Standard to Meet
| Compound Assessment
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Human Toxicity
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Compound causes one or more of the following:- cholestasis
- steatosis
- phospholipidosis
- fibrosis
- cell death
in humans; or exemplifies an in vitro mechanism underlying one of these toxicities.
| The primary target of aflatoxins is the hepatic system. Acute effects include hemorrhagic necrosis of the liver and bile duct proliferation while chronic effects include hepatocellular carcinoma. Acute exposure can result in aflatoxicosis, which manifests as severe, acute hepatotoxicity with a case fatality rate of approximately 25%.Hepatocellular carcinoma as a result of chronic exposure has been well documented, generally in association with hepatitis B virus or other risk factors.
References:
1. Public Health Strategies for Preventing Aflatoxin Exposure workgroup report for the International Mycotoxin Workshop, sponsored by WHO and CDC, held in Geneva in July 2005.
2. I.Dvorackova 1990 Aflatoxins and human health CRC Press 1990
3. Mohamed IF Shariff et al. Current Trends in Hepatocellular Carcinoma: Aflatoxin B1, Expert Rev Gastroenterol Hepatol. 2009;3(4):353-367.
4. Current Trends in Hepatocellular Carcinoma: Aflatoxin B1
5. C.P.Wild et al. The toxicology of aflatoxins as a basis for public health decisions, Mutagenesis vol.17 no.6 pp.471-481, 2002
6. Strosnider H et al. 2006 Workgroup Report: Public Health Strategies for Reducing Aflatoxin Exposure in Developing Countries. Environ Health Perspect 114(12): 1898-1903
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Toxicity occurs via one or more of the following mechanisms:- mitochondrial disruption
- inhibition of lipid transport or metabolism
- nuclear receptor modulation
- complexation of phospholipids
| Yes
Reference: 1. Sara Hale Henry et al. Reducing Liver Cancer-- Global Control of Aflatoxin Science 1999: Vol. 286 no. 5449 pp. 2453-2454
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Therapeutic target.
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Biochemical mechanism of toxicity.
| AFB1 is activated by cytochromes P450 (CYP3A4 and 1A2) to AFB1-8,9-exoepoxide and AFB1-8,9-endo-epoxide, which can covalently bind to nucleic acids or proteins, provoking cell membrane damage, necrosis and mutagenesis in the affected cells. The exo-epoxide binds to DNA to form the predominant 8,9-dihydro-8- (N7-guanyl)-9-hydroxy-AFB1 (AFB1-N7-Gua) adduct that confers the mutagenic properties of the compound.
Subsequently AFB1 was shown to induce formation of reactive oxygen species, lipid peroxidation and formation of 8-hydroxydeoxyguanosine in vivo and in vitro. The ability of AFB1 to induce oxidative damage to cells and DNA may, in addition to the formation of AFB1-DNA adducts, play an important role in AFB1 carcinogenicity. References: 1. Frances Trail et al. Molecular biology of aflatoxin biosynthesis Microbiology (1995), 141,755-765 2. R. Liu et al. In vitro toxicity of aflatoxin B1 and its photodegradation products in HepG2 cells, J. Appl. Toxicol. 2011, doi:10.1002/jat.1669
3. Shen H.M et al. Detection of elevated reactive oxygen species level in cultures rat hepatocytes treated with aflatoxin B1. Free Rad. Biol. Med. 1996, 21, 139-146. 4. R. J. Verma, Aflatoxin Cause DNA Damage, Int J Hum Genet, 4(4): 231-236 (2004)
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PK-ADME
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PK parameters 1:
- recommended dose
- Cmax
- Vd
- half-life
| About 80% of a total dose of AFB1 is excreted in 1 week. The plasma half-life is 36.5 min, volume of distribution 14% of body weight and body clearance is 1.25 L/kg/h. Aflatoxin M1 is mostly excreted within 48 h of ingestion.
Reference:
1. R. J. Verma Aflatoxin Cause DNA Damage Int J Hum Genet, 4(4): 231-236 (2004)
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Therapeutic window.1
| For cereals a maximum level of 2 μg/kg for aflatoxin B1 and for maize and rice a maximum level of 5 μg/kg for aflatoxin B1 has been established COMMISSION REGULATION (EU) No 165/2010 setting maximum levels for certain contaminants in foodstuffs as regards aflatoxins
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Metabolically activated (optional), active metabolite known and available for testing.2
| AFB1 8, 9-epoxide is generally accepted as the active electrophilic form of AFB1 that may attack nucleophilic nitrogen, oxygen and sulphur heteroatoms in cellular constituents. This highly reactive substance may combine with DNA bases such as guanine to produce alterations in DNA. This may be the most important product from the carcinogenic point of view.
Other major metabolites in the human include AFM1, aflatoxicol, AFLH1, AFP1, AFB2á and AFB1-2, 2-dihydrodiol (detoxification products). Reference: 1. R. J. Verma, Aflatoxin Cause DNA Damage, Int J Hum Genet, 4(4): 231-236 (2004)
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Omics and IC50 Data
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Gene expression profiles known.3
| Jossé R et al. Early target genes of aflatoxin B1 in human hepatic cells, Public on Dec 07, 2010
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Proteomics profiles known.3
| Yuan Li et al. Proteome analysis of aflatoxin B1-induced hepatocarcinogenesis in tree shrew (Tupaia belangerichinensis) and functional identification of candidate protein peroxiredoxin II, Proteomics 2008, 8, 1490–1501
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Metabonomics profiles known.3
| Limin Zhang et al. Systems Responses of Rats to Aflatoxin B1 Exposure Revealed with Metabonomic Changes in Multiple Biological Matrices, J. Proteome Res., 2011, 10 (2), pp 614-623
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Fluxomics profiles known.3
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Epigenomics profiles known.3
| 1. Z. Herceg Epigenetics and cancer: towards an evaluation of the impact of environmental and dietary factors, Mutagenesis (2007) 22 (2): 91-103 (page 96) 2. Zhang YJ et al. High frequency of promoter hypermethylation of RASSF1A and p16 and its relationship to aflatoxin B1-DNA adduct levels in human hepatocellular carcinoma. Mol. Carcinog. 2002;35:85-92 3. Zhang YJ et al. Inactivation of the DNA repair gene O6-methylguanine-DNA methyltransferase by promoter hypermethylation and its relationship to aflatoxin B1-DNA adducts and p53 mutation in hepatocellular carcinoma. Int. J. Cancer 2003;103:440-444
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Observed IC50 for in vitro cellular efficacy.4
| RTL-W1, a cell line derived from the normal liver of a mature rainbow trout: EC50 for inhibition of DNA synthesis was 0.05 µg/ml D.G. Bechtel et al. Effects of aflatoxin B1 in a liver cell line from rainbow trout (Oncorhynchus mykiss), Toxicology in Vitro Volume 8, Issue 3, June 1994, Pages 317-328
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Observed IC50 for in vitro cellular toxicity studies. 4
| HepG2: 1 microM
Ch. McKean et al. Comparative acute and combinative toxicity of aflatoxin B1 and T-2 toxin in animals and immortalized human cell lines J. Appl. Toxicol. 2006; 26: 139–147
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Physical Properties
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Accepted and listed within the ToxCast/Tox21 program.5
| Not included in phase I and II ToxCast List
soluble in DMSO (-1 < log P < 6, i.e., log of the octanol/water partition coefficient; 97.5% meet this criteria) Log P 2.04 (predicted ACD/Labs from ChemSpider) meets criteria molecular weight range 250-1000 (90% meet this criteria) Aflatoxin B1 312.3 g/mol meets criteria
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Defined and confirmed structure and isomeric form(s).
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Substance stability.
| Sensitivity to light[Sigma Aldrich A6636 MSDS]
The amount of aflatoxin in water did not vary after 100 days of storage at 10°C. Little changes in concentration of AFB 1in deionized water solution after 140 days at 25°C Reference: 1. Garcia ME, Blanco JL, Suarez G. Aflatoxins B, and G1 solubility in standard solutions and stability during cold storage. Mycotoxin Research 1994 Vol. 10 (1994)
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Soluble in buffer solution at 30 times the in vitro IC50 for toxicity.6
| 0.01 mg/ml (25°C after 24 hours mixing); 0.05-0.09 mg/ml soluble with lower stability and probable formation of crystals
Reference Garcia ME, Blanco JL, Suarez G. Aflatoxins B, and G1 solubility in standard solutions and stability during cold storage. Mycotoxin Research 1994 Vol. 10 (1994) estimated intrinsic solubility: 0.414 mg/ml estimated solubility in pure water at pH 7.0: 0.414 mg/ml estimated solubility in water at pH 7.4: 0.414 mg/ml Calculations performed using ACD/PhysChem v 9.14
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Solubility in DMSO 100 times buffer solubility.
| Soluble Sigma Aldrich Product Information Sheet
20mg/ml Enzo Lifesciences Aflatoxin B1 Product Informaton
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Vessel binding properties.7
| Adsorbtion to glass.
Reference
Rodricks IV. Note on adsorption of aflatoxin standards to glass. I Assoc Offic Anal Chern 1969; 52:979-980
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Commercial availability at > 95% (> 99% is preferred).
| Sigma Aldrich (A 6636) 1mg/31.30€ purity >98% Sigma Aldrich A6636 Product details
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Vapor pressure. (Non-volatile)
| estimated vapor pressure: 1.74E-09 mmHg (Calculation performed using EPI Suite v4.10)
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Criteria Notes
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1. | The in vivo therapeutic window is used to estimate an appropriate concentration for in vitro toxicity assays. This in vitro concentration should also be consistent with the exposure implied by pharmacokinetics parameters. |
2. | We prefer compounds that require metabolic activation, although standards that are active in themselves will be accepted if they have otherwise valuable properties. We require knowing the active metabolite, and we prefer compounds where the metabolite is stable and can be independently tested in order to verify the mechanism of toxicity as well as of metabolic activation in the test cell line. |
3. | Literature data for at least one, but not necessarily all, of the ‘omics datasets is desired. This requirement can be waived in special cases. |
4. | The IC50’s for in vitro efficacy and toxicity should be consistent with the therapeutic ratio observed in the clinic. These parameters will be dependent on specific cell type and culture conditions, but differences of more than 30-fold in the in vitro vs. in vivo therapeutic ratios should be considered suspect and carefully justified. |
5. | This is not a requirement, but compounds utilized in the EPA testing program can be assumed to have physical properties verified to be suitable for in vitro cellular assays. |
6. | Sparing soluble compounds may be assayed for solubility in serum and the percent serum used specified here. |
7. | This property will be measured when a sample of compound becomes available. |
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