Towards personalised medicine in autoimmune hepatitis: Measurement of thiopurine metabolites results in higher biochemical response rates.

BACKGROUND & AIMS: Patients with autoimmune hepatitis (AIH) usually receive maintenance therapy with thiopurines, such as azathioprine (AZA) or mercaptopurine. Genetic polymorphisms in AZA metabolism can lead to variations in thioguanine nucleotide (TGN) and 6-methylmercaptopurine, both of which can cause adverse drug reactions (ADRs). In inflammatory bowel disease, a therapeutic TGN range (225-450 pmol/8x108 erythrocytes) has been identified to optimise effectiveness. We evaluated the benefits of a personalised medicine approach to thiopurine dosing, in comparison to standard weight-based dosing. METHODS: A retrospective matched cohort study of 214 patients with AIH who were seen at King's College between 1999-2019 was performed. Metabolite levels were measured in 109 patients. The control group included 105 patients on weight-based thiopurine dosing with no metabolite monitoring. RESULTS: Biochemical response (BR) occurred more frequently at 6-month follow-up in patients with metabolite monitoring compared to those on a weight-based regimen (77% vs. 60%, p = 0.008). This remained true with data analysis based on clinicians who measure metabolites and those who do not (BR at 6 months: 84% vs. 64%, p = 0.016). Patients with BR had TGN levels within the therapeutic range of 225-450 pmol/8x108 erythrocytes significantly more often than those who failed to achieve or lost BR (40% vs. 13%, p <0.0001). Moreover, TGN levels within the pre-defined therapeutic range predicted more stable disease within 6 months of testing compared to levels outside the range (p <0.0001). A high proportion of patients with sub-therapeutic TGN levels (75-225 pmol/8x108 erythrocytes) remained in BR (75% vs. 81%, p = 0.589) with fewer ADRs (44% vs. 86%, p = 0.0002) when compared to patients with therapeutic TGN levels. CONCLUSION: A strategy of personalised medicine using metabolite levels can optimise treatment regimens in AIH, resulting in fewer ADRs whilst maintaining BR. LAY SUMMARY: This study looked to see if measuring the breakdown products of a medication used in autoimmune hepatitis increases the chances of gaining good control of the disease, when compared to a group of patients who were on a dose of this medication based on their weight. A group of 214 patients with autoimmune hepatitis were split into 2 groups: roughly half had their medication dose adjusted according to measurements of breakdown products in the blood, whilst the other half received their weight-based dose as normal. The results confirmed that using a personalised approach and checking drug breakdown products resulted in fewer side effects and potentially improved control of disease.

Decreased Peripheral Blood ALKBH5 Correlates with Markers of Autoimmune Response in Systemic Lupus Erythematosus.

Although it has been proved that the epigenetic modification of DNA and histones is involved in the pathogenesis of systemic lupus erythematosus (SLE), there is no study to explore whether the modification of N6-methyladenosine (m6A) in RNA is involved. In this study, the mRNA levels of m6A "writers" (METTL3, MTEEL14, and WTAP), "erasers" (FTO and ALKBH5), and "readers" (YTHDF2) in peripheral blood were determined by quantitative reverse transcription-polymerase chain reaction (qRT-PCR). The results demonstrated that the mRNA levels of METTL3, WTAP, FTO, ALKBH5, and YTHDF2 in peripheral blood from SLE patients were significantly decreased. The levels of ALKBH5 mRNA in SLE patients were associated with anti-dsDNA, antinucleosome, rash, and ulceration. Multivariate logistic regression analysis showed that the level of ALKBH5 mRNA in peripheral blood is a risk factor of SLE (P < 0.001). Moreover, our results suggested that there was a positive correlation between m6A"writers" (METTL3 and WTAP), "erasers" (FTO and ALKBH5), and "readers" (YTHDF2) in SLE patients. This study suggests that the mRNA level of ALKBH5 in peripheral blood may be involved in the pathogenesis of SLE.

Azathioprine and the neurologist.

Neurologists are very familiar with using corticosteroids and are aware of their considerable risk of adverse effects with prolonged use. Thus, we frequently consider alternative immunosuppression or corticosteroid sparing agents. However, unlike other specialties, such as rheumatology, there are few indications for corticosteroid-sparing agents in neurology and so our experience is less extensive; even these indications may reduce further as more disease-modifying treatments become available for neurological conditions. Azathioprine is perhaps the most commonly used corticosteroid-sparing agent in neurology. This review aims to remind neurologists of important aspects of azathioprine prescribing, focussing on enhancing patient safety and clinician confidence in its prescribing.

The relationship among occupational irradiation, DNA methylation status, and oxidative damage in interventional physicians.

Ionizing radiation can induce deoxyribonucleic acid (DNA) methylation pattern change, and ionizing radiation-induced oxidative damage may also affect DNA methylation status. However, the influence of low-dose ionizing radiation, such as occupational radiation exposure, on DNA methylation is still controversial.By investigating the relationship between occupational radiation exposure and DNA methylation changes, we evaluated whether radiation-induced oxidative damage was related to DNA methylation alterations and then determined the relationship among occupational radiation level, DNA methylation status, and oxidative damage in interventional physicians.The study population included 117 interventional physicians and 117 controls. We measured global methylation levels of peripheral blood leukocyte DNA and expression level of DNA methyltransferase (Dnmts) and homocysteine (Hcy) in serum to assess the DNA methylation status of the body. We measured 8-hydroxy-2'-deoxyguanosine (8-OHDG) and 4-hydroxynonenal (4-HNE) levels as indices of oxidative damage. Relevance analysis between multiple indices can reflect the relationship among occupational radiation exposure, DNA methylation changes, and oxidative damage in interventional physicians.The expression levels of Dnmts, 4-HNE, and 8-OHDG in interventional physicians were higher than those in controls, while there was no statistical difference in total DNA methylation rate and expression of Hcy between interventional physicians and controls. Total cumulative personal dose equivalent in interventional physicians was positively correlated with the expression levels of Dnmts, 8-OHDG, and 4-HNE. The expression levels of 8-OHDG in interventional physicians were negatively correlated with global DNA methylation levels and positively correlated with the expression levels of Hcy.Occupational radiation exposure of interventional physicians has a certain effect on the expression of related enzymes in the process of DNA methylation, while ionizing radiation-induced oxidative damage also has a certain effect on DNA methylation. However, there was no evidence that dose burden of occupational exposure was associated to changes of DNA methylation status of interventional physicians, since it is rather unclear which differences are observed among the effects produced by radiation exposure and oxidative damage.

Retrospective Data Analysis of the Influence of Age and Sex on TPMT Activity and Its Phenotype-Genotype Correlation.

BACKGROUND: Therapeutic efficacy and toxicity of thiopurine drugs (used as anticancer and immunosuppressant agents) are affected by thiopurine S-methyltransferase (TPMT) enzyme activity. TPMT genotype and/or phenotype is used to predict the risk for adverse effects before drug administration. Inosine triphosphate pyrophosphatase (ITPA) is another enzyme involved in thiopurine metabolism. In this study, we aimed to evaluate (a) frequency of various TPMT phenotypes and genotypes, (b) correlations between them, (c) influence of age and sex on TPMT activity, and (d) distribution of ITPA variants among various TPMT subgroups. METHODS: TPMT enzyme activity was determined by LC-MS/MS. TPMT (*2,*3A-C) and ITPA (rs1127354, rs7270101) genotypes were determined using a customized TaqMan® OpenArray®. RESULTS: TPMT enzyme activity varied largely (6.3-90 U/mL). The frequency of low, intermediate, normal, and high activity was 0.5% (n = 230), 13.1% (n = 5998), 86.1% (n = 39448), and 0.28% (n = 126), respectively. No significant difference in TPMT activity in relation to age and sex was found. Genotype analysis revealed the frequency of variant TPMT alleles was 6.73% (*3A, n = 344), 0.05% (*3B, n = 2), 2.22% (*3C, n = 95), and 0.42% (*2, n = 19). Analysis of paired phenotype and genotype showed that TPMT activity in samples with variant allele(s) was significantly lower than those without variant alleles. Lastly, an equal distribution of ITPA variants was found among normal and abnormal TPMT activity. CONCLUSIONS: This retrospective data analysis demonstrated a clustering of variant TPMT genotypes with phenotypes, no significant influence of age and sex on TPMT activity, and an equal distribution of ITPA variants among various TPMT subgroups.

Correlation between Thiopurine S-Methyltransferase Genotype and Adverse Events in Inflammatory Bowel Disease Patients.

Background and Objectives: In patients with inflammatory bowel diseases (IBD), the use of azathioprine results in adverse events at a rate of 5% to 20%. The aim of the study was to assess a possible correlation between genetic variability of the enzyme thiopurine S-methyltransferase (TPMT) and the development of toxicity to azathioprine. Materials and Methods: A retrospective, single center, blind, case-control study was conducted on 200 IBD patients, of whom 60 cases suspended azathioprine due to toxicity (leukopenia, pancreatitis, hepatitis, and nausea or vomiting), and 140 controls continued treatment with the drug without adverse events. Results: In the entire cohort, only 8 cases of heterozygous mutations of TPMT were observed, corresponding to 4% mutated haplotype rate, much lower than that reported in literature (close to 10%). No homozygous mutation was found. Regarding the TPMT allelic variants, we did not find any statistically significant difference between patients who tolerated azathioprine and those who suffered from adverse events. (OR = 0.77, 95% CI = 0.08-7.72; p = 0.82). Conclusions: According to our study, in IBD patients, the search for TPMT gene mutations before starting treatment with azathioprine is not helpful in predicting the occurrence of adverse events. Importantly, patients with allelic variants should not be denied the therapeutic option of azathioprine, as they may tolerate this drug.

Development and validation of a UPLC-UV method for the quantification of thiopurine methyltransferase enzyme activity in human erythrocytes.

Thiopurines are drugs widely used for the treatment of autoimmune conditions, inflammatory bowel disease or acute lymphoblastic leukemia. Determination of thiopurine methyltransferase activity (TPMT), a major determinant of thiopurines toxicity, has been suggested before implementing thiopurine treatment. An ultraperformance liquid chromatography (UPLC) method was developed and validated for the quantification of TPMT enzyme activity based on the conversion of 6-mercaptopurine (6-MP) to 6-methylmercaptopurine (6-MMP) using S-adenosyl-L-methionine (SAM) as methyl donor in red blood cell lysates (RBC). This method was improved from a previous laborious high performance liquid chromatography (HPLC) method, using a lower volume of injection and with a shorter runtime. After incubation and protein precipitation 6-MMP was separated on a HSS-T3 (2.1 × 50 mm, 1.8 µm) column and monitored by UV detection (290 nm). A change on the organic solvent used to dissolve 6-MP resulted in a reduction of interference by endogenous or non-enzymatic methylated 6-MMP. A full validation of the 6-MMP assay was performed according to the FDA and EMA guidelines. The method was linear from 0.125 to 2 nmol/mL, with acceptable values of accuracy and precision. The method was applied in 106 patients treated with thiopurines whose TPMT activity was previously quantified by HPLC. Evaluation through Bland-Altman plot showed that TPMT activities were in agreement between both methods.

Thiopurine Methyltransferase Genetic Polymorphisms and Activity and Metabolic Products of Azathioprine in Patients with Inflammatory Bowel Disease.

BACKGROUND: Thiopurine S-methyltransferase (TPMT) is a cytoplasmic enzyme that catalyzes thiopurine drugs such as 6-mercaptopurine, 6-thioguanine, and azathioprine. There is a correlation between thiopurine drug metabolism, response, and toxicity and genetic polymorphism of TPMT. The aim of this study is to assess TPMT genetic polymorphisms activity and metabolic products of AZA in patients with IBD. METHODS: Blood samples were obtained from 50 IBD unrelated patients from a private laboratory. We used polymerase chain reaction-restriction length polymorphism (PCR-RFLP) and allele-specific PCRbased assays to determine the TPMT gene for the different variants. A high-performance liquid chromatography system (HPLC) was carried out to determine the whole blood 6-TGN concentration. Determination of serum TMPT activity was done by ELISA kit. RESULTS: In IBD patients, 46/50 (92%) subjects were homozygous for the wild-type allele (TPMT*1/*1). Mutant TPMT*1/*2 and TPMT*1/*3C alleles were found in 4/46 (8%) and 3/47 (6%) of IBD patients, respectively. TPMT*1/*3B variant was not detected in any of the IBD patients. TPMT enzyme activity was higher in wild-type than that mutant variants TPMT*1/*2 and TPMT*1/*3C, suggesting that there are statistically significant differences between 6-TG levels and polymorphisms of TMPT enzyme. 6-TG levels significantly increased in IBD patients mutant variants TPMT*1/*2 and TPMT*1/*3C. CONCLUSIONS: Our results showed that TPMT polymorphisms are associated with 6-TGN levels in patients using AZA. This study suggests that AZA dosage may be determined according to the high or low prevalence of a TPMT genotype. Moreover, the results present the determination of metabolite for assessing possible safe effective dosage of the drug.

Red Blood cell IMPDH activity in adults and children with or without azathioprine: Relationship between thiopurine metabolites, ITPA and TPMT activities.

Inosine monophosphate dehydrogenase (IMPDH) is considered as the limiting enzyme of thiopurine metabolism for the formation of 6-thioguanine nucleotides (6-TGN). No data are available on the influence of RBC IMPDH activity on the metabolism of thiopurine drugs in individuals with IBD. The aims of this study were as follows: (a) to carry out a phenotypic study of RBC IMPDH activity in adults and children treated or not with azathioprine (AZA) for autoimmune diseases, and (b) to investigate the relationship between the activities of IMPDH, thiopurine metabolites, inosine triphosphatase (ITPA) and thiopurine methyltransferase (TPMT). IMPDH activity was determined in 97 adults and 67 children treated or not with AZA. 6-Thioguanine nucleotides (6-TGN), 6-methylmercaptopurine nucleotide (6-MeMPN) levels, and ITPA as well as TPMT activities were measured in RBCs by HPLC. Using the Gaussian mixture model, distribution of IMPDH activity was evaluated. Influence of age, sex and AZA treatment on IMPDH activity was also assessed. A bimodal distribution in IMPDH activity was found with 87% of patients exhibiting normal activity and 13% of patients with high activity. No influence of age, sex and AZA therapy was found. There is no relationship between TPMT, ITPA and IMPDH activities. A negative correlation between IMPDH activity and 6-MeMPN was shown in adults and children (rs = -0.335 P = 0.014 and rs = -0.383 P = 0.012, respectively). Our results suggest that AZA-treated patients exhibiting lower IMPDH activity could have higher Me-6MPN levels with higher risk of hepatotoxicity. We demonstrated that RBC matrix could be an interesting alternative to lymphocyte matrix to monitor thiopurine metabolites and enzyme activity.

Amplification strategy for sensitive detection of methyltransferase activity based on surface plasma resonance techniques.

In this work, a newly developed surface plasma resonance (SPR) system for the sensitive detection of M.SssI activity has been designed based on double signal amplification with DNA chain cyclic reactions and AuNPs. In the absence of M.SssI, hairpin DNA 1 (HP1) can be cleaved into s1 fragments catalyzed by HpaII. The s1 fragments can then trigger a recycling process of hairpin DNA 2 (HP2) hybridization and subsequently release massive s2 and s3 in the solution of Nt.AlwI and HPII. AuNPs-DNA can be captured on gold film by the released s2 and s3 to produce a strong SPR signal. Whereas in the presence of M.SssI, methylated HP1 cannot be cleaved by HpaII, thus produce a weak SPR signal. The SPR signals are dependent on the M.SssI concentration in the range from 0.5 to 50 U/mL. The successful detection of M.SssI activity in clinical serum samples and inhibition of M.SssI using 5-Aza and 5-Aza-dC indicate a great potential of this strategy for building new monitoring platform in bioanalysis and clinical biomedicine.

Thiopurine S-methyltransferase activity in Nigerians: phenotypes and activity reference values.

OBJECTIVES: This study assessed the activity of thiopurine S-methyltransferase (TPMT) in Nigerians with a view to providing data on susceptibility to thiopurine toxicity, and as well generate reference activity values for clinical use. RESULTS: TPMT activity, expressed as the amount of 6MMP in ng/mL after 1 h incubation at 37 °C per haemoglobin (U/g Hb), varied between 2.34 and 63.50 U/g Hb in the study population. Poor metabolic phenotypes, characterised by an activity values below 8.41 U/g Hb, were observed in 20% of the study subjects. Intermediate metabolizers had activity values between 8.41 and 16.13 U/g Hb. Fast and very fast metabolizers were characterised by activity values of 16.20-56.22 and > 56.22 U/g Hb, respectively. These findings suggest that a potentially huge discordance between TPMT phenotype and genotype exist in Nigerians, and emphasizes the superiority of a prior determination of TPMT metabolic phenotype in ensuring the safety of thiopurine drug administration in the population.

Monitoring recommendations for oral azathioprine, methotrexate and cyclosporin in a paediatric dermatology clinic and literature review.

BACKGROUND/OBJECTIVES: Systemic oral immunomodulators azathioprine, methotrexate and cyclosporin are widely used in paediatric dermatology. Routine blood tests are performed to minimise drug-related adverse events. However, the frequency of monitoring tests may lead to significant fearful experiences for patients. We reviewed haematological abnormalities and clinical side-effects in a paediatric clinic population commencing immunomodulators for dermatological conditions, where haematological profiles are monitored less frequently than in current recommendations. METHODS: A retrospective chart review of children started on azathioprine, methotrexate or cyclosporin for a dermatological condition between 2001-2015 from a primarily paediatric, private dermatology practice was performed. Blood tests were done at baseline, 1 month, 2 months and then 3-monthly for children on azathioprine. Children on methotrexate and cyclosporin had tests done at baseline, after 1 month and then 3-monthly. RESULTS: In total, 242 children were included in this study. Azathioprine, methotrexate and cyclosporin cohorts had 95, 97 and 50 patients treated for a mean duration of 656, 758 and 313 days, respectively. Isolated abnormal blood tests indicated the cessation of azathioprine in 3/95 (3%), methotrexate in 5/97 (5%) and cyclosporin in 2/50 (4%) of patients. Abnormal blood test results were not associated with any reported clinical side-effects in the azathioprine (P = 0.726), methotrexate (P = 0.06) or cyclosporin groups (P = 0.250). CONCLUSION: In our experience, less frequent monitoring did not result in any significant adverse events over a 15-year period. We suggest that haematological monitoring during immunosuppressants use can be safely reduced from current recommendations.

Addition of Allopurinol for Altering Thiopurine Metabolism to Optimize Therapy in Patients with Inflammatory Bowel Disease.

Thiopurine drugs, including azathioprine and 6-mercaptopurine, are used commonly in patients with inflammatory bowel disease for maintenance of remission. Although generally well tolerated, adverse effects lead to discontinuation in a significant minority of patients. Pharmacogenomic studies have suggested that metabolic breakdown of azathioprine in an individual is genetically determined. Coupled with the fact that certain thiopurine metabolites, notably 6-thioguanine nucleotide and 6-methylmercaptopurine, are associated with antiinflammatory effects and adverse effects, respectively, some investigators have examined intentionally shunting the metabolism of azathioprine toward increasing 6-thioguanine nucleotide levels by using low doses of the xanthine oxidoreductase inhibitor allopurinol to improve efficacy and decrease toxicity of azathioprine in patients with inflammatory bowel disease. We performed a search of the MEDLINE and Embase databases for basic and clinical research reports of this modality. Pertinent articles were retrieved, reviewed, and assessed by the authors. Case series, cohort studies, and one randomized trial have investigated adding allopurinol to azathioprine therapy in patients with inflammatory bowel disease. Most reports primarily examined metabolite levels in these patients. In general, the literature suggests that this modality was successful at significantly increasing 6-thioguanine nucleotide levels while decreasing 6-methylmercaptopurine levels. Several small reports have suggested that patients with increased 6-thioguanine nucleotide levels had improved symptoms or symptom remission. Adverse effects and discontinuation rates remained similar or were improved in patients who were taking a thiopurine and started allopurinol. In conclusion, the addition of allopurinol may be an option for optimizing thiopurine metabolite production in select patients with low 6-thioguanine nucleotide levels. Appropriate care and monitoring of these patients are mandatory to prevent neutropenia or other adverse effects.

Validation of a high-performance liquid chromatography method for thiopurine S-methyltransferase activity in whole blood using 6-mercaptopurine as substrate.

BACKGROUND: Variation in metabolism, toxicity and therapeutic efficacy of thiopurine drugs is largely influenced by genetic polymorphisms in the thiopurine S-methyltransferase (TPMT) gene. Determination of TPMT activity is routinely performed in patients to adjust drug therapy. METHODS: We further optimized a previously established high-performance liquid chromatography (HPLC) method by measuring TPMT activity in whole blood instead of isolated erythrocytes, which is based on conversion of 6-mercaptopurine to 6-methylmercaptopurine using S-adenosyl-methionine as methyl donor. RESULTS: The simplified TPMT whole-blood method showed similar or better analytical and diagnostic performance compared with the former erythrocyte assay. The whole-blood method was linear for TPMT activities between 0 and 40 nmol/(mL·h) with a quantification limit of 0.1 nmol/(mL·h). Within-day imprecision and between-day imprecision were ≤5.1% and ≤8.5%, respectively. The optimized method determining TPMT activity in whole blood (y) showed agreement with the former method determining TPMT activity in erythrocytes (x) (n=45, y=1.218+0.882x; p>0.05). Phenotype-genotype concordance (n=300) of the whole-blood method was better when TPMT activity was expressed per volume of whole blood (specificity 92.2%), whereas correction for hematocrit resulted in lower genotype concordance (specificity 86.9%). A new cutoff for the whole-blood method to distinguish normal from reduced TPMT activity was determined at ≤6.7 nmol/(mL·h). CONCLUSIONS: This optimized TPMT phenotyping assay from whole blood using 6-MP as substrate is suitable for research and routine clinical analysis.

A Role for Thiopurine Metabolites in the Synergism Between Thiopurines and Infliximab in Inflammatory Bowel Disease.

BACKGROUND: Interactions between principal cytotoxic thiopurine metabolites, that is 6-thioguanine nucleotides [6-TGN], and infliximab [IFX] and anti-IFX antibodies [Abs] may contribute to higher effectiveness of IFX-thiopurine combination therapy than monotherapies in inflammatory bowel disease. METHODS: To examine if thiopurine metabolites influenced trough IFX and anti-IFX Abs, 89 patients previously assessed for anti-IFX Abs were included. To assess if IFX influenced thiopurine metabolites, eight patients who had responded to 12 weeks of intensified IFX at a constant thiopurine dosing were included. RESULTS: In the first cohort, IFX-thiopurine combination therapy reduced anti-IFX Ab detection [8/40; 20%] as compared with IFX monotherapy [22/49; 45%], odds ratio [OR] 0.31 [0.12-0.80], p < 0.05. 6-TGN was significantly lower in anti-IFX Ab-positive patients (50 pmol/8 × 108 red blood cells [RBC] vs 105, p < 0.01). All anti-IFX Ab-positive patients had 6-TGN < 117 pmol/8 × 108 RBC (sensitivity 100% [63-100], specificity 47% [29-65], area under the curveROC = 0.82, p < 0.01). Trough IFX was similar between anti-IFX Ab-negative patients in IFX monotherapy and IFX-thiopurine combination therapy [5.1 µg/mL vs 4.9, p = 0.76]. 6-TGN and IFX did not correlate [rP = 0.04, p = 0.83; rS = 0.02, p = 0.89, respectively]. In the second cohort, trough IFX increased during IFX intensification [ΔIFX median 6.5 µg/mL, p = 0.02], but 6-TGN was stable [6-TGN at Weeks 0, 4, 8, 12: 90 pmol/8 × 108 RBC, 93, 101, 90; p > 0.05]. Methylated mercaptopurine metabolite associations were consistently negative. CONCLUSIONS: Superior effect of IFX-thiopurine combination therapy over monotherapies partly relates to decrease in anti-IFX Abs, which associates with 6-TGN levels and has a lower therapeutic threshold than during thiopurine monotherapy. Additional benefit likely ascribes to synergy between different anti-inflammatory modes of action rather than direct drug interactions.

Genetic Variants of Pre-microRNAs A-499G(rs3746444) and T-196a2C(rs11614913) with Ulcerative Colitis (UC) and Investigated with Thiopurine-S-Methyltransferase (TPMT) Activity.

BACKGROUND: Abnormal expression and different splicing of miRNAs are involved in several human inflammatory disorders. It has been suggested that gene variants of miRNAs may be associated with increased risk of ulcerative colitis (UC). We aimed to evaluate the association of two SNPs (miRNA-A-499G(rs3746444) and miRNA-T196a2C(rs11614913)) with the risk of UC and monitor their effect on thiopurine-S-methyltransferase (TPMT) activity in Kurdish population of Iran. METHODS: This case-control study was performed on 210 UC patients and 212 healthy individuals. Genotyping assay was performed using PCR-RFLP and the TPMT-activity was measured via non-extraction-HPLC method. RESULTS: We found that the existence of GG genotypes and G allele of miRNA-A-499G SNPs significantly increased the risk of UC by 1.76 and 1.32 times, respectively. The distribution of GG genotype (23.8% vs. 16%, χ2 = 4.2, p = 0.041) and G allele (46.4% vs. 39.4%, χ2 = 4, p = 0.046) of miRNA-A-499G, were significantly higher in UC patients compared to control group. Our results indicate that miRNA SNPs (miRNA-T-196a2C and miRNA-A-499G) have no significant effect on TPMT activity of studied population. CONCLUSIONS: Our results, for the first time, demonstrate that the GG genotype and G allele of miRNA-A-499G significantly increase the risk of UC. However, miRNA SNPs showed no significant effect on TPMT activity in studied population.

American Gastroenterological Association Institute Technical Review on the Role of Therapeutic Drug Monitoring in the Management of Inflammatory Bowel Diseases.

Therapeutic drug monitoring (TDM), which involves measurement of drug or active metabolite levels and anti-drug antibodies, is a promising strategy that can be used to optimize inflammatory bowel disease therapeutics. It is based on the premise that there is a relationship between drug exposure and outcomes, and that considerable inter-individual variability exists in how patients metabolize the drug (pharmacokinetics) and the magnitude and duration of response to therapy (pharmacodynamics). Therefore, the American Gastroenterological Association has prioritized clinical guidelines on the role of TDM in the management of inflammatory bowel disease. To inform these clinical guidelines, this technical review was developed in accordance with the GRADE (Grading of Recommendations Assessment, Development, and Evaluation) framework for interventional and prognostic studies, and focused on the application of TDM for biologic therapy, specifically anti-tumor necrosis factor-α agents, and for thiopurines. Focused questions address the benefits and risks of a strategy of reactive TDM (in patients with active inflammatory bowel disease) to guide treatment changes compared with empiric treatment changes, and the benefits and risks of a strategy of routine proactive TDM (during routine clinical care in patients with quiescent disease) compared with no routine TDM. Additionally, the review addresses the benefits and risks of routine measurement of thiopurine methyltransferase enzyme activity or genotype before starting thiopurine therapy compared with empiric weight-based dosing and explores the performance of different trough drug concentrations for anti-tumor necrosis factor agents and thiopurines to inform clinical decision making when applying TDM in a reactive setting. Due to a paucity of data, this review does not address the role of TDM for more recently approved biologic agents, such as vedolizumab or ustekinumab.

Multicentric Case-Control Study on Azathioprine Dose and Pharmacokinetics in Early-onset Pediatric Inflammatory Bowel Disease.

BACKGROUND: Early-onset inflammatory bowel disease (IBD) is generally aggressive, with a high probability of complications and need of surgery. Despite the introduction of highly effective biological drugs, treatment with azathioprine continues to be important even for early-onset IBD; however, in these patients azathioprine response seems to be reduced. This study evaluated azathioprine doses, metabolite concentrations, and their associations with patients' age in children with IBD treated at 6 tertiary pediatric referral centers. METHODS: Azathioprine doses, metabolites, and clinical effects were assessed after at least 3 months of therapy in 17 early-onset (age < 6 yr, cases) and 51 nonearly-onset (aged > 12 and <18 yrs, controls) patients with IBD. Azathioprine dose was titrated on therapeutic efficacy (response and adverse effects). Azathioprine metabolites and thiopurine methyltransferase activity were determined by high-performance liquid chromatography with ultra violet-vis detection (HPLC-UV) methods. RESULTS: Frequency of patients in remission was similar among early-onset and control groups, respectively (82% and 84%, P value = 0.72). Early-onset patients required higher doses of azathioprine (median 2.7 versus 2.0 mg·kg·d, P value = 1.1 × 10). Different doses resulted in comparable azathioprine active thioguanine nucleotide metabolite concentrations (median 263 versus 366 pmol/8 × 10 erythrocytes, P value = 0.41) and methylmercaptopurine nucleotide concentrations (median 1455 versus 1532 pmol/8 × 10 erythrocytes, P value = 0.60). Lower ratios between thioguanine nucleotide metabolites and azathioprine doses were found in early-onset patients (median 98 versus 184 pmol/8 × 10 erythrocytes·mg·kg·d, P value = 0.017). Interestingly, early-onset patients presented also higher thiopurine methyltransferase activity (median 476 versus 350 nmol methylmercaptopurine/mg hemoglobin/h, P-value = 0.046). CONCLUSIONS: This study demonstrated that patients with early-onset IBD present increased inactivating azathioprine metabolism, likely because of elevated activity of the enzyme thiopurine methyltransferase.