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Biomedical subjects

W Lu

Publications and source records attributed to W Lu.

At least 343 records · Page 19Linked to original sources
PubMed1993

Echicetin: a snake venom protein that inhibits binding of von Willebrand factor and alboaggregins to platelet glycoprotein Ib.

Echicetin, a new protein isolated from Echis carinatus venom by reverse phase and ion exchange chromatography specifically inhibited agglutination of fixed platelets induced by several platelet glycoprotein Ib (GPIb) agonists, such as bovine von Willebrand factor (vWF), alboaggregins, and human vWF in the presence of botrocetin. Unlike alboaggregins, echicetin bound to GPIb but did not induce agglutination of washed or fixed platelets. In contrast to disintegrins, it did not block adenosine 5'-diphosphate (ADP)-induced platelet aggregation in the presence of fibrinogen. The apparent molecular weight of echicetin measured on sodium dodecyl sulfate (SDS) gel electrophoresis was 26 Kd under nonreducing conditions. On reduction, echicetin showed 16 and 14-Kd subunits suggesting that the molecule is a dimer. Reduced echicetin retained its binding activity and its inhibitory effect on the agglutination of fixed platelets induced by bovine vWF. 125I-echicetin bound to fixed platelets with high affinity (kd = 30 +/- 1.8 nmol/L) at 45,000 +/- 2,400 binding sites per platelet. The binding was selectively inhibited by a monoclonal antibody to the 45-Kd N-terminal domain of platelet GPIb, but not by monoclonal antibodies to other regions on GPIb. Binding of 125I-bovine vWF to fixed platelets was strongly inhibited by echicetin. In contrast, bovine vWF showed a much weaker inhibitory activity on binding of 125I-echicetin to platelets. The half life of echicetin in blood was approximately 170 minutes with no detectable degradation. Echicetin significantly prolonged the bleeding time of mice, suggesting that it may inhibit vWF binding to GPIb in vivo as well as in vitro.

Animals↗
PubMed1993

Binding of amino acid side chains to preformed cavities: interaction of serine proteinases with turkey ovomucoid third domains with coded and noncoded P1 residues.

In the association of serine proteinases with their cognate substrates and inhibitors an important interaction is the fitting of the P1 side chain of the substrate or inhibitor into a preformed cavity of the enzyme called the S1 pocket. In turkey ovomucoid third domain, which is a canonical protein proteinase inhibitor, the P1 residue is Leu18. Here we report the values of equilibrium constants, Ka, for turkey ovomucoid third domain and 13 additional Leu18X variants with six serine proteinases: bovine alpha chymotrypsin A, porcine pancreatic elastase, subtilisin Carlsberg, Streptomyces griseus proteinases A and B, and human leukocyte elastase. Eight of the Xs are coded amino acids: Ala, Ser, Val, Met, Gln, Glu, Lys, and Phe, and five are noncoded: Abu, Ape, Ahx, Ahp, and Hse. They were chosen to simplify the interamino acid comparisons. In the homologous series of straight-chain side chains Ala, Abu, Ape, Ahx, Ahp, free energy of binding decreases monotonically with the side-chain length for chymotrypsin with large binding pocket, but even for this enzyme shows curvature. For the two S. griseus enzymes a minimum appears to be reached at Ahp. A minimum is clearly evident for the two elastases, where increasing the side-chain length from Ahx to Ahp greatly weakens binding, but much more so for the apparently more rigid pancreatic enzyme than for the more flexible leukocyte enzyme. beta-Branching (Ape/Val) is very deleterious for five of the six enzymes; it is only slightly deleterious for the more flexible human leukocyte elastase. The effect of gamma-branching (Ahx/Leu), of introduction of heteroatoms (Abu/Ser), (Ape/Hse), and (Ahx/Met), and of introduction of charge (Gln/Glu) and (Ahp/Lys) are tabulated and discussed. An important component of the free energy of interaction is the distortion of the binding pocket by bulky or branched side chains. Most of the variants studied were obtained by enzymatic semisynthesis. X18 variants of the 6-18 peptide GlyNH2 were synthesized and combined with natural reduced peptide 19-56. Disulfide bridges were formed. The GlyNH2 was removed and the reactive-site peptide bond X18-Glu19 was synthesized by complex formation with proteinase K. The resultant complexes were dissociated by sudden pH drop. This kinetically controlled dissociation afforded virgin, reactive-site-intact inhibitor variants.

Amino Acid Sequence↗
PubMed1993

Selective activation of cardiac angiotensinogen gene expression in post-infarction ventricular remodeling in the rat.

Recent studies in both experimental animals and man have demonstrated the unique efficacy of converting enzyme inhibitors to prevent or attenuate ventricular remodeling after myocardial infarction. Concomitantly, evidence for a trophic role of the renin-angiotensin system (RAS), as well as for the existence of an intracardiac tissue-resident RAS, has been presented, raising the question whether altered regulation of this cardiac RAS may be associated with the process of ventricular remodeling. We conducted the present study to examine whether cardiac angiotensinogen gene expression is altered after myocardial infarction. Experiments were performed in rats 5 and 25 days after ligation of the left coronary artery or sham operation. Coronary artery ligation resulted in relative infarct sizes averaging 29% and 36% of total left ventricular mass at 5 and 25 days and in marked elevations of left ventricular end-diastolic pressure (LVEDP). Angiotensinogen mRNA levels, measured by solution hybridization assay and confirmed in a second, independent experimental group by RNAse protection assay, were significantly elevated in the non-infarcted portion of the left ventricle at 5 days after infarction when compared to the sham group (22.1 + 3.3 vs. 13.4 +/- 2.0 fg/microgram total RNA; ratio of densitometric absorbance for angiotensinogen/beta-actin: 0.356 +/- 0.041 vs. 0.156 +/- 0.02), and showed a significant correlation with infarct size (r = 0.93). At 25 days, angiotensinogen gene expression had returned to control values. Similarly, no significant differences in angiotensinogen mRNA levels between animals with and without infarction were found in other cardiac tissues (atria, right ventricle). Plasma renin activity was significantly increased over baseline in the infarct group at 5, but not at 25 days. Our results demonstrate that acute hemodynamic embarrassment early after LV infarction is associated with augmented angiotensinogen gene expression. The potential significance of this finding is discussed.

Angiotensinogen↗
PubMed1993

Genetic and molecular analysis of REC114, an early meiotic recombination gene in yeast.

Four new meiotic recombination genes were previously isolated by selecting for mutations that rescue the meiotic lethality of rad52 spo13 strains. One of these genes, REC114, is described here, and the data confirm that REC114 is a meiosis-specific recombination gene with no detectable function in mitosis. REC114 is located on chromosome XIII approximately 4.9 cM from CIN4. The nucleotide sequence reveals an open reading frame of 1262 bp, consensus intron splice sites close to the 3' end, and indicates that the second exon codes for only seven amino acids. In the promoter region, a URS1 consensus sequence (TGGGCGGCTA), identical to the URS1 found in the promoter of SPO16, is present 93 bp upstream of the translation start site. Northern-blot hybridization demonstrates that REC114 is transcribed only during meiosis and that it is not expressed in the absence of the IME1 gene product, even when IME2 is constitutively expressed.

Alleles↗
PubMed1993

Microcomputer-based cardiac field simulation model.

Cardiac field simulation is one of the frontier subjects in electrocardiogram theory study. The paper describes a complete cardiac simulation model implemented on an IBM-PC/AT microcomputer. This model uses a new algorithm for excitation propagation simulation. In comparison with the previous rule-based algorithms, the new algorithm shows better in simulation speed and simulation accuracy.

Algorithms↗
PubMed1993

Early identification of human immunodeficiency virus-infected asymptomatic subjects susceptible to zidovudine by quantitative viral coculture and reverse transcription-linked polymerase chain reaction.

The effect of zidovudine (500 mg/day) on 32 asymptomatic subjects seropositive for human immunodeficiency virus (HIV) was evaluated by monitoring the concentrations of infections HIV-carrying blood mononuclear cells and serum virus particles. After 3 months of treatment, a significant reduction in cellular virus load (P < .001) and a marginal decrease in serum viremia (P = .068) were noted. After 6 months, 14 patients (44%) maintained a > or = 50% reduction in virus load, 12 patients (37%) had a virus load that declined by > 50% at 3 months but returned to the initial level at 6 months, and 6 patients (19%) retained their initial virus load. Thus, virus load measurements permit reliable follow-up of antiviral therapy on an individual basis and may enable the identification of patients for whom zidovudine is efficacious.

Base Sequence↗
PubMed1993

High concentration of peripheral blood mononuclear cells harboring infectious virus correlates with rapid progression of human immunodeficiency virus type 1-related diseases.

In a cohort of 103 asymptomatic seropositive subjects (Centers for Disease Control and Prevention [CDC] stage II/III) followed for 2 years, the concentration of peripheral blood mononuclear cells harboring infectious human immunodeficiency virus (HIV) type 1 (viral burden) was correlated with the rate of decrease of CD4 cell count (RD-CD4; R = .857). Rapidly progressing patients (RD-CD4 > or = 60%; n = 18) had a high viral burden (mean +/- SE, 572 +/- 202 cells/mL) and an 89% progression to CDC IV-A-C, while stable patients (RD-CD4 < 30%; n = 55) had a low viral burden (mean +/- SE, 28 +/- 4 cells/mL) and remained asymptomatic. Slowly progressing patients (RD-CD4 > or = 30 and < 60%; n = 30) showed an intermediate viral burden (mean +/- SE, 131 +/- 9 cells/mL) and a 10% CDC IV-A-C progression. Quantitative determination of infectious virus in blood cells adds important information on the prognosis of HIV-1 infection.

Adult↗
PubMed1993

Lack of isolate-specific neutralizing activity is correlated with an increased viral burden in rapidly progressing HIV-1-infected patients.

OBJECTIVE: To delineate the interaction between in vivo HIV replication and host antiviral immunity during disease progression in order to elucidate the pathogenesis of AIDS. DESIGN: In a cohort of HIV-seropositive patients, the serum concentration of viral particles, the blood concentration of mononuclear cells harbouring infectious virus and the serum titre of isolate-specific neutralizing antibodies were correlated with the rates of CD4+ T-cell depletion and disease progression. METHODS: Using a quantitative reverse-transcriptase linked polymerase chain reaction assay, the concentration of viral particles was measured in blood samples from 103 initially symptom-free subjects who were followed up for > or = 24 months. The concentration of infectious virus and the neutralizing antibodies to autologous HIV isolates were assessed in 37 out of the 103 subjects. The rate of decrease in CD4 cells over the 24 months was calculated for each subject. RESULTS: Rapidly progressing patients (rate of decrease in CD4 cells > or = 60%) had a high concentration of viral particles and a high concentration of infectious virus associated with an undetectable serum titre of isolate-specific neutralizing antibodies. Stable patients (rate of decrease in CD4 cells < 30%) had a low concentration of infectious virus and either a low concentration of viral particles with the absence of isolate-specific neutralizing antibodies or a high concentration of viral particles with the presence of isolate-specific neutralizing antibodies. Slowly progressing patients (rate of decrease in CD4 cells > or = 30 and < 60%) showed an intermediate profile. CONCLUSIONS: Progression to AIDS is associated with a shift in the balance between viral replication and host immunity that increases the concentration of infected cells and destroys the CD4+ T-lymphocyte population.

Acquired Immunodeficiency Syndrome↗
PubMed1993

Exposure of platelet fibrinogen receptors by zinc ions: role of protein kinase C.

Previous studies demonstrated that Zn2+ at a concentration of 50 microM increases the number of fibrinogen receptors exposed on ADP-stimulated platelets and that higher concentrations of Zn2+ induce platelet aggregation that appears to be mediated by receptors associated with the glycoprotein IIb/IIIa complex. The purpose of this study was to identify the mechanism by which Zn2+ modulates exposure of fibrinogen receptors on the surface of human washed platelets. We determined that Zn2+ (300-800 microM)-induced platelet aggregation that was not accompanied by the release of [14C]serotonin was not blocked by ADP scavenging enzymes and 5'-p-fluorosulfonylbenzoyl-adenosine, an affinity label for ADP binding sites, but it was inhibited by disintegrins, staurosporine, and EDTA. Zn2+ (50-200 microM) showed a synergistic effect on platelet aggregation and platelet release caused by ADP and N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine, a Zn2+ chelator, and inhibited ADP-induced platelet aggregation that was reversed by Zn2+ (50 microM). Zn2+ (200 microM) increased the number of fibrinogen binding sites and the affinity of albolabrin (a disintegrin isolated from Trimeresurus albolabris snake venom that has been shown to bind to the fibrinogen receptor) on ADP-activated platelets. On the other hand, Zn2+ (100-800 microM) did not increase fibrinogen binding to the purified receptor. Incubation of platelets with Zn2+ (200 microM) resulted in the phosphorylation of a 47-kDa protein that was blocked by staurosporine, an inhibitor of protein kinase C. In conclusion, Zn2+ ions activate protein kinase C and enhance fibrinogen receptor exposure on the surface of platelets stimulated by ADP.

Adenosine Diphosphate↗
PubMed1993

Production and characterization of VP4/VP7 reassortant swine rotaviruses derived from Gottfried and OSU parental strains.

The ability of viral glycoproteins (VP) VP4/VP7 reassortant swine rotaviruses (RV) to induce cross-neutralizing antibody against parental serotypes was investigated in guinea pigs. Using selective culture conditions, we produced 10 reassortant viruses that contained gene segment 4 of the OSU RV strain and gene segment 9 of the Gottfried RV strain. These reassortant RV grew to high titer in cell culture and were neutralized by monospecific antisera against both parental RV strains. The reassortant RV were chemically inactivated with binary ethylenimine, adjuvanted with aluminum hydroxide, and used to produce antisera in guinea pigs. The hyperimmune antisera had high neutralization titer against both parent RV strains. These results indicate that several of the reassortant RV may be capable of inducing neutralizing antibodies to VP4 and VP7 and may have future use as bivalent vaccine strains.

Animals↗
PubMed1993

[Taxonomic study on strain 1254 and its mutant 113].

The mutant 113 was obtained from a natural non-antibiotic producing Streptomyces sp. 1254 by UV irradiation. It produced a group of novel anthracycline compounds designated mutactimycins. Strain 1254 was placed in the genus Streptomyces on the basis of its morphological characteristics and chemical properties of cells. According to Williams's numerical taxonomical data based on more than 50 physiological tests of a total of 375 type strains, the strain 1254 is considered to be more resemble to S. omiyaensis in the cluster of S. exfoliatus. The whole cell hydrolysate of mutant 113 contains DL-DAP, arabinose, galactose and rhamnose, but its cell envelope does not contain mycolic acids. Comparing with all genera of cell chemotype IV without mycolic acids and with Sacchrothrix which contains taxonomically significant rhamnose, mutant 113 shows differences with them respectively on FA composition or MK and PL patterns. The conclusion we can draw now is that mutant 113 doesn't belong to the same genus Streptomyces as its parent strain 1254 does, and is more close to the genus Sacchrothris.

Antibiotics, Antineoplastic↗
PubMed1992

Characterization of three alboaggregins purified from Trimeresurus albolabris venom.

Alboaggregins (AL-A, AL-B, AL-C) isolated from Trimeresurus albolabris snake venom represent a new family of proteins which bind to platelet glycoprotein Ib (GPIb). These alboaggregins were purified to homogeneity with ion exchange HPLC (Mono-Q column) and hydrophobic HPLC (TSK Phenyl-5PW column). On SDS-polyacrylamide gel electrophoresis, apparent molecular weights of AL-A, AL-B and AL-C were 52 kDa, 26 kDa, and 121 kDa respectively, under nonreducing conditions. Upon reduction, each alboaggregin showed two types of chains with apparent molecular weights in the range of 15-20 kDa. All three alboaggregins agglutinated formalin-fixed platelets. Agglutination activities and binding of labeled alboaggregins to GPIb were specifically inhibited by the monoclonal antibody AK2 which is directed against the 45 kDa N-terminal region on GPIb, but not by monoclonal antibodies against other epitopes on GPIb. 125I-alboaggregin binding to platelets was not altered by the presence of thrombin. Alboaggregins did not bind to GPIIb/IIIa. Alboaggregins were competitive inhibitors for 125I-bovine vWF binding to platelets. Mutual competition studies between AL-A, AL-B and AL-C for the binding of labeled bovine vWF and AL-B to platelets demonstrated that AL-B and AL-C had a significantly higher affinity than AL-A.

Agglutination↗
PubMed1992

In situ hybridization histochemistry: a new method for processing material stored for several years.

We describe here a protocol developed to detect specific mRNAs by in situ hybridization using tissue sections that were not treated to inactivate RNase and were stored in cryoprotectant solution for several years. Brains from rats, monkeys and humans were sectioned at 50 microns and stored free floating in an ethylene glycol based cryoprotective solution at -20 degrees C. Rat brain sections were kept in cryoprotective solution for 3 days, 1 month and 2 months. Control sections were cut and mounted immediately on gelatin-coated slides and stored at -80 degrees C. Monkey brain sections were stored in cryoprotective solution for up to 5 years. Human sections were tested after storage for one year. Oligonucleotide probes that were complementary to human preproenkephalin mRNA (amino acid sequences 130-145), rat preproenkephalin mRNA (sequences 388-435) and rat tyrosine hydroxylase mRNA (sequences 1441-1488) were labeled with 35S-dATP and terminal deoxynucleotidyl transferase. To prevent possible RNase contamination from mounting the tissue sections onto gelatin coated slides, the in situ hybridization was performed in sterile culture dishes. Following each step, solutions were aspirated out of the dish. The amount of probe necessary for each section was 45 microliters (rat), 450 microliters (monkey), and 350 microliters (human). Using this protocol, the detection of specific mRNAs in rat brain sections was more specific with less non-specific background as compared to control sections that were processed after they were mounted onto gelatin-coated sides. Excellent resolution was also obtained from monkey brain sections that were stored in cryoprotectant for up to 31 months and in human brain sections stored for 12 months.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗