Differential potencies of naturally occurring regioisomers of nitrolinoleic acid in PPARgamma activation.
Previous studies demonstrated that the naturally occurring electrophile and PPARgamma ligand, nitrolinoleic acid (NO(2)-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 PPARgamma activation, NO(2)-LA was separated into three fractions which were identified by NMR (13-NO(2)-LA, 12-NO(2)-LA, and a mixture of 9- and 10-NO(2)-LA) and characterized for PPARgamma interactions. A competition radioligand binding assay showed that all three NO(2)-LA fractions had similar binding affinities for PPARgamma (IC(50) = 0.41-0.60 microM) that were comparable to that of the pharmaceutical ligand, rosiglitazone (IC(50) = 0.25 microM). However, when PPARgamma-dependent transcription activation was examined, there were significant differences observed among the NO(2)-LA fractions. Each isomer behaved as a partial agonist in this reporter gene assay; however, the 12-NO(2) derivative was the most potent with respect to maximum activation of PPARgamma and an EC(50) of 0.045 microM (compare with the rosiglitazone EC(50) of 0.067 microM), while the 13-NO(2) and 9- and 10-NO(2) derivatives were considerably less effective with EC(50) values of 0.41-0.62 microM. We conclude that the regioisomers of NO(2)-LA are not functionally equivalent. The 12-NO(2) derivative appears to be the most potent in PPARgamma-dependent transcription activation, whereas the weaker PPARgamma agonists, 13-NO(2) and 9- and 10-NO(2), may be relatively more important in signaling via other, PPARgamma-independent pathways in which this family of nitrolipid electrophiles is implicated.
Alexander
Richard L
RL
Department of Biochemistry, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27101, USA.
Wright
Marcus W
MW
Gorczynski
Michael J
MJ
Smitherman
Pamela K
PK
Akiyama
Taro E
TE
Wood
Harold B
HB
Berger
Joel P
JP
King
S Bruce
SB
Morrow
Charles S
CS
D001667:Binding, Competitive; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D002999:Clone Cells; D004305:Dose-Response Relationship, Drug; D005260:Female; D017930:Genes, Reporter; D006801:Humans; D020128:Inhibitory Concentration 50; D008041:Linoleic Acids / Q000737:chemistry / Q000494:pharmacology*; D008156:Luciferases / Q000378:metabolism; D009574:Nitro Compounds / Q000737:chemistry / Q000494:pharmacology*; D019906:Nuclear Magnetic Resonance, Biomolecular; D047495:PPAR gamma / Q000819:agonists / Q000235:genetics / Q000378:metabolism*; D011869:Radioligand Assay; D000077154:Rosiglitazone; D013237:Stereoisomerism; D045162:Thiazolidinediones / Q000378:metabolism; D015533:Transcriptional Activation / Q000187:drug effects; D014161:Transduction, Genetic
C501855:10-nitro-9,12-octadecadienoic acid; D008041:Linoleic Acids; D009574:Nitro Compounds; D047495:PPAR gamma; D045162:Thiazolidinediones; D000077154:Rosiglitazone; D008156:Luciferases