Physiologically based kinetic modeling of bioactivation and detoxification of the alkenylbenzene methyleugenol in human as compared with rat

Unraveling Interspecies Differences in the Phase I Hepatic Metabolism of Alternariol and Alternariol Monomethyl Ether: Closing Data Gaps for a Comprehensive Risk Assessment

The Alternaria mycotoxins alternariol (AOH) and alternariol 9-O-monomethyl ether (AME) are pervasive food contaminants known to exert adverse effects in vitro, yet their toxicokinetics remain inadequately understood. Thus, this study endeavors to elucidate the qualitative and quantitative aspects of the phase I metabolism of AOH and AME. To pursue this goal, reduced nicotinamide adenine dinucleotide phosphate (NADPH)-fortified porcine, rat, and human liver microsomes were incubated for 0-10 min with AOH or AME within a concentration range of 1-100 and 1-50 μM, respectively. The decline in the parent toxin concentration was monitored via liquid chromatography coupled to tandem mass spectrometry, whereas coupling to high-resolution mass spectrometry provided insights into the composition of the arising metabolic mixture. The collected quantitative data allowed us to calculate the hepatic intrinsic clearance rates of AOH and AME, marking a notable contribution to the field. Moreover, we unveiled interspecies differences in the pattern and rate of the phase I metabolism of the investigated mycotoxins. The presented findings lay the groundwork for physiologically based toxicokinetic modeling aimed at estimating local concentrations of these mycotoxins in specific organs, enhancing our understanding of their mode of action and adverse health effects.

Toxins in Botanical Drugs and Plant-derived Food and Feed - from Science to Regulation: A Workshop Review

In September 2022, the 3rd International Workshop on pyrrolizidine alkaloids (PAs) and related phytotoxins was held on-line, entitled 'Toxins in botanical drugs and plant-derived food and feed - from science to regulation'. The workshop focused on new findings about the occurrence, exposure, toxicity, and risk assessment of PAs. In addition, new scientific results related to the risk assessment of alkenylbenzenes, a distinct class of herbal constituents, were presented. The presence of PAs and alkenylbenzenes in plant-derived food, feed, and herbal medicines has raised health concerns with respect to their acute and chronic toxicity but mainly related to the genotoxic and carcinogenic properties of several congeners. The compounds are natural constituents of a variety of plant families and species widely used in medicinal, food, and feed products. Their individual occurrence, levels, and toxic properties, together with the broad range of congeners present in nature, represent a striking challenge to modern toxicology. This review tries to provide an overview of the current knowledge on these compounds and indicates needs and perspectives for future research.

Urinary Excretion of Mercapturic Acids of the Rodent Carcinogen Methyleugenol after a Single Meal of Basil Pesto: A Controlled Exposure Study in Humans

Methyleugenol (ME), found in numerous plants and spices, is a rodent carcinogen and is classified as "possibly carcinogenic to humans". The hypothesis of a carcinogenic risk for humans is supported by the observation of ME-derived DNA adducts in almost all human liver and lung samples examined. Therefore, a risk assessment of ME is needed. Unfortunately, biomarkers of exposure for epidemiological studies are not yet available. We hereby present the first detection of N-acetyl-l-cysteine conjugates (mercapturic acids) of ME in human urine samples after consumption of a popular ME-containing meal, pasta with basil pesto. We synthesized mercapturic acid conjugates of ME, identified the major product as N-acetyl-S-[3'-(3,4-dimethoxyphenyl)allyl]-l-cysteine (E-3'-MEMA), and developed methods for its extraction and LC-MS/MS quantification in human urine. For conducting an exposure study in humans, a basil cultivar with a suitable ME content was grown for the preparation of basil pesto. A defined meal containing 100 g of basil pesto, corresponding to 1.7 mg ME, was served to 12 participants, who collected the complete urine at defined time intervals for 48 h. Using d6-E-3'-MEMA as an internal standard for LC-MS/MS quantification, we were able to detect E-3'-MEMA in urine samples of all participants collected after the ME-containing meal. Excretion was maximal between 2 and 6 h after the meal and was completed within about 12 h (concentrations below the limit of detection). Excreted amounts were only between 1 and 85 ppm of the ME intake, indicating that the ultimate genotoxicant, 1'-sulfooxy-ME, is formed to a subordinate extent or is not efficiently detoxified by glutathione conjugation and subsequent conversion to mercapturic acids. Both explanations may apply cumulatively, with the ubiquitous detection of ME DNA adducts in human lung and liver specimens arguing against an extremely low formation of 1'-sulfooxy-ME. Taken together, we hereby present the first noninvasive human biomarker reflecting an internal exposure toward reactive ME species.

FEMA GRAS assessment of derivatives of basil, nutmeg, parsley, tarragon and related allylalkoxybenzene-containing natural flavor complexes

In 2015, the Expert Panel of the Flavor and Extract Manufacturers Association (FEMA) initiated a program for the re-evaluation of the safety of over 250 natural flavor complexes (NFCs) used as flavoring ingredients in food. In this publication, tenth in the series, NFCs containing a high percentage of at least one naturally occurring allylalkoxybenzene constituent with a suspected concern for genotoxicity and/or carcinogenicity are evaluated. In a related paper, ninth in the series, NFCs containing anethole and/or eugenol and relatively low percentages of these allylalkoxybenzenes are evaluated. The Panel applies the threshold of toxicological concern (TTC) concept and evaluates relevant toxicology data on the NFCs and their respective constituent congeneric groups. For NFCs containing allylalkoxybenzene constituent(s), the estimated intake of the constituent is compared to the TTC for compounds with structural alerts for genotoxicity and when exceeded, a margin of exposure (MOE) is calculated. BMDL₁₀ values are derived from benchmark dose analyses using Bayesian model averaging for safrole, estragole and methyl eugenol using EPA's BMDS software version 3.2. BMDL₁₀ values for myristicin, elemicin and parsley apiole were estimated by read-across using relative potency factors. Margins of safety for each constituent congeneric group and MOEs for each allylalkoxybenzene constituent for each NFC were determined that indicate no safety concern. The scope of the safety evaluation contained herein does not include added use in dietary supplements or any products other than food. Ten NFCs, derived from basil, estragon (tarragon), mace, nutmeg, parsley and Canadian snakeroot were determined or affirmed as generally recognized as safe (GRAS) under their conditions of intended use as flavor ingredients based on an evaluation of each NFC and the constituents and congeneric groups therein.

Food-Borne Chemical Carcinogens and the Evidence for Human Cancer Risk

Commonly consumed foods and beverages can contain chemicals with reported carcinogenic activity in rodent models. Moreover, exposures to some of these substances have been associated with increased cancer risks in humans. Food-borne carcinogens span a range of chemical classes and can arise from natural or anthropogenic sources, as well as form endogenously. Important considerations include the mechanism(s) of action (MoA), their relevance to human biology, and the level of exposure in diet. The MoAs of carcinogens have been classified as either DNA-reactive (genotoxic), involving covalent reaction with nuclear DNA, or epigenetic, involving molecular and cellular effects other than DNA reactivity. Carcinogens are generally present in food at low levels, resulting in low daily intakes, although there are some exceptions. Carcinogens of the DNA-reactive type produce effects at lower dosages than epigenetic carcinogens. Several food-related DNA-reactive carcinogens, including aflatoxins, aristolochic acid, benzene, benzo[a]pyrene and ethylene oxide, are recognized by the International Agency for Research on Cancer (IARC) as causes of human cancer. Of the epigenetic type, the only carcinogen considered to be associated with increased cancer in humans, although not from low-level food exposure, is dioxin (TCDD). Thus, DNA-reactive carcinogens in food represent a much greater risk than epigenetic carcinogens.

Alkenylbenzenes in Foods: Aspects Impeding the Evaluation of Adverse Health Effects

Alkenylbenzenes are naturally occurring secondary plant metabolites, primarily present in different herbs and spices, such as basil or fennel seeds. Thus, alkenylbenzenes, such as safrole, methyleugenol, and estragole, can be found in different foods, whenever these herbs and spices (or extracts thereof) are used for food production. In particular, essential oils or other food products derived from the aforementioned herbs and spices, such as basil-containing pesto or plant food supplements, are often characterized by a high content of alkenylbenzenes. While safrole or methyleugenol are known to be genotoxic and carcinogenic, the toxicological relevance of other alkenylbenzenes (e.g., apiol) regarding human health remains widely unclear. In this review, we will briefly summarize and discuss the current knowledge and the uncertainties impeding a conclusive evaluation of adverse effects to human health possibly resulting from consumption of foods containing alkenylbenzenes, especially focusing on the genotoxic compounds, safrole, methyleugenol, and estragole.

Assessment of the predictive capacity of a physiologically based kinetic model using a read-across approach

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Potential regulatory application of PBK modelling information to assist read-across.

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Presents workflow to read across PBK model information from data-rich to data-poor chemicals.

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Describes appropriate analogue selection based on a set of specific criteria.

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Uses estragole and safrole as source chemicals for a target chemical - methyleugenol.

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Example of PBK model validation where in vivo kinetic data are lacking.

With current progress in science, there is growing interest in developing and applying Physiologically Based Kinetic (PBK) models in chemical risk assessment, as knowledge of internal exposure to chemicals is critical to understanding potential effects in vivo. In particular, a new generation of PBK models is being developed in which the model parameters are derived from in silico and in vitro methods. To increase the acceptance and use of these “Next Generation PBK models”, there is a need to demonstrate their validity. However, this is challenging in the case of data-poor chemicals that are lacking in kinetic data and for which predictive capacity cannot, therefore, be assessed. The aim of this work is to lay down the fundamental steps in using a read across framework to inform modellers and risk assessors on how to develop, or evaluate, PBK models for chemicals without in vivo kinetic data. The application of a PBK model that takes into account the absorption, distribution, metabolism and excretion characteristics of the chemical reduces the uncertainties in the biokinetics and biotransformation of the chemical of interest. A strategic flow-charting application, proposed herein, allows users to identify the minimum information to perform a read-across from a data-rich chemical to its data-poor analogue(s). The workflow analysis is illustrated by means of a real case study using the alkenylbenzene class of chemicals, showing the reliability and potential of this approach. It was demonstrated that a consistent quantitative relationship between model simulations could be achieved using models for estragole and safrole (source chemicals) when applied to methyleugenol (target chemical). When the PBK model code for the source chemicals was adapted to utilise input values relevant to the target chemical, simulation was consistent between the models. The resulting PBK model for methyleugenol was further evaluated by comparing the results to an existing, published model for methyleugenol, providing further evidence that the approach was successful. This can be considered as a “read-across” approach, enabling a valid PBK model to be derived to aid the assessment of a data poor chemical.

Estragole DNA adduct accumulation in human liver HepaRG cells upon repeated in vitro exposure

Accumulation of N²-(trans-isoestragol-3'-yl)-2'-deoxyguanosine (E-3'-N²-dG) DNA adducts derived from the alkenylbenzene estragole upon repeated dose exposure was investigated since the repair of this adduct was previously shown to be inefficient. To this end human HepaRG cells were exposed to repeating cycles of 2 h exposure to 50 μM estragole followed by 22 h repair to mimic daily exposure. The E-3'-N²-dG DNA adduct levels were quantified by LC-MS/MS after each cycle. The results show accumulation of E-3'-N²-dG DNA adducts at a rate of 17.53 adducts/10⁸ nts/cycle. This rate at the dose level calculated by physiologically based kinetic (PBK) modeling to result in 50 μM was converted to a rate expected at average human daily intake of estragole. The predicted time estimated to reach adduct levels reported at the BMD10 of the related alkenylbenzene methyleugenol of 10-100 adducts /10⁸ nts upon average human daily intake of estragole amounted to 8-80 (in rat) or 6-57 years (in human). It is concluded that the persistent nature of the E-3'-N²-dG DNA adducts may contribute to accumulation of substantial levels of DNA adducts upon prolonged dietary exposure.

DNA double strand break repair as cellular response to genotoxic asarone isomers considering phase I metabolism

The phenylpropenes α-asarone and β-asarone are widely spread in the marsh plant Acorus calamus. Both isomers are classified as carcinogenic in rodents. However, the respective genotoxic mechanisms are not elucidated so far. The present study gives deeper insights into the genotoxic effects of asarone isomers as well as their known oxidative phase I metabolites, (E)-3'-oxoasarone and asarone epoxide. We show that asarone metabolites highly increase DNA strand breaks after 1 h of incubation, markedly metabolic activation contributes to their carcinogenic mode of action. All test compounds act as aneugens and potently enhance the amounts of micronuclei in binuclear cells. However, a prolonged incubation time of 24 h results in a decrease of DNA damage. This work suggests that asarone metabolites also induce DNA double strand breaks , why we put a strong focus on homologous recombination and non-homologous end joining. The obtained results herein indicate that asarone epoxide-induced DNA strand breaks are repaired via a homologous repair pathway.

Mode of action-based risk assessment of genotoxic carcinogens

The risk assessment of chemical carcinogens is one major task in toxicology. Even though exposure has been mitigated effectively during the last decades, low levels of carcinogenic substances in food and at the workplace are still present and often not completely avoidable. The distinction between genotoxic and non-genotoxic carcinogens has traditionally been regarded as particularly relevant for risk assessment, with the assumption of the existence of no-effect concentrations (threshold levels) in case of the latter group. In contrast, genotoxic carcinogens, their metabolic precursors and DNA reactive metabolites are considered to represent risk factors at all concentrations since even one or a few DNA lesions may in principle result in mutations and, thus, increase tumour risk. Within the current document, an updated risk evaluation for genotoxic carcinogens is proposed, based on mechanistic knowledge regarding the substance (group) under investigation, and taking into account recent improvements in analytical techniques used to quantify DNA lesions and mutations as well as "omics" approaches. Furthermore, wherever possible and appropriate, special attention is given to the integration of background levels of the same or comparable DNA lesions. Within part A, fundamental considerations highlight the terms hazard and risk with respect to DNA reactivity of genotoxic agents, as compared to non-genotoxic agents. Also, current methodologies used in genetic toxicology as well as in dosimetry of exposure are described. Special focus is given on the elucidation of modes of action (MOA) and on the relation between DNA damage and cancer risk. Part B addresses specific examples of genotoxic carcinogens, including those humans are exposed to exogenously and endogenously, such as formaldehyde, acetaldehyde and the corresponding alcohols as well as some alkylating agents, ethylene oxide, and acrylamide, but also examples resulting from exogenous sources like aflatoxin B1, allylalkoxybenzenes, 2-amino-3,8-dimethylimidazo[4,5-f] quinoxaline (MeIQx), benzo[a]pyrene and pyrrolizidine alkaloids. Additionally, special attention is given to some carcinogenic metal compounds, which are considered indirect genotoxins, by accelerating mutagenicity via interactions with the cellular response to DNA damage even at low exposure conditions. Part C finally encompasses conclusions and perspectives, suggesting a refined strategy for the assessment of the carcinogenic risk associated with an exposure to genotoxic compounds and addressing research needs.

The safety evaluation of food flavoring substances: the role of genotoxicity studies

The Flavor and Extract Manufacturers Association (FEMA) Expert Panel relies on the weight of evidence from all available data in the safety evaluation of flavoring substances. This process includes data from genotoxicity studies designed to assess the potential of a chemical agent to react with DNA or otherwise cause changes to DNA, either in vitro or in vivo. The Panel has reviewed a large number of in vitro and in vivo genotoxicity studies during the course of its ongoing safety evaluations of flavorings. The adherence of genotoxicity studies to standardized protocols and guidelines, the biological relevance of the results from those studies, and the human relevance of these studies are all important considerations in assessing whether the results raise specific concerns for genotoxic potential. The Panel evaluates genotoxicity studies not only for evidence of genotoxicity hazard, but also for the probability of risk to the consumer in the context of exposure from their use as flavoring substances. The majority of flavoring substances have given no indication of genotoxic potential in studies evaluated by the FEMA Expert Panel. Examples illustrating the assessment of genotoxicity data for flavoring substances and the consideration of the factors noted above are provided. The weight of evidence approach adopted by the FEMA Expert Panel leads to a rational assessment of risk associated with consumer intake of flavoring substances under the conditions of use.

Physiologically based kinetic modelling-facilitated reverse dosimetry to predict in vivo red blood cell acetylcholinesterase inhibition following exposure to chlorpyrifos in the Caucasian and Chinese population

Organophosphates have a long history of use as insecticides over the world. The aim of the present study was to investigate the interethnic differences in kinetics, biomarker formation, and in vivo red blood cell acetylcholinesterase inhibition of chlorpyrifos (CPF) in the Chinese and the Caucasian population. To this purpose, physiologically based kinetic models for CPF in both the Chinese and Caucasian population were developed, and used to study time- and dose-dependent interethnic variation in urinary biomarkers and to convert concentration-response curves for red blood cell acetylcholinesterase inhibition to in vivo dose-response curves in these 2 populations by reverse dosimetry. The results obtained revealed a marked interethnic difference in toxicokinetics of CPF, with lower urinary biomarker levels at similar dose levels and slower CPF bioactivation and faster chlorpyrifos-oxon detoxification in the Chinese compared with the Caucasian population, resulting in 5- to 6-fold higher CPF sensitivity of the Caucasian than the Chinese population. These differences might be related to variation in the frequency of single-nucleotide polymorphisms for the major biotransformation enzymes involved. To conclude, the interethnic variation in kinetics of CPF may affect both its biomarker-based exposure assessment and its toxicity and risk assessment and physiologically based kinetic modeling facilitates the characterization and quantification of these interethnic variations.

Levels of methyleugenol and eugenol in instant herbal beverages available on the Indonesian market and related risk assessment

The presence and accompanying risks of methyleugenol and eugenol in herbal beverages available on the Indonesian market were evaluated. Methyleugenol was detected in 49 out of 114 samples, at levels amounting to 2.6-443.7 μg/g, while 4 samples contained eugenol at 21.4-101.2 μg/g. The EDI resulting from drinking these preparations amounted to 0.1-51.2 μg/kg bw/day and 1.1-3.3 μg/kg bw/day, respectively for samples targeted at adults and children. A BMDL₁₀ value of 22.2 mg/kg bw/day for methyleugenol was defined using literature data and model averaging. MOE values were below 10,000 for 46 samples (40.4%), indicating a priority for risk management when assuming daily lifelong consumption, while the EDI for 4 samples containing eugenol did not exceed the ADI of 2.5 mg/kg bw thus did not raise a concern for human health. Using Haber's rule to correct for less than lifetime exposure, consumption of methyleugenol via these beverages would be of low concern when consumed for less than 2 weeks/year during a lifetime. This conclusion holds for herbal beverages collected by targeted sampling, not for all herbal beverages on the Indonesian market. The study provides data that can support establishment of a maximum permitted level (MPL) for methyleugenol in herbal beverages in Indonesia.

Natural occurrence of genotoxic and carcinogenic alkenylbenzenes in Indonesian jamu and evaluation of consumer risks

The consumer risks of jamu, Indonesian traditional herbal medicines, was assessed focussing on the presence of alkenylbenzene containing botanical ingredients. Twenty-three out of 25 samples contained alkenylbenzenes at levels ranging from 3.8 to 440 μg/kg, with methyleugenol being the most frequently encountered alkenylbenzene. The estimated daily intake (EDI) resulting from jamu consumption was estimated to amount to 0.2-171 μg/kg bw/day for individual alkenylbenzenes, to 0.9-203 μg/kg bw/day when adding up all alkenylbenzenes detected, and to 0.9-551 μg/kg bw/day when expressed in methyleugenol equivalents using interim relative potency (REP) factors. The margin of exposure (MOE) values obtained were generally <10,000 indicating a priority for risk management when assuming daily consumption during a lifetime. Using Haber's rule it was estimated that two weeks consumption of these jamu only once would not raise a concern (MOE >10,000). However, when considering use for two weeks every year during a lifetime, 5 samples still raise a concern. It is concluded that the consumption of alkenylbenzene containing jamu can be of concern especially when consumed on a daily basis for longer periods of time on a regular basis.

Methyleugenol and selected oxidative metabolites affect DNA-Damage signalling pathways and induce apoptosis in human colon tumour HT29 cells

Previously the food carcinogen methyleugenol was found to be cytotoxic and genotoxic in multiple cell lines and in primary hepatocytes. In this study, the question addressed was whether methyleugenol and the selected oxidative metabolites, 1'-hydroxymethyleugenol, methyleugenol-2',3'-epoxide and 3'-oxomethylisoeugenol trigger a DNA damage response in the human colon carcinoma HT29 cell line. Most notably investigations by flow cytometry revealed that the metabolites induce an accumulation of HT29 cells in the G₂ phase of the cell cycle. DNA damage response is characterised by a time-delayed phosphorylation of ATM (ataxia-telangiectasia, mutated)/ATR (ATM- and Rad3-related) kinases and checkpoint kinase 1 after 2 h of incubation, and the tumour suppressor protein p53 only after 24 h of incubation. The test compounds induced apoptotic cell death indicated by cleavage of caspase 3 and poly-(ADP-ribose)-polymerase after a prolonged incubation time up to 72 h. In addition, activation of ATM/ATR-signalling cascade might contribute to apoptosis induction to a certain extent. However, clarification of this relationship awaits experimental confirmation.

Risk assessment of combined exposure to alkenylbenzenes through consumption of plant food supplements containing parsley and dill

A risk assessment was performed of parsley- and dill-based plant food supplements (PFS) containing apiol and related alkenylbenzenes. First, the levels of the alkenylbenzenes in the PFS and the resulting estimated daily intake (EDI) resulting from use of the PFS were quantified. Since most PFS appeared to contain more than one alkenylbenzene, a combined risk assessment was performed based on equal potency or using a so-called toxic equivalency (TEQ) approach based on toxic equivalency factors (TEFs) for the different alkenylbenzenes. The EDIs resulting from daily PFS consumption amount to 0.74-125 µg kg^-1 bw for the individual alkenylbenzenes, 0.74-160 µg kg^-1 bw for the sum of the alkenylbenzenes, and 0.47-64 µg kg^-1 bw for the sum of alkenylbenzenes when expressed in safrole equivalents. The margins of exposure (MOEs) obtained were generally below 10,000, indicating a priority for risk management if the PFS were to be consumed on a daily basis. Considering short-term use of the PFS, MOEs would increase above 10,000, indicating low priority for risk management. It is concluded that alkenylbenzene intake through consumption of parsley- and dill-based PFS is only of concern when these PFS are used for long periods of time.

Study on inter-ethnic human differences in bioactivation and detoxification of estragole using physiologically based kinetic modeling

Considering the rapid developments in food safety in the past decade in China, it is of importance to obtain insight into what extent safety and risk assessments of chemicals performed for the Caucasian population apply to the Chinese population. The aim of the present study was to determine physiologically based kinetic (PBK) modeling-based predictions for differences between Chinese and Caucasians in terms of metabolic bioactivation and detoxification of the food-borne genotoxic carcinogen estragole. The PBK models were defined based on kinetic constants for hepatic metabolism derived from in vitro incubations using liver fractions of the two ethnic groups, and used to evaluate the inter-ethnic differences in metabolic activation and detoxification of estragole. The models predicted that at realistic dietary intake levels, only 0.02% of the dose was converted to the ultimate carcinogenic metabolite 1′-sulfooxyestragole in Chinese subjects, whereas this amounted to 0.09% of the dose in Caucasian subjects. Detoxification of 1′-hydroxyestragole, mainly via conversion to 1′-oxoestragole, was similar within the two ethnic groups. The 4.5-fold variation in formation of the ultimate carcinogenic metabolite of estragole accompanied by similar rates of detoxification may indicate a lower risk of estragole for the Chinese population at similar levels of exposure. The study provides a proof of principle for how PBK modeling can identify differences in ethnic sensitivity and provide a more refined risk assessment for a specific ethnic group for a compound of concern.

Determination and risk assessment of naturally occurring genotoxic and carcinogenic alkenylbenzenes in basil-containing sauce of pesto

A risk assessment of basil-based pesto sauces containing methyleugenol and related alkenylbenzenes was performed based on their levels detected in a series of pesto sauces available on the Dutch market. The estimated daily intake (EDI) values of alkenylbenzenes as a result of consumption of the different pesto sauces amounted to 1.2–44.3 μg/kg bw for individual alkenylbenzenes, 14.3–43.5 μg/kg bw when adding up the alkenylbenzene levels assuming equal potency, and 17.3–62.9 μg/kg bw when expressed in methyleugenol equivalents using alkenylbenzenes defined toxic equivalency factors (TEF). The margin of exposure approach (MOE), used to evaluate the potential risks, resulted in MOE values that were generally lower than 10000 indicating a priority for risk management when assuming daily consumption. The levels of methyleugenol detected in the pesto sauces would allow consumption of 1.1–29.8, 7.5–208, 15.1–416.5, and 32.4–892.5 g of pesto sauce on a daily basis, once a week, once every two weeks, and once a month, respectively, to achieve MOE values above the 10000 limit indicating low priority for risk management. It is concluded that consumption of pesto sauces would only be of concern if consumed on a daily basis over longer periods of time.

Physiologically based kinetic modeling of the bioactivation of myristicin

The present study describes physiologically based kinetic (PBK) models for the alkenylbenzene myristicin that were developed by extension of the PBK models for the structurally related alkenylbenzene safrole in rat and human. The newly developed myristicin models revealed that the formation of the proximate carcinogenic metabolite 1′-hydroxymyristicin in liver is at most 1.8 fold higher in rat than in human and limited for the ultimate carcinogenic metabolite 1′-sulfoxymyristicin to (2.8–4.0)-fold higher in human. In addition, a comparison was made between the relative importance of bioactivation for myristicin and safrole. Model predictions indicate that for these related compounds, the formation of the 1′-sulfoxy metabolites in rat and human liver is comparable with a difference of <2.2-fold over a wide dose range. The results from this PBK analysis support that risk assessment of myristicin may be based on the BMDL₁₀ derived for safrole of 1.9–5.1 mg/kg bw per day. Using an estimated daily intake of myristicin of 0.0019 mg/kg bw per day resulting from the use of herbs and spices, this results in MOE values for myristicin that amount to 1000–2700, indicating a priority for risk management. The results obtained illustrate that PBK modeling provides insight into possible species differences in the metabolic activation of myristicin. Moreover, they provide an example of how PBK modeling can facilitate a read-across in risk assessment from a compound for which in vivo toxicity studies are available to a related compound for which tumor data are not reported, thus contributing to alternatives in animal testing.

Evaluation of Interindividual Human Variation in Bioactivation and DNA Adduct Formation of Estragole in Liver Predicted by Physiologically Based Kinetic/Dynamic and Monte Carlo Modeling

Estragole is a known hepatocarcinogen in rodents at high doses following metabolic conversion to the DNA-reactive metabolite 1'-sulfooxyestragole. The aim of the present study was to model possible levels of DNA adduct formation in (individual) humans upon exposure to estragole. This was done by extending a previously defined PBK model for estragole in humans to include (i) new data on interindividual variation in the kinetics for the major PBK model parameters influencing the formation of 1'-sulfooxyestragole, (ii) an equation describing the relationship between 1'-sulfooxyestragole and DNA adduct formation, (iii) Monte Carlo modeling to simulate interindividual human variation in DNA adduct formation in the population, and (iv) a comparison of the predictions made to human data on DNA adduct formation for the related alkenylbenzene methyleugenol. Adequate model predictions could be made, with the predicted DNA adduct levels at the estimated daily intake of estragole of 0.01 mg/kg bw ranging between 1.6 and 8.8 adducts in 10(8) nucleotides (nts) (50th and 99th percentiles, respectively). This is somewhat lower than values reported in the literature for the related alkenylbenzene methyleugenol in surgical human liver samples. The predicted levels seem to be below DNA adduct levels that are linked with tumor formation by alkenylbenzenes in rodents, which were estimated to amount to 188-500 adducts per 10(8) nts at the BMD10 values of estragole and methyleugenol. Although this does not seem to point to a significant health concern for human dietary exposure, drawing firm conclusions may have to await further validation of the model's predictions.

Matrix-derived combination effects influencing absorption, distribution, metabolism and excretion (ADME) of food-borne toxic compounds: implications for risk assessment

Absorption, distribution, metabolism and excretion (ADME) of food-borne toxic compounds may be influenced by other compounds or constituents present in the food.

Evaluation of the interindividual human variation in bioactivation of methyleugenol using physiologically based kinetic modeling and Monte Carlo simulations

The present study aims at predicting the level of formation of the ultimate carcinogenic metabolite of methyleugenol, 1'-sulfooxymethyleugenol, in the human population by taking variability in key bioactivation and detoxification reactions into account using Monte Carlo simulations. Depending on the metabolic route, variation was simulated based on kinetic constants obtained from incubations with a range of individual human liver fractions or by combining kinetic constants obtained for specific isoenzymes with literature reported human variation in the activity of these enzymes. The results of the study indicate that formation of 1'-sulfooxymethyleugenol is predominantly affected by variation in i) P450 1A2-catalyzed bioactivation of methyleugenol to 1'-hydroxymethyleugenol, ii) P450 2B6-catalyzed epoxidation of methyleugenol, iii) the apparent kinetic constants for oxidation of 1'-hydroxymethyleugenol, and iv) the apparent kinetic constants for sulfation of 1'-hydroxymethyleugenol. Based on the Monte Carlo simulations a so-called chemical-specific adjustment factor (CSAF) for intraspecies variation could be derived by dividing different percentiles by the 50th percentile of the predicted population distribution for 1'-sulfooxymethyleugenol formation. The obtained CSAF value at the 90th percentile was 3.2, indicating that the default uncertainty factor of 3.16 for human variability in kinetics may adequately cover the variation within 90% of the population. Covering 99% of the population requires a larger uncertainty factor of 6.4. In conclusion, the results showed that adequate predictions on interindividual human variation can be made with Monte Carlo-based PBK modeling. For methyleugenol this variation was observed to be in line with the default variation generally assumed in risk assessment.

Free radical metabolism of methyleugenol and related compounds

Methyleugenol, the methyl ether of eugenol, both of which are flavorant constituents of spices, has been listed by the National Toxicology Program's Report on Carcinogens as reasonably anticipated to be a human carcinogen. This finding is based on the observation of increased incidence of malignant tumors at multiple tissue sites in experimental animals of different species. By contrast, eugenol is not listed. In this study, we show that both methyleugenol and eugenol readily undergo peroxidative metabolism in vitro to form free radicals with large hyperfine interactions of the methylene allylic hydrogen atoms. These large hyperfine splittings indicate large electron densities adjacent to those hydrogen atoms. Methyleugenol undergoes autoxidation such that the commercial product contains 10-30 mg/L hydroperoxide and is capable of activating peroxidases without the presence of added hydrogen peroxide. Additionally, the hydroperoxide is not a good substrate for catalase, which demonstrates that these antioxidant defenses will not be effective in protecting against methyleugenol exposure.

Formation of hepatic DNA adducts by methyleugenol in mouse models: drastic decrease by Sult1a1 knockout and strong increase by transgenic human SULT1A1/2

Methyleugenol--a natural constituent of herbs and spices--is hepatocarcinogenic in rodent models. It can form DNA adducts after side-chain hydroxylation and sulfation. We previously demonstrated that human sulfotransferases (SULTs) 1A1 and 1A2 as well as mouse Sult1a1, expressed in Salmonella target strains, are able to activate 1'-hydroxymethyleugenol (1'-OH-ME) and 3'-hydroxymethylisoeugenol (3'-OH-MIE) to mutagens. Now we investigated the role of these enzymes in the formation of hepatic DNA adducts by methyleugenol in the mouse in vivo. We used FVB/N mice [wild-type (wt)] and genetically modified strains in this background: Sult1a1 knockout (ko), transgenic for human SULT1A1/2 (tg) and the combination of both modifications (ko-tg). Methyleugenol (50mg/kg body mass) formed 23, 735, 3770 and 4500 N (2)-(trans-methylisoeugenol-3'-yl)-2'-deoxyguanosine adducts per 10(8) 2'-deoxyribonucleosides (dN) in ko, wt, ko-tg and tg mice, respectively. The corresponding values for an equimolar dose of 1'-OH-ME were 12, 1490, 12 400 and 13 300 per 10(8) dN. Similar relative levels were observed for the minor adduct, N (6)-(trans-methylisoeugenol-3'-yl)-2'-deoxyadenosine. Thus, the adduct formation by both compounds was nearly completely dependent on the presence of SULT1A enzymes, with human SULT1A1/2 producing stronger effects than mouse Sult1a1. Moreover, a dose of 0.05 mg/kg methyleugenol (one-fourth of the estimated average daily exposure of humans) was sufficient to form detectable adducts in humanized (ko-tg) mice. Although 3'-OH-MIE was equally mutagenic to 1'-OH-ME in Salmonella strains expressing human SULT1A1 or 1A2, it only formed 0.14% of hepatic adducts in ko-tg mice compared with an equimolar dose of 1'-OH-ME, suggesting an important role of detoxifying pathways for this isomer in vivo.

Chemical Compositions of the Rhizome, Leaf and Stem Oils from Malaysian Hornstedtia leonurus

The chemical compositions of the essential oil of the rhizome, leaf and stem of Hornstedtia leonurus Retz., collected from Negeri Sembilan, Malaysia, are reported for the first time. The essential oils were extracted using hydrodistillation and analyzed by gas chromatography (GC-FID) and gas chromatography/mass spectrometry (GC/MS). Seventeen (96.4%), thirteen (89.2%) and nine components (98.8%) were successfully identified from the rhizome, stem and leaf oils, respectively. Phenylpropanoids were found to be the major fraction, with methyleugenol being the most abundant compound in all oils with percentage compositions of 76.4% (rhizome), 80.3% (stem) and 74.5% (leaf).

Physiologically based kinetic models for the alkenylbenzene elemicin in rat and human and possible implications for risk assessment

The present study describes physiologically based kinetic (PBK) models for the alkenylbenzene elemicin (3,4,5-trimethoxyallylbenzene) in rat and human, based on the PBK models previously developed for the structurally related alkenylbenzenes estragole, methyleugenol, and safrole. Using the newly developed models, the level of metabolic activation of elemicin in rat and human was predicted to obtain insight in species differences in the bioactivation of elemicin and read across to the other methoxy allylbenzenes, estragole and methyleugenol. Results reveal that the differences between rat and human in the formation of the proximate carcinogenic metabolite 1'-hydroxyelemicin and the ultimate carcinogenic metabolite 1'-sulfoxyelemicin are limited (<3.8-fold). In addition, a comparison was made between the relative importance of bioactivation for elemicin and that of estragole and methyleugenol. Model predictions indicate that compound differences in the formation of the 1'-sulfoxymetabolites are limited (<11-fold) in rat and human liver. The insights thus obtained were used to perform a risk assessment for elemicin using the margin of exposure (MOE) approach and read across to the other methoxy allylbenzene derivatives for which in vivo animal tumor data are available. This reveals that elemicin poses a lower priority for risk management as compared to its structurally related analogues estragole and methyleugenol. Altogether, the results obtained indicate that PBK modeling provides an important insight in the occurrence of species differences in the metabolic activation of elemicin. Moreover, they provide an example of how PBK modeling can facilitate a read across in risk assessment from compounds for which in vivo toxicity studies are available to a compound for which only limited toxicity data have been described, thus contributing to the development of alternatives for animal testing.