On the Transport of Vanadium in the Blood Serum.

The complexation of the VO2+ ion in several systems that can model the physiological conditions of its transport in blood serum was studied using electron paramagnetic resonance (EPR) spectroscopy. Particularly, the ternary systems formed by (i) VO2+ and two high-molecular-mass components of blood serum, human serum apo-transferrin (hTf) and human serum albumin (HSA); (ii) VO2+, hTf, and bL; and (iii) VO2+, HSA, and bL, where bL is one of the six most important low-molecular-mass bioligands of the blood serum (bL = lactate, citrate, oxalate, phosphate, glycine, or histidine), were examined. The results indicate that, in aqueous solution, transferrin is a stronger binder than albumin, and at the physiological ratio, most of the VO2+ ion is present as (VO)2hTf, and a small amount as (VO)2dHSA, the dinuclear species formed by albumin where the two metal ions are interacting and the spin state S is 1. Among the bL ligands, only lactate and citrate are able to bind VO2+ in the presence of transferrin or albumin, the others not interacting at all. Finally, the quaternary systems formed by (i) VO2+, hTf, HSA, and lactate and (ii) VO2+, hTf, HSA, and citrate were studied. In these cases, the results suggest that the predominant species is (VO)2hTf, followed by the mixed complexes VO2+-hTf-lactate or VO2+-hTf-citrate, whereas (VO)2dHSA and [(VO)2(citrH-1)2]4- are minor components at physiological pH. The conclusions of this study give new insights on how the VO2+ ion distributes among the blood serum components and is transported in the plasma toward the target sites in the organism.