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Biomedical subjects

L Chan

Publications and source records attributed to L Chan.

At least 217 records · Page 12Linked to original sources
PubMed1996

Recognition of tetrahedral 1,10-phenanthroline-cuprous chelates by transcriptionally active complexes does not depend on the sequence of the promoter.

BACKGROUND: The open complex formed at the initiation site of transcription within the active site of RNA polymerase is unique to actively transcribing genes and is thus an ideal target for the design of transcription inhibitors. Many redoxactive tetrahedral cuprous chelates of 1,10-phenanthroline (OP) or derivatives cleave the single-stranded template, principally at sequence positions -7 to -3, whereas the redox-inactive tetrahedral cuprous chelate of 2, 9-dimethyl-OP (neocuproine) blocks transcription, but does not cleave. The octahedral (OP)3-Fe2+ chelate has no effect. Different promoters can give different cleavage patterns. We therefore searched for structural determinants of the open complex that are important in the cleavage reaction. RESULTS: Using site-directed mutagenesis, we systematically altered the nucleotides at the cleavage sites of the Escherichia coli lac UV-5-RNA polymerase open complex (positions -6 to -4), which are highly variable in E. coli promoters. Surprisingly, these changes had little effect on catalytic activity, on transcription inhibition by the cuprous complex of neocuproine and on the cleavage patterns generated by the cuprous chelates of OP derivatives. The scission pattern of a lac UV-5 promoter mutant in which the cleavage sites have the sequence of the trp EDCBA promoter is that of the lac UV-5 promoter, not the trp EDCBA promoter. CONCLUSIONS: Nucleotide-specific interactions are not responsible for the observed cleavage patterns. The recognition of the tetrahedral OP chelate must be due to a specific structure of the single-stranded regions, determined by RNA polymerase-DNA interactions in the upstream regulatory region.

Chelating Agents↗
PubMed1996

Adenovirus-mediated gene transfer: strategies and applications in lipoprotein research.

Adenovirus-mediated gene transfer into mammalian liver is a highly efficient process that can result in transduction frequencies approaching 100%. Coupled with efficient expression levels from these vectors, the transfer of genes encoding a variety of enzymes, ligands and receptors has resulted in physiologically significant effects on lipoprotein metabolism. Adenovirus vectors have not only proved useful in the study of lipoprotein metabolism, they may also ultimately be used for hepatic gene therapy of inherited monogenic and polygenic disorders. The main hurdle to overcome before this technology can be therapeutically applied is the relatively short duration of expression in immunocompetent hosts. Apparently, cytolytic T-lymphocyte-mediated rejection of the transduced hepatocytes is caused by low-level expression of adenovirus genes. Several strategies have been recently employed in an attempt to circumvent this immune response and prolong transgene expression.

Adenoviruses, Human↗
PubMed1996

Pre-operative parental anxiety.

This study attempts to identify the incidence and specific sources of anxiety in the parents of children admitted to hospital for elective surgery, to isolate factors associated with increased anxiety and to identify useful ameliorative measures. One hundred parents were interviewed and completed a questionnaire before their child's surgery. Parental anxiety levels were measured using the Leeds scale for self-assessment of anxiety. Anxiety-related illness was identified in 47% of parents, who were significantly more concerned than others about all aspects of their children's hospitalisation. No factors were identified which could predict which parents were at high risk of developing an anxiety state. When questioned about educational and interventional measures which they felt would be reassuring, the same factors were identified by 'anxious' and 'non-anxious' parents. As all parents agree on useful ameliorative factors, a general advice and education programme would be appropriate.

Adult↗
PubMed1996

Burnout and its correlates in emergency physicians: four years' experience with a wellness booth.

OBJECTIVE: To measure the degree of burnout among emergency physicians (EPs) and to identify and rank predictive factors. METHODS: Using the Maslach Burnout Inventory as well as a 79-item questionnaire, a cross-sectional survey was conducted for physician registrants at the Annual Scientific Assemblies of the American College of Emergency Physicians from 1992 to 1995. Degrees of burnout were stratified into low, moderate, and high ranges. Univariate and stepwise multiple regression analyses were conducted to identify and rank correlates to burnout scores. RESULTS: Of 1,272 registrants taking the inventory, 60% registered in the moderate to high burnout ranges. Twenty-one correlates were identified. These were classified broadly in terms of negative perceptions of self, negative practice habits and attitudes, and unhealthy lifestyles. The most highly ranked correlates were: self-recognition of burnout, lack of job involvement, negative self-assessment of productivity, dissatisfaction with career, sleep disturbances, increased number of shifts per month, dissatisfaction with specialty services, intent to leave the practice within 10 years, higher levels of alcohol consumption, and lower levels of exercise. Age and years of practice were not significant predictors of burnout. Projected attrition rates were 7.5% over 5 years and 25% over 10 years. CONCLUSIONS: Elevated levels of burnout exist among a substantial percentage of surveyed EPs. However, there is evidence for a "survivor" category of practitioners for whom burnout either does not develop or is a reversible process. The projected attrition rate over 5 and 10 years appears to be no greater than that of the average medical specialty.

Adaptation, Psychological↗
PubMed1996

Systemic toxicity from ocular homatropine.

Toxidromes are well known to emergency physicians. An unclear or incomplete history and subtle findings on physical examination make the diagnosis of poisonings challenging. This article reports a patient who had an acute onset of visual hallucinations, pressured speech, and mania. Although she denied taking any medications, she was ultimately diagnosed as having anticholinergic toxicity. On further questioning of family members, it was discovered that she was being treated for anterior uveitis with 5% homatropine. This case illustrates the potential role of ocular medications in systemic toxicity. Patients often do not consider eyedrops to be medications, and their use may be overlooked in the medical history. It also is important to educate patients and medical staff in methods to minimize systemic toxicity when using ocular medication.

Acute Disease↗
PubMed1996

Analysis of CA repeat polymorphisms places three human gene loci on the 8p linkage map.

The gene loci for luteinizing hormone-releasing hormone (LHRH), the beta-3 adrenergic receptor (ADRB3), and heregulin (HGL) have been assigned to the short arm of human chromosome 8, but the positions of these loci on the human genetic linkage map have not been previously reported. We have isolated simple tandem repeat polymorphisms (STRPs) for these loci. These STRPs enabled us to determine the genetic map locations for these genes.

Base Sequence↗
PubMed1996

Secondary oxalosis: a cause of delayed recovery of renal function in the setting of acute renal failure.

Oxalosis, or calcium oxalate deposition in the tissues, may develop in patients with inherited disorders of oxalate metabolism or can occur secondary to other diseases. In this study, a case of renal oxalosis probably secondary to excessive parenteral vitamin C administration in a patient with acute post-traumatic oliguric renal failure is reported. Oxalate deposits may have contributed to further worsening and delayed recovery of renal function. The elimination of the source of excess vitamin C and its presumed effect on oxalate production, together with enhanced removal of oxalate during aggressive dialysis, resulted in prompt recovery of renal function. Secondary oxalosis represents a possible cause of delayed recovery of renal function in patients with acute renal failure who are receiving vitamin C supplementation if excess dosage of that supplementation is given. Vitamin C supplementation, if utilized, should be carefully monitored in patients receiving artificial renal replacement therapy.

Ascorbic Acid↗
PubMed1996

Color Doppler flow as an indicator of nodal metastasis in solid breast masses.

Tumor metastases are dependent on angiogenesis. This prospective study evaluates the role of color Doppler sonographic signals in (1) detecting blood flow in solid breast masses, (2) differentiating between benign and malignant breast tumors, and (3) identifying women at risk for axillary lymph node metastasis. Ultrasonographically proved solid breast masses from 95 women were evaluated with color Doppler imaging for the presence of blood flow. A characteristic curvilinear or branching signal pattern, labeled the "rim sign," was noted to be either present or absent at the periphery of the mass in all cases. The color Doppler sonographic signals in 86 patients with pathologic results were correlated with the occurrence of malignancy and axillary lymph node metastasis. Fifty-three of the 86 patients (62%) had benign breast disease and 33 patients (38%) had malignant tumors. Sixteen (30%) of the benign tumors and 20 (61%) of the malignant cancers demonstrated a positive rim sign. A positive rim sign has a 61% sensitivity and a 70% specificity for the prediction of breast malignancy. In the malignant masses, nodal involvement occurred in 50% of patients with a positive rim sign and 10% of patients with a negative rim sign. A negative rim sign has a negative predictive value of 90% for nodal metastasis. Color Doppler imaging can detect blood flow in both malignant and benign solid breast masses. A positive rim sign is a poor prognostic factor whereas a negative rim sign is a good prognostic indicator for axillary nodal metastases.

Adult↗
PubMed1996

Apolipoprotein B mRNA editing protein: a tool for dissecting lipoprotein metabolism and a potential therapeutic gene for hypercholesterolemia.

Apolipoprotein (apo) B mRNA editing protein is an essential catalytic component of the apoB mRNA editing enzyme complex. Its cDNA has been cloned recently from rats and humans. In the presence of other proteins of the editing enzyme complex, it will deaminate nucleotide 6666 in apoB mRNA, a cytidine residue, converting it to uridine. The end result of this reaction is the production of apoB-48 in place of apoB-100. The editing protein exists as a homodimer. It imparts editing activity to HepG2, a human hepatoma cell line, causing these cells to start producing apoB-48 in addition to apoB-100. Therefore, it can be used as a therapeutic agent to reduce apoB-100 production. Preliminary experiments in our laboratory indicate that somatic gene transfer of the editing protein is highly effective in lowering plasma low density lipoproteins.

APOBEC-1 Deaminase↗
PubMed1996

Restriction fragment length polymorphism of the human apo B and apo AII gene regions among type II diabetics.

Levels of plasma low density lipoproteins (LDL) are positively, and high density lipoproteins (HDL) are negatively correlated with an increased risk for atherosclerosis. The frequencies of restriction fragment length polymorphism (RFLP) of the genes for apoB, a major LDL apolipoprotein, and apoAII, a major HDL apolipoprotein, were studied in 45 Tunisian diabetics and an equal number of sex and age matched controls. Southern blot analysis of an EcoR1 apoB polymorphism and an Msp1 apo AII polymorphism indicates that there was no statistically significant difference in the incidence of different genotypes or alleles among diabetics compared to controls.

Adult↗
PubMed1995

Tissue-specific expression and cholesterol regulation of acylcoenzyme A:cholesterol acyltransferase (ACAT) in mice. Molecular cloning of mouse ACAT cDNA, chromosomal localization, and regulation of ACAT in vivo and in vitro.

Acyl-coenzyme A:cholesterol acyltransferase (ACAT) catalyzes the esterification of cholesterol with long chain fatty acids and is believed to play an important part in the development of atherosclerotic lesions. To facilitate the study of ACAT's role in this process, we have used the human ACAT K1 clone previously described (Chang, C. C. Y., Huh, H. Y., Cadigan, K. M. and Chang, T. Y. (1993) J. Biol. Chem. 268, 20747-20755) to isolate mouse ACAT cDNA from a liver cDNA library. The 3.7-kilobase cDNA clone isolated contains a 1620-base pair open reading frame which encodes a protein of 540 amino acids. The predicted mouse ACAT protein is 87% identical to the protein product of human ACAT K1 and shares many of the same secondary structural features, including two transmembrane domains, a leucine heptad motif consistent with dimer or multimer formation, and five regions homologous to the "signature sequences" found in other enzymes that catalyze acyl adenylation followed by acyl thioester formation and acyl transfer. Using the cDNA as a hybridization probe, we mapped the gene encoding mouse ACAT to chromosome 1 in a region syntenic to human chromosome 1 where the ACAT gene is located. Northern blot analysis and RNase protection assays of mouse tissues revealed that ACAT mRNA is expressed most highly in the adrenal gland, ovary, and preputial gland and is least abundant in skeletal muscle, adipose tissue, heart, and brain. To study the dietary regulation of ACAT mRNA expression in mouse tissues, we fed C57BL/6J mice a high-fat, high-cholesterol (HF/HC) atherogenic diet for 3 weeks and measured ACAT mRNA levels in various tissues by RNase protection. The HF/HC diet had little effect on ACAT mRNA levels in the small intestine, aorta, adrenal, or peritoneal macrophages, whereas hepatic ACAT mRNA levels were doubled in mice fed the atherogenic diet. ACAT activity in liver microsomes was similarly increased in cholesterol-fed mice, suggesting that mouse ACAT is regulated at least in part at the level of mRNA abundance. Additionally, a significant positive correlation was observed between ACAT activity and microsomal free cholesterol levels in chow- and cholesterol-fed mice, supporting the concept of cholesterol availability as a regulator of ACAT. To further investigate the regulation of ACAT activity under controlled conditions, ACAT-deficient Chinese hamster ovary cells were stably transfected with the mouse ACAT cDNA clone driven by a cytomegalovirus promoter. Two transfected Chinese hamster ovary cell lines that expressed the mouse ACAT transgene regained the ability to esterify cholesterol.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1995

Partial structure of the mouse glucokinase gene.

A complementary DNA for glucokinase (GK) was cloned from mouse liver total RNA by a combination of the polymerase chain reaction (PCR) and mouse liver cDNA library screening. Liver- and beta-cell-specific exons 1 were isolated by PCR using mouse and rat genomic DNAs. These clones were then used to screen a mouse genomic library; three genomic clones were isolated and characterized. The mouse GK gene spans over 20 kb, containing 11 exons including a liver- or beta-cell-specific exon 1, which encodes a tissue-specific 15-aa peptide at the N-terminus of the protein. Both types of GK contain 465 amino acid residues. The predicted amino acid sequence of mouse beta-cell-specific GK showed 98 and 96% identity to the rat and human enzymes, respectively; the corresponding values are 98 and 95%, respectively, for the liver-specific GK. Several transcription factor-binding consensus sequences are identified in the 5' flanking region of the mouse GK gene.

Amino Acid Sequence↗
PubMed1995

Very low density lipoprotein receptor binds and mediates endocytosis of urokinase-type plasminogen activator-type-1 plasminogen activator inhibitor complex.

Very low density lipoprotein receptor (VLDL-R) was found to be expressed in bovine mammary gland and the human breast carcinoma cell line MCF-7 as an M(r) 105,000 variant, and in Chinese hamster ovary (CHO) cells transfected with human VLDL-R cDNA as an M(r) 130,000 variant. The receptor was purified by ligand affinity chromatography with immobilized M(r) 40,000 receptor-associated protein (RAP). The purified receptor was found to bind urokinase-type plasminogen activator-type-1 plasminogen activator inhibitor complex (u-PA.PAI-1), while there was no or very weak binding of active site blocked u-PA (DFP-u-PA), PAI-1 or u-PA-type-2 plasminogen activator inhibitor complex. The binding of u-PA.PAI-1 was blocked by RAP. The transfected CHO cells had an efficient, RAP-sensitive endocytosis of u-PA.PAI-1, severalfold higher than non-transfected parental CHO cells. u-PA.PAI-1 endocytosis was partially inhibited by DFP-u-PA, which blocks binding of the complex to the u-PA receptor. RAP and DFP-u-PA sensitive u-PA.PAI-1 endocytosis was also observed in MCF-7 cells, which were without detectable levels of other RAP-binding endocytosis receptors. These results show that VLDL-R represents a novel endocytosis mechanism for u-PA receptor-bound u-PA.PAI-1.

Amino Acid Sequence↗
PubMed1995

Alternative mRNA splicing and differential promoter utilization determine tissue-specific expression of the apolipoprotein B mRNA-editing protein (Apobec1) gene in mice. Structure and evolution of Apobec1 and related nucleoside/nucleotide deaminases.

Apolipoprotein (apo) B mRNA editing consists of a C-->U conversion involving the first base of the codon CAA, encoding Gln 2153, to UAA, a stop codon. Editing occurs in the intestine only in most mammals, and in both the liver and intestine in a few mammalian species including mouse. We have cloned the cDNA for the mouse apoB mRNA editing protein, apobec1. Expression of mouse apobec1 cDNA in HepG2 cells results in the editing of the intracellular apoB mRNA. The cDNA predicts a 229-amino acid protein showing 92, 66, and 70% identity to the rat, rabbit, and human proteins, respectively. Based on the estimated values of divergence of apobec1 sequences in terms of the numbers of synonymous and non-synonymous suhstitutions per site, we found that apobec1 is a fairly rapidly evolving protein. Sequence comparison among mammalian apobec1 sequences has permitted the identification of seven conserved regions that may be functionally important for editing activity. We present a phylogenetic tree relating apobec1 sequences to double-stranded RNA adenosine deaminase and other nucleotide/nucleoside deaminases. Northern blot analysis indicates that apobec1 mRNA exists in two different sizes, a approximately 2.2-kilobase (kb) form in small intestine and a approximately 2.4-kb form in liver, spleen, kidney, lung, muscle, and heart. To study the molecular basis for the different sized apobec1 mRNAs, we cloned the apobec1 gene and characterized its exon-intron organization together with the sequences expressed in the hepatic and intestinal mRNA. The mouse apobec1 gene contains 8 exons and spans approximately 25 kb, and is located in chromosome 6. The major hepatic mRNA contains all 8 exons, whereas the major small intestinal mRNA misses the first 3 exons and its transcription is initiated in exon 4. The intestinal mRNA also contains at its 5' end a unique 102-nucleotide piece that is absent in the liver mRNA. We also identified two alternatively spliced hepatic apobec1 mRNAs with different acceptor sites in exon 4. Transient expression studies using promoter-reporter gene constructs in HeLa, Hepa, and Caco-2 cells indicate that the 5'-flanking sequences of the liver mRNA (i.e. upstream of exon 1) have predominantly hepatic promoter activity and the 5'-flanking sequences of the major small intestine mRNA (i.e. upstream of exon 4) have preferential intestinal promoter activity.(ABSTRACT TRUNCATED AT 400 WORDS)

APOBEC-1 Deaminase↗
PubMed1995

Lipoprotein lipase: role of intramolecular disulfide bonds in enzyme catalysis.

Lipoprotein lipase (LPL) catalyzes the hydrolysis of the triacylglycerol component of triacylglycerol-rich lipoproteins. There are 4 cysteine pairs that are completely conserved among LPLs of all species known. We examined the functional importance of each of the cysteine pairs in enzyme catalysis by examining LPLs produced in Cos cells by transfection. Immunoreactive LPL was produced by vectors encoding the wildtype LPL and each of the 4 cysteine-pair mutant LPLs. Enzyme activity was detectable in the wildtype enzyme, but not in 3 of the 4 Cys-->Ser mutant enzymes (C216S/C239S, C264S/C275S, and C278S/C283S). Interestingly, LPL activity was also present in the mutant (C418S/C438S), which affects the C-terminal cysteine pair, with a specific activity approximately 50% higher than that of wildtype. There is evidence that LPL contains two distinct domains consisting of the N-terminal three-quarters of the sequence connected by a flexible region to the C-terminal domain comprising the rest of the molecule. The conservation of catalytic function despite the disruption of the only disulfide bridge in the C-terminal domain of LPL indicates that the two domains can function independently of each other in enzyme catalysis.

Amino Acid Sequence↗
PubMed1995

Apolipoprotein B messenger RNA editing: an update.

Apolipoprotein (apo) B mRNA editing consists of a C-->U conversion of the first base of the codon CAA encoding glutamine 2153 in apoB mRNA to UAA, a stop codon. The cDNA for an apoB mRNA editing protein was recently cloned in rat and human. The human protein contains 236 amino acid residues and exists as a homodimer. The editing protein edits apoB mRNA in vitro only in the presence of tissue complementation factors. There is a leucine-rich motif spanning residues 173-210 of the protein which may be involved in homodimer formation and/or interaction with complementation factors. The requirements for these factors support the existence of an editosome involved in apoB mRNA editing.

APOBEC-1 Deaminase↗
PubMed1995

Cost analysis of stapling versus suturing for skin closure.

A randomized, prospective study was performed to test the null hypothesis that there is no difference between the cost of stapling and suturing for skin closure of selected linear lacerations. Appropriate wounds were randomly assigned to be closed by staples or sutures. Wound lengths, skin closure times, and the number of staples or the number and types of sutures used were recorded. Costs for materials and labor were calculated. The average total cost per case was $17.69 (with suture kit) and $7.84 (without suture kit) for the staple Group compared with $21.58 for the suture Group (P = .0001 for each). It is concluded that stapling is less costly than suturing and that the advantage appears to increase as laceration length increases.

Adult↗