Toxicokinetics of chloroethanol in the rat after single oral administration

Ifosfamide - History, efficacy, toxicity and encephalopathy

In this review we trace the passage of fundamental ideas through 20^th century cancer research that began with observations on mustard gas toxicity in World War I. The transmutation of these ideas across scientific and national boundaries, was channeled from chemical carcinogenesis labs in London via Yale and Chicago, then ultimately to the pharmaceutical industry in Bielefeld, Germany. These first efforts to checkmate cancer with chemicals led eventually to the creation of one of the most successful groups of cancer chemotherapeutic drugs, the oxazaphosphorines, first cyclophosphamide (CP) in 1958 and soon thereafter its isomer ifosfamide (IFO). The giant contributions of Professor Sir Alexander Haddow, Dr. Alfred Z. Gilman & Dr. Louis S. Goodman, Dr. George Gomori and Dr. Norbert Brock step by step led to this breakthrough in cancer chemotherapy. A developing understanding of the metabolic disposition of ifosfamide directed efforts to ameliorate its side-effects, in particular, ifosfamide-induced encephalopathy (IIE). This has resulted in several candidates for the encephalopathic metabolite, including 2-chloroacetaldehyde, 2-chloroacetic acid, acrolein, 3-hydroxypropionic acid and S-carboxymethyl-L-cysteine. The pros and cons for each of these, together with other IFO metabolites, are discussed in detail. It is concluded that IFO produces encephalopathy in susceptible patients, but CP does not, by a "perfect storm," involving all of these five metabolites. Methylene blue (MB) administration appears to be generally effective in the prevention and treatment of IIE, in all probability by the inhibition of monoamine oxidase in brain potentiating serotonin levels that modulate the effects of IFO on GABAergic and glutamatergic systems. This review represents the authors' analysis of a large body of published research.

Assessing the genotoxicity and carcinogenicity of 2-chloroethanol through structure activity relationships and in vitro testing approaches

The detection of 2-chloroethanol in foods generally follows an assumption that the pesticide ethylene oxide has been used at some stage in the supply chain. In this situation the Pesticide Residues in Food Regulation (EC) 396/2005 requires 2-chloroethanol to be assessed as if equivalent to ethylene oxide, which has been classified as a genotoxic carcinogen. This review investigated whether this is an appropriate risk assessment approach for 2-chloroethanol. This involved an assessment of existing genotoxicity and carcinogenicity data, application of Structure Activity Based Read Across for carcinogenicity assessment, biological reactivity in the ToxTracker assay and micronuclei formation in HepaRG cells. Although we identified there is an absence of a standard oral bioassay for 2-chloroethanol, carcinogenicity weight-of-evidence assessment along with data on relevant structural analogues do not show evidence for carcinogenicity for 2-chloroethanol. The absence of genotoxicity was demonstrated for 2-chloroethanol and suitable analogues. In contrast, ethylene oxide showed reactivity towards markers indicative of direct DNA damage which is consistent with what is known about its mode-of-action. These data facilitate the understanding of 2-chloroethanol and given that it is not a genotoxic carcinogen suggest it must be assessed relative to non-cancer endpoints and a health protective Reference Dose should be established on that basis.

Analysis of ethylene oxide in ice creams manufactured with contaminated carob bean gum (E410)

Residues of ethylene oxide (EO), a banned fumigant in the EU, were found at amounts above the maximum residue limit (MRL) in carob (locust) bean gum (additive E410). The pesticide entered the food chain via stabiliser blends that are used as minor ingredients in the manufacture of ice cream. Consequently, all products that contained the non-compliant ingredient were withdrawn or recalled in several countries across the EU, in most cases irrespective of whether the pesticide residue was detectable or not in the final product. This is the first report of a reliable method to determine EO and its metabolite/marker compound 2-chloroethanol (2-CE), either together or independently in ice cream, with a limit of quantification at 0.01 mg EO/kg and recovery in the range of 87-104% across the levels investigated (0.01, 0.02 and 0.06 mg EO/kg). The method applies QuEChERS extraction and isotope dilution gas chromatography coupled with tandem mass spectrometry (GC-MS/MS). High resolution mass spectrometry (HRMS) confirmed the specificity of low mass ions. Data on the stability of EO and 2-CE under thermal conditions revealed that 2-CE is relatively stable in an ice cream matrix (ca. 80% recovery of spiked material). Importantly, this study also demonstrates that not EO, but 2-CE is the predominant analyte detected in the contaminated samples, which is new information of significance in terms of the overall risk assessment of EO in foodstuffs.

Toxicokinetics of bis(2-chloroethoxy)methane following intravenous administration and dermal application in male and female F344/N rats and B6C3F1 mice

In the National Toxicology Program's toxicity studies, rats were more sensitive than mice to Bis(2-chloroethoxy)methane (CEM) - induced cardiac toxicity following dermal application to male and female F344/N rats and B6C3F1 mice. Thiodiglycolic acid (TDGA) is a major metabolite of CEM in rats. It has been implicated that chemicals metabolized to TDGA cause cardiac toxicity in humans. Therefore, the toxicokinetics of CEM and TDGA were investigated in male and female F344/N rats and B6C3F1 mice following a single intravenous administration or dermal application of CEM to aid in the interpretation of the toxicity data. Absorption of CEM following dermal application was rapid in both species and genders. Bioavailability following dermal application was low but was higher in rats than in mice with females of both species showing higher bioavailability than males. CEM was rapidly distributed to the heart, thymus, and liver following both routes of administration. Plasma CEM C(max) and AUC(∞) increased proportionally with dose, although at the dermal dose of 400mg/kg in rats and 600mg/kg in mice non-linear kinetics were apparent. Following dermal application, dose-normalized plasma CEM C(max) and AUC(∞) was significantly higher in rats than in mice (p-value<0.0001 for all comparisons except for C(max) in the highest dose groups where p-value=0.053). In rats, dose-normalized plasma CEM C(max) and AUC(∞) was higher in females than in males: however, the difference was significant only at the lowest dose (p-value=0.009 for C(max) and 0.056 for AUC(∞)). Similar to rats, female mice also showed higher C(max) and AUC(∞) in females than in male: the difference was significant only for C(max) at the lowest dose (p-value=0.002). Dose-normalized heart CEM C(max) was higher in rats than in mice and in females than their male counterparts. The liver CEM C(max) was lower compared to that of heart and thymus in both rats and mice following intravenous administration and in rats following dermal application. This is likely due to the rapid metabolism of CEM in the liver as evidenced by the high concentration of TDGA measured in the liver. Dose-normalized plasma and heart TDGA C(max) values were higher in rats compared to mice. In rats, females had higher plasma and heart TDGA C(max) than males; however, there was no gender difference in plasma or heart TDGA C(max) in mice. These findings support the increased sensitivity of rats compared to mice to CEM-induced cardiac toxicity. Data also suggest that, either CEM C(max) or AUC can be used to predict the CEM-induced cardiac toxicity. Although, both plasma and heart TDGA C(max) was consistent with the observed species difference and the gender difference in rats, the gender difference in mice to cardiac toxicity could not be explained based on the TDGA data. This animal study suggests that toxicologically significant concentrations of CEM and TDGA could possibly be achieved in the systemic circulation and/or target tissues in humans as a result of dermal exposure to CEM.

Protective effects of fomepizole on 2-chloroethanol toxicity

2-Chloroethanol (2-CE) is a widely used industrial solvent. In Taiwan, Taiwanese farmers apply 2-CE on grape-vines to accelerate grape growth, a practice that in some cases have caused poisoning in humans. Thus, there is strong interest in identifying antidotes to 2-CE. This study examines the protective role in 2-CE intoxicated rats. Alcohol dehydrogenase and glutathione were hypothesized to be important in the metabolism of 2-CE. This study used fomepizole, an alcohol dehydrogenase inhibitor, and chemicals that affected glutathione metabolism to study 2-CE toxicity. Notably, fomepizole 5 mg/kg significantly increased median lethal dose (LD50) of 2-CE from 65.1 to 180 mg/kg and reduced the production of a potential toxic metabolite chloroacetaldehyde (CAA) in animal plasma. In contrast, disulfiram (DSF), an aldehyde dehydrogenase inhibitor, increased the toxicity of 2-CE on the lethality in rats. Additional or pretreatment with N-acetylcysteine (NAC) and fomepizole significantly reduced plasma CAA concentrations. Fomepizole also significantly reduced 2-CEinhibited glutathione activity. Otherwise, pretreatment with NAC for 4 days followed by co-treatment with fomepizole significantly decreased formation of the metabolic CAA. These results indicated that its catalytic enzyme might play a vital role during 2-CE intoxication, and the combination of fomepizole and NAC could be a protective role in cases of acute 2-CE intoxication.

[14C]bis(2-chloroethoxy)methane: comparative absorption, distribution, metabolism and excretion in rats and mice

bis(2-Chloroethoxy)methane (BCM) is used primarily as a precursor in the synthesis of polysulfide elastomers. After administration of [(14)C]BCM, radioactivity is readily absorbed from the gastrointestinal tract and moderately absorbed through skin. Following absorption, BCM-derived radioactivity is rapidly distributed to all tissues, rapidly metabolized and excreted primarily in urine. Minimal effects of sex, species or dose in the range studied (0.1-10 mg kg(-1)) were observed on the fate of BCM in rats and mice after all routes of administration. The major metabolite (about 40% of the dose) of BCM in rat was isolated and identified as thiodiglycolic acid (TDGA) indicating that the ether linkage of BCM is cleaved to form 2-chloroethyl fragments that may be further metabolized to 2-chloracetaldehyde, conjugated with glutathione and the latter subsequently metabolized to TDGA. 2-chloroacetaldehyde has also been shown to be cardiotoxic, possibly accounting for BCM cardiotoxicity observed in repeated dose studies.

Molecular mechanisms of chloroacetaldehyde-induced cytotoxicity in isolated rat hepatocytes

2-Chloroacetaldehyde (CAA) induced a loss in hepatocyte viability in a concentration- and time-dependent manner. Three phases before cytotoxicity ensued could be distinguished. Glutathione (GSH) was depleted immediately upon addition of CAA but only partial depletion occurred with subtoxic CAA concentrations. GSH-depleted hepatocytes were much more susceptible to CAA toxicity, indicating that CAA was detoxified by GSH. The second phase of changes involved a steady decrease in protein thiol levels, mitochondrial respiration, transmembrane potential and ATP levels. The third phase involved lipid peroxidation which commenced at around 60 min with a CAA concentration that caused 50% cytotoxicity in 120 min. Addition of antioxidants (diphenylphenylenediamine, butylated hydroxyanisole) and iron chelators (desferoxamine) at 40 min prevented lipid peroxidation and delayed CAA-induced cytotoxicity without restoring protein thiols, hepatocyte respiration or preventing further ATP depletion. Addition of dithiothreitol at 40 min, however, restored protein thiols and hepatocyte respiration, and prevented further ATP depletion and cytotoxicity. CAA-induced hepatocyte cytotoxicity therefore involved reversible thiol protein adduct formation, mitochondrial toxicity and lipid peroxidation.

The comparative disposition of [14C]-fotemustine in non-tumourous and tumourous mice

The distribution and excretion of radioactivity from [14C]-fotemustine was examined in mice with melanomas at different stages of development to determine whether the disease state substantially alters the disposition of the drug and its metabolites. Normal BDF1 mice and mice that had been subcutaneously grafted with B16 melanoma either 1, 3, 7, 14 or 21 days previously were used. The animals were killed at either 5 min, or at 3, 24 or 96 h after receiving an intravenous dose of [14C]-fotemustine (20 mg/kg) and were examined either by whole-body autoradiography or by liquid scintillation counting of excreta and tissues of interest. The majority of the [14C]-fotemustine dose was excreted in the urine, with similar amounts being measured in both non-tumourous animals (61.6% +/- 13.1%) and tumourous mice grafted 14 days previously (67.2% +/- 5.7%). Small amounts of radioactivity, again similar in both non-tumourous and tumourous mice, were recovered in the faeces (5.4% +/- 5.6% and 3.6% +/- 1.8%, respectively) and as carbon dioxide (7% +/- 3.5% and 6.4% +/- 1%, respectively), with minimal amounts being expired as chloroethanol (less than 1%). When mice were examined 5 min after dosing, there was extensive tissue distribution accounting for 75% +/- 10% of the dose. The highest concentrations determined by both whole-body autoradiography and liquid scintillation counting were measured in the excretory organs, with 33 and 28 micrograms Eq/g being found in the liver and kidney, respectively. High levels were also seen in the lung and plasma (19.8 and 19.5 micrograms Eq/g, respectively). Analysis of variance indicated that groups of tissues, such as the excretory organs, blood and plasma or the pigmented tissues, showed distinct but inconsistent patterns. Only tumours at 14 and 21 days of development were suitable for examination, and these showed levels of 12.1 micrograms Eq/g; however, the tumour-to-plasma ratio increased from between approx. 0.5 and 0.6 at 5 min to approx. 2 at 96 h after dosing, suggesting retention within the melanoma, whereas the ratio for the femur remained at approx. 1. Whole-body autoradiography showed that the distribution in the tumour was not uniform, but rather was concentrated in the peripheral area (presumably viable cells) as opposed to the central necrotic region. Thus, the high and sustained concentration of radioactivity found in the active cells of the melanoma may provide an explanation for the high efficacy of the drug.

Nucleophilic selectivity as a determinant of carcinogenic potency (TD50) in rodents: a comparison of mono- and bi-functional alkylating agents and vinyl chloride metabolites

Using published data, the carcinogenic potency (TD50) in rodents of a series of monofunctional alkylating agents, bifunctional antitumor drugs and the vinyl chloride (VC) metabolites chloroethylene oxide (CEO) and chloroacetaldehyde (CAA) was compared to their nucleophilic selectivity (Swain and Scott's constant s or initial ratio of 7-/O6-alkylguanine in DNA). A positive correlation between the log of TD50 estimates and the s values for a series of 14, mostly monofunctional, alkylating agents was observed. This linear relationship also included 2 bifunctional chloroethylnitrosoureas, although their carcinogenic potency was compared to their initial 7-/O6-alkylguanine ratio rather than their s values (n = 16, r = 0.91, p less than 0.005). In addition, the carcinogenic potency of 2 alkyl sulfates, which is not yet known accurately, may correlate with their nucleophilic selectivity through the same relationship. By contrast, 2 methyl halides and 5 bifunctional antitumor drugs (nitrogen mustards and azyridinyl derivatives) did not follow this linear relationship: at similar nucleophilic selectivity, they were more potent carcinogens than the above 18 alkylating agents; this may hold true for CEO and CAA too, although further carcinogenicity experiments are needed to calculate their precise TD50 values. The possible molecular mechanisms involved in tumor induction by these agents are discussed on the basis of these findings. Comparison of the estimated TD50 for CEO, CAA and VC in rodents confirms that CEO is the ultimate carcinogenic metabolite of VC and suggests that only a very small proportion of metabolically generated CEO is available for DNA alkylation in vivo.

N-acetyl-S-(2-hydroxyethyl)-L-cysteine as a potential tool in biological monitoring studies? A critical evaluation of possibilities and limitations

In mammalian species, including man, N-acetyl-S-(2-hydroxyethyl)-L-cysteine (2-HEMA) is a common urinary metabolite of a large number of structurally different xenobiotic chemicals. It is a common urinary end product of glutathione pathway metabolism of a variety of chemicals possessing electrophilic properties and, in most cases, also a genotoxic potential. Five different chemically reactive intermediates, with different electrophilic properties, may be involved in the formation of 2-HEMA. An inventory of chemicals known to lead to the formation of 2-HEMA, or based on their chemical structure expected to do so, is presented. Furthermore, an attempt is made to evaluate the possibilities and limitations in terms of the potential use of urinary 2-HEMA as a tool in biomonitoring studies. Two other related, sulfur-containing urinary metabolites, i.e. N-acetyl-(S-carboxymethyl)-L-cysteine and thio-diacetic acid, are proposed as possible alternatives to urinary 2-HEMA. It is suggested that 2-HEMA might be seen as a potentially useful and sensitive signal parameter for the assessment of exposure of animals and man to a variety of electrophilic and therefore potentially toxic xenobiotic chemicals.

Hepatic fatty acid conjugation of 2-chloroethanol and 2-bromoethanol in rats

To study the formation of fatty acid conjugates of 2-chloroethanol (2-CE) and 2-bromoethanol (2-BE), rats were administered (by gavage) 50 mg/kg of 2-CE and 2-BE in mineral oil and sacrificed on fifth day of the treatment. Hepatic microsomal lipids were extracted, and the fatty acid esters were separated by preparative thin-layer chromotography. The ester fraction was further purified by reverse-phase, high-performance liquid chromatography and analyzed by ammonia chemical ionization mass spectrometry. Pseudomolecular ions (M + NH4+, base peak) at m/z 336/338, 362/364, and 364/366 in a ratio of 3:1 and 380/382 and 408/410 in a ratio of 1:1 confirmed the in vivo formation of 2-chloroethyl palmitate, 2-chloroethyl oleate, 2-chloroethyl stearate, 2-bromoethyl palmitate, and 2-bromoethyl stearate, respectively. These results demonstrate the formation of fatty acid conjugates of 2-CE and 2-BE in vivo. These fatty acid conjugates may be retained in the body for a longer time and cause toxic manifestations.

Roles of etheno-DNA adducts in tumorigenicity of olefins

Cyclic DNA adducts bearing an "etheno" structure have been described to occur after interaction with metabolites of halogenated olefins. Extensive work has been published on adducts of vinyl chloride, both in vitro and in vivo. The major DNA adduct of vinyl chloride is 7-(2-oxoethyl)guanine, but an important minor adduct appears to be N2,3-ethenoguanine. Other etheno adducts, i.e., 1, N6-ethenoadenine and 3, N4-ethenocytosine, are readily formed with DNA, vinyl chloride, and a metabolizing system in vitro and with RNA in vivo, but usually are not detected as DNA adducts in vivo. Other compounds that have been studied with respect to possible formation of etheno DNA adducts are vinyl bromide (which is more or less completely analogous to vinyl chloride), acrylonitrile, vinyl acetate and vinyl carbamate. Proposals of possible structures of DNA adducts with an etheno structure have been promutagenic potential of these lesions which may lead to misincorporation of wrong DNA bases in newly synthesized DNA.