An investigation of the chemical stability of arsenosugars in simulated gastric juice and acidic environments using IC-ICP-MS and IC-ESI-MS/MS© US Government.

Abstract

A more quantitative extraction of arsenic-containing compounds from seafood matrices is essential in developing better dietary exposure estimates. More quantitative extraction often implies a more chemically aggressive set of extraction conditions. However, these conditions may result in undesirable chemical changes in the native arsenicals which may further complicate the toxicological risk assessment. This balance between quantitative extraction and species-specific integrity may be best addressed by using simulated gastric juice as an extraction solvent to mimic 'bioavailability'. This, conceptually, should extract the bioavailable fraction and induce any chemical changes that would occur because of ingestion. The most chemically labile species associated with seafood are thought to be the arsenosugars and for this reason their chemical stability is investigated in this study. Four arsenosugars (3-[5'-deoxy-5'-(dimethylarsinoyl)-beta-ribofuranosyloxy]-2-hydroxypropylene glycol, As(328); 3-[5'-deoxy-5'-(dimethylarsinoyl)-beta-ribofuranosyloxy]-2-hydroxypropanesulfonic acid, As(392); 3-[5'-deoxy-5'-(dimethylarsinoyl)-beta-ribofuranosyloxyl-2-hydroxypropyl hydrogen sulfate, As(408); and 3-[5'-deoxy-5'-(dimethylarsinoyl)-beta-ribofuranosyloxy]-2-hydroxypropyl-2,3-hydroxypropyl phosphate, As(482)) were isolated from seaweed extracts and subjected to simulated gastric juice and acidic conditions which mimic the stomach's pH of 1.1. Three acid solutions were used to test the chemical stability of the arsenosugars: simulated gastric juice, 78 mM nitric acid and 78 mM hydrochloric acid. The composition of the solutions was monitored over time (up to 48 h) using IC-ICP-MS for detection. The arsenosugars were found to degrade at the rate of 1.4% per h at 38 degrees C and 12.2% per h at 60 degrees C. The plots of percent conversion versus time were found to be independent of the starting arsenosugar and all had r2 values of greater than 0.97. A single common degradation product was observed in all the stability studies. A mass balance between the starting arsenosugar (As(392), As(408) and As(482)) and the degradation product was conducted with each set of experiments. This mass balance indicated that the degradation process did not produce any unchromatographable species. This degradation product was tentatively identified as As(254) as determined by ESI-MS/MS spectral data. An acid hydrolysis mechanism was proposed for the formation of As(254) from each of the native arsenosugars by hydrolysis at the C-1 carbon on the ribose ring.

Cyanobacteria produce arsenosugars

“…flagelliforme) powder was shown to contain an arsenosugar (oxo-arsenosugar-glycerol, Oxo-Gly), [26] this has not been demonstrated in isolated species [25] or axenic cultures of Nostoc. Although Yin et al [10] demonstrated As methylation by an arsM gene product in cyanobacteria including Synechocystis and Nostoc, they have not yet investigated arsenosugar production (because their aim was to check methylated species, only samples prepared by HNO 3 and microwave treatments, in which sugars might not be preserved, [28] were analysed). If it is substantiated that cyanobacteria have a mechanism to produce arsenosugars, their new role in the natural cycling of As in the environment as a source of arsenosugars will be elucidated.…”

Speciation Analysis of Arsenics in Commercial Hijiki by High Performance Liquid Chromatography-tandem-mass Spectrometry and High Performance Liquid Chromatography-inductively Coupled Plasma Mass Spectrometry

“…Gamble et al 32) reported that AsSug 408 and AsSug 482 were degraded to DMA via AsSug 328 in a basic environment. In acidic conditions, the formation of AsSug 254 26) and an increase in DMA with heating 33) were also reported. Both of our Boso hijiki products (#6 and #7) contained DMA at the concentration of 0.8 µg/kg dw hijiki, while the DMA levels in two raw hijiki samples (#8 and #9) were much lower (0.2 µg/kg dw hijiki), and these changes in DMA amount may be enhanced by heating.…”

“…The existence of AsSug 391 in Hijiki fusiforme was reported by Edmonds et al 10) Formation of AsSug 254 from AsSugs 328, 392, 408 and 482 in acidic environments has been reported. 26) Even though AsBe was recently detected in six kinds of marine algae, 27) its contamination from epifauna should be examined more carefully. Therefore, further study is necessary to confirm the existence of AsSug 254 and AsBe in hijiki seaweed.…”

Changes in proportions of arsenic species within an Ecklonia radiata food chain

“…[31] In the present study, Gly-riboside and PO 4 -riboside were the major arsenoribosides found in animal tissues (Tables A6 and A8). As the animals' digestive systems are mainly alkaline to neutral and not likely to experience low pH for long periods, degradation of arsenoribosides to OH-riboside, shown to occur slowly at low pH, [9,45] would probably not occur in these organisms.…”

“…[4,5] Thioarsenoribosides have also been found in molluscs. [6][7][8] At low pH (∼1), arsenoribosides degrade to 5-dimethylarsinoyl-α/β-ribofuranose (OH-riboside) [9] whereas at high pH (∼11), they are stable. [10] Anaerobic decomposition of arsenoribosides produces 2-dimethylarsinoyl ethanol (Me 2 As(O)-CH 2 -CH 2 OH; DMAE), [11] whereas aerobic decomposition produces OH-riboside, dimethylarsinate (DMA) and inorganic arsenic.…”