Arsenic Metabolites in Human Urine after Ingestion of an Arsenosugar

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Abstract
Background: Arsenic-containing carbohydrates (arsenosugars) are common constituents of marine algae, including those species used as human food. The toxicology of these compounds has not been fully evaluated. Methods: Arsenic metabolites in human urine were monitored over a 4-day period after ingestion of a synthetic specimen of arsenosugar. The metabolites were determined by HPLC-inductively coupled plasma mass spectrometry, and structural assignments were confirmed with liquid chromatography-electrospray ionization mass spectrometry. Results: Approximately 80% of the total ingested arsenic was excreted in the urine during the 4 days of the experiment. There was a lag-period of ∼13 h before substantial quantities of arsenic appeared in the urine, and the excretion rate peaked between 22 and 31 h. At least 12 arsenic metabolites were detected, only 3 of which could be positively identified. Dimethylarsinate (DMA) was the major metabolite, constituting 67% of the total arsenicals excreted. A new urinary arsenic metabolite, dimethylarsinoylethanol, represented 5% of the total arsenicals, whereas trimethylarsine oxide was present as a trace (0.5%) constituent. One other significant metabolite cochromatographed with a reduced DMA standard, and hence was possibly dimethylarsinous acid. The second most abundant metabolite in the urine (20% of the total arsenic) remained unidentified, whereas the rest of the excreted arsenic was made up of several trace metabolites and small amounts of unchanged arsenosugar. Conclusions: Arsenosugars are biotransformed by humans to at least 12 arsenic metabolites, the toxicologies of which are currently unknown.