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Biomedical subjects

Thomas Meyer

Publications and source records attributed to Thomas Meyer.

At least 55 records · Page 3Linked to original sources
PubMed2004

Epidemiology of HHV-8 infection in HIV-positive patients with and without Kaposi sarcoma: diagnostic relevance of serology and PCR.

BACKGROUND: Kaposi's sarcoma (KS) remains the most common neoplasm in HIV-infected patients. Human herpesvirus 8 (HHV-8) infection is etiologically associated with KS. Diagnostic procedures with regard to HHV-8 infection are not routinely performed in HIV-infected patients; diagnostic and prognostic value of HHV-8 serology or PCR are unknown in this setting. Epidemiological data concerning HHV-8 infection of HIV-infected patients in Germany are rare. OBJECTIVES: To assess prevalence of HHV-8 infection in a cohort of HIV-infected patients with and without KS in Germany and to correlate this to manifestations and clinical course of KS. STUDY DESIGN: HHV-8 serology was performed in 483 patients in routine care for HIV-infection in northern Germany. HHV-8 DNA was analyzed by PCR in peripheral blood mononuclear cells (PBMC) of 293 patients; in a subgroup multiple samples were analyzed. History and manifestations of KS were recorded. RESULTS: HHV-8 antibodies were detected using IFT in 91% of 33 patients with KS and 52% of 398 patients without KS. In 36 of 293 (12.3%) patients HHV-8 DNA was detected in PBMC. In general, HHV-8 DNA was not continuously detected when multiple samples from the same patient were analyzed. Patients with KS history were more likely to be PCR positive than those without (45.5% versus 7.8%). In patients with active KS HHV-8 DNA was detected more frequently than in patients with disease remission. HHV-8 DNA was not detected in serologically negative patients. However, three patients with KS history in full remission for several years were seronegative. CONCLUSIONS: HIV-infected patients were frequently found to be positive for HHV-8 antibodies. The number of patients positive for viral DNA in PBMC was much smaller. Single PCR-examinations were of little value for prognosis, but repeated detection of HHV-8 DNA represents an increased risk of disease activity.

Base Sequence↗
PubMed2004

In vivo antitumor activity of NVP-AEW541-A novel, potent, and selective inhibitor of the IGF-IR kinase.

IGF-IR-mediated signaling promotes survival, anchorage-independent growth, and oncogenic transformation, as well as tumor growth and metastasis formation in vivo. NVP-AEW541 is a pyrrolo[2,3-d]pyrimidine derivative small molecular weight kinase inhibitor of the IGF-IR, capable of distinguishing between the IGF-IR (IC50 = 0.086 microM) and the closely related InsR (IC50 = 2.3 microM) in cells. As expected for a specific IGF-IR kinase inhibitor, NVP-AEW541 abrogates IGF-I-mediated survival and colony formation in soft agar at concentrations that are consistent with inhibition of IGF-IR autophosphorylation. In vivo, this orally bioavailable compound inhibits IGF-IR signaling in tumor xenografts and significantly reduces the growth of IGF-IR-driven fibrosarcomas. Thus, NVP-AEW541 represents a class of selective, small molecule IGF-IR kinase inhibitors with proven in vivo antitumor activity and potential therapeutic application.

3T3 Cells↗
PubMed2004

QT-screen: high-throughput cardiac safety pharmacology by extracellular electrophysiology on primary cardiac myocytes.

Cardiac safety pharmacology focuses mostly on the drug-induced prolongation of the QT interval in the electrocardiogram. A prolonged QT interval is an important indicator for an increased risk of severe ventricular arrhythmia. Guidelines demand safety tests addressing QT prolongation in vitro and in vivo before a drug enters clinical trials. If safety risks will be detected not until an advanced stage of preclinical drug development, a considerable sum of money has already been invested into the drug development process. To prevent this, high-throughput systems have been developed to obtain information on the potential toxicity of a substance earlier. We will discuss in this publication that the QT-Screen system, which is based on primary cardiac myocytes, is able to provide a sufficient throughput for secondary screening. With this system, extracellular field potentials can be recorded from spontaneously beating cultures of mammalian or avian ventricular cardiac myocytes simultaneously on 96 channels. The system includes software-controlled and automated eight-channel liquid handling, data acquisition, and analysis. These features allow a user-friendly and unsupervised operation. The throughput is over 100 compounds in six replicates and with full dose-response relationships per day. This equals a maximum of approximately 6,000 data points per day at an average cost for consumables of 0.20 US pennies (U.S.) per data point. The system is intended for a non-good laboratory practice-compliant screening; however, it can be adapted to be used in a good laboratory practice environment.

Action Potentials↗
PubMed2004

Low-dose immunosuppression reduces the incidence of post-transplant lymphoproliferative disease in pediatric liver graft recipients.

OBJECTIVES: In pediatric solid organ transplantation, the Epstein-Barr virus (EBV)-related lymphoproliferative disorders (PTLD) still play a major role in post-transplant morbidity and mortality. The aim of the study was to determine the incidence of PTLD in pediatric patients with liver transplant who receive low-dose immunosuppression protocols. METHODS: All pediatric patients (n = 269) received a dual immunosuppression therapy consisting of cyclosporine A (initial trough levels, 170-200 microg/L; trough levels for maintenance immunosuppression after 1 year, 80-100 microg/L) and prednisolone (starting dose, 60 mg/m2). Steroids were reduced to 30 mg/m2 after 1 week, followed by a weekly tapering to 5 mg/m2. Seventy-seven of 269 patients were switched to tacrolimus therapy. The authors evaluated the significance of EBV-DNA monitoring by quantitative polymerase chain reaction in identifying patients at risk for PTLD. RESULTS: Patient survival was 90.3%; graft survival was 85.9%. Eight patients lost their grafts because of chronic rejection. The incidence of PTLD was low (0.7%), although a significant EBV viral load was found in 42.4% of the patients. One third of the patients with a viral load of 3,000 genomes/10(5) cells or greater had clinical signs of EBV infection. CONCLUSIONS: The authors conclude that low-dose immunosuppressive protocols significantly reduce the incidence of PTLD. In patients treated with that regimen, the monitoring of EBV viral load seems not to be helpful. It can be assumed that low-dose immunosuppression does not suppress EBV-specific cytotoxic CD8+ T cells, thus allowing the host to control EBV infection without the risk of PTLD. Our low-dose immunosuppression protocol did not increase the risk of chronic rejection.

Adolescent↗
PubMed2004

Confusion by frequent changes in staging of exocrine pancreatic carcinoma.

OBJECTIVES: The TNM/pTNM classification of anatomic extent before treatment is the strongest predictor of outcome in exocrine pancreatic carcinoma. Frequent changes in staging, published by the UICC in 1987, 1997, and 2002, lead to considerable problems. METHODS: The data on 272 patients with resection of a pancreatic ductal adenocarcinoma between 1978 and 1997 were analyzed. RESULTS: Two hundred sixty-five tumors were assigned to a higher pT category in 1997. Of them, 70 were reassigned to a lower pT category in 2002. No patient fulfilled the criteria of pT4 in 2002. Eighty-seven tumors were assigned to a higher pathologic stage in 1997. In 2002, 151 tumors were assigned to a lower pathologic stage. No patient was assigned to pathologic stage III. The staging systems of 1987 and 1997 are able to identify subgroups of patients with superior prognosis. The staging system of 2002 includes the same 12 patients in stage I as the classification of 1997. However, stage II contains an inhomogeneous group of 193 patients with poor prognosis. CONCLUSIONS: Changes in the TNM classification require a conversion of the data. Analysis and comparison of published results are very difficult and sometimes impossible if classification systems change too often. The present classification is well qualified for treatment choice and gives good information on prognosis after resection. It should be unchanged for at least 10 years.

Adult↗
PubMed2004

Nucleocytoplasmic shuttling of STAT transcription factors.

The signal transducer and activator of transcription (STAT) proteins have initially been described as cytoplasmic proteins that enter the nucleus only after cytokine treatment of cells. Contrary to this assumption, it was demonstrated that STATs are constantly shuttling between nucleus and cytoplasm irrespective of cytokine stimulation. This happens both via carrier-dependent as well as carrier-independent transportation. Moreover, it was also recognized that cytokine stimulation triggers nuclear retention of dimeric STATs, rather than affecting the rate of nuclear import. In summary, it is increasingly being appreciated that STAT nucleocytoplasmic cycling determines the quality of cytokine signaling and also constitutes an important area for microbial intervention.

Biological Transport↗
PubMed2004

Human papillomaviruses in transplant-associated skin cancers.

BACKGROUND: Human papillomavirus (HPV) infection has been suggested to be involved in the development of nonmelanoma skin cancer, the most common malignancy after solid-organ transplantation. OBJECTIVE: The objective of this study was to analyze the prevalence of different HPV types in squamous cell carcinomas (SCC) and basal cell carcinomas (BCC) of transplant recipients and nonimmunosuppressed patients. METHODS: To include the complete spectrum of HPV types in skin lesions, a comprehensive polymerase chain reaction assay with five different primer combinations was used. RESULTS: For SCC, HPV DNA was detected more frequently in tumors of transplant recipients (12/16, 75%) than of nonimmunosuppressed patients (7/19, 37%). In contrast, the HPV detection rate was similar in BCC specimens (4/8 or 50% in transplanted patients; 27/56 or 48% in nonimmunosupressed patients). Overall, 22 different HPV types were identified. HPV types 5 and 8 were detected predominately in SCC from transplant recipients. The amount of viral DNA was slightly higher in SCC of transplanted than in nonimmunosuppressed patients, but much lower than in both cutaneous and genital warts. CONCLUSIONS: Cutaneous infections with HPV5 and HPV8 may represent an increased risk for SCC development in transplant recipients. The mechanisms by which these viruses may contribute to skin cancer development still remain unclear.

Adult↗
PubMed2004

Human papillomavirus and overexpression of P16INK4a in nonmelanoma skin cancer.

BACKGROUND: P16INK4a overexpression has been identified as a specific biomarker in high-risk human papillomavirus (HPV)-infected cervical (pre)cancer lesions. OBJECTIVE: To evaluate the overexpression of this cyclin-dependent kinase inhibitor in skin tumors depending on HPV infections, we analyzed normal skin, benign skin disease, and skin cancer specimens. METHODS: Biopsies of 23 patients with normal histology (3), psoriasis (2), verrucae vulgaris (2), actinic keratoses (5), squamous cell carcinoma (SCC) in situ (3), Bowen's carcinoma (1), and SCC (7) were analyzed. Specimens of 23 patients were immunostained using the monoclonal antibody E6H4 specific for p16INK4a. HPV status was assessed by a polymerase chain reaction (PCR) system to detect all currently known HPV types. MY (MY09/MY11 and MYN9/MYN10)-, CP (CP65/CP70 and CP66/CP69)-nested PCR, and three single PCR methods CN1, CN3, and CN4 were used in a first step, and HPV typing was performed by restriction fragment length polymorphism analysis. Only beta-globin-positive patients were included in this study. RESULTS: HPV DNA was detected in all actinic keratoses, SCC in situ, Bowen's carcinoma, and SCC, in 50% (one of two) of verrucae vulgaris, in 66% (two of three) of normal skin, and in none of two psoriasis. P16INK4a expression was not detected in normal skin, psoriasis, and verrucae vulgares. Overexpression of p16INK4a was detected in a subset of dysplastic cells (10% to 80%) of all skin (pre)cancer lesions such as actinic keratoses, SCC in situ, Bowen's carcinoma, and SCC infected with HPV independent of sun exposure. CONCLUSION: P16INK4a appears to be overexpressed in a portion of dysplastic cells from actinic keratoses and SCC. Further studies to examine the association of HPV infection and the overexpression of p16INK4a are warranted.

Aged↗
PubMed2004

Micro-electrode arrays in cardiac safety pharmacology: a novel tool to study QT interval prolongation.

Drug-induced QT interval prolongation is now a major concern in safety pharmacology. Regulatory authorities such as the US FDA and the European Medicines Agency require in vitro testing of all drug candidates against the potential risk for QT interval prolongation prior to clinical trials. Common in vitro methods include organ models (Langendorff heart), conventional electrophysiology on cardiac myocytes, and heterologous expression systems of human ether-a-go-go-related gene (hERG) channels. A novel approach is to study electrophysiological properties of cultured cardiac myocytes by micro-electrode arrays (MEA). This technology utilises multi channel recording from an array of embedded substrate-integrated extracellular electrodes using cardiac tissue from the ventricles of embryonic chickens. The detected field potentials allow a partial reconstruction of the shape and time course of the underlying action potential. In particular, the duration of action potentials of ventricular myocytes is closely related to the QT interval on an ECG. This novel technique was used to study reference substances with a reported QT interval prolonging effect. These substances were E4031, amiodarone, quinidine and sotalol. These substances show a significant prolongation of the field potential. However, verapamil, a typical 'false positive' when using the hERG assay does not cause any field potential prolongation using the MEA assay. Whereas the heterologous hERG assay limits cardiac repolarisation to just one channel, the MEA assay reflects the full range of mechanisms involved in cardiac action potential regulation. In summary, screening compounds in cardiac myocytes with the MEA technology against QT interval prolongation can overcome the problem of a single cell assay to potentially report 'false positives'.

Action Potentials↗
PubMed2004

[Dramatic increase in lymphogranuloma venereum among homosexual men in Hamburg].

Classical sexually transmitted diseases, including syphilis and gonorrhea, have recently increased significantly among homosexual men in Hamburg. During the last year we also observed an increase in patients with lymphogranuloma venereum (LGV) at the ifi-institute in Hamburg. In 2003, we identified 4 homosexual patients with LGV in different clinical stages. None of the patients has traveled outside Germany. Three of these patients were HIV-infected. In all cases Chlamydia trachomatis was identified by SDA (strand displacement amplification) in genital swabs or lymph node aspirates. In three cases sequencing of ompA PCR products was performed and in each instance revealed the C. trachomatis serovar L2. Other important genital pathogens were excluded by specific PCR tests, bacteriological and serological tests. LGV should be included in the differential diagnosis of anogenital and oral erosions, especially in homosexual patients and HIV-infected patients. Novel nucleic acid amplification tests can be used for the rapid and reliable diagnosis of LGV by identifying Chlamydia trachomatis.

Adult↗
PubMed2003

Coupling to Gs and G(q/11) of histamine H2 receptors heterologously expressed in adult rat atrial myocytes.

The predominant histamine receptor subtype in the supraventricular and ventricular tissue of various mammalian species is the H2 receptor (H2-R) subtype, which is known to couple to stimulatory G proteins (Gs), i.e. the major effects of this autacoid are an increase in sinus rate and in force of contraction. To investigate histamine effects in H2-R-transfected rat atrial myocytes, endogenous GIRK currents and L-type Ca2+ currents were used as functional assays. In H2-R-transfected myocytes, exposure to His resulted in a reversible augmentation of L-type Ca2+ currents, consistent with the established coupling of this receptor to the Gs-cAMP-PKA signalling pathway. Mammalian K+ channels composed of GIRK (Kir3.x) subunits are directly controlled by interaction with betagamma subunits released from G proteins, which couple to seven-helix receptors. In mock-transfected atrial cardiomyocytes, activation of muscarinic K+ channels (IK(ACh)) was limited to Gi-coupled receptors (M2R, A1R). In H2-R-overexpressing cells, histamine activated IK(ACh) via Gs-derived betagamma subunits since the histamine-induced current was insensitive to pertussis toxin. These data indicate that overexpression of Gs-coupled H2-R results in a loss of target specificity due to an increased agonist-induced release of Gs-derived betagamma subunits. When IK(ACh) was maximally activated by GTP-gamma-S, histamine induced an irreversible inhibition of the inward current in a fraction of H2-R-transfected cells. This inhibition is supposed to be mediated via a G(q/11)-PLC-mediated depletion of PIP2, suggesting a partial coupling of overexpressed H2-R to G(q/11). Dual coupling of H2-Rs to Gs and Gq is demonstrated for the first time in cardiac myocytes. It represents a novel mechanism to augment positive inotropic effects by activating two different signalling pathways via one type of histamine receptor. Activation of the Gs-cAMP-PKA pathway promotes Ca2+ influx through phosphorylation of L-type Ca2+ channels. Simultaneous activation of Gq-signalling pathways might result in phosphoinositide turnover and Ca2+ release from intracellular stores, thereby augmenting H2-induced increases in [Ca2+]i.

Animals↗
PubMed2003

Identification of a new chemical class of potent angiogenesis inhibitors based on conformational considerations and database searching.

The vascular endothelial growth factor (VEGF) tyrosine kinase receptors KDR and Flt-1 are targets of current interest in anticancer drug research. PTK787/ZK222584 is a potent inhibitor of these enzymes in clinical evaluation as an antiangiogenic agent. The development of a hypothesis concerning the bioactive conformation of this compound has led to the discovery of a new class of potent inhibitors of KDR and Flt-1, the anthranilamides. This could be achieved with a limited experimental effort, which only involved the testing of one archive compound and the synthesis and testing of one appropriate analogue.

Angiogenesis Inhibitors↗
PubMed2003

Biological application of microelectrode arrays in drug discovery and basic research.

Electrical activity of electrogenic cells in neuronal and cardiac tissue can be recorded by means of microelectrode arrays (MEAs) that offer the unique possibility for non-invasive extracellular recording from as many as 60 sites simultaneously. Since its introduction 30 years ago, the technology and the related culture methods for electrophysiological cell and tissue assays have been continually improved and have found their way into many academic and industrial laboratories. Currently, this technology is attracting increased interest owing to the industrial need to screen selected compounds against ion channel targets in their native environment at organic, cellular, and sub-cellular level. As the MEA technology can be applied to any electrogenic tissue (i.e., central and peripheral neurons, heart cells, and muscle cells), the MEA biosensor is an ideal in vitro system to monitor both acute and chronic effects of drugs and toxins and to perform functional studies under physiological or induced pathophysiological conditions that mimic in vivo damages. By recording the electrical response of various locations on a tissue, a spatial map of drug effects at different sites can be generated, providing important clues about a drug's specificity. In this survey, examples of MEA biosensor applications are described that have been developed for drug screening and discovery and safety pharmacology in the field of cardiac and neural research. Additionally, biophysical basics of recording and concepts for analysis of extracellular electrical signals are presented.

Action Potentials↗
PubMed2003

DNA binding controls inactivation and nuclear accumulation of the transcription factor Stat1.

Cytokine-dependent gene transcription greatly depends on the tyrosine phosphorylation ("activation") of Stat proteins at the cell membrane. This rapidly leads to their accumulation in the nucleus by an unknown mechanism. We performed microinjections of recombinant Stat1 protein to show that nuclear accumulation of phosphorylated Stat1 can occur without cytokine stimulation of cells. Microinjection of Stat1 antibody and treatment of cells with kinase or phosphatase inhibitors revealed that nuclear accumulation is a highly dynamic process sustained by Stat1 nucleocytoplasmic cycling and continuous kinase activity. By characterizing nuclear accumulation mutants, it is demonstrated that nuclear import and nuclear retention are two separate steps leading up to nuclear accumulation, with nonspecific DNA binding of activated Stat1 being sufficient for nuclear retention. Critical for nuclear buildup of Stat1 and the subsequent nuclear export is the point of time of tyrosine dephosphorylation, because our data indicate that activated Stat1 is incapable of leaving the nucleus and requires dephosphorylation to do so. It is demonstrated that the inactivation of Stat1 is controlled by its exchange reaction with DNA, whereby DNA binding protects Stat1 from dephosphorylation in a sequence-specific manner. Thus, during nuclear accumulation, a surprisingly simple mechanism integrates central aspects of cytokine-dependent gene regulation, for example, receptor monitoring, promoter occupancy, and transcription factor inactivation.

Active Transport, Cell Nucleus↗
PubMed2003

Differential regulation of 5' splice variants of the glutamate transporter EAAT2 in an in vivo model of chemical hypoxia induced by 3-nitropropionic acid.

Defective glutamate uptake has been implicated as a pathogenic event of neuronal damage related to cerebral ischemia and hypoxia. In several models of ischemia-hypoxia, a reduced immunoreactivity and altered RNA expression of excitatory amino acid transporter 2 (EAAT2), the major excitatory amino acid transporter, have been reported. However, the gene regulation of EAAT2 under these conditions is incompletely understood. In this study, we investigated alternative splicing of EAAT2 in an in vivo mouse model of chemical hypoxia as induced by 3-nitropropionic acid (3-NP). The neurotoxin 3-NP is an inhibitor of mitochondrial energy production. Furthermore, it is known to inhibit glutamate reuptake directly, representing at least one of the mechanisms responsible for 3-NP-induced neurodegeneration. Here we report an expression analysis of five known (mEAAT2/5UT1-5) and two novel (mEAAT2/5UT6, -7) 5' splice variants of EAAT2 using semiquantitative PCR. The RNA expression was studied at 2, 12, 24, 48, and 72 hr and 7 days after 3-NP administration. mEAAT2/5UT4 and mEAAT2/5UT5 were up-regulated in the frontal cortex and down-regulated in the hippocampus 12-72 hr after chemical hypoxia. In the cerebellum, there was an increased expression of mEAAT2/5UT4 and a down-regulation of mEAAT2/5UT5. mEAAT2/5UT3 show a different regional expression pattern, being regulated in the cerebellum only. mEAAT2/5UT1-7 encoded distinct 5' regulatory sequences, including conserved elements of translational control. It is easily conceivable that expression alterations of 5' splice variants of EAAT2 are related to glutamate transporter malfunction after chemical hypoxia. Our findings contribute to the hypothesis that RNA splicing events can serve as a molecular mechanism of posthypoxic gene regulation.

Alternative Splicing↗
PubMed2003

Association of human papillomavirus infections with cutaneous tumors in immunosuppressed patients.

Besides immunosuppression and UV radiation, human papillomavirus (HPV) infection was also suggested to be involved in the development of non-melanoma skin cancer, the most common malignancy after transplantation. In this study we used a comprehensive PCR assay to analyze the prevalence of individual HPV types in different skin lesions from transplant and non-transplant patients. HPV DNA was detected more frequently in squamous cell carcinomas (SCCs) of transplant recipients (75%) than the same lesion was in non-immunosuppressed patients (47%). Similar HPV prevalences were found in cutaneous warts (91% vs 94%), pre-malignant skin tumors (38% vs 36%), and normal skin specimens (17% vs 16%) of both patient populations. Overall, more than 40 different HPV types were identified. HPV types 5 and 8 were found more frequently in SCCs (26%) than in pre-cancerous (5%) or benign lesions (1%). All HPV 5- and HPV 8-positive SCCs were from immunosuppressed patients, indicating that infection with HPV 5 and HPV 8 may present an increased risk of SCC development in these patients.

Base Sequence↗