Background: This study investigated the inhibitory effect of berberine (BBR) on lipopolysaccharide (LPS) induced cyclooxygenase-2 (COX-2) expression via the mitogen activated protein kinase (MAPK) signalling cascade pathways in human peripheral blood monocytes (PBMC).
Methods: PBMC from whole blood were isolated and cultured for up to 24 hours after division into 5 groups treated with LPS, LPS + BBR 25 micromol/L, LPS + BBR 50 micromol/L or LPS + BBR 100 micromol/L and untreated. Monocytes were extracted for RT-PCR and Western blot analyses to examine COX-2 mRNA and protein activated expression of p38 mitogen activated protein kinase (p38MAPK), Jun N-terminal kinase (JNK) and extracellular regulated kinases 1/2 (ERK1/2) signalling pathways.
Results: COX-2 mRNA and protein expression decreased to a minimum at 12 hours after BBR treatment (P < 0.05). With the increasing concentration of BBR treatment, the COX-2 expression decreased progressively (P < 0.01). With BBR treatment for 6, 12 or 24 hours at three doses, ERK1/2 protein expression was significantly inhibited. For the JNK pathway, only with the treatment of BBR at the concentration of 100 micromol/L was JNK protein expression inhibited compared with the LPS stimulation group (P < 0.01). Irrespective of the BBR concentration, no difference was shown between the BBR group and the LPS group for p38MAPK protein expression. Human monocytes COX-2 mRNA, by RT-PCR, and protein expression, by Western blot analysis, were inhibited when incubated with PD98059, SP600125 and SB203580 (P < 0.05).
Conclusions: Berberine inhibits COX-2 expression via the ERK1/2 signalling pathway and, possibly, at a high dosage via the JNK pathway. P38MAPK may have no relationship with the effect of BBR in PBMC. Berberine inhibited COX-2 mRNA and protein expression in a dose dependent manner and suppressed COX-2 expression to a minimal level after 12 hours of berberine treatment.