Sulforaphane and alpha-lipoic acid upregulate the expression of the pi class of glutathione S-transferase through c-jun and Nrf2 activation.

The anticarcinogenic effect of dietary organosulfur compounds has been partly attributed to their modulation of the activity and expression of phase II detoxification enzymes. Our previous studies indicated that garlic allyl sulfides upregulate the expression of the pi class of glutathione S-transferase (GSTP) through the activator protein-1 pathway. Here, we examined the modulatory effect of sulforaphane (SFN) and alpha-lipoic acid (LA) or dihydrolipoic acid (DHLA) on GSTP expression in rat Clone 9 liver cells. Cells were treated with LA or DHLA (50-600 micromol/L) or SFN (0.2-5 micromol/L) for 24 h. Immunoblots and real-time PCR showed that SFN, LA, and DHLA dose dependently induced GSTP protein and mRNA expression. Compared with the induction by the garlic organosulfur compound diallyl trisulfide (DATS), the effectiveness was in the order of SFN > DATS > LA = DHLA. The increase in GSTP enzyme activity in cells treated with 5 micromol/L SFN, 50 micromol/L DATS, and 600 micromol/L LA and DHLA was 172, 75, 122, and 117%, respectively (P < 0.05). A reporter assay showed that the GSTP enhancer I (GPEI) was required for GSTP induction by the organosulfur compounds. Electromobility gel shift assays showed that the DNA binding of GPEI to nuclear proteins reached a maximum at 0.5-1 h after SFN, LA, and DHLA treatment. Super-shift assay revealed that the transcription factors c-jun and nuclear factor erythroid-2 related factor 2 (Nrf2) were bound to GPEI. These results suggest that SFN and LA in either its oxidized or reduced form upregulate the transcription of the GSTP gene by activating c-jun and Nrf2 binding to the enhancer element GPEI.

Induction of heme oxygenase 1 and inhibition of tumor necrosis factor alpha-induced intercellular adhesion molecule expression by andrographolide in EA.hy926 cells.

Andrographolide is the most abundant diterpene lactone in Andrographis paniculata, which is widely used as a traditional medicine in Southeast Asia. Heme oxygenase 1 (HO-1) is an antioxidant enzyme encoded by a stress-responsive gene. HO-1 has been reported to inhibit the expression of adhesion molecules in vascular endothelial cells (EC). Intercellular adhesion molecule (ICAM-1) is an inflammatory biomarker that is involved in the adhesion of monocytes to EC. In this study, we investigated the effect of andrographolide on the expression of ICAM-1 induced by tumor necrosis factor alpha (TNF-alpha) in EA.hy926 cells and the possible mechanisms involved. Andrographolide (2.5-7.5 microM) inhibited the TNF-alpha-induced expression of ICAM-1 in a dose-dependent manner and resulted in a decrease in HL-60 cell adhesion to EA.hy926 cells (p < 0.05). In parallel, andrographolide significantly induced the expression of HO-1 in a concentration-dependent fashion (p < 0.05). Andrographolide increased the rate of nuclear translocation of nuclear factor erythroid 2-related 2 (Nrf2) and induced antioxidant response element-luciferase reporter activity. Transfection with HO-1-specific small interfering RNA knocked down HO-1 expression, and the inhibition of expression of ICAM-1 by andrographolide was significantly reversed. These results suggest that stimulation of Nrf2-dependent HO-1 expression is involved in the suppression of TNF-alpha-induced ICAM-1 expression exerted by andrographolide.