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Differential Potencies of Naturally Occurring Regioisomers of Nitrolinoleic Acid in PPARγ Activation

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journal contribution
posted on 2009-01-20, 00:00 authored by Richard L. Alexander, Marcus W. Wright, Michael J. Gorczynski, Pamela K. Smitherman, Taro E. Akiyama, Harold B. Wood, Joel P. Berger, S. Bruce King, Charles S. Morrow
Previous studies demonstrated that the naturally occurring electrophile and PPARγ ligand, nitrolinoleic acid (NO2-LA), exists as a mixture of four regioisomers [Alexander, R. L., et al. (2006) Biochemistry 45, 7889−7896]. We hypothesized that these alternative isomers have distinct bioactivities; therefore, to determine if the regioisomers are quantitatively or qualitatively different with respect to PPARγ activation, NO2-LA was separated into three fractions which were identified by NMR (13-NO2-LA, 12-NO2-LA, and a mixture of 9- and 10-NO2-LA) and characterized for PPARγ interactions. A competition radioligand binding assay showed that all three NO2-LA fractions had similar binding affinities for PPARγ (IC50 = 0.41−0.60 μM) that were comparable to that of the pharmaceutical ligand, rosiglitazone (IC50 = 0.25 μM). However, when PPARγ-dependent transcription activation was examined, there were significant differences observed among the NO2-LA fractions. Each isomer behaved as a partial agonist in this reporter gene assay; however, the 12-NO2 derivative was the most potent with respect to maximum activation of PPARγ and an EC50 of 0.045 μM (compare with the rosiglitazone EC50 of 0.067 μM), while the 13-NO2 and 9- and 10-NO2 derivatives were considerably less effective with EC50 values of 0.41−0.62 μM. We conclude that the regioisomers of NO2-LA are not functionally equivalent. The 12-NO2 derivative appears to be the most potent in PPARγ-dependent transcription activation, whereas the weaker PPARγ agonists, 13-NO2 and 9- and 10-NO2, may be relatively more important in signaling via other, PPARγ-independent pathways in which this family of nitrolipid electrophiles is implicated.

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