Primary structure of the propeptide and factor VIII-binding domain of bovine von Willebrand factor

A 2811 base-pair cDNA, encoding the amino-terminal part of the bovine pre-pro-von Willebrand factor, was characterized and sequenced. The deduced amino acid sequence shares significant homology with the human von Willebrand antigen II and the amino-terminal part of the factor VIII-binding domain of von Willebrand factor. In contrast to human, there is no RGD motif in the bovine von Willebrand antigen II. High levels of Cys, characteristic of D domains, are also found in bovine and the Cys position is markedly conserved between the two species.

Absence of cross-reactivity of SR90107A/ORG31540 pentasaccharide with antibodies to heparin-PF4 complexes developed in heparin-induced thrombocytopenia

New carbohydrate-based anticoagulants devoid of the side effects of unfractionated heparin are currently under development and show a major potential for patients with heparin-induced thrombocytopenia (HIT) who still require efficient antithrombotic therapy. As HIT is usually associated with antibodies to heparin-platelet factor 4 (H-PF4) complexes, cross-reactivity of the heparin pentasaccharide SR90107A/ORG31540 was tested in the presence of PF4 with the plasma from 49 patients with HIT. No cross-reactivity was observed whatever the pentasaccharide concentrations. Although more extensive studies are required for excluding its total absence of immunogenicity and pathogenicity, this pentasaccharide is a candidate for use in emergency situations in patients with HIT.

Molecular characterization of glucokinase from Escherichia coli K-12

glk, the structural gene for glucokinase of Escherichia coli, was cloned and sequenced. Overexpression of glk resulted in the synthesis of a cytoplasmic protein with a molecular weight of 35,000. The enzyme was purified, and its kinetic parameters were determined. Its Km values for glucose and ATP were 0.78 and 3.76 mM, respectively. Its Vmax was 158 U/mg of protein. A chromosomal glk-lacZ fusion was constructed and used to monitor glk expression. Under all conditions tested, only growth on glucose reduced the expression of glk by about 50%. A fruR mutation slightly increased the expression of glk-lacZ, whereas the overexpression of plasmid-encoded fruR+ weakly decreased expression. A FruR consensus binding motif was found 123 bp upstream of the potential transcriptional start site of glk. Overexpression of glk interfered with the expression of the maltose system. Repression was strongest in strains that exhibited constitutive mal gene expression due to endogenous induction and, in the absence of a functional MalK protein, the ATP-hydrolyzing subunit of the maltose transport system. It was least effective in wild-type strains growing on maltose or in strains constitutive for the maltose system due to a mutation in malT rendering the mal gene expression independent of inducer. This demonstrates that free internal glucose plays an essential role in the formation of the endogenous inducer of the maltose system.

Impaired prothrombin consumption in Bernard-Soulier syndrome is corrected in vitro by human factor VIII

The Bernard-Soulier syndrome (BSS) is characterized by thrombocytopenia with giant platelets, a prolonged bleeding time with defective platelet adhesion to the subendothelium related to a defect in platelet membrane glycoprotein Ib (GPIb) and a decreased prothrombin consumption. The mechanism of the latter abnormality remains unknown. In this study, we showed that this defect was corrected by the addition of purified human factor VIII (FVIII) to blood from four patients with BSS. The correction of prothrombin consumption was almost complete at concentrations between 1.5 and 3 IU/ml of FVIII procoagulant activity (VIII:C) and partially abolished by a monoclonal antibody which neutralizes VIII:C. This correction was specific for FVIII and was not observed after addition of purified human FIX. It was obtained, in the same magnitude range, with FVIII complexed to von Willebrand factor (vWF) but not with free vWF. These data provide a new insight into the knowledge of the physiological interaction between the platelet membrane and the vWF-FVIII complex facilitating plasma coagulation activation and may lead to helpful therapeutic advances.

Detection by denaturing gradient gel electrophoresis of an Arg1689Cys mutation in a Chinese patient with mild hemophilia A

OBJECTIVE

To detect gene defects of factor VIII (F VIII) in Chinese hemophilia A patients.

METHODS

3' end of exon 14 of F VIII gene from a mild hemophilia A patient of Chinese origin was amplified by polymerase chain reaction (PCR) and identified mutations by denaturing gradient gel electrophoresis (DGGE) combining with direct sequencing.

RESULTS

An upward shift band was detected by DGGE in W381. Direct sequencing demonstrated a C to T transition resulting in substitution of Arg1689Cys within a thrombin activation site of mature F VIII protein, which created a unique a thrombin activation site of mature F VIII protein, which created a unique PstI site in amplified fragment of F VIII.

CONCLUSIONS

The association of PCR and DGGE can detect a single base substitution; the Arg1689Cys mutation that inhibited activation of F VIII by thrombin is a molecular defect associated with hemophilia A in W381.

Requirement of prestimulated THP-1 monocytic cells for endothelial cell activation. Involvement of TNF alpha

Blood monocytes spontaneously activate endothelial cells in culture, leading to adhesion of monocytic cells onto the endothelial surface and overproduction of endothelial proteins such as von Willebrand factor (vWf) and plasminogen activator inhibitor type 1 (PAI-1). To overcome the difficulty in obtaining quiescent monocytes, we studied the ability of promonocytic THP-1 cells to activate endothelial cells. Lipopolysaccharide (LPS)-prestimulated and untreated THP-1 cells were cocultured with resting human umbilical vein endothelial cells (HUVEC) for 3 and 24 h in the presence of colimycin to neutralize LPS traces. Addition of untreated THP-1 cells had little effect on HUVEC adhesiveness. Addition of prestimulated THP-1 cells was followed by a noticeable adhesion after 3 h which reversed to basal values within 24 h. Under these conditions HUVEC adhesion molecules, E-selectin, VCAM-1 and ICAM-1, were increased at 3 h with only ICAM-1 remaining overexpressed at 24 h. Diffusible endothelial proteins such as soluble E-selectin, PAI-1 and vWf to a minimal extent, increased in supernatants from HUVEC cocultured for 24 h with prestimulated THP-1 cells. In those cocultures, TNF alpha concentrations peaked at 3 h whereas IL-1 beta levels progressively rose until 24 h. Addition of an anti-TNF alpha antibody decreased by 40% E-selectin and ICAM-1 induction and suppressed PAI-1 overproduction with a weak effect on vWf. An anti-IL-1 beta antibody had negligible effects on HUVEC adhesion molecules, PAI-1 or vWf production. These results provide evidence that promonocytic THP-1 cells require prestimulation in order to activate HUVEC and that TNF alpha contributes to this phenomenon.

Abnormal proteolytic processing of von Willebrand factor Arg611 Cys and Arg611His

The structural and functional properties of plasma and platelet vWF were studied in 8 patients (5 unrelated families) with vWD demonstrating a mutation at position 611 (R611C or R611H). Following reduction, electrophoresis and immunoblotting with a polyclonal anti-reduced vWF antibody, abnormal proteolysis of vWF was demonstrated in plasma and to a lesser extent in platelets from all patients, leading to the formation of a unique 209 kDa fragment undetectable in control as well as in type 2A, 2B or 2N vWF. Immunoblotting with MoAbs to reduced vWF showed that the C-terminal end of the 209 kDa fragment was located beyond residue 1744 of the subunit and that its N-terminus was between residues 523 and 1114. Multimeric analysis of patients vWF showed an abnormal pattern in both plasma and platelets, with a moderate decrease of the HMW multimers together with a significant increase of the lowest MW forms. The specific sensitivity of vWF R611C and vWF R611H to proteolysis was further evidenced using V-8 protease. In all patient's samples the enzyme produced a unique monomeric 80 kDa fragment, absent in V-8 digested normal vWF, which overlapped the N-terminal part of the subunit. The functional analysis of vWF showed a markedly decreased affinity of mutated plasma vWF for platelet GPIb in the presence of ristocetin. Infusion of DDAVP in two of these patients did not lead to significant platelet count change. It induced a limited increase of the HMW multimers in plasma together with a poor correction of the vWF binding to platelet GPIb. In conclusion, our data demonstrate that in addition to a normal proteolysis, vWF mutated at position 611 undergoes a specific cleavage in plasma and platelets. In contrast to the increased proteolysis observed in type 2A and 2B patients' plasma, this additional cleavage produced a unique 209 kDa species but maintained a HMW multimer-like structure of vWF R611C and R611H.

Physical, chemical and biological evaluations of CMD-A2-Gd-DOTA. A new paramagnetic dextran polymer

PURPOSE

We investigated the synthesis and physical, chemical and biological characterisation of a carboxymethyl-dextran polymer substituted with the paramagnetic macrocyclic complex Gd-DOTA using an amino spacer.

MATERIAL AND METHODS

The product was synthesised in 4 steps. Using rigorous purification conditions in each step, a polymer was obtained, i.e. CMD-A2-Gd-DOTA, whose polydispersity profile was comparable to the initial dextran (I = 1.66-Mw = 50.5 kDa). Approximately 22% of the glucose groups were replaced by Gd-DOTA and 39% were replaced by carboxyl groups. The paramagnetic efficacy of the polymer was 3 times higher than Gd-DOTA alone, which suggests that the injected doses of Gd(III) can be reduced. The vascular residence time of the polymer was measured in rats and rabbits, showing that the pharmacokinetics of the product is similar whatever the dose. Forty-five percent of the product was excreted in urine after 24 h and 1.64% was found in the liver. No acute toxicity was observed at the maximum dose injected (> 5 mmol Gd/kg) and the general biocompatibility of the product tested in vitro was comparable to that of Gd-DOTA.

RESULTS AND CONCLUSION

These results show the advantages of using paramagnetic macrocyclic complexes in the synthesis of macromolecules to preserve biological stability, in contrast with linear chelates. Additional studies will be carried out to demonstrate the benefits of this type of product, particularly in functional imaging.

[Drug-induced taste disorders]

Taste disorders may have diverse uncomfortable consequences such as reduced quality of life, weight loss and possibly professional disability. The sense of taste depends on many factors. Thus various conditions may cause taste disorders, drugs being one of them. The list of drugs being able to cause taste disorders as adverse drug reaction is long and there are many such cases reported to the Swiss Drug Monitoring Center (SANZ). The possibility of an unwanted side effect should be taken into account if a patient complains about taste disorders, such as reduced or changed sense of taste.

Bacterial gastroenteritis among hospitalized patients in a Danish County, 1991-93

BACKGROUND

Denmark has in recent years experienced an increase in the number of bacterial gastrointestinal infections.

METHODS

We have reviewed patients hospitalized with culture-confirmed bacterial gastroenteritis in Roskilde County during 1991-93.

RESULTS

Two hundred and seven patients were included; 68 were children (< 15 years). The microorganism isolated was Salmonella in 61% of the cases, Campylobacter in 20% and Yersinia enterocolitica in 13%. Ninety-three per cent of the patients had diarrhea, 74% had fever (> 38 degrees C), and 66% abdominal pain. Blood in stools was most frequent in patients infected with Campylobacter. Leukocytosis was rare. Twenty-four patients had bacteremia. Reactive arthritis occurred in 4.8%. Three patients died, all infected with zoonotic Salmonella types. Three stool cultures were made for 115 patients, and in 73% all 3 cultures were positive.

CONCLUSIONS

Bacterial gastroenteritis requiring hospitalization affects mainly children and young adults. Infections due to zoonotic Salmonella types were more severe than Campylobacter and Y. enterocolitica gastroenteritis. It seems necessary to make at least three stool cultures to secure a bacteriologic diagnosis.

Characterization of recombinant von Willebrand factors mutated on cysteine 509 or 695

The interacting domain of vWF with platelet GPIb has been shown to overlap the large A1 loop formed by the intra-chain disulfide bond linking Cys 509 to Cys 695. In order to further investigate the role of the conformation of this region, we have expressed in COS-7 cells three mutated full-length recombinant vWFs (rvWFs) in which the substitutions Cys509Gly, Cys509Arg or Cys695Gly have been introduced by site-directed mutagenesis. SDS-agarose gel electrophoresis demonstrated an impaired multimerization of the mutants with undetectable high molecular weight multimers and a decrease of the relative amounts of the intermediate sized multimers. Binding analysis showed that rvWFC509G and rvWFC509R did not interact with botrocetin but spontaneously interacted with GPIb; the latter binding remained unchanged in the presence of ristocetin. This indicates that the substitution of Cys509 by Gly or Arg creates a conformation of vWF that increases its binding to GPIb. In contrast, rvWFC695G which did not react with botrocetin was also unable to interact with GPIb even in the presence of ristocetin, indicating that sequences interacting with GPIb are masked and/or disrupted. In conclusion, the substitution of each of the Cys509 and 695 results in mutant proteins which may be "locked" into active or inactive conformations in regard to the binding to platelet GPIb receptor.

Impaired IgG-dependent anaphylaxis and Arthus reaction in Fc gamma RIII (CD16) deficient mice

The family of receptors for IgG (Fc gamma R) plays an essential role in antibody-mediated effector functions of the immune system. However, the specific contribution of each of the Fc gamma R classes to in vivo immune reactions is still unclear. Here, we demonstrate that mice deficient for the ligand-binding alpha chain of Fc gamma RIII lack NK cell-mediated antibody-dependent cytotoxicity and phagocytosis of IgG1-coated particles by macrophages. Strikingly, these mice lack IgG-mediated mast cell degranulation, are resistant to IgG-dependent passive cutaneous anaphylaxis, and exhibit an impaired Arthus reaction. These results indicate a prominent role for Fc gamma RIII in inflammatory and anaphylactic responses, making this receptor a potential target in immunotherapy.

Presence of autoantibodies to interleukin-8 or neutrophil-activating peptide-2 in patients with heparin-associated thrombocytopenia

Eighty-seven patients with heparin-associated thrombocytopenia (HAT) showed either a positive heparin platelet aggregometry test result and/or the presence of antibodies to heparin-platelet factor 4 (H-PF4) complexes by enzyme-linked immunosorbent assay (ELISA). Fifteen of these patients lacked antibodies to H-PF4, and plasma from these patients was analyzed for the presence of antibodies to PF4-related chemokines, Neutrophil-activating peptide-2 (NAP-2) and interleukin-8 (IL-8). Of these 15 patients, 6 showed antibodies to IL-8 and 3 to the platelet basic protein (PBP)-derived protein, NAP-2. Antibodies to IL-8 and NAP-2 were not observed in control patients (n = 38), patients with HAT and H-PF4 autoantibodies (n = 72), patients with autoimmune diseases (n = 21), or patients with non-HAT thrombocytopenia (n = 30). Five of these nine patients with anti-IL-8 or anti-NAP-2 developed thrombosis during heparin treatment, which is not statistically different from the patients with H-PF4 antibodies. The existence of autoantibodies to IL-8 and NAP-2 in HAT patients highlights the significance of chemokines in the pathogenesis of HAT. The contribution of heparin in vitro was minimal in patients with anti-IL-8 and anti-NAP-2 antibodies, suggesting a biologic difference from the majority of patients with HAT and anti-PF4 antibodies. It may be that antibodies to IL-8 and NAP-2 have weaker affinity for heparin and that the ELISA system may not reflect in vivo heparin-chemokine complex formation. Alternatively, antichemokine autoantibodies may predate heparin exposure, and the role of heparin in initiating HAT may be to mobilize the chemokines and to target them to platelets, neutrophils, or endothelial cells. Subsequent chemokine-binding autoantibodies then lead to cell activation resulting in thrombocytopenia and thrombosis.

Multiple founder haplotypes of mitochondrial DNA in Amerindians revealed by RFLP and sequencing

The mitochondrial DNA (mtDNA) of 139 individuals from eight tribes which belong to four linguistic groups of the Brazilian Amazon Region was studied both by RFLP and by sequencing of the D-loop region. RFLP analysis showed that 41 haplotypes (29%) belonged to haplogroup A, 39 (28%) to haplogroup B, 38 (27%) to haplogroup C, 19 (14%) to haplogroup D, and 2 (< 2%) could not be assigned to any of the four haplogroups. Among the 92 individuals analyzed by direct sequencing of the D-loop region, we observed 43 different haplotypes defined by 48 polymorphic points, while one haplotype could not be assigned to any of the clusters previously described. Joint analysis of data obtained by RFLP and by sequencing of mtDNA demonstrated that, regardless of the method of analysis, the mtDNA haplotypes of contemporary Amerindians cluster into four groups, similar to those previously described, even though 7% of the total sample or 12% of the haplotypes have discrepancies between results obtained by RFLP and sequencing. In addition to supporting the prevalence of four major haplogroups among contemporary Amerindians, our data are compatible with multiple founder haplotypes in each haplogroup, based on: i) a high prevalence of unusual haplotypes: ii) presence of multiple polymorphic sites shared by different haplogroups; iii) relative differences in nucleotide diversity based on RFLP or sequencing within the different haplogroups.

Molecular basis of von Willebrand disease

von Willebrand disease (vWD), the most common congenital bleeding disorder in man, is related to quantitative and/or qualitative abnormalities of von Willebrand factor (vWF), a protein necessary for platelet-vessel wall interactions and for carrying factor VIII. Distinct abnormalities of vWF are responsible for the three main types of vWD. Types 1 and 3 are defined by a quantitative defect of vWF whereas type 2, comprising subtypes 2A, 2B, 2M and 2N, refers to patients with a qualitative defect of vWF. Recent progress in the molecular biology of vWF has led to the identification of the molecular basis of vWD in a significant number of patients. Type 2A is characterized by a decreased platelet-dependent function of vWF and includes subtypes IIA and IIC. In all the cases of subtype IIA, aa substitutions have been identified in the A2 domain of vWF which contains a proteolytic site. In the rare subtype IIC, some aa substitutions or insertion have been found within the propeptide of vWF. In type 2B, defined by an increased affinity of vWF for platelet GPIb, various aa substitutions or insertions have been localized within the A1 domain containing binding sites for GPIb, collagen, heparin and sulfatides. In type 2N, characterized by a defective binding of vWF to factor VIII, several aa substitutions have been identified within the factor VIII-binding domain in the N-terminal part of vWF. The identification of gene defects is difficult in types 1 and 3 of vWD. Whereas various abnormalities (gross, partial or point deletions, point insertions, nonsense mutations) have been shown to be at the origin of the quantitative vWF defect in type 3, the molecular basis of type 1 is still unknown in most cases. A data base of gene defects in vWD has been recently established. Its updating may contribute to consider a future classification of vWD based on the nature of the gene defect. Furthermore, the characterization of mutations in vWD presents a more fundamental interest in providing further insight into the structure-function relationship and the synthesis of vWF.

Overexpression of the Xenopus Xl-fli gene during early embryogenesis leads to anomalies in head and heart development and erythroid differentiation

The product of the Xl-fli gene, a Xenopus laevis transcription factor of the ets family, specifically expressed in several lineage of migratory cells during Xenopus development (Meyer et al., Int. J. Dev. Biol. 39: 909-919, 1995) was overproduced during Xenopus embryogenesis, upon microinjection of a synthetic transcript in the fertilized egg or in the early embryo. This results in anomalies of the antero-posterior and dorso-ventral polarities, and in tissue differentiation, particularly in the eye- and head cartilage development, as well as erythroid differentiation (absence of erythrocyte differentiation in the circulating blood, often accompanied by ectopic localization of mature erythrocytes, leading to important hemangiomas). Cytological examination reveals at gastrulation the existence of abnormal cells separating the different embryonic layers, suggesting modifications of the cellular adhesion properties. The possible involvement of the fli gene in controlling the dissemination of migratory cells is discussed.

Generation of antibodies to heparin-PF4 complexes without thrombocytopenia in patients treated with unfractionated or low-molecular-weight heparin

The incidence of antibodies to heparin-PF4 complexes (H-PF4) has been evaluated in patients who were under heparin therapy for more than 7 days: 109 patients treated with unfractionated heparin (UH) and 100 patients with low-molecular-weight heparin (LMWH). The presence of antibodies was identified in 17% of the former group and 8% of the latter. In both the UH and the LMWH groups, IgM antibodies were found in all but four patients who showed IgA antibodies. IgG isotypes were only detected in five patients and were consistently associated to either IgM or IgA antibodies. The follow-up of H-PF4 antibodies in 76 patients treated with UH from 1 to > or = 12 days showed a relationship between the incidence of antibodies and the duration of therapy. Despite the presence of anti-H-PF4 antibodies there was no thrombocytopenia (<150 10(9)/L) in the patients. A significant drop of platelets requiring the discontinuation of heparin was observed, however, in three patients, but their platelet count consistently remained >150 10(9)/L. Our study demonstrates that the induction of antibodies to H-PF4 is a frequent phenomenon in patients treated with UH or with LMWH. The absence of thrombocytopenia and of clinical complications in these patients demonstrates that other conditions must be associated with H-PF4 antibodies for inducing type II HIT: optimal concentrations of heparin and PF4 in the blood circulation to allow the formation of macromolecular H-PF4 complexes, presence of activated platelets that present an increased binding of H-PF4 complexes, increased expression of FcgammaRIIA receptors, or presence of their H 131 phenotype. We conclude that the measurement of antibodies to H-PF4 complexes allows the detection of heparin-treated patients at risk of developing type II HIT.