PPARalpha agonists inhibit nitric oxide production by enhancing iNOS degradation in LPS-treated macrophages.
OBJECTIVE
Nitric oxide (NO) production through the inducible nitric oxide synthase (iNOS) pathway is increased in response to pro-inflammatory cytokines and bacterial products. In inflammation, NO has pro-inflammatory and regulatory effects. Peroxisome proliferator-activated receptors (PPARs), members of the nuclear steroid receptor superfamily, regulate not only metabolic but also inflammatory processes. The aim of the present study was to investigate the role of PPARalpha in the regulation of NO production and iNOS expression in activated macrophages.


METHODS
The effects of PPARalpha agonists were investigated on iNOS mRNA and protein expression, on NO production and on the activation of transcription factors NF-kappaB and STAT1 in J774 murine macrophages exposed to bacterial lipopolysaccharide (LPS).


RESULTS
PPARalpha agonists GW7647 and WY14643 reduced LPS-induced NO production in a dose-dependent manner as measured by the accumulation of nitrite into the culture medium. However, PPARalpha agonists did not alter LPS-induced iNOS mRNA expression or activation of NF-kappaB or STAT1 which are important transcription factors for iNOS. Nevertheless, iNOS protein levels were reduced by PPARalpha agonists in a time-dependent manner. The reduction was markedly greater after 24 h incubation than after 8 h incubation. Treatment with the proteasome inhibitors, lactacystin or MG132, reversed the decrease in iNOS protein levels caused by PPARalpha agonists.


CONCLUSIONS
The results suggest that PPARalpha agonists reduce LPS-induced iNOS expression and NO production in macrophages by enhancing iNOS protein degradation through the proteasome pathway. The results offer an additional mechanism underlying the anti-inflammatory effects of PPARalpha agonists.
Paukkeri
E-L
EL
The Immunopharmacology Research Group, Medical School, University of Tampere and Research Unit, Tampere University Hospital, Tampere, Finland.
Leppänen
T
T
Sareila
O
O
Vuolteenaho
K
K
Kankaanranta
H
H
Moilanen
E
E
D000111:Acetylcysteine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002087:Butyrates / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D007976:Leupeptins / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000037:antagonists & inhibitors / Q000494:pharmacology; D008264:Macrophages / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D051379:Mice; D016328:NF-kappa B / Q000187:drug effects / Q000378:metabolism; D009569:Nitric Oxide / Q000037:antagonists & inhibitors* / Q000096:biosynthesis; D052247:Nitric Oxide Synthase Type II / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D047493:PPAR alpha / Q000819:agonists* / Q000378:metabolism; D010671:Phenylurea Compounds / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D046988:Proteasome Endopeptidase Complex / Q000187:drug effects / Q000378:metabolism; D011743:Pyrimidines / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D012333:RNA, Messenger / Q000187:drug effects / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050794:STAT1 Transcription Factor / Q000187:drug effects / Q000378:metabolism
D002087:Butyrates; C453899:GW 7647; D007976:Leupeptins; D008070:Lipopolysaccharides; D016328:NF-kappa B; D047493:PPAR alpha; D010671:Phenylurea Compounds; D011743:Pyrimidines; D012333:RNA, Messenger; D050794:STAT1 Transcription Factor; C494080:Stat1 protein, mouse; C067713:lactacystin; D009569:Nitric Oxide; C006253:pirinixic acid; D052247:Nitric Oxide Synthase Type II; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde; D000111:Acetylcysteine