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A Wong

Publications and source records attributed to A Wong.

At least 145 records · Page 8Linked to original sources
PubMed1994

Mutations in the catalase-peroxidase gene from isoniazid-resistant Mycobacterium tuberculosis isolates.

Isoniazid resistance in Mycobacterium tuberculosis has been associated with total deletion of the katG gene, which codes for catalase-peroxidase production. To determine whether this is a common mechanism of drug resistance, 9 isolates of isoniazid-resistant and 1 of isoniazid-sensitive M. tuberculosis were analyzed by polymerase chain reaction amplification of a 237-bp sequence of the katG gene. Amplification was observed in the isoniazid-sensitive isolate and in 8 resistant isolates; in only 1 isoniazid-resistant isolate was there no amplification of the expected band, suggesting gene deletion. DNA sequencing showed that 8 of the 9 isolates had point mutations, deletions, or insertions of 1-3 bases. Evidence corroborating the presence of mutations in the katG gene was obtained by single-strand conformation polymorphism analysis in these 8 isolates. Thus, mutations as well as insertions and deletions in the katG gene can account for inactive catalase peroxidase, leading to isoniazid resistance; gene deletion occurs only infrequently, in approximately 11% of cases.

Bacterial Proteins↗
PubMed1994

Stabilization and multidose use of exametazime for cerebral perfusion studies.

The efficient use of exametazime for cerebral blood flow imaging is restricted by the short useful life of the reconstituted kit due to the instability of the primary complex. It is therefore recommended that 99Tcm-exametazime be used within half an hour after preparation allowing only a single patient dose to be prepared from one vial of exametazime. The shelf-life of 'cold' reconstituted exametazime has been extended by means of stannous enhancement. Freshly prepared stannous fluoride solution, 0.8 ml (5.4 micrograms SnF2), was mixed with 0.5 ml (42 micrograms) exametazime solution followed by the addition of up to 1500 MBq pertechnetate. The radiochemical purity of the chelate was 91% (S.D. 3.6%, n = 3). The rate of conversion of the primary complex (kc = 0.012 +/- 0.011 h-1) was considerably slower than the rate of degradation obtained using the recommended method of preparation (kc = 0.17 +/- 0.02 h-1). Radiochemical purity levels greater than 80% were maintained for up to 2.5 h after preparation and the level of free pertechnetate did not exceed 7%. There was only a slight deterioration of the cold reconstituted exametazime on storage of 0.3 +/- 0.1% per day. However, exametazime reconstituted up to 3 weeks previously produced more than 80% purity. The mean radiochemical purity obtained in 22 studies was 90% with a range of 81-98%. Clinical validation was performed in a blinded study of 38 patients using single photon emission computed tomography (SPECT). There was no significant difference between the images obtained using the tin enhancement method of preparation and the manufacturer's method (chi 2 = 3.62, P = 0.16).(ABSTRACT TRUNCATED AT 250 WORDS)

Drug Stability↗
PubMed1994

Community photoscreening of six to nine month old infants for amblyopiogenic risk factors.

Photorefraction (PR) is gaining acceptance as potentially the most effective objective screening technique for amblyopia risk factors in the preverbal child. This study determined the validity and feasibility of using the Auckland eccentric photorefractor in the detection of amblyopiogenic factors in six to nine month old infants in an established community-based vision screening program. Photographs were analysed and compared to results of clinical examination including cycloplegic refraction. Amblyopia risk factors were present in 7.2% of the infants clinically examined. Analysis only of readable photographs in children who were also clinically examined, gave sensitivities ranging from 71% to 79%, and specificities ranging from 81% to 86%. Inclusion in the analysis of photo-failures lowered sensitivity figures to 56% to 61%, and specificity to 63% to 70%. Photofailures were predominantly due to poor operator technique. Calculation of kappa scores indicated fair observer reliability. In conclusion, PR could provide a feasible and sufficiently reliable screening technique in the infant, but requires adequate training and auditing of screening personnel performance for optimum effectiveness.

Amblyopia↗
PubMed1994

Selection of functional signal peptide cleavage sites from a library of random sequences.

The export of proteins to the periplasmic compartment of bacterial cells is mediated by an amino-terminal signal peptide. After transport, the signal peptide is cleaved by a processing enzyme, signal peptidase I. A comparison of the cleavage sites of many exported proteins has identified a conserved feature of small, uncharged amino acids at positions -1 and -3 relative to the cleavage site. To determine experimentally the sequences required for efficient signal peptide cleavage, we simultaneously randomized the amino acid residues from positions -4 to +2 of the TEM-1 beta-lactamase enzyme to form a library of random sequences. Mutants that provide wild-type levels of ampicillin resistance were then selected from the random-sequence library. The sequences of 15 mutants indicated a bias towards small amino acids. The N-terminal amino acid sequence of the mature enzyme was determined for nine of the mutants to assign the new -1 and -3 residues. Alanine was present in the -1 position for all nine of these mutants, strongly supporting the importance of alanine at the -1 position. The amino acids at the -3 position were much less conserved but were consistent with the -3 rules derived from sequence comparisons. Compared with the wild type, two of the nine mutants have an altered cleavage position, suggesting that sequence is more important than position for processing of the signal peptide.

Amino Acid Sequence↗
PubMed1994

Genetic contamination of Dahl SS/Jr rats. Impact on studies of salt-sensitive hypertension.

The Dahl salt-sensitive rat (SS/Jr) is a widely used animal model of salt-sensitive hypertension. SS/Jr rats are believed to be highly inbred and uniformly sensitive to the hypertensinogenic effects of sodium chloride, but we have recently observed that SS/Jr rats from Harlan Sprague Dawley, Inc, exhibit considerable variability in their blood pressure response to supplemental dietary salt. To test the possibility that commercially available SS/Jr rats are genetically contaminated and therefore no longer fully inbred, we performed molecular genetic studies and blood pressure measurements in several groups of SS/Jr rats purchased from Harlan Sprague Dawley. We found molecular evidence of heterozygosity and/or atypical allelic variants involving loci on at least five different chromosomes. Many of the rats also failed to exhibit a salt-sensitive blood pressure phenotype. We conclude that SS/Jr rats being sold by the only commercial vendor of Dahl rats in the United States are genetically contaminated and resistant to the hypertensinogenic effects of salt. These findings raise serious questions about the interpretation of research conducted with SS/Jr rats obtained from Harlan Sprague Dawley.

Animals↗
PubMed1994

Diagnosis of premature rupture of the membranes by the identification of alpha-feto-protein in vaginal secretions.

Premature rupture of membranes (PROM) is sometimes difficult to diagnose. This report proposes the use of alpha-feto-protein (AFP) values in vaginal secretions for diagnostic tests. Our investigation took place in two separate phases. The first phase validated the AFP test using an immuno-enzymatic assay method and determined a threshold value from a sample of 167 female patients (Group 1: 133 patients with an extremely low probability of PROM, and Group 2: 54 patients with confirmed PROM). In the second phase the test was applied to a sample of 145 female patients (Group 3) with suspected, but unconfirmed, PROM. Results from alpha-feto-protein (AFP) evaluation were compared with data obtained from clinical, echographic and other tests. The positive/negative threshold adopted was an AFP concentration of 30 micrograms/l. For the two first groups, 1 and 2, sensitivity and specificity was in the 98% to 99% confidence level. For Group 3, sensitivity and specificity results at the 30 micrograms/l threshold value were 94.5% and 95.4% respectively. Quantitative measurement of AFP determined by immuno-enzymatic assay of vaginal secretions with a threshold of 30 micrograms/l is a reliable, simple and rapid diagnostic test. Results obtained are significantly better than the measurement of pH, the determination of prolactin, and more practical than diamino-oxidase (DAO) assays.

Female↗
PubMed1994

IgG3 reactive rheumatoid factor in rheumatoid arthritis: etiologic and pathogenic considerations.

Rheumatoid factor (RF) is a polyclonal autoantibody directed against the Fc portion of IgG. Although the role of RF in patients with rheumatoid arthritis (RA) is unclear, immune complexes that form between RF and IgG can activate the classical complement (C) pathway, leading to pathogenic outcomes involving inflammatory events and tissue damage. The specificity of serum RF and RF produced by rheumatoid synovial cells (RSC) is different. Serum RF has specificity for rabbit IgG and human IgG subclasses IgG1, 2, and 4, but binds poorly to IgG3. The affinity of serum RF for IgG Fc is low, having an association constant of 10(4)-10(5) M-1. RSC RF, however, has specificity for human IgG and high avidity for IgG3. Because of this greater specificity and avidity for IgG3, and because RSC RF may be pathogenically more important than serum RF, an important role for IgG3-reactive RF in RA may exist. Binding of RF to IgG may be dependent on the allotype and glycosylation of IgG. Infectious agents present in RA patients may directly or indirectly induce the production of certain RF. In this communication, we review and expand on several observations examining the role of IgG3-reactive RF in RA including: 1) binding differences between RF derived from RSC and serum; 2) glycosylation characteristics of IgG and its interaction with RF; 3) apparent allotype dependent binding of IgG3-reactive RF; and 4) possible relationship between infectious agents and the production of IgG3-reactive RF. Taken together, these observations suggest an important role for IgG3-reactive RF in better understanding the etiology and pathogenesis of RA.

Amino Acid Sequence↗
PubMed1994

Assessment of the validity of the INR system for patients with liver impairment.

The INR system was developed to standardize PT reporting in patients on oral anticoagulants. We prospectively collected blood samples from 29 patients with liver impairment (INR 1.5-3.5). Control patients were on warfarin (n = 31). PT's were measured on an ACL-300 with three thromboplastin reagents. INR's were calculated using instrument specific ISI's. Other tests performed were FDP's, fibrinogen, aPTT, factors II, V, VII and X. The INR's for each patient in the study population using the three thromboplastin reagents were significantly different (p = 0.0001). Those for the control population were not (p = 0.0658). Fibrinogen, factors V, II and X were different at the 5% level of significance between the populations. FDP's were detected in 17 study subjects. The INR system is not valid for comparison of patients with liver impairment because different reagents do not give the same INR for the same sample. It is, however, no less valid than the use of PT with different thromboplastin reagents. Further study is recommended.

Adult↗
PubMed1994

[Cardiac amyloidosis secondary to multiple myeloma detected by echocardiography].

The authors present the clinical history of a 70-year-old male with arterial hypertension who sought medical advice because of dyspnea on exertion, orthopnea and episodes of paroxysmal nocturnal dyspnea. The electrocardiogram showed left arterial hemiblock and abnormalities of ventricular repolarization compatible with a left lateral endocardiac lesion. Echocardiography revealed a hypertrophied left ventricle with a small ventricular cavity, compatible with an infiltrative-restrictive myopathy. Blood chemistry showed creatinine 4.9 mg/dl, BUN 133 mg/dl and alkaline phosphatase 204 i.v. The patient expired because of intractable heart failure. The histopathological examination of a piece of myocardium (authorized by the family) stained with Congo red confirmed the presence of abundant, diffuse deposits of amyloid, as had been suspected because of the echocardiographic findings.

Aged↗
PubMed1994

Electrocautery-induced ignition of tonsillar packing.

A recent case of ignition of a bismuth-subgallate pack during routine tonsillectomy prompted this investigation of local oxygen levels. Similar conditions were reproduced in the laboratory to determine their influence on the flammability of materials commonly used to aid in haemostasis. Cotton tonsil packs soaked in saline, adrenalin, or adrenalin and bismuth were compared. During spontaneous ventilation through an age-appropriate uncuffed endotracheal tube, an air leak rarely occurred. However, when assisted ventilation was used, an airway leak produced an elevated oxygen concentration in 8 of 10 children. This was associated with increased combustibility of the packs, regardless of solution mixture. The addition of bismuth further increased combustibility. Partially saturated packs appeared to be more combustible than fully saturated packs.

Child↗
PubMed1994

A comparative study of prothrombinase and thrombin inhibitors in a novel rabbit model of non-occlusive deep vein thrombosis.

A quantitative and non-occlusive deep vein thrombosis model was developed in rabbits. We used this model to test the antithrombotic activity of the prothrombinase complex inhibitors factor rXai and its chemical analog glutamyl-glycyl-arginyl chloromethyl ketone inactivated human factor Xa (EGR-Xai), along with the thrombin inhibitors D-phenylalanyl-prolyl-arginyl chloromethyl ketone (PPACK) and heparin. Dose dependent effects of the inhibitors during constant infusion were monitored. Measurements included thrombus weights, hemostatic parameters and both cuticle and ear bleeding times. In this model, factor rXai and EGR-Xai had comparable in-vivo efficacy, and showed 80%-93% inhibition at plasma levels of 6.5 nM (rXai) and 8 nM (EGR-Xai). Effects on ex-vivo clotting times varied among the inhibitors. At 80-100% thrombus inhibition, factor rXai and EGR-Xai had no statistically significant effect, while PPACK extended thrombin clotting time (TCT) times 2.3-fold, and heparin prolonged both activated partial thromboplastin time (APTT), prothrombin time (PT) and TCT ex-vivo clotting times 6.9-, 1.2-, and 7-fold respectively. At these dosages, cuticle and ear bleeding times were prolonged for all inhibitors and showed increases of 177%-389% (cuticle) and 45%-129% (ear). Our results demonstrate that direct inhibition of prothrombinase complex assembly is effective in arresting venous thrombosis.

Amino Acid Chloromethyl Ketones↗
PubMed1994

Polymorphism at codon 36 of the p53 gene.

A polymorphism at codon 36 in exon 4 of the p53 gene was identified by single strand conformation polymorphism (SSCP) analysis and direct sequencing of genomic DNA PCR products. The polymorphic allele, present in the heterozygous state in genomic DNAs of four of 100 individuals (4%), changes the codon 36 CCG to CCA, eliminates a FinI restriction site and creates a BccI site. Including this polymorphism there are four known polymorphisms in the p53 coding sequence.

Base Sequence↗
PubMed1993

Preoperative concurrent 5-fluorouracil infusion, mitomycin C and pelvic radiation therapy in tethered and fixed rectal carcinoma.

PURPOSE: This is a Phase I/II study of preoperative concurrent radiation and chemotherapy in tethered and fixed rectal carcinoma. This study examined the curative resectability, the acute toxicities during chemo-radiation and the surgical complications. METHODS AND MATERIALS: Between 1986 and 1990, 46 patients were treated with preoperative pelvic radiation (4000 cGy in 20 fractions in 4 weeks), 5-Fluorouracil infusion (20 mg/m2, days 1-4 and 15-18) and Mitomycin C (8 mg/m2, day 1). This was followed by surgery 6 to 8 weeks later. 30 patients had tethered tumors and 16 patients had fixed tumors. RESULTS: After preoperative chemo-radiation, 41 patients (89%) underwent curative resection. Two patients (4%) had no residual tumor found (T0N0M0). Seven patients (15%) had nodal metastases. Two patients developed grade 3 neutropenia (WBC = 1-2 x 10(9)/L) during chemo-radiation. Five patients had delay in perineal wound healing. One patient had an anastomotic leak. Four patients developed stomal stenosis which required surgical revision. The 2-year actuarial survival was 73%. The 2-year local relapse rate was 16%. Patients with fixed carcinoma had a higher incidence of local failure (38% vs. 10%) and the difference was statistically significant (p = 0.0036). The 2-year distant failure rate was 41%, and the rates were similar for both tethered and fixed carcinomas. CONCLUSION: Preoperative pelvic radiation, chemotherapy and surgery could achieve a curative resection rate of 89% in tethered and fixed rectal carcinomas. However, distant metastases remained the major cause of failure.

Adenocarcinoma↗
PubMed1993

Survival benefit of tamoxifen therapy in adenocarcinoma of pancreas. A case-control study.

BACKGROUND: Clinical data suggest tamoxifen may improve the survival of patients with unresectable ductal adenocarcinoma of pancreas. METHODS: Eighty patients (50 women and 30 men) with biopsy-documented unresectable or incompletely resected ductal adenocarcinoma of the pancreas were treated with 20 mg of tamoxifen twice daily. The survival of the tamoxifen-treated group was compared with that of a case-control group of another 80 patients with pancreatic cancer, matched for age, sex, TNM stage, and bypass procedure versus biopsy. RESULTS: The median survival times for the tamoxifen-treated group versus controls were 7 and 3 months, respectively (P < 0.0001). For women older than 60 years of age and treated with tamoxifen, the median survival time was 12 months. Multivariate analysis of the 160 patients showed that tamoxifen therapy, female sex, absence of metastases at diagnosis, and bypass procedure are all of independent prognostic significance for prolonged survival. CONCLUSIONS: Patients with unresectable or incompletely resected ductal adenocarcinoma of pancreas may have a prolonged survival benefit while receiving tamoxifen treatment. This potential benefit is most prominent in older women.

Adenocarcinoma↗
PubMed1993

Human Tcrb-V6.10 is a pseudogene with Alu repetitive sequences in the promoter region.

Tcrb-V6.10 represents an abnormal human V gene with an Alu insertion in the promoter, a point mutation of a conserved Cys at position 23, and a missing nonamer within the usually conserved recombinase signal sequence. Here it is shown that b-V6.10 is found in the genome of most individuals, is normally located in the Tcrb-V locus on chromosome 7, but is not rearranged or transcribed. Thus, it is likely that the abnormal signal sequence precludes recombination and that the Alu insertion results in a disabled promoter, indicating the functional importance of the affected regions. Tcrb-V6.10 probably evolved by duplication of an ancestral Tcrb V13-V6-V5 cassette, like other members of the large b-V6 subfamily, and more recently became inactivated into a pseudogene.

Base Sequence↗
PubMed1993

Diethylnitrosamine- and partial hepatectomy-induced decrease in alpha 2u-globulin mRNA level in the rat liver.

Changes in gene expression in the rat liver were investigated by analyzing cDNA libraries for liver mRNAs from adult male rats injected with a chemical carcinogen diethylnitrosamine (DEN). Differential screening using normal and DEN-treated liver cDNAs as probes demonstrated that some of the mRNA species had noticeably lower abundance in the DEN-treated liver than in the untreated liver. Surprisingly, most of those clones were found to code for alpha 2u-globulin (A2uG), an abundant protein in the male rat liver. Further analysis by in situ hybridization revealed that the decrease in the A2uG mRNA level occurred in the area where liver cells were proliferating due to DEN treatment and/or partial hepatectomy (PH). The findings indicate coincidence of cell proliferation with a decrease in the A2uG gene expression in the adult male rat liver, implying that the A2uG-related change favors chemical carcinogen-induced cell growth.

Alpha-Globulins↗