Structural Origins of the Insulin-mimetic Activity of Bis(acetylacetonato)oxovanadium(IV)

Marvin W Makinen,Matthew J Brady

doi:10.1074/jbc.m110798200

Marvin W Makinen, Matthew J Brady

Open Access

https://doi.org/10.1074/jbc.m110798200

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Journal: Journal of Biological Chemistry	Publication Date: Apr 1, 2002
Citations: 51	License type: cc-by

Affiliation: University of Chicago

Abstract

We have investigated the interaction of bis(acetylacetonato)oxovanadium(IV) (VO(acac)(2)) with bovine serum albumin (BSA) by EPR and angle-selected electron nuclear double resonance, correlating results with assays of glucose uptake by 3T3-L1 adipocytes. EPR spectra of VO(acac)(2) showed no broadening in the presence of BSA; however, electron nuclear double resonance titrations of VO(acac)(2) in the presence of BSA were indicative of adduct formation of VO(acac)(2) with albumin of 1:1 stoichiometry. The influence of VO(acac)(2) on uptake of 2-deoxy-d-[1-(14)C]glucose by serum-starved 3T3-L1 adipocytes was measured in the presence and absence of BSA. Glucose uptake was stimulated 9-fold in the presence of 0.5 mm VO(acac)(2), 17-fold in the presence of 0.5 mm VO(acac)(2) plus 1 mm BSA, and 22-fold in the presence of 100 nm insulin. BSA had no influence on glucose uptake, on the action of insulin, or on glucose uptake in the presence of VOSO(4). The maximum insulin-mimetic effect of VO(acac)(2) was observed at VO(acac)(2):BSA ratios less than or equal to 1.0. Similar results were obtained also with bis(maltolato)oxovanadium(IV). These results suggest that the enhanced insulin-mimetic action of organic chelates of VO(2+) may be dependent on adduct formation with BSA and possibly other serum transport proteins.

Highlights

In the past several years the clinical potential of vanadium compounds in the treatment of type II diabetes has changed from low to high because of the introduction of an organic chelate of oxovanadium(IV) known as KP-102 into phase I trials [1]
We have investigated the interaction of bis(acetylacetonato)oxovanadium(IV) (VO(acac)2) with bovine serum albumin (BSA) by EPR and angle-selected electron nuclear double resonance, correlating results with assays of glucose uptake by 3T3-L1 adipocytes
Similar results were obtained with bis(maltolato)oxovanadium(IV). These results suggest that the enhanced insulin-mimetic action of organic chelates of VO2؉ may be dependent on adduct formation with BSA and possibly other serum transport proteins

Summary

EXPERIMENTAL PROCEDURES

Reagents—Vanadyl sulfate hydrate and bis(acetylacetonato)oxovanadium(IV) were purchased from Aldrich. After 5 min at room temperature, the assay was terminated by addition of 50 ␮l of 200 mM 2-deoxy-D-glucose and washing the cells three times with phosphate-buffered isotonic saline on ice. Adipocytes were collected in 0.5 ml of distilled water, and 2-deoxyglucose uptake was determined by liquid scintillation counting. Concentrated stock solutions of VOSO4 were prepared by dissolving vanadyl sulfate hydrate in a small volume of H2O under a nitrogen atmosphere, and aliquots were added to a solution of BSA in buffered isotonic saline to result in 1 mM final concentration of each. This solution was used for suspension of adipocytes for glucose uptake measurements. EPR spectra were simulated with use of the program WINEPR2.11 (Bruker Instruments, Inc., Bellerica, MA) as described previously [27]

RESULTS AND DISCUSSION

AЌ go

KRBH ϩ BSA