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Biomedical subjects

W M Huang

Publications and source records attributed to W M Huang.

At least 19 recordsLinked to original sources
PubMed2003

Total anomalous pulmonary venous draining to inferior vena cava.

A 12-year-old girl complained of tachycardia and dyspnea after exertion but without cyanosis. Her echocardiogram showed an ASD and a widened inferior vena cava. A difference in PO2 between inferior and superior vena cava was evident. An anastomosis between left atrium and pulmonary vein, and a long oval pericardium to cover the opening of the descending vein and ASD into left atrium were performed during cardiopulmonary bypass. The patient recovered without complications.

Child↗
PubMed2002

Analysis of a Leptospira interrogans locus containing DNA replication genes and a new IS, IS1502.

A region of the Leptospira interrogans serovar pomona genome encoding DNA replication genes was characterized. This region, designated the ppa-ntrC locus, includes 19 open reading frames and a new insertion sequence, IS1502. Although this locus resembles replication origins from many eubacteria, it lacks several genes common to homologous loci. Some replication-related genes were previously located near rrf, and may have been moved to that location by homologous recombination between short sequence elements common to both loci. Further analysis showed that the ppa-ntrC region has undergone substantial change during spirochete evolution. Transcription analysis using RT-PCR revealed uniquely organized polycistronic mRNAs in the ppa-ntrC locus. The dnaN and recF intergenic region of serovar pomona was different from the homologous sites of 41 L. interrogans serovars by the presence of IS1502. The distribution of IS1502 throughout pathogenic Leptospira species varies. This result suggests that IS1502 may have been recently introduced into Leptospira.

Bacterial Proteins↗
PubMed2001

Effect of relative humidity on mixed aerosols in atmosphere.

In this study, the effects of relative humidity on the deliquescent point and size of internally mixed aerosols diameter, NH4NO3 and (NH4)2SO4 were investigated using a Tandem Differential Mobility Analyzer (TDMA) with a relative humidity conditioner. The growth of mixed aerosols appears to have two deliquescent steps. The first one was at about 61.2-61.3%, but the second one was at around 77-78%. At the first deliquescence point, growth ratio at phase change was 7.5%, which agrees with the growth ratio of ammonium nitrate aerosol. Growth ratio of phase change at the second deliquescence point was about 20%, lower than the growth ratio of ammonium sulfate aerosol. In the relative humidity range of 80-85%, the growth ratio of the mixed aerosols reached 60%. In other words, it appears that growth ratio increases with the size of aerosol. Furthermore, a theoretical growth model of mixed aerosols was developed and applied to estimate the amount of composition of the mixed aerosols dissolved at each deliquescence point. The results also show that some of ammonium sulfate already dissolved at the first deliquescence point according to the theoretical growth model.

Aerosols↗
PubMed2000

A bacterial genome in flux: the twelve linear and nine circular extrachromosomal DNAs in an infectious isolate of the Lyme disease spirochete Borrelia burgdorferi.

We have determined that Borrelia burgdorferi strain B31 MI carries 21 extrachromosomal DNA elements, the largest number known for any bacterium. Among these are 12 linear and nine circular plasmids, whose sequences total 610 694 bp. We report here the nucleotide sequence of three linear and seven circular plasmids (comprising 290 546 bp) in this infectious isolate. This completes the genome sequencing project for this organism; its genome size is 1 521 419 bp (plus about 2000 bp of undetermined telomeric sequences). Analysis of the sequence implies that there has been extensive and sometimes rather recent DNA rearrangement among a number of the linear plasmids. Many of these events appear to have been mediated by recombinational processes that formed duplications. These many regions of similarity are reflected in the fact that most plasmid genes are members of one of the genome's 161 paralogous gene families; 107 of these gene families, which vary in size from two to 41 members, contain at least one plasmid gene. These rearrangements appear to have contributed to a surprisingly large number of apparently non-functional pseudogenes, a very unusual feature for a prokaryotic genome. The presence of these damaged genes suggests that some of the plasmids may be in a period of rapid evolution. The sequence predicts 535 plasmid genes >/=300 bp in length that may be intact and 167 apparently mutationally damaged and/or unexpressed genes (pseudogenes). The large majority, over 90%, of genes on these plasmids have no convincing similarity to genes outside Borrelia, suggesting that they perform specialized functions.

Base Sequence↗
PubMed2000

The role of genomics in approaching the study of Borrelia DNA replication.

The identification of chromosomal and episomal origins of replication in the genome of the causative agent of Lyme disease, the spirochete Borrelia burgdorferi, has been greatly facilitated by genomics. Analysis of genome features, including strand compositional asymmetries, organizational similarities to other bacterial origins of replication, and the presence of homologues of genes involved in replication and partitioning, have contributed to the identification of a collection of putative origins of replication within the Borrelia genome. This analysis has provided the basis for the experimental verification of origins in the linear chromosome and in the linear plasmid Ip28-2. Information generated during the study of these origins will significantly contribute to the understanding of the mechanisms of replication and partitioning in Borrelia.

Amino Acid Sequence↗
PubMed1999

Sparfloxacin selects gyrase mutations in first-step Mycoplasma hominis mutants, whereas ofloxacin selects topoisomerase IV mutations.

The role of mutations in the genes for GyrA and ParC in quinolone resistance in Mycoplasma hominis was studied. Selection with sparfloxacin gave mutations at GyrA83 (Ser-->Leu; Escherichia coli numbering) or GyrA87 (Glu-->Lys), and mutants had increased levels of resistance to sparfloxacin (8- to 16-fold) but not to ofloxacin. Selection with ofloxacin gave changes at ParC80 (Ser-->Ile) or ParC84 (Glu-->Lys), and mutants were four- to eightfold more resistant to ofloxacin but not to sparfloxacin. Selection of second-step mutants from strains with ParC mutations with either quinolone yielded double mutants with additional mutations at GyrA83 (Ser-->Trp or Ser-->Leu) or GyrA87 (Glu-->Lys). Second-step selection of GyrA mutants gave additional mutations at ParC80 (Ser-->Ile) or ParC84 (Glu-->Lys). Two-step mutants showed high levels of resistance to ofloxacin (MICs, 64 to 128 microg/ml) and moderate levels of resistance to sparfloxacin (MICs, 2 to 8 microg/ml). The primary target of ofloxacin in first-step mutants of Mycoplasma hominis was ParC, whereas that for sparfloxacin was GyrA.

Anti-Infective Agents↗
PubMed1999

Independent effects of preload, afterload, and contractility on left ventricular torsion.

Shortening of oblique left ventricular (LV) fibers results in torsion. A unique relationship between volume and torsion is therefore expected, and the effects of load and contractility on torsion should be predictable. However, volume-independent behavior of torsion has been observed, and the effects of load on this deformation remain controversial. We used magnetic resonance imaging (MRI) with tagging to study the relationships between load and contractility, and torsion. In ten isolated, blood-perfused canine hearts, ejection was controlled by a servopump: end-diastolic volume (EDV) was controlled by manipulating preload parameters and end-systolic volume (ESV) by manipulating afterload using a three-element windkessel model. MRI was obtained at baseline, two levels of preload alteration, two levels of afterload alteration, and dobutamine infusion. An increase in EDV resulted in an increase in torsion at constant ESV (preload effect), whereas an increase in ESV resulted in a decrease in torsion at constant EDV (afterload effect). Dobutamine infusion increased torsion in association with an increase in LV peak-systolic pressure (PSP), even at identical EDV and ESV. Multiple regression showed correlation of torsion with preload (EDV), afterload (ESV), and contractility (PSP; r = 0.67). Furthermore, there was a close linear relationship between torsion and stroke volume (SV) and ejection fraction (EF) during load alteration, but torsion during dobutamine infusion was greater than expected for the extent of ejection. Preload and afterload influence torsion through their effects on SV and EF, and there is an additional direct inotropic effect on torsion that is independent of changes in volume but rather is force dependent. There is therefore potential for the torsion-volume relation to provide a load-independent measure of contractility that could be measured noninvasively.

Animals↗
PubMed1999

[The development of mouse bioreactor expressing human tissue plasminogen activator (tPA) in mammary gland by transfecting spermatozoa in testicular duct].

The most established methods for development of transgenic animals are the microinjection of DNA into the fertilized eggs, but it is still a procedure of certain complexity and high cost. Therefore, the idea of using sperm as a vehicle to carry exogenous DNA into eggs is very attractive, and there have been some successful reports. Though the methods are rather simple they sometimes have low reproducibility. To improve the technique we transinfected the spermatozoa in testicular duct, not in vitro, to produce mice which expressed human tissue plasminogen activator (tPA) in mammary gland. The results demonstrated that: (1) 5 transinfected mice mated 10 female mice in 10 days after operation, (2) 79 founders were developed and 42 survived, (3) using PCR to detect foreign DNA integrated into the genome of founders, 7 out of 42 founders were positive (16.67%), (4) The expression level of tPA was 48-80 ng/ml in the milk of 5 PCR positive founders and (5) the foreign DNA integrated into the genome was detected in 2 out of 4 1st offspring by PCR technique.

Animals↗
PubMed1998

Bipolar localization of Bacillus subtilis topoisomerase IV, an enzyme required for chromosome segregation.

In Bacillus subtilis, parE and parC were shown to be essential genes for the segregation of replicated chromosomes. Disruption of either one of these genes resulted in failure of the nucleoid to segregate. Purified ParE and ParC proteins reconstituted to form topoisomerase IV (topo IV), which was highly proficient for ATP-dependent superhelical DNA relaxation and decatenation of interlocked DNA networks. By immunofluorescence microscopy and by directly visualizing fluorescence by using green fluorescence protein fusions, we determined that ParC is localized at the poles of the bacteria in rapidly growing cultures. The bipolar localization of ParC required functional ParE, suggesting that topo IV activity is required for the localization. ParE was found to be distributed uniformly throughout the cell. On the other hand, fluorescence microscopy showed that the GyrA and GyrB subunits of gyrase were associated with the nucleoid. Our results provide a physiologic distinction between DNA gyrase and topo IV. The subcellular localization of topo IV provides physical evidence that it may be part of the bacterial segregation machinery.

Artificial Gene Fusion↗
PubMed1998

Development of quinolone-resistant Campylobacter fetus bacteremia in human immunodeficiency virus-infected patients.

Campylobacter fetus subspecies fetus has been recognized as a cause of systemic illness in immunocompromised hosts, including relapsing bacteremia in human immunodeficiency virus (HIV)-infected patients. Acquired resistance to quinolone therapy, while reported for a variety of bacteria, including Campylobacter jejuni, has not been previously documented for C. fetus. Two cases of quinolone-resistant C. fetus bacteremia were detected in HIV-infected patients. Cloning and nucleotide sequencing of the C. fetus gyrA gene in the 2 resistant isolates demonstrated a G-to-T change that led to an Asp-to-Tyr amino acid substitution at a critical residue frequently associated with quinolone resistance. In addition, comparison of the pre- and posttreatment isolates from 1 patient documented outer membrane protein changes temporally linked with the development of resistance. Relapsing C. fetus infections in quinolone-treated HIV-infected patients may be associated with the acquisition of resistance to these agents, and this resistance may be multifactorial.

AIDS-Related Opportunistic Infections↗
PubMed1998

p53 gene therapy in a rat model of hepatocellular carcinoma: intra-arterial delivery of a recombinant adenovirus.

p53 tumor suppressor gene therapy has been proposed for cancers characterized by inactivation of p53 function, and successful therapy will require efficient strategies for gene delivery. To maximize transgene expression in tumors, a clinical strategy has been proposed to treat neoplasms in the liver via hepatic artery administration of a recombinant adenovirus encoding wild-type p53 (rAd-p53). We have developed a syngeneic rat model using a p53mut hepatocellular carcinoma cell line (McA-RH7777) that results in multifocal liver tumor nodules to provide experimental support for this strategy. Treatment of McA-RH7777 cells with rAd-p53 in vitro resulted in efficient transgene expression, growth suppression, and apoptosis. Intrahepatic artery dosing with rAd-p53 or an adenovirus encoding beta-galactosidase (rAd-betagal) increased transgene expression in tumor tissue and decreased systemic exposure when compared with i.v. dosing. Daily hepatic artery dosing of rAd-p53 suppressed tumor growth when compared with untreated rats or animals treated with rAd-betagal. These data demonstrate the potential for arterial gene delivery to tumors using recombinant adenoviruses, and support continued investigation of rAd-p53 gene therapy for liver malignancies.

Adenoviridae↗
PubMed1997

Genomic sequence of a Lyme disease spirochaete, Borrelia burgdorferi.

The genome of the bacterium Borrelia burgdorferi B31, the aetiologic agent of Lyme disease, contains a linear chromosome of 910,725 base pairs and at least 17 linear and circular plasmids with a combined size of more than 533,000 base pairs. The chromosome contains 853 genes encoding a basic set of proteins for DNA replication, transcription, translation, solute transport and energy metabolism, but, like Mycoplasma genitalium, it contains no genes for cellular biosynthetic reactions. Because B. burgdorferi and M. genitalium are distantly related eubacteria, we suggest that their limited metabolic capacities reflect convergent evolution by gene loss from more metabolically competent progenitors. Of 430 genes on 11 plasmids, most have no known biological function; 39% of plasmid genes are paralogues that form 47 gene families. The biological significance of the multiple plasmid-encoded genes is not clear, although they may be involved in antigenic variation or immune evasion.

Biological Transport↗
PubMed1997

Telomeres of the linear chromosomes of Lyme disease spirochaetes: nucleotide sequence and possible exchange with linear plasmid telomeres.

Bacteria of the spirochaete genus Borrelia have linear chromosomes about 950 kbp in size. We report here that these linear chromosomes have covalently closed hairpin structures at their termini that are similar but not identical to those reported for linear plasmids carried by these organisms. Nucleotide sequence analysis of the chromosomal telomeric regions indicates that unique, apparently functional genes lie within a few hundred bp of each of the telomeres, and that there is an imperfect 26 bp inverted repeat at the two telomeres. In addition, we characterize a major chromosomal length polymorphism within the right telomeric regions of various Borrelia isolates, and show that sequences similar to those near the right telomere are often found on linear plasmids in B. burgdorferi (sensu stricto) isolates from nature. Sequences similar to a number of other regions of the chromosome, including those near the left telomere, were not found on B. burgdorferi plasmids. These observations suggest that there has been historical exchange of genetic information between the linear plasmids and the right end of the linear chromosome.

Amino Acid Sequence↗
PubMed1997

The new model of age-dependent changes in bone mineral density.

To theoretically and quantitively describe the phenomena that bone mineral density (BMD) was changed with, the three-exponential model was proposed. Our results showed that BMD in radius and ulna in a sample of 36,879 healthy people ranging in age from 2 to 100 years fit the three-exponential equation well. Bone mass loss in Chinese women was faster than that in Chinese men. The method to accurately calculate the peak BMD and the corresponding age was given. The peak BMD and age for Chinese men and women in radius were 0.7469 g/cm2 and 35 years old, and 0.7051 g/cm2 and 33 years old respectively. The peak BMD and age in ulna were 0.7515 g/cm2 and 35 years old for Chinese men, and 0.6904 g/cm2 and 31 years old for Chinese women. Peak BMD in Chinese women was lower than in men. Peak BMD occurred slightly earlier in Chinese women. We concluded that our model could successfully characterize the regularity of bone mass accumulation and loss during the whole lifetime. The quantitive relationship was very useful in the diagnosis of osteoporosis.

Adolescent↗
PubMed1996

Characterization of genes encoding topoisomerase IV of Mycoplasma genitalium.

A type-II toposiomerase (Topo-IV) encoded by the parC and parE genes in Escherichia coli and Salmonella typhimurium is thought to be involved in cell septation and in the decatenation of newly replicated chromosomes. We have identified parC and parE homologs in the pleomorphic, wall-less organism Mycoplasma genitalium. Since the mechanics of cell septation in conventional eubacterial species is believed to be mediated by cell-wall constituents, there is no clear understanding of what coordinates that process in wall-less species. The presence of par genes in this bacterium, which has the smallest genome of any free-living organism, suggests that Topo-IV has been evolutionarily conserved because of an essential role in mediating cell division.

Bacterial Proteins↗
PubMed1996

Bacterial diversity based on type II DNA topoisomerase genes.

Type II DNA topoisomerases are essential and ubiquitous DNA metabolic enzymes that alter DNA topology. Eubacteria have two indispensable type II DNA topoisomerases, DNA gyrase encoded by gyrB and gyrA and topoisomerase IV encoded by parE and parC. These genes belong to a single family whose members span both eukaryotes and prokaryotes. The highly conserved motifs in these genes provide a rationale for the design of universal primers used in the polymerase chain reaction in order to systematically generate a data set suitable for bacterial diversity studies at the macro-diversity level, as well as at the micro-diversity level displaying individual species and isolates. This family of genes is the subject of intensive biochemical and genetic analyses, which provide an opportunity for comprehensive understanding of sequence conservation and variability and their relationship to function. These genes are ideally suited for microbial identification and biodiversity analyses.

Amino Acid Sequence↗
PubMed1995

The recA gene of Borrelia burgdorferi.

The nucleotide sequence of the Borrelia burgdorferi (Bb) Sh-2-82 recA gene has been determined using PCR-based approaches without the construction of a genomic library. The gene should encode a protein of 365 amino acids which is highly homologous to other known RecA proteins. It represents a new homolog from a distinct phylogenetic branch of eubacteria. Although, previous reports concluded that recA is absent from Bb, the identification presented here conclusively shows its presence and reaffirms the ubiquity of RecA in prokaryotes.

Amino Acid Sequence↗