Bioactivation of aflatoxin B1 by turkey liver microsomes: responsible cytochrome P450 enzymes

Human CYP1A1-activated aneugenicity of aflatoxin B1 in mammalian cells and its combined effect with benzo(a)pyrene

Aflatoxin B1 (AFB1) is the most toxic mycotoxin and a proven human carcinogen that requires metabolic activation, known by cytochrome P450 (CYP) 1A2 and 3A4. Previous evidence showed that AFB1 is activated by human recombinant CYP1A1 expressed in budding yeast. Yet, the toxicity, in particular the genotoxicity of the reactive metabolites formed from AFB1 remains unclear. Humans could be exposed to both AFB1 and benzo(a)pyrene (BaP) simultaneously, thus we were interested in their combined genotoxic effects subsequent to metabolic activation by CYP1A1. In this study, molecular docking of AFB1 to human CYP1A1 indicated that AFB1 is valid as a substrate. In the incubations with AFB1 in human CYP1A1-expressed microsomes, AFM1 as a marking metabolite of AFB1 was detected. Moreover, AFB1 induced micronucleus formation in a Chinese hamster V79-derived cell line and in a human lung epithelial BEAS-2B cell line, both expressing recombinant human CYP1A1, V79-hCYP1A1 and 2B-hCYP1A1 cells, respectively. Immunofluorescence of centromere protein B stained micronuclei was dominant in AFB1-treated BEAS-2B cells exposed to AFB1, suggesting an aneugenic effect. Moreover, AFB1 elevated the levels of ROS, 8-OHdG, AFB1-DNA adduct, and DNA breaks in 2B-hCYP1A1 cells, compared with those in the parental BEAS-2B cells. Meanwhile, AFB1 increased CYP1A1, RAD51, and γ-H2AX protein levels in 2B-hCYP1A1 cells, which were attenuated by the CYP1A1 inhibitor bergamottin. Co-exposure of AFB1 with BaP increased 8-OHdG, RAD51, and γ-H2AX levels (indicating DNA damage). In conclusion, AFB1 could be activated by human CYP1A1 for potent aneugenicity, which may be further enhanced by co-exposure to BaP.

Chicken CYP1A5 is able to hydroxylate aflatoxin B1 to aflatoxin M1

Aflatoxin B1 (AFB1), a naturally-occurring mycotoxin, can cause severe toxicological and carcinogenic effects in livestock and humans. Given that the chicken is one of the most important food-producing animals, knowledge regarding AFB1 metabolism and enzymes responsible for AFB1 transformation in the chicken has important implications for chicken production and food safety. Previously, we have successfully expressed chicken CYP1A5 and CYP3A37 monooxygenases in E. coli, and reconstituted them into a functional CYP system consisting of CYP1A5 or CYP3A37, CPR and cytochrome b5. In this study, we aimed to investigate the roles of CYP1A5 and CYP3A37 in the bioconversion of AFB1 to AFM1. Our results showed that chicken CYP1A5 was able to hydroxylate AFB1 to AFM1. The formation of AFM1 followed the typical Michaelis-Menten kinetics. The kinetics parameters of Vmax and Km were determined as 0.83 ± 0.039 nmol/min/nmol P450 and 26.9 ± 4.52 μM respectively. Docking simulations further revealed that AFB1 adopts a "side-on" conformation in chicken CYP1A5, facilitating the hydroxylation of the C9a atom and the production of AFM1. On the other hand, AFB1 assumes a "face-on" conformation in chicken CYP3A37, leading to the displacement of the C9a atom from the heme iron and explaining the lack of AFM1 hydroxylation activity. The results demonstrate that chicken CYP1A5 possesses efficient hydroxylase activity towards AFB1 to form AFM1.

Involvement of glyphosate in disruption of biotransformation P450 enzymes and hepatic lipid metabolism in chicken

The current study investigated the potentially harmful consequences of pure glyphosate or Roundup® on CYP family members and lipid metabolism in newly hatched chicks. On the sixth day, 225 fertilized eggs were randomly divided into three treatments: (1) the control group injected with deionized water, (2) the glyphosate group injected with 10 mg pure glyphosate/Kg egg mass and (3) the Roundup group injected 10 mg the active ingredient glyphosate in Roundup®/Kg egg. The results of the study revealed a reduction in hatchability in chicks treated with Roundup®. Moreover, change of Lipid concentration in serum and the liver-treated groups. Additionally, increased liver function enzymes and increased oxidative stress in the glyphosate and Roundup® groups. Furthermore, liver tissues showed histological changes and several lipid deposits in glyphosate-treated groups. Hepatic CYP1A2 and CYP1A4 expressions were significantly increased (p < .05) after glyphosate exposure, and suppression of CYP1C1 mRNA expression was significant (p < .05) after Roundup® exposure. The pro-inflammatory cytokines genes IFN-γ and IL-1β expression were significantly increased (p < .05) after Roundup® exposure. In addition, there were significant differences in the levels of expression genes which are related to lipid synthesis or catabolism in the liver. In conclusion, in ovo glyphosate exposure caused disruption of biotransformation, pro-inflammatory and lipid metabolism in chicks.

The metabolism and biotransformation of AFB1: Key enzymes and pathways

Aflatoxins B₁ (AFB₁) is a hepatoxic compound produced by Aspergillus flavus and Aspergillus parasiticus, seriously threatening food safety and the health of humans and animals. Understanding the metabolism of AFB₁ is important for developing detoxification and intervention strategies. In this review, we summarize the AFB₁ metabolic fates in humans and animals and the key enzymes that metabolize AFB₁, including cytochrome P450s (CYP450s) for AFB₁ bioactivation, glutathione-S-transferases (GSTs) and aflatoxin-aldehyde reductases (AFARs) in detoxification. Furthermore, AFB₁ metabolism in microbes is also summarized. Microorganisms specifically and efficiently transform AFB₁ into less or non-toxic products in an environmental-friendly approach which could be the most desirable detoxification strategy in the future. This review provides a wholistic insight into the metabolism and biotransformation of AFB₁ in various organisms, which also benefits the development of protective strategies in humans and animals.

The Mechanism Underlying the Extreme Sensitivity of Duck to Aflatoxin B1

Most metabolites of aflatoxin B1 (AFB1), especially exo-AFB1-8,9-epoxide (AFBO), can induce the production of reactive oxygen species (ROS) to vary degrees, causing oxidative stress and liver damage, and ultimately induce liver cancer in humans and animals. Duck is one of the most sensitive animals to AFB1, and severe economic losses are caused by duck AFB1 poisoning every year, but the exact mechanism of this high sensitivity is still unclear. This review highlights significant advances in our understanding of the AFB1 metabolic activation, like cytochrome P450s (CYPs), and AFB1 metabolic detoxification, like glutathione S-transferases (GSTs) in poultry. In addition, AFB1 may have other metabolic pathways in poultry, such as the mutual conversion of AFB1 and aflatoxicol (AFL) and the process of AFBO to produce AFB1-8,9-dihydrodiol (AFB1-dhd) and further metabolize it into detoxification substances. This review also summarized some exogenous regulatory substances that can alleviate AFB1-induced oxidative stress.

Phase-1 bioactivation mechanisms of aflatoxin through AhR, CAR and PXR nuclear receptors and the interactions with Nigella sativa seeds and thymoquinone in broilers

Aflatoxins (AFs) are metabolised in two main phases in the liver. Cytochrome p450 enzyme (CYP) 1A1 and CYP2A6 are expressed through AhR, CAR and PXR nuclear receptors in phase-1 biotransformation of AFs. This study is the first to examine phase-1 biotransformation mechanisms of AF and the activity of Nigella sativa seed (NS) and its active ingredient thymoquinone (TQ) on these enzymes and receptors at the molecular level in broilers. Six groups of one day old broiler chicken (20 animals per group) were fed either control feed or a diet containing Aspergillus parasiticus NRRL 2999 culture material (total AFs 2 mg/kg), TQ (300 mg/kg), and NS (5%), either alone or as AF + TQ and AF + NS. Randomly selected from each group, 10 chicks were necropsied, and the livers were removed. Histopathological examination and serum biochemistry results revealed that AF caused hydropic and fatty degenerations, periportal inflammatory infiltrations, acinar arrangement, and biliary duct proliferation in livers and a significant increase at AST, ALT, ALP and GGT levels while significant decreases at serum cholesterol and total protein levels. These aflatoxicosis lesions and deteriorations in biochemistry levels were significantly ameliorated by NS or TQ (p < 0.05). AF was immunohistochemically found to increase strongly the nuclear receptors of AhR, PXR, CAR, and the enzyme activity of CYP1A1 and CYP2A6 responsible for its metabolism, leading to the emergence of toxic effects. Addition of TQ or NS to AF-containing diets improved the negative effects of AF on these receptors and enzymes significantly (p < 0.05). It was concluded that TQ and NS successfully alleviated liver injury by inhibiting or reducing the bioactivation of AF through phase-1 nuclear receptors and CYP-450 enzymes modulation.

Disruption of cytochrome P450 enzymes in the liver and small intestine in chicken embryos in ovo exposed to glyphosate

Glyphosate is the active component of several commercial formulations as in Roundup®. The present study was investigated the toxic effects of pure glyphosate or Roundup® on the liver and small intestine of chick embryos. On day 6, a total of 180 fertile eggs injected with deionized water (control group), 10 mg pure glyphosate, or 10 mg of the active ingredient glyphosate in Roundup®/kg egg mass. The results showed an increase in relative weights of the liver in embryos that treated with Roundup®. Furthermore, oxidative stress was observed in the embryos treated with glyphosate or Roundup®, increased total superoxide dismutase, and content of malondialdehyde in the liver and intestine; moreover, decrease of glutathione peroxidase in the liver with increased in the intestine compared with the control. Besides, glutamic-pyruvic transaminase was increased in Roundup® group compared with other groups. Moreover, histopathological alterations in the liver and intestine tissues were observed in treated groups. Suppression of hepatic CYP1A2, CYP1A4, CYP1B1, and MDR1 mRNA expression after exposed to Roundup®. Furthermore, inhibition of CYP1A4 in the duodenum, CYP1A4, and MRP2 in the jejunum in embryos exposed to glyphosate or Roundup®. In addition, glyphosate treatment caused an increase of CYP3A5, CYP1C1, and IFNY mRNA expression in the jejunum and CYP1A2 expression in the ileum, while IFN-Y gene increase in embryos treated with Roundup®. In conclusion, in ovo exposure to glyphosate caused histopathological alterations and induced oxidative stress in the liver and small intestines. Moreover, the expression of cytochrome P450, MDR1, and MRP2 transporters was also modulated in the liver and small intestines for chick embryos.

An unusually high production of hepatic aflatoxin B1-dihydrodiol, the possible explanation for the high susceptibility of ducks to aflatoxin B1

A study was conducted to determine the enzymatic kinetic parameters V_max, K_M, and intrinsic clearance (CL_int) for the hepatic in vitro production of aflatoxin B₁-dihydrodiol (AFB₁-dhd) from aflatoxin B₁ (AFB₁) in four commercial poultry species, ranging in sensitivity to AFB₁ from highest (ducks) to lowest (chickens). Significant but small differences were seen for V_max, while large significant differences were observed for K_M. However, the largest inter-species differences were observed for the CL_int parameter, with ducks being extraordinarily efficient in converting AFB₁ into AFB₁-dhd. Since AFB₁-dhd is considered the metabolite responsible for the acute toxic effects of AFB₁, the high hepatic production of AFB₁-dhd from AFB₁ in ducks is the possible biochemical explanation for the extraordinary high sensitivity of this poultry species to the adverse effects of AFB₁.

Study on the inhibitory effect of furafylline and troleandomycin in the 7-methoxyresorufin-O-demethylase and nifedipine oxidase activities in hepatic microsomes from four poultry species using high-performance liquid chromatography coupled with fluorescence and ultraviolet detection

The present study reports the in vitro studies with furafylline and troleandomycin (TAO) as specific inhibitors of activities 7-methoxyresorufin-O-demethylase (MROD) and nifedipine oxidase, catalyzed by cytochrome P450 1 A2 (CYP1 A2) and 3A4 human enzymes, respectively, in hepatic microsomes of quail, duck, turkey and chicken. The results suggest that in chicken and quail the MROD activity is carried out by orthologs CYP1 A4 and 1 A5, meanwhile in duck and turkey by a CYP1 A5 ortholog. The nifedipine oxidase activity is carried out by orthologs of the CYP3A family in the four bird species. The use of furafylline and TAO significantly decreased these activities (P < 0.05) and suggested that the biotransformation of resorufin methyl ether (RME) may be related to more than one avian ortholog.

Dual Role of Dietary Curcumin Through Attenuating AFB1-Induced Oxidative Stress and Liver Injury via Modulating Liver Phase-I and Phase-II Enzymes Involved in AFB1 Bioactivation and Detoxification

It is well understood that liver cytochrome p450 enzymes are responsible for AFB1 bioactivation, while phase-II enzymes regulated by the transcription factor nuclear factor-erythroid-2-related factor 2 (Nrf2) are involved in detoxification of AFB1. In this study, we explored the potential of curcumin to prevent AFB1-induced liver injury by modulating liver phase-I and phase-II enzymes along with Nrf2 involved in AFB1 bioactivation and detoxification. Arbor Acres broiler were divided into four groups including control group (G1; fed only basal feed), curcumin alone-treated group (G2; 450 mg/kg feed), AFB1-fed group (G3; 5 mg/kg feed), and curcumin plus AFB1 group (G4; 5 mg AFB1+450 mg curcumin/kg feed). After 28 days, liver and blood samples were collected for different analyses. Histological and phenotypic results revealed that AFB1-induced liver injury was partially ameliorated by curcumin supplementation. Compared to AFB1 alone-treated group, serum biochemical parameters and liver antioxidant status showed that curcumin supplementation significantly prevented AFB1-induced liver injury. RT-PCR and western blot results revealed that curcumin inhibited CYP enzymes-mediated bioactivation of AFB1 at mRNA and protein level. Transcription factor Nrf2, its downstream genes such as GSTA3, and GSTM2 mRNA, and protein expression level significantly upregulated via dietary curcumin. In addition, GSTs enzyme activity was enhanced with dietary curcumin which plays a crucial role in AFB1-detoxification. Conclusively, the study provided a scientific basis for the use of curcumin in broiler's diet and contributed to explore the multi-target preventive actions of curcumin against AFB1-induced liver injury through the modulation of phase-I and phase-II enzymes, and its potent anti-oxidative effects.

Aflatoxin B1 Induced Systemic Toxicity in Poultry and Rescue Effects of Selenium and Zinc

Among many challenges, exposure to aflatoxins, particularly aflatoxin B₁ (AFB₁), is one of the major concerns in poultry industry. AFB₁ intoxication results in decreased meat/egg production, hepatotoxicity, nephrotoxicity, disturbance in gastrointestinal tract (GIT) and reproduction, immune suppression, and increased disease susceptibility. Selenium (Se) and zinc (Zn), in dietary supplementation, offer easy, cost-effective, and efficient ways to neutralize the toxic effect of AFB₁. In the current review, we discussed the impact of AFB₁ on poultry industry, its biotransformation, and organ-specific noxious effects, along with the action mechanism of AFB₁-induced toxicity. Moreover, we explained the biological and detoxifying roles of Se and Zn in avian species as well as the protection mechanism of these two trace elements. Ultimately, we discussed the use of Se and Zn supplementation against AFB₁-induced toxicity in poultry birds.

The aflatoxin B1 -fumonisin B1 toxicity in BRL-3A hepatocytes is associated to induction of cytochrome P450 activity and arachidonic acid metabolism

Human oral exposure to aflatoxin B₁ (AFB₁ ) and fumonisin B₁ (FB₁ ) is associated with increased hepatocellular carcinoma. Although evidence suggested interactive AFB₁ -FB₁ hepatotoxicity, the underlying mechanisms remain mostly unidentified. This work was aimed at evaluating the possible AFB₁ -FB₁ interplay to induce genetic and cell cycle toxicities in BRL-3A rat hepatocytes, reactive oxygen species (ROS) involvement, and the AFB₁ metabolizing pathways cytochrome P450 (CYP) and arachidonic acid (ArAc) metabolism as ROS contributors. Flow cytometry of stained BRL-3A hepatocytes was used to study the cell cycle (propidium iodide), ROS intracellular production (DCFH-DA, HE, DAF-2 DA), and phospholipase A activity (staining with bis-BODIPY FL C11-PC). The CYP1A activity was assessed by the 7-ethoxyresorufin-O-deethylase (EROD) assay. Despite a 48-h exposure to FB₁ (30 μM) not being genotoxic, the AFB₁ (20 μM)-induced micronucleus frequency was overcome by the AFB₁ -FB₁ mixture (MIX), presumably showing toxin interaction. The mycotoxins blocked G1/S-phase, but only MIX caused cell death. Overall, the oxidative stress led these alterations as the pretreatment with N-acetyl-l-cysteine reduced such toxic effects. While AFB₁ had a major input to the MIX pro-oxidant activity, with CYP and ArAc metabolism being ROS contributors, these pathways were not involved in the FB₁ -elicited weak oxidative stress. The MIX-induced micronucleus frequency in N-acetyl-l-cysteine pretreated cells was greater than that caused by AFB₁ without antioxidants, suggesting enhanced AFB₁ direct genotoxicity probably owing to the higher CYP activity and ArAc metabolism found in MIX. The metabolic pathways modulation by AFB₁ -FB₁ mixtures could raise its hepatocarcinogenic properties.

Efficacy and insecticidal properties of some essential oils against Caryedon serratus (Oliver)-a storage pest of groundnut

During storage groundnut is attacked by number of stored grain pest and management of these insect pests particularly bruchid beetle, Caryedon serratus (Oliver) is of prime importance as they directly damage the pod and kernels. Hence, some essential oils were tested for their insecticidal and fungicidal properties. Highest total bruchid mortality was recorded with the application of neem oil and pongamia oil at 10% (v/w) concentration and lowest in eucalyptus oil at 5% (v/w). Number of eggs laid was recorded 2.3 in neem oil 10% (v/w) which was lowest and significantly superior over untreated control and was at par with castor oil 10% (v/w) which recorded 2.5 eggs per 100 g of groundnut pods. There was no adult emergence in the groundnut pods treated with castor oil, eucalyptus oil, neem oil and pongamia oil at 10% (v/w) concentration. Groundnut pods treated with castor oil, eucalyptus oil, neem oil and pongamia oil at 10% (v/w) and neem oil at 5% (v/w) concentrations recorded no damage to pods and kernels and also zero per cent weight loss. These oils effectively influenced groundnut bruchid establishment and reduce damage besides reduction in aflatoxin contamination.

Metabolism of aflatoxins: key enzymes and interindividual as well as interspecies differences

Aflatoxins are potent hepatocarcinogen in animal models and suspected carcinogen in humans. The most important aflatoxin in terms of toxic potency and occurrence is aflatoxin B1 (AFB1). In this review, we mainly summarized the key metabolizing enzymes of AFB1 in animals and humans. Moreover, the interindividual and the interspecies differences in AFB1 metabolism are highly concerned. In human liver, CYP3A4 plays an important role in biotransforming AFB1 to the toxic product AFB1-8,9-epoxide. In human lung, CYP2A13 has a significant activity in metabolizing AFB1 to AFB1-8,9-epoxide and AFM1-8,9-epoxide. The epoxide of AFB1-8,9-epoxide could conjugate with glutathione to reduce the toxicity by glutathione-S-transferase (GST). In poultry species, CYP2A6, CYP3A37, CYP1A5, and CYP1A1 are responsible for bioactivation of AFB1. There are interindividual variations in the rate of activation of aflatoxins in various species, and there are also differences between children and adults. The age and living regions are important factors affecting resistance of species to AFB1. The rate of AFB1-8,9-epoxide formation and its conjugation with glutathione are key parameters in interspecies and interindividual differences in sensitivity to the toxic effect of AFB1. This review provides an important information for key metabolizing enzymes and the global metabolism of aflatoxins in different species.

Aflatoxicosis chemoprevention by probiotic Lactobacillius and lack of effect on the major histocompatibility complex

Turkeys are extremely sensitive to aflatoxin B1 (AFB1) which causes decreased growth, immunosuppression and liver necrosis. The purpose of this study was to determine whether probiotic Lactobacillus, shown to be protective in animal and clinical studies, would likewise confer protection in turkeys, which were treated for 11 days with either AFB1 (AFB; 1 ppm in diet), probiotic (PB; 1 × 10(11) CFU/ml; oral, daily), probiotic + AFB1 (PBAFB), or PBS control (CNTL). The AFB1 induced drop in body and liver weights were restored to normal in CNTL and PBAFB groups. Hepatotoxicity markers were not significantly reduced by probiotic treatment. Major histocompatibility complex (MHC) genes BG1 and BG4, which are differentially expressed in liver and spleens, were not significantly affected by treatments. These data indicate modest protection, but the relatively high dietary AFB1 treatment, and the extreme sensitivity of this species may reveal limits of probiotic-based protection strategies.

Aflatoxin B1: toxicity, bioactivation and detoxification in the polyphagous caterpillar Trichoplusia ni

Trichoplusia ni caterpillars are polyphagous foliage-feeders and rarely likely to encounter aflatoxin B1 (AFB1), a mycotoxin produced by Aspergillus flavus and A. parasiticus, in their host plants. To determine how T. ni copes with AFB1, we evaluated the toxicity of AFB1 to T. ni caterpillars at different developmental stages and found that AFB1 tolerance significantly increases with larval development. Diet incorporation of AFB1 at 1 μg/g completely inhibited larval growth and pupation of newly hatched larvae, but 3 μg/g AFB1 did not have apparent toxic effects on larval growth and pupation of caterpillars that first consume this compound 10 days after hatching. Piperonyl butoxide, a general inhibitor of cytochrome P450 monooxygenases (P450s), reduced the toxicity of AFB1, suggesting that AFB1 is bioactivated in T. ni and this bioactivation is mediated by P450s. Some plant allelochemicals, including flavonoids such as flavones, furanocoumarins such as xanthotoxin and imperatorin, and furanochromones such as visnagin, that induce P450s in other lepidopteran larvae ameliorated AFB1 toxicity, suggesting that P450s are also involved in AFB1 detoxification in T. ni.

Characterization of chicken cytochrome P450 1A4 and 1A5: inter-paralog comparisons of substrate preference and inhibitor selectivity

The chicken (Gallus gallus) is one of the most economically important domestic animals and also an avian model species. Chickens have two CYP1A genes (CYP1A4 and CYP1A5) which are orthologous to mammalian CYP1A1 and CYP1A2. Although the importance of chicken CYP1As in metabolism of endogenous compounds and xenobiotics is well recognized, their enzymatic properties, substrate preference and inhibitor selectivity remain poorly understood. In this study, functional enzymes of chicken CYP1A4 and CYP1A5 were successfully produced in Escherichia coli (E. coli). The substrate preference and inhibitor specificity of the two chicken CYP1As were compared. Kinetic results showed that the enzymatic parameters (K(m), V(max), V(max)/K(m)) for ethoxyresorufin O-deethylase (EROD) and benzyloxyresorufin O-debenzylase (BROD) differed between CYP1A4 and CYP1A5, while no significant difference was observed for methoxyresorufin O-demethylase (MROD). Lower K(m) of CYP1A4 for BROD suggests that CYP1A4 has a greater binding affinity to benzyloxyresorufin than either ethoxyresorufin or methoxyresorufin. The highest V(max)/K(m) ratio was seen in BROD activity for CYP1A4 and in MROD for CYP1A5 respectively. These results indicate that substrate preference of chicken CYP1As is more notably distinguished by BROD activity and CYP1A5 prefers shorter alkoxyresorufins resembling its mammalian ortholog CYP1A2. Differential patterns of MROD inhibition were observed between CYP1As and among the five CYP inhibitors (α-naphthoflavone, furafylline, piperonyl butoxide, erythromycin and ketoconazole). α-Naphthoflavone was determined to be a potent MROD inhibitor of both CYP1A4 and CYP1A5. In contrast, no or only a trace inhibitory effect (<15%) was observed by erythromycin at a concentration of 500 μM. Stronger inhibition of MROD activity was found in CYP1A5 than CYP1A4 by relatively small molecules α-naphthoflavone, piperonyl butoxide and furafylline. AROD kinetics and inhibition profiles between chicken CYP1A4 and CYP1A5 demonstrate that the two paralogous members of the CYP1A subfamily have distinct enzymatic properties, reflecting differences in the active site geometry between CYP1A4 and CYP1A5. These findings suggest that CYP1A4 and CYP1A5 play partially overlapping but distinctly different physiological and toxicological roles in the chicken.

Influence of broccoli extract and various essential oils on performance and expression of xenobiotic- and antioxidant enzymes in broiler chickens

The aim of our present study was to examine the regulation of xenobiotic- and antioxidant enzymes by phytogenic feed additives in the intestine and the liver of broilers. A total of 240 male Ross-308 broiler chickens (1 d old) were fed a commercial starter diet for 2 weeks. On day 15, the birds were assigned to six treatment groups of forty birds each. The control (Con) group was fed a diet without any additive for 3 weeks. The diet of group sulforaphane (SFN) contained broccoli extract providing 0.075 g/kg SFN, whereas the diets of the other four groups contained 0.15 g/kg essential oils from turmeric (Cuo), oregano (Oo), thyme and rosemary (Ro). Weight gain and feed conversion were slightly impaired by Cuo and Oo. In the jejunum SFN, Cuo and Ro increased the expression of xenobiotic enzymes (epoxide hydrolases 1 and 2 and aflatoxin B1 aldehyde reductase) and of the antioxidant enzyme haeme oxygenase regulated by an 'antioxidant response element' (ARE) compared to group Con. In contrast to our expectations in the liver, the expression of these enzymes was decreased by all the additives. Nevertheless, all the additives increased the Trolox equivalent antioxidant capacity of the jejunum and the liver and reduced Fe-induced lipid peroxidation in the liver. We conclude that the up-regulation of ARE genes in the small intestine reduces oxidative stress in the organism and represents a novel mechanism by which phytogenic feed additives improve the health of farm animals.