The different inhibitory effects of Huang-Lian-Jie-Du-Tang on cyclooxygenase 2 and 5-lipoxygenase

Huang-Lian-Jie-Du-Tang (HLJDT), a famous traditional Chinese prescription with wide anti-inflammatory applications, is an aqueous extract of four herbal materials: Rhizoma coptidis, Radix scutellariae, Cortex phellodendri, and Fructus gardeniae. Its effects on the cyclooxygenase (COX)-2 and 5-lipoxygenase (5-LOX) pathways are thought to be responsible for its anti-inflammatory activity. However, our previous work found that the inhibitory effects of HLJDT act on the 5-LOX pathway but not on the COX pathway. The possibility that HLJDT inhibits COX-2- or 5-LOX-catalyzed eicosanoid generation by downregulating enzyme expression requires further investigation. To observe the effects of HLJDT and its four major components (baicalin, baicalein, berberine and geniposide) on COX-2- or 5-LOX-catalyzed eicosanoid generation and to distinguish the effects of HLJDT on enzyme activity from those on enzyme expression. The topical anti-inflammatory activities and inhibition of eicosanoid formation of HLJDT and its components were observed in an arachidonic acid (AA)-induced mouse ear edema model. Macrophage-based systems were established to observe the effects of the drugs on enzyme activity and enzyme expression of COX-2 and 5-LOX. Further experiments were carried out to confirm these effects at the mRNA and protein levels. Topical treatment of HLJDT significantly inhibited AA-induced mouse ear edema and reduced PGE2 and LTB4 release in the edematous ears. Baicalein, geniposide, and berberine also ameliorated the symptoms and suppressed eicosanoid generation with varying efficacies. Cell-based assays showed that HLJDT and baicalein inhibited the PGE2 levels by decreasing COX-2 enzyme expression without affecting COX-2 enzyme activity in RAW 246.7 murine macrophages. The other experiments on rat peritoneal macrophages indicated that HLJDT and baicalein exerted significant inhibition on LTB4 production by decreasing 5-LOX enzyme activity. The real-time PCR and western blotting data demonstrated that HLJDT and baicalein reduced COX-2 expression at the mRNA and protein levels, whereas no inhibition on 5-LOX expression was observed. HLJDT can suppress eicosanoid generation via both the COX and LOX pathways, which definitely contributes to its topical anti-inflammatory activity. We have confirmed that its dual inhibition on the COX and LOX pathways mainly result from the downregulation of COX-2 expression and direct inhibition of 5-LOX activity, respectively. Baicalein worked