Induction of detoxifying enzymes by garlic organosulfur compounds through transcription factor Nrf2: effect of chemical structure and stress signals.
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.
Chen
Chi
C
Department of Pharmaceutics, Ernest Mario School of Pharmacy, Rutgers, The State University of New Jersey, 160 Frelinghuysen Road, Piscataway, NJ 08854, USA.
Pung
Daniel
D
Leong
Vasco
V
Hebbar
Vidya
V
Shen
Guoxiang
G
Nair
Sujit
S
Li
Wenge
W
Kong
A-N Tony
AN
D000498:Allyl Compounds / Q000494:pharmacology*; D006528:Carcinoma, Hepatocellular / Q000188:drug therapy; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D005737:Garlic / Q000737:chemistry*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects / Q000502:physiology; D017930:Genes, Reporter / Q000235:genetics; D006419:Heme Oxygenase (Decyclizing) / Q000378:metabolism; D051547:Heme Oxygenase-1; D006801:Humans; D008658:Inactivation, Metabolic / Q000502:physiology; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D008565:Membrane Proteins; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000378:metabolism*; D051267:NF-E2-Related Factor 2; D010946:Plants, Medicinal / Q000737:chemistry; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D015534:Trans-Activators / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D000498:Allyl Compounds; D004268:DNA-Binding Proteins; D008565:Membrane Proteins; D051267:NF-E2-Related Factor 2; C495635:NFE2L2 protein, human; D047428:Protein Kinase Inhibitors; D015534:Trans-Activators; C496541:HMOX1 protein, human; D006419:Heme Oxygenase (Decyclizing); D051547:Heme Oxygenase-1; D016660:NAD(P)H Dehydrogenase (Quinone); C447479:NQO1 protein, human; D011493:Protein Kinase C; D048031:JNK Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D020929:Mitogen-Activated Protein Kinase Kinases