Uptake and metabolic effects of insulin mimetic oxovanadium compounds in human erythrocytes.

The uptake of the oxidation products of two oxovanadium(IV) compounds, [N,N'-ethylenebis(pyridoxylaminato)]oxovanadium(IV), V(IV)O(Rpyr(2)en), and bis-[3-hydroxy-1,2-dimethyl-4-pyridinonato]oxovanadium(IV), V(IV)O(dmpp)(2), by human erythrocytes was studied using (51)V and (1)H NMR and EPR spectroscopy. V(IV)O(Rpyr(2)en) in aerobic aqueous solution is oxidized to its V(V) counterpart and the neutral form slowly enters the cells by passive diffusion. In aerobic conditions, V(IV)O(dmpp)(2) originates V(V) complexes of 1:1 and 1:2 stoichiometry. The neutral 1:1 species is taken up by erythrocytes through passive diffusion in a temperature-dependent process; its depletion from the extracellular medium promotes the dissociation of the negatively charged 1:2 species, and the protonation of the negatively charged 1:1 species. The identity of these complexes is not maintained inside the cells, and the intracellular EPR spectra suggest N(2)O(2) or NO(3) intracellular coordinating environments. The oxidative stress induced by the oxovanadium compounds in erythrocytes was not significant at 1mM concentration, but was increased by both vanadate and oxidized V(IV)O(dmpp)(2) at 5mM. Only 1mM oxidized V(IV)O(dmpp)(2) significantly stimulated erythrocytes glucose intake (0.75+/-0.13 against 0.37+/-0.17mM/h found for the control, p<0.05).