Inhibition of monoacylglycerol lipase by troglitazone, N-arachidonoyl dopamine and the irreversible inhibitor JZL184: comparison of two different assays

BACKGROUND AND PURPOSE Drugs used clinically usually have a primary mechanism of action, but additional effects on other biological targets can contribute to their effects. A potentially useful additional target is the endocannabinoid metabolizing enzyme monoacylglycerol lipase (MGL). We have screened a range of drugs for inhibition of MGL and compared the observed potencies using different MGL enzyme assays. EXPERIMENTAL APPROACH MGL activity was screened using recombinant human MGL (cell lysates and purified enzyme) with 4-nitrophenyl acetate (NPA) as substrate. 2-Oleolyglycerol metabolism by rat cerebellar cytosolic MGL and by recombinant MGL was also investigated. KEY RESULTS Among the 96 compounds screened in the NPA assay, troglitazone, CP55,940, N-arachidonoyl dopamine and AM404 inhibited NPA hydrolysis by the lysates with IC50 values of 1.1, 4.9, 0.78 and 3.1 mu M, respectively. The potency for troglitazone is in the same range as its primary pharmacological activity, activation of peroxisome proliferator-activated receptor (PPAR) gamma. Among PPAR gamma ligands, the potency order towards human MGL was troglitazone > ciglitazone > rosiglitazone > 15-deoxy-Delta(12,14)-prostaglandin J(2) approximate to CAY 10415 > CAY 10514. In contrast to the time-dependent inhibitor JZL184, the potency of troglitazone was dependent upon the enzyme assay system used. Thus, troglitazone inhibited rat cytosolic 2-oleoylglycerol hydrolysis less potently (IC50 41 mu M) than hydrolysis of NPA by the human MGL lysates. CONCLUSIONS AND IMPLICATIONS 'Hits' in screening programmes for MGL inhibitors should be assessed in different MGL assays. Troglitazone may be a useful lead for the design of novel, dual action MGL inhibitors/PPAR gamma activators.