N. K. H. de Boer

Thiopurine therapy in inflammatory bowel disease patients: Analyses of two 8-year intercept cohorts†

Background: Thiopurines have proven efficacy in long‐term maintenance therapy of inflammatory bowel disease (IBD). Limited data are available with regard to factors predicting effectiveness and failure of long‐term thiopurine use in IBD patients. Methods: The data in this retrospective study are based on an 8‐year intercept cohort of previous or present thiopurine‐using IBD patients. Both cohorts are assessed by descriptive and statistical analysis aimed at determining thiopurine effectiveness and the variables that are predictive for failure of thiopurine therapy. Results: In all, 363 IBD patients were included (60% female), 63% with Crohns disease and 33% with ulcerative colitis. Overall, thiopurines were continued in 145/363 (40%) and discontinued in 208/363 (57%) patients. The proportion of patients still using thiopurines at 3, 6, 12, 24, and 60 months was 73%, 69%, 63%, 51%, and 42%, respectively. Patients discontinued thiopurines due to adverse events (39%), refractoriness (16%), and ongoing remission / patients request (4%). 6‐methylmercaptopurine (6‐MMP) concentration and 6‐MMP/6‐thioguanine nucleotides (6‐TGN) ratio were significant higher in the failure group. Prolonged continuation of thiopurines was associated with a decreased risk of discontinuation. Conclusions: Azathioprine and 6‐mercaptopurine were considered effective in ≈40% of IBD patients after 5 years of treatment. A quarter of the patients discontinued thiopurines within 3 months, mostly due to adverse events. A high 6‐MMP concentration or 6‐MMP/6‐TGN ratio was associated with therapeutic failure. If thiopurine use was successfully initiated in the first months, its use was usually extended over many years, as long‐term use was associated with continuation of therapy. (Inflamm Bowel Dis 2010)

Bacterial population analysis of human colon and terminal ileum biopsies with 16S rRNA-based fluorescent probes: Commensal bacteria live in suspension and have no direct contact with epithelial cells

Background: The commensal intestinal microflora has important metabolic and perhaps also immune modulatory functions. Evidence has accumulated that the microflora plays a role in the pathogenesis of inflammatory bowel disease. Therefore, there is a growing interest in the intestinal microflora and its interaction with the host. Presumably, this interaction takes place at the mucus layer. In this study, we investigated the microflora that is present at the mucus layer and addressed the following questions. Does a specific mucus‐adherent microflora exist? Is there direct contact between commensal bacteria and epithelial cells? Methods: Snap‐frozen biopsies were taken of 5 colon regions and of the terminal ileum in 9 subjects with a normal colon. Fecal samples were also collected. Bacteria were detected in cryosections with fluorescent in situ hybridization (FISH) with 16S ribosomal (r)RNA‐targeted probes for all bacteria and specific probes for the major representatives of anaerobic microflora (bifidobacteria, Bacteroides, clostridia, atopobia) and aerobic microflora (Enterobacteriaceae, enterococci, streptococci, lactobacilli). Results: With this sensitive technique, bacteria were only observed at the luminal side of the intestinal mucus layer. Very few microcolonies were present at the mucus layer, and the composition of the bacterial microflora present in the feces was similar to that at the mucus layer of the terminal ileum and colon regions. Conclusions: We did not observe direct contact between bacteria and epithelial cells. The equal distribution of bacterial species suggests that intestinal commensal bacteria live in suspension in the lumen and that there is no specific mucus‐adherent microflora.

Detection of immune deposits in skin lesions of patients with Wegener's granulomatosis.

BACKGROUND Wegeners granulomatosis (WG) is considered a pauci-immune systemic vasculitis based on the absence of immune deposits in renal biopsies of patients with active disease. In animal models of antineutrophil cytoplasmic antibody (ANCA) associated glomerulonephritis, immune deposits along the glomerular capillary wall are present at early stages of lesion development. These deposits are degraded rapidly, resulting in “pauci-immune” lesions. OBJECTIVE To test the hypothesis that immune deposits can also be detected in early lesions of patients with WG, thereby initiating an inflammatory reaction that, in time, is augmented in the presence of ANCA, resulting in pauci-immune lesions later on. METHODS The presence of immune deposits in skin biopsies taken within 48 hours of lesion development was investigated. Direct immunofluorescence was used to examine 32 skin biopsies for the presence of immune deposits (IgG, IgA, IgM, C3c). When possible, a comparison was made between the immunofluorescence findings in renal and skin biopsies taken at the same time. RESULTS Four of 11 biopsies taken at initial presentation and four of 21 biopsies taken at the onset of a relapse of WG showed IgG and/or IgA containing immune deposits in the subepidermal blood vessels. All nine renal biopsies showed pauci-immune glomerulonephritis, irrespective of the presence (n=5) or absence (n=4) of immune deposits in the skin biopsy. CONCLUSION A substantial number of skin biopsies showed immune deposits during active disease. These results could support the hypothesis that immune complexes may trigger vasculitic lesions in WG.

6-Thioguanine treatment in inflammatory bowel disease: a critical appraisal by a European 6-TG working party.

Recently, the suggestion to use 6-thioguanine (6-TG) as an alternative thiopurine in patients with inflammatory bowel disease (IBD) has been discarded due to reports about possible (hepato) toxicity. During meetings arranged in Vienna and Prague in 2004, European experts applying 6-TG further on in IBD patients presented data on safety and efficacy of 6-TG. After thorough evaluation of its risk-benefit ratio, the group consented that 6-TG may still be considered as a rescue drug in stringently defined indications in IBD, albeit restricted to a clinical research setting. As a potential indication for administering 6-TG, we delineated the requirement for maintenance therapy as well as intolerance and/or resistance to aminosalicylates, azathioprine, 6-mercaptopurine, methotrexate and infliximab. Furthermore, indications are preferred in which surgery is thought to be inappropriate. The standard 6-TG dosage should not exceed 25 mg daily. Routine laboratory controls are mandatory in short intervals. Liver biopsies should be performed after 6–12 months, three years and then three-yearly accompanied by gastroduodenoscopy, to monitor for potential hepatotoxicity, including nodular regenerative hyperplasia (NRH) and veno-occlusive disease (VOD). Treatment with 6-TG must be discontinued in case of overt or histologically proven hepatotoxicity.

Long-term follow-up of children exposed intrauterine to maternal thiopurine therapy during pregnancy in females with inflammatory bowel disease.

Inflammatory bowel disease (IBD) affects a substantial number of female patients in their reproductive years. Therefore, many physicians face the dilemma whether thiopurines, prescribed to maintain remission, can be taken safely during pregnancy. Data on long‐term development outcome of children exposed to maternal thiopurine therapy are very limited.

The effect of allopurinol and low-dose thiopurine combination therapy on the activity of three pivotal thiopurine metabolizing enzymes: Results from a prospective pharmacological study

INTRODUCTION Thiopurine therapy is often discontinued in inflammatory bowel disease (IBD) patients. The xanthine oxidase (XO) inhibitor allopurinol has previously shown to enhance thiopurine efficacy and to prevent adverse reactions, the mechanism of this beneficial interaction is not completely clarified. The aim of this study is to observe possible effects of allopurinol and low-dose thiopurine combination therapy on the activity of three pivotal thiopurine metabolizing enzymes. METHODS A prospective study of IBD patients failing thiopurine therapy due to a skewed thiopurine metabolism was performed. Patients were treated with allopurinol and azathioprine or mercaptopurine. Xanthine oxidase, hypoxanthine-guanine phosphoribosyl transferase (HGPRT) and thiopurine S-methyl transferase (TPMT) activities, and thiopurine metabolites concentrations were measured during thiopurine monotherapy, and after 4 and 12 weeks of combination therapy. RESULTS Of fifteen IBD patients, XO activity decreased from 0.18 (IQR 0.08-0.3) during thiopurine monotherapy to 0.14 (IQR 0.06-0.2) and 0.11 (IQR 0.06-0.2; p=0.008) mU/hour/ml at 4 and 12 weeks, respectively. HGPRT activity increased from 150 (IQR 114-176) to 180 (IQR 135-213) and 204 nmol/(h×mg protein) (IQR 173-213; p=0.013). TPMT activity seemed not to be affected. 6-Thioguanine nucleotide concentrations increased from 138 (IQR 119-188) to 235 (223-304) and to 265 pmol/8×10^8 (IQR 188-344), whereas 6-methyl mercaptopurine ribonucleotides concentrations decreased from 13230 (IQR 7130-17420) to 690 (IQR 378-1325) and 540 (IQR 240-790) pmol/8×10^8 at 4 and 12 weeks of combination therapy (both p<0.001). CONCLUSION Allopurinol and thiopurine combination-therapy seems to increase HGPRT and decrease XO activity in IBD patients, which at least in part may explain the observed changes in thiopurine metabolite concentrations.

Allopurinol safely and effectively optimises thiopurine metabolites in patients with autoimmune hepatitis

Ten percent of patients with autoimmune hepatitis (AIH) are nonresponsive or intolerant to thiopurine therapy. A skewed metabolism, leading to the preferential generation of (hepato)toxic thiopurine metabolites (6‐MMPs) instead of the metabolic active 6‐tioguanine (thioguanine) nucleotides (6‐TGNs), may explain this unfavourable outcome. Co‐administration of allopurinol to low‐dose thiopurine therapy may effectively revert this deviant metabolism, as has been shown in inflammatory bowel disease.

Azathioprine or mercaptopurine-induced acute pancreatitis is not a disease-specific phenomenon

Aliment Pharmacol Ther 31, 1322–1329

Extended Thiopurine Metabolite Assessment During 6-Thioguanine Therapy for Immunomodulation in Crohn's Disease

The proposed metabolic advantage of 6‐thioguanine (6‐TG) is the direct conversion into the pharmacologically active 6‐thioguaninenucleotides (6‐TGN). The authors assessed metabolic characteristics of 6‐TG treatment in patients with Crohns disease (N = 7) on therapy with 20 mg 6‐TG. 6‐thioguanine‐monophosphate (6‐TGMP), 6‐thioguanine‐diphosphate (6‐TGDP), and 6‐thioguanine‐triphosphate (6‐TGTP) were measured by high‐performance liquid chromatography analysis in erythrocytes. Thiopurine S‐methyltransferase activity and total 6‐TGN levels were determined by standard methods. High interindividual variance in metabolite measurements was observed. Main metabolites were 6‐TGTP (median = 531 pmol/8 × 108 red blood cells) and 6‐TGDP (median = 199 pmol/8 × 108 red blood cells). Traces of 6‐TGMP (median = 39 pmol/8 × 108 red blood cells) and 6‐TG (2 patients) could be detected. 6‐TGN levels correlated with 6‐TGTP levels (r = 0.929, P = .003) and with the sum of separate nucleotides (r = 0.929, P = .003). No correlations were established between TPMT activity (median = 13 pmol/h/107) and 6‐TG metabolites. The 1‐step metabolism of 6‐TG still leads to high interindividual variance in metabolite concentrations. Total 6‐TGN level monitoring may suffice for clinical practice.

On the limitation of 6-tioguaninenucleotide monitoring during tioguanine treatment

Background : Tioguanine (thioguanine) has been proposed as a rescue thiopurine for azathioprine or mercaptopurine intolerant inflammatory bowel disease patients. The use of tioguanine leads to high 6‐tioguaninenucleotide (6‐thioguaninenucleotide) levels in red blood cells but, contra‐intuitively, these have yet not been associated with an increased risk of myelotoxicity.