Arsenic interactions with lipid particles containing iron.

While arsenic is toxic to all multicellular organisms, some organisms become tolerant by an unknown mechanism. We have recently uncovered an inducible tolerance mechanism in insects, which is based on a sequestration of toxins and pathogens by lipid particles. To examine whether arsenic interacts with lipid particles from mammals we compared binding of arsenic to lipid particles from insect and pig plasma after separation of lipid particles by low-density gradient centrifugation. Arsenic was found in both organisms in an area of the gradient, which corresponds to lipid-rich lipid particles. Since iron is known to affect arsenic toxicity in some organisms, we asked whether iron may be present in lipid particles. When low density cell (LDC) gradient fractions were analysed for the presence of iron we detected a peak in very low-density fractions similar to those that carried arsenic. This could indicate that arsenic interacts with lipid particles that contain iron and, if arsenic is removed from the plasma by lipid particles, that would also reduce iron-containing lipid particles at the time of arsenic emergence in the plasma. To test this assumption we measured the iron content in plasma at various time periods after the toxin ingestion. This time course revealed that iron is depleted in plasma fractions when arsenic shows a peak. Our data suggest that arsenic interacts with invertebrate and vertebrate lipid particles that are associated with proteins that may lead to detoxification by cell-free or cellular sequestration mechanisms.