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Biomedical subjects

D Meyer

Publications and source records attributed to D Meyer.

At least 19 recordsLinked to original sources
PubMed1992

Aurin tricarboxylic acid inhibits platelet adhesion to collagen by binding to the 509-695 disulphide loop of von Willebrand factor and competing with glycoprotein Ib.

Aurin tricarboxylic acid (ATA) is known to inhibit ristocetin-induced platelet agglutination but not arachidonic acid-, epinephrine- or ADP-induced aggregation. Its capacity to abolish human von Willebrand factor (vWF)-platelet interactions was further investigated by measurement of platelet adhesion to collagen, platelet agglutination tests and binding studies. In flowing blood using parallel-plate perfusion chambers and human collagen, ATA inhibited platelet adhesion to completion in a dose-dependent manner only at the highest shear rate tested (2,600 s-1). It was without effect at 100 and 650 s-1. ATA completely abolished vWF-dependent platelet agglutination induced by ristocetin, botrocetin and asialo-vWF, respectively. 125I-vWF binding to ristocetin- and botrocetin-treated platelets, to heparin and to sulfatides as well as 125I-botrocetin binding to vWF was competitively inhibited by ATA. By contrast, binding of 125I-vWF to collagen was not affected. To further localize the domain of vWF interacting with ATA, experiments of inhibition of binding of selected 125I-monoclonal antibodies (MoAbs) to immobilized vWF by ATA were performed. Our data led to the conclusion that: 1) the interaction of ATA with vWF involves sequences of the A1 disulphide loop of vWF (residues 509-695) and close epitopes which interact with GPIb and 2) the inhibition of platelet adhesion by ATA occurs only at a high shear rate where vWF is known to play a key role. Thus ATA, which blocks the vWF/GPIb pathway by interfering with vWF and not with platelets, is a potential tool in preventing the early stages of thrombosis.

Aurintricarboxylic Acid↗
PubMed1992

Characterization of recombinant von Willebrand factor corresponding to mutations in type IIA and type IIB von Willebrand disease.

Type IIA and IIB von Willebrand disease (vWD) result from defects in von Willebrand factor (vWF). Although both type IIA and IIB vWD are characterized by the absence of high molecular weight multimers in plasma, vWF from patients with type IIA vWD demonstrates a decreased affinity for the platelet receptor glycoprotein Ib (GPIb), whereas vWF from patients with type IIB vWD show an increased affinity for GPIb. To investigate how structural alterations in vWF affect its interaction with GPIb, we reproduced the reported potential mutations in type IIA and IIB vWD in vWF cDNA and expressed the recombinant proteins in COS-1 cells. The type IIA vWF potential mutation was represented by a G-->A transversion which results in the substitution of Lys for Glu at position 875 in the mature vWF subunit (rvWFLys875). The type IIB vWF mutation corresponds to a duplicated ATG codon, resulting in three contiguous methionines starting at position 540-541 in the normal vWF sequence (rv-WFduplMet540-541). The subunit composition and multimeric structure of both mutant proteins were similar to the wild-type rvWF. The rvWFLys875 bound to fixed platelets in the presence of ristocetin similar to wild-type rvWF. The rvWFduplMet540-541 bound to fixed platelets in the absence of agonist. The rvWFLys875 appears to interact normally with GPIb, and the decreased affinity for the platelet receptor observed in plasma is probably a consequence of prior reduction in multimeric size resulting from the defect. In contrast, the duplication of Met540-541 increases the reactivity of vWF for its platelet receptor.

Amino Acid Sequence↗
PubMed1992

Shear rate-dependent impairment of thrombus growth on collagen in nonanticoagulated blood from patients with von Willebrand disease and hemophilia A.

Thrombus formation on collagen fibrils was quantified at venous (100/s) and arterial (650/s and 2,600/s) wall shear rates in blood from patients with various subtypes of von Willebrand disease (vWD) and with hemophilia A (HA). Nonanticoagulated blood was drawn directly from an antecubital vein over purified type III collagen fibrils exposed in parallel-plate perfusion chambers. Blood-collagen interactions were differentiated and quantified by morphometry as platelet adhesion, thrombus height, thrombus volume, and deposition of fibrin strands. Sixteen patients with vWD, including four type III, six type I, four type IIA, and two type IIB, were compared with 26 normal subjects and nine patients with HA, including six severe HA and three mild HA. Platelet adhesion and thrombus formation at 2,600/s were significantly decreased in blood from patients with vWD type III, IIA, and IIB, but not in blood from patients with type I and in HA. The abnormal thrombus formation was apparently not related to the decreased levels of factor VIII (F.VIII), because thrombus height and volume were normal in severe and mild HA. Thrombus formation at 650/s was also significantly decreased in patients with vWD type III, IIA, and IIB and slightly reduced in type I. Significant reduction in thrombus volume and height was also observed in blood from patients with severe HA, but not in mild HA. Thrombus dimensions were not affected at 100/s in the vWD subtypes. However, significantly decreased thrombus height and virtually absent fibrin deposition were observed in blood from patients with severe HA. Apparently, F.VIII supports thrombus formation at low and intermediate shear conditions, presumably through the generation of thrombin. In contrast, von Willebrand factor (vWF) mediates not only platelet adhesion, but also thrombus formation at intermediate and high shear rates. Thus, the relative contribution of coagulation (F.VIII) and platelet function (vWF) in thrombus formation appears to be shear rate dependent, but having optimal effects at different shear conditions.

Biomechanical Phenomena↗
PubMed1992

Epitope mapping by cDNA expression of a monoclonal antibody which inhibits the binding of von Willebrand factor to platelet glycoprotein IIb/IIIa.

In order to study the structure-function relationship of von Willebrand Factor (vWF), we have located the epitope of a well-characterized monoclonal antibody (MAb) to vWF (MAb 9). This MAb reacts with the C-terminal portion of the vWF subunit, SPII fragment [amino acids (aa) 1366-2050], which includes an Arg-Gly-Asp (RGD) sequence at positions 1744-1746, and totally inhibits vWF and SPII binding to platelet membrane glycoprotein IIb/IIIa (GPIIb/IIIa). A recombinant DNA library was constructed by cloning small (250-500 nucleotides) vWF cDNA fragments into the lambda gt11 vector and these inserts were expressed as fusion proteins with beta-galactosidase. Immunological screening of the library with 125I-MAb 9 identified three immunoreactive clones. vWF inserts were amplified by the PCR and their sequences demonstrated overlapping nucleotides from positions 7630 to 7855 of vWF cDNA, coding for aa residues 1698-1773 of the mature subunit, indicating that this is the epitope of MAb 9. vWF-beta-galactosidase fusion protein reacted with 125I-MAb 9 by Western blotting. In a solid-phase radioimmunoassay, the purified fusion proteins decreased the binding of vWF to 125I-MAb 9 by 50%, and this inhibition was dose-dependent between 3.5 and 120 nM. Therefore the epitope of MAb 9 is located within aa 1698-1773 of the vWF subunit, which includes the RGD sequence implicated in the binding of adhesive proteins of GPIIb/IIIa.

Antibodies, Monoclonal↗
PubMed1992

Evidence that a secondary binding and protecting site for factor VIII on von Willebrand factor is highly unlikely.

A binding domain for Factor VIII (F.VIII) has been previously identified on the N-terminal portion of human von Willebrand Factor (vWF) subunit [amino acids (AA) 1-272]. In order to characterize other possible structures of vWF involved in its capacity to bind and to protect F.VIII against human activated protein C (APC), we used a series of purified vWF fragments overlapping the whole sequence of the subunit. Among those were fragments SpIII (dimer; AA 1-1365), SpII (dimer; AA 1366-2050) and SpI (monomer; AA 911-1365) generated by Staphylococcus aureus V8 proteinase, a P34 species (monomer; AA 1-272) obtained with plasmin, a monomeric 39/34 kDa dispase fragment (AA 480-718) and a tetrameric III-T2 fragment (AA 273-511/674-728) produced from SpIII by trypsin. Three other fragments without precise extremities were located using selected monoclonal antibodies to vWF. Two C-terminal fragments of 270 and 260 kDa, overlapping SpI and SpII, were respectively generated from vWF with trypsin and protease 1 from Crotalus atrox venom. An N-terminal 120 kDa fragment, overlapping P34 and 39/34 kDa fragments, was produced by protease 1. Our results show that vWF bound to F.VIII and protected it from degradation by APC in a dose-dependent way. Among the C-terminal and central vWF fragments (SpII, tryptic 270 kDa, 260 kDa, SpI, 39/34 kDa and III-T2), none had the capacity to bind or to protect F.VIII, even at high concentrations. The three N-terminal fragments (SpIII, 120 kDa and P34) bound to F.VIII in a dose-dependent and saturable fashion. SpIII and the 120 kDa fragment had the capacity to protect F.VIII in a dose-dependent way. In contrast, the P34 species did not significantly protect F.VIII, even when using high concentrations of the fragment. In conclusion, the N-terminal end of vWF subunit (AA 1-272) plays a crucial role in binding to F.VIII, but requires additional structures of the 120 kDa fragment to protect it against APC. In addition, the presence of a secondary binding and/or protecting domain on other portions of the vWF subunit (potentially destroyed during the proteolysis of vWF) is highly unlikely.

Antibodies↗
PubMed1992

Comparison of the primary structure of the functional domains of human and porcine von Willebrand factor that mediate platelet adhesion.

Porcine von Willebrand factor (vWF) directly aggregates human platelets in vitro indicating a conformational difference between the human and porcine molecules. We amplified and directly sequenced 1242 nucleotides of porcine vWF cDNA that encodes functional domains which mediate the binding of vWF to platelets and subendothelium. The deduced amino acid sequence corresponds to residues 473-891 of the human mature vWF subunit and is 79% homologous with the human protein. Significant differences are found in two discontinuous segments thought to be involved in the binding of vWF to platelet glycoprotein Ib. Porcine vWF lacks four contiguous residues in the first segment and has two positively charged arginine residues in the second. Three point mutations associated with human type IIB von Willebrand disease in the first segment of a botrocetin binding site are at the same position as mismatches between the pig and human. The second segment of the botrocetin site is highly conserved while the third segment shows only a 60% homology.

Amino Acid Sequence↗
PubMed1992

Tooth contacts in eccentric mandibular positions and facial morphology.

Correlations between facial morphology and tooth contacts in excursive mandibular positions were studied in 75 men aged 20 to 33 years. The morphology of the dentition was verified on dental casts and the face was measured by use of roentgen cephalometry. No correlation was observed between facial morphology and the number of tooth contacts in the retruded position; however, wide dental arches and jaws displayed many contacts on protrusion. Numerous contacts on the functional side in group function were noted in individuals with a facial morphology associated with distal occlusion, such as Angle class II, division 1. Wide dental arches were associated with multiple functional-side contacts whereas tooth contacts on the nonfunctional side were related to the inclination of the mandible. A "long-face" morphology was related to contacts on the nonfunctional side. There was a negative correlation between the extent of the overbite (vertical overlap) and the number of tooth contacts on the nonfunctional side.

Adult↗
PubMed1992

Defects in type IIA von Willebrand disease: a cysteine 509 to arginine substitution in the mature von Willebrand factor disrupts a disulphide loop involved in the interaction with platelet glycoprotein Ib-IX.

Type IIA von Willebrand disease (vWD) is characterized by the loss of high and intermediate weight multimers of von Willebrand factor (vWF) from plasma. The 3' end of exon 28 in the vWF gene from four type IIA vWD patients was amplified by the polymerase chain reaction, cloned and sequenced. Sequencing identified two potential missense mutations resulting in the amino acid substitutions Arg 834-->Gln and Glu 875-->Lys in the mature vWF subunit within an area of vWF where mutations in type IIA vWD have been reported. Neither of these amino acid substitutions was found in over 100 normal alleles tested by allele specific oligonucleotide hybridization. A polymorphism (Val 802-->Leu) was identified in another patient. Other areas of exon 28 were analysed by denaturing gradient gel electrophoresis (DGGE) and DNA from one patient demonstrated an irregular DGGE pattern on the 5' end of the exon. Sequencing demonstrated an amino acid substitution of an arginine for cysteine at position 509 adjacent to an area of vWF where defects associated with type IIB vWD have been found. This substitution was not found in 100 normal chromosomes tested by restriction enzyme digestion. The Cys 509-->Arg substitution eliminates an intramolecular disulphide bridge formed by Cys 509 and Cys 695 which is important to maintain the configuration of vWF functional domains that interact with platelet glycoprotein Ib-IX.

Arginine↗
PubMed1992

Replacement therapy with virus-inactivated plasma concentrates in von Willebrand disease.

In von Willebrand disease, the goal of treatment is to correct the two laboratory hallmarks of abnormal hemostasis, i.e. the deficiency of factor VIII (FVIII) and the prolonged bleeding time (BT). Since desmopressin (DDAVP) is able to achieve both these goals in the majority of patients, it is the treatment of choice. Some patients, however, are not responsive or become refractory to DDAVP. In these, blood products maintain an important therapeutic role, and there is a need to assess the efficacy of the recently available virus-inactivated plasma concentrates, which contain both FVIII and von Willebrand factor and carry a low risk of transmitting blood-borne viruses. Our survey of the data reported in the literature indicates that all available concentrates are similarly effective in attaining high and sustained levels of FVIII after infusion. Although they often shorten or normalize the prolonged BT, that effect is less uniform. Since concentrates appear efficacious in the majority of clinical situations that require the use of blood products, they should be preferred, because of their greater safety, to cryoprecipitate produced by blood banks, which cannot be virus inactivated.

Bleeding Time↗
PubMed1992

Characterization of an endothelial protein in the developing rabbit kidney.

A new protein (EnPo 1 antigen) abundant on endothelial cells and glomerular podocytes has been characterized by means of the mouse monoclonal antibody EnPo 1. Following electrophoretical separation of rabbit kidney homogenates EnPo 1 recognized a protein with a molecular weight of 110 kDa and an isoelectric point of 5.9 in Western blots. Using immunohistological techniques, the EnPo 1 antigen has been localized in high concentrations on glomerular podocytes of different developmental stages. Furthermore, the EnPo 1 antigen was expressed on endothelial cells of all adult rabbit organs tested so far. Detailed analysis of neonatal rabbit kidney revealed the abundance of EnPo 1 antigen on both differentiated vessels as well as on immature endothelial cells and endothelium of the microvasculature. Thus, for the first time a marker for in situ investigations of angiogenic processes within the mammalian kidney is available. Analysis of kidney cryosections by confocal laser scan microscopy revealed a direct connection between mature and differentiating vessels in the outer kidney cortex. Furthermore, two differentially organized cell populations discriminated by their EnPo 1 binding pattern were localized in the embryonic renal cortex. Morphologically, these cells were not distinguishable from other mesenchymal cells.

Animals↗
PubMed1992

Activation of rat liver perisinusoidal lipocytes by transforming growth factors derived from myofibroblastlike cells. A potential mechanism of self perpetuation in liver fibrogenesis.

Rat liver perisinusoidal lipocytes (PL) cultured on uncoated plastic transform spontaneously within 6-10 d to myofibroblastlike cells (MFBlC). Parallel to the transformation the TGF alpha- and TGF beta 1-mRNA expression increased and was highest in MFBlC. Competitive radioligand binding assays demonstrated that in contrast to untransformed PL the MFBlC synthesize and secrete transforming growth factor (TGF)-alpha (15 fmol/cell per 24 h) and predominantly the latent form of TGF beta 1 (0.2 fmol/cell per 24 h). Medium conditioned by MFBlC (MFBcM) significantly stimulated PL proliferation with little effect on PL proteoglycan synthesis. By transient acidification of the MFBcM, known to activate the latent form of TGF beta 1, the stimulatory effect on PL proteoglycan synthesis was enhanced and furthermore PL transformation (measured by expression of iso-alpha smooth muscle actin and loss of retinylpalmitate) was accelerated. Preincubation of this medium with neutralizing antibodies to TGF beta resulted in (a) the growth inhibitory effect was converted to a growth stimulation and (b) the stimulatory effect on proteoglycan synthesis was abolished. In summary our data indicate that progressive activation of PL on plastic (transformation to MFBlC) leads to an enhanced expression of the TGF alpha- and TGF beta 1-mRNAs and secretion of the corresponding proteins. Medium conditioned by MFBIC stimulates proliferation, transformation, and PG synthesis of untransformed PL. These mechanisms are suggested to be relevant in self perpetuation of liver fibrogenesis.

Adipose Tissue↗
PubMed1992

[Balanced facial hydrophilicity of ioversol: a qualitative approach of hydrophilicity].

Chimiotoxicity of iodinated contrast media is essentially due to non specific hydrophobic interactions with biologic proteins and membranes. These hydrophobic interactions depend both on the whole molecular lipophilicity and on the spatial accessibility of lipophilic molecular areas. Measurements of lipophilicity by partition coefficient, partially take into account the spatial localisation of hydrophilic groups around the lipophilic area due to the 1,3,5-triiodo-benzene. These measurements have to be completed by an accurate knowledge of the three-dimensional localisation of hydrophilic groups to improve the biocompatibility of polyiodinated contrast media. The concept of evenly distributed facial hydrophilicity aims to minimize the accessibility to lipophilic area by a localisation of hydrophilic group on each plan of the benzene ring. The molecular structure of ioversol allows to put this concept in concrete form thanks to a tertiary anilide group which imposes on one hydroxy group to be located on each face of the 1,3,5-triiodo-benzene ring, providing facial hydrophilic protection.

Contrast Media↗
PubMed1992

Effect of combined peribulbar and retrobulbar injection of large volumes of anesthetic agents on the intraocular pressure.

A prospective randomized study was done in 79 patients undergoing elective routine cataract surgery in which the Kelman phacoemulsification technique was used with placement of an intraocular lens. In all the patients anesthesia was induced with both a peribulbar and a retrobulbar injection of a large volume (total 10.5 mL) of local anesthetic. The patients were randomly assigned to receive either the peribulbar (39 patients) (group 1) or the retrobulbar (40 patients) (group 2) injection first. The intraocular pressure (IOP) was measured five times during anesthesia. The mean elevation in IOP immediately after the first injection was 0.4 mm Hg in group 1, compared with 2.0 mm Hg in group 2. Twenty minutes after both injections had been given and a Super Pinky pressure device had been placed on the eye, the mean decrease in IOP from the preoperative value was 3.1 mm Hg in group 1 and 4.8 mm Hg in group 2. We conclude that a combined peribulbar and retrobulbar approach is a safe and effective alternative method of regional anesthesia for cataract surgery.

Aged↗
PubMed1992

Myasthenia gravis-like syndrome induced by topical ophthalmic preparations. A case report.

This case study reports on a 64-year-old female who presented for cataract surgery. She relayed a history of allergic responses to local anesthetics such as xylocaine, but was otherwise in good health. Upon instilling ophthalmic preparations into her eyes during routine ocular examination, she developed general muscular weakness but not other allergic-like symptoms. Further investigation established her myasthenic-like syndrome to be precipitated by an ophthalmic mydriatic preparation. She was able to undergo uneventful cataract surgery and enjoy 20/20 vision postoperatively, with proper management.

Cataract Extraction↗
PubMed1992

Molecular study of von Willebrand disease: identification of potential mutations in patients with type IIA and type IIB.

The defective von Willebrand Factor (vWF) in type IIA von Willebrand disease (vWD) has decreased binding affinity for platelet membrane glycoprotein Ib (GPIb) while in type IIB vWD, the abnormal vWF has increased affinity for this receptor. Segments of exon 28 of the vWF gene were amplified by the polymerase chain reaction and sequenced in two patients with type IIA and two patients with type IIB vWD. One type IIB patient showed an arginine to tryptophan substitution at amino acid residue 543 in the mature vWF and the other patient had a valine to methionine change at residue 553. Including these two new cases, substitutions at residues 543 and 553 now account for more than half of the documented mutations in patients with type IIB vWD. One patient with type IIA vWD showed an isoleucine to threonine change at amino acid 865. This substitution has been reported in another patient with type IIA vWD. The other patient showed a novel proline to serine change at residue 885. The C to T nucleotide transition which causes the amino acid change was not found in over 100 normal chromosomes tested by allele specific oligonucleotide hybridization and was linked to type IIA vWD in the family. This potential mutation is more carboxyterminal in the vWF subunit than other reported mutations in type IIA vWD. It is apparent that mutations associated with type IIA vWD are not as tightly grouped as defects in type IIB vWD, supporting the evidence that the type IIA vWD phenotype is generated by diverse mechanisms.

Base Sequence↗
PubMed1992

South African obstetricians' views on caesarean section.

The widespread increase in the rate of caesarean sections performed in the Western world has become a cause for concern. In this country, two systems of health care exist, one provided by the State and the other based on private practice. A high incidence of caesarean sections has been reported, especially among private practitioners. This study investigated doctors' perceptions of caesarean section practices and explored the availability of facilities which could help to reduce the high caesarean section rate. Questionnaires were mailed to all registered obstetricians. Of these 45.2% (233) responded. Findings indicate that private obstetricians are more likely to perform caesarean sections even though they do have good facilities available to monitor or assess difficult deliveries. Other factors influencing their practice are also explored.

Attitude of Health Personnel↗