Selective inhibition of COX-2 by a standardized CO2 extract Humulus lupulus in vitro and its activity in a mouse model of Zymosan-induced arthritis

Abstract A standardized CO 2 extract from HUMULUS LUPULUS L. (hop extract) was investigated for its selective COX-1/2 inhibitory properties. An IN VITRO model of inflammation using lipopolysaccharide (LPS)-stimulated human peripheral blood mononuclear cells (PBMC) was used as a model to investigate the effect of hop extract on PGE 2 production. COX-1/2 selective inhibition by the hop extract was investigated in a COX-1 whole blood assay (WBA) and a COX-2 WBA. To evaluate the IN VIVO activity of hop extract, it was administered orally to C57BL/6 mice in which inflammation of the right joint was induced by injecting zymosan intra-articularly. EX VIVO PGE 2 production of LPS-stimulated blood cells was determined. Also, the effect of hop extract on healthy and arthritic cartilage was investigated as well as effects on inflammatory joint swelling. Hop extract inhibited PGE 2 production by LPS-stimulated PBMC without compromising the metabolic activity of these cells. Furthermore, hop extract showed a decline in PGE 2 production in the COX-2 whole blood assay (WBA) with an IC 50 of 20.4 μg/mL, while in the COX-1 WBA no inhibition of PGE 2 production was observed. This indicates a COX-2 selective inhibition. The COX-1 inhibitor SC-560 inhibited PGE 2 production in the COX-1 WBA but not in the COX-2 WBA. At 2 μM, celecoxib inhibited PGE 2 production in the COX-2 WBA by 92 % and in the COX-1 WBA by 50 %. When hop extract was administered orally to C57BL/6 mice in which joint inflammation was induced with zymosan, PGE 2 production in EX VIVO LPS-stimulated whole blood was significantly decreased by 24 %, suggesting that hop extract becomes bioavailable. Furthermore, oral administration of hop extract showed no negative or positive effects on healthy cartilage proteoglycan synthesis, or on zymosan-induced arthritic cartilage proteoglycan synthesis. However, no effect of oral administration of 1.25 mg hop extract daily was observed on joint swelling. In conclusion, this standardized CO 2 extract of HUMULUS LUPULUS could be a useful agent for intervention strategies targeting inflammatory disorders and/or inflammatory pain.