Mojtaba S. Taleshi

Arsenic-Containing Lipids Are Natural Constituents of Sashimi Tuna

Arsenic occurs naturally in many types of seafood as water- and fat-soluble organoarsenic compounds. Although water-soluble compounds have been well characterized, the fat-soluble compounds, so-called arsenolipids, have until recently remained unknown. We report that sashimi-grade tuna fish, with a total arsenic content of 5.9 microg of As/g dry mass, contains approximately equal quantities of water- and fat-soluble arsenic. The water-soluble arsenic comprised predominantly arsenobetaine (>95%) with a trace of dimethylarsinate. Two fat-soluble compounds, which together accounted for about 40% of the lipid-arsenic, were isolated and characterized. The first was identified as 1-dimethylarsinoylpentadecane [(CH(3))(2)As(O)(CH(2))(14)CH(3)] by comparison of HPLC/mass spectrometric data and accurate mass data with those of an authenticated synthesized standard. The second arsenolipid was postulated as 1-dimethylarsinoyl all-cis-4,7,10,13,16,19-docosahexane from mass spectrometric data and analogy with non-arsenic-containing lipids found in fish. The remaining fat-soluble arsenic consisted of less polar arsenolipids of currently unknown structure. This is the first identification of arsenolipids in commonly consumed seafood.

In vitro toxicological characterization of two arsenosugars and their metabolites

Scope In their recently published Scientific Opinion on Arsenic in Food, the European Food Safety Authority concluded that a risk assessment for arsenosugars is currently not possible, largely because of the lack of relevant toxicological data. To address this issue, we carried out a toxicological in vitro characterization of two arsenosugars and six arsenosugar metabolites. Methods and results The highly pure synthesized arsenosugars, DMAV-sugar-glycerol and DMAV-sugar-sulfate, investigated in this study, as well as four metabolites, oxo-dimethylarsenoacetic acid (oxo-DMAAV), oxo-dimethylarsenoethanol (oxo-DMAEV), thio-DMAAV and thio-DMAEV, exerted neither cytotoxicity nor genotoxicity up to 500 μM exposure in cultured human bladder cells. However, two arsenosugar metabolites, namely dimethyl-arsinic acid (DMAV) and thio-dimethylarsinic acid (thio-DMAV), were toxic to the cells; thio-DMAV was even slightly more cytotoxic than arsenite. Additionally, intestinal bioavailability of the arsenosugars was assessed applying the Caco-2 intestinal barrier model. The observed low, but significant transfer rates of the arsenosugars across the barrier model provide further evidence that arsenosugars are intestinally bioavailable. Conclusion In a cellular system that metabolizes arsenosugars, cellular toxicity likely arises. Thus, in strong contrast to arsenobetaine, arsenosugars cannot be categorized as nontoxic for humans and a risk to human health cannot be excluded.

Identification of arsenolipids with GC/MS

Arsenic-containing hydrocarbons have recently been reported as natural constituents of fish oil. We report a simple method for determining these compounds by GC/MS. Application of the methodology will delineate the distribution of these novel arsenic compounds in foods, and facilitate an assessment of the toxicological implications.

Synthesis and Characterization of Arsenolipids: Naturally Occurring Arsenic Compounds in Fish and Algae

Arsenic-containing lipids (arsenolipids) are natural products present in fish and algae. Because these compounds occur in foods, there is considerable interest in their human toxicology. We report the synthesis and characterization of seven arsenic-containing lipids, including six natural products. The compounds comprise dimethylarsinyl groups attached to saturated long-chain hydrocarbons (three compounds), saturated long-chain fatty acids (two compounds), and monounsaturated long chain fatty acids (two compounds). The arsenic group was introduced through sodium dimethylarsenide or bis(dimethylarsenic) oxide. The latter route provided higher and more reproducible yields, and consequently, this pathway was followed to synthesize six of the seven compounds. Mass spectral properties are described to assist in the identification of these compounds in natural samples. The pure synthesized arsenolipids will be used for in vitro experiments with human cells to test their uptake, biotransformation, and possible toxic effects.

In vitro intestinal bioavailability of arsenosugar metabolites and presystemic metabolism of thio-dimethylarsinic acid in Caco-2 cells

Two arsenosugar metabolites show in vitro intestinal bioavailability similar to that of arsenite, and much higher than that of arsenosugars.

In vitro toxicological characterisation of arsenic-containing fatty acids and three of their metabolites.

Arsenic-containing fatty acids are bioavailable and toxic to human liver cells in culture.

Arsenolipids in oil from blue whiting Micromesistius poutassou – evidence for arsenic-containing esters

Arsenic-containing lipids in the oil from the blue whiting fish (Micromesistius poutassou) were separated into three broad polarity groups and investigated by HPLC and mass spectrometry. A total of 11 arsenolipids including 4 new compounds were identified. The polar lipid fraction constituting 24% of the total arsenolipid content (which totalled 2.16 μg As/g) contained four known dimethylarsinoyl fatty acids and three known dimethylarsinoyl hydrocarbons. The less polar fraction (ca 30% of the total arsenolipids) contained four new dimethylarsinoyl hydrocarbons with chain lengths 22–30 carbons, in addition to more complex arsenicals that hydrolysed to known dimethylarsinoyl fatty acids suggesting they were conjugated carboxylic acids, presumably esters. The rest of the lipid-soluble arsenic (ca 45% of the total) remained in the non-polar fraction together with the bulk of the fish oil lipids, a complex mixture of compounds that precluded identification of the small amounts of arsenolipids.

A method for screening arsenolipids in fish oils by HPLC-ICPMS

We present a method for screening lipid-soluble arsenic compounds (arsenolipids) in fish oils by reversed-phase HPLC-ICPMS using a gradient elution with ethanol and acetate buffer at pH 6. Two different approaches were tested to reduce changes in arsenic response due to the carbon effect: addition of a supplementary methanol solution directly to the spray chamber or addition of methanol post-column through a T-piece. The latter method proved to be the best option for maintaining constant response for several arsenolipids covering a wide range of polarities. With the optimized method it is possible to perform a screening of at least three groups of arsenolipids with different polarities in 90 min with detection limits ranging from 5 to 11 μg As L−1, depending on the analyzed compound. The method was applied to the screening of arsenolipids in fractions obtained from cod liver oil and capelin oil, which include arsenic-containing fatty acids, arsenic-containing hydrocarbons and another group of lower polarity and unknown character.

Arsenic-containing hydrocarbons and arsenic-containing fatty acids: Transfer across and presystemic metabolism in the Caco-2 intestinal barrier model.

SCOPE Arsenic-containing hydrocarbons (AsHCs) and arsenic-containing fatty acids (AsFAs) represent two classes of arsenolipids occurring naturally in marine food. Toxicological data are yet scarce and an assessment regarding the risk to human health has not been possible. Here, we investigated the transfer and presystemic metabolism of five arsenolipids in an intestinal barrier model. METHODS AND RESULTS Three AsHCs and two AsFAs were applied to the Caco-2 intestinal barrier model. Thereby, the short-chain AsHCs reached up to 50% permeability. Transport is likely to occur via passive diffusion. The AsFAs showed lower intestinal bioavailability, but respective permeabilities were still two to five times higher as compared to arsenobetaine or arsenosugars. Interestingly, AsFAs were effectively biotransformed while passing the in vitro intestinal barrier, whereas AsHCs were transported to the blood-facing compartment essentially unchanged. CONCLUSION AsFAs can be presystemically metabolised and the amount of transferred arsenic is lower than that for AsHCs. In contrast, AsHCs are likely to be highly intestinally bioavailable to humans. Since AsHCs exert strong toxicity in vitro and in vivo, toxicity studies with experimental animals as well as a human exposure assessment are needed to assess the risk to human health related to the presence of AsHCs in seafood.

Characterization of trace metals in source identification of tar balls deposited along the southern coast of the Caspian Sea

ABSTRACT The southern coast of the Caspian Sea, Iran, is frequently affected by tar balls deposition. Tar balls on the shores, as oil pollution warnings, attract a huge public concern and will have long-term impacts to the marine environment. The concentrations of seven metals (Ni, V, Co, Mn, Fe, Cr, and Cu) were studied in tar ball samples collected from five different locations and analyzed using ICP-OES. Co/Ni and V/Ni markers are fairly uniform in the tar balls, and it indicates that the tar balls are from an identical source. V/(V + Ni) ratios of the tar balls were compared with those of Kazakhstan and Azerbaijan crude oils. The results showed that the ratio measured in tar balls remained quite stable, at a value of approximately 0.57, which is comparable to the value of Kazakhstan crude oil, which was approximately 0.44. The data show that a remarkable difference exists in Azerbaijan crude oils, which varies between 0.03 and 0.18, and that of tar balls. It may be concluded that, based on the V/(V + Ni) ratios, the majority of the tar balls were probably formed from the Kazakhstan crude oil.