Possible inhibitory mechanism of Curcuma drugs on CYP3A4 in 1α,25 dihydroxyvitamin D3 treated Caco-2 cells

Curcuma longa and C. zedoaria, belonging to genus Curcuma, have become prevalent as supplements in East Asia. Curcumin is the most well-studied bioactive component isolated from rhizomes of C. longa and other Curcuma species except C. zedoaria. In this study, we investigated the affects of C. longa, C. zedoaria from Japan and curcumin on CYP3A4. Caco-2 cells, in which CYP3A4 expression was induced by 1α,25-(OH)2-D3, were used to mimic the metabolism of small intestine. Caco-2 cells were treated with methanol extracts from two Curcuma rhizomes (0.1 mg/ml) or curcumin (30 μM) for 72 h. Both extracts significantly decreased the activity of CYP3A4 by about 85–98%. The 50% inhibitory concentrations of C. longa and C. zedoaria extracts were 0.019 and 0.014 mg/ml, respectively. They caused a 60–70% decrease in CYP3A4 protein. Otherwise, curcumin treatment caused a 30–40% decrease in CYP3A4 catalytic activity and a 38% decrease in CYP3A4 protein expression. Moreover, it was found that both Curcuma extracts and curcumin treatment had no influence on CYP3A4 mRNA expression. Our results suggested that administration of Curcuma drugs might inhibit the catalytic activity of intestinal CYP3A4. However, curcumin was not the major compound responsible for this inhibitory effect.