BACKGROUND AND AIMS: Arsenic contamination remains a leading public health concern. Folic acid (FA) supplementation enhances one carbon metabolism (OCM) which facilitates arsenic metabolism and excretion. Here, we aimed to identify metabolomic profiles and OCM metabolites associated with arsenic exposure and explore changes attributed to arsenic changes induced by FA supplementation.

METHODS: The double-blind, randomized FACT trial included 610 arsenic-exposed Bangladeshi adults. Arsenic exposure was assessed by the concentrations of four blood arsenic species (bAs: arsenite [AsIII], arsenate [AsV], monomethyl- [MMA] and dimethy- arsenicals [DMA]), and arsenic metabolism was assessed by the relative distribution of three arsenic species in urine (%uInAsIII+V, %uMMA, %uDMA). Annotated- (n=723) and unannotated (n=41,375) metabolomic features were analyzed by high-resolution mass spectrometry.   OCM metabolites (n=11) were measured in plasma using LC-MS/MS. We conducted metabolomic-wide approach to examine metabolomic signatures associated with arsenic biomarkers and FA supplementation.

RESULTS: At baseline, prior to supplementation, cystathionine was positively associated with the concentrations of all bAs species, while S-adenosylmethionine, S-adenosylhomocysteine, cysteine, and methionine were negatively associated with %uInAs (FDR<0.05). Choline, betaine, and dimethylglycine were negatively associated with %uMMA and positively with %uDMA (FDR<0.05). Metabolomic profiling identified 8 unique metabolites and 812 metabolomic features (FDR<0.05) associated with bAs (mostly AsV), and 66 metabolites and 285 metabolomic features with %uAs (mostly %uInAs). Metabolic pathways enriched for bAs and %uAs were similar, highlighting phenylalanine, tyrosine and tryptophan biosynthesis. Finally, FA-induced %uInAs change was positively associated with four metabolites ([14-Me-15.0]-isopalmitic acid, 3-methylglutaconate, indole-3-aldehyde, and oxaloacetic acid), consistent across two FA doses, 3 of which share links to acetyl-CoA metabolism.

CONCLUSIONS: The identified OCM metabolites affirmed and expanded our understanding of arsenic biotransformation. Metabolites and metabolic features identified in association with arsenic exposure, methylation capacity and FA-induced %uInAs change may aid in the discovery of mechanisms underlying arsenic-induced health outcomes such as arsenical skin lesions and diabetes.