Arsenic compounds marine animals

Arsenobetaine was the first arsenic compound identified in a marine animal when it was isolated in 1977 in a crystalline form from the tail muscle of the western rock lobster Panulirus cygnus (48). The large body of work that followed established that arsenobetaine was by far the predominant form of arsenic in marine animals (Table VI). It occurs at all trophic levels, although there is a tendency for it to be present at higher concentrations (or at least constitute the greater percentage... 

Although arsenobetaine was first reported as the natural major arsenical in marine animals almost 30 years ago, there is still no clear biosynthetic scheme for this compound. An early proposal was that oxo-arsenosugars were the likely precursors based on several observations. First, oxo-arsenosugars are abundant in marine algae and they occur together with arsenobetaine in animals that feed on algae. Second, laboratory experiments simulating environmental conditions produced oxo-DMAE, which appealed as a possible intermediate in the formation of arsenobetaine... 

Acute toxicity decreases in the following order As(III) > As(V) > MAA > DMAA, suggesting that the acute toxicity of arsenic compounds diminishes with progressive methylation. Arsenobetaine [22], arsenocholine [23], trimethylarsine oxide [24], DMAA [24], MAA [24], and As(III) [22] have so far been fed to mice to estimate their toxicities, as summarized in TABLE 1. For arsenobetaine, the most ubiquitous arsenical in marine animals, an acute LD50 cannot be obtained because arsenobetaine administered orally to mice at a dose of 10 g per kg of body weight did not cause any toxic symptoms. The other trimethylated compounds, arsenocholine and trimethylarsine oxide, are 200 to 300 times less toxic than arsenic trioxide. 

C. Marine Animals Toxicological Considerations Biotransformation of Marine Arsenic Compounds... 

The application of high-sensitivity ICP-MS detectors coupled to HPLC has enabled the detection of trace arsenic compounds present in marine animals. Thus, arsenocholine has been reported as a trace constituent (<0.1% of the total arsenic) in fish, molluscs, and crustaceans (37) and was found to be present in appreciable quantities (up to 15%) in some tissues of a marine turtle (110). Earlier reports (46,47) of appreciable concentrations of arsenocholine in some marine animals appear to have been in error (32). Phosphatidylarsenocholine 45 was identified as a trace constituent of lobster digestive gland following hydrolysis of the lipids and detection of GPAC in the hydrolysate by HPLC/ICP-MS analysis (70). It might result from the substitution of choline with arsenocholine in enzyme systems for the biogenesis of phosphatidylcholine (111). 

C. Rojima, T. Sakurai, M. Ochiai H. Rumata, W. Qu, M. P. Waalkes, R. Fujiwara, Cytotoxicological aspects of the organic arsenic compound arsenobetaine in marine animals, Appl. Organomet. Chem., 16 (2002), 421-426. 

Arsenobetaine, arsenosugars and arsenocholine are organoarsenicals less toxic for animals and humans than inorganic arsenic compounds, and have been found in certain marine organisms and in seafoods. They are excreted rapidly in urine (about 70% of the dose in 24h) . Natural arsenic is a pure one-isotope element ( As) and had to be labelled with radioactive arsenic for metabolic studies. As has been chosen as the most suitable isotope for tracer investigations. 

Arsenic compounds were determined in the marine lungworm Arenicola marina collected from Odensee Fjord, Denmark [159]. In contrast to most other marine animals, A. marina contained most water-soluble arsenic in inorganic forms, and arsenobetaine 54 was present as a minor constituent (6% only). Other arsenic compounds detected in A. marina were dimethylarsinate 47 (4%), tetramethylarsonium ion 53 (1.5%), arsenocholine 55 (<1%), and two arsenosugars (56, 57, 1% and 3%, respectively). A new arsenobetaine, i.e. trimethylarsoniopropionate (62), previously only reported in fish, was also present in trace amounts (<1%). 

Trimethylarsine oxide has been reported in several marine animals, where it is almost always a trace constituent. The one exception is the fish Kyphosus sydney-anus, which has trimethylarsine oxide as the major arsenical (25). That trimethylarsine oxide is not more widespread is perhaps surprising since it is likely to be a metabolite of the same pathway producing methylarsonate and dimethylarsinate, both of which are more commonly found. Trimethylarsine oxide chromatographs rather poorly on cation-exchange columns often used for determining arsenic species, and the resultant poor detection limits for this compound may partly explain the data indicating its apparent absence in many samples. Trimethylarsine oxide is usually only rarely reported in terrestrial organisms, but more recent work (with better detection limits) has shown it to be present in various terrestrial plants and two lichen samples (26). 

Although marine animals contain many arsenic compounds, most species contain arsenobetaine as the major arsenical. Fish tend to have a simple pattern of arsenic compounds dominated by arsenobetaine. The silver drummer Kyphosus sydney-anus, however, contains trimethylarsine oxide as its major arsenical (25). Crustaceans also generally contain arsenobetaine as a high percentage of their total arsenic. It should be noted, however, that most work on fish and crustaceans has examined the muscle tissue, and the pattern of compounds may be more complex in other tissues (88). 

Lipid arsenic compounds also occur in marine animals (34,110). The compounds originally present in the lipid fraction were subjected to base and/or acid hydrolysis, and the water-soluble products identified by HPLC-ICPMS. In this way, phosphatidylarsenocholine (see Fig. 2, compound 18) and a phosphatidyl-arsenosugar (see Fig. 2, compound 5) were identified in the digestive gland of lobster (34), and evidence was presented for the presence of lipids containing arsenocholine and dimethylated arsenic moieties in shark tissues (110). 

Of particular interest, however, is the presence of arsenobetaine as a major arsenical in many species of fungi (20). In addition, several fungal species contain arsenocholine and/or tetramethylarsonium ion, and Sparassis crispa contains arsenocholine as the major arsenical (20). These three arsenic compounds had traditionally been considered metabolites of marine animals before their discovery in fungi. 

Another frequently determined element is arsenic, and comparably harsh conditions have to be applied for acid digestion if total arsenic has to be determined. In occupational medicine, however, it is of particular interest to distinguish between the arsenic which originates from the exposure at the workplace, etc., and that which was ingested with marine animals. It was demonstrated that arsenic species relevant in occupational medicine are determined quantitatively in urine by HGAAS without an acid digestion [42]. Aromatic arsenic compounds, however, such as arsenobetaine, which are excreted after ingestion of marine animals, are not determined. 

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