Membrane transport of vanadium compounds and the interaction with the erythrocyte membrane

In the present work, the membrane transport and the biotransformation of vanadate, bis(maltolato)oxovanadium (VO(ma)(2)), and vanadyl acetylacetonate (VO(acac)(2)) were investigated to explore the relationship with their insulin-like activity. Cellular uptake kinetics were performed by ICP-AES and EPR. The uptake of VO(acac)(2) and VO(ma)(2) by human erythrocytes showed intracellular vanadium level higher than NaVO3 and the membrane transport of these two vanadyl complexes was presumed to be via the passive diffusion mechanism. A fraction of vanadyl was oxidized to anionic vanadium(V) species and also entered the cells by the anion channel. The stability of VO(acac)(2) and VO(ma)(2) to oxidation in human erythrocyte membrane vesicles was investigated using EPR. VO(ma)(2) was found to be more sensitive to oxidation than VO(acac)(2) in aqueous buffer solution. However, in the presence of membrane vesicles, the oxidation of VO(ma)(2) and VO(acac)(2) was retarded and the differences between them became insignificant. Thus, the lifetime of vanadium complexes might be prolonged in physiological fluids. The interaction with membranes appears to be important in the stabilization of vanadyl complexes. Meanwhile, structural changes of membrane proteins were also observed. The higher uptake of the vanadyl complexes and the observed changes of membrane proteins might attribute to their insulin-mimetic mechanisms and toxicities. (C) 2002 Elsevier Science B.V. All rights reserved.