Lipophilic aldehydes and related carbonyl compounds in rat and human urine

An Overview of NRF2-Activating Compounds Bearing α,β-Unsaturated Moiety and Their Antioxidant Effects

The surge of scientific interest in the discovery of Nuclear Factor Erythroid 2 (NFE2)-Related Factor 2 (NRF2)-activating molecules underscores the importance of NRF2 as a therapeutic target especially for oxidative stress. The chemical reactivity and biological activities of several bioactive compounds have been linked to the presence of α,β-unsaturated structural systems. The α,β-unsaturated carbonyl, sulfonyl and sulfinyl functional groups are reportedly the major α,β-unsaturated moieties involved in the activation of the NRF2 signaling pathway. The carbonyl, sulfonyl and sulfinyl groups are generally electron-withdrawing groups, and the presence of the α,β-unsaturated structure qualifies them as suitable electrophiles for Michael addition reaction with nucleophilic thiols of cysteine residues within the proximal negative regulator of NRF2, Kelch-like ECH-associated protein 1 (KEAP1). The physicochemical property such as good lipophilicity of these moieties is also an advantage because it ensures solubility and membrane permeability required for the activation of the cytosolic NRF2/KEAP1 system. This review provides an overview of the reaction mechanism of α,β-unsaturated moiety-bearing compounds with the NRF2/KEAP1 complex, their pharmacological properties, structural activity-relationship and their effect on antioxidant and anti-inflammatory responses. As the first of its kind, this review article offers collective and comprehensive information on NRF2-activators containing α,β-unsaturated moiety with the aim of broadening their therapeutic prospects in a wide range of oxidative stress-related diseases.

Method Validation and Characterization of the Associated Uncertainty for Malondialdehyde Quantification in Exhaled Breath Condensate

There are several methods for quantifying malondialdehyde (MDA), an oxidative stress biomarker, in exhaled breath condensate (EBC). However, due to the very diluted nature of this biological matrix, a high variability is observed at low concentrations. We aimed to optimize a 2,4-dinitrophenylhydrazine-based method using liquid chromatography coupled to tandem mass spectrometry and characterize the uncertainty associated with this method. We investigated the following parameters for the method validation: calibration linearity, limit of detection (LOD), precision, recovery, and matrix effect. The results were used to identify the main sources of uncertainty and calculating the combined uncertainty. The applicability of this method was evaluated in an ongoing epidemiological study by analyzing 164 EBC samples collected from different professional groups in subway environments. The optimized method was sensitive (LOD: 70 pg/mL), precise (inter-day variation < 19%) and accurate (recovery range: 92–106.5%). The calculated analytical uncertainty was the highest at the LOQ level and reached 23%. Although the analytical uncertainty was high at low MDA concentrations, it was significantly lower than that the observed inter-individual variability. Hence, this method performs sufficiently well and can be recommended for future use in epidemiological researches relying on between-subject differences.

Maternal Exposure to Oxidized Soybean Oil Impairs Placental Development by Modulating Nutrient Transporters in a Rat Model

INTRODUCTION

As an exogenous food contaminant, dietary oxidized lipid impairs growth and development, and triggers chronic diseases in humans or animals. This study explores the effects of soybean oil with different oxidative degree on the placental injury of gestational rats.

METHODS AND RESULTS

Thirty-two female adult rats are randomly assigned to four groups. The control group is fed the purified diet with fresh soybean oil (FSO), and the treatment groups are fed purified diets with lipid content replaced by oxidized soybean oil (OSO) at 200, 400, and 800 mEqO2 kg-1 from conception until delivery. On day 20 of gestation, OSO decreased placental and embryonic weights as the oxidative degree increased linearly and quadratically. The expression of Bax showed a linear increase, and Bcl-2 decreased as the oxidative degree increased. The expression of Fosl1 and Esx1 is linearly and quadratically decreased in OSO-treated groups than FSO group. OSO decreased the level of IL-10 but increased expression of IL-1β in placenta and plasma. OSO remarkably upregulates levels of Fatp1 and Glut1 and decreases expression of Snat2 and Glut3.

CONCLUSION

OSO aggravates placental injury by modulating nutrient transporters and apoptosis-related genes, impedes placental growth and development, and ultimately leads to the decrease of fetal weight.

Hexanal inhalation affects cognition and anxiety-like behavior in mice

Hexanal is a 6-carbon aldehyde that smells like green leaves and urine to mammals. However, its physiological effects remain unclear. In particular, the effects of hexanal inhalation on the central nervous system have not been clarified. We investigated hexanal inhalation in mice and conducted a series of behavioral experiments to examine the neuropsychological effects of hexanal. After inhaling hexanal emissions for 30 min, mice were subjected to an open field test, a hot plate test, a grip strength test, an elevated plus maze test, a Y-maze test, a tail suspension test, and a forced swim test to examine the effects of hexanal odor on mouse behavior. Compared to controls, mice that inhaled hexanal exhibited reduced anxiety-like behavior in the elevated plus maze test. In addition, mice that inhaled hexanal displayed significantly improved spatial cognitive ability in the Y-maze test. However, in some behavioral experiments there was no significant difference between control mice and mice that inhaled hexanal. The results of this study suggest that hexanal inhalation causes anxiolytic effects and improves cognitive function in mice. These findings may have implications for safety management procedures and determining the effective use of household goods containing hexanal, though further work is required.

The Antioxidant Role of Soy and Soy Foods in Human Health

Oxidative stress seems to play a role in many chronic diseases, such as cardiovascular diseases, diabetes, and some cancers. Research is always looking for effective approaches in the prevention and treatment of these pathologies with safe strategies. Given the central role of nutrition, the identification of beneficial healthy foods can be the best key to having a safe and at the same time effective approach. Soy has always aroused great scientific interest but often this attention is galvanized by the interaction with estrogen receptors and related consequences on health. However, soy, soy foods, and soy bioactive substances seem to have antioxidant properties, suggesting their role in quenching reactive oxygen species, although it was frequently mentioned but not studied in depth. The purpose of this review is to summarize the scientific evidence of the antioxidant properties of soy by identifying the human clinical trials available in the literature. A total of 58 manuscripts were individuated through the literature search for the final synthesis. Soy bioactive substances involved in redox processes appear to be multiple and their use seems promising. Other larger clinical trials with adequate standardization and adequate choice of biomarkers will fill the gap currently existing on the suggestive role of soy in antioxidant mechanisms.

The in Vivo Antioxidant Effects of (-)-Epigallocatechin-3-Gallate Consumption in Healthy Postmenopausal Women Measured by Urinary Excretion of Secondary Lipid Peroxidation Products

The present study was carried out to determine whether the consumption of epigallocatechin (EGCG), the major bioactive green tea catechin, exerts a positive effect on lowering in vivo lipid peroxidation, a measure of oxidative stress, in healthy postmenopausal women. Urinary excretion of secondary lipid peroxidation products, a measure of in vivo lipid peroxidation, was determined in 40 participants randomly assigned to consume a green tea catechin extract (843.0 ± 44.0 mg EGCG/d) or placebo capsules for 12 months. Urine samples were analyzed for individual polar and nonpolar lipophilic aldehydes and related carbonyl compounds by high-performance liquid chromatography (HPLC) at the beginning and at the end of the 12-month intervention period. Results show that two nonpolar aldehydes, nonanal and decatrienal, were both 48% lower (p < 0.005) following consumption of EGCG. These results indicate that a modest degree of in vivo antioxidant activity exists with long-term EGCG consumption, which could slightly limit oxidative damage associated with lipid peroxidation and the onset and progression of chronic diseases.

Electrochemical impedance spectroscopy measurements for determination of derivatized aldehydes in several matrices

A simple, selective and sensitive electrochemical method is described for the determination of different aldehydes at glassy carbon electrode using electrochemical impedance spectroscopy (EIS). The measurements were performed after their derivatization with 2,4-dinitrophenylhydrazine (DNPH) in acidic medium. The impedance measurements were investigated in the frequency range from 100 mHz to 100 kHz at a potential of 1.0 V versus Ag/AgCl. The Nyquist plots were modeled with a Randle's equivalent circuit. The charge transfer resistance was identified as the dependent parameter on relevant concentration of aldehydes (determined as their hydrazones). Under the optimized conditions, the linearity was established over the concentration range of 1000-0.05 μmol L^-1. The limits of detection (LODs) obtained were from 0.097 to 0.0109 μmol L^-1. Finally, the developed method has been applied to the determination of aldehydes in drinking water, orange juice and apple vinegar samples with relative standard deviations (RSDs) < 3.1% and acceptable recovery rate (around of 80%).

Chromatographic determination of low-molecular mass unsaturated aliphatic aldehydes with peroxyoxalate chemiluminescence detection after fluorescence labeling with 4-(N,N-dimethylaminosulfonyl)-7-hydrazino-2,1,3-benzoxadiazole

A highly sensitive, selective and reproducible chromatographic method is described for determination of low-molecular mass unsaturated aliphatic aldehydes in human serum. The method combines fluorescent labeling using 4-(N,N-Dimethylaminosulfonyl)-7-hydrazino-2,1,3-benzoxadiazole with peroxyoxalate chemiluminescence. The derivatives were separated on a reversed-phase column C8 isocratically using a mixture of acetonitrile and 90mM imidazole-HNO3 buffer (pH 6.4, 1:1, % v/v). The calibration ranges were: 20-420nM for methylglyoxal, 16-320nM for acrolein, 15-360nM for crotonaldehyde and 20-320nM for trans-2-hexenal. The detection limits were ranged from 4.4 to 6.5nM (88-130fmol/injection), the recovery results were within the range of 87.4-103.8% and the intra and inter-day precision results were lower than 5.5%. The proposed validated method has been successfully applied to healthy, diabetic and rheumatic arthritis patients' sera with simple pretreatment method. In conclusion, this new method is suitable for routine analysis of large numbers of clinical samples for assessment of the oxidative stress state in patients.

Effect of high stearic acid containing fat on markers forin vivolipid peroxidation

The objective of this study was to determine the effect of high stearic acid (SA) diets versus high polyunsaturated fatty acid (PUFA) diets on several measures of lipid peroxidation in vivo. Sprague-Dawley rats were fed diets that differed only in the fat source (8% by weight) for 19 weeks. High SA fats were beef tallow (BT) and cocoa butter (CB), high PUFA fats were soybean oil (SO) and menhaden oil (MO). Urine was analyzed for lipophilic aldehydes, the secondary products of lipid peroxidation, by HPLC. Decreases (P<0.05) were found for 4 nonpolar lipophilic aldehydes and related carbonyl compounds (NPC) and 4 polar lipophilic aldehydes and related carbonyl compounds (PC) when the BT-fed group was compared to the SO-fed group. Decreases were also found to be significant for total NPC (P<0.01) and total PC (P<0.05) between BT and SO-fed groups. Serum increase in resistance to oxidation (P<0.01) was found in the BT group when compared to the SO group. The differences in urine and serum measurements in the present experiment indicate lower level of lipid peroxidation in vivo due to the consumption of high SA containing BT diet compared to high PUFA containing SO diet without raising serum triglycerides and cholesterol levels significantly for the BT-fed groups.

Quantification of pentafluorobenzyl oxime derivatives of long chain aldehydes by GC-MS analysis

Negative ion mass spectrometric techniques, for compounds having good ionization properties, such as pentafluorobenzyl derivatives, are believed to be more sensitive than positive ion methods. Preparation of PFB oximes of fatty aldehydes from crude lipid extracts is problematic due to the release of free aldehydes from plasmalogens during derivatization. Accordingly, in these studies plasmalogens were removed by silicic acid column chromatography prior to pentafluorobenzyl derivatization. This simple purification step to remove plasmalogens is shown to facilitate the quantification of long-chain aldehydes by analysis of their pentafluorobenzyl oxime derivatives utilizing gas chromatography-mass spectrometry in the negative ion chemical ionization mode. The limit of detection for long chain fatty aldehydes using this method is 0.5 pmol and it is linear over two orders of magnitude. Silicic acid column chromatography followed by electrospray ionization mass spectrometry demonstrated that plasmalogens were removed (the detection limit for this analyses was <or=0.3 pmol). Furthermore, we have exploited the utility and sensitivity of this method to identify increases in hexadecanal and octadecanal in 3-amino-1,2,4-triazole treated human neutrophils.

Detection of primary and secondary oxidation products by Fourier transform infrared spectroscopy (FTIR) and 1H nuclear magnetic resonance (NMR) in sunflower oil during storage

The oxidation of sunflower oil, stored in closed receptacles at room temperature for a period of 10 years, was monitored using Fourier transform infrared spectroscopy (FTIR) and 1H nuclear magnetic resonance (NMR). The objective was to understand the evolution of the oxidation process in sunflower oil under the conditions above mentioned. These techniques provide information about the oxidative status of several oil samples and the primary and some of the secondary oxidation products formed in the oxidation process. The results obtained show that, under these conditions, sunflower oxidation takes place in a different way to that at higher temperatures with aeration. The 1H NMR spectra show that in the first oxidation stages of the process only hydroperoxides supporting cis, trans-conjugated double bonds are formed and that at more advanced stages hydroperoxides having trans, trans-conjugated double bonds are generated, with the latter always being in a smaller proportion than the former. In addition, the presence of hydroxy derivatives supporting cis, trans-conjugated double bonds among the primary oxidation compounds is shown for the first time. Also, from early oxidation stages onward and unlike the process at 70 degrees C with aeration, it is noticeable that 4-hydroxy- trans-2-alkenals are formed in much higher proportions than 4-hydroperoxy- trans-2-alkenals. This fact could be associated with the presence of hydroxy derivatives with cis, trans-conjugated double bonds among the primary oxidation products and the limited concentration of oxygen during the oxidation. Furthermore, relationships between some oxidation conditions and the oxidation level of the samples were statistically analyzed.

Urinalysis of 4-hydroxynonenal, a marker of oxidative stress, using stir bar sorptive extraction–thermal desorption–gas chromatography/mass spectrometry

A simple and fast method for the measurement of 4-hydroxynonenal (4HNE), a highly toxic end-product of lipid peroxidation, in urine samples is described. The method combines stir bar sorptive extraction (SBSE) with two derivatization steps, followed by thermal desorption and GC/MS. 4HNE is derivatized in situ with O-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine and the oxime is extracted from the aqueous phase with SBSE. The 4HNE-oxime is further acylated by headspace derivatization prior to thermal desorption. Derivatization reactions and extraction were optimized in terms of reagent quantities, temperature and time. The method is linear over a concentration range of 0.5-5 ng mL(-1) with a correlation coefficient of 0.997. The limit of detection and limit of quantitation are 22 and 75 pg mL(-1) urine, respectively. The high sensitivity of the method allows the measurement of physiological concentrations of 4HNE in urine samples.

New method for HPLC separation and fluorescence detection of malonaldehyde in normal human plasma

A new method for the detection of free and total malonaldehyde (MDA) in human plasma samples based on the derivatization of MDA with 9-fluorenylmethoxycarbonyl hydrazine (FMOC-hydrazine) in an acidic medium was developed. Derivatization was achieved after 4 h at 50 degrees C. The derivatized samples were analyzed by HPLC using a reversed-phase C18 column with fluorescence detection (Ex=270 nm, Em=310 nm). The benefit of this direct injection of deproteinized plasma is to avoid the use of an internal standard. The detection limit was 0.1 pmol (4.0 nmol/L). The recovery of MDA spiked in different human plasma samples was 95.3% (n=25; R.S.D. 5.1%) for the hydrolysation procedure. The total and free MDA in plasma of 15 healthy male volunteers are 426+/-29.8 nmol/L and 153+/-9.6 nmol/L, respectively.

Identification of linoleic acid free radicals and other breakdown products using spin trapping with liquid chromatography-electrospray tandem mass spectrometry

Linoleic acid radical products formed by radical reaction (Fenton conditions) were trapped using 5,5-dimethyl-1-pyrrolidine-N-oxide (DMPO) and analysed by reversed-phase liquid chromatography coupled to electrospray mass spectrometry (LC-MS). The linoleic acid radical species detected as DMPO spin adducts comprised oxidized linoleic acid and short-chain radical species that resulted from the breakdown of carbon and oxygen centred radicals. Based on the m/z values, the short-chain products were identified as alkyl and carboxylic acid DMPO radical adducts that exhibited different elution times. The ions identified as DMPO radical adducts were studied by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The LC-MS/MS spectra of linoleic acid DMPO radical adducts exhibited the fragment ion at m/z 114 and/or the loss of neutral molecule of 113 Da (DMPO) or 131 Da (DMPO + H2O), indicated to be DMPO adducts. The short-chain products identified allowed inference of the radical oxidation along the linoleic acid chain by abstraction of hydrogen atoms in carbon atoms ranging from C-8 to C-14. Other ions containing the fragment ion at m/z 114 in the LC-MS/MS spectra were attributed to DMPO adducts of unsaturated aldehydes, hydroxy-aldehydes and oxocarboxylic acids. The identification of aldehydic products formed by radical oxidation of linoleic acid peroxidation products, as short-chain product DMPO adducts, is a means of identifying lipid peroxidation products.

Exposure to hexanal odor induces extraordinary Fos expression in the medial preoptic area and amygdala of Fyn tyrosine kinase-deficient mice

Our previous study revealed that the odor of hexanal, which is derived from the wood chips used as bedding, influenced mouse maternal behavior and induced the neonatal death of Fyn-deficient (fyn(-/-)) pups born of fyn(-/-) parents. To clarify what regions of the brain are involved in this effect, we examined which brain regions of fyn(-/-) and Fyn-heterozygous (fyn(+/-)) females were activated by hexanal odor using Fos immunohistochemistry. Hexanal induced Fos immunoreactivity in the primary olfactory cortex and in the medial and central amygdala of both fyn(+/-) and fyn(-/-) mice. In fyn(-/-) females, hexanal also induced the activation of the medial preoptic area and the basolateral and posteriomedial cortical amygdala, which are known to be involved in the control of maternal and emotional behavior.

Exposure to hexanal odor influences maternal behavior and induces neonatal death in Fyn tyrosine kinase-deficient mice

Fyn-deficient pups born of Fyn-deficient parents die because they fail to suckle within 1-2 days after birth. Here we demonstrate that the neonatal death phenotype was influenced by the genetic background and an environmental odor. The odor of hexanal (C6-aldehyde) partially impaired mouse maternal behavior and induced the neonatal death of Fyn-deficient pups born of Fyn-deficient parents. This death phenotype was first observed in the breeding environment using autoclaved chips of Douglas fir. An analysis of the volatile chemicals in the autoclaved chips revealed an approximately 10-fold greater amount of hexanal than in non-autoclaved chips. Hexanal influenced the length of time virgin female mice engage in the maternal crouching behavior. In addition, Fyn-deficient females exhibited defects in the maternal behavior of nest building and pup retrieval, regardless of exposure to hexanal. These observations provide new insights into the regulation of maternal behavior by environmental and genetic factors.

Measurement by reversed-phase high-performance liquid chromatography of malondialdehyde in normal human urine following derivatisation with 2,4-dinitrophenylhydrazine

A selective and sensitive method based on derivatisation with 2,4-dinitrophenylhydrazine (DNPH) and consecutive HPLC gradient separation is described for the determination of malondialdehyde (MDA) in urine. Preparation of urine samples involved a one-step derivatisation/extraction procedure. Separation was achieved using a Waters SymmetryC(18) column (3.9 x 150 mm) and linear gradient of acetonitrile in water (from 30% to 70% in 30 min). The overall detection limit of the method was 56 nM of MDA in urine. The recovery of MDA was 94.3+/-8.6%. MDA in urine of healthy volunteers, measured using the method of standard additions, was 0.019+/-0.012 microM/mmol creatinine. MDA in the same samples measured using the 2-thiobarbituric acid (TBA) assay was 0.181+/-0.063 microM/mmol creatinine. We demonstrate that the commonly used TBA assay in conjunction with HPLC may overestimate the MDA concentration in human urine by almost 10-fold.

Spontaneous urinary chemiluminescence and diet. An intervention study in humans

Spontaneous urinary visible chemiluminiscence has been measured in samples from a diet intervention study in humans. For a month, two groups, each of 21 male volunteers, received either a Mediterranean-type diet or an occidental (high-fat) diet. Urinary chemiluminescence levels (in 10(3) cpm) were 8.5 +/- 3.1 and 6.0 +/- 2.0 for the high-fat and Mediterranean-type diets, respectively. The differences obtained were statistically significant. These results reflect differences in the oxidative stress associate to both diets and support the proposal that spontaneous urinary chemiluminiscence constitutes a complementary index of systemic oxidative stress.

Urinary aldehydes as indicators of lipid peroxidation in vivo

The excretion of malondialdehyde (MDA), lipophilic aldehydes and related carbonyl compounds in rat and human urine was investigated. MDA was found to be excreted mainly in the form of two adducts with lysine, indicating that its predominant reaction in vivo is with the lysine residues of proteins. Adducts with the phospholipid bases serine and ethanolamine and the nucleic acid bases guanine and deoxyguanosine also were found. Except for the adduct with deoxyguanosine (dG-MDA), the excretion of these compounds increased with peroxidative stress imposed in the form of vitamin E deficiency or the administration of iron or carbon tetrachloride. Marked differences in the concentration of dG-MDA in different tissues were correlated with their content of fatty acids having three or more double bonds, the putative source of MDA. Fourteen nonpolar and eleven polar lipophilic aldehydes and other carbonyl compounds were identified as their 2,4-diphenylhydrazine derivatives in rat urine. The excretion of five nonpolar and nine polar compounds was increased under conditions of peroxidative stress. The profile of lipophilic aldehydes obtained for human urine resembled that for rat urine. Except for a reported 4-hydroxynon-2-enal conjugate with mercapturic acid, the conjugated forms of the lipophilic aldehydes excreted in urine remain unidentified. Aldehyde excretion is influenced by numerous factors that affect the formation of lipid peroxides in vivo such as energy status, physical activity and environmental temperature, as well as by wide variations in the intake of peroxides in the diet. Consequently, urinalysis for aldehydic products of lipid peroxidation is an unreliable indicator of the general state of peroxidative stress in vivo.

Vitamin E and probucol reduce urinary lipophilic aldehydes and renal enlargement in streptozotocin-induced diabetic rats

Diabetes mellitus is characterized by complications affecting several organs, including the kidney. Lipid peroxidation increases in diabetes and has been implicated in the pathogenesis of diabetic complications. In this study, we examined the ability of two antioxidants, vitamin E and probucol, to reduce lipid peroxidation in vivo and renal hypertrophy, an early stage of diabetic nephropathy, in rats. Animals were divided into four groups: non-diabetic, diabetic, diabetic treated with vitamin E, and diabetic treated with probucol. Animals were given antioxidants by intraperitoneal injection after induction of diabetes by streptozotocin injection. After 7 wk, lipid peroxidation in vivo was measured by analyzing urinary excretion of lipophilic aldehydes and related carbonyl compounds (LACC) as 2,4-dinitrophenylhydrazones by high-performance liquid chromatography. A number of urinary lipophilic nonpolar and polar aldehydes and related carbonyl compounds were identified, almost all of which increased in diabetes. Antioxidant treatment resulted in significantly decreased excretion of urinary LACC excretion. Antioxidant treatment of diabetic rats reduced renal hypertrophy. There was a high correlation between kidney weight and urinary LACC. Since LACC are accepted markers of lipid peroxidation, these results indicate that antioxidants can reduce the elevated lipid peroxidation of diabetes and may slow the onset of diabetic nephropathy.

Response of urinary lipophilic aldehydes and related carbonyl compounds to factors that stimulate lipid peroxidation in vivo

Peroxidation of lipids results in the formation of a number of aldehydic and other carbonyl-containing secondary degradation products. The effect of peroxidative stimuli mediated by vitamin E deficiency, a diet high in polyunsaturated fatty acids (containing cod liver oil), and carbon tetrachloride administration on urinary excretion of a number of lipophilic aldehydes and related carbonyl compounds was examined in rats. These secondary lipid peroxidation products were measured as 2,4-dinitrophenylhydrazine derivatives. All three treatments increased urinary excretion of secondary lipid peroxidation products, although the pattern of excretion of these products varied somewhat among the treatments. Significant increases were found in butanal, hexanal, octanal, butan-2-one, pentan-2-one, hex-2-enal, hepta-2,4-dienal, 4-hydroxyhex-2-enal, 4-hydroxyoct-2-enal, 4-hydroxynon-2-enal, and a number of unidentified carbonyl compounds. These results suggest that urinary excretion of these lipophilic secondary lipid peroxidation products is a useful and noninvasive marker of whole-body lipid peroxidation.