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Biomedical subjects

Holger K Eltzschig

Publications and source records attributed to Holger K Eltzschig.

At least 19 recordsLinked to original sources
PubMed2006

ATP release from activated neutrophils occurs via connexin 43 and modulates adenosine-dependent endothelial cell function.

Extracellular ATP liberated during hypoxia and inflammation can either signal directly on purinergic receptors or can activate adenosine receptors following phosphohydrolysis to adenosine. Given the association of polymorphonuclear leukocytes (PMNs) with adenine-nucleotide/nucleoside signaling in the inflammatory milieu, we hypothesized that PMNs are a source of extracellular ATP. Initial studies using high-performance liquid chromatography and luminometric ATP detection assays revealed that PMNs release ATP through activation-dependent pathways. In vitro models of endothelial barrier function and neutrophil/endothelial adhesion indicated that PMN-derived ATP signals through endothelial adenosine receptors, thereby promoting endothelial barrier function and attenuating PMN/endothelial adhesion. Metabolism of extracellular ATP to adenosine required PMNs, and studies addressing these metabolic steps revealed that PMN express surface ecto-apyrase (CD39). In fact, studies with PMNs derived from cd39(-/-) mice showed significantly increased levels of extracellular ATP and lack of ATP dissipation from their supernatants. After excluding lytic ATP release, we used pharmacological strategies to reveal a potential mechanism involved in PMN-dependent ATP release (eg, verapamil, dipyridamole, brefeldin A, 18-alpha-glycyrrhetinic acid, connexin-mimetic peptides). These studies showed that PMN ATP release occurs through connexin 43 (Cx43) hemichannels in a protein/phosphatase-A-dependent manner. Findings in human PMNs were confirmed in PMNs derived from induced Cx43(-/-) mice, whereby activated PMNs release less than 15% of ATP relative to littermate controls, whereas Cx43 heterozygote PMNs were intermediate in their capacity for ATP release (P<0.01). Taken together, our results identify a previously unappreciated role for Cx43 in activated PMN ATP release, therein contributing to the innate metabolic control of the inflammatory milieu.

Adenosine↗
PubMed2006

Irradiation-induced pneumonitis mediated by the CD95/CD95-ligand system.

Pneumonitis is a dose-limiting side effect of radiotherapy. However, the underlying mechanisms of irradiation-induced pneumonitis are unclear. Several observations suggest that the CD95/CD95-ligand (CD95L) system is involved in this process. Therefore, we examined the development of pneumonitis in CD95- and CD95L-deficient and wild-type mice after single irradiation with 0 or 12.5 Gy by measuring breathing frequency, pulmonary resistance, and histopathologic changes. Although wild-type mice developed pathognomonic alterations characteristic of pneumonitis (judged by alveolar wall thickness, interstitial edema, and interstitial and peribronchial inflammation) that paralleled increased breathing frequency ratio on days 5-70 (P < .03) with a maximum at day 37 (12.5 Gy, mean ratio = 1.05, 95% confidence interval [CI] = 1.01 to 1.08; P = .004 versus 0 Gy, mean ratio = 0.997, 95% CI = 0.976 to 1.02; P = .05) and pulmonary resistance (day 42, 12.5 Gy, mean = 0.51, 95% CI = 0.44 to 0.58 versus 0 Gy, mean = 0.40, 95% CI = 0.32 to 0.47; P = .03) after irradiation, no such changes were detected in CD95- or CD95L-deficient mice. This report demonstrates for the first time, to our knowledge, that the CD95/CD95L system is important for the development of irradiation-induced pneumonitis.

Animals↗
PubMed2006

Use of a hanging-weight system for isolated renal artery occlusion during ischemic preconditioning in mice.

Renal failure from ischemia contributes to morbidity and mortality. Ischemic preconditioning (IP) represents a powerful strategy for kidney protection, and recent advances in transgenic mice may help elucidate its molecular mechanisms. However, murine IP is technically challenging and experimental details significantly influence results. Thus we developed a novel model for renal IP using a hanging-weight system for isolated renal artery occlusion. In contrast to previous models, this technique eliminates the need for clamping the vascular pedicle (artery/vein). In fact, assessment of renal injury after different time periods of ischemia (10-60 min) revealed highly reproducible increases in plasma creatinine and potassium levels, while creatinine clearance, urinary flow and potassium/sodium excretion were significantly attenuated. Using different numbers of IP cycles, we found maximal protection with four cycles of 4 min of ischemia-reperfusion. In contrast, no significant renal protection was observed with IP of the vascular pedicle. To assess transcriptional responses in this model, we isolated RNA from preconditioned kidneys and found time-dependent induction of erythropoietin mRNA and plasma levels with IP. Taken together, this model provides highly reproducible renal injury and protection by IP, thus minimizing variability associated with previous techniques based on clamping of the renal pedicle. Further studies on renal ischemia/IP in mice may consider this technique.

Animals↗
PubMed2006

Systematic evaluation of a novel model for cardiac ischemic preconditioning in mice.

Cardioprotection by ischemic preconditioning (IP) remains an area of intense investigation. To further elucidate its molecular basis, the use of transgenic mice seems critical. Due to technical difficulty associated with performing cardiac IP in mice, we developed an in situ model for cardiac IP using a hanging-weight system for coronary artery occlusion. This technique has the major advantage of eliminating the necessity of intermittently occluding the coronary artery with a knotted suture. To systematically evaluate this model, we first demonstrated correlation of ischemia times (10-60 min) with infarct sizes [3.5 +/- 1.3 to 42 +/- 5.2% area at risk (AAR), Evan's blue/triphenyltetrazolium chloride staining]. IP (4 x 5 min) and cold ischemia (27 degrees C) reduced infarct size by 69 +/- 6.7% and 84 +/- 4.2%, respectively (n = 6, P < 0.01). In contrast, lower numbers of IP cycles did not alter infarct size. However, infarct sizes were distinctively different in mice from different genetic backgrounds. In addition to infarct staining, we tested cardiac troponin I (cTnI) as marker of myocardial infarction in this model. In fact, plasma levels of cTnI were significantly lower in IP-treated mice and closely correlated with infarct sizes (R(2) = 0.8). To demonstrate transcriptional consequences of cardiac IP, we isolated total RNA from the AAR and showed repression of the equilibrative nucleoside transporters 1-4 by IP in this model. Taken together, this study demonstrates highly reproducible infarct sizes and cardiac protection by IP, thus minimizing the variability associated with knot-based coronary occlusion models. Further studies on cardiac IP using transgenic mice may consider this technique.

Animals↗
PubMed2006

Endothelial catabolism of extracellular adenosine during hypoxia: the role of surface adenosine deaminase and CD26.

Extracellular levels of adenosine increase during hypoxia. While acute increases in adenosine are important to counterbalance excessive inflammation or vascular leakage, chronically elevated adenosine levels may be toxic. Thus, we reasoned that clearance mechanisms might exist to offset deleterious influences of chronically elevated adenosine. Guided by microarray results revealing induction of endothelial adenosine deaminase (ADA) mRNA in hypoxia, we used in vitro and in vivo models of adenosine signaling, confirming induction of ADA protein and activity. Further studies in human endothelia revealed that ADA-complexing protein CD26 is coordinately induced by hypoxia, effectively localizing ADA activity at the endothelial cell surface. Moreover, ADA surface binding was effectively blocked with glycoprotein 120 (gp120) treatment, a protein known to specifically compete for ADA-CD26 binding. Functional studies of murine hypoxia revealed inhibition of ADA with deoxycoformycin (dCF) enhances protective responses mediated by adenosine (vascular leak and neutrophil accumulation). Analysis of plasma ADA activity in pediatric patients with chronic hypoxia undergoing cardiac surgery demonstrated a 4.1 +/- 0.6-fold increase in plasma ADA activity compared with controls. Taken together, these results reveal induction of ADA as innate metabolic adaptation to chronically elevated adenosine levels during hypoxia. In contrast, during acute hypoxia associated with vascular leakage and excessive inflammation, ADA inhibition may serve as therapeutic strategy.

Adenosine Deaminase↗
PubMed2006

Effect of synthetic colloids on major histocompatibility complex class II expression.

STUDY OBJECTIVE: Synthetic colloids are used for perioperative fluid management. We hypothesized that their use may be associated with changes in major histocompatibility complex (MHC) class II expression. This could affect patients' morbidity and mortality during clinical intervention. SETTING: University research laboratory. SUBJECTS: Whole blood samples from healthy volunteers. INTERVENTIONS: Whole blood samples from healthy volunteers (n = 6) were incubated with different concentrations of hydroxyethyl starch (HES) from maize and potato (pHES), dextran, and polygelin (gelatine) for 24 hours with or without 100 U/mL human interferon gamma (IFN-gamma; stimulus for MHC class II expression). The expression of human leukocyte antigen (HLA): HLA-DR, HLA-DQ, and HLA-DP was detected simultaneously by a fluoresceinisothiocyanate (FITC)-labeled antibody and analyzed by flow cytometry on lymphocytes and monocytes. MEASUREMENTS AND MAIN RESULTS: Hydroxyethyl starch, pHES, and dextran induced a significant increase in HLA expression. The induction of MHC class II was independent of the structure (50 mg/mL: control, 8.7+/-1.4%; HES, 28 +/- 9.7%; pHES, 29.8 +/- 11.7%; and dextran, 50.2 +/- 8.1%). In contrast, polygelin increased HLA expression only at the highest concentration of gelatine (5 mg/mL, 7.8 +/- 1%; 50 mg/mL, 7.6 +/- 0.8%; 100 mg/mL, 7.3 +/- 1%; 200 mg/mL,16.2 +/- 2.3%). The addition of IFN-gamma decreased HLA expression in presence of highest concentration of HES and dextran. CONCLUSION: In an ex vivo laboratory setting, we demonstrate that high concentrations of plasma expanders are associated with increased HLA expression on lymphocytes and monocytes. However, further in vivo studies are necessary to demonstrate the clinical significance of this observation.

Colloids↗
PubMed2006

HIF-dependent induction of adenosine A2B receptor in hypoxia.

Adenosine has been widely associated with hypoxia of many origins, including those associated with inflammation and tumorogenesis. A number of recent studies have implicated metabolic control of adenosine generation at sites of tissue hypoxia. Here, we examine adenosine receptor control and amplification of signaling through transcriptional regulation of endothelial and epithelial adenosine receptors. Initial studies confirmed previous findings indicating selective induction of human adenosine A2B receptor (A2BR) by hypoxia. Analysis of the cloned human A2BR promoter identified a functional hypoxia-responsive region, including a functional binding site for hypoxia-inducible factor (HIF) within the A2BR promoter. Further studies examining HIF-1alpha DNA binding and HIF-1alpha gain and loss of function confirmed strong dependence of A2BR induction by HIF-1alpha in vitro and in vivo mouse models. Additional studies in endothelia overexpressing full-length A2BR revealed functional phenotypes of increased barrier function and enhanced angiogenesis. Taken together, these results demonstrate transcriptional coordination of A2BR by HIF-1alpha and amplified adenosine signaling during hypoxia. These findings may provide an important link between hypoxia and metabolic conditions associated with inflammation and angiogenesis.

Base Sequence↗
PubMed2006

Effect of hydroxyethyl starch on vascular leak syndrome and neutrophil accumulation during hypoxia.

OBJECTIVE: Several studies have suggested that intravenous hydroxyethyl starch treatment may dampen acute inflammatory responses. It is well documented that limited oxygen delivery to tissues (hypoxia) is common in acute inflammation, and numerous parallels exist between acute responses to hypoxia and to inflammation, including the observation that both are associated with increased vascular leakage and neutrophil infiltration of tissues. Therefore, we compared functional influences of hydroxyethyl starch on normoxic or posthypoxic endothelia. DESIGN: Laboratory study. SETTING: University hospital. SUBJECTS: Cultured human microvascular endothelial cells and mice (C57BL/6/129 svj). INTERVENTIONS: We measured functional influences of hydroxyethyl starch on normoxic or posthypoxic endothelia. MEASUREMENTS AND MAIN RESULTS: Studies to assess endothelial barrier function in vitro indicated that the addition of hydroxyethyl starch promotes endothelial barrier in a dose-dependent fashion and hydroxyethyl starch-barrier effects are increased following endothelial hypoxia exposure (human microvascular endothelial cells, 48 hrs, 2% oxygen). Treatment of human microvascular endothelial cells with hydroxyethyl starch resulted in a dose-dependent increase in 157-phosphorylated vasodilator-stimulated phosphoprotein, a protein responsible for controlling the geometry of actin-filaments. Neutrophil adhesion was decreased in the presence of physiologically relevant concentrations of hydroxyethyl starch in vitro, particularly after endothelial hypoxia exposure. Using a murine model of normobaric hypoxia, increases in vascular leakage and pulmonary edema associated with hypoxia exposure (4 hrs at 8% oxygen) were decreased in animals treated with intravenous hydroxyethyl starch. Increases of tissue neutrophil accumulation following hypoxia exposure were dampened in hydroxyethyl starch-treated mice. CONCLUSIONS: Taken together, these results indicate that hypoxia-induced increases in vascular leakage and acute inflammation are attenuated by hydroxyethyl starch treatment.

Acute Disease↗
PubMed2006

Acute hemodynamic collapse after induction of general anesthesia for emergent pulmonary embolectomy.

Patients undergoing pulmonary embolectomy often experience hemodynamic deterioration during induction of general anesthesia (GA). Therefore, we studied the incidence and possible risk factors for hemodynamic deterioration during GA induction. Fifty-two consecutive patients undergoing emergent pulmonary embolectomy at our institution were included. Hemodynamic collapse after GA induction was defined as hypotension refractory to vasopressor, inotrope, or fluid administration, requiring cardiopulmonary resuscitation followed by urgent institution of cardiopulmonary bypass (CPB). Demographic variables, comorbidities, specific location of thromboemboli, preoperative inotropic support, and anesthetic drugs used for GA induction were evaluated as possible risk factors. After GA induction, hemodynamic collapse occurred in 19% of patients (n = 10). However, the occurrence of hemodynamic instability was not predicted by any of the evaluated risk factors. In addition, the incidence of in-hospital mortality did not differ between hemodynamically stable or unstable patients (10%; 4 of 42 versus 10%; 1 of 10 patients, respectively). In conclusion, hemodynamic deterioration after GA induction develops frequently during emergent pulmonary embolectomy. On the basis of our experience from this study and the unpredictable nature of hemodynamic deterioration, we suggest that patients undergoing pulmonary embolectomy should be prepared and draped before GA induction, and a cardiac surgical team should immediately be available for emergent institution of cardiopulmonary bypass.

Acute Disease↗
PubMed2006

The usefulness of transesophageal echocardiography during intraoperative cardiac arrest in noncardiac surgery.

According to guidelines established by the American Society of Anesthesiologists and the Society of Cardiovascular Anesthesiologists, life-threatening hemodynamic disturbances are classified as a category I indication for the intraoperative use of transesophageal echocardiography (TEE). However, the usefulness of TEE during intraoperative cardiac arrest and its impact on patient management have not been rigorously investigated. Using our departmental TEE database, we identified a population of 22 patients who underwent noncardiac surgical procedures and experienced unexpected intraoperative hemodynamic collapse requiring the initiation of Advanced Cardiac Life Support procedures between the time of induction of general anesthesia and the termination of the surgical procedure. Results of TEE examinations, patient records, detailed operative records, and outcome of patients were reviewed for the utility of TEE to diagnose the etiology of the hemodynamic collapse. Furthermore, the impact on subsequent patient management was evaluated. A primary suspected diagnosis of the underlying pathological process was established in 19 of 22 patients with TEE, including 9 with thromboembolic events, 6 with acute myocardial ischemia, 2 with hypovolemia, and 2 patients with pericardial tamponade. A definitive diagnosis could not be made in 3 patients with TEE. In 18 patients, TEE guided specific management beyond implementation of Advanced Cardiac Life Support protocols, including the addition of surgical procedures in 12 patients. Fourteen patients survived to leave the operating room, and 7 of these patients were eventually discharged from the hospital. Thus, TEE may provide additional diagnostic information in patients with intraoperative cardiac arrest and may directly guide specific, potentially life-saving therapy.

Adult↗
PubMed2006

Nucleotide metabolism and cell-cell interactions.

Interactions between the vascular endothelium and polymorphonuclear leukocytes (PMNs) are central to PMN emigration into inflamed tissues, and to neutrophil-endothelial crosstalk pathways that modulate inflammatory responses and vascular barrier function. For example, during episodes of inflammation, the transendothelial migration (TEM) of PMNs potentially disturbs vascular barrier and gives rise to intravascular fluid extravasation and edema. However, because of the close special relationship between PMNs and the vascular endothelium, TEM creates an ideal situation for neutrophil-endothelial crosstalk. While investigating innate mechanisms to dampen intravascular fluid loss and edema occurring during TEM, we observed that PMNs release adenine nucleotides after activation (adenosine triphosphate [ATP] and adenosine monophosphate [AMP]). ATP and AMP are metabolized by endothelial cell-surface enzymes, the ecto-apyrase (CD39, metabolizes ATP to AMP) and the 5'-ecto-nucleotidase (CD73, metabolizes AMP to adenosine). Adenosine generated in this fashion can activate endothelial adenosine receptors, leading to increases in intracellular cyclic AMP and resealing of the endothelial junctions, thereby promoting vascular barrier function. This crosstalk pathway provides an endogenous mechanism to dampen vascular leak syndrome during neutrophil-endothelial interaction. In other words, during TEM, neutrophils close the door behind them.

5'-Nucleotidase↗
PubMed2005

HIF-1-dependent repression of equilibrative nucleoside transporter (ENT) in hypoxia.

Extracellular adenosine (Ado) has been implicated as central signaling molecule during conditions of limited oxygen availability (hypoxia), regulating physiologic outcomes as diverse as vascular leak, leukocyte activation, and accumulation. Presently, the molecular mechanisms that elevate extracellular Ado during hypoxia are unclear. In the present study, we pursued the hypothesis that diminished uptake of Ado effectively enhances extracellular Ado signaling. Initial studies indicated that the half-life of Ado was increased by as much as fivefold after exposure of endothelia to hypoxia. Examination of expressional levels of the equilibrative nucleoside transporter (ENT)1 and ENT2 revealed a transcriptionally dependent decrease in mRNA, protein, and function in endothelia and epithelia. Examination of the ENT1 promoter identified a hypoxia inducible factor 1 (HIF-1)-dependent repression of ENT1 during hypoxia. Using in vitro and in vivo models of Ado signaling, we revealed that decreased Ado uptake promotes vascular barrier and dampens neutrophil tissue accumulation during hypoxia. Moreover, epithelial Hif1alpha mutant animals displayed increased epithelial ENT1 expression. Together, these results identify transcriptional repression of ENT as an innate mechanism to elevate extracellular Ado during hypoxia.

Adenosine↗
PubMed2005

Role of transesophageal echocardiography in patients with suspected aortic dissection.

Patients with acute aortic dissection of the ascending aorta benefit from rapid surgical intervention. We report a patient with suspected acute aortic dissection based on history and transthoracic echocardiography findings. This patient was taken to the operating room without further workup, where transesophageal echocardiography (TEE) revealed acute myocardial infarction and mitral regurgitation due to papillary muscle rupture. The patient underwent coronary bypass grafting and mitral valve replacement. This case demonstrates that intraoperative TEE can be used as a primary diagnostic modality to rule out aortic dissection, and can provide a definitive etiology for cardiogenic shock before a planned surgical intervention.

Aged↗