Thiopurine Methyltransferase Activity Research Articles

Thiopurine S-methyl Transferase (TPMT) Enzyme Level in Healthy Sudanese Population

Background: Thiopurine drugs have limited use due to their toxicity, related to the enzyme thiopurine S-methyl transferase (TPMT) activity, which varies between individuals. This is the first study in Sudan, which aimed to assess the TPMT phenotypic status of healthy Sudanese volunteers. Methods: A total of 177 healthy volunteers from Sudan were included in the study. TPMT enzymatic activities were measured using the ELISA serum protocol. We used SPSS to analyze the data and determined enzyme level categories and normal range with Z scores and quartile tests. The Sudan Medical Specialization Board (SMSB) Ethical Committee approved the study. Results: There were 117 males and 60 females among the volunteers, with ages ranging from 16 to 70 years and a mean age ± SD of 28.0 ±1 0.2, median = 24. Most candidates were from the Afro-Asiatic linguistic group (64.5%), followed by Nilo-Saharan (18.6%) and Niger-Kordofanian (16.9%). The TPMT enzyme level ranged between 0.17 and 9.5 ng/ml, with a mean of 2.26 ± 0.75 ng/ml. The quartile classification included very low enzyme (<0.76 ng/ml) seen in 4 candidates (2.3%), intermediate low (0.76-1.4 ng/ml) seen in 34 (19.2%), the normal range (1.5 – 3.75 ng/ml) seen in 119 (67.2%), and high enzyme activity (>3.76 ng/ml) seen in 20 (11.3%). No significant correlations between age, sex, and ethnic groups were recorded. Conclusion: The normal TPMT enzyme activity is between 1.5 and 3.76 ng/ml. A higher prevalence of TPMT deficiency was recorded and compared with international studies. Pretreatment screening using serum ELISA test for TPMT enzyme activity should be used to predict the risk of toxicity.

Agranulocytosis Induced by Overdosage of Mercaptopurine: A Case Report

Drug-induced agranulocytosis (DIAG) is a rare but potentially fatal hematological complication. Thiopurines, such as mercaptopurine (6-MP), are widely used in the treatment of chronic inflammatory bowel diseases (IBD), but can cause myelotoxicity due to the accumulation of active metabolites. We report the case of a 48-year-old woman with ulcerative colitis who developed severe agranulocytosis following an accidental overdose of 6-MP. The patient presented with febrile pancytopenia with a neutrophil count of 0.04 G/L. Bone marrow examination revealed normal cellularity with an inversion of the maturation pyramid of the granulocyte lineage. A treatment combining growth factors (filgrastim) and antibiotics (tazobactam) was initiated, leading to progressive improvement over 5 weeks. The toxicity of 6-MP is mainly due to the accumulation of 6-thioguanine nucleotides (6-TGN). The polymorphism of the gene encoding the enzyme thiopurine S-methyltransferase (TPMT) can influence the risk of myelotoxicity. Two strategies are proposed to minimize this risk: evaluation of TPMT activity with dosage adjustment, or regular monitoring of blood counts with gradual dose increase. This case highlights the importance of rigorous biological monitoring when initiating 6-MP treatment, regardless of the TPMT test. Increased vigilance is necessary when using immunosuppressive drugs in the treatment of IBD to optimize efficacy and minimize toxicity.

Genotype and Phenotype Correlation of the TPMT∗8 Allele in Thiopurine Metabolism

Thiopurine 6-mercaptopurine (6-MP) is metabolized by thiopurine methyl transferase (TPMT). TPMT genetic variation results in some individuals having reduced or absent TPMT enzyme activity. If these individuals take a full thiopurine dose, life-threatening adverse events can occur. Testing identifies patients with reduced or absent TPMT activity and is recommended prior to initiation of therapy. The TPMT*8 allele, defined by c.644G>A (p.Arg215His), is common among individuals of African ancestry (∼2.3% minor allele frequency), but is not included in genotyping recommendations due to its uncertain function. Here, a clinical TPMT enzyme activity assay was used to assess TPMT activity in red blood cells from 982 patients, including those with *1/*8 (n=22), *3A/*8 (n=1), and *3C/*8 (n=1) TPMT diplotypes. The average 6-MMP production (primary TPMT product measured clinically) was 3.08 ± 0.16 nmol/mL/hr for *1/*8 individuals, compared to 3.77 ± 0.03 nmol/mL/hr for normal metabolizers (p=0.0001) and 2.39 ± 0.06 nmol 6-MMP/mL/hr for intermediate metabolizers (p<0.0001). Individuals with a TPMT*1/*8 diplotype demonstrated reduced 6-MP metabolism between that of normal metabolizers and intermediate metabolizers, suggesting that TPMT*8 is a reduced function allele.

Autoimmune Hepatitis Management: Recent Advances and Future Prospects

Autoimmune hepatitis (AIH) is a varied inflammatory chronic liver disease. AIH’s prevalence varies and has increased recently. Diagnosis involves the discovery of histologic features following liver biopsy and serologic testing. Clinical features vary, and up to 40% of patients may be asymptomatic. Evaluating thiopurine methyltransferase (TMPM) activity before treatment is crucial for an optimal response. The primary treatment goal is biochemical remission, normalized serum IgG, and liver enzymes. Induction therapy typically involves azathioprine and corticosteroids. Close monitoring of liver function tests and serum immunoglobulin levels is essential. Medications can be tapered after achieving biochemical remission. Liver transplantation may be required for refractory disease or cirrhosis. Further therapeutic approaches are needed, particularly for non-responders to first-line treatments.

P798 Study of the concordance between the enzymatic activity of Thiopurine S-methyltransferase and polymorphisms in the TPMT gene in patients with Inflammatory Bowel Disease

Abstract Background Thiopurine therapy is associated with an increased risk of serious adverse events in patients with Inflammatory Bowel Disease (IBD). Thiopurine S-methyltransferase (TPMT) is the enzyme responsible for metabolism, and its determination helps identify patients at risk of toxicity. This study aims to explore the level of correspondence between the TPMT genotype and enzymatic activity (phenotype) with the objective of preventing adverse events prior to the commencement of thiopurine therapy. Methods Consecutive patients with IBD, Crohn’s Disease (CD) or Ulcerative Colitis (UC), were included. Genotype was conducted for the most prevalent TPMT variants (TPMT*2, TPMT*3B, TPMT*3C), TPMT enzymatic activity assessment, and quantification of 6-thioguanine nucleotide (6-TGN) levels. Adverse effects were documented, along with the administration of biologics, mesalazine, ACE inhibitors or allopurinol. The primary objective was to evaluate the concordance between TPMT genotype and phenotype. Secondary objectives included determining the prevalence of genotype and phenotype within our patient cohort, 6-TGN serum levels, the prevalence of adverse events and identifying potential pharmacological inducers of the phenotype. Results A total of 218 patients were included (131 with CD and 81 with UC). Thirteen patients did not initiate thiopurines, and 34.63% (71/205) had discontinued treatment. The most observed adverse events were myelotoxicity (15.12%), gastrointestinal toxicity (12.20%), and hepatic toxicity (5.37%). TPMT activity exhibited a trimodal distribution, with 87.61% (191/218) having normal activity, 11.47% having intermediate activity, and 1% having low activity. Genotypically, 90.83% (198/218) had a wild-type genotype, 8.72% (18/218) had a heterozygous genotype, and 0.5% (1/218) had a homozygous genotype. The concordance index between phenotype and genotype was calculated at 0.57. Significantly, myelotoxicity was associated with the presence of genotypic variants (p=0.004). 6-TGN levels did not correlate with TPMT activity and concurrent medications did not affect TPMT activity . Conclusion The proactive assessment of TPMT (phenotype or genotype) before initiating thiopurine therapy effectively mitigates the occurrence of myelotoxicity in IBD patients. Importantly, the level of concordance between TPMT activity and genotype is moderate, with genotyping serving as the more reliable approach for preselecting patients susceptible to myelotoxic reactions.

Determination of Thiopurine S-Methyltransferase (TPMT) Activity in Human Erythrocytes by Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS).

Thiopurine methyltransferase (TPMT) is a cytosolic enzyme involved in the metabolism of thiopurine medications that are used in the treatment of multiple malignant and nonmalignant immunologic conditions. Polymorphisms in the TPMT gene associated with low enzyme activity can produce pronounced pharmacologic effects during therapy. The determination of TPMT erythrocyte activity is a valuable adjunct test to genotyping for the assignment of TPMT phenotype, especially in the presence of indeterminate genotypes. We present a method for the determination TPMT activity in human erythrocytes whereby we utilize LC-MS/MS to measure the amount of 6-methylmercaptopurine formed in red blood cell (RBC) lysates using 6-mercaptopurine as substrate and S-adenosylmethionine (SAM) as methyl donor. This method has been successfully implemented and proven to be reliable for use in human specimens.

SERS spectroscopy as a tool for the study of thiopurine drug pharmacokinetics in a model of human B leukemia cells

Thiopurine drugs are immunomodulatory antimetabolites relevant for pediatric patients characterized by dose-dependent adverse effects such as myelosuppression and hepatotoxicity, often related to inter-individual differences, involving the activity of important enzymes at the basis of their biotransformation, such as thiopurine S-methyltransferase (TPMT).Surface Enhanced Raman Scattering (SERS) spectroscopy is emerging as a bioanalytical tool and represents a valid alternative in terms of affordable costs, shorter analysis time and easier sample preparation in comparison to the most employed methods for pharmacokinetic analysis of drugs.The aim of this study is to investigate mercaptopurine and thioguanine pharmacokinetics by SERS in cell lysates of a B-lymphoblastoid cell line (NALM-6), that did (TPMT*1) or did not (MOCK) overexpress the wild-type form of TPMT as an in vitro cellular lymphocyte model to discriminate between cells with different levels of TPMT activity on the base of the amount of thioguanosine nucleotides (TGN) metabolites formed.SERS analysis of the cell lysates was carried out using SERS substrates constituted by Ag nanoparticles deposited on paper and parallel samples were used for quantification of thiopurine nucleotides with liquid chromatography-tandem mass spectrometry (LC-MS/MS).A direct SERS detection method has been set up that could be a tool to study thiopurine drug pharmacokinetics in in vitro cellular models to qualitatively discriminate between cells that do and do not overexpress the TPMT enzyme, as an alternative to other more laborious techniques.Results underlined decreased levels of TGN and increased levels of methylated metabolites when TPMT was overexpressed, both after mercaptopurine and thioguanine treatments.A strong positive correlation (Spearman's rank correlation coefficient rho = 0.96) exists between absolute quantification of TGMP (pmol/1 x 106 cells), obtained by LC-MS/MS, and SERS signal (intensity of TGN at 915 cm−1).In future studies, we aim to apply this method to investigate TPMT activity in pediatric patients’ leukocytes.

The Role of Pharmacogenetics in the Therapeutic Response to Thiopurines in the Treatment of Inflammatory Bowel Disease: A Systematic Review.

This study focuses on the use of thiopurines for treating inflammatory bowel diseases (IBD). These drugs undergo enzymatic changes within the body, resulting in active and inactive metabolites that influence their therapeutic effects. The research examines the role of genetic polymorphisms in the enzyme thiopurine S-methyltransferase (TPMT) in predicting the therapeutic response and adverse effects of thiopurine treatment. The TPMT genotype variations impact the individual responses to thiopurines. Patients with reduced TPMT activity are more susceptible to adverse reactions (AEs), such leukopenia, hepatotoxicity, pancreatitis, and nausea, which are common adverse effects of thiopurine therapy. The therapeutic monitoring of the metabolites 6-thioguanine nucleotides (6-TGN) and 6-methyl mercaptopurine (6-MMP) is proposed to optimize treatment and minimize AEs. Patients with higher 6-TGN levels tend to have better clinical responses, while elevated 6-MMP levels are linked to hepatotoxicity. Genotyping for TPMT before or during treatment initiation is suggested to tailor dosing strategies and enhance treatment efficacy while reducing the risk of myelosuppression. In conclusion, this study highlights the importance of considering genetic variations and metabolite levels in optimizing thiopurine therapy for IBD patients, focusing on balance therapeutic efficacy with the prevention of adverse effects and contributing to personalized treatment and better patient outcomes.

Transcriptome analysis reveals involvement of thiopurine S-methyltransferase in oxidation-reduction processes

Thiopurine S-methyltransferase (TPMT) is an important enzyme involved in the deactivation of thiopurines and represents a major determinant of thiopurine-related toxicities. Despite its well-known importance in thiopurine metabolism, the understanding of its endogenous role is lacking. In the present study, we aimed to gain insight into the molecular processes involving TPMT by applying a data fusion approach to analyze whole-genome expression data. The RNA profiling was done on whole blood samples from 1017 adult male and female donors to the Estonian biobank using Illumina HTv3 arrays. Our results suggest that TPMT is closely related to genes involved in oxidoreductive processes. The in vitro experiments on different cell models confirmed that TPMT influences redox capacity of the cell by altering S-adenosylmethionine (SAM) consumption and consequently glutathione (GSH) synthesis. Furthermore, by comparing gene networks of subgroups of individuals, we identified genes, which could have a role in regulating TPMT activity. The biological relevance of identified genes and pathways will have to be further evaluated in molecular studies.

B-225 Assessment of the Genotype Frequency of Thiopurine Methyltransferase (TPMT) Deficiency in a Large Cohort of Patients With Immune Mediated Inflammatory Disease and Cancer

Abstract Background Thiopurine methyltransferase (TPMT) alleles (*1/*2/*3A/*3B/*3C) are routinely genotyped to determine the metabolizer status of patients that plan to undergo thiopurine therapies (6-Mercaptopurine and Azathioprine). Screening of these alleles allows for personalized patient dosing and reduces the risk of severe or even fatal myelosuppression. The objective of this study was to determine the genotype frequency of TPMT deficiency in a large clinical cohort of patients with immune mediated inflammatory diseases and cancer. Methods All genotyping was performed in a reference clinical laboratory. Patient specimens were tested using genomic DNA isolated from whole blood. Clinical patient diagnoses were physician provided (international classification of disease, ICD-10). The genomic DNA was tested for the presence of three single nucleotide polymorphisms (SNPs) in the TPMT gene coding region and known to associate with reduced TPMT activity (rs1800462-Exon 5, rs1800460-Exon 7 and rs1142345-Exon 10). These polymorphisms determine the presence of *2/*3A/*3B/*3C alleles. Testing occurred from 10/26/2000 to 9/9/2022. Three different testing technologies were used during the 22 years of testing (PCR-RFLP from 2000 to 2003, Taqman™ chemistries from 2004 to 2015, and Luminex™ xMAP™ bead-based since 2016). Results A total of 219 129 patients were tested (mean age: 38 yrs, 56% female). As presented in the Table the genotype frequency for the wild type *1/*1 was 90.8% (95%CI: 90.7–90.9%), it was 9.0% (95%CI: 8.8–9.1%) for the heterozygous and 0.22% (95%CI: 0.020–0.024%) for homozygous variant, with similar frequency across disease states. The TPMT *1/*3B genotype frequency was very rare (&amp;lt;0.1%, n = 5) and the *3B/*3C homozygous variant (which cannot be distinguished from the *1/*3A) was calculated to have a frequency of 1:7 706 230 (95%CI: 1:7 043 228–1:8 369 232) and lower than initial estimates. Conclusion We estimated the frequency of TPMT genotypes in the largest cohort reported to date. The occurrence of the *3B/*3C genotype may be rarer than initially estimated.

Genome-Wide Association Study for the Genetic Determinants of Thiopurine Methyltransferase Protein Expression in Human Livers and Racial Differences.

Polymorphisms in the Thiopurine S-Methyltransferase (TPMT) gene are associated with decreased TPMT activity, but little is known about their impact on TPMT protein expression in the liver. This project is to conduct a genome-wide association study (GWAS) to identify single nucleotide polymorphisms (SNPs) associated with altered TPMT protein expression in human livers and to determine if demographics affect hepatic TPMT protein expression. Human liver samples (n = 287) were genotyped using a whole genome genotyping panel and quantified for TPMT protein expression using a Data-Independent Acquisition proteomics approach. Thirty-one SNPs were found to be associated with differential expression of TPMT protein in the human livers. Subsequent analysis, conditioning on rs1142345, a SNP associated with the TPMT*3A and TPMT*3C alleles, showed no additional independent signals. Mean TPMT expression is significantly higher in wildtype donors compared to those carrying the known TPMT alleles, including TPMT*3A, TPMT*3C, and TPMT*24 (0.107 ± 0.028 vs. 0.052 ± 0.014pmol/mg total protein, P = 2.2 × 10-16). After removing samples carrying the known TPMT variants, European ancestry donors exhibited significantly higher expression than African ancestry donors (0.109 ± 0.026 vs. 0.090 ± 0.041pmol/mg total protein, P = 0.020). The GWAS identified 31 SNPs associated with TPMT protein expression in human livers. Hepatic TPMT protein expression was significantly lower in subjects carrying the TPMT*3A, TPMT*3C, and TPMT*24 alleles compared to non-carriers. European ancestry was associated with significantly higher hepatic TPMT protein expression than African ancestry, independent of known TPMT variants.

Impact of Duodenal Pathology on Oral Drug Bioavailability and Disease Outcomes in Pediatric Crohn’s Disease

Crohn's disease with upper gastrointestinal tract involvement occurs more often in children than adults and has the potential to interfere with oral drug absorption. We aimed to compare disease outcomes in children receiving oral azathioprine for the treatment of Crohn's disease with (DP) and without (NDP) duodenal pathology at diagnosis. Duodenal villous length, body mass index (BMI), and laboratory studies were compared in DP vs. NDP during the first year post-diagnosis, using parametric/nonparametric tests and regression analysis (SAS v9.4); the data are reported as the median (interquartile range) or the mean ± standard deviation. Thiopurine metabolite concentration (pmol/8 × 108 erythrocytes) 230-400 was considered therapeutic for 6-thioguanine nucleotides (6-TGN), and >5700 was considered hepatotoxic for 6-methylmercaptopurine (6-MMPN). Twenty-six of the fifty-eight children enrolled (29 DP, 29 NDP) started azathioprine for standard medical care, including nine DP and ten NDP who had normal thiopurine methyltransferase activity. Duodenal villous length was significantly shorter in DP vs. NDP (342 ± 153 vs. 460 ± 85 μm; p < 0.001) at diagnosis; age, sex, hemoglobin, and BMI were comparable between groups. A trend toward lower 6-TGN was observed in the DP vs. NDP subset receiving azathioprine (164 (117, 271) vs. 272 (187, 331); p = 0.15). Compared to NDP, DP received significantly higher azathioprine doses (2.5 (2.3, 2.6) vs. 2.2 (2.0, 2.2) mg/kg/day; p = 0.01) and had an increased relative risk of sub-therapeutic 6-TGN. At 9 months post-diagnosis, children with DP had significantly lower hemoglobin (12.5 (11.7, 12.6) vs. 13.1 (12.7, 13.3) g/dL; p = 0.01) and BMI z-scores (-0.29 (-0.93, -0.11) vs. 0.88 (0.53, 0.99); p = 0.02) than children with NDP. For children with Crohn's disease, duodenal pathology, marked by villous blunting, increased the risk of sub-therapeutic 6-TGN levels, despite higher azathioprine dosing during the first year post-diagnosis. Lower hemoglobin and BMI z-scores at 9 months post-diagnosis suggest the impaired absorption/bioavailability of nutrients, as well as oral drugs, in children with duodenal disease.

Improving outpatient care in adult inflammatory bowel disease: effect of implementation of a reminder checklist in the electronic health records (IBD-ERS)—a pilot study

Studies have shown that patients with inflammatory bowel disease (IBD) do not receive age appropriate preventive care services at the same rate as the general population. Providers extract information on...

PACSIN2 as a modulator of autophagy and mercaptopurine cytotoxicity: mechanisms in lymphoid and intestinal cells.

PACSIN2 variants are associated with gastrointestinal effects of thiopurines and thiopurine methyltransferase activity through an uncharacterized mechanism that is postulated to involve autophagy. This study aims to clarify the role of PACSIN2 in autophagy and in thiopurine cytotoxicity in leukemic and intestinal models. Higher autophagy and lower PACSIN2 levels were observed in inflamed compared with non-inflamed colon biopsies of inflammatory bowel disease pediatric patients at diagnosis. PACSIN2 was identified as an inhibitor of autophagy, putatively through inhibition of autophagosome formation by a protein-protein interaction with LC3-II, mediated by a LIR motif. Moreover, PACSIN2 resulted a modulator of mercaptopurine-induced cytotoxicity in intestinal cells, suggesting that PACSIN2-regulated autophagy levels might influence thiopurine sensitivity. However, PACSIN2 modulates cellular thiopurine methyltransferase activity via mechanisms distinct from its modulation of autophagy.

Azathioprine-induced severe pancytopenia: A serious complication in a patient with normal TPMT activity

Azathioprine is an immunomodulator commonly used in renal transplant recipients and to treat lupus erythematous, and inflammatory bowel disease, and as second-line therapy in cases of rheumatoid arthritis. Here, we present a case of non-segmental vitiligo treated with low-dose azathioprine developing life-threatening pancytopenia with febrile neutropenia and trephine biopsy-proven drug-induced myelosuppression. The patient needed broad-spectrum antibiotics and granulocyte colony-stimulating factor (G-CSF) support with intermittent transfusion of blood products to completely recover from myelosuppression. It took almost a month for the patient to completely recover from the cytotoxicity caused by azathioprine. Interestingly, the patient had normal thiopurine methyl transferase (TPMT) activity and wild-type TPMT allele. We tried to outline how these types of patients can be managed and to emphasize the need for continuous monitoring of blood counts in patients receiving azathioprine to prevent life-threatening cytopenia even with normal TPMT activity and wild-type TPMT allele.

Azathioprine‐induced pancytopenia: A case report

AbstractAzathioprine (AZA) is commonly used as immunosuppressive therapy for autoimmune diseases, including systemic lupus erythematosus (SLE). Myelosuppression is a common side effect of AZA. Here we report a case of severe myelosuppression following AZA therapy in a 15‐year‐old girl despite a normal thiopurine methyltransferase (TPMT) level. She had been receiving AZA for SLE and presented with neutropenic fever and pancytopenia. AZA was stopped. After stopping AZA, her blood counts steadily improved. When TPMT genotyping results were normal, AZA was reintroduced. Pancytopenia reappeared after starting AZA, despite normal TPMT genotype. AZA was replaced with mycophenolate mofetil which consequently resulted in improvement of blood counts. It is essential to understand the temporal relationship between AZA use and pancytopenia onset in patients with normal TPMT activity. This case illustrates that regular monitoring of blood cell counts should be routine practice after starting AZA regardless of TPMT activity.

Passive smoking and thiopurine methyl transferase genotyping in 6-mercaptopurine-induced myelosuppression in Egyptian children with acute lymphoblastic leukemia

6-mercaptopurine (6-MP) is a crucial component drug used to treat childhood acute lymphoblastic leukemia (ALL) in the maintenance phase. Thiopurine S-methyltransferase (TPMT) is an enzyme that metabolizes thiopurine drugs like 6-MP. In patients taking thiopurine medications, lack of TPMT activity is linked to an increased risk of myelosuppression. Patients with TPMT polymorphisms are more likely to develop mercaptopurine-induced myelosuppression. The goal of this study was to see how passive smoking and TPMT genetic variations affected 6-MP-induced myelosuppression in Egyptian ALL children. This study included 100 children: 50 with acute lymphoblastic leukemia in the maintenance phase of treatment who had a history of passive smoking and 50 age-matched healthy controls. 6-MP was given to patients in the maintenance phase, and myelosuppression was monitored at the end of this phase by comparing WBC counts to those obtained at the start of treatment. After six months of 6-MP administration, there was no significant association between cotinine levels and WBC count (as evidence of myelosuppression), although there was a significant correlation between TPMT genotypes and WBC count, with 75% of hetero genotype patients suffering from severe declines in WBC count and 91% of wild genotype people undergoing mild to moderate decreases in WBC count.

Genome‐Wide Association Study for the Genetic Determinants of Thiopurine S‐Methyltransferase Protein Expression in the Liver

HypothesisSinge nucleotide polymorphisms will be associated with differential expression of Thiopurine S‐Methyltransferase (TPMT) in the liver.MethodsNormal human liver samples (n=288) were acquired from University of Minnesota Liver Tissue Cell Distribution System, the Cooperative Human Tissue Network, and XenoTech LCC (Lenexa, KS, USA). Absolute quantification of TPMT in liver microsomes was calculated using a DIA total protein approach (DIA‐TPA). Human liver samples were genotyped using the Illumina Multi‐Ethnic Global Assay (Illumina, Miami, USA).ResultsAfter accounting for population stratification, genome‐wide association study (GWAS) analysis was conducted on 243 human liver samples. There were 30 genetic variants, all located on chromosome 6, that passed our genome‐wide threshold (P &lt; 5.0 x 10‐8) after Bonferroni correction. Further GWAS analysis conditioning on rs1142345 (TPMT*3C/TPMT*3A), the strongest signal within the dataset and a known nonfunctional TPMT allele, showed no other independent signals. The presumed homozygous wild‐type TPMT subjects had a 1.97‐fold higher expression of TPMT than the TPMT*3A heterozygotes (0.1056 pmol/mg ± 0.0289 pmol/mg vs. 0.0536 pmol/mg ± 0.0143 pmol/mg, p‐value: 8.4e‐14).When comparing TPMT expression by ancestry, European ancestry donors (n= 214) had significantly higher expression than African ancestry donors (n= 34) when removing TPMT*3A carriers (0.1085 pmol/mg ± 0.0260 pmol/mg vs. 0.0860 pmol/mg ± 0.0416 pmol/mg, p‐value: 0.004.ConclusionFor the first time, we quantified absolute TPMT protein expression in the liver using a liquid chromatography tandem mass spectrometry based DIA‐TPA proteomics approach and conducted a GWAS to identify genetic variants affecting hepatic TPMT protein expression. The only independent genetic signal from the GWAS was from the TPMT*3A haplotype, which is comprised of two nonsynonymous SNPs rs1800460 and rs1142345. Previous in vitrostudies investigating the effect of common polymorphisms on TPMT expression in COS‐1 cells demonstrated that TPMT*3A is almost a complete loss of detectable TPMT due to its rapid degradation rate.1 This is in line with our expression data, where heterozygous carriers of TPMT*3A had about half the amount of TPMT as wild‐type subjects.We also discovered that donors with African ancestry had significantly less TPMT expression than donors with European ancestry after removing samples that had known TPMT polymorphisms (TPMT*3A/*3B/*3C). A previous study reported patients of Afro‐Caribbean ancestry had significantly lower TPMT activity than those of European or South Asian descent.2 Future studies need to be conducted to determine if the difference in TPMT expression by ancestry is due to genetic polymorphisms or other factors.

LC-MS/MS Method for Measurement of Thiopurine Nucleotides (TN) in Erythrocytes and Association of TN Concentrations With TPMT Enzyme Activity.

Monitoring concentrations of thiopurine metabolites is used clinically to prevent adverse effects in patients on thiopurine drug therapy. We developed a LC–MS/MS method for the quantification of 6-thioguanine (6-TG) and 6-methylmercaptopurine (6-MMP) in red blood cells (RBCs). This method utilizes an automated cell washer for RBC separation from whole blood samples and washing of the separated RBCs. The lower limit of quantification of the method was 0.2 μmol/L for 6-TG (∼50 pmol/8 × 108 RBC) and 4 μmol/L for 6-MMP (∼1,000 pmol/8 × 108 RBC). The total imprecision of the assay was <3.0%. The upper limit of linearity for 6-TG and 6-MMP was 7.5 μmol/L and 150 μmol/L, respectively. The stability of the thiopurine metabolites under pre- and post-analytically relevant conditions was also evaluated. A good agreement was observed between this method and validated LC–MS/MS methods from three laboratories, except for ∼40% low bias for 6-MMP observed in one of the methods. The assessment of the association between 6-TG and 6-MMP concentrations with thiopurine S-methyltransferase (TPMT) phenotype and genotype demonstrated a statistically significant difference in the thiopurine metabolite concentrations between the TPMT groups with normal and intermediate activity of 6-MMP (p < 0.0001), while the difference in 6-TG concentrations was statistically not significant (p = 0.096). Among the samples with normal TPMT activity, higher concentrations of 6-MMP (p = 0.015) were observed in pediatric samples than in the samples of adults. No statistically significant differences were observed in the distributions of 6-TG and 6-MMP concentrations among the evaluated genotypes.

Pharmacogenetics-based personalized treatment in patients with inflammatory bowel disease: A review

The development of treatment options has revolutionized the prognosis of inflammatory bowel disease (IBD). However, a particular group of patients still experience therapeutic failure or drug side effects. Although the high inter-patient variability in therapy is associated with clinical factors, including age, disease behavior, and disease duration, they attribute only a small proportion of inter-individual variability. Thus, pharmacogenetics evaluating associations between specific genetic variations and drug responses or side effects have focused on optimizing therapeutic efficacy and minimizing toxicity in IBD treatment. Thiopurine S-methyltransferase (TPMT) and nudix hydrolase 15 (NUDT15) are well-established predictive markers of thiopurine-induced myelosuppression. Low TPMT activity is related to increased 6-thioguanine nucleotide levels, subsequently leading to myelotoxicity. NUDT15 variants are strongly associated with thiopurine-induced early leukopenia in Asians, with a lower incidence of TPMT-deficient allele. The Korean Association for the Study of Intestinal Diseases guidelines recommend pretreatment determination of NUDT15 genotypes, especially in East Asians, and NUDT15 R139C measurement has been approved for clinical use since 2019. Several studies have attempted to identify powerful genetic markers for personalized medicine. In this article, we review the identified pharmacogenetics of currently available drugs, focusing on 5-aminosalicylic acid, glucocorticosteroids, thiopurines, and anti-tumor necrosis factor-alpha agents.