Drug Response And Metabolism In Crohn\u27s Disease

Inflammatory bowel disease (IBD) is an illness of chronic intestinal inflammation comprised of Crohn\u27s disease (CD) and ulcerative colitis (UC). Specialists rely heavily on drugs that target a dysregulated immune system. There is a staggering degree of variation in drug response in CD. Our understanding of drug metabolism and response in IBD is limited. Gaining new insights into IBD-specific modifications of drug metabolism may allow for improved drug efficacy and reduced toxicity. Cytochrome P450 (CYP) 3A4 is the most relevant determinant of drug metabolism and exposure for medications prescribed today. CYP3A4 is highly expressed in the liver, but is also important to intestinal drug metabolism. Little is known about CYP3A4 activity in disease states. We tested the hypothesis that CD affects the activity, expression and regulation of CYP3A4. Acute, non-hepatic inflammatory states are reported to reduce hepatic CYP3A4 activity. Using midazolam pharmacokinetics and the cholesterol metabolite, 4β- hydroxycholesterol as in vivo probes of CYP3A4 activity, we were able to demonstrate and confirm that CYP3A4 activity is lower in CD. Conversely, we were unable to show, using in vitro modeling, that differences in CYP3A4 activity were due to differential nuclear receptor-signaling in CD. CYP3A4 plays a key role in hepatic and intestinal first-pass metabolism, likely in concert with the xenobiotic exporter, P-glycoprotein (P-gp). The intestinal and colonic ii expression of CYP3A4 in CD has not been well characterized. Using an immunobloting technique, we were able to demonstrate that the intestinal and colonic expression of CYP3A4 are reduced in CD. Lastly, nuclear receptors such as FXR and PXR are important regulators of CYP3A4. Both are down-regulated in IBD. This may have important consequences for drug response in IBD. We confirm that a novel single nucleotide polymorphism in FXR results in a reduction in its downstream products in vivo and reveal a link between genetic variation in FXR and outcomes of CD severity, such as risk and time to surgery, particularly relevant to women affected by CD. Ultimately, these studies demonstrate the impact of CD on drug metabolism pathways and offer insight into the overlap between CD pathogenesis and drug metabolism

Impact of Transporter Polymorphisms on Drug Development: Is It Clinically Significant?

Drug transporters are becoming increasingly recognized as relevant to the drug development process. This may be a reflection of increasing target complexity and the need for high-affinity interaction with drug targets that minimize off-target side effects. Moreover, as new molecular entities (NMEs) become larger in size and amphipathic in nature, interaction with drug transporters, both uptake as well as efflux, becomes increasingly likely. In some cases transporters may limit the absorption or organ-specific entry of NMEs, whereas in other cases transporters may enhance their absorption or tissue accumulation. Indeed, in some cases, transporters may prove to be a therapeutic target. Accordingly, a better understanding of potentially clinically relevant drug transporter polymorphisms earlier in the drug development process is highly desirable. In this review we examine key transporters that are important to the absorption, distribution, and excretion of a large number of drugs in clinical use. Importantly, we provide our assessment of the potential impact of known polymorphisms in such transporters and discuss whether there is sufficient evidence to incorporate these polymorphisms in the drug development process

Attenuation of bile acid-mediated FXR and PXR activation in patients with Crohn’s disease

Bile acids are endogenous ligands of nuclear receptors pregnane X (PXR) and farnesoid X (FXR). PXR and FXR regulate pathways that are impaired in inflammatory bowel disease (IBD). Decreases in PXR and FXR activity are documented in IBD; however reasons for this are unknown. We aimed to assess the effect of Crohn’s disease (CD) on the plasma bile acid composition in vivo and the resultant impact on PXR and FXR activation. A cross-sectional study evaluated the plasma concentrations of 12 bile acids in addition to 4β-hydroxycholesterol (4βOHC), an in vivo probe of the PXR target-gene cytochrome 3A4 (CYP3A4) and the FXR target-gene, fibroblast growth factor (FGF) 19 in individuals with (n = 74) and without (n = 71) CD. An in vitro model was used to assess the impact of CD-specific changes in the plasma bile acid composition on PXR and FXR activation. Decreases in glycochenodeoxycholic acid, taurocholic acid and lithocholic acid were seen in CD with increases in glycodeoxycholic acid and glycocholic acid relative to the total plasma bile acid profile. In vitro, increasing concentrations of bile acids applied in the same ratio as seen in the study cohorts resulted in decreased activation of both PXR and FXR in the CD model. In vivo, plasma 4βOHC (CD = 18.68 ng/ml ± 13.02 ng/ml, non-CD = 46.38 ng/ml ± 40.70 ng/ml, p ≤ 0.0001) and FGF19 (CD = 0.276 pg/L ± 0.189 pg/L, non-CD = 0.485 pg/L ± 0.42 pg/L, p = 0.0002) concentrations were lower in CD versus controls. Ultimately, CD-specific changes in the plasma bile acid composition lead to reduced activation of FXR and PXR target genes in vitro and in vivo

High infliximab trough concentrations are associated with sustained histologic remission in inflammatory bowel disease: a prospective cohort study

Background: The threshold concentration of infliximab during maintenance therapy has not been well-defined in relation to histologic remission. The aim of the study is to dentify the maintenance-phase infliximab concentration associated with histologic remission in inflammatory bowel disease patients (IBD). Methods: A prospective cohort study was carried out in 104 IBD patients seen at a tertiary care centre in London, Canada. Infliximab trough concentrations were collected during the maintenance phase of treatment and compared between participants with and without evidence of histologic remission. Participants were additionally evaluated for sustained histologic remission, and relapse to active disease. Results: Participants in histologic remission attained higher mean concentrations of infliximab during the maintenance phase (10.34 ± 0.69 μg/ml) compared to those with persistent disease activity (6.23 ± 0.67 μg/ml, p-value \u3c 0.0001). Additionally, during the maintenance phase, sustained histologic remission was also associated with a higher mean concentration of infliximab (10.81 ± 5.46 μg/ml) compared to those who relapsed to active disease (5.68 ± 3.70, p \u3c 0.001). Overall, participants with a mean infliximab trough concentration greater than 8ug/ml were more likely to have histologic remission (area under the receiver operating characteristic curve, AUROC = 0.72, 95%CI = 0.65–0.84, p \u3c 0.0001) and sustained histologic remission (AUC = 0.77, 95%CI = 0.63–0.91, p = 0.002). Conclusion: Maintenance-phase infliximab trough concentrations greater than 8 μg/ml, which is higher than the currently recommended target concentration, are highly associated with histologic remission and sustained histologic remission

Genetic variation in the farnesoid X-receptor predicts Crohn’s disease severity in female patients

The farnesoid X receptor (FXR) is implicated in Crohn\u27s disease (CD) pathogenesis. It is unclear how genetic variation in FXR impacts CD severity versus genetic variation in nuclear receptors such as pregnane X receptor (PXR) and the multi-drug resistance protein 1 (MDR1, ABCB1). To evaluate FXR-1G \u3e T as a genomic biomarker of severity in CD and propose a plausible molecular mechanism. A retrospective study (n = 542) was conducted in a Canadian cohort of CD patients. Genotypic analysis (FXR-1G \u3e T, MDR1 3435C \u3e T and PXR -25385C \u3e T) as well as determination of the FXR downstream product, fibroblast growth factor (FGF) 19 was performed. Primary outcomes included risk and time to first CD-related surgery. The effect of estrogen on wild type and variant FXR activity was assessed in HepG2 cells. The FXR-1GT genotype was associated with the risk of (odds ratio, OR = 3.34, 95% CI = 1.58–7.05, p = 0.002) and earlier progression to surgery (hazard ratio, HR = 3.00, 95% CI = 1.86–4.83, p \u3c 0.0001) in CD. Female carriers of the FXR-1GT genotype had the greatest risk of surgery (OR = 14.87 95% CI = 4.22–52.38, p \u3c 0.0001) and early progression to surgery (HR = 6.28, 95% CI = 3.62–10.90, p \u3c 0.0001). Women carriers of FXR-1GT polymorphism had a three-fold lower FGF19 plasma concentration versus women with FXR-1GG genotype (p \u3c 0.0001). In HepG2 cells cotransfected with estrogen receptor (ER) and FXR, presence of estradiol further attenuated variant FXR activity. MDR1 and PXR genotypes were not associated with surgical risk. Unlike MDR1 and PXR, FXR-1GT genetic variation is associated with earlier and more frequent surgery in women with CD. This may be through ER-mediated attenuation of FXR activation

Identification and Characterization of Trimethylamine-N-oxide Uptake and Efflux Transporters

Trimethylamine-N-oxide (TMAO) is a recently identified predictor of cardiovascular and chronic kidney disease. TMAO is primarily generated through gut-microbiome mediated conversion of dietary choline and carnitine to TMA, which is converted to TMAO by hepatic flavin monooxygenase 3 (FMO3) and subsequently undergoes renal elimination. We investigated the role of uptake and efflux drug transporters in TMAO disposition in vitro and in vivo. After screening a large array of uptake transporters, we show organic cation transporter 2 (OCT2) is the key transporter for TMAO cellular uptake. In Oct1/2 knockout mice, we observed increased plasma TMAO levels with reduced renal retention, suggesting the importance of Oct2 in facilitating the uptake of TMAO into renal tubular cells in vivo. Multiple transporters of the ATP-binding cassette (ABC) family, including ABCG2 (BCRP) and ABCB1 (MDR1), were capable of TMAO efflux. In human subjects, clinical, dietary, and pharmacogenetic covariates were evaluated for contribution to TMAO levels in a cohort of dyslipidemic patients (n = 405). Interestingly, genetic variation in ABCG2, but not other transporters, appeared to play a role in modulating TMAO exposure

Pretreatment HLADQA1-HLADRB1 Testing for the Prevention of Azathioprine-Induced Pancreatitis in Inflammatory Bowel Disease: A Prospective Cohort Study

INTRODUCTION:Azathioprine-induced pancreatitis is an idiosyncratic and unpredictable response, occurring in up to 7% of azathioprine-exposed patients with inflammatory bowel disease (IBD). The haplotype HLADQA1-HLADRB1*07:01A\u3eC is strongly associated with azathioprine-induced pancreatitis in IBD. We aimed to evaluate whether pretreatment HLADQA1-HLADRB1*07:01A\u3eC screening will reduce the risk of azathioprine-induced pancreatitis.METHODS:Participants with IBD were screened for HLADQA1-HLADRB1*07:01A\u3eC, and participants with a variant genotype were excluded from azathioprine treatment. Wild-type participants were started on azathioprine and followed for 3 months. The incidence of pancreatitis was compared with unscreened historical controls.RESULTS:HLADQA1-HLADRB1*07:01A\u3eC screening resulted in an 11-fold reduction in the incidence of azathioprine-induced pancreatitis (n = 1/328 or 0.30% vs n = 13/373 or 3.4%). In propensity score-matched cohorts (age and sex), HLA DQA1-HLADRB1*07:01A\u3eC screening was significantly associated with a reduction in the incidence of AZA-induced pancreatitis independent of weight, glucocorticoid exposure, and smoking status (adjusted odds ratio = 0.075, 95% confidence interval = 0.01-0.58, P = 0.01). Up to 45% (n = 271/599) of participants were excluded from azathioprine therapy based on the haplotype in the HLADQA1-HLADRB1*07:01A\u3eC-screened cohort.DISCUSSION:HLADQA1-HLADRB1*07:01A\u3eC screening reduced the risk of azathioprine-induced pancreatitis; however, using this strategy to guide the use of azathioprine therapy in IBD may eliminate a large proportion of patients from being eligible for treatment with azathioprine. In regions where there is access to other IBD therapies, and given the short-term and long-term toxicities associated with azathioprine, HLADQA1-HLADRB1*07:01A\u3eC-screening may be a clinically relevant strategy for enhancing the safe use of azathioprine in IBD. In addition, cost-effectiveness analyses are needed to further solidify the utility of HLADQA1-HLADRB1*07:01A\u3eC screening in IBD populations