Publications by authors named "Brad Johnston"

12 Publications

  • Page 1 of 1

Systematic reviews experience major limitations in reporting absolute effects.

J Clin Epidemiol 2016 Apr 10;72:16-26. Epub 2015 Nov 10.

Department of Clinical Epidemiology & Biostatistics, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada; Department of Medicine, McMaster University, 1280 Main St W, Hamilton, Ontario L8S 4L8, Canada.

Objectives: Expressing treatment effects in relative terms yields larger numbers than expressions in absolute terms, affecting the judgment of the clinicians and patients regarding the treatment options. It is uncertain how authors of systematic reviews (SRs) absolute effect estimates are reported in. We therefore undertook a systematic survey to identify and describe the reporting and methods for calculating absolute effect estimates in SRs.

Study Design And Setting: Two reviewers independently screened title, abstract, and full text and extracted data from a sample of Cochrane and non-Cochrane SRs. We used regression analyses to examine the association between study characteristics and the reporting of absolute estimates for the most patient-important outcome.

Results: We included 202 SRs (98 Cochrane and 104 non-Cochrane), most of which (92.1%) included standard meta-analyses including relative estimates of effect. Of the 202 SRs, 73 (36.1%) reported absolute effect estimates for the most patient-important outcome. SRs with statistically significant effects were more likely to report absolute estimates (odds ratio, 2.26; 95% confidence interval: 1.08, 4.74). The most commonly reported absolute estimates were: for each intervention, risk of adverse outcomes expressed as a percentage (41.1%); number needed to treat (26.0%); and risk for each intervention expressed as natural units or natural frequencies (24.7%). In 12.3% of the SRs that reported absolute effect estimates for both benefit and harm outcomes, harm outcomes were reported exclusively as absolute estimates. Exclusively reporting of beneficial outcomes as absolute estimates occurred in 6.8% of the SRs.

Conclusions: Most SRs do not report absolute effects. Those that do often report them inadequately, thus requiring users of SRs to generate their own estimates of absolute effects. For any apparently effective or harmful intervention, SR authors should report both absolute and relative estimates to optimize the interpretation of their findings.
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http://dx.doi.org/10.1016/j.jclinepi.2015.11.002DOI Listing
April 2016

Simultaneous quantitation of delamanid (OPC-67683) and its eight metabolites in human plasma using UHPLC-MS/MS.

J Chromatogr B Analyt Technol Biomed Life Sci 2015 Oct 6;1002:78-91. Epub 2015 Aug 6.

Otsuka Pharmaceutical Development & Commercialization (OPDC), 2440 Research Boulevard, Rockville, MD 20850, USA.

Delamanid (OPC-67683) is a novel nitro-dihydroimidazo-oxazole derivative that is being developed by Otsuka Pharmaceutical Co., Ltd., Japan (referred to as Otsuka hereafter) for the treatment of tuberculosis (TB). An ultra-high performance liquid chromatographic-tandem mass spectrometry (UHPLC-MS/MS) method has been developed and validated for the determination of OPC-67683 and its eight metabolites, DM-6704, DM-6705, DM-6706, DM-6717, DM-6718, DM-6720, DM-6721 and DM-6722 in human plasma to support regulated clinical development. During method development several technical challenges such as poor chromatography, separation of structural isomers, conversion of the analytes, instability in matrix and long cycle time were encountered and overcome. A protein precipitation extraction (PPE) was used to extract plasma samples (50μL) and the resulting extracts were analyzed using reversed phase UHPLC-MS/MS with a electrospray (ESI) and selected reaction monitoring (SRM). The method was fully validated over the calibration curve range of 1.00-500ng/mL for all nine analytes with linear regression and 1/x(2) weighting according to regulatory guidance for bioanalysis. Based on three inter-day precision and accuracy runs, the between-run % relative standard deviation (RSD) for all nine analytes varied from 0.0 to 11.9% and the accuracy ranged from 92.7% to 102.5% of nominal at all quality controls (QC) concentrations, including the lower limit of quantitation (LLOQ) QC at 1.00ng/mL. The extraction recovery of OPC-67683 and its eight metabolites were above 95%. Various short term and long term solution and matrix stability were established including the stability of OPC-67683 and its eight metabolites in human plasma for 708 days at -70°C. Although this method has been used to support regulated clinic studies during the last decade and over ten thousand samples have been analyzed, this is the first time that the method development process and validation data have been published.
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http://dx.doi.org/10.1016/j.jchromb.2015.07.058DOI Listing
October 2015

A volumetric method for quantifying atherosclerosis in mice by using microCT: comparison to en face.

PLoS One 2011 Apr 18;6(4):e18800. Epub 2011 Apr 18.

Department of Metabolic Disorders, Amgen Inc., Thousand Oaks, California, United States of America.

Precise quantification of atherosclerotic plaque in preclinical models of atherosclerosis requires the volumetric assessment of the lesion(s) while maintaining in situ architecture. Here we use micro-computed tomography (microCT) to detect ex vivo aortic plaque established in three dyslipidemic mouse models of atherosclerosis. All three models lack the low-density lipoprotein receptor (Ldlr(-/-)), each differing in plaque severity, allowing the evaluation of different plaque volumes using microCT technology. From clearly identified lesions in the thoracic aorta from each model, we were able to determine plaque volume (0.04-3.1 mm(3)), intimal surface area (0.5-30 mm(2)), and maximum plaque (intimal-medial) thickness (0.1-0.7 mm). Further, quantification of aortic volume allowed calculation of vessel occlusion by the plaque. To validate microCT for future preclinical studies, we compared microCT data to intimal surface area (by using en face methodology). Both plaque surface area and plaque volume were in excellent correlation between microCT assessment and en face surface area (r(2) = 0.99, p<0.0001 and r(2) = 0.95, p<0.0001, respectively). MicroCT also identified internal characteristics of the lipid core and fibrous cap, which were confirmed pathologically as Stary type III-V lesions. These data validate the use of microCT technology to provide a more exact empirical measure of ex vivo plaque volume throughout the entire intact aorta in situ for the quantification of atherosclerosis in preclinical models.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0018800PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3078927PMC
April 2011

L-5F, an apolipoprotein A-I mimetic, inhibits tumor angiogenesis by suppressing VEGF/basic FGF signaling pathways.

Integr Biol (Camb) 2011 Apr 1;3(4):479-89. Epub 2011 Feb 1.

David Geffen School of Medicine, University of California Los Angeles, 10833 Le Conte Avenue, Los Angeles, CA 90095-5347, USA.

We recently reported that apolipoprotein A-I (apoA-I) and apoA-I mimetic peptides inhibit tumor growth and improve survival in a mouse model of ovarian cancer. The current study was designed to examine whether inhibition of angiogenesis is one of the mechanisms for the observed anti-tumorigenic effects. The apoA-I mimetic peptide L-5F had no affect on proliferation and cell viability of human umbilical vascular endothelial cells (HUVECs) in the basal state; however, treatment with L-5F at 1, 3, and 10 μg ml(-1), dose-dependently inhibited both vascular endothelial growth factor (VEGF)- and basic fibroblast growth factor (bFGF)-induced proliferation, cell viability, migration, invasion and tube formation in HUVECs. L-5F inhibited VEGF- and bFGF-induced activation of their corresponding receptors, VEGFR2 and FGFR1, as well as downstream signaling pathways, including Akt and ERK1/2. MicroCT scanning and immunohistochemistry staining demonstrated that daily injection of L-5F (10 mg kg(-1)) decreased both the quantity and size of tumor vessels in mice. L-5F treated mice showed significantly reduced levels of VEGF in both tumor tissue and the circulation, which is consistent with in vitro data showing that L-5F inhibited production and secretion of VEGF from mouse and human ovarian cell lines in the absence and presence of exogenously added lysophosphatidic acid, a potent tumor promoter. In conclusion, our data that L-5F inhibits angiogenesis suggests that apoA-I mimetic peptides may serve as novel anti-angiogenesis agents for the treatment of angiogenesis-associated diseases, including cancer.
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http://dx.doi.org/10.1039/c0ib00147cDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3248743PMC
April 2011

Which medications used in paediatric practice have demonstrated natural health product-drug interactions?: Part B: Clinical commentary.

Paediatr Child Health 2006 Dec;11(10):673-4

Complementary and Alternative Research and Education (CARE) Program, Stollery Children's Hospital, and Department of Pediatrics, University of Alberta, Edmonton, Alberta.

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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2528602PMC
http://dx.doi.org/10.1093/pch/11.10.673DOI Listing
December 2006

Which medications used in paediatric practice have demonstrated natural health product-drug interactions?: Part A: Evidence-based answer and summary.

Paediatr Child Health 2006 Dec;11(10):671-2

Complementary and Alternative Research and Education (CARE) Program, Stollery Children's Hospital, and Department of Pediatrics, University of Alberta, Edmonton, Alberta.

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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2528601PMC
http://dx.doi.org/10.1093/pch/11.10.671DOI Listing
December 2006

Product stewardship in wollastonite production.

Inhal Toxicol 2008 Nov;20(14):1199-214

Everest Consulting Associates, Cranbury, New Jersey, USA.

In July 2002, NYCO Minerals, Inc., discovered a heretofore unknown contaminant in its wollastonite ore. The contaminant was first believed to be tremolite asbestos. Immediate efforts were made to eliminate this material. Additional studies were initiated to fully characterize the contaminant and its distribution in the ore body. Subsequent study by NYCO and their consultants led to the identification of the contaminant as a transition material (TM) intermediate between tremolite and talc. In vitro dissolution rate measurements indicated that the TM dissolved much more rapidly than tremolite asbestos. This article provides background information on wollastonite mineralogy and NYCO's product stewardship program (PSP). At present, NYCO Minerals uses selective mining to control the trace levels of TM in the ore and finished product verified by periodic monitoring of workplace air and finished product.
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http://dx.doi.org/10.1080/08958370802136749DOI Listing
November 2008

Rhodamine 123 permeability through the catfish intestinal wall: Relationship to thermal acclimation and acute temperature change.

Comp Biochem Physiol C Toxicol Pharmacol 2006 Nov 3;144(3):205-15. Epub 2006 Sep 3.

Department of Comparative Biomedical Sciences, School of Veterinary Medicine, Louisiana State University, Skip Bertman Drive, Baton Rouge, LA 70803, USA.

Temperature is known to influence xenobiotic retention in fish. The effect of acute and acclimatory temperature change upon Rhodamine 123 (Rho123) permeability through an in vitro catfish multi-segment (3) everted sac intestinal wall model was examined in a 9 cell matrix of acclimation and assay temperatures (10, 20 and 30 degrees C). Changes in Rho123 permeability were examined in context with membrane fluidity, xenobiotic solubility and intestinal morphology. When assayed at the acclimation temperature greater Rho123 permeability was noted at warmer acclimation temperatures for the proximal and middle intestinal segments, while the distal segment exhibited little change and apparent compensation across temperatures. Rho123 permeability was increased as assay temperatures were elevated above the acclimation temperature for most comparisons. Cold acclimation significantly increased total intestinal length (43.2%) and proximal intestine weights while total body weights did not differ. Brush border membranes (BBM) increased fluidity with increased assay temperatures, however, composite anisotropy lines were not significantly different between acclimation treatments. In an additive manner, the membrane probe DPH exhibited increased solubility in BBM with increases in acclimation and assay temperatures. Compositely, these results suggest that acclimation and acute temperature change may differentially influence xenobiotic permeability among intestinal segments with interacting mechanisms.
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http://dx.doi.org/10.1016/j.cbpc.2006.08.007DOI Listing
November 2006

Gefitinib modulates the function of multiple ATP-binding cassette transporters in vivo.

Cancer Res 2006 May;66(9):4802-7

Departments of Pharmaceutical Sciences, Hematology-Oncology, and Molecular Pharmacology, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA.

The 4-anilinoquinazoline (4-AQ) derivative gefitinib (Iressa) is an oral epidermal growth factor receptor tyrosine kinase inhibitor. Oral administration of 4-AQ molecules, such as gefitinib, inhibits ATP-binding cassette (ABC) transporter-mediated drug efflux and strongly increases the apparent bioavailability of coadministered drug molecules that are transporter substrates. Based on in vitro studies investigating 4-AQ interactions with several transporters, these effects have primarily been attributed to the inhibition of breast cancer resistance protein (BCRP; ABCG2). Although 4-AQ shows in vitro inhibition of P-glycoprotein [multidrug resistance protein (MDR1); ABCB1], the in vivo effect on this and other transporters is not known. In our studies, pretreatment of Abcg2(-/-) and Mdr1(a/b)(-/-) mice with gefitinib increased oral absorption and decreased systemic clearance of topotecan, a model substrate, indicating that additional transporters were inhibited. These results were extended to human orthologues using engineered cell lines to show that gefitinib inhibited the efflux of BCRP and MDR1 substrates and restored vincristine sensitivity in MDR1-expressing cells. Although gefitinib inhibited BCRP more potently than MDR1 (10-fold), the inhibition of both transporters occurred at clinically relevant concentrations (e.g., 1-5 micromol/L). These studies illustrate the broad implications for the therapeutic combination of gefitinib or other 4-AQ molecules with agents that are BCRP and MDR1 substrates. 4-AQ molecules may offer a means to increase the low and variable oral drug absorption of transporter substrates while decreasing interpatient variability and reversing tumor drug resistance.
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http://dx.doi.org/10.1158/0008-5472.CAN-05-2915DOI Listing
May 2006

Integrating complementary and alternative medicine into academic medical centers: experience and perceptions of nine leading centers in North America.

BMC Health Serv Res 2005 Dec 20;5:78. Epub 2005 Dec 20.

CARE Program, Department of Pediatrics, University of Alberta, Edmonton, Alberta, Canada.

Background: Patients across North America are using complementary and alternative medicine (CAM) with increasing frequency as part of their management of many different health conditions. The objective of this study was to develop a guide for academic health sciences centers that may wish to consider starting an integrative medicine program.

Methods: We queried North American leaders in the field of integrative medicine to identify initial sites. Key stakeholders at each of the initial sites visited were then asked to identify additional potential study sites (snowball sampling), until no new sites were identified. We conducted structured interviews to identify critical factors associated with success and failure in each of four domains: research, education, clinical care, and administration. During the interviews, field notes were recorded independently by at least two investigators. Team meetings were held after each visit to reach consensus on the information recorded and to ensure that it was as complete as possible. Content analysis techniques were used to identify key themes that emerged from the field notes.

Results: We identified ten leading North American integrative medical centers, and visited nine during 2002-2003. The centers visited suggested that the initiation of an integrative medicine program requires a significant initial outlay of funding and a motivated "champion". The centers had important information to share regarding credentialing, medico-legal issues and billing for clinical programs; identifying researchers and research projects for a successful research program; and strategies for implementing flexible educational initiatives and establishing a functional administrative structure.

Conclusion: Important lessons can be learned from academic integrative programs already in existence. Such initiatives are timely and feasible in a variety of different ways and in a variety of settings.
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http://dx.doi.org/10.1186/1472-6963-5-78DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1343546PMC
December 2005

Mrp4 confers resistance to topotecan and protects the brain from chemotherapy.

Mol Cell Biol 2004 Sep;24(17):7612-21

Department of Pharmaceutical Sciences, St. Jude Children's Research Hospital, 332 N. Lauderdale, Memphis, TN 38105-2794, USA.

The role of the multidrug resistance protein MRP4/ABCC4 in vivo remains undefined. To explore this role, we generated Mrp4-deficient mice. Unexpectedly, these mice showed enhanced accumulation of the anticancer agent topotecan in brain tissue and cerebrospinal fluid (CSF). Further studies demonstrated that topotecan was an Mrp4 substrate and that cells overexpressing Mrp4 were resistant to its cytotoxic effects. We then used new antibodies to discover that Mrp4 is unique among the anionic ATP-dependent transporters in its dual localization at the basolateral membrane of the choroid plexus epithelium and in the apical membrane of the endothelial cells of the brain capillaries. Microdialysis sampling of ventricular CSF demonstrated that localization of Mrp4 at the choroid epithelium is integral to its function in limiting drug penetration into the CSF. The topotecan resistance of cells overexpressing Mrp4 and the polarized expression of Mrp4 in the choroid plexus and brain capillary endothelial cells indicate that Mrp4 has a dual role in protecting the brain from cytotoxins and suggest that the therapeutic efficacy of central nervous system-directed drugs that are Mrp4 substrates may be improved by developing Mrp4 inhibitors.
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http://dx.doi.org/10.1128/MCB.24.17.7612-7621.2004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC506999PMC
September 2004

Determination of plasma topotecan and its metabolite N-desmethyl topotecan as both lactone and total form by reversed-phase liquid chromatography with fluorescence detection.

J Chromatogr B Analyt Technol Biomed Life Sci 2003 Feb;784(2):225-32

Department of Pharmaceutical Sciences, St. Jude Children's Research Hospital, 332 N. Lauderdale, 38105, Memphis, TN, USA.

Topotecan (TPT) undergoes hepatic N-demethylation forming N-desmethyl topotecan (NDS). To evaluate the effect of drug-drug interactions on NDS disposition in children receiving TPT we developed and validated a sensitive and specific HPLC-fluorescence detection method for lactone and total (lactone plus carboxylate) TPT and NDS. Deproteinized plasma is vortexed, centrifuged, and the methanolic extract diluted with water for the lactone form of NDS and TPT or diluted with 1.5% phosphoric acid for NDS and TPT total. A 100 microL sample is injected onto a Varian ChromGuard RP column attached to an Agilent SB-C(18) reversed-phase analytical column held at 50 degrees C. The mobile phase (flow-rate, 0.8 mL/min) consists of methanol-aqueous buffer (27:73, v/v) (75 mM potassium phosphate and 0.2% triethylamine, pH 6.5). TPT and NDS were detected with excitation and emission wavelengths set at 376 and 530 nm, respectively. The standard curves for both forms of TPT ranged from 0.25 to 80 ng/mL, and for NDS ranged from 0.10 to 8.0 ng/mL. Within-day and between-day precision (% RSD) was
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http://dx.doi.org/10.1016/s1570-0232(02)00798-5DOI Listing
February 2003