Toxicology Letters 215 (2012) 214–218 Contents lists available at SciVerse ScienceDirect Toxicology Letters jou rn al h om epa ge: www.elsevier.com/locate/toxlet Arsenic urinary speciation in Mthfr deficient mice injected with sodium arsenate Bogdan Wlodarczyk a,c,∗ , Ofer Spiegelstein a , Denise Hill a , X. Chris Le b , Richard H. Finnell a,c a Center for Environmental and Genetic Medicine, Institute of Biosciences and Technology, Texas A&M University System Health Science Center, Houston, TX 77030, USA b Department of Laboratory Medicine and Pathology, University of Alberta, Edmonton, Canada T6G 2G3 c Dell Pediatric Research Institute, College of Natural Sciences, University of Texas at Austin, 1400 Barbara Jordan Boulevard, Austin, TX 78723, USA h i g h l i g h t s I On control diet the Mthfr -/- mice excreted less arsenic than the Mthfr +/- and Mthfr +/+ . I No differences in arsenic excretion were observed in mice on folate deficient diet. I Homocysteine transsulfuration pathway can modulate arsenic toxicity. a r t i c l e i n f o Article history: Received 5 September 2012 Received in revised form 19 October 2012 Accepted 22 October 2012 Available online 30 October 2012 Keywords: Sodium arsenate Urinary arsenic species Mthfr knockout mouse Toxicokinetics a b s t r a c t In most mammalian species, arsenic biotransformation occurs primarily by biomethylation and reduction reactions, with dimethylarsinic acid being the predominant metabolite excreted in the urine. Methyle- netetrahydrofolate reductase (Mthfr) plays a key role in folate metabolism by channeling one-carbon units between nucleotide synthesis and methylation reactions. In the study on transgenic Mtfhr knock- out mice we investigated: (1) whether Mthfr is an important determinant in arsenic biotransformation by performing urinary arsenic speciation, and (2) whether dietary folate deficiency alters arsenic bio- transformation in these mice. The Mthfr mice fed folate replete or folate deficient diet were injected with sodium arsenate 1 mg/kg, and placed in metabolic cages for a urine collection. The urine was analyzed for arsenic species. Additionally, folate and homocysteine plasma level was analyzed in Mthfr mice. When fed a folate control diet, the Mthfr -/- mice excreted significantly less of the total arsenic in urine than did the Mthfr +/+ and Mthfr +/- mice. The Mthfr -/- had significantly lower levels of pentavalent arsenic in their urine than did the Mthfr +/+ mice. The wild type mice excreted significantly less pentavalent arsenic when they were fed folate deficient diet comparing to control diet. The current data suggest that both the Mthfr status and food folate level modulate in a significant manner excretion of arsenic in mice, following intraperitoneal administration of sodium arsenate. Published by Elsevier Ireland Ltd. 1. Introduction Methylenetetrahydrofolate reductase (MTHFR) is an enzyme that plays a key role in folate metabolism. It catalyzes the conversion of 5,10-methylenetetrahydrofolate (5-10-MTHF) to 5- methyltetrahydrofolate (5-MTHF), which is the principal methyl donor in the homocysteine to methionine remethylation cycle. Homocysteine can also be remethylated via alternative reactions driven by betaine:homocysteine methyltransferase (BHMT), where betaine is the methyl group donor (DiBello et al., 2010). Through regulating the usage of 5-10-MTHF, methyleneterahydrofolate ∗ Corresponding author at: Dell Pediatric Research Institute, College of Natural Sciences, University of Texas at Austin, 1400 Barbara Jordan Boulevard, Austin, TX 78723, USA. Tel.: +1 512 495 3002; fax: +1 512 495 4945. E-mail address: bwlodarczyk@austin.utexas.edu (B. Wlodarczyk). reductase also regulates supply of this substrate for nucleotide syn- thesis via thymidylate synthase (Schwahn & Rozen, 2001). Inorganic arsenic biotransformation in most mammalian species occurs mainly in the liver by the means of series of reduc- tion and biomethylation reactions (Carter et al., 2003). In order for the first step of the biomethylation reaction to occur, arse- nate (As V) must be reduced to arsenite (As III). As III serves as a substrate for a methyltransferase that generates monomethylar- sonate (MMA V) (Lin et al., 2002; Vahter & Concha, 2001). MMA V is then reduced to monomethylarsonous acid (MMA III), which is biomethylated to dimethylarsinic acid (DMAV), the major arsenic metabolite excreted in the urine (Vahter & Marafante, 1989; Vahter, 2002). The last step of arsenic biotransformation is the reduction of DMA V to dimethylarsinous acid DMA III (Chowdhury et al., 2006). Both biomethylation reactions that are catalyzed by methyl- transferases require S-adenosylmethionine (SAM), which serves as the methyl donor (Aposhian, 1997; Vahter and Envall, 1983). The metabolic process that generates SAM occurs primarily via 0378-4274/$ – see front matter. Published by Elsevier Ireland Ltd. http://dx.doi.org/10.1016/j.toxlet.2012.10.014