Carnosic acid induces the NAD(P)H: quinone oxidoreductase 1 expression in rat clone 9 cells through the p38/nuclear factor erythroid-2 related factor 2 pathway

The anticarcinogenic effect of rosemary has been partly attributed to the modulation of the activity and expression of phase II detoxification enzymes. Here we compared the effects of phenolic diterpenes from rosemary on the expression of NAD(P)H: quinone oxidoreductase 1 (NQO1) in rat Clone 9 liver cells. Cells were treated with 1‐20 mmol/L of carnosic acid (CA) or carnosol (CS) for 24 h. Both CA and CS dose dependently increased NQO1 enzyme activity and protein expression, and the induction potency of CA was stronger than that of CS. The increase in NQO1 enzyme activity in cells treated with 10 mmol/L CA and CS was 4.1- and 1.9-fold, respectively (P , 0.05). RT-PCR showed that CA and CS induced NQO1 mRNA in a dose-dependent manner. Furthermore, CA dose dependently induced transcription of nuclear factor erythroid-2 related factor 2 (Nrf2) and antioxidant response element (ARE)-luciferase reporter activity. Silencing of Nrf2 expression alleviated NQO1 protein expression and ARE-luciferase activity by CA. Moreover, the phosphorylation of p38 was mainly stimulated in the presence of CA. Pretreatment with SB203580 or silencing of p38 expression inhibited Nrf2 activation and NQO1 induction. These results suggest that the increased NQO1 expression by CA is likely related to the p38-Nrf2 pathway and help to clarify the possible molecular mechanism of action of rosemary phenolic compounds in drug metabolism and cancer prevention. J. Nutr. doi: 10.3945/jn.111.146779.