Houttuynia cordata, a novel and selective COX-2 inhibitor with anti-inflammatory activity

Ethnopharmacological relevance: Houttuynia cordata Thunb. (Saururaceae; HC) has been long used in traditional oriental medicine for the treatment of inflammation diseases. Modern research has implicated inducible cyclooxygenase-2 (COX-2) as a key regulator of the inflammatory process. Aim of the study: In the present study, we aimed to investigate the effect of HC on COX-2. We examined the effects of HC on lipopolysaccharide (LPS)-induced prostaglandin (PG) E₂ production, an indirect indicator of COX-2 activity, and COX-2 gene and protein expression in mouse peritoneal macrophages. Materials and methods: LPS-induced mouse peritoneal macrophages were employed as an in vitro model system. LPS-induced PGE₂ production was assessed by enzyme-linked immunosorbant assay and COX-2 protein expression was assessed by Western blot assay. Results: The results showed that HC was able to inhibit the release of LPS-induced PGE₂ from mouse peritoneal macrophages (IC50 value: 44.8 μg/mL). Moreover, the inhibitory activity of HC essential oil elicited a dose-dependent inhibition of COX-2 enzyme activity (IC50 value: 30.9 μg/mL). HC was also found to cause reduction in LPS-induced COX-2 mRNA and protein expression, but did not affect COX-1 expression. The non-steroidal anti-inflammatory drug (NSAID) and specific COX-2 inhibitor NS398 functioned similarly in LPS-induced mouse peritoneal macrophages. Conclusion: Taken together, our data suggest HC mediates inhibition of COX-2 enzyme activity and can affect related gene and protein expression. HC works by a mechanism of action similar to that of NSAIDs. These results add a novel aspect to the biological profile of HC.