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Biomedical subjects

D Meyer

Publications and source records attributed to D Meyer.

At least 361 records · Page 20Linked to original sources
PubMed1990

Synthetic RGDS-containing peptides of von Willebrand factor inhibit platelet adhesion to collagen.

We compared the effect of a synthetic dodecapeptide of residues 400-411 of the gamma chain of fibrinogen (gamma Fg 400-411) and of three synthetic peptides (15 to 18 aminoacids), of human von Willebrand Factor (vWF), containing the 1744-1747 Arg-Gly-Asp-Ser (RGDS) sequence, upon platelet adhesion to collagen in flowing blood. Both types of peptides are known to inhibit the binding of adhesive proteins to platelet membrane glycoprotein IIb/IIIa (GPIIb/IIIa). Collagen was coated onto plastic cover slips and exposed in parallel-plate perfusion chambers to reconstituted human blood at various shear rates for 5 min at 37 degrees C. At a shear rate of 2,600 s-1, RGDS peptides inhibited platelet adhesion to collagen in a dose-dependent manner and appeared to be more potent inhibitors than the gamma Fg 400-411 on a molar basis. No synergetic effect between RGDS and gamma Fg 400-411 peptides was observed. These results suggest that the RGDS peptides affect adhesion by inhibiting the GPIIb/IIIa-vWF interaction and confirm the involvement of this platelet receptor in vWF-mediated platelet adhesion to collagen at high shear rate.

Amino Acid Sequence↗
PubMed1990

Ristocetin and botrocetin involve two distinct domains of von Willebrand factor for binding to platelet membrane glycoprotein Ib.

We have evidence that ristocetin and botrocetin mediate binding of von Willebrand Factor (vWF) to platelet glycoprotein Ib (GPIb) through two distinct domains on the vWF molecule. This was established by using monoclonal antibodies (MAbs) to vWF and synthetic peptides derived from the sequence of vWF. MAb 322 and MAb NMC/vW4 both recognize native vWF as well as fragments containing the GPIb-binding domain of vWF, obtained with the following enzymes: trypsin (116 kDa), V-8 protease (SpIII, 320 kDa) and V-8 protease plus subtilisin (33-28 kDa). Nevertheless, the lack of reciprocal displacement between the two MAbs in experiments of competitive inhibition for binding to vWF demonstrate that their respective epitopes are separate. Both MAbs inhibit 125I-vWF binding to platelet membrane GPIb and vWF-dependent platelet agglutination induced by ristocetin. However, only MAb NMC/vW4 inhibits these functions in the presence of botrocetin and when ristocetin-induced platelet agglutination is inhibited by MAb 322, botrocetin is still able to restore the agglutination. The involvement of two distinct domains of vWF for binding to GPIb in the presence of ristocetin or botrocetin was confirmed in experiments of binding of 125I-vWF to platelets using a competitor synthetic peptides corresponding to the GPIb binding domain of vWF (Cys 474 to Pro 488 and Ser 692 to Pro 708). At a final concentration of 2.5 mM both peptides inhibit more than 90% of the binding of vWF to ristocetin-treated platelets but are unable to modify this binding in the presence of botrocetin. In conclusion our data suggest that botrocetin and ristocetin involve distinct sites on vWF for binding to GPIb.

Antibodies, Monoclonal↗
PubMed1990

Familial variant of antithrombin III (AT III Bligny, 47Arg to His) associated with protein C deficiency.

The association of a variant of antithrombin III (AT III Bligny) and protein C deficiency is described in a 36-year-old patient having suffered from severe thrombotic episodes. His mother has protein C deficiency and showed a single episode of thrombophlebitis following surgery. His father, sister and daughter have the variant AT III and are asymptomatic. The abnormal AT III was characterized in plasma by the discrepancy between a normal progressive activity and a reduced heparin cofactor activity. This variant AT III was purified, separated from the normal protein by heparin-Sepharose chromatography and was eluted with increased NaCl concentrations. At pH 7.4, the variant AT III eluted at lower (0.3 to 0.5 M) NaCl concentrations than normal (1 to 1.5 M) AT III, thus demonstrating a decreased affinity for heparin. At pH 6.0, however, the abnormal molecule bound more avidly to heparin-Sepharose and was eluted like normal AT III at pH 7.4. Similarly, the heparin enhancement of intrinsic fluorescence of the variant AT III, markedly reduced at pH 7.4, was normalized at pH 6.0. The abnormal AT III showed a normal antiprotease activity, a normal molecular weight by SDS-PAGE, but displayed only a partial immunological identity with the normal protein. Analysis of amplified genomic DNA from this patient by dot-blot demonstrates a heterozygous substitution of arginine by histidine at position 47.

Adult↗
PubMed1990

Skeletal scintigraphy in patients with bilateral retinoblastoma.

One hundred-seventeen radionuclide bone scans were performed on 46 patients with bilateral retinoblastoma between diagnosis and 19 years from diagnosis for the purpose of detecting skeletal metastases or other malignant neoplasms of bone that might develop in this group of patients at high risk for a second malignancy. Only one child, who had been symptomatic for 1.5 years, had a scan positive for metastasis at diagnosis. Scans in three additional children became positive (in one after the development of metastatic disease involving bone and soft tissue but not bone marrow 2 years after the diagnosis of retinoblastoma, and in two others after the development of osteosarcoma at 10.5 and 16 years from the diagnosis of retinoblastoma). Our data indicate that bone scans should not remain as part of the initial staging of patients with bilateral retinoblastoma unless there is clinical or pathologic evidence of extraocular disease at diagnosis. The performance of skeletal scintigraphy also is not warranted, with the expectation of diagnosing a second malignant neoplasm (namely osteosarcoma).

Bone Neoplasms↗
PubMed1990

Removal of radiation-induced cataracts in patients treated for retinoblastoma.

Experience with removal of radiation-induced cataract in patients treated for retinoblastoma is limited. We retrospectively reviewed the records of 38 patients with retinoblastoma (42 eyes) who underwent removal of radiation-induced cataract from 1973 to 1989. Nineteen eyes (45%) without macular tumors or severe radiation complications had final visual acuities in the range of 20/20 to 20/50. One eye (2.4%) developed a rhegmatogenous retinal detachment and four eyes (9.5%) were noted to have amblyopia after cataract removal. Three eyes (7%) developed retinoblastoma recurrence, one with extension of retinoblastoma into the subconjunctival space through the previous sclerotomy. Exenteration was performed and the patient was alive after 8 years. Cataract removal can be visually beneficial in selected patients with radiation-induced cataracts.

Adolescent↗
PubMed1990

Theoretical analysis of factors influencing recovery of ventilation distributions from inert gas washout data.

A method is presented that allows to calculate distributions of ventilation from measured time courses of inert gas washout. In the mathematical description of the washout process a discontinuous algorithm is applied: For each individual breath inspiratory and expiratory tidal volumes, endexpiratory alveolar volume, and dead space inspiration are taken into account. Furthermore, volume reduction of the alveolar gas according to the gas exchange ratio is considered. Commonly in ventilation analysis, the specific ventilation serves as abscissa of the density of the ventilation distribution. As at a given location the specific ventilation changes with varying tidal volumes even if the distribution pattern of the ventilation amongst the lung remains unchanged, the normalized specific ventilation is newly introduced instead. This quantity is defined to be the ratio of regional alveolar ventilation and regional endexpiratory alveolar volume divided by the total alveolar ventilation. The normalized specific ventilation reflects the distribution of the ventilation independently of variations in tidal volume and respiratory frequency. Furthermore, it allows direct comparison of ventilation distributions that are determined at varying alveolar ventilations. Ventilation distributions are approximated by the transformed beta distribution which is parameterized by its mean, variance, and skewness. In order to evaluate simplifications introduced in former studies and to quantify their effects on the resulting ventilation distributions, washout time courses are generated in a computer simulation from the comprehensive discontinuous algorithm and are used to recover ventilation distributions by means of accordingly simplified algorithms. Furthermore, the influence of errors that may occur in the measurement of tidal volumes are assessed. The results of these studies are summarized as follows: Serious errors are introduced in the recovered distributions if ventilation is modelled as a continuous process and if physiological variations in tidal volumes or endexpiratory alveolar volumes or dead space inspiration are neglected. Modelling the entire dead space as common dead space or as local dead space only, entails significant errors as well. Statistical errors of 2% in the measured volumes practically do not have any impacts on the recovered distributions whereas systematic errors significantly deteriorate the results. In conclusion, in ventilation analysis it is essential to apply a discontinuous description of the inert gas washout process that accounts for dead space inspiration and variations in the above mentioned quantities. In addition it is important to obtain all measured values with the highest achievable precision.

Computer Simulation↗
PubMed1990

Significance of dinucleoside tetraphosphate production by cultured tumor cells exposed to the presence of ethanol.

The use of 30 to 50% ethanol solutions to extract the nucleotides from HTC and A-459 cells results in dinucleoside tetraphosphate (Ap4X) levels 3-30-fold as high as those obtained by 5% classical trichloracetic acid extraction, while ATP levels are identical in both cases. The amplification factor varies with the percentage of ethanol and duration of contact between the cells and the extraction mixture. It remains constant for the HTC cells during cell growth, but exhibits a maximum for the A-459 cells towards the end of the exponential growth period. The incorporation of radioactivity in Ap4X when [alpha-32P]ATP is added to the extraction mixture suggests an Ap4X neosynthesis in the presence of ethanol. The results carried out in the presence of pyrophosphate, EDTA and zinc acetate strongly suggest that aminoacyl-tRNA synthetases could be responsible for the increase in Ap4A content with ethanol treatment. Nevertheless, the effect of ethanol is probably not the result of an activation of these enzymes, but rather, as already suggested by earlier results in our laboratory, the result of a fast inactivation of the degradation enzymes.

Adenosine Triphosphate↗
PubMed1990

Decreased expression of the glutathione S-transferases alpha and pi genes in human renal cell carcinoma.

Using the polymerase chain reaction (PCR), a human kidney glutathione S-transferase (GST) alpha cDNA clone (GST alpha 12 K) was synthesized; it is identical to a known liver GST alpha cDNA clone except for one base change (G----A), indicating that an alpha class gene expressed in human kidney is similar to one expressed in human liver. Comparisons were made in the expression of GST alpha and GST pi between renal cell carcinoma and adjacent non-neoplastic tissue. Messenger RNA expression in 30 cases was determined by Northern blotting, and GST protein from nine of these cases was analyzed by HPLC. The GST alpha gene products were expressed at near-zero levels. The GST pi gene product was the predominant GST in tumors, but was decreased in absolute amount compared with control tissue, the tumor/control ratios for the GST pi gene obtained by Northern blots and HPLC analysis being 0.50 +/- 0.07 and 0.36 +/- 0.07 respectively. The resulting pattern in renal cell carcinoma therefore shows a predominance of GST pi. Since it is assumed that renal cell carcinoma derives from the proximal tubular epithelial cells which are high in GST alpha, this implies a dedifferentation in the GST expression pattern.

Blotting, Northern↗
PubMed1990

Expression in Escherichia coli of a recombinant fragment (Ile 914-Leu 1364) of human von Willebrand factor containing a collagen binding domain.

Previous studies have shown that a collagen binding domain of human von Willebrand factor (vWF) resides on a fragment named SpI obtained by digestion with Staphylococcus aureus V8 protease which corresponds to residues Gly 911-Glu 1365 of the mature plasma vWF subunit. We have subcloned a fragment of a full-length cDNA encoding vWF into an expression vector which uses an inducible lambda PL promoter. The predicted product expressed by this plasmid is a fusion protein consisting of 16 amino acids (aa) of the lambda cII protein and aa Ile 914-Leu 1364 of human vWF. This fusion protein was shown to be expressed as insoluble inclusion bodies by induced E. coli harbouring the recombinant vector and was partially purified from bacterial debris and renatured. Partially purified bacterial extract run on SDS-polyacrylamide gels contained a major band representing 50-70% of the visualized proteins and corresponded to the predicted fusion protein. This band reacted with both polyclonal antibodies against human vWF and monoclonal antibodies (MAbs) which recognize the SpI fragment of plasma vWF. The radiolabelled partially purified bacterial extract was shown to bind specifically to human fibrillar collagen types I and III. This binding, which was a function of radiolabelled ligand and collagen concentrations, did not occur on monomeric denatured collagen. It was inhibited by both unlabelled bacterial extract and plasma vWF and also by a MAb against vWF SpI, which has the property of inhibiting vWF/collagen interaction. Our data demonstrate that this recombinant vWF SpI fragment, which can be obtained in large amounts, is a useful model for localizing the epitopes of monoclonal antibodies and then for studying the mechanism of vWF/collagen interaction.

Base Sequence↗
PubMed1990

The synthesis of glycosaminoglycans in isolated hepatocytes during experimental liver fibrogenesis.

During human and experimental liver fibrogenesis, the pattern of glycosaminoglycans in fibrotic liver matrix is greatly changed by severalfold increases of hyaluronic acid, chondroitin sulfate, and dermatan sulfate, respectively. The present study aimed to determine whether hepatocytes take part during fibrogenesis in the alteration of the glycosaminoglycan profile in liver matrix. Rats received thioacetamide orally for 2 and 10 weeks, respectively. After 10 weeks a typical micronodular cirrhosis had developed. Hepatocytes isolated at these time points were characterized by light and electron microscopy and incubated for up to 4 h in suspension cultures in [35S]-sulfate and [3H]-glucosamine containing medium to study the synthesis and intra-/extracellular distribution of total and specific types of glycosaminoglycans. A biphasic change of glycosaminoglycan synthesis in hepatocytes was found. After 2 weeks of TAA-treatment parenchymal cells synthesized about 25% more labeled glycosaminoglycans than control liver cells, but at 10 weeks the synthesis was reduced by more than 40%. Thus, between 2 and 10 weeks of TAA-treatment hepatocellular glycosaminoglycan synthesis decreased by more than 50%. The major portion of newly synthesized glycosaminoglycans was nitrous acid labile and, hence, identified as heparan sulfate. Its fractional synthesis decreased from 0.90 in control cells to 0.84 (2 weeks TAA) and 0.76 (10 weeks TAA), respectively. Thus, the absolute synthesis of heparan sulfate was reduced by 50% in hepatocytes from cirrhosis liver. Eighty to 90% of labeled glycosaminoglycans remained cell-associated. Hyaluronic acid was detected neither in normal hepatocytes nor in hepatocytes from injured liver. We conclude from these data that parenchymal liver cells will not contribute actively to the accumulation of galactosaminoglycans (chondroitin sulfate, dermatan sulfate) and hyaluronic acid in the extracellular matrix during fibrogenesis. The diminished rate of synthesis of heparan sulfate in hepatocytes from cirrhotic liver might explain its fractional decrease in cirrhotic liver matrix.

Animals↗
PubMed1990

Preparation of factor-VIII-depleted plasma with antibodies and its use for the assay of factor VIII.

Standardized factor VIII (FVIII)-deficient plasma is necessary for the clotting assay of this protein. Ethical considerations and prevalence of HIV seropositivity in hemophilia A patients have required the replacement of severe hemophilia A plasma by another specific substrate for FVIII clotting assays. FVIII-deficient plasma was prepared by immunodepletion using polyclonal anti-von-Willebrand factor (vWF) and monoclonal anti-FVIII antibodies coated to agarose beads. This plasma, deficient in both FVIII and vWF, allows the evaluation of FVIII activity with a detection limit of 1% as compared to normal plasma. This immunodepleted plasma was compared to plasma from severe hemophilia A for the FVIII determination in plasma from normal subjects, severe and mild hemophiliacs, patients with von Willebrand disease and dicoumarol-treated patients. In all cases, similar values were obtained with both reagents at various levels of FVIII, with a correlation coefficient of 0.994. Such a good correlation was also obtained for the assay of FVIII in concentrates and in plasma from hemophiliacs following infusion. This immunodeficient plasma thus represents a suitable reagent for the FVIII clotting assay and provides an accurate alternative to the use of hemophilic plasma.

Antibodies↗
PubMed1990

Prenatal diagnosis in type IIA von Willebrand disease.

A prenatal diagnosis for fetal disease was performed at 20 weeks gestation in a severely affected patient with type IIA von Willebrand disease. In the fetal cord blood sample obtained under ultrasound guidance, the level of von Willebrand ristocetin cofactor activity was similar to that of von Willebrand factor antigen, and all the multimers were present. These results were compared to those obtained in 51 normal fetuses of similar gestational age (19-21 weeks). Normal fetuses showed slightly lower levels of von Willebrand factor than normal adults and in addition to all adult multimers, the presence of unusual large forms. This data compared with the case, allowed the exclusion of the diagnosis of type IIA von Willebrand disease in our patient's fetus. This was confirmed at birth in the cord blood.

Adult↗