Biomedical subjects

D Meyer

Publications and source records attributed to D Meyer.

At least 55 records · Page 3Linked to original sources

PubMed2002

Identification of a new type 2M von Willebrand disease mutation also at position 1324 of von Willebrand factor.

Type 2M von Willebrand disease (VWD) refers to variants with decreased platelet-dependent function that is not associated with the loss of high molecular weight (HMW) von Willebrand factor (VWF) multimers. This category includes the so-called "phenotype B" responsible for inexistent ristocetin-induced but normal botrocetin-induced binding of VWF to platelet glycoprotein lb. The missense mutation G1324S was identified in the first patient reported to display "phenotype B". We report here on the identification in four members of a French family of a missense mutation also affecting this glycine residue but changing it into an alanine residue. These individuals are heterozygous for this mutation and two of them display an additional quantitative VWF deficiency resulting from a stop codon at position 2470. After transient transfection in Cos-7 cells, the mutated recombinant protein harbouring the G1324A substitution was shown to exhibit normal multimers and inexistent ristocetin-induced but normal botrocetin-induced binding to GPIb, confirming the classification of this new mutation as a type 2M VWD mutation.

Adult↗

PubMed2001

Specific von Willebrand factor-cleaving protease in thrombotic microangiopathies: a study of 111 cases.

Retrospective studies of patients with thrombotic microangiopathies (TMAs) have shown that a deficient activity of von Willebrand factor (vWF)-cleaving protease is involved in thrombotic thrombocytopenic purpura (TTP) but not in the hemolytic-uremic syndrome (HUS). To further analyze the relevance of this enzymatic activity in TMA diagnosis, a 20-month multicenter study of vWF-cleaving protease activity was conducted in adult patients prospectively enrolled in the acute phase of TMA. Patients with sporadic (n = 85), intermittent (n = 21), or familial recurrent (n = 5) forms of TMA (66 manifesting as TTP and 45 as HUS) were included. TMA was either idiopathic (n = 42) or secondary to an identified clinical context (n = 69). vWF-cleaving protease activity was normal in 46 cases (7 TTP and 39 HUS) and decreased in 65 cases (59 TTP and 6 HUS). A protease inhibitor was detected in 31 cases and was observed only in patients manifesting TTP with a total absence of protease activity. Among the 111 patients, mean vWF antigen levels were increased and the multimeric distribution of vWF was very heterogeneous, showing either a defect of the high-molecular-weight forms (n = 40), a normal pattern (n = 21), or the presence of unusually large multimers (n = 50). Statistical analysis showed that vWF-protease deficiency was associated with the severity of thrombocytopenia (P <.01). This study emphasizes that vWF-cleaving protease deficiency specifically concerns a subgroup of TMA corresponding to the TTP entity.

ADAM Proteins↗

PubMed2001

Functional mapping of anti-factor IX inhibitors developed in patients with severe hemophilia B.

Development of inhibitory antibodies is a serious complication of treatment with repeated factor IX infusions in a minority of patients with hemophilia B. Such antibodies detected in 8 patients have been characterized. Typing studies revealed that patients' immune response toward factor IX is highly heterogeneous and involves immunoglobulin G (IgG) antibodies, preferentially IgG1 and IgG4. The preservation of the sequence and the 3-dimensional orientation of the amino acids constituting one epitope are highly important for the assembly of an antibody-antigen complex. To localize the epitopes on the factor IX molecule, an original approach was designed using a set of factor X chimeras carrying regions of factor IX. Results showed that some patients' antibodies were directed against both the domain containing the gamma-carboxy glutamic acid residues (Gla domain) and the protease domain of factor IX. In contrast, no binding was observed to the epidermal growth factor-like domains or to the activation peptide. Functional characterization showed that the purified IgG from patients' serum inhibited the factor VIIIa-dependent activation of factor X. Moreover, patients' IgG directed against the Gla domain inhibited the binding of factor IX to phospholipids as well as the binding of factor VIII light chain to factor IXa. These data demonstrate that inhibitors appearing in patients with severe hemophilia B display specificity against restricted functional domains of factor IX.

Antibody Specificity↗

PubMed2001

Recoil momentum spectroscopy of highly charged ion collisions on magneto-optically trapped Na.

We have used a cold ( T<<1 mK), laser-cooled target of Na atoms confined in a magneto-optical trap to study electron capture processes during highly charged ion-sodium atom collisions at keV energies. Momentum distributions of target ions were determined by employing time-of-flight and position sensitive detection of the Na ions, produced during the collisions and extracted by a weak electric field. In this way impact parameter sensitive information about multielectron capture processes is obtained.

Journal Article↗

PubMed2001

Tissue Doppler imaging consistently detects myocardial abnormalities in patients with hypertrophic cardiomyopathy and provides a novel means for an early diagnosis before and independently of hypertrophy.

BACKGROUND: Left ventricular hypertrophy (LVH), the clinical hallmark of familial hypertrophic cardiomyopathy (FHCM), is absent in a significant number of subjects with causal mutations. In transgenic rabbits that fully recapitulate the FHCM phenotype, reduced myocardial tissue Doppler (TD) velocities accurately identified the mutant rabbits, even in the absence of LVH. We tested whether humans with FHCM also consistently showed reduced myocardial TD velocities, irrespective of LVH. METHODS AND RESULTS: We performed 2D and Doppler echocardiography and TD imaging in 30 subjects with FHCM, 13 subjects who were positive for various mutations but did not have LVH, and 30 age- and sex-matched controls (all adults; 77% women). LV wall thickness and mass were significantly greater in FHCM subjects (P<0.01 versus those without LVH and controls). There were no significant differences in 2D echocardiographic, mitral, and pulmonary venous flow indices between mutation-positives without LVH and controls. In contrast, systolic and early diastolic TD velocities were significantly lower in both mutation-positives without LVH and in FHCM patients than in controls (P<0.001). Reduced TD velocities had a sensitivity of 100% and a specificity of 93% for identifying mutation-positives without LVH. CONCLUSIONS: Myocardial contraction and relaxation velocities, detected by TD imaging, are reduced in FHCM, including in those without LVH. Before and independently of LVH, TD imaging is an accurate and sensitive method for identifying subjects who are positive for FHCM mutations.

Adult↗

PubMed2001

Mixed lineage kinase-dependent JNK activation is governed by interactions of scaffold protein JIP with MAPK module components.

It has been proposed that JNK-interacting proteins (JIP) facilitate mixed lineage kinase-dependent signal transduction to JNK by aggregating the three components of a JNK module. A new model for the assembly and regulation of these modules is proposed based on several observations. First, artificially induced dimerization of dual leucine zipper-bearing kinase (DLK) confirmed that DLK dimerization is sufficient to induce DLK activation. Secondly, under basal conditions, DLK associated with JIP is held in a monomeric, unphosphorylated and catalytically inactive state. Thirdly, JNK recruitment to JIP coincided with significantly decreased affinity of JIP and DLK. JNK promoted the dimerization, phosphorylation and activation of JIP-associated DLK. Similarly, treatment of cells with okadaic acid inhibited DLK association with JIP and resulted in DLK dimerization in the presence of JIP. In summary, JIP maintains DLK in a monomeric, unphosphorylated, inactive state. Upon stimulation, JNK-JIP binding affinity increases while JIP-DLK interaction affinity is attenuated. Dissociation of DLK from JIP results in subsequent DLK dimerization, autophosphorylation and module activation. Evidence is provided that this model holds for other MLK-dependent JNK modules.

Adenosine Triphosphate↗

PubMed2001

CYP98A3 from Arabidopsis thaliana is a 3'-hydroxylase of phenolic esters, a missing link in the phenylpropanoid pathway.

The 4- and 5-hydroxylations of phenolic compounds in plants are catalyzed by cytochrome P450 enzymes. The 3-hydroxylation step leading to the formation of caffeic acid from p-coumaric acid remained elusive, however, alternatively described as a phenol oxidase, a dioxygenase, or a P450 enzyme, with no decisive evidence for the involvement of any in the reaction in planta. In this study, we show that the gene encoding CYP98A3, which was the best possible P450 candidate for a 3-hydroxylase in the Arabidopsis genome, is highly expressed in inflorescence stems and wounded tissues. Recombinant CYP98A3 expressed in yeast did not metabolize free p-coumaric acid or its glucose or CoA esters, p-coumaraldehyde, or p-coumaryl alcohol, but very actively converted the 5-O-shikimate and 5-O-d-quinate esters of trans-p-coumaric acid into the corresponding caffeic acid conjugates. The shikimate ester was converted four times faster than the quinate derivative. Antibodies directed against recombinant CYP98A3 specifically revealed differentiating vascular tissues in stem and root. Taken together, these data show that CYP98A3 catalyzes the synthesis of chlorogenic acid and very likely also the 3-hydroxylation of lignin monomers. This hydroxylation occurs on depsides, the function of which was so far not understood, revealing an additional and unexpected level of networking in lignin biosynthesis.

Arabidopsis↗

PubMed2001

Persistence of stable intragraft cell chimerism in rat liver allografts after drug-induced tolerance.

BACKGROUND: Drug-induced tolerance of rat liver allografts is well documented. We analyzed cellular events during immunosuppressive therapy on day (d) 10 and in the late phase (d 100) after transplantation to assess for characteristics in the intrahepatic leukocyte (IHL) population in the phase of tolerance. METHODS: Lewis rats served as recipients of Dark Agouti rat livers. Temporary immunosuppression with either cyclosporine (CsA) monotherapy (3 mg/kg/d) or triple therapy that consisted of a subtherapeutic CsA dosage (0.25 mg/kg/d) and monoclonal antibodies directed against the interleukin-2 receptor (IL-2R, CD25) and the intercellular adhesion molecule-1 (ICAM-1, CD54) was administered from postoperative d 0 to d 13. Cell migration and cell activation within liver grafts was assessed by standard histology and flow cytometry. IHL apoptosis was detected by terminal deoxynucleotidyl transferase-mediated dUTP-digoxigenin nick end labeling (TUNEL). RESULTS: Both CsA monotherapy and triple therapy prolonged liver allograft survival to more than 100 d and led to the induction of donor-specific tolerance. Untreated recipients rejected their allografts within 14 d. In both groups, donor-specific IHLs initially dropped to 18% to 25% on d 10, but they rebounded to as much as 40% on d 100 as a common characteristic of both groups. Within this population, donor-specific T cells were dominant. In both groups, increased numbers of activated (IL-2R+) CD8+ T lymphocytes were present on d 100. No accumulation of apoptotic IHL was observed on d 100. Their proportion was unchanged in the triple therapy group and slightly decreased in the CsA group compared to the syngeneic controls. CONCLUSIONS: The present study reveals that tolerant liver allografts are repopulated by donor-specific T lymphocytes. This phenomenon is independent of the type of applied immunosuppression. The persistence of activated CD8+ T cells in the phase of proven donor-specific tolerance on d 100 indicates that liver tolerance is associated with the state of a permanent intragraft immune activation. It seems that the coexistence of donor cells with infiltrating recipient cells within liver grafts, termed intrahepatic cell chimerism, is characteristic for tolerated liver allografts.

Animals↗

PubMed2001

Expression, activity, and subcellular localization of the Yin Yang 1 transcription factor in Xenopus oocytes and embryos.

Yin Yang 1 (YY1) is a multifunctional transcription factor that acts as an activator, repressor, or initiator of transcription of numerous cellular and viral genes. Previous studies in tissue culture model systems suggest YY1 plays a role in development and differentiation in multiple cell types, but the biological role of YY1 in vertebrate oocytes and embryos is not well understood. Here we analyzed expression, activity, and subcellular localization profiles of YY1 during Xenopus laevis development. Abundant levels of YY1 mRNA and protein were detected in early stage oocytes and in all subsequent stages of oocyte and embryonic development through to swimming larval stages. The DNA binding activity of YY1 was detected only in early oocytes (stages I and II) and in embryos after the midblastula transition (MBT), which suggested that its potential to modulate gene expression may be specifically repressed in the intervening period of development. Experiments to determine transcriptional activity showed that addition of YY1 recognition sites upstream of the thymidine kinase promoter had no stimulatory or repressive effect on basal transcription in oocytes and post-MBT embryos. Although the apparent transcriptional inactivity of YY1 in oocytes could be explained by the absence of DNA binding activity at this stage of development, the lack of transcriptional activity in post-MBT embryos was not expected given the ability of YY1 to bind its recognition elements. Subsequent Western blot and immunocytochemical analyses showed that YY1 is localized in the cytoplasm in oocytes and in cells of developing embryos well past the MBT. These findings suggest a novel mode of YY1 regulation during early development in which the potential transcriptional function of the maternally expressed factor is repressed by cytoplasmic localization.

Animals↗

PubMed2001

Cargo of kinesin identified as JIP scaffolding proteins and associated signaling molecules.

The cargo that the molecular motor kinesin moves along microtubules has been elusive. We searched for binding partners of the COOH terminus of kinesin light chain, which contains tetratricopeptide repeat (TPR) motifs. Three proteins were found, the c-jun NH(2)-terminal kinase (JNK)-interacting proteins (JIPs) JIP-1, JIP-2, and JIP-3, which are scaffolding proteins for the JNK signaling pathway. Concentration of JIPs in nerve terminals requires kinesin, as evident from the analysis of JIP COOH-terminal mutants and dominant negative kinesin constructs. Coprecipitation experiments suggest that kinesin carries the JIP scaffolds preloaded with cytoplasmic (dual leucine zipper-bearing kinase) and transmembrane signaling molecules (the Reelin receptor, ApoER2). These results demonstrate a direct interaction between conventional kinesin and a cargo, indicate that motor proteins are linked to their membranous cargo via scaffolding proteins, and support a role for motor proteins in spatial regulation of signal transduction pathways.

Adaptor Proteins, Signal Transducing↗

PubMed2001

The arginine-552-cysteine (R1315C) mutation within the A1 loop of von Willebrand factor induces an abnormal folding with a loss of function resulting in type 2A-like phenotype of von Willebrand disease: study of 10 patients and mutated recombinant von Willebrand factor.

The study identified 10 patients from 6 families with prolonged bleeding time, decreased von Willebrand factor (vWF) ristocetin cofactor activity (RCoF) to vWF:Ag (antigen) ratio, and reduced ristocetin-induced platelet agglutination as well as ristocetin- or botrocetin-induced binding of plasma vWF to platelet glycoprotein Ib (GpIb). In addition, all patients showed a decrease of intermediate-molecular-weight (intermediate-MW) and high-molecular-weight (HMW) multimers of vWF. In the heterozygous state, a cysteine-to-threonine (C --> T) transversion was detected at nucleotide 4193 of the VWF gene of all patients and lead to the arginine (R)522C substitution in the A1 loop of vWF mature subunit (R1315C in the preprovWF). By in vitro mutagenesis of full-length complementary DNA (cDNA) of vWF and transient expression in COS-7 cells, the mutated C552 recombinant vWF (C552rvWF) was found to exhibit decreased expression, abnormal folding, and lack of intermediate-MW and HMW multimers. In addition, direct binding of botrocetin to C552rvWF, as well as ristocetin- and botrocetin-induced binding of C552rvWF to GpIb, was markedly decreased. Although being localized in an area of the A1 loop of vWF where most of the type 2B mutations that induce a gain-of-function have been identified, the R552C mutation induces a 2A-like phenotype with a decrease of intermediate-MW and HMW multimers as well as a loss-of-function of vWF in the presence of either ristocetin or botrocetin. (Blood. 2001;97:952-959)

Adult↗

PubMed2001

Reproductive behavioral changes during the ovarian cycle of lesser bushbabies (Galago moholi) in captivity.

Behavioral patterns were quantified in seven heterosexual lesser bushbaby (Galago moholi) pairs during the estrous cycle to determine the relative significance of behavioral and nonbehavioral components of female sexuality in mate attraction. Increases in the occurrence of several male behaviors indicating female attractiveness were initiated during vaginal swelling when the female was sexually nonreceptive. Female behavioral estrus, as indicated by intromission, was confined to a portion of vaginal opening coinciding with proestrous and vaginal estrous smears. Female attractiveness was maintained for much of the period of vaginal opening, whereas female receptivity ended a day or two earlier than attractiveness. Female receptive and proceptive behaviors were not well defined or extensive, and few female behaviors exhibited significant changes during the cycle. Scent-marking behaviors, such as urine washes, and male grooms, were generally elevated outside the behavioral estrous period. In G. moholi, male sexual arousal appears to be elicited primarily by female attractiveness, while behavioral components of female sexuality appear to be less important in influencing mate attraction.

Animals↗

PubMed2001

A double-blind, multicentered study comparing the accuracy of diagnostic markers to predict short- and long-term clinical events and their utility in patients presenting with chest pain.

BACKGROUND: Millions of patients present annually with chest pain, but only 10% have myocardial infarction (MI). We recently reported comparative sensitivity and specificity of available markers in the diagnosis of MI; however, optimum interpretation of marker results requires prognostic follow-up data. HYPOTHESIS: The study was undertaken to study the accuracy of CK-MB subforms, troponin I and T, myoglobin, and CK-MB in predicting clinical events at 30 days and 6 months. METHODS: In all, 955 consecutive patients with chest pain were enrolled in a prospective, multicenter, double-blind study to test the prognostic accuracy of these markers. RESULTS: Myocardial infarction was diagnosed in 119 by CK-MB mass criteria and unstable angina (UA) in 203 patients by clinical criteria. Follow-up at 30 days and 6 months was available in 824 and 724 patients, respectively, with mortalities of 2.8 and 4.14%, respectively. Cumulative 6-month mortality was 5.6% in MI, 4.4% in UA, and 3.0% in others. Revascularization was reported in 9.3% of patients by 6 months. A positive test on each of the markers except myoglobin was predictive of revascularization. The composite endpoint of death or revascularization occurred in 107 patients by 6 months and a positive result on each of the markers was predictive of this composite endpoint (p < 0.05). The relative risk of death or revascularization for patients who did not have MI but tested positive on each of the markers was > 1.0 but did not reach statistical significance. CONCLUSIONS: With the possible exception of myoglobin, each of the diagnostic markers displayed similar prognostic performance in patients with chest pain presenting to emergency departments. The most appropriate markers to triage patients with chest pain, which has both adequate early diagnostic sensitivity and prognostic accuracy, are the CK-MB subforms.

Adult↗

PubMed2001

Orthotopic liver/small bowel transplantation in rats: a microsurgical model inducing tolerance.

Liver cirrhosis in patients with short bowel syndrome is successfully treated in humans by simultaneous liver/small bowel transplantation. However, until now, a clinically relevant experimental rat model for this procedure has not existed. We therefore established a protocol that, for the first time in rats, allows the simultaneous transplantation of arterialized liver and small bowel into an orthotopic position. Short-term immunosuppression induced not only allograft acceptance but tolerance (as demonstrated by indicator heart/skin transplantation). The immunosuppressive dose required to achieve this result was dramatically less than that of protocols for successful small bowel transplantation alone. Immunohistochemistry detected a transient rejection crisis before tolerance. During this crisis, apoptotic recipient-type T lymphocytes, mainly CD8+ cells, accumulated in the liver but not in the small bowel allograft. The initiation of T-cell apoptosis is one possible explanation for the specific immunosuppressive effect of the liver allograft, which also supports the simultaneously transplanted small bowel allograft in our model.

Animals↗

PubMed2001

P792: a rapid clearance blood pool agent for magnetic resonance imaging: preliminary results.

An original MRI contrast agent, called P792, is described. P792 is a gadolinium macrocyclic compound based on a Gd-DOTA structure substituted by hydrophilic arms. The chemical structure of P792 has been optimized in order to provide (1) a high r(1) relaxivity in the clinical field for MRI: 29 mM(-1)xs(-1) at 60 MHz, (2) a high biocompatibility profile and (3) a high molecular volume: the apparent hydrodynamic volume of P792 is 125 times greater than that of Gd-DOTA. As a result of this high molecular volume, P792 presents an unusual pharmacokinetic profile, as it is a Rapid Clearance Blood Pool Agent (RCBPA) characterized by limited diffusion across the normal endothelium. The original pharmacokinetic properties of this RCBPA are expected to be well suited to MR coronary angiography, angiography, perfusion imaging (stress and rest), and permeability imaging (detection of ischemia and tumor grading). Further experimental imaging studies are ongoing to define the clinical value of this compound.

Animals↗

PubMed2001

How safe is adventure tourism in New Zealand? An exploratory analysis.

The paper reports findings from a multidisciplinary programme of research, the major aims of which were to determine the nature and extent of the New Zealand adventure tourism injury problem. Analysis of hospital discharge and mortality data for a 15-year period identified adventure tourism-related activities as contributing to approximately 20% of overseas visitor injuries, and 22% of fatalities. Activities that commonly involve independent-unguided adventure tourism, notably mountaineering, skiing and tramping, contributed most to injury and fatality incidence. Horse riding and cycling activities were identified from hospital discharge data and adventure tourism operators' reported client injury-incidence, as the commercial adventure tourism activities most frequently involved in client injuries. Falls were the most common injury events, and a range of client, equipment, environmental and organisational risk factors were identified. Possible interventions to reduce injury risk among overseas and domestic adventure tourists are discussed.

Accidents↗

PubMed2001

Pattern visual evoked potential in the diagnosis of functional visual loss.

OBJECTIVE: To study the pattern visual evoked potential (P-VEP) in the diagnosis of functional visual loss. STUDY DESIGN: Retrospective study of observational case series. PARTICIPANTS: Seventy-two subjects whose best corrected visual acuity (VA) was 20/50 or worse, with or without visual field defect, and whose visual abnormalities could not be explained by the findings of ophthalmologic and neurologic examination were included in this study. MAIN OUTCOME MEASURES: To compare the P-VEP estimated acuity to the initial subjective VA and to the best-performed VA. RESULTS: Seventy-two subjects with functional visual loss had normal P-VEPs. The initial subjective VA was 20/50 in 9 subjects and < or =20/200 in 42 subjects. After clinical examination and reassurance, the best-performed VA was > or =20/50 in 53 subjects and < or =20/200 in 8 subjects. The discrepancy between the P-VEP estimated acuity and the best-performed VA was less than 3 lines of Snellen acuity in 63 of 72 (87.5%) subjects and more than 4 lines in 6 subjects. These six subjects were three women with loss of vision of unknown origin and three men with injury-related visual loss. CONCLUSIONS: P-VEP has the advantage of objectively predicting VA and is a useful test in the diagnosis of functional visual loss.

Adolescent↗

PubMed2001

Nitroglycerin alters alveolar type II cell ultrastructure after ischemia and reperfusion.

BACKGROUND: Although administration of nitric oxide (NO) has been suggested to reduce pulmonary reimplantation response, concerns remain about cytotoxic side effects. METHODS: Using light and electron microscopy, we examined the effects of the NO donor nitroglycerin (NTG) (0.1 mg/ml) as a supplement to the preservation solution Celsior on the structural integrity of rat lungs after extracorporeal ischemia (4 hours at 10 degrees C) and reperfusion (50 minutes) (IR). We performed evaluation in comparison with Celsior alone after IR using either standard antegrade perfusion through the pulmonary artery or retrograde perfusion through the left atrium as an alternative way to improve the preservation quality. Untreated, non-ischemic lungs served as controls (n = 5 per group). We recorded respiratory and hemodynamic parameters during reperfusion. Tissue collection using systematic uniform random sampling was representative for the whole organ and allowed stereologic quantification of structures. RESULTS: After IR, histochemistry revealed no breaks in the alveolo-capillary barrier and we detected no alveolar flooding. Edema formed in the peribronchovascular cuffs, of which the volume fraction was increased (p =.008). Vasoconstriction of the smaller arteries accompanied antegrade flush, which occurred neither after administration of NTG nor after retrograde flush, as shown by immunostaining for alpha-smooth muscle actin. Treatment with NTG was associated with focal disintegration of Type II cells, which displayed edematous swelling of distinct cell compartments and lysis of mitochondria and cells. Nitroglycerin prevented alveolar collapse, which was increased in the other IR groups (p = 0.013). We observed alterations in intra-alveolar surfactant components. CONCLUSION: These findings indicate pathologic effects of NTG treatment on alveolar epithelial integrity. Therefore, we suggest further critical evaluation of NTG/NO for therapeutic use in lung transplantation.

Animals↗