Two-dimensional HPLC coupled to ICP-MS and electrospray ionisation (ESI)-MS/MS for investigating the bioavailability in vitro of arsenic species from edible seaweed

Abstract

Edible seaweed consumption is a route of exposure to arsenic. However, little attention has been paid to estimate the bioaccessibility and/or bioavailability of arsenosugars in edible seaweed and their possible degradation products during gastrointestinal digestion. This work presents first use of combined inductively coupled plasma mass spectroscopy (ICP-MS) with electrospray ionization tandem mass spectrometry (ESI-MS/MS) with two-dimensional HPLC (size exclusion followed by anion exchange) to compare the qualitative and quantitative arsenosugars speciation of different edible seaweed with that of their bioavailable fraction as obtained using an in vitro gastrointestinal digestion procedure. Optimal extraction conditions for As species from four seaweed namely kombu, wakame, nori and sea lettuce were selected as a compromise between As extraction efficiency and preservation of compound identity. For most investigated samples, the use of ammonium acetate buffer as extractant and 1 h sonication in a water bath followed by HPLC-ICP-MS resulted in 40-61% of the total As to be found in the buffered aqueous extract, of which 86-110% was present as arsenosugars (glycerol sugar, phosphate sugar and sulfonate sugar for wakame and kombu and glycerol sugar and phosphate sugar for nori). The exception was sea lettuce, for which the arsenosugar fraction (glycerol sugar, phosphate sugar) only comprised 44% of the total extracted As. Interestingly, the ratio of arsenobetaine and dimethylarsinic acid to arsenosugars in sea lettuce extracts seemed higher than that for the rest of investigated samples. After in vitro gastrointestinal digestion, approximately 11-16% of the total As in the solid sample was found in the dialyzates with arsenosugars comprising 93-120% and 41% of the dialyzable As fraction for kombu, wakame, nori and sea lettuce, respectively. Moreover, the relative As species distribution in seaweed-buffered extracts and dialyzates was found to be very similar. Collection of specific fractions from the size-exclusion column to be analysed using anion-exchange HPLC-ESI-MS/MS enabled improved chromatographic selectivity, particularly for the less retained arsenosugar (glycerol sugar), facilitating confirmation of the presence of arsenosugars in seaweed extracts and dialyzates. Using this approach, the presence of arsenobetaine in sea lettuce samples was also confirmed.

Arsenic: bioaccessibility from seaweed and rice, dietary exposure calculations and risk assessment

“…The concentrations were comparable with concentrations found by some researchers but much lower compared with others (Laparra et al 2003;Wei et al 2003;Koch et al 2007;Rose et al 2007;Nakamura et al 2008;LlorenteMirandes et al 2011;Garcia-Sartal et al 2012;Oguri et al 2014). In the current study, not many seaweed products were investigated, but the products investigated were obtained from different shops throughout the Netherlands and were imported from regions in the world with high As levels.…”

Arsenic relative bioavailability from diet and airborne exposures: Implications for risk assessment

“…Williams et al (2009), Maulvault et al (2011), and Garcia-Sartal et al (2012 provided estimates of the bioaccessibility of total As, which do not support evaluation of iAs risks. Oguri et al, 2014 provided estimates of the amount of bioaccessible iAs consumed daily, which is of interest in estimating risks associated with dietary consumption of iAs.…”

“…Five studies were identified that examined As bioaccessibility in marine seafood and seaweed, and in freshwater crayfish using in vitro test systems (Leufroy et al, 2012;Williams et al, 2009;Maulvault et al, 2011;Garcia-Sartal et al, 2012;Oguri et al, 2014). Leufroy et al (2012) used a continuous leaching procedure adapted from Dufailly et al (2008) comprising saliva, gastric and intestinal phases to assess As bioaccessibility in 30 seafood samples consisting of mussel, scallop, shrimp, crab, periwinkle, saithe, salmon, smoked salmon, tuna and canned tuna.…”

“…As was not speciated in this study, so the fraction of iAs in the bioaccessible As is unknown. Garcia-Sartal et al (2012) used an in vitro system consisting of a gastric phase and an intestinal phase to assess As bioaccessibility in four edible seaweed samples (kombu, wakame, nori and sea lettuce). An analytical method comprising a two-dimensional HPLC coupled to ICP-MS and electrospray ionization encompassing capability was used to quantify arsenosugars.…”

Algae as nutritional and functional food sources: revisiting our understanding

“…By estimating As bioaccessibility through the human GI tract using modifications of methods developed by nutritionists for estimating Fe uptake, Garcia-Sartal et al (2012) concluded that only a fraction (7–15%) of the inorganic As and arsenosugars in cooked algae such as kombu, wakame, nori, and sea lettuce is bioaccessible. More research is needed to understand how different cooking processes, the particular algal food matrix, and the gut microbiome modify arsenosugar bioaccessibility and then better definition of the interaction of other As species produced in the body with cellular metabolites and macromolecules before their excretion (NRC 2013; Molin et al 2015; Carlin et al 2016).…”