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

Association of genetic polymorphisms with mercapturic acids in the urine of young healthy subjects before and after exposure to outdoor air pollution

We aimed to identify the relationship between variations in metabolic genes and human urinary changes in mercapturic acids (MAs), including CEMA, HMPMA, SPMA, HPMA and HEMA, before and after air pollution exposure. Genotype detection for 47 relevant single nucleotide polymorphisms (SNPs) collected by literature research was performed. Five MAs expression levels in the urinary samples of 50 young healthy individuals with short-term exposure to clean, polluted and purified air at five time points were detected by targeted online solid-phase extraction liquid chromatography tandem mass spectrometry (SPE-LC-MS/MS), followed with associations of SNPs with MAs changes. Difference in MAs between polluted and clean/purified air was significantly associated with 21 SNPs mapped into 9 genes. Five SNPs in GSTP1 showed the most prominent association with the changes in SPMA expression, indicating that those SNPs in GSTP1 and SPMA might serve as biomarkers for susceptibility and the prognosis of lung cancer.

Characterization of the association between cigarette smoking intensity and urinary concentrations of 2-hydroxyethyl mercapturic acid among exclusive cigarette smokers in the National Health and Nutrition Examination Survey (NHANES) 2011-2016

BACKGROUND

2-Hydroxyethyl mercapturic acid (2HEMA, N-acetyl-S-(2-hydroxyethyl)-L-cysteine) is a urinary metabolite of several volatile organic compounds including acrylonitrile and ethylene oxide, which are found in cigarette smoke.

METHODS

We measured 2HEMA concentrations in urine specimens collected during the National Health and Nutrition Examination Survey (2011-2016) from eligible participants aged >12 years (N = 7,416). We developed two multiple linear regression models to characterize the association between cigarette smoking and 2HEMA concentrations wherein the dependent variable was 2HEMA concentrations among participants who exclusively smoked cigarettes at the time of specimen collection and the independent variables included sex, age, race/ethnicity, creatinine, diet, and either cigarettes smoked per day (CPD) or serum cotinine.

RESULTS

We detected 2HEMA in 85% of samples tested among exclusive cigarette smokers, and only 40% of specimens from non-smokers. When compared to exclusive cigarette smokers who smoked 1-9 CPD, smoking 10-19 CPD was associated with 36% higher 2HEMA (p < 0.0001) and smoking >19 CPD was associated with 61% higher 2HEMA (p < 0.0001). Additionally, 2HEMA was positively associated with serum cotinine.

CONCLUSIONS

This study demonstrates that cigarette smoking intensity is associated with higher urinary 2HEMA concentrations and is likely a major source of acrylonitrile and/or ethylene oxide exposure.

Harmonization of acronyms for volatile organic compound metabolites using a standardized naming system

Increased interest in volatile organic compound (VOC) exposure has led to an increased need for consistent, systematic, and informative naming of VOC metabolites. As analytical methods have expanded to include many metabolites in a single assay, the number of acronyms in use for a single metabolite has expanded in an unplanned and inconsistent manner due to a lack of guidance or group consensus. Even though the measurement of VOC metabolites is a well-established means to investigate exposure to VOCs, a formal attempt to harmonize acronyms amongst investigators has not been published. The aim of this work is to establish a system of acronym naming that provides consistency in current acronym usage and a foundation for creating acronyms for future VOC metabolites.

Simultaneous determination of mercapturic acids derived from ethylene oxide (HEMA), propylene oxide (2-HPMA), acrolein (3-HPMA), acrylamide (AAMA) and N,N-dimethylformamide (AMCC) in human urine using liquid chromatography/tandem mass spectrometry

Mercapturic acids are highly important and specific biomarkers of exposure to carcinogenic substances in occupational and environmental medicine. We have developed and validated a reliable, specific and very sensitive method for the simultaneous determination of five mercapturic acids derived from several high-production chemicals used in industry, namely ethylene oxide, propylene oxide, acrylamide, acrolein and N,N-dimethylformamide. Analytes are enriched and cleaned up from urinary matrix by offline solid-phase extraction. The mercapturic acids are subsequently separated by means of high-performance liquid chromatography on a Luna C8 (2) column and specifically quantified by tandem mass spectrometric detection using isotopically labelled analytes as internal standards. The limits of detection (LODs) for N-acetyl-S-2-carbamoylethylcysteine (AAMA) and N-acetyl-S-2-hydroxyethylcysteine (HEMA) were 2.5 microg/L and 0.5 microg/L urine, while for N-acetyl-S-3-hydroxypropylcysteine (3-HPMA), N-acetyl-S-2-hydroxypropylcysteine (2-HPMA) and N-acetyl-S-(N-methylcarbamoyl)cysteine (AMCC) it was 5 microg/L. These LODs were sufficient to detect the background exposure of the general population. We applied the method on spot urine samples of 28 subjects of the general population with no known occupational exposure to these substances. Median levels for AAMA, HEMA, 3-HPMA, 2-HPMA and AMCC in non-smokers (n = 14) were 52.6, 2.0, 155, 7.1 and 113.6 microg/L, respectively. In smokers (n = 14), median levels for AAMA, HEMA, 3-HPMA, 2-HPMA and AMCC were 243, 5.3, 1681, 41.7 and 822 microg/L, respectively. Due to the simultaneous quantification of these mercapturic acids, our method is well suited for the screening of workers with multiple chemical exposures as well as the determination of the background excretion of the general population.

Disposition and metabolism of 1,6-dimethylnaphthalene in rats

The distribution, excretion and metabolism of 1,6-dimethylnaphthalene following i.p. administration of a single dose of 20 mg/kg to rats, was investigated using radiotracer [3H] and a gas chromatography-mass spectrometry technique (GC-MS). After 72 h, about 94% of the given dose was excreted in urine and feces. In organs and tissues, the highest concentration during the first hours after administration was detected in fat, liver, spleen and kidneys. Then gradual decline of tritium was noticed in all examined tissues. In urine, the following substances were identified and quantified by GC peak areas: unchanged 1,6-dimethylnaphthalene, 1-methyl-hydroxynaphthalenes, 1-hydroxymethyl-6-methylnaphthalene, 1,6-dimethyl-thionaphthalene, 6-methyl-1-naphthoic aldehyde, 6-methyl-1-naphthoic acid, 1,6-dimethyl-thionaphthalene and 1,6-dimethyl-methylthionaphthalene.

Identification and quantitative determination of glutathione-related urinary metabolites of fotemustine, a new anti-cancer agent

1. Potential sulphur-containing metabolites of the anticancer agent, fotemustine, were synthesized, namely thiodiacetic acid (TDA), S-2-hydroxyethyl N-acetyl-L-cysteine (2-HE-NAC), N-acetyl-L-cysteine (NAC), S-methyl N-acetyl-L-cysteine (M-NAC), S-carboxymethyl-L-cysteine (CM-Cys), S-carboxymethyl N-acetyl-L-cysteine (CM-NAC), their corresponding sulphoxides and sulphones. Their chemical structures and stabilities were confirmed and derivatization methods were developed for their analysis by sulphur-selective g.l.c. (g.l.c.-FPD) and g.l.c.-mass spectrometry. 2. Four methods for isolation of potential metabolites of fotemustine were developed. Quantification of metabolites, derived in various ways was carried out by g.l.c.-atomic emission detection (AED) or g.l.c.-mass spectrometry. 3. Male Wistar rats (n = 4) were given a single i.p. dose of 40 mg/kg fotemustine. Urine excretion of TDA (18.4 +/- 1.9% in 24 h) and TDA sulphoxide (12.0 +/- 1.6% in 24 h) was significant; 32.7 +/- 4.6% of the fotemustine dose was excreted as TDA, and TDA sulphoxide in 48 h. NAC was excreted in rat urine at 1% of the dose. No other potential glutathione-derived metabolites of fotemustine were excreted. 4. Male Wistar rats (n = 4) were also treated i.p. with fotemustine at 5, 20 and 40 mg/kg, to investigate dose dependency and the time course of excretion of TDA. Excretion of TDA in 48 h urine decreased from 32 +/- 2 to 17 +/- 2% dose (mean +/- SD) with increasing dose of fotemustine.

Thioethers in urine of sterilization personnel exposed to ethylene oxide

Biological monitoring of exposure to ethylene oxide (EO) was carried out in 31 hospital workers in the sterilization facilities of five hospitals. The excretion of total thioethers was determined in the urine of sterilization workers. An occupational nonexposed group served as a control (n = 31). The air EO level was not monitored routinely, however, peak concentrations of EO up to 200 p.p.m. were detected mainly when the sterilization chambers were open. Our results show a significant difference in urinary thioether excretion between the exposed and control groups (P less than 0.001). Sterilization workers seem to absorb significant quantities of EO. We feel that other alternative and more sensitive methods for detecting thioether metabolites of EO should be carried out to confirm our results.

Monitoring of oxidative free radical damage in vivo: analytical aspects

Free radical damage is an important factor in many pathological and toxicological processes. During the last decade a wide range of methods has been developed to determine free radical damage in various biological fluids and at various stages of development. This review offers an overview of the state of the art of monitoring free radical damage in vivo, with special emphasis on the analytical aspects of non-invasive methods.

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.

Metabolism of the chloroethylnitrosoureas

1. The chemical degradation and metabolism of the 2-chloroethylnitrosoureas (CENUSs) have been critically reviewed with the objective of gaining a better understanding of factors that could aid in the design of new, more effective, anticancer drugs. 2. The CENUs are chemically unstable under normal physiological conditions and can rapidly degrade to give a variety of reactive intermediates capable of carbamoylating proteins and/or alkylating both proteins and DNA. 3. Carbamoylation is thought to make a minimal contribution to the cytotoxic effect of the CENUs, although it may be involved in some of the unwanted side-effects. It would seem desirable, therefore, to design new CENUs with low carbamoylating activity. 4. The main action of the CENUs is by alkylation of DNA via a chloroethyldiazo-hydroxide intermediate. Chloroethylation is important, as opposed to hydroxyethylation, since the former leads to inter-strand DNA cross-linking via an intramolecular rearrangement with the removal of chloride. It is this inter-strand cross-linking which prevents subsequent DNA repair and loss of cytotoxicity. 5. Metabolism usually, although not exclusively, leads to deactivation of the CENUs either by dechlorination or denitrosation of the molecule, generally with the former being the dominant route. These reactions occur very rapidly, and before chemical degradation can take place, and can be an important determinant in the final cytotoxicity. Moreover, both these pathways involve the cytochrome P-450 system and can be induced with phenobarbital.(ABSTRACT TRUNCATED AT 250 WORDS)