Publications by authors named "Janet Cheng"

17 Publications

  • Page 1 of 1

Evaluation of an in-house developed multiplex real-time PCR for the detection of IMP, OXA-23, GES carbapenemases and the transmissible colistin-resistant mcr gene on the BD MAX™ open system.

Diagn Microbiol Infect Dis 2018 Jan 4;90(1):67-69. Epub 2017 Oct 4.

National University Hospital, Department of Laboratory Medicine, Division of Microbiology, Singapore 119074, Republic of Singapore; National Public Health Laboratory, Ministry of Health, 3 Biopolis Drive, Synapse #05-14/16, Singapore 138623, Republic of Singapore.

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http://dx.doi.org/10.1016/j.diagmicrobio.2017.09.010DOI Listing
January 2018

Predominance of clarithromycin-susceptible Mycobacterium massiliense subspecies: Characterization of the Mycobacterium abscessus complex at a tertiary acute care hospital.

J Med Microbiol 2017 Oct 6;66(10):1443-1447. Epub 2017 Sep 6.

National University Hospital, Department of Laboratory Medicine, Division of Microbiology, Singapore 119074, Republic of Singapore.

To characterize members of the Mycobacterium abscessus complex, with an emphasis on the correlation between species identification and clarithromycin associated genetic polymorphisms that contribute to inducible and constitutive macrolide resistance. PCR and sequencing analysis was used to elucidate the subspecies, erm(41) genotypes and the presence of rrl mutations. M. abscessus subsp. massiliense was the dominant subspecies (70.2 %), followed by M. abscessus subsp. abscessus (23.8 %) and M. abscessus subsp. bolletii (5.9 %). The majority of M. abscessus and M. bolletii isolates possessed T28 erm(41) sequevar and were inducibly resistant to clarithromycin. All M. massiliense carried the truncated erm(41) and were largely clarithromycin-susceptible (98.3 %). Constitutive resistance involving rrl mutations was rare and seen in only 2 isolates (2.2 %). Subspecies identification was insufficient to predict clarithromycin susceptibility and required the genetic resistance to be determined via sequencing. In our context, rrl mutations were uncommon and may not be an essential test.
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http://dx.doi.org/10.1099/jmm.0.000576DOI Listing
October 2017

Agonistic Human Antibodies Binding to Lecithin-Cholesterol Acyltransferase Modulate High Density Lipoprotein Metabolism.

J Biol Chem 2016 Feb 7;291(6):2799-811. Epub 2015 Dec 7.

Cardiometabolic Disorders,

Drug discovery opportunities where loss-of-function alleles of a target gene link to a disease-relevant phenotype often require an agonism approach to up-regulate or re-establish the activity of the target gene. Antibody therapy is increasingly recognized as a favored drug modality due to multiple desirable pharmacological properties. However, agonistic antibodies that enhance the activities of the target enzymes are rarely developed because the discovery of agonistic antibodies remains elusive. Here we report an innovative scheme of discovery and characterization of human antibodies capable of binding to and agonizing a circulating enzyme lecithin cholesterol acyltransferase (LCAT). Utilizing a modified human LCAT protein with enhanced enzymatic activity as an immunogen, we generated fully human monoclonal antibodies using the XenoMouse(TM) platform. One of the resultant agonistic antibodies, 27C3, binds to and substantially enhances the activity of LCAT from humans and cynomolgus macaques. X-ray crystallographic analysis of the 2.45 Å LCAT-27C3 complex shows that 27C3 binding does not induce notable structural changes in LCAT. A single administration of 27C3 to cynomolgus monkeys led to a rapid increase of plasma LCAT enzymatic activity and a 35% increase of the high density lipoprotein cholesterol that was observed up to 32 days after 27C3 administration. Thus, this novel scheme of immunization in conjunction with high throughput screening may represent an effective strategy for discovering agonistic antibodies against other enzyme targets. 27C3 and other agonistic human anti-human LCAT monoclonal antibodies described herein hold potential for therapeutic development for the treatment of dyslipidemia and cardiovascular disease.
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http://dx.doi.org/10.1074/jbc.M115.672790DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4742745PMC
February 2016

A Novel Mycobacterium cosmeticum-Like Bacterium Isolated from the Ear Swab of a Patient with Otitis Externa.

Case Rep Infect Dis 2015 17;2015:825819. Epub 2015 Mar 17.

Department of Laboratory Medicine, Microbiology Unit, National University Hospital, Singapore 119074.

We describe the identification and characterization of a novel nontuberculous mycobacterium (NTM), isolated from an ear swab of an adult male patient with chronic otitis externa. Genetically, the bacterium is most closely related to Mycobacterium cosmeticum; however, growth and biochemical features indicate that it is distinctly different. Here, we highlight for the first time an unusual NTM that is a probable cause of ear infection.
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http://dx.doi.org/10.1155/2015/825819DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4381726PMC
April 2015

Clinical utility of RD1, RD9 and hsp65 based PCR assay for the identification of BCG in vaccinated children.

BMC Res Notes 2013 Oct 29;6:434. Epub 2013 Oct 29.

Department of Laboratory Medicine, Microbiology Unit, National University Hospital, Singapore 119074, Republic of Singapore.

Background: Mycobacterium bovis Bacille Calmette-Guérin (BCG) vaccine is widely administered to prevent tuberculosis. Vaccine complications are rare. However, when BCG-related adverse reactions arise there is a need to rapidly and reliably identify BCG from other members of the Mycobacterium tuberculosis complex (TBC). PCR assays based on the detection of the regions of difference (RD), in particular RD1 and RD9, have been invaluable in the identification of BCG. Prior to this study, specimens were identified through HPLC analysis at a local reference laboratory taking up to 2 weeks for a result. We sought to expedite the identification process by validating a RD1, RD9 and hsp65 PCR assay for the identification and differentiation of BCG from TBC.

Findings: In last past 3 years, we validated the RD1, RD9 and hsp65 PCR assay for 16 mycobacterial isolates obtained from children who had experienced adverse reactions to BCG vaccination. In these cases, the clinician required a definitive identification of the isolate. The RD1 and RD9 PCR profiles indicated that all 16 isolates were BCG whilst amplification of the hsp65 target functioned as a PCR positive control. When tested against clinical M. tuberculosis (MTB), reference and non-tuberculous mycobacteria the PCR assay demonstrated 100% sensitivity and specificity.

Conclusions: The RD1, RD9 and hsp65 PCR assay is a useful tool for the rapid and reliable identification of BCG. Its ease of use has allowed it to be implemented in our clinical microbiology laboratory.
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http://dx.doi.org/10.1186/1756-0500-6-434DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4228461PMC
October 2013

Pandemic influenza triage in the clinical setting.

Prehosp Disaster Med 2010 Mar-Apr;25(2):99-104

University of California Los Angeles Center for Public Health and Disasters, Los Angeles, California 90024, USA.

Introduction: There has been much federal and local health planning for an influenza pandemic in the United States, but little is known about the ability of the clinical community to deal quickly and effectively with a potentially overwhelming surge of pandemic influenza patients.

Problem: The attitudes and expectations of emergency physicians, emergency nurses, hospital nursing supervisors, hospital administrators, and infection control personnel concerning clinical care in a pandemic were assessed.

Methods: Key informant structured interviews of 46 respondents from 34 randomly selected emergency receiving hospitals in Los Angeles County were conducted using an Institutional Review Board-approved protocol. The interview asked about supplies/resources, triage, quality of care, and decision-making. At the conclusion of each interview, the informant was asked to provide the contact information for at least two others within their respective professional group. Interviews were transcribed and coded for key themes using qualitative analytical software.

Results: There was little salience that an influx of variably ill patients with influenza would force stratified healthcare decision-making. There also was a general lack of preparation to address the ethics and practices of triaging patients in the clinical setting of a pandemic.

Conclusions: Guidelines must be developed in concert with public health, medical society, and legislative authorities to help clinicians define, adopt, and communicate to the public those practice standards that will be followed in a mass population, infectious disease emergency.
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http://dx.doi.org/10.1017/s1049023x00007792DOI Listing
July 2010

Fusion partners can increase the expression of recombinant interleukins via transient transfection in 2936E cells.

Protein Sci 2010 Feb;19(2):357-62

Department of Protein Science, Amgen, Inc., Seattle, Washington 98119, USA.

The expression levels of five secreted target interleukins (IL-11, 15, 17B, 32, and IL23 p19 subunit) were tested with three different fusion partners in 2936E cells. When fused to the N-terminus, human serum albumin (HSA) was found to enhance the expression of both IL-17B and IL-15, cytokines which did not express at measurable levels on their own. Although the crystallizable fragment of an antibody (Fc) was also an effective fusion partner for IL-17B, Fc did not increase expression of IL-15. Fc was superior to HSA for the expression of the p19 subunit of IL-23, but no partner led to measurable levels of IL-32gamma secretion. Glutathione S-transferase (GST) did not enhance the expression of any target and suppressed the production of IL-11, a cytokine which expressed robustly both on its own and when fused to HSA or Fc. Cleavage of the fusion partner was not always possible. The use of HSA or Fc as N-terminal fusions can be an effective technique to express difficult proteins, especially for applications in which the fusion partner need not be removed.
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http://dx.doi.org/10.1002/pro.307DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2865725PMC
February 2010

An integrative genomic analysis identifies Bhmt2 as a diet-dependent genetic factor protecting against acetaminophen-induced liver toxicity.

Genome Res 2010 Jan 18;20(1):28-35. Epub 2009 Nov 18.

Department of Genetics and Genomics, Roche Palo Alto, Palo Alto, California 94304, USA.

Acetaminophen-induced liver toxicity is the most frequent precipitating cause of acute liver failure and liver transplant, but contemporary medical practice has mainly focused on patient management after a liver injury has been induced. An integrative genetic, transcriptional, and two-dimensional NMR-based metabolomic analysis performed using multiple inbred mouse strains, along with knowledge-based filtering of these data, identified betaine-homocysteine methyltransferase 2 (Bhmt2) as a diet-dependent genetic factor that affected susceptibility to acetaminophen-induced liver toxicity in mice. Through an effect on methionine and glutathione biosynthesis, Bhmt2 could utilize its substrate (S-methylmethionine [SMM]) to confer protection against acetaminophen-induced injury in vivo. Since SMM is only synthesized in plants, Bhmt2 exerts its beneficial effect in a diet-dependent manner. Identification of Bhmt2 and the affected biosynthetic pathway demonstrates how a novel method of integrative genomic analysis in mice can provide a unique and clinically applicable approach to a major public health problem.
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http://dx.doi.org/10.1101/gr.097212.109DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2798828PMC
January 2010

Changing trends and allergens in the patch test standard series: a mayo clinic 5-year retrospective review, january 1, 2001, through december 31, 2005.

Arch Dermatol 2008 Jan;144(1):67-72

Department of Dermatology, Mayo Clinic, 200 First St SW, Rochester, MN 55905, USA.

Objective: To present and interpret results of patch testing with the Mayo Clinic standard series over 5 years.

Design: Retrospective study. A standardized patch testing technique was used. Data were recorded on a standardized computer program from January 1, 2001, to December 31, 2005, and analyzed.

Setting: Tertiary referral center.

Patients: Patients who were referred for patch testing.

Intervention: Patch testing with the "standard series," ie, a standard series of allergens used by most clinicians to identify the most common offending allergens in patients with allergic contact dermatitis.

Main Outcome Measures: Number of patients patch tested, allergens used over this period, and rates of allergic patch test reactions to allergens.

Results: A total of 3854 patients (mean age, 55.1 years; age range, 6.2-99.4 years; 2576 female [66.8%]) were tested. All dermatologists in the department performed patch testing. The mean number of allergens included was 69.3 (range, 6-87). There were 2664 patients with at least 1 positive reaction (69.1%) and 1933 with 2 or more positive reactions (50.2%). Metals, fragrances, topical antibiotics, preservatives, and individual allergens used in hair-care products, topical corticosteroids, glues, plastics, and rubber were still the most common allergen groups associated with allergic patch test reactions.

Conclusions: We describe the structure of the patch testing service at our referral center. Ongoing analysis of our patch test reaction rates allows us to recommend broad, clinically relevant, and up-to-date allergens for testing.
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http://dx.doi.org/10.1001/archdermatol.2007.2DOI Listing
January 2008

The structure of Dasatinib (BMS-354825) bound to activated ABL kinase domain elucidates its inhibitory activity against imatinib-resistant ABL mutants.

Cancer Res 2006 Jun;66(11):5790-7

Bristol-Myers Squibb Company, Pharmaceutical Research Institute, Princeton, New Jersey, USA.

Chronic myeloid leukemia (CML) is caused by the constitutively activated tyrosine kinase breakpoint cluster (BCR)-ABL. Current frontline therapy for CML is imatinib, an inhibitor of BCR-ABL. Although imatinib has a high rate of clinical success in early phase CML, treatment resistance is problematic, particularly in later stages of the disease, and is frequently mediated by mutations in BCR-ABL. Dasatinib (BMS-354825) is a multitargeted tyrosine kinase inhibitor that targets oncogenic pathways and is a more potent inhibitor than imatinib against wild-type BCR-ABL. It has also shown preclinical activity against all but one of the imatinib-resistant BCR-ABL mutants tested to date. Analysis of the crystal structure of dasatinib-bound ABL kinase suggests that the increased binding affinity of dasatinib over imatinib is at least partially due to its ability to recognize multiple states of BCR-ABL. The structure also provides an explanation for the activity of dasatinib against imatinib-resistant BCR-ABL mutants.
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http://dx.doi.org/10.1158/0008-5472.CAN-05-4187DOI Listing
June 2006

In silico pharmacogenetics of warfarin metabolism.

Nat Biotechnol 2006 May;24(5):531-6

Department of Genetics and Genomics, Roche Palo Alto S3-1, 3431 Hillview Ave., Palo Alto, California 94304, USA.

Pharmacogenetic approaches can be instrumental for predicting individual differences in response to a therapeutic intervention. Here we used a recently developed murine haplotype-based computational method to identify a genetic factor regulating the metabolism of warfarin, a commonly prescribed anticoagulant with a narrow therapeutic index and a large variation in individual dosing. After quantification of warfarin and nine of its metabolites in plasma from 13 inbred mouse strains, we correlated strain-specific differences in 7-hydroxywarfarin accumulation with genetic variation within a chromosomal region encoding cytochrome P450 2C (Cyp2c) enzymes. This computational prediction was experimentally confirmed by showing that the rate-limiting step in biotransformation of warfarin to its 7-hydroxylated metabolite was inhibited by tolbutamide, a Cyp2c isoform-specific substrate, and that this transformation was mediated by expressed recombinant Cyp2c29. We show that genetic variants responsible for interindividual pharmacokinetic differences in drug metabolism can be identified by computational genetic analysis in mice.
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http://dx.doi.org/10.1038/nbt1195DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1459533PMC
May 2006

Patch test results from the Mayo Clinic Contact Dermatitis Group, 1998-2000.

J Am Acad Dermatol 2005 Sep;53(3):416-21

Mayo Clinic Contact Dermatitis Group, Department of Dermatology, Mayo Clinic, Rochester, Minnesota 55905, USA.

Background: Patch testing is a diagnostic tool for the evaluation of patients with suspected allergic contact dermatitis. A standard series of allergens similar to that used by the North American Contact Dermatitis Group (NACDG) is used at Mayo Clinic.

Objective: Our aim was to report the results of patch testing with a standard series at Mayo Clinic from July 1, 1998, to Dec 31, 2000 and to compare our findings with those of the NACDG during the same period.

Methods: The results of patch testing with the standard series at Mayo Clinic were examined. Positive reaction rates were compared between Mayo Clinic and the NACDG.

Results: During the 30-month period, 1324 Mayo Clinic patients were patch tested with a standard series of allergens (mean, 60 allergens), whereas the NACDG standard series during this period included 50 allergens. Overall, 917 patients (69.3%) had at least one positive reaction and 606 patients (45.8%) had two or more positive reactions. The 10 allergens used both by Mayo Clinic and by the NACDG that most frequently caused positive reactions were nickel sulfate hexahydrate, balsam of Peru (Myroxylon pereirae), neomycin sulfate, cobalt chloride, fragrance mix, potassium dichromate (0.25%), thimerosal, bacitracin, formaldehyde, and glutaraldehyde. Statistically significant differences in positive reaction rates (P < .05) were observed for 12 of the 43 allergens common to both Mayo Clinic and the NACDG.

Conclusion: With large standard patch test series, one can identify commonly encountered and potentially relevant contact allergens.
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http://dx.doi.org/10.1016/j.jaad.2005.04.077DOI Listing
September 2005

Irritant contact dermatitis precipitating allergic contact dermatitis.

Dermatitis 2005 Jun;16(2):87-8; quiz 55-6

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June 2005

Granuloma annulare presenting as contact dermatitis.

Dermatitis 2005 Mar;16(1):34-7

Department of Dermatology, Mayo Clinic, 4500 San Pablo Road, Jacksonville, FL 32224, USA.

Granuloma annulare is a benign idiopathic disorder of the dermis that has various clinical presentations and an unknown etiology. We discuss a patient who presented with a contact dermatitis that demonstrated granuloma annulare on biopsy. The most likely etiologic agent was a substance known as FAZ (an exhaust product of Kodak DryView laser imaging film), to which the patient was exposed in his occupation.
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March 2005

In silico genetics: identification of a functional element regulating H2-Ealpha gene expression.

Science 2004 Oct;306(5696):690-5

Department of Genetics and Genomics, Roche Palo Alto, 3431 Hillview Avenue, Palo Alto, CA 94304-1397, USA.

Computational tools can markedly accelerate the rate at which murine genetic models can be analyzed. We developed a computational method for mapping phenotypic traits that vary among inbred strains onto haplotypic blocks. This method correctly predicted the genetic basis for strain-specific differences in several biologically important traits. It was also used to identify an allele-specific functional genomic element regulating H2-Ealpha gene expression. This functional element, which contained the binding sites for YY1 and a second transcription factor that is probably serum response factor, is located within the first intron of the H2-Ealpha gene. This computational method will greatly improve our ability to identify the genetic basis for a variety of phenotypic traits, ranging from qualitative trait information to quantitative gene expression data, which vary among inbred mouse strains.
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http://dx.doi.org/10.1126/science.1100636DOI Listing
October 2004

Comparative studies of active site-ligand interactions among various recombinant constructs of human beta-amyloid precursor protein cleaving enzyme.

Arch Biochem Biophys 2003 Feb;410(2):307-16

Department of Chemical Enzymology, Hopewell, NJ, USA.

Amyloid precursor protein (APP) cleaving enzyme (BACE) is the enzyme responsible for beta-site cleavage of APP, leading to the formation of the amyloid-beta peptide that is thought to be pathogenic in Alzheimer's disease (AD). Hence, BACE is an attractive pharmacological target, and numerous research groups have begun searching for potent and selective inhibitors of this enzyme as a potential mechanism for therapeutic intervention in AD. The mature enzyme is composed of a globular catalytic domain that is N-linked glycosylated in mammalian cells, a single transmembrane helix that anchors the enzyme to an intracellular membrane, and a short C-terminal domain that extends outside the phospholipid bilayer of the membrane. Here we have compared the substrate and active site-directed inhibitor binding properties of several recombinant constructs of human BACE. The constructs studied here address the importance of catalytic domain glycosylation state, inclusion of domains other than the catalytic domain, and incorporation into a membrane bilayer on the interactions of the enzyme active site with peptidic ligands. We find no significant differences in ligand binding properties among these various constructs. These data demonstrate that the nonglycosylated, soluble catalytic domain of BACE faithfully reflects the ligand binding properties of the full-length mature enzyme in its natural membrane environment. Thus, the use of the nonglycosylated, soluble catalytic domain of BACE is appropriate for studies aimed at understanding the determinants of ligand recognition by the enzyme active site.
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http://dx.doi.org/10.1016/s0003-9861(02)00690-2DOI Listing
February 2003