Altered expression of methylenetetrahydrofolate reductase modifies response to methotrexate in mice.
OBJECTIVE
Folates provide one-carbon units for nucleotide synthesis and methylation reactions. A common polymorphism (677C-->T) in methylenetetrahydrofolate reductase (MTHFR) encodes an enzyme with reduced activity. Response to the antifolate methotrexate (MTX) may be modified in 677TT individuals because MTHFR converts nonmethylated folates, used for thymidine and purine synthesis, to 5-methyltetrahydrofolate, used in homocysteine remethylation to methionine. To study potential interactions between MTHFR activity and MTX, we examined the impact of decreased and increased MTHFR expression on MTX response in mice.


METHODS
Mthfr-deficient (Mthfr and Mthfr) and wild-type (Mthfr) mice were injected with MTX or saline and assessed for hematological parameters (hematocrit, hemoglobin, red, and white blood cell numbers), plasma homocysteine, nephrotoxicity, hepatotoxicity, and splenic 2'-deoxyuridine 5'-triphosphate/2'-deoxythymidine 5'-triphosphate ratios. MTHFR-overexpressing transgenic mice (MTHFR-Tg) were generated, metabolites and folate distributions were measured, and response to MTX was assessed.


RESULTS
MTX-treated Mthfr and Mthfr mice displayed hyperhomocysteinemia and decreased hematocrit, hemoglobin, and red blood cell numbers compared with wild-type animals. Mthfr mice also showed increased nephrotoxicity and hepatotoxicity. MTHFR-Tg mice were generated and confirmed to have increased levels of MTHFR with altered distributions of folate and thiols in a tissue-specific manner. After MTX treatment, MTHFR-Tg mice exhibited the same decreases in hematological parameters as Mthfr-deficient mice, and significantly decreased thymidine synthesis (higher 2'-deoxyuridine 5'-triphosphate/2'-deoxythymidine 5'-triphosphate ratios) compared with wild-type mice, but they were protected from MTX-induced hyperhomocysteinemia.


CONCLUSIONS
Underexpression and overexpression of Mthfr/MTHFR increase MTX-induced myelosuppression but have distinct effects on plasma homocysteine and nephrotoxicity. Pharmacogenetic analysis of polymorphisms in folate-dependent enzymes may be useful in optimization of MTX therapy.
Departments of Human Genetics and Pediatrics, McGill University Health Centre, Montreal Children's Hospital Research Institute, Montreal, Quebec, Canada.
Basak
B
Celtikci
Daniel
D
Leclerc
Andrea K
AK
Lawrance
Liyuan
L
Deng
Hana C
HC
Friedman
Natalia I
NI
Krupenko
Sergey A
SA
Krupenko
Stepan
S
Melnyk
S Jill
SJ
James
Alan C
AC
Peterson
Rima
R
Rozen
D000818:Animals; D002478:Cells, Cultured; D005260:Female; D015870:Gene Expression / Q000502:physiology; D006710:Homocysteine / Q000097:blood; D007165:Immunosuppression Therapy; D007166:Immunosuppressive Agents / Q000009:adverse effects / Q000494:pharmacology; D007674:Kidney Diseases / Q000139:chemically induced; D008297:Male; D008727:Methotrexate / Q000009:adverse effects / Q000494:pharmacology*; D042965:Methylenetetrahydrofolate Reductase (NADPH2) / Q000235:genetics*; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008954:Models, Biological; D020641:Polymorphism, Single Nucleotide
D007166:Immunosuppressive Agents; D006710:Homocysteine; D042965:Methylenetetrahydrofolate Reductase (NADPH2); D008727:Methotrexate