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Julie A Johnson

Publications and source records attributed to Julie A Johnson.

30 records · Page 2Linked to original sources
PubMed2004

Comparison of cytochrome P450 2C9 genotyping methods and implications for the clinical laboratory.

STUDY OBJECTIVE: To compare the accuracy, speed, and cost of two methodologies used for genotyping known variants in the cytochrome P450 (CYP) 2C9 metabolizing enzyme gene. DESIGN: Comparative study. SETTING: University research center. SAMPLES: Fifteen-milliliter mouthwash samples collected from 253 subjects participating in a warfarin pharmacogenomic study. INTERVENTION: Genotyping for the isoleucine-to-leucine change at codon 359 (Ile359Leu [*3] polymorphism) was performed by using the Pyrosequencing and polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) methods in all 253 samples. Genotyping for the arginine-to-cysteine change at codon 144 (Arg144Cys [*2] polymorphism) was performed by using Pyrosequencing in all samples and by PCR-RFLP in a random subset of 136 samples. MEASUREMENTS AND MAIN RESULTS: Comparisons of genotyping success rates, time efficiency, and cost analyses were conducted for Pyrosequencing and PCR-RFLP at each variant site. Pyrosequencing and PCR-RFLP produced similar success rates on the first genotyping attempt for the Arg144Cys variant (93.3% vs 90.4%, respectively) and the Ile359Leu variant (83.8% vs 79.1%, respectively). With Pyrosequencing, genotyping 96 samples for either polymorphism could be performed in 1 hour. In contrast, genotyping 96 samples by RFLP took 10 hours for the Arg144Cys variant and 20 hours for the Ile359Leu variant. Total cost/sample for Arg144Cys genotyping was dollars 1.90 with PCR-Pyrosequencing and dollars 3.14 with PCR-RFLP. Total cost/sample for Ile359Leu genotyping was dollars 1.88 with PCR-Pyrosequencing and dollars 10.18 with PCR-RFLP CONCLUSION: Compared with RFLP, genotype determination by Pyrosequencing is a more time-efficient, cost-effective, and robust method for CYP2C9 genotyping. Because of its wide applicability and ease of use, Pyrosequencing is a promising technology for future pharmacogenomic investigations.

Alleles↗
PubMed2003

Beta 1-adrenergic receptor polymorphisms and antihypertensive response to metoprolol.

OBJECTIVES: Marked interpatient variability exists in blood pressure response to beta-blocker monotherapy. We tested the hypothesis that 2 common polymorphisms in the gene for beta(1)-adrenergic receptor are associated with antihypertensive response to metoprolol in patients with uncomplicated hypertension. METHODS: Forty hypertensive men and women aged 35 to 65 years were studied. Baseline studies included 24-hour ambulatory blood pressure monitoring. Patients took 50 mg metoprolol twice daily with weekly titration to response or 200 mg twice daily. After a minimum of 4 weeks at stable dose, treatment phase 24-hour ambulatory blood pressure monitoring was repeated. The codon 49 and 389 genotypes for beta(1)-adrenergic receptor were determined by polymerase chain reaction with restriction fragment length polymorphism. Multilinear regression was performed to determine the impact of genotype and other variables on blood pressure response to metoprolol. RESULTS: Patients homozygous for Arg at codon 389 had a nearly 3-fold greater reduction in daytime diastolic blood pressure (-13.3% +/- 8.4% versus -4.5% +/- 8.2%, P =.0018) compared with those who carried the variant allele. The haplotype pair (diplotype) for beta(1)-adrenergic receptor was also a significant predictor of response, with patients having the Ser49Arg389/Ser49Arg389 diplotype demonstrating a decline in blood pressure of 14.7 mm Hg versus 0.5 mm Hg in patients with the Gly49Arg389/Ser49Gly389 diplotype. In multiregression analysis, baseline daytime diastolic blood pressure, codon 389 genotype, and codon 49 genotype were significant predictors of blood pressure after treatment. CONCLUSIONS: Our data suggest that beta(1)-adrenergic receptor polymorphisms are important determinants of antihypertensive response to metoprolol. In the future, codon 49 and 389 genotypes or beta(1)-adrenergic receptor haplotypes might be used to predict the diastolic blood pressure response to metoprolol in patients with hypertension.

Adrenergic beta-1 Receptor Antagonists↗
PubMed2003

A haplotype-based algorithm for multilocus linkage disequilibrium mapping of quantitative trait loci with epistasis.

For tightly linked loci, cosegregation may lead to nonrandom associations between alleles in a population. Because of its evolutionary relationship with linkage, this phenomenon is called linkage disequilibrium. Today, linkage disequilibrium-based mapping has become a major focus of recent genome research into mapping complex traits. In this article, we present a new statistical method for mapping quantitative trait loci (QTL) of additive, dominant, and epistatic effects in equilibrium natural populations. Our method is based on haplotype analysis of multilocus linkage disequilibrium and exhibits two significant advantages over current disequilibrium mapping methods. First, we have derived closed-form solutions for estimating the marker-QTL haplotype frequencies within the maximum-likelihood framework implemented by the EM algorithm. The allele frequencies of putative QTL and their linkage disequilibria with the markers are estimated by solving a system of regular equations. This procedure has significantly improved the computational efficiency and the precision of parameter estimation. Second, our method can detect marker-QTL disequilibria of different orders and QTL epistatic interactions of various kinds on the basis of a multilocus analysis. This can not only enhance the precision of parameter estimation, but also make it possible to perform whole-genome association studies. We carried out extensive simulation studies to examine the robustness and statistical performance of our method. The application of the new method was validated using a case study from humans, in which we successfully detected significant QTL affecting human body heights. Finally, we discuss the implications of our method for genome projects and its extension to a broader circumstance. The computer program for the method proposed in this article is available at the webpage http://www.ifasstat.ufl.edu/genome/~LD.

Algorithms↗
PubMed2003

Drug receptor/effector polymorphisms and pharmacogenetics: current status and challenges.

The pharmacogenetics literature of drug receptors and effector proteins is in its relative infancy compared to that of drug metabolism pharmacogenetics. Nonetheless, in a short time period, numerous studies have demonstrated that receptor/effector polymorphisms contribute to variable drug response. We review the current status, and list challenges that confront drug target pharmacogenetics before we can use genetic information in drug-therapy decision-making. We focus our review on G protein coupled receptors (GPCRs), which represent over 50% of all drug targets, and use specific examples from the beta-adrenergic receptor pharmacogenetic literature to illustrate important issues. Recent resequencing efforts of GPCR genes suggest that they have more coding region and nonsynonymous polymorphisms than non-GPCR genes, thus making GPCRs important foci for pharmacogenetic investigation. Our inability to use drug target genetic information to guide in the selection of drug therapy is due to several factors, including (i) the relatively subtle functional effects of the single gene polymorphisms, which do not account for enough of the drug response variability to accurately predict response and (ii) inconsistencies between studies. The latter may be due to some studies having inadequate sample sizes, studying different drug response phenotypes and patient populations, difficulties in identifying and measuring a valid drug response phenotype, and focusing on single polymorphisms in single genes, rather than haplotypes or multiple genes. To move the field to the point of clinical application, future studies will need to be larger, and will have to consider the complexity of the drug response, either by inclusion of polymorphisms from signal transduction proteins and other proteins relevant to the drug response, or through a genomics approach. Finally, the literature suggests that, for those drugs with multiple pharmacologic effects, or effects in multiple organs, the genetic contribution to each drug response phenotype will have to be considered separately. The knowledge necessary to move forward on all these fronts is not yet available, but will be increasingly accessible over the next few years.

Amino Acid Sequence↗
PubMed2003

The evolving role of nesiritide in advanced or decompensated heart failure.

Nesiritide is a recombinant form of human brain natriuretic peptide (BNP) that is structurally and biochemically identical to endogenously produced BNP. In humans, BNP is important in hemodynamic and neurohormonal equilibrium, helping to maintain adequate vascular volume and pressure in response to volume overload. The pharmacodynamic effects of nesiritide mimic the biologic effects of BNP. The molecular biology and actions of nesiritide and BNP are reviewed, with the therapeutic rationale for nesiritide in patients with acute or advanced decompensated heart failure highlighted. In addition, recommendations for its administration are provided, and unresolved therapeutic considerations are discussed.

Heart Failure↗
PubMed2002

Molecular diagnostics as a predictive tool: genetics of drug efficacy and toxicity.

There is a rapidly growing body of evidence linking genetic polymorphisms with functional changes in proteins that are responsible for the metabolism and disposition of many medications. Likewise, polymorphisms in genes encoding the targets of medications (e.g. receptors) can alter the pharmacodynamics of the drug response by changing receptor sensitivity. As a result, the inherited basis of drug effects is often polygenic in nature, and thus more challenging to define. However, technological advances, coupled with new insights into the molecular pharmacology of medications and the functional consequences of polymorphisms in the human genome, are providing the tools needed to elucidate genetic determinants of drug response, and translate functional genomics into personalized medicine.

Drug Design↗
PubMed2002

Beta-adrenergic receptor polymorphisms: cardiovascular disease associations and pharmacogenetics.

The beta-adrenergic receptors (betaAR) play important roles in cardiovascular function and disease, and both agonists and antagonists are widely used in various settings for treatment of cardiovascular disease. Both the beta1AR and beta2AR genes have several polymorphisms that are common in the population and result in encoding of different amino acids. More importantly, in vitro functional studies suggest that these polymorphisms have functional significance. In this review we summarize the literature on the relationship between the betaAR polymorphisms and cardiovascular disease as well as the literature on the impact of these polymorphisms on drug response. Additionally, the polymorphisms in both the beta1AR and beta2AR genes are in linkage disequilibrium; thus, the relevance of single polymorphism vs. haplotype analysis is discussed. Further study of the betaAR genetic polymorphisms is likely to enhance our understanding of cardiovascular disease and improve our use of beta-agonists and beta-antagonists in treatment of cardiovascular disease.

Amino Acid Sequence↗
PubMed2002

Pharmacogenetics of cardiovascular drugs.

Pharmacogenetics is a field aimed at understanding the genetic contribution to inter-patient variability in drug efficacy and toxicity. Treatment of cardiovascular disease is, in most cases, guided by evidence from well-controlled clinical trials. Given the solid scientific basis for the treatment of most cardiovascular diseases, it is common for patients with a given disease to be treated in essentially the same manner. Thus, the clinical trials have been very informative about treating large groups of patients with a given disease, but are slightly less informative about the treatment of individual patients. Pharmacogenetics and pharmacogenomics have the potential of taking the information derived from large clinical trials and further refining it to select the drugs with the greatest likelihood for benefit, and least likelihood for harm, in individual patients, based on their genetic make-up. In this paper, the current literature on cardiovascular pharmacogenetics is emphasised, and how the use of pharmacogenetic/pharmacogenomic information may be particularly useful in the future in the treatment of cardiovascular diseases is also highlighted.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2002

Dobutamine pharmacodynamics during dobutamine stress echocardiography and the impact of beta-blocker withdrawal: a report from the Women's Ischemic Syndrome Evaluation Study.

STUDY OBJECTIVES: To determine the pharmacodynamic parameters of dobutamine during dobutamine stress echocardiography (DSE) and to determine how beta-blocker withdrawal the evening before DSE affects responses to dobutamine during DSE. DESIGN: Retrospective analysis. SETTING: University medical center. PATIENTS: One hundred thirty-six women who had chest pain or other symptoms suggestive of myocardial ischemia and were considered to have a clinical indication for coronary angiography MEASUREMENTS AND MAIN RESULTS: Patients underwent DSE with dobutamine dosages titrated from 5 to 40 microg/kg/minute. The infusion was terminated if the patient reached target heart rate or symptoms developed. Those taking beta-blockers withheld their doses the evening before DSE. Traditional pharmacodynamic modeling revealed a wide range in responses to dobutamine. Data for 62% of patients not taking beta-blockers were described by the Emax (maximum heart rate response to dobutamine) model, whereas data for only 39% of patients taking beta-blockers were best described by this model (p = 0.01). Patients taking beta-blockers also had a smaller mean increment in left ventricular ejection fraction (10.8% +/- 4.2% vs 14.1% +/- 9.3%, p < 0.01), a trend toward a higher ED50 (dobutamine dosage rate causing half the maximum heart-rate response; median 16.8 microg/kg/min, p = 0.12) and a lower sigmoidicity factor determining the shape of the curve (median 2.1, p = 0.03). CONCLUSION: The response to dobutamine exhibits wide interpatient variability, even in the absence of beta-blockade. Nonetheless, in the absence of beta-blockers, in most patients the dobutamine response reaches a plateau by the time the maximum infusion rate (40 microg/kg/min) is reached. Withdrawal of beta-blockers the evening before DSE may be inadequate time for elimination of beta-blocker effect, requiring the addition of atropine to achieve the desired response during DSE.

Adrenergic beta-Antagonists↗
PubMed2002

Collection of genomic DNA by the noninvasive mouthwash method for use in pharmacogenetic studies.

STUDY OBJECTIVE: To determine long-term stability, quantity, and quality of genomic DNA samples collected in buccal cells by the mouthwash method, for use in pharmacogenetic studies. DESIGN: Prospective analysis. SETTING: University pharmacogenomics center in Florida and medical centers in Puerto Rico and the United States participating in a multicenter international trial. SUBJECTS: Ten volunteers at the pharmacogenomics center and 201 participants in the ongoing multicenter clinical trial. INTERVENTION: Stability of genomic DNA was determined by measuring DNA yield from mouthwash samples obtained from six volunteers and stored at room temperature over 90 days and from 201 clinical trial samples that were stored and shipped at room temperature. Whether DNA yield was higher with three 5-ml mouthwash rinses versus one 10-ml rinse was evaluated in four volunteers. Quality of genomic DNA was assessed on 32 randomly selected samples from the six volunteers in the stability study, by determining the success rate of DNA amplification with polymerase chain reaction (PCR) testing and by genotyping. MEASUREMENTS AND MAIN RESULTS: For the stability studies, the quantity of genomic DNA decreased over time with storage at room temperature (overall p < 0.01), with the largest declines occurring at 60 and 90 days. Median DNA recovery at 30 and 90 days was 59% and 28% of that at baseline, respectively. Mean +/- standard deviation, median, and range for recovery of genomic DNA from the 201 samples were 45.2 +/- 55 microg, 25.2 microg, and 1-330 microg, respectively. Median recoveries of DNA from the one-rinse and three-rinse methods were not statistically significantly different (9.1 vs 10.5 microg). All samples were amplified successfully by PCR and genotyped, indicating quality of the DNA samples. CONCLUSION: The mouthwash method for collection of genomic DNA is a simple, inexpensive, and noninvasive method that poses less risk than venipuncture and may be used in a variety of settings. Genomic DNA in mouthwash is stable for prolonged periods at room temperature, and the quantity of DNA recovered from this method is more than sufficient for pharmacogenetic studies. Such an approach should be valuable to pharmacogenetic researchers and others who are conducting genetic research.

DNA↗
PubMed2002

Pharmacogenetics, pharmacogenomics, and cardiovascular therapeutics: the way forward.

The completion of sequencing of the human genome will be the vanguard for numerous advances in medicine. The first discernible application is likely to occur in pharmacogenomics, a field focused on the influence of genetic differences on the variability in patients' response to medications. While an inherited basis for drug response has been recognized for some time, it is the confluence of molecular biology, high-throughput genotyping, and bioinformatics that has made it practical to study the genetic basis of variability to medications on a large scale. Pharmacogenomics may enable clinicians to prospectively identify patients most likely to derive benefit from a drug, with minimal likelihood of adverse events. This DNA-based approach to predicting clinical drug efficacy and toxicity would shift the current prescribing paradigm from its empirical nature to a more patient-specific model, ushering in a new era of personalized medicine. Polymorphisms in drug metabolizing enzymes, drug targets, and disease pathogenesis genes are associated with therapeutic effect to cardiovascular pharmacotherapy. Moreover, pharmacogenomics and functional genomics are expected to have a profound impact on the process of drug discovery and development. Finally, pharmacogenomics is likely to transform the way clinical trials are conducted by allowing for the selection of a more homogeneous study population, thereby reducing the size and cost of clinical investigation.

Cardiovascular Agents↗