The nitrated fatty acid, 10-nitrooleate inhibits the neutrophil chemotaxis via peroxisome proliferator-activated receptor gamma in CLP-induced sepsis in mice

Abstract

The inhibition of polymorphonuclear neutrophils' (PMNs) migration to the source of injury is among the most prominent aspects of immunosuppression following sepsis, although the precise mechanisms involved remain unclear and multifaceted. Increasing evidence connects this immunosuppression to nitric oxide (NO), as NO production is a classic feature of inflammation probably through neutrophil activation and migration. Nitrated fatty acids (NFA) such as 10-nitrooleate (OA-NO2), nitrolinoleic acid etc. produced endogenously by the non-enzymatic reaction of NO with unsaturated fatty acids, are found to be potent activators of the transcription factor, peroxisome proliferator-activated receptor gamma (PPARγ). Upregulation of PPARγ during immunosuppression and the subsequent inhibition of neutrophil migration in sepsis have been reported. However, the interplay of OA-NO2, NO and PPARγ in polymicrobial-induced immunosuppression has not been established. Hence to understand this, we have studied the role of OA-NO2 in blood PMNs migration, the effects of iNOS inhibitor on PMNs migration and PPARγ activity in cecal ligation and puncture (CLP)-induced sepsis in mice. We found increased expression of PPARγ and its DNA-binding activity in the lungs and blood PMNs from CLP mice. CLP or OA-NO2 treatment inhibited PMNs' migration in response to fMLP stimulation. Pharmacological inhibition of iNOS resulted in decreased PPARγ DNA-binding activity with a concomitant increase in the migration of PMNs to the site of infection. OA-NO2 treatment also inhibited the production of inflammatory cytokines (TNFα and IL-1β) secretion from PMNs stimulated with lipopolysaccharide. We have also established that, OA-NO2 mediated inhibition of PMNs migration in vivo and ex vivo are regulated through PPARγ-dependent pathway. This study further highlights the fact that the activation of PPARγ by the NFA has a pivotal role in PMNs' migration and immunosuppression.