1255 - Folate Metabolic Pathway Single Nucleotide Polymorphisms a Predictive Pharmacogenetic Marker of Methotrexate Related Adverse Events in Indian (Asian) Patients with Rheumatoid Arthritis

Monday, November 7, 2011: 9:00 AM-6:00 PM
Hall F2 - Poster Hall (McCormick Place West)
Yogita Ghodke1, Arvind Chopra2, Amrutesh S. Puranik1, Pooja Shintre3, Anjali Radkar4, Kalpana Joshi5 and Bhushan Patwardhan5, 1University of Minnesota, Minneapolis, MN, 2Centre for Rheumatic Diseases, Pune, India, 3Sinhgad College of Engineering, Pune, India, 4Gokhale Institute of Politics and Economics, Pune, India, 5Symbiosis International University, Pune - 411042, India
Presentation Number: 1255

Background/Purpose: Methotrexate (MTX) is a folate analogue and the best tolerated DMARD but is limited by major interpatient variability in clinical response and unpredictable toxicity. Though the increasingly recognized association of single nucleotide polymorphisms (SNPs) of the folate metabolic pathway is published little is known about Indian population. We present the results of a pharmacogenetic study in Indian RA patients on MTX. We hypothesized the role of SNPs in MTX pharmacokinetics (PK) and MTX related adverse events (AE).

Methods: 322 RA patients (Female 86%, RF 79%) undergoing supervised MTX therapy for > 3 months; were randomly selected from a community rheumatology clinic; maximum (usually limited by tolerability) MTX dose 3.75-20 mg, median 17.5mg. We retrospectively analyzed standard CRF but recalled several patients to confirm events. Hepatic, gastrointestinal (nausea, vomiting, gastritis, diarrhea) , pain in abdomen, bone marrow, skin rash/aggravated nodules, mucositis, hair-loss and central nervous system related were identified as significant AE. Any one or combinations of above events were noted as “overall AE”. 12 SNPs in 9 genes of folate metabolism (including transporters) were genotyped using PCR-RFLP and Real-time Taqman allelic discrimination. Toxicogenetic index was calculated as the sum of homozygous variant genotypes carried by an individual (Arthritis Rheum 2006; 54(2):607-12). The genotypes which showed significant association (P<0.05) in the binary logistic regression analysis were taken into consideration for calculating toxicogenetic index.  The presence of the 4 genotypes was summed as a composite index to constitute a toxicogenetic index for each patient (index range 0–4). PK analysis was performed on 94 patients by determining plasma MTX and metabolite 7-OH MTX levels at 0, 2 and 8 hr by HPLC and plasma Hcy at 0hr.

Result:

 

No of patients

Hepatic

Bone marrow

Pain in abdomen

Overall
AE

TS 5UTR
2R/2R vs. 3R/3R and 2R/3R

57 vs. 259

1.3(0.6-2.8)

4.9(1.7-13.6)*

0.8(0.2-3)

1.5(0.8-2.9)

TS 3 UTR
6bp/6bp vs. 6bp/6bp and 0bp/0bp

65 vs. 257

1.4(0.7-3)

0.1(0.3-3)

1.1(0.3-4)

2.8(1.4-5.6)*

GGH C401T
TT vs. CC and CT

124 vs.198

2.3(1.3-4.1)*

1.1(0.4-2.9)

1.0(0.3-3)

1.7(1.0-2.8)*

SHMT1 C1420T
CC vs. CT and TT

8 vs. 304

0.7(0.1-4.1)

1.3(0.1-4.7)

6.9(1.1-46.1)*

1.7(0.3-9.7)

<>(1) The table shows occurrence of AE by risk genotype (Values are odds ratio (95% confidence interval: *P < 0.05). The toxicogenetic index ranged from 0 to 4. An index of 4 was associated with~3 fold higher likelihood of side effect compared with an index of 0 (= 0.0001). (2) Pharmacokinetic analysis shows that the patients with risk genotype have significantly high plasma concentration of MTX at 2hr (TS 5UTR *2R/2R), 8hr (TS 6bp/6bp) and its active metabolite 7-OH MTX at 8 hr. (SHMT1 CC).

Conclusion: Our findings revealed newer risk association with MTX related AE in Indian (Asian) RA cohort. Pharmacokinetic studies do show some associations with genetic polymorphisms but need to be further validated. Our observations propose that a toxicogenetic index can provide a means of profiling patients who develop AE to MTX and may be useful in establishing the likelihood of occurrence of AE to MTX. However, prospective studies with large no of patients will be necessary to reveal the predictive value of this pharmacogenetic marker.


Keywords: methotrexate (MTX), polymerase chain reaction (PCR), polymorphism and rheumatoid arthritis (RA)

Disclosure: Y. Ghodke, None; A. Chopra, None; A. S. Puranik, None; P. Shintre, None; A. Radkar, None; K. Joshi, None; B. Patwardhan, None.