Involvement of cytochrome P450, glutathione S-transferase, and epoxide hydrolase in the metabolism of aflatoxin B1 and relevance to risk of human liver cancer

Lactobacillus salivarius Ameliorates AFB1-induced hepatotoxicity via PINK1/Parkin-mediated mitophagy in Geese

Aflatoxin B1 (AFB1) is commonly found in feed ingredients and foods all over the world, posing a significant threat to food safety and public health in animals and humans. Lactobacillus salivarius (L. salivarius) was recorded to improve the intestinal health and performance of chickens. However, whether L. salivarius can alleviate AFB1-induced hepatotoxicity in geese was unknown. A total of 300 Lande geese were randomly assigned to five groups: control group, AFB1 low-dose group (L), L. salivarius+AFB1 low-dose group (LL), AFB1 high dosage groups (H), L. salivarius+AFB1 high dosage groups (LH), respectively. The results showed that the concentrations of ALT, AST, and GGT significantly increased after exposure to AFB1. Similarly, severe damage of hepatic morphology was observed including the hepatic structure injury and inflammatory cell infiltration. The oxidative stress was evidenced by the elevated concentrations of MDA, and decreased activities of GSH-Px, GSH and SOD. The observation of immunofluorescence, real-time PCR, and western blotting showed that the expression of PINK1 and the value of LC3II/LC3I were increased, but that of p62 significantly decreased after AFB1 exposure. Moreover, the supplementation of L. salivarius effectively improved the geese performance, ameliorated AFB1-induced oxidative stress, inhibited mitochondrial mitophagy and enhanced the liver restoration to normal level. The present study demonstrated that L. salivarius ameliorated AFB1-induced the hepatotoxicity by decreasing the oxidative stress, and regulating the expression of PINK1/Parkin-mediated mitophagy in the mitochondria of the geese liver. Furthermore, this investigation suggested that L. salivarius might serve as a novel and safe additive for preventing AFB1 contamination in poultry feed.

CYP2E1 deficit mediates cholic acid-induced malignant growth in hepatocellular carcinoma cells

BACKGROUND

Increased level of serum cholic acid (CA) is often accompanied with decreased CYP2E1 expression in hepatocellular carcinoma (HCC) patients. However, the roles of CA and CYP2E1 in hepatocarcinogenesis have not been elucidated. This study aimed to investigate the roles and the underlying mechanisms of CYP2E1 and CA in HCC cell growth.

METHODS

The proteomic analysis of liver tumors from DEN-induced male SD rats with CA administration was used to reveal the changes of protein expression in the CA treated group. The growth of CA-treated HCC cells was examined by colony formation assays. Autophagic flux was assessed with immunofluorescence and confocal microscopy. Western blot analysis was used to examine the expression of CYP2E1, mTOR, AKT, p62, and LC3II/I. A xenograft tumor model in nude mice was used to examine the role of CYP2E1 in CA-induced hepatocellular carcinogenesis. The samples from HCC patients were used to evaluate the clinical value of CYP2E1 expression.

RESULTS

CA treatment significantly increased the growth of HCC cells and promoted xenograft tumors accompanied by a decrease of CYP2E1 expression. Further studies revealed that both in vitro and in vivo, upregulated CYP2E1 expression inhibited the growth of HCC cells, blocked autophagic flux, decreased AKT phosphorylation, and increased mTOR phosphorylation. CYP2E1 was involved in CA-activated autophagy through the AKT/mTOR signaling. Finally, decreased CYP2E1 expression was observed in the tumor tissues of HCC patients and its expression level in tumors was negatively correlated with the serum level of total bile acids (TBA) and gamma-glutamyltransferase (GGT).

CONCLUSIONS

CYP2E1 downregulation contributes to CA-induced HCC development presumably through autophagy regulation. Thus, CYP2E1 may serve as a potential target for HCC drug development.

Mass Spectrometry-Based Method to Measure Aflatoxin B1 DNA Adducts in Formalin-Fixed Paraffin-Embedded Tissues

Aflatoxin B1 (AFB1) is a potent human liver carcinogen produced by certain molds, particularly Aspergillus flavus and Aspergillus parasiticus, which contaminate peanuts, corn, rice, cottonseed, and ground and tree nuts, principally in warm and humid climates. AFB1 undergoes bioactivation in the liver to produce AFB1-exo-8,9-epoxide, which forms the covalently bound cationic AFB1-N7-guanine (AFB1-N7-Gua) DNA adduct. This adduct is unstable and undergoes base-catalyzed opening of the guanine imidazolium ring to form two ring-opened diastereomeric 8,9-dihydro-8-(2,6-diamino-4-oxo-3,4-dihydropyrimid-5-yl-formamido)-9-hydroxy-aflatoxin B1 (AFB1-FapyGua) adducts. The AFB1 formamidopyrimidine (Fapy) adducts induce G → T transversion mutations and are likely responsible for the carcinogenic effects of AFB1. Quantitative liquid chromatography-mass spectrometry (LC-MS) methods have shown that AFB1-N7-Gua is eliminated in rodent and human urine, whereas ring-opened AFB1-FapyGua adducts persist in rodent liver. However, fresh frozen biopsy tissues are seldom available for biomonitoring AFB1 DNA adducts in humans, impeding research advances in this potent liver carcinogen. In contrast, formalin-fixed paraffin-embedded (FFPE) specimens used for histopathological analysis are often accessible for molecular studies. However, ensuring nucleic acid quality presents a challenge due to incomplete reversal of formalin-mediated DNA cross-links, which can preclude accurate quantitative measurements of DNA adducts. In this study, employing ion trap or high-resolution accurate Orbitrap mass spectrometry, we demonstrate that ring-opened AFB1-FapyGua adducts formed in AFB1-exposed newborn mice are stable to the formalin fixation and DNA de-cross-linking retrieval processes. The AFB1-FapyGua adducts can be detected at levels comparable to those in a match of fresh frozen liver. Orbitrap MS2 measurements can detect AFB1-FapyGua at a quantification limit of 4.0 adducts per 108 bases when only 0.8 μg of DNA is assayed on the column. Thus, our breakthrough DNA retrieval technology can be adapted to screen for AFB1 DNA adducts in FFPE human liver specimens from cohorts at risk of this potent liver carcinogen.

Key Role of Porcine Cytochrome P450 2A19 in the Bioactivation of Aflatoxin B1 in the Liver

The metabolic transformation of aflatoxin B1 (AFB1) in pigs remains understudied, presenting a gap in our toxicological understanding compared with extensive human-based research. Here, we found that the main products of AFB1 in porcine liver microsomes (PLMs) were AFB1-8,9-epoxide (AFBO), the generation of which correlated strongly with the protein levels and activities of cytochrome P450 (CYP)3A and CYP2A. In addition, we found that porcine CYP2A19 can transform AFB1 into AFBO, and its metabolic activity was stronger than the other CYPs we have reported, including CYP1A2, CYP3A29, and CYP3A46. Furthermore, we stably transfected all identified CYPs in HepLi cells and found that CYP2A19 stable transfected HepLi cells showed more sensitivity in AFB1-induced DNA adducts, DNA damage, and γH2AX formation than the other three stable cell lines. Moreover, the CYP2A19 N297A mutant that lost catalytic activity toward AFB1 totally eliminated AFB1-induced AFB1-DNA adducts and γH2AX formations in CYP2A19 stable transfected HepLi cells. These results indicate that CYP2A19 mainly mediated AFB1-induced cytotoxicity through metabolizing AFB1 into a highly reactive AFBO, promoting DNA adduct formation and DNA damage, and lastly leading to cell death. This study advances the current understanding of AFB1 bioactivation in pigs and provides a promising target to reduce porcine aflatoxicosis.

Comparative metabolism of aflatoxin B1 in mouse, rat and human primary hepatocytes using HPLC-MS/MS

Aflatoxin B1 (AFB1) is a highly hepatotoxic and carcinogenic mycotoxin produced by Aspergillus species. The compound is mainly metabolized in the liver and its metabolism varies between species. The present study quantified relevant AFB1- metabolites formed by mouse, rat, and human primary hepatocytes after treatment with 1 µM and 10 µM AFB1. The use of liquid chromatographic separation coupled with tandem mass spectrometric detection enabled the selective and sensitive determination of phase I and phase II metabolites of AFB1 over incubation times of up to 24 h. The binding of AFB1 to macromolecules was also considered. The fastest metabolism of AFB1 was observed in mouse hepatocytes which formed aflatoxin P1 as a major metabolite and also its glucuronidated form, while AFP1 occurred only in traces in the other species. Aflatoxin M1 was formed in all species and was, together with aflatoxin Q1 and aflatoxicol, the main metabolite in human cells. Effective epoxidation led to high amounts of DNA adducts already 30 min post-treatment, especially in rat hepatocytes. Lower levels of DNA adducts and fast DNA repair were found in mouse hepatocytes. Also, protein adducts arising from reactive intermediates were formed rapidly in all three species. Detoxification via glutathione conjugation and subsequent formation of the N-acetylcysteine derivative appeared to be similar in mice and in rats and strongly differed from human hepatocytes which did not form these metabolites at all. The use of qualitative reference material of a multitude of metabolites and the comparison of hepatocyte metabolism in three species using advanced methods enabled considerations on toxification and detoxification mechanisms of AFB1. In addition to glutathione conjugation, phase I metabolism is strongly involved in the detoxification of AFB1.

A doxycycline-inducible CYP3A4-Caco-2 cell line as a model for evaluating safety of aflatoxin B1 in the human intestine

Exposure of humans to aflatoxin B1 (AFB1) via ingestion of contaminated agricultural products is a major concern for human health throughout the world because epoxidized AFB1, biotransformed from AFB1 by hepatic CYP3A4, is strongly hepatotoxic and hepatocarcinogenic. Intestinal epithelial cells serve as a physical and physiological barrier against xenobiotics via their intercellular tight junction (TJ) seals and the metabolizing enzyme CYP3A4. However, the effect of AFB1 on the intestinal barrier remains unclear. Here, we investigated the influence of AFB1 on these physical and physiological intestinal barriers by means of an in vitro human intestinal model utilizing doxycycline-inducible CYP3A4-expressing Caco-2 cells, in which CYP3A4 activity is comparable to that in the adult human intestine. Cellular toxicity of AFB1 in induced Caco-2 cells (i.e., cells in which expression of CYP3A4 is induced by doxycycline) was approximately 5 times that of uninduced Caco-2 cells. Exposure to 16 µM AFB1 did not decrease the transepithelial electric resistance (TEER; a measure of TJ barrier integrity) in monolayers of uninduced Caco-2 cells to 95.8 % of that in vehicle-treated cells; in contrast, in induced Caco-2 cells, TEER was reduced to 28.8 %. Exposure to 16 µM AFB1 increased paracellular permeation of 4- and 20-kDa dextrans (paracellular permeation markers) through monolayers of induced Caco-2 cells to 5.4 and 5.2 times that through uninduced Caco-2 cells. These results together show that ingested AFB1 can modulate the intestinal barrier, and that inducible CYP3A4-expressing Caco-2 cells are a promising tool for evaluating the safety of food contaminants in the human intestine.

Total flavonoids of Rhizoma Drynariae protect hepatocytes against aflatoxin B1-induced oxidative stress and apoptosis in broiler chickens

Aflatoxin B1 (AFB1) is a common mycotoxin in food and in the environment that lead to multi-organ injury in humans and animals. The objective of this study was to evaluate the detoxification properties of dietary total flavonoids of Rhizoma drynariae (TFRD), a Chinese herbal, on aflatoxin B1 (AFB1)-induced hepatic oxidative damage and apoptosis of liver of broiler chickens. A total of 160 healthy specific pathogen free (SPF) 21-day-old broilers were randomly allocated to 4 groups, including the CON group (basal diet), TFRD group (basal diet with 125 mg/kg TFRD), AFB1 group (100 μg/kg body weight), and AFB1 (100 μg/kg body weight) + TFRD (basal diet with 125 mg/kg TFRD) group. The exposure of AFB1 continued for seven days. The results showed that TFRD treatment alleviated the abnormal changes of growth performance and liver morphology, reduced serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels. Moreover, TFRD promoted the antioxidant capacity of serum, increased the activities of total superoxide dismutase (T-SOD), oxidized glutathione (GSSG) and glutathione (GSH) (p < 0.05), while decreased MDA contents (p > 0.05). Meanwhile, supplementation of TFRD significantly increased the expression of antioxidant-related genes (SOD, CAT, GST, and GPX1) in liver (p < 0.05). Furthermore, we found that AFB1 was involved in the regulation of PI3K/AKT signaling pathway, leading to hepatocyte apoptosis. At the same time, TFRD treatment inhibited AFB1-induced apoptosis and significantly changed mRNA expression of apoptosis-related genes, including PI3K, AKT, Bax, and Bcl-2 (p < 0.05). The results indicated that TFRD could alleviate AFB1-induced liver injury in broiler chickens.

Zinc Oxide Nanoparticles Ameliorate Dimethylnitrosamine-Induced Renal Toxicity in Rat

Dimethylnitrosamine (DMN) is an established carcinogen. It is toxic to several organs, viz., the liver, kidney, and lungs, and immune system. Several drugs have been used in the past to modulate its toxicity using experimental animal models. The present study was designed to investigate the effect of zinc oxide nanoparticles (ZnONPs) on renal toxicity caused by DMN in laboratory rat. Since oxidative mechanisms are mainly involved in its toxicity, the proposed study focuses on the amelioration of oxidative stress response by ZnONPs, if any. The present results show that administration of ZnONPs (50 mg/kg body weight/rat) to DMN (2 μl/100 g body weight/rat)-treated rats diminuted the concentration of malonaldehyde, H₂O₂, and NO in the kidney. However, reduced glutathione (GSH) concentration increased after ZnONP treatment. Results on glutathione S-transferase and glutathione peroxidase favored its antioxidative effects. These results are supported by the recovery of oxidative DNA damage and less pronounced histopathological changes in the kidney. It is hypothesized that ZnONPs might be toxic to renal tissue; however, its strong therapeutic/antioxidative potential helps in ameliorating DMN-induced renal toxicity in rat.

Recombinant Expression of Trametes versicolor Aflatoxin B1-Degrading Enzyme (TV-AFB1D) in Engineering Pichia pastoris GS115 and Application in AFB1 Degradation in AFB1-Contaminated Peanuts

Aflatoxins seriously threaten the health of humans and animals due to their potential carcinogenic properties. Enzymatic degradation approach is an effective and environmentally friendly alternative that involves changing the structure of aflatoxins. In this study, Trametes versicolor aflatoxin B₁-degrading enzyme gene (TV-AFB₁D) was integrated into the genome of Pichia pastoris GS115 by homologous recombination approach. The recombinant TV-AFB₁D was expressed in engineering P. pastoris with a size of approximately 77 kDa under the induction of methanol. The maximum activity of TV-AFB₁D reached 17.5 U/mL after the induction of 0.8% ethanol (v/v) for 84 h at 28 °C. The AFB₁ proportion of 75.9% was degraded using AFB₁ standard sample after catalysis for 12 h. In addition, the AFB₁ proportion was 48.5% using AFB₁-contaminated peanuts after the catalysis for 18 h at 34 °C. The recombinant TV-AFB₁D would have good practical application value in AFB₁ degradation in food crops. This study provides an alternative degrading enzyme for the degradation of AFB₁ in aflatoxin-contaminated grain and feed via enzymatic degradation approach.

QuEChERS LC-MS/MS Screening Method for Mycotoxin Detection in Cereal Products and Spices

We developed and validated a screening method for mycotoxin analysis in cereal products and spices. Ultra-high-performance liquid chromatography coupled with tandem mass spectrometry (UHPLC-MS/MS) was used for the analysis. Dispersive solid-phase extractions (d-SPEs) were used for the extraction of samples. Ochratoxin A (OTA), zearalenone (ZEA), aflatoxins (AFLA; AFB1, AFB2, AFG1, AFG2), deoxynivalenol (DON), fumonisin (FUMO; FB1, FB2, FB3), T2, and HT2 were validated in maize. AFLA and DON were validated in black pepper. The method satisfies the requirements of Commission Regulation (EC) no. 401/2006 and (EC) no. 1881/2006. The screening target concentration (STC) was under maximum permitted levels (MLs) for all mycotoxins validated. The method's performance was assessed by two different proficiencies and tested with 100 real samples.

The gut microbiome: an orchestrator of xenobiotic metabolism

Microbes inhabiting the intestinal tract of humans represent a site for xenobiotic metabolism. The gut microbiome, the collection of microorganisms in the gastrointestinal tract, can alter the metabolic outcome of pharmaceuticals, environmental toxicants, and heavy metals, thereby changing their pharmacokinetics. Direct chemical modification of xenobiotics by the gut microbiome, either through the intestinal tract or re-entering the gut via enterohepatic circulation, can lead to increased metabolism or bioactivation, depending on the enzymatic activity within the microbial niche. Unique enzymes encoded within the microbiome include those that reverse the modifications imparted by host detoxification pathways. Additionally, the microbiome can limit xenobiotic absorption in the small intestine by increasing the expression of cell-cell adhesion proteins, supporting the protective mucosal layer, and/or directly sequestering chemicals. Lastly, host gene expression is regulated by the microbiome, including CYP450s, multi-drug resistance proteins, and the transcription factors that regulate them. While the microbiome affects the host and pharmacokinetics of the xenobiotic, xenobiotics can also influence the viability and metabolism of the microbiome. Our understanding of the complex interconnectedness between host, microbiome, and metabolism will advance with new modeling systems, technology development and refinement, and mechanistic studies focused on the contribution of human and microbial metabolism.

Morphological and Transcriptomic Analysis of the Inhibitory Effects of Lactobacillus plantarum on Aspergillus flavus Growth and Aflatoxin Production

Lactobacillus plantarum, as a natural bio-preservative, has attracted a great deal of attention in recent years. In this study, 22 L. plantarum strains were tested against the aflatoxin-producing fungus, Aspergillus flavus; strain IAMU80070 showed the highest antifungal activity. At a concentration of 5 × 105 colony-forming units (CFU) mL-1, it completely inhibited A. flavus growth and decreased aflatoxin production by 93%. Furthermore, ultrastructural examination showed that IAMU80070 destroyed the cellular structure of hyphae and spores. To explore the inhibitory effect of IAMU80070 on A. flavus at the transcriptional level, transcriptome data were obtained and subjected to Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses. The aflatoxin biosynthetic process was the most significantly downregulated functional category, while genes implicated in the synthesis and organization of cell wall polysaccharides were upregulated. Quantitative real-time PCR results verified the credibility and reliability of the RNA sequencing data. These results provided insight into the transcriptome of A. flavus in response to the antagonistic effects of L. plantarum IAMU80070.

Metal Ions in Activated Carbon Improve the Detection Efficiency of Aflatoxin-Producing Fungi

Aflatoxins (AF), produced by several Aspergillus species, are visible under ultraviolet light if present in high amounts. AF detection can be improved by adding activated carbon, which enhances the observation efficiency of weakly AF-producing fungi. However, commercial activated carbon products differ in their characteristics, making it necessary to investigate which characteristics affect method reproducibility. Herein, the addition of 10 activated carbon products resulted in different AF production rates in each case. The differences in the production of aflatoxin G₁ (AFG₁) were roughly correlated to the observation efficiency in the plate culture. Trace element analysis showed that the concentrations of several metal ions differed by factors of >100, and the carbons that most effectively increased AFG₁ production contained higher amounts of metal ions. Adding 5 mg L^-1 Fe or Mg ions increased AFG₁ production even without activated carbon. Furthermore, co-addition of both ions increased AFG₁ production stably with the addition of carbon. When varying the concentration of additives, only AFG₁ production increased in a concentration-dependent manner, while the production of all the other AFs decreased or remained unchanged. These findings suggest that a key factor influencing AF production is the concentration of several metal ions in activated carbon and that increasing AFG₁ production improves AF detectability.

Significant change of cytochrome P450s activities in patients with hepatocellular carcinoma

The lack of information concerning individual variation in drug-metabolizing enzymes is one of the most important obstacles for designing personalized medicine approaches for hepatocellular carcinoma (HCC) patients. To assess cytochrome P450 (CYP) in the metabolism of endogenous and exogenous molecules in an HCC setting, the activity changes of 10 major CYPs in microsomes from 105 normal and 102 HCC liver tissue samples were investigated. We found that CYP activity values expressed as intrinsic clearance (CL_int) differed between HCC patients and control subjects. HCC patient samples showed increased CL_int for CYP2C9, CYP2D6, and CYP2E1 compared to controls. Meanwhile, CYP1A2, CYP2C8, and CYP2C19 CL_int values decreased and CYP2A6, CYP2B6, and CYP3A4/5 activity was unchanged relative to controls. For patients with HCC accompanied by fibrosis or cirrhosis, the same activity changes were seen for the CYP isoforms, except for CYP2D6 which had higher values in HCC patients with cirrhosis. Moreover, CYP2D6*10 (100C>T), CYP2C9*3 (42614 A>C), and CYP3A5*3 (6986A>G) polymorphisms had definite effects on enzyme activities. In the HCC group, the CL_int of CYP2D6*10 mutant homozygote was decreased by 95% compared to wild-type samples, and the frequency of this homozygote was 2.8-fold lower than the controls.

In conclusion, the activities of CYP isoforms were differentially affected in HCC patients. Genetic polymorphisms of some CYP enzymes, especially CYP2D6*10, could affect enzyme activity. CYP2D6*10 allelic frequency was significantly different between HCC patients and control subjects. These findings may be useful for personalizing the clinical treatment of HCC patients as well as predicting the risk of hepatocarcinogenesis.

Anti-mutagenic and Anti-oxidant Potencies of Cetraria Aculeata (Schreb.) Fr., Cladonia Chlorophaea (Flörke ex Sommerf.) Spreng. and Cetrelia olivetorum (Nyl.) W.L. Culb. & C.F. Culb.)

In this study, the mutagenic and anti-mutagenic effects of methanol extract of three lichen species (Cetraria aculeata, Cladonia chlorophaea and Cetrelia olivetorum) were investigated by using E. coli-WP2, Ames-Salmonella (TA1535 and TA1537) and sister chromatid exchange (SCE) test systems. The results obtained from bacterial test systems demonstrated that methanol extracts of three lichen species have strong anti-mutagenic potencies on TA1535, TA1537 strains and to a lesser extent on E. coli-WP2 strain. The anti-oxidant level of human lymphocytes cells was determined in order to clarify the mechanism underlying the anti-mutagenic effects of these lichen species. Co-treatments of 5, 10 and 20 µg/mL concentrations of these three lichen species with AFB decreased the frequencies of SCE and the level of MDA and increased the amount of SOD, GSH and GPx which decreased by aflatoxin. The findings of this work have clearly demonstrated that Cetraria aculeata, Cladonia chlorophaea and Cetrelia olivetorum have significant anti-mutagenic effects which are thought to be partly due to the anti-oxidant activities and the interaction capability of lichen extracts with mutagen agents (Sodium azide, acridin, N-methyl-N'-nitro-N-nitrosoguanidine and aflatoxin B₁).

Curcumin Successfully Inhibited the Computationally Identified CYP2A6 Enzyme-Mediated Bioactivation of Aflatoxin B1 in Arbor Acres broiler

Cytochrome P450 enzymes are often responsible for the toxic and carcinogenic effects of toxicants, such as aflatoxin B1 (AFB1). The human hepatic CYP2A6 enzyme mediates the oxidative metabolism of several procarcinogens. In this study, we characterized a partial sequence of CYP2A6 gene from Arbor Acres (AA) broiler and studied its role in AFB1 bioactivation. Moreover, the effect of curcumin on CYP2A6 is illustrated. Six groups of AA broiler were treated for 28 days including the control group (fed only basal diet), curcumin alone-treated group (450 mg/kg feed), the group fed AFB1-contaminated feed (5 mg/kg feed) plus the low (150 mg), medium (300 mg) or high (450 mg) of curcumin, and the group fed AFB1-contaminated diet alone (5 mg/kg feed). After the end of treatment period, liver samples were collected for different analyses. The results revealed that the histopathological examination showed clear signs of liver toxicity in AA broliers in AFB1-fed group, but curcumin-supplementation in feed prevented partially AFB1-induced liver toxicity. Liver and body weights were recorded to study the AFB1 harmful effects. We noted an obvious increase in liver weight and decrease in body weight in AFB1-fed group. But, the administration of curcumin partially ameliorated the increase in liver weight and decrease in body weight in a dose-dependent manner. The results (RT-PCR and Elisa) revealed that mRNA and protein expression level enhanced in AFB1-fed group. Consistently, CYP2A6 enzyme activity also increased in AFB1-fed group, suggesting that AA broiler CYP2A6 actively involved in bioactivation of AFB1. However, curcumin treatment inhibited CYP2A6 at mRNA and protein levels in AFB1 treated AA broiler in a dose-dependent manner. Maximum inhibition of liver CYP2A6 enzyme activity in AA broiler has been achieved at a dose of 450 mg/kg curcumin. This is the first study identifying and confirming the role of CYP2A6 enzyme in AFB1 bioactivation in AA broiler liver (in vivo), and the hepatoprotective role of curcumin via inhibiting CYP2A6 expression and enzyme activity. The study contributed to identify an important CYP enzyme involved in AFB1 bioactivation in broilers and thus could pave the way for the prevention of the harmful effects of AFB1 in broilers.

Novel Aflatoxin-Degrading Enzyme from Bacillus shackletonii L7

Food and feed contamination by aflatoxin (AF)B₁ has adverse economic and health consequences. AFB₁ degradation by microorganisms or microbial enzymes provides a promising preventive measure. To this end, the present study tested 43 bacterial isolates collected from maize, rice, and soil samples for AFB₁-reducing activity. The higher activity was detected in isolate L7, which was identified as Bacillus shackletonii. L7 reduced AFB₁, AFB₂, and AFM₁ levels by 92.1%, 84.1%, and 90.4%, respectively, after 72 h at 37 °C. The L7 culture supernatant degraded more AFB₁ than viable cells and cell extracts; and the degradation activity was reduced from 77.9% to 15.3% in the presence of proteinase K and sodium dodecyl sulphate. A thermostable enzyme purified from the boiled supernatant was designated as Bacillus aflatoxin-degrading enzyme (BADE). An overall 9.55-fold purification of BADE with a recovery of 39.92% and an activity of 3.85 × 10³ U·mg-1 was obtained using chromatography on DEAE-Sepharose. BADE had an estimated molecular mass of 22 kDa and exhibited the highest activity at 70 °C and pH 8.0, which was enhanced by Cu2+ and inhibited by Zn2+, Mn2+, Mg2+, and Li⁺. BADE is the major protein involved in AFB₁ detoxification. This is the first report of a BADE isolated from B. shackletonii, which has potential applications in the detoxification of aflatoxins during food and feed processing.

Biodegradation of Mycotoxins: Tales from Known and Unexplored Worlds

Exposure to mycotoxins, secondary metabolites produced by fungi, may infer serious risks for animal and human health and lead to economic losses. Several approaches to reduce these mycotoxins have been investigated such as chemical removal, physical binding, or microbial degradation. This review focuses on the microbial degradation or transformation of mycotoxins, with specific attention to the actual detoxification mechanisms of the mother compound. Furthermore, based on the similarities in chemical structure between groups of mycotoxins and environmentally recalcitrant compounds, known biodegradation pathways and degrading organisms which hold promise for the degradation of mycotoxins are presented.

Scientific concepts and applications of integrated discrete multiple organ co-culture technology

Over several decades, animals have been used as models to investigate the human-specific drug toxicity, but the outcomes are not always reliably extrapolated to the humans in vivo. Appropriate in vitro human-based experimental system that includes in vivo parameters is required for the evaluation of multiple organ interaction, multiple organ/organ-specific toxicity, and metabolism of xenobiotic compounds to avoid the use of animals for toxicity testing. One such versatile in vitro technology in which human primary cells could be used is integrated discrete multiple organ co-culture (IdMOC). IdMOC system adopts wells-within-well concept that facilitates co-culture of cells from different organs in a discrete manner, separately in the respective media in the smaller inner wells which are then interconnected by an overlay of a universal medium in the large containing well. This novel in vitro approach mimics the in vivo situation to a great extent, and employs cells from multiple organs that are physically separated but interconnected by a medium that mimics the systemic circulation and provides for multiple organ interaction. Applications of IdMOC include assessment of multiple organ toxicity, drug distribution, organ-specific toxicity, screening of anticancer drugs, metabolic cytotoxicity, etc.

Modulation of the spleen transcriptome in domestic turkey (Meleagris gallopavo) in response to aflatoxin B1 and probiotics

Poultry are highly susceptible to the immunotoxic effects of the food-borne mycotoxin aflatoxin B1 (AFB1). Exposure impairs cell-mediated and humoral immunity, limits vaccine efficacy, and increases the incidence of costly secondary infections. We investigated the molecular mechanisms of AFB1 immunotoxicity and the ability of a Lactobacillus-based probiotic to protect against aflatoxicosis in the domestic turkey (Meleagris gallopavo). The spleen transcriptome was examined by RNA sequencing (RNA-seq) of 12 individuals representing four treatment groups. Sequences (6.9 Gb) were de novo assembled to produce over 270,000 predicted transcripts and transcript fragments. Differential expression analysis identified 982 transcripts with statistical significance in at least one comparison between treatment groups. Transcripts with known immune functions comprised 27.6 % of significant expression changes in the AFB1-exposed group. Short exposure to AFB1 suppressed innate immune transcripts, especially from antimicrobial genes, but increased the expression of transcripts from E3 ubiquitin-protein ligase CBL-B and multiple interleukin-2 response genes. Up-regulation of transcripts from lymphotactin, granzyme A, and perforin 1 could indicate either increased cytotoxic potential or activation-induced cell death in the spleen during aflatoxicosis. Supplementation with probiotics was found to ameliorate AFB1-induced expression changes for multiple transcripts from antimicrobial and IL-2-response genes. However, probiotics had an overall suppressive effect on immune-related transcripts.

Screening a strain of Aspergillus niger and optimization of fermentation conditions for degradation of aflatoxin B₁

Aflatoxin B₁, a type of highly toxic mycotoxin produced by some species belonging to the Aspergillus genus, such as Aspergillus flavus and Aspergillus parasiticus, is widely distributed in feed matrices. Here, coumarin was used as the sole carbon source to screen microorganism strains that were isolated from types of feed ingredients. Only one isolate (ND-1) was able to degrade aflatoxin B₁ after screening. ND-1 isolate, identified as a strain of Aspergillus niger using phylogenetic analysis on the basis of 18S rDNA, could remove 26.3% of aflatoxin B₁ after 48 h of fermentation in nutrient broth (NB). Optimization of fermentation conditions for aflatoxin B₁ degradation by selected Aspergillus niger was also performed. These results showed that 58.2% of aflatoxin B₁ was degraded after 24 h of culture under the optimal fermentation conditions. The aflatoxin B₁ degradation activity of Aspergillus niger supernatant was significantly stronger than cells and cell extracts. Furthermore, effects of temperature, heat treatment, pH, and metal ions on aflatoxin B₁ degradation by the supernatant were examined. Results indicated that aflatoxin B₁ degradation of Aspergillus niger is enzymatic and this process occurs in the extracellular environment.

Aflatoxin B₁ degradation by a Pseudomonas strain

Aflatoxin B1 (AFB1), one of the most potent naturally occurring mutagens and carcinogens, causes significant threats to the food industry and animal production. In this study, 25 bacteria isolates were collected from grain kernels and soils displaying AFB1 reduction activity. Based on its degradation effectiveness, isolate N17-1 was selected for further characterization and identified as Pseudomonas aeruginosa. P. aeruginosa N17-1 could degrade AFB₁, AFB₂ and AFM₁ by 82.8%, 46.8% and 31.9% after incubation in Nutrient Broth (NB) medium at 37 °C for 72 h, respectively. The culture supernatant of isolate N17-1 degraded AFB₁ effectively, whereas the viable cells and intra cell extracts were far less effective. Factors influencing AFB1 degradation by the culture supernatant were investigated. Maximum degradation was observed at 55 °C. Ions Mn²⁺ and Cu²⁺ were activators for AFB1 degradation, however, ions Mg²⁺, Li⁺, Zn²⁺, Se²⁺, Fe³⁺ were strong inhibitors. Treatments with proteinase K and proteinase K plus SDS significantly reduced the degradation activity of the culture supernatant. No degradation products were observed based on preliminary LC-QTOF/MS analysis, indicating AFB₁ was metabolized to degradation products with chemical properties different from that of AFB₁. The results indicated that the degradation of AFB₁ by P. aeruginosa N17-1 was enzymatic and could have a great potential in industrial applications. This is the first report indicating that the isolate of P. aeruginosa possesses the ability to degrade aflatoxin.

The role of epoxide hydrolases in health and disease

Epoxide hydrolases (EH) are ubiquitously expressed in all living organisms and in almost all organs and tissues. They are mainly subdivided into microsomal and soluble EH and catalyze the hydration of epoxides, three-membered-cyclic ethers, to their corresponding dihydrodiols. Owning to the high chemical reactivity of xenobiotic epoxides, microsomal EH is considered protective enzyme against mutagenic and carcinogenic initiation. Nevertheless, several endogenously produced epoxides of fatty acids function as important regulatory mediators. By mediating the formation of cytotoxic dihydrodiol fatty acids on the expense of cytoprotective epoxides of fatty acids, soluble EH is considered to have cytotoxic activity. Indeed, the attenuation of microsomal EH, achieved by chemical inhibitors or preexists due to specific genetic polymorphisms, is linked to the aggravation of the toxicity of xenobiotics, as well as the risk of cancer and inflammatory diseases, whereas soluble EH inhibition has been emerged as a promising intervention against several diseases, most importantly cardiovascular, lung and metabolic diseases. However, there is reportedly a significant overlap in substrate selectivity between microsomal and soluble EH. In addition, microsomal and soluble EH were found to have the same catalytic triad and identical molecular mechanism. Consequently, the physiological functions of microsomal and soluble EH are also overlapped. Thus, studying the biological effects of microsomal or soluble EH alterations needs to include the effects on both the metabolism of reactive metabolites, as well as epoxides of fatty acids. This review focuses on the multifaceted role of EH in the metabolism of xenobiotic and endogenous epoxides and the impact of EH modulations.

Implications of time-series gene expression profiles of replicative senescence

Although senescence has long been implicated in aging-associated pathologies, it is not clearly understood how senescent cells are linked to these diseases. To address this knowledge gap, we profiled cellular senescence phenotypes and mRNA expression patterns during replicative senescence in human diploid fibroblasts. We identified a sequential order of gain-of-senescence phenotypes: low levels of reactive oxygen species, cell mass/size increases with delayed cell growth, high levels of reactive oxygen species with increases in senescence-associated β-galactosidase activity (SA-β-gal), and high levels of SA-β-gal activity. Gene expression profiling revealed four distinct modules in which genes were prominently expressed at certain stages of senescence, allowing us to divide the process into four stages: early, middle, advanced, and very advanced. Interestingly, the gene expression modules governing each stage supported the development of the associated senescence phenotypes. Senescence-associated secretory phenotype-related genes also displayed a stage-specific expression pattern with three unique features during senescence: differential expression of interleukin isoforms, differential expression of interleukins and their receptors, and differential expression of matrix metalloproteinases and their inhibitory proteins. We validated these phenomena at the protein level using human diploid fibroblasts and aging Sprague-Dawley rat skin tissues. Finally, disease-association analysis of the modular genes also revealed stage-specific patterns. Taken together, our results reflect a detailed process of cellular senescence and provide diverse genome-wide information of cellular backgrounds for senescence.

Definition of metabolism-dependent xenobiotic toxicity with co-cultures of human hepatocytes and mouse 3T3 fibroblasts in the novel integrated discrete multiple organ co-culture (IdMOC) experimental system: results with model toxicants aflatoxin B1, cyclophosphamide and tamoxifen

The integrated discrete multiple organ co-culture system (IdMOC) allows the co-culturing of multiple cell types as physically separated cells interconnected by a common overlying medium. We report here the application of IdMOC with two cell types: the metabolically competent primary human hepatocytes, and a metabolically incompetent cell line, mouse 3T3 fibroblasts, in the definition of the role of hepatic metabolism on the cytotoxicity of three model toxicants: cyclophosphamide (CPA), aflatoxin B1 (AFB) and tamoxifen (TMX). The presence of hepatic metabolism in IdMOC with human hepatocytes was demonstrated by the metabolism of the P450 isoform 3A4 substrate, luciferin-IPA. The three model toxicants showed three distinct patterns of cytotoxic profile: TMX was cytotoxic to 3T3 cells in the absence of hepatocytes, with slightly lower cytotoxicity towards both 3T3 cells and hepatocytes in the IdMOC. AFB was selective toxic towards the human hepatocytes and relatively noncytotoxic towards 3T3 cells both in the presence and absence of the hepatocytes. CPA cytotoxicity to the 3T3 cells was found to be significantly enhanced by the presence of the hepatocytes, with the cytotoxicity dependent of the number of hepatocytes, and with the cytotoxicity attenuated by the presence of a non-specific P450 inhibitor, 1-aminobenzotriazole. We propose here the following classification of toxicants based on the role of hepatic metabolism as defined by the human hepatocyte-3T3 cell IdMOC assay: type I: direct-acting cytotoxicants represented by TMX as indicated by cytotoxicity in 3T3 cells in the absence of hepatocytes; type II: metabolism-dependent cytotoxicity represented by AFB1 with effects localized within the site of metabolic activation (i. e. hepatocytes); and type III: metabolism-dependent cytotoxicity with metabolites that can diffuse out of the hepatocytes to cause toxicity in cells distal from the site of metabolism, as exemplified by CPA.

Mutations in the p53 Tumor Suppressor Gene: Important Milestones at the Various Steps of Tumorigenesis

Inactivation of the p53 tumor suppressor is a frequent event in tumorigenesis. In most cases, the p53 gene is mutated, giving rise to a stable mutant protein whose accumulation is regarded as a hallmark of cancer cells. Mutant p53 proteins not only lose their tumor suppressive activities but often gain additional oncogenic functions that endow cells with growth and survival advantages. Interestingly, mutations in the p53 gene were shown to occur at different phases of the multistep process of malignant transformation, thus contributing differentially to tumor initiation, promotion, aggressiveness, and metastasis. Here, the authors review the different studies on the involvement of p53 inactivation at various stages of tumorigenesis and highlight the specific contribution of p53 mutations at each phase of cancer progression.

Higher susceptibility to aflatoxin B(1)-related hepatocellular carcinoma in glycine N-methyltransferase knockout mice

In both humans and rodents, males are known to be more susceptible than females to hepatocarcinogenesis. We have previously reported that glycine N-methyltransferase (GNMT) interacts with aflatoxin B(1) (AFB(1)) and reduces both AFB(1)-DNA adduct formation and hepatocellular carcinoma (HCC) in mice. We also reported that 50% of the males and 100% of the females in a small group of Gnmt null (Gnmt-/-) mice developed HCC, with first dysplastic hepatocellular nodules detected at mean ages of 17 and 16.5 months, respectively. In our study, we tested our hypothesis that male and female Gnmt-/- mice are susceptible to AFB(1) carcinogenesis, and that the absence of Gnmt expression may accelerate AFB(1)-induced liver tumorigenesis. We inoculated Gnmt-/- and wild-type mice intraperitoneally with AFB(1) at 7 days and 9 weeks of age and periodically examined them using ultrasound. Dysplastic hepatocellular nodules were detected in six of eight males and five of five females at 12.7 and 12 months of ages, respectively. Dysplastic hepatocellular nodules from 5/8 (62.5%) male and 4/5 (80%) female Gnmt-/- mice were diagnosed as having HCC, ∼6 months earlier than AFB(1)-treated wild-type mice. Results from microarray and real-time PCR analyses indicate that five detoxification pathway-related genes were downregulated in AFB(1)-treated Gnmt-/- mice: Cyp1a2, Cyp3a44, Cyp2d22, Gsta4 and Abca8a. In summary, we observed overall higher susceptibility to AFB(1)-related HCC in Gnmt-/- mice, further evidence that GNMT overexpression is an important contributing factor to liver cancer resistance.

Role of reactive metabolites in drug-induced hepatotoxicity

Drugs are generally converted to biologically inactive forms and eliminated from the body, principally by hepatic metabolism. However, certain drugs undergo biotransformation to metabolites that can interfere with cellular functions through their intrinsic chemical reactivity towards glutathione, leading to thiol depletion, and functionally critical macromolecules, resulting in reversible modification, irreversible adduct formation, and irreversible loss of activity. There is now a great deal of evidence which shows that reactive metabolites are formed from drugs known to cause hepatotoxicity, such as acetaminophen, tamoxifen, isoniazid, and amodiaquine. The main theme of this article is to review the evidence for chemically reactive metabolites being initiating factors for the multiple downstream biological events culminating in toxicity. The major objectives are to understand those idiosyncratic hepatotoxicities thought to be caused by chemically reactive metabolites and to define the role of toxic metabolites.

Aflatoxin B1 exposure, hepatitis B virus infection, and hepatocellular carcinoma in Taiwan

To evaluate the role of aflatoxin B1 (AFB1) exposure on risk of hepatocellular carcinoma (HCC), a case-control study nested within a community-based cohort was conducted. Baseline blood and urine samples were used to determine the level of AFB1-albumin adducts and urinary AFB1 metabolites. Conditional logistic regression analysis was used to calculate odds ratios (OR) and 95% confidence intervals (95% CI) to assess the effect of AFB1 exposure on risk of HCC. The adjusted ORs (95% CIs) were 1.54 (1.01-2.36) and 1.76 (1.18-2.58), respectively, for those with AFB1-albumin adducts and urinary AFB1 metabolite levels above the mean compared with those with levels below the mean. When compared with subjects in the lowest quartile of urinary AFB1 metabolites, there was an increase in risk of HCC, with adjusted ORs (95% CIs) of 0.57 (0.14-2.43), 1.43 (0.32-6.42), and 4.91 (1.18-20.48; Ptrend=0.02), respectively, among noncarriers of hepatitis B virus (HBV) infection. The adjusted OR (95% CI) was 7.49 (5.13-10.93) for carriers of hepatitis B surface antigen compared with noncarriers, regardless of AFB1 status. The ORs (95% CI) were 10.38 (5.73-18.82) and 15.13 (7.83-29.25) for carriers of hepatitis B surface antigens with levels of AFB1-albumin adducts and urinary AFB1 metabolites above the mean, respectively. The combined effect of aflatoxin exposure and HBV infection did not differ by duration of follow-up. Consistent with our previous study with fewer subjects, these data show that AFB1 exposure is a risk factor for HCC risk. However, in this larger study, the effect of combined AFB1 exposure and HBV infection is more consistent with an additive than a multiplicative model.

Rainbow trout (Oncorhynchus mykiss) and ultra-low dose cancer studies

Cancer risk assessment utilizing rodents requires extrapolation across five orders of magnitude to estimate the Virtually Safe Dose (VSD). Regulatory agencies rely upon the Linear Extrapolated Dose (LED) except when sufficient information on mechanism of action justifies alternative models. Rainbow trout (Oncorhynchus mykiss) has been utilized at Oregon State University as a model for human cancer for forty years. Low cost and high capacity, made possible by our unique facility, along with low spontaneous background and high sensitivity, allow design and conduct of statistically challenging studies not possible in rodents. Utilization of custom microarrays demonstrates similarities in gene expression in trout and human hepatocellular carcinoma (HCC). We have completed one study employing over 42,000 trout with dibenzo[a,l]pyrene (DBP) and determined the dose resulting in 1 additional cancer in 5000 animals, a 50-fold enhancement over the mouse ED(01) study. Liver tumor incidence at low dose deviated significantly from linearity (concave down), whereas, DBP-DNA adductions deviated slightly (convex up). A second study is underway with aflatoxin B(1) (AFB(1)). Results to date indicate AFB(1) at low dose, in contrast to DBP, elicits a linear dose-response function on the log-log scale which falls below the LED with a slope slightly greater than 1.0. Such studies demonstrate the statistical power of the trout cancer model and strengthen the case for incorporation of these data-sets into risk assessment for these environmental human carcinogens.

Molecular Cloning and Expression of a Novel Cytochrome P450 from Turkey Liver with Aflatoxin B1Oxidizing Activity

Cytochromes P450 are members of a superfamily of oxidative hemoprotein enzymes that metabolize a variety of endogenous and exogenous compounds. Previous studies in our laboratory have shown that efficient P450-mediated activation underlies the extreme sensitivity of poultry, specifically turkeys, to the toxic effects of the mycotoxin aflatoxin B1 (AFB1). Using 3'- and 5'-rapid amplification of cDNA ends (RACE), we amplified from turkey liver RNA a full-length 1.73 kb cDNA predicted to be 528 amino acids with 94.7% sequence identity to a CYP1A5 from chicken liver. A truncated construct of the turkey CYP1A5 gene with 29 amino acids deleted from the hydrophobic NH2-terminal region was cloned and heterologously expressed in Escherichia coli. The expressed protein from E. coli membranes had a CO-binding spectrum typical of P450s, and it catalyzed the O-dealkylation of the CYP1A prototype substrates ethoxyresorufin and methoxyresorufin. CYP1A5-mediated O-dealkylation of methoxyresorufin was completely inhibited by alpha-naphthoflavone, a specific CYP1A inhibitor. Inhibitors to other mammalian P450s (3A4, 2D, 2E, and 3A1) either slightly inhibited this activity or not at all. CYP1A5 oxidized AFB1 to form two metabolites: the reactive intermediate, AFB1 -8,9-epoxide (AFBO), and aflatoxin M1 (AFM1). Because of the importance of AFBO and AFM1 in the toxicity of AFB1, we conclude that this P450 probably plays some role in the well-known hypersensitivity of turkeys to AFB1. To our knowledge, this is the first P450 cloned and sequenced from turkeys, the species in which the toxicity of AFB1 was first discovered.

Hepatocellular carcinoma and polymorphisms in carcinogen-metabolizing and DNA repair enzymes in a population with aflatoxin exposure and hepatitis B virus endemicity

High rates of hepatocellular carcinoma (HCC) in The Gambia, West Africa, are primarily due to a high prevalence of chronic hepatitis B virus infection and heavy aflatoxin exposure via groundnut consumption. We investigated genetic polymorphisms in carcinogen-metabolizing (GSTM1, GSTT1, HYL1*2) and DNA repair (XRCC1) enzymes in a hospital-based case-control study. Incident HCC cases (n = 216) were compared with frequency-matched controls (n = 408) with no clinically apparent liver disease. Although the prevalence of variant genotypes was generally low, in multivariable analysis (adjusting for demographic factors, hepatitis B virus, hepatitis C virus, and TP53 status), the GSTM1-null genotype [odds ratio (OR), 2.45; 95% confidence interval (95% CI), 1.21-4.95] and the heterozygote XRCC1-399 AG genotype (OR, 3.18; 95% CI, 1.35-7.51) were significantly associated with HCC. A weak association of the HYL1*2 polymorphism with HCC was observed but did not reach statistical significance. GSTT1 was not associated with HCC. The risk for HCC with null GSTM1 was most prominent among those with the highest groundnut consumption (OR, 4.67; 95% CI, 1.45-15.1) and was not evident among those with less than the mean groundnut intake (OR, 0.64; 95% CI, 0.20-2.02). Among participants who had all three suspected aflatoxin-related high-risk genotypes [GSTM1 null, HLY1*2 (HY/HH), and XRCC1 (AG/GG)], a significant 15-fold increased risk of HCC was observed albeit with imprecise estimates (OR, 14.7; 95% CI, 1.27-169). Our findings suggest that genetic modulation of carcinogen metabolism and DNA repair can alter susceptibility to HCC and that these effects may be modified by environmental factors.

Interindividual differences in response to chemoprotection against aflatoxin-induced hepatocarcinogenesis: implications for human biotransformation enzyme polymorphisms

It is now evident that most, if not all, of the remarkable species differences in susceptibility to AFB hepatocarcinogenesis is due in large part, if not exclusively, to differences in biotransformation. Certainly the relative rate of oxidative formation of the proximate carcinogen, AFB-8,9-exo-epoxide, is an important determinant of species and interindividual differences in susceptibility to AFB. However, mice produce relatively large amounts of exo-AFBO, yet are highly resistant to AFB-hepatocarcinogenesis because they express a particular form of GST with remarkably high catalytic activity toward the exo-epoxide of AFB. Rats, which are highly susceptible to AFB hepatocarcinogenesis,can be made resistant through dietary induction of an orthologous form of GST that is normally expressed in only very small amounts. Based on these findings in laboratory animal models, there is great interest in identifying chemicals and/or specific dietary constituents that could offer protection against AFB-hepatocarcinogenesis to humans. Current experimental strategies have focused on the antiparasitic drug, oltipraz, which induces protection in rats and has also shown some promise in humans. The mechanism of protection in rats appears to be via induction of an alpha class GST with high catalytic activity toward AFBO (rGSTA5-5). vet human alpha class GST proteins that are constitutively expressed in the liver (hGSTA1 and hGSTA2) have little, if any activity toward AFBO. Rather, it appears that mu class GSTs may be responsible for the very low, but potentially significant, detoxification activity toward AFBO. Oltipraz and certain dietary constituents may induce mu class GSTs in human liver, and this could afford some protection against the genotoxic effects of AFBO. However, it also appears that oltipraz, and perhaps certain dietary constituents, act as competitive inhibitors of human CYP1A2. As CYP1A2 appears to mediate most of the activation of AFB to exo-AFBO in human liver at low dietary concentrations of AFB encountered in the human diet, much of the putative protective effects of oltipraz could be mediated via inhibition of CYP1A2 rather than induction of GSTs. There is now evidence that human microsomal epoxide hydrolase (mEH) could play a role in protecting human DNA from the genotoxic effects of AFB, although the importance of this detoxification pathway, relative to mu class GSTs, remains to be elucidated. Oltipraz is an effective inducer of mEH in rats (Lamb Franklin, 2000), and thus induction of this pathway in humans could also potentially contribute to the protective effects of this drug toward AFB genotoxicity. Because the dihydrodiol of AFB may contribute indirectly to the carcinogenic effects of AFB via protein adduction and subsequent hepatotoxicity, the recently characterized human aflatoxin aldehyde reductase (AFAR) may also offer some protection against AFB-induced carcinogenicity in humans. Current and future dietary and/or chemointervention strategies aimed at reducing the carcinogenic effects of AFB in humans should consider all of the possible mechanistic approaches for modifying AFB-induced genotoxicity.

A polymorphism in the gene for microsomal epoxide hydrolase is associated with pre-eclampsia

OBJECTIVE

Microsomal epoxide hydrolase is an important enzyme involved in the metabolism of endogenous and exogenous toxicants. Polymorphic variants of the human epoxide hydrolase gene vary in enzyme activity. We determined whether genetic variability in the gene encoding for microsomal epoxide hydrolase contributes to individual differences in susceptibility to the development of pre-eclampsia with or without the syndrome of Haemolysis, Elevated Liver enzymes, and Low Platelets (HELLP).

METHODS

A total of 183 non-pregnant women with a history of pre-eclampsia, 96 of whom had concurrently developed the HELLP syndrome, and 151 healthy female controls were genotyped for the 113Tyr-->His polymorphism in exon 3 and the 139His-->Arg polymorphism in exon 4 of the epoxide hydrolase gene by a polymerase chain reaction-restriction fragment length polymorphism assay. Chi-square analysis was used for statistical evaluation of differences in polymorphic rates.

RESULTS

In pre-eclampsia a higher frequency (29%) of the high activity genotype Tyr113 Tyr113 in exon 3 was found as compared to controls (16%, OR 2.0, 95% CI 1.2-3.7). There was no difference between groups for the 139His-->Arg polymorphism. In women with a history of pre-eclampsia, no difference in epoxide hydrolase genotypes was found between women who either did or did not develop the HELLP syndrome. In addition, a significant association was found between predicted EPHX activity and pre-eclampsia.

CONCLUSIONS

Women with the high activity genotype in exon 3, which could reflect differences in metabolic activation of endogenous or exogenous toxic compounds, may have enhanced susceptibility to pre-eclampsia. However, polymorphisms in the epoxide hydrolase gene do not seem to influence the risk for concurrent development of the HELLP syndrome.