Single nucleotide polymorphism profiling across the methotrexate pathway in normal subjects and patients with rheumatoid arthritis

Methotrexate intoxication: Beyond the adverse events

AIM

Methotrexate (MTX) is the first-line disease-modifying antirheumatic drug in rheumatoid arthritis (RA). However, this anchor may cause some side effects that may range from nausea to mortality. The clinical features of MTX toxicity are under-researched. In this study, we aimed to find out the potential predisposing factors and outcomes of the MTX toxicity (n = 31).

METHODS

The data were collected from 31 patients whose ages ranged from 25 to 81 years, who were suffering from immune-mediated inflammatory diseases and major MTX-related toxicity.

RESULTS

Out of 31 patients, six (19.4%) used MTX every day, and 13 (41.9%) patients had renal insufficiency who were admitted to the hospital because of mucositis (90.3%) and fever (71%). While using MTX, 27 patients (87.1%) were discharged after the treatment and four patients (12.9%) died.

CONCLUSIONS

Although MTX has high efficacy for the toxicity ratio, wrong use and dosage of MTX may be harmful to patients. Thus, patients should be informed about the proper use of MTX.

The association between reduced folate carrier-1 gene 80G/A polymorphism and methotrexate efficacy or methotrexate related-toxicity in rheumatoid arthritis: A meta-analysis

Methotrexate (MTX), the most commonly used anti-rheumatic drug against RA, enters the cell via the action of the reduced folate carrier 1(RFC1). A major polymorphism of the RFC1 gene, 80G/A, has been reported to influence the activity of RFC1, resulting in variable intracellular MTX-polyglutamate (MTX-PG) levels. However, the association studies addressing the RFC1 80G/A polymorphism and MTX efficacy or toxicity in Rheumatoid arthritis (RA) has yielded conflicting results. In the present meta-analysis, we aimed to evaluate the association between the RFC1 80G/A polymorphism and MTX efficacy or toxicity in RA patients. A total 17 studies met our inclusion criteria. Among them, 12 studies with 2049 subjects reported the association between the RFC1 80G/A and MTX response, and 12 studies involving 2627 subjects were on MTX-related toxicity. Meta-analysis revealed significant association between RFC1 80G/A polymorphism and MTX efficacy (odds ratio (OR) for the A allele=1.29, 95% confidence interval (CI) 1.05-1.67, P=0.02; for AA genotype: OR=1.49, 95%CI 1.17-1.907, P=0.001). However, no association could be detected in the analysis of MTX-related toxicity. Stratification by ethnic population also indicated an association between this polymorphism and MTX efficacy in Asian group (P=0.002 for A allele; P=0.003 for AA genotype), but not in the Caucasian group (P=0.15 for A allele; P=0.05 for AA genotype). In both Asian and Caucasian sub-groups, no influence of the RFC1 80G/A polymorphism on MTX toxicity can be detected. In conclusion, the RFC1 G80A polymorphism is associated with responsiveness to MTX therapy, but may not be associated with MTX toxicity in RA patients.

Pharmacogenetics of inflammatory bowel disease

Pharmacogenetic studies have been performed for almost all classes of drugs that have been used in IBD but very few have generated consistent findings or have been replicated. The genetic test that has been approved for clinical practice is TPMT testing prior to starting treatment with thiopurine drugs. Research in IBD pharmacogenetics has focused on prediction of drug efficacy and toxicity by identifying polymorphisms in the genes encoding enzymes that are involved in metabolic pathways. Recent research has mainly focused on therapeutic agents such as azathioprine, methotrexate, aminosalicylates, corticosteroids, infliximab and adalimumab. Future pharmaceutical trials should include pharmacogenetic research to test appropriate candidate genes in a prospective manner and correlate genetic associations with trial outcomes and relevant functional data.

Influence of genetic polymorphisms of FPGS, GGH, and MTHFR on serum methotrexate levels in Chinese children with acute lymphoblastic leukemia

PURPOSE

To investigate the correlation between common genetic polymorphisms of folylpolyglutamate synthase (FPGS), gamma-glutamyl hydrolase (GGH), and methylenetetrahydrofolate reductase (MTHFR) and serum levels of methotrexate (MTX) in Chinese children with acute lymphoblastic leukemia (ALL).

METHODS

Ninety-one children with ALL who received high-dose MTX were recruited. The polymorphisms FPGS (rs1544105 G>A), GGH (rs3758149 C>T), and MTHFR (rs1801133 C>T) were genotyped through polymerase chain reaction-restriction fragment length polymorphism analysis. Serum MTX was measured by fluorescence polarization immunoassay. The association between targeted polymorphisms and MTX concentration-to-dose (C/D) ratios was assessed, and between targeted polymorphisms and the percent of MTX above the therapeutic threshold (40 µmol/L).

RESULTS

The minor allele frequencies of rs1544105 G (34.1%), rs3758149 T (19.2%), and rs1801133 C (48.4%) observed in our population were significantly lower than those reported for European populations (64.2, 30.8, and 69.0%, respectively). The association between the GGH rs3758149 polymorphism and MTX C/D was gender-specific; in girls, the MTX C/D at 24 h of GGH rs3758149 CC carriers (12.09 μmol/L per g/m(2)) was significantly lower than that of CT or TT carriers (16.80 μmol/L per g/m(2)). The percent of serum MTX above the therapeutic threshold in GGH rs3758149 CC carriers (18.3%) was significantly lower than that of CT and TT carriers (38.7%). The MTX C/D ratios at 24 h and the percent of MTX >40 µmol/L for the A-T-T (three variant alleles) haplotype were significantly higher than those for other haplotypes combined (P < 0.05).

CONCLUSIONS

These data indicate that FPGS rs1544105, GGH rs3758149, and MTHFR rs1801133 polymorphisms contribute to the variability of MTX pharmacokinetics, and their genotyping may be useful to reduce toxicities associated with MTX therapy.

Pharmacogenetics in rheumatoid arthritis

Rheumatoid arthritis (RA) is a systemic inflammatory arthritis leading to severe joint damage and associated with high morbidity and mortality. Disease-modifying antirheumatic drugs (DMARDs) are the mainstay of treatment in RA. DMARDs not only relieve the clinical signs and symptoms of RA but also inhibit the radiographic progression of disease. In the last decade, a new class of disease-modifying medications, the biologic agents, has been added to the existing spectrum of DMARDs in RA. However, patients' response to these agents is not uniform with considerable variability in both efficacy and toxicity. There are no reliable means of predicting an individual patient's response to a given DMARD prior to initiation of therapy. In this chapter, the current published literature on the pharmacogenetics of traditional DMARDS and the newer biologic DMARDs in RA is highlighted. Pharmacogenetics may help individualize drug therapy in patients with RA in the near future.

Old drugs, old problems: where do we stand in prediction of rheumatoid arthritis responsiveness to methotrexate and other synthetic DMARDs?

Methotrexate (MTX) is the central drug in the management of rheumatoid arthritis (RA) and other immune mediated inflammatory diseases. It is widely used either in monotherapy or in association with other synthetic and biologic disease modifying anti-rheumatic drugs (DMARDs). Although comprehensive clinical experience exists for MTX and synthetic DMARDs, to date it has not been possible to preview correctly whether or not a patient will respond to treatment with these drugs. Predicting response to MTX and other DMARDs would allow the selection of patients based on their likelihood of response, thus enabling individualized therapy and avoiding unnecessary adverse effects and elevated costs. However, studies analyzing this issue have struggled to obtain consistent, replicable results and no factor has yet been recognized to individually distinguish responders from nonresponders at treatment start. Variables possibly influencing drug effectiveness may be disease-, patient- or treatment-related, clinical or biological (genetic and nongenetic). In this review we summarize current evidence on predictors of response to MTX and other synthetic DMARDs, discuss possible causes for the heterogeneity observed and address its translation into daily clinical practice.

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.

Pharmacogenomics in rheumatoid arthritis

Rheumatoid arthritis (RA) is a systemic inflammatory arthritis that leads to severe joint damage and is associated with high morbidity and mortality. Disease-modifying antirheumatic drugs (DMARDs) are the mainstay of treatment in RA. DMARDs not only relieve the clinical signs and symptoms of RA but also inhibit the radiographic progression of disease. Recently, a new class of disease-modifying medications, the biologic agents, has been added to the existing spectrum of DMARDs in RA. However, patients' response to these agents is not uniform, with considerable variability in both efficacy and toxicity. There are no reliable means of predicting an individual patient's response to a given DMARD prior to initiation of therapy. In this chapter, the current published literature on the pharmacogenomics of traditional DMARDs and the newer biologic DMARDs in RA is highlighted. Pharmacogenomics may help individualize drug therapy in patients with RA in the near future.

The use of low dose methotrexate in rheumatoid arthritis - are we entering a new era of therapeutic drug monitoring and pharmacogenomics?

Methotrexate (MTX) is one of the most commonly used medications in the treatment of rheumatoid arthritis (RA). It has proven efficacy as a sole agent as well as in combination with other disease modifying anti-rheumatic agents (DMARDs) including the newer biological agents. MTX is generally well tolerated although there are a number of potentially serious adverse effects. Of these, haematopoietic suppression, hepatotoxicity and pulmonary toxicity are the more severe and patients are therefore required to have appropriate monitoring while they remain on MTX. In the past, attempts at therapeutic drug monitoring using serum MTX concentrations have been unsuccessful. However, MTX is taken into red blood cells (RBC) where up to four glutamates are added to form MTX polyglutamates (MTXPG(n)). More recently it has been suggested that higher RBC MTXPG(3-5) concentrations may be associated with improved disease control. Genetic variations in enzymes involved in the uptake of MTX into cells and its metabolism are also being examined for their ability to predict drug response and potential for adverse events. While it is unlikely that a single genetic variant will predict efficacy or toxicity there is preliminary evidence that a "pharmacogenetic index" that takes into account the effects of multiple genetic variants maybe useful. Although in their infancy at present, both therapeutic drug monitoring using MTXPG concentrations and pharmacogenomics of MTX may prove useful in the future and are worthy of further investigation.

Racial or ethnic differences in allele frequencies of single-nucleotide polymorphisms in the methylenetetrahydrofolate reductase gene and their influence on response to methotrexate in rheumatoid arthritis

BACKGROUND

The anti-folate drug methotrexate (MTX) is commonly used to treat rheumatoid arthritis.

OBJECTIVE

To determine the allele frequencies of five common coding single-nucleotide polymorphisms (SNPs) in the methylenetetrahydrofolate reductase (MTHFR) gene in African-Americans and Caucasians with rheumatoid arthritis and controls to assess whether there are differences in allele frequencies among these ethnic or racial groups and whether these SNPs differentially affect the efficacy or toxicity of MTX.

METHODS

Allele frequencies in the 677, 1298 and 3 additional SNPs in the MTHFR coding region in 223 (193 Caucasians and 30 African-Americans) patients with rheumatoid arthritis who previously participated in one of two prospective clinical trials were characterised, and genotypes were correlated with the efficacy and toxicity of MTX. Another 308 subjects with rheumatoid arthritis who participated in observational studies, one group predominantly Caucasian and the other African-American, as well as 103 normal controls (53 African-Americans and 50 Caucasians) were used to characterise allele frequencies of these SNPs and their associated haplotypes.

RESULTS

Significantly different allele frequencies were seen in three of the five SNPs and haplotype frequencies between Caucasians and African-Americans. Allele frequencies were similar between patients with rheumatoid arthritis and controls of the same racial or ethnic group. Frequencies of the rs4846051C, 677T and 1298C alleles were 0.33, 0.11 and 0.13, respectively, among African-Americans with rheumatoid arthritis. Among Caucasians with rheumatoid arthritis, these allele frequencies were 0.08 (p<0.001 compared with African-Americans with rheumatoid arthritis), 0.30 (p = 0.002) and 0.34 (p<0.001), respectively. There was no association between SNP alleles or haplotypes and response to MTX as measured by the mean change in the 28-joint Disease Activity Score from baseline values. In Caucasians, the 1298 A (major) allele was associated with a significant increase in MTX-related adverse events characteristic of a recessive genetic effect (odds ratio 15.86, 95% confidence interval 1.51 to 167.01; p = 0.021), confirming previous reports. There was an association between scores of MTX toxicity and the rs4846051 C allele, and haplotypes containing this allele, in African-Americans, but not in Caucasians.

CONCLUSIONS

: These results, although preliminary, highlight racial or ethnic differences in frequencies of common MTHFR SNPs. The MTHFR 1298 A and the rs4846051 C alleles were associated with MTX-related adverse events in Caucasians and African-Americans, respectively, but these findings should be replicated in larger studies. The rs4846051 SNP, which is far more common in African-Americans than in Caucasians, can also be proved to be a useful ancestry informative marker in future studies on genetic admixture.

Pharmacogenetic of antirheumatic treatments: clinical implications

Preliminary pharmacogenetic data suggest that germline genetic informations might be of value in individualizing disease-modifying antirheumatic drugs (DMARDs) therapy in various autoimmune chronic inflammatory diseases. Either DMARDs small molecules (DMARDs-SM) or DMARDs biological therapies (DMARDs-BT) might be selected for their lower toxicity or better efficacy based on single-nucleotide polymorphisms (SNPs) of genes governing the metabolism of drugs, or the response of immune cells to proinflammatory molecules, or the proinflammatory molecular activity of immune cells. Data available for one DMARDs-SM, methotrexate, suggest that a careful assessment of the SNPs of four enzymes involved in the folate metabolism allow one to construct a genetic index of toxicity (toxicogenetic index) that might be employed in daily practice to find the patient's most at risk. Only the full knowledge of the various gene polymorphisms controlling the phenotypic manifestations of the inflammatory-immunological milieu of each rheumatic disease will allow one to obtain the clear definition of a personalized medicine. Few different cytokine gene SNPs seem to be of importance in determining the susceptibility to diseases, or the aggressiveness of diseases. The role of genetics in affecting a possible clinical response to DMARDs-BT targeting specific inflammatory molecules or their receptors still has to be defined. However, the available data suggest that cytokine (and/or receptors) gene SNPs might indeed play a role in determining the biological effects, hence the clinical effectiveness of DMARDs-BT. Crucial to this aim will be the prospective analysis of clinical benefits and safety on the basis of the at baseline stratification of gene SNPs in each chronic inflammatory rheumatic disease before starting any new DMARDs-SM or DMARDs-BT.

Pharmacogenomics in the treatment of rheumatoid arthritis: clinical implication and perspective

Rheumatoid arthritis (RA) is a chronic inflammatory disease. The inflammatory process of the joint destroys articular architecture and causes a significant disability. The efficacy of disease modifying antirheumatic drugs such as methotrexate, sulfasalazine and biological response modifiers, is widely accepted. However, the outcome of the treatment with these agents is known to vary among patients. The application of the pharmacogenomics is expected to reduce toxicities and enhance the desirable effects of therapeutic agents for RA. Recently, pharmacogenomic studies on methotrexate, sulfasalazine and tumor necrosis factor-α inhibitors have been reported. These investigations suggest that the pharmacogenomic approach is useful for the treatment of RA, although there are points to be considered before the translation of the pharmacogenomic data into clinical practice. This review focuses on the latest information on the pharmacogenomics of antirheumatic drugs and its clinical implication in the treatment of RA.

Efficacy and toxicity of methotrexate in early rheumatoid arthritis are associated with single-nucleotide polymorphisms in genes coding for folate pathway enzymes

OBJECTIVE

To determine associations of methotrexate (MTX) efficacy and toxicity with single-nucleotide polymorphisms (SNPs) in genes coding for folate pathway enzymes in patients with early rheumatoid arthritis (RA).

METHODS

Patients (n=205) with active RA received MTX at an initial dosage of 7.5 mg/week, which was increased to 15 mg/week and combined with folic acid (1 mg/day) after 4 weeks. If the Disease Activity Score in 44 joints (DAS44) was >2.4 at 3 months, MTX was increased to 25 mg/week. MTX efficacy was evaluated at 3 and 6 months and compared for genotypes in 3 analyses: patients with and without good response (DAS44<or=2.4), patients with and without good improvement (DeltaDAS44>1.2), and patients with and without moderate improvement (DeltaDAS44>0.6). The association between MTX-related adverse drug events (ADEs) and genotype was evaluated by comparing genotypes between patients with and without ADEs, specifically pneumonitis, gastrointestinal ADEs, skin and mucosal ADEs, and elevated liver enzyme levels. The following SNPs were analyzed: methylenetetrahydrofolate reductase (MTHFR) 677C>T, MTHFR 1298A>C, dihydrofolate reductase (DHFR) -473G>A, DHFR 35289G>A, and reduced folate carrier 80G>A. In case of significant differences, odds ratios (ORs) were calculated.

RESULTS

At 6 months, MTHFR 1298AA was associated with good improvement relative to 1298C (OR 2.3, 95% confidence interval [95% CI] 1.18-4.41), which increased with increased copies of the MTHFR 677CC haplotype. In contrast, MTHFR 1298C allele carriers developed more ADEs (OR 2.5, 95% CI 1.32-4.72).

CONCLUSION

Patients with MTHFR 1298AA and MTHFR 677CC showed greater clinical improvement with MTX, whereas only the MTHFR 1298C allele was associated with toxicity. In the future, MTHFR genotypes may help determine which patients will benefit most from MTX treatment.

Screening for new MTHFR polymorphisms and NTD risk

The enzyme, 5,10-methylenetetrahydrofolate reductase (MTHFR) plays a key role in cellular folate metabolism. The A222V (677C->T) polymorphism is a confirmed neural tube defect (NTD) risk factor within Irish and other populations. To search for other unknown single nucleotide polymorphisms (SNPs) that might play a role in the etiology of NTDs, we examined the entire MTHFR coding region in healthy individuals (n = 100). SNPs were identified using sequencing and database analysis and allele frequencies were determined in our Irish population. We identified P39P (116C->T; T allele frequency 0.13) and previously reported R594Q (1793G->A; Q allele frequency 0.07). We screened a large ethnically homogeneous Irish NTD cohort (n>1,300) for P39P and R594Q. A possible association between NTD cases and P39P (P = 0.034) was found but this was not confirmed by transmission disequilibrium testing. R594Q also showed some evidence of a NTD case association (P = 0.07). Further analysis indicated these observations are due to linkage disequilibrium with A222V (677C->T), and therefore these new SNPs are unlikely to be independent risk factors for NTDs. As rates of NTDs differ between ethnic groups, we examined allele and genotype frequencies of P39P and R594Q within African-American and American-Caucasian populations. This is the first NTD association study of both R594Q and the novel P39P. The association with NTD risk reported for these SNPs is driven by the linkage disequilibrium with the A222V (677C->T) NTD risk factor.

Pharmacogenetics of methotrexate

Methotrexate (MTX) has proven efficient in the treatment of a number of malignancies, as well as non-malignant disorders characterized by a rapid cellular growth. Yet some patients might develop resistance, while others could have toxic side effects. MTX achieves its cytotoxicity through the inhibition of folate-dependent enzymes, suggesting that the genes controlling their activity or the levels of folate cofactors can modulate drug efficacy and, thus, the sensitivity of a patient to MTX. Indeed, several studies, conducted mostly in leukemia and rheumatoid arthritis patients, have addressed the potential for tailoring MTX therapy based on a patient's genetics. Several genetic variants have been shown to have a predictive role, among which the most frequently studied are those of methylenetetrahydrofolate reductase and thymidylate synthase genes. The other candidates, as well as gene-gene interactions, which may be even more important for the prediction of disease outcomes than the individual gene effects, are also briefly discussed.