Piperine inhibits TNF-alpha induced adhesion of neutrophils to endothelial monolayer through suppression of NF-kappaB and IkappaB kinase activation.

Piperine displays antipyretic, analgesic, insecticidal and anti-inflammatory activities. It is the first amide to be isolated from Piper species. In the process of identifying non-steroidal anti-inflammatory small molecules from the natural sources, we demonstrate here that piperine inhibits adhesion of neutrophils to endothelial monolayer. The inhibition of neutrophils to endothelial monolayer by piperine is due to its ability to block the tumor necrosis factor-alpha (TNF-alpha) induced expression of cell adhesion molecules i.e. ICAM-1 (intercellular adhesion molecule-1), VCAM-1 (vascular cell adhesion molecule-1) and E-selectin as analyzed by cell-ELISA and confirmed by flow cytometry. Further, we demonstrate that inhibition of ICAM-1 by piperine is reversible. As nuclear factor-kappaB (NF-kappaB) is known to control the transcriptional regulation of cell adhesion molecules hence, we measured the effect of piperine on NF-kappaB in the cytoplasm and in the nucleus of endothelial cells. We observed that pretreatment of endothelial cells with piperine blocks the nuclear translocation and activation of NF-kappaB via blocking the phosphorylation and degradation of its inhibitory protein, IkappaBalpha. Piperine blocks the phosphorylation and degradation of IkappaBalpha by attenuating TNF-alpha induced IkappaB kinase activity. These results suggest a possible mechanism of anti-inflammatory activity of piperine. Therefore, piperine or its structural analogues could be used for the development of new anti-inflammatory molecules.