The metabolism of crotyl phosphate, crotyl alcohol and crotonaldehyde

Daily Exposure to Environmental Volatile Organic Compounds Triggers Oxidative Damage: Evidence from a Large-Scale Survey in China

Volatile organic compounds (VOCs) are ubiquitous environmental pollutants and have been implicated in adverse health outcomes. In this study, concentrations of 11 VOC metabolites (mVOCs) and three oxidative stress biomarkers (8-oxo-7,8-dihydro-2'-deoxyguanosine, 8-oxo-7,8-dihydro-guanosine, and dityrosine) were determined in 205 urine samples collected from 12 cities across mainland China. Urinary ∑11mVOC concentrations ranged from 498 to 1660 ng/mL, with a geometric mean (GM) value of 1070 ng/mL. The factorial analysis revealed that cooking, solvents, and vehicle emissions were the three primary sources of VOC exposure. A significant regional variation was clearly found in ∑11mVOC concentrations across four regions in China, with high urine VOC concentrations found in North and South China (GM: 1450 and 1340 ng/mL). The multiple linear regression model revealed that most mVOCs were significantly positively correlated with three oxidative stress markers (β range: 0.06-0.22). Mixture effect regression showed that isoprene, crotonaldehyde, acrolein, and benzene were the strongest contributors to oxidative stress. Approximately 80% of the participants have HQ values greater than 1.0 for 1,3-butadiene and benzene, suggesting that their exposure doses were close to potential adverse health effects. Our findings provide comprehensive information on human exposure and potential health risks of VOCs in China.

Exposure to volatile organic compounds is a risk factor for diabetes: A cross-sectional study

Currently, more studies showed that environmental chemicals were associated with the development of diabetes. However, the effect of volatile organic compounds (VOCs) on diabetes remained uncertain and needed to be studied. This cross-sectional study examined whether exposure to low levels of VOCs was associated with diabetes, insulin resistance (TyG index) and glucose-related indicators (FPG,HbA1c, insulin) in the general population by using the NHANES dataset (2013-2014 and 2015-2016). We analyzed the association between urinary VOC metabolism (mVOCs) and these indicators in 1409 adults by multiple linear regression models or logistic regression models, further Bayesian kernel machine regression (BKMR) models were performed for mixture exposure analysis. The results showed positive associations between multiple mVOCs and diabetes, TyG index, FPG, HbA1c and insulin, respectively. Among them, HPMMA concentration in urine was significantly positively correlated with diabetes and related indicators (TyG index, FPG and HbA1c), and the concentration of CEMA was significantly positively correlated with insulin. The positive association of mVOCs with diabetes and its related indicators was more significant in the female group and in the 40-59 years group. Thus, our study suggested that exposure to VOCs affected insulin resistance and glucose homeostasis, further affecting diabetes levels, which had important public health implications.

Comparison of urinary mercapturic acid excretions in users of various tobacco/nicotine products

Urinary mercapturic acids (MAs) are detoxification products for electrophiles occurring in the human body. They are suitable biomarkers of exposure to directly acting electrophilic chemicals or to chemicals which generate the electrophile during its metabolism. We determined the urinary excretion of 19 MAs in habitual users of combustible cigarettes (CCs), electronic cigarettes (ECs), heated tobacco products (HTPs), oral tobacco (OT), and nicotine replacement therapy (NRT) products, and nonusers (NUs) of any tobacco/nicotine products. The 19 MAs are assumed to be physiologically formed primarily from 15 toxicants with three of them belonging to IARC Group 1 (human carcinogen), seven to Group 2A (probable human carcinogen), four to Group 2B (possible human carcinogen), and one to Group 3 (not classifiable as carcinogen). Smoking (CC) was found to be associated with significantly elevated exposure to ethylene oxide (or ethylene), 1,3-butadiene, benzene, dimethylformamide, acrolein, acrylamide, styrene, propylene oxide, acrylonitrile, crotonaldehyde, and isoprene compared with the other user groups and NU. Users of HTPs revealed slight elevation in the MAs related to acrolein, acrylamide, and crotonaldehyde compared with the other non-CC groups. Vaping (EC) was not found to be associated with any of the MAs studied. In conclusion, the determination of urinary MAs is a useful tool for assessing the exposure to toxicants (mainly potential carcinogens) in users of various tobacco/nicotine products. Our data also give cause to clarify the role of vaping (EC) in urinary excretion of DHPMA (precursor: glycidol).

Crotonaldehyde-induced vascular relaxation and toxicity: Role of endothelium and transient receptor potential ankyrin-1 (TRPA1)

INTRODUCTION

Crotonaldehyde (CR) is an electrophilic α,β-unsaturated aldehyde present in foods and beverages and is a minor metabolite of 1,3-butadiene. CR is a product of incomplete combustion, and is at high levels in smoke of cigarettes and structural fires. Exposure to CR has been linked to cardiopulmonary toxicity and cardiovascular disease.

OBJECTIVE

The purpose of this study was to examine the direct effects of CR in murine blood vessels (aorta and superior mesenteric artery, SMA) using an in vitro system.

METHODS AND RESULTS

CR induced concentration-dependent (1-300 μM) relaxations (75-80%) in phenylephrine (PE) precontracted aorta and SMA. Because the SMA was 20× more sensitive to CR than aorta (SMA EC50 3.8 ± 0.5 μM; aorta EC50 76.0 ± 2.0 μM), mechanisms of CR relaxation were studied in SMA. The CR-induced relaxation at low concentrations (1-30 μM) was inhibited by: 1) mechanically-impaired endothelium; 2) Nω-Nitro-L-arginine methyl ester hydrochloride (L-NAME); 3) guanylyl cyclase (GC) inhibitor (ODQ); 4) transient receptor potential ankyrin-1 (TRPA1) antagonist (A967079); and, 5) by non-vasoactive level of nicotine (1 μM). Similarly, a TRPA1 agonist, allyl isothiocyanate (AITC; mustard oil), stimulated SMA relaxation dependent on TRPA1, endothelium, NO, and GC. Consistent with these mechanisms, TRPA1 was present in the SMA endothelium. CR, at higher concentrations (100-300 μM), induced tension oscillations (spasms) and irreversibly impaired contractility (a vasotoxic effect enhanced by impaired endothelium).

CONCLUSIONS

CR relaxation depends on a functional endothelium and TRPA1, whereas vasotoxicity is enhanced by endothelium dysfunction. Thus, CR is both vasoactive and vasotoxic along a concentration continuum.

Urinary biomonitoring of subjects with different smoking habits. Part I: Profiling mercapturic acids

BACKGROUND

While tobacco smoke contains thousands of chemicals, some of which are carcinogenic to humans, the content of electronic cigarette smoke is less known. This work aimed to assess and compare the exposure associated with different smoking habits by profiling urinary mercapturic acids as biomarkers of toxic compounds.

METHODS

In this pilot study, sixty-seven healthy adults with different smoking habits were investigated: 38 non-smokers (NS), 7 electronic cigarette users (ECU), and 22 traditional tobacco smokers (TTS). Seventeen urinary mercapturic acids, metabolites of 1,3-butadiene (DHBMA, MHBMA), 4-chloronitrobenze (NANPC), acrolein (3-HPMA), acrylamide (AAMA, GAMA), acrylonitrile (CEMA), benzene (SPMA), crotonaldehyde (CMEMA, HMPMA), ethylating agents (EMA), methylating agents (MMA), ethylene oxide (HEMA), N,N-dimethylformamide (AMCC), propylene oxide (2-HPMA), styrene (PHEMA), and toluene (SBMA), were quantified, along with urinary nicotine and cotinine.

RESULTS

Median urinary cotinine was 0.4, 1530 and 1772 μg/L in NS, ECU and TTS, respectively. Most mercapturic acids were 2-165 fold-higher in TTS compared to NS, with CEMA, MHBMA, 3-HPMA and SPMA showing the most relevant increases. Furthermore, some mercapturic acids were higher in ECU than NS; CEMA and 3-HPMA, in particular, showed significant increases and were 1.8 and 4.9 fold-higher, respectively.

CONCLUSIONS

This study confirms that tobacco smoking is a major source of carcinogenic chemicals such as benzene and 1,3-butadiene; electronic cigarette use is a minor source, mostly associated with exposure to chemicals with less carcinogenic potential such as acrylonitrile and acrolein.

Crotonaldehyde exposure in U.S. tobacco smokers and nonsmokers: NHANES 2005-2006 and 2011-2012

INTRODUCTION

Crotonaldehyde is an α,β-unsaturated carbonyl compound that is a potent eye, respiratory, and skin irritant. Crotonaldehyde is a major constituent of tobacco smoke and its exposure can be quantified using its urinary metabolite N-acetyl-S-(3-hydroxypropyl-1-methyl)-L-cysteine (HPMM). A large-scale biomonitoring study is needed to determine HPMM levels, as a measure of crotonaldehyde exposure, in the general U.S.

POPULATION

MATERIALS AND METHODS

Urine samples were obtained as part of the National Health and Nutrition Examination Survey 2005-2006 and 2011-2012 from participants who were at least six-years-old (N = 4692). Samples were analyzed for HPMM using ultra performance liquid chromatography - tandem mass spectrometry. Exclusive tobacco smokers were distinguished from non- tobacco users through a combination of self-reporting and serum cotinine data.

RESULTS

Detection rate of HPMM among eligible samples was 99.9%. Sample-weighted, median urinary HPMM levels for smokers and non-users were 1.61 and 0.313 mg/g creatinine, respectively. Multivariable regression analysis among smokers showed that HPMM was positively associated with serum cotinine, after controlling for survey year, urinary creatinine, age, sex, race, poverty level, body mass index, pre-exam fasting time, and food intake. Other significant predictors of urinary HPMM include sex (female > male), age (children > non-user adults), race (non-Hispanic Blacks < non-Hispanic Whites).

CONCLUSIONS

This study characterizes U.S. population exposure to crotonaldehyde and confirms that tobacco smoke is a major exposure source. Urinary HPMM levels were significantly higher among exclusive combusted tobacco users compared to non-users, and serum cotinine and cigarettes per day were significant predictors of increased urinary HPMM. This study also found that sex, age, ethnicity, pre-exam fasting time, and fruit consumption are related to urinary HPMM levels.

Determination of two mercapturic acids related to crotonaldehyde in human urine: influence of smoking

Crotonaldehyde, an αβ-unsaturated aldehyde, and a potent alkylating agent, is present in many foods and beverages, ambient air and tobacco smoke. A previous study indicated that two metabolites, 3-hydroxy-1- methylpropylmercapturic acid (HMPMA) and 2-carboxy1-1-methylethylmercapturic acid (CMEMA), were excreted in rat urine after subcutaneous injection of crotonaldehyde. Herein, we report the development of a method based on liquid chromatography with tandem mass spectrometry (LC-MS/MS) and deuterated analytes as internal standards, for the determination of HMPMA and CMEMA in human urine. The limits of quantification of the method were 92 and 104 ng/mL for HMPMA and CMEMA, respectively. The calibration curves for both compounds were linear up to 7500 ng/mL with R2 >0.99. It was found that cigarette smokers excreted about three to five-fold more HMPMA, and only slightly elevated amounts of CMEMA, in their urine compared to non-smokers. In smokers, we also found significant correlations between the urinary excretion levels of HMPMA (but not CMEMA) and several markers of exposure for smoking, including the daily cigarette consumption, carbon monoxide in exhaled breath, salivary cotinine, and nicotine plus five of its major metabolites in urine. Smoking cessation or switching from smoking conventional cigarettes to experimental cigarettes with lower crotonaldehyde delivery led to significant reductions of urinary HMPMA excretion, but not CMEMA excretion. Alcohol consumption did not influence either urinary HMPMA or CMEMA excretion. We conclude that HMPMA is a potentially useful biomarker for smoking-related exposure to crotonaldehyde.

The involvement of TRP channels in sensory irritation: a mechanistic approach toward a better understanding of the biological effects of local irritants

Peripheral nerves innervating the mucosae of the nose, mouth, and throat protect the organism against chemical hazards. Upon their stimulation, characteristic perceptions (e.g., stinging and burning) and various reflexes are triggered (e.g., sneezing and cough). The potency of a chemical to cause sensory irritation can be estimated by a mouse bioassay assessing the concentration-dependent decrease in the respiratory rate (50 % decrease: RD50). The involvement of the N. trigeminus and its sensory neurons in the irritant-induced decrease in respiratory rates are not well understood to date. In calcium imaging experiments, we tested which of eight different irritants (RD50 5-730 ppm) could induce responses in primary mouse trigeminal ganglion neurons. The tested irritants acetophenone, 2-ethylhexanol, hexyl isocyanate, isophorone, and trimethylcyclohexanol stimulated responses in trigeminal neurons. Most of these responses depended on functional TRPA1 or TRPV1 channels. For crotyl alcohol, 3-methyl-1-butanol, and sodium metabisulfite, no activation could be observed. 2-ethylhexanol can activate both TRPA1 and TRPV1, and at low contractions (100 µM) G protein-coupled receptors (GPCRs) seem to be involved. GPCRs might also be involved in the mediation of the responses to trimethylcyclohexanol. By using neurobiological tools, we showed that sensory irritation in vivo could be based on the direct activation of TRP channels but also on yet unknown interactions with GPCRs present in trigeminal neurons. Our results showed that the potency suggested by the RD50 values was not reflected by direct nerve-compound interaction.

Effects of smoking cessation on eight urinary tobacco carcinogen and toxicant biomarkers

We determined the persistence at various times (3, 7, 14, 21, 28, 42, and 56 days) of eight tobacco smoke carcinogen and toxicant biomarkers in the urine of 17 smokers who stopped smoking. The biomarkers were 1-hydroxy-2-(N-acetylcysteinyl)-3-butene (1) and 1-(N-acetylcysteinyl)-2-hydroxy-3-butene (2) [collectively called MHBMA for monohydroxybutyl mercapturic acid] and 1,2-dihydroxy-4-(N-acetylcysteinyl)butane (3) [DHBMA for dihydroxybutyl mercapturic acid], metabolites of 1,3-butadiene; 1-(N-acetylcysteinyl)-propan-3-ol (4, HPMA for 3-hydroxypropyl mercapturic acid), a metabolite of acrolein; 2-(N-acetylcysteinyl)butan-4-ol (5, HBMA for 4-hydroxybut-2-yl mercapturic acid), a metabolite of crotonaldehyde; (N-acetylcysteinyl)benzene (6, SPMA for S-phenyl mercapturic acid), a metabolite of benzene; (N-acetylcysteinyl)ethanol (7, HEMA for 2-hydroxyethyl mercapturic acid), a metabolite of ethylene oxide; 1-hydroxypyrene (8) and its glucuronides (1-HOP), metabolites of pyrene; and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (9) and its glucuronides (total NNAL), a biomarker of exposure to 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). These biomarkers represent some of the major carcinogens and toxicants in cigarette smoke: 1,3-butadiene, acrolein, crotonaldehyde, benzene, ethylene oxide, polycyclic aromatic hydrocarbons (PAH), and NNK. With the exception of DHBMA, levels of which did not change after cessation of smoking, all other biomarkers decreased significantly after 3 days of cessation (P < 0.001). The decreases in MHBMA, HPMA, HBMA, SPMA, and HEMA were rapid, nearly reaching their ultimate levels (81-91% reduction) after 3 days. The decrease in total NNAL was gradual, reaching 92% after 42 days, while reduction in 1-HOP was variable among subjects to about 50% of baseline. Since DHBMA did not change upon smoking cessation, there appear to be sources of this metabolite other than 1,3-butadiene. The results of this study demonstrate that the tobacco smoke carcinogen/toxicant biomarkers MHBMA, HPMA, HBMA, SPMA, HEMA, 1-HOP, and NNAL are related to smoking and are good indicators of the impact of smoking on human exposure to 1,3-butadiene, acrolein, crotonaldehyde, benzene, ethylene oxide, PAH, and NNK.

Influence of smoking charcoal filter tipped cigarettes on various biomarkers of exposure

Charcoal (CC) filters of cigarettes are known to significantly reduce a series of volatile constituents in mainstream smoke, including reactive alpha,beta-unsaturated aldehydes such as acrolein and crotonaldehyde. We performed a randomized, crossover, 2-wk brand-switching study with 39 smokers. Twenty of the subjects smoked cellulose acetate (CA) filter tipped cigarettes during wk 1 of the study; the remaining 19 subjects smoked CC filter tipped cigarettes during wk 1. In wk 2, the subjects switched to the corresponding brand with the other filter type, with similar smoking machine-derived tar and nicotine yields. Daily cigarette consumption, carbon monoxide in exhaled breath, salivary cotinine, and urinary nicotine equivalents (molar sum of nicotine plus five major metabolites) did not change significantly when switching to the cigarettes with the other filter type. Urinary excretion rates of 3-hydroxy-1-methylpropylmercapturic acid (metabolite of crotonaldehyde), monohydroxybutenylmercapturic acid (metabolite of 1,3-butadiene), and S-phenylmercapturic acid (metabolite of benzene) were significantly lower when smoking CC compared to CA filter tipped cigarettes. The reduction in amount of 3-hydroxypropylmercapturic acid (metabolite of acrolein) was of borderline significance. Other mercapturic acids and thioethers (the latter is a summary parameter that indicates the exposure to electrophilic compounds) were not or were only slightly reduced upon smoking CC filter tipped cigarettes. We conclude that smoking CC filter tipped cigarettes does not change the uptake of carbon monoxide and nicotine when compared to CA filter tipped cigarettes with similar tar and nicotine yields, but significantly reduces the exposure to toxicologically relevant smoke constituents such as acrolein, crotonaldehyde, 1,3-butadiene, and benzene.

Detection of carboxylic acids and inhibition of hippuric acid formation in rats treated with 3-butene-1,2-diol, a major metabolite of 1,3-butadiene

Epidemiological studies have indicated that 1,3-butadiene exposure is associated with an increased risk of leukemia. In human liver microsomes, 1,3-butadiene is rapidly oxidized to butadiene monoxide, which can then be hydrolyzed to 3-butene-1,2-diol (BDD). In this study, BDD and several potential metabolites were characterized in the urine of male B6C3F1 mice and Sprague-Dawley rats after BDD administration (i.p.). Rats given 1420 micromol kg(-1) BDD excreted significantly greater amounts of BDD relative to rats administered 710 micromol kg(-1) BDD. Rats administered 1420 or 2840 micromol kg(-1) BDD excreted significantly greater amounts of BDD per kilogram of body weight than mice given an equivalent dose. Trace amounts of 1-hydroxy-2-butanone and the carboxylic acid metabolites, crotonic acid, propionic acid, and 2-ketobutyric acid, were detected in mouse and rat urine after BDD administration. Because of the identification of the carboxylic acid metabolites and because of the known ability of carboxylic acids to conjugate coenzyme A, which is critical for hippuric acid formation, the effect of BDD treatment on hippuric acid concentrations was investigated. Rats given 1420 or 2272 micromol kg(-1) BDD had significantly elevated ratios of benzoic acid to hippuric acid in the urine after treatment compared with control urine. However, this effect was not observed in mice administered 1420 or 2840 micromol kg(-1) BDD. Collectively, the results demonstrate species differences in the urinary excretion of BDD and show that BDD administration in rats inhibits hippuric acid formation. The detection of 1-hydroxy-2-butanone and the carboxylic acids also provides insight regarding pathways of BDD metabolism in vivo.

Determination of mercapturic acid excretions in exposure control to toxicants

Toxicants can be converted in vivo by a variety of biotransformation reactions into substances that are more, equally, or less noxious than the parent compound. Although conjugation with glutathione is a process that usually results in less harmful products, these products might subsequently form new metabolites that exert more toxicity than the parent compound. These conjugation reactions are catalyzed by several classes of glutathione-S-transferase isoenzymes and thus result in the urinary or biliary excretion of N-acetyl-L-cysteine-S-conjugates (mercapturic acids). Inasmuch as GSH-S-transferase activity varies among different tissues, urinary excretion of mercapturic acids might reflect tissue-specific toxicity. Urinary mercapturic acids are biomarkers of internal and, in some cases, effective dose. The utility of these markers is, however, limited to times shortly after exposure. Studies on possible human deficiencies in some GSH-S-transferases might help us better understand interindividual variations in susceptibility to different toxicants and thus the differences in the pathway of mercapturic acid excretion pattern.

Depletion of the reduced glutathione level in the liver and production of the mutagens in the intestine in the mice inducing hepatoma by feeding on a high level dose of sorbic acid

Mutagenicity was detected using Salmonella typhimurium TA98 in the acidic components of the intestinal contents of mice, in which a high incidence of hepatoma had been reported due to feeding on a diet containing 15% sorbic acid (Ishizawa et al., 1980). Furthermore, the glutathione level in the liver of the 15% sorbic acid group was decreased to 40% of the amount found in controls after a 3-month feeding period, and this low level was maintained for long periods (12 months) until the end of the experiments. There was also a close correlation between the extent of depletion of the hepato-glutathione level and the concentration of sorbic acid added to the diet. Consequently, the hepatoma which developed in mice fed a 15% sorbic acid diet was considered to be induced both by the depletion of the hepato-glutathione level over the long periods, and by the gradual production of various mutagens in the intestine which were absorbed and transferred to liver to be metabolically activated.

Isolation and identification of mercapturic acids of cinnamic aldehyde and cinnamyl alcohol from urine of female rats

Rats dosed with cinnamic aldehyde (I) excreted two mercapturic acids in the urine. The major one was identified as N-acetyl-S-(1-phenyl-3-hydroxypropyl)cysteine (V). The minor one was identified as N-acetyl-S-(1-phenyl-2-carboxy ethyl)cysteine (VI). The ratio appeared to be V : VI = 4 : 1. The hydroxy mercapturic acid (V) was also isolated from urine of rats dosed with cinnamyl alcohol (II). The total mercapturic acid excretion as percentage of the dose was 14.8 +/- 1.9% for cinnamic aldehyde (250 mg/kg) (n = 4) and 8.8 +/- 1.7% for cinnamyl alcohol (n = 4) (125 mg/kg). Inhibition of the alcohol dehydrogenase by pyrazole (206 mg/kg) diminished the thioether excretion of cinnamyl alcohol to 3.3 +/- 1.4% of the dose (n = 8). Cinnamic aldehyde has been proposed to be an intermediate in the mercapturic acid formation of cinnamyl alcohol.

The metabolism of S-carboxyalkylcysteines in man

1. The ingestion of S-(2-carboxy-1-methylethyl)-, S-(2- carboxy-1-methylpropyl)-, S-(1-carboxy-2methylpropyl)- and S-(2-carboxyethyl)-L-cysteine by man was followed by the excretion in the urine of the unchanged amino acid and the N-acetylated compounds. 2. In the rat the fraction of S-(2-carboxy-1-methylethyl)-L-[U-14C]cysteine acetylated increased as the dose level decreased. 3. The significance of these results for the excretion of S-carboxyalkyl-cysteines in man is discussed.

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

1. 3-Hydroxypropylmercapturic acid, i.e. N-acetyl-S-(3-hydroxypropyl)-l-cysteine, was isolated, as its dicyclohexylammonium salt, from the urine of rats after the subcutaneous injection of each of the following compounds: allyl alcohol, allyl formate, allyl propionate, allyl nitrate, acrolein and S-(3-hydroxypropyl)-l-cysteine. 2. Allylmercapturic acid, i.e. N-acetyl-S-allyl-l-cysteine, was isolated from the urine of rats after the subcutaneous injection of each of the following compounds: triallyl phosphate, sodium allyl sulphate and allyl nitrate. The sulphoxide of allylmercapturic acid was detected in the urine excreted by these rats. 3. 3-Hydroxypropylmercapturic acid was identified by g.l.c. as a metabolite of allyl acetate, allyl stearate, allyl benzoate, diallyl phthalate, allyl nitrite, triallyl phosphate and sodium allyl sulphate. 4. S-(3-Hydroxypropyl)-l-cysteine was detected in the bile of a rat dosed with allyl acetate.