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Biomedical subjects

T Meyer

Publications and source records attributed to T Meyer.

At least 127 records · Page 7Linked to original sources
PubMed2001

Resistance analyses in HIV infected patients with a history of multiple antiretroviral treatment regimens.

OBJECTIVE: To assess HIV-1 isolate based resistance profiles from extensively pretreated patients and effects of a resistance guided switch of antiretroviral therapy. METHODS: In a prospective study phenotypic and genotypic resistance analyses were performed on HIV infected individuals with failure of the current therapy and history of at least three antiretroviral regimens. Antiretroviral therapy was changed according to the results. Viral load and CD4 lymphocyte counts were measured at baseline, after 10 (SD 2), and 24 (2) weeks. RESULTS: All patients (n=52) failed their actual regimen. Currently versus ever previously taking the specific drug, resistance associated mutations and phenotypic resistance to AZT and 3TC were found in over 80% of individuals; resistance to DDI and D4T was detected in less than 10% of cases. A resistance guided switch of therapy was followed by a median decrease of viral load of 0.5 log10 units after 24 weeks. Individuals resistant to two or more drugs compared with patients with resistance to less than two drugs of ongoing treatment, were switched to a regimen containing DDI, D4T, and a PI or NNRTI. After 10 (SD 2) weeks viral load decrease was pronounced in patients with resistance to at least two drugs in the previous regimen. CONCLUSIONS: Among different RTI, the profile of clinically relevant resistance indicates pronounced differences when looking at separate drugs. Regarding virological response, in the context of available drugs, resistance tested with currently used methods is of limited value in extensively pretreated patients and seems to have its value primarily in first or second switch of therapy.

Adult↗
PubMed2001

Purification and properties of human melanoma cell tissue factor.

Tissue factor (TF) is a transmembrane glycoprotein that acts as a receptor for nonactivated and activated factor VII (FVII) and triggers the coagulation cascade. TF plays an important role in hemostasis, but may also have noncoagulation functions in vascular development, angiogenesis, and tumor cell metastasis. In tumor cells, analysis of the role of TF has been hampered by the lack of purified TF. In this study, TF antigen was identified on human A375 malignant melanoma cells using flow cytometry. We further purified TF apoprotein 2,000-fold to homogeneity from A375 melanoma cells using immunoaffinity chromatography. On SDS-polyacrylamide gel electrophoresis under reduction, purified TF apoprotein gave two major protein bands corresponding to molecular weights of 53 and 34 to 36 KD. The identity of these forms of TF was confirmed by Western blotting using a polyclonal antibody against human brain TF. Under reduction, the TF antibody bound with a monomeric form of TF (53 KD), and without reduction, to several forms of TF (34 to 128 KD). Preliminary carbohydrate analysis suggested that TF is a glycoprotein and contains about 22% total carbohydrates. The coagulant activity of the purified apoprotein was reconstituted by the addition of phospholipids. The effects of varying concentrations (0 to 8 microg) of polyclonal antibodies to TF and FVII on TF procoagulant activity were studied. Both antibodies inhibited more than 70% of the procoagulant activity of TF in an FX activation assay. The complex formation between purified TF apoprotein and FVIIa was demonstrated by using an enzyme-linked immunosorbent assay. TF formed a complex with FVIIa in a concentration-dependent and saturable manner. We conclude that in human melanoma cells, TF occurs in monomeric and heterodimeric forms and appears to have similar properties as reported for TF from other sources.

Antibodies↗
PubMed2001

Synthesis and antibacterial activity of 5- and 6-hydroxy substituted 4-aminoquinolines and derivatives.

The synthesis and antimicrobial activity of 4-amino-8-methylquinolines 8, 11 substituted with a hydroxy- or methoxy-group at 5- and at 6-position have been investigated. The title compounds could be prepared by a six-step procedure according to the literature starting from commercially available anilines 1. The novel 4-aminoquinolines 8,11 exhibited slight antibacterial activity against Gram-positive and Gram-negative bacteria.

Anti-Bacterial Agents↗
PubMed2001

Flow analysis in vascular shunts that bypass the carotid artery.

When blood flow through a carotid artery is impaired and vascular surgery is necessary to restore adequate circulation a vascular shunt can be applied to maintain cerebral blood flow. Several vascular shunts are commercially available, but there is only limited test data on their flow capacity. The purpose of this study is to determine the flow capacity of three vascular shunt systems. A theoretical model has been developed for this purpose. To validate the model, in vitro flow measurements were taken. Application of the model showed that all shunts cause a decrease in blood flow. The amount of flow decrease varied widely from 13% (Javid shunt) to 55% (Pruitt-Inahara). In vitro measurements confirmed the validity of the model. In conclusion, it is important for the vascular surgeon to realise that vascular shunts show large differences in flow capacity. Of the three investigated shunts, the Javid has the highest flow capacity.

Arteriovenous Shunt, Surgical↗
PubMed2001

[Biophysical basics of aerosol therapy in bronchial asthma].

For an effective inhalation therapy with aerosols the drug itself but also the inhalation device have to be considered. Several biophysical parameters influence the deposition in different regions of the respiratory tract. Particle size and the breathing pattern of the patient are the most important factors and have to be considered.

Aerosols↗
PubMed2001

[Regional chemotherapy--perfusion of the extremities].

Hyperthermic isolated limb perfusion with cytostatic drugs (HILP) is indicated in locoregional recurrences of malignant melanoma of the limbs. As a neoadjuvant treatment it is also used for non-curatively resectable soft tissue sarcoma or their recurrences on the extremities. Up to now, melphalan is still the standard drug in HILP for malignant melanoma. With melphalan, complete response can be achieved in 65-80% for clinically detectable in transit metastases (+/- regional lymph node metastases). The combination of tumor necrosis factor (TNF) alpha with melphalan has considerably improved response rates of HILP in sarcoma. In more than 80% of the patients the otherwise necessary amputation of the limb can be avoided. The combination of TNF with other drugs than melphalan could possibly further improve results of HILP in sarcoma patients. The high rate of local recurrences of malignant melanoma after HILP poses an unsolved problem yet.

Antineoplastic Agents↗
PubMed2001

Highly efficient isolation of porcine islets of Langerhans for xenotransplantation: numbers, purity, yield and in vitro function.

UNLABELLED: Xenogeneic transplantation of porcine islets of Langerhans is regarded as a potential future treatment for diabetes mellitus. Despite considerable biotechnological progress, however, it is still very difficult and often unreliable to isolate sufficient numbers of highly purified, intact islets from the porcine pancreas with good in vitro function. OBJECTIVE: Of this study was to describe an efficient and reliable method to isolate sufficient numbers of highly purified islets of Langerhans with good in vitro function from adult as well as from young hybrid pigs. METHODS: Islets were isolated from the pancreas of young (4-6 months) hybrid pigs and old (2-3 years) retired breeders using Liberase PI and digestion-filtration. Average islet size was detected by dithizone staining of tissue sections prior to isolation; only organs with an average islet size > or = 200 microns were used. Density gradient purification with OptiPrep was performed in a COBE 2991 cell processor. Viability was investigated using fluorescence staining. Perifusion studies were carried out to asses in vitro function of isolated islets. RESULTS: Islets were successfully isolated from young hybrid pigs (3,671 +/- 598 IEQ/g) and old retired breeders (5,182 +/- 545 IEQ/g). After purification islet purity was 92% for retired breeders and 87% for young hybrid pigs. Yield after purification was still not satisfactory: 64% for retired breeders (3,209 +/- 444 IEQ/g) and 44% for young hybrid pigs (1,669 +/- 386 IEQ/g). Viability of isolated islets was 80-95%. Perifusion studies of porcine islets showed sufficient insulin release upon glucose challenge; however, the level of insulin release depended on the density of islets within the perifusion chamber. Low temperature culture (24 degrees C) prior to perifusion studies had no detrimental effect on insulin release. Long-term culture over 11 days was followed by a dramatic loss of islet function. CONCLUSIONS: If xenograft rejection can be overcome and the risk of xenosis can be minimised, sufficient numbers of purified porcine islets with good in vitro function can be isolated to serve as a potential source for islet transplantation in diabetic patients.

Animals↗
PubMed2001

Importance of human papillomaviruses for the development of skin cancer.

The frequent detection of HPV DNA in non-melanoma skin cancers was shown in several studies; however, the role of HPV in the development of these cancers remains speculative. We analyzed different skin tumors, normal skin, and hair follicles for HPV DNA using a PCR system designed to detect all HPV types known so far. HPV DNA was found in 93% of common warts, 69% of squamous cell carcinomas (SCC), 52% of basal cell carcinomas (BCC), 41% of actinic keratoses, 31% of extragenital Bowen's disease, 22% of keratoacanthomas, 16% of normal skin tissues and 47% of hair follicles. No individual HPV type predominated in any of the skin tumors. The number of HPV genomes in individual neoplasms (SCC and BCC) seems to be less than I per cancer cell. These results indicate that a direct role of HPV in skin cancerogenesis remains questionable. Possibly, mechanisms different from the activity of HPV oncoproteins in genital cancers are involved in skin neoplastic transformation.

Adolescent↗
PubMed2000

Localized biphasic changes in phosphatidylinositol-4,5-bisphosphate at sites of phagocytosis.

Phagocytosis requires localized and transient remodeling of actin filaments. Phosphoinositide signaling is believed to play an important role in cytoskeletal organization, but it is unclear whether lipids, which can diffuse along the membrane, can mediate the focal actin assembly required for phagocytosis. We used imaging of fluorescent chimeras of pleckstrin homology and C1 domains in live macrophages to monitor the distribution of phosphatidylinositol-4,5-bisphosphate (4,5-PIP(2)) and diacylglycerol, respectively, during phagocytosis. Our results reveal a sequence of exquisitely localized, coordinated steps in phospholipid metabolism: a focal, rapid accumulation of 4,5-PIP(2) accompanied by recruitment of type Ialpha phosphatidylinositol phosphate kinase to the phagosomal cup, followed by disappearance of the phosphoinositide as the phagosome seals. Loss of 4,5-PIP(2) correlated with mobilization of phospholipase Cgamma (PLCgamma) and with the localized formation of diacylglycerol. The presence of 4, 5-PIP(2) and active PLCgamma at the phagosome was shown to be essential for effective particle ingestion. The temporal sequence of phosphoinositide metabolism suggests that accumulation of 4,5-PIP(2) is involved in the initial recruitment of actin to the phagocytic cup, while its degradation contributes to the subsequent cytoskeletal remodeling.

Actins↗
PubMed2000

Neurologic outcome of controlled compressed-air diving.

The authors compared the neurologic, neuropsychological, and neuroradiologic status of military compressed-air divers without a history of neurologic decompression illness and controls. No gross differences in the neuropsychometric test results or abnormal neurologic findings were found. There was no correlation between test results, diving experience, and number and size of cerebral MRI lesions. Prevalence of cerebral lesions was not increased in divers. These results suggest that there are no long-term CNS sequelae in military divers if diving is performed under controlled conditions.

Adult↗
PubMed2000

Spatial sensing in fibroblasts mediated by 3' phosphoinositides.

The directed movement of fibroblasts towards locally released platelet-derived growth factor (PDGF) is a critical event in wound healing. Although recent studies have implicated polarized activation of phosphoinositide (PI) 3-kinase in G protein-mediated chemotaxis, the role of 3' PI lipids in tyrosine kinase-triggered chemotaxis is not well understood. Using evanescent wave microscopy and green fluorescent protein-tagged Akt pleckstrin homology domain (GFP-AktPH) as a molecular sensor, we show that application of a shallow PDGF gradient triggers a markedly steeper gradient in 3' PI lipids in the adhesion zone of fibroblasts. Polar GFP-AktPH gradients, as well as a new type of radial gradient, were measured from front to rear and from the periphery to the center of the adhesion zone, respectively. A strong spatial correlation between polarized 3' PI production and rapid membrane spreading implicates 3' PI lipids as a direct mediator of polarized migration. Analysis of the temporal changes of 3' PI gradients in the adhesion zone revealed a fast diffusion coefficient (0.5 microm(2)/s) and short lifetime of 3' PIs of <1 min. Together, this study suggests that the tyrosine kinase-coupled directional movement of fibroblasts and their radial membrane activity are controlled by local generation and rapid degradation of 3' PI second messengers.

3T3 Cells↗
PubMed2000

Depletion of phosphatidylinositol 4,5-bisphosphate by activation of phospholipase C-coupled receptors causes slow inhibition but not desensitization of G protein-gated inward rectifier K+ current in atrial myocytes.

G protein-gated inwardly rectifier K+ current in atrial myocytes (I(K(ACh))) upon stimulation with acetylcholine (ACh) shows a fast desensitizing component (t(1/2) approximately 5 s). After washout of ACh, I(K(ACh)) recovers from fast desensitization within < 30 s. A recent hypothesis suggests that fast desensitization is caused by depletion of phosphatidylinositol 4,5-bisphosphate (PtIns(4,5)P(2)), resulting from costimulation of phospholipase C (PLC)-coupled M3 receptors (M3AChR). The effects of stimulating two established PLC-coupled receptors, alpha-adrenergic and endothelin (ET(A)), on I(K(ACh)) were studied in rat atrial myocytes. Stimulation of these receptors caused activation of I(K(ACh)) and inhibition of the M2AChR-activated current. In myocytes loaded with GTPgammaS (guanosine 5'-3-O-(thio)triphosphate), causing stable activation of I(K(ACh)), inhibition via alpha-agonists and ET-1 was studied in isolation. Stimulation of either type of receptor under this condition, via G(q/11), caused a slow inhibition (t(1/2) approximately 50 s) by about 70%. No comparable effect on GTPgammaS-activated I(K(ACh)) was induced by ACh, suggesting that PLC-coupled M3AChRs are not functionally expressed in rat myocytes, which was supported by the finding that M3AChR transcripts were not detected by reverse transcriptase-polymerase chain reaction in identified atrial myocytes. Supplementing the pipette solution with PtIns(4,5)P(2) significantly reduced inhibition of I(K(ACh)) but had no effect on fast desensitization. From these data it is concluded that stimulation of PLC-coupled receptors causes slow inhibition of I(K(ACh)) by depletion of PtIns(4,5)P(2), whereas fast desensitization of I(K(ACh)) is not related to PtIns(4,5)P(2) depletion. As muscarinic stimulation by ACh does not exert inhibition of I(K(ACh)) comparable to stimulation of alpha(1)- and ET(A) receptors, expression of functional PLC-coupled muscarinic receptors in rat atrial myocytes is unlikely.

Acetylcholine↗
PubMed2000

Surgical therapy for distant metastases of malignant melanoma.

BACKGROUND: Manifestation of distant metastases in melanoma patients commonly indicates a poor prognosis. The aim of the current study was to examine the role of surgical treatment in these patients. METHODS: Data from 444 patients with distant melanoma metastases were gathered prospectively from January 1978 through December 1997. Characteristics of the primary tumor, time until the first occurrence of distant metastases, frequency and site of distant metastases, surgical therapy, and survival were evaluated by univariate and multivariate analyses. RESULTS: Histology, Breslow thickness, Clark level, and pT and pN categories (UICC 1997) significantly influenced the median interval from initial diagnosis to manifestation of distant metastases. The most common single localization was the lung (n = 83), followed by distant lymph node (n = 79), and skin metastases (n = 51). One hundred seventy-four patients received surgical treatment (39%) and 111 (25%) patients received surgical treatment with curative resection (R0, UICC 1997), most frequently in distant lymph node or skin metastases (57% and 59%, respectively). Median survival time and 2-year survival rate for all patients were 7 months and 15.8%, respectively, 17 months and 36.1% following curative resection, 6 months and 12.7% after incomplete resection (n = 63) (P < 0.0001). Conservatively treated patients survived for a median of only 4 months with a 2-year survival of 8.1%. Multivariate survival analysis showed localization of the primary tumor (head/neck/trunk vs. extremities), the number of involved sites, and surgical therapy to be independent prognostic factors. CONCLUSIONS: Surgical therapy of distant metastases was most beneficial when complete removal of metastatic tissue was achieved. Selection of patients for surgical excision should be determined by individual patient indications.

Adult↗
PubMed2000

Cardiac troponin I elevation in acute pulmonary embolism is associated with right ventricular dysfunction.

OBJECTIVES: The purpose of this study was to evaluate the prevalence and diagnostic utility of cardiac troponin I to identify patients with right ventricular (RV) dysfunction in pulmonary embolism. BACKGROUND: Right ventricular overload resulting from elevated pulmonary resistance is a common finding in major pulmonary embolism. However, biochemical markers to assess the degree of RV dysfunction have not been evaluated so far. METHODS: In this prospective, double-blind study we included 36 study patients diagnosed as having acute pulmonary embolism. RESULTS: Among the whole study population, 14 patients (39%) had positive troponin I tests. Ten of 16 patients (62.5%) with RV dilatation had increased serum troponin I levels, while only 4 of 14 patients (28.6%) with elevated troponin I values had a normal RV diameter as assessed by echocardiography, indicating that positive troponin I tests were significantly associated with RV dilatation (p = 0.009). Patients with positive troponin I tests had significantly more segmental defects in ventilation/perfusion lung scans than patients with normal serum troponin I (p = 0.0002). CONCLUSIONS: Our data demonstrate that more than one-third of patients clinically diagnosed as having pulmonary embolism presented with elevated serum troponin I concentrations. Troponin I tests helped to identify patients with RV dilatation who had significantly more segmental defects in lung scans. Thus, troponin I assays are useful to detect minor myocardial damage in pulmonary embolism.

Acute Disease↗
PubMed2000

Differential RNA cleavage and polyadenylation of the glutamate transporter EAAT2 in the human brain.

We cloned four novel transcripts of the excitatory amino acid transporter 2, named EAAT2/3UT1-4, resulting from differential cleavage and polyadenylation. Tandem poly (A) sites were found to be functional at 72, 654, 973 nucleotides and more than 2 kb downstream of the stop codon. A tissue-specific expression was identified for 3'-variants of the EAAT2 RNA, most prominently for EAAT2/3UT4 (hippocampus>cortex>>cerebellum>thalamus) as demonstrated by Northern blot analysis and quantitative PCR. We conclude, that alternative poly (A) selection may contribute to the reported differential EAAT2 protein expression under normal and diseased conditions.

Base Sequence↗
PubMed2000

Nucleocytoplasmic translocation of Stat1 is regulated by a leucine-rich export signal in the coiled-coil domain.

Signal transducer and activator of transcription (Stat) proteins are latent transcription factors that reside in the cytoplasm before activation. On cytokine-induced tyrosine phosphorylation, these molecules dimerize and accumulate transiently in the nucleus. No specific signals mediating these processes have been identified to date. In this report, we examine the nuclear export of Stat1. We find that treatment of cells with the export inhibitor leptomycin B does not affect steady-state localization of Stat1 but impedes nuclear export after IFNgamma-induced nuclear accumulation. We identify a conserved leucine-rich helical segment in the coiled-coil domain of Stat1, which is responsible for the efficient nuclear export of this protein. Mutation of two hallmark leucines within this segment greatly attenuate the back transport of Stat1 in the cytoplasm. When fused to a carrier protein, the Stat1 export sequence can mediate nuclear export after intranuclear microinjection. We show that prolonging the nuclear presence of Stat1 by inhibiting nuclear export reduces the transcriptional response to stimulation with IFNgamma. These data suggest that Stats are actively exported from the nucleus via several separate pathways and link this activity to transcriptional activation.

Amino Acid Sequence↗
PubMed2000

In vivo therapy of malignant melanoma by means of antagonists of alphav integrins.

Integrin alphavbeta3 (vitronectin receptor) has been implicated in human malignant melanoma progression and angiogenesis as a receptor that provides survival signals. However, little is known about the therapeutic potential of antagonists of alphavbeta3. In this report, we characterize the activities of 2 antagonists of alphavbeta3 integrins: a human specific monoclonal antibody (MAb), 17E6, and a cyclic RGD peptide that blocked cell adhesion and induced detachment of previously substrate-attached cells in vitro. In vivo, alphavbeta3 antagonists behaved as anti-tumor drugs in a dose- and time-dependent manner. Moreover, different therapeutic treatments proved to be effective even in the therapy of established macroscopic tumor masses, thus supporting the use of these antagonists in clinical therapy. Using a panel of 6 human melanomas and 5 carcinomas, MAb 17E6 efficiently blocked the in vivo tumor growth of melanomas expressing alphavbeta3 as xenografts but did not affect the alphavbeta3-negative (although alphav integrin-positive) tumors. This demonstrated that alphavbeta3 is a pivotal integrin for the growth of human melanomas. Furthermore, since MAb 17E6 does not recognize murine alphavbeta3, the effect is due only to the direct anti-tumor activity and not to the well-known anti-angiogenic activity of alphav-integrin antagonists. Taken together, our results confirm the essential role of alphavbeta3 integrin in the growth of human malignant melanoma in vivo and provide strong evidence of the therapeutic potential of alphav-integrin antagonists for the treatment of such tumors.

Animals↗