Pharmacogenetic study of methylenetetrahydrofolate reductase and thymidylate synthase in Japanese and assessment of ethnic and gender differences

Genetic polymorphisms of enzyme proteins and transporters related to methotrexate response and pharmacokinetics in a Japanese population

Background

Methotrexate (MTX) is currently the anchor drug widely used worldwide in the treatment of rheumatoid arthritis (RA). However, the therapeutic response to MTX has been shown to vary widely among individuals, genders and ethnic groups. The reason for this has been not clarified but it is considered to be partially due to several mechanisms in the cellular pathway of MTX including single-nucleotide polymorphisms (SNPs). The purpose of this study was to investigate the allelic frequencies in different ethnic and/or population groups in the 10 polymorphisms of enzyme proteins and transporters related to the MTX response and pharmacokinetics including MTHFR, TYMS, RFC1, FPGS, GGH, ABCB1, ABCC2 and ABCG2 in unrelated healthy Japanese adults and patients with RA.

Methods

Ten polymorphisms, methylenetetrahydrofolate reductase (MTHFR) 1298, thymidylate synthase (TYMS) 3'-UTR, reduced folate carrier 1 (RFC1) 80 and−43, folypolyglutamyl synthase (FPGS) 1994, γ-glutamyl hydrolase (GGH) 452 and−401, the ABC transporters (ABCB1 3435, ABCC2 IVS23 + 56, ABCG2 914) of enzyme proteins and transporters related to MTX response and pharmacokinetics in 299 unrelated healthy Japanese adults and 159 Japanese patients with RA were investigated to clarify their contributions to individual variations in response and safety to MTX and establish personalized MTX therapy. SNPs were evaluated using real-time polymerase chain reaction (PCR).

Results

Comparison of allelic frequencies in our study with other ethnic/population groups of healthy adults and RA patients showed significant differences in 10 polymorphisms among healthy adults and 7 among RA patients. Allelic frequencies of MTHFR 1298 C, FPGS 1994A and ABCB1 3435 T were lower in Japanese than in Caucasian populations and those of ABCC2 IVS23 + 56 C and ABCG2 914A were higher in Japanese than in Caucasian/European populations in both healthy adults and RA patients. Allelic frequencies of MTHFR 1298 C, GGH−401 T, ABCB1 3435 T, and ABCG2 914A were higher in healthy Japanese adults than in an African population, and those of RFC1 80A, RFC1−43C and ABCC2 IVS23 + 56 C in healthy Japanese adults were lower than in Africans. However, no significant differences were seen in the distribution of allelic frequencies between healthy Japanese adults and RA patients.

Conclusion

The variations in allelic frequencies in different ethnic and/or population groups in healthy adults and RA patients may contribute to individual variations in MTX response and toxicity.

Thymidylate synthase genetic polymorphism and plasma total homocysteine level in a group of Turkish patients with rheumatoid arthritis: relationship with disease activity and methotrexate toxicity

BACKGROUND

The polymorphism of thymidylate synthase (TS) gene and homocysteine are reported to have a relationship to methotrexate (MTX) metabolism, with conflicting results. The aim of this study was to determine homocysteine levels and the frequency of TS gene triple repeat (TS3R) and double repeat (TS2R) polymorphisms in a group of Turkish RA patients and evaluate its association with MTX toxicity and disease activity.

METHODS

Sixty-four patients with RA and 31 control subjects with a mean age of 48.7 ± 12.5 and 46.2 ± 13.4 years, were enrolled to the study. Demographic characteristics were obtained and number of patients with MTX-related adverse affects, were recorded in the patient group. The homocysteine levels and TS2R/TS3R polymorphisms of the TS gene were analyzed and the distribution of genotypes according to MTX toxicity and disease activity, were determined.

RESULTS

The demographic properties were similar between the patient and control subjects. Folic acid supplementation with a mean dose of 5mg folic acid/week, was present in all patients. Thirty-six of the 64 patients showed adverse effects to MTX treatment. The frequency of TS2R and TS3R polymorphisms were found to be similar in the patient and control groups. TS2R and TS3R gene polymorphisms were found to be similar in patients with and without MTX-related adverse events. The mean homocysteine level was also similar in patients with and without TS gene polymorphism, but was found to be higher (12.45μmol/L vs 10.7μmol/L) in patients with MTX-related side effects than in patients without side effects. The mean level of homocysteine was correlated with levels of ESR in the patient group.

CONCLUSIONS

In conclusion, homocysteine levels might effect the disease activity and toxicity of MTX but 2R and 3R polymorphisms in the TS gene, were not related with MTX-related toxicity in RA patients receiving folate supplementation. Further studies are needed to illuminate the polymorphisms in other enzymes that might be responsible from the MTX toxicity in patients suffering from RA.

Effect of genetic polymorphisms in the folate pathway on methotrexate therapy in rheumatic diseases

Methotrexate (MTX) is the first-line treatment for rheumatoid arthritis and is frequently used in the management of other forms of inflammatory arthritis. It is currently challenging to predict which patients will achieve adequate disease control and which patients will develop adverse effects while taking MTX. As an analog of dihydrofolic acid, MTX enters cells through the reduced folate carrier-1 protein, and is polyglutamated. MTX polyglutamates inhibit key enzymes in the folate pathway to produce an anti-inflammatory effect. It has been suggested that genetic polymorphisms in the folate pathway may influence intracellular folate and MTX polyglutamates pools, and thus MTX response. However, studies to identify genetic predictors have yielded inconclusive results. Nonreplication across studies has been attributed to insufficient statistical power as well as pharmacological and clinical confounders. Prospective studies, standardizing the definitions of response and toxicity, and application of genome-wide approaches may advance the search for genetic predictors of MTX response.

Methylenetetrahydrofolate reductase polymorphisms and interaction with smoking and alcohol consumption in lung cancer risk: a case-control study in a Japanese population

Background

Cigarette smoking is an established risk factor of lung cancer development while the current epidemiological evidence is suggestive of an increased lung cancer risk associated with alcohol consumption. Dietary folate, which is present in a wide range of fresh fruits and vegetables, may be a micronutrient that has a beneficial impact on lung carcinogenesis. Methylenetetrahydrofolate reductase (MTHFR) plays a crucial role in regulating folate metabolism, which affects both DNA synthesis/repair and methylation. We examined if smoking or alcohol consumption modify associations between MTHFR polymorphisms and lung cancer risk.

Methods

We evaluated the role of the MTHFR C677T (rs1801133) and A1298C (rs1801131) polymorphisms in a case-control study comprised of 462 lung cancer cases and 379 controls in a Japanese population. Logistic regression was used to assess the adjusted odds ratios (OR) and 95% confidence intervals (95% CI).

Results

The TT genotype of the C677T polymorphism was significantly associated with an increased risk of lung cancer (OR = 2.27, 95% CI = 1.42 - 3.62, P < 0.01) while the A1298C polymorphism was not associated with lung cancer risk. The minor alleles of both polymorphisms behaved in a recessive fashion. The highest risks were seen for 677TT-carriers with a history of smoking or excessive drinking (OR = 6.16, 95% CI = 3.48 - 10.9 for smoking; OR = 3.09, 95% CI = 1.64 - 5.81 for drinking) compared with C-carriers without a history of smoking or excessive drinking, but no interactions were seen. The 1298CC genotype was only associated with increased risk among non-smokers (P < 0.05), and smoking was only associated with increased risks among 1298A-carriers (P < 0.01), but no significant interaction was seen. There was a synergistic interaction between the A1298C polymorphism and drinking (P < 0.05). The highest risk was seen for the CC-carriers with excessive drinking (OR = 7.24, 95% CI = 1.89 - 27.7) compared with the A-carriers without excessive drinking).

Conclusions

The C677T polymorphism was significantly associated with lung cancer risk. Although the A1298C polymorphism was not associated with lung cancer risk, a significant interaction with drinking was observed. Future studies incorporating data on folate intake may undoubtedly lead to a more thorough understanding of the role of the MTHFR polymorphisms in lung cancer development.

A phase I/II and pharmacogenomic study of pemetrexed and cisplatin in patients with unresectable, advanced gastric carcinoma

This phase I/II study was conducted to determine the maximum recommended dose of pemetrexed when given in combination with a fixed dose of cisplatin, and the efficacy, toxicity and association of 5,10-methylenetetrahydrofolate reductase (MTHFR) variants with this pemetrexed--cisplatin combination, in patients with unresectable, advanced gastric carcinoma. Patients 18-70 years of age, with stage IV disease or post-surgery recurrence, no earlier palliative chemotherapy, 0 or 1 Eastern Cooperative Oncology Group performance status, were included. The cisplatin dose was 75 mg/m. In phase I, the initial dose of pemetrexed was 600 mg/m, escalated in 100 mg/m increments. In phase II, efficacy, including overall response rate, overall survival, as well as toxicity and MTHFR pharmacogenetics were investigated. Phase I enrolled 16 patients; 700 mg/m was defined as pemetrexed recommended dose. Thirteen serious adverse events were reported; the most common grade 3/4 toxicities were haematologic (10 of 13, 76.9%). Phase II enrolled 73 patients, 69 qualified for safety and 68 for efficacy analysis; 65 for pharmacogenomic analysis. Overall response rate was 23.5% (14.1%, 35.4%), disease control rate 55.9%, median overall survival 11.8 months (95% confidence interval, 7.2-18.5 months), progression-free survival 4.9 months (95% confidence interval, 2.8-7.1 months), and median response duration 5.4 months. Patients with MTHFR A1298C variants had median overall survival of 6.6 months, significantly shorter than patients with the wild type (median 18.5 months, P=0.001). The pemetrexed--cisplatin combination in patients with advanced gastric cancer generates modest efficacy and a manageable toxicity profile. The reduced overall survival in patients with MTHFR A1298C polymorphism variants deserves further investigation.

Preliminary study to identify the predictive factors for the response to methotrexate therapy in patients with rheumatoid arthritis

To identify the major factors predicting the response to Methotrexate (MTX) therapy in rheumatoid arthritis (RA) patients, we evaluated the relationship between the response to MTX and factors such as the concentration of MTX-polyglutamates (MTX-PGs) in erythrocytes (RBCs), genotypes of thymidylate synthase (TYMS) 5'-UTR (2R/3R) and 3'-UTR (-6/+6), 5,10-methylenetetrahydrofolate reductase (MTHFR) C677T and A1298C, and other patient-related factors. Thirty-six Japanese RA patients were enrolled in this cohort study. The concentrations of MTX-PGs in RBCs were measured, and polymorphisms were determined using PCR-RFLP method. As an indicator of the accumulated capacity of MTX-PGs in the RBCs of each patient, the MTX dose/MTX-PGs (AC-MPG, l/week) was calculated. The response to MTX therapy was assessed using the MTX dose for a>or=50% decrease in CRP level (MTX dose for 50%CRP, mg/week), and the relationships between MTX dose for 50%CRP and various other factors were evaluated using multiple linear regression analysis. The MTX dose was 6.9+/-0.3 mg/week and the MTX-PGs concentration in RBCs was 97.3+/-8.1 nmol/l (n=36, blood samples=95, mean+/-S.D.). The range of MTX dose for 50%CRP was 2.0-13.0 mg/week. Most individual AC-MPG levels showed no change during the evaluation period (coefficient of variation=5.9%). Based on the results of multiple linear regression analysis, AC-MPG, TYMS 3'-UTR (-6/+6), and ESR at the start of MTX therapy were associated with the MTX dose for 50%CRP. AC-MPG, TYMS 3'-UTR (-6/+6), and ESR might be the major predictive factors for the response to MTX therapy in Japanese RA patients.

Plasma total homocysteine level and methylenetetrahydrofolate reductase 677C>T genetic polymorphism in Japanese patients with rheumatoid arthritis

Hyperhomocysteinemia is a known risk factor of cardiovascular disease. Homocysteine has been also linked to inflammation in rheumatoid arthritis (RA). In this study, we investigated the relationship between plasma homocysteine levels and single nucleotide polymorphism (SNP) of the gene coding for methylenetetrahydrofolate reductase (MTHFR), an enzyme involved in the biosynthesis of homocysteine, and the correlation between the plasma homocysteine levels and generally used inflammatory markers (C-reactive protein, erythrocyte sedimentation rate and matrix metalloproteinase-3) in 96 Japanese patients with RA. Plasma homocysteine levels in patients with the MTHFR 677TT genotype were significantly higher than in those with the 677CC genotype (p < 0.05). In addition, plasma homocysteine levels were increased along with the elevation of general inflammatory markers. Therefore, we conclude that homocysteine might affect the inflammatory status of patients, and the MTHFR 677C>T SNP could be a predictive factor of hyperhomocysteinemia in patients with RA.

Magnifying endoscopic observation of the gastric mucosa, particularly in patients with atrophic gastritis

The gastric mucosal surface was observed using the magnifying fibergastroscope (FGS-ML), and the fine gastric mucosal patterns, which were even smaller than one unit of gastric area, were examined at a magnification of about 30. For simplicification, we classified these patterns by magnifying endoscopy in the following ways; FP, FIP, FSP, SP and MP, modifying Yoshii's classification under the dissecting microscope. The FIP, which was found to have round and long elliptical gastric pits, is a new addition to our endoscopic classification. The relationship between the FIP and the intermediate zone was evaluated by superficial and histological studies of surgical and biopsy specimens. The width of the band of FIP seems to be related to the severity of atrophic gastritis. Also, the transformation of FP to FIP was assessed by comparing specimens taken from the resected and residual parts of the stomach, respectively. Moreover, it appears that severe gastritis occurs in the gastric mucosa which shows a FIP. Therefore, we consider that the FIP indicates the position of the atrophic border.