Berberine Decreased Inducible Nitric Oxide Synthase mRNA Stability through Negative Regulation of Human Antigen R in Lipopolysaccharide-Induced Macrophages

Berberine, a major isoquinoline alkaloid found in medicinal herbs, has been reported to possess anti-inflammatory effects; however, the underlying mechanisms responsible for its actions are poorly understood. In the present study, we investigated the inhibitory effects of berberine and the molecular mechanisms involved in lipopolysaccharide (LPS)-treated RAW 264.7 and THP-1 macrophages and its effects in LPS-induced septic shock in mice. In both macrophage cell types, berberine inhibited the LPS-induced nitric oxide (NO) production and inducible NO synthase (iNOS) protein expression, but it had no effect on iNOS mRNA transcription. Suppression of LPS-induced iNOS protein expression by berberine occurred via a human antigen R (HuR)-mediated reduction of iNOS mRNA stability. Molecular data revealed that the suppression on the LPS-induced HuR binding to iNOS mRNA by berberine was accompanied by a reduction in nucleocytoplasmic HuR shuttling. Pretreatment with berberine reduced LPS-induced iNOS protein expression and the cytoplasmic translocation of HuR in liver tissues and increased the survival rate of mice with LPS-induced endotoxemia. These results show that the suppression of iNOS protein expression by berberine under LPS-induced inflammatory conditions is associated with a reduction in iNOS mRNA stability resulting from inhibition of the cytoplasmic translocation of HuR.