Pifithrin-α, a pharmacological inhibitor of p53, downregulates lipopolysaccharide-induced nitric oxide production via impairment of the MyD88-independent pathway.

The effect of pifithrin (PFT)-α, a pharmacological inhibitor of p53, on lipopolysaccharide (LPS)-induced nitric oxide (NO) production in RAW 264.7 macrophage-like cells was examined. PFT-α inhibited the production of NO but not tumor necrosis factor (TNF)-α in response to LPS. PFT-α inhibited LPS-induced NO production via reduced expression of an inducible NO synthase (iNOS). Moreover, PFT-α inhibited LPS-induced iNOS expression in p53-silenced cells. PFT-α inhibited the production of interferon (IFN)-β, characteristic of the MyD88-independent pathway of LPS signaling, whereas it did not affect the activation of nuclear factor (NF)-κB and mitogen-activated protein kinases in the MyD88-dependent pathway. PFT-α inhibited poly I:C-induced NO production whereas it did not inhibit IFN-β-induced NO production. Further, PFT-α reduced the expression of IFN regulatory factor 3 that leads to the IFN-β production in the MyD88-independent pathway. The most upstream event impaired by PFT-α was the reduced expression of TNF receptor-associated factor (TRAF) 3 in the MyD88-independent pathway. PFT-α also reduced the in vivo expression of iNOS in the livers of mice injected with LPS. Taken together, PFT-α was suggested to inhibit LPS-induced NO production via impairment of the MyD88-independent pathway and attenuated LPS-mediated inflammatory response.