Induction of detoxifying enzymes by garlic organosulfur compounds through transcription factor Nrf2: effect of chemical structure and stress signals

• Published in: Free radical biology & medicine Vol. 37; no. 10; pp. 1578 - 1590
• Main Authors: Chen, Chi, Pung, Daniel, Leong, Vasco, Hebbar, Vidya, Shen, Guoxiang, Nair, Sujit, Li, Wenge, Tony Kong, A.-N.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15-11-2004
• Subjects: Allyl Compounds - pharmacology; Antioxidant response element; Calcium/calmodulin-dependent protein kinase; Carcinoma, Hepatocellular - drug therapy; Diallyl disulfide; Diallyl trisulfide; DNA-Binding Proteins - metabolism; Enzyme Activation - drug effects; Enzyme Activation - physiology; Free radicals; Garlic - chemistry; Garlic organosulfur compounds; Gene Expression Regulation, Neoplastic - drug effects; Gene Expression Regulation, Neoplastic - physiology; Genes, Reporter - genetics; Heme Oxygenase (Decyclizing) - metabolism; Heme Oxygenase-1; Humans; Inactivation, Metabolic - physiology; JNK Mitogen-Activated Protein Kinases - metabolism; Kelch-like ECH-associating protein 1; Membrane Proteins; Mitogen-Activated Protein Kinase Kinases - metabolism; Mitogen-activated protein kinases; NAD(P)H Dehydrogenase (Quinone) - metabolism; NF-E2-Related Factor 2; Nuclear factor E2-related factor; p38 Mitogen-Activated Protein Kinases - metabolism; Plants, Medicinal - chemistry; Protein Kinase C - antagonists & inhibitors; Protein Kinase C - metabolism; Protein Kinase Inhibitors - pharmacology; Signal Transduction - drug effects; Signal Transduction - physiology; Thiol antioxidants; Trans-Activators - metabolism; Tumor Cells, Cultured; Keap 1; CaMK; DMSO; SAR; DPS; JNK; HO1; MTS; Diallyl trisulfide; DADS; Nrf2; RT-PCR; Kelch-like ECH-associating protein 1; DME; GSH; Antioxidant response element; OSC; Mitogen-activated protein kinases; Nrf2-FL; Thiol antioxidants; NQO1; DATS; Diallyl disulfide; Free radicals; Nrf2-DN; Nuclear factor E2-related factor; TBST; GST; PKC; DPTS; SUL; Garlic organosulfur compounds; MAPK; Calcium/calmodulin-dependent protein kinase; NAC; ARE; DAS; DPDS; ERK
• ISSN: 0891-5849; 1873-4596
• DOI: 10.1016/j.freeradbiomed.2004.07.021

Garlic organosulfur compounds (OSCs) are recognized as a group of potential chemopreventive compounds. It is known that garlic OSCs can modulate drug metabolism systems, especially various phase II detoxifying enzymes, though the mechanism underlying their inductive effect on these enzymes remains largely unknown. In the present study, we investigated the transcriptional levels of NAD(P)H:quinone oxidoreductase 1 (NQO1) and heme oxygenase 1 (HO1) genes, the reporter activity mediated by antioxidant response element (ARE), and the protein level of transcription factor nuclear factor E2-related factor 2 (Nrf2), after administration of three major garlic OSCs—diallyl sulfide (DAS), diallyl disulfide (DADS), and diallyl trisulfide (DATS)—in human hepatoma HepG2 cells. Our results showed that ARE activation and Nrf2 protein accumulation were well correlated with phase II gene expression induction. The structure–activity relationship study indicated that the third sulfur in the structure of OSCs contributed substantially to their bioactivities, and that allyl-containing OSCs were more potent than propyl-containing OSCs. To better understand the signaling events involved in the upregulation of detoxifying enzymes by DATS, ARE activity and Nrf2 protein levels were examined after transient transfection of HepG2 cells with mutant Nrf2, cotreatment with antioxidants, and pretreatment with protein kinase inhibitors. DATS-induced ARE activity was inhibited by dominant-negative Nrf2 Kelch-like ECH-associating protein 1 and constructs. Cotreatment with thiol antioxidants decreased the ARE activity and Nrf2 protein level induced by DATS. Three major mitogen-activated protein kinases (MAPKs)—extracellular signal-regulated protein kinase, c-Jun N-terminal kinase, and p38-were activated by DATS treatment. However, the inhibition of these MAPKs did not affect DATS-induced ARE activity. Pretreatment with various upstream protein kinase inhibitors showed that the protein kinase C pathway was not directly involved in DATS-induced ARE activity, but instead the calcium-dependent signaling pathway appeared to play a role in the DATS-induced cytoprotective effect.