Biochemical basis for the extreme sensitivity of turkeys to aflatoxin B(1)

LC-MS/MS determination of N-acetyl-l-cysteine in chicken plasma

N-acetyl-l-cysteine (NAC) shows beneficial effects in cases of aflatoxicosis and heat stress in poultry but little is known about its pharmacokinetics in chickens. Therefore, the study aimed to develop and validate a sensitive LC-MS/MS analytical method for quantitative analysis of NAC in chicken plasma. A split calibration curve approach was used for determination of NAC in chicken plasma. Standard curves for low (0.05-2.5 μg/ml) and high (2.5-100 μg/ml) ranges of concentrations were prepared. The standard curves for low (r2 = 0.9987) and high (r2 = 0.9899) concentrations were linear within the tested range. The limits of detection (LOD) and of quantification (LOQ) for the standard at low concentrations were 0.093 and 0.28 μg/ml, respectively. The accuracy was from 97.35 to 101.33%. The values of LOD and LOQ for the standard at high concentrations were 0.76 and 2.30 μg/ml, respectively. The accuracy was between 99.77 and 112.14%. The intra- and inter-day precisions for all concentrations from both standards did not exceed 8.57% and 10.69%, respectively. The recovery for all concentrations was between 92.45 and 105.52%. The validated method for determination of NAC in chicken plasma can be applied in future pharmacokinetic studies in chickens without dilution of samples and their repeated analysis.

Aflatoxin B1 in poultry liver: Toxic mechanism

Aflatoxin B1 (AFB1) is the most common carcinogenic toxin in livestock and poultry feed, seriously endangering poultry production and public health. Liver is the most important organ for the metabolism of exogenous and endogenous substances in the body. AFB1 produces toxicity under the biotransformation of cytochrome P450 microparticle oxidase (CYP450). Hepatocytes are the most important cells for synthesizing CYP450 enzymes, so that AFB1 has the most significant effect on the liver. AFB1 can induce liver cell damage in poultry through a variety of molecular mechanisms, and the main of damage mechanisms have been discovered so far include oxidative damage, promoting apoptosis, influencing hepatocyte gene expression, interfering with hepatocyte autophagy, pyroptosis and necroptosis. This article reviewed the molecular mechanism of AFB1 inducing liver injury in poultry, hopefully, to provid a new direction and theoretical basis for the development of a new AFB1 detoxification method.

Research update on aflatoxins toxicity, metabolism, distribution, and detection: A concise overview

Serious health risks associated with the consumption of food products contaminated with aflatoxins (AFs) are worldwide recognized and depend predominantly on consumed AF concentration by diet. A low concentration of aflatoxins in cereals and related food commodities is unavoidable, especially in subtropic and tropic regions. Accordingly, risk assessment guidelines established by regulatory bodies in different countries help in the prevention of aflatoxin intoxication and the protection of public health. By assessing the maximal levels of aflatoxins in food products which are a potential risk to human health, it's possible to establish appropriate risk management strategies. Regarding, a few factors are crucial for making a rational risk management decision, such as toxicological profile, adequate information concerning the exposure duration, availability of routine and some novel analytical techniques, socioeconomic factors, food intake patterns, and maximal allowed levels of each aflatoxin in different food products which may be varied between countries.

Detoxication and bioconversion of aflatoxin B1 by yellow mealworms (Tenebrio molitor): A sustainable approach for valuable larval protein production from contaminated grain

Yellow mealworm (Tenebrio molitor) is a supplementary protein source for food and feed and represents a promising solution to manage grain contaminated with Aflatoxin B₁ (AFB₁). In this study, AFB₁ present in different concentrations in wheat bran was treated and removed via bioconversion by yellow mealworm of different instars, with emphasis on the bioconversion performance and metabolism of AFB₁. Upon application of wheat bran spiked with 100 μg/kg AFB₁ to 5th-6th instar yellow mealworms, the conversion rate of AFB₁ was up to 87.85 %. Low level of AFB₁ (< 2 μg/kg) was accumulated in the larval bodies, and the survival rate, development and nutrition contents of yellow mealworm were not significantly affected. It was revealed that 1 kg of wheat bran contaminated with AFB₁ increased the weight of yellow mealworms from 138 g to 469 g, containing approximately 103 g of protein. The bioconversion of AFB₁ by yellow mealworms led to generation of 13 metabolites in the frass and 3 metabolites in the larvae. AFB₁ was detoxicated and removed via phase I metabolism comprising reduction, dehydrogenation, hydration, demethylation, hydroxylation, decarbonylation and ketoreduction, followed by phase II metabolism involving conjugation of amino acid, glucoside and glutathione (GSH). The toxicity of AFB₁ metabolites was deemed lower than that of AFB₁ according to their structures. This study provides a sustainable approach and theoretical foundation on using yellow mealworms for cleaner grain contamination management and valuable larval protein production via bioconversion of food and feed contaminated by AFB₁.

PINK1/Parkin-mediated mitophagy as a protective mechanism against AFB1-induced liver injury in mice

Aflatoxin B₁ (AFB₁) can cause oxidative stress leading to mitochondrial damage and subsequent liver injury. Although it is well-known that damaged mitochondria are eliminated by PINK1/Parkin-mediated mitophagy, this mechanism has not yet been characterized in the context of AFB₁-induced liver injury. In this study, male wild-type C57BL/6N mice were divided into groups 1-4, which were then orally administered 0, 0.5, 0.75, and 1 mg/kg body weight AFB₁ for 28 d, respectively. Our results demonstrated that oxidative stress, NLRP3-inflammasome activation, and mitochondrial damage were dose-dependently augmented in AFB₁-induced liver injury. Additionally, PINK1/Parkin-mediated mitophagy peaked in the groups that had received a mid-dose of AFB₁ (0.75 mg/kg), which was attenuated slightly in high-dose groups. Afterward, we further characterized AFB₁-induced liver injury by comparing wild-type C57BL/6N mice with Parkin knockout (Parkin^-/-) mice. We found that the restricted mitophagy in Parkin^-/- mice was associated with increased oxidative stress, NLRP3-inflammasome activation, mitochondrial damage, and liver injury. Taken together, these results indicate that PINK1/Parkin-mediated mitophagy plays an important role in attenuating AFB₁-induced liver injury in mice.

Aflatoxin B1-activated heterophil extracellular traps result in the immunotoxicity to liver and kidney in chickens

Aflatoxin B1 (AFB1) is a mycotoxin with strong toxicity and play a large proportion in aspergillosis. Heterophil extracellular traps (HETs) was considered as an innate immune response of chickens to resist pathogens. AFB1 has been reported to trigger macrophages extracellular traps (METs) in THP-1 cells and RAW264.7 cells, but whether AFB1 could also activate HETs release, and the mechanism underlying AFB1-activated HETs in chicken remains unclear. In this study, we confirmed that AFB1could induce HETs release, which was a network of DNA-based structures consist of citrullinated histone 3 (citH3) and elastase. Meanwhile, AFB1-activated HETs rely on the glycolytic process to provide energy, NADPH oxidase and p38 signaling pathway. Moreover, it has been verified that AFB1-activated HETs release could significantly increase the biochemical indexes of liver (ALT and AST) and kidney (CRE and BUN) in serum. In addition, histopathological observation showed that AFB1 caused swelling, necrosis and vacuolation of hepatocytes in liver, and necrosis, exfoliated of nephrocyte in kidney. Further investigation demonstrated that AFB1 significantly decreased the levels of SOD and GSH-PX but increased the level of MDA, and meanwhile induced the mRNA expressions of TNF-α, IL-6 and IL-1β, iNOS, COX-2, NLRP3, caspase-1, caspase-3 and caspase-11. However, all these AFB1-induced biochemical indexes and histopathological changes were effectively alleviated by DNase I (the standard degradant for HETs). In conclusion, it has preliminary confirmed that AFB1-activated HETs formation contributed to the immunotoxicity in chicken and provide new strategies for the therapy in aspergillosis.

Acute toxicity and metabolism of pesticides in birds

The median lethal dose of pesticide in acute oral toxicity, used as a conservative index in avian risk assessment, varies by the species with differences of less than one order of magnitude, depending on body size, feeding habit, and metabolic enzyme activity. The profiles of pesticide metabolism in birds with characteristic conjugations are basically common to those in mammals, but less information is available on their relevant enzymes. The higher toxicity of some pesticides in birds than in mammals is due to the lower activity of avian metabolic enzymes. The bioaccumulation in birds is limited for very hydrophobic pesticides resistant to metabolic degradation. Several in silico approaches using the descriptors of a pesticide molecule have recently been employed to estimate the profiles of acute oral toxicity and bioaccumulation.

Protective effect of glutathione S-transferase enzyme activity against aflatoxin B1 in poultry species: relationship between glutathione S-transferase enzyme kinetic parameters, and resistance to aflatoxin B1

Comparative studies designed to investigate the role of glutathione S-transferase (GST) activity on the enzyme catalyzed trapping of aflatoxin B1-8,9-epoxide (AFBO) with glutathione, and the relationship with aflatoxin B1 (AFB1) resistance have not been conducted in poultry. Hepatic cytosolic fractions of chickens, quail, turkeys and ducks were used to measure in vitro the enzymatic parameters maximal velocity (Vmax), Michaelis-Menten constant (Km) and intrinsic clearance (CLint) for GST activity. AFB1 used ranged from 2.0 to 157.5 µM and the AFB1-GSH produced was identified and quantitated by HPLC. Significant differences were found in GST Vmax values, being the highest in chickens, followed by quail, ducks and turkeys. The Km values were also significantly different, with chickens < ducks < turkeys < quail. Chickens had the higher CLint value in contrast to ducks. Differences by sex showed that duck females had a higher CLint value than the turkey and quail, whereas duck males had a CLint close to that of turkey. The ratio "AFBO production /AFB1-GSH production" follows the order duck>turkey>quail>chicken, in agreement with the known poultry sensitivity. The extremely high "AFB1 epoxidation activity/ GST activity" ratio observed in ducks might be the explanation for the development of hepatocellular carcinoma in this species.

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.

CYP1A2, 2A13, and 3A4 network and interaction with aflatoxin B1

Aspergillus fungi are known to produce aflatoxins, among which aflatoxin B1 (AFB1) is the most potent carcinogen that is metabolised by cytochrome P450 (CYP450). In the liver, AFB1 is metabolised into exo-8,9-epoxide by the CYP1A2 enzymes. The resulting epoxide can react with guanine to cause DNA damage. Natural inhibitors are being identified. However, the modes of action are poorly understood. In the current study, we have investigated the mode of action of AFB1 with CYP1A2, CYP3A4 and CYP2A13 using molecular dynamic simulation (MD simulation) approaches. The interaction network and paths among CYP1A2, CYP3A4, and CYP2A13 have been investigated using the STRING database and PathLinker plugin of Cytoscape. CYP3A4 is the most active protein involved in interactions with AFB1 during its metabolism. Residues 362ARG, 445SER, 450LEU and 451PHE of CYP1A2 are important, interacting with AFB1 and converting it to toxic exo-AFB1-8,9-epoxide (AFBEX). The pathway shows that microsomal epoxide hydrolase (EPHX1) may acts as initiator in the signalling pathway where CYP1A2, CYP3A4 and CYP2A13 interact in a sequential order. The interaction network shows there to be a strong association in expression among CYP1A2, CYP3A4 and CYP2A13 along with other metabolising enzymes. The complex of AFB1 and CYP1A2 was found to be stable during the MD simulation. This study provides a better understanding of the mode of action between AFB1 and CYP1A2, CYP3A4 and CYP2A13 which relates to the effective management of AFB1 toxicity. EPHX1 in the protein network may be an ideal target when designing inhibitors to prevent the toxin’s activation. Peptide inhibitors may be designed to block the substrate site residues of CYP1A2 in order to prevent the conversion from AFB1 into AFBEX. This would either neutralise or reduce its toxicity.

Insights into Aflatoxin B1 Toxicity in Cattle: An In Vitro Whole-Transcriptomic Approach

Aflatoxins, and particularly aflatoxin B1 (AFB1), are toxic mycotoxins to humans and farm animal species, resulting in acute and chronic toxicities. At present, AFB1 is still considered a global concern with negative impacts on health, the economy, and social life. In farm animals, exposure to AFB1-contaminated feed may cause several untoward effects, liver damage being one of the most devastating ones. In the present study, we assessed in vitro the transcriptional changes caused by AFB1 in a bovine fetal hepatocyte-derived cell line (BFH12). To boost the cellular response to AFB1, cells were pre-treated with the co-planar PCB 3,3′,4,4′,5-pentachlorobiphenyl (PCB126), a known aryl hydrocarbon receptor agonist. Three experimental groups were considered: cells exposed to the vehicle only, to PCB126, and to PCB126 and AFB1. A total of nine RNA-seq libraries (three replicates/group) were constructed and sequenced. The differential expression analysis showed that PCB126 induced only small transcriptional changes. On the contrary, AFB1 deeply affected the cell transcriptome, the majority of significant genes being associated with cancer, cellular damage and apoptosis, inflammation, bioactivation, and detoxification pathways. Investigating mRNA perturbations induced by AFB1 in cattle BFH12 cells will help us to better understand AFB1 toxicodynamics in this susceptible and economically important food-producing species.

Involvement of hepatic lipid droplets and their associated proteins in the detoxification of aflatoxin B1 in aflatoxin-resistance BALB/C mouse

The highly potent carcinogen, Aflatoxin B₁, induces liver cancer in many animals including humans but some mice strains are highly resistant. This murine resistance is due to a rapid detoxification of AFB₁. Hepatic lipid droplets (LDs) ultimately impact the liver functions but their potential role in AFB₁ detoxification has not been addressed. This study describes the structural and functional impacts on hepatic LDs in BALB/C mice after exposure to 44 (low dose) or 663 (high dose) μg AFB₁/kg of body weight. After 7 days, the liver of AFB₁-dosed mice did not accumulate any detectable AFB₁ or its metabolites and this was associated with a net increase in gene transcripts of the AhR-mediating pathway. Of particular interest, the livers of high-dose mice accumulated many more LDs than those of low-dose mice. This was accompanied with a net increase in transcript levels of LD-associated protein-encoding genes including Plin2, Plin3 and Cideb and an alteration in the LDs lipid profiles that could be likely due to the induction of lipoxygenase and cyclooxygenase genes. Interestingly, our data suggest that hepatic LDs catalyze the in vitro activation of AFB₁ into AFB₁-exo-8,9-epoxide and subsequent hydrolysis of this epoxide into its corresponding dihydrodiol. Finally, transcript levels of CYP1A2, CYP1B1, GSTA3 and EH1 genes were elevated in livers of high-dose mice. These data suggest new roles for hepatic LDs in the trapping and detoxifying of aflatoxins.

Adverse Effects, Transformation and Channeling of Aflatoxins Into Food Raw Materials in Livestock

Aflatoxins are wide-spread harmful carcinogenic secondary metabolites produced by Aspergillus species, which cause serious feed and food contaminations and affect farm animals deleteriously with acute or chronic manifestations of mycotoxicoses. On farm, both pre-harvest and post-harvest strategies are applied to minimize the risk of aflatoxin contaminations in feeds. The great economic losses attributable to mycotoxin contaminations have initiated a plethora of research projects to develop new, effective technologies to prevent the highly toxic effects of these secondary metabolites on domestic animals and also to block the carry-over of these mycotoxins to humans through the food chain. Among other areas, this review summarizes the latest findings on the effects of silage production technologies and silage microbiota on aflatoxins, and it also discusses the current applications of probiotic organisms and microbial products in feeding technologies. After ingesting contaminated foodstuffs, aflatoxins are metabolized and biotransformed differently in various animals depending on their inherent and acquired physiological properties. These mycotoxins may cause primary aflatoxicoses with versatile, species-specific adverse effects, which are also dependent on the susceptibility of individual animals within a species, and will be a function of the dose and duration of aflatoxin exposures. The transfer of these undesired compounds from contaminated feed into food of animal origin and the aflatoxin residues present in foods become an additional risk to human health, leading to secondary aflatoxicoses. Considering the biological transformation of aflatoxins in livestock, this review summarizes (i) the metabolism of aflatoxins in different animal species, (ii) the deleterious effects of the mycotoxins and their derivatives on the animals, and (iii) the major risks to animal health in terms of the symptoms and consequences of acute or chronic aflatoxicoses, animal welfare and productivity. Furthermore, we traced the transformation and channeling of Aspergillus-derived mycotoxins into food raw materials, particularly in the case of aflatoxin contaminated milk, which represents the major route of human exposure among animal-derived foods. The early and reliable detection of aflatoxins in feed, forage and primary commodities is an increasingly important issue and, therefore, the newly developed, easy-to-use qualitative and quantitative aflatoxin analytical methods are also summarized in the review.

Aflatoxin B1 induces S phase arrest by upregulating the expression of p21 via MYC, PLK1 and PLD1

Aflatoxin B1 (AFB1), a member of the aflatoxin family, is a common contaminant in foods and feeds, and AFB1 exposure is associated with various clinical conditions. Thus far, research on the toxicity of AFB1 has mainly focused on its induction of liver cancer, but little research has been reported on renal toxicity, especially with regards to the underlying molecular mechanisms. In this study, we found that AFB1 treatment significantly induced kidney damage and reduced kidney weight. The human kidney cell line HEK293T was used to further study the molecular mechanism of the toxicity of AFB1 to kidney cells. We found that AFB1 significantly and dose-dependently induced S phase arrest and upregulated p21 mRNA and protein expression. Upstream of p21, three negative regulators, PLK1, MYC, and PLD1, were significantly downregulated under AFB1 treatment. Consistently, p21 was upregulated, and PLK1, MYC and PLD1 were downregulated in mouse kidney after AFB1 treatment. Interestingly, AFB1 also decreased the physical interaction between PLK1 and MYC and weakened the stability of the MYC protein. Importantly, overexpression of PLK1, MYC and PLD1 significantly blocked the upregulation of p21 and attenuated the S phase arrest caused by AFB1. In summary, AFB1 markedly induces kidney damage and strongly induces S phase arrest by upregulating the expression of p21 via PLK1, PLD1 and MYC, which represents a noval mechanism of the renal toxicity of AFB1.

Altered Gene Response to Aflatoxin B1 in the Spleens of Susceptible and Resistant Turkeys

Susceptibility and/or resistance to aflatoxin B₁ (AFB₁) is a threshold trait governed principally by glutathione S transferase (GST)-mediated detoxification. In poultry, domesticated turkeys are highly sensitive to AFB₁, most likely due to dysfunction in hepatic GSTs. In contrast, wild turkeys are comparatively resistant to aflatoxicosis due to the presence of functional hepatic GSTAs and other possible physiological and immunological interactions. The underlying genetic basis for the disparate GST function in turkeys is unknown as are the broader molecular interactions that control the systemic response. This study quantifies the effects of dietary AFB₁ on gene expression in the turkey spleen, specifically contrasting genetically distinct domesticated (DT, susceptible) and Eastern wild (EW, resistant) birds. Male turkey poults were subjected to a short-term AFB₁ treatment protocol with feed supplemented with 320 ppb AFB₁ beginning on day 15 of age and continuing for 14 days. Spleen tissues were harvested and subjected to deep RNA sequencing and transcriptome analysis. Analysis of differential gene expression found the effects of AFB₁ treatment on the spleen transcriptomes considerably more prominent in the DT birds compared to EW. However, expression of the differentially expressed genes (DEGs) was directionally biased, with the majority showing higher expression in EW (i.e., down-regulation in DT). Significantly altered pathways included FXR/RXR and LXR/RXR activation, coagulation system, prothrombin activation, acute phase response, and atherosclerosis signaling. Differential extra-hepatic expression of acute phase protein genes was confirmed by quantitative real time PCR (qRT-PCR) in the original experiment and additional turkey lines. Results demonstrate that wild turkeys possess a capacity to more effectively respond to AFB₁ exposure.

Differential Transcriptome Responses to Aflatoxin B₁ in the Cecal Tonsil of Susceptible and Resistant Turkeys

The nearly-ubiquitous food and feed-borne mycotoxin aflatoxin B₁ (AFB₁) is carcinogenic and mutagenic, posing a food safety threat to humans and animals. One of the most susceptible animal species known and thus a good model for characterizing toxicological pathways, is the domesticated turkey (DT), a condition likely due, at least in part, to deficient hepatic AFB₁-detoxifying alpha-class glutathione S-transferases (GSTAs). Conversely, wild turkeys (Eastern wild, EW) are relatively resistant to the hepatotoxic, hepatocarcinogenic and immunosuppressive effects of AFB₁ owing to functional gene expression and presence of functional hepatic GSTAs. This study was designed to compare the responses in gene expression in the gastrointestinal tract between DT (susceptible phenotype) and EW (resistant phenotype) following dietary AFB₁ challenge (320 ppb for 14 days); specifically in cecal tonsil which functions in both nutrient absorption and gut immunity. RNAseq and gene expression analysis revealed significant differential gene expression in AFB₁-treated animals compared to control-fed domestic and wild birds and in within-treatment comparisons between bird types. Significantly upregulated expression of the primary hepatic AFB₁-activating P450 (CYP1A5) as well as transcriptional changes in tight junction proteins were observed in AFB₁-treated birds. Numerous pro-inflammatory cytokines, TGF-β and EGF were significantly down regulated by AFB₁ treatment in DT birds and pathway analysis suggested suppression of enteroendocrine cells. Conversely, AFB₁ treatment modified significantly fewer unique genes in EW birds; among these were genes involved in lipid synthesis and metabolism and immune response. This is the first investigation of the effects of AFB₁ on the turkey gastro-intestinal tract. Results suggest that in addition to the hepatic transcriptome, animal resistance to this mycotoxin occurs in organ systems outside the liver, specifically as a refractory gastrointestinal tract.

Bush sophora root polysaccharide could help prevent aflatoxin B1-induced hepatotoxicity in the primary chicken hepatocytes

The aim of this study was to evaluate the effects of bush sophora root polysaccharide (BSRPS) on the aflatoxin B1 (AFB1)-induced hepatotoxicity and to explore the underlying mechanisms. The primary chicken hepatocytes were used as the model in the present experiment. The results showed that AFB1 induced hepatotoxicity of chicken hepatocytes in a dose dependent manner as demonstrated by decreasing cell viability and increasing LDH activity, ALT and AST levels. AFB1 at 0.16 μM significantly increased the levels of hepatic cytochrome P450 1A5 (CYP450 1A5) mRNA and malondialdehyde (MDA) and decreased the activity and mRNA level of manganese superoxide dismutase(SOD2) and the glutathione peroxidases (GSH-Px) activity in the hepatocytes compared with the blank control. BSRPS at 8.93 μM, 17.86 μM, and 35.72 μM supplementation could significantly reverse the above-mentioned changes induced by AFB1, and 17.86 μM of BSRPS has the largest effects on protecting the AFB1-induced hepatocytes damage. Knock-down of SOD2 by SOD2-specific siRNA significantly eliminated the protective effects of BSRPS on AFB1-induced the increase of CYP450 1A5 mRNA levels and hepatotoxicity. These results suggested that the BSRPS has protective effects on AFB1-induced hepatotoxicity by down-regulating CYP450 1A5 mRNA level via up-regulating SOD2 expression in the primary chicken hepatocytes.

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.

Detoxification, metabolism, and glutathione pathway activity of aflatoxin B1 by dietary lactic acid bacteria in broiler chickens

Lactic acid bacteria (LAB) and the glutathione (GSH) pathway are protective against aflatoxin, but information on the effect of LAB on aflatoxin metabolism and GSH activity in farm animals is scarce. This study aimed to investigate the effects of LAB and aflatoxin B (AFB) on growth performance, aflatoxin metabolism, and GSH pathway activity using 480 male Arbor Acres broiler chickens from d 1 to 35 of age. Diets were arranged in a 2 × 2 factorial design, including AFB at 0 or 40 µg/kg of feed and LAB at 0 or 3 × 10 cfu/kg of feed, and the LAB was a mixture of equal amounts of , , and . The results showed that there were highly significant ( < 0.01) effects of AFB toxicity, LAB protection, and their interaction on ADFI, ADG, and G:F of broilers during d 1 to 35. Compared with the AFB diet, the LAB diet reduced ( < 0.05) the residues of AFB in the liver, kidney, serum, ileal digesta, and excreta on d 14 by 121.5, 80.6, 43.7, 47.0, and 26.5%, respectively, and on d 35 by 40.6, 60.2, 131.7, 37.9, and 32.9%, respectively, whereas the LAB diet increased ( < 0.05) the contents of aflatoxin M, a metabolite of AFB, in the liver, kidney, serum, and ileal digesta on d 14 by 98.2, 154.2, 168.6, 19.1, and 34.1%, respectively, and in the kidney and serum on d 35 by 32.6 and 142.2%, respectively. For the activity of the GSH pathway in the liver and duodenal mucosa, there were significant ( ≤ 0.01) effects of LAB and AFB on reduced GSH, glutathione S-transferases (GST), and glutathione reductase (GR) on d 14 and 35; compared with the control diet, the LAB diet increased ( < 0.05) GSH, GST, and GR by a range of 11.6 to 86.1%, and compared with the AFB diet, the LAB diet increased ( < 0.05) GSH, GST, and GR by a range of 24.1 to 146.9%. In the liver, there were interactions ( < 0.05) on GSH and GST on d 14 and on GSH on d 35; in the mucosa, interactions were significant ( ≤ 0.01) on GSH and GR on d 14 and on GST on d 35. It can be concluded that LAB is effective in the detoxification of AFB by modulating toxin metabolism and activating the GSH pathway in animals.

Sensitivity of Arbor Acres broilers and chemoprevention of aflatoxin B1-induced liver injury by curcumin, a natural potent inducer of phase-II enzymes and Nrf2

In this study, we scrutinized the effects of curcumin and AFB₁ supplemented diet alone or in combination on phase-ӀӀ enzymes. Histopathological examination showed that after 28 days, AFB1 (5.0 mg/kg diet) induced liver injury in broilers, but curcumin supplementation partially ameliorated liver injury in a dose-dependent manner. RT-PCR data revealed that AFB₁ significantly (p < 0.01) down-regulated Nrf2 and its downstream genes mRNA expression level. Moreover, Western blot analysis showed that Nrf2, GSTM2, and GSTA3 protein expression level was markedly (p < 0.01) reduced in AFB₁-fed group. However, curcumin supplementation ameliorated AFB₁-induced liver injury via enhancing phase-ӀӀ enzymes expressions and activity. HPLC results showed that curcumin increased AFB₁-GSH conjugation in-vitro in liver cytosol. Surprisingly, similar trends were noted in mRNA, protein expression level of Nrf2 and its downstream genes at day 35, one week after the withdrawal of AFB₁ and curcumin from the diet, showing the preventive effects of curcumin.

Comparative Toxicokinetics and Plasma Protein Binding of Ochratoxin A in Four Avian Species

Ochratoxin A (OTA, 0.25 mg/kg body weight) was absorbed rapidly ( T_max = 0.31-1.88 h) in all avian species (broiler chickens, laying hens, turkeys, and Muscovy ducks) but more slowly in broiler chickens ( T_max = 1.43-4.63 h). The absolute oral bioavailability was complete in these bird species (88.0-109.6%). Ducks have a significantly higher volume of distribution ( V_d) and turkeys a lower V_d compared to chickens and layers (broiler chickens, 0.27 ± 0.12 L/kg; layers, 0.23 ± 0.08 L/kg; turkeys, 0.18 ± 0.04 L/kg; ducks, 0.76 ± 0.44 L/kg). This difference in V_d can be attributed to the species-dependent differences in plasma protein binding of OTA, namely ranging between 82.2 and 88.9% in ducks and between 96.5 and 98.8% in turkeys. No significant gender differences were found in toxicokinetics or plasma protein binding.

Biochemical basis for the age-related sensitivity of broilers to aflatoxin B1

In this study, we investigated the mechanism underlying age-related susceptibility in broilers to aflatoxin B1 (AFB1). The results showed that AFB1 induced significant changes in serum alkaline phosphatase (ALP), alanine aminotransferase (ALT), aspartate aminotransferase (AST), gamma-glutamyl transferase (GGT) activity & liver superoxide dismutase (SOD), malonaldehyde (MDA), glutathione peroxidase (GSH-Px) and glutathione S-transferase (GST) activity at day 7, 21 and 42 relative to control group. However, AFB1-induced changes in serum biochemical parameters and liver antioxidant activities become less severe with increasing age of broilers. Particularly, liver cytosolic GST activity increases with the age of broilers, crucial for the detoxification of AFB1. The mRNA expression level of Cytochrome P450 (CYP) enzymes was significantly higher at day 7, and decreases at day 21 and 42. While, the mRNA expression level of liver GSTA3, GSTA4 and EPHX1 increases with age of broilers. Maximum AFB1 residues level was detected at day 42 relative to day 7 and 21. While, AFM1 residues level increases (p < 0.05) from day 7 to 21, but decreases (p > 0.05) at day 42. Most importantly, our data confirmed the efficient AFB1-bioactivation by CYP enzymes and deficient detoxification of GST enzymes at younger age (∼7-day old) compared to older age. In summary, the age-related changes particularly in phase-I and phase-II enzymes mainly responsible for AFB1 bioactivation and detoxification may be partially accountable for the increased susceptibility of younger broilers (∼7-day old) compared to older broilers.

Comparative Response of the Hepatic Transcriptomes of Domesticated and Wild Turkey to Aflatoxin B₁

The food-borne mycotoxin aflatoxin B₁ (AFB₁) poses a significant risk to poultry, which are highly susceptible to its hepatotoxic effects. Domesticated turkeys (Meleagris gallopavo) are especially sensitive, whereas wild turkeys (M. g. silvestris) are more resistant. AFB₁ toxicity entails bioactivation by hepatic cytochrome P450s to the electrophilic exo-AFB₁-8,9-epoxide (AFBO). Domesticated turkeys lack functional hepatic GST-mediated detoxification of AFBO, and this is largely responsible for the differences in resistance between turkey types. This study was designed to characterize transcriptional changes induced in turkey livers by AFB₁, and to contrast the response of domesticated (susceptible) and wild (more resistant) birds. Gene expression responses to AFB₁ were examined using RNA-sequencing. Statistically significant differences in gene expression were observed among treatment groups and between turkey types. Expression analysis identified 4621 genes with significant differential expression (DE) in AFB₁-treated birds compared to controls. Characterization of DE transcripts revealed genes dis-regulated in response to toxic insult with significant association of Phase I and Phase II genes and others important in cellular regulation, modulation of apoptosis, and inflammatory responses. Constitutive expression of GSTA3 was significantly higher in wild birds and was significantly higher in AFB₁-treated birds when compared to controls for both genetic groups. This pattern was also observed by qRT-PCR in other wild and domesticated turkey strains. Results of this study emphasize the differential response of these genetically distinct birds, and identify genes and pathways that are differentially altered in aflatoxicosis.

Selenomethionine Alleviates AFB1-Induced Damage in Primary Chicken Hepatocytes by Inhibiting CYP450 1A5 Expression via Upregulated SelW Expression

This study aims to evaluate the protective effects of selenomethionine (SeMet) on aflatoxin B1 (AFB1)-induced hepatotoxicity in primary chicken hepatocytes. Cell viability and lactic dehydrogenase activity assays revealed the dose dependence of AFB1 toxicity to chicken hepatocytes. AFB1 concentrations of >0.05 μg/mL significantly reduced glutathione and total superoxide dismutase levels and increased the malondialdehyde concentration and cytochrome P450 enzyme 1A5 (CYP450 1A5) mRNA levels (P < 0.05). AFB1, however, did not affect CYP450 3A37 mRNA levels. Supplementation with 2 μM SeMet protected against AFB1-induced changes and significantly increased selenoprotein W (SelW) mRNA levels (P < 0.05). Additionally, SelW knockdown attenuated the protective effect of SeMet on AFB1-induced damage and significantly increased the level of CYP450 1A5 expression (P < 0.05). Therefore, SeMet alleviates AFB1-induced damage in primary chicken hepatocytes by improving SelW expression, thus inhibiting CYP450 1A5 expression.

Ameliorative Effects of Neutral Electrolyzed Water on Growth Performance, Biochemical Constituents, and Histopathological Changes in Turkey Poults during Aflatoxicosis

Different in vitro and in silico approaches from our research group have demonstrated that neutral electrolyzed water (NEW) can be used to detoxify aflatoxins. The objective of this investigation was to evaluate the ability of NEW to detoxify B-aflatoxins (AFB₁ and AFB₂) in contaminated maize and to confirm detoxification in an in vivo experimental model. Batches of aflatoxin-contaminated maize were detoxified with NEW and mixed in commercial feed. A total of 240 6-day-old female large white Nicholas-700 turkey poults were randomly divided into four treatments of six replicates each (10 turkeys per replicate), which were fed ad libitum for two weeks with the following dietary treatments: (1) control feed containing aflatoxin-free maize (CONTROL); (2) feed containing the aflatoxin-contaminated maize (AF); (3) feed containing the aflatoxin-contaminated maize detoxified with NEW (AF + NEW); and (4) control feed containing aflatoxin-free maize treated with NEW (NEW). Compared to the control groups, turkey poults of the AF group significantly reduced body weight gain and increased feed conversion ratio and mortality rate; whereas turkey poults of the AF + NEW group did not present significant differences on productive parameters. In addition, alterations in serum biochemical constituents, enzyme activities, relative organ weight, gross morphological changes and histopathological studies were significantly mitigated by the aflatoxin-detoxification procedure. From these results, it is concluded that the treatment of aflatoxin-contaminated maize with NEW provided reasonable protection against the effects caused by aflatoxins in young turkey poults.

Curcumin Prevents Aflatoxin B₁ Hepatoxicity by Inhibition of Cytochrome P450 Isozymes in Chick Liver

This study was designed to establish if Curcumin (CM) alleviates Aflatoxin B₁ (AFB₁)-induced hepatotoxic effects and to determine whether alteration of the expression of cytochrome P450 (CYP450) isozymes is involved in the regulation of these effects in chick liver. One-day-old male broilers (n = 120) were divided into four groups and used in a two by two factorial trial in which the main factors included supplementing AFB₁ (< 5 vs. 100 μg/kg) and CM (0 vs. 150 mg/kg) in a corn/soybean-based diet. Administration of AFB₁ induced liver injury, significantly decreasing albumin and total protein concentrations and increasing alanine aminotransferase and aspartate aminotransferase activities in serum, and induced hepatic histological lesions at week 2. AFB₁ also significantly decreased hepatic glutathione peroxidase, catalase, and glutathione levels, while increasing malondialdehyde, 8-hydroxydeoxyguanosine, and exo-AFB₁-8,9-epoxide (AFBO)-DNA concentrations. In addition, the mRNA and/or activity of enzymes responsible for the bioactivation of AFB₁ into AFBO-including CYP1A1, CYP1A2, CYP2A6, and CYP3A4-were significantly induced in liver microsomes after 2-week exposure to AFB₁. These alterations induced by AFB₁ were prevented by CM supplementation. Conclusively, dietary CM protected chicks from AFB₁-induced liver injury, potentially through the synergistic actions of increased antioxidant capacities and inhibition of the pivotal CYP450 isozyme-mediated activation of AFB₁ to toxic AFBO.

Bioactivation and Regioselectivity of Pig Cytochrome P450 3A29 towards Aflatoxin B₁

Due to unavoidable contaminations in feedstuff, pigs are easily exposed to aflatoxin B₁ (AFB₁) and suffer from poisoning, thus the poisoned products potentially affect human health. Heretofore, the metabolic process of AFB₁ in pigs remains to be clarified, especially the principal cytochrome P450 oxidases responsible for its activation. In this study, we cloned CYP3A29 from pig liver and expressed it in Escherichia coli, and its activity has been confirmed with the typical P450 CO-reduced spectral characteristic and nifedipine-oxidizing activity. The reconstituted membrane incubation proved that the recombinant CYP3A29 was able to oxidize AFB₁ to form AFB₁-exo-8,9-epoxide in vitro. The structural basis for the regioselective epoxidation of AFB₁ by CYP3A29 was further addressed. The T309A mutation significantly decreased the production of AFBO, whereas F304A exhibited an enhanced activation towards AFB₁. In agreement with the mutagenesis study, the molecular docking simulation suggested that Thr309 played a significant role in stabilization of AFB₁ binding in the active center through a hydrogen bond. In addition, the bulk phenyl group of Phe304 potentially imposed steric hindrance on the binding of AFB₁. Our study demonstrates the bioactivation of pig CYP3A29 towards AFB₁ in vitro, and provides the insight for understanding regioselectivity of CYP3A29 to AFB₁.

Hepatic Transcriptome Responses of Domesticated and Wild Turkey Embryos to Aflatoxin B₁

The mycotoxin, aflatoxin B₁ (AFB₁) is a hepatotoxic, immunotoxic, and mutagenic contaminant of food and animal feeds. In poultry, AFB₁ can be maternally transferred to embryonated eggs, affecting development, viability and performance after hatch. Domesticated turkeys (Meleagris gallopavo) are especially sensitive to aflatoxicosis, while Eastern wild turkeys (M. g. silvestris) are likely more resistant. In ovo exposure provided a controlled AFB₁ challenge and comparison of domesticated and wild turkeys. Gene expression responses to AFB₁ in the embryonic hepatic transcriptome were examined using RNA-sequencing (RNA-seq). Eggs were injected with AFB₁ (1 μg) or sham control and dissected for liver tissue after 1 day or 5 days of exposure. Libraries from domesticated turkey (n = 24) and wild turkey (n = 15) produced 89.2 Gb of sequence. Approximately 670 M reads were mapped to a turkey gene set. Differential expression analysis identified 1535 significant genes with |log₂ fold change| ≥ 1.0 in at least one pair-wise comparison. AFB₁ effects were dependent on exposure time and turkey type, occurred more rapidly in domesticated turkeys, and led to notable up-regulation in cell cycle regulators, NRF2-mediated response genes and coagulation factors. Further investigation of NRF2-response genes may identify targets to improve poultry resistance.

Prevention of Aflatoxin B1 Hepatoxicity by Dietary Selenium Is Associated with Inhibition of Cytochrome P450 Isozymes and Up-Regulation of 6 Selenoprotein Genes in Chick Liver

BACKGROUND

The involvement of cytochrome P450 (CYP450) isozymes and the selenogenome in selenium-mediated protection against aflatoxin B1 (AFB1)-induced adverse effects in broilers remains unclear.

OBJECTIVE

This study was designed first to determine whether selenium could reduce AFB1-induced hepatotoxic effects and then to determine whether these effects were due to changes in the CYP450 isozymes and selenogenome expression in the liver of chicks.

METHODS

Male avian broilers (aged 120 d) were allocated to 4 groups with 5 replicates of 6 birds to be included in a 2-by-2 factorial trial in which the main factors included supplementation of AFB1 (<5 compared with 100 μg/kg) and selenium (0.2 compared with 0.5 mg/kg) in a corn/soybean-based diet for 4 wk. Serum biochemistry, hepatic histology, and mRNA and/or activities of hepatic antioxidant enzymes, CYP450 isozymes, and 26 selenoproteins were analyzed at week 2 and/or 4.

RESULTS

Administration of AFB1 induced liver injury, decreasing (P < 0.05) total protein and albumin concentrations by 33.3-43.8% and increasing (P < 0.05) alanine aminotransferase and aspartate aminotransferase activities by 26.0-33.8% in serum, and induced hepatic necrosis and bile duct hyperplasia at week 2. AFB1 also decreased (P < 0.05) hepatic activities of glutathione peroxidase (GPX), thioredoxin reductase (TXNRD), and catalase, and the glutathione concentration by 13.1-59.9% and increased (P < 0.05) malondialdehyde, 8-hydroxydeoxyguanosine and exo-AFB1-8,9-epoxide (AFBO) DNA concentrations by 17.9-1200%. In addition, the mRNA and activity of enzymes responsible for the bioactivation of AFB1 into AFBO, which included CYP450 A1, 1A2, 2A6, and 3A4, were significantly induced (P < 0.05) by 29.2-271% in liver microsomes after 2-wk exposure to AFB1. These alterations induced by AFB1 were prevented by selenium supplementation. Dietary selenium supplementation increased (P < 0.05) mRNA and/or activities of 6 selenoprotein genes (Gpx3, Txnrd1, Txnrd2, Txnrd3, iodothyronine deiodinase 2, and selenoprotein N) in the liver of AFB1-treated groups at week 2.

CONCLUSIONS

Dietary selenium protected chicks from AFB1-induced liver injury, potentially through the synergistic actions of inhibition of the pivotal CYP450 isozyme-mediated activation of AFB1 to toxic AFBO, and increased antioxidant capacities by upregulation of selenoprotein genes coding for antioxidant proteins.

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.

Response of the hepatic transcriptome to aflatoxin B1 in domestic turkey (Meleagris gallopavo)

Dietary exposure to aflatoxin B₁ (AFB₁) is detrimental to avian health and leads to major economic losses for the poultry industry. AFB₁ is especially hepatotoxic in domestic turkeys (Meleagris gallopavo), since these birds are unable to detoxify AFB₁ by glutathione-conjugation. The impacts of AFB₁ on the turkey hepatic transcriptome and the potential protection from pretreatment with a Lactobacillus-based probiotic mixture were investigated through RNA-sequencing. Animals were divided into four treatment groups and RNA was subsequently recovered from liver samples. Four pooled RNA-seq libraries were sequenced to produce over 322 M reads totaling 13.8 Gb of sequence. Approximately 170,000 predicted transcripts were de novo assembled, of which 803 had significant differential expression in at least one pair-wise comparison between treatment groups. Functional analysis linked many of the transcripts significantly affected by AFB₁ exposure to cancer, apoptosis, the cell cycle or lipid regulation. Most notable were transcripts from the genes encoding E3 ubiquitin-protein ligase Mdm2, osteopontin, S-adenosylmethionine synthase isoform type-2, and lipoprotein lipase. Expression was modulated by the probiotics, but treatment did not completely mitigate the effects of AFB₁. Genes identified through transcriptome analysis provide candidates for further study of AFB₁ toxicity and targets for efforts to improve the health of domestic turkeys exposed to AFB₁.

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.

Cytochrome P450 isoforms are differently up-regulated in aflatoxin B₁-exposed human lymphocytes and monocytes

CONTEXT

Aflatoxins (AFs) are highly hazardous mycotoxins with potent carcinogenic, mutagenic and immune disregulatory properties. Cytochrome P450 (CYP) isoforms are central for enhanced AFB₁ toxicity in situ. It remains to be seen whether and how these AFB₁ activators work in human leukocytes.

OBJECTIVE

To investigate the involvement of CYP isoforms in AFB₁ toxicity of circulating mononuclear cells, we examined the impact of environmentally relevant levels of AFB1 on lymphocytes and monocytes.

MATERIALS AND METHODS

Very low and moderate doses of AFB₁ with/without CYP inducers on transcription of key CYP isoforms and toll-like receptor 4 (TLR4) were examined in human lymphocytes, monocytes and HepG2 cells; cell cycle distribution and viability were also analyzed in AFB₁-exposed lymphocytes and monocytes.

RESULTS

Only CYP1A1, CYP1B1, CYP3A4, CYP3A5 and CYP3A7 expressed in lymphocytes and monocytes. TLR4 much more expressed in monocytes than in lymphocytes, but HepG2 showed little TLR4 transcription. While CYP1A1, CYP1B1 and CYP3A4 were highly induced by AFB₁ in monocytes, in lymphocytes only CYP1A1 was induced. Among CYP1A1, CYP1B1 and CYP3A4 only CYP1A1 responded to low and moderate levels of AFB₁. Enhanced transcripts of CYPs by AFB₁ yielded little synergies on TLR4 transcription in lymphocytes and monocytes. Cell cycle arrest and necrosis were also detected in AFB₁-exposed lymphocytes and monocytes.

CONCLUSIONS

Our novel findings indicate that AFB₁ more intensively stimulates CYP genes expression in monocytes than in lymphocytes. Mechanistically, this could explain a more pronounced immunotoxicity of AFB₁ in myeloid than in lymphoid lineage cells in vitro/situ/vivo.

Heterologous expression and functional characterization of avian mu-class glutathione S-transferases

Hepatic glutathione S-transferases (GSTs: EC2.5.1.1.8) catalyze the detoxification of reactive electrophilic compounds, many of which are toxic and carcinogenic intermediates, via conjugation with the endogenous tripeptide glutathione (GSH). Glutathione S-transferase (GST)-mediated detoxification is a critical determinant of species susceptibility to the toxic and carcinogenic mycotoxin aflatoxin B1 (AFB1), which in resistant animals efficiently detoxifies the toxic intermediate produced by hepatic cytochrome P450 bioactivation, the exo-AFB1-8,9-epoxide (AFBO). Domestic turkeys (Meleagris gallopavo) are one of the most sensitive animals known to AFB1, a condition associated with a deficiency of hepatic GST-mediated detoxification of AFBO. We have recently shown that unlike their domestic counterparts, wild turkeys (Meleagris gallopavo silvestris), which are relatively resistant, express hepatic GST-mediated detoxification activity toward AFBO. Because of the importance of GSTs in species susceptibility, and to explore possible GST classes involved in AFB1 detoxification, we amplified, cloned, expressed and functionally characterized the hepatic mu-class GSTs tGSTM3 (GenBank accession no. JF340152), tGSTM4 (JF340153) from domestic turkeys, and a GSTM4 variant (ewGSTM4, JF340154) from Eastern wild turkeys. Predicted molecular masses of tGSTM3 and two tGSTM4 variants were 25.6 and 25.8kDa, respectively. Multiple sequence comparisons revealed four GSTM motifs and the mu-loop in both proteins. tGSTM4 has 89% amino acid sequence identity to chicken GSTM2, while tGSTM3 has 73% sequence identity to human GSTM3 (hGSTM3). Specific activities of Escherichia coli-expressed tGSTM3 toward 1-chloro-2,4-dinitrobenzene (CDNB) and peroxidase activity toward cumene hydroperoxide were five-fold greater than tGSTM4 while tGSTM4 possessed more than three-fold greater activity toward 1,2-dichloro-4-nitrobenzene (DCNB). The two enzymes displayed equal activity toward ethacrynic acid (ECA). However, none of the GSTM proteins had AFBO detoxification capability, in contrast to recombinant alpha-class GSTs shown in our recent study to possess this important activity. In total, our data indicate that although turkey hepatic GSTMs may contribute to xenobiotic detoxification, they probably play no role in detoxification of AFBO in the liver.

Alpha-class glutathione S-transferases in wild turkeys (Meleagris gallopavo): characterization and role in resistance to the carcinogenic mycotoxin aflatoxin B1

Domestic turkeys (Meleagris gallopavo) are one of the most susceptible animals known to the toxic effects of the mycotoxin aflatoxin B₁ (AFB₁), a potent human hepatocarcinogen, and universal maize contaminant. We have demonstrated that such susceptibility is associated with the inability of hepatic glutathione S-transferases (GSTs) to detoxify the reactive electrophilic metabolite exo-AFB₁-8,9-epoxide (AFBO). Unlike their domestic counterparts, wild turkeys, which are relatively AFB₁-resistant, possess hepatic GST-mediated AFBO conjugating activity_. Here, we characterized the molecular and functional properties of hepatic alpha-class GSTs (GSTAs) from wild and domestic turkeys to shed light on the differences in resistance between these closely related strains. Six alpha-class GST genes (GSTA) amplified from wild turkeys (Eastern and Rio Grande subspecies), heritage breed turkeys (Royal Palm) and modern domestic (Nicholas strain) turkeys were sequenced, and catalytic activities of heterologously-expressed recombinant enzymes determined. Alpha-class identity was affirmed by conserved GST domains and four signature motifs. All GSTAs contained single nucleotide polymorphisms (SNPs) in their coding regions: GSTA1.1 (5 SNPs), GSTA1.2 (7), GSTA1.3 (3), GSTA2 (3), GSTA3 (1) and GSTA4 (2). E. coli-expressed GSTAs possessed varying activities toward GST substrates 1-chloro-2,4-dinitrobenzene (CDNB), 1,2-dichloro-4-nitrobenzene (DCNB), ethacrynic acid (ECA), cumene hydroperoxide (CHP). As predicted by their relative resistance, livers from domestic turkeys lacked detectable GST-mediated AFBO detoxification activity, whereas those from wild and heritage birds possessed this critical activity, suggesting that intensive breeding and selection resulted in loss of AFB₁-protective alleles during domestication. Our observation that recombinant tGSTAs detoxify AFBO, whereas their hepatic forms do not, implies that the hepatic forms of these enzymes are down-regulated, silenced, or otherwise modified by one or more mechanisms. These data may inform of possible molecular mechanisms of resistance to AFB₁, and may also have the benefit of identifying genetic markers which could be used to enhance AFB₁ resistance in modern domestic strains.

Modulation of DNA damage and alteration of gene expression during aflatoxicosis via dietary supplementation of Spirulina (Arthrospira) and Whey protein concentrate

Spirulina (SPN) and Whey protein (WPC) are being touted as functional foods with a number of health benefits. SPN is blue green algae while WPC is a protein complex derived from milk and both have strong antioxidant activity and provoke a free radical scavenging enzyme system. The aim of the present study was to evaluate the antioxidant potentials of SPN and WPC to regulate the alteration of genes' expression and counteract oxidative stress in rats during aflatoxecosis. Eighty male Sprague-Dawley rats were divided into eight groups, which included the control group, the group fed with aflatoxins (AFs)-contaminated diet (2.5 mg/kg diet) for 30 day, the group treated orally with WPC (300 mg/kg b.w.), the group treated orally with SPN (50 mg/kg b.w), the group treated orally with WPC plus SPN and the groups fed with AFs-contaminated diet and treated orally with WPC, SPN and/or WPC. Oxidative stress markers and gene expression were assayed in liver and testis and the damage of DNA was evaluated by DNA fragmentation and micronucleus tests. The results demonstrated that supplementation of SPN and/or WPC reduced the oxidative stress induced by AFs as indicated by decreased lipid peroxidation level, increased glutathione content and up-regulated PHGPx gene expression. Both agents succeed to inhibit DNA damage as indicated by the down-regulation of Fas gene expression, and decreased the percentage of DNA fragmentation and micronucleated erythrocytes. Moreover, WPC was found to be effective than SPN and the combined treatment was more effective than the single treatment. It could be concluded that both SPN and WPC induced a protective action and regulated the alteration of genes expression induced by AFs; however, the combined treatment may be useful than the single treatment.

Functional characterization of alpha-class glutathione s-transferases from the Turkey (meleagris gallopavo)

Six Alpha-class glutathione S-transferase (GST) subunits were cloned from domestic turkey livers, which are one of the most susceptible animals known to the carcinogenic mycotoxin aflatoxin B₁. In most animals, GST dysfunction is a risk factor for susceptibility toward AFB₁, and we have shown that turkeys lack GSTs with affinity toward the carcinogenic intermediate exo-aflatoxin B(1)-8-9-epoxide (AFBO). Conversely, mice are resistant to AFB₁ carcinogenesis, due to high constitutive expression of mGSTA3 that has high affinity toward AFBO. When expressed in Escherichia coli, all six tGSTA subunits possessed conjugating activities toward substrates 1-chloro-2,4-dinitrobenzene (CDNB), 1,2-dichloro-4-nitrobenzene (DCNB), ethacrynic acid (ECA), and cumene hydroperoxide (CHP) with tGSTA1.2 appearing most active. Interestingly, tGSTA1.1, which lacks one of the four Alpha-class signature motifs, possessed enzymatic activities toward all substrates. All had comparable activities toward AFBO conjugation, an activity absent in turkey liver cytosols. E. coli-expressed mGSTA3 conjugated AFBO with more than 3-fold greater activity than that of tGSTAs and had higher activity toward GST prototype substrates. Mouse hepatic cytosols had approximately 900-fold higher catalytic activity toward AFBO compared with those from turkey. There was no apparent amino acid profile in tGSTAs that might correspond to specificity toward AFBO, although tGSTA1.2, which had slightly higher AFBO-trapping ability, shared Tyr¹⁰⁸ with mGSTA3, a residue postulated to be critical for AFBO trapping activity in mammalian systems. The observation that recombinant tGSTAs detoxify AFBO, whereas their hepatic forms do not, implies that the hepatic forms of these enzymes are silenced by one or more regulatory mechanisms.

Cytochrome P450 enzymes involved in the metabolism of aflatoxin B1 in chickens and quail

A study was conducted to identify the cytochrome P450 (CYP, CYP450) enzyme orthologs involved in the bioactivation of aflatoxin B(1) (AFB(1)) into the highly toxic metabolite known as aflatoxin-8,9-epoxide (AFBO) in quail and chicken hepatic microsomes. The strategies used included the use of specific CYP450 inhibitors and the correlation of prototype substrate activities with AFBO production. Additionally, the presence of the enzymes was qualitatively determined using an immunoblotting technique. The results showed that both quail and chicken microsomes have CYP1A1, CYP1A2, CYP2A6, and CYP3A4 enzymatic activity. A strong relationship between CYP1A1 and CYP2A6 activities and AFB(1) bioactivation was found in both species. Inhibition studies provided more evidence for the role of CYP2A6 in the bioactivation of AFB(1). The immunoblot results showed clear bands for the CYP2A6 and CYP3A4 orthologs in both species. The results of the present study indicate that CYP2A6 and, to a lesser extent, CYP1A1 are responsible for the bioactivation of AFB(1) into AFBO in both quail and chicken hepatic microsomes.