I. Goldwaser et al., L-glutamic acid gamma-monohydroxamate - A potentiator of vanadium-evoked glucose metabolism in vitro and in vivo, J BIOL CHEM, 274(37), 1999, pp. 26617-26624
We report that the vanadium ligand L-Glu(gamma)HXM potentiates the capacity
of free vanadium ions to activate glucose uptake and glucose metabolism in
rat adipocytes in vitro (by 4-5-fold) and to lower blood glucose levels in
hyperglycemic rats in vivo (by 5-7-fold). A molar ratio of two L-Glu(gamma
)HXM molecules to one vanadium ion was most effective. Unlike other vanadiu
m ligands that potentiate the insulinomimetic actions of vanadium, L-Glu(ga
mma)HXM partially activated lipogenesis in rat adipocytes in the absence of
exogenous vanadium, This effect was not manifested by D-Glu(gamma)HMM, At
10-20 mu M L-Glu(gamma)HXM, lipogenesis was activated 9-21%, This effect wa
s approximately g-fold higher (140 +/- 15% of maximal insulin response) in
adipocytes derived from rats that had been treated with vanadium for severa
l days. Titration of vanadium(lV) with L-Glu(gamma)HXM led to a rapid decre
ase in the absorbance of vanadium(IV) at 765 nm, and V-51 NMR spectroscopy
revealed that the chemical shift of vanadium(IV) at -490 ppm disappeared wi
th the appearance of a signal characteristic to vanadium(V) (-530 ppm) upon
adding one equivalent of L-Glu(gamma)HXM. In summary, L-Glu(gamma)HXM is h
ighly active in potentiating vanadium-activated glucose metabolism in vitro
and in vivo and facilitating glucose metabolism in rat adipocytes in the a
bsence of exogenous vanadium probably through conversion of trace intracell
ular vanadium into an active insulinomimetic compound. We propose that the
active species is either a 1:1 or 2:1 L-Glu(gamma)HXM vanadium complex in w
hich the endogenous vanadium(IV) has been altered to vanadium(V), Finally w
e demonstrate that L-Glu(gamma)HXM- and L-Glu(gamma)HXM vanadium-evoked lip
ogenesis is arrested by wortmannin and that activation of glucose uptake in
rat adipocytes is because of enhanced translocation of GLUT4 from low dens
ity microsomes to the plasma membrane.