CD14hi monocytes (expressing low levels of B2R) was unchanged. Moreover, the capacity of genetically B2R-deficient bone marrow cells to promote endothelial repair in vivo was markedly impaired as compared with wild-type bone marrow cells. B2R expression was reduced on CD34+CXCR4+mononuclear cells and endothelial repair–promoting early outgrowth cells, but not on CD14himonocytes, from CAD patients as compared with healthy subjects. B2R stimulation induced CD18 activation in early outgrowth cells of healthy subjects, but not in early outgrowth cells of CAD patients. Adenoviral B2R overexpression enhanced in vivo vascular recruitment and rescued impaired endothelial repair capacity of early outgrowth cells from CAD patients. Conclusions— We newly report that bradykinin/B2R signaling may promote endothelial repair after arterial injury by selective recruitment and functional activation of B2R-expressing circulating mononuclear cell subsets. In CAD patients, B2R downregulation on endothelial repair–promoting circulating mononuclear cells substantially impairs the bradykinin-dependent endothelial repair, representing a novel mechanism promoting endothelial injury in CAD patients.

Novel Insights Into the Critical Role of Bradykinin and the Kinin B2 Receptor for Vascular Recruitment of Circulating Endothelial Repair–Promoting Mononuclear Cell Subsets

Background— Endothelial injury is considered critical for progression of atherosclerosis and its complications in coronary artery disease (CAD). The endothelial-supportive effects of bradykinin have mainly been attributed to activation of the resident endothelium. Here we newly investigate the role of bradykinin and its B2 receptor for the recruitment and functional activation of circulating mononuclear cell subsets with endothelial-repair promoting capacity, such as CD34+CXCR4+cells, at sites of arterial injury. Methods and Results— Bradykinin-B2-receptor (B2R) blockade by icatibant substantially impaired recruitment of circulating CD34+CXCR4+ mononuclear cells (expressing high levels of B2R) to endothelial cells in vitro and to injured arterial wall in vivo, whereas recruitment of CD14hi monocytes (expressing low levels of B2R) was unchanged. Moreover, the capacity of genetically B2R-deficient bone marrow cells to promote endothelial repair in vivo was markedly impaired as compared with wild-type bone marrow cells. B2R expression was reduced on CD34+CXCR4+mononuclear cells and endothelial repair–promoting early outgrowth cells, but not on CD14himonocytes, from CAD patients as compared with healthy subjects. B2R stimulation induced CD18 activation in early outgrowth cells of healthy subjects, but not in early outgrowth cells of CAD patients. Adenoviral B2R overexpression enhanced in vivo vascular recruitment and rescued impaired endothelial repair capacity of early outgrowth cells from CAD patients. Conclusions— We newly report that bradykinin/B2R signaling may promote endothelial repair after arterial injury by selective recruitment and functional activation of B2R-expressing circulating mononuclear cell subsets. In CAD patients, B2R downregulation on endothelial repair–promoting circulating mononuclear cells substantially impairs the bradykinin-dependent endothelial repair, representing a novel mechanism promoting endothelial injury in CAD patients.