Inorganic and methylated thioarsenates pass the gastrointestinal barrier

Arsenic forms different species that are toxic for humans. Toxicity to internal organs is, however, only relevant if the respective species passes the gastrointestinal barrier. Thioarsenates were known to be produced by gut microbiota and to be toxic to bladder and liver cells, but their intestinal transport was largely unknown. Using a Caco-2 cell model, we show here that dimethylmonothioarsenate has the highest cellular retention and intestinal transport of all methylated species. Mono- and trithioarsenate show little cellular retention like arsenate, but their intestinal transport is much higher than that of arsenate; for trithioarsenate, it is almost as high as that for arsenite. The transport of all thioarsenates increases in the absence of phosphate. With the present study, we link previous reports of thioarsenate formation and toxicity by proving their bioavailability and confirm the relevance of their consideration in As risk assessments.