Synthesis, analysis and toxicological characterization of arsenolipids

Lipid-soluble arsenic compounds, so-called arsenolipids, are present in seafoods, where they can represent a significant source of dietary arsenic. There are several types of arsenolipids, the main ones comprising compounds containing arsenic bound to fatty acids, hydrocarbons or phospholipids More recent studies have indicated the presence also of arsenic-containing glycerides in fish. Because arsenic is a well-known toxic element, and arsenolipids occur in common marine foods, the toxicity of these compounds and their human health consequences are of high scientific and public health interest. In a recent joint project, the research groups from the University of Potsdam and the University of Graz produced alarming preliminary results from cytotoxicity tests showing that arsenic- containing hydrocarbons were as toxic as inorganic arsenic. To further assess risks to human health related to the presence of arsenolipids in food, this project will address five important aspects: (i) We will synthesize and characterize high quality standards of two arsenic-phospholipids and four arsenic- triglycerides; (ii) We will characterize the toxicological profile of these six newly synthesized arsenolipids in cultured human liver and brain-associated cells in comparison with arsenite and the arsenic-hydrocarbons; (iii)we will study the transfer of arsenic-hydrocarbons and the six newly synthesized arsenolipids across the blood-brain barrier and the blood-CSF barrier to assess brain bioavailability of the respective arsenolipids; (iv) We will study toxicity of the six newly synthesized arsenolipids in the nematode Caenorhabditis elegans, a model organism for the investigation of neural development in animals, in comparison with inorganic arsenic and arsenic-hydrocarbons; and (v) we will assess in mice the toxicokinetics of the arsenolipids via gavage. Collectively, the results from this research will clarify the toxic potential of arsenolipids naturally present in our foods, and provide a basis for future regulations concerning safe limits of these compounds in foods.

The human health consequences of arsenic in food has been the subject of increasing research interest over the last two decades, and led, in 2016, to the European Commission introducing regulations with strict limits on the allowable amount of toxic inorganic arsenic in certain foods. The situation with arsenolipids, however, was not addressed at that time, even though recent results had suggested that these arsenicals were often present in seafood, and preliminary tests with human cells had indicated that they could be cytotoxic. The current project investigated the distribution and significance of arsenolipids in our foods and, through both in vitro and in vivo studies explored their potential toxicity, particularly neurotoxicity, to humans, with the collective goal of providing sound data on which regulatory authorities could frame future realistic and safe guidelines for arsenic in foods. Thus, in the course of this joint project with our partners in Potsdam, we: (1) identified more than 20 new arsenolipids present in organisms including those used as seafoods, quantified the distribution of selected arsenolipids in foods in Japan (a high seafood-consuming country), and, based on a market basket survey, estimated daily intake of arsenolipids; (2) synthesised 10 new arsenolipids which served as pure standards for developing new analytical methods, and for use in toxicity studies by our project collaborators in Potsdam; (3) used in vitro experiments to show that arsenic hydrocarbons enhanced the permeability of a blood-brain barrier model and disturbed neuronal networks in human brain cells; (4) found in whole animal experiments that arsenic hydrocarbons reduced survival and development in the nematode Caenorhabditis elegans, whereas other arsenolipids were much less harmful; (5) in further whole animal experiments with mice exposed to an arsenic hydrocarbon, we demonstrated that this arsenolipid can cross the blood brain barrier and preferentially accumulates in the mammalian brain; and (6) in studies with nursing mothers on a fish-rich diet, we showed that arsenic hydrocarbons naturally present in the fish were readily transferred to the mothers' milk with a transfer efficiency 100-fold higher than that for arsenobetaine, a harmless, major water-soluble form of arsenic in fish. Collectively these studies have demonstrated the neurotoxic potential of arsenic hydrocarbons, naturally occurring arsenolipids commonly present in seafoods, and highlights the need to investigate their effects on the infant brain during crucial early developmental stages.