Phytochemical-induced changes in gene expression of carcinogen-metabolizing enzymes in cultured human primary hepatocytes

Abstract

1. The naturally occurring compounds curcumin (CUR), 3,3'-diindolylmethane (DIM), isoxanthohumol (IXN), 8-prenylnaringenin (8PN), phenethyl isothiocyanate (PEITC) and sulforaphane (SFN) protect animals against chemically induced tumours. Putative chemoprotective mechanisms include modulated expression of hepatic biotransformation enzymes. However, few, if any, studies have used human primary cells as test models. 2. The present study investigated the effects of these phytochemicals on the expression of four carcinogenesis-relevant enzymes--cytochrome P450 (CYP)1A1 and 1A2, NAD(P)H:quinone oxidoreductase (NQO1) and glutathione S-transferase A1 (GSTA1)--in primary cultures of freshly isolated human hepatocytes. 3. Quantitative RT-PCR analyses demonstrated that CYP1A1 was up-regulated by PEITC and DIM in a dose-dependent manner. CYP1A2 transcription was significantly activated following DIM, IXN, 8PN and PEITC treatments. DIM exhibited a remarkably effective induction response of CYP1A1 (474-, 239- and 87-fold at 50, 25 and 10 microM, respectively) and CYP1A2 (113-, 70- and 31-fold at 50, 25 and 10 microM, respectively), that was semiquantitatively reflected in protein levels. NQO1 expression responded to PEITC (11 x at 25 microM), DIM (4.5 x at 50 microM) and SFN (5 x at 10 microM) treatments. No significant effects on GSTA1 transcription were seen. 4. The findings show novel and unexpected effects of these phytochemicals on the expression of human hepatic biotransformation enzymes that play key roles in chemical-induced carcinogenesis.

Molecular basis for chemoprevention by sulforaphane: a comprehensive review

“…SF also induced expression of GST A1/2 isoforms and NQO1 in primary rat hepatocytes in a dose-response and time-course manner [49], although prolonged treatment was required to obtain GST induction levels comparable to those obtained in hepatoma cell lines [29]. Similar results were observed in primary cultures of freshly isolated human hepatocytes where NQO1 expression responded to SF but no significant effects on GSTA1 transcription were seen [50]. SF induced phase 2 detoxification enzymes, UDPG1A1 and GSTA1 mRNA expression in human hepatocytes, although UGT1A1 induction was subject to inter-individual variation [36].…”

Molecular Targets of Dietary Phenethyl Isothiocyanate and Sulforaphane for Cancer Chemoprevention

“…It has been shown that PEITC induces the expression of several xenobiotic-metabolizing CYPs which could potentially activate carcinogens. In cultured human primary hepatocytes, it was also shown that PEITC dose-dependently upregulated the expression of carcinogen-activating enzymes CYP1A1 and CYP1A2 using quantitative polymerase chain reaction analyses (20). On the other hand, activities of CYPs have been shown to be inhibited by PEITC.…”

Effects of food natural products on the biotransformation of PCBs

“…Studies in animals have shown that natural products present in food and herbal drugs will induce synthesis of P450 isoforms in the 1, 2 and 3 families (Table 1). Phytochemicals known to induce CYP1A1 and CYP1A2 synthesis include isothiothiocyanates, indole-3-carbinol and its condensation products (including di-indolylmethane), flavonoids and tea polyphenolic compounds (Gross-Steinmeyer et al, 2004;Moon et al, 2006). The herbal drug, St. John's wort, which has the active component, hyperforin, induces hepatic CYP3A4 (Komoroski et al, 2004).…”