Publications by authors named "Markus Klinger"

31 Publications

Abdominal aortic aneurysm and virus infection: a potential causative role for cytomegalovirus infection?

J Med Virol 2021 Feb 25. Epub 2021 Feb 25.

Department of Surgery, Division of Vascular Surgery, Medical University of Vienna, Vienna, Austria.

An abdominal aortic aneurysm (AAA) is a multifactorial disease with a variety of genetic and environmental risk factors, but the exact mechanism of AAA formation and progression is still not well understood. The present study investigated the frequency of cytomegalovirus (CMV), Epstein-Barr virus (EBV), and papillomavirus types 6 and 11 (HPV6 and HPV11), their impact on clinical manifestations of cardiovascular diseases, and their possible association with inflammation in patients with AAA and healthy volunteers. Genotyping of CMV UL75, EBV LMP-1, and HPV6 and HPV11 E6 was performed by polymerase chain reaction (PCR), while the viral DNA loads were measured by quantitative real-time PCR (qRT-PCR). Cytokine levels were determined by enzyme-linked immunosorbent assays (ELISAs). The CMV UL75 was detected more frequently in the blood of patients with AAA than in the blood of healthy volunteers (32.7% vs. 6.3%, p < 0.0001). Neither EBV LMP-1 nor HPV6 E6 was found in blood and aortic wall biopsies, while the HPV11 E6 was detected in 36.4% of AAA walls. The CMV infection in patients with AAA was associated with an increased risk of hypertension and coronary artery disease (CAD) (OR 9.057; 95% CI: 1.141 - 71.862, p = 0.037; OR 2.575; 95% CI: 1.002 - 6.615, p = 0.049, respectively). Additionally, CMV-infected patients with AAA had higher TNF-α levels compared with non-infected subjects (p = 0.017). Our findings suggest that CMV infection can stimulate local inflammation in the aorta but is not a direct cause of most abdominal aortic aneurysms. This article is protected by copyright. All rights reserved.
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http://dx.doi.org/10.1002/jmv.26901DOI Listing
February 2021

Polymorphisms in the IL-6 and TNF-α gene are associated with an increased risk of abdominal aortic aneurysm.

Int J Cardiol 2021 Apr 6;329:192-197. Epub 2021 Jan 6.

Department of Surgery, Division of Vascular Surgery, Medical University of Vienna, Vienna, Austria.

Background: An abdominal aortic aneurysm (AAA) is a complex disease of the aging population that is associated with inflammation and the cellular immune response. To investigate the influence of interleukin (IL)-6 and tumor necrosis factor (TNF)-α single nucleotide polymorphisms (SNPs) on the risk of AAA formation and progression, the frequency of AAA and its associated risk factors were determined.

Method: Four SNPs in the IL-6 (-174G/C, rs1800795; -572G/C, rs1800796) and TNF-α (-238G/A, rs361525; -308G/A, rs1800629) genes were studied by the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) in patients with AAA and healthy volunteers. The mRNA expression and plasma IL-6 and TNF-α levels were also determined.

Results: A mutation detected in at least one allele of the IL-6 -174G/C SNP was associated with a 2-fold increased risk of AAA occurrence (OR: 2.08; 95% CI: 1.15-3.76; p = 0.014, in the dominant model). An increased risk of AAA incidence among heterozygous carriers of the TNF-α - 308G/A genotype was observed (OR: 2.06; 95% CI: 1.17-3.62; p = 0.011, in the overdominant model). The wild-type genotypes of the IL-6 -174G/C and the TNF-α -308G/A SNPs coexisted more frequently in healthy subjects than in AAA patients and was associated with decreased risk of AAA (p < 0.001). Moreover, elevated levels of IL-6 and TNF-α were associated with an increased risk of hypertension (p < 0.001 and p = 0.022, respectively).

Conclusions: The IL-6 -174G/C and the TNF-α -238G/A gene polymorphisms are associated with an increased risk of abdominal aortic aneurysm development.
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http://dx.doi.org/10.1016/j.ijcard.2020.12.051DOI Listing
April 2021

Inverse probability of treatment analysis of open vs endovascular repair in ruptured infrarenal aortic aneurysm - Cohort study.

Int J Surg 2020 Aug 15;80:218-224. Epub 2020 Jun 15.

Department of Surgery, Division of Vascular Surgery, Medical University of Vienna, Austria. Electronic address:

Background: To compare open repair (OR) with EVAR for the management of ruptured infrarenal abdominal aortic aneurysms (RAAA) in a cohort study over a time period of 15 years with inverse probability of treatment weights.

Material And Methods: From 2000/01 through 2015/12 136 patients were treated for RAAA, 98 (72.1%) underwent OR, 38 (27.9%) were treated with EVAR. Thirty-day and long-term mortality (survival) were analyzed in this IRB-approved retrospective cohort study. Treatment modalities were compared using inverse probability of treatment weights to adjust for imbalances in demographic data and risk factors.

Results: EVAR patients were older (75.11 ± 7.17 vs 69.79 ± 10.24; p=0.001). There was no statistical difference in gender, hypertension, COPD, CAD, or diabetes. GFR was significantly higher in OR patients (71.4 ± 31.09 vs. 53.68 ± 25.73). Postoperative dialysis was required more frequently in EVAR patients: 11% vs. 2% (p = 0.099). In the OR group, adjusted cumulative survival was 70.4% (61.1, 81.1) at 30 days, 47.0% (37.1, 59.6) at one year and 38.3% (28.6, 51.3) at 5 years. In the EVAR group the corresponding numbers were 77.0% (67.7, 87.5), 67.5% (57.0, 80.0) and 41.7% (30.4, 57.4), respectively.

Conclusion: There is evidence for EVAR patients exhibiting a benefit in one-year survival, while patients treated with OR may have more favorable long-term survival given they survive for at least one year. Herein we provide a statistically rigorous comparison of OR and EVAR in short and long-term outcomes with up to 15 years of follow-up.
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http://dx.doi.org/10.1016/j.ijsu.2020.05.090DOI Listing
August 2020

2029C/T and 1377C/T and -7C/A Polymorphisms Are Associated with the Occurrence of Abdominal Aortic Aneurysm.

J Immunol 2020 06 13;204(11):2900-2909. Epub 2020 Apr 13.

Division of Vascular Surgery, Department of Surgery, Medical University of Vienna, A-1090 Vienna, Austria.

TLRs are a family of signaling sensors that play a crucial role in the host immune response and are involved in the modulation of inflammatory processes. To study their contribution to abdominal aortic aneurysm (AAA) formation and development, we determined the frequency of , , , and single-nucleotide polymorphisms (SNPs) and investigated the association between polymorphisms and the risk of AAA incidence. A total of 104 patients with AAAs and 112 healthy, unrelated volunteers were screened for the presence of (2029C/T and 2258G/A), (1377C/T, 1234C/T, and -7C/A), (896A/G, 1196C/T, and 3266G/A), and (-1237T/C, -1486T/C, 1174G/A, and 2848C/T) SNPs by using PCR-RFLP analysis. The heterozygous genotype of the 2029C/T SNP was more common in patients with AAA than in healthy subjects ( < 0.0001) and was associated with at least an 8-fold increased risk of AAA incidence ( < 0.001). The wild-type genotype of the -7C/A SNP was associated with a 3-fold increased risk of hypertension ( = 0.026). The heterozygous genotype 1377C/T and -7C/A SNPs were less common in patients with AAA than in healthy subjects ( < 0.0001 and = 0.0004, respectively) and were associated with a decreased risk of AAA occurrence ( < 0.001 and = 0.0012, respectively). No relation to AAA risk was found for SNPs. Heterozygous genotypes of the 2029C/T and 1377C/T and -7C/A SNPs may serve as genetic biomarkers of AAA incidence.
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http://dx.doi.org/10.4049/jimmunol.1901014DOI Listing
June 2020

Author Correction: Organic Power Electronics: Transistor Operation in the kA/cm Regime.

Sci Rep 2020 Apr 10;10(1):6473. Epub 2020 Apr 10.

Dresden Integrated Center for Applied Physics and Photonic Materials, Technische Universität Dresden, Nöthnitzer Str. 61, 01187, Dresden, Germany.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.
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http://dx.doi.org/10.1038/s41598-020-63130-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7148371PMC
April 2020

Insight into the expression of toll-like receptors 2 and 4 in patients with abdominal aortic aneurysm.

Mol Biol Rep 2020 Apr 7;47(4):2685-2692. Epub 2020 Mar 7.

Division of Vascular Surgery, Department of Surgery, Medical University of Vienna, Vienna General Hospital, Vienna, Austria.

An abdominal aortic aneurysm (AAA) is a relatively common, life-threatening disease prevalent in persons over the age of 65. In recent years, an increasing number of studies have suggested that pattern-recognition receptors (PRRs), including Toll-like receptors (TLRs), may serve as important regulators in the development of AAAs. In this study, we evaluated the TLR2 and TLR4 expression in the aortic wall and blood of patients with AAA. The TLR2 and TLR4 mRNA expression were significantly higher in the blood of patients with AAA than in the blood of healthy volunteers (p = 0.009 and p = 0.010, respectively). The expression of TLR2 and TLR4 transcripts was also higher in the blood compared with the aortic wall tissue of AAA patients (p = 0.001 for both). Higher TLR2 protein expression was observed in the aortic wall of AAA patients compared with the blood (p = 0.026). A significantly higher concentration of TNF-α and IL-4 in patients with AAA than in healthy volunteers (p < 0.001 for both) was noticed. This study suggests that TLR2 may play a role in the inflammatory response in the aorta, both locally and systemically, in patients with AAA.
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http://dx.doi.org/10.1007/s11033-020-05366-xDOI Listing
April 2020

Non-Linear Self-Heating in Organic Transistors Reaching High Power Densities.

Sci Rep 2018 Jun 28;8(1):9806. Epub 2018 Jun 28.

Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP), Technische Universität Dresden, Nöthnitzer Str. 61, 01187, Dresden, Germany.

The improvement of the performance of organic thin-film transistors is driven by novel materials and improved device engineering. Key developments are a continuous increase of the charge carrier mobility, a scale-down of transistor dimensions, and the reduction of contact resistance. Furthermore, new transistor designs such as vertical devices are introduced to benefit from drastically reduced channel length while keeping the effort for structuring moderate. Here, we show that a strong electrothermal feedback occurs in organic transistors, ultimately leading to output characteristics with regions of S-shaped negative differential resistance. For that purpose, we use an organic permeable-base transistor (OPBT) with outstanding current densities, where a strong and reproducible, non-linear electrothermal feedback is revealed. We derive an analytical description of the temperature dependent current-voltage behavior and offer a rapid investigation method for material systems, where a temperature-activated conductivity can be observed.
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http://dx.doi.org/10.1038/s41598-018-27689-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6023904PMC
June 2018

A Pulse-Biasing Small-Signal Measurement Technique Enabling 40 MHz Operation of Vertical Organic Transistors.

Sci Rep 2018 May 16;8(1):7643. Epub 2018 May 16.

Chair for Circuit Design and Network Theory (CCN), Technische Universität Dresden, Helmholtzstr. 18, 01069, Dresden, Germany.

Organic/polymer transistors can enable the fabrication of large-area flexible circuits. However, these devices are inherently temperature sensitive due to the strong temperature dependence of charge carrier mobility, suffer from low thermal conductivity of plastic substrates, and are slow due to the low mobility and long channel length (L). Here we report a new, advanced characterization circuit that within around ten microseconds simultaneously applies an accurate large-signal pulse bias and a small-signal sinusoidal excitation to the transistor and measures many high-frequency parameters. This significantly reduces the self-heating and therefore provides data at a known junction temperature more accurate for fitting model parameters to the results, enables small-signal characterization over >10 times wider bias I-V range, with ~10 times less bias-stress effects. Fully thermally-evaporated vertical permeable-base transistors with physical L = 200 nm fabricated using C fullerene semiconductor are characterized. Intrinsic gain up to 35 dB, and record transit frequency (unity current-gain cutoff frequency, f) of 40 MHz at 8.6 V are achieved. Interestingly, no saturation in f - I and transconductance (g - I) is observed at high currents. This paves the way for the integration of high-frequency functionalities into organic circuits, such as long-distance wireless communication and switching power converters.
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http://dx.doi.org/10.1038/s41598-018-26008-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5955934PMC
May 2018

Analysis of host Toll-like receptor 3 and RIG-I-like receptor gene expression in patients with abdominal aortic aneurysm.

J Vasc Surg 2018 12 19;68(6S):39S-46S. Epub 2018 Mar 19.

Department of Surgery, Medical University of Vienna, Vienna, Austria.

Objective: Abdominal aortic aneurysm (AAA) is a vascular disease relatively common in the elderly population. Although some events that contribute to the development and progression of AAA are known, there are limited data examining the association of Toll-like receptor 3 (TLR3) and RIG-I-like receptor expression with the pathogenesis of AAAs. In this study, we investigated the gene and protein expression of TLR3 and RIG-I-like receptors (RIG-I and MDA5) in aortic wall and blood of AAA patients and examined the relationship between their expression and immune response.

Methods: Total RNA was extracted from aortic wall tissues and blood samples collected from 20 patients with AAA and blood samples of 17 healthy volunteers without aortic aneurysm. To evaluate the DDX58 (RIG-I), IFIH1 (MDA5), and TLR3 gene expression level, quantitative real-time polymerase chain reaction was used. Extracellular cytokine and pattern recognition receptor levels were quantified by enzyme-linked immunosorbent assays.

Results: TLR3, RIG-I, and MDA5 were constitutively expressed in both aortic tissues and blood samples from AAA patients and healthy volunteers. In patients with AAA, higher TLR3 expression in aortic tissues than in blood was found (P = .004). The DDX58 messenger RNA expression was higher in blood of patients with AAA compared with healthy subjects (P = .021). A significantly higher level of plasma interleukin 4 was noticed in patients with AAA than in healthy individuals (P = .008).

Conclusions: This study suggests that RIG-I and TLR3 seem to be important factors in the pathogenesis of AAA.
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http://dx.doi.org/10.1016/j.jvs.2017.10.087DOI Listing
December 2018

NGAL and MMP-9/NGAL as biomarkers of plaque vulnerability and targets of statins in patients with carotid atherosclerosis.

Clin Chem Lab Med 2017 Nov;56(1):147-156

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Background: Neutrophil gelatinase associated lipocalin (NGAL) is expressed in atherosclerotic lesions and was recently implicated in the pathogenesis of cardiovascular pathologies. Statins are known to exert stabilizing effects on atherosclerotic plaque. The aims of our study were (1) to investigate the association of serum NGAL and metalloproteinase (MMP)-9/NGAL complex with the vulnerability of the atherosclerotic plaque, and (2) to reveal the effects of statin treatment on circulating NGAL and MMP-9/NGAL levels in patients with carotid artery stenosis.

Methods: We examined the levels of NGAL and MMP-9/NGAL in blood samples from 136 patients with carotid artery stenosis by specific enzyme-linked immunosorbent assays.

Results: Patients with vulnerable plaques, as determined by ultrasound (plaques with decreased echogenicity) and histological analysis (type VI according to the classification of American Heart Association [AHA]), displayed the highest levels of NGAL (both p<0.0001) and MMP-9/NGAL complex (p=0.0004 and p=0.004, respectively). Moreover, patients with symptomatic carotid atherosclerosis had significantly higher NGAL levels compared to asymptomatic patients (p=0.0007). The statin-treated group (n=108) demonstrated lower NGAL (73.9 vs. 128.0 μg/L, p<0.0001) and MMP-9/NGAL (28.9 vs. 40.6 μg/L, p=0.046) as compared to the non-statin group (n=28). Furthermore, in multivariate regression analysis NGAL, but not MMP-9/NGAL levels, were independently associated with symptomatic carotid artery stenosis. In addition, statin treatment was independently associated with lower NGAL levels.

Conclusions: Circulating NGAL and MMP-9/NGAL are associated with plaque vulnerability in patients with carotid artery stenosis. Statin treatment could contribute to plaque stabilization by reducing circulating NGAL and MMP-9/NGAL levels.
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http://dx.doi.org/10.1515/cclm-2017-0156DOI Listing
November 2017

Organic Power Electronics: Transistor Operation in the kA/cm Regime.

Sci Rep 2017 03 17;7:44713. Epub 2017 Mar 17.

Dresden Integrated Center for Applied Physics and Photonic Materials, Technische Universität Dresden, Nöthnitzer Str. 61, 01187, Dresden, Germany.

In spite of interesting features as flexibility, organic thin-film transistors have commercially lagged behind due to the low mobilities of organic semiconductors associated with hopping transport. Furthermore, organic transistors usually have much larger channel lengths than their inorganic counterparts since high-resolution structuring is not available in low-cost production schemes. Here, we present an organic permeable-base transistor (OPBT) which, despite extremely simple processing without any high-resolution structuring, achieve a performance beyond what has so far been possible using organic semiconductors. With current densities above 1 kA cm and switching speeds towards 100 MHz, they open the field of organic power electronics. Finding the physical limits and an effective mobility of only 0.06 cm V s, this OPBT device architecture has much more potential if new materials optimized for its geometry will be developed.
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http://dx.doi.org/10.1038/srep44713DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5356189PMC
March 2017

The cell-wall active mannuronan C5-epimerases in the model brown alga Ectocarpus: From gene context to recombinant protein.

Glycobiology 2016 09 29;26(9):973-983. Epub 2016 Mar 29.

Sorbonne Universités, UPMC Univ Paris 06, UMR 8227, Integrative Biology of Marine Models, Station Biologique de Roscoff, CS 90074, Roscoff, France CNRS, UMR 8227, Integrative Biology of Marine Models, Station Biologique de Roscoff, CS 90074, Roscoff, France

Mannuronan C5-epimerases (ManC5-Es) catalyze in brown algae the remodeling of alginate, a major cell-wall component which is involved in many biological functions in these organisms. ManC5-Es are present as large multigenic families in brown algae, likely indicating functional specificities and specializations. ManC5-Es control the distribution pattern of (1-4) linked β-d-mannuronic acid (M) and α-l-guluronic acid (G) residues in alginates, giving rise to widely different polysaccharide compositions and sequences, depending on tissue, season, age, or algal species. As such they are also a source of powerful new tools for the biotechnological and enzymatic processing of alginates, to match the growing interest for food hydrocolloids and in biomedical and nanotechnological applications. We report here the first heterologous production of a ManC5-E of brown algal origin that is successfully refolded in an active form. The activity was measured by H NMR and by an indirect enzymatic assay using a known bacterial alginate lyase. The transcript expression as a function of the developmental program of the brown alga Ectocarpus, together with the bioinformatic analyses of the corresponding gene context of this multigenic family, is also presented.
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http://dx.doi.org/10.1093/glycob/cww040DOI Listing
September 2016

Advanced Organic Permeable-Base Transistor with Superior Performance.

Adv Mater 2015 Dec 20;27(47):7734-9. Epub 2015 Oct 20.

Institut für Angewandte Photophysik, Technische Universität Dresden, George-Bähr-Str. 1, 01062, Dresden, Germany.

An optimized vertical organic permeable-base transistor (OPBT) competing with the best organic field-effect transistors in performance, while employing low-cost fabrication techniques, is presented. The OPBT stands out by its excellent power efficiency at the highest frequencies.
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http://dx.doi.org/10.1002/adma.201502788DOI Listing
December 2015

Clinical Usefulness of a Novel Freehand 3D Imaging Device for Radio-Guided Intraoperative Sentinel Lymph Node Detection in Malignant Melanoma.

Clin Nucl Med 2015 Sep;40(9):e436-40

From the *Department of Nuclear Medicine and Endocrinology, Linz General Hospital, Medical Faculty, Johannes Kepler University, Linz, Austria; †Department of Dermatology, Linz General Hospital, Medical Faculty, Johannes Kepler University, Linz, Austria; ‡2nd Surgical Department, Linz General Hospital, Medical Faculty, Johannes Kepler University, Linz, Austria; §Department of Oral and Maxillofacial Surgery, Linz General Hospital, Medical Faculty, Johannes Kepler University, Linz, Austria; ∥Department of Radiology, University of Southern California, Los Angeles, CA; ¶Nuclear Medicine & PET/CT Centre, Santa Maria della Misericordia Hospital, Rovigo, Italy; and **University Clinic of Nuclear Medicine, Medical University of Innsbruck, Innsbruck, Austria.

Introduction: Patients with invasive malignant melanoma are commonly referred for sentinel lymph node (SLN) detection. A recently proposed 3D tomographic imaging modality is freehand SPECT (declipseSPECT). This "bedside system" was originally developed to enable minimal-invasive image-guided surgery. The aim of this retrospective analysis was to assess the clinical use of this freehand detector device for image-guided lymphatic mapping in melanoma patients.

Materials And Methods: Thirty-nine patients (12 female and 27 male subjects) were included (age, 30-79 years). All of them had at least one location of melanoma with tumoral stage pT1b or greater in 37 and pTx in 2 patients in different sites of the body (abdomen in 4, back in 14, head and neck in 5, lower extremity in 6, and upper extremity in 10 patients). Lymphoscintigraphy was performed with 65 to 127 MBq Tc-nanocolloid. A 2-day protocol was applied with SPECT-CT acquisition (Brightview XCT, Philips) at day 1 and surgery using radio-guided freehand SPECT at day 2. SPECT-CT data were integrated into the 3D navigation system to enable fast and direct localization of the SLN by displaying the depth of the node from the skin surface and lateral margins in relation to the gamma probe.

Results: Comparable preoperative imaging and intraoperative localization was observed in 18 patients. In 14 cases, more lymph nodes were resected than detected by SPECT-CT including 1 patient without evidence of an SLN because this node was located close to the primary right ear tumor. In 10 of these patients, intraoperative freehand SPECT revealed additional sites of lymph nodes. In 7 cases, more findings were detected by SPECT-CT than surgically removed. The procedure was safe and easy to perform, and the time of surgical intervention using freehand SPECT was in the range of 36 to 133 minutes (mean time, 66.56 minutes).

Conclusions: Freehand SPECT detected more SLN compared with SPECT-CT, and the tracking system provided precise anatomical localization of the radioactive-labeled SLNs.
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http://dx.doi.org/10.1097/RLU.0000000000000882DOI Listing
September 2015

Quantification of free formaldehyde in carrageenan and processed Eucheuma seaweed using high-performance liquid chromatography.

Food Addit Contam Part A Chem Anal Control Expo Risk Assess 2015 22;32(2):152-60. Epub 2014 Dec 22.

a DuPont Nutrition Biosciences ApS , Brabrand , Denmark.

In 2010 the European Commission placed a limit on the amount of free formaldehyde in carrageenan and processed Eucheuma seaweed (PES) of 5 mg kg(-1). Formaldehyde is not used in carrageenan and PES processing and accordingly one would not expect free formaldehyde to be present in carrageenan and PES. However, surprisingly high levels up to 10 mg kg(-1) have been found using the generally accepted AOAC and Hach tests. These findings are, per proposed reaction pathways, likely due to the formation of formaldehyde when sulphated galactose, the backbone of carrageenan, is hydrolysed with the strong acid used in these conventional tests. In order to minimise the risk of false-positives, which may lead to regulatory non-compliance, a new high-performance liquid chromatography (HPLC) method has been developed. Initially, carrageenan or PES is extracted with 2-propanol and subsequently reacted with 2,4-dinitrophenylhydrazine (DNPH) to form the chromophore formaldehyde-DNPH, which is finally quantified by reversed-phase HPLC with ultraviolet light detection at 355 nm. This method has been found to have a limit of detection of 0.05 mg kg(-1) and a limit of quantification of 0.2 mg kg(-1). Recoveries from samples spiked with known quantities of formaldehyde were 95-107%. Using this more specific technique, 20 samples of carrageenan and PES were tested for formaldehyde. Only one sample had a detectable content of formaldehyde (0.40 mg kg(-1)), thus demonstrating that the formaldehyde content of commercial carrageenan and PES products are well below the European Commission maximum limit of 5 mg kg(-1).
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http://dx.doi.org/10.1080/19440049.2014.992049DOI Listing
December 2015

Application of diffusion-edited NMR spectroscopy for selective suppression of water signal in the determination of monomer composition in alginates.

Magn Reson Chem 2011 Sep 4;49(9):584-91. Epub 2011 Aug 4.

Department of Chemistry, Swedish University of Agricultural Sciences, 750 07 Uppsala, Sweden.

Alginate is a linear copolymer of 1-4 linked β-D-mannuronic acid (M) and 1-4 linked α-L-guluronic acid (G). The physical properties of these polysaccharides such as gel properties and viscosity are largely correlated to the monomer composition (M/G ratio), the sequence of the polymer and the molecular weight. Determination of the M/G ratio is therefore important and NMR spectroscopy is among the most common methods used to accurately obtain this ratio. Instead of using time consuming, possibly sample altering, acid hydrolysis to reduce the viscosity of the alginate sample prior to analysis, samples of low concentrations can be used. However, this results in a water peak in the NMR spectrum that is several orders of magnitude larger than the alginate signals and water suppression is required. In this article, a diffusion-edited NMR experiment that suppresses the water peak while retaining the signals of interest has been used to enable correct M/G ratio determination. This approach exploits the difference in translational diffusion between the larger alginate molecules and the smaller water molecules. Using this method, the monomer composition of 20 different alginate powders was determined. The diffusion parameters were optimized to allow measurement for samples covering a large range of M/G ratios and viscosities. Thus, such method should be useful for analyzing large numbers of unknown alginate samples using, for example, automation procedures.
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http://dx.doi.org/10.1002/mrc.2789DOI Listing
September 2011

Sinusoidal obstruction syndrome impairs long-term outcome of colorectal liver metastases treated with resection after neoadjuvant chemotherapy.

Ann Surg Oncol 2011 Feb 16;18(2):421-30. Epub 2010 Sep 16.

Department of Surgery, Medical University of Vienna, Vienna, Austria.

Background: Chemotherapy-induced liver injury is a considerable problem in patients undergoing surgery for colorectal liver metastases, since an increase in postoperative morbidity and mortality has been observed. We investigated whether liver damage had further implications on long-term outcome in these patients.

Materials And Methods: Liver specimens from 196 patients resected for colorectal liver metastases were evaluated for chemotherapy-associated hepatic damage in the nontumorous liver. Injury patterns were correlated with recurrence free (RFS) and overall survival (OS). Factors leading to sinusoidal injury were identified.

Results: Patients who developed grade 2 or 3 sinusoidal dilatation had a significantly shorter RFS (hazard ratio [HR] 2.05; 95% confidence interval [95% CI] 1.23-3.39, P = .005) and OS (HR 2.90; 95% CI 1.61-6.19, P < .001), compared to patients without this alteration. Those patients also had significantly more intrahepatic recurrences (66.7% vs 30.5%, P = .003). Other patterns of chemotherapy-associated liver damage (nonalcoholic steatohepatitis, fibrosis) were not associated with impaired survival. Factors indicating sinusoidal injury were oxaliplatin-based chemotherapy, tumor size >5 cm, and elevated alkaline phosphatase or gamma glutamyltransferase.

Conclusions: Sinusoidal obstruction syndrome due to oxaliplatin-based chemotherapy may not only compromise perioperative outcome, but can lead to early recurrence and decreased survival in the long term. Strategies to prevent this condition are clearly needed.
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http://dx.doi.org/10.1245/s10434-010-1317-4DOI Listing
February 2011

Liver resection remains a safe procedure after neoadjuvant chemotherapy including bevacizumab: a case-controlled study.

Ann Surg 2010 Jul;252(1):124-30

Department of Surgery, Medical University of Vienna, Vienna, Austria.

Objective: This study was conducted to analyze if the combination of Bevacizumab with standard chemotherapy increases postoperative morbidity and mortality after resection of colorectal liver metastases as compared with resection after chemotherapy alone. Parameters contributing to an increased morbidity were evaluated.

Summary Background Data: Most patients referred for colorectal liver metastases are treated with neoadjuvant chemotherapy before hepatic surgery. Targeted agents like the vascular endothelial growth factor-antagonist Bevacizumab are increasingly added to standard therapy to prolong survival; however, little is known about the consequences of this policy in the perioperative period.

Methods: One hundred-two patients treated between 2005 and 2009, who received neoadjuvant chemotherapy combined with Bevacizumab (CHT + B) were identified. A cohort of 112 patients treated without chemotherapy alone before resection served as the control group (CHT). Complications were graded within an established staging system and the therapeutic consequences were laid down. Uni- and multivariate analysis of factors contributing to postoperative complications in the CHT + B group was performed using a logistic regression model.

Results: Postoperative complications occurred in 45 (44%, CHT + B) and 38 (34%, CHT) patients, respectively (P = 0.216). The incidence of severe complications requiring surgical or radiologic intervention or leading to organ failure was 10.8% in the CHT + B group and 7.1% in the CHT group (P = 0.350). Increased age, low serum albumin, resection of more than 3 liver segments and synchronous bowel procedures requiring an anastomosis were associated with an increased morbidity rate in the multivariate regression analysis. No patient died in either group.

Conclusions: The addition of Bevacizumab to standard chemotherapy before resection of colorectal liver metastases does not seem to increase postoperative morbidity. Caution should be given to extended resections >3 liver segments and synchronous bowel anastomoses.
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http://dx.doi.org/10.1097/SLA.0b013e3181deb67fDOI Listing
July 2010

Effect of polymer cross-links on oxygen diffusion in glassy PMMA films.

ACS Appl Mater Interfaces 2009 Mar;1(3):661-7

Center for Oxygen Microscopy and Imaging and Centre for DNA Nanotechnology, Department of Chemistry, University of Aarhus, Langelandsgade 140, Arhus, Denmark.

Oxygen diffusion coefficients, D, have been measured in poly(methyl methacrylate) (PMMA) films containing small amounts of a cinnamic acid derived cross-linker. In the technique employed, the time evolution of oxygen sorption into the film was monitored using the phosphorescence of singlet oxygen as a spectroscopic probe. Although the effect of adding up to 1 mol % of the cross-linker is clearly manifested in the molecular weight and T(g) of these samples, values of D are only moderately influenced. Nevertheless, a systematic decrease in the value of D is discernible as the extent of cross-linking is increased. Although it is reasonable to expect that, in a glassy polymer, cross-linking should not significantly perturb the local motions and confined changes in free volume that influence the translational motion of a small penetrant such as oxygen, our data indicate that even small amounts of a cross-linker can, nevertheless, have a noticeable and potentially meaningful effect. Although UV irradiation of the polymer films disrupts the cinnamic acid derived cross-linker via a [2 + 2] cycloreversion reaction, the photoinduced changes observed in D appear, rather, to reflect degradation reactions in the PMMA-based polymer.
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http://dx.doi.org/10.1021/am800197jDOI Listing
March 2009

Bevacizumab improves pathological response of colorectal cancer liver metastases treated with XELOX/FOLFOX.

Ann Surg Oncol 2010 Aug 23;17(8):2059-65. Epub 2010 Feb 23.

Department of General Surgery, Hepatobiliary Service, Medical University of Vienna, Vienna, Austria.

Background: Histological response of colorectal cancer liver metastases to chemotherapy may be graded based on the extent of tumor regression. The knowledge about the effect of bevacizumab, if given in addition to fluoropyrimidines and oxaliplatin, on tumor regression and its consequences on clinical outcome is limited.

Materials And Methods: Resected liver metastases from patients of 2 prospective nonrandomized trials (fluoropyrimidines and oxaliplatin +/- bevacizumab) were analyzed retrospectively. Histological response was analyzed according to an established tumor regression grading for colorectal cancer liver metastases. Tumor regression grades (TRGs) were correlated to progression-free and overall survival.

Results: Bevacizumab improved tumor regression to chemotherapy significantly. Improvement in histological response was translated into a significant prolongation of progression-free and overall survival.

Conclusions: Classifying histological response based on tumor regression grades qualifies to predict the outcome of patients with colorectal cancer liver metastases. Tumor regression grading provides a standardized pathological response evaluation, against which radiologic response on chemotherapy including biologicals can be prospectively evaluated.
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http://dx.doi.org/10.1245/s10434-010-0972-9DOI Listing
August 2010

Influence of hepatic resection margin on recurrence and survival in intrahepatic cholangiocarcinoma.

Ann Surg Oncol 2008 Oct 7;15(10):2787-94. Epub 2008 Aug 7.

Department of Surgery, Hepatobiliary Service, Medical University of Vienna, Waehringer Guertel 18-20, 1090, Vienna, Austria.

Background: Intrahepatic cholangiocarcinoma (ICC) is a rare disease in the Western world, hence little is known about its optimal surgical management. We analyzed whether hepatic resection margin is a prognostic factor for local or distant recurrence and survival in patients resected with curative intent.

Methods: Seventy-four patients underwent potentially curative surgery for ICC at our institution from 1994 to 2007. Demographic, and tumor- and surgery-related details including hepatic resection margin were recorded, patients were followed up for recurrence and survival. All patients were resected using modern dissection devices (CUSA or Waterjet).

Results: Fifty-nine patients (80%) underwent R0 resection, 15 (20%) had a resection margin greater than 10 mm (wide margin, WM) and 38 (51%) between 1 and 10 mm (close margin, CM). In 14 patients (19%), hepatic resection margin was involved on histological examination; perioperative mortalities were excluded from analysis (n = 7). Forty-seven patients developed recurrence (WM, CM, and R1): hepatic recurrence was observed in 40%, 58%, and 50% of patients; extrahepatic spread occurred in 27, 16, and 14%; and 33, 26, and 36% had no recurrence of disease so far (P = 0.755). There was no difference between groups regarding local versus disseminated hepatic recurrence. Median recurrence free survival was 11.4 months (WM), 9.8 months (CM), and 9.9 months (R1), respectively (P = 0.880). Median overall survival was 27.2 months (WM), 29.7 months (CM), and not reached in the R1 group, (P = 0.350).

Conclusion: Hepatic resection margin seems to play a minor role in the prognosis of ICC as long as complete tumor clearance can be achieved with a modern liver dissection technique.
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http://dx.doi.org/10.1245/s10434-008-0081-1DOI Listing
October 2008

Caspase-cleaved cytokeratin 18 and 20 S proteasome in liver degeneration.

J Clin Lab Anal 2007 ;21(5):277-81

Department of Anesthesiology and Intensive Care, General Hospital Vienna, Medical University of Vienna, Austria.

Apoptosis of epithelial hepatocytes plays a pivotal role in acute as well as in chronic liver diseases. The cleavage of cytokeratin-18 (CK-18) by caspases is an early event in the apoptotic process. We therefore sought to investigate serum levels of CK-18 and 20S proteasome in patients with liver cirrhosis, primary graft dysfunction (PDF), and acute liver failure (ALF), and in healthy volunteers. Enzyme-linked immunosorbent assay (ELISA) was utilized to measure the concentration of M30, a fragment of CK-18 cleaved at Asp396 (M30 neoantigen), and the concentration of 20S proteasome. Serum levels of the CK-18 neoepitope M30 were significantly increased in ALF, primary graft dysfunction, and liver cirrhosis vs. healthy controls (1,993.6+/-124.7 U/L, 2,238.1+/-235.9 U/L, and 673.6+/-86.5 U/L vs. 66.8+/-29.1 U/L, respectively, P<0.001). Similar results were detected with the evaluation of 20S proteasome (124,014.5+/-13,235.6 ng/mL, 76,993.2+/-15,720.1 ng/mL, and 2,395.9+/-1,098.2 ng/mL vs. 1,074.5+/-259.4 ng/mL, respectively; P<0.001). Detection of CK-18 neoepitope M30 and 20S proteasome may represent a novel marker of tracing apoptotic epithelium, respectively mirroring degenerative liver processes in affected patient population.
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http://dx.doi.org/10.1002/jcla.20180DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6648973PMC
December 2007

Inhibition of xenograft tumor growth and down-regulation of ErbB receptors by an antibody directed against Lewis Y antigen.

J Pharmacol Exp Ther 2006 Dec 8;319(3):1459-66. Epub 2006 Sep 8.

Institute of Pharmacology, Center of Biomolecular Medicine and Pharmacology, Medical University of Vienna, Waehringer Str. 13a, A-1090 Vienna, Austria.

The blood group-related Lewis Y antigen is expressed on the majority of human cancers of epithelial origin with only limited expression on normal tissue. Therefore, the Lewis Y antigen represents an interesting candidate for antibody-based treatment strategies. Previous experiments showed that the humanized Lewis Y-specific monoclonal antibody, IGN311, reduced ErbB-receptor-mediated stimulation of mitogen-activated protein kinase by altering receptor recycling. Here, we tested whether binding of IGN311 to growth factor receptors is relevant also to inhibition of tumor growth in vivo. Prolonged incubation with IGN311 of human tumor cell lines, which express high levels of ErbB1 (A431) or ErbB2 (SK-BR-3), resulted in down-regulation of the receptors and inhibition of cell proliferation. IGN311 inhibited the growth of tumors derived from A431 cells xenografted in nude mice. Treatment with IGN311 was associated with a down-regulation of ErbB1 in the excised tumor tissue. Importantly, these effects of IGN311 were also mimicked by the Fab fragment of IGN311. These data indicate that tumor cell growth inhibition by IGN311 cannot solely be accounted for by invoking cellular and humoral immunological mechanisms. A direct effect on signaling via binding to Lewis Y glycosylated growth factor receptors on tumor cells is also likely to contribute to the therapeutic effect of IGN311 in vivo.
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http://dx.doi.org/10.1124/jpet.106.107318DOI Listing
December 2006

Vaccination with cetuximab mimotopes and biological properties of induced anti-epidermal growth factor receptor antibodies.

J Natl Cancer Inst 2005 Nov;97(22):1663-70

Department of Pathophysiology, Medical University of Vienna, Vienna, Austria.

Background: The monoclonal antibody cetuximab (IMC-225, Erbitux) inhibits epidermal growth factor receptor (EGFR) signaling and has been approved for metastatic colon cancer therapy. However, to achieve effective titers, passive antibody therapies must be repeatedly administered over long periods. To overcome this limitation, we aimed to generate a vaccine inducing continuously available "cetuximab-like" antibodies in vivo using the mimotope approach.

Methods: We used the phage display technique to identify four peptides structurally mimicking the cetuximab epitope. We coupled two of these peptides to an immunogenic carrier protein, and we vaccinated four groups (n = 8) of BALB/c mice intraperitoneally with 10 microg of the mimotope conjugates, a control peptide conjugate, or the carrier protein alone. We assessed antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity mediated by the induced antibodies against EGFR-overexpressing human A431 carcinoma cells. We then tested receptor internalization capacity of the induced antibodies with fluorescently labeled EGFR, and we assayed their growth inhibitory potential toward A431 cells with a [3H]thymidine proliferation assay.

Results: Mimotope-induced antibodies recognized EGFR, and both types of antibody-mediated cytotoxic effects were elicited by these antibodies. In both cellular cytotoxicity assays, the mimotope-induced antibodies exhibited specific lysis of more than 50%. The induced antibodies caused internalization of the receptor from the cell surface into endocytic vesicles and inhibited growth of EGFR-expressing cells to a similar extent as cetuximab [67% (95% confidence interval {CI} = 55% to 79%) and 69% (95% CI = 55% to 84%), respectively].

Conclusions: Epitope-specific immunization is feasible for active anti-EGFR immunotherapy. The in vitro biologic features of mimotope-induced antibodies are similar to those of the monoclonal antibody cetuximab.
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http://dx.doi.org/10.1093/jnci/dji373DOI Listing
November 2005

Singlet oxygen microscope: from phase-separated polymers to single biological cells.

Acc Chem Res 2004 Nov;37(11):894-901

Department of Chemistry, University of Aarhus, DK-8000 Arhus, Denmark.

The lowest excited electronic state of molecular oxygen, singlet molecular oxygen (a1Deltag), is an intermediate in many chemical and biological processes. Tools and methods have been developed to create singlet-oxygen-based optical images of heterogeneous samples that range from phase-separated polymers to biological cells. Such images provide unique insight into a variety of oxygen-dependent phenomena, including the photoinitiated death of cells.
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http://dx.doi.org/10.1021/ar040075yDOI Listing
November 2004

Generation of Peptide mimics of the epitope recognized by trastuzumab on the oncogenic protein Her-2/neu.

J Immunol 2004 Jul;173(1):394-401

BioLife Science, and Department of Pathophysiology, Medical University of Vienna, Waehringer Guertel 18-20, A-1090 Vienna, Austria.

Immunizations with the oncogenic protein Her-2/neu elicit Abs exerting diverse biological effects--depending on epitope specificity, tumor growth may be inhibited or enhanced. Trastuzumab (herceptin) is a growth-inhibitory humanized monoclonal anti-Her-2/neu Ab, currently used for passive immunotherapy in the treatment of breast cancer. However, Ab therapies are expensive and have to be repeatedly administered for long periods of time. In contrast, active immunizations produce ongoing immune responses. Therefore, the study aims to generate peptide mimics of the epitope recognized by trastuzumab for vaccine formulation, ensuring the subsequent induction of tumor growth inhibitory Abs. We used the phage display technique to generate epitope mimics, mimotopes, complementing the screening Ab trastuzumab. Five candidate mimotopes were isolated from a constrained 10 mer library. These peptides were specifically recognized by trastuzumab, and showed distinctive mimicry with Her-2/neu in two experimental setups. Subsequently, immunogenicity of a selected mimotope was examined in BALB/c mice. Immunizations with a synthetic mimotope conjugated to tetanus toxoid resulted in Abs recognizing Her-2/neu in a blotted cell lysate as well as on the SK-BR-3 cell surface. Analogous to trastuzumab, the induced Abs caused internalization of the receptor from the cell surface to endosomal vesicles. These results indicate that the selected mimotopes are suitable for formulation of a breast cancer vaccine because the resulting Abs show similar biological features as trastuzumab.
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http://dx.doi.org/10.4049/jimmunol.173.1.394DOI Listing
July 2004

Antibodies directed against Lewis-Y antigen inhibit signaling of Lewis-Y modified ErbB receptors.

Cancer Res 2004 Feb;64(3):1087-93

Department of Surgery, University of Vienna, Vienna, Austria.

The majority of cancer cells derived from epithelial tissue express Lewis-Y (LeY) type difucosylated oligosaccharides on their plasma membrane. This results in the modification of cell surface receptors by the LeY antigen. We used the epidermal growth factor (EGF) receptor family members ErbB1 and ErbB2 as model systems to investigate whether the sugar moiety can be exploited to block signaling by growth factor receptors in human tumor cells (i.e., SKBR-3 and A431, derived from a breast cancer and a vulval carcinoma, respectively). The monoclonal anti-LeY antibody ABL364 and its humanized version IGN311 immunoprecipitated ErbB1 and ErbB2 from detergent lysates of A431 and SKBR-3, respectively. ABL364 and IGN311 blocked EGF- and heregulin-stimulated phosphorylation of mitogen-activated protein kinase [MAPK = extracellular signal-regulated kinase 1/2] in SKBR-3 and A431 cells. The effect was comparable in magnitude with that of trastuzumab (Herceptin) and apparently noncompetitive with respect to EGF. Stimulation of MAPK by ErbB was dynamin dependent and contingent on receptor internalization. ABL364 and IGN311 changed the intracellular localization of fluorescent EGF-containing endosomes and accelerated recycling of intracellular [(125)I]EGF to the plasma membrane. Taken together, these observations show that antibodies directed against carbohydrate side chains of ErbB receptors are capable of inhibiting ErbB-mediated signaling. The ability of these antibodies to reroute receptor trafficking provides a mechanistic explanation for their inhibitory action.
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http://dx.doi.org/10.1158/0008-5472.can-03-2435DOI Listing
February 2004

The human D2 dopamine receptor synergizes with the A2A adenosine receptor to stimulate adenylyl cyclase in PC12 cells.

Neuropsychopharmacology 2003 Jul 30;28(7):1317-27. Epub 2003 Apr 30.

Institute of Pharmacology, University of Vienna, A-1090 Wien, Austria.

The adenosine A(2A) receptor and the dopamine D(2) receptor are prototypically coupled to G(s) and G(i)/G(o), respectively. In striatal intermediate spiny neurons, these receptors are colocalized in dendritic spines and act as mutual antagonists. This antagonism has been proposed to occur at the level of the receptors or of receptor-G protein coupling. We tested this model in PC12 cells which endogenously express A(2A) receptors. The human D(2) receptor was introduced into PC12 cells by stable transfection. A(2A)-agonist-mediated inhibition of D(2) agonist binding was absent in PC12 cell membranes but present in HEK293 cells transfected as a control. However, in the resulting PC12 cell lines, the action of the D(2) agonist quinpirole depended on the expression level of the D(2) receptor: at low and high receptor levels, the A(2A)-agonist-induced elevation of cAMP was enhanced and inhibited, respectively. Forskolin-stimulated cAMP formation was invariably inhibited by quinpirole. The effects of quinpirole were abolished by pretreatment with pertussis toxin. A(2A)-receptor-mediated cAMP formation was inhibited by other G(i)/G(o)-coupled receptors that were either endogenously present (P(2y12)-like receptor for ADP) or stably expressed after transfection (A(1) adenosine, metabotropic glutamate receptor-7A). Similarly, voltage activated Ca(2+) channels were inhibited by the endogenous P(2Y) receptor and by the heterologously expressed A(1) receptor but not by the D(2) receptor. These data indicate functional segregation of signaling components. Our observations are thus compatible with the proposed model that D(2) and A(2A) receptors are closely associated, but they highlight the fact that this interaction can also support synergism.
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http://dx.doi.org/10.1038/sj.npp.1300181DOI Listing
July 2003

Removal of the carboxy terminus of the A2A-adenosine receptor blunts constitutive activity: differential effect on cAMP accumulation and MAP kinase stimulation.

Naunyn Schmiedebergs Arch Pharmacol 2002 Oct 28;366(4):287-98. Epub 2002 Aug 28.

Institute of Pharmacology, University of Vienna, 1090 Vienna, Austria.

The A(2A)-adenosine receptor has an extended carboxy terminus (approximately 120 amino acids), the role of which is poorly defined. In human endothelial cells and in HEK293 cells, the A(2A)-receptor controls at least two independent signalling pathways, i.e. increased cyclic adenosine 3',5'-monophosphate (cAMP) formation via its cognate G protein G(s) and increased phosphorylation of mitogen-activated protein kinase (MAP kinase) by recruiting p21(ras). In order to address the role of the carboxy terminus in signal transfer, we generated HEK293 cells that stably expressed the full-length (wt) receptor and truncated versions [A(2A)-R(1-360) and A(2A)-R(1-311)] at comparable levels (approximately 0.5 pmol/mg) in the plasma membrane. The effects of truncation were divergent with respect to the two effectors regulated by the receptor. In intact cells carrying A(2A)-R(wt) and A(2A)-R(1-360), cAMP accumulation was more potently activated by an A(2A)-agonist than in cells expressing A(2A)-R(1-311). Similarly, A(2A)-R(wt) and A(2A)-R(1-360)--but not A(2A)-R(1-311)--caused constitutive (=agonist-independent) elevation of cAMP which was reversed by the addition of A(2A)-antagonists. In membranes prepared from these cells, however, the three receptors displayed no constitutive activity in stimulating adenylyl cyclase and they did not differ in apparent agonist affinity. Truncation of the A(2A)-receptor did also not decrease the potency of an A(2A)-agonist to stimulate MAP kinase in intact cells. We conclude that the carboxy terminus defines both (a) the level of constitutive activity, i.e. the equilibrium R<--> R*, in intact cells only, indicating a role for a component that is lost upon cell lysis, and (b) the efficiency of signal transfer in alternative pathways.
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http://dx.doi.org/10.1007/s00210-002-0617-zDOI Listing
October 2002

MAP kinase stimulation by cAMP does not require RAP1 but SRC family kinases.

J Biol Chem 2002 Sep 24;277(36):32490-7. Epub 2002 Jun 24.

Institute of Pharmacology, University of Vienna, Währinger Strasse 13a, A-1090 Vienna, Austria.

The small G protein RAP1 and the kinase B-RAF have been proposed to link elevations of cAMP to activation of ERK/mitogen-activated protein (MAP) kinase. In order to delineate signaling pathways that link receptor-generated cAMP to the activation of MAP kinase, the human A(2A)-adenosine receptor, a prototypical G(s)-coupled receptor, was heterologously expressed in Chinese hamster ovary cells (referred as CHO-A(2A) cells). In CHO-A(2A) cells, the stimulation of the A(2A)-receptor resulted in an activation of RAP1 and formation of RAP1-B-RAF complexes. However, overexpression of a RAP1 GTPase-activating protein (RAP1GAP), which efficiently clamped cellular RAP1 in the inactive GDP-bound form, did not affect A(2A)-agonist-mediated MAP kinase stimulation. In contrast, the inhibitor of protein kinase A H89 efficiently suppressed A(2A)-agonist-mediated MAP kinase stimulation. Neither dynamin-dependent receptor internalization nor receptor-promoted shedding of matrix-bound growth factors accounted for A(2A)-receptor-dependent MAP kinase activation. PP1, an inhibitor of SRC family kinases, blunted both the A(2A)-receptor- and the forskolin-induced MAP kinase stimulation (IC(50) = 50 nm); this was also seen in PC12 cells, which express the A(2A)-receptor endogenously, and in NIH3T3 fibroblasts, in which cAMP causes MAP kinase stimulation. In the corresponding murine fibroblast cell line SYF, which lacks the ubiquitously expressed SRC family kinases SRC, YES, and FYN, forskolin barely stimulated MAP kinase; this reduction was reversed in cells in which c-SRC had been reintroduced. These findings show that activation of MAP kinase by cAMP requires a SRC family kinase that lies downstream of protein kinase A. A role for RAP1, as documented for the beta(2)-adrenergic receptor, is apparently contingent on receptor endocytosis.
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http://dx.doi.org/10.1074/jbc.M200556200DOI Listing
September 2002