Innovating Thiopurine Therapeutic Drug Monitoring: A Systematic Review and Meta-Analysis on DNA-Thioguanine Nucleotides (DNA-TG) as an Inclusive Biomarker in Thiopurine Therapy.

BACKGROUND AND OBJECTIVE: Thioguanine (TG), azathioprine (AZA), and mercaptopurine (MP) are thiopurine prodrugs commonly used to treat diseases, such as leukemia and inflammatory bowel disease (IBD). 6-thioguanine nucleotides (6-TGNs) have been commonly used for monitoring treatment. High levels of 6-TGNs in red blood cells (RBCs) have been associated with leukopenia, the cutoff levels that predict this side effect remain uncertain. Thiopurines are metabolized and incorporated into leukocyte DNA. Measuring levels of DNA-incorporated thioguanine (DNA-TG) may be a more suitable method for predicting clinical response and toxicities such as leukopenia. Unfortunately, most methodologies to assay 6-TGNs are unable to identify the impact of NUDT15 variants, effecting mostly ethnic populations (e.g., Chinese, Indian, Malay, Japanese, and Hispanics). DNA-TG tackles this problem by directly measuring thioguanine in the DNA, which can be influenced by both TPMT and NUDT15 variants. While RBC 6-TGN concentrations have traditionally been used to optimize thiopurine therapy due to their ease and affordability of measurement, recent developments in liquid chromatography-tandem mass spectrometry (LC-MS/MS) techniques have made measuring DNA-TG concentrations in lymphocytes accurate, reproducible, and affordable. The objective of this systematic review was to assess the current evidence of DNA-TG levels as marker for thiopurine therapy, especially with regards to NUDT15 variants. METHODS: A systematic review and meta-analysis were performed on the current evidence for DNA-TG as a marker for monitoring thiopurine therapy, including methods for measurement and the illustrative relationship between DNA-TG and various gene variants (such as TPMT, NUDT15, ITPA, NT5C2, and MRP4). PubMed and Embase were systematically searched up to April 2024 for published studies, using the keyword "DNA-TG" with MeSH terms and synonyms. The electronic search strategy was augmented by a manual examination of references cited in articles, recent reviews, editorials, and meta-analyses. A meta-analysis was performed using R studio 4.1.3. to investigate the difference between the coefficients (Fisher's z-transformed correlation coefficient) of DNA-TG and 6-TGNs levels. A meta-analysis was performed using RevMan version 5.4 to investigate the difference in DNA-TG levels between patients with or without leukopenia using randomized effect size model. The risk of bias was assessed using the Newcastle-Ottowa quality assessment scale. RESULTS: In this systematic review, 21 studies were included that measured DNA-TG levels in white blood cells for either patients with ALL (n = 16) or IBD (n = 5). In our meta-analysis, the overall mean difference between patients with leukopenia (ALL + IBD) versus no leukopenia was 134.15 fmol TG/µg DNA [95% confidence interval (CI) (83.78-184.35), P < 0.00001; heterogeneity chi squared of 5.62, I2 of 47%]. There was a significant difference in DNA-TG levels for patients with IBD with and without leukopenia [161.76 fmol TG/µg DNA; 95% CI (126.23-197.29), P < 0.00001; heterogeneity chi squared of 0.20, I2 of 0%]. No significant difference was found in DNA-TG level between patients with ALL with or without leukopenia (57.71 fmol TG/µg DNA [95% CI (- 22.93 to 138.35), P < 0.80]). DNA-TG monitoring was found to be a promising method for predicting relapse rates in patients with ALL, and DNA-TG levels are likely a better predictor for leukopenia in patients with IBD than RBC 6-TGNs levels. DNA-TG levels have been shown to correlate with various gene variants (TPMT, NUDT15, ITPA, and MRP4) in various studies, points to its potential as a more informative marker for guiding thiopurine therapy across diverse genetic backgrounds. CONCLUSIONS: This systematic review strongly supports the further investigation of DNA-TG as a marker for monitoring thiopurine therapy. Its correlation with treatment outcomes, such as relapse-free survival in ALL and the risk of leukopenia in IBD, underscores its role in enhancing personalized treatment approaches. DNA-TG effectively identifies NUDT15 variants and predicts late leukopenia in patients with IBD, regardless of their NUDT15 variant status. The recommended threshold for late leukopenia prediction in patients with IBD with DNA-TG is suggested to be between 320 and 340 fmol/µg DNA. More clinical research on DNA-TG implementation is mandatory to improve patient care and to improve inclusivity in thiopurine treatment.

MUC13 Cell Surface Mucin Limits Salmonella Typhimurium Infection by Protecting the Mucosal Epithelial Barrier.

BACKGROUND & AIMS: MUC13 cell surface mucin is highly expressed on the mucosal surface throughout the intestine, yet its role against bacterial infection is unknown. We investigated how MUC13 impacts Salmonella typhimurium (S Tm) infection and elucidated its mechanisms of action. METHODS: Muc13-/- and wild-type littermate mice were gavaged with 2 isogenic strains of S Tm after pre-conditioning with streptomycin. We assessed clinical parameters, cecal histology, local and systemic bacterial load, and proinflammatory cytokines after infection. Cecal enteroids and epithelial cell lines were used to evaluate the mechanism of MUC13 activity after infection. The interaction between bacterial SiiE and MUC13 was assessed by using siiE-deficient Salmonella. RESULTS: S Tm-infected Muc13-/- mice had increased disease activity, histologic damage, and higher local and systemic bacterial loads. Mechanistically, we found that S Tm binds to MUC13 through its giant SiiE adhesin and that MUC13 acts as a pathogen-binding decoy shed from the epithelial cell surface after pathogen engagement, limiting bacterial invasion. In addition, MUC13 reduces epithelial cell death and intestinal barrier breakdown by enhancing nuclear factor kappa B signaling during infection, independent of its decoy function. CONCLUSIONS: We show for the first time that MUC13 plays a critical role in antimicrobial defense against pathogenic S Tm at the intestinal mucosal surface by both acting as a releasable decoy limiting bacterial invasion and reducing pathogen-induced cell death. This further implicates the cell surface mucin family in mucosal defense from bacterial infection.

Gut inflammation and adaptive immunity amplify acetaminophen toxicity in bowel and liver.

BACKGROUND AND AIM: Prevention of liver failure arising from accidental or deliberate paracetamol (acetaminophen [APAP]) overdose remains a vexed health problem despite well-publicized guidelines for its early detection and treatment. It is recognized that the gut may aggravate liver pathology, via the gut-liver axis. The main aim of this study was to assess the role of the colon in APAP-induced liver toxicity. METHODS: Liver necrosis and colitis were studied following sublethal doses of APAP administered intraperitoneally to C57Bl/6 wild-type (WT) mice, as well as to C57Bl/6 Winnie mice, which develop a spontaneous colitis caused by a SNP in Muc2, and WT mice with acute DSS-induced colitis. Repeated APAP exposure was studied in WT and Rag1 ko mice that lack mature T and B lymphocytes. RESULTS: APAP overdose resulted in significant colonic injury in WT mice (P < 0.05), which resolved by 24 h. Underlying colitis was not associated with liver necrosis, but colitis exacerbated APAP-induced liver injury and extended APAP-colonic injury. Prior APAP exposure exacerbated both APAP-liver and APAP-colonic injury more so in WT than Rag1 ko mice. APAP impaired barrier function with increased intestinal permeability and associated bacterial translocation to the liver and spleen in mice with the Winnie phenotype. CONCLUSIONS: This study identifies novel roles for APAP in causing colitis, the amplification of APAP-liver toxicity where there is underlying colitis, and involvement of immune memory in APAP-toxicity. The latter could be key for decoding the poorly understood but important clinical entity of chronic APAP liver failure.

An Extremes of Phenotype Approach Confirms Significant Genetic Heterogeneity in Patients with Ulcerative Colitis.

BACKGROUND AND AIMS: Ulcerative colitis [UC] is a major form of inflammatory bowel disease globally. Phenotypic heterogeneity is defined by several variables including age of onset and disease extent. The genetics of disease severity remains poorly understood. To further investigate this, we performed a genome wide association [GWA] study using an extremes of phenotype strategy. METHODS: We conducted GWA analyses in 311 patients with medically refractory UC [MRUC], 287 with non-medically refractory UC [non-MRUC] and 583 controls. Odds ratios [ORs] were calculated for known risk variants comparing MRUC and non-MRUC, and controls. RESULTS: MRUC-control analysis had the greatest yield of genome-wide significant single nucleotide polymorphisms [SNPs] [2018], including lead SNP = rs111838972 [OR = 1.82, p = 6.28 × 10-9] near MMEL1 and a locus in the human leukocyte antigen [HLA] region [lead SNP = rs144717024, OR = 12.23, p = 1.7 × 10-19]. ORs for the lead SNPs were significantly higher in MRUC compared to non-MRUC [p < 9.0 × 10-6]. No SNPs reached significance in the non-MRUC-control analysis (top SNP, rs7680780 [OR 2.70, p = 5.56 × 10-8). We replicate findings for rs4151651 in the Complement Factor B [CFB] gene and demonstrate significant changes in CFB gene expression in active UC. Detailed HLA analyses support the strong associations with MHC II genes, particularly HLA-DQA1, HLA-DQB1 and HLA-DRB1 in MRUC. CONCLUSIONS: Our MRUC subgroup replicates multiple known UC risk variants in contrast to non-MRUC and demonstrates significant differences in effect sizes compared to those published. Non-MRUC cases demonstrate lower ORs similar to those published. Additional risk and prognostic loci may be identified by targeted recruitment of individuals with severe disease.

MUC1-mediated Macrophage Activation Promotes Colitis-associated Colorectal Cancer via Activating the Interleukin-6/ Signal Transducer and Activator of Transcription 3 Axis.

BACKGROUND & AIMS: MUC1 is abnormally expressed in colorectal cancer, including colitis-associated colorectal cancer (CAC), but its role in tumorigenesis is unclear. This study investigated MUC1's effects in murine models of colitis and CAC and elucidated mechanisms of action. METHODS: Colitis and CAC were induced in mice by exposure to dextran sodium sulfate or azoxymethane plus dextran sodium sulphate. Clinical parameters, immune cell infiltration, and tumor development were monitored throughout disease progression. Experiments in knockout mice and bone marrow chimeras were combined with an exploration of immune cell abundance and function. RESULTS: Deficiency of Muc1 suppressed inflammation, inhibited tumor progression, increased abundance of CD8+ T lymphocytes, and reduced abundance of macrophages in colon tumors. Bone marrow chimeras showed promotion of CAC was primarily mediated by Muc1-expressing hematopoietic cells, and that MUC1 promoted a pro-tumoral immunosuppressive macrophage phenotype within tumors. Mechanistic studies revealed that Muc1 deficiency remarkably reduced interleukin-6 levels in the colonic tissues and tumors that was mainly produced by infiltrating macrophages at day 21, 42, and 85. In bone marrow-derived macrophages, MUC1 promoted responsiveness to chemoattractant and promoted activation into a phenotype with high Il6 and Ido1 expression, secreting factors which inhibited CD8+ T cell proliferation. MUC1 potently drives macrophages to produce interleukin-6, which in turn drives a pro-tumorigenic activation of signal transducer and activator of transcription 3 in colon epithelial tumor and stromal cells, ultimately increasing the occurrence and development of CAC. CONCLUSIONS: Our findings provide cellular and molecular mechanisms for the pro-tumorigenic functions of MUC1 in the inflamed colon. Therapeutic strategies to inhibit MUC1 signal transduction warrant consideration for the prevention or therapy of CAC.

Secreted NF-κB suppressive microbial metabolites modulate gut inflammation.

Emerging evidence suggests that microbiome-host crosstalk regulates intestinal immune activity and predisposition to inflammatory bowel disease (IBD). NF-κB is a master regulator of immune function and a validated target for the treatment of IBD. Here, we identify five Clostridium strains that suppress immune-mediated NF-κB activation in epithelial cell lines, PBMCs, and gut epithelial organoids from healthy human subjects and patients with IBD. Cell-free culture supernatant from Clostridium bolteae AHG0001 strain, but not the reference C. bolteae BAA-613 strain, suppresses inflammatory responses and endoplasmic reticulum stress in gut epithelial organoids derived from Winnie mice. The in vivo responses to Clostridium bolteae AHG0001 and BAA-613 mirror the in vitro activity. Thus, using our in vitro screening of bacteria capable of suppressing NF-κB in the context of IBD and using an ex vivo organoid-based approach, we identify a strain capable of alleviating colitis in a relevant pre-clinical animal model of IBD.

Successful Manipulation of the Gut Microbiome to Treat Spontaneous and Induced Murine Models of Colitis.

Background and Aims: There is clinical interest in the sustainability or otherwise of prebiotic, microbial, and antibiotic treatments to both prevent and treat inflammatory bowel diseases. This study examined the role of antibiotic manipulation of the gut microbiome to treat spontaneous and induced murine models of colitis. Methods: Symptomatic, histological, molecular, and microbial ecology and bioinformatic readouts were used to study the effect of a 10-day antibiotic cocktail and then follow-up over 2 months in the spontaneous Winnie colitis mouse preclinical model of ulcerative colitis and also the indirect antibiotic and Winnie microbiotic gavage effects in an acute dextran sodium sulfate-induced colitis model in wild-type mice. Results: The antibiotics elicited a striking reduction in both colitis symptoms and blinded histological colitis scores, together with a convergence of the microbial taxonomy of the spontaneous colitis and wild-type control mice, toward a taxonomic phenotype usually considered to be dysbiotic. The improvement in colitis was sustained over the following 8 weeks although the microbial taxonomy changed. In vitro, fecal waters from the antibiotic-treated colitis and wild-type mice suppressed the inflammatory tenor of colonic epithelial cells, and gavaged cecal slurries from these mice moderated the acute induced colitis. Conclusion: The results clearly show the possibility of a sustained remission of colitis by microbial manipulation, which is relevant to clinical management of inflammatory bowel diseases. The beneficial effects appeared to depend on the microbial metabolome rather than its taxonomy.

Advances in Thiopurine Drug Delivery: The Current State-of-the-Art.

Thiopurines (mercaptopurine, azathioprine and thioguanine) are well-established maintenance treatments for a wide range of diseases such as leukemia, inflammatory bowel disease (IBD), systemic lupus erythematosus (SLE) and other inflammatory and autoimmune diseases in general. Worldwide, millions of patients are treated with thiopurines. The use of thiopurines has been limited because of off-target effects such as myelotoxicity and hepatotoxicity. Therefore, seeking methods to enhance target-based thiopurine-based treatment is relevant, combined with pharmacogenetic testing. Controlled-release formulations for thiopurines have been clinically tested and have shown promising outcomes in inflammatory bowel disease. Latest developments in nano-formulations for thiopurines have shown encouraging pre-clinical results, but further research and development are needed. This review provides an overview of novel drug delivery strategies for thiopurines, reviewing modified release formulations and with a focus on nano-based formulations.

A Nucleotide Analog Prevents Colitis-Associated Cancer via Beta-Catenin Independently of Inflammation and Autophagy.

BACKGROUND & AIMS: Chronic bowel inflammation increases the risk of colon cancer; colitis-associated cancer (CAC). Thiopurine treatments are associated with a reduction in dysplasia and CAC in inflammatory bowel disease (IBD). Abnormal Wnt/ß-catenin signalling is characteristic of >90% of colorectal cancers. Immunosuppression by thiopurines is via Rac1 GTPase, which also affects Wnt/ß-catenin signalling. Autophagy is implicated in colonic tumors, and topical delivery of the thiopurine thioguanine (TG) is known to alleviate colitis and augment autophagy. This study investigated the effects of TG in a murine model of CAC and potential mechanisms. METHODS: Colonic dysplasia was induced by exposure to azoxymethane (AOM) and dextran sodium sulfate (DSS) in wild-type (WT) mice and mice harboring intestinal epithelial cell-specific deletion of autophagy related 7 gene (Atg7ΔIEC). TG or vehicle was administered intrarectally, and the effect on tumor burden and ß-catenin activity was assessed. The mechanisms of action of TG were investigated in vitro and in vivo. RESULTS: TG ameliorated DSS colitis in wild-type but not Atg7ΔIEC mice, demonstrating that anti-inflammatory effects of locally delivered TG are autophagy-dependent. However, TG inhibited CAC in both wild-type and Atg7ΔIEC mice. This was associated with decreased ß-catenin activation/nuclear translocation demonstrating that TG's inhibition of tumorigenesis occurred independently of anti-inflammatory and pro-autophagic actions. These results were confirmed in cell lines, and the dependency on Rac1 GTPase was demonstrated by siRNA knockdown and overexpression of constitutively active Rac1. CONCLUSIONS: Our findings provide evidence for a new mechanism that could be exploited to improve CAC chemoprophylactic approaches.

MUC13 promotes the development of colitis-associated colorectal tumors via ß-catenin activity.

Many adenocarcinomas, including colorectal cancer (CRC), overexpress the MUC13 cell surface mucin, but the functional significance and mechanisms are unknown. Here, we report the roles of MUC13 in colonic tumorigenesis and tumor progression. High-MUC13 expression is associated with poor survival in two independent patient cohorts. In a comprehensive series of in vivo experiments, we identified a critical role for MUC13 in the development of this malignancy, by promoting survival and proliferation of tumor-initiating cells and driving an immunosuppressive environment that protects tumors from checkpoint inhibitor immunotherapy. In Muc13-deficient mice, fewer tumors are generated after exposure to carcinogens and inflammation, they have markedly reduced ß-catenin signaling, have more tumor-infiltrating CD103+ dendritic cells and CD8+ T lymphocytes, fewer myeloid-derived suppressor cells, and are rendered sensitive to checkpoint inhibitor immunotherapy (anti-PD-L1). Mechanistically, we show that MUC13 protects ß-catenin from degradation, by interacting with GSK-3ß, which increases ß-catenin nuclear translocation and promotes its signaling, thereby driving cancer initiation, progression, invasion, and immune suppression. Therefore, MUC13 is a potential marker of poor prognosis in colorectal cancer, and inhibiting MUC13 may be useful in the treatment of colitis-associated cancer and sensitizing tumors to immunotherapy.

Association of Genetic Variants in NUDT15 With Thiopurine-Induced Myelosuppression in Patients With Inflammatory Bowel Disease.

Importance: Use of thiopurines may be limited by myelosuppression. TPMT pharmacogenetic testing identifies only 25% of at-risk patients of European ancestry. Among patients of East Asian ancestry, NUDT15 variants are associated with thiopurine-induced myelosuppression (TIM). Objective: To identify genetic variants associated with TIM among patients of European ancestry with inflammatory bowel disease (IBD). Design, Setting, and Participants: Case-control study of 491 patients affected by TIM and 679 thiopurine-tolerant unaffected patients who were recruited from 89 international sites between March 2012 and November 2015. Genome-wide association studies (GWAS) and exome-wide association studies (EWAS) were conducted in patients of European ancestry. The replication cohort comprised 73 patients affected by TIM and 840 thiopurine-tolerant unaffected patients. Exposures: Genetic variants associated with TIM. Main Outcomes and Measures: Thiopurine-induced myelosuppression, defined as a decline in absolute white blood cell count to 2.5 × 109/L or less or a decline in absolute neutrophil cell count to 1.0 × 109/L or less leading to a dose reduction or drug withdrawal. Results: Among 1077 patients (398 affected and 679 unaffected; median age at IBD diagnosis, 31.0 years [interquartile range, 21.2 to 44.1 years]; 540 [50%] women; 602 [56%] diagnosed as having Crohn disease), 919 (311 affected and 608 unaffected) were included in the GWAS analysis and 961 (328 affected and 633 unaffected) in the EWAS analysis. The GWAS analysis confirmed association of TPMT (chromosome 6, rs11969064) with TIM (30.5% [95/311] affected vs 16.4% [100/608] unaffected patients; odds ratio [OR], 2.3 [95% CI, 1.7 to 3.1], P = 5.2 × 10-9). The EWAS analysis demonstrated an association with an in-frame deletion in NUDT15 (chromosome 13, rs746071566) and TIM (5.8% [19/328] affected vs 0.2% [1/633] unaffected patients; OR, 38.2 [95% CI, 5.1 to 286.1], P = 1.3 × 10-8), which was replicated in a different cohort (2.7% [2/73] affected vs 0.2% [2/840] unaffected patients; OR, 11.8 [95% CI, 1.6 to 85.0], P = .03). Carriage of any of 3 coding NUDT15 variants was associated with an increased risk (OR, 27.3 [95% CI, 9.3 to 116.7], P = 1.1 × 10-7) of TIM, independent of TPMT genotype and thiopurine dose. Conclusions and Relevance: Among patients of European ancestry with IBD, variants in NUDT15 were associated with increased risk of TIM. These findings suggest that NUDT15 genotyping may be considered prior to initiation of thiopurine therapy; however, further study including additional validation in independent cohorts is required.

A well-tolerated and rapidly acting thiopurine for IBD?

Thiopurine drugs continue to be a cornerstone of inflammatory bowel disease (IBD) treatment. Thiopurines are economical compared with many newer medical treatments for IBD, other chronic inflammatory diseases and leukaemia, although they are not without their shortcomings. These include a slow-onset therapeutic action and many adverse drug reactions. This feature article surveys published data, unpublished in vitro and in vivo experiments, as well as clinical experience, underpinning a rationale for bringing a novel thiopurine drug formulation to market. This formulation has a rapid action making it suitable for the induction and maintenance treatment of IBD and avoids most thiopurine-associated adverse reactions.

The role of IL-22 in the resolution of sterile and nonsterile inflammation.

In a broad sense, inflammation can be conveniently characterised by two phases: the first phase, which is a pro-inflammatory, has evolved to clear infection and/or injured tissue; and the second phase concerns regeneration of normal tissue and restitution of normal physiology. Innate immune cell-derived pro-inflammatory cytokines and chemokines activate and recruit nonresident immune cells to the site of infection, thereby amplifying the inflammatory responses to clear infection or injury. This phase is followed by a cytokine milieu that promotes tissue regeneration. There is no absolute temporal distinction between these two phases, and cytokines may have dual pleiotropic effects depending on the timing of release, inflammatory microenvironment or concentrations. IL-22 is a cytokine with reported pro- and anti-inflammatory roles; in this review, we contend that this protein has primarily a function in restitution of normal tissue and physiology.

Entyvio lengthen dose-interval study: lengthening vedolizumab dose interval and the risk of clinical relapse in inflammatory bowel disease.

BACKGROUND: Vedolizumab (VDZ), an α4ß7 anti-integrin antibody, is efficacious in the induction and maintenance of remission in ulcerative colitis (UC) and Crohn's disease (CD). In the GEMINI long-term safety study, enrolled patients received 4-weekly VDZ. Upon completion, patients were switched to 8-weekly VDZ in Australia. The clinical success rate of treatment de-escalation for patients in remission on VDZ has not been described previously. AIM: To determine the proportion of patients who relapsed after switching from 4 to 8-weekly VDZ, the mean time to relapse, and the recapture rate when switching back to 8-weekly dosing. MATERIALS AND METHODS: This was a retrospective, observational, multicenter study of patients previously recruited into GEMINI long-term safety in Australia. Data on the demographics and biochemical findings were collected. RESULTS: There were 34 patients [23 men, mean age 49.1 (±13.1) years] and their mean disease duration was 17.6 (±8.5) years. The mean 4-weekly VDZ infusion duration was 286.5 (±48.8) weeks. A total of five (15%) patients relapsed on dose-interval increase (4/17 UC, 1/17 CD) at a median duration from dose interval lengthening to flare of 14 weeks (interquartile range=6-25). Eighty percent (4/5) of patients re-entered remission following dose-interval decrease back to 4-weekly. No clinical predictors of relapse could be determined because of the small cohort size. CONCLUSION: The risk of patients relapsing when switching from 4 to 8-weekly VDZ ∼15% and is similar between CD and UC. Dose-interval decrease recaptures 80% of patients who relapsed. Therapeutic drug monitoring of VDZ may be of clinical relevance.

Anti-TNF Therapeutic Drug Monitoring in Postoperative Crohn's Disease.

BACKGROUND: Anti-TNF prevents postoperative Crohn's disease recurrence in most patients but not all. This study aimed to define the relationship between adalimumab pharmacokinetics, maintenance of remission and recurrence. METHODS: As part of a study of postoperative Crohn's disease management, some patients undergoing resection received prophylactic postoperative adalimumab. In these patients, serum and fecal adalimumab concentration and serum anti-adalimumab antibodies [AAAs] were measured at 6, 12 and 18 months postoperatively. Levels of Crohn's disease activity index [CDAI], C-reactive protein [CRP] and fecal calprotectin [FC] were assessed at 6 and 18 months postoperatively. Body mass index and smoking status were recorded. A colonoscopy was performed at 6 and/or 18 months. RESULTS: Fifty-two patients [32 on monotherapy and 20 on combination therapy with thiopurine] were studied. Adalimumab concentration did not differ significantly between patients in endoscopic remission vs recurrence [Rutgeerts ≥ i2] [9.98µg/mL vs 8.43 µg/mL, p = 0.387]. Patients on adalimumab monotherapy had a significantly lower adalimumab concentration [7.89 µg/mL] than patients on combination therapy [11.725 µg/mL] [p = 0.001], and were significantly more likely to have measurable AAA [31% vs 17%, p = 0.001]. Adalimumab concentrations were lower in patients with detectable AAA compared with those without [3.59 µg/mL vs 12.0 µg/mL, p < 0.001]. Adalimumab was not detected in fecal samples. Adalimumab serum concentrations were lower in obese patients compared with in non-obese patients [p = 0.046]. CONCLUSION: Adalimumab concentration in patients treated with adalimumab to prevent symptomatic endoscopic recurrence postoperatively is, for most patients, well within the therapeutic window, and is not significantly lower in patients who develop recurrence compared with in those who remain in remission. Mechanisms of anti-TNF failure to prevent postoperative recurrence remain to be determined in these patients.

Colonic thioguanine pro-drug: Investigation of microbiome and novel host metabolism.

Thiopurines are analogues of endogenous purines. They are pro-drugs which require the purine salvage pathway to convert them to the active drug nucleotides (TGN). These drugs are used to maintain clinical remission in patients with inflammatory bowel diseases. In our recent Gut paper, we showed that thioguanine worked quickly to improve colitis in the absence in the host animal of the key guanine salvage enzyme, hypoxanthine-guanine-phosphoribosyltransferase (HPRT). Current evidence favours the proposition that active drug delivery to the host lacking HPRT requires translocation of TGN-loaded bacteria across the inflamed mucosal barrier, and most likely delivery by phagocytosis. Alternatively, the efficacy of thioguanine in treating colitis could be mediated by modulation of the community of the microbiota in the intestine, or there are novel host pathways for conversion of the thioguanine pro-drug to TGN.

Critical assessment of thioguanine treatment for inflammatory bowel diseases: Is it time to rehabilitate this treatment?

OBJECTIVE: The potential therapeutic effect of thioguanine in the management of inflammatory bowel disease (IBD) is hindered due to association with vascular hepatotoxicity. The study aimed to assess the evidence for efficacy of thioguanine in IBD management and the association with nodular regenerative hyperplasia (NRH) and other thioguanine-related hepatotoxicities. METHODS: Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were used for literature search. Due to the lack of randomized controlled trials (RCTs), the search was extended to observational studies. Quality of the included studies were graded A to C based on evaluation tools used to determine efficacy (subjective and objective grading tools) and nodular regenerative hyperplasia safety (liver biopsy and imaging tools). RESULTS: Two hundred and ninety studies were identified, but following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines only 13 studies were evaluated for efficacy and safety of thioguanine. Outcome measures were consistent across the included studies. Thioguanine appeared efficacious and well-tolerated in patients who were intolerant/non-responsive to existing immunomodulators. There was a trend toward a positive association between dose of thioguanine and NRH but not with other adverse events such as liver biochemical abnormalities or with portal hypertension. CONCLUSIONS: The evidence to support thioguanine treatment is limited to observational studies. While encouraging, there is a need for prospective RCTs to determine the role of thioguanine in the management of IBD.