Sulforaphane- and Phenethyl Isothiocyanate–Induced Inhibition of Aflatoxin B1–Mediated Genotoxicity in Human Hepatocytes: Role of GSTM1 Genotype and CYP3A4 Gene Expression

Abstract

Primary cultures of human hepatocytes were used to investigate whether the dietary isothiocyanates, sulforaphane (SFN), and phenethyl isothiocyanate (PEITC) can reduce DNA adduct formation of the hepatocarcinogen aflatoxin B(1) (AFB). Following 48 h of pretreatment, 10 and 50 microM SFN greatly decreased AFB-DNA adduct levels, whereas 25muM PEITC decreased AFB-DNA adducts in some but not all hepatocyte preparations. Microarray and quantitative reverse transcriptase (RT)-PCR analyses of gene expression in SFN and PEITC-treated hepatocytes demonstrated that SFN greatly decreased cytochrome P450 (CYP) 3A4 mRNA but did not induce the expression of either glutathione S-transferase (GST) M1 or GSTT1. The protective effects of SFN required pretreatment; cotreatment of hepatocytes with SFN and AFB in the absence of pretreatment had no effect on AFB-DNA adduct formation. When AFB-DNA adduct formation was evaluated by GST genotype, the presence of one or two functional alleles of GSTM1 was associated with a 75% reduction in AFB-DNA adducts, compared with GSTM1 null. In conclusion, these results demonstrate that the inhibition of AFB-DNA adduct formation by SFN is dependent on changes in gene expression rather than direct inhibition of catalytic activity. Transcriptional repression of genes involved in AFB bioactivation (CYP3A4 and CYP1A2), but not transcriptional activation of GSTs, may be responsible for the protective effects of SFN. Although GSTM1 expression was not induced by SFN, the presence of a functional GSTM1 allele can afford substantial protection against AFB-DNA damage in human liver. The downregulation of CYP3A4 by SFN may have important implications for drug interactions.

Aflatoxicosis: Lessons from Toxicity and Responses to Aflatoxin B1 in Poultry

“…Human enzymes hGSTA1 and hGSTA2 have little AFBO-conjugating activity [57,59,68]. Instead, some AFB1-SG adducts are produced by the mu-class GST (GSTM) enzyme hGSTM1 [59,[68][69][70][71]. Although hGSTM1 forms more AFB1-SG adducts from the endo stereoisomer, it is able to detoxify mutagenic exo-AFBO [68].…”

Staying a Step Ahead of Cancer

“…For instance, consumption of a known amount of the phytonutrient sulforaphane does not guarantee absorption of a predicted amount of anti-cancer molecule since differences in the glutathione S transferase M1 gene influences the metabolic rate of sulforaphane, a phytonutrient present in broccoli. The faster it is metabolized, the faster it is expelled from the body , Gasper et al 2005, Gross-Steinmeyer et al 2010, Joseph et al 2004, Lampe 2007, Lampe 2009, McWalter et al 2004, Riedl, Saxon and Diaz-Sanchez 2009, Ritz, Wan and Diaz-Sanchez 2007, Traka et al 2008. Similarly, a number of the nutrients, e.g.…”

A mechanistic insight into 3,4-methylenedioxymethamphetamine (“ecstasy”)-mediated hepatotoxicity

“…As previously mentioned, GSH depletion was stronger upon co-exposure and rendering the cellular GSH pool, which correlates with these findings of stimulation of new GSH synthesis. SFN can effectively increase GSH levels when it is administrated before the oxidative stress is promoted (Gross-Steinmeyer et al 2010;GuerreroBeltran et al 2010). Therefore, our studies could indicate an early up-regulation after a 24-h exposure, although it will not be sufficient to observe elevated cellular GSH levels upon HHMA exposure.…”