Ethacrynic acid and its glutathione conjugate as inhibitors of glutathioneS-transferases

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Abstract
1. The diuretic drug ethacrynic acid (EA) is a potent reversible inhibitor of rat and human glutathione S-transferases (GST), with I50-values (πm) of 4.6–6.0, 0.3–1.9 and 3.3–4.8 π, π and π-class, respectively. 2. The reversible inhibition by the glutathione conjugate of EA is even stronger for π and π-class, with I50-values (πm) of 0.8–2.8 and I50 for the π-class is 11. 3. Inhibition of rat and human π-class GST also occurs by covalent binding of ethacrynic acid. 14C-ethacrynic acid, 0.8nmol EA per nmol π-class GST could be incorporated, resulting in 65-93% inhibition of the catalytic activity. 4. Owing to the chemical nature of the covalent binding (Michael addition), this reaction should be reversible. Indeed, full restoration of the catalytic activity of GST P1-1 inactivated by covalently-bound EA was reached in about 125 h by incubation with an excess of glutathione. 5. EA has been used to inhibit GST in biological systems. The reversible covalent binding may very well play a role in the observed inhibition of GST by EA in vivo.