Biospeciation of various antidiabetic VIVO compounds in serum

The interactions of various insulin mimetic oxovanadium(IV) compounds with serum proteins were studied in model systems and in ex vivo samples. For the modeling study, an earlier in situ method was extended and applied to the formation of ternary complexes of apotransferrin (apoTf)–VIVO–maltol (mal) and 1,2-dimethyl-3-hydroxy-4(1H)-pyridinone (dhp). Both systems were evaluated via simultaneous CD and EPR measurements. Determination of the formation constants of the ternary complexes allowed the calculation of more accurate stability constants for the VIVO–apoTf parent complexes and establishment of a better model for drug speciation in serum. It was found that dhp and the synergistic carbonate are non-competitive binders. Based on the stability constants obtained for VIVO–apoTf complexes and estimated for VIVO–HSA (= human serum albumin), modeling calculations were performed on the distribution of VIVO among the components of blood serum. The results were confirmed by HPLC-ICP-MS (liquid chromatography-inductively coupled plasma spectroscopy-mass spectrometry) measurements. The ex vivo interactions of the VIVO complexes formed with mal, picolinic acid (pic) and dhp with serum protein standards and also with human serum samples were evaluated. The proteins were firstly separated by (HPLC), and the V content of each fraction was determined by ICP-MS. All the studied VIVO compounds displayed similar chromatographic profiles, associated almost exclusively with apotransferrin as predicted by the modeling calculations. Under physiological conditions, the interactions with HSA of all of the species under study were negligible. Therefore Tf seems to be the main VIVO transporter in the serum under in vitro conditions, and this association is practically independent of the chemical form in which VIVO is administered.