Determination of 4-hydroxynonenal by high-performance liquid chromatography with electrochemical detection

Electrochemical approaches based on micro- and nanomaterials for diagnosing oxidative stress

This review article comprehensively discusses the various electrochemical approaches for measuring and detecting oxidative stress biomarkers and enzymes, particularly reactive oxygen/nitrogen species, highly reactive chemical molecules, which are the byproducts of normal aerobic metabolism and can oxidize cellular components such as DNA, lipids, and proteins. First, we address the latest research on the electrochemical determination of reactive oxygen species generating enzymes, followed by detection of oxidative stress biomarkers, and final determination of total antioxidant activity (endogenous and exogenous). Most electrochemical sensing platforms exploited the unique properties of micro- and nanomaterials such as carbon nanomaterials, metal or metal oxide nanoparticles (NPs), conductive polymers and metal-nano compounds, which have been mainly used for enhancing the electrocatalytic response of sensors/biosensors. The performance of the electroanalytical devices commonly measured by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) in terms of detection limit, sensitivity, and linear range of detection is also discussed. This article provides a comprehensive review of electrode fabrication, characterization and evaluation of their performances, which are assisting to design and manufacture an appropriate electrochemical (bio)sensor for medical and clinical applications. The key points such as accessibility, affordability, rapidity, low cost, and high sensitivity of the electrochemical sensing devices are also highlighted for the diagnosis of oxidative stress. Overall, this review brings a timely discussion on past and current approaches for developing electrochemical sensors and biosensors mainly based on micro and nanomaterials for the diagnosis of oxidative stress.

Biomarkers of oxidative stress and reproductive complications

Oxidative stress is the result of an imbalance between the formation of reactive oxygen species (ROS) and the levels of enzymatic and non-enzymatic antioxidants. The assessment of biological redox status is performed by the use of oxidative stress biomarkers. An oxidative stress biomarker is defined as any physical structure or process or chemical compound that can be assessed in a living being (in vivo) or in solid or fluid parts thereof (in vitro), the determination of which is a reproducible and reliable indicator of oxidative stress. The use of oxidative stress biomarkers allows early identification of the risk of developing diseases associated with this process and also opens up possibilities for new treatments. At the end of the last century, interest in oxidative stress biomarkers began to grow, due to evidence of the association between the generation of free radicals and various pathologies. Up to now, a significant number of studies have been carried out to identify and apply different oxidative stress biomarkers in clinical practice. Among the most important oxidative stress biomarkers, it can be mentioned the products of oxidative modifications of lipids, proteins, nucleic acids, and uric acid as well as the measurement of the total antioxidant capacity of fluids in the human body. In this review, we aim to present recent advances and current knowledge on the main biomarkers of oxidative stress, including the discovery of new biomarkers, with emphasis on the various reproductive complications associated with variations in oxidative stress levels.

Novel sample treatment method for the determination of free (E)-4-hydroxy-2-nonenal in meat products by liquid chromatography/tandem mass spectrometry using 4-hydroxy-2-nonenal-d3 as internal standard

RATIONALE

(E)-4-Hydroxy-2-nonenal (HNE) is a reactive secondary product of lipid oxidation with biological significance. The analysis of HNE is a challenge due to its volatility and high activity. Developing sample preparation and analytical tools for the determination of free HNE is crucial for better understanding the actual level of free HNE in meat products.

METHODS

Liquid nitrogen freezing, subzero-temperature extraction and derivatization were employed for meat sample treatment. Liquid chromatography/tandem mass spectrometry with electrospray ionization in negative ion mode was used for the determination of free HNE after isotope-coded derivatization.

RESULTS

High repeatability and good recoveries with a limit of quantification as low as 0.25 pmol/g were found. Nineteen out of 24 samples, including chilled/processed meat products and meat-based instant foods, were found to contain free HNE with a range of 0.014-1.160 nmol/g.

CONCLUSIONS

The proposed method showed satisfactory reliability, sensitivity and accuracy. We believe that such a sample preparation strategy will provide a powerful tool for better understanding the actual level of free HNE in meat products.

4-hydroxy-2-alkenals in foods: a review on risk assessment, analytical methods, formation, occurrence, mitigation and future challenges

Undoubtedly, significant advances were performed concerning 4-hydroxy-2-alkenals research on foods, and their formation by double oxidation of polyunsaturated fatty acids. But further studies are still needed, especially on their occurrence in foods enriched with n-3 and n-6 fatty acids, as well as in foods for infants and processed foods. Major factors concerning the formation of 4-hydroxy-2-alkenals were discussed, namely the influence of fatty acids composition, time/temperature, processing conditions, salt, among others. Regarding mitigation, the most effective strategies are adding phenolic extracts to foods matrices, as well as other antioxidants, such as vitamin E. Exposure assessment studies revealed 4-hydroxy-2-alkenals values that could not be considered a risk for human health. However, these toxic compounds remain unaltered after digestion and can easily reach the systemic circulation. Therefore, it is crucial to develop in vivo research, with the inclusion of the colon phase, as well as, cell membranes of the intestinal epithelium. In conclusion, according to our review it is possible to eliminate or effectively decrease 4-hydroxy-2-alkenals in foods using simple and economic practices.

Mechanisms of the pH- and Oxygen-Dependent Oxidation Activities of Artesunate

Artemisinin was discovered in 1971 as a constituent of the wormwood genus plant (Artemisia annua). This plant has been used as an herbal medicine to treat malaria since ancient times. The compound artemisinin has a sesquiterpene lactone bearing a peroxide group that offers its biological activity. In addition to anti-malarial activity, artemisinin derivatives have been reported to exert antitumor activity in cancer cells, and have attracted attention as potential anti-cancer drugs. Mechanisms that might explain the antitumor activities of artemisinin derivatives reportedly induction of apoptosis, angiogenesis inhibitory effects, inhibition of hypoxia-inducible factor-1α (HIF-1α) activation, and direct DNA injury. Reactive oxygen species (ROS) generation is involved in many cases. However, little is known about the mechanism of ROS formation from artemisinin derivatives and what types of ROS are produced. Therefore, we investigated the iron-induced ROS formation mechanism by using artesunate, a water-soluble artemisinin derivative, which is thought to be the underlying mechanism involved in artesunate-mediated cell death. The ROS generated by the coexistence of iron(II), artesunate, and molecular oxygen was a hydroxyl radical or hydroxyl radical-like ROS. Artesunate can reduce iron(III) to iron(II), which enables generation of ROS irrespective of the iron valence. We found that reduction from iron(III) to iron(II) was activated in the acidic rather than the neutral region and was proportional to the hydrogen ion concentration.

Enzymatic and non-enzymatic detoxification of 4-hydroxynonenal: Methodological aspects and biological consequences

4-Hydroxynonenal (HNE), an electrophilic end-product deriving from lipid peroxidation, undergoes a heterogeneous set of biotransformations including enzymatic and non-enzymatic reactions. The former mostly involve red-ox reactions on the HNE oxygenated functions (phase I metabolism) and GSH conjugations (phase II) while the latter are due to the HNE capacity to spontaneously condense with nucleophilic sites within endogenous molecules such as proteins, nucleic acids and phospholipids. The overall metabolic fate of HNE has recently attracted great interest not only because it clearly determines the HNE disposal, but especially because the generated metabolites and adducts are not inactive molecules (as initially believed) but show biological activities even more pronounced than those of the parent compound as exemplified by potent pro-inflammatory stimulus induced by GSH conjugates. Similarly, several studies revealed that the non-enzymatic reactions, initially considered as damaging processes randomly involving all endogenous nucleophilic reactants, are in fact quite selective in terms of both reactivity of the nucleophilic sites and stability of the generated adducts. Even though many formed adducts retain the expected toxic consequences, some adducts exhibit well-defined beneficial roles as documented by the protective effects of sublethal concentrations of HNE against toxic concentrations of HNE. Clearly, future investigations are required to gain a more detailed understanding of the metabolic fate of HNE as well as to identify novel targets involved in the biological activity of the HNE metabolites. These studies are and will be permitted by the continuous progress in the analytical methods for the identification and quantitation of novel HNE metabolites as well as for proteomic analyses able to offer a comprehensive picture of the HNE-induced adducted targets. On these grounds, the present review will focus on the major enzymatic and non-enzymatic HNE biotransformations discussing both the molecular mechanisms involved and the biological effects elicited. The review will also describe the most important analytical enhancements that have permitted the here discussed advancements in our understanding of the HNE metabolic fate and which will permit in a near future an even better knowledge of this enigmatic molecule.

Measurement and Clinical Significance of Biomarkers of Oxidative Stress in Humans

Oxidative stress is the result of the imbalance between reactive oxygen species (ROS) formation and enzymatic and nonenzymatic antioxidants. Biomarkers of oxidative stress are relevant in the evaluation of the disease status and of the health-enhancing effects of antioxidants. We aim to discuss the major methodological bias of methods used for the evaluation of oxidative stress in humans. There is a lack of consensus concerning the validation, standardization, and reproducibility of methods for the measurement of the following: (1) ROS in leukocytes and platelets by flow cytometry, (2) markers based on ROS-induced modifications of lipids, DNA, and proteins, (3) enzymatic players of redox status, and (4) total antioxidant capacity of human body fluids. It has been suggested that the bias of each method could be overcome by using indexes of oxidative stress that include more than one marker. However, the choice of the markers considered in the global index should be dictated by the aim of the study and its design, as well as by the clinical relevance in the selected subjects. In conclusion, the clinical significance of biomarkers of oxidative stress in humans must come from a critical analysis of the markers that should give an overall index of redox status in particular conditions.

The Oxidative and Inflammatory State in Patients with Acute Renal Graft Dysfunction Treated with Tacrolimus

Objective. To determine the oxidative stress/inflammation behavior in patients with/without acute graft dysfunction (AGD) with Tacrolimus. Methods. Cross-sectional study, in renal transplant (RT) recipients (1-yr follow-up). Patients with AGD and without AGD were included. Serum IL-6, TNF-α, 8-isoprostanes (8-IP), and Nitric Oxide (NO) were determined by ELISA; C-reactive protein (CRP) was determined by nephelometry; lipid peroxidation products (LPO) and superoxide dismutase (SOD) were determined by colorimetry. Results. The AGD presentation was at 5.09 ± 3.07 versus 8.27 ± 3.78 months (p < 0.001); CRP >3.19 mg/L was found in 21 versus 19 in the N-AGD group (p = 0.83); TNF-α 145.53 ± 18.87 pg/mL versus 125.54 ± 15.92 pg/mL in N-AGD (p = 0.64); IL-6 2110.69 ± 350.97 pg/mL versus 1933.42 ± 235.38 pg/mL in N-AGD (p = 0.13). The LPO were higher in AGD (p = 0.014): 4.10 ± 0.69 µM versus 2.41 ± 0.29 µM; also levels of 8-IP were higher in AGD 27.47 ± 9.28 pg/mL versus 8.64 ± 1.54 pg/mL (p = 0.01). Serum levels of NO in AGD were lower 138.44 ± 19.20 µmol/L versus 190.57 ± 22.04 µmol/L in N-AGD (p = 0.042); antioxidant enzyme SOD activity was significantly diminished in AGD with 9.75 ± 0.52 U/mL versus 11.69 ± 0.55 U/mL in N-AGD (p = 0.012). Discussion. Patients with RT present with a similar state of the proinflammatory cytokines whether or not they have AGD. The patients with AGD showed deregulation of the oxidative state with increased LPO and 8-IP and decreased NO and SOD.

Effect of Bleeding on Hemoglobin Contents and Lipid Oxidation in the Skipjack Muscle

Skipjack samples were prepared using two different killing methods, namely, struggling death in iced sea water (control) and instant death by mechanical bleeding. The hemoglobin content in the bled muscles was significantly lower than that in the control. 4-Hydroxyhexenal content in the bled muscles was significantly lower than that in the control over 2 d of storage at 0 degrees C.

Effects of NaCl on 4-Hydroxy-2-hexenal Formation in Yellowtail Meat Stored at 0 °C

Changes in the 4-hydroxy-2-hexenal (HHE) and malonaldehyde (MA) contents were investigated in the meat of the yellowtail Seriola quinqueradiate containing 0, 0.3, 0.6, and 0.9 M NaCl stored at 0 degrees C for 7 days. After 7 days of storage, the HHE content was significantly lower and the MA content significantly higher in the meat containing NaCl than in the control without NaCl.

Oxidative stress and neurodegenerative disorders

Living cells continually generate reactive oxygen species (ROS) through the respiratory chain during energetic metabolism. ROS at low or moderate concentration can play important physiological roles. However, an excessive amount of ROS under oxidative stress would be extremely deleterious. The central nervous system (CNS) is particularly vulnerable to oxidative stress due to its high oxygen consumption, weakly antioxidative systems and the terminal-differentiation characteristic of neurons. Thus, oxidative stress elicits various neurodegenerative diseases. In addition, chemotherapy could result in severe side effects on the CNS and peripheral nervous system (PNS) of cancer patients, and a growing body of evidence demonstrates the involvement of ROS in drug-induced neurotoxicities as well. Therefore, development of antioxidants as neuroprotective drugs is a potentially beneficial strategy for clinical therapy. In this review, we summarize the source, balance maintenance and physiologic functions of ROS, oxidative stress and its toxic mechanisms underlying a number of neurodegenerative diseases, and the possible involvement of ROS in chemotherapy-induced toxicity to the CNS and PNS. We ultimately assess the value for antioxidants as neuroprotective drugs and provide our comments on the unmet needs.

Aldehyde reactivity with 2-thiobarbituric acid and TBARS in freeze-dried beef during accelerated storage

When lipid oxidation is evaluated in freeze-dried beef, a yellow 450-nm-absorbing pigment develops during the 2-thiobarbituric acid (TBA) assay. TBA analysis and high performance liquid chromatography (HPLC) were applied to measure oxidative changes in salted freeze-dried beef patties (15% fat) initially during storage at 49°C. The TBA pink pigment (λ(max)=532 nm) was most pronounced in unstored salted freeze-dried beef, and yellow pigment (λ(max)=450 nm) predominated in stored samples. An in vitro study of TBA reactivity of different aldehydes, known to be secondary lipid oxidation products, showed that alkanals and alk-2-enals favored TBARS(450) formation, while alka-2,4-dienals favored TBARS(532). Values of TBARS(450) from 95°C TBA incubation were lower than those from 25°C incubation (P<0.05), indicating that the yellow chromophore from the aldehyde-TBA complex was less thermally stable than the pink pigment. 5-Hydroxymethyl-2-furfural, an aldehyde produced from Maillard reaction, also produced strong TBARS(450). Propional, butanal and 5-hydroxymethyl-2-furfural (HMF), were tentatively identified in freeze-dried beef during accelerated storage at 49°C, and have the potential to yield TBARS @450.

Shotgun lipidomics analysis of 4-hydroxyalkenal species directly from lipid extracts after one-step in situ derivatization

4-Hydroxyalkenal species are a class of peroxidative products of polyunsaturated fatty acids, which serve as "toxic second messengers" in cellular systems. Investigation of their cellular role is hindered due to the lack of sensitive, reliable, robust method for identification and quantification of these metastable metabolites. Herein, we explored the facile Michael adduct of carnosine with 4-hydroxyalkenal species and developed a sensitive, facile, shotgun lipidomics-based method for quantification of these compounds directly from organic solvent lipid extracts of biological samples. In the study, we extensively examined the factors that may affect the accurate quantification of 4-hydroxyalkenal species and found that this method possessed high reproducibility (<8%) and nearly 3 orders of linear dynamic range with a limit of quantification at lower than 0.56 fmol/μL. Mass levels of 4-hydroxyalkenal species in various biological samples, including mouse heart, kidney, liver, and skeletal muscle, were determined by this developing method. In addition, the effects of sample collection methods and sample storage time on 4-hydroxyalkenal mass levels were also determined. We believe that development of this novel methodology should provide a powerful tool for us to better understand the role of 4-hydroxyalkenal species in biological processes.

The determination of glutathione-4-hydroxynonenal (GSHNE), E-4-hydroxynonenal (HNE), and E-1-hydroxynon-2-en-4-one (HNO) in mouse liver tissue by LC-ESI-MS

Glutathione (GSH) conjugation of 4-hydroxy-2(E)-nonenal (HNE) is an efficient means of cellular detoxification. HNE is a byproduct of lipid peroxidation which has shown toxicity but also signaling roles. E-1-hydroxynon-2-en-4-one (HNO) is another byproduct of lipid peroxidation which has the same molecular weight as HNE. This study presents the LC-MS detection of GS-HNE, HNE, and HNO in tissue samples without derivatization and with minimal sample preparation. Tissue samples were taken from wild-type mice and knock-out mice, which have been bred without the RLIP76 transfer protein. Extraction procedures were developed to determine GS-HNE and HNE levels in the mouse liver tissue. A gradient elution LC-MS method was developed for GS-HNE analysis using electrospray ionization and selected ion monitoring (SIM). The HNE/HNO method involves isocratic elution due to instability issues. Higher levels of GSHNE, HNE, and HNO were found in the knock-out animals, due to the absence of the RLIP76 transport mechanism.

Effect of NaCl on the lipid peroxidation-derived aldehyde, 4-hydroxy-2-nonenal, formation in boiled pork

Pork was boiled at 100 degrees C for 5, 10 and 15 min and stored at 0 degrees C, and changes in the 4-hydroxynonenal (HNE), malonaldehyde (MA) and fatty acid (FA) contents were analyzed immediately and 3 days later. The HNE, MA and FA contents in all samples were not significantly different from each other. Pork samples containing none (control), 1% and 2% NaCl were boiled at 100 degrees C for 5 min and stored at 0 degrees C, and changes in the HNE, MA and FA contents and cooking yields were immediately analyzed and after 0, 1, 2 and 3 days. Cooking losses in the NaCl-containing samples were significantly lower than those of the control. The HNE contents in the control samples of boiled pork had significantly increased after 3 days of storage, while the contents in the NaCl-containing samples were significantly lower than those of the control after 1, 2 and 3 days of storage. The MA contents in all samples were not significantly different from each other. All FA contents analyzed had decreased in all samples after 3 days of storage. The decrease ratio of highly unsaturated fatty acids was lowest in the sample containing 2% NaCl.

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.

Time-dependent effect of p-aminophenol (PAP) toxicity in renal slices and development of oxidative stress

p-Aminophenol (PAP), a metabolite of acetaminophen, is nephrotoxic. This study investigated PAP-mediated changes as a function of time that occur prior to loss of membrane integrity. Experiments further evaluated the development of oxidative stress by PAP. Renal slices from male Fischer 344 (F344) rats (N = 4-6) were exposed to 0.1, 0.25, and 0.5 mM PAP for 15-120 min under oxygen and constant shaking at 37 degrees C. Pyruvate-stimulated gluconeogenesis, adenine nucleotide levels, and total glutathione (GSH) levels were diminished in a concentration- and time-dependent manner prior to detection of a rise in lactate dehydrogenase (LDH) leakage. Glutathione disulfide (GSSG) levels were increased by PAP suggesting the induction of oxidative stress. Western blot analysis confirmed a rise in 4-hydroxynonenal (4-HNE)-adducted proteins in tissues exposed to 0.1 and 0.25 mM PAP for 90 min. The appearance of 4-HNE-adducted proteins at the 0.1 mM concentration of PAP occurred prior to development of increased LDH leakage. Pretreatment with 1 mM glutathione (GSH) for 30 min only partially reduced PAP toxicity as LDH values were less severely depleted relative to tissues not pretreated with GSH. In contrast, pretreatment for 15 min with 2 mM ascorbic acid completely protected against PAP toxicity. Further studies showed that ascorbic acid pretreatment prevented PAP-mediated depletion of GSH. In summary, PAP rapidly depletes GSH and adenine nucleotides and inhibits gluconeogenesis prior to a rise in LDH leakage. PAP induces oxidative stress as indicated by an increase in GSSG and 4-HNE-adducted proteins. Ascorbic acid pretreatment prevents PAP toxicity by maintaining GSH status.

Solid phase extraction and liquid chromatography-tandem mass spectrometry for the evaluation of 4-hydroxy-2-nonenal in pork products

This research was aimed at setting up an analytical method for the determination in pork products of 4-hydroxy-2-nonenal (4-HNE), an aldehyde produced from the oxidation of omega-6-polyunsaturated fatty acids. Such a compound mediates various biological effects, but it is considered to be very toxic to mammalian cells at levels higher than physiological ones. The methods used for the determination of 4-HNE in biological fluids, such as blood, were found to be unsuitable for meat samples because both the repeatability and the recovery in spiked samples were unsatisfactory. A new method, based on solid phase extraction and HPLC-MS/MS, was therefore developed and validated. The limit of detection of 4-HNE in spiked samples was 0.043 mg/kg, and the recovery was approximately 60% depending on the concentration. Good linearity was observed in the range of 0.1-10 mg/kg, and repeatability and interday and intraday precision expressed as relative standard deviation were <10%. The method has been successfully applied to the determination of the aldehyde in samples of various pork products. 4-HNE was present in some products, especially the smoked and/or cooked ones, at levels that might not be a real risk for human health.

Measurement of 4-hydroxynonenal in small volume blood plasma samples: modification of a gas chromatographic-mass spectrometric method for clinical settings

4-Hydroxynon-2-enal (4-HNE) is one of the major aldehydic products of lipid peroxidation (LPO) and is involved in a number of pathophysiological processes. Since LPO products are useful indicators for oxidative stress in vivo, a number of detection methods for LPO products in biological tissues were developed. However, none of these methods is presently used in clinical settings. In order to introduce LPO products as biomarkers in clinical studies a suitable GC-MS method for 4-HNE detection was adapted to meet clinical requirements. As one result, the minimal sample volume could be decreased to 50 microl of plasma so that the method might even be suitable for pediatric purposes. The best internal standard (I.S.) for 4-HNE detection by GC-MS 9,9,9-D(3)-4-hydroxynon-2-enal was introduced by van Kuijk et al. [Anal. Biochem., 224 (1995) 420]. However, because of its limited availability, benzaldehyde-ring-d(5), 4-hydroxybenzaldehyde, and 2,5-dihydroxybenzaldehyde were tested to find an alternative. Out of these three, 4-hydroxybenzaldehyde was shown to serve best as I.S. To examine the applicability of the adapted method, tests on the stability of 4-HNE in samples during storage were carried out. It was shown that plasma samples need to be stored at -80 degrees C or less to avoid greater loss of 4-HNE. Samples with 4-HNE concentrations close to the physiological level were shown to be stable over 22 months at -80 degrees C. The introduction of a new and easily available I.S., reduction of the sample volume, and information about sample stability provided by this study facilitate 4-HNE determination in most clinical settings.

Method for analysis of 4-hydroxy-2-(E)-nonenal with solid-phase microextraction

A simple analytical method for 4-hydroxy-2-(E)-nonenal (HNE) using solid-phase microextraction (SPME) fiber was developed. HNE or the derivative of HNE formed by reaction with 2,4-dinitrophenylhydrazine (DNPH) was extracted from the sample solution by immersing the SPME fiber into the solution, and the amount of HNE was quantified by HPLC. The extraction conditions of HNE and HNE-DNPH were examined, using standard solutions, with respect to fiber coating, NaCl concentration, rate of stirring, adsorption temperature, and adsorption time. The recovery of HNE reached 80%, and the quantification limits of HNE and HNE-DNPH using standard compounds were 14.1 pmol/10 mL and 486.5 fmol/10 mL, respectively. This method can be applied to the detection of HNE in oxidized oil or samples of porcine liver.

Micellar electrokinetic chromatography separation and laser-induced fluorescence detection of the lipid peroxidation product 4-hydroxynonenal

4-Hydroxnonenal (HNE) is a product of lipid peroxidation in biological systems that causes a variety of harmful biological effects. A method for identifying HNE based on derivatization with the fluorescent reagent dansylhydrazine (5-(dimethylamino)naphthalene-1-sulphonehydrazine (DNSH) followed by micellar electrokinetic chromatography separation laser-induced fluorescence detection has been developed. The derivatization reaction has also been investigated for significant experimental parameters and rat brain homogenates with induced lipid peroxidation have been analysed for HNE contents. The limit of detection (3 S/N) was 30 nM or 0.3 fmol in the injected sample.

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.

Effect of aldehyde lipid oxidation products on myoglobin

The effects of aldehyde lipid oxidation products on myoglobin (Mb) were investigated at 37 degrees C and pH 7.2. Oxymyoglobin (OxyMb) oxidation increased in the presence of 4-hydroxynonenal (4-HNE) compared to controls (P < 0.05). Preincubation of metmyoglobin (MetMb) with aldehydes rendered the heme protein a poorer substrate for enzymatic MetMb reduction compared to controls, and the effect was inversely proportional to preincubation time; unsaturated aldehydes were more effective than saturated aldehydes (P < 0.05). The order of MetMb reduction as affected by preincubation was control > hexanal > heptanal > octanal > nonanal = decanal = hexenal > heptenal = octenal > nonenal = decenal = 4-HNE (P < 0.05). Preincubation of MetMb with 4-HNE enhanced the subsequent ability of the heme protein to act as a prooxidant in both liposomes and microsomes when compared to controls (P < 0.05); the effect was reduced in microsomes containing elevated concentrations of alpha-tocopherol (P < 0.05). MetMb preincubation with mono-unsaturated aldehydes enhanced the catalytic activity of MetMb to a greater degree than saturated aldehydes (P < 0.05). These results suggest that aldehyde lipid oxidation products can alter Mb stability by increasing OxyMb oxidation, decreasing the ability of MetMb to be enzymatically reduced and enhancing the prooxidant activity of MetMb.

Lipophilic aldehydes and related carbonyl compounds in rat and human urine

Rat and human urine samples were analyzed for lipophilic aldehydes and other carbonyl products of lipid peroxidation. The following compounds were identified as their 2,4-dinitrophenyl hydrazones by cochromatography with pure standards using three solvent systems: butanal, butan-2-one, pentan-2-one, hex-2-enal, hexanal, hepta-2,4-dienal, hept-2-enal, octanal, non-2-enal, deca-2,4-dienal, 4-hydroxyhex-2-enal, and 4-hydroxynon-2-enal. In general, fasted rats excreted less of these compounds than fed rats, indicating they were partially of dietary origin or that the endogenous compounds were excreted in a form not susceptible to hydrazone formation. The compounds excreted in human urine were similar to those excreted in rat urine but were present in lower concentrations. Identification of the conjugated forms of the lipophilic aldehydes and related carbonyl compounds excreted in urine may be a source of information about their reactions in vivo.

Determination of 4-hydroxy-2-nonenal in primary rat hepatocyte cultures by liquid chromatography with laser induced fluorescence detection

An HPLC (high performance liquid chromatography) method with laser induced fluorescence (LIF) detection is described for the determination of 4-hydroxy-2-nonenal (HNE) formed from lipid peroxidation in rat hepatocytes. Carbonyl compounds were fluorescently labelled by incubating the hepatocyte samples with a tagging reagent, 4-(2-carbazoylpyrrolidin-1-yl)-7-nitro-2,1,3-benzoxadiazole (NBD-ProCZ), at 60 degrees C for 10 min. The hydrazone derivatives were extracted with a C18 solid phase extraction (SPE) cartridge and separated on a reversed-phase HPLC column. The detection limit was 2.5 fmol or 0.5 nM (5 microL injection) of HNE in the cell homogenate. Method precision (C.V.) was 5% at the 5 nM level. The method has been used to determine free HNE in rat hepatocyte samples treated with several pro-oxidant toxins. A significant HNE increase (from 4 to 27.6 pmol/10(6) cells) was observed with the samples treated by allyl alcohol. The results were in accordance with those for malondialdehyde formation as measured by a thiobarbituric acid (TBA) assay.

Lipid peroxidation and biogenic aldehydes: from the identification of 4-hydroxynonenal to further achievements in biopathology

The formation, reactivity and toxicity of aldehydes originating from lipid peroxidation of cellular membranes are reviewed. Very reactive aldehydes, namely 4-hydroxyalkenals, were first shown to be formed in autoxidizing chemical systems. It was subsequently shown that 4-hydroxyalkenals are formed in biological conditions, i.e. during lipid peroxidation of liver microsomes incubated in the NADPH-Fe systems. Our studies carried out in collaboration with Hermann Esterbauer which led to the identification of 4-hydroxynonenal (4-HNE) are reported. 4-HNE was the most cytotoxic aldehyde and was then assumed as a model molecule of oxidative stress. Many other aldehydes (alkanals, alk-2-enals and dicarbonyl compounds) were then identified in peroxidizing liver microsomes or hepatocytes. The in vivo formation of aldehydes in liver of animals intoxicated with agents that promote lipid peroxidation was shown in further studies. In a first study, evidence was forwarded for aldehydes (very likely alkenals) bound to liver microsomal proteins of CCl4 or BrCCl3-intoxicated rats. In a second study, 4-HNE and a number of other aldehydes (alkanals and alkenals) were identified in the free (non-protein bound) form in liver extracts from bromobenzene or allyl alcohol-poisoned mice. The detection of free 4-HNE in the liver of CCl(4) or BrCC1(3)-poisoned animals was obtained with the use of an electrochemical detector, which greatly increased the sensitivity of the HPLC method. Furthermore, membrane phospholipids bearing carbonyl groups were demonstrated in both in vitro (incubation of microsomes with NADPH-Fe) and in vivo (CC1(4) or BrCCl(3) intoxication) conditions. Finally, the results concerned with the histochemical detection of lipid peroxidation are reported. The methods used were based on the detection of lipid peroxidation-derived carbonyls. Very good results were obtained with the use of fluorescent reagents for carbonyls, in particular with 3-hydroxy-2-naphtoic acid hydrazide (NAH) and analysis with confocal scanning fluorescence microscopy with image video analysis. The significance of formation of toxic aldehydes in biological membranes is discussed.

Polyenylphosphatidylcholine prevents carbon tetrachloride-induced lipid peroxidation while it attenuates liver fibrosis

BACKGROUND/AIMS

Polyenylphosphatidylcholine protects against alcoholic cirrhosis in the baboon and carbon tetrachloride-induced cirrhosis in rats. This study addresses the possible mechanism of the protective effect of polyenylphosphatidylcholine.

METHODS

For 8 weeks, rats were injected with either carbon tetrachloride in peanut oil or peanut oil alone (control), and pair-fed nutritionally adequate liquid diets with equivalent amounts of linoleic acid either as polyenylphosphatidylcholine or as safflower oil. Other rats were injected for 9 weeks with heterologous albumin and fed the same liquid diets. Lipid peroxidation was measured by F2-isoprostanes and 4-hydroxynonenal.

RESULTS

Carbon tetrachloride-induced lipid peroxidation was strikingly attenuated with polyenylphosphatidylcholine supplementation. Levels of hepatic F2-isoprostanes and 4-hydroxynonenal paralleled liver fibrotic scores and collagen accumulation. Polyenylphosphatidylcholine also attenuated the fibrosis induced in rats with human albumin, but in this case, levels of hepatic 4-hydroxynonenal did not change, nor were they significantly affected by polyenylphos-phatidylcholine. Neither carbon tetrachloride injection nor polyenylphosphatidylcholine treatment changed the arachidonic acid content (a major precursor of F2-isoprostanes and 4-hydroxynonenal) in liver phospholipids, and hepatic vitamin E was not significantly altered.

CONCLUSIONS

The hepatic protection of polyenylphosphatidylcholine against carbon tetrachloride appears to be due, at least in part, to an antioxidant effect, whereas the protection against heterologous albumin-induced fibrosis suggests that an additional mechanism, such as stimulation of collagenase activity, may also be responsible.

Determination of the lipid peroxidation product (E)-4-hydroxy-2-nonenal in clinical samples by gas chromatography--negative-ion chemical ionisation mass spectrometry of the O-pentafluorobenzyl oxime

(E)-4-Hydroxy-2-nonenal (HNE) is a highly reactive product of the free radical-stimulated lipid peroxidation of phospholipid-bound arachidonic acid in cellular membranes. We describe a sensitive and specific method for the determination of HNE in clinical samples. The method is based on the formation of the O-pentafluorobenzyl (O-PFB) oxime derivative of HNE, which is then extracted and cleaned up by solid-phase extraction. The HNE O-PFB oxime is then analysed without further derivatisation by capillary column gas chromatography-negative ion chemical ionisation mass spectrometry (GC-NICI-MS) using selected-ion monitoring. Concentrations down to the pmol range were achieved using deuterated HNE as an internal standard. The method was used to determine HNE in the cerebrospinal fluid and plasma of patients with Parkinson's disease, the plasma of patients with HIV-1 infection and AIDS and in inflamed mucosal biopsy specimens from patients with inflammatory bowel disease.

Analytical technologies for lipid oxidation products analysis

Productive investigation of the contribution of oxidative stress to human disease is facilitated by the design and application of suitable analytical technologies for oxidation product analysis. Lipid oxidation, including polyunsaturated fatty acid and cholesterol oxidation, produces a variety of products that can function as indexes of the extent of oxidation. These products include fatty acid hydroperoxides and hydroxides, aldehydes, prostanoids, hydrocarbons, and cholesterol hydroperoxides and hydroxides, epoxides, and carbonyls. Some of these oxidation products have biological activities that can contribute to tissue damage in unique ways. This paper reviews the state-of-the-art for chromatographic analysis of these products through a discussion of advances that have taken place since 1990.

Lipid peroxidation. Biopathological significance

Peroxidation of unsaturated lipids, initially studied in the chemistry of oil and fat rancidity, has become a problem of increasing interest in the biological field, because of its proposed role in a variety of pathological conditions. The general mechanism of the process, the formation of toxic aldehydes capable to react with protein and non protein thiols, and the overall effects in cellular membranes are reviewed. The possible implications of lipid peroxidation as one of the main mechanisms of cellular damage in both toxic injury and other pathological conditions are discussed.