P Irving

Mechanism of allopurinol induced TPMT inhibition

Up to 1/5 of patients with wildtype thiopurine-S-methyltransferase (TPMT) activity prescribed azathioprine (AZA) or mercaptopurine (MP) demonstrate a skewed drug metabolism in which MP is preferentially methylated to yield methylmercaptopurine (MeMP). This is known as thiopurine hypermethylation and is associated with drug toxicity and treatment non-response. Co-prescription of allopurinol with low dose AZA/MP (25-33%) circumvents this phenotype and leads to a dramatic reduction in methylated metabolites; however, the biochemical mechanism remains unclear. Using intact and lysate red cell models we propose a novel pathway of allopurinol mediated TPMT inhibition, through the production of thioxanthine (TX, 2-hydroxymercaptopurine). In red blood cells pre-incubated with 250 μM MP for 2h prior to the addition of 250 μM TX or an equivalent volume of Earles balanced salt solution, there was a significant reduction in the concentration of MeMP detected at 4h and 6h in cells exposed to TX (4 h, 1.68, p=0.0005, t-test). TX acts as a direct TPMT inhibitor with an apparent Ki of 0.329 mM. In addition we have confirmed that the mechanism is relevant to in vivo metabolism by demonstrating raised urinary TX levels in patients receiving combination therapy. We conclude that the formation of TX in patients receiving combination therapy with AZA/MP and allopurinol, likely explains the significant reduction of methylated metabolites due to direct TPMT inhibition.

Small bowel MR enterography: problem solving in Crohn’s disease

AbstractMagnetic resonance enterography (MRE) is fast becoming the first-line radiological investigation to evaluate the small bowel in patients with Crohn’s disease. It can demonstrate both mural and extramural complications. The lack of ionizing radiation, together with high-contrast resolution, multiplanar capability and cine-imaging make it an attractive imaging modality in such patients who need prolonged follow-up. A key question in the management of such patients is the assessment of disease activity. Clinical indices, endoscopic and histological findings have traditionally been used as surrogate markers but all have limitations. MRE can help address this question. The purpose of this pictorial review is to (1) detail the MRE protocol used at our institution; (2) describe the rationale for the MR sequences used and their limitations; (3) compare MRE with other small bowel imaging techniques; (4) discuss how MRE can help distinguish between inflammatory, stricturing and penetrating disease, and thus facilitate management of this difficult condition. Main Messages • MR enterography (MRE) is the preferred imaging investigation to assess Crohn’s disease. T2-weighted, post-contrast and diffusion-weighted imaging (DWI) can be used.• MRE offers no radiation exposure, high-contrast resolution, multiplanar ability and cine imaging.• MRE can help define disease activity, a key question in the management of Crohn’s disease.• MRE can help distinguish between inflammatory, stricturing and penetrating disease.• MRE can demonstrate both mural and extramural complications.

The impact of introducing thioguanine nucleotide monitoring into an inflammatory bowel disease clinic

Background:  Thioguanine nucleotides (TGNs) are the active product of thiopurine metabolism. Levels have been correlated with effective clinical response. Nonetheless, the value of TGN monitoring in clinical practice is debated. We report the influence of introducing TGN monitoring into a large adult inflammatory bowel disease (IBD) clinic.

Improving quality of care in inflammatory bowel disease: what changes can be made today?

BACKGROUND AND AIMS There are a number of gaps in our current quality of care for patients with inflammatory bowel diseases. This review proposes changes that could be made now to improve inflammatory bowel disease care. METHODS Evidence from the literature and clinical experience are presented that illustrate best practice for improving current quality of care of patients with inflammatory bowel diseases. RESULTS Best care for inflammatory bowel disease patients will involve services provided by a multidisciplinary team, ideally delivered at a centre of excellence and founded on current guidelines. Dedicated telephone support lines, virtual clinics and networking may also provide models through which to deliver high-quality, expert integrated patient care. Improved physician-patient collaboration may improve treatment adherence, producing tangible improvements in disease outcomes, and may also allow patients to better understand the benefits and risks of a disease management plan. Coaching programmes and tools that improve patient self-management and empowerment are likely to be supported by payers if these can be shown to reduce long-term disability. CONCLUSIONS Halting disease progression before there is widespread bowel damage and disability are ideal goals of inflammatory bowel disease management. Improving patient-physician communication and supporting patients in their understanding of the evidence base are vital for ensuring patient commitment and involvement in the long-term management of their condition. Furthermore, there is a need to create more centres of excellence and to develop inflammatory bowel disease networks to ensure a consistent level of care across different settings.

Interleukin 6 Increases Production of Cytokines by Colonic Innate Lymphoid Cells in Mice and Patients With Chronic Intestinal Inflammation

Background & Aims Innate lymphoid cells (ILCs) are a heterogeneous group of mucosal inflammatory cells that participate in chronic intestinal inflammation. We investigated the role of interleukin 6 (IL6) in inducing activation of ILCs in mice and in human beings with chronic intestinal inflammation. Methods ILCs were isolated from colons of Tbx21-/- × Rag2-/- mice (TRUC), which develop colitis; patients with inflammatory bowel disease (IBD); and patients without colon inflammation (controls). ILCs were characterized by flow cytometry; cytokine production was measured by enzyme-linked immunosorbent assay and cytokine bead arrays. Mice were given intraperitoneal injections of depleting (CD4, CD90), neutralizing (IL6), or control antibodies. Isolated colon tissues were analyzed by histology, explant organ culture, and cell culture. Bacterial DNA was extracted from mouse fecal samples to assess the intestinal microbiota. Results IL17A- and IL22-producing, natural cytotoxicity receptor–negative, ILC3 were the major subset of ILCs detected in colons of TRUC mice. Combinations of IL23 and IL1α induced production of cytokines by these cells, which increased further after administration of IL6. Antibodies against IL6 reduced colitis in TRUC mice without significantly affecting the structure of their intestinal microbiota. Addition of IL6 increased production of IL17A, IL22, and interferon-γ by human intestinal CD3-negative, IL7-receptor–positive cells, in a dose-dependent manner. Conclusions IL6 contributes to activation of colonic natural cytotoxicity receptor–negative, CD4-negative, ILC3s in mice with chronic intestinal inflammation (TRUC mice) by increasing IL23- and IL1α-induced production of IL17A and IL22. This pathway might be targeted to treat patients with IBD because IL6, which is highly produced in colonic tissue by some IBD patients, also increased the production of IL17A, IL22, and interferon-γ by cultured human colon CD3-negative, IL7-receptor–positive cells.

A Biochemical Mechanism for the Role of Allopurinol in TPMT Inhibition

Introduction Hypermethylation of thiopurines has been associated with drug toxicity and non-response to treatment. In such patients the use of low dose thiopurines with concomitant allopurinol is advocated12. Allopurinol is observed to cause a reduction in methylated metabolites of thiopurines; however the biochemical mechanisms remain incompletely understood. Using an intact erythrocyte model we propose a novel pathway of allopurinol mediated thiopurine- S- methyltransferase (TPMT) inhibition, through the production of 2-hydroxy-6-thiopurine (2OH6MP). Methods EDTA whole blood was obtained from healthy volunteers; the plasma and top 5 th were removed and the red cells washed with 0.9% saline. 150 μL of Earl9s balanced salt solution was added to 100 μL of packed red cells. Cells were incubated with 250 μM of 6-mercaptopurine (6-MP) for 0, 2, 4 and 6 h at 37°C. In the second experiment cells were pre-incubated for 2 h with 280 μM of 2OH6MP prior to the addition of 250 μM 6-MP for either 2 or 4 h. At the end of the incubation period, the media was removed and the red cells lysed with 15% perchloric acid after the addition of dithiotreitol. Methylated thiopurine-metabolites were reduced to the base by boiling at 100°C for 1 h. 75 μL of the red cell lysates and supernatant media were separated by reverse phase HPLC to detect the methylated metabolites of 6-MP. Results In packed red cells there was an increase in the concentration of 6-methylmercaptopurine (6-MeMP) detected at each time point. However, the rate of 6-MeMP production remained constant (mean 0.825 pmol L −1 h −1 , SEM ± 0.038). The concentration of 6-MeMP observed in the media was up to 7-fold lower than the concentration in red cells (mean 0.133 pmol L −1 h −1 , SEM ± 0.009). In red cells pre-incubated with 2OH6MP prior to the addition of 6-MP there was a significant reduction in the rate of 6-MeMP production at both 2 (0.878 pmol L −1 h −1 vs 0.135 pmol L −1 h −1 , p −1 h −1 vs 0.096 pmol L −1 h −1 , p Conclusion The data suggests that 6-MP enters red blood cells, where it undergoes methylation to 6-MeMP. The presence of 2OH6MP leads to a reduction in the rate of 6-MeMP production, most likely through direct inhibition of TPMT. We propose that 6-MP undergoes preferential oxidation via aldehyde oxidase, producing 2OH6MP, which leads to feed-back inhibition of TMPT and thereby a reduction in methylated thiopurine-metabolites. This mechanism may explain why patients treated with a combination of thiopurine and allopurinol have dramatically decreased methylated metabolites.

Thiopurines Dosed to a Therapeutic 6-Thioguanine Level in Combination with Adalimumab Are More Effective Than Subtherapeutic Thiopurine-based Combination Therapy or Adalimumab Monotherapy During Induction and Maintenance in Patients with Long-standing Crohnʼs Disease

Background: The benefit of concomitant immunomodulation with adalimumab (ADA) in Crohns disease is poorly understood. We aimed to compare ADA monotherapy with combination therapy with thiopurines, stratified by thioguanine nucleotides (TGNs). Methods: Retrospective observational study of ADA induction and maintenance. Thiopurines were classified according to TGNs (>235 pmol/8 × 108 red blood cell therapeutic). Results: At induction, response was more frequent in combination than ADA monotherapy (83% versus 61%, P = 0.02) and with therapeutic compared with subtherapeutic TGNs (87% versus 70% P = 0.011). Among 280 maintenance semesters in 91 patients, remission was higher with combination than monotherapy (81% versus 60%, P < 0.0001) and therapeutic versus subtherapeutic TGNs (85% versus 58%, P = 0.004). Therapeutic TGN (odds ratio [OR] 4.32, 95% CI, 1.41–13.29, P = 0.01) and albumin (OR 1.09, 95% CI, 1.01–1.18, P = 0.03) were predictors of response to induction. Therapeutic TGN (OR 3.71, 95% CI, 1.87–7.34, P < 0.0001) and ileal disease (OR 0.21, 95% CI, 0.08–0.57, P = 0.002) were predictors of remission semesters. Concomitant immunomodulation at induction was associated with longer time to failure (69 versus 36 months, P = 0.009). Therapeutic TGN at induction (P = 0.03) and male sex (P = 0.026) were associated with time to failure. Conclusions: Combination therapy was superior to ADA monotherapy for induction and during maintenance. This benefit was increased further when thiopurines resulted in therapeutic TGNs. Early use of adequately dosed thiopurines (≥3 months before starting ADA) was associated with improved clinical outcomes.

Vedolizumab: toward a personalized therapy paradigm for people with ulcerative colitis

Ulcerative colitis (UC) is a chronic relapsing and remitting inflammatory bowel disease, with a characteristic leukocytic infiltration of the mucosa. Immunosuppression including anti-TNF-α therapy is a mainstay of treatment for many; however, systemic immunosuppression is not universally effective and is associated with potential side effects. The gut-tropic integrin α4β7, which is expressed on leukocytes, mediates migration from the circulation to the intestinal mucosa. Vedolizumab is a monoclonal antibody which blocks the egress of leukocytes via α4β7, preventing accumulation in the mucosa, and attenuating inflammation without systemic immunosuppression. Vedolizumab has been evaluated in UC in a phase III trial, demonstrating efficacy as both an induction and a maintenance agent. In this article, we review the clinical trial data and also explore the growing body of “real-world” effectiveness data, investigating response and remission rates of vedolizumab in clinical practice. In addition, we review the increasing volume of data supporting the reassuring safety profile associated with vedolizumab.

Optimising use of thiopurines in inflammatory bowel disease

ABSTRACT Introduction: Thiopurines are central to inflammatory bowel disease (IBD) therapeutics, either as monotherapy or in combination with newer biologic therapies, however it is only recently that focus has increased on improving effectiveness and tolerability through optimisation. Areas covered: We review the role of thiopurines in IBD and the importance of the timing of initiation of therapy. Drug metabolism and pharmacogenetics have increasingly played a role in determining dosing and dose optimisation and we review the rationale for this in both thiopurine monotherapy and in combination with biologic agents. We also discuss allopurinol co-therapy as a strategy for enhancing both efficacy and tolerability of thiopurine therapy. Although immunomodulators carry safety considerations, we discuss methods of optimisation to minimise side-effects and maximise safety to ensure the broadest number of patients can benefit. Expert commentary: We provide a practical guide to drug initiation and dose optimisation in a clinical setting, and address potential treatment duration. The forward view considers the place for thiopurines in the treatment of IBD, and how the application of the plethora of genetic data may help inform thopurine therapy in the future.

638 5-Aminosalicylate (5-ASA) Induced Nephrotoxicity in Inflammatory Bowel Disease

Introduction Nephrotoxicity is a rare idiosyncratic reaction to 5-ASA therapy. The precise pathogenic mechanisms are unknown. This study aims to a) describe the clinical features of this rare complication b) explore underlying mechanisms and c) identify clinically useful predictive genetic markers so these drugs can be avoided, or monitoring intensified, in high-risk patients. Here we report the clinical features. Methods Patients were identified and recruited from 185 sites (130 UK). Inclusion criteria included normal renal function prior to commencing 5-ASA, ≥50% rise in creatinine after starting 5-ASA and medical opinion implicating 5-ASA justified drug withdrawal. An adjudication panel assessed causality from case report forms using the validated Liverpool Adverse Drug Reaction Causality Assessment Tool. Results 154 patients were recruited. 19 patients were excluded following adjudication. The cohort included patients with Crohn’s disease, ulcerative colitis and indeterminate colitis (42%, 55%, 4% respectively). 74% of cases were male. Nephrotoxicity was seen with all aminosalicylates including 1 patient treated with topical therapy only. Nephrotoxicity occurred at a median age of 36.5 yrs (range 15.4–88.4 yrs). Two patients had a confirmed family history of 5-ASA-induced nephrotoxicity. 78% were detected by routine blood monitoring. Only 45% of cases recovered completely after drug withdrawal, with 18 requiring renal replacement therapy (14 transplantation). The median time for peak creatinine after commencing 5-ASA was 3.5 yrs (range 0.16–43.4 yrs). There was no evidence that time on 5-ASA treatment was associated with a higher peak creatinine or the likelihood of full recovery (p = 0.87). Women were more likely to reach full recovery than men (p = 0.00148; OR 8.26; CI 2.46–34.94). There was no evidence that early withdrawal of 5-ASA led to a higher likelihood of complete recovery. There was no difference in recovery between the three disease groups on logistic regression analysis. Conclusion This is the largest and most detailed study of 5-ASA induced nephrotoxicity to date. Whilst the incidence is low, the morbidity is high with 13% of patients requiring renal replacement therapy and 55% of patients failing to return to a normal creatinine after 5-ASA withdrawal. The next step is to carry forward these patients to a genome-wide association analysis, to be performed in February 2013. Disclosure of Interest None Declared