Gas chromatographic-electron impact mass spectrometric screening procedure for unknown hydroxyaldehydic lipid peroxidation products after pentafluorobenzyloxime derivatization

Formation of the mutagenic DNA lesion 1,N2-ethenoguanine induced by heated cooking oil and identification of causative agents

BACKGROUND

The DNA-damaging compounds in heated cooking oil were identified as guanosine adducts. Heated vegetable oil was subjected to deep-frying conditions at 170 °C for 45 min, reacted with isopropylidene guanosine (ipG) at pH 7.4, and the resulting compounds were separated by high-performance liquid chromatography (HPLC).

RESULTS

Two adducts, 8-hydroxy-ipG and 1,N2-etheno-ipG, were identified in the reaction mixture. One of the major components in heated cooking oil, 2,4-heptadienal (HDE), efficiently produced etheno-ipG from ipG in the presence of tBuOOH. An oxidized HDE solution was fractionated using HPLC to identify causative agents, and each fraction was tested for etheno-ipG formation. In addition to the known lipid peroxidation product, 4,5-epoxy-2-heptenal, two unknown polar components with potent etheno-ipG formation activity were discovered. Based on Mass and UV spectra, their structures were identified as 6-oxo- and 6-hydroxy-2,4-HDE. Similarly, 6-oxo- and 6-hydroxy-2,4- decadienal (DDE) were formed from 2,4-DDE. Significant amounts of 6-oxo- and 6-hydroxy-2,4-alkadienal were detected in the heated cooking oil. These compounds induced the formation of 1,N2-ethenoguanine in nucleosides and DNA, especially in the presence of tBuOOH. Moreover, the formation of 6-oxo- and 6-OH-HDE from 2,4-HDE was accelerated in the presence of hemin and tBuOOH.

CONCLUSION

The results suggest that these compounds are not only generated during the oil heating process but also produced from 2,4-alkadienal through digestion under normal physiological conditions, especially after ingesting heme- and alkyl-OOH-containing diets. Moreover, these compounds can be formed within cells under oxidative stress, potentially linking them to gastrointestinal carcinogenesis.

Chemical Penetration Enhancers Increase Hydrogen Peroxide Uptake in C. elegans for In Vivo Fast Photochemical Oxidation of Proteins

Fast photochemical oxidation of proteins (FPOP) is a hydroxyl radical protein footprinting method that covalently labels solvent-accessible amino acids by photolysis of hydrogen peroxide. Recently, we expanded the use of FPOP for in vivo (IV-FPOP) covalent labeling in C. elegans. In initial IV-FPOP studies, 545 proteins were oxidatively modified in all body systems within the worm. Here, with the use of chemical penetration enhancers (CPEs), we increased the number of modified proteins as well as the number of modifications per protein to gain more structural information. CPEs aid in the delivery of hydrogen peroxide inside C. elegans by disturbing the highly ordered lipid bilayer of the worm cuticle without affecting worm viability. IV-FPOP experiments performed using the CPE azone showed an increase in oxidatively modified proteins and peptides. This increase correlated with greater hydrogen peroxide uptake by C. elegans quantified using a chemical fluorophore demonstrating the efficacy of using CPEs with IV-FPOP. Mass spectrometry proteomics data are available via ProteomeXchange with identifier PXD019290.

Membrane Oxidation in Cell Delivery and Cell Killing Applications

Cell delivery or cell killing processes often involve the crossing or disruption of cellular membranes. We review how, by modifying the composition and properties of membranes, membrane oxidation can be exploited to enhance the delivery of macromolecular cargoes into live human cells. We also describe how membrane oxidation can be utilized to achieve efficient killing of bacteria by antimicrobial peptides. Finally, we present recent evidence highlighting how membrane oxidation is intimately engaged in natural biological processes such as antigen delivery in dendritic cells and in the killing of bacteria by antimicrobial peptides. Overall, the insights that have been recently gained in this area should facilitate the development of more effective delivery technologies and antimicrobial therapeutic approaches.

Monounsaturated fatty acids are substrates for aldehyde generation in tellurite-exposed Escherichia coli

Reactive oxygen species (ROS) damage macromolecules and cellular components in nearly all kinds of cells and often generate toxic intracellular byproducts. In this work, aldehyde generation derived from the Escherichia coli membrane oxidation as well as membrane fatty acid profiles, protein oxidation, and bacterial resistance to oxidative stress elicitors was evaluated. Studies included wild-type cells as well as cells exhibiting a modulated monounsaturated fatty acid (MUFA) ratio. The hydroxyaldehyde 4-hydroxy 2-nonenal was found to be most likely produced by E. coli, whose levels are dependent upon exposure to oxidative stress elicitors. Aldehyde amounts and markers of oxidative damage decreased upon exposure to E. coli containing low MUFA ratios, which was paralleled by a concomitant increase in resistance to ROS-generating compounds. MUFAs ratio, lipid peroxidation, and aldehyde generation were found to be directly related; that is, the lower the MUFAs ratio, the lower the peroxide and aldehyde generation levels. These results provide additional evidence about MUFAs being targets for membrane lipid oxidation and their relevance in aldehyde generation.

Structural characterization of alpha,beta-unsaturated aldehydes by GC/MS is dependent upon ionization method

alpha,beta-unsaturated aldehydes are toxic products of lipid peroxidation. Detection and characterization of these aldehydes is important in many human disease states as well as in the food industry. Our study shows that electron ionization-mass spectrometry (EI-MS) and positive-ion chemical ionization-mass spectrometry (PICI-MS), but not electron capture negative ionization-mass spectrometry (ECNI-MS), can be used to detect the C4-hydroxylation state of alpha,beta-unsaturated aldehydes derivatized with pentafluorobenzyl hydroxylamine alone. EI-MS and PICI-MS spectra of 4-hydroxy-2-alkenals contained a fragment with m/z 252, whereas spectra of 2-alkenals contained a fragment with m/z 250. These fragments are consistent with fragmentation between C3 and C4 with transfer of two hydrogens from C4 and the C4 hydroxyl group in the case of 4-hydroxy-2-alkenals. In addition, EI-MS and PICI-MS were able to distinguish 4-hydroxy-2-alkenals and 2-alkenals from 4-keto-2-alkenals and 4-hydroxyalkanals. On the other hand, ECNI-MS provided complex spectra regarding C4-hydroxylation state. Furthermore, the syn- and anti-configurations of PFB-oximes had different resultant spectra using ECNI-MS, but not with EI-MS or PICI-MS. These data indicate that EI-MS and PICI-MS are more amenable for structural analysis of alpha,beta-unsaturated aldehydes than ECNI-MS.

Critical aspects of the determination of pentafluorobenzyl derivatives of aldehydes by gas chromatography with electron-capture or mass spectrometric detection

This work presents a thorough study of some aspects critical to the quantitative performance of methods for the determination of volatile aldehydes previously derivatized to pentafluorobenzyl hydroxylamine oximes. The conclusions of the study are further applied to the validation of an optimized procedure for the determination of oxidation-related aldehydes from wine. Aspects studied include the chromatographic injection, the analytical performance of electron-capture detection (ECD) or MS detection, and the way in which the derivatization is carried out. Different injection techniques have been optimized and compared (classical splitless-hot injection; cold splitless; and large volume solvent split injection). All of them were carried out in a programmed temperature vaporization (PTV) injector, with a 350 microL internal volume liner (3.4 mm internal diameter). Classical splitless injection of hexane extracts is troublesome and requires large carrier gas flows (>10 mL min(-1)). Cold splitless injection was clearly superior. Large volume solvent split injection has been also optimized. ECD has been found to lack the necessary selectivity for the determination of unsaturated aldehydes in wine, although the quantitation of several minor aldehydes is possible. MS detection has proven to be superior for the determination of these compounds in wine. The way in which the reagent is applied is also critical and for the case of wine is important to ensure that the reagent is applied after some of the major wine aldehydes have been eliminated. The finally proposed method is extremely sensitive. Method detection limits ranged from 0.002 microg L(-1) (for unsaturated aldehydes) to 0.73 microg L(-1) (for phenylacetaldehyde) and precision (measured as relative standard deviation) is < or =6% in all cases. The method makes it possible to determine quantitatively in a single run the wine aldehydes with sensory significance (isobutyraldehyde, 2-methylbutanal, isovaleraldehyde, (E)-2-hexenal, (E)-2-heptenal, (E)-2-octenal, (E)-2-nonenal, methional and phenylacetaldehyde).

Review: derivatization in mass spectrometry-6. Formation of mixed derivatives of polyfunctional compounds

The review describes chemical transformations of multifunctional compounds (amino acids and peptides, amino alcohols, amino thiols, hydroxy acids, oxo acids, oxo alcohols, compounds containing simultaneously three or more different groups etc.) by using step-wise or one-step modification or protection of functional groups. Some chemical aspects of mixed derivatization performed for improving the physical-chemical properties and mass spectral characteristics are discussed. Application of mixed derivatization to qualitative and quantitative analysis of various multifunctional compounds mainly in biological fluids and other matrices by gas chromatography/mass spectrometry in electron ionization, chemical ionization, negative-ion chemical ionization and selected ion monitoring modes is considered.

Review: derivatization in mass spectrometry--5. Specific derivatization of monofunctional compounds

The present paper is complementary to the foregoing reviews and describes some additional methods of the derivatization of particular functional groups mainly to enhance the structural information content of electron ionization and chemical ionization mass spectra. Derivatization approaches for the modification of unsaturated compounds, alcoholic, carboxylic, carbonyl, amine and other functional groups, are discussed. Derivatization for separation and quantitative determination of chiral enantiomeric compounds is also considered. Preliminary chemical and physicalchemical degradation for structure elucidation of high molecular weight compounds (biopolymers, synthetic polymers) is mentioned. Chemical aspects of derivatizations and characteristic mass spectral features of derivatives are described briefly. Some particular applications of chemical modification, in conjunction with mass spectral measurements for the analysis of various important bioorganic compounds and compounds in biological fluids, air, environmental etc., are considered.

Fatty acid cytotoxicity to human lens epithelial cells

Data obtained with the neutral red cytotoxicity assay reveal that human lens epithelial cells in culture are highly sensitive to low micromolar concentrations of unsaturated, cis-configured fatty acids in the following order: arachidonic acid>linolenic acid=linoleic acid=oleic acid, whereas the saturated fatty acids are much less effective. Though the cytotoxic effects of the unsaturated fatty acids could not be discerned from effects of their oxidation products, the fact that oleic acid is equally cytotoxic as linoleic acid or linolenic acid as well as previously reported findings with bovine lens epithelial cells support the idea that the unsaturated fatty acid molecules directly account for the cytotoxicity and not their products of lipid peroxidation. Bleb formation and cell retraction are early morphological signs of fatty acid-induced lens cell damage. These cellular alterations are accompanied by an aggregation of intermediate filaments in a first step, whereas the disorganization of microfilaments occurs at a later time and only at higher fatty acid concentrations. Measurements of protein-, RNA- and DNA-synthesis turned out to be much less sensitive parameters for the fatty acid-induced damage of lens cells. The uptake rate of linoleic acid by human lens cells is relatively high (4.35 fmol sec(-1) per 1000 cells), 30 and 50% higher as compared with diploid human embryonal lung fibroblasts and chemically transformed mouse fibroblasts, respectively. Saturation kinetics in combination with competition between linoleic acid, oleic acid and palmitic acid on one hand and ineffectiveness of trypsin and DIDS treatment on the other hand hint at cytoplasmic fatty acid binding proteins as receptors with high binding affinity (5.55 micromol l(-1), calculated for the linoleic acid-albumin complex) to be involved in the fatty acid uptake in human lens cells. Cellular fatty acid uptake is mainly influenced by the albumin concentrations present in physiological solutions. Albumin determinations in aqueous humor from 177 cataract patients reveal an age-dependent, statistically significant albumin rise with average values below 2 micromol l(-1) up to the age of 40 years to about 4 micromol l(-1) at the age between 80 and 90 years with single values up to 10 micromol l(-1). Using physiological fatty acid mixtures it is demonstrated that fatty acid-induced lens cell damage is strongly increased by elevated albumin concentrations found in aqueous humor of the elderly, who already have cataracts. Free fatty acid induced lens cell damage as a possible cause for age-dependent cataracts as well as a molecular link between systemic diseases such as diabetes and cataract formation is discussed.

Analysis of 3'-phosphoglycolaldehyde residues in oxidized DNA by gas chromatography/negative chemical ionization/mass spectrometry

Deoxyribose oxidation in DNA represents a biologically important facet of oxidative DNA damage that gives rise to protein-DNA cross-links and base adducts. Toward the goal of quantifying deoxyribose oxidation chemistry in cells, we report a method for the quantification of 3'-phosphoglycolaldehyde (PGA) residues, which likely arise from 3'-oxidation of deoxyribose in DNA. The method exploits the aldehyde moiety in PGA by derivatization as a stable oxime with pentafluorobenzylhydroxylamine, followed by solvent extraction and gas chromatography/negative chemical ionization/mass spectrometry. A stable isotopically labeled [(13)C(2)]PGA was synthesized and used as an internal standard. The assay showed a linear response over the range of 30 fmol to 300 pmol, and its precision was verified by analysis of a synthetic, PGA-containing oligodeoxynucleotide. The limit of detection in the presence of DNA was 30 fmol per sample, corresponding to two molecules of PGA in 10(6) nucleotides for 170 microg of DNA. Samples were exposed to 0-100 Gy of (60)Co gamma-radiation, which resulted in a linear dose-response of 1.5 PGA residues per 10(6) nucleotides per Gy and a radiation chemical yield (G-value) of 0.0016 micromol/J. When compared to the total quantity of deoxyribose oxidation occurring under the same conditions (141 oxidation events per 10(6) nucleotides per Gy; determined by plasmid topoisomer analysis), PGA formation occurs in 1% of deoxyribose oxidation events. This small fraction is consistent with current models of limited solvent accessibility of the 3'-position of deoxyribose, although partitioning of 3'-chemistry could lead to other damage products that would increase the fraction of oxidation at this site in deoxyribose.

Microwave-assisted derivatization of volatile carbonyl compounds with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine

A method for the determination of carbonyl compounds, either directly from gaseous phase or following a volatilization from liquid or solid samples after trapping on Tenax TA is presented. Following solvent desorption, the carbonyls are derivatized using O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine. The reaction is accomplished in a microwave oven using closed vessels to minimize reaction time compared to conventional methodology. The solvent for the chemical reaction was selected according to the requirements of microwave energy interaction and solubility. After gas chromatographic separation of the corresponding oximes, they are detected using electron impact mass spectrometry in single ion monitoring mode. Quantification is carried out using internal standardization with 3-fluorobenzaldehyde, resulting in limits of detection in the ppm range following the calibration graph method. The optimized conditions provide for good recoveries and fast reaction rates for the volatile carbonyls studied so far.

Linoleic acid peroxidation--the dominant lipid peroxidation process in low density lipoprotein--and its relationship to chronic diseases

Modern separation and identification methods enable detailed insight in lipid peroxidation (LPO) processes. The following deductions can be made: (1) Cell injury activates enzymes: lipoxygenases generate lipid hydroperoxides (LOOHs), proteases liberate Fe ions--these two processes are prerequisites to produce radicals. (2) Radicals attack any activated CH2-group of polyunsaturated fatty acids (PUFAs) with about a similar probability. Since linoleic acid (LA) is the most abundant PUFA in mammals, its LPO products dominate. (3) LOOHs are easily reduced in biological surroundings to corresponding hydroxy acids (LOHs). LOHs derived from LA, hydroxyoctadecadienoic acids (HODEs), surmount other markers of LPO. HODEs are of high physiological relevance. (4) In some diseases characterized by inflammation or cell injury HODEs are present in low density lipoproteins (LDL) at 10-100 higher concentration, compared to LDL from healthy individuals.