Jamie Gregor

Breast cancer resistance protein (ABCG2) and drug disposition : intestinal expression, polymorphisms and sulfasalazine as an in vivo probe

Breast cancer resistance protein (BCRP) is an efflux transporter expressed in tissues that act as barriers to drug entry. Given that single nucleotide polymorphisms (SNPs) in the ABCG2 gene encoding BCRP are common, the possibility exists that these genetic variants may be a determinant of interindividual variability in drug response. The objective of this study is to confirm the human BCRP-mediated transport of sulfasalazine in vitro, evaluate interindividual variation in BCRP expression in human intestine and to determine the role of ABCG2 SNPs to drug disposition in healthy patients using sulfasalazine as a novel in vivo probe. To evaluate these objectives, pinch biopsies were obtained from 18 patients undergoing esophagogastro–duodenoscopy or colonoscopy for determination of BCRP expression in relation to genotype. Wild-type and variant BCRP were expressed in a heterologous expression system to evaluate the effect of SNPs on cell-surface trafficking. A total of 17 healthy individuals participated in a clinical investigation to determine the effect of BCRP SNPs on sulfasalazine pharmacokinetics. In vitro, the cell surface protein expression of the common BCRP 421 C>A variant was reduced in comparison with the wild-type control. Intestinal biopsy samples revealed that BCRP protein and mRNA expression did not significantly differ between patients with 34GG/421CC versus patients with 34GG/421CA genotypes. Remarkably, in subjects with 34GG/421CA genotype, sulfasalazine area under the concentration–time curve was 2.4-fold greater compared with 34GG/421CC subjects (P<0.05). This study links commonly occurring SNPs in BCRP with significantly increased oral sulfasalazine plasma exposure in humans. Accordingly, sulfasalazine may prove to have utility as in vivo probe for assessing the clinical impact of BCRP for the disposition and efficacy of drugs.

Prospective Study of Clinical and Histological Safety of Pure and Uncontaminated Canadian Oats in the Management of Celiac Disease

BACKGROUND Pure oats are safe for most patients with celiac disease, but concerns regarding contamination by other grains limit their consumption. The Canadian Celiac Association recently released guidelines governing the production of pure oats. The objective was to test the safety of a product manufactured under these guidelines. METHODS Fifteen adults with established, biopsy-confirmed celiac disease of ≥ 1 year duration were challenged with 350 g/wk of pure oats for 12 weeks. Symptom scores, weight, hemoglobin, ferritin, albumin, and tissue transglutaminase (tTG) were assessed at weeks 0, 6, and 12. Duodenal biopsies were obtained before and after oat challenge and assessed based on the modified Marsh-Oberhuber score. Compliance with a gluten-free diet was monitored with random food diaries. RESULTS Fifteen patients completed the study and were analyzed in intention-to-treat and per-protocol analyses. There were no significant changes in symptom scores, weight, hemoglobin, ferritin, or albumin during oat consumption. The tTG remained negative in all patients, and the histology scores did not significantly change during oat challenge. The only relapse occurred in a patient who became noncompliant with her gluten-free diet. CONCLUSION The findings support the safety of pure, uncontaminated oats manufactured under Canadian Celiac Association guidelines for patients with celiac disease.

The human proton-coupled folate transporter (hPCFT): modulation of intestinal expression and function by drugs

Folic acid is a vitamin essential for thymidylate and purine synthesis. The human proton-coupled folate transporter (hPCFT) has recently been identified as a pH-dependent folic acid transporter, and mutations in this transporter have been linked to hereditary folic acid malabsorption. In this study, we assessed hPCFT-mediated transport activity in vitro, intersubject variability of intestinal expression in relation to blood folates, and the relationship of proton-pump inhibitor (PPI) therapy on hPCFT expression in vivo. We created a Madin-Darby canine kidney strain II (MDCKII) cell line stably expressing hPCFT to evaluate its drug substrates and inhibitors. Intestinal pinch biopsies (duodenum, ileum, colon) were collected from patients undergoing routine endoscopy procedures, and expressed levels of hPCFT were determined by RT-PCR. When assessed using MDCKII-hPCFT cells, folic acid and methotrexate were found to be high-affinity hPCFT substrates. Sulfasalazine and pyrimethamine were noted to inhibit hPCFT activity with Ki values of 42.3 and 161.7 micromol/l, respectively. hPCFT was localized to the brush-border membrane of enterocytes with highest expression in the duodenum and reduced levels in the ileum and colon. When we assessed hPCFT expression in a subset of patients who were receiving PPI therapy, a near 50% reduction in duodenal hPCFT mRNA expression was noted. These results suggest that hPCFT transporter activity can be modulated by many drugs in clinical use, and expression of this transporter in the gastrointestinal tract is higher in the duodenum than more distal sites (duodenum > ileum > colon). Importantly, we note that PPI drug use appears to be associated with reduced hPCFT expression in vivo.

Intestinal CYP3A4 and midazolam disposition in vivo associate with VDR polymorphisms and show seasonal variation.

Vitamin D, whose levels vary seasonally with sunlight, is activated to 1α,25-dihydroxyvitamin D(3) that binds the vitamin D receptor (VDR) and transcriptionally regulates intestinal CYP3A4 expression. We genotyped VDR polymorphisms and determined their associations with intestinal CYP3A4 and with midazolam pharmacokinetics, and whether intestinal CYP3A4 levels/activity varied seasonally. The VDR BsmIG > A (rs1544410) polymorphism was significantly associated with CYP3A4 jejunal expression/activity, with CYP3A4 duodenal mRNA, and with midazolam area under the curve (AUC). Intestinal CYP3A4 expression/activity was significantly higher in biopsies with the VDR promoter polymorphisms Cdx2-3731G > A and GATA-1012A > G that increase VDR activation of target genes. Duodenal CYP3A4 mRNA was significantly higher between April and September than between October and March. Midazolam p.o. AUC and oral bioavailability trended higher October through March compared to April through September. These data suggest VDR polymorphisms are predictors of intestinal CYP3A4, and that CYP3A4 intestinal expression varies seasonally--likely related to annual changes in UV sunlight and vitamin D levels.

Screening for colorectal cancer: the cost to find an advanced adenoma

OBJECTIVE:Cancer Care Ontario has recommended a program to screen for colorectal cancer using fecal occult blood testing (FOBT). Patients who test positive on FOBT will require further investigation. We examined the cost of finding an advanced adenoma in these patients using four different strategies.METHODS:Using decision analysis software (DATA 3.5, TreeAge Software, Boston, MA), we considered four strategies for evaluating patients referred for a positive FOBT: 1) flexible sigmoidoscopy to the splenic flexure, 2) flexible sigmoidoscopy with air contrast barium enema (ACBE), 3) virtual colonoscopy, and 4) colonoscopy. If an adenoma was found in any of the first three methods, colonoscopy and polypectomy were performed. An advanced adenoma was defined as a villous adenoma, tubular adenoma ≥10 mm, high grade dysplasia, or cancer. Values for probabilities, test characteristics and costs (

Predictive factors associated with immunosuppressive agent use in ulcerative colitis: a case–control study

CDN) were estimated from a MEDLINE literature review, local costs, and OHIP fee codes. Patients with adenomas identified as well as direct medical costs from a third party payer perspective were calculated.RESULTS:Assuming a probability of adenoma of 16.9%, the cost for each strategy (compared to no investigation) was as follows: flexible sigmoidoscopy to the splenic flexure,

Pharmacokinetic profiles for oral and subcutaneous methotrexate in patients with Crohn's disease.

226; flexible sigmoidoscopy with ACBE,

Retrospective analysis of disease association and outcome in histologically confirmed ischemic colitis

424; virtual colonoscopy,

Self-Screening for Malnutrition Risk in Outpatient Inflammatory Bowel Disease Patients Using the Malnutrition Universal Screening Tool (MUST)

597; and colonoscopy,

Functional Characterization of Genetic Variants in the Apical Sodium-Dependent Bile Acid Transporter (ASBT; SLC10A2)

387. The cost to clear a patient of adenoma(s) was