Biomedical subjects

A Marx

Publications and source records attributed to A Marx.

At least 19 recordsLinked to original sources

PubMed2001

Structure of a fast kinesin: implications for ATPase mechanism and interactions with microtubules.

We determined the crystal structure of the motor domain of the fast fungal kinesin from Neurospora crassa (NcKin). The structure has several unique features. (i) Loop 11 in the switch 2 region is ordered and enables one to describe the complete nucleotide-binding pocket, including three inter-switch salt bridges between switch 1 and 2. (ii) Loop 9 in the switch 1 region bends outwards, making the nucleotide-binding pocket very wide. The displacement in switch 1 resembles that of the G-protein ras complexed with its guanosine nucleotide exchange factor. (iii) Loop 5 in the entrance to the nucleotide-binding pocket is remarkably long and interacts with the ribose of ATP. (iv) The linker and neck region is not well defined, indicating that it is mobile. (v) Image reconstructions of ice-embedded microtubules decorated with NcKin show that it interacts with several tubulin subunits, including a central beta-tubulin monomer and the two flanking alpha-tubulin monomers within the microtubule protofilament. Comparison of NcKin with other kinesins, myosin and G-proteins suggests that the rate-limiting step of ADP release is accelerated in the fungal kinesin and accounts for the unusually high velocity and ATPase activity.

Adenosine Triphosphatases↗

PubMed2001

Mutations of tau protein in frontotemporal dementia promote aggregation of paired helical filaments by enhancing local beta-structure.

The microtubule-associated protein tau is a natively unfolded protein in solution, yet it is able to polymerize into the ordered paired helical filaments (PHF) of Alzheimer's disease. In the splice isoforms lacking exon 10, this process is facilitated by the formation of beta-structure around the hexapeptide motif PHF6 ((306)VQIVYK(311)) encoded by exon 11. We have investigated the structural requirements for PHF polymerization in the context of adult tau isoforms containing four repeats (including exon 10). In addition to the PHF6 motif there exists a related PHF6* motif ((275)VQIINK(280)) in the repeat encoded by the alternatively spliced exon 10. We show that this PHF6* motif also promotes aggregation by the formation of beta-structure and that there is a cross-talk between the two hexapeptide motifs during PHF aggregation. We also show that two of the tau mutations found in hereditary frontotemporal dementias, DeltaK280 and P301L, have a much stronger tendency for PHF aggregation which correlates with their high propensity for beta-structure around the hexapeptide motifs.

Amino Acid Motifs↗

PubMed2001

The development of lymphomas in families with autoimmune lymphoproliferative syndrome with germline Fas mutations and defective lymphocyte apoptosis.

Lymphomas were studied in kindreds with autoimmune lymphoproliferative syndrome (ALPS; Canale-Smith syndrome), a disorder of lymphocyte homeostasis usually associated with germline Fas mutations. Fas (CD95/APO-1) is a cell surface receptor that initiates programmed cell death, or apoptosis, of activated lymphocytes. Lymphoma phenotype was determined by immunohistochemistry, frequency of CD3(+)CD4(-)CD8(-) T-cell-receptor alpha/beta cells by flow cytometry, nucleotide sequences of the gene encoding Fas (APT1, TNFRSF6), and the percentage of lymphocytes undergoing apoptosis in vitro. Of 223 members of 39 families, 130 individuals possessed heterozygous germline Fas mutations. Eleven B-cell and T-cell lymphomas of diverse types developed in 10 individuals with mutations in 8 families, up to 48 years after lymphoproliferation was first documented. Their risk of non-Hodgkin and Hodgkin lymphomas, respectively, was 14 and 51 times greater than expected (each P <.001). Investigation of these 10 patients and their relatives with Fas mutations revealed that all had defective lymphocyte apoptosis and most had other features of ALPS. The tumor cells retained the heterozygous Fas mutations found in the peripheral blood and manifested defective Fas-mediated killing. These data implicate a role for Fas-mediated apoptosis in preventing B-cell and T-cell lymphomas. Inherited defects in receptor-mediated lymphocyte apoptosis represent a newly appreciated risk factor for lymphomas.

Adult↗

PubMed2001

[Danaparoid (Orgaran) as an antiocoagulant for mechanical autotransfusion with Cell Saver 5 (Hemonetics)].

We investigated Danaparoid Sodium (Orgaran) as anticoagulant using three different concentrations (9, 4,5 or 3 U/ml anticoagulant solution) for the use in the autotransfusion device Cell Saver 5 (Haemonetics). Fresh units of whole blood packs were mixed in the reservoir in a proportion of 5:1 with the anticoagulant solution. Having started the Cell Saver 5 in the automatic mode, the amount of Danaparoid in the retransfusion blood was determined (chromogenic Antifactor-Xa test). The lowest concentration of the anticoagulant was applied in 4 patients with Heparin-induced Thrombocytopenia Type II undergoing total hip arthroplasty. There was a correlation between the concentration in the reservoir and in the retransfusion blood. None of the patients showed a disturbance of his coagulation system. One of them had slight clotting in the reservoir. We recommend the use of the lower concentrations tested: 4,5 U/ml or, particularly for patients with renal insufficiency or low body weight or expected high retransfusion volumes, 3 U/ml as anticoagulant concentrations. If the autotransfusion device is used according to the manufacturer's instructions there may be virtually no risk of clotting in the Cell Saver or of inhibition of the coagulation system in the patient.

Anticoagulants↗

PubMed2001

Thymic epithelial tumors can develop along two different pathogenetic pathways.

To investigate genetic abnormalities associated with the development of thymic epithelial tumors, we performed microsatellite analysis of 26 thymomas belonging to three different World Health Organization types (A, B3, and C) using 48 repeats. The most frequent aberration seen was loss of heterozygosity (LOH) in the region 6q23.3-25.3 detected in 11 tumors (45.8% of informative cases). Further consistent LOHs were detected in regions 3p22-24.2, 3p14.2 (FHIT gene locus), 5q21 (APC), 6p21, 6q21-22.1, 7p21-22, 8q11.21-23, 13q14 (RB), and 17p13.1 (p53). Microsatellite instability was extremely rare, occurring in one type B3 thymoma only, although, at 12.5% of the analyzed loci. Comparing the allelotypes of the analyzed thymomas, we were able to identify two pathogenetic pathways these tumors develop along, characterized by the 6q23.3-25.3 and 5q21 LOHs, respectively. The APC aberration on 5q21 showed significant associations with LOH in the 3p22-24.2, 13q14, and 17p13.1 regions. Interestingly, type A thymomas presented with consistent LOH in the region 6q23.3-25.5 only, they did not reveal any aberrations in the APC, RB, and p53 gene loci or regions 3p22-24.2 and 8q11.21-23. The absence of these aberrations might be the reason for the well-known benign behavior of type A thymomas as compared to types B3 and C tumors.

Adult↗

PubMed2001

A new monoclonal antibody against vitellogenin from rainbow trout (Oncorhynchus mykiss).

Monoclonal antibodies were developed against vitellogenin (vtg) of rainbow trout. This protein is used as a biochemical response to the exposure with estrogenic compounds. Several mice were immunized with purified vtg and the spleen cells of these mice were fused with myeloma cells. The resulting hybridoma cells were screened with an enzyme immunoassay for the production of specific anti-vtg antibodies. Twelve positive cell lines were detected. The hybridoma cell line B8D8 was adjusted to serum free medium; it produced monoclonal antibodies with a high selectivity and sensitivity. A detection limit of 5 microg/l vtg was achieved with a competitive enzyme immunoassay applying a preincubation step and a streptavidin-biotin amplification system (ABC system). Cross-reactivity with vtg of other species was detected with roach (Rutilus rutilus), flounder (Platichthys flesus) and dab (Limanda limanda). The assay was applied to rainbow trout (Oncorhynchus mykiss), which were exposed for six months to defined concentrations of effluents (10%, 20%, 30% and 40%) and surface water. Increased vtg levels in male fish are correlated with the increasing levels of effluent. The effluent levels in the exposure experiments are relevant for effluent loadings of the Berlin waterways during the seasons of the year.

Animals↗

PubMed2001

Inhibition of protein synthesis by the T cell receptor-inducible human TDAG51 gene product.

The T cell death associated gene 51 (TDAG51) was shown to be required for T cell receptor (TCR)-dependent induction of Fas/Apo1/CD95 expression in a murine T cell hybridoma. Despite the absence of a nuclear localization sequence and a nucleic acid binding domain, it was suggested to be localized in the nucleus and to function as a transcription factor regulating Fas-expression. However, we demonstrate that the human (h)TDAG51 protein is localized in the cytoplasm and the nucleoli, suggesting a role in ribosome biogenesis and/or translation regulation. Indeed, it strongly inhibited translation of a luciferase mRNA in a reticulocyte translational extract. Furthermore, cotransfection of hTDAG51 and the luciferase gene into 293T cells resulted in a strong inhibition of luciferase mRNA translation. Our findings were further strengthened by isolating in a yeast two-hybrid screen three proteins which are involved in the regulation of translation. We speculate that hTDAG51 couples TCR signaling to inhibition of protein biosynthesis in activated T lymphocytes.

Animals↗

PubMed2001

[Removal of lepirudin used as an anticoagulant in mechanical autotransfusion with Cell-Saver 5].

UNLABELLED: Former studies demonstrated that small amounts of heparin might remain in the prepared retransfusion blood during intraoperative autotransfusion. This could lead to serious complications in patients suffering from heparin-induced-thrombocytopenia type II (HIT II). Lepirudin is an approved anticoagulant in HIT II-patients. We studied to what extent lepirudin is washed out during the preparation of retransfusion blood, when it is used as anticoagulant for the autotransfusion device cell saver 5. METHODS: We investigated four different concentrations of lepirudin solutions, 5 mg, 10 mg, 20 mg and 30 mg per litre normal saline. In order to imitate a clinical situation, each lepirudin solution was mixed with human blood in a 1:5-ratio and put into the reservoir of the cell saver. The device was started in the automatic mode using 1000 ml saline as washing solution. Several runs were carried out (five times using the 5 mg/l solution, ten times the 10 mg/l, eleven times the 20 mg/l and eleven times the 30 mg/l solution). The lepirudin concentration in the prepared retransfusion blood was measured. RESULTS: The median percentage reduction of the lepirudin content from the reservoir blood to the retransfusion blood was 100% for the 5 mg/l, 90.4% for the 10 mg/l, 94.3% for the 20 mg/l and 86.3% for the 30 mg/l solution. The differences of percentage reduction are not significant. But the different lepirudin concentrations in the anticoagulant solution have a significant influence on the lepirudin concentration in the retransfusion blood. The lepirudin concentration (median) in the retransfusion blood was 0.00 microgram/ml for the 5 mg/l, 0.16 microgram/ml for the 10 mg/l, 0.19 microgram/ml for the 20 mg/l and 0.66 microgram/l for the 30 mg/l lepirudin solution. CONCLUSION: Lepirudin as an anticoagulant for intraoperative autotransfusion is effectively eliminated using the cell saver 5 device in the automatic mode with 1000 ml saline as washing solution. A clinically relevant disturbance of coagulation is not to be expected, even if the highest concentration of lepirudin anticoagulant solution investigated in this study is used.

Anticoagulants↗

PubMed2001

[Anatomy of the dorsal mid-hand arteries--anatomic study and review of the literature].

By dissections of 20 cold-preserved hands, we investigated the dorsal metacarpal arteries (DMA) with regard to reliability, origin and anastomoses. The first dorsal metacarpal artery showed a trifurcation with three vessels: Ramus ulnaris (A. metacarpalis dorsalis I), Ramus medialis and Ramus radialis (A. ulnodorsalis pollicis). The DMA II to IV were observed medially in their respective intermetacarpal spaces. The A. metacarpalis dorsalis V was unreliable in reaching the skin of dorsal proximal phalanges as in the DMA IV. Most reliable for reaching the skin of dorsal proximal phalanges were the radial arteries--first, second and third dorsal metacarpal arteries. The dorsal digital arteries originate close to one another at the level of the metacarpophalangeal joints. There was an increase of epifascial position, from radial to ulnar. Irregular palmar intermetacarpal anastomoses were found proximal to the ligamentum metacarpale transversum profundum but nearly consistently in the web space.

Arteries↗

PubMed2001

[Covering defects of the basal finger area by pedicled flaps anastomosed to the doral metacarpal arteries].

Between 1993 and 1998, 12 distally based dorsal metacarpal artery flaps were used to cover defects of the fingers and palm. All flaps were raised from the dorsum of the hand. Eleven flaps allowed direct closure of the donor site area; one case required a full-thickness skin graft. Nine flaps healed uneventfully. Distal marginal flap necrosis occurred in three cases. All of these were used to cover defects at the distal part of the middle phalanx.

Adolescent↗

PubMed2001

Evidence for distinct mechanisms in the shaping of the CD4 T cell repertoire in histologically distinct myasthenia gravis-associated thymomas.

The major histocompatibility complex (MHC) class II is involved both in thymocyte maturation and peptide presentation and might thus play a key role in the pathogenesis of paraneoplastic myasthenia gravis (MG) in thymomas. To further investigate this issue, we analyzed and scored the expression of epithelial class II expression in 35 thymomas (medullary, MDT; mixed, MXT; cortical and well differentiated thymic carcinoma, CT/WDTC) and correlated it with the histological tumor subtype, prevalence of MG and thymocyte maturation, which was analyzed by flow cytometry and RT-PCR. Our results show that both MHC class II expression and thymocyte maturation are highly dependent on the histological tumor subtype. CT/WDTC retain features of the normal outer thymic cortex, namely substantial MHC class II expression together with normal early thymocyte maturation until late phases of positive selection, but disturbed terminal thymopoiesis. By contrast, MDT and MXT retain features of the normal inner cortex and the medulla with low to absent class II expression and highly abnormal early thymocyte maturation including impaired positive selection, while terminal T cell maturation in MXT appeared undisturbed. There was no correlation between MHC class II expression and MG status for a given tumor subtype. In conclusion, our results provide evidence for a different histogenesis of cortical thymomas and well differentiated carcinomas on the one hand and mixed and medullary thymomas on the other. Decreased expression levels of MHC class II, although of crucial importance for abnormal intratumorous maturation, are not sufficient to explain the emergence of paraneoplastic MG.

CD4-Positive T-Lymphocytes↗

PubMed2000

Thymomas alter the T-cell subset composition in the blood: a potential mechanism for thymoma-associated autoimmune disease.

Thymomas are the only tumors that are proven to generate mature T cells from immature precursors. It is unknown, however, whether intratumorous thymopoiesis has an impact on the peripheral T-cell pool and might thus be related to the high frequency of thymoma-associated myasthenia gravis. This study shows, using fluorescence-activated cell sorting-based analyses and T-cell proliferation assays, that thymopoiesis and T-cell function in thymomas correspond with immunologic alterations in the blood. Specifically, the proportion of circulating CD45RA(+)CD8(+) T cells is significantly increased in patients with thymoma compared with normal controls, in accordance with intratumorous T-cell development that is abnormally skewed toward the CD8(+) phenotype. Moreover, it is primarily the proportion of circulating CD45RA(+)CD8(+) T cells that decreases after thymectomy. The results also demonstrate that T cells reactive toward recombinant autoantigens are distributed equally between thymomas and blood, whereas T-cell responses to foreign antigen (ie, tetanus toxoid) are seen only among circulating T cells and not among thymoma-derived T cells. These functional studies support the hypothesis that thymopoiesis occurring within thymomas alters the peripheral T-cell repertoire. Because many thymomas are enriched with autoantigen-specific T cells, a disturbance of circulating T-cell subset composition by export of intratumorous T cells may contribute to paraneoplastic autoimmune disease arising in patients with thymoma. (Blood. 2000;96:3872-3879)

Adolescent↗

PubMed2000

The influence of the radicality of resection and dose of postoperative radiation therapy on local control and survival in carcinomas of the upper aerodigestive tract.

PURPOSE: To evaluate dose concepts in postoperative irradiation of carcinomas of the upper aerodigestive tract according to the radicality of resection. PATIENTS AND METHODS: In a retrospective analysis, the charts of 257 patients with histologically-proven carcinoma of the upper aerodigestive tract (40 T1, 80 T2, 53 T3, 84 T4 tumors, with nodal involvement in 181 cases) were reviewed according to the radicality of resection and dose of irradiation administered. Sixty-four patients had tumor-free resection margins (> 3 mm), 66 patients had close resection margins (< 3 mm), and 101 patients had R1 resections, and 26 patients had R2 resections. A median dose of 56 Gy was applied to the primary tumor bed and the cervical lymphatics (2 Gy/fraction, 5 fractions/week). In cases of R1 or R2 resection, or of close margins (< 3 mm), the tumor bed or, respectively, tumor residuals were boosted with doses up to a median of 66 Gy. Locoregional tumor control and survival was investigated by uni- and multivariate analyses according to T-, N-stage, grade of resection, total dose of radiation, and presence or absence of extracapsular tumor spread and lymphangiosis carcinomatosa. RESULTS: An overall 3- and 5-year survival rate of 60% and 45%, respectively, was achieved. Rates for freedom from locoregional recurrence were 77% and 72% at 3 and 5 years, respectively. The survival rates according to the grade of resection at 5 years were 67% for patients resected with tumor-free margins, 59% for patients resected with close margins, 26% for patients with R1 resection, and 27% for patients with R2 resection. Within a median follow-up period of 4.7 years for living patients, a total of 67 recurrences (26%) were observed (in 9% of patients resected with tumor-free margins, in 27% with close margins, in 37% of R1 resected, and in 19% of R2 resected patients). Freedom from locoregional recurrence at 3 years was achieved in 100% of the patients resected with tumor-free margins, in 92% of patients resected with close surgical margins, in 87% of R1 and 69% of R2 resected patients. In multivariate Cox-regression analysis, the variables grade of resection (p = 0.00031) and total dose of irradiation (p = 0.0046) were found as factors influencing locoregional control. Variables influencing survival according to multivariate analysis are T-stage (p = 0.0057), N-stage (p = 0.024), grade of resection (p = 0.000015), total dose of irradiation (p < 0. 000000). Extracapsular tumor spread and lymphangiosis carcinomatosa are factors of borderline significance (p = 0.055, p = 0.066). CONCLUSION: In postoperative radiotherapy of head and neck carcinomas, doses adapted to the risk of locoregional recurrent disease should be applied. Patients with R1 and R2 resections should be treated with doses of more than 68 Gy (2 Gy/fraction, 5 fractions/week) (with close margins [< 3 mm] more than 66 Gy) to achieve an improvement in locoregional control and survival.

Adult↗

PubMed2000

Widespread paralytic poliomyelitis in Pakistan: A case-control study to determine risk factors and implications for poliomyelitis eradication.

Despite substantial efforts to eradicate poliomyelitis by administering oral poliovirus vaccine through routine immunization and annual national immunization days (NIDs), Pakistan reported 22% (1147) of the worldwide cases in 1997. Reasons for continued high poliomyelitis incidence include failure to vaccinate, vaccine failure, or inadequate immunization strategies. A case-control study was conducted to measure vaccination status and reasons for undervaccination among 66 poliomyelitis cases and 130 age- and neighborhood-matched controls. Cases were undervaccinated through routine immunization (matched odds ratio [MOR], 0.3; 95% confidence interval [CI], 0.1-0.5); however, NID immunization was similar for cases and controls (MOR, 0.6; 95% CI, 0.3-1.2). Reasons for undervaccination included not being informed, considering vaccination unimportant, and long distances to vaccination sites. Failure to vaccinate through routine immunization was a major risk factor for poliomyelitis in Pakistan. Successful NIDs alone will not interrupt poliovirus circulation in Pakistan, and children remain at risk unless routine immunization is strengthened or additional supplementary immunization is provided.

Case-Control Studies↗

PubMed2000

Response to nitrogen starvation in Corynebacterium glutamicum.

Proteins strongly synthesized in Corynebacterium glutamicum during nitrogen restriction were examined by two-dimensional gel electrophoresis and microsequencing. Two main groups of enzymes were identified beside miscellaneous proteins, enzymes involved (i) in protein synthesis, and (ii) in carbon metabolism. Biochemical measurements revealed an increase of oxygen consumption during nitrogen starvation, indicating an enhanced energy demand of the cells. By Northern hybridizations, an increased transcription for the gap and fda genes upon nitrogen deprivation was shown.

Amino Acid Sequence↗

PubMed2000

Aluminum Bis(trifluoromethylsulfonyl)amides: New Highly Efficient and Remarkably Versatile Catalysts for C - C Bond Formation Reactions.

Superacid-derived aluminum catalysts R(2)AlNTf(2) (2 - 5 mol%) are highly efficient and versatile and are suitable promoters for the allylation and pentadienylation of aldehydes, aldol reactions, aldol cross-coupling of ketones, and Michael additions (several products are shown). Furthermore, they can be converted into chemoselective Lewis acids. Tf=trifluoromethanesulfonyl.

Journal Article↗

PubMed2000

Mechanisms of ischemic preconditioning in skeletal muscle.

BACKGROUND: Ischemic preconditioning (IP) (one or more cycles each consisting of a short period of ischemia and a short period of reperfusion, before the sustained ischemia) reduces ischemia-related organ damage in heart and skeletal muscle but the underlying mechanisms are not clear. This study was intended to assess the possible involvement of K(ATP) channels and of adenosine receptors in IP of skeletal muscle in a rat model of skeletal muscle ischemia. MATERIALS AND METHODS: Groups of 8-15 rats were given the following in vivo treatments: ischemia-reperfusion (I-R: 2.5 h tourniquet-induced ischemia of the right hindlimb, then 2 h reperfusion); IP (three cycles of 5 min ischemia, then 5 min reperfusion) before I-R; cromakalim and I-R; glibenclamide, cromakalim, and I-R; glibenclamide, IP, and I-R; [R]-N(6)-[1-methyl-2-phenylethyl]adenosine (R-PIA) and I-R; adenosine and I-R; and glibenclamide, IP, and I-R. Parameters of muscle function (postischemic maximal force, performance, contraction index, and force after 1 min of stimulation) were then assessed in vitro in the extensor digitorum longus muscle. RESULTS: Pretreatment with either IP or the K(ATP) channel opener cromakalim significantly improved postischemic muscle function. The protective effect of cromakalim was not seen when the K(ATP) channel blocker glibenclamide was added. Glibenclamide, however, did not block IP-induced protection. Pretreatment with the adenosine A(1) receptor agonist 8-(p-sulfophenyl)-theophyllin (8-SPT) or with adenosine did not improve postischemic muscle function. The adenosine receptor agonist did not block IP-induced protection against ischemic damage. CONCLUSIONS: The results show significant improvements in postischemic skeletal muscle function after IP or cromakalim pretreatment but they do not support a role for K(ATP) channels or for adenosine receptors in IP of skeletal muscle.

Animals↗

PubMed2000

Monoclonal antibody-based enzyme immunoassay for mercury(II) determination.

A monoclonal antibody (K3C6) was developed against Hg(II) and applied in different enzyme immunoassay (EIA) formats to determine the test system with the highest sensitivity. A detection limit of 1. 0 microg/L Hg(II) could be achieved with a competitive format in contrast to a detection limit of 2.1 microg/L Hg(II) with a noncompetitive EIA. A competitive displacement EIA yielded the best detection limit of 0.4 microg/L Hg(II) and was well suited to measuring real samples. For this purpose different water samples were diluted at least 1:10 to avoid matrix effects and subsequently spiked with 1 microg/L HgCl(2). Recovery of the spiked samples was between 80 and 120%.

Absorption↗