Identification of novel dual Peroxisome Proliferator-Activated Receptor alpha/gamma ligands and characterization of their biochemical properties by 3D structural studies

The Peroxisome Proliferator-Activated Receptors (PPARs) belong to the nuclear receptor superfamily and are involved in several physiological and pathological processes. Agonists of the {alpha} and {gamma} subtypes, such as fibrates and glitazones, are currently used to treat patients with metabolic disorders. Therefore, aim of this study was to find novel compounds able to activate both receptors. We analyzed two enantiomers, LT127 (enantiomer S) and LT160 (enantiomer R), in cell assay with Gal4-PPAR fusion proteins and show that the (R) form is a full agonist whereas the (S) form is a partial agonist of PPAR{gamma} . The two compounds are also potent full agonists of PPAR{alpha}. They induce the differentiation of 3T3-L1 murine fibroblasts into adipocytes and regulate the expression of PPAR target genes in adipose tissue and liver. To understand the molecular basis underlying the activity of these ligands, we crystallized the ligand binding domain (LBD) of PPAR{gamma} and by comparing the two crystal structures we show that the stabilization of helix 12 determines the partial agonist behavior of LT127. Moreover, the comparison of the PPAR{gamma} /LT127 structure with a data set of the same complex, collected after a different ligand soaking time, offers a dynamical view of the events provoked by the entrance of the partial agonist in the LBD. In conclusion, these results identify novel PPAR{alpha}/{gamma} dual agonists and show the structural basis of their activity on PPAR{gamma}