Molecular analysis of thiopurine S-methyltransferase alleles in Taiwan aborigines and Taiwanese

Taiwan guidelines for the diagnosis and management of pediatric atopic dermatitis: Consensus statement of the Taiwan Academy of Pediatric Allergy, Asthma and Immunology

Atopic dermatitis (also known as atopic eczema) is a chronic relapsing inflammatory skin disease commonly seen in children, with increasing prevalence over the past few decades in many countries including Taiwan. The management of pediatric atopic dermatitis can be challenging, particularly as treatment options are expanding with the emergence of novel systemic and topical anti-inflammatory medications in recent years. The Taiwan Academy of Pediatric Allergy, Asthma and Immunology (TAPAAI) has developed the Taiwan guidelines for the diagnosis and management of pediatric atopic dermatitis, which provides a concise overview of its epidemiology, clinical characteristics and diagnosis, mechanisms, treatments, and education. The contents of this guideline integrate the principles of recent national and international guidelines for the diagnosis and management of atopic dermatitis, latest research findings, and expert opinions of experienced pediatric allergy specialists in Taiwan. For practical purposes, this guideline presents simplified and easy-to-use diagnostic criteria and severity grading for pediatric atopic dermatitis. A stepwise treatment algorithm is also proposed to expedite rational, cost-effective, and evidence-based management strategy. This guideline, developed based on current best evidence and real-world experience of pediatric allergy experts in Taiwan, is intended to facilitate practical, up-to-date management of pediatric atopic dermatitis among physicians.

Population pharmacokinetics of azathioprine active metabolite in patients with inflammatory bowel disease and dosage regimens optimisation

Azathioprine is a first-line drug used to maintain the remission of inflammatory bowel disease (IBD). As a prodrug, azathioprine is metabolised to produce active 6-thioguanine nucleotides (6-TGN). There are large individual variations in the pharmacokinetics/pharmacodynamics of 6-TGN in patients with IBD. Here, we aimed to develop a model to quantitatively investigate factors that affect 6-TGN pharmacokinetics to formulate a dosage guideline for azathioprine. Data were collected prospectively from 100 adult patients with IBD who were receiving azathioprine. Patients were genotyped for two single-nucleotide polymorphisms (TPMT*3C c.719A > G and NUDT15 c.415C > T). Using high-performance liquid chromatography, we measured 156 steady-state trough concentrations of 6-TGN within the range 0.09 to 1.16 mg/L (ie 133-1733 pmol per 8 × 10⁸ RBC). The covariates analysed included sex, age, body-weight, laboratory tests and concomitant medications. A population pharmacokinetic model was established using "non-linear mixed-effects modelling" software and the "first-order conditional estimation method with interaction." Body-weight, TPMT*3C polymorphisms and co-therapy with mesalazine were found to be important factors influencing the clearance of 6-TGN. A dosage guideline for azathioprine was developed based on the PPK model that enables individualised azathioprine dosing in adult patients with different body-weights, TPMT*3C genotypes and co-administration with mesalazine.

Hair Trace Element Levels in Han and Indigenous Hualien Inhabitants in Taiwan

The objective of the present study was to assess the impact of ethnicity on hair trace element content in Han and aboriginal inhabitants of Hualien in Taiwan. Fifty Han (female/male = 35/15) and 50 aboriginal (female/male = 40/10) Hualien inhabitants aged 40-60 years were involved in the present study. Anthropometric data and dietary patterns were recorded. Hair mineral, essential, and toxic trace element levels were assessed using inductively coupled plasma mass spectrometry at NexION 300D (PerkinElmer Inc., USA) equipped with ESI SC-2 DX4 autosampler (Elemental Scientific Inc., USA). No group difference in gender, age, body weight, height, or physical activity was observed. Fish intake was more frequent in Han inhabitants, whereas aborigines consumed significantly more nuts. Indigenous people were characterized by higher hair Al (45%), Ca (threefold), Co (71%), Fe (twofold), I (74%), K (60%), Mg (2.5-fold), Na (62%), P (6%), Sn (78%), and V (46%) content. In turn, Han Hualien inhabitants had higher hair Be (twofold), Li, Se, Si levels as compared to indigenous counterparts. Multiple regression analysis demonstrated that ethnicity was significantly associated with hair Ca (β = 0.302), Mn (β = 0.284), P (β = 0.387), and Se (β = - 0.310) levels after adjustment for other confounders. At the same time, the overall models were significant for Ca, Mn, Se, and As. The obtained data may provide a background for monitoring and correction of trace element status in patients of different ethnic groups. However, further detailed studies are required to highlight the mechanisms underlying the observed associations.

Relationship between Azathioprine metabolites and therapeutic efficacy in Chinese patients with neuromyelitis optica spectrum disorders

BACKGROUND

Neuromyelitis optica spectrum disorders (NMOSD) are demyelinating autoimmune diseases in the central nervous system (CNS) that are characterized by a high relapse rate and the presence of anti-aquaporin 4 antibodies (AQP4-IgG) in the serum. Azathioprine (AZA) is a first-line immunomodulatory drug that is widely used for the treatment of patients with NMOSD. However, the efficacy and safety of AZA vary in different individuals.

METHOD

Thirty-two patients with NMOSD who regularly took AZA were enrolled in the study at Beijing Tiantan Hospital, Capital Medical University. The efficacy of AZA was evaluated using the expanded disability status scale (EDSS) and the annual relapse rate (ARR). The erythrocyte concentrations of AZA metabolites were detected using an LC-MS/MS method.

RESULTS

The erythrocyte concentrations of 6-thioguanine nucleotides (6-TGNs) and 6-methylmercaptopurine nucleotides (6-MMPNs) were 202.03 ± 63.35 pmol/8*10⁸ RBC and 1618.90 ± 1607.06 pmol/8*10⁸ RBC, respectively. After the patients had received AZA therapy for more than one year, the EDSS score decreased from 5.21 ± 0.24 to 2.57 ± 0.33 (p < 0.0001), and the ARR decreased from 1.41 ± 0.23 to 0.36 ± 0.09 (p < 0.0001). The 6-TGN and 6-MMPN levels were significantly different between the non-relapsed and relapsed groups (p < 0.0001, p = 0.006, respectively). A higher ARR was significantly correlated with higher erythrocyte concentrations of 6-TGNs (p < 0.0001) and 6-MMPNs (p = 0.004).

CONCLUSION

AZA can reduce the EDSS score and ARR in NMOSD patients. Additionally, the efficacy of AZA is significantly related to the erythrocyte concentrations of 6-TGNs and 6-MMPNs. Within the safe upper limits, a higher concentration of 6-TGNs is associated with better efficacy of AZA.

TRIAL REGISTRATION NUMBER

ISRCTN16551495 , retrospectively registered on May 22, 2017.

Mercaptopurine/Methotrexate maintenance therapy of childhood acute lymphoblastic leukemia: clinical facts and fiction

The antileukemic mechanisms of 6-mercaptopurine (6MP) and methotrexate (MTX) maintenance therapy are poorly understood, but the benefits of several years of myelosuppressive maintenance therapy for acute lymphoblastic leukemia are well proven. Currently, there is no international consensus on drug dosing. Because of significant interindividual and intraindividual variations in drug disposition and pharmacodynamics, vigorous dose adjustments are needed to obtain a target degree of myelosuppression. As the normal white blood cell counts vary by patients' ages and ethnicity, and also within age groups, identical white blood cell levels for 2 patients may not reflect the same treatment intensity. Measurements of intracellular levels of cytotoxic metabolites of 6MP and MTX can identify nonadherent patients, but therapeutic target levels remains to be established. A rise in serum aminotransferase levels during maintenance therapy is common and often related to high levels of methylated 6MP metabolites. However, except for episodes of hypoglycemia, serious liver dysfunction is rare, the risk of permanent liver damage is low, and aminotransferase levels usually normalize within a few weeks after discontinuation of therapy. 6MP and MTX dose increments should lead to either leukopenia or a rise in aminotransferases, and if neither is experienced, poor treatment adherence should be considered. The many genetic polymorphisms that determine 6MP and MTX disposition, efficacy, and toxicity have precluded implementation of pharmacogenomics into treatment, the sole exception being dramatic 6MP dose reductions in patients who are homozygous deficient for thiopurine methyltransferase, the enzyme that methylates 6MP and several of its metabolites. In conclusion, maintenance therapy is as important as the more intensive and toxic earlier treatment phases, and often more challenging. Ongoing research address the applicability of drug metabolite measurements for dose adjustments, extensive host genome profiling to understand diversity in treatment efficacy and toxicity, and alternative thiopurine dosing regimens to improve therapy for the individual patient.

Frequency of thiopurine S-methyltransferase mutant alleles in indigenous and admixed Guatemalan patients with acute lymphoblastic leukemia

Thiopurine S-methyltransferase (TPMT) polymorphisms affect the enzyme's activity and are predictive for the efficacy and toxicity of thiopurine treatment of acute lymphoblastic leukemia (ALL), autoimmune diseases and organ transplants. Because inter-ethnic differences in the distribution of these polymorphisms have been documented, we sequenced the TMPT gene in 95 Guatemalans, yet identified no new alleles. We also determined the frequency of the TPMT 2, 3A, 3B and 3C alleles in 270 admixed and 177 indigenous pediatric patients with ALL and healthy subjects from Guatemala using TaqMan assays and DNA sequencing. Among the 447 subjects genotyped, 10.0 % of the ALL cases and 13.6 % of the healthy controls were heterozygous for one of the four TPMT variants screened. The genotype frequencies in ALL and control populations were 0.7 and 1.7 % for TPMT 1/ 2, 7.4 and 10 % for TPMT 1/3A, 0.3 and 0 % for TPMT 1/B, and 1.5 and 1.1 % for TPMT 1/C, respectively (p = 0.30). No statistically significant differences between admixed and indigenous ALL (p = 0.67) or controls (p = 0.41) groups were detected; however, 17 % of the admixed healthy group bore one TPMT mutant allele, and they have one of the highest reported frequencies of TPMT mutant allele carriers. Because of the clinical implications of these variants for therapeutic response, TPMT allele testing should be considered in all Guatemalan patients to reduce adverse side-effects from thiopurine drug treatments.

Inter and intra-ethnic differences in the distribution of the molecular variants of TPMT, UGT1A1 and MDR1 genes in the South Indian population

Molecular variants of polymorphic drug metabolizing enzymes and drug transporters are attributed to differences in individual's therapeutic response and drug toxicity in different populations. We sought to determine the genotype and allele frequencies of polymorphisms for major phase II drug-metabolizing enzymes (TPMT, UGT1A1) and drug transporter (MDR1) in South Indians. Allelic variants of TPMT (*2,*3A,*3B,*3C & *8), UGT1A1 (TA)6>7 and MDR1 (2677G>T/A & 3435C>T) were evaluated in 450-608 healthy South Indian subjects. Genomic DNA was extracted by phenol-chloroform method and genotype was determined by PCR-RFLP, qRT-PCR, allele specific PCR, direct sequencing and SNaPshot techniques. The frequency distributions of TPMT, UGT1A1 and MDR1 gene polymorphisms were compared between the individual 4 South Indian populations viz., Tamilian, Kannadiga, Andhrite and Keralite. The combined frequency distribution of the South Indian populations together, was also compared with that of other major populations. The allele frequencies of TPMT*3C, UGT1A1 (TA)7, MDR1 2677T, 2677A and 3435T were 1.2, 39.8, 60.3, 3.7, and 61.6% respectively. The other variant alleles such as TPMT*2, *3A, *3B and *8 were not identified in the South Indian population. Sub-population analysis showed that the distribution of UGT1A1 (TA)6>7 and MDR1 allelic variants differed between the four ethnic groups. However, the frequencies of TPMT*3C allele were similar in the four South Indian populations. The distribution of TPMT, UGT1A1 and MDR1 gene polymorphisms of the South Indian population was significantly different from other populations.

Thiopurine S-methyltransferase activity in three major Asian populations: a population-based study in Singapore

OBJECTIVE

The distribution of thiopurine methyltransferase (TPMT) activity in Asian populations has not been well documented. We studied the TPMT phenotype in three major Asian ethnic groups in Singapore, namely the Chinese (Ch), Malays (Mal) and Indians (Ind), with the aim of carrying out a comprehensive survey of the distribution of TPMT activity in Asians.

METHODS

A radiochemical assay was used to measure the enzymatic activity of TPMT in the red blood cells (RBCs) of 479 healthy adults (Ch=153, Mal=163 and Ind=163). Cut-off points for intermediate TPMT activity were validated using a receiver operating curve (ROC) analysis. PCR-based methods were used to screen for the TPMT*3C, TPMT*3A and TPMT*6 variants.

RESULTS

The histogram of the combined population cohort showed a bimodal distribution of TPMT activity, with no subject having low TPMT activity (<5 units). In total, TPMT variants were detected in 14 subjects (*1/*3C in 13 subjects; *1/*3A in one subject). We observed significant inter-ethnic differences in terms of TPMT activity (p<0.001), with the Malays showing a higher median activity than the Chinese or Indians (17.8 units vs 16.4 units). The Malays also showed a higher methylation rate--with a cut-off point for intermediate TPMT activity of 11.3 units--than the Chinese (9.9 units) or Indians (9.4 units). A high phenotype-genotype correlation of >97% was observed in all three races. We also genotyped 418 childhood leukaemias. The combined analysis of subjects participating in this and a previous study--1585 subjects--showed that 4.7% of Chinese (n=30/644), 4.4% of Malays (n=24/540) and 2.7% of Indians (n=11/401) were heterozygous at the TPMT gene locus.

CONCLUSION

This is the first comprehensive TPMT phenotype and genotype study in Asian populations, particularly in the Malays and Indians.

Frequency of the thiopurine S-methyltransferase alleles in the ancient genetic population isolate of Sardinia

BACKGROUND

Thiopurine S-methyltransferase (TPMT) is an enzyme involved in the normal metabolic inactivation of thiopurine drugs. Patients with intermediate or no TPMT activity are at risk of toxicity after receiving standard doses of thiopurine drugs and it was shown that inter-individual differences in response to these drugs is largely determined by genetic variation at the TPMT locus.

OBJECTIVE

This study was designed to investigate in the Sardinian population the frequency distribution of four of the most common variants accounting for TPMT deficiency and to conduct comparative analyses with other populations in order to obtain insights into the main factors that have shaped diversity at the TPMT locus in Sardinia.

METHODS

DNA was extracted in 259 Sardinians and the frequencies of allelic variants of TPMT were determined using polymerase chain reaction-restriction fragment length polymorphism technique.

RESULTS

Among the 259 Sardinians genotyped, 6.95% were found to be heterozygous for one of four TPMT variants screened; for each variant the frequency estimate was 1.74%, 0.58%, 0.39% and 0.77% for TPMT*2, TPMT*3A, TPMT*3B and TPMT*3C respectively.

CONCLUSIONS

Although Sardinia does not show reduced diversity at the TPMT locus, the spectrum of TPMT allele frequencies affords evidence of remarkable influence of genetic drift and founder effects throughout its population history. In the broad context of the European TPMT diversity, the Sardinians come out as outliers, an observation consistent with previous genetic inferences that Sardinia has features of a genetic isolate.