Abstract
EFSA was asked to deliver a scientific opinion on the risks to public health related to the presence of aflatoxins in food. The risk assessment was confined to aflatoxin B1 (AFB 1), AFB 2, AFG 1, AFG 2 and AFM 1. More than 200,000 analytical results on the occurrence of aflatoxins were used in the evaluation. Grains and grain‐based products made the largest contribution to the mean chronic dietary exposure to AFB 1 in all age classes, while ‘liquid milk’ and ‘fermented milk products’ were the main contributors to the AFM 1 mean exposure. Aflatoxins are genotoxic and AFB 1 can cause hepatocellular carcinomas (HCC s) in humans. The CONTAM Panel selected a benchmark dose lower confidence limit (BMDL ) for a benchmark response of 10% of 0.4 μg/kg body weight (bw) per day for the incidence of HCC in male rats following AFB 1 exposure to be used in a margin of exposure (MOE ) approach. The calculation of a BMDL from the human data was not appropriate; instead, the cancer potencies estimated by the Joint FAO /WHO Expert Committee on Food Additives in 2016 were used. For AFM 1, a potency factor of 0.1 relative to AFB 1 was used. For AFG 1, AFB 2 and AFG 2, the in vivo data are not sufficient to derive potency factors and equal potency to AFB 1 was assumed as in previous assessments. MOE values for AFB 1 exposure ranged from 5,000 to 29 and for AFM 1 from 100,000 to 508. The calculated MOE s are below 10,000 for AFB 1 and also for AFM 1 where some surveys, particularly for the younger age groups, have an MOE below 10,000. This raises a health concern. The estimated cancer risks in humans following exposure to AFB 1 and AFM 1 are in‐line with the conclusion drawn from the MOE s. The conclusions also apply to the combined exposure to all five aflatoxins.
Summary
Following a request from the European Commission, the Panel on Contaminants in the Food Chain (CONTAM Panel) has provided a scientific opinion on the human health risks related to the presence of aflatoxins in food. The opinion evaluates the toxicity of aflatoxins to humans, estimates the dietary exposure of the European Union (EU) population to aflatoxins and assesses the human health risks to the EU population due to the estimated dietary exposure. Aflatoxin B1 (AFB1), aflatoxin B2 (AFB2), aflatoxin G1 (AFG1), aflatoxin G2 (AFG2) and aflatoxin M1 (AFM1) are considered in the risk assessment. Aflatoxin total typically refers to the sum of AFB1, AFB2, AFG1 and AFG2. The risk assessment carried out by the CONTAM Panel of EFSA in 2007 was used as a starting point.
AFB1, AFB2, AFG1 and AFG2 are mycotoxins produced primarily by toxigenic strains of the fungi Aspergillus flavus and Aspergillus parasiticus . In addition to the above‐mentioned four aflatoxins, these fungi also form other substances such as aflatoxicol and sterigmatocystin. The most frequently found aflatoxin in contaminated food samples is AFB1 and the three others are generally not found in the absence of AFB1. Aflatoxin‐producing fungi are found in areas with a hot, humid climate and aflatoxins in food are a result of both pre‐ and post‐harvest fungal contamination. Climate change is anticipated to impact on the presence of aflatoxins in food in Europe. AFM1 is the hydroxylated metabolite of AFB1 and is found in milk and dairy products obtained from livestock that have ingested contaminated feed, and also in human milk.
AFB1 is absorbed in the small intestine and distributed to the liver where it undergoes first pass metabolism. The metabolism of AFB1 in humans and laboratory animals has been well‐characterised with CYP1A2, 2B6, 3A4, 3A5, 3A7, 2A13 and GSTM1 all catalysing aflatoxin metabolism in humans. AFB1, AFG1 and AFM1 are converted to their respective epoxides, which can bind covalently to both DNA and proteins. AFB2 and AFG2 cannot form the 8,9‐epoxide. AFB1 and its metabolites are both excreted via the faecal and the urinary route. The percentage excreted via both routes varies according to the species. AFM1 is also excreted in milk. A limited amount of new information has become available regarding the toxicokinetics of AFB1 in humans since the previous assessment by the CONTAM Panel in 2007. The new data on humans show that absorption of AFB1 and/or its metabolites into the systemic circulation is rapid and high.
In short‐term studies (7–90 days), AFB1 had multiple negative effects on rodents including inhibition of normal growth, liver and kidney damage, as well as sustained alterations in the intestinal microbiota. For AFG1, AFG2, AFB2 or AFM1, no new short‐term toxicity or gut microbiota studies were identified. AFB1 affects reproductive and developmental parameters and aflatoxins, especially AFB1, can produce an immunotoxic effect in rodents. The no‐observed‐adverse‐effect‐levels (NOAELs) for these effects were around 30 μg/kg body weight (bw) per day.
AFB1 is a genotoxic and carcinogenic substance. CYP3A and CYP1A2 activity is important for AFB1 genotoxicity. Upon epoxidation, DNA adducts such as AFB1‐N7‐gua and AFB1‐FAPY are formed and can lead to G‐to‐T transversions. In addition to DNA adduct formation, a broad spectrum of cellular effects has been reported in response to AFB1 exposure. In humans living in areas where hepatitis B virus (HBV) infection and AFB1 exposure are prevalent, hepatocellular carcinoma (HCC) samples show a mutational hotspot (G‐to‐T transversion) at codon 249 of the TP53 gene, which is considered to be a signature mutation for aflatoxin‐induced HCC.
There is evidence for genotoxic effects of AFB1 in pregnant mice, fetuses and young animals. Pregnancy appears to enhance the sensitivity to the genotoxicity of AFB1 for the mothers, possibly due to elevated levels of CYP1A2 and CYP3A enzymes. A study with in utero exposure showed a greater mutational impact of the lesions in the fetus. Early postnatal exposure resulted in higher adduct levels in the liver compared to adult animals.
Besides DNA adduct formation, AFB1 induces oxidative stress including modulation of antioxidant defence systems. Considering the potential sequence of events towards HCC, oxidative stress might compromise critical AFB1 detoxification pathways (e.g. glutathione (GSH) conjugation) and/or induce additional DNA lesions.
In contrast to AFB1, fewer studies are available regarding the genotoxicity of the other aflatoxins. When comparing the genotoxicity of the different aflatoxins, most studies have indicated that AFB1 is the most genotoxic compound. AFG1 is slightly less genotoxic than AFB1; AFB2 and AFG2 are less genotoxic than AFB1. It is not possible, based on these data, to make a quantitative comparison of the genotoxic potency of these compounds. The genotoxic potency can be summarised as AFB1 > AFG1 ≈ aflatoxicol » AFM1 based on the γH2AX in‐cell western technique in cultured human liver cells, while AFB2 and AFG2 showed no effects.
AFB1, AFG1 and AFM1 are carcinogenic when delivered orally via the diet or by gavage. There is limited evidence for the carcinogenicity of AFB2 and inadequate evidence for carcinogenicity of AFG2. AFB1 is more potent than AFG1 with respect to liver carcinogenicity but AFG1 induced a higher incidence of kidney tumours than AFB1. AFB1 is also more potent than AFM1 with respect to liver carcinogenicity by approximately 10‐fold.
AF‐alb (AFB1‐lys), urinary AF‐N7‐gua and urinary AFM1 are all biomarkers of exposure that have been validated against dietary intake of aflatoxin. However, the levels of these biomarkers cannot be converted reliably into dietary exposures in individuals. As AF‐alb (AFB1‐lys) better reflects longer‐term exposure (i.e. several weeks), it tends to be most widely used, while urinary AFM1 and AF‐N7‐gua are suitable biomarkers for recent exposure.
The epidemiological studies reported since 2006 have added to the weight of evidence that aflatoxin exposure is associated with a risk of developing HCC, with a higher risk for people infected with either HBV or hepatitis C virus (HCV). Data suggest that HBV infection of the liver alters the expression of the genes coding for the enzymes, which metabolise/detoxify aflatoxins such as an induction of CYP enzymes or decrease in glutathione S‐transferase (GST) activity. This may provide one mechanistic basis for the higher risk of liver cancer among HBV‐infected individuals exposed to aflatoxins.
Child health is an emerging area of interest for the field of aflatoxin‐related health outcomes but not yet suitable for use in risk assessment. Child growth has been assessed in a growing body of evidence outside European populations but with limited replicability in the observed associations. The evidence related to the remaining child health outcomes is sparse, heterogeneous and with methodological limitations.
The CONTAM Panel considers that liver carcinogenicity of aflatoxins remains the pivotal effect for the risk assessment. In view of the genotoxic properties of aflatoxins, the CONTAM Panel considered that it was not appropriate to establish a tolerable daily intake. Based on studies in animals, the CONTAM Panel selected a BMDL10 of 0.4 μg/kg bw per day for the incidence of HCC in male rats following AFB1 exposure to be used in a margin of exposure (MOE) approach. The calculation of a BMDL from the human data was not appropriate; instead, the cancer potencies estimated by the Joint FAO/WHO Expert Committee on Food Additives (JECFA) in 2016 were used.
Differences in carcinogenic potency are reported for the different aflatoxins. For AFM1, JECFA concluded, based on a study in Fischer rats, that AFM1 induces liver cancer with a potency one‐tenth that of AFB1. No new evidence has become available that necessitates a change to this conclusion and a potency factor of 0.1 was used in this assessment for AFM1. For the other aflatoxins, the available in vivo data are not sufficient to derive potency factors. In the absence of such potency factors, the CONTAM Panel applied equal potency factors for AFB1, AFB2, AFG1 and AFG2 as used in previous assessments.
Chronic dietary exposure to AFB1, AFM1 and AFT (the sum of AFB1, AFB2, AFG1 and AFG2) +AFM1 was estimated using a data set comprising 209,802 analytical results from 69,166 samples. The highest AFB1 and AFT mean concentrations were obtained for the food category ‘legumes, nuts and oilseeds’ (in particular for pistachios, peanuts and ‘other seeds’). As expected, the highest AFM1 mean concentrations were reported for ‘milk and dairy products’ and milk‐based foods belonging to the food category ‘food for infants and small children’. For adults, the mean lower bound (LB) exposure to AFB1 ranged from 0.22 to 0.49 ng/kg bw per day and the mean UB exposure from 1.35 to 3.25 ng/kg bw per day. For the younger age groups, the mean LB exposure to AFB1 ranged from 0.08 to 1.78 ng/kg per day and the mean upper bound (UB) exposure from 0.58 to 6.95 ng/kg per day. The LB P95 exposure to AFB1 ranged from 0.62 to 1.36 ng/kg bw per day for adults and from 0.35 to 6.22 ng/kg bw per day for the younger age groups. The UB P95 exposure to AFB1 ranged from 2.76 to 6.78 ng/kg bw per day and from 2.79 to 14.01 ng/kg bw per day, respectively. The highest estimated exposure to AFM1 was in infants with a mean exposure of 1.6/2.0 ng/kg bw per day (LB/UB) and a P95 exposure of 6.2/7.9 ng/kg bw per day. Overall, ‘grains and grain‐based products’ made the largest contribution to the LB mean chronic dietary exposure to AFB1 in all age classes. The main subcategories driving the contribution of this food category were ‘grains for human consumption’ (in particular corn grain), ‘bread and rolls’ and ‘fine bakery wares’. The food categories ‘liquid milk’ and ‘fermented milk products’ were the main contributors to the overall AFM1 mean exposure throughout all age groups.
Based on a BMDL10 of 0.4 μg/kg bw per day for the induction of HCC by AFB1 in male rats, MOE values (minimum to maximum) range from 5,000 to 225 for the mean LB exposure to AFB1 and from 690 to 58 for the mean UB exposure to AFB1 across dietary surveys and age groups. The MOE values range from 1,143 to 64 for the P95 LB exposure to AFB1 and from 145 to 29 for the P95 UB exposure to AFB1 across dietary surveys and age groups. The calculated MOEs are below 10,000, which raises a health concern. For AFM1, based on the BMDL10 of 0.4 μg/kg bw per day derived for AFB1 and a potency factor of 0.1, MOE values that range from 100,000 to 2,564 for the mean LB exposure estimates, from 66,667 to 2,020 for the mean UB exposure estimates, from 33,333 to 642 for the P95 LB exposure estimates, and from 25,000 to 508 for the P95 UB exposure estimates across dietary surveys and age groups have been calculated. The CONTAM Panel noted that the calculated MOEs are less than 10,000 for some surveys, particularly for the younger age groups, which raises a health concern. The estimated cancer risks in humans following exposure to AFB1 are in‐line with the conclusion drawn from the animal data. This conclusion also applies to AFM1 and AFT + AFM1.
The CONTAM Panel recommends that data that would allow the derivation of potency factors are generated. Research designed to quantify the relationship between biomarker levels and dietary intake at the individual level, integrating exposure over time with biomarker levels, is recommended. Such study would be performed in populations with an indigenous dietary exposure to aflatoxin resulting in measurable biomarker levels. More data are needed regarding the occurrence of aflatoxicol and aflatoxin M2 (AFM2), to clarify whether these substances should be included in the risk assessment. There is a need to continue to monitor aflatoxin occurrence in the light of potential increases due to climate change using methods with high levels of sensitivity for detection.
Reference
EFSA CONTAM Panel (EFSA Panel on Contaminants in the Food Chain), Schrenk, D, Bignami, M, Bodin, L, Chipman, JK, del Mazo, J, Grasl‐Kraupp, B, Hogstrand, C, Hoogenboom, LR, Leblanc, J‐C, Nebbia, CS, Nielsen, E, Ntzani, E, Petersen, A, Sand, S, Schwerdtle, T, Vleminckx, C, Marko, D, Oswald, IP, Piersma, A, Routledge, M, Schlatter, J, Baert, K, Gergelova, P and Wallace, H, 2020. Scientific opinion – Risk assessment of aflatoxins in food. EFSA Journal 2020;18(3):6040, 112 pp. https://doi.org/10.2903/j.efsa.2020.6040
No comments:
Post a Comment