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D Meyer

Publications and source records attributed to D Meyer.

At least 73 records · Page 4Linked to original sources
PubMed2001

Comparing qualitative and quantitative spectroscopic techniques for the detection of the effect of direct iron loading of mammalian cell cultures.

Iron overload augments diseases of the liver and microorganism infection as well as deregulates the immune system. In vitro analysis of the effects of iron loading and its chelation involves determining the amount of iron constituting overload, which metal sources and cell lines to use and reliable assay methods. The uptake of 500 microM FeSO4 or FeEDTA by CEMss, U937 or leukocytes was confirmed by inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Excess iron increased CEMss viability (assessed by MTT, XTT, Trypan- and Alamar Blue) by an average of 18% (P = 0.034). Flow cytometry indicated dye-viable cells to be undergoing apotosis/necrosis while still confirming an increase (9%, P < 0.001) in excess iron-induced viability. The iron chelator desferioxamine (DFO) when added in addition to Fe, reversed the effects of excess iron (and vice versa) and had detrimental effects when used on its own (33% inhibition of viability as measured by dyes and 10.85%; P = 0.0427 assessed by flow cytometry). The 4 dyes demonstrated different levels of sensitivity in detecting the influence of iron or DFO but gave a related, qualitative picture while flow cytometry and ICP-AES data was more quantitative.

Cell Culture Techniques↗
PubMed2001

Selective inactivation of Von Willebrand factor binding to glycoprotein IIb/IIIa and to inhibitor monoclonal antibody 9 by site-directed mutagenesis.

INTRODUCTION: The purpose of this study was to assess the requirement for the RGD sequence of von Willebrand factor (VWF) for its binding to the beta3 chain of integrins and the structural basis for the specificity of monoclonal antibody (MoAb) 9 which specifically binds to VWF and inhibits this interaction. MATERIAL AND METHODS: : Seven point mutations were introduced into VWF by site-directed mutagenesis. Mutated recombinant VWF were tested for their multimeric pattern and their ability to bind to purified GPIIb/IIIa, thrombin-activated platelets and MoAb 9. RESULTS: All recombinant VWF were fully multimerized. The conservative Arg 1744 to Lys substitution into the RGD sequence resulted in an 80% loss of function whereas the Arg to Ala change led to a total loss of function. The two substitutions however did not impair the binding to MoAb 9. In contrast Arg 1715 to Ala substitution had no effect on the binding to GPIIb/IIIa but the binding of the corresponding mutated recombinant VWF to MoAb 9 was strikingly decreased. CONCLUSION: Direct evidence of the role of the structure and the charge of Arg 1744 into the RGD sequence were established by changing Arg to Lys (KGD) and to Ala (AGD). Our results also demonstrate that Arg 1715 is not essential in the function but it is necessary for maintaining the conformation recognized by MoAb 9 specific for the GPIIb/IIIa-binding domain of VWF.

Amino Acid Substitution↗
PubMed2001

How selection shapes variation of the human major histocompatibility complex: a review.

The nature of polymorphism and molecular sequence variation in the genes of the human major histocompatibility complex (MHC) provides strong support for the idea that these genes are under selection. With the understanding that selection shapes MHC variation new questions have become the focus of study. What is the mode of selection that accounts for MHC polymorphism? Is variation maintained by pathogen pressure or by reproductive mechanisms? Discerning between these requires drawing on information from studies on association between HLA genes and infectious diseases, reproductive success and mating preferences relative to HLA genotypes, and theoretical studies that compare the outcomes of different selection regimes. The pattern that has emerged suggests that several types of selection are plausible for the maintenance of HLA polymorphism.

Alleles↗
PubMed2001

Type 2 von Willebrand disease causing defective von Willebrand factor-dependent platelet function.

Type 2 von Willebrand disease causing defective von Willebrand factor-dependent platelet function comprises mainly subtypes 2A, 2B and 2M. The diagnosis of type 2 von Willebrand disease may be guided by the observation of a disproportionately low level of ristocetin cofactor activity or collagen-binding activity relative to the von Willebrand factor antigen level. The decreased platelet-dependent function is often associated with an absence of high molecular weight multimers (types 2A and 2B), but the high molecular weight multimers may also be present (type 2M and some type 2B), and supranormal multimers may exist (as in the Vicenza variant). Today, the identification of mutations in particular domains of the pre-provon Willebrand factor is helpful to classify these variants and to provide further insight into the structure-function relationship and the biosynthesis of von Willebrand factor. Thus, mutations in the D2 domain, involved in the multimerization process, are found in patients with type 2A, formerly named IIC von Willebrand disease. Mutations in the D3 domain characterize the Vicenza variant, or type IIE patients. Mutations in the A1 domain may modify the binding of von Willebrand factor multimers to platelets, either increasing (type 2B) or decreasing (types 2M and 2A/2M) the affinity of von Willebrand factor for platelets. In type 2A disease, molecular abnormalities identified in the A2 domain, which contains a specific proteolytic site, are associated with alterations in folding that impair the secretion of von Willebrand factor or increase its susceptibility to proteolysis. Finally, a mutation localized in the C terminus cysteine knot domain, which is crucial for the dimerization of von Willebrand factor subunit, has been identified in a rare subtype 2A, formerly named IID.

Amino Acid Sequence↗
PubMed2001

Type 2N von Willebrand disease: clinical manifestations, pathophysiology, laboratory diagnosis and molecular biology.

Type 2N von Willebrand disease encompasses all patients with factor VIII deficiency caused by a markedly decreased affinity of von Willebrand factor for factor VIII. It is recessively inherited and clinically similar to mild haemophilia. The differential biological diagnosis is of major importance for providing the optimal treatment and relevant genetic counselling. This accurate diagnosis is based on an evaluation of the factor VIII-binding capacity of plasma von Willebrand factor. Furthermore, molecular biology techniques allow the identification of missense mutations in the von Willebrand factor gene. All of these induce the substitution of amino acid residues located in the N terminal part of the mature von Willebrand factor molecule, which contains the factor VIII binding site. Most of them induce a classical type 2N von Willebrand disease phenotype with factor VIII deficiency but a normal level and multimeric pattern of von Willebrand factor.

Clinical Laboratory Techniques↗
PubMed2001

Abnormal von Willebrand factor in bleeding angiodysplasias of the digestive tract.

BACKGROUND & AIMS: Involvement of an abnormal von Willebrand factor in the bleeding expression of gastrointestinal angiodysplasias has been suggested but not assessed by prospective studies. METHODS: To address this issue, 27 patients with either nonbleeding (group A, n = 9) or bleeding (group B, n = 9) digestive angiodysplasias or telangiectasias or diverticular hemorrhage (group C, n = 9) were enrolled. In all patients, an analysis of von Willebrand factor and a screening for the most common disorders associated with an acquired von Willebrand disease were performed. RESULTS: In all patients from groups A and C, von Willebrand factor was normal, and no underlying disease could be found. In contrast, all but 1 patient from group B had a variable selective loss of the largest multimeric forms of von Willebrand factor, associated in 7 cases with a stenosis of the aortic valve. CONCLUSIONS: This study indicates that most patients with bleeding angiodysplasia or telangiectasia have a deficiency of the largest multimers of von Willebrand factor induced by a latent acquired von Willebrand disease. Because these multimers are the most effective in promoting primary hemostasis at the very high shear conditions related to these vascular malformations, we suggest that their deficiency is likely to contribute to the bleeding diathesis.

Adult↗
PubMed2001

[Small bowel transplantation as an experimental and clinical replacement procedure].

Small bowel transplantation as an experimental and clinical replacement procedure. The routine use of human small bowel isografts as a treatment for mucosal defects, e. g. in the hypopharynx, demonstrates clearly that early surgical problems with this procedure have almost been solved. However, human small bowel allografts show a high risk for complications after transplantation. They provoke severe rejection episodes in the recipients which have to be treated with high-dose immunosuppression. These rejection episodes are of major interest for our own experimental research in rats: Video-microscopy (clinically established as zoom-endoscopy) makes early recognition and immediate therapy of these events possible. Concommittant liver transplantation from the identical donor even eliminate them. However, further research of the specific small bowel immune system is needed, to make this organ transplantation even clinically more successful.

Adult↗
PubMed2001

Effects of three penetration enhancers on transcorneal permeation of cyclosporine.

PURPOSE: To investigate the permeation of cyclosporin A (CsA) through fresh and frozen human corneas in the presence and absence of three penetration enhancers: benzalkonium chloride (BZCl), dimethylsulfoxide (DMSO), and Cremophor-EL. METHODS: Human corneas, unsuitable for transplantation, were either freshly used for permeability experiments or snap-frozen in liquid nitrogen and stored at -85 degrees C. CsA permeation through either fresh or thawed frozen corneal tissue was determined using a flow-through diffusion apparatus (20 degrees C for 24 hours). Flux rates for CsA were determined in the presence and absence of the penetration enhancers 0.01% BZCl, 20% DMSO, and Cremophor-EL (10% and 20%). Analysis of variance and Duncan's multiple-range test were used to test for steady state, and an unpaired Student t test with Welch's correction was used to test for differences between the mean flux values at each time point. A significance level of 5% was used for all of the statistical tests. RESULTS: No statistically significant differences in flux values of CsA could be detected between fresh and frozen corneas. In the presence of Cremophor-EL (10% and 20%) and 0.01% BZCl, statistically significant increases in flux values of CsA before 16 hours and after 16 hours, respectively, could be observed. In the presence of 20% DMSO, no statistically significant increases in flux values could be detected. CONCLUSIONS: The permeation of CsA through human corneas appeared to be enhanced by the presence of BZCl and Cremophor-EL. Additionally, it was shown that the flux rate of CsA across fresh and frozen corneas was not significantly different.

Adolescent↗
PubMed2001

Preclinical profile of the monodisperse iodinated macromolecular blood pool agent P743.

RATIONALE AND OBJECTIVES: To summarize the chemical synthesis, physicochemical characterization, pharmacokinetic behavior, and biological evaluation of P743, a new macromolecular iodinated contrast medium. METHODS: The synthesis and molecular modeling of the iodinated macromolecule P743 are described. The pharmacokinetic profile was established in rabbits and rats. Acute toxicity in mice, renal tolerance in normal rabbits, and renal tolerance in uninephrectomized, dehydrated rats undergoing selective intrarenal injection was evaluated. In vitro permeability effects on isolated mastocytes and on the coagulation pathways were carried out. Computed tomography vascular imaging was performed after intravenous injection of P743 (300 mg I/kg) in rabbits and compared with the nonspecific nonionic agent iobitridol. RESULTS: P743 is a monodisperse, macromolecular iodinated contrast medium. In both rabbits and rats, P743 showed a pharmacokinetic profile consistent with that of a rapid-clearance blood-pool agent. Its diffusion through the endothelium was found to be low in vitro, thus confirming early confinement of this macromolecule, unlike nonspecific contrast media. In both species, P743 was excreted by glomerular filtration. Acute toxicity disclosed no mortality at the highest volume that could be injected into mice, leading to a median lethal dose greater than 8.9 g I/kg. Renal tolerance was found to be good in both euvolemic rabbits and uninephrectomized, dehydrated rats. No histamine or leukotriene B4 release was found on RBL-2H3 isolated mastocytes. P743 did not interfere with the coagulation pathways. Imaging experiments confirmed that P743 remains in the vascular compartment for a longer time than does iobitridol, thus allowing vascular enhancement that is twice as high as that of iobitridol in the recirculation phase. CONCLUSIONS: The pharmacokinetic and imaging profiles of P743, a new, monodisperse, macromolecular blood-pool iodinated contrast medium, were consistent with those of a rapid-clearance blood-pool agent. Its initial safety profile is satisfactory. Further experimental imaging studies are required to define the clinical interest in such molecules.

Animals↗
PubMed2001

Physicochemical and biological evaluation of P792, a rapid-clearance blood-pool agent for magnetic resonance imaging.

RATIONALE AND OBJECTIVES: To summarize the physicochemical characterization, pharmacokinetic behavior, and biological evaluation of P792, a new monogadolinated MRI blood-pool agent. METHODS: The molecular modeling of P792 was described. The r1 relaxivity properties of P792 were measured in water and 4% human serum albumin at different magnetic fields (20, 40, 60 MHz). The stability of the gadolinium complex was assessed. The pharmacokinetic and biodistribution profiles were studied in rabbits. Renal tolerance in dehydrated rats undergoing selective intrarenal injection was evaluated. Hemodynamic safety in rats and in vitro histamine and leukotriene B4 release were also tested. RESULTS: The mean diameter of P792 is 50.5 A and the r1 relaxivity of this monogadolinium contrast agent is 29 L x mmol(-1) x s(-1) at 60 MHz. The stability of the gadolinium complex in transmetallation is excellent. The pharmacokinetic and biodistribution profiles are consistent with that of a rapid-clearance blood-pool agent: P792 is mainly excreted by glomerular filtration, and its diffusion across normal endothelium is limited. Renal and hemodynamic safety is comparable to that of the nonspecific agent gadolinium-tetraazacyclododecane tetraacetic acid. No histamine or leukotriene B4 release was found in RBL-2H3 isolated mastocytes. CONCLUSIONS: The relaxivity of P792 at clinical field is very high for a monogadolinium complex without protein binding. The pharmacokinetic and biodistribution profiles are consistent with those of a rapid-clearance blood-pool agent. Its initial safety profile is satisfactory. Experimental and clinical studies are underway to confirm the potential of P792 in MRI.

Acute Kidney Injury↗
PubMed2001

Osteoporosis in a north american adult population with celiac disease.

OBJECTIVE: Osteoporosis, common in European and South American adults with celiac disease, has not been reported in those patients with celiac disease residing in North America. We therefore evaluated bone density in a group of patients from the United States. METHODS: Patients (105 women and 23 men) with celiac disease, who had completed a questionnaire and had bone mineral density (BMD) measured by dual energy x-ray absorptiometry, were evaluated. The patients were an average age of 56 yr old (range 21-83 yr) and had been on a gluten-free diet from 0 months to 46 yr (mean 7.5 yr). RESULTS: Osteoporosis (T score < -2.5) was present in 34% of the patients at the lumbar spine, 27% at the femoral neck, and 36% at the radius. Low bone mass (T score between -1.0 and -2.5) was present in 38% at the lumbar spine, 44% at the femoral neck, and 32% at the radius. When compared to age-matched controls, men were more severely affected than women. BMD did not differ between those on a gluten-free diet and those who had not begun therapy. BMD was remeasured 16 +/- 2 months after beginning a gluten-free diet in 5 patients; it increased by 7.5% at the femoral neck (p < 0.02). In 16 patients who had followed a gluten-free diet for an average of 12 yr, BMD remained stable over an additional 2 yr of observation. CONCLUSIONS: Osteoporosis and low bone mass often affect North American adults with celiac disease, whether or not they are on dietary therapy. Routine screening for osteoporosis is indicated in patients with celiac disease.

Absorptiometry, Photon↗
PubMed2001

spiel ohne grenzen/pou2 is required during establishment of the zebrafish midbrain-hindbrain boundary organizer.

The vertebrate midbrain-hindbrain boundary (MHB) organizes patterning and neuronal differentiation in the midbrain and anterior hindbrain. Formation of this organizing center involves multiple steps, including positioning of the MHB within the neural plate, establishment of the organizer and maintenance of its regional identity and signaling activities. Juxtaposition of the Otx2 and Gbx2 expression domains positions the MHB. How the positional information is translated into activation of Pax2, Wnt1 and Fgf8 expression during MHB establishment remains unclear. In zebrafish spiel ohne grenzen (spg) mutants, the MHB is not established, neither isthmus nor cerebellum form, the midbrain is reduced in size and patterning abnormalities develop within the hindbrain. In spg mutants, despite apparently normal expression of otx2, gbx1 and fgf8 during late gastrula stages, the initial expression of pax2.1, wnt1 and eng2, as well as later expression of fgf8 in the MHB primordium are reduced. We show that spg mutants have lesions in pou2, which encodes a POU-domain transcription factor. Maternal pou2 transcripts are distributed evenly in the blastula, and zygotic expression domains include the midbrain and hindbrain primordia during late gastrulation. Microinjection of pou2 mRNA can rescue pax2.1 and wnt1 expression in the MHB of spg/pou2 mutants without inducing ectopic expression. This indicates an essential but permissive role for pou2 during MHB establishment. pou2 is expressed normally in noi/pax2.1 and ace/fgf8 zebrafish mutants, which also form no MHB. Thus, expression of pou2 does not depend on fgf8 and pax2.1. Our data suggest that pou2 is required for the establishment of the normal expression domains of wnt1 and pax2.1 in the MHB primordium.

Animals↗
PubMed2001

Circulating procoagulant microparticles in women with unexplained pregnancy loss: a new insight.

One of the frequently proposed mechanisms for pregnancy losses refers to uteroplacental thrombosis. However the contribution of classical thrombotic risk factors remains questionable and, if real, does not account for a large number of pregnancy losses. The aim of this study was to investigate the presence of circulating procoagulant microparticles, a new marker of cell activation already associated with various prothrombotic clinical settings. Microparticles were assessed by an original prothrombinase assay on platelet depleted plasma obtained from 74 women with a history of pregnancy loss without apparent cause and 50 controls. Patients were studied at least 2 months after the last obstetrical event and were classified into 2 groups: 49 women with at least 3 consecutive spontaneous abortions at or before the 10th postmenstrual week and 25 with at least one fetal death beyond the 10th postmenstrual week. Among the 74 patients, 41 had increased levels of circulating microparticles, 29 belonging to the group of early pregnancy loss (59%) and 12 to the group of late pregnancy loss (48%). The high prevalence of increased levels of procoagulant microparticles in both groups makes this new marker very promising for the understanding, follow up and therapeutical handling of pregnancy loss.

Abortion, Habitual↗
PubMed2001

Cortical lens opacities in the young patient--an indication for a lipogram?

AIM: To determine the characteristics and prevalence of lenticular opacification in patients with underlying dyslipidaemia. METHODS: Eighty patients of both genders and all ages (18-90 years) were enrolled in the trial if they met the inclusion criteria for dyslipidaemia. Patients were included if their fasting serum cholesterol and triglyceride concentrations were > 5.2 mmol/l and > 2.3 mmol/l, respectively, when measured on three separate occasions over a 1-month period. Patients were excluded if they suffered from any condition known to cause or predispose them to elevated lipid levels or lenticular opacification. Lenticular changes were assessed by means of a slit-lamp through the fully dilated pupil and other physical signs were documented subsequent to thorough physical evaluation. RESULTS: In addition to the classic clinic signs of dyslipidaemia, 31% of patients had cortical lens opacities. Cortical opacities were twice as prevalent as Achilles tendon thickening (16.3%) in our study, the second most prevalent sign of elevated lipid levels. In the subgroup of patients aged under 50 years, 55% had lenticular opacities, predominantly cortical (80%). CONCLUSIONS: Cortical lens opacification was the most prevalent sign of dyslipidaemia and it occurred at a relatively young age in our trial population in those patients who were affected. Cortical lenticular opacification should be regarded as an indication for blood lipid profile evaluation.

Adolescent↗
PubMed2001

Ser968Thr mutation within the A3 domain of von Willebrand factor (VWF) in two related patients leads to a defective binding of VWF to collagen.

We report the identification of a new mutation of von Willebrand Factor (VWF) gene within exon 30 occurring in two related patients (mother and daughter) with a hemorrhagic syndrome. A T-->A transvertion at nucleotide 5441 was found changing the serine 968 to threonine of the mature VWF subunit (S1731T of the preproVWF). The Ser968Thr mutation is located within the VWF A3 domain which interacts with type I and III collagens. Both patients were found to be heterozygous for the mutation. The propositus (daughter) exhibited a slightly prolonged bleeding time, levels of VWF:Ag and VWF:RCo at the lower limit of normal, contrasting with normal levels of VIII:C. Her mother exhibited borderline bleeding time and moderately decreased levels of VWF and VIII:C. In both patients multimeric structure of VWF and ristocetin- as well as botrocetin-induced binding of VWF to GPIb were normal; however both patients repeatedly showed decreased binding of VWF to collagen. The Ser968Thr substitution was reproduced by site-directed mutagenesis on the full-length cDNA of VWF. The mutated recombinant VWF (rVWF), T968rVWF, and the hybrid S/T968rVWF were transiently expressed by COS-7 cells. Both rVWF exhibited normal multimeric pattern and normal ristocetin- as well as botrocetin-induced binding to GPIb. T968rVWF showed significantly decreased binding to collagen while the hybrid S/T968rVWF bound to collagen in a similar way to that of the patients' plasma VWF. Thus, our data demonstrate that the Ser968Thr mutation of the VWF A3 domain is clearly responsible for the abnormal binding of VWF to collagen observed in both patients. The Ser968Thr substitution of the VWF is the first mutation identified in two patients leading to a decreased affinity of VWF for collagen and a normal multimeric structure.

Adolescent↗
PubMed2001

Defect of heparin binding in plasma and recombinant von Willebrand factor with type 2 von Willebrand disease mutations.

The aim of our study was to characterise heparin-binding properties of mutated von Willebrand factor (VWF) in 24 patients plasmas with type 2 von Willebrand disease (VWD). and in 15 recombinant VWF (rVWF) with the corresponding mutations. Binding of mutated rVWF or plasma VWF was compared to that of WT-rVWF or normal pool plasma VWF. Four mutations, at positions C509, V551, R552 and R611 lead to significantly decreased binding to heparin in both plasma and rVWF. Interestingly, whereas these four residues are distant in the primary structure of VWF-A1domain, they are close to each other in its three-dimensional structure. Structural analysis suggested how folding problems and destabilisation due to these mutations could induce reorganisation of surface regions involved in heparin binding. In contrast, no heparin-binding defect was found associated with different type 2 VWF mutants, at positions G561, E596, I662, R543, R545, V553, R578 or L697.

Amino Acid Substitution↗
PubMed2000

Susceptibility locus for Alzheimer's disease on chromosome 10.

The apolipoprotein E (APOE) gene is the only genetic risk factor that has so far been linked to risk for late-onset Alzheimer's disease (LOAD). However, 50 percent of Alzheimer's disease cases do not carry an APOE4 allele, suggesting that other risk factors must exist. We performed a two-stage genome-wide screen in sibling pairs with LOAD to detect other susceptibility loci. Here we report evidence for an Alzheimer's disease locus on chromosome 10. Our stage one multipoint lod score (logarithm of the odds ratio for linkage/no linkage) of 2.48 (266 sibling pairs) increased to 3.83 in stage 2 (429 sibling pairs) close to D10S1225 (79 centimorgans). This locus modifies risk for Alzheimer's disease independent of APOE genotype.

Age of Onset↗