Studies of whole blood-associated acetaldehyde levels in teetotalers

N-vinyl compounds: studies on metabolism, genotoxicity, carcinogenicity

Several N-vinyl compounds are produced in high volumes and are widely employed in the production of copolymers and polymers used in chemical, pharmaceutical, cosmetic and food industry. Hence, information on their genotoxicity and carcinogenicity is requisite. This review presents hitherto available information on the carcinogenicity and genotoxicity of N-vinyl compounds as well as their metabolism potentially generating genotoxic and carcinogenic derivatives. The genotoxicity and carcinogenicity of the investigated N-vinyl compounds vary widely from no observed carcinogenicity tested in lifetime bioassays in two rodent species (up to very high doses) to carcinogenicity in rats at very low doses in the absence of apparent genotoxicity. Despite of the presence of the vinyl group potentially metabolized to an epoxide followed by covalent binding to DNA, genotoxicity was observed for only one of the considered N-vinyl compounds, N-vinyl carbazole. Carcinogenicity was investigated only for two, of which one, N-vinyl pyrrolidone was carcinogenic (but not genotoxic) and ranitidine was neither carcinogenic nor genotoxic. As far as investigated, neither a metabolically formed epoxide nor a therefrom derived diol has been reported for any of the considered N-vinyl compounds. It is concluded that the information collected in this review will further the understanding of the carcinogenic potentials of N-vinyl compounds and may eventually allow approaching their prediction and prevention. A suggestion how to prevent genotoxicity in designing of N-vinyl compounds is presented. However, the available information is scarce and further research especially on the metabolism of N-vinyl compounds is highly desirable.

Fetal Alcohol Spectrum Disorder: Embryogenesis Under Reduced Retinoic Acid Signaling Conditions

Fetal Alcohol Spectrum Disorder (FASD) is a complex set of developmental malformations, neurobehavioral anomalies and mental disabilities induced by exposing human embryos to alcohol during fetal development. Several experimental models and a series of developmental and biochemical approaches have established a strong link between FASD and reduced retinoic acid (RA) signaling. RA signaling is involved in the regulation of numerous developmental decisions from patterning of the anterior-posterior axis, starting at gastrulation, to the differentiation of specific cell types within developing organs, to adult tissue homeostasis. Being such an important regulatory signal during embryonic development, mutations or environmental perturbations that affect the level, timing or location of the RA signal can induce multiple and severe developmental malformations. The evidence connecting human syndromes to reduced RA signaling is presented here and the resulting phenotypes are compared to FASD. Available data suggest that competition between ethanol clearance and RA biosynthesis is a major etiological component in FASD.

Biomarkers of Alcohol Consumption in Body Fluids - Possibilities and Limitations of Application in Toxicological Analysis

BACKGROUND

Ethyl alcohol is the most popular legal drug, but its excessive consumption causes social problems. Despite many public campaigns against alcohol use, car accidents, instances of aggressive behaviour, sexual assaults and deterioration in labor productivity caused by inebriated people is still commonplace. Fast and easy diagnosis of alcohol consumption is required in order to introduce proper and effective therapy, and is crucial in forensic toxicology analysis. The easiest method to prove alcohol intake is determination of ethanol in body fluids or in breath. However, since ethanol is rapidly metabolized in the human organism, only recent consumption can be detected using this method. Because of that, the determination of alcohol biomarkers was introduced for monitoring alcohol consumption over a wider range of time.

OBJECTIVE

The objective of this study was to review published studies focusing on the sample preparation methods and chromatographic or biochemical techniques for the determination of alcohol biomarkers in whole blood, plasma, serum and urine.

METHODS

An electronic literature search was performed to discuss possibilities and limitations of application of alcohol biomarkers in toxicological analysis.

RESULTS

Authors described the markers of alcohol consumption such as: ethanol, its nonoxidative metabolites (ethyl glucuronide, ethyl sulfate, phosphatidylethanol, ethyl phosphate, fatty acid ethyl esters) and oxidative metabolites (acetaldehyde and acetaldehyde adducts). We also discussed issues concerning the detection window of these biomarkers, and possibilities and limitations of their use in routine analytical toxicology for monitoring alcohol consumption or sobriety during alcohol therapy.

Acetaldehyde inhibits retinoic acid biosynthesis to mediate alcohol teratogenicity

Alcohol consumption during pregnancy induces Fetal Alcohol Spectrum Disorder (FASD), which has been proposed to arise from competitive inhibition of retinoic acid (RA) biosynthesis. We provide biochemical and developmental evidence identifying acetaldehyde as responsible for this inhibition. In the embryo, RA production by RALDH2 (ALDH1A2), the main retinaldehyde dehydrogenase expressed at that stage, is inhibited by ethanol exposure. Pharmacological inhibition of the embryonic alcohol dehydrogenase activity, prevents the oxidation of ethanol to acetaldehyde that in turn functions as a RALDH2 inhibitor. Acetaldehyde-mediated reduction of RA can be rescued by RALDH2 or retinaldehyde supplementation. Enzymatic kinetic analysis of human RALDH2 shows a preference for acetaldehyde as a substrate over retinaldehyde. RA production by hRALDH2 is efficiently inhibited by acetaldehyde but not by ethanol itself. We conclude that acetaldehyde is the teratogenic derivative of ethanol responsible for the reduction in RA signaling and induction of the developmental malformations characteristic of FASD. This competitive mechanism will affect tissues requiring RA signaling when exposed to ethanol throughout life.

Recognition of malondialdehyde-modified proteins by the C terminus of complement factor H is mediated via the polyanion binding site and impaired by mutations found in atypical hemolytic uremic syndrome

Atypical hemolytic uremic syndrome (aHUS) is a severe thrombotic microangiopathy characterized by uncontrolled complement activation against endothelial and blood cells. Mutations in the C-terminal target recognition domains 19-20 of complement regulator factor H (FH) are strongly associated with aHUS, but the mechanisms triggering disease onset have remained unresolved. Here we report that several aHUS-related mutations alter the binding of FH19-20 to proteins where lysines have reacted with malondialdehyde (MDA). Although FH19-20 did not interact with MDA-modified hexylamine, lysine-containing peptides, or a proteolytically degraded protein, it bound to MDA-modified polylysine. This suggests that FH19-20 recognizes only clustered MDA adducts. Binding of MDA-modified BSA to FH19-20 was ionic by nature, depended on positive residues of FH19-20, and competed with the polyanions heparin and DNA. This could not be explained with the mainly neutral adducts known to form in MDA modification. When positive charges of lysines were eliminated by acetic anhydride instead of MDA, the acetylated BSA started to bind FH19-20. Together, these results indicate that negative charges on the modified proteins dominate the interaction with FH19-20. This is beneficial for the physiological function of FH because by binding to the negative charges of the modified target, FH could prevent excess complement activation initiated by naturally occurring antibodies recognizing MDA epitopes with multiple different structures. We propose that oxidative stress leading to formation of MDA adducts is a common feature for triggers of aHUS and that failure of FH in protecting MDA-modified surfaces from complement activation is involved in the pathogenesis of the disease.

Novel Objective Biomarkers of Alcohol Use: Potential Diagnostic and Treatment Management Tools in Dual Diagnosis Care

Alcohol use disorders are highly prevalent conditions that generate a large fraction of the total public health burden. These disorders are concentrated in mentally ill populations, in which reliability of self-reporting of alcohol consumption may be especially compromised. The application of objective biomarkers for alcohol use may therefore play an important role in these patients. This article provides a description and comparative overview of traditional versus novel biomarkers of alcohol consumption. Greater professional familiarity with and use of novel biomarkers as diagnostic and treatment management tools may enhance clinical standards and research on alcohol use in patients with a dual diagnosis.

Challenging dogma: thresholds for genotoxic carcinogens? The case of vinyl acetate

Although many questions remain unanswered, the general principle of the sequence of events leading to cancer after exposure to genotoxic carcinogens has become increasingly clear. This helps to understand the parameters that influence the shape of the dose-effect curve for carcinogenesis, including metabolic activation and inactivation of carcinogens, DNA repair, cell cycle control, apoptosis, and control by the immune system. A linear dose-response relationship with no observable threshold seems to be a conservative but adequate description for the carcinogenic activity of many genotoxic carcinogens, such as aflatoxin B1, the tobacco-specific nitrosoketone NNK, and probably N,N-diethylnitrosamine. However, extrapolation models connecting the high-level risk to the zero intercept have clearly resulted in overestimations of risk. Vinyl acetate is an example that is discussed extensively in this review. At extremely high and toxic doses, vinyl acetate is carcinogenic in rats and mice and causes chromosomal aberrations. In tissues of contact, vinyl acetate is converted to acetic acid and acetaldehyde. Only when threshold levels are achieved do critical steps in the mechanism ultimately leading to cancer become active, namely pH reduction in exposed cells of more than 0.15 units leading to cytotoxicity, damage to DNA, and regenerative proliferation. Consistent with the known exposure to endogenous acetic acid and acetaldehyde, tissues sustain a certain level of exposure without adverse effects. Physiological modeling shows that the conditions necessary for carcinogenesis are in place only when threshold levels of vinyl acetate are exceeded. The example of vinyl acetate underlines the importance of toxicological research that unequivocally identifies genotoxic carcinogens acting through a threshold process.

Biochemical markers of alcohol use in pregnant women

OBJECTIVES

To describe the serious health consequences of alcohol (ethanol) use, especially as they relate to pregnancy and the development of fetal alcohol syndrome (FAS) and fetal alcohol effects (FAE). The classic markers of alcohol exposure, including blood/breath alcohol, gamma-glutamyl transferase (gammaGT), mean corpuscular volume (MCV), hemoglobin-associated acetaldehyde (HAA) and carbohydrate deficient transferrin (CDT), are valuable and their methods of analysis are reviewed.

CONCLUSIONS

Since both FAS and FAE represent two of the leading preventable causes of mental retardation and birth defects, identification of alcohol use early in pregnancy is important to avoid adverse fetal outcomes. Unfortunately, the diagnosis of FAS and FAE is usually made after birth, when alcohol damage has become irreversible and permanent. The clinical laboratory can help prevent this damage and make a valuable contribution in assessing prenatal alcohol use. The clinical utility of blood/breath alcohol, gammaGT, MCV, HAA and CDT in alcohol use identification, especially in pregnancy, is substantial. Although none of the markers singularly has adequate sensitivity and specificity for screening, their diagnostic utility increases when measured as a panel. This is especially true in detecting alcohol use in pregnancy where the presence of several positive markers was correlated with the presence of alcohol-related fetal effects.

Prevalence of ethanol consumption may be higher in women than men in a university health service population as determined by a biochemical marker: whole blood-associated acetaldehyde above the 99th percentile for teetotalers

To estimate ethanol consumption by university students attending a student health facility, a biochemical marker of alcohol intake [whole blood associated acetaldehyde (WBAA)] was quantified by fluorimetric HPLC. Over a two year period we studied blood samples, coded by date and sex, from 645 females and 332 males, and compared the results to previously established reference ranges for teetotalers by sex. Men had higher absolute values for WBAA than women (9.9 versus 9.5 microM in the present study). However, significantly greater numbers of women (74%) than men (44%) had WBAA levels above the 99th percentile for teetotalers. Variations occurred during the academic year, with significant elevations occurring in the late fall and winter months. Testing of WBAA levels in a student health service may be important especially for women to facilitate counseling on the dangers of alcohol abuse.

Stable acetaldehyde adducts: structural characterization of acetaldehyde adducts of human hemoglobin N-terminal beta-globin chain peptides

Acetaldehyde is the first oxidation product of ethanol in vivo. Our earlier work showed that with sufficient acetaldehyde, five of the six possible sites of the peptide pentalysine were modified as a Schiff base (Braun KP, et al: J Biol Chem 270:11263-11266, 1995). However, we were unable to deduce unequivocally which site was unmodified. Lysine residues, as well as the amine terminal valine residues, in hemoglobin have been implicated as target structures for acetaldehyde adducts resulting from ethanol consumption. Hemoglobin adducts of acetaldehyde have been used clinically as a marker of ethanol consumption, but the chemical nature of these adducts remains undefined. As part of our continuing structural characterization of acetaldehyde-protein adduct formation, we studied the peptides Val-His-Leu-Thr-Pro and Val-His-Leu-Thr-Pro-Val-Glu-Lys, from the amine terminus of the beta-globin chain of hemoglobin, in vitro. Both peptides have at least one potential site for adduct formation. In the octapeptide, the N-terminal amine group of Val as well as the epsilon-amine group of the lysine sidechain can potentially be modified by acetaldehyde. We used mass spectrometry, carbon-13 nuclear magnetic resonance, and Raman spectroscopy and characterized stable Schiff base acetaldehyde adducts of these two peptides at both reactive sites. The identification of stable Schiff base adducts with the N-terminal peptides of the beta-chain of hemoglobin as well as with epsilon-amino groups of lysine provides another possible means of monitoring ethanol consumption. The functional implications of these stable Schiff bases remains undefined.

A structural assignment for a stable acetaldehyde-lysine adduct

Acetaldehyde is the first oxidation product of ethanol in vivo. Lysine residues in proteins such as hemoglobin have been implicated as target structures for acetaldehyde adducts resulting from ethanol consumption. Although the presence of both stable and unstable acetaldehyde-hemoglobin adducts has been established, the structural characterization of the adducts has received relatively little attention. As a model for such adduct formation, we studied the peptide pentalysine in vitro. Pentalysine has several potential sites for adduct formation. The amino-terminal amine group as well as the epsilon-amine groups of each lysine side chain can serve as potential sites for modification by acetaldehyde. Mass spectrometry, nuclear magnetic resonance, and Raman spectroscopy were employed to demonstrate that acetaldehyde forms a stable linkage to lysine amine groups via a Schiff base.