The Relationship Between The Single Nucleotide Polymorphism In The Adenosine Pathway And The Treatment Of Methotrexate In Rheumatoid Arthritis

Background Rheumatoid arthritis (RA) is an inflammatory and immune-mediated disease involving joints and a variety of major organ systems. In China the prevalence of RA is 0.32-0.36 percent. RA is one of the important reasons which cause the destruction of joints and the loss of function. Methotrexate (MTX) has proven to reduce disease activity and delay or stabilize the development of bone erosions. MTX is also cheap and can be in combination with other disease modifying antirheumatic drug (DMARD) or biological agents, so it is the most widely used DMARD for the treatment of RA. However, only 45%-65% of the patients experience good clinical response, and 10%-30% discontinue therapy due to side effects. Adenosine is a potent anti-inflammatory agent, and some of the antiproliferative effects of MTX are thought to be mediated through this mechanism. MTX directly or indirectly inhibits several enzymes of the adenosine pathway, including aminoimidazole carboxamide ribonucleotide transformylase (ATIC), methionine synthase (MTR), methionine synthase reductase (MTRR), adenosine monophosphate deaminase (AMPD), adenosine deaminase (ADA) and so on.Based on the progress of pharmacogenetics research in the past ten years; the difference of individual gene is the main factor of efficacy and toxicity of treatment. Genetic variants in the adenosine pathway had been studied in the international about the efficacy and toxicity of MTX, for instance ATIC, MTR and MTRR. The report from individual may vary. The single nucleotide polymorphism (SNP) of these genes were analysed by real-time fluorescent quantitative polymerase chain reaction. The aim of the current study was to determine associations between the efficacy and toxicity of MTX and SNPs in gene coding for the adenosine pathway enzyme ATIC,MTR,MTRR in patients with RA and to provide the initiatory clues for the individualized therapy in RA.Objectives To determine the allele frequencies of three single nucleotide polymorphisms (ATIC C347G/rs2372536 , MTRR A66G/rs1801394 , MTR A2756G/rs1805087) in three genes coding for enzymes related to the release of adenosine in RA patients and controls, the relationship between it and the treatment of methotrexate in rheumatoid arthritis.Methods A total of 359 patients with RA were divided into MTX group(n=116), MTX+other DMARDs group (n=152), other DMARDs with no MTX group(n=91),who were diagnosed as having RA as defined by the American College of Rheumatology 1987 revised criteria.The clinical and laboratory measurements were evaluated before observation and 12, 24 weeks later.Efficacy (evaluated by ACR20) and toxicity of the drugs were also collected. Real-time fluorescent quantitative PCR was conducted to test gene mutation in RA patients and 340 healthy controls. The association between MTX-related adverse events and genotype was also assessed.The following polymorphisms were determined: ATIC 347C>G,MTR 2756A>G及MTRR 66A>G.Results1. There was no significant difference of frenquency among ATIC 347 CC,CG,GG,MTR 2756AA,AG,GG及MTRR 66AA,AG,GG between RA patients and the healthy controls.2 In MTX group (n=107), 72 %( n=77) of the patients have the good clinical response; there was no statistical significance with 347CC, CG, GG between in effect patients and ineffective ones. There was no statistical significance between MTR or MTRR polymorphisms with good clinical response of the RA patients who have been treated with MTX. But to the RA patients who have MTR AA and MTRR AA genotypes, those with MTR AG and MTRR AG/GG genotypes had a depressed risk with the efficacy of MTX (OR=0.19,95% CI,0.04-0.88,P=0.03).3 There are 32.7 percent (n=35) of the patients exhibit adverse drug reaction,more likely to experience gastrointestinal side effects, levels of liver enzymeelevated,and so on. The ATIC G allele carriers(22.4%) experienced a great frequency of side effects than the CC carriers (OR=2.67, 95%CI, 1.27-5.59,P<0.05). There was no statistical significance between MTR,MTRR and toxicity of MTX-related adverse events.4 In the MTX+other DMARDs group and other DMARDs with no MTX group, there was no statistical significance between the three SNPs with good clinical response and toxicity to MTX treatment.Conclusion1. Polymorphisms in the ATIC gene is not associated with good clinical response to MTX treatment, but the ATIC347 G allele was associated with the toxicity of MTX, most of them are gastrointestinal side effects .2. Polymorphisms in the MTR or MTRR gene are not associated with good clinical response and toxicity to MTX treatment, but the cumulative genotypes was associated with the good clinical response of patients who take MTX.