In vitro kinetics of amiodarone and its major metabolite in two human liver cell models after acute and repeated treatments

The limited value of in vitro toxicity data for the in vivo extrapolation has been often attributed to the lack of kinetic data. Here the in vitro kinetics of amiodarone (AMI) and its mono-N-desethyl (MDEA) metabolite was determined and modelled in primary human hepatocytes (PHH) and HepaRG cells, after single and repeated administration of clinically relevant concentrations. AMI bioavailability was influenced by adsorption to the plastic and the presence of protein in the medium (e.g. 10% serum protein reduced the uptake by half in HepaRG cells). The cell uptake was quick (within 3h), AMI metabolism was efficient and a dynamic equilibrium was reached in about a week after multiple dosing. In HepaRG cells the metabolic clearance was higher than in PHH and increased over time, as well as CYP3A4. The interindividual variability in MDEA production in PHHs was not proportional to the differences in CYP3A4 activities, suggesting the involvement of other CYPs and/or AMI-related CYP inhibition. After repeated treatment AMI showed a slight potential for bioaccumulation, whereas much higher intracellular MDEA levels accumulated over time, especially in the HepaRG cells, associated with occurrence of phospholipidosis. The knowledge of in vitro biokinetics is important to transform an actual in vitro concentration-effect into an in vivo dose-effect relationship by using appropriate modelling, thus improving the in vitro-to-in vivo extrapolation.

Comprehensive summary--Predict-IV: A systems toxicology approach to improve pharmaceutical drug safety testing

This special issue of Toxicology in Vitro is dedicated to disseminating the results of the EU-funded collaborative project "Profiling the toxicity of new drugs: a non animal-based approach integrating toxicodynamics and biokinetics" (Predict-IV; Grant 202222). The project's overall aim was to develop strategies to improve the assessment of drug safety in the early stage of development and late discovery phase, by an intelligent combination of non animal-based test systems, cell biology, mechanistic toxicology and in silico modeling, in a rapid and cost effective manner. This overview introduces the scope and overall achievements of Predict-IV.

Emerging health issues of cyanobacterial blooms

This paper describes emerging issue related to cyanobacterial dynamics and toxicity and human health risks. Data show an increasing cyanobacteria expansion and dominance in many environments. However there are still few information on the toxic species fitness, or on the effects of specific drivers on toxin production. Open research fields are related to new exposure scenario (cyanotoxins in water used for haemodialysis and in food supplements); to new patterns of co-exposure between cyanotoxins and algal toxins and/or anthropogenic chemicals; to dynamics affecting toxicity and production of different cyanotoxin variants under environmental stress; to the accumulation of cyanotoxins in the food web. In addition, many data gaps exist in the characterization of the toxicological profiles, especially about long term effects.

Toxicity of palytoxin after repeated oral exposure in mice and in vitro effects on cardiomyocytes

Palytoxin (PLTX) is a highly toxic hydrophilic polyether detected in several edible marine organisms from intra-tropical areas, where seafood poisoning were reported. Symptoms usually start with gastro-intestinal malaise, often accompanied by myalgia, muscular cramps, dyspnea and, sometimes, arrhythmias. Monitoring programs in the Mediterranean Sea have detected PLTX-like molecules in edible mollusks and echinoderms. Despite the potential exposure of the human population and its high toxic potential, the toxicological profile of the molecule is still an issue. Thus, the effects of repeated oral administration of PLTX in mice were investigated. Seven days of PLTX administration caused lethality and toxic effects at doses ≥ 30 μg/kg/day. A NOAEL was estimated equal to 3 μg/kg/day, indicating a quite steep dose-response curve. This value, due to the limited number of animal tested, is provisional, although represents a sound basis for further testing. Macroscopic alterations at gastrointestinal level (gastric ulcers and intestinal fluid accumulation) were observed in mice dead during the treatment period. Histological analysis highlighted severe inflammation, locally associated with necrosis, at pulmonary level, as well as hyper-eosinophilia and fiber separation in myocardium. A cardiac damage was supported by the in vitro effect of the toxin on cardiomyocytes, indicating a severe and irreversible impairment of their electrical properties: electrophysiological recordings detected a progressive cell depolarization, arrest of action potentials and beating.

The use of biomarkers of toxicity for integrating in vitro hazard estimates into risk assessment for humans

The role that in vitro systems can play in toxicological risk assessment is determined by the appropriateness of the chosen methods, with respect to the way in which in vitro data can be extrapolated to the in vivo situation. This report presents the results of a workshop aimed at better defining the use of in vitro-derived biomarkers of toxicity (BoT) and determining the place these data can have in human risk assessment. As a result, a conceptual framework is presented for the incorporation of in vitro-derived toxicity data into the risk assessment process. The selection of BoT takes into account that they need to distinguish adverse and adaptive changes in cells. The framework defines the place of in vitro systems in the context of data on exposure, structural and physico-chemical properties, and toxicodynamic and biokinetic modeling. It outlines the determination of a proper point-of-departure (PoD) for in vitro-in vivo extrapolation, allowing implementation in risk assessment procedures. A BoT will need to take into account both the dynamics and the kinetics of the compound in the in vitro systems. For the implementation of the proposed framework it will be necessary to collect and collate data from existing literature and new in vitro test systems, as well as to categorize biomarkers of toxicity and their relation to pathways-of-toxicity. Moreover, data selection and integration need to be driven by their usefulness in a quantitative in vitro-in vivo extrapolation (QIVIVE).

Contamination by Microcystis and microcystins of blue-green algae food supplements (BGAS) on the Italian market and possible risk for the exposed population

Blue green algae supplements (BGAS) are generally proposed as health-promoting natural products for their purported beneficial effects. Spirulina spp. and Aphanizomenon flos aquae are mainly used in BGAS production. They are usually collected from the natural environment, where other potentially toxic cyanobacteria can be present, making possible BGAS contamination by cyanotoxins, with potential risk for human health. In this work we apply a combined approach, by using chemical and molecular techniques, on BGAS of 17 brands available in Italy. Samples containing Spirulina-only were free of contamination. The Aphanizomenon flos aquae-based samples were contaminated by highly variable levels of microcystins (MC-LR and MC-LA congeners), up to 5.2 μg MC-LR equivalents per gram product. The highest variability (up to 50 fold) was among batches of the same brand, although intra-batch differences were also evidenced. PCR analyses were positive only for the presence of Microcystis sp., identified as the toxin-producing species responsible for contamination. At the maximum contamination levels found, a risk for consumers can be expected following chronic or sub-chronic exposure to a reasonable daily BGAS consumption of 4 g. The need for a strict monitoring by producers and Health Authority to assure an adequate protection for consumers is underscored.

Toxicokinetics as a key to the integrated toxicity risk assessment based primarily on non-animal approaches

Toxicokinetics (TK) is the endpoint that informs about the penetration into and fate within the body of a toxic substance, including the possible emergence of metabolites. Traditionally, the data needed to understand those phenomena have been obtained in vivo. Currently, with a drive towards non-animal testing approaches, TK has been identified as a key element to integrate the results from in silico, in vitro and already available in vivo studies. TK is needed to estimate the range of target organ doses that can be expected from realistic human external exposure scenarios. This information is crucial for determining the dose/concentration range that should be used for in vitro testing. Vice versa, TK is necessary to convert the in vitro results, generated at tissue/cell or sub-cellular level, into dose response or potency information relating to the entire target organism, i.e. the human body (in vitro-in vivo extrapolation, IVIVE). Physiologically based toxicokinetic modelling (PBTK) is currently regarded as the most adequate approach to simulate human TK and extrapolate between in vitro and in vivo contexts. The fact that PBTK models are mechanism-based which allows them to be 'generic' to a certain extent (various extrapolations possible) has been critical for their success so far. The need for high-quality in vitro and in silico data on absorption, distribution, metabolism as well as excretion (ADME) as input for PBTK models to predict human dose-response curves is currently a bottleneck for integrative risk assessment.

Human glutathione transferases catalyzing the conjugation of the hepatoxin microcystin-LR

Many cyanobacterial species are able to produce cyanotoxins as secondary metabolites. Among them, microcystins (MC) are a group of around 80 congeners of toxic cyclic heptapeptides. MC-LR is the most studied MC congener, in view of its high acute hepatotoxicity and tumor promoting activity. Humans may be exposed to cyanotoxins through several routes, the oral one being the most important. The accepted pathway for MC-LR detoxication and excretion in the urine is GSH conjugation. The GSH adduct (GS-MCLR) formation has been shown to occur spontaneously and enzymatically, catalyzed by glutathione transferases (GSTs). The enzymatic reaction has been reported but not characterized both in vitro and in vivo in animal and plant species. No data are available on humans. In the present work, the MC-LR conjugation with GSH catalyzed by five recombinant human GSTs (A1-1, A3-3, M1-1, P1-1, and T1-1) has been characterized for the first time. All GSTs are able to catalyze the reaction; kinetic parameters K(m), k(cat), and their relative specific activities to form GS-MCLR were derived (T1-1 > A1-1 > M1-1 > A3-3 ≫ P1-1). In the range of MC tested concentrations used (0.25-50 μM) GSTT1-1 and A1-1 showed a typical saturation curve with similar affinity for MC-LR (≈80 μM; k(cat) values 0.18 and 0.10 min(-1), respectively), A3-3 and M1-1 were linear, whereas GSTP1-1 showed a temperature-dependent sigmoidal allosteric curve with a k(cat) = 0.11 min(-1). The enzymes mainly expressed in the liver and gastrointestinal tract, GSTA1-1, T1-1, and M1-1, seemed to be mainly involved in the MC-LR detoxification after oral exposure, whereas P1-1 kinetics and location in the skin suggest a role related to dermal exposure. Considering the high frequency of some GST polymorphism, especially M1 and T1 gene deletion, with complete loss in activity, this information could be the first step to identify groups of individual at higher risk associated with MC exposure.

Alternative (non-animal) methods for cosmetics testing: current status and future prospects-2010

The 7th amendment to the EU Cosmetics Directive prohibits to put animal-tested cosmetics on the market in Europe after 2013. In that context, the European Commission invited stakeholder bodies (industry, non-governmental organisations, EU Member States, and the Commission's Scientific Committee on Consumer Safety) to identify scientific experts in five toxicological areas, i.e. toxicokinetics, repeated dose toxicity, carcinogenicity, skin sensitisation, and reproductive toxicity for which the Directive foresees that the 2013 deadline could be further extended in case alternative and validated methods would not be available in time. The selected experts were asked to analyse the status and prospects of alternative methods and to provide a scientifically sound estimate of the time necessary to achieve full replacement of animal testing. In summary, the experts confirmed that it will take at least another 7-9 years for the replacement of the current in vivo animal tests used for the safety assessment of cosmetic ingredients for skin sensitisation. However, the experts were also of the opinion that alternative methods may be able to give hazard information, i.e. to differentiate between sensitisers and non-sensitisers, ahead of 2017. This would, however, not provide the complete picture of what is a safe exposure because the relative potency of a sensitiser would not be known. For toxicokinetics, the timeframe was 5-7 years to develop the models still lacking to predict lung absorption and renal/biliary excretion, and even longer to integrate the methods to fully replace the animal toxicokinetic models. For the systemic toxicological endpoints of repeated dose toxicity, carcinogenicity and reproductive toxicity, the time horizon for full replacement could not be estimated.

Polymorphic DNA repair and metabolic genes: a multigenic study on gastric cancer

Risk factors for gastric cancer (GC) include inter-individual variability in the inflammatory response to Helicobacter pylori infection, in the ability of detoxifying DNA reactive species and repairing DNA damage generated by oxidative stress and dietary carcinogens. To evaluate the association between polymorphic DNA repair genes and GC risk, a case-control study including 314 histologically confirmed GC patients and 548 healthy controls was conducted in a GC high-risk area in Tuscany, Italy. Polymorphic variants of base excision repair (APE1-D148E, XRCC1-R194W, XRCC1-R399Q and OGG1-S326C), nucleotide excision repair (XPC-PAT, XPA-23G>A, ERCC1-19007T>C and XPD-L751Q), recombination (XRCC3-T241M) and alkylation damage reversal (MGMT-L84F) were tested for their potential role in the development of GC by using logistic regression models. The same population was also characterised for GSTT1 and GSTM1 variant alleles to search for possible functional interactions between metabolic and DNA repair genotypes by two-way interactions using multivariate logistic models. No significant association between any single DNA repair genotype and GC risk was detected with a borderline association with the XPC-PAT homozygous genotype [odds ratio (OR) =1.42; 95% confidence interval (CI) 0.94-2.17]. Gene-gene interaction analysis revealed combinations of unfavourable genotypes involving either multiple DNA repair polymorphisms or DNA repair and GST-specific genotypes. The combination of the XPC-PAT and the XPA variant alleles significantly increased GC risk (OR=2.15; 95% CI 1.17-3.93, P=0.0092). A significant interaction was also found between the APE1 wild-type genotype and either the single GSTT1 (OR=4.90; 95% CI 2.38-10.11, P=0.0079) or double GSTM1-GSTT1 null (OR=7.84; 95% CI 3.19-19.22, P=0.0169) genotypes or the XPA-mutant allele (OR=3.56; 95% CI 1.53-8.25, P=0.0012). These findings indicate that a complex interaction between host factors such as oxidative stress, antioxidant capacity and efficiency of multiple DNA repair pathways underlies the inter-individual variability in GC risk.

Caco-2/TC7 cell line characterization for intestinal absorption: how reliable is this in vitro model for the prediction of the oral dose fraction absorbed in human?

Caco-2 cell line is one of the most used in vitro model to study intestinal absorption of compounds at screening level. Several clones have been isolated from Caco-2 cell line and characterized for their activities. Among them, TC7 clone was isolated from a late passage of the parental Caco-2 line and has shown to consist of a more homogeneous population with respect to the most representative functions of the small intestinal enterocytes, with more developed intercellular junctions. On the basis of these characteristics, it was selected within the framework of the EU A-Cute-Tox project to check its suitability to predict intestinal transport. In the present study, drugs, synthetic or natural chemicals have been characterized for their absorption profile in TC7 cells cultivated on semi-permeable filters for 21 days. The absorption experiments have been performed with the highest nontoxic concentration as determined in a preliminary set of cytotoxicity tests. The apparent permeability coefficient (P(app)) has been extrapolated by calculating the passage of the test compound from the donor to the receiver compartment as a time function. The samples have been collected at different time intervals and the concentration of the test compounds analyzed by analytical methods (HPLC, GC, GC/MS). The P(app) obtained with the TC7 clone are comparable to those obtained with the parental cell line. However, some drawbacks related to the experimental system have been highlighted (i.e. low mass balance, adsorption to the plastics), on the basis of which some compounds were excluded from the analysis. In order to check the predictability of the model, a regression analysis has been performed by plotting P(app) values vs. the fraction absorbed in humans (FA, expressed as % of the administered dose). Additional elaborations have highlighted that the specific absorption pathway (passive, active and carrier-mediated) and other factors (i.e. efflux proteins and/or metabolic activity) can strongly affect the robustness of the prediction model. On the basis of the obtained results, TC7 clone has shown to be a model for passive diffusion as reliable as the parental cell line. However, we have remarked the non-suitability of the TC7 cells to predict intestinal absorption: (i) for highly lipophilic compounds; (ii) for poorly absorbed compounds; or (iii) when transporter-mediated routes and/or first pass metabolism are involved. The preliminary study of those factors likely influencing compound biokinetics, as well as the characterization of the cellular model with respect to metabolic and transporter competence, would help in the interpretation of data.

Health risk evaluation associated to Planktothrix rubescens: An integrated approach to design tailored monitoring programs for human exposure to cyanotoxins

Increasing concern for human health related to cyanotoxin exposure imposes the identification of pattern and level of exposure; however, current monitoring programs, based on cyanobacteria cell counts, could be inadequate. An integrated approach has been applied to a small lake in Italy, affected by Planktothrix rubescens blooms, to provide a scientific basis for appropriate monitoring program design. The cyanobacterium dynamic, the lake physicochemical and trophic status, expressed as nutrients concentration and recycling rates due to bacterial activity, the identification/quantification of toxic genotype and cyanotoxin concentration have been studied. Our results indicate that low levels of nutrients are not a marker for low risk of P. rubescens proliferation and confirm that cyanobacterial density solely is not a reliable parameter to assess human exposure. The ratio between toxic/non-toxic cells, and toxin concentrations, which can be better explained by toxic population dynamic, are much more diagnostic, although varying with time and environmental conditions. The toxic fraction within P. rubescens population is generally high (30-100%) and increases with water depth. The ratio toxic/non-toxic cells is lowest during the bloom, suggesting a competitive advantage for non-toxic cells. Therefore, when P. rubescens is the dominant species, it is important to analyze samples below the thermocline, and quantitatively estimate toxic genotype abundance. In addition, the identification of cyanotoxin content and congeners profile, with different toxic potential, are crucial for risk assessment.

Exposure to low levels of hexavalent chromium: target doses and comparative effects on two human pulmonary cell lines

Intracellular reduction of hexavalent chromium [Cr(VI)] is associated with the production of reactive oxygen species (ROS) and subsequent oxidative damage to different intracellular molecules like DNA, proteins and lipids is believed to contribute to the process of carcinogenesis. Aim of this study was to develop a model to establish a relationship between intracellular and macromolecule-bound chromium and some biomarkers of oxidative stress in two in vitro cell lines. Human lung adenocarcinoma (A549) and human bronchial epithelial (BEAS2B) cells were exposed for 3, 8 and 24 hours to relatively low doses (0.5--1--2 microM) of Cr(VI), i.e., to concentrations similar to what measured and reported by some authors in unexposed subjects and chromate workers. The results show that the differential cytotoxicity of Cr(VI) on the A549 and BEAS2B cell lines may be related both to their different polymorphism of Glutathione S-transferases genes and probably to their unlike permeability to Cr(VI). The glutathione decrease and the induction of HO-1 observed only in BEAS2B cells after Cr(VI) exposure strengthen the idea that glutathione S-transferases activity may accelerate the reduction of Cr(VI) to Cr(III) with the concomitant induction of oxidative stress. In conclusion, the determination of intracellular Cr in cellular models can be considered an important step in comparing in vitro and in vivo models on the basis of target doses and a promising approach to study the effects of pneumotoxic compounds.

Evidences for CYP3A4 autoactivation in the desulfuration of dimethoate by the human liver

Dimethoate (DIM) is an organophosphorothionate (OPT) pesticide used worldwide as a systemic insecticide and acaricide. It is characterized by low-to-moderate acute mammalian toxicity; similarly to the other OPT pesticides, its mode of action is mediated by the inhibition of acetylcholinesterase (AChE), exerted by its toxic metabolite dimethoate-oxon or omethoate (OME), which is also used as a direct acting pesticide. Human hepatic DIM bioactivation to the toxic metabolite OME has been characterized by using c-DNA expressed human CYPs and human liver microsomes (HLM) also in the presence of CYP-specific chemical inhibitors, with a method based on AChE inhibition. The obtained kinetic parameters and AChE IC(50) have been compared with those previously obtained with other OPTs, indicating a lower efficiency in DIM desulfuration reaction and a lower potency in inhibiting AChE. Results showed that, similarly to the other OPTs tested so far, at low DIM concentration OME formation is mainly catalysed by CYP1A2, while the role of 3A4 is relevant at high DIM levels. Differently from the other OPTs, DIM desulfuration reaction showed an atypical kinetic profile, likely due to CYP3A4 autoactivation. The sigmoidicity degree of the activity curve increased with the level of CYP3A4 in HLM or disappeared in the presence of a CYP3A4 chemical inhibitor. This atypical kinetic behaviour can be considered one of the possible explanations for the recent findings that among patients hospitalized following OPT intoxication, DIM ingestion gave different symptoms and more severe poisoning (23.1% of fatal cases versus total) than chlorpyrifos (8% of deaths), which has a lower LD(50) value. Since DIM-poisoned patients poorly responded to pralidoxime, the possibility to use CYP3A4 inhibitors could be considered as a complementary treatment.

Cholinesterase inhibition and alterations of hepatic metabolism by oral acute and repeated chlorpyrifos administration to mice

Chlorpyrifos (CPF) is a broad spectrum organophosphorus insecticide bioactivated in vivo to chlorpyrifos-oxon (CPFO), a very potent anticholinesterase. A great majority of available animal studies on CPF and CPFO toxicity are performed in rats. The use of mice in developmental neurobehavioural studies and the availability of transgenic mice warrant a better characterization of CPF-induced toxicity in this species. CD1 mice were exposed to a broad range of acute (12.5-100.0mg/kg) and subacute (1.56-25mg/kg/day from 5 to 30 days) CPF oral doses. Functional and biochemical parameters such as brain and serum cholinesterase (ChE) and liver xenobiotic metabolizing system, including the biotransformation of CPF itself, have been studied and the no observed effect levels (NOELs) identified. Mice seem to be more susceptible than rats at least to acute CPF treatment (oral LD(50) 4.5-fold lower). The species-related differences were not so evident after repeated exposures. In mice a good correlation was observed between brain ChE inhibition and classical cholinergic signs of toxicity. After CPF-repeated treatment, mice seemed to develop some tolerance to CPF-induced effects, which could not be attributed to an alteration of P450-mediated CPF hepatic metabolism. CPF-induced effects on hepatic microsomal carboxylesterase (CE) activity and reduced glutathione (GSH) levels observed at an early stage of treatment and then recovered after 30 days, suggest that the detoxifying mechanisms are actively involved in the protection of CPF-induced effects and possibly in the induction of tolerance in long term exposure. The mouse could be considered a suitable experimental model for future studies on the toxic action of organophosphorus pesticides focused on mechanisms, long term and age-related effects.

Lindane may modulate the female reproductive development through the interaction with ER-beta: an in vivo-in vitro approach

Lindane (gamma-HCH) is a persistent environmental pollutant that may act as endocrine disrupter, affecting the nervous, immune and reproductive system, possibly through endocrine-mediated mechanisms. Since both estrogen receptors (ER-alpha and -beta) have shown to be target for endocrine disruption, we investigated the role of gamma-HCH on the development of female reproductive system. For an in vivo evaluation of gamma-HCH effects during prenatal period, pregnant CD1 mice were treated p.o. on gestational days 9-16 with 15 mg/kg bw/day of gamma-HCH and vehicle. The in vivo findings in treated F1 pups - in the absence of signs of systemic toxicity - included increase in the absolute and relative and absolute uterus weight revealed on post-natal day 22, earlier vaginal patency and reduced diameters of primary oocytes at fully sexual maturity. No effects on steroid hormone metabolism (aromatase, testosterone catabolism) were observed. Thus, gamma-HCH elicited subtle effects on female reproductive development likely mediated by ER-beta-mediated pathway(s), without a concurrent impairment of steroid hormone metabolism. Furthermore, to verify whether the endocrine interference of gamma-HCH is attributable to stimulation of ER-beta-mediated pathway(s), its effect has been evaluated in vitro on a cell line, LNCaP, expressing only functional ER-beta. In vitro treatments revealed a concentration-related effect on LNCaP cell viability and proliferation. Significantly, the contemporary addition of a pure anti-estrogen, the ER antagonist ICI 182,780, completely reversed gamma-HCH effects indicating an ER-beta-mediated action. Our findings indicate that gamma-HCH may act as endocrine disruptor during the female reproductive system development and ER-beta as a potential target for this compound and other endocrine disrupting chemicals as well.

Effects of the pesticide clorpyrifos on an in vitro model of intestinal barrier

Clorpyrifos (CPF), one of the most widely used organophosphorothionate pesticide can be detected as residues in food and drinking water; therefore the oral route is the major route of exposure for the general population, including children, following household use of this insecticide. Aim of this work was to investigate the possible acute cytotoxic effects of CPF on intestine and the integrity of the epithelial barrier, using Caco-2/TC7 cells as intestinal in vitro model. High level of CPF found inside the cells, corresponding to about 80% of the nominal concentration tested (30, 50 and 250microM), chosen as representative of the concentrations attainable in the intestinal lumen after actual levels of human oral exposure. In these conditions, no cytotoxicity in terms of cellular viability was observed. However, at the highest CPF nominal concentration (250microM) the impairment of barrier integrity was evidenced, due only to the parent compound, since no CPF metabolites could be detected in our experimental conditions. CPF itself was demonstrated to interfere with the tight junction on this in vitro model of epithelial intestinal cells, altering the barrier integrity and very likely the absorption of other co-administered chemicals.

Foetal and adult human CYP3A isoforms in the bioactivation of organophosphorothionate insecticides

In humans organophosphorothionate pesticides (OPT) prenatal exposure has been demonstrated. Since OPT-induced neurodevelopmental effects may be due to in situ bioactivation by foetal enzymes, the catalytic activity of the foetal CYP3A7 toward chlorpyrifos (CPF), parathion (PAR), malathion (MAL) and fenthion (FEN) has been assessed by using recombinant enzymes. A comparison with the adult isoforms CYP3A4 and CYP3A5 has been also carried out. CYP3A7 was able to produce significant levels of oxon or sulfoxide from the four OPTs in the range of tested concentrations (0.05-200 microM). When the efficiencies of CYP3A isoforms were compared, the ranking, expressed as CLi values, were: CPF=3A4>3A5>3A7; PAR=3A4>>3A7>>3A5; MAL=3A4>3A7>3A5; FEN (sulfoxide formation)=3A4>3A5>>3A7. The CYP3A5 efficiency appeared to be more dependent on the single insecticide than its related isozyme CYP3A4. Our results indicate that the levels of toxic metabolite formed in situ by CYP3A7 from CPF, MAL and PAR but not from FEN have the chance to inhibit acetylcholinesterase, following prenatal exposure to OPTs. However, due to the smaller weight of foetal liver, the contribution to total OPT biotransformation is relatively low. On the other hand, our results clearly indicate that at low CPF concentrations, the formation of the non-toxic metabolites is highly favoured in the foetus.

Metabolic and genetic factors contributing to alcohol induced effects and fetal alcohol syndrome

Alcohol-related damages on newborns and infants include a wide variety of complications from facial anomalies to neurodevelopmental delay, known as fetal alcohol syndrome (FAS). However, only less than 10% of women drinking alcohol during pregnancy have children with FAS. Understanding the risk factors increasing the probability for newborn exposed in utero to alcohol to develop FAS is therefore a key issue. The involvement of genetics as a one risk factor in FAS has been suggested by animal models and by molecular epidemiological studies on different populations, bearing allelic variants for those enzymes, such as ADH e CYP2E1, involved in ethanol metabolism. Indeed, one of the major factors determining the peak blood alcohol exposure to the fetus is the metabolic activity of the mother, in addition to placental and fetal metabolism, explaining, at least partially, the risk of FAS. The different rates of ethanol metabolism may be the result of genetic polymorphisms, the most relevant of which have been described in the paper.

Short-Term Effects of Adolescent Methylphenidate Exposure on Brain Striatal Gene Expression and Sexual/Endocrine Parameters in Male Rats

Exposure to methylphenidate (MPH) during adolescence is the elective therapy for attention deficit/hyperactivity disorder (ADHD) children, but raises major concerns for public health, due to possibly persistent neurobehavioral changes. Rats (30- to 44-days old) were administered MPH (2 mg/kg, i.p once daily) or saline (SAL). At the end of the treatment we collected plasma, testicular, liver, and brain (striatum) samples. The testes and liver were used to evaluate conventional reproductive and metabolic endpoints. Testes of MPH-exposed rats weighed more and contained an increased quantity of sperm, whereas testicular levels of testosterone (TST) were markedly decreased. The MPH treatment exerted an inductive effect on enzymatic activity of TST hydroxylases, resulting in increased hepatic TST catabolism. These findings suggest that subchronic MPH exposure in adolescent rats could have a trophic action on testis growth and a negative impact on TST metabolism. We have analyzed striatal gene expression profiles as a consequence of MPH exposure during adolescence, using microarray technology. More than 700 genes were upregulated in the striatum of MPH-treated rats (foldchange >1.5). A first group of genes were apparently involved in migration of immature neural/glial cells and/or growth of novel axons. These genes include matrix proteases (ADAM-1, MMP14), their inhibitors (TIMP-2, TIMP-3), the hyaluronan-mediated motility receptor (RHAMM), and growth factors (transforming growth factor-beta3 [TGF-beta3] and fibroblast growth factor 14 [FGF14]). A second group of genes were suggestive of active axonal myelination. These genes mediate survival of immature cells after contact with newly produced axonal matrix (laminin B1, collagens, integrin alpha 6) and stabilization of myelinating glia-axon contacts (RAB13, contactins 3 and 4). A third group indicated the appearance and/or upregulation of mature processes. The latter included genes for: K+ channels (TASK-1, TASK-5), intercellular junctions (connexin30), neurotransmitter receptors (adrenergic alpha 1B, kainate 2, serotonin 7, GABA-A), as well as major proteins responsible for their transport and/or anchoring (Homer 1, MAGUK MPP3, Shank2). All these genes were possibly involved in synaptic plasticity, namely the formation, maturation, and stabilization of new neural connections within the striatum. MPH treatment seems to potentiate synaptic plasticity, which is an age-dependent developmental phenomenon that adolescent rats are very likely to show, compared to adults. Our observations suggest that adolescent MPH exposure causes only transient changes in reproductive and hormonal parameters, and a more enduring enhancement of neurobehavioral plasticity.

Individual susceptibility and alcohol effects:biochemical and genetic aspects

The large interethnic and interindividual variability in alcohol-induced toxic effects comes from a combination of genetic and environmental factors, influencing ethanol toxicokinetics. The hepatic enzymatic systems involved in ethanol metabolism are alcohol dehydrogenase (ADH), aldehyde dehydrogenase (ALDH) and microsomal P4502E1 (CYP2E1). ADH oxidizes ethanol to acetaldehyde, which is very efficiently oxidized to acetate by ALDH. About 10% of moderate quantities of ethanol is metabolised by CYP2E1; the percentage increases when ADH is saturated. During ethanol metabolism reactive oxygen species and hydroxyethyl radicals are generated, causing oxidative stress, responsible for most ethanol-induced liver damage. For their critical role in detoxifying radicals, glutathione S-transferase are gaining attention in the etiology of alcoholism. All these enzymes have been shown to be polymorphic, giving rise to altered phenotypes. For this reason recent studies have looked for a correlation between metabolic variability and differences in alcohol abuse-related effects.

Malathion detoxification by human hepatic carboxylesterases and its inhibition by isomalathion and other pesticides

The organophosphorothioate (OPT) pesticide malathion (MAL) in mammals is readily hydrolyzed by mammalian carboxylesterases (CE). The reaction competes with the CYP-catalyzed formation of malaoxon (MOX), the toxic metabolite. Alterations or individual variations in CE activity may result in increased MOX formation, enhancing MAL toxicity. We have characterized the human hepatic CE activity in a panel of 18 human liver microsomes as well as the inhibitory effect of IsoMAL, a major impurity of MAL commercial formulations, parathion (PAR), chlorpyrifos (CPF), and chlorpyrifos-oxon (CPFO). CE activity showed a low level of variation among individuals (4-fold). The reaction consists of two different phases, differing in their affinity for mal (k(m1)=0.25-0.69 microm; K(m2)=10.3-26.8 microM). The relatively low K(m1) values confirmed that human CE efficiently detoxify MAL. IsoMAL was shown to be a potent noncompetitive inhibitor of MAL detoxification (K(i)=0.6 microM), with a higher inhibitory potency than CPF and PAR (K(i)=7.5 microM and 50 microM, respectively). These two latter compounds very likely act as mixed inhibitors. CPFO showed the highest inhibitory potency toward CE-mediated detoxification, being characterized by a K(i)=22 nM. The present results provide useful information for a better understanding of possible interactions between different OPTs and for assessing the potential cumulative risk for exposure to OPT mixtures.

Interleukin-1 gene polymorphisms and gastric cancer risk in a high-risk Italian population

OBJECTIVES

Host genetic factors, including the IL1 gene cluster, play a key role in determining the long-term outcome of Helicobacter pylori infection. The aim of the study was to investigate the relationship between selected IL1 loci polymorphisms and gastric cancer risk in an Italian population.

METHODS

In a case-control study we compared the IL1B-31 and IL1B+3954 biallelic and IL1RN pentaallelic variable number of tandem repeats (VNTR) polymorphisms in 185 gastric cancer patients and 546 controls randomly sampled from the general population of an area at high gastric cancer risk (Tuscany, Central Italy).

RESULTS

Genotype frequencies of the IL1B-31 T/C, IL1B+3954 C/T, and IL1RN polymorphisms among our population controls were in Hardy-Weinberg equilibrium. In multivariate analyses, no increase in gastric cancer risk was observed for the IL1B-31*C- and IL1B+3954*T- carriers; a significant 50% increase emerged for IL1RN*2 allele carriers (OR = 1.49; 95% CI: 1.01-2.21). Analyses based on combined genotypes showed also that the association with IL1RN*2 allele was limited to two-variant allele carriers who were also homozygous for the IL1B-31*T allele (OR = 2.23; 95% CI: 1.18-4.23) with a statistically significant interaction between these two genotypes (p= 0.043). Haplotype analysis showed an increased risk for the haplotype IL1RN*2/IL1B-31*T.

CONCLUSIONS

Our results suggest that host genetic factors (such as the IL1RN and the IL1B-31 polymorphisms) interact in the complex process of gastric carcinogenesis in this high-risk Italian population. Overall, this effect appears more modest than previously reported in other populations, supporting the hypothesis that other still-to-be-defined factors are important in gastric carcinogenesis. These findings might be due to a haplotype effect.

Organophosphorothionate pesticides inhibit the bioactivation of imipramine by human hepatic cytochrome P450s

The drug-toxicant interaction between the antidepressant imipramine (IMI) and three organophosphorothionate pesticides (OPTs), to which humans may be chronically and simultaneously exposed, has been investigated in vitro. Concentrations of IMI (2-400 microM) and OPTs (< or =10 microM) representative of actual human exposure have been tested with recombinant human CYPs and human liver microsomes (HLM). The different CYPs involved in IMI demethylation to the pharmacologically active metabolite desipramine (DES) were CYP2C19 > CYP1A2 > CYP3A4. The OPTs significantly inhibited (up to >80%) IMI bioactivation catalyzed by the recombinant CYPs tested, except CYP2D6, and by HLM; the inhibition was dose-dependent and started at low pesticide concentrations (0.25-2.5 microM). The OPTs, having lower K(m) values, efficiently competed with IMI for the enzyme active site, as in the case of CYP2C19. However, with CYP1A2 and CYP3A4, a time- and NADPH-dependent mechanism-based inactivation also occurred, consistently with irreversible inhibition due to the release of the sulfur atom, binding to the active CYP during OPT desulfuration. At low IMI and OPT concentrations, lower IC50 values have been obtained with recombinant CYP1A2 (0.7-1.1 microM) or with HLM rich in 1A2-related activity (2-10.8 microM). The K(i) values (2-14 microM), independent on substrate concentrations, were quite low and similar for the three pesticides. Exposure to OPTs during IMI therapeutic treatments may lead to decreased DES formation, resulting in high plasma levels of the parent drug, eventual impairment of its pharmacological action and possible onset of adverse drug reactions (ADRs).

GSTT1 andGSTM1 gene polymorphisms and gastric cancer in a high-risk italian population

Glutathione S-Transferases (GSTs) are a family of phase II enzymes involved in the detoxification of potential carcinogens and provided of a strong antioxidant function by neutralizing electrophiles and free radicals. The GSTM1 and GSTT1 isoenzymes exhibit deletion polymorphisms, resulting in a lack of activity, and the null genotypes have been associated with increased cancer risk at several sites, including the stomach, although with contrasting results. We carried out a case-control study to evaluate whether these polymorphisms modulate the risk of developing gastric cancer (GC). Genotypes for GSTM1 and GSTT1 were obtained from a series of 175 histologically confirmed GC patients and a large series of 546 healthy controls randomly sampled from the general population of Tuscany, an area at high GC risk. No difference in the frequency of GSTM1 null genotype was observed between cases and controls, whereas the GSTT1 null genotype was more frequent among cases (p = 0.04). Multivariate single-gene analyses adjusted for possible confounders showed that the GSTT1 null genotype, but not the GSTM1 null genotype, was associated with an increased GC risk. Combined-genotype analyses showed a significantly increased GC risk only for the double null (GSTM1-GSTT1) genotype (OR = 2.27; 95% CI: 1.14-4.53). A statistically significant positive interaction between the 2 null genotypes was observed (p = 0.02). Our findings suggest that only subjects lacking both GSTM1 and GSTT1 activity are at increased GC risk. This study provides further support to the hypothesis that the risk of developing GC is influenced by inter-individual variation in both carcinogen detoxification and antioxidant capacity. (c) 2005 Wiley-Liss, Inc.

Bioactivation, toxicokinetics and acute effects of chloroform in Fisher 344 and Osborne Mendel male rats

Chloroform has been regarded as a renal carcinogen, based on results obtained with Osborne Mendel (OM) rats. Fisher 344 (F344) rats, considered representative of OM rats on the basis of comparable acute toxic effects, have been used in most of the studies aimed to elucidate the mechanisms of kidney tumour induction. In the present work, in vitro and in vivo chloroform bioactivation in the liver and kidney of F344 and OM rats has been reported, as well as additional toxicokinetics and acute toxicity information. Complete similarity of chloroform metabolism and toxicokinetics was evidenced in the two rat strains. Chloroform metabolism was fully saturated at the OM rat bioassay doses (90-180 mg kg(-1) body wt.), working at a maximal rate of 40-50 micro mol (14)CO(2) expired kg(-1) h(-1). No acute hepatotoxicity, nephrotoxicity or consequent cell proliferation was evidenced at 180 mg kg(-1) body wt. chloroform. In the rat liver, phosgene was confirmed as the major metabolite. Renal microsomes from both F344 and OM rats in vitro were unable to produce any oxidative metabolite; at variance, adducts due to oxidative and reductive metabolites were detected in vivo. Our results indicated the presence in the rat kidney of electrophilic metabolites other than phosgene, representing either oxidative metabolites formed elsewhere and sufficiently stable to be transported to the kidney or electrophilic metabolites secondary to the formation of reductive radicals. Therefore, the rat kidney represents a suitable model to study the toxicological effects, including genotoxicity, of chloroform metabolites in the absence of cytotoxic effects produced by phosgene formed in situ.

MALATHION BIOACTIVATION IN THE HUMAN LIVER: THE CONTRIBUTION OF DIFFERENT CYTOCHROME P450 ISOFORMS

Among organophosphorothioate (OPT) pesticides, malathion is considered relatively safe for use in mammals. Its rapid degradation by carboxylesterases competes with the cytochrome P450 (P450)-catalyzed formation of malaoxon, the toxic metabolite. However, impurities in commercial formulations are potent inhibitors of carboxylesterase, allowing a dramatic increase in malaoxon formation. Malathion desulfuration has been characterized in human liver microsomes (HLMs) with a method based on acetylcholinesterase inhibition that is able to detect nanomolar levels of oxon. The active P450 isoforms have been identified by means of a multifaceted strategy, including the use of cDNA-expressed human P450s and correlation, immunoinhibition, and chemical inhibition studies in a panel of phenotyped HLMs. HLMs catalyzed malaoxon formation with a high level of variability (>200-fold). One or two components (K(mapp1) = 53-67 microM; K(mapp2) = 427-1721 microM) were evidenced, depending on the relative specific P450 content. Results from different approaches indicated that, at low malathion concentration, malaoxon formation is catalyzed by CYP1A2 and, to a lesser extent, 2B6, whereas the role of 3A4 is relevant only at high malathion levels. These results are in line with those found with chlorpyrifos, diazinon, azynphos-methyl, and parathion, characterized by the presence of an aromatic ring in the molecule. Since malathion has linear chains as substituents at the thioether sulfur, it can be hypothesized that, independently from the chemical structure, OPTs are bioactivated by the same P450s. These results also suggest that CYP1A2 and 2B6 can be considered as possible metabolic biomarkers of susceptibility to OPT-induced toxic effects at actual human exposure levels.

Toxicology investigations with cell culture systems: 20 years after

From almost 20 years the "in vitro" model has gained a wide ground in toxicological investigation, providing advanced tools, reliable protocols, mechanistic information. These advancements have been done thanks to different approaches, addressed at improving chemical testing and validating procedures, at exploring the cellular and molecular basis of toxicity, at studying the modifications that xenobiotics undergo in the cellular environment. In this review the most advanced cellular models, the mechanisms of cell death, the techniques to monitor gene activation, following chemical exposure, is highlighted. Moreover the more recent in vitro models to approach the biotransformation issue will be presented.

Metabolism of chloroform in the human liver and identification of the competent P450s

The oxidative and reductive cytochrome P450 (P450)-mediated chloroform bioactivation has been investigated in human liver microsomes (HLM), and the role of human P450s have been defined by integrating results from several experimental approaches: cDNA-expressed P450s, selective chemical inhibitors and specific antibodies, correlation studies in a panel of phenotyped HLM. HLM bioactivated CHCl(3) both oxidatively and reductively. Oxidative reaction was characterized by two components, suggesting multiple P450 involvement. The high affinity process was catalyzed by CYP2E1, as clearly indicated by kinetic studies, correlation with chlorzoxazone 6-hydroxylation (r = 0.837; p < 0.001), and inhibition by monoclonal antihuman CYP2E1 and 4-methylpyrazole. The low affinity phase of oxidative metabolism was essentially catalyzed by CYP2A6. This conclusion was supported by the correlation with coumarin 7-hydroxylase (r = 0.777; p < 0.01), inhibition by coumarin and by the specific antibody, in addition to results with heterologously expressed P450s. Chloroform oxidation was poorly dependent on pO(2), whereas the reductive metabolism was highly inhibited by O(2). The production of dichloromethyl radical was significant only at CHCl(3) concentration > or =1 mM, increasing linearly with substrate concentration. CYP2E1 was the primary enzyme involved in the reductive reaction, as univocally indicated by all the different approaches. The reductive pathway seems to be scarcely relevant in the human liver, since it is active only at high substrate concentrations, and in strictly anaerobic conditions. The role of human CYP2E1 in CHCl(3) metabolism at low levels, typical of actual human exposure, provides insight into the molecular basis for eventual difference in susceptibility to chloroform-induced effects due to either genetic, pathophysiological, or environmental factors.

CYP-specific bioactivation of four organophosphorothioate pesticides by human liver microsomes

The bioactivation of azinphos-methyl (AZIN), chlorpyrifos (CPF), diazinon (DIA), and parathion (PAR), four widely used organophosphorothioate (OPT) pesticides has been investigated in human liver microsomes (HLM). In addition, the role of human cytochrome P450 (CYPs) in OPT desulfuration at pesticide levels representative of human exposure have been defined by means of correlation and immunoinhibition studies. CYP-mediated oxon formation from the four OPTs is efficiently catalyzed by HLM, although showing a high variability (>40-fold) among samples. Two distinct phases were involved in the desulfuration of AZIN, DIA, and PAR, characterized by different affinity constants (K(mapp1) = 0.13-9 microM and K(mapp2) = 5- 269 microM). Within the range of CPF concentrations tested, only the high-affinity component was evidenced (K(mapp1) = 0.27-0.94 microM). Oxon formation in phenotyped individual HLM showed a significant correlation with CYP1A2-, 3A4-, and 2B6-related activities, at different levels depending on the OPT concentration. Anti-human CYP1A2, 2B6, and 3A4 antibodies significantly inhibited oxon formation, showing the same OPT concentration dependence. Our data indicated that CYP1A2 is mainly involved in OPT desulfuration at low pesticide concentrations, while the role of CYP3A4 is more significant to the low-affinity component of OPT bioactivation. The contribution of CYP2B6 to total hepatic oxon formation was relevant in a wide range of pesticide concentrations, being a very efficient catalyst of both the high- and low-affinity phase. These results suggest CYP1A2 and 2B6 as possible metabolic biomarkers of susceptibility to OPT toxic effect at the actual human exposure levels.

Kinetic parameters of OPT pesticide desulfuration by c-DNA expressed human CYPs

The role of different cytochrome P450 isoforms (CYPs) in the desulfuration of four organophosphorothionate pesticides (OPTs), namely diazinon (DIA), azinphos-methyl (AZ), chlorpyrifos (CPF) and parathion (PARA), at OPT levels representative of actual human exposure has been investigated. For this purpose c-DNA expressed human CYPs and a method, based on acetylcholinesterase (AChE) inhibition, able to detect nM levels of oxon have been used. Our results indicate that the four tested OPTs at low concentration were mainly desulfurated by CYP2B6, 2C19 and 1A2, showing K(m) values in the range 0.8-5 μM and the highest efficiency (intrinsic clearance (ICL)) values. CYP3A4 was generally endowed with high K(m) and resulted linear up to 25-100 μM OPT, concentrations saturating the most efficient CYPs. The tentative extrapolation of the relative contribution of single CYPs, taking into account the average content of different isoforms in the human liver, indicate that CYP1A2 is the major responsible for oxon formation. Indeed this CYP catalyses the 50-90% of desulfuration reaction, depending on the OPT. As CYP3A4 activity is not completely saturated up to 100 μM OPT, and due to the high hepatic content, its contribution to oxon formation may result relevant in poisoning episodes, when individuals are exposed at high doses of OPTs.

The relevance of xenobiotic metabolism in the interindividual susceptibility to chemicals

Biotransformation enzymes may catalyze either detoxication or bioactivation reactions; indeed, many xenobiotics exert their toxic effects after metabolic activation to electrophilic chemicals, interacting with nucleophilic sites on cellular macromolecules. On the other hand, by increasing xenobiotic hydrophilicity, the drug-metabolizing enzymes favors excretion of lipophilic chemicals, not allowing their bioaccumulation up to toxic levels. The expression of the enzymes of the drug-metabolizing system is modulated by genetic, pathological, developmental, environmental and dietary factors. Genetic polymorphism resulting in interindividual and interethnic variation in xenobiotic metabolism is responsible for differences in the susceptibility to chemical-induced toxicity and carcinogenicity, allowing the identification of people at increased risk. Moreover, differences in drug metabolism may correspond to variability in drug response during pharmacological therapy, which can be manifest either as adverse reactions or as a lack of benefit.