Development of three stable isotope dilution assays for the quantitation of (E)-2-butenal (crotonaldehyde) in heat-processed edible fats and oils as well as in food

Elevated hemoglobin adducts derived from crotonaldehyde in healthy smokers and oral cancer patients by nanoflow liquid chromatography tandem mass spectrometry☆

Hemoglobin adducts derived from reactive chemicals have been used as exposure biomarkers in vivo. We previously identified and quantified adducted peptides derived from acrolein in human hemoglobin after trypsin digestion. In this study, we characterized the Schiff base and Michael adducts of crotonaldehyde in human hemoglobin after NaBH4 reduction to the stable adducts with a respective mass increase of 54.0470 and 72.0575 Da, determined by high-resolution mass spectrometry. We developed a workflow based on nanoflow liquid chromatography nanoelectrospray ionization tandem mass spectrometry to simultaneously quantify 29 adducted peptides derived from acrolein and crotonaldehyde in one drop of blood from smoking oral cavity cancer patients, healthy smokers, and healthy nonsmokers. Levels of ten adducted peptides were significantly elevated in smokers, despite their cancer status, and the adduct levels correlate with the extent of cigarette smoking. Comparing the adduct levels at the same site, the Michael adduct of acrolein is much higher than that of crotonaldehyde. Multivariate analysis by orthogonal partial least squares discriminant analysis suggests that the Michel adducts of acrolein at α-Lys-7, α-His-50, β-Lys-17, and the Schiff base adduct of crotonaldehyde at β-Lys-59 are the predominate contributors. This is the first report on the structural characterization of human hemoglobin adducts of crotonaldehyde and the detection and quantification of these adducts in human subjects. Our results reveal that cigarette smoking plays a major role in forming these adducted peptides which might serve as potential biomarkers for exposure to acrolein and crotonaldehyde.

Crotonaldehyde paralyzes arteries by inducing impairment of ion channels, vascular histiocytic injury, overproduction of reactive oxygen species, mitochondrial damage, and autophagy

Humans are ubiquitously exposed to crotonaldehyde (CRA) endogenously and exogenously. Deeper knowledge of the pharmacological and toxicological characteristics and the mechanisms of CRA on vasculature is urgently needed for prevention of its harmfulness. The effects of acute and prolonged exposure to CRA were studied in rat isolated arteries and arterial smooth muscle cells (ASMCs). Instant exposure to CRA (1-300 μM) concentration-dependently declined the tension of pre-constricted arteries with an irreversible depression on the contractility. Prolonged exposure of rat coronary arteries (RCAs) to CRA concentration- and time-dependently depressed the arterial contractile responsiveness to various vasoconstrictors including depolarization, U46619, serotonin and Bay K8644 (an agonist of voltage-gated Ca2+ channels (VGCCs)). In fresh RCA ASMCs, CRA abated depolarization-induced elevation of intracellular Ca2+ ([Ca2+]i). Electrophysiological study revealed that acute exposure to CRA depressed the functions of Ca2+-activated Cl- channels (CaCCs), voltage-gated K+ (Kv) channels and inward rectifier K+ (Kir) channels in RCA ASMCs. Prolonged exposure of RCAs to CRA reduced the expressions of these ion channels in RCA ASMCs, disordered tissue frames, injured arterial cells, and increased autophagosomes in both ASMCs and endothelial cells. In rat aortic smooth muscle cells (A7r5), CRA exposure decreased the cell viability, elevated the intracellular levels of reactive oxygen species, reduced the mitochondrial membrane potential, and enhanced autophagy. Taken together, the present study for the first time portrays a clearer panoramic outline of the vascular effects and the mechanisms of CRA on arteries, demonstrates that CRA impairs arterial contractility, depresses VGCCs, CaCCs, Kv channels and Kir channels, reduces cell viability, and destroys the arterial histiocytes, and suggests that excessive oxidative stress, mitochondrial dysfunction and autophagy underlie these vascular damages. These findings are significant for the comprehensive evaluation of the vicious effects of CRA on arteries and suggest potential preventive strategies.

Acrolein: formation, health hazards and its controlling by dietary polyphenols

Acrolein, a highly reactive toxic aldehyde, is a common dietary and environmental contaminant which can also be generated endogenously. Exposure to acrolein has been positively associated with some pathological conditions, such as atherosclerosis, diabetes mellitus, stroke, and Alzheimer's disease. At the cellular level, acrolein induces various harmful effects, particularly protein adduction and oxidative damages. Polyphenols are a group of secondary plant metabolites ubiquitously presented in fruits, vegetables, and herbs. Recent evidence has gradually solidified the protective role of polyphenols by working as acrolein scavengers and regulator of acrolein toxicities. This was largely attributed to the ability of polyphenols as antioxidants and sacrificial nucleophiles in trapping acrolein. This review discussed the exposure and toxicity of acrolein, summarized the known and anticipated contribution of polyphenols in ameliorating acrolein contamination and its health hazards.

Online Exploring the Gaseous Oil Fumes from Oleic Acid Thermal Oxidation by Synchrotron Radiation Photoionization Mass Spectrometry

Cooking oil fumes are an intricate and dynamic mixture containing a variety of poisonous and hazardous substances, and their real-time study remains challenging. Based on tunable synchrotron radiation photoionization mass spectrometry (SR-PIMS), isomeric/isobaric compounds in the gaseous oil fumes from oleic acid thermal oxidation were determined in real time and distinguished by photoionization efficiency (PIE) curve simulation combined with multiple linear regression (MLR) analysis. A series of common carcinogens such as formaldehyde, acetaldehyde, acrolein, and several unreported chemicals including diethyl ether and formylcyclohexane were successfully characterized. Moreover, time-resolved profiles of certain components in gaseous oil fumes were monitored for 55 h. Distinct evolutionary processes were observed, indicating the consumption and formation of parent molecules, intermediates, and final products.

Theanine in Tea: An Effective Scavenger of Single or Multiple Reactive Carbonyl Species at the Same Time

Reactive carbonyl species (RCS) are generated during thermal food processing, and their accumulation in the body increases the risk of various chronic diseases. Herein, the RCS-scavenging ability of theanine, a unique nonproteinogenic amino acid, was evaluated in terms of the scavenging rate, reaction kinetics, and reaction pathway using LC-MS/MS. Three major products of theanine conjugated with acrolein (ACR) and glyoxal (GO) were prepared and identified using nuclear magnetic resonance. Thereafter, the simultaneous reactions of four types of RCS (namely, ACR, crotonaldehyde, methylglyoxal, and GO) with theanine were discussed in RCS-theanine and RCS-tea models. Under different reaction ratios, theanine could nonspecifically scavenge the four coexisting RCS by forming adducts with them. The amount of theanine-RCS adducts in green and black tea was more than that of catechin (epigallocatechin gallate, epigallocatechin, epicatechin gallate, and epicatechin)-RCS adducts despite the lower content of theanine than catechins. Thus, theanine, as a food additive and dietary supplement, could demonstrate new bioactivity as a promising RCS scavenger in food processing.

Assessment of exposure to volatile organic compounds through urinary concentrations of their metabolites in pet dogs and cats from the United States

Volatile organic compounds (VOCs) are ubiquitous environmental pollutants, exposure to which is associated with birth defects, neurocognitive and reproductive impairments, and cancer. Little is known, however, about VOC exposure in pet dogs and cats, which represent sentinels for human exposure as well as having value as companion animals. In this study, we determined 38 VOC metabolites (VOCMs) in urine samples collected from 47 dogs and 42 cats from the Albany area of New York State. Seventeen (in cats) to twenty (in dogs) VOCMs were found at detection frequencies (DFs) above 60%. The creatinine-adjusted geometric mean (GM) concentrations of individual VOCMs ranged from 5.43 (EMA) to 761 μg/g (3HPMA) in dog urine and 0.824 (SBMA) to 278 μg/g (ATCA) in cat urine. The ∑20 VOCM concentration in dog urine was 2280 μg/g (geometric mean) and the ∑17 VOCM concentration in cat urine was 847 μg/g. Eight individual VOCMs were significantly more abundant in dog than in cat urine, and the urinary concentrations of several VOCMs in dogs were comparable to those reported for human tobacco smokers. Metabolites of acrolein accounted for 43% of ∑20 VOCM concentration in dogs, whereas those of cyanide and benzene accounted for 60% of ∑17 VOCM concentration in cats. Based on acrylamide exposure doses, calculated hazard quotients were above 1 in 77% of dogs and 50% of cats studied, and cancer risk values (using a benchmark of 10^-6) from exposure to acrylamide exceeded 1 for all dogs and cats. This is the first study to report VOCM concentrations in urine collected from pet dogs and cats and highlights the need to identify sources and health implications of VOCs exposure in these animals.

Particulate matters, aldehydes, and polycyclic aromatic hydrocarbons produced from deep-frying emissions: comparisons of three cooking oils with distinct fatty acid profiles

It is recognized that hazardous emissions produced from frying oils may be related to oil properties, particularly the fatty acid composition. However, investigations have been limited and partial. In this work, the emissions from deep-frying foods with three oils (palm, olive, and soybean oils) with distinct fatty acid profiles were comprehensively examined in a simulated kitchen, and the interrelationship among emitted substances, oil quality parameters, and fatty acids profiles was explored. Firstly, palm oil emitted the highest number concentration of total particle matters ((3895 ± 1796) × 103 #/cm3), mainly in the Aitken mode (20-100 nm). We observed a positive correlation between particle number concentration and levels of palmitic acid, a major saturated fatty acid (SAFA) (rs = 0.73, p < 0.05), and total polar compounds (TPC) (rs = 0.68, p < 0.05) in the fried oil, a degradation marker which was also positively correlated with that of black carbon (BC) (rs = 0.68, p < 0.05). Secondly, soybean oil emitted the highest level of gaseous aldehydes (3636 ± 607 μg/m3), including acrolein, propinoaldehyde, crotonaldehyde, hexanal, and trans-2-heptenal; the total aldehyde concentration were positively correlated with α-linolenic acid (ALA) percentage (rs = 0.78, p < 0.01), while hexanal and trans-2-heptenal were with linoleic acid (LA) (rs = 0.73 and 0.67, p < 0.05). LA and ALA were two major polyunsaturated fatty acids in non-tropical plant oils. Thirdly, palm oil emitted the most particle-bound polycyclic aromatic hydrocarbons (PAHs), and a positive association was discovered between two PAHs and SAFA percentage. Olive oil seems superior to soybean and palm oils with regards to toxic emissions during deep-frying.

Formation of naphthoquinones and anthraquinones by carbonyl-hydroquinone/benzoquinone reactions: A potential route for the origin of 9,10-anthraquinone in tea

The reaction of 2-alkenals (crotonaldehyde and 2-pentenal) with hydroquinones (hydroquinone and tert-butylhydroquinone) and benzoquinones (benzoquinone, methylbenzoquinone, and methoxybenzoquinone) was studied as a potential route for the endogenous formation of naphthoquinones and anthraquinones in foods. Polycyclic quinones were produced at a low water activity, within a wide pH range, and in the presence of air. 9,10-Anthraquinone formation had an activation energy of 46.1 ± 0.1 kJ·mol^-1, and a reaction pathway for the formation of the different naphthoquinones and anthraquinones is proposed. These reactions also took place in tea, therefore suggesting that the common tea pollutant 9,10-anthraquinone is also a process-induced contaminant. In fact, when four commercial teas (from a total of eight studied teas) were heated at 60 °C for 72 h, they significantly (p < 0.05) increased the amount of this toxicant. Reduction of 9,10-anthraquinone formation in teas is suggested to be carried out by reducing/scavenging its precursors.

Identification of acrolein as the reactive carbonyl responsible for the formation of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx)

Reaction mixtures of reactive carbonyls and creatinine were submitted to high temperature and studied to identify the reactive carbonyl(s) responsible for 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) formation. MeIQx was produced by reaction of acrolein and creatinine within a wide pH range and with an activation energy of 81.1 ± 1.4 kJ/mol. No additional reactants were required, although methylglyoxal, ammonia, and formaldehyde also participated in the reaction. Nevertheless, these additional reactants were produced in situ from either acrolein or creatinine. A reaction pathway that both explains the formation of MeIQx and is valid for the formation of other heterocyclic aromatic amines (HAAs) with the structure of quinoxaline is proposed. Obtained results demonstrate the key role of reactive carbonyls present in foods (the food carbonylome) on HAA formation. Because creatinine is ubiquitous in proteinaceous foods, the control of the food carbonylome seems to be the key point to control HAA formation in foods.

Identification of Precursors and Formation Pathway for the Heterocyclic Aromatic Amine 2-Amino-3-methylimidazo(4,5-f)quinoline (IQ)

Food processing is responsible for the destruction of some health hazards, but it is responsible for the formation of new ones. Among them, the formation of heterocyclic aromatic amines (HAAs) has received a considerable attention because of their carcinogenicity. In spite of this, HAA formation is still poorly understood. This study was undertaken to identify precursors and formation pathways for 2-amino-3-methylimidazo(4,5-f)quinoline (IQ). IQ was produced by reaction of acrolein, crotonaldehyde, creatinine, and ammonia. Reaction conditions were studied, and its activation energy (E_a) was determined to be 77.0 ± 1.3 kJ/mol. IQ formation was always accompanied by the formation of the HAA 2-amino-3,4-dimethylimidazo(4,5-f)quinoline (MeIQ), which was produced with an E_a of 72.2 ± 0.4 kJ/mol. A reaction pathway for the competitive formation of IQ and MeIQ is proposed. Obtained results demonstrate the significant role of reactive carbonyls (the food carbonylome) in HAA formation and provide evidences for designing HAA mitigation strategies.

Interaction of Acrylamide, Acrolein, and 5-Hydroxymethylfurfural with Amino Acids and DNA

Acrylamide, acrolein, and 5-hydroxymethylfurfural (HMF) are food-borne toxicants produced during the thermal processing of food. The α,β-unsaturated carbonyl group or aldehyde group in their structure can react easily with the amino, imino, and thiol groups in amino acids, proteins, and DNA via Michael addition and nucleophilic reactions in food and in vivo. This work reviews the interaction pathways of three toxins with amino acids and the cytotoxicity and changes after the digestion and absorption of the resulting adducts. Their interaction with DNA is also discussed. Amino acids ubiquitously exist in foods and are added as nutrients or used to control these food-borne toxicants. Hence, the interaction widely occurring in foods would greatly increase the internal exposure of these toxins and their derived compounds after food intake. This review aims to encourage further investigation on toxin-derived compounds, including their types, exposure levels, toxicities, and pharmacokinetics.

Carbonyl-Phenol Adducts: An Alternative Sink for Reactive and Potentially Toxic Lipid Oxidation Products

Different from the well-characterized function of phenolics as antioxidants, their function as lipid-derived carbonyl scavengers is mostly unknown. However, phenolics react with lipid-derived carbonyls as a function of the nucleophilicity of their reactive groups and the electronic effects and steric hindrances present in the reactive carbonyls. Furthermore, the reaction produces a wide variety of carbonyl-phenol adducts, some of which are stable and have been isolated and characterized but others polymerize spontaneously. This perspective updates present knowledge about the lipid-derived carbonyl trapping ability of phenolics, its competition with carbonyl-amine reactions produced in foods, and the presence of carbonyl-phenol adducts in food products.

Generation of Desired Aroma-Active as Well as Undesired Toxicologically Relevant Compounds during Deep-Frying of Potatoes with Different Edible Vegetable Fats and Oils

Deep-frying leads to the generation of various degradation products providing desired properties, like aroma, taste, or color, but some can have adverse effects on human health. The study investigated the influence of frying oils differing in their fatty acid compositions on the generation of desirable and undesirable compounds during deep-frying of potato chips. Selected key odorants and toxicologically relevant compounds (acrolein, acrylamide, furan, and glycidamide) were quantitated by stable isotope dilution assays. Significantly higher concentrations of (E,E)-2,4-decadienal and (E,Z)-2,4-decadienal were found in chips fried with oils rich in linoleic acid, the precursor of the 2,4-decadienals. In contrast, the amounts of Strecker aldehydes and pyrazines were similar. Oils rich in linolenic acid revealed the highest amounts of the toxicologically relevant (E)-2-alkenal acrolein, whereas oils mainly consisting of monounsaturated or saturated fatty acids led to a clearly lower amount. Acrylamide and glycidamide concentrations in chips also showed a clear dependence on the used frying medium, in contrast to furan, whose amount was more or less similar in all chips.

Toxicologically Relevant Aldehydes Produced during the Frying Process Are Trapped by Food Phenolics

The lipid-derived carbonyl trapping ability of phenolic compounds under common food processing conditions was studied by determining the presence of carbonyl-phenol adducts in both onions fried in the laboratory and commercially crispy fried onions. Four carbonyl-phenol adducts produced between quercetin and acrolein, crotonaldehyde, or (E)-2-pentenal were prepared and characterized by (1)H and (13)C nuclear magnetic resonance (NMR) spectroscopy and high performance liquid chromatography coupled to high resolution mass spectrometry (HPLC-HRMS). The synthesized compounds were 2-(3,4-dihydroxyphenyl)-3,5,8-trihydroxy-9,10-dihydro-4H,8H-pyrano[2,3-f]chromen-4-one (4), 2-(3,4-dihydroxyphenyl)-3,5,8-trihydroxy-10-methyl-9,10-dihydro-4H,8H-pyrano[2,3-f]chromen-4-one (5), 2-(3,4-dihydroxyphenyl)-3,5-dihydroxy-8-methyl-4H,8H-pyrano[2,3-f]chromen-4-one (9), and 2-(3,4-dihydroxyphenyl)-8-ethyl-3,5-dihydroxy-4H,8H-pyrano[2,3-f]chromen-4-one (10). When onions were fried in fresh rapeseed oil spiked with acrolein, crotonaldehyde, and (E)-2-pentenal (2.7 μmol/g of oil), adduct 10 was the major compound produced, and trace amounts of adducts 4 and 5, but not of adduct 9, were also detected. In contrast, compound 4 was the major adduct present in commercially crispy fried onions. Compound 10 was also present to a lower extent, and trace amounts of compound 5, but not of compound 9, were also detected. These data suggested that lipid-derived carbonyl-phenol adducts are formed in food products under standard cooking conditions. They also pointed to a possible protective role of food polyphenols, which might contribute to the removal of toxicologically relevant aldehydes produced during deep-frying, assuming that the formed products are stable during food consumption in the human organism.

Detection of 1,N(2)-propano-2'-deoxyguanosine adducts in genomic DNA by ultrahigh performance liquid chromatography-electrospray ionization-tandem mass spectrometry in combination with stable isotope dilution

Crotonaldehyde (Cro) is one of widespread and genotoxic α,β-unsaturated aldehydes and can react with the exocyclic amino group of 2'-deoxyguanosine (dG) in genomic DNA to form 1,N(2)-propano-2'-deoxyguanosine (ProdG) adducts. In this study, two diastereomers of high purity were prepared, including non-isotope and stable isotope labeled ProdG adducts, and exploited stable isotope dilution-based calibration method. By taking advantage of synthesized ProdG standards, we developed a sensitive ultrahigh performance liquid chromatography-electrospray ionization-tandem mass spectrometry (UHPLC-ESI-MS/MS) method for accurate quantification of two diastereomers of ProdG adducts. In addition to optimization of the UHPLC separation, ammonium bicarbonate (NH4HCO3) was used as additive in the mobile phase for enhancing the ionization efficiency to ProdG adducts and facilitating MS detection. The limits of detection (LODs, S/N=3) and the limits of quantification (LOQs, S/N=10) are estimated about 50 amol and 150 amol, respectively. By the use of the developed method, both diastereomers of ProdG adducts can be detected in untreated human MRC5 cells with a frequency of 2.4-3.5 adducts per 10(8) nucleotides. Crotonaldehyde treatment dramatically increases the levels of ProdG adducts in human MRC5 in a concentration-dependent manner.

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) formation and fate: an example of the coordinate contribution of lipid oxidation and Maillard reaction to the production and elimination of processing-related food toxicants

Major chemical reactions dealing with carbonyl chemistry in foods (Maillard reaction and lipid oxidation) play a role in PhIP formation and fate, pointing to this and analogous heterocyclic aromatic amines as outcomes of this chemistry.

Isotope-labeling studies on the formation pathway of acrolein during heat processing of oils

Acrolein (2-propenal) is classified as a foodborne toxicant and was shown to be present in significant amounts in heated edible oils. Up to now, its formation was mainly suggested to be from the glycerol part of triacylglycerides, although a clear influence of the unsaturation of the fatty acid moiety was also obvious in previous studies. To unequivocally clarify the role of the glycerol and the fatty acid parts in acrolein formation, two series of labeled triacylglycerides were synthesized: [(13)C(3)]-triacylglycerides of stearic, oleic, linoleic, and linolenic acid and [(13)C(54)]-triacylglycerides with labeled stearic, oleic, and linoleic acid, but with unlabeled glycerol. Heating of each of the seven intermediates singly in silicon oil and measurement of the formed amounts of labeled and unlabeled acrolein clearly proved the fatty acid backbone as the key precursor structure. Enzymatically synthesized pure linoleic acid and linolenic acid hydroperoxides were shown to be the key intermediates in acrolein formation, thus allowing the discussion of a radical-induced reaction pathway leading to the formation of the aldehyde. Surprisingly, although several oils contained high amounts of acrolein after heating, deep-fried foods themselves, such as donuts or French fries, were low in the aldehyde.