Prevalence of TPMT polymorphism in Indian patients requiring immunomodulator therapy and its clinical significance

Detailed resume of S-methyltransferases: Categories, structures, biological functions and research advancements in related pathophysiology and pharmacotherapy

Methylation is a vital chemical reaction in the metabolism of many drugs, neurotransmitters, hormones, and exogenous compounds. Among them, S-methylation plays a significant role in the biotransformation of sulfur-containing compounds, particularly chemicals with sulfhydryl groups. Currently, only three S-methyltransferases have been reported: thiopurine methyltransferase (TPMT), thiol methyltransferase (TMT), and thioether methyltransferase (TEMT). These enzymes are involved in various biological processes such as gene regulation, signal transduction, protein repair, tumor progression, and biosynthesis and degradation reactions in animals, plants, and microorganisms. Furthermore, they play pivotal roles in the metabolic pathways of essential drugs and contribute to the advancement of diseases such as tumors. This paper reviews the research progress on relevant structural features, metabolic mechanisms, inhibitor development, and influencing factors (gene polymorphism, S-adenosylmethionine level, race, sex, age, and disease) of S-methyltransferases. We hope that a better comprehension of S-methyltransferases will help to provide a reference for the development of novel strategies for related disorders and improve long-term efficacy.

Therapeutic drug monitoring in inflammatory bowel disease: A practical approach

The global burden of inflammatory bowel diseases (IBD) is estimated at 4.9 million and the global prevalence exceeds 0.3%. Multiple newer therapeutic agents have broadened the options for the therapy of IBD in the last three decades. Thiopurines, however, have retained their place as maintenance therapy in IBD, especially in resource-constrained setting. But thiopurines have narrow therapeutic range, often needing discontinuation due to side effects or lack of efficacy. Biologic agents revolutionized the treatment of IBD, but the efficacy is lost in 50% of patient after one year. These outcomes are often due to inadequate drug concentrations that may lead to the development of antibodies as well as pharmacodynamic failure. Therapeutic drug monitoring (TDM) was proposed to reduce loss of response and to optimize the therapy in patients on thiopurine and biologic therapy. TDM is based on exposure-response relationship, suggesting a positive correlation between elevated serum anti-TNF concentrations and favorable therapeutic outcomes. TDM has multiple facets. This article discusses the benefits, evidence and limitations of TDM. The practical use of TDM in clinical practice is highlighted. Newer developments in the field and their relevance in practice are discussed.

A bioinformatics approach to the identification of novel deleterious mutations of human TPMT through validated screening and molecular dynamics

Polymorphisms of Thiopurine S-methyltransferase (TPMT) are known to be associated with leukemia, inflammatory bowel diseases, and more. The objective of the present study was to identify novel deleterious missense SNPs of TPMT through a comprehensive in silico protocol. The initial SNP screening protocol used to identify deleterious SNPs from the pool of all TPMT SNPs in the dbSNP database yielded an accuracy of 83.33% in identifying extremely dangerous variants. Five novel deleterious missense SNPs (W33G, W78R, V89E, W150G, and L182P) of TPMT were identified through the aforementioned screening protocol. These 5 SNPs were then subjected to conservation analysis, interaction analysis, oncogenic and phenotypic analysis, structural analysis, PTM analysis, and molecular dynamics simulations (MDS) analysis to further assess and analyze their deleterious nature. Oncogenic analysis revealed that all five SNPs are oncogenic. MDS analysis revealed that all SNPs are deleterious due to the alterations they cause in the binding energy of the wild-type protein. Plasticity-induced instability caused by most of the mutations as indicated by the MDS results has been hypothesized to be the reason for this alteration. While in vivo or in vitro protocols are more conclusive, they are often more challenging and expensive. Hence, future research endeavors targeted at TPMT polymorphisms and/or their consequences in relevant disease progressions or treatments, through in vitro or in vivo means can give a higher priority to these SNPs rather than considering the massive pool of all SNPs of TPMT.

Prevalence of polymorphisms in thiopurine metabolism and association with adverse outcomes: a South Asian region-specific systematic review and meta-analysis

Background: Prevalence and impact of thiopurine S-methyltransferase (TPMT) and Nudix hydrolase (NUDT15) minor allele frequencies in South Asian population is unclear.Methods: We searched PubMed and Embase with keywords-TPMT and NUDT15 combined with South Asian countries. We included studies reporting frequency of TPMT and NUDT15 polymorphisms. We estimated the pooled prevalence of TPMT and NUDT15 polymorphisms and their impact on pooled odds ratio of adverse events with thiopurines.Results: We included 26 studies in our analysis. The pooled prevalence of NUDT15 and TPMT polymorphisms was 16.5% (95% CI: 13.09-20.58) and 4.57% (95% CI: 3.66-5.68), respectively. In patients with adverse effects, the pooled prevalence of NUDT15 and TPMT polymorphism was 49.51% (95% C.I. 21.69-77.64) and 9.47% (95% C.I. 5.39-16.11), respectively. The odds ratio (OR) of adverse events with presence of TPMT polymorphisms was 3.65 (95% C.I., 1.43-9.28). The pooled OR for adverse events in presence of NUDT15 polymorphism was 12.63 (95% C.I., 3.68-43.26).Conclusion: NUDT15 were reported more frequently than the TPMT polymorphisms in South Asian population and were more frequently associated with adverse events. These findings may have implications for preemptive testing amongst South Asian population and immigrants prior to starting thiopurines.

Thiopurine-induced Myelosuppression with Severe Sepsis in a Patient with Crohn's Disease: A Case Report

Thiopurines by their glucocorticoid-sparing property help in maintaining remission for patients with inflammatory bowel disease (IBD), when glucocorticoids are reduced and withdrawn. However, due to bone marrow suppression, it cannot be used in various conditions where it is indicated. A 17-year-old patient presented with pancytopenia with neutropenic sepsis and alopecia after 3 weeks of starting azathioprine for her underlying Crohn's disease. Thiopurine S-methyltransferase (TPMT;*2, *3A, *3C) analysis resulted in a wild-type genotype, whereas homozygous Nudix hydrolase 15 (NUDT 15 C415T) variant was positive. Azathioprine was stopped immediately, and she was started on broad-spectrum antibiotics that led to some clinical improvements initially, but later on, the patient developed intestinal obstruction along with postoperative complications leading to death. In this report, we highlight a case of serious hematological toxicity associated with azathioprine use in a patient with Crohn's disease with homozygous NUDT 15 variant, thus favoring the implementation of a pharmacogenomic approach before starting azathioprine, particularly in the Asian population.

How to cite this article

Debnath P, Nair S, Jain S, Udgirkar S, Contractor Q, Rathi P. Thiopurine-induced Myelosuppression with Severe Sepsis in a Patient with Crohn's Disease: A Case Report. Indian J Crit Care Med 2021;25(2):228-230.

Prior presentation of case report at professional meeting

The case was presented in abstract form at the American College of Gastroenterology Annual Scientific Meeting, held at San Antonio, TX, USA 2019.

Informed consent for publication of case details

Obtained from patient's relatives.

Optimising management strategies of inflammatory bowel disease in resource-limited settings in Asia

Over the 21st century, inflammatory bowel disease (IBD) has become a global disease with increasing prevalence reported in the Asian subcontinent as a result of rapid urbanisation, industrialisation, and westernisation of lifestyles. Although rates of surgery have shown a temporal decrease globally because of the increasing availability of new drugs and early initiation of effective therapy, health-care costs associated with IBD have continued to rise. The increase in IBD prevalence in resource-limited countries poses a substantial health-care burden. Drugs are not universally accessible or available. An optimised and practical management strategy of IBD in resource-limited countries in Asia is urgently needed. Special consideration should be made to balance the risk of undertreatment (and suboptimal disease control) because of financial constraints with the risk of overtreatment, which is associated with side-effects and costly therapeutics. In this Series paper, we summarise the current approach in optimising conventional therapies, use of other therapies, and de-escalation of biologics in low-resource settings in Asia. The long-term objective is to strive for more effective and affordable therapies with sustained durability of benefit.

Prevalence of TPMT, ITPA and NUDT 15 genetic polymorphisms and their relation to 6MP toxicity in north Indian children with acute lymphoblastic leukemia

PURPOSE

Toxicity of 6-Mercaptopurine (6MP) is related to single nucleotide polymorphism (SNP) in genes coding for metabolizing enzymes, with TPMT analysis being recommended prior to maintenance therapy. However, ITPA and NUDT15 polymorphisms appear more important in the Asian population.

METHOD

In this study 63 consecutive patients with ALL, entering maintenance phase of therapy, were evaluated for TPMT, ITPA and NUDT15 polymorphisms by PCR RFLP and confirmed by sequencing. Hematological and hepatic toxicities were monitored for 36 weeks. The groups with and without any of the three studied polymorphisms (Risk SNP + and Risk SNP-) were compared.

RESULTS

Eighteen (28.6%) patients had major polymorphisms, 17 being heterozygous. ITPA(198CA): 11(17.5%); NUDT (415CT): 6(9.5%) and TPMT*3C: in 2(3.1%). Mean cumulative dose of 6MP was lower: 10927 mg/m² in group with one of the polymorphisms compared to 12533 mg/m² in the group without a polymorphism (p = 0.009). The group with Risk SNP + tolerated lesser weeks of full-dose 6MP chemotherapy (20.81 vs 30.40 weeks; p = 0.001). Risk of neutropenia > 3 weeks was pronounced in Risk SNP + group. The individual TPMT, ITPA and NUDT15 polymorphism subgroups had similar cumulative 6MP dose and chemotherapy interruptions. There was no difference in the average cumulative dose of methotrexate in the two groups. No significant hepatotoxicity was noted.

CONCLUSION

Polymorphisms in ITPA and NUDT15 have a greater prevalence in the north Indian population. Patients with these SNPs tolerate lower doses of 6MP.

Thiopurine metabolite level and toxicity in Indians with inflammatory bowel disease

Background and Aim

A lower dose requirement and higher toxicity of thiopurine is reported in Asian patients with inflammatory bowel disease (IBD) as compared with Caucasian patients. These reports are based on thiopurine methyltransferase measurement studies rather than metabolite estimation.We studied the utility of thiopurine metabolite estimation in Indian patients with IBD and compared dose and toxicity with Asian and Caucasian patients.

Methods

In this prospective study, 6-thioguanine nucleotide (6-TGN) and 6-methylmercaptopurine levels were determined by HPLC in 76 IBD patients treated with thiopurines. The levels were correlated with dose, disease activity, and toxicity. The dose-related metabolite levels and toxicity were compared with Caucasian and Asian patients reported in literature.

Results

Of the 76 patients (32 women, mean age: 35.9 [SD: 14.54] years, 36 Crohn's disease and 40 ulcerative colitis), 1 non-compliant patient had undetectable level of metabolites. Of the 75 patients, 21(28%) had therapeutic level of 6-TGN, 37(49%) had subtherapeutic level and 17(23%) had supratherapeutic level. The 6-methylmercaptopurine levels ranged up to 4971 pmol/8 × 10⁸ red blood cells. Six (8%) patients showed toxicity. Thiopurine dose was optimized in 20 (26.31%) patients. Dose-based metabolite levels were comparable to Asian and Caucasian patients. The toxicity (8%) observed in our patients was less than that reported (12-39%).

Conclusion

Half of the patients in this study had low and a quarter had high 6-TGN levels. One-fourth of the patients needed dose modification. The dose-based metabolite levels were comparable and the toxicity was less than that reported in Asian and Caucasian patients.

Pharmacogenetics of inflammatory bowel disease: a focus on Crohn's disease

Crohn's disease is an inflammatory bowel disease showing a high heterogeneity in phenotype and a strong genetic component. The treatment is complex, due to different severity of clinical parameters and to the fact that therapies only permit to control symptoms and to induce remission for short periods. Moreover, all categories of drugs present a great interindividual variability both in terms of efficacy and side effects appearance. For this reason, the identification of specific genomic biomarkers involved in drugs response will be of great clinical utility in order to foresee drug's efficacy and to prevent adverse reactions, permitting a more personalized therapeutic approach. In this review, we focus the attention on the pharmacogenetic studies regarding drugs commonly utilized in Crohn's disease treatment.

Nucleoside diphosphate-linked moiety X-type motif 15 C415T variant as a predictor for thiopurine-induced toxicity in Indian patients

BACKGROUND AND AIM

Interindividual variation seen in the thiopurine metabolism is attributed to the genetic variant in thiopurine methyltransferase (TPMT) gene leading to myelosuppression. In Asians, the thiopurine-induced toxicity is not completely explained by TPMT variants. Literature indicates that a newer genetic variant in nucleoside diphosphate-linked moiety X-type motif 15 (NUDT15) gene is associated with thiopurine intolerance. We aimed to determine the risk allele frequency of NUDT15 genetic variant and its association with thiopurine-induced toxicity in Indian patients.

METHODS

In this pilot study, 69 patients on thiopurine therapy were analyzed. The frequencies of thiopurine-induced leukopenia were recorded. NUDT15 (C415T) and TPMT (*2, *3A, *3B, and *3C) genotyping was performed using amplification refractory mutation system-polymerase chain reaction and restriction fragment length polymorphism technique. Results were validated by DNA sequencing.

RESULTS

The NUDT15 CC, CT, and TT genotypes were found to be 86.9%, 11.5%, and 1.5%, respectively, whereas TPMT genetic variants were absent. Of 60 patients without NUDT15 variant, none developed leukopenia, whereas of nine patients with NUDT15 variant, six developed leukopenia (P-value < 0.0001). The mean thiopurine dose of 1.01 and 0.73 mg/kg/day for patients with wild and mutant NUDT15 alleles, respectively, was statistically significant (P < 0.01). The sensitivity and specificity for NUDT15 variant were 100% and 95.2%, respectively.

CONCLUSIONS

The NUDT15 risk allele frequency was 7.2%. There are 6/69 (8.7%) patients who developed leukopenia and harbored NUDT15 variant, thus showing a strong association for thiopurine-induced toxicity. Hence, NUDT15 genotyping may be considered before thiopurine therapy in Indian patients.

TPMT and ITPA genetic variants in Lithuanian inflammatory bowel disease patients: Prevalence and azathioprine-related side effects

PURPOSE

Inter-individual thiopurine metabolism variability can influence treatment outcomes in inflammatory bowel disease (IBD) patients. Genetic polymorphisms in thiopurine methyltransferase (TPMT) and inosine triphosphate pyrophosphatase (ITPA) were linked with toxicity of azathioprine (AZA). The aim of the study was to investigate frequencies of TPMT and ITPA polymorphisms in Lithuanian IBD patients and analyze their association with AZA-related adverse events.

MATERIALS/METHODS

Polymorphisms in TPMT (TPMT*2,*3B,*3C,*3A) and ITPA (rs1127354, rs7270101) genes were determined using PCR-RFLP and TaqMan(®) genotyping assays. 551 consecutive Lithuanian IBD patients were genotyped. The use of AZA and its side effects were assessed retrospectively according to hospital medical records.

RESULTS

Frequencies of TPMT*3A, TPMT*3B and TPMT*3C alleles were 3.1%, 0.5% and 0.1%, respectively. TPMT*2 genetic variant was not detected in the study group. The distribution of minor alleles for ITPA rs1127354 and rs7270101 polymorphisms was 9.9% and 10.5%, respectively. AZA was prescribed in 82 patients and it provoked myelotoxicity in 11%, hepatotoxicity in 6.1%, dyspepsia in 6.1%, and pancreatitis in 3.6% of cases. Among patients who had AZA-related myelotoxicity, 11.1% were TPMT compound heterozygous, 44.4% had heterozygous genotype (P<0.01). Frequencies of ITPA minor alleles were similar among the patients with and without AZA-related side effects.

CONCLUSION

Frequencies of TPMT and ITPA variant alleles in Lithuanian IBD group were similar to those observed in the Northern-Eastern Europe Caucasian populations. Polymorphisms in TPMT might be associated with myelotoxicity and leukopenia in AZA treated patients, while ITPA variant alleles appear not to be linked with treatment-related side effects.