Development of a competitive immunoassay for the determination of N-(2-hydroxyethyl)valine adducts in human haemoglobin and its application in biological monitoring

High-throughput, simultaneous quantitation of hemoglobin adducts of acrylamide, glycidamide, and ethylene oxide using UHPLC-MS/MS

Ethylene oxide (EO), acrylamide (AA) and glycidamide (GA) exposures are associated with mammary tumors in animals. Currently available information about human exposure to these chemicals is limited creating the need for analytical methods to assess their exposure. We developed a sensitive ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method to simultaneously quantitate hemoglobin (Hb) N-terminal valine adducts of AA (HbAA), GA (HbGA), and EO (HbEO) using modified Edman reaction. The limits of detection of this method were 3.9, 4.9 and 12.9 in pmol/g Hb for HbAA, HbGA and HbEO, respectively. The among-day and within-day precision for all analytes determined with three levels of quality control pools ranged from 2.2-13.0% in percent coefficient of variation (%CV). The accuracy determined by standard addition was between 94 and 111% among all analytes. The median HbAA, HbGA and HbEO values in 34 self-reported non-smokers were 64.9, 45.3 and 113.6 pmol/g Hb and in 70 self-reported smokers were 127.8, 69.6 and 237.1 pmol/g Hb, respectively. HbAA, HbGA, and HbEO were detectable in all samples suggesting that the described method is suitable for measuring hemoglobin adducts of AA, GA and EO in the general population. This high throughput method can process 148 samples in 8 h. The HbEO/HbGA ratio appears independent of the HbAA levels in non-smokers and decreases with increasing HbAA concentration in smokers. This new method is suitable for measuring human exposure to AA, GA and EO and can provide further insight into the metabolism of these chemicals in humans.

The application of mass spectrometry in molecular dosimetry: ethylene oxide as an example

Mass spectrometry plays an increasingly important role in the search for and quantification of novel chemically specific biomarkers. The revolutionary advances in mass spectrometry instrumentation and technology empower scientists to specifically analyze DNA and protein adducts, considered as molecular dosimeters, derived from reactions of a carcinogen or its active metabolites with DNA or protein. Analysis of the adducted DNA bases and proteins can elucidate the chemically reactive species of carcinogens in humans and can serve as risk-associated biomarkers for early prediction of cancer risk. In this article, we review and compare the specificity, sensitivity, resolution, and ease-of-use of mass spectrometry methods developed to analyze ethylene oxide (EO)-induced DNA and protein adducts, particularly N7-(2-hydroxyethyl)guanine (N7-HEG) and N-(2-hydroxyethyl)valine (HEV), in human samples and in animal tissues. GC/ECNCI-MS analysis after HPLC cleanup is the most sensitive method for quantification of N7-HEG, but limited by the tedious sample preparation procedures. Excellent sensitivity and specificity in analysis of N7-HEG can be achieved by LC/MS/MS analysis if the mobile phase, the inlet (split or splitless), and the collision energy are properly optimized. GC/ECNCI-HRMS and GC/ECNCI-MS/MS analysis of HEV achieves the best performance as compared with GC/ECNCI-MS and GC/EI-MS. In conclusion, future improvements in high-throughput capabilities, detection sensitivity, and resolution of mass spectrometry will attract more scientists to identify and/or quantify novel molecular dosimeters or profiles of these biomarkers in toxicological and/or epidemiological studies.

Development of a competitive immunoassay for the determination of N-(2-hydroxypropyl)valine adducts in human haemoglobin and its application in biological monitoring

Propylene oxide (PO) is an important industrial compound and a directly acting mutagen. Human exposure to PO can be monitored by the determination of haemoglobin adducts. An immunoassay that quantifies the N-terminal adduct N-(2-hydroxypropyl)valine in whole haemoglobin was developed and its potential usefulness as a tool for biologically monitoring occupational exposure was demonstrated. Analytical reliability was confirmed in a comparative study with GC-MS (range 3.7-992 nmol g-1 haemoglobin (Hb), correlation coefficient 0.99, n=10). The assay has been configured as a competitive enzyme-linked immunosorbent assay to facilitate the rapid throughput of samples. The assay employs a whole blood matrix and has a working range of 2-250 pmol g-1 Hb. It does not appear to be affected by structurally similar metabolites and has been used to determine adducts in human blood samples. The first results in potentially exposed workers indicate the assay's high potential usefulness in routine occupational biomonitoring of exposure to PO.

Monitoring drug-protein interaction

A variety of therapeutic drugs can undergo biotransformation via Phase I and Phase II enzymes to reactive metabolites that have intrinsic chemical reactivity toward proteins and cause potential organ toxicity. A drug-protein adduct is a protein complex that forms when electrophilic drugs or their reactive metabolite(s) covalently bind to a protein molecule. Formation of such drug-protein adducts eliciting cellular damages and immune responses has been a major hypothesis for the mechanism of toxicity caused by numerous drugs. The monitoring of protein-drug adducts is important in the kinetic and mechanistic studies of drug-protein adducts and establishment of dose-toxicity relationships. The determination of drug-protein adducts can also provide supportive evidence for diagnosis of drug-induced diseases associated with protein-drug adduct formation in patients. The plasma is the most commonly used matrix for monitoring drug-protein adducts due to its convenience and safety. Measurement of circulating antibodies against drug-protein adducts may be used as a useful surrogate marker in the monitoring of drug-protein adducts. The determination of plasma protein adducts and/or relevant antibodies following administration of several drugs including acetaminophen, dapsone, diclofenac and halothane has been conducted in clinical settings for characterizing drug toxicity associated with drug-protein adduct formation. The monitoring of drug-protein adducts often involves multi-step laboratory procedure including sample collection and preliminary preparation, separation to isolate or extract the target compound from a mixture, identification and determination. However, the monitoring of drug-protein adducts is often difficult because of short half-lives of the protein adducts, sampling problem and lack of sensitive analytical techniques for the protein adducts. Currently, chromatographic (e.g. high performance liquid chromatography) and immunological methods (e.g. enzyme-linked immunosorbent assay) are two major techniques used to determine protein adducts of drugs in patients. The present review highlights the importance for clinical monitoring of drug-protein adducts, with an emphasis on methodology and with a further discussion of the application of these techniques to individual drugs and their target proteins.