n-Propyl gallate suppresses lipopolysaccharide-induced inducible nitric oxide synthase activation through protein kinase Cδ-Mediated up regulation of heme oxygenase-1 in RAW264.7 macrophages

n-Propyl gallate is a synthetic phenolic antioxidant with potential anti-inflammatory effects. However, the underlying mechanism remains largely unknown. In the present study, we showed that n-propyl gallate increases the expression and activity of the heme oxygenase-1 (Ho-1), a stress-inducible protein with potent anti-inflammatory activity, in RAW264.7 macrophages. The inhibition of the HO-1 activity by treatment with zinc (II) protoporphyrin IX (ZnPP) or by knockdown of the HO-1 expression with small interference RNA significantly reversed the inhibitory effect of n-Propyl gallate on activations of nuclear factor-xB (NF-x13) and inducible nitric oxide synthase (iNOS) induced by lipopolysaccharide (LPS). An additional mechanism study using inhibitors of signaling kinases revealed the involvement of protein kinase CS (PKC delta) in the expression of HO-1 induced by n-Propyl gallate. Consistent with these results, n-Propyl gallate increased the intracellular levels of phosphorylated PKC delta in concentration-and time-dependent manners. The inhibitory effects of nPropyl gallate on LPS-induced iNOS expression and nitric oxide production were also significantly attenuated by pretreatment with the PUS inhibitor, rottlerin, or by transfection with PKC delta (K376R), a kinase-inactive form of PKC delta. Taken together, these findings provide the first evidence that n-Propyl gallate exerts its antiinflammatory effect through PKC delta-mediated up-regulation of HO-1 in macrophages.