Aminoacid-derivatised picolinato-oxidovanadium(IV) complexes: Characterisation, speciation and ex vivo insulin-mimetic potential

Esbak, Hossein and Enyedy, Éva Anna and Kiss, Tamás and Yoshikawa, Yutaka and Sakurai, Hiromu and Garribba, Eugenio and Rehder, Dieter (2009) Aminoacid-derivatised picolinato-oxidovanadium(IV) complexes: Characterisation, speciation and ex vivo insulin-mimetic potential. JOURNAL OF INORGANIC BIOCHEMISTRY, 103 (4). pp. 590-600. ISSN 0162-0134

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Abstract

The proligands PicMe-AaR (PicMe = methoxipicolyl-5-amide, where the amide substituent is an amino acid AaR = HisH, HisMe, IleH, IleMe, TrpH, TrpMe, HTyrEt, tBuTyrMe, HThrMe, tBuThrMe) and the complexes [VO(Pic-AaR)2] have been synthesised and characterised. A detailed EPR study of the VO2+/Pic-His systems in water revealed the predominance of the complex [VO(Pic-His)H2O] in the pH range 2–6, with tridentate coordination of Pic-His via the picolinate moiety and imidazole-Nδ. Speciation analyses of the binary systems VO2+/Pic-Aa (Aa = His, Ile, Trp) and the ternary systems VO2+/Pic-Aa/B (Aa = His, Ile; B = citrate (cit), lactate (lac), phosphate) showed a predominance of the ternary complexes [VO(Pic-Aa)(cit/lac)] and [VO(Pic-Aa)(cit/lac)OH]− in the physiological pH regime. If, in addition, human serum albumin (HAS) and apotransferrin (Tf) are present, with all of the low and high molecular mass constituents in their blood serum concentrations, about two thirds of VO2+ is bound to the protein, while there is still a sizable amount of ternary complex [VO(Pic-Aa)(cit/lac)] present (about 1/4 for Pic-His and 1/3 for Pic-Ile) when the vanadium(IV) concentration is relatively high; at lower concentrations Tf is the predominant binder. Insulin-mimetic studies for VO2+/Pic-Aa (Aa = His, Ile, Tyr and Trp), based on a lipolysis assay with rat adipocytes, provided IC50 values of 0.41(1) for VO2+/Pic-His and VO2+/Pic-Ile, which compares with 0.87(17) for VOSO4.

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