Lipid-soluble Arsenic Compounds Research Articles

Exposure to arsenolipids and inorganic arsenic from marine-sourced dietary supplements

Dietary supplements sourced from marine environments, such as fish oils and seaweed-based supplements, are widely consumed to boost nutrient intakes, including by vulnerable populations such as pregnant women. Like other marine foods, these supplements are also a potential source of exposure to arsenic, including the known toxic species, inorganic arsenic, and the cytotoxic, lipid-soluble arsenic compounds, arsenic hydrocarbons. A study of 32 marine-sourced supplements found higher total arsenic concentrations (>1000 ng g−1) in supplements made from seaweed, krill and calanus oil, and in fish and fish liver products marketed as “unprocessed”. Inorganic arsenic was only detectable in the seaweed samples, and was elevated (8900 ng g−1) in one product. Arsenic hydrocarbons were not detected in krill oil samples but were present at concentrations from 169 to 2048 ng g−1 in “unprocessed” fish and fish liver oil, and calanus oil. Survey data from the New Hampshire Birth Cohort Study (NHBCS) found 13.5% of pregnant women (n = 1997) reported taking fish oil supplements; and of those, most did so daily (75.6%, 6 or more times per week). Only a small percentage (9%) of those who reported consuming fish oil used products associated with higher arsenic levels. Higher urinary arsenic concentrations were found among women who consumed fish oil compared with those who did not, and specifically higher arsenobetaine and dimethyl arsenic concentrations. Dietary supplements are becoming common components of modern diets, and some marine-sourced dietary supplements are a source of inorganic arsenic and arsenic hydrocarbons.

A 2-O-Methylriboside Unknown Outside the RNA World Contains Arsenic.

Lipid-soluble arsenic compounds, also called arsenolipids, are ubiquitous marine natural products of currently unknown origin and function. In our search for clues about the possible biological roles of these compounds, we investigated arsenic metabolism in the unicellular green alga Dunaliella tertiolecta, and discovered an arsenolipid fundamentally different from all those previously identified; namely, a phytyl 5-dimethylarsinoyl-2-O-methyl-ribofuranoside. The discovery is of particular interest because 2-O-methylribosides have, until now, only been found in RNA. We briefly discuss the significance of the new lipid in biosynthesis and arsenic biogeochemical cycling.

Biosynthesis of arsenolipids by the cyanobacterium Synechocystis sp. PCC 6803

Environmental context Arsenic biotransformation processes play a key role in the cycling of arsenic in aquatic systems. We show that a freshwater cyanobacterium can convert inorganic arsenic into arsenolipids, and the conversion efficiency depends on the arsenic concentration. The role of these novel arsenic compounds remains to be elucidated. Abstract Although methylated arsenic and arsenosugars have been verified in various freshwater organisms, lipid-soluble arsenic compounds have not been identified. Here, we report investigations with the model organism cyanobacterium Synechocystis sp. PCC 6803 wild type and ΔarsM (arsenic(III) S-adenosylmethionine methyltransferase) mutant strain, which lacks the enzymes for arsenic methylation cultured in various concentrations of arsenate (AsV). Although Synechocystis accumulated higher arsenic concentrations at the higher exposure levels, the bioaccumulation factor decreased with increasing AsV. The accumulated arsenic in the cells was partitioned into water-soluble and lipid-soluble fractions; lipid-soluble arsenic was found in Synechocystis wild type cells (3–35% of the total depending on the level of arsenic exposure), but was not detected in Synechocystis ΔarsM mutant strain showing that ArsM was required for arsenolipid biosynthesis. The arsenolipids present in Synechocystis sp. PCC 6803 were analysed by high performance liquid chromatography–inductively coupled plasma–mass spectrometry, high performance liquid chromatography–electrospray mass spectrometry, and high resolution tandem mass spectrometry. The two major arsenolipids were characterised as arsenosugar phospholipids based on their assigned molecular formulas C47H88O14AsP and C47H90O14AsP, and tandem mass spectrometric data demonstrated the presence of the phosphate arsenosugar and acylated glycerol groups.

The high diversity of arsenolipids in herring fillet (Clupea harengus)

Arsenolipids represent a relevant step in the biosynthesis of organoarsenicals from inorganic arsenic compounds. Their fate after human consumption is still uncertain.By means of a HPLC-ICP-MS/ESI-Q-TOF-MS method, 16 lipid soluble arsenic compounds, including seven formerly unknown organoarsenicals, have been identified in commercial herring fillet.The structural assignment was done by exact mass and high resolution MS/MS data. This is the first identification of arsenolipids in herring (Clupea harengus). They contribute with (3.6±0.2)mgkg−1 arsenic to 62.3% of the total arsenic content of (5.7±0.3)mg of arsenic per kg dry mass. Current studies indicate that a metabolization by humans to cancerous dimethylarsinic acid is very likely. The presented results are highly relevant as herring is a very popular food fish species in Europe. Moreover, the screening of different fish species revealed that arsenolipids are more widespread than previously assumed.

Comprehensive analysis of lipophilic arsenic species in a brown alga (Saccharina latissima).

Approaches for the unambiguous identification of lipophilic arsenic species in Saccharina latissima (sugar kelp) have been studied. Parallel use of high resolution ICPMS and electrospray ionization (ESI)-MS after separation revealed that Saccharina latissima contained three distinct classes of lipophilic As-species, a family of arsenic containing phospholipids (AsPL), all including As in the form of As-sugar-PO4, As-containing hydrocarbons (AsHC), and As-containing polyunsaturated fatty acids (AsFA). For detailed identification, the use of phospholipases, in particular phospholipase A2, was essential to define the fatty acid composition (determination of regioisomers) of the lipids without purification of the sample, while fragmentation of the molecules by MS(2) measurements alone did not supply this information. Some of the identified AsPL contained unsaturated fatty acids (C16:1, C18:1 to C18:3), but saturated fatty acids dominated the AsPL. The fatty acid bound to the position 2″ was predominantly C16:0. Complete lipid hydrolysis showed that this alga did not contain arsenic containing fatty acids (AsFA) bound to complex lipids. Our investigations indicate that in addition to RP-HPLC-ICPMS/ESI-MS a range of different derivatization methods should be used for the comprehensive identification of unknown lipid-soluble arsenic compounds.

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.

Phosphatidylarsenocholine, one of the major arsenolipids in marine organisms: Synthesis and metabolism in mice

Marine organisms contain arsenic at high levels, both in water-soluble and lipid-soluble forms. In contrast to the accumulated knowledge on water-soluble arsenic compounds, toxicological properties of lipid-soluble arsenic compounds (arsenolipids) have been little understood. Therefore, this study was aimed to clarify the metabolism of phosphatidylarsenocholine, one of the major arsenolipids so far identified in marine organisms. Phosphatidylarsenocholine (dipalmitoyl) was synthesized from phosphatidylcholine (dipalmitoyl) and arsenocholine by the transphosphatidylation reaction with phospholipase D and its synthesis was confirmed by LC/ESI-MS analysis. When phosphatidylarsenocholine was orally administered to mice at 45μg As/mouse, arsenic was excreted mainly in urine almost in parallel with the time elapsed. The excretion rate was considerably slow compared to the case of water-soluble arsenic compounds but more than 90% of the administered arsenic was excreted within 144h after administration. Analysis by LC/ESI-MS revealed that the major urinary metabolite was arsenobetaine, although small amounts of arsenocholine were detected in urine up to 72h. These results allowed us to conclude that phosphatidylarsenocholine is mostly absorbed from the gastrointestinal tract in mice, metabolized to arsenobetaine and slowly excreted mainly in urine.

Water-Soluble and Lipid-Soluble Arsenic Compounds in Japanese Flying Squid Todarodes pacificus

Water-soluble and lipid-soluble arsenic compounds in Japanese flying squid Todarodes pacificus were analyzed. Regardless of the tissues, the major water-soluble arsenic compound was identified as arsenobetaine by LC/ESI-MS analysis, as reported for a number of marine animals. Lipid-soluble arsenic compounds were found at relatively high levels in liver and testis. LC/ESI-MS analysis of water-soluble arsenic compounds released from liver phospholipids by either chemical hydrolysis or phospholipase D hydrolysis demonstrated that the major arsenolipids are dimethylarsinic acid (DMA)-containing glycerophospholipid (phosphatidyldimethylarsinic acid) and DMA-containing sphingomyelin where the choline moiety of sphingomyelin is replaced by DMA. This is the first work to report the presence of DMA-containing phospholipids in marine invertebrates.

Determination of Arsenic Species in Fish Oil After Acid Digestion

Arsenic speciation is of increasing interest to the food industry, as concerns about high total arsenic concentrations in food can often be alleviated to a great extent if the ratio of toxic, less toxic and non-toxic arsenic compounds in the sample is known. The lipid matrix of fish oil is a challenge in the determination of arsenic species, as current methods for this type of analysis require the analyte to be water-soluble. In this study, two sample preparation techniques were applied. One the one hand water-soluble species were extracted with methanol/water, on the other, acid digestion was applied to release lipid-soluble arsenic compounds into the aqueous phase. Ion chromatography – inductively coupled plasma mass spectrometry (IC-ICP-MS) was used for separation and sensitive element-specific detection of arsenic compounds. Additional experiments, including alkaline hydrolysis, were carried out to find out more about the type of lipids arsenic is bound to in fish oil. Up to eight different arsenic species were detected and quantified in fish oil with dimethylarsinate being the major compound both in the aqueous extract and in the acid digest. No inorganic arsenic was detected in the aqueous extract, and the maximum concentration of arsenate determined in the acid digest was 0.05 µg g−1. The total arsenic concentration determined by ICP-MS ranged from <0.1 to 5 µg g−1. With regard to the mass balance, approximately 1% of the total arsenic content was extractable with methanol/water, whereas the sum of arsenic species quantified after acid digestion yielded 85–100% of the total arsenic content. It was confirmed that the large fraction of arsenic in fish oil not extractable on an aqueous basis consists of organoarsenic compounds. This new approach in sample preparation makes the complete characterization of the arsenic content in the sample possible with regard to the respective species, providing necessary information required for risk assessment.

Arsenocholine- and dimethylated arsenic- containing lipids in starspotted shark Mustelus manazo

We have investigated lipid-soluble arsenic compounds present in the tissues of a demersal shark, the starspotted shark Mustelus manazo. Arsenic compounds were extracted with chloroform–methanol from several tissues taken from each of five individuals, subjected to mild alkaline hydrolysis and fractionated into alkali-labile and alkali-stable fractions. Ordinary muscle, kidney and brain contained alkali-labile arsenic compounds; liver, stomach, heart and gall bladder contained alkali-stable compounds; and intestine, skin, dark muscle, spleen and bone contained both types of arsenic compounds. After further hydrolysis, the hydrolysates from ordinary muscle and liver were chromatographed with HPLC–ICP–MS. Arsenocholine was detected in the hydrolysates from the muscle, suggesting that arsenolecithins were present in the tissues. However, dimethyl-­arsinic acid was detected in the hydrolysates from the liver, suggesting the presence of di-­methylated arsenolipid in it. Copyright © 1999 John Wiley & Sons, Ltd.

Selenium and arsenic in biology: their chemical forms and biological functions.

Based on the recent development of analytical methods, sensitive systems for the analysis and speciation of selenium and arsenic have been established. A palladium addition technique was developed for the accurate determination of selenium in biological samples using graphite furnace atomic absorption analysis. For the speciation of the elements, combined methods of HPLC either with ICP-AES or with ICP-MS were found to work well. These systems were applied to the elucidation of the chemical form of the elements in natural samples. Some chemical properties of the selenium-mercury complex in dolphin liver were elucidated: i.e., it was a cationic, water-soluble, low molecular weight compound containing selenium and mercury in a 1:1 molar ratio, and was shown to be different from a known selenium-mercury complex, bis(methylmercuric)selenide. The major selenium compound excreted in human urine was revealed to be other than any of those previously identified (TMSe, selenate, and selenite). TMSe, a suspected major metabolite in urine, was found, if at all, in low levels. The major water-soluble, and lipid-soluble arsenic compounds in a brown seaweed, U. pinnatifida (WAKAME), were rigorously identified, and the results were compared with other data on marine algae and animals. The major organic arsenic compounds (termed "arseno-sugars") in marine algae commonly contain 5-deoxy-5-dimethylarsinyl-ribofuranoside moiety. There are various kinds of arseno-sugar derivatives containing different side-chains attached to the anomeric position of the sugar, and the distribution of each arsenic species seems to be related to algal species. The arseno-sugar (A-XI) is present in every alga so far examined, is metabolized to lipids, and possibly may play some specific role in the algal cells. On the other hand, the major arsenic compound in fish, crustacea and molluscs has been identified as arsenobetaine, which is an arseno-analog of glycinebetaine, a very common osmo-regulator in living organisms. Arsenobetaine is not detected in marine algae while arseno-sugars are not present in marine animals except for some molluscs which contain both compounds in considerable amounts. Arsenobetaine is present in the urine of human beings who have eaten foods derived from marine animals.

Chemical form of arsenic in marine macroalgae

AbstractChemical forms of water‐soluble and lipid soluble arsenic compounds in marine macroalgae, including edible algae, are reviewed. Major watersoluble arsenic compounds inalgae are arseniccontaining ribofuranosides (ACRs). Red and green algae contain mainly a glycerophospho derivative at the glycerol terminal while brown algae contain a sulfate or sulfonate derivatives at the glycerol terminal together with a glycerophospho derivative. Brown algae which belong to the Sargasso species contain significant amounts of inorganic arsenic in the form of arsenate. Lipid‐soluble arsenic identified in a brown algae (Undaria pinnatifida) was an acylated derivative of an ACR. Thirty‐eight marine algae were analyzed by HPLC/ICP/MS and their arsenic compounds are characterized. The characterization of arsenic compounds may show their role in the chemical taxonomy of algae species in addition to giving an understanding of the toxicological and geochemical implication of the element.