Reduced infiltration and increased apoptosis of leukocytes at sites of inflammation by systemic administration of a membrane-permeable IκBα repressor

Objective. NF-kappaB activation is associated with several inflammatory disorders, including rheumatoid arthritis (RA), making this family of transcription factors a good target for the development of antiinflammatory treatments. Although inhibitors of the NF-kappaB pathway are currently available, their specificity has not been adequately determined. IkappaBalpha is a physiologic inhibitor of NF-kappaB and a potent repressor experimentally when expressed in a nondegradable form. We describe here a novel means for specifically regulating NF-kappaB activity in vivo by administering a chimeric molecule comprising the super-repressor IkappaBalpha (srIkappaBalpha) fused to the membrane-transducing domain of the human immunodeficiency virus Tat protein (Tat-srIkappaBalpha). Methods. The Wistar rat carrageenan-induced pleurisy model was used to assess the effects of in vivo administration of Tat-srIkappaBalpha on leukocyte infiltration and on cytokine and chemokine production. Results. Systemic administration of Tat-srIkappaBalpha diminished infiltration of leukocytes into the site of inflammation. Analysis of the recruited inflammatory cells confirmed uptake of the inhibitor and reduction of the NF-kappaB activity. These cells exhibited elevated caspase activity, suggesting that NF-kappaB is required for the survival of leukocytes at sites of inflammation. Analysis of exudates, while showing decreases in the production of the proinflammatory cytokines tumor necrosis factor a and interleukin-1beta, also revealed a significant increase in the production of the neutrophil chemoattractants cytokine-induced neutrophil chemoattractant 1 (CINC-1) and CINC-3 compared with controls. This result could reveal a previously unknown feedback mechanism in which infiltrating leukocytes may down-regulate local production of these chemokines. Conclusion. These results provide new insights into the etiology of inflammation and establish a strategy for developing novel therapeutics by regulating the signaling activity of pathways known to function in RA.