Arsonoliposome interaction with thiols: effect of pegylation and arsonolipid content of arsonoliposomes on their integrity during incubation in glutathione.

Increased toxicity of arsonoliposomes towards cancer cells may be attributed to interaction between arsonolipids and cellular thiols which, would result in reduction of As(V) to the more toxic As(Ill). Cancer cells with high thiol contents may thus be more sensitive to arsonoliposomes, providing that the arsonolipid molecules that are incorporated in the liposome membrane can interact with thiol-containing compounds. For examination of this possibility we investigate the effect of incubating various compositions of arsonoliposomes with glutathione, on their integrity. If glutathione does interact with the As(V) of the arsonolipid headgroup, this should result in an alteration of the arsonoliposome membrane stability. We followed arsonoliposome integrity by measuring the release of vesicle-encapsulated calcein from arsonoliposomes with different lipid compositions, during incubation in glutathione. The results of this study show that the effect of glutathione on arsonoliposome integrity is higher (arsonoliposomes are less stable) when the arsonolipid content of their membranes increases. This indicates that arsonolipid molecules interact with glutathione, and in some cases, depending on the rigidity of their membranes; this interaction leads to a (higher or lower) destabilization of arsonoliposomes. The destabilizing effect of glutathione was higher for arsonoliposomes that were previously found to be less stable during incubation in serum proteins or, in other words, have lower membrane rigidity. In the case of pegylated-arsonoliposomes membrane destabilization was minimal and this may be related to the high stability demonstrated previously for these specific arsonoliposomes, or, it may indicate that pegylation results in prevention (total or partial) of arsonolipid-As interaction with thiols (perhaps because of steric repulsion).