Simultaneous determination of homologues of vitamin E and coenzyme Q and products of α-tocopherol oxidation

Concepts and principles for new rapid simple liquid chromatography method for quantification of antioxidants resveratrol, vitamin E, and coenzyme Q10 in capsules with high-performance liquid chromatography with a photo-diode array detector

Principles and problems in the development of simultaneous liquid chromatography (LC) analytical methods for potent antioxidative molecules resveratrol, tocopherol, and coenzyme Q10 in capsules, have been investigated and systematically compared and summarized. For these purposes, experiments within the full polarity spectrum of LC techniques. were tested and recorded. The whole range of polarities included: Alkyl C18 bonded reversed phase, phenyl, cyanopropyl, diol, and the most polar base silica-filled column matrixes have been used. The summarized results concluded that all mentioned LC techniques could be used for the determination of the mentioned group of the three analytes with different run characteristics and efficiency. These successes could be achieved after careful analyses of molecular physicochemical data of analytes. They are especially organic solubilities. The ultraviolet spectral absorption characteristics of each analyte and the mobile phase constituents for appropriate separation were very important to be known. The ultimate targets were the development method with the isocratic mode of separation yielding symmetrical peak shapes for the best sensitivity and accuracy, with the shortest run time and best reproducibility. From an analytical point of view important for LC, the three analytes have quite distinct characteristics that contribute to successful method development. These features are their organic solvent and water solubility, molecular polarities, and ultraviolet-absorption characteristics, like spectra and absorptivities. All these mentioned parameters were taken into account for solving complications appearing in the development of rapid LC methods for the simultaneous determination of three antioxidant molecules.

Levels of Coenzyme Q10 and Several COQ Proteins in Human Astrocytoma Tissues Are Inversely Correlated with Malignancy

In a previous study, we reported the alterations of primary antioxidant enzymes and decreased citrate synthase (CS) activities in different grades of human astrocytoma tissues. Here, we further investigated coenzyme Q₁₀ (CoQ₁₀) levels and protein levels of polyprenyl diphosphate synthase subunit (PDSS2) and several COQ proteins required for CoQ₁₀ biosynthesis in these tissues. We found that the level of endogenous CoQ₁₀, but not of exogenous α-tocopherol, was higher in nontumor controls than in all grades of astrocytoma tissues. The levels of COQ3, COQ5, COQ6, COQ7, COQ8A, and COQ9, but not of COQ4, were lower in Grade IV astrocytoma tissues than in controls or low-grade (Grades I and II) astrocytomas, but PDSS2 levels were higher in astrocytoma tissues than in controls. Correlation analysis revealed that the levels of CoQ₁₀ and COQ proteins were negatively correlated with malignancy degree and positively correlated with CS activity, whereas PDSS2 level was positively correlated with malignancy. Moreover, lower level of mitochondrial DNA-encoded cytochrome c oxidase subunit 2 was not only associated with a higher malignancy degree but also with lower level of all COQ proteins detected. The results revealed that mitochondrial abnormalities are associated with impaired CoQ₁₀ maintenance in human astrocytoma progression.

The role of vitamin E acetate (VEA) and its derivatives in the vaping associated lung injury: systematic review of evidence

Small scale observational evidence suggested that Vitamin E (VE) might play beneficial role in human and animal respiratory conditions of various origin by stabilizing surfactant functions. The intra-aleveolar VE level is directly proportionate to the lung's response to inflammation. Electronic cigarette or vaping associated lung injury was a dominantly respiratory syndrome in the United States with seemingly strong association between potential Vitamin E acetate inhalation exposure and the onset of symptoms. This systematic review intended to assess if there was previous evidence of any potential respiratory/gastrointestinal toxicity associated with Vitamin E acetate or any of its derivatives. A systematic review was constructed and prospectively registered at PROSPERO to search important clinical databases between 2000 and 2020 for full text human articles investigating the effect of VEA or any of its derivatives administered via any route (oral/parenteral/aerosolised) in adults with any respiratory conditions. Out of 363 records investigating the effect of VEA and/or its derivatives/isomers in (any) lung injury (inflammatory, oxidative, infective, asthma/COPD) seven articles qualified. The papers reported various surrogate outcomes (APACHEII score, spirometry, etc) with equivocal results. There was one case report of harmful exposure to both Vitamin E (intramuscular) and Vitamin E acetate (topical). The present review found evidence of neither harm nor any significant clinical improvement associated with the administration of VEA or any derivatives via any route in adult inflammatory lung conditions however, the articles were of low-level evidence. Further studies are needed to correct flaws in research to explore the role of Vitamin E in pulmonology.

Analytical Method Development for Coq10 Determination in Human Plasma Using HPLC-UV and HPLC/MS/MS

Background:

CoQ10 is a very important compound which is found in every tissue of our organism. It participates in the processes of cellular respiration and ATP production. Also, it acts as a strong antioxidant. In an organism, it is represented in two forms: oxidized (ubiquinone) and reduced (ubiquinol). Its low blood level may be a signal for a list of diseases.

Materials and Methods:

This study developed and compared two methods of CoQ10 determination in order to find the fastest and the most convenient one. The first one involved HPLC-UV with the wavelength of ubiquinone determination equivalent to 290 nm and 275 nm for ubiquinol, respectively. The second one was carried out on an HPLC/MS/MS system utilizing Electrospray Ionization (ESI) and triple quadrupole mass analyzer for quantification in MRM positive mode.

Results:

Two methods of ubiquinol and ubiquinone determination were developed and validated. HPLC-UV included sample preparation based on liquid-liquid extraction. The LLOQ was 0.50 µg/ml. HPLC-MS/MS method sample preparation was based on protein precipitation. The LLOQ was 0.10 µg/ml.

Conclusion:

During the investigation, a conclusion was drawn that the HPLC-UV method is too insensitive for simultaneous determination of ubiquinol and ubiquinone. Furthermore, ubiquinol is very unstable and during exogenous factors’ exposure, it rapidly turns into ubiquinone. While, the HPLCMS/ MS method turned out to be sensitive, selective, rapid as it provides an accurate determination of both forms of CoQ10 in spiked human plasma.

Physicochemical aspects of reaction of ozone with galactolipid and galactolipid-tocopherol layers

The impact of reaction of galactolipids with ozone on the physicochemical properties of their monolayers was examined. In Megli and Russo (Biochim Biophys Acta, 1778:143–152, 2008), Cwiklik and Jungwirth (Chem Phys Lett, 486:99–103, 2010), Jurkiewicz et al. (Biochim Biophys Acta, 1818:2388–2402, 2012), Khabiri et al. (Chem Phys Lett, 519:93–99, 2012), and Conte et al. (Biochim Biophys Acta, 1828:510–517, 2013), the properties of layers formed from model mixtures composed of chosen lipids and selected oxidation products were studied, whereas in this work, question was raised as to how the oxidation reactions taking place in situ affect the physical properties of the galactolipid layers. So, set experiment should take into account the effect of all reaction products. The mechanical characteristics of monolayers of monogalactosyldiacyl-glycerol (MGDG) and digalactosyldiacylglycerol (DGDG) were determined by Langmuir trough technique, and the electrical properties of liposomes formed from these lipids by measuring their electrophoretic mobility. Considerable loss of galactolipid molecules forming monolayers was found at ozone concentrations (in aqueous medium) higher than 0.1 ppm with a stronger effect measured for MGDG. That goes along with the greater amounts of MDA found in the extracts of oxidized MGDG films compared with DGDG. Based on this, it was concluded that an additional galactose group present in DGDG molecules acts protectively under oxidative conditions. The surface tension of the solutions (of small volume) contacting the oxidized galactolipids films was significantly reduced, indicating the presence of soluble in polar media, surface active reaction products. The presence of α-tocopherol in mixtures with tested galactolipids at a molar ratio of lipid to tocopherol equal to 1.7:1 caused some inhibition of lipid oxidation, reducing the decrease of amount of lipid particles forming the monolayer. Here, also protective effect of α-tocopherol was greater for the MGDG compared to DGDG.

Analytical problems with the determination of coenzyme Q10 in biological samples

The article discusses analytical problems related to the determination of coenzyme Q10 in biological samples. The assaying of coenzyme Q10 in complex samples, such as plasma, tissues, or food items requires meticulous sample preparation prior to final quantification. The process typically consists of the following steps: deproteinization, extraction, and ultimately reduction of extract volumes. At times drying under a gentle stream of neutral gas is applied. In the case of solid samples, a careful homogenization is also required. Each step of the sample preparation process can be a source of analytical errors that may lead to inaccurate results. The main aim of this work is to point to sources of analytical errors in the preparation process and their relation to physicochemical properties of coenzyme Q10. The article also discusses ways of avoiding and reducing the errors.

Serum Levels of Vitamin E Are Associated With Early Recurrence of Atrial Fibrillation After Electric Cardioversion

Background—

Oxidative stress is suggested to play a role in favoring the occurrence of atrial fibrillation (AF). We analyzed whether vitamin E, a known antioxidant, or markers of oxidative stress are associated with AF recurrence in patients undergoing electric cardioversion.

Methods and Results—

A total of 144 patients (83 men; mean age, 71.1±5.4 years) underwent successful biphasic electric cardioversion of nonvalvular persistent AF. At baseline, urinary 8-isoprostaglandin F2α and serum soluble NOX2-derived peptide (sNOX2-dp), high-sensitivity C-reactive protein (hs-CRP), and vitamin E levels were measured in each patient. All patients underwent 3 months of clinical follow-up, including an office visit with ECG every week or in cases of symptom recurrence. During the follow-up, 94 patients maintained sinus rhythm, whereas 50 experienced AF recurrence. In unadjusted analysis, left atrial diameter and levels of urinary isoprostanes and serum sNOX2-dp and hs-CRP were significantly higher and serum vitamin E lower in patients with AF recurrence. In multivariable Cox analysis, serum vitamin E (hazard ratio, 0.734; 95% CI, 0.605–0.891; P <0.001) and, to a lesser extent, hs-CRP ( P =0.047) remained significantly associated with AF recurrence. Urinary isoprostanes and serum sNOX2-dp levels were inversely correlated with serum vitamin E level ( r =−0.626, P <0.001, and r =−0.460, P <0.001, respectively).

Conclusions—

The study shows that low serum vitamin E levels are associated with AF recurrence in patients who underwent cardioversion. Because vitamin E inversely correlated with oxidative stress, the findings reinforce the hypothesis of an interplay between oxidative stress and AF.

Determination of in plasma samples by dual-electrode amperometric detection and liquid chromatography

Co-Q10 is a lipid-soluble benzoquinone that is an important factor in free radical scavenging, mitochondrial membrane stability and ATP synthesis. Dietary Co-Q10 is a powerful antioxidant that has been useful in lessening the damage associated with ischemia-reperfusion injuries and aiding in the recovery of myocardial function after myocardial infarction. However, the role of dietary Co-Q10 in oxidative damage and repair is not well understood. Previous LC-EC methods have used packed carbon bed electrodes with high overpotentials that were sufficient to oxidize and reduce several biological compounds, thereby decreasing the selectivity that can be achieved with EC detection. Thin-layer cell dual electrode detection enables monitoring of reduced and oxidized forms of Co-Q10 simultaneously and selectively. The oxidation (+0.45 V vs. Ag/AgCl) and reduction (-0.4 V vs. Ag/AgCl) electrode potentials were optimized to oxidize and reduce the electroactive quinone moiety. The reduced form of Co-Q10 was prepared from the commercially available oxidized form using a Jones reductor. Confirmation of its formation was determined using the current ratios of the peak and half wave potentials from previously generated hydrodynamic voltammograms, using the oxidized form with electrodes in a series configuration. This analytical system was successfully applied to determine basal concentrations of oxidized (510 nM) and reduced (500 nM) Co-Q10 in human plasma. Peak identity of oxidized and reduced Co-Q10 was confirmed by two orthogonal methods: by the current ratios at +0.45 V and +0.25 V and -0.4 V and -0.2 V (vs. Ag/AgCl) as well as by retention time. Detection limits were determined to be 5 nM, with a linear range of three orders of magnitude.

Tocopheryl quinones and mitochondria

In the past, the role of tocopherols and tocopheryl hydroquinones as antioxidants in mitochondria has been examined. However, structural properties of tocopherols and tocopheryl quinones (arrangement of polar/apolar moieties) have also been recognized as being crucial for the selective transport of RRR-alpha-congeners compared with other tocopherols in the cell, suggesting that these properties might be generally important for the binding of vitamin E-related compounds to proteins and enzymes in mitochondria. Therefore, direct modulation of mitochondrial activities, such as bioenergetics, production of reactive oxygen species and apoptosis, not exclusively related to the redox activity of these compounds is increasingly studied. This overview focuses on the influence of alpha-/gamma-tocopheryl quinones and their parent alpha-/gamma-tocopherols on mitochondrial functions, including formation of tocopheryl quinones, their analytical aspects, their potential as alternative substrates and their inhibitory activity for some mitochondrial functions. It is shown that the understanding of how tocopheryl quinones and tocopherols interfere with mitochondrial functions on the molecular level is still incomplete and that a better comprehension requires further research activities.

Determination of total cholesterol in serum by high-performance liquid chromatography with electrochemical detection

A simple and sensitive HPLC method that does not require derivatization for determining cholesterol has been developed. Investigation of voltammetric behavior of cholesterol showed that cholesterol could be oxidized on a glassy carbon electrode in non-aqueous solvents. This was applied to the development of a method by HPLC with electrochemical detection (HPLC-ED). The HPLC-ED was optimized using the separation of cholesterol and oxysterols including 26-hydroxycholesterol and 24S-hydroxycholesterol. The separation was carried out with a Develosil C30-UG-3 column; acetonitrile-2-propanol (9:1, v/v) containing 50mM LiClO(4) as a mobile phase; and an applied potential at 1.9V versus Ag/AgCl. The current peak height was linearly related to the amount of cholesterol injected from 0.5-100 microM (r>0.999). The detection limit (S/N=3) of cholesterol was 0.36 microM (1.8 pmol). Cholesterol at 100 microM was directly detected with a relative standard deviation (RSD) of less than 1.0% (n=8). Total cholesterol and free cholesterol in control human serum were determined by the present method with the recovery of more than 90% and the RSD (n=6) of less than 3.0%.

Comprehensive Analysis of Vitamin E Constituents in Human Plasma by Liquid Chromatography−Mass Spectrometry

The present paper describes the development and validation of a normal-phase liquid chromatography-mass spectrometry (NP-HPLC-MS) method for the screening and quantification of vitamin E constituents in human plasma and food matrixes. Liquid-liquid extraction combined with isotope dilution was applied to extract the lipophilic target analytes. Baseline separation of alpha-tocopherylacetate, alpha-tocopherol, alpha-tocotrienol, alpha-tocopherylquinone, beta-tocopherol, gamma-tocopherol, beta-tocotrienol, gamma-tocotrienol, delta-tocopherol, and delta-tocotrienol was achieved utilizing a normal-phase amine column operated with n-hexane and 1,4-dioxane as solvents. Detection was achieved by positive-ion atmospheric-pressure chemical ionization (APCI). Key features of the method are lower limits of detection, 3-51 nmoles/L; lower limits of quantification, 8-168 nmoles/L; linearity coefficients, 0.9778-0.9989; linear ranges, 0.01-29 micromol/L; recoveries, 53-92%; accuracies, 99-103%; intraday precisions, 2-17%; interday precisions, 5-18%; and suppression values, 0-29%. Fragmentation of tocopherols was studied by tandem mass spectrometry, and a fragmentation scheme for tocotrienols/tocopherols is postulated. Neutral-loss and precursor-ion scan experiments were performed for targeted discovery of oxidation products of tocopherols in human blood and fish oil, the latter being an important food component. The presented data suggest that this method will help to expand the number of quantified/discovered vitamin E constituents detected in food products and analyzed during human/animal trials in order to give a more comprehensive picture to nutritionists about the fate of vitamin E.

Ubiquinol-10/lipids ratios in consecutive patients with different angiographic findings

OBJECTIVE

Information concerning un-supplemented plasma concentrations of ubiquinol-10 in coronary artery disease patients is still controversial. The aim of this study is to determine the levels of plasma ubiquinol-10 and ratios of ubiquinol-10 to plasma lipids in consecutive patients with different angiographic findings.

SUBJECTS AND METHODS

Thirty-six consecutive patients who underwent coronary angiography were split in two groups with different atherosclerotic changes. These patients were un-supplemented with antioxidants and were not treated by lipid-lowering medication. We have measured a plasma level of ubiquinol-10 using high-performance liquid chromatography with coulometric detection. Conventional plasma lipids, markers of oxidative stress and other widely accepted risk factors of atherosclerosis have been determined too.

RESULTS

Plasma ubiquinol-10 to low-density lipoprotein cholesterol (LDL-C) ratios in patients with different angiographic findings have been found as 180+/-69 and 132+/-43, respectively (p=0.020). The ubiquinol-10/LDL-C ratio was significantly lower in angiographically positive patients. There were also significant differences in ubiquinol-10 per total cholesterol (109+/-47 and 80+/-26, respectively; p=0.031), per triglycerides (426+/-191 and 237+/-86, respectively; p=0.002) and per the sum of triglycerides and total cholesterol (86+/-35 and 61+/-20, respectively; p=0.013).

CONCLUSIONS

There have not been found any significant differences between levels of widely accepted risk factors for genesis and progress of atherosclerotic changes in these two groups of patients. Only the level of triglycerides and the total cholesterol minus high-density lipoprotein cholesterol/high-density lipoprotein cholesterol ratio were significantly higher in patients with stenosis. This ratio correlated with the ubiquinol-10/LDL-C ratio, which was significantly lower in patients with stenosis. Our results indicate that the ratio of ubiquinol-10/LDL-C is likely to be a risk factor for atherogenesis.

Vitamin E metabolism

The aim of this paper is to provide an overview of vitamin E metabolism. The topics covered include: major classes of vitamin E metabolites; their production pathways and route of excretion; possible biological activities of vitamin E metabolites; and use of vitamin E metabolites as markers of oxidant generation. Recent investigations into vitamin E metabolism have also highlighted important new areas of research, such as the potential for high dose vitamin E supplementation to interfere with drug metabolism, as well as alternative methods to alter vitamin E bioavailability in vivo. These issues will also be discussed in the review.

Addition products of alpha-tocopherol with lipid-derived free radicals

The addition products of alpha-tocopherol with lipid-derived free radicals have been reviewed. Free radical scavenging reactions of alpha-tocopherol take place via the alpha-tocopheroxyl radical as an intermediate. If a suitable free radical is present, an addition product can be formed from the coupling of the free radical with the alpha-tocopheroxyl radical. The addition products of alpha-tocopherol with lipid-peroxyl radicals are 8a-(lipid-dioxy)-alpha-tocopherones, which are hydrolyzed to alpha-tocopherylquinone. On the other hand, the carbon-centered radicals of lipids prefer to react with the phenoxyl radical of alpha-tocopherol to form 6-O-lipid-alpha-tocopherol under anaerobic conditions. The addition products of alpha-tocopherol with peroxyl radicals (epoxylinoleoyl-peroxyl radicals) produced from cholesteryl ester and phosphatidylcholine were detected in the peroxidized human plasma using a high-sensitive HPLC procedure with postcolumn reduction and electrochemical detection. Thus, the formation of these addition products provides us with much information on the antioxidant function of vitamin E in biological systems.

HPLC method for simultaneous determination of retinol, alpha-tocopherol and coenzyme Q10 in human plasma

A simple HPLC method with UV detection is proposed for the simultaneous determination of three lipophilic vitamins: all-trans-retinol, alpha-tocopherol and coenzyme Q(10) (ubiquinone) in human plasma. The following chromatographic conditions were used: RP-18 column, a mobile phase consisted of methanol -n-hexane 72:28 (v/v) and UV detector set at 324, 292 and 276 nm for all-trans-retinol, alpha-tocopherol and coenzyme Q(10), respectively. The linearity range was 0.35-70 microM for all-trans-retinol, 0.23-44 microM for alpha-tocopherol and 0.12-23 microM for coenzyme Q(10). Deproteinised plasma samples were extracted with n-hexane prior to the analysis. The within-day and between day reproducibilities were 1.5 and 3.7% for all-trans-retinol, 4.0 and 5.8% for alpha-tocopherol and 2.3 and 3.1% for coenzyme Q(10), respectively. Using the proposed method the following recoveries were achieved: 91% for all-trans-retinol, 86% for alpha-tocopherol and 88% for coenzyme Q(10). The method was applied to the determination of the levels of retinol, tocopherol and coenzyme Q(10) in plasma of healthy children and children treated by elimination diet.

The analysis of the zero-order and the second derivative spectra of retinol acetate, tocopherol acetate and coenzyme Q10 and estimation of their analytical usefulness for their simultaneous determination in synthetic mixtures and pharmaceuticals

The aim of the present work was to develop a simple and rapid method of retinol acetate, tocopherol acetate and coenzyme Q(10) determination in pharmaceuticals without involving any preparation operations like separation or masking. The values of second derivative amplitude at 212 nm for tocopherol, 351 nm for retinol and 222 nm for coenzyme were used for construction of calibration graphs. Beer's law is obeyed in the concentration range 0.5-20, 0.5-7.5 and 0.5-30 microg ml(-1) for retinol acetate, tocopherol acetate and coenzyme, respectively. The elaborated procedures were successfully applied to the simultaneous determination of studied compounds in their binary synthetic mixtures and in commercial preparations with high reliability and repeatability. Spectral properties of retinol acetate allows to determine its contents in ternary mixture which includes Vitamin E and coenzyme Q(10).

Redox-interaction of α-tocopheryl quinone with isolated mitochondrial cytochrome bc1 complex

The homogenous distribution of vitamin E in lipid membranes is a prerequisite for its universal function as lipophilic antioxidant. Its antioxidant activity leads to the irreversible formation of alpha-tocopheryl quinone (TQ) in those membranes. Very little is known about the interference of TQ with redox-cycling enzymes normally interacting with ubiquinone (UQ), which exerts important bioenergetic functions in the mitochondrial respiratory chain. One of the most complex redox reactions of the respiratory chain is the interaction of reduced UQ (UQH(2)) with the cytochrome bc(1) complex (ubiquinol:cytochrome c reductase, EC 1.10.2.2). The aim of this study was to elucidate the influence of TQ on the electron transfer from UQH(2) to cytochrome c via the isolated mitochondrial cytochrome bc(1) complex. Although TQ is present in substoichiometric amounts with respect to UQ in mitochondria and in our experiments with isolated bc(1) complex, we observed a decrease of the total electron transfer rate via the bc(1) complex with increasing amounts of TQ. Both reduced TQ (TQH(2)) and UQH(2) are able to reduce b-cytochromes in the bc(1) complex, however, they act in a completely different way. While reduction of b-cytochromes by UQH(2) can occur both via the Q(o) and the Q(i) pocket of the cytochrome bc(1) complex, TQH(2) can preferably reduce b-cytochromes via the Q(i) pocket. These differences are also reflected by the extremely low turnover numbers of the bc(1) activity for TQ/TQH(2) compared to UQ/UQH(2) suggesting that TQ/TQH(2) acts as a weak competitive inhibitor for binding sites of UQ/UQH(2). In contrast, the oxidation properties of TQ and UQ are similar. Furthermore, oxidized TQ was observed to decrease the O(2)(*)(-) release rate of UQH(2)-consuming cytochrome bc(1) complex. These findings suggest that the irreversible oxidation of vitamin E to TQ in mitochondrial membranes causes a downregulation of respiratory activities as well as a lower O(2)(*)(-) formation rate by the cytochrome bc(1) complex.

Measurement of reduced and oxidized coenzyme Q9 and coenzyme Q10 levels in mouse tissues by HPLC with coulometric detection

BACKGROUND

Ubiquinone-responsive multiple respiratory chain dysfunction due to coenzyme Q(10) (CoQ(10)) deficiency has been previously identified in muscle biopsies. However, previous methods are unreliable for estimating CoQ(10) redox status in tissue. We developed an accurate method for measuring tissue concentrations of reduced and oxidized coenzyme Q (CoQ).

METHODS

Mouse tissues were weighed in the frozen state and homogenized with cold 1-propanol on ice. After solvent extraction, centrifugation and filtration, the filtrate was subsequently analyzed by reversed-phase HPLC with coulometric detection.

RESULTS

Reference calibration curves were used to determine reduced and oxidized coenzyme Q(9) (CoQ(9)) and CoQ(10) concentrations in tissues. The method is sensitive ( approximately 15 microg/l), reproducible (6% CV) for CoQ(9) and CoQ(10), and linear up to 20 mg/l for CoQ(9) and CoQ(10). Analytical recoveries were 90-104%. In mouse tissues the amounts of total CoQ (TQ) ranged from 261 to 1737 nmol/g of protein. Total CoQ(9) levels are comparable with the values of those previously reported. CoQ is found to be mostly in the reduced form in mouse liver ( approximately 87%), heart ( approximately 60%), and muscle tissues ( approximately 58%); in the brain, most of the CoQ is in the oxidized state ( approximately 65%).

CONCLUSION

This procedure provides a precise, sensitive, and direct assay method for the determination of reduced and oxidized CoQ(9) and CoQ(10) in mouse hindleg muscle, heart, brain, and liver tissues.

Impurities from polypropylene microcentrifuge tubes as a potential source of interference in simultaneous analysis of multiple lipid-soluble antioxidants by HPLC with electrochemical detection

High-performance liquid chromatography (HPLC) with electrochemical detection was used to analyze lipidsoluble antioxidants and micronutrients in plasma. Small amounts of plasma samples are often extracted in polypropylene (PP) microcentrifuge tubes before HPLC analysis due to its convenience. We therefore investigated the effect of impurities released from different PP tubes during extraction on the electrochemical detection of retinol, lutein, α-tocopherol, γ-tocopherol, retinyl palmitate, β-carotene and total coenzyme Q

Analysis of vitamin E and its oxidation products by HPLC with electrochemical detection

A sensitive HPLC procedure with postcolumn reduction and electrochemical detection was developed for the analysis of vitamin E and its oxidation products, alpha-tocopherylquinone, epoxy-alpha-tocopherylquinones, and 8a-(lipid-dioxy)-alpha-tocopherones. After the separation on a reversed-phase column, on-line zinc-catalyzed reduction allowed the detection of alpha-tocopherylquinone and epoxy-alpha-tocopheryl-quinones, whereas platinum-catalyzed reduction allowed the detection of 8a-(lipid-dioxy)-alpha-tocopherones. The lowest detectable level of each compound was about 0.2 pmol at the signal-to-noise ratio of 3. This method was applied to the detection of alpha-tocopherol products in peroxidized human plasma. When the plasma was peroxidized by the addition of a free radical initiator, peaks corresponding to alpha-tocopherylquinone, epoxy-alpha-tocopherylquinones, and the addition products of alpha-tocopherol with peroxyl radicals derived from cholesteryl ester hydroperoxides and PC hydroperoxides were observed. The amount of these oxidation products in the plasma increased with the depletion of endogenous alpha-tocopherol. The results indicate that the method is useful to detect the oxidation products formed by the peroxyl radical-trapping reactions of alpha-tocopherol in biological systems.

Attention to relative response across sequential electrodes improves quantitation of coulometric array

HPLC separations coupled with coulometric electrode-based detectors offer potential to evaluate complex biological samples, but analytical approaches to such samples are still being defined. Coulometric electrode array systems use response ratio (as ratio conformity), for quantitation and qualitative characterization. We investigated the influence of changing the ratio conformity requirement (ratio window, RW) on quantitative consistency of the system. Sixty-one serum metabolites were analyzed in three cohorts of ad libitum/dietary restricted rats with two RW settings. RW 30 uses channels with <30% ratio variation (vs standard) to quantitate, whereas RW 100 generally uses all channels. Quantitation between the two approaches differed in 29/671, 61/976, and 264/976 metabolites in cohorts A, B, and C, respectively. The changes were 23.0 +/- 16.6, 31.9 +/- 28.6, and 23.6 +/- 17.1% (+/- SD). Correlation analysis showed that 11, 7, and 21% of the 61 metabolites had r(2) < 0.9 in cohorts A, B, and C, respectively. Inspection of HPLC chromatograms revealed that most of the metabolites with changed levels possessed common characteristics (e.g., shoulder peaks, low signal/noise ratios, coeluting peaks). Analysis demonstrated that RW 30 provided precise quantitation, whereas RW 100 did not. These data suggest that narrow ratio window increases quantitative accuracy in coulometric electrode array analysis of the metabolome(s) of complex biological samples (e.g., sera, mitochondria).

Comparison of gas chromatography-mass spectrometry and liquid chromatography-tandem mass spectrometry methods to quantify alpha-tocopherol and alpha-tocopherolquinone levels in human plasma

Two mass spectrometric methods were established for the quantitative analyses of alpha-tocopherol (TH) and its oxidation product alpha-tocopherolquinone (TQ) in human plasma. Both methods make use of isotopically labeled internal standards of different levels of deuteration (d3-TH and d6-TQ). Plasma (100 microl) was saponified in the presence of a mixture of antioxidants, and then TH and TQ were extracted with hexane. With the GC-MS method, the analytes were first converted into O-trimethylsilyl derivatives before analysis in the selective ion monitoring mode. The derivatization procedure led to the quantitative conversion of TQ into the O-trimethylsilyl derivative of tocopherolhydroquinone, giving rise to a more stable molecule with less fragmentation than for TQ. The increased stability of the molecule resulted in an enhanced contribution of the base peak to the total observed ions and therefore an increased sensitivity of the base peak for quantification. With the liquid chromatography-tandem mass spectrometry (LC-MS/MS) method, TH and TQ were detected by multiple reaction monitoring after positive electrospray ionization. The GC-MS and LC-MS/MS methods showed nearly the same accuracy (>95%) and the same within-day precisions, with less than 5 and 10% for TH and TQ, respectively. The between-day precision and the limit of quantification for TQ in plasma were better by LC-MS/MS (4%; 3 nM) than by GC-MS (21%; 10 nM). Analysis and method validation were carried out with plasma samples obtained from a male volunteer pre- and postexercise. Both techniques showed that the ratio of TQ/TH was elevated by 35% immediately after exercise and had returned to basal levels when measured 24 h later.

Chromatographic analysis of alpha-tocopherol and related compounds in various matrices

Tocopherols and tocotrienols (Vitamin E) are part of a group of "minor components" of main interest, present in the unsaponifiable fraction of many samples. Their importance in biological, metabolical and nutritional studies makes determination of tocopherols and related compounds of major interest. Present work critically reviews the different ways to perform sample pre-treatment and analysis of these compounds, related to the matrices, other analytes to be measured, sensitivity, and simplicity. The review includes well referenced tables that provide in-depth summaries of methodology for the chromatographic analysis of alpha-tocopherol and related compounds in foods, pharmaceuticals, plants, animal tissues and other matrices.

Long-chain n-3 fatty acids specifically affect rat coagulation factors dependent on vitamin K: relation to peroxidative stress

Fatty acids of marine origin have been shown to affect blood coagulation in the rat. In an attempt to gain insight into the mechanisms of this phenomenon, we studied the effects of dietary linseed and fish oils on the liver antioxidant status and plasma coagulation parameters in rats on a time-course basis. Dietary enrichment in eicosapentaenoic and docosahexaenoic acids resulted in strong hypocoagulation after only 1 week and a concomitant increase in liver lipid peroxidation and tocopherolquinone content. Enrichment in linolenic acid induced similar increases in lipid peroxidation and tocopherol catabolism but negligible alteration of coagulation. A significant correlation between plasma factor II coagulant activity and liver tocopherolquinone was found in fish oil- but not in linseed oil-fed rats. Although ingestion of tocopherolquinone led to high levels of this compound in the liver, it had only marginal effects on coagulation factors. Thus, it seems unlikely that this vitamin E metabolite could be involved in the lowering of vitamin K-dependent clotting factors through inhibition of gamma-glutamylcarboxylase. Rather, our results indicate that the effects of the n-3 fatty acids of fish oil on vitamin K-dependent coagulation factors are specific and independent of liver tocopherolquinone levels.