Procyanidin dimer B1 and trimer C1 impair inflammatory response signalling in human monocytes

The way specific procyanidins exert their anti-inflammatory effects is not fully understood. This study has investigated the capacity of different procyanidins to modulate lipopolysaccharide (LPS)-induced reactive oxygen species (ROS) production in THP1 human monocytes and their effects on the redox regulated protein kinases activity: IkB kinase beta (IKKb) and the extracellular signal-regulated kinase (ERK). LPS-triggered increase of ROS was prevented by cell pre-incubation with procyanidins. LPS induced ERK1/2 activation through phosphorylation, which was inhibited by all the compounds tested, the most active being epigallocatechin (EG), followed by epigallocatechin gallate (EGCG) and C1. Procyanidins inhibited IKKb activity in vitro. C1 and procyanidin extract (PE) exerted the maximal IKKb inhibition, followed by EGCG and dimer B1. Catechin exerted a slight but significant IKKb inhibition, in contrast to epicatechin, which was ineffective. In conclusion, procyanidins reduce the LPS-induced production of ROS and they exert their anti-inflammatory effects by inhibiting ERK1/2 and IKKb activity.