Coumarin metabolism, toxicity and carcinogenicity: relevance for human risk assessment

Effects of umbelliferone in a murine model of allergic airway inflammation

The therapeutic effects of umbelliferone (30, 60 and 90 mg/kg), a coumarin isolated from Typha domingensis (Typhaceae) were investigated in a mouse model of bronchial asthma. BALB/c mice were immunized and challenged by nasal administration of ovalbumin. Treatment with umbelliferone (60 and 90 mg/kg) caused a marked reduction of cellularity and eosinophil numbers in bronchoalveolar lavage fluids from asthmatic mice. In addition, a decrease in mucus production and lung inflammation were observed in mice treated with umbelliferone. A reduction of IL-4, IL-5, and IL-13, but not of IFN-gamma, was found in bronchoalveolar lavage fluids of mice treated with umbelliferone, similar to that observed with dexamethasone. The levels of ovalbumin-specific IgE were not significantly altered after treatment with umbelliferone. In conclusion, our results demonstrate that umbelliferone attenuates the alteration characteristics of allergic airway inflammation. The investigation of the mechanisms of action of this molecule may contribute for the development of new drugs for the treatment of asthma.

Negative ion electrospray ionization mass spectrometry and computational studies on substituted 7-hydroxycoumarins

Twenty-two substituted 7-hydroxycoumarins were studied by negative ion electrospray ionization collision- induced dissociation (CID) mass spectrometry. Fragmentation pathways were also investigated by computation method using the B3LYP density functional theory. In general, the most important fragmentations of the 7- hydroxycoumarin [M - H](-) ions were the elimination of CO(2) and CO which agreed with the calculated energies of the proposed fragmentation reactions. In most cases, methyl group elimination was also favorable. Methyl group elimination occurred in three different ways, the most interesting being hydrogen rearrangement from a neighboring alkyl group to a ring carbon, which led to a benzyl radical formation. In some cases, CH(2)CO elimination was observed as well. Isomeric compounds gave rise to different CID spectra.

Aquatic toxicity assessment of the additive 6-methylcoumarine using four experimental systems

The toxicity assessment of chemicals is one of the main issues in the current policies in order to protect the health of the environment and human beings. Food and cosmetic additives have been extensively studied in relation to their toxicity to humans, but data about their ecotoxicological effects are scarce. The aim of this study was to evaluate the toxic effects of the additive 6-methylcoumarine in the aquatic milieu using a test battery comprising experimental model systems from different trophic levels. The inhibition of bioluminiscence was studied in the bacteria Vibrio fischeri (decomposer), the inhibition of growth was evaluated in the alga Chlorella vulgaris (producer) and immobilization was studied in the cladoceran Daphnia magna (first consumer). Finally, several end points were evaluated in the RTG-2 salmonid fish cell line, including neutral red uptake, protein content, methylthiazol tetrazolium salt metabolization, glucose-6-phosphate dehydrogenase activity, lactate dehydrogenase activity and leakage, and morphology. The sensitivity of the test systems employed was as follows: V. fischeri > D. magna > C. vulgaris > RTG-2 cell line. The results show that 6-methylcoumarine is not expected to produce acute toxic effects on the aquatic biota. However, chronic and synergistic effects with other chemicals cannot be excluded and should be further investigated.

The composition of alcohol products from markets in Lithuania and Hungary, and potential health consequences: a pilot study

AIMS

The rates of alcohol-attributable mortality in Lithuania and Hungary have been shown to be higher than those in most other European countries. Quality of alcohol products is investigated as a possible explanation.

METHODS

In a descriptive pilot study, a convenience sample of alcohol products was collected from local city markets in both countries (Lithuania n = 10, Hungary n = 15) and chemical analyses, including some that have not been done in prior studies, were conducted. The parameters studied were alcoholic strength, volatiles (methanol, acetaldehyde, higher alcohols), ethyl carbamate, anions (including nitrate) and inorganic elements (including lead). Additionally, a multi-target screening analysis for toxicologically relevant substances was conducted.

RESULTS

The majority of samples (64%) had an alcohol content between 35% vol. and 40% vol., being in accordance with the typical strength of legal spirits in Europe. Three samples containing significantly higher concentrations of alcohol above 60% vol. were found to be unrecorded alcohol products, defined as any alcohol that is outside of legal and taxed production. Screening analysis showed that those samples contained various flavourings, including the hepatotoxic substance coumarin, at concentrations above the legal limit for foods. All other substance classes under study were found to be at levels of no toxicological concern.

CONCLUSIONS

Although some problems with the quality of the alcohol samples were found, there is insufficient evidence from this pilot study to conclude that alcohol quality has an influence on health as reflected in alcohol-attributable mortality rates. Given the extent of alcohol-attributable disease burden in central and eastern European countries, future research should focus on collection of large, representative samples, particularly of unrecorded sources, which was the most problematic product group in our study.

Generation of recombinant alpaca VHH antibody fragments for the detection of the mycotoxin ochratoxin A

To develop sensor technologies based on genetically engineered recognition elements, recombinant antibodies characterised by high stability are a prerequisite. Here we describe the first successful isolation of recombinant alpaca single-domain antibody fragments with high affinity to the mycotoxin ochratoxin A (OTA). Variable domains (VHH) of heavy-chain antibodies binding to OTA were cloned from an immunised alpaca. Selected VHH clones clustered in four major groups, based on protein sequence similarity. Six representative VHH antibody fragments were produced in Escherichia coli and characterised for their sensitivity and specificity by indirect competitive enzyme-linked immunosorbent assays. OTA concentrations causing 50% inhibition (IC50) ranged from 12 ng/ml for antibody fragment OCH-62 to 442 ng/ml for antibody fragment OCH-40. The IC50 of OCH-62 for ochratoxin B, an OTA analogue, was 476 ng/ml. No significant cross-reactivity was observed with common food constituents with structural similarities with parts of OTA, such as L-phenylalanine and coumarin. The performance of OCH-62 for detection of OTA in food matrices was comparable to the performance in buffer (white wine: IC50=17 ng/ml; red wine: IC50=21 ng/ml; instant coffee: IC50=17 ng/ml). In a membrane-based flow-through immunoassay, used for fast visual screening of samples, OCH-62 showed a cut-off level of 10 ng/ml OTA. Thereby, OCH-62 ranked among the best recombinant antibody fragments described for mycotoxins and is an excellent candidate for the design of food contamination sensors based on nanotechnology.

Differential inhibition of cytochromes P450 3A4 and 3A5 by the newly synthesized coumarin derivatives 7-coumarin propargyl ether and 7-(4-trifluoromethyl)coumarin propargyl ether

The abilities of 7-coumarin propargyl ether (CPE) and 7-(4-trifluoromethyl)coumarin propargyl ether (TFCPE) to act as mechanism-based inactivators of P450 3A4 and 3A5 in the reconstituted system have been investigated using 7-benzyloxy-4-(trifluoromethyl)coumarin (BFC) and testosterone as probes. CPE inhibited the BFC O-debenzylation activity of P450 3A4 in a time-, concentration-, and NADPH-dependent manner characteristic of a mechanism-based inactivator with a half-maximal inactivation (K(I)) of 112 microM, a maximal rate of inactivation (k(inact)) of 0.05 min(-1), and a t(1/2) of 13.9 min. Similarly, TFCPE inhibited the BFC O-debenzylation activity of P450 3A4 in a time-, concentration-, and NADPH-dependent manner with a K(I) of 14 microM, a k(inact) of 0.04 min(-1), and a t(1/2) of 16.5 min. Parallel losses of P450 3A4 enzymatic activity and heme were observed with both compounds as measured by high-performance liquid chromatography and reduced CO spectra. Interestingly, neither compound inhibited the BFC O-debenzylation activity of P450 3A5. Reactive intermediates of CPE and TFCPE formed by P450 3A4 were trapped with glutathione, and the resulting adducts were identified using tandem mass spectral analysis. Metabolism studies using TFCPE resulted in the identification of a single metabolite that is formed by P450 3A4 but not by P450 3A5 and that may play a role in the mechanism-based inactivation.

Effects of naturally occurring coumarins on hepatic drug-metabolizing enzymes in mice

Cytochromes P450 (P450s) and glutathione S-transferases (GSTs) constitute two important enzyme families involved in carcinogen metabolism. Generally, P450s play activation or detoxifying roles while GSTs act primarily as detoxifying enzymes. We previously demonstrated that oral administration of the linear furanocoumarins, isopimpinellin and imperatorin, modulated P450 and GST activities in various tissues of mice. The purpose of the present study was to compare a broader range of naturally occurring coumarins (simple coumarins, and furanocoumarins of the linear and angular type) for their abilities to modulate hepatic drug-metabolizing enzymes when administered orally to mice. We now report that all of the different coumarins tested (coumarin, limettin, auraptene, angelicin, bergamottin, imperatorin and isopimpinellin) induced hepatic GST activities, whereas the linear furanocoumarins possessed the greatest abilities to induce hepatic P450 activities, in particular P450 2B and 3A. In both cases, this corresponded to an increase in protein expression of the enzymes. Induction of P4502B10, 3A11, and 2C9 by xenobiotics often is a result of activation of the pregnane X receptor (PXR) and/or constitutive androstane receptor (CAR). Using a pregnane X receptor reporter system, our results demonstrated that isopimpinellin activated both PXR and its human ortholog SXR by recruiting coactivator SRC-1 in transfected cells. In CAR transfection assays, isopimpinellin counteracted the inhibitory effect of androstanol on full-length mCAR, a Gal4-mCAR ligand-binding domain fusion, and restored coactivator binding. Orally administered isopimpinellin induced hepatic mRNA expression of Cyp2b10, Cyp3a11, and GSTain CAR(+/+) wild-type mice. In contrast, the induction of Cyp2b10 mRNA by isopimpinellin was attenuated in the CAR(-/-) mice, suggesting that isopimpinellin induces Cyp2b10 via the CAR receptor. Overall, the current data indicate that naturally occurring coumarins have diverse activities in terms of inducing various xenobiotic metabolizing enzymes based on their chemical structure.

HPLC analysis and safety assessment of coumarin in foods

Coumarin is a component of natural flavourings including cassia, which is widely used in foods and pastries. The toxicity of coumarin has raised some concerns and food safety authorities have set a maximum limit of 2mg/kg for foods and beverages in general, and a maximum level of 10mg/l for alcoholic beverages. An efficient method for routine analysis of coumarin is liquid chromatography with diode array detection. The optimal sample preparation for foods containing cinnamon was investigated and found to be cold extraction of 15g sample with 50mL of methanol (80%, v/v) for 30min using magnetic stirring. In the foods under investigation, appreciable amounts of coumarin were found in bakery products and breakfast cereals (mean 9mg/kg) with the highest concentrations up to 88mg/kg in certain cookies flavoured with cinnamon. Other foods such as liqueurs, vodka, mulled wine, and milk products did not have coumarin concentrations above the maximum level. The safety assessment of coumarin containing foods, in the context of governmental food controls, is complicated as a toxicological basis for the maximum limits appears to be missing. The limits were derived at a time when a genotoxic mechanism was assumed. However, this has since been disproven in more recent studies. Our exposure data on coumarin in bakery products show that there is still a need for a continued regulation of coumarin in foods. A toxicological re-evaluation of coumarin with the aim to derive scientifically founded maximum limits should be conducted with priority.

Synthesis and antitumor studies on novel Co(II), Ni(II) and Cu(II) metal complexes of bis(3-acetylcoumarin)thiocarbohydrazone

The synthesis, structure, physico-chemical investigation and biological studies of some metal complexes of thiocarbohydrazone ligands are described. The ligand is obtained by condensation of N,N'-thiocarbohydrazide with 3-acetylcoumarin. The metal complexes of Co(II), Ni(II) and Cu(II) with bis(3-acetylcoumarin)thiocarbohydrazone were synthesized and isolated as solid products and characterized by analytical means as well as by spectral techniques such as FT-IR, (1)H NMR and EPR and UV spectrometry. The ligand acts as bidentate, through NO or NN, neutral in coordinating the M(II) ions. The bonding sites are the azomethine nitrogen, lactone carbonyl oxygen and respective anion counterparts. The metal complexes exhibit either octahedral or distorted octahedral structures. The complexes are found to be soluble in dimethylformamide and dimethylsulphoxide. Molar conductance values in dimethylsulphoxide indicate the non-electrolytic nature of the complexes. The compounds tested in present study have shown promising cytotoxic activity when screened using the in vitro method and at the same time were shown to have good activity when tested using the Ehrlich Ascites Carcinoma model. Preliminary antimicrobial screening shows the promising results against both bacterial and fungal strains.

A comparative human health risk assessment of p-dichlorobenzene-based toilet rimblock products versus fragrance/surfactant-based alternatives

A comparison of the human health risk to consumers using one of two types of toilet rimblock products, either a p-dichlorobenzene-based rimblock or two newer fragrance/surfactant-based alternatives, was conducted. Rimblock products are designed for global use by consumers worldwide and function by releasing volatile compounds into indoor air with subsequent exposure presumed to be mainly by inhalation of indoor air. Using the THERdbASE exposure model and experimentally determined emission data, indoor air concentrations and daily intake values were determined for both types of rimblock products. Modeled exposure concentrations from a representative p-dichlorobenzene rimblock product are an order of magnitude higher than those from the alternative rimblock products due to its nearly pure composition and high sublimation rate. Lifetime exposure to p-dichlorobenzene or the subset of fragrance components with available RfD values is not expected to lead to non-cancer-based adverse health effects based on the exposure concentrations estimated using the THERdbASE model. A similar comparison of cancer-based effects was not possible as insufficient data were available for the fragrance components.

Determination of eugenol, anethole, and coumarin in the mainstream cigarette smoke of Indonesian clove cigarettes

Indonesian clove cigarettes (kreteks), typically have the appearance of a conventional domestic cigarette. The unique aspects of kreteks are that in addition to tobacco they contain dried clove buds (15-40%, by wt.), and are flavored with a proprietary "sauce". Whereas the clove buds contribute to generating high levels of eugenol in the smoke, the "sauce" may also contribute other potentially harmful constituents in addition to those associated with tobacco use. We measured levels of eugenol, trans-anethole (anethole), and coumarin in smoke from 33 brands of clove-flavored cigarettes (filtered and unfiltered) from five kretek manufacturers. In order to provide information for evaluating the delivery of these compounds under standard smoking conditions, a quantification method was developed for their measurement in mainstream cigarette smoke. The method allowed collection of mainstream cigarette smoke particulate matter on a Cambridge filter pad, extraction with methanol, sampling by automated headspace solid-phase microextraction, and subsequent analysis using gas chromatography/mass spectrometry. The presence of these compounds was confirmed in the smoke of kreteks using mass spectral library matching, high-resolution mass spectrometry (+/-0.0002 amu), and agreement with a relative retention time index, and native standards. We found that when kreteks were smoked according to standardized machine smoke parameters as specified by the International Standards Organization, all 33 clove brands contained levels of eugenol ranging from 2,490 to 37,900 microg/cigarette (microg/cig). Anethole was detected in smoke from 13 brands at levels of 22.8-1,030 microg/cig, and coumarin was detected in 19 brands at levels ranging from 9.2 to 215 microg/cig. These detected levels are significantly higher than the levels found in commercial cigarette brands available in the United States.

Drug discovery and computational evolutionary analysis

Drug discovery remains a difficult business with a very high level of attrition. Many steps in this long process use data generated from various species. One key challenge is to successfully translate the pre-clinical findings of target validation and safety studies in animal models to diverse human beings in the clinic. Advanced computational evolutionary analysis techniques combined with the increasing availability of sequence information enable the application of systematic evolutionary approaches to targets and pathways of interest to drug discovery. These analyses have the potential to increase our understanding of experimental differences observed between species.

Compounds from Ageratum conyzoides: isolation, structural elucidation and insecticidal activity

This work aimed at identifying plant compounds with insecticidal activity against Diaphania hyalinata (L.) (Lepidoptera: Pyralidae), Musca domestica (L.) (Diptera: Muscidae), Periplaneta americana (L.) (Blattodea: Blattidae) and Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae). The plant species used were: basil (Ocimum selloi Benth.), rue (Ruta graveolens L.), lion's ear (Leonotis nepetaefolia L.), Jimson weed (Datura stramonium L.), 'baleeira' herb (Cordia verbenaceae L.), mint (Mentha piperita L.), wild balsam apple (Mormodica charantia L.) and billy goat weed (Ageratum conyzoides L.). Firstly, the insecticidal activities of hexane and ethanol plant extracts were evaluated against adults of R. dominica. Among them, only the hexane extract of A. conyzoides showed insecticidal activity. The hexane extract of this plant species was therefore fractionated by silica gel column chromatography to isolate and purify its bioactive chemical constituents. Three compounds were identified using IR spectra, (1)H NMR, (13)C NMR, HMBC and NOE after gel chromatography: 5,6,7,8,3', 4', 5'-heptamethoxyflavone, 5,6,7,8,3'-pentamethoxy-4', 5'-methylenedioxyflavone and coumarin. The complete assignment of (13)C NMR to 5,6,7,8,3'-pentamethoxy-4', 5'-methylenedioxyflavone was successfully made for the first time. 5,6,7,8,3'-Pentamethoxy-4', 5'-methylenedioxyflavone did not show any insecticidal activity against the four insect species tested. 5,6,7,8,3', 4', 5'-Heptamethoxyflavone showed low activity against D. hyalinata and R. dominica and was not toxic to M. domestica or P. americana. In contrast, coumarin showed insecticidal activity against all four insect pest species tested, with the following order of susceptibility: R. dominica < P. americana < D. hyalinata < M. domestica after 24 h exposure.

CYP2A6 polymorphisms: is there a role for pharmacogenomics in preventing coumarin-induced hepatotoxicity in lymphedema patients?

Lymphedema is a chronic progressive and significantly disabling disease that affects over 150 million people worldwide. Coumarin is an effective pharmacological treatment, but is banned in some countries due to incidences of hepatotoxicity in rats and mice, and the rare finding of similar hepatotoxicity in humans. Cytochrome P450 (CYP)2A6 is the major enzyme involved in metabolizing coumarin to 7-hydroxycoumarin. A reduction in CYP2A6 activity will lead to shunting of coumarin into other metabolic pathways. In particular, coumarin is metabolized by CYP3A4 to form 3-hydroxycoumarin, the major metabolite in mice and rats. It has been shown that an increase in the 3-hydroxycoumarin ratio is associated with an increased production of the significant cytotoxic product o-hydroxyphenylacetylacetaldehyde (o-HPA), suggesting that a shunting of coumarin metabolism away from 7-hydroxylation is the cause of the toxicity. Hence, poor CYP2A6 metabolizers are more likely to metabolize coumarin via the cytotoxic pathway. Identifying these patients, and not treating them with coumarin, may reduce the incidence of toxicity associated with this drug. The technology to do so exists, but more information is required regarding the mechanism of coumarin toxicity.

Comparison of coumarin-induced toxicity between sandwich-cultured primary rat hepatocytes and rats in vivo: a toxicogenomics approach

Sandwich-cultured primary rat hepatocytes are often used as an in vitro model in toxicology and pharmacology. However, loss of liver-specific functions, in particular, the decline of cytochrome P450 (P450) enzyme activity, limits the value of this model for prediction of in vivo toxicity. In this study, we investigated whether a hepatic in vitro system with improved metabolic competence enhances the predictability for coumarin-induced in vivo toxicity by using a toxicogenomics approach. Therefore, primary rat hepatocytes were cultured in sandwich configuration in medium containing a mixture of low concentrations of P450 inducers, phenobarbital, dexamethasone, and beta-naphthoflavone. The toxicogenomics approach used enabled comparison of similar mechanistic end-points at the molecular level between in vitro and in vivo conditions, namely, compound-induced changes in multiple genes and signaling pathways. Toxicant-induced cytotoxic effects and gene expression profiles observed in hepatocytes cultured in modified medium and hepatocytes cultured in standard medium (without inducers) were compared with results from a rat in vivo study. Coumarin was used as a model compound because its toxicity depends on bioactivation by P450 enzymes. Metabolism of coumarin toward active metabolites, coumarin-induced cytotoxicity, and gene expression modulation were more pronounced in hepatocytes cultured in modified medium compared with hepatocytes cultured in standard medium. In addition, more genes and biological pathways were similarly affected by coumarin in hepatocytes cultured in modified medium and in vivo. In conclusion, these experiments showed that for coumarin-induced toxicity, sandwich-cultured hepatocytes maintained in modified medium better represent the situation in vivo compared with hepatocytes cultured in standard medium.

A safety assessment of coumarin taking into account species-specificity of toxicokinetics

Coumarin (1,2-benzopyrone) is a naturally occurring fragrant compound found in a variety of plants and spices. Exposure to the general public is through the diet and from its use as a perfume raw material in personal care products. High doses of coumarin by the oral route are known to be associated with liver toxicity in rodents. Chronic oral bioassays conducted in the 1990s reported liver tumors in rats and mice and lung tumors in mice, raising concerns regarding the safety of coumarin. Since then, an extensive body of research has focused on understanding the etiology of these tumors. The data support a conclusion that coumarin is not DNA-reactive and that the induction of tumors at high doses in rodents is attributed to cytotoxicity and regenerative hyperplasia. The species-specific target organ toxicity is shown to be related to the pharmacokinetics of coumarin metabolism, with data showing rats to be particularly susceptible to liver effects and mice to be particularly susceptible to lung effects. A quantitative human health risk assessment that integrates both cancer and non-cancer effects is presented, confirming the safety of coumarin exposure from natural dietary sources as well as from its use as a perfume in personal care products.

Pharmacogenomics: its role in re-establishing coumarin as treatment for lymphedema

Although there remains some significant controversy regarding the use and benefits of coumarin (5,6-benzo-alpha pyrone), it would seem that targeted appropriate and monitored use of the drug does have a significant role in the treatment of lymphedemas. The particular benefits are its cost and ease of administration. Given today's demands for high level investigative clinical trials, it would be virtually impossible to conduct a study large enough to make any significant conclusions about hepatotoxic effects. However, it seems without doubt that the majority of studies conducted thus far suggest that coumarin (and other benzopyrones, i.e., the ruto-sides, which do not have hepatotoxic effects and which are often discussed in aggregate with coumarin) is effective in treating lymphedema, particularly when used in conjunction with complex physical therapy. The use of pharmacogenomics could significantly lower the risk of coumarin-associated hepatotoxicity, by targeting the use of coumarin to those with functional CYP2A6. Further research in this area will be required to re-evaluate the cost- benefit ratio and to determine the potential for the reintroduction of coumarin as a potent treatment for lymphedema. The perceived negative image of coumarin should not be allowed to carry across to the other benzopyrones, as they still confer a significant benefit in the management of lymphedemas.

Metabolism of coumarin by human P450s: a molecular modelling study

The oxidative metabolism of coumarin via several human cytochrome P450 (CYP) enzymes from families CYP1, CYP2 and CYP3 is rationalized in terms of molecular modelling studies carried out on the key interactions with various amino acid residues in the relevant active sites. The findings from modelling by homology with the CYP2C5 crystallographic template are in agreement with the known metabolism of coumarin in human P450s from the CYP1, CYP2 and CYP3 families, which has been published recently, and with independently reported information from site-directed mutagenesis studies.

Molecular mechanisms of toxicity of important food-borne phytotoxins

At present, there is an increasing interest for plant ingredients and their use in drugs, for teas, or in food supplements. The present review describes the nature and mechanism of action of the phytochemicals presently receiving increased attention in the field of food toxicology. This relates to compounds including aristolochic acids, pyrrolizidine alkaloids, beta-carotene, coumarin, the alkenylbenzenes safrole, methyleugenol and estragole, ephedrine alkaloids and synephrine, kavalactones, anisatin, St. John's wort ingredients, cyanogenic glycosides, solanine and chaconine, thujone, and glycyrrhizinic acid. It can be concluded that several of these phytotoxins cause concern, because of their bioactivation to reactive alkylating intermediates that are able to react with cellular macromolecules causing cellular toxicity, and, upon their reaction with DNA, genotoxicity resulting in tumors. Another group of the phytotoxins presented is active without the requirement for bioactivation and, in most cases, these compounds appear to act as neurotoxins interacting with one of the neurotransmitter systems. Altogether, the examples presented illustrate that natural does not equal safe and that in modern society adverse health effects, upon either acute or chronic exposure to phytochemicals, can occur as a result of use of plant- or herb-based foods, teas, or other extracts.

Metabolic Detoxification Determines Species Differences in Coumarin-Induced Hepatotoxicity

Hepatotoxicity of coumarin is attributed to metabolic activation to an epoxide intermediate, coumarin 3,4-epoxide (CE). However, whereas rats are most susceptible to coumarin-induced hepatotoxicity, formation of CE is greatest in mouse liver microsomes, a species showing little evidence of hepatotoxicity. Therefore, the present work was designed to test the hypothesis that detoxification of CE is a major determinant of coumarin hepatotoxicity. CE can either rearrange spontaneously to o-hydroxyphenylacetaldehyde (o-HPA) or be conjugated with gluatathione (GSH). o-HPA is hepatotoxic and is further detoxified by oxidation to o-hydroxyphenylacetic acid (o-HPAA). In vitro experiments were conducted using mouse liver microsomes to generate a constant amount of CE, and cytosols from F344 rats, B6C3F1 mice, and human liver were used to characterize CE detoxification. All metabolites were quantified by HPLC methods with UV detection. In rats and mice, GSH conjugation occurred non-enzymatically and through glutathione-S-transferases (GSTs), and the kinetics of GSH conjugation were similar in rats and mice. In rat liver cytosol, oxidation of o-HPA to o-HPAA was characterized with a high affinity K(m) of approximately 12 microM, and a V(max) of approximately 1.5 nmol/min/mg protein. In contrast, the K(m) and V(max) for o-HPA oxidation in mouse liver cytosol were approximately 1.7 microM and 5 nmol/min/mg protein, respectively, yielding a total intrinsic clearance through oxidation to o-HPAA that was 20 times higher in mouse than in rats. Human cytosols (two separate pools) detoxified CE through o-HPA oxidation with an apparent K(m) of 0.84 microM and a V(max) of 5.7 nmol/min/mg protein, for a net intrinsic clearance that was more than 50 times higher than the rat. All species also reduced o-HPA to o-hydroxyphenylethanol (o-HPE), but this was only a major reaction in rats. In the presence of a metabolic reaction replete with all necessary cofactors, GSH conjugation accounted for nearly half of all CE metabolites in rat and mouse, whereas the GSH conjugate represented only 10% of the metabolites in human cytosol. In mouse, o-HPAA represented the major ring-opened metabolite, accounting for the remaining 50% of metabolites, and in human cytosol, o-HPAA was the major metabolite, representing nearly 90% of all CE metabolites. In contrast, no o-HPAA was detected in rats, whereas o-HPE represented a major metabolite. Collectively, these in vitro data implicate o-HPA detoxification through oxidation to o-HPAA as the major determinant of species differences in coumarin-induced hepatotoxicity.

Daphnetin induced differentiation of human renal carcinoma cells and its mediation by p38 mitogen-activated protein kinase

Daphnetin has been shown to be a potent in vitro anti-proliferative agent to the human renal cell carcinoma (RCC) cell line, A-498. In the present study, we investigated its effects on mitogen-activated protein kinase (MAPK) signalling along with cell cycle events and cellular differentiation. Daphnetin-activated p38, however, higher concentrations were required to inhibit ERK1/ERK2. In addition, it did not activate SAPK or induce apoptosis, but instead inhibited S phase cell cycle transition of A-498 cells at low concentrations and time of exposure. In addition, a late G(1), early S phase inhibition was observed at higher concentrations and time of exposure, indicating that the mechanism of daphnetin-induced differentiation was concentration dependent. Increased expression of the epithelial differentiation markers cytokeratins 8 and 18, correlated with increasing concentrations of daphnetin, while pre-treatment with a specific p38-inhibitor, served to limit this effect. There was no evidence that P-glycoprotein (P-gp) mediated multi-drug resistance (MDR) played a role in the anti-proliferative activity of daphnetin. Consequently, we concluded that p38 MAP kinase is intrinsically involved in mediating the effect of daphnetin in A-498 cells, suggesting that this drug may act by promotion of cellular maturation, and consequently may represent a novel low toxic approach for the treatment of poorly differentiated RCCs.

Apoptosis and cell cycle disturbances induced by coumarin and 7-hydroxycoumarin on human lung carcinoma cell lines

Coumarin and 7-hydroxycoumarin have anti-tumour actions in vitro and in vivo. There are no previous reports on the cytostatic and apoptotic actions of coumarin and 7-hydroxycoumarin in non-small cell lung carcinoma (NSCLC) cell lines. Here we report on: (1) the inhibition of cell proliferation, (2) the phase in which cell cycle arrest occurs, and (3) the induction of apoptosis. Inhibition of cell proliferation was determined by 3H-thymidine incorporation. The effects on cell cycle phases were determined at 100 microg/ml of coumarin or 7-hydroxycoumarin using propidium iodide and flow cytometry. Higher concentrations were used to study apoptosis, detected by: (1) morphological cell changes, (2) subG1 peak detection and (3) Annexin-V assay. Peripheral blood mononuclear cells (PBMC) stimulated with phytohemagglutinin were used as controls. The actions of these compounds depended on drug concentrations and on histological cell type. Coumarin and 7-hydroxycoumarin inhibited cell growth by inducing cell cycle arrest in the G1 phase in all the lung carcinoma cell lines. Apoptosis required large concentrations of the coumarin compounds and was observed in adenocarcinomas. Apoptosis was not associated with intra-nucleosomal DNA fragmentation. Apoptosis was not observed in squamous lung carcinoma cell lines, but an increase in G1 cell cycle arrest was detected. In PBMC, only large concentrations of the coumarin compounds elicited a cystostatic action. Coumarins in combination with other anti-neoplastic drugs might increase the effectiveness of NSCLC treatments.

Liquid chromatographic determination of the glutathione conjugate and ring-opened metabolites formed from coumarin epoxidation

Species differences in the biotransformation of coumarin are thought to play an important role in its toxicity. Since the putative toxic metabolite is coumarin 3,4-epoxide (CE), methods to measure the metabolites of CE were developed. The glutathione (GSH) conjugate of CE (CE-SG) at the 3-position was purified by reversed-phase (RP)-high performance liquid chromatography (HPLC), and characterized by mass spectrometry (MS) and nuclear magnetic resonance spectroscopy (NMR). An RP-HPLC method was developed to quantify CE-SG in hepatic microsomal mixtures and a separate RP-HPLC method was also developed to quantify the three ring-opened coumarin metabolites; o-hydroxyphenylacetic acid (o-HPAA), o-hydroxyphenylethanol (o-HPE) and o-hydroxyphenylacetaldehyde (o-HPA) in hepatic microsomal mixtures. Detection limits for all four products of coumarin epoxidation exceeded 3.5 ng/ml and recovery from hepatic microsomal mixtures was essentially quantitative with RSD values less than 8%. Species differences in o-HPA detoxification were consistent with sensitivity to coumarin, thereby demonstrating that these methods have utility in addressing the fate of CE and its contribution to toxicity.

Synthesis of N-acetyl-S-(3-coumarinyl)-cysteine methyl ester and HPLC analysis of urinary coumarin metabolites

N-Acetyl-S-(3-coumarinyl)cysteine, a metabolite of coumarin in rodents, has been synthesized as methyl ester. A new synthetic route to prepare N-acetyl-S-(3-coumarinyl)-D,L-cysteine methyl ester comprises reaction of 3-mercaptocoumarin with N-acetyl-3-chloro-D,L-alanine methyl ester. N-acetyl-S-(4-coumarinyl)-L-cysteine was obtained by reaction of 3-bromocoumarin and N-acetyl-L-cysteine. A method for the determination of N-acetyl-S-(3-coumarinyl)cysteine as its methyl ester in urine by HPLC has been developed.

Comparative metabolism and kinetics of coumarin in mice and rats

Coumarin, a well recognized rat hepatotoxicant, also causes acute, selective necrosis of terminal bronchiolar Clara cells in the mouse lung. Further, chronic oral gavage administration of coumarin at 200 mg/kg, a dose that causes Clara cell death, resulted in a statistically significant increased incidence of alveolar/bronchiolar adenomas and carcinomas in B6C3F1 mice. In contrast, mouse lung tumors were not observed at the 100 and 50 mg/kg dose levels in the oral gavage study, or in CD-1 mice following chronic intake of coumarin at levels equivalent to 276 mg/kg in diet. The current studies were designed to determine the impact of oral gavage vs dietary administration on the pharmacokinetics and metabolism of coumarin in CD-1 and B6C3F1 mice and F344 rats. Following the administration of 200 mg/kg 14C-coumarin via oral gavage, lung C(max) values (total 14C-associated radioactivity) were five- and 37-fold greater than those resulting from a 50 mg/kg oral gavage dose or 1000 ppm in diet, respectively. Coumarin (200 mg/kg) pharmacokinetics and metabolism was also examined in F344 rats following oral gavage dosing. Total 14C-coumarin associated radioactivity in plasma was 3.5-fold lower than in the mouse, and the plasma half-life in rats was five-times longer than in mice. Using non-radiolabeled compound (200 mg/kg), coumarin and products of the coumarin 3,4-epoxidation pathway were quantitated in plasma and urine after oral gavage administration to mice and rats. 7-Hydroxycoumarin (7-HC) was quantitated in mouse plasma and urine. o-Hydroxyphenylacetic acid (o-HPAA) reached a concentration of 37 microg/ml in plasma, and accounted for 41% of the dose in the urine, whereas the C(max) for 7-hydroxycoumarin was 3 microg/ml, and represented 7% of the administered dose. In the rat, the plasma C(max) for o-HPAA was 6 microg/ml, and accounted for 12% of the dose. The coumarin C(max) in rat plasma was comparable to that in mouse. Coumarin 3,4-epoxide (CE) and its rearrangement product o-hydroxyphenylacetaldehyde (o-HPA) and o-hydroxyphenylethanol (o-HPE), were not detected at any time point in plasma or urine. This analysis of coumarin and CE pharmacokinetics in rodents suggests that the differential tumor response in the mouse oral gavage and dietary bioassays is a function of the route of exposure, whereas species differences in lung toxicity between mice and rats result from heightened local bioactivation in the mouse lung.

Concentrations of nine alkenylbenzenes, coumarin, piperonal and pulegone in Indian bidi cigarette tobacco

Indian-made bidi cigarettes sold in the United States are available in a variety of exotic (e.g. clove, mango) and candy-like (e.g. chocolate, raspberry) flavors. Because certain tobacco flavorings contain alkenylbenzenes and other toxic or carcinogenic chemicals, we measured the concentration of flavor-related compounds in bidi tobacco using a previously developed method. Twenty-three brands of bidis were sampled using automated headspace solid-phase microextraction and subsequently analyzed for 12 compounds by gas chromatography-mass spectrometry. Two alkenylbenzene compounds, trans-anethole and eugenol, were found in greater than 90% of the brands analyzed. Methyleugenol, pulegone and estragole were each detected in 30% or more of the brands, whereas safrole and elemicin were not detected in any of the brands. The flavor-related compounds with the highest tobacco concentrations were eugenol (12,000 microg/g tobacco) and trans-anethole (2200 microg/g tobacco). The highest eugenol and trans-anethole concentrations found in bidi tobacco were about 70,000 and 7500 times greater, respectively, than the highest levels previously found in US cigarette brands. Measurement of these compounds is crucial to evaluation of potential risks associated with inhaling highly concentrated flavor-related compounds from bidis or other tobacco products.

Species differences in coumarin metabolism: a molecular modelling evaluation of CYP2A interactions

1. An account of the differences in coumarin metabolism between several mammalian species, including man, is reported. 2. The metabolism of coumarin via 7-hydroxylation in the human (CYP2A6) and mouse (CYP2A5) enzymes is explained in terms of molecular modelling of the active site interactions, whereas the rat orthologue (CYP2A1) exhibits 3,4-epoxidation of coumarin, which is also consistent with the modelled interaction between enzyme and substrate. 3. In addition, quantitative structure-activity relationships (QSARs) for coumarin 7-hydroxylation in wild-type and mutant CYP2A5 show the importance of amino acid residue properties for substrate binding, whereas QSARs for CYP2A6 substrates indicate the importance of hydrogen bonding and lipophilicity for favourable interactions with the enzyme.

Effects of Melilotus officinalis on acute inflammation

Our study investigated the effects of Melilotus officinalis L. extract, containing 0.25% coumarin, on acute inflammation induced with oil of turpentine in male rabbits. The results were compared with those from a group treated with hydrocortisone sodium hemisuccinate and one injected with coumarin before inflammation was induced. The effects were evaluated by measuring serum citrulline, a test of in vitro phagocytosis, total leukocyte count and differential leukocyte count expressed as a percentage. M. officinalis had antiinflammatory effects because it reduced the activation of circulating phagocytes and lowered citrulline production. These properties were similar to those of hydrocortisone sodium hemisuccinate and coumarin. In the bone marrow acute phase response, M. officinalis had an inhibitory action that was lower than that of hydrocortisone sodium hemisuccinate and similar to coumarin.

Studies on the disposition, metabolism and hepatotoxicity of coumarin in the rat and Syrian hamster

The hepatotoxicity, metabolism and disposition of coumarin has been compared in male Sprague-Dawley rats and Syrian hamsters. The treatment of rats for 12, 24 and 42 weeks with diets containing 0.2 and 0.5% coumarin resulted in hepatotoxicity and increased relative liver weights. While levels of cytochrome P450 (CYP) and CYP-dependent enzymes were decreased, levels of reduced glutathione (GSH) and activities of UDP glucuronosyltransferase, gamma-glutamyltransferase and GSH S-transferase were increased. In contrast, coumarin produced few hepatic changes in the Syrian hamster. Following a single oral dose of 25 mg/kg [3-14C]coumarin, radioactivity was rapidly excreted by the rat and Syrian hamster with the urine containing 63.5 and 89.9%, respectively, and the faeces 38.0 and 12.4%, respectively, of the administered dose after 96 h. The biliary excretion of radioactivity was greater in the rat than in the Syrian hamster. Analysis of 0-24-h urine samples revealed that both species were poor 7-hydroxylators of coumarin. In the rat, treatment with 0.5% coumarin in the diet for 24 weeks was found to increase the urinary excretion of single oral gavage doses of 25 and 300 mg/kg [3-14C]coumarin. The marked species difference in hepatotoxicity between the rat and Syrian hamster observed in this study may be at least partially attributable to differences in coumarin disposition. However, additional studies are required to elucidate the metabolic pathways of coumarin in both species.

Identification of the cytochromes P450 that catalyze coumarin 3,4-epoxidation and 3-hydroxylation

Coumarin, a widely used fragrance ingredient, is a rat liver and mouse lung toxicant. Species differences in toxicity are metabolism-dependent, with injury resulting from the cytochrome P450-mediated formation of coumarin 3,4-epoxide (CE). In this study, the enzymes responsible for coumarin activation in liver and lung were determined. Recombinant human and rat CYP1A forms and recombinant human CYP2E1 readily catalyzed CE production. Coinhibition with CYP1A1/2 and CYP2E1 antibodies blocked CE formation by 38, 84, and 67 to 92% (n = 3 individual samples) in mouse, rat, and human hepatic microsomes, respectively. Although CYP1A and 2E forms seem to be the most active catalysts of CE formation in liver, studies conducted with the mechanism-based inhibitor 5-phenyl-pentyne demonstrated that CYP2F2 is responsible for up to 67% of CE formation in whole mouse lung microsomes. In contrast to the CE pathway, coumarin 3-hydroxylation is a minor product of coumarin in liver microsomes from mice, rats, and humans and is catalyzed predominately by CYP3A and CYP1A forms, confirming that CE and 3-hydroxycoumarin are formed via distinct metabolic pathways.

Unexpected tumour findings in lifetime rodent bioassay studies--what to do?

Currently, the majority of substances tested in lifetime bioassays in rodents are not mutagenic and, therefore, at the most weakly carcinogenic, generally by epigenetic mechanisms. It thus appears obvious that only marginal increases of tumour incidences can be expected in lifetime bioassays and that, therefore, every aspect of a potential carcinogenic effect must be thoroughly evaluated. This paper describes a series of key factors, which should be looked at in order to exclude that the lifetime bioassay in question is flawed for design, technical or qualification reasons. It also provides some hints whether there is indeed a real effect and not just a variation of the spontaneous tumour incidences. Tumour findings must be seen in the context of the animal model, the pharmcokinetics and pharmcodynamics of the test substance, as well as any other observation in the present or other studies with the test substance, including non-tumour findings and--in particular--potential precursor lesions and effects on feed intake and survival. The possibility that the observed carcinogenic effects may be species-specific and not relevant for man is discussed. It is also important to check what findings are reported with similar substances or substances with the same pharmacological effect. Data from additional investigations on material of the same study and/or mechanistic studies are often needed to support the final risk assessment.

Changes in the expression of cytochrome P450 isozymes and related carcinogen metabolizing enzyme activities in Schistosoma mansoni-infected mice

Mixed-function oxidase enzymes metabolize most xenobiotic agents. Western blotting was used to investigate the effect of Schistosoma mansoni infection on the expression of various cytochrome P450 (CYP) isozymes and specific enzyme assays to study related metabolic functions in mouse liver microsomes. Male BK-TO mice were infected with 200 cercariae per mouse and their livers were assayed at 6, 15, 30 and 45 days post-infection (p.i.) and compared with appropriately matched controls. The expression of each of the CYP isozymes (1A1, 2B1/2, 2C6, and 4A) was either unaffected or transiently increased up to 30 days post-infection. By 45 days, a significant loss of signal was observed, particularly for CYP 1A1 and 2B1 /2 where no signal could be detected. Evidence supporting these findings was obtained from enzyme assays specific for particular CYP isozymes. The activity of ethoxyresorufin O-deethylase (CYP 1A1) was reduced by 97% and that of pentoxyresorufin O-depentylase (CYP 2B1 /2) by 96% at 45 days p.i. Similarly, the activity of ethoxycoumarin hydroxylase was progressively reduced over the period under study. It is believed that N-nitrosamines are activated principally by N-nitrosodimethylamine N-demethylase I which was significantly increased at both 30 and 45 days p.i. To further investigate metabolic competency following S. mansoni infection, the in vitro binding of benzo(a)pyrene metabolites to DNA was measured, using isolated liver microsomes to activate benzo(a)pyrene. Benzo(a)-pyrene-DNA adduct formation was markedly increased at 6,15 and 30 days with a maximum at 15 days, but decreased at 45 days p.i. It was concluded that S. mansoni infection changes the expression of different CYP isozymes and also the activity of phase I drug-metabolizing enzymes at different periods of infection and may thus change the liver's capacity to activate or detoxify many endogenous and exogenous compounds. Such alterations may also change the therapeutic actions of drugs that are primarily metabolized by the P450 system, when administered to patients with schistosomiasis.

Lack of effect of coumarin on the formation of micronuclei in an in vivo mouse micronucleus assay

Coumarin was tested for its potential to cause genotoxic effects in mouse bone marrow cells using an in vivo micronucleus assay. Male and female Swiss mice were administered a single oral dose of coumarin at 50, 100 or 200 mg/kg by gavage in corn oil vehicle. Control animals received only the vehicle. Groups of male mice were also administered mitomycin C at 0.75 mg/kg and served as positive controls. At 24 h after treatment, mice from all dose levels, and at 48 h after treatment, mice from the high dose level only were sacrificed. Bone marrow cells were collected and assayed for the presence of micronuclei. Coumarin did not cause any increase in the incidence of micronucleated polychromatic erythrocytes in male or female mice at any of the dose levels, the positive control mitomycin C produced a significant increase. There was no evidence of coumarin or mitomycin C treatment related cytotoxicity to bone marrow cells. The results of this study demonstrate that coumarin is negative in the mouse in vivo micronucleus assay.

The in vivo dermal absorption and metabolism of [4-14C] coumarin by rats and by human volunteers under simulated conditions of use in fragrances

The disposition and metabolic fate of [4-14C]coumarin in a 70% aqueous ethanol solution was studied in male Lister Hooded rats after occluded dermal application and in three male volunteers after an exposure designed to simulate that which may be encountered when using an alcohol-based perfumed product. In both cases, the 6-h exposure was 0.02 mg/cm(2) (rats 0.023 mg/kg and humans 0.77 mg/kg). In both, coumarin was quickly absorbed, distributed and excreted in urine and feces, although fecal excretion of coumarin in humans was only 1% of the applied dose as opposed to 21% in rats. Total absorption was 72% of the applied dose with rats and 60% with humans. Peak plasma radioactivity in both was at 1 h. The mean plasma half-life of coumarin and metabolites was approximately 1.7 h for humans and 5 h for rats. In humans, coumarin was primarily metabolized to and excreted in urine as 7-hydroxycoumarin glucuronide and 7-hydroxycoumarin sulfate. Small amounts of unconjugated 7-hydroxycoumarin and o-hydroxyphenylacetic acid (o-HPAA) were also excreted. In rats, about twenty metabolites were present, but only o-HPAA was identified. These studies show the rat is a very poor model for humans and toxicity in the rat cannot be extrapolated to humans.

Lack of effect of coumarin on unscheduled DNA synthesis in the in vivo rat hepatocyte DNA repair assay

The ability of coumarin to induce UDS in male Sprague-Dawley CD rat hepatocytes in vivo was assessed using the unscheduled DNA synthesis (UDS) assay. From a preliminary toxicity study the oral maximum tolerated dose (MTD) of coumarin was determined to be 320 mg/kg body weight. For the UDS studies, rats were treated with 0 (corn oil control), 32 (one-tenth the MTD), 107 (one-third the MTD) and 320 (MTD) mg/kg coumarin via oral gavage. Rats were also treated with 20mg/kg body weight dimethylnitrosamine (DMN) or 50mg/kg body weight 2-acetylaminofluorene (2-AAF) as positive controls for the 2-4 hr and 12-16 hr expression of UDS, respectively. Hepatocytes were isolated by liver perfusion either 2-4 hr or 12-16 hr after treatment and cultured in medium containing [methyl-(3)H]thymidine for 4 hr and assessed for UDS by grain counting of autoradiographs. Coumarin treatment at doses of 32-320 mg/kg body weight had no statistically significant or dose-related effect on UDS in rat hepatocytes either 2-4 hr or 12-16 hr after dosing. In contrast, both DMN 2-4 hr after dosing and 2-AAF 12-16 hr after dosing produced significant increases in UDS assessed as the net nuclear grain count. Both genotoxins also increased the percentage of hepatocyte nuclei with greater than 5 net grains. Treatment with coumarin, DMN and 2-AAF had no statistically significant effect on the proportion of rat hepatocytes undergoing replicative DNA synthesis. In summary, this study demonstrates that coumarin does not induce UDS in hepatocytes of male Sprague-Dawley CD rats after oral administration at doses up to the MTD of 320 mg/kg. The responsiveness of the animals used in this study to genotoxic agents was demonstrated by the clear induction of DNA repair after treatment with DMN and 2-AAF.