Biosynthesis of mercapturic acids from allyl alcohol, allyl esters and acrolein

Disease-associated acrolein: A possible diagnostic and therapeutic substrate for in vivo synthetic chemistry

Acrolein, a highly reactive α,β-unsaturated aldehyde, is a compound to which humans are exposed in many different situations and often causes various human diseases. This paper summarizes the reports over the past twenty-five years regarding disease-associated acrolein detected in clinical patients and the role acrolein plays in various diseases. In several diseases, it was found that the increased acrolein acts as a pathogenetic factor. Thus, we propose the utility of over-produced acrolein as a substrate for a promising therapeutic or diagnostic method applicable to a wide range of diseases based on an in vivo synthetic chemistry strategy.

Potential Adverse Public Health Effects Afforded by the Ingestion of Dietary Lipid Oxidation Product Toxins: Significance of Fried Food Sources

Exposure of polyunsaturated fatty acid (PUFA)-rich culinary oils (COs) to high temperature frying practices generates high concentrations of cytotoxic and genotoxic lipid oxidation products (LOPs) via oxygen-fueled, recycling peroxidative bursts. These toxins, including aldehydes and epoxy-fatty acids, readily penetrate into fried foods and hence are available for human consumption; therefore, they may pose substantial health hazards. Although previous reports have claimed health benefits offered by the use of PUFA-laden COs for frying purposes, these may be erroneous in view of their failure to consider the negating adverse public health threats presented by food-transferable LOPs therein. When absorbed from the gastrointestinal (GI) system into the systemic circulation, such LOPs may significantly contribute to enhanced risks of chronic non-communicable diseases (NCDs), e.g. cancer, along with cardiovascular and neurological diseases. Herein, we provide a comprehensive rationale relating to the public health threats posed by the dietary ingestion of LOPs in fried foods. We begin with an introduction to sequential lipid peroxidation processes, describing the noxious effects of LOP toxins generated therefrom. We continue to discuss GI system interactions, the metabolism and biotransformation of primary lipid hydroperoxide LOPs and their secondary products, and the toxicological properties of these agents, prior to providing a narrative on chemically-reactive, secondary aldehydic LOPs available for human ingestion. In view of a range of previous studies focused on their deleterious health effects in animal and cellular model systems, some emphasis is placed on the physiological fate of the more prevalent and toxic α,β-unsaturated aldehydes. We conclude with a description of targeted nutritional and interventional strategies, whilst highlighting the urgent and unmet clinical need for nutritional and epidemiological trials probing relationships between the incidence of NCDs, and the frequency and estimated quantities of dietary LOP intake.

Urinary acrolein metabolite levels in severe acute alcoholic hepatitis patients

Alcohol-associated liver disease (ALD) remains a major health concern worldwide. Alcohol consumption gives rise to reactive/toxic acrolein, a pathogenic mediator of liver injury in experimental ALD. Elevated acrolein adducts and metabolites are detectable in blood and urine. This study evaluates the major urinary acrolein metabolite, 3-hydroxypropylmercapturic acid (HPMA), in patients with acute alcoholic hepatitis (AAH) and examines its association with disease severity and markers of hepatic inflammation and injury. Urine HPMA was significantly higher in patients with severe [model for end-stage liver disease (MELD) ≥ 20] AAH compared with nonsevere AAH (MELD ≤ 19) or non-alcohol-consuming controls, suggesting that urine HPMA is a novel noninvasive biomarker in severe AAH. The association between HPMA and MELD in patients with AAH was nonlinear. In patients with nonsevere AAH, there was a positive trend, although not significant, whereas in severe AAH the association was negative, indicative of extensive injury and glutathione depletion. Consistent with the multifactorial etiology of ALD, our data identified strong combined effects of HPMA and proinflammatory cytokines on hepatocyte cell death, thereby supporting the pathogenic role of acrolein in liver injury. HPMA, together with IL-1β, showed robust associations with cytokeratin 18 caspase-cleaved fragment (CK18-M30; adjusted R² = 0.812, P = 0.016) and cytokeratin 18 full-length protein (CK18-M65; adjusted R² = 0.670, P = 0.048); similarly, HPMA, with IL-8, correlated with CK18-M30 (adjusted R² = 0.875, P = 0.007) and CK18-M65 (adjusted R² = 0.831, P = 0.013). The apoptosis index (CK18-M30:CK18-M65 ratio) strongly correlated with HPMA, together with IL-1β (adjusted R² = 0.777, P = 0.022) or tumor necrosis factor-α (TNFα; adjusted R² = 0.677, P = 0.046). In patients with severe AAH, IL-1β, IL-8, and TNFα are the predominant proinflammatory cytokines that interact with HPMA and play important mediating roles in influencing the extent/pattern of liver cell death. NEW & NOTEWORTHY This is the first study to examine the urinary acrolein metabolite 3-hydroxypropylmercapturic acid (HPMA) in alcoholic liver disease. HPMA was higher in patients with severe acute alcoholic hepatitis (AAH) compared with controls or nonsevere AAH and may be a novel selective, noninvasive biomarker for severe AAH. Consistent with the multifactorial etiology of alcohol-associated liver disease, we identified strong combined effects of HPMA and proinflammatory cytokines (IL-1β, IL-8, and TNFα) on the extent/pattern of liver cell death, thereby supporting the pathogenic role of acrolein.

Comparison of Biomarkers of Tobacco Exposure between Premium and Discount Brand Cigarette Smokers in the NHANES 2011-2012 Special Sample

Background: Increased cigarette costs have inadvertently strengthened the appeal of discounted brands to price-sensitive smokers. Although smokers perceive discounted brands as having poorer quality, little is known about their delivery of toxic tobacco smoke constituents compared with premium-branded tobacco products.Methods: We investigated the differences between discount and premium brand smokers using the National Health and Nutrition Examination Survey 2011-2012 Special Smoker Sample. Our analyses focused on demographic differences and 27 biomarkers of harmful and potentially harmful constituents (HPHC) listed by the FDA, including volatile organic compounds, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol and its glucuronide [4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol glucuronide; reported as total NNAL (tNNAL)], metals, and polycyclic aromatic hydrocarbons (PAHs). Data were analyzed using linear regression models adjusting for potential confounders.Results: A total of 976 non-tobacco users and 578 recent cigarette smokers were eligible for analysis, of which 141 (26.0% weighted) smoked discount brand cigarettes and 437 (74.0% weighted) smoked premium. Discount brand smokers were older, predominantly non-Hispanic white, and had higher serum cotinine. Discount brand smokers had significantly higher levels of 13 smoking-related biomarkers, including tNNAL, uranium, styrene, xylene, and biomarkers of exposure to PAHs (naphthalene, fluorene, and phenanthrene), compared with premium brand smokers.Conclusions: These findings suggest that discount cigarette use is associated with higher exposure to several carcinogenic and toxic HPHCs.Impact: These results may have important regulatory implications for product standards, as higher exposures could lead to a greater degree of harm. Cancer Epidemiol Biomarkers Prev; 27(5); 601-9. ©2018 AACR.

Exposure assessment of process-related contaminants in food by biomarker monitoring

Exposure assessment is a fundamental part of the risk assessment paradigm, but can often present a number of challenges and uncertainties. This is especially the case for process contaminants formed during the processing, e.g. heating of food, since they are in part highly reactive and/or volatile, thus making exposure assessment by analysing contents in food unreliable. New approaches are therefore required to accurately assess consumer exposure and thus better inform the risk assessment. Such novel approaches may include the use of biomarkers, physiologically based kinetic (PBK) modelling-facilitated reverse dosimetry, and/or duplicate diet studies. This review focuses on the state of the art with respect to the use of biomarkers of exposure for the process contaminants acrylamide, 3-MCPD esters, glycidyl esters, furan and acrolein. From the overview presented, it becomes clear that the field of assessing human exposure to process-related contaminants in food by biomarker monitoring is promising and strongly developing. The current state of the art as well as the existing data gaps and challenges for the future were defined. They include (1) using PBK modelling and duplicate diet studies to establish, preferably in humans, correlations between external exposure and biomarkers; (2) elucidation of the possible endogenous formation of the process-related contaminants and the resulting biomarker levels; (3) the influence of inter-individual variations and how to include that in the biomarker-based exposure predictions; (4) the correction for confounding factors; (5) the value of the different biomarkers in relation to exposure scenario's and risk assessment, and (6) the possibilities of novel methodologies. In spite of these challenges it can be concluded that biomarker-based exposure assessment provides a unique opportunity to more accurately assess consumer exposure to process-related contaminants in food and thus to better inform risk assessment.

Recent Progress in Analytical Methods for Determination of Urinary 3-Hydroxypropylmercapturic Acid, a Major Metabolite of Acrolein

3-Hydroxypropylmercapturic acid (3-HPMA), a major metabolite of acrolein in urine, has been recognized as a noninvasive biomarker of exposure to cigarette smoke. Since acrolein is formed endogenously from polyamines and is also formed during oxidative stress and aggravates tissue damage by changing protein activity through its conjugation in pathological lesions, it is thought that the urinary 3-HPMA level is useful as a biomarker to monitor the severity of several diseases related to acrolein. To study the correlation between 3-HPMA and disease severity, it is important to understand the properties of analytical methods for determination of 3-HPMA. In this article, we summarize the analytical methods for determination of urinary 3-HPMA and discuss the utility of 3-HPMA as one of the biomarkers for the diagnosis of brain infarction.

Acrolein Exposure in U.S. Tobacco Smokers and Non-Tobacco Users: NHANES 2005-2006

BACKGROUND

Acrolein is a highly reactive α,β unsaturated aldehyde and respiratory irritant. Acrolein is formed during combustion (e.g., burning tobacco or biomass), during high-temperature cooking of foods, and in vivo as a product of oxidative stress and polyamine metabolism. No biomonitoring reference data have been reported to characterize acrolein exposure for the U.S.

OBJECTIVES

Our goals were to a) evaluate two acrolein metabolites in urine--N-acetyl-S-(3-hydroxypropyl)-L-cysteine (3HPMA) and N-acetyl-S-(2-carboxyethyl)-L-cysteine (CEMA)--as biomarkers of exposure to acrolein for the U.S. population by age, sex, race, and smoking status; and b) assess tobacco smoke as a predictor of acrolein exposure.

METHODS

We analyzed urine from National Health and Nutrition Examination Survey (NHANES 2005-2006) participants ≥ 12 years old (n = 2,866) for 3HPMA and CEMA using ultra-high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry (UPLC/ESI-MSMS). Sample-weighted linear regression models stratified for non-tobacco users versus tobacco smokers (as defined by serum cotinine and self-report) characterized the association of urinary 3HPMA and CEMA with tobacco smoke exposure, adjusting for urinary creatinine, sex, age, and race/ethnicity.

RESULTS

3HPMA and CEMA levels were higher among tobacco smokers (cigarettes, cigars, and pipe users) than among non-tobacco users. The median 3HPMA levels for tobacco smokers and non-tobacco users were 1,089 and 219 μg/g creatinine, respectively. Similarly, median CEMA levels were 203 μg/g creatinine for tobacco smokers and 78.8 μg/g creatinine for non-tobacco users. Regression analysis showed that serum cotinine was a significant positive predictor (p < 0.0001) of both 3HPMA and CEMA among tobacco smokers.

CONCLUSIONS

Tobacco smoke was a significant predictor of acrolein exposure in the U.S. population.

Thermally induced process-related contaminants: the example of acrolein and the comparison with acrylamide: opinion of the Senate Commission on Food Safety (SKLM) of the German Research Foundation (DFG)

α,β-Unsaturated aliphatic carbonyl compounds are naturally widespread in food, but are also formed during the thermal treatment of food. This applies, for example, to the genotoxic carcinogen acrylamide (AA), but also to acrolein (AC), the simplest α,β-unsaturated aldehyde. First observations indicate that human exposure to AC may be higher than the exposure to AA. The DFG Senate Commission on Food Safety therefore compared data on AC and AA available in the scientific literature, evaluating current knowledge on formation, occurrence, exposure, metabolism, biological effects, toxicity, and carcinogenicity and defined knowledge gaps as well as research needs in an opinion on November 19, 2012, in German. The English version was agreed on April 17, 2013.

Formation of a vitamin C conjugate of acrolein and its paraoxonase-mediated conversion into 5,6,7,8-tetrahydroxy-4-oxooctanal

Vitamin C (ascorbic acid) has been reported to participate in Michael addition reactions in vitro to form vitamin C conjugates with alpha,beta-unsaturated aldehydes, such as acrolein. This study shows evidence for the formation and metabolism of the vitamin C conjugate of acrolein (AscACR) in cultured human monocytic THP-1 cells exposed to acrolein diacetate. By using (18)O and (13)C labeling in combination with liquid chromatography-tandem mass spectrometry, AscACR was shown to undergo hydrolytic conversion of the ascorbyl lactone into an intermediate carboxylic acid. Subsequent decarboxylation of the carboxylic acid yielded 5,6,7,8-tetrahydroxy-4-oxooctanal (THO). When THP-1 cells were pretreated with ascorbic acid (1 mM, 18 h) and then exposed to acrolein diacetate, THO was detected as its pentafluorobenzyl oxime derivative in the cell lysates and medium. Treatment of THP-1 cells with both ascorbic acid and acrolein diacetate was required for THO formation. The formation of THO from AscACR was facilitated by the lactonase enzymes, human recombinant paraoxonases 1 and 2. THP-1 cells exhibited PON activity, which explains the catalytic conversion of AscACR into THO in these cells. THO was formed in addition to metabolites of the glutathione conjugate of acrolein, indicating that THO formation contributes to the elimination of acrolein in a cellular environment.

Acrolein health effects

Acrolein is a chemical used as an intermediate reactive aldehyde in chemical industry. It is used for synthesis of many organic substances, methionine production, and methyl chloride refrigerant. The general population is exposed to acrolein via smoking, second-hand smoke, exposure to wood and plastic smoke. Firefighters and population living or working in areas with heavy automotive traffic may expose to higher level of acrolein via inhalation of smoke or automotive exhaust. Degradation of acrolein in all environmental media occurs rapidly, therefore, environmental accumulation is not expected. Acrolein degrade in 6A days when applied to surface water, and it has not been found as a contaminant in municipal drinking water. Acrolein vapor may cause eye, nasal and respiratory tract irritations in low level exposure. A decrease in breathing rate was reported by volunteers acutely exposed to 0.3A ppm of acrolein. At similar level, mild nasal epithelial dysplasia, necrosis, and focal basal cell metaplasia have been observed in rats. The acrolein effects on gastrointestinal mucosa in the animals include epithelial hyperplasia, ulceration, and hemorrhage. The severity of the effects is dose dependent. Acrolein induces the respiratory, ocular, and gastrointestinal irritations by inducing the release of peptides in nerve terminals innervating these systems. Levels of acrolein between 22 and 249 ppm for 10 min induced a dose-related decrease in substance P (a short-chain polypeptide that functions as a neurotransmitter or neuromodulator).

A comparative 90-day toxicity study of allyl acetate, allyl alcohol and acrolein

Allyl acetate (AAC), allyl alcohol (AAL), and acrolein (ACR) are used in the manufacture of detergents, plastics, pharmaceuticals, and chemicals and as agricultural agents. A metabolic relationship exists between these chemicals in which allyl acetate is metabolized to allyl alcohol and subsequently to the highly reactive, alpha,beta-unsaturated aldehyde, acrolein. Due to the weaker reactivity of the protoxicants, allyl acetate and allyl alcohol, relative to acrolien we hypothesized the protoxicants would attain greater systemic exposure and therefore deliver higher doses of acrolein to the internal organs. By extension, the higher systemic exposure to acrolein we hypothesized should lead to more internal organ toxicity in the allyl acetate and allyl alcohol treated animals relative to those treated with acrolein. To address our hypothesis we compared the range of toxicities produced by all three chemicals in male and female Fischer 344/N rats and B6C3F1 mice exposed 5 days a week for 3 months by gavage in 0.5% methylcellulose. Rats (10/group) were dosed with 0-100mg/kg allyl acetate, 0-25mg/kg allyl alcohol, or 0-10mg/kg acrolein. Mice (10/group) were dosed with 0-125mg/kg allyl acetate, 0-50mg/kg allyl alcohol, or 0-20mg/kg acrolein. The highest dose of allyl acetate and acrolein decreased survival in both mice and rats. The primary target organ for the toxicity of all three chemicals in both species and sexes was the forestomach; squamous epithelial hyperplasia was observed following exposure to each chemical. In both species the highest allyl acetate dose group exhibited forestomach epithelium necrosis and hemorrhage and the highest dose of acrolein led to glandular stomach hemorrhage. Liver histopathology was the most apparent with allyl acetate, was also observed with allyl alcohol, but was not observed with acrolein. All chemicals had effects on the hematopoietic system with allyl acetate having the most pronounced effect. When dosed at quantities limited by toxicity, allyl acetate and allyl alcohol produce higher levels of urinary mercapturic acids than the minimally toxic dose of acrolein. This observation is likely due to biotransformation of allyl acetate and ally alcohol to acrolein that occurs after absorption and suggests that these chemicals are protoxicants that increase systemic exposure of acrolein. Increased systemic exposure to acrolein is likely responsible for the differences in hepatic toxicological profile observed with these chemicals.

Acrolein: sources, metabolism, and biomolecular interactions relevant to human health and disease

Acrolein (2-propenal) is ubiquitously present in (cooked) foods and in the environment. It is formed from carbohydrates, vegetable oils and animal fats, amino acids during heating of foods, and by combustion of petroleum fuels and biodiesel. Chemical reactions responsible for release of acrolein include heat-induced dehydration of glycerol, retro-aldol cleavage of dehydrated carbohydrates, lipid peroxidation of polyunsaturated fatty acids, and Strecker degradation of methionine and threonine. Smoking of tobacco products equals or exceeds the total human exposure to acrolein from all other sources. The main endogenous sources of acrolein are myeloperoxidase-mediated degradation of threonine and amine oxidase-mediated degradation of spermine and spermidine, which may constitute a significant source of acrolein in situations of oxidative stress and inflammation. Acrolein is metabolized by conjugation with glutathione and excreted in the urine as mercapturic acid metabolites. Acrolein forms Michael adducts with ascorbic acid in vitro, but the biological relevance of this reaction is not clear. The biological effects of acrolein are a consequence of its reactivity towards biological nucleophiles such as guanine in DNA and cysteine, lysine, histidine, and arginine residues in critical regions of nuclear factors, proteases, and other proteins. Acrolein adduction disrupts the function of these biomacromolecules which may result in mutations, altered gene transcription, and modulation of apoptosis.

Relationship between machine-derived smoke yields and biomarkers in cigarette smokers in Germany

In order to determine whether smokers of cigarettes in the contemporary yield ranges of the German market (0.1-1.0mg nicotine, 1-10mg tar) differ in their actual exposure to various smoke constituents, we performed a field study with 274 smokers and 100 non-smokers. The following biomarkers were determined: In 24-h urine: Nicotine equivalents (molar sum of nicotine, cotinine, trans-3'-hydroxycotinine and their respective glucuronides), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL, metabolite of the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, NNK), 3-hydroxypropylmercapturic acid (metabolite of acrolein), trans,trans-muconic acid, S-phenylmercapturic acid (metabolites of benzene), 1-hydroxypyrene (metabolite of pyrene); in saliva: Cotinine and trans-3'-hydroxycotinine; in exhaled air: Carbon monoxide; in blood: Methyl-, hydroxyethyl-, cyanoethyl- (biomarker of acrylonitrile) and carbamoylethylvaline (biomarker of acrylamide) hemoglobin adducts. All biomarkers were found to be significantly higher in smokers compared to non-smokers and showed strong correlations with the daily cigarette consumption. Biomarker levels and per cigarette increases in smokers were at most weakly related to the machine-derived smoke yields. It is concluded that machine-derived yields of cigarettes from the contemporary German cigarette market have little or no impact on the actual smoking-related exposure determined by suitable biomarkers.

Quantitative urinalysis of the mercapturic acid conjugates of allyl formate using high-resolution NMR spectroscopy

As end products of xenobiotic metabolism via glutathione conjugation, mercapturic acids (MCAs) can be used as markers to indicate exposure to allylic compounds as well as the rate and efficiency of their excretion. In addition, the formation of certain MCAs indicates metabolism via the known toxin acrolein, a strong electrophile. High-resolution 1H NMR spectroscopy has been employed to quantitatively measure the presence of MCAs in the urine of Sprague-Dawley rats, collected in the 8 h following 25 and 50 mgkg(-1) i.p. doses of allyl formate (AF), a model toxin. 3-Hydroxypropylmercapturic acid (HPMA) was found to be the only 1H NMR-observable MCA excreted in the urine, exhibiting a percentage recovery of approximately 20% at the 25 mgkg(-1) dose level, and approximately 30% at the 50 mgkg(-1) dose level.

Sulfoxides as urinary metabolites of S-allyl-L-cysteine in rats: evidence for the involvement of flavin-containing monooxygenases

S-Allyl-L-cysteine (SAC), a component of garlic and a metabolite of allyl halides, is a known substrate for multiple flavin-containing monooxygenases (FMOs). In the current study, we characterize the in vivo SAC metabolism by investigating the presence of SAC, N-acetyl-S-allyl-L-cysteine (NASAC), and their corresponding sulfoxides in the urine of rats given SAC (200 or 400 mg/kg i.p.). In some experiments, rats were given aminooxyacetic acid (AOAA), an inhibitor of cysteine conjugate beta-lyase, or methimazole, an alternative FMO substrate, 30 min prior to treatment with 200 mg/kg SAC. Nearly 40 to 50% of the dose was recovered in the 24-h collection period. In all treatment groups, the majority of the metabolites were excreted within 8 h. The major metabolites detected were NASAC and NASAC sulfoxide (NASACS; nearly 30-40% and 5-10% of the dose, respectively). Only small amounts of the dose (approximately 1.5%) were recovered as SAC and SAC sulfoxide (SACS). Methimazole pretreatment significantly reduced amounts of both SACS and NASACS detected in the urine when compared with rats given SAC only, whereas AOAA pretreatment had no effect. In vitro assays using rat liver microsomes were also carried out to compare the sulfoxidation rates of SAC and NASAC. The results showed that SAC was much more readily oxidized than NASAC. Collectively, the results provide evidence for the involvement of FMOs in the in vivo metabolism of SAC and that SAC is a much better substrate for FMOs than its corresponding mercapturic acid.

Prevention of diabetes-induced albuminuria in transgenic rats overexpressing human aldose reductase

Studies using pharmacologic inhibitors have implicated the enzyme aldose reductase in the pathogenesis of albuminuria and diabetic renal disease. However, a clear conclusion is not easily drawn from such studies since these pharmacologic inhibitors have nonspecific properties. To examine further the role of aldose reductase, we have overexpressed the human enzyme in a transgenic rat model. Transgene expression in the kidney was predominantly localized to the outer stripe of the outer medulla, compatible with the histotopography of the straight (S3) proximal tubule. The effect of enzyme overexpression on diabetes-induced renal function and structure was then investigated. Contrary to what may have been anticipated from the previous enzyme inhibition studies, diabetes-induced albuminuria was completely prevented by the overexpression of aldose reductase. No effect of overexpression of aldose reductase on renal structure nor on urinary excretion of beta2-microglobulin and N-acetyl-beta-D-glucosaminidase was observed in this transgenic rat model. In conclusion, our study strongly suggests that multiple roles for aldose reductase may give it a more complex place in diabetic nephropathy than is currently recognized.

High-performance liquid chromatographic-tandem mass spectrometric determination of 3-hydroxypropylmercapturic acid in human urine

A sensitive and specific high-performance liquid chromatographic-tandem mass spectrometric (HPLC-MS-MS) method was developed for the determination of 3-hydroxypropylmercapturic acid (3-HPMA) in human urine. Samples were extracted using ENV+ cartridges and then injected onto a C8 Superspher Select B column with acetonitrile and formic acid as eluent (5:95, v/v). N-Acetylcysteine was used as internal standard for HPLC-MS-MS. Linearity was given in the tested range of 50-5000 ng/ml urine. The limit of quantification was 50 ng/ml. Precision, as C.V., in the tested range of 50-5000 ng/ml was 1.47-6.04%. Accuracy ranged from 87 to 114%. 3-HPMA was stable in human urine at 37 degrees C for 24 h. The method was able to quantify 3-HPMA in urine of non-smokers and smokers.

In vivo absorption, metabolism, and urinary excretion of alpha,beta-unsaturated aldehydes in experimental animals. Relevance to the development of cardiovascular diseases by the dietary ingestion of thermally stressed polyunsaturate-rich culinary oils

Thermal stressing of polyunsaturated fatty acid (PUFA)- rich culinary oils according to routine frying or cooking practices generates high levels of cytotoxic aldehydic products (predominantly trans-2-alkenals, trans,trans-alka-2,4-dienals, cis,trans-alka-2, 4-dienals, and n-alkanals), species arising from the fragmentation of conjugated hydroperoxydiene precursors. In this investigation we demonstrate that typical trans-2-alkenal compounds known to be produced from the thermally induced autoxidation of PUFAs are readily absorbed from the gut into the systemic circulation in vivo, metabolized (primarily via the addition of glutathione across their electrophilic carbon-carbon double bonds), and excreted in the urine as C-3 mercapturate conjugates in rats. Since such aldehydic products are damaging to human health, the results obtained from our investigations indicate that the dietary ingestion of thermally, autoxidatively stressed PUFA-rich culinary oils promotes the induction, development, and progression of cardiovascular diseases.

Bioactivation of benzylic and allylic alcohols via sulfo-conjugation

Although sulfo-conjugation, in general, has been regarded as a detoxification process in the xenobiotic metabolism, there is a substantial body of data supporting that the same reaction can also lead to activation of certain types of chemical carcinogens and mutagens. Examples include some aromatic amines and amides, alkenylbenzenes, methyl-substituted polyaromatic hydrocarbons, nitrotoluenes and nitrosamines. The N- or O-hydroxy derivatives of these compounds undergo sulfonation to form extremely reactive sulfuric acid esters that can play a role as ultimate carcinogenic/mutagenic metabolites. Previous studies from several laboratories have shown that hydroxymethyl polyarenes, such as hydroxymethylbenz[a]anthracenes, 6-hydroxymethylbenzo[a]pyrene, and 1-hydroxymethylpyrene, are activated to reactive benzylic sulfuric acid esters, preferentially by rat hepatic hydroxysteroid sulfotransferase. Some aromatic hydrocarbons bearing the secondary benzylic hydroxy functionality can also yield electrophilic sulfate esters in the presence of hepatic sulfotransferase activity. Thus, benzylic mono- and dihydroxy derivatives of cyclopenta[cd]pyrene form mutagenic and DNA binding species when incubated with rat liver cytosol and the sulfo-group donor, 3'-phosphoadenosine-5'-phosphosulfate. 1-Hydroxy-3-methylcholanthrene that also possesses the cyclopenta-fused ring system appears to be metabolically activated through sulfo-conjugation. Likewise, benzo[a]pyrene tetraol might be activated through sulfuric acid esterification at one of two benzylic hydroxyl groups. Methylene-bridged polyarenols represent another potential group of cyclic secondary benzylic alcohols that can be activated by sulfotransferases. Certain non-polycyclic aromatic type benzylic alcohols have also been proposed to undergo sulfotransferase-mediated activation. Besides benzylic sulfonation, sulfuric acid esterification of certain allylic alcohols can produce reactive species.

Mixed effects of 2,6-dithiopurine against cyclophosphamide mediated bladder and lung toxicity in mice

2,6-Dithiopurine (DTP) has been proposed as a possible chemopreventive agent because of its ability to react with electrophiles. Acrolein, an electrophilic metabolite of cyclophosphamide (CP) involved in the toxicities of this anticancer drug, can be scavenged by DTP. The present study examined the effect of DTP treatment on CP-mediated bladder and lung toxicity in male ICR mice. Mice fed a diet containing 4% DTP that were treated intraperitoneally (i.p.) with 350 mg/kg CP showed no significant bladder damage (measured as bladder blood content at 48 h) with respect to the group fed a control diet. DTP (50 and 100 mg/kg), given i.p. 0.5 and 7 h after the initial injection of CP, also prevented the bladder damage when compared with the group receiving CP alone. Surprisingly, although neither parenteral CP nor DTP alone caused any mortality at these doses, the combined treatment resulted in 67% mortality within 3 days. At 24 h after CP + DTP, blood urea nitrogen was elevated 6-fold and urine volumes decreased by 70%. Histopathological analyses revealed a diffuse myocardial degeneration and necrosis, severe granular degeneration in the liver, abundant cellularity and infiltrates in interalveolar spaces in the lung and swollen nephron epithelial cells with some necrosis. All mice survived treatment when the dose of CP was lowered to 250 and 25-75 mg/kg DTP was given i.p. 0.5 and 7 h after CP. These DTP regimens reduced the degree of CP-induced lung toxicity, measured by [3H]thymidine incorporation into lung DNA 7 days after CP, in a dose-dependent manner. DTP (75 mg/kg) also reduced CP-induced lung fibrosis estimated by lung hydroxyproline content 28 days after CP. Analyses of urine from mice given CP + DTP revealed large amounts of the metabolic product dithiouric acid, smaller amounts of the parent DTP and several smaller peaks. The major unique metabolite peak was collected and analyzed by mass spectrometry, but did not correspond to either acrolein-DTP or acrolein-dithiouric acid. Thus, either very small amounts of an acrolein adduct are generated, the adduct is broken down to an unidentified product, or the ability of DTP to prevent CP-induced lung and bladder damage is related to some other mechanism. The possibility that mercapturic acid metabolites of acrolein released the parent electrophile in the urine was not supported by the finding that probenecid did not prevent CP-induced bladder toxicity.

Allylmercapturic acid as urinary biomarker of human exposure to allyl chloride

OBJECTIVE

To evaluate the use of urinary mercapturic acids as a biomarker of human exposure to allyl chloride (3-chloropropene) (AC). During three regular shut down periods in a production factory for AC, both types of variables were measured in 136 workers involved in maintenance operations.

METHODS

Potential airborne exposure to AC was measured by personal air monitoring in the breathing zone. In total 205 workshifts were evaluated. During 99 workshifts no respiratory protection equipment was used. Mercapturic acid metabolites were measured in urinary extracts by gas chromatography-mass spectrometry (GC-MS).

RESULTS

During 86 work shifts when no respiratory protection was used the air concentrations of AC were below the Dutch eight hour time weighted average (8 h-TWA) occupational exposure limit (OEL) of AC (3 mg/m3), whereas in 13 workshifts the potential exposure, as measured by personal air monitoring, exceeded the OEL (3.3 to 17 mg/m3). With the aid of GC-MS, 3-hydroxypropylmercapturic acid (HPMA) was identified as a minor and allylmercapturic acid (ALMA) as a major metabolite of AC in urine samples from the maintenance workers exposed to AC. The concentrations of ALMA excreted were in a range from < 25 micrograms/l (detection limit) to 3550 micrograms/l. The increases in urinary ALMA concentrations during the workshifts correlated well with the 8h-TWA air concentrations of AC (r = 0.816, P = 0.0001, n = 39). Based on this correlation, for AC a biological exposure index (BEI) of 352 micrograms ALMA/g creatinine during an eight hour workshift is proposed. In some urine samples unexpectedly high concentrations of ALMA were found. Some of these could definitely be attributed to dermal exposure to AC. In other cases garlic consumption was identified as a confounding factor.

CONCLUSION

The mercapturic acid ALMA was identified in urine of workers occupationally exposed to airborne AC and the increase in ALMA concentrations in urine during a workshift correlated well with the 8 h-TWA exposure to AC. Garlic consumption, but not smoking, is a potential confounding factor for this biomarker of human exposure to AC.

Urinary mutagenicity and thioethers in nonsmokers: role of environmental tobacco smoke (ETS) and diet

The urinary excretion of mutagens and thioethers was investigated in a controlled diet study and in two field studies. A diet containing charcoal-broiled meat and other items rich in mutagenic compounds increased the urinary mutagenicity as assessed in Salmonella typhimurium strain TA98 with metabolic activation approximately 46-fold compared to a diet low in mutagens. The excretion of thioethers after ingestion of the diet rich in mutagens also increased significantly when compared to the diet low in mutagens. The increase was associated with the content of preformed thioethers in the diet. In the first field study with 21 nonsmokers, urinary mutagenicity as assessed in Salmonella typhimurium strain TA98 and excretion of thioethers showed no relation to either the self-reported exposure to environmental tobacco smoke (ETS) or to serum cotinine concentrations used as an objective marker for ETS exposure. In the second field study, urinary mutagenicity was determined with a tobacco-smoke sensitive Salmonella typhimurium strain YG1024 with metabolic activation. No correlation was found between the mutagenic activity in urine and ETS exposure duration, nicotine on the personal sampler, cotinine in saliva and cotinine in urine. Our results suggest that real-life ETS exposure does not measurably increase either urinary mutagen or urinary thioether excretion. Furthermore, diet seems to be the most important source for both urinary mutagen and thioether excretion in nonsmokers.

Potential role of the flavin-containing monooxygenases in the metabolism of endogenous compounds

Several xenobiotics and their corresponding cysteine S-conjugates are metabolized in vivo to cysteine S-conjugate sulfoxides and/or N-acetylcysteine S-conjugate sulfoxides. Homocysteine S-conjugates, such as methionine and ethionine, are also metabolized in vivo to sulfoxides. The enzymatic basis for these metabolic reactions is not known. Recently, the rat liver and kidney S-benzyl-L-cysteine S-oxidase activities were found to be associated with flavin-containing monooxygenases that are structurally and immunochemically related to known FMO1 isoforms. Further evidence for FMO1 being the major FMO isoform involved in S-benzyl-L-cysteine sulfoxidation was obtained from kinetic studies with cDNA-expressed rabbit FMOs. Endogenous cysteine S-conjugates, e.g. cysteinylcatecholamines, cysteinylleukotrienes, lanthionine and djenkolic acid may also be substrates for FMOs, since S-benzyl-L-cysteine can be considered a model for these compounds. Methionine, an endogenous homocysteine S-conjugate, was shown to be a substrate for cDNA-expressed rabbit FMO1, FMO2, and FMO3, however, the methionine sulfoxidation reaction was preferentially catalyzed by FMO3. These results suggest that FMOs may also play a role in the in vivo metabolism of endogenous homocysteine S-conjugates.

Fate and effects of acrolein

Acrolein is a highly toxic, reactive, and irritating aldehyde that occurs as a product of organic pyrolysis, as a metabolite of a number of compounds, and as a residue in water when used for the control of aquatic organisms. It is an intermediate in the production of acrylic acid, DL-methionine, and numerous other agents. Its major direct use is as a biocide for the control of aquatic flora and fauna. It is introduced to the environment from a variety of sources, including organic combustion such as automobile exhaust, cigarette smoke, and manufacturing and cooking emissions, as well as direct biocidal applications. Organic combustion from both fixed and mobile sources is the significant source of acrolein in the atmosphere; it represents up to 8% of the total aldehydes generated from vehicles and residential fireplaces and 13% of total atmospheric aldehydes. This reactive aldehyde also occurs in organisms as a metabolite of allyl alcohol, allylamine, spermine, spermidine, and the anticancer drug cyclophosphamide, and as a product of UV radiation of the skin lipid triolein. Furthermore, small amounts are found in foods; when animal or vegetable fats are overheated, however, large amounts are produced. Most human contact occurs during exposure to smoke from cigarettes, automobiles, industrial processes, and structural and vegetation fires. Besides cigarette smoke, occupational exposures are a common mode of human contact, particularly in industries that involve combustion of organic compounds. Firefighters, in particular, are exposed to extremely high levels during the extinguishment and overhaul phases of their work. Water may contain significant levels of the herbicide. It has been found in paper mill and municipal effluents at 20-200 micrograms/L, and at 30 micrograms/L as far as 64 km downstream from the point of application. The USEPA-recommended water quality criteria for freshwater are only 1.2 micrograms/L (24-hr avg) and 2.7 micrograms/L (maximum ceiling). Acrolein is highly reactive, and intercompartmental transport is limited. However, it is eliminated from aqueous environments by volatilization and hydration to beta-hydroxypropanal, after which biotransformation occurs, with a half-life of 7-10 d. The Koc for acrolein is 24, and it is not likely to be retained in soil; activated carbon adsorbs only 30% from solution. Thus, the aldehyde is either leached extensively in moist soil or volatilizes quickly from dry soil. It is eliminated from air by reaction with .OH (half-life, 0.5-1.2 d), NOx (half-life, 16 d), and O3 (half-life, 59 d), as well as by photolysis and wet deposition. As expected from its high water solubility, bioaccumulation is low. Acrolein is highly toxic by all routes of exposure. The respiratory system is the most common target: exposure causes localized irritation, respiratory distress, pulmonary edema, cellular necrosis, and increased susceptibility to microbial diseases. Additionally, acute inhalation studies verify that it is a severe respiratory irritant that affects respiratory rates. Respiratory rate depression may have a protective effect by minimizing vapor inhalation, thereby explaining the subadditive effect of acrolein when combined with the other toxic combustion by-products CO and HCHO. Liquid contact with the skin and eyes causes severe irritation, opaque or cloudy corneas, and localized epidermal necrosis, but no allergic contact dermatitis. The cardiovascular system is affected, resulting in increased blood pressure, platelet aggregation, and quick cessation of beating in perfused rat hearts. It may also inhibit mitochondrial oxidative phosphorylation in the myocardium. Acute LD50s and LC50s are low. Levels are 7-46 mg/kg and 18-750 mg/m3, respectively, in rats; aquatic organisms are affected above 11.4 micrograms/L.(ABSTRACT TRUNCATED)

Nephrotoxicity of the 1:1 acrolein-glutathione adduct in the rat

Previous metabolic studies in rats have suggested in vivo formation of the acrolein-glutathione (acrolein-GSH) adduct following administration of the highly reactive alpha, beta-unsaturated aldehyde acrolein. Early studies by several investigators demonstrated that similar compounds such as alpha, beta-unsaturated aldehyde-cysteine adducts have toxic (carcinostatic) activity against Ehrlich ascites tumor cells implanted in mice. The current studies investigated the in vivo toxicity associated with the acrolein-GSH adduct in the male Sprague-Dawley rat. The 1:1 acrolein-GSH adduct was synthesized and characterized by physical-chemical methods. Rats given the acrolein-GSH adduct intravenously at 0.5 or 1 mmol/kg developed nephrotoxicity characterized by glucosuria, proteinuria, elevation in serum urea nitrogen, and gross and histologic changes of the kidney. The toxicity was not affected by pretreatment of rats with pyrazole, an alcohol dehydrogenase inhibitor; disulfiram, an inhibitor of aldehyde dehydrogenases; or probenecid, a renal organic anion transport inhibitor. Administration of a similar but nonaldehydic glutathione conjugate, S-n-propylglutathione, did not result in nephrotoxicity in the rat. The nephrotoxicity induced by the acrolein-GSH adduct was inhibited by acivicin, a gamma-glutamyl-transpeptidase inhibitor. These results indicate that the acrolein-GSH adduct requires processing through the first step of the renal mercapturic acid synthesis pathway to be activated to a toxic species.

Uptake of tobacco smoke constituents on exposure to environmental tobacco smoke (ETS)

For the purpose of risk evaluation, passive smoking is frequently regarded as low-dose cigarette smoking. However, since the physical, chemical and biological properties of mainstream smoke (MS), which is inhaled by the smoker and environmental tobacco smoke (ETS), which is breathed by the passive smoker are quite different, risk extrapolation from active smoking to passive smoking is of doubtful value. In a series of experimental exposure studies we compared the uptake of tobacco smoke constituents by active and passive smoking. The results show that biomarkers which were found to be elevated after experimental ETS exposure, such as nicotine and cotinine in plasma and urine as well as thioethers in urine, indicate gas-phase exposure in passive smokers, but particle-phase exposure in active smokers. Biomarkers which should indicate the uptake of particle-bound, genotoxic substances with ETS, such as urinary mutagenicity, metabolites of polycyclic aromatic hydrocarbons (PAH) and DNA adducts, were not found to be elevated even after extremely high ETS exposure. From these results we conclude that a risk evaluation for passive smoking on the basis of dosimetric data is currently not possible.

The physiological consequences of glutathione variations

The major low molecular weight thiol inside cells, the tripeptide glutathione (GSH), is of importance for protection of the cell against oxidative challenge, for thiol homeostasis required to guarantee basic functions, and for defence mechanisms against xenobiotics. Since the pathophysiological significance of a perturbed GSH status in human disease is less clear, this review evaluates the consequences of in vivo variations of GSH. Owing to intracellular GSH concentrations above 2 mM depletion of GSH as such has little metabolic consequences unless an additional stress is superimposed. The kinetic properties of GSH-dependent enzymes imply that loss of up to 90% of intracellular GSH may still be compatible with cellular integrity. Mitochondrial GSH, which accounts for about 10% of total cellular GSH, may define the threshold beyond that toxicity commences. Thus, in cases of severe GSH-depletion a substitution of GSH as a therapeutic measure seems justified. Such a severe depletion of GSH has been described for some diseases such as liver dysfunction, AIDS or pulmonary fibrosis.

Mercapturic acids, protein adducts, and DNA adducts as biomarkers of electrophilic chemicals

The possibilities and limitations of using mercapturic acids and protein and DNA adducts for the assessment of internal and effective doses of electrophilic chemicals are reviewed. Electrophilic chemicals may be considered as potential mutagens and/or carcinogens. Mercapturic acids and protein and DNA adducts are considered as selective biomarkers because they reflect the chemical structure of the parent compounds or the reactive electrophilic metabolites formed during biotransformation. In general, mercapturic acids are used for the assessment of recent exposure, whereas protein and DNA adducts are used for the assessment of semichronic or chronic exposure. 2-Hydroxyethyl mercapturic acid has been shown to be the urinary excretion product of five different reactive electrophilic intermediates. Classification of these electrophiles according to their acid-base properties might provide a tool to predict their preference to conjugate with either glutathione and proteins or with DNA. Constant relationships appear to exist in the cases of 1,2-dibromoethane and ethylene oxide between urinary mercapturic acid excretion and DNA and protein adduct concentrations. This suggests that mercapturic acids in some cases may also play a role as a biomarker of effective dose. It is concluded that simultaneous determination of mercapturic acids, protein and DNA adducts, and other metabolites can greatly increase our knowledge of the specific roles these biomarkers play in internal and effective dose assessment. If the relationship between exposure and effect is known, similar to protein and DNA adducts, mercapturic acids might also be helpful in (individual) health risk assessment.

Cyclophosphamide toxicity. Characterising and avoiding the problem

Cyclophosphamide, an orally active alkylating agent, is widely used to treat a variety of malignant and nonmalignant disorders. Although it has some tumour selectivity, it also possesses a wide spectrum of toxicities. The requirement of metabolic activation before cyclophosphamide exerts either its therapeutic or toxic effects is well established, but has not led to effective counter-measures. Clinically, damage to the bladder (haemorrhagic cystitis), immunosuppression (when not desired) and alopecia are the most significant toxicities associated with cyclophosphamide. Cardiotoxicity is also a possibility when very high doses are given. Preventing these toxicities has focused on modifications of the treatment regimens and, in the case of haemorrhagic cystitis, the administration of a drug which is excreted in the urine where it inactivates the bladder-toxic species. As treatment regimens for cancer become more effective in prolonging a patient's life, and as cyclophosphamide receives increasing use for nonmalignant disorders, the potential for cyclophosphamide-induced cancers, particularly in the bladder, must be recognised. Although the toxicities associated with cyclophosphamide are serious, this agent remains a highly effective drug in many situations. Research on the pathways which play an important role in activating this drug may improve our ability to target particular diseases and decrease unwanted side effects.

Allyl alcohol- and acrolein-induced toxicity in isolated rat hepatocytes

Incubation of isolated hepatocytes with allyl alcohol results in GSH depletion and subsequent cytotoxicity which is prevented by pyrazole, an inhibitor of alcohol dehydrogenase. Both GSH depletion and cytotoxicity were much more rapid when hepatocytes were incubated with acrolein, the reactive metabolite, and were not affected by pyrazole. However, cytotoxicity of both allyl alcohol and acrolein was enhanced by the aldehyde dehydrogenase inhibitors cyanamide and disulfiram. Malondialdehyde, a lipid peroxidation product, was also formed when hepatocytes were incubated with either agent, and treatment of the hepatocytes with a ferric ion chelator, desferrioxamine, or an antioxidant delayed the cytotoxicity without affecting GSH depletion. Although no GSSG was formed and addition of disulfide reductant dithiothreitol did not restore GSH levels, cytotoxicity was prevented if dithiothreitol was added some time after either agent.

3-Hydroxypropylmercapturic acid: a biologic marker of exposure to allylic and related compounds

3-Hydroxypropylmercapturic acid [3-OHPrMCA, S-(3-hydroxypropyl)-N-acetyl-L-cysteine] was quantitatively measured by high-performance liquid chromatography (HPLC) in the urine of rats given allylamine.HCl (5, 25, 50, 100 and 150 mg kg-1), acrolein (13 mg kg-1), allylalcohol (64 mg kg-1), allylchloride (76 mg kg-1), allylbromide (120 mg kg-1), allylcyanide (115 mg) and cyclophosphamide (160 mg kg-1) by gavage in water. 3-OHPrMCA was measured by HPLC in 24-h urine collections; the lower detection limit was 1.25 micrograms or 5.6 nmol ml-1. Various doses of allylamine resulted in 3-OHPrMCA excretion at a fairly constant percentage of the dose, ca. 44-48% at 0-24 h and 3% at 24-48 h, indicating rapid metabolism through glutathione conjugation in the first 24h. Similarly, 3-OHPrMCA was recovered in the urine of rats given acrolein (78.5%), allylalcohol (28.3%), allylchloride (21.5%), allylbromide (3.0%), allylcyanide (3.7%) and cyclophosphamide (2.6%). These data indicate that 3-OHPrMCA can be used as a marker of exposure to allylic and other compounds that lead to the metabolic formation of acrolein.

In vivo metabolism of the cardiovascular toxin, allylamine

Previous evidence from this laboratory demonstrated that allylamine, a known cardiovascular toxin, is metabolized in vitro to acrolein, which has been hypothesized to act as a distal toxin. In this study, 3-hydroxypropylmercapturic acid was isolated and identified by MS, NMR, and 2D-NMR spectroscopy as the sole urinary metabolite of allylamine metabolism in vivo. Parallel experiments showed reduced glutathione (GSH) depletion in several organs (most marked in aorta, blood, and lung), which is consistent with GSH conjugation of the proposed acrolein intermediate. These findings indicate that allylamine was metabolized in vivo to a highly reactive aldehyde which was converted to a mercapturic acid through a GSH conjugation pathway; the exact mechanisms of cellular damage remain unclear.

Protection of rat embryos in culture against the embryotoxicity of acrolein using exogenous glutathione

The aldehyde acrolein is embryotoxic in vivo and in vitro. Since acrolein is reactive towards thiols, glutathione was evaluated for its protective effects against the in vitro embryotoxicity of acrolein. Day 10 rat embryos were cultured in the presence of acrolein and glutathione, either concurrently or sequentially, and evaluated for embryo deaths, malformations, growth retardation, and content of glutathione and protein. Acrolein, added alone at the initiation of the culture period, was embryolethal to 64 and 100% of the embryos at 120 and 160 microM respectively. At acrolein concentrations of 80 and 120 microM, 50 and 100%, respectively, of the surviving embryos were malformed. In addition, both of these concentrations of acrolein produced growth retardation manifested by significant decreases in the yolk sac diameter, crown-rump and head lengths, number of somites, and morphological score. Concurrent exposure to 100 or 500 microM glutathione markedly protected embryos against all of these effects. To study the mechanism of the protective effect of glutathione against the embryotoxicity of acrolein, the effects of sequential addition of acrolein and glutathione were determined. When rat embryos were cultured in the presence of acrolein for 2 hr prior to exposure to glutathione, even 500 microM glutathione could not offer any protection against the embryolethality, teratogenicity, and growth retardation induced by acrolein. However, a 6-hr preincubation with 500 microM glutathione, prior to exposure to acrolein (in the absence of exogenous glutathione), significantly decreased the incidence of embryo deaths at 160 microM acrolein and brought the number of deaths and malformations among embryos exposed to 120 microM acrolein down to a level not significantly different from control; unlike the embryos exposed concurrently to acrolein and glutathione, however, the sequential treatment with glutathione and acrolein did not protect against growth retardation. While there were some changes in the total glutathione and protein content of embryos and yolk sacs with acrolein exposure, none of the treatments had any overall effect on the glutathione concentration per mg protein. Thus, exogenous glutathione can protect against the in vitro embryotoxicity of acrolein. We propose that this protection is mediated in part by a direct interaction between glutathione and acrolein, added concurrently to the serum medium, and in part by an indirect effect on the embryo of glutathione added prior to acrolein.

Enhancement of the embryotoxicity of acrolein, but not phosphoramide mustard, by glutathione depletion in rat embryos in vitro

The intracellular thiol glutathione is known to protect cells against the toxicity of certain drugs and reactive intermediates. In this study, the role of glutathione in protecting the embryo against two embryolethal and teratogenic metabolites of cyclophosphamide, and anticancer drug, was assessed in vitro using the rat whole embryo culture system. Day 10.5 rat embryos were cultured in rat serum medium containing phosphoramide mustard (1, 10, or 25 microM) or acrolein (10, 25, 50 or 100 microM), with and without buthionine sulfoximine (10 or 100 microM), a compound which depletes glutathione by inhibiting its synthesis. After 45 hr, embryos were assessed for viability, malformations, growth and development, and the glutathione content of embryos exposed to buthionine sulfoximine alone was assayed. The glutathione levels of the embryos and their yolk sacs were decreased significantly by 100 microM buthionine sulfoximine, whereas 10 microM buthionine sulfoximine decreased glutathione levels in the yolk sacs only. Phosphoramide mustard alone, at concentrations of 10 and 25 microM, did not produce embryo deaths but did cause malformations and growth retardation in 100% of the exposed embryos. The addition of buthionine sulfoximine (100 microM) had no effect on the teratogenicity or growth-retarding effects of phosphoramide mustard. Acrolein alone produced a 25 and 48% incidence of embryo deaths at 50 and 100 microM, respectively, and a 46% incidence of embryo malformations, as well as significant growth retardation, among the surviving embryos at 100 microM. Buthionine sulfoximine (10 or 100 microM) significantly enhanced the embryotoxic effects of acrolein. The addition of 10 microM buthionine sulfoximine resulted in 100% embryolethality at 100 microM acrolein; this buthionine sulfoximine concentration decreased the EC50 values for embryo deaths and malformations to 50% of those for acrolein alone. The addition of 100 microM butionine sulfoximine significantly potentiated the embryolethality of acrolein at 25, 50 and 100 microM; the combination of 100 microM acrolein plus 100 microM buthionine sulfoximine was 100% embryolethal. The incidence of embryo malformations was enhanced significantly at 10 and 25 microM acrolein by 100 microM buthionine sulfoximine. The EC50 values for embryo deaths and malformations were decreased to 50 and 20%, respectively, of those values for acrolein alone. Both butionine sulfoximine concentrations produced significant growth retardation at all acrolein concentrations compared to either acrolein or buthionine sulfoximine alone.(ABSTRACT TRUNCATED AT 400 WORDS)

Examination of the differential hepatotoxicity of diallyl phthalate in rats and mice

In this study we confirmed that diallyl phthalate (DAP) is more hepatotoxic to rats than to mice, and we demonstrated the same species difference in toxicity for allyl alcohol (AA). The data suggest that the toxicity of DAP probably results from AA cleaved from DAP. To determine if the species difference in susceptibility to hepatotoxicity resulted from differences in the disposition and metabolism of DAP, Fischer-344 rats and B6C3F1 mice were given [14C]DAP, 1, 10, or 100 mg/kg po or 10 mg/kg iv, and placed in metabolism cages for 24 hr. In rats, 25-30% of the DAP was excreted as CO2, and 50-70% appeared in the urine within 24 hr. In mice, 6-12% of the DAP was excreted as CO2, and 80-90% was excreted in the urine within 24 hr. Monoallyl phthalate (MAP), allyl alcohol, 3-hydroxypropylmercapturic acid (HPMA), and an unidentified polar metabolite (PM) were found in the urine of rats and mice dosed with DAP. The polar metabolite was present in the urine of rats dosed with DAP or AA, indicating that the compound is a metabolite of AA. There was no difference between the species in the quantity of AA excreted, but mice excreted more MAP (39 vs 33%), HPMA (28 vs 17%), and PM (20 vs 8%) than rats. Because DAP is metabolized to AA, a potent periportal hepatotoxicant, and because the mouse produced more HPMA than rats, we postulate that the differential hepatotoxicity of DAP is related to the extent of glutathione conjugation with allyl alcohol or acrolein (the active metabolite of AA).

The embryolethality and teratogenicity of acrolein in cultured rat embryos

Acrolein, a three-carbon unsaturated aldehyde, is teratogenic to rats in vivo following intraamniotic administration but has been reported not to be teratogenic in vitro in the rat whole embryo culture system. In this study the effects of acrolein on rat embryos cultured in the standard medium consisting of rat serum were assessed over a narrow-concentration range. Additionally, a comparison was done of the effects of culture in a serum medium vs. a serum-free medium. In the serum medium acrolein caused 100% embryolethality at 140 microM and was found to be teratogenic in the concentration range of 80-120 microM. In the serum-free medium acrolein was 100% embryolethal at 20 microM and was teratogenic in the range of 5-15 microM. The EC50 for malformations in the serum medium was 137 microM, whereas that for embryolethality was 115 microM; the EC50s for malformations and embryolethality in the serum-free medium were 2.8 microM and 8.3 microM, respectively. Malformations were observed in the brain, facial area, and heart in addition to blebs and twisted or kinked bodies. Decreases in yolk sac diameter, crown-rump length, head length, number of somites, morphological score, and protein content were observed within the teratogenic ranges in each type of medium. Thus acrolein is teratogenic and embryolethal in vitro as well as in vivo. Dissociation between embryolethality and teratogenicity was seen in the serum-free medium. The slope of the acrolein log concentration-response curve in the serum-free medium was twice that in the serum medium, indicating that acrolein may have a different mechanism of action in this medium.

QSAR for upper-respiratory tract irritation

A recent paper by Muller and Greff (Fd. Chem. Toxicol., 22 (1984) 661) presents QSAR equations for upper respiratory tract irritation by compounds falling into various chemical families. In the present paper the relationships are analysed further. It is found that a general QSAR equation, covering a diverse range of structures, correlates the biological activity reported by Muller and Greff with a single physicochemical parameter, TB'. The parameter TB' is the boiling point at atmospheric pressure (TB), adjusted for compounds with Trouton constants different from 22 cal deg-1 mol-1: TB' = (Tr X TB/22) + 40(1 - Tr/22) where Tr is the Trouton constant. Some of the compounds studied were found to be more irritant than predicted by the general equation: their enhanced activity can be rationalised in terms of their chemical reactivity as electrophiles, their metabolism to electrophiles, or their hydrolysis to more irritant products.

Teratogenicity and embryolethality of acrolein and structurally related compounds in rats

Acrolein, a metabolite of the anticancer agent cyclophosphamide, is teratogenic to rats after intraamniotic administration. It is not known whether acrolein or a metabolite of acrolein is responsible for the teratogenicity of this compound. We assessed the teratogenicity and embryolethality of acrolein and five structurally related compounds: acrylic acid, allyl alcohol, glycidol, glyceraldehyde, and propionaldehyde by intraamniotic injections in Sprague-Dawley rats on day 13 of gestation. All compounds tested were significantly embryolethal with at least one concentration of the drug. Acrolein was the most embryolethal of the drugs, causing a significant increase in resorptions with as little as 0.1 micrograms/fetus; the other drugs were embryolethal at doses 100-10,000 times that of acrolein. Acrolein was also the most teratogenic of the drugs tested; a dose as low as 5 micrograms/fetus caused a significant increase in the incidence of fetal malformations. Of the other compounds tested, only glycidol at a dose of 1,000 micrograms/fetus induced a significant number of malformed fetuses compared to control. These results suggest that it is acrolein itself that is responsible for its teratogenicity.

A new pathway of acrolein metabolism in rats

The excretion of metabolites of acrolein in rat urine after single oral administration of 10 mg/kg was investigated. S-Carboxyethylmercapturic acid (S-carboxyethyl-N-acetyl-cysteine), or S-(propionic acid methyl ester)mercapturic acid, was found as the major metabolite. An unidentified metabolite was found in expired air. Acrylic acid and methyl acrylate are suggested as intermediates in the metabolism of acrolein.

Mutagenic properties of allylic and alpha, beta-unsaturated compounds: consideration of alkylating mechanisms

1. Allyl and allylic compounds may exert alkylating activities by SN1, SN2 and SN2' mechanisms. This direct alkylating potential can be determined quantitatively by a modified 4-NBP (4-nitrobenzyl pyridine) test. 2. The alkylating activities in a systematically selected series of allyl and allylic compounds correlate well with the direct mutagenic potential as determined in the Ames test using Salmonella typhimurium TA 100 as tester strain. 3. The allylic structure is a prerequisite for these types of activities since structurally related molecules lacking the allylic moiety are inactive in this respect. 4. The potency of both the alkylating and mutagenic activity is determined by the strength of the leaving group: --OSO2CH3 greater than I greater than Br greater than Cl greater than--NCS. 5. Indirect mutagenicity, through metabolic activation of the olefinic bond (by addition of S9 mix to the tester medium), can be ruled out for practically all compounds, the only exception found being 2,3-dichloro-1-propene where an increase of mutagenicity is encountered after addition of S9 mix; mechanistic explanations for this exception are provided. 6. Analogous activation is demonstrated for benzyl halides, the alkylating potency of which is even higher than that of genuine allylic compounds. 7. A variety of methyl- and chlorine-substituted allyl compounds has been included in the study: both groups increase activity, either by +I (CH3) or by +M effects (Cl). 8. alpha, beta-Unsaturated carbonyl compounds, e.g. acrolein and crotonaldehyde, also display direct mutagenic activity which is due to a completely different mechanism: covalent binding to nucleophilic sites of DNA bases by Michael addition. Methyl and other alkyl substitutions decrease the mutagenic potential in this type of compound. The corresponding alcohols, also displaying mutagenic activity but to a lesser degree, are metabolically activated by ADH (alcohol dehydrogenase) of the tester strain microbes to the aldehydes or ketones.

Correlation of alkylating and mutagenic activities of allyl and allylic compounds: standard alkylation test vs. kinetic investigation

Thirty-nine allylic and non-allylic compounds have been tested in the standard 4-(p-nitrobenzyl)pyridine (NBP) alkylating procedure and the Salmonella typhimurium mutagenicity assay. Fourteen of these were found directly mutagenic (without addition of S-9 mix activating enzyme system). With twelve of these compounds, a good correlation of alkylating and mutagenic potencies was established; the remaining two do not meet the chemical conditions of the NBP procedure on account of HCl elimination with these two compounds. The other 25 substances were inactive in both systems. The quantitative correlation proved to be almost linear in the lower activity ranges (E approximately 2; revertants/muml approximately 600). The reasons for some deviations from the linear relationship have been analyzed and discussed on the basis of structural features. In addition to the standard alkylation test, a modified NBP-test was performed in order to obtain kinetic data and activation energy values. The results with 6 representative allylic compounds show that the overall correlation is not substantially improved above that of the standard procedure: nonetheless, additional information on reaction characteristics is obtained with some substances.