Toxicity and metabolism of arsenolipid mixtures

Because of the unique chemistry of arsenic, it occurs in nature in various forms that determine its toxicity. Inorganic arsenic is highly toxic to humans, found commonly in low amounts in non- contaminated drinking water and terrestrial food; whereas organic arsenic compounds are considered generally much less toxic, but occur in significantly larger quantities in seafood. Some of these organic arsenic compounds are lipid-soluble that are collectively referred to as arsenolipids. At the moment, the toxicity of arsenolipids is still not clear, but recent toxicity studies have shown that some individual arsenolipids were highly toxic in human cells and that they have the potential to cross the intestinal and blood-brain barrier. Therefore, further toxicity studies are urgently needed for a risk assessment of arsenolipids. Humans are unavoidable exposed to different arsenolipids in varying amounts when ingesting seafood. So far, toxicity studies of arsenolipids have been performed only with individual arsenolipid compounds. However, for a realistic risk assessment, the toxicological characterization of arsenolipids as an arsenolipid mixture, simulating the exposure of humans eating seafood, would need to be performed. Herein, the main aims of this research project include the study of the bioavailability and toxicity of arsenolipid mixtures, consisting of arsenic fatty acids, arsenic hydrocarbons and arsenosugar phospholipids, in human intestinal, human liver and human brain cells, and the identification and quantification of their metabolic products with sensitive analytical methods in these cell lines. Arsenolipid mixtures of arsenic fatty acids, arsenic hydrocarbons and arsenosugar phospholipids, consisting of various individual compounds, will be isolated from naturally occurring and commercially available lipid sources, such as krill or fish oils, used primarily as dietary supplements or animal feed, and edible algae, which are predominantly used in Asian cooking, according to scientifically published and established methods. Afterwards, individual and combined arsenolipid mixtures will be applied on human cells. The toxicity in the cells will be measured in all human cell cultures, genotoxicity will be assessed in liver cells and the bioavailability will be examined in intestinal cells. Arsenic metabolites and the arsenic content in the cells are examined at specific times during the bioavailability tests with sensitive analytical methods and techniques developed specifically for measurement of the total arsenal content and arsenic compounds. The main researchers for this project are Dr. Michael Stiboller (applicant), Prof. Dr. Tanja Schwerdtle from the University of Potsdam, Germany (foreign research institution) and Assoc. Prof. Dr. Georg Raber from the University of Graz, Austria (home research institution).

Arsenic occurs naturally in various chemical forms that determine its toxicity. Inorganic arsenic is highly toxic to humans, whereas organic arsenic compounds are considered generally much less toxic. Some of these organic arsenic compounds are fat-soluble that are collectively referred to as arsenolipids and occur predominantly in seafood. At the moment, the toxicity of arsenolipids is still not clear, but recent toxicity studies have shown that some individual arsenolipids were highly toxic in human cells and that they have the potential to cross physiological barriers like the blood-brain barrier. Therefore, further toxicity studies are urgently needed for a risk assessment of arsenolipids. Humans are unavoidable exposed to different arsenolipids in varying amounts when ingesting seafood. So far, toxicity studies of arsenolipids have been performed only with individual arsenolipid compounds. In this research project, for a more realistic risk assessment, the toxicological characterization of arsenolipids as an arsenolipid mixture has been performed. To do so, novel procedures for the isolation and purification of arsenolipids from natural commercially available marine sources such as fish oil and edible algae have been developed to obtain highly pure mixtures of arsenic containing hydrocarbons, arsenic containing fatty acids and arsenosugar phospholipids, three common and human health relevant groups of arsenolipids found in various seafood like marine fish and algae. This natural product approach of obtaining arsenolipids in high purity provides an alternative and straightforward way to chemical synthesis. The toxicity of arsenolipid mixtures was investigated in human liver cells with well-established cytotoxicity methods. Bioavailability of arsenolipid mixtures, and the identification and quantification metabolic products were performed with sensitive analytical methods. Purified mixtures of arsenic hydrocarbons were highly bioavailable in human liver cells and showed a substantial toxicity in the low micro molar range. Arsenic hydrocarbons biotransformed to arsenic fatty acids and corresponding sulfur containing arsenic hydrocarbons. These results were in accordance with previous studies of single compounds of highly pure synthesized arsenic hydrocarbons. Arsenosugar phospholipids was applied for the first time in a human cell line. These compounds showed a strongly reduced cellular bioavailability in comparison to arsenic hydrocarbons. However, metabolic transformations could be observed in human liver cells. Thus, at the moment, a toxic potential of arsenosugar phospholipids cannot be excluded. In this project, it could be demonstrated that natural extracts of arsenolipids can be applied in human cells and are a viable option for future toxicity and metabolic studies. The developed purification strategies for environmental- and human health relevant arsenolipids and their successful application human cells will broaden and support innovative arsenolipid research and markedly contribute to an urgently needed risk assessment of arsenolipids, since a potential hazard for humans cannot be excluded.