5 research outputs found
Genetic Variation in the Proximal Promoter of ABC and SLC Superfamilies: Liver and Kidney Specific Expression and Promoter Activity Predict Variation
Membrane transporters play crucial roles in the cellular uptake and efflux of an array of small molecules including nutrients, environmental toxins, and many clinically used drugs. We hypothesized that common genetic variation in the proximal promoter regions of transporter genes contribute to observed variation in drug response. A total of 579 polymorphisms were identified in the proximal promoters (â250 to +50 bp) and flanking 5âČ sequence of 107 transporters in the ATP Binding Cassette (ABC) and Solute Carrier (SLC) superfamilies in 272 DNA samples from ethnically diverse populations. Many transporter promoters contained multiple common polymorphisms. Using a sliding window analysis, we observed that, on average, nucleotide diversity (Ï) was lowest at approximately 300 bp upstream of the transcription start site, suggesting that this region may harbor important functional elements. The proximal promoters of transporters that were highly expressed in the liver had greater nucleotide diversity than those that were highly expressed in the kidney consistent with greater negative selective pressure on the promoters of kidney transporters. Twenty-one promoters were evaluated for activity using reporter assays. Greater nucleotide diversity was observed in promoters with strong activity compared to promoters with weak activity, suggesting that weak promoters are under more negative selective pressure than promoters with high activity. Collectively, these results suggest that the proximal promoter region of membrane transporters is rich in variation and that variants in these regions may play a role in interindividual variation in drug disposition and response
Effects of Ketoconazole on the In Vivo Biotransformation and Hepatobiliary Transport of the Thrombin Inhibitor AZD0837 in Pigs
Combined in Vitroâin Vivo Approach To Assess the Hepatobiliary Disposition of a Novel Oral Thrombin Inhibitor
Combined in Vitroâin Vivo Approach To Assess the Hepatobiliary Disposition of a Novel Oral Thrombin Inhibitor
Two
clinical trials and a large set of in vitro transporter experiments
were performed to investigate if the hepatobiliary disposition of
the direct thrombin inhibitor prodrug AZD0837 is the mechanism for
the drugâdrug interaction with ketoconazole observed in a previous
clinical study. In Study 1, [<sup>3</sup>H]ÂAZD0837 was administered
to healthy male volunteers (<i>n</i> = 8) to quantify and
identify the metabolites excreted in bile. Bile was sampled directly
from the jejunum by duodenal aspiration via an oro-enteric tube. In
Study 2, the effect of ketoconazole on the plasma and bile pharmacokinetics
of AZD0837, the intermediate metabolite (AR-H069927), and the active
form (AR-H067637) was investigated (<i>n</i> = 17). Co-administration
with ketoconazole elevated the plasma exposure to AZD0837 and the
active form approximately 2-fold compared to placebo, which may be
explained by inhibited CYP3A4 metabolism and reduced biliary clearance,
respectively. High concentrations of the active form was measured
in bile with a bile-to-plasma AUC ratio of approximately 75, indicating
involvement of transporter-mediated excretion of the compound. AZD0837
and its metabolites were further investigated as substrates of hepatic
uptake and efflux transporters in vitro. Studies in MDCK-MDR1 cell
monolayers and P-glycoprotein (P-gp) expressing membrane vesicles
identified AZD0837, the intermediate, and the active form as substrates
of P-gp. The active form was also identified as a substrate of the
multidrug and toxin extrusion 1 (MATE1) transporter and the organic
cation transporter 1 (OCT1), in HEK cells transfected with the respective
transporter. Ketoconazole was shown to inhibit all of these three
transporters; in particular, inhibition of P-gp and MATE1 occurred
in a clinically relevant concentration range. In conclusion, the hepatobiliary
transport pathways of AZD0837 and its metabolites were identified
in vitro and in vivo. Inhibition of the canalicular transporters P-gp
and MATE1 may lead to enhanced plasma exposure to the active form,
which could, at least in part, explain the clinical interaction with
ketoconazole
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Genetic variation in the proximal promoter of ABC and SLC superfamilies: liver and kidney specific expression and promoter activity predict variation.
Membrane transporters play crucial roles in the cellular uptake and efflux of an array of small molecules including nutrients, environmental toxins, and many clinically used drugs. We hypothesized that common genetic variation in the proximal promoter regions of transporter genes contribute to observed variation in drug response. A total of 579 polymorphisms were identified in the proximal promoters (-250 to +50 bp) and flanking 5' sequence of 107 transporters in the ATP Binding Cassette (ABC) and Solute Carrier (SLC) superfamilies in 272 DNA samples from ethnically diverse populations. Many transporter promoters contained multiple common polymorphisms. Using a sliding window analysis, we observed that, on average, nucleotide diversity (pi) was lowest at approximately 300 bp upstream of the transcription start site, suggesting that this region may harbor important functional elements. The proximal promoters of transporters that were highly expressed in the liver had greater nucleotide diversity than those that were highly expressed in the kidney consistent with greater negative selective pressure on the promoters of kidney transporters. Twenty-one promoters were evaluated for activity using reporter assays. Greater nucleotide diversity was observed in promoters with strong activity compared to promoters with weak activity, suggesting that weak promoters are under more negative selective pressure than promoters with high activity. Collectively, these results suggest that the proximal promoter region of membrane transporters is rich in variation and that variants in these regions may play a role in interindividual variation in drug disposition and response