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Douglas Clark

Publications and source records attributed to Douglas Clark.

7 recordsLinked to original sources
PubMed2006

In silico pharmacogenetics of warfarin metabolism.

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.

Animals↗
PubMed2006

Vivo motion and force measurement of surgical needle intervention during prostate brachytherapy.

In this paper, we present needle insertion forces and motion trajectories measured during actual brachytherapy needle insertion while implanting radioactive seeds in the prostate glands of 20 different patients. The needle motion was captured using ultrasound images and a 6 degree-of-freedom electromagnetic-based position sensor. Needle velocity was computed from the position information and the corresponding time stamps. From in vivo data we found the maximum needle insertion forces to be about 15.6 and 8.9 N for 17 gauge (1.47 mm) and 18 gauge (1.27 mm) needles, respectively. Part of this difference in insertion forces is due to the needle size difference (17G and 18G) and the other part is due to the difference in tissue properties that are specific to the individual patient. Some transverse forces were observed, which are attributed to several factors such as tissue heterogeneity, organ movement, human factors in surgery, and the interaction between the template and the needle. However, theses insertion forces are significantly responsible for needle deviation from the desired trajectory and target movement. Therefore, a proper selection of needle and modulated velocity (translational and rotational) may reduce the tissue deformation and target movement by reducing insertion forces and thereby improve the seed delivery accuracy. The knowledge gleaned from this study promises to be useful for not only designing mechanical/robotic systems but also developing a predictive deformation model of the prostate and real-time adaptive controlling of the needle.

Brachytherapy↗
PubMed2006

Understanding our drugs and our diseases.

Analysis of mouse genetic models of human disease-associated traits has provided important insight into the pathogenesis of human disease. As one example, analysis of a murine genetic model of osteoporosis demonstrated that genetic variation within the 15-lipoxygenase (Alox15) gene affected peak bone mass, and that treatment with inhibitors of this enzyme improved bone mass and quality in rodent models. However, the method that has been used to analyze mouse genetic models is very time consuming, inefficient, and costly. To overcome these limitations, a computational method for analysis of mouse genetic models was developed that markedly accelerates the pace of genetic discovery. It was used to identify a genetic factor affecting the rate of metabolism of warfarin, an anticoagulant that is commonly used to treat clotting disorders. Computational analysis of a murine genetic model of narcotic drug withdrawal suggested a potential new approach for treatment of narcotic drug addiction. Thus, the results derived from computational mouse genetic analysis can suggest new treatment strategies, and can provide new information about currently available medicines.

Animals↗
PubMed2005

Antidiabetic drugs and heart failure risk in patients with type 2 diabetes in the U.K. primary care setting.

OBJECTIVE: To assess the effects of antidiabetic drugs on the risk of heart failure in patients with type 2 diabetes. RESEARCH DESIGN AND METHODS: We conducted a retrospective cohort study with a newly diagnosed diabetes cohort of 25,690 patients registered in the U.K. General Practice Research Database, 1988-1999. We categorized person-time drug exposures to monotherapies in insulin, sulfonylureas (SUs), metformins, and other oral hypoglycemic agents (i.e., acarbose, guar gum) and combination therapy including insulin, combination therapy without insulin, and triple combination therapy with or without insulin. A drug-free time interval served as a reference category. Cox interval-wise (piece-wise) regression analyses were used. The main outcome was incident heart failure. RESULTS: Among 43,390 drug exposure intervals for 25,690 patients who had a mean follow-up period of 2.5 years, 1,409 patients developed heart failure. Heart failure occurred most frequently in SU monotherapy exposure. After adjusting for duration of diabetes, the timing and order of treatments received, and known risk factors for heart failure, we found no differential effects among type-specific therapies. Patients with any drug use within the first year after diabetes diagnosis had a 4.75-fold higher risk (hazard ratio) for heart failure than those with drug-free status but had no increased risk during subsequent years. CONCLUSIONS: In conclusion, the use of any pharmacological therapy for type 2 diabetes appears to be associated with an increased risk of heart failure. This risk does not persist beyond the first year after diagnosis of diabetes and does not appear to differ among the types of drug therapy examined. This observation suggests that the severity of diabetes or the preclinical duration of diabetes and the need for drug therapy, and not the therapy itself, is an explanation for heart failure in patients with type 2 diabetes.

Adult↗
PubMed2003

Relating sensation seeking and the von Restorff Isolation Effect.

Sensation seeking was examined in a short-term memory task involving the serial recall of a 10-item list of consonants with (isolated) and without (non-isolated) a distinctively larger item in the fifth position. 126 students were given the Sensation Seeking Scale Form-V and 32 10-item lists to memorize in a 1 by 3 mixed design. Sensation seeking was a between-subject factor and Blocks (Trials 1-16 and 17-32), Isolation (isolated and nonisolated), and Duration (2 sec. and 10 sec.) were within-subject factors. Generally nonisolated lists and the larger letters (the von Restorff Isolation Effect) were better recalled, with the latter being stronger at the shorter duration. Only the high sensation-seeking group showed a Blocks effect for lists with an isolated item such that there was a greater number of items correct per list in Block 1 than in Block 2. This finding is consistent with the argument that higher scores on sensation seeking are associated with greater cortical arousal and better memory for newness and change. Students with high sensation-seeking scores showed superior memory for the isolated list when it contained an isolate if allowed more processing time. It is argued that high sensation-seeking scores were associated with more effective transfer of items from shorter to longer-term memory. A rapid nontime-dependent perceptual process was used to explain the isolation effect. The poorer overall list performance for the lists with the isolate was explained in terms of the intense nature of the isolate.

Adult↗