Extraction and Determination of Vitamin K1 in Foods by Ultrasound-Assisted Extraction, SPE, and LC-MS/MS

Vitamin K₁ is one of the important hydrophobic vitamins in fat-containing foods. Traditionally, lipase is employed in the determination of vitamin K₁ to remove the lipids, which makes the detection complex, time-consuming, and insensitive. In this study, the determination of vitamin K₁ in fat-containing foods was developed based on ultrasound-assisted extraction (UAE), solid-phase extraction (SPE) combined with liquid chromatography–tandem mass spectrometry (LC-MS/MS). The optimal conditions for extraction of vitamin K₁ were material–liquid ratio of 1:70 (g/mL), extraction temperature of 50 °C, extraction power of 700 W, extraction time of 50 min, material-wash fluid ratio of 1:60 (g/mL), and 8 mL of hexane/anhydrous ether (97:3, v/v) as the elution solvent. Then, vitamin K₁ was analyzed on a ZORBAX SB-C18 column (50 mm × 2.1 mm, 1.8 μm) by gradient elution with water (0.01% formic acid) and methanol (0.01 formic acid + 2.5 mmol/L ammonium formate) as the mobile phase. The limit of detection (LOD) and limit of quantification (LOQ) were 0.05 and 0.16 μg/kg, respectively. Calibration curve was linear over the range of 10–500 ng/mL (R² > 0.9988). The recoveries at three spiked levels were between 80.9% and 119.1%. The validation and application indicated that the proposed method was simple and sensitive in determination of vitamin K₁ in fat-containing foods.

Purification and Characterization of the Principal Antimutagenic Bioactive as Ethoxy-Substituted Phylloquinone from Spinach (Spinacea oleracea L.) Based on Evaluation in Models Including Human Lymphoblast TK+/- Cells

During in vitro analysis, spinach (Spinacea oleracea L.) leaf extracts displayed varying antimutagenicity when analyzed in models including human lymphoblast (TK^+/-) cell line (thymidine kinase gene mutation assay) and Escherichia coli MG1655 (rifampicin resistance assay) against chemically (ethyl methanesulfonate and 5-azacytidine) induced mutagenicity. Highest antimutagenicity was displayed by the quinone extract. The principal bioactive compound exhibited fluorescence in TLC at 366 nm (termed C4) resolved at R_f 0.32 and t_R 15.2 min in TLC and HPLC, respectively. On the TLC plate, three spots (C1-C3), observed at 254 nm, displayed comparatively lesser antimutagenicity. Furthermore, biochemical and spectroscopic analyses using MALDI-TOF MS and NMR indicated the nature of the potent compound (C4) as an ethoxy-substituted phylloquinone derivative [2-ethoxy-3-((E)-3,7,11,15-tetramethylhexadec-2-enyl)naphthalene-1,4-dione]. The C4 compound did not display any cytotoxicity and hence possesses significant nutraceutical-based intervention possibility to combat the onset of mutation-associated disease(s).

5'-monohydroxyphylloquinone is the dominant naphthoquinone of PSI in the green alga Chlamydomonas reinhardtii

Thylakoid membranes contain two types of quinones, benzoquinone (plastoquinone) and naphthoquinone, which are involved in photosynthetic electron transfer. Unlike the benzoquinone, the chemical species of naphthoquinone present (phylloquinone, menaquinone-4 and 5'-monohydroxyphylloquinone) varies depending on the oxygenic photosynthetic organisms. The green alga Chlamydomonas reinhardtii has been used as a model organism to study the function of the naphthoquinone bound to PSI. However, the level of phylloquinone and the presence of other naphthoquinones in this organism remain unknown. In the present study, we found that 5'-monohydroxyphylloquinone is the predominant naphthoquinone in cell and thylakoid extracts based on the retention time during reverse phase HPLC, absorption and mass spectrometry measurements. It was shown that 5'-monohydroxyphylloquinone is enriched 2.5-fold in the PSI complex as compared with thylakoid membranes but that it is absent from PSI-deficient mutant cells. We also found a small amount of phylloquinone in the cells and in the PSI complex and estimated that accumulated 5'-monohydroxyphylloquinone and phylloquinone account for approximately 90 and 10%, respectively, of the total naphthoquinone content. The ratio of these two naphthoquinones remained nearly constant in the cells and in the PSI complexes from logarithmic and stationary cell growth stages. We conclude that both 5'-monohydroxyphylloquinone and phylloquinone stably co-exist as major and minor naphthoquinones in Chlamydomonas PSI.

Vitamin K1 accumulation in tobacco plants overexpressing bacterial genes involved in the biosynthesis of salicylic acid

Phylloquinone (Vitamin K(1)) is an essential component of the photosynthetic electron transfer. As isochorismate is required for the biosynthesis of Vitamin K(1), isochorismate synthase (ICS) activity is expected to be present in all green plants. In bacteria salicylic acid (SA) is synthesized via a two step pathway involving ICS and isochorismate pyruvate lyase (IPL). The effect of the introduction in tobacco plants of the bacterial ICS and IPL genes on the endogenous isochorismate pathway was investigated. Transgenic tobacco plants in which IPL was targeted to the chloroplast suffered severe growth retardation and had low Vitamin K(1) content. Probably because isochorismate was channeled towards SA production, the plants were no longer able to produce normal levels of Vitamin K(1). Transgenic tobacco plants in which the bacterial ICS was present in the chloroplast showed higher Vitamin K(1) contents than wild type plants.

Indirect identification of isoprenoid quinones inEscherichia coli by LC-MS with atmospheric pressure chemical ionization in negative mode

A novel analytical method was applied for identification of isoprenoid quinones in Escherichia coli by liquid chromatography atmospheric press chemical ionization mass spectrometry in negative mode (LC-NI-APCI-MS). Extraction and clean-up of sample were carried out on Sep-Pak Plus Silica solid-phase extraction cartridges. Ubiquinone-7 (UQ-7), Ubiquinone-8 (UQ-8) and Mequinone-8 (MK-8) were determined directly using combined information on retention time, molecular ion mass, fragment ion masses and UV characteristic spectrometry without any standard reagent. It was found that UQ-8 was the major component of isoprenoid quinones in Escherichia coli under aerobic condition. Compared with UQ-8, the relative abundance of UQ-7 and MK-8 is only 15% and 14%, respectively. The average recoveries of UQ-6, UQ-10 and vitamin K(1) in Escherichia coli were investigated by standard spiking experiment. The recoveries were achieved in the range from 94 to 106%, and the relative standard deviations (RSD) of the triplicate analysis of the spiked samples (UQ-6, UQ-10 and vitamin K(1)) ranged from 3 to 8%. The detection limits of LC-NI-APCI-MS were estimated to be 5, 40 and 0.8 microg/g dry cell for UQ-6, UQ-10 and vitamin K(1), respectively.

Simultaneous determination of vitamin K analogs in human serum by sensitive and selective high-performance liquid chromatography with electrochemical detection

OBJECTIVES

We report a sensitive and selective method for the simultaneous determination of vitamin K1 and K2 analogs (VKs) with high-performance liquid chromatography in which a platinum catalyst reduction column and an electrochemical detector operated in the oxidation mode are incorporated into the detection system. We also applied this trace analysis method to the simultaneous determination of VKs in human serum to investigate the physiologic and pathophysiologic roles of VKs in the bone metabolism.

METHODS

Our high-performance liquid chromatographic method with postcolumn catalyst reduction and electrochemical detection was applied for the simultaneous determination of VKs in human serum samples. After separation of VKs on a reversed-phase separation column by using a mixture of ethanol and methanol (1:1, v/v), containing 0.025 M of sodium perchlorate as the mobile phase, the VKs were reduced once in a platinum catalyst reduction column connected online and then monitored quantitatively by an electrochemical detector with a glassy carbon working electrode operated in the oxidation mode (+0.6 V versus Ag/AgCl).

RESULTS

VKs were clearly separated from each other within 80 min. The detection limits at a signal-to-noise ratio of 3 were 2 to 10 pg for VKs. Quantitative recovery from serum was obtained in the range of 86% to 91% for VKs. The average coefficients of variation of within-day and between-day assays were 1.6% to 2.1% and 2.4% to 3.6%, respectively, for all VKs.

CONCLUSIONS

This method was sensitive and selective for detection of VKs and was satisfactory in the simultaneous determination of VKs in small volumes of human serum.

Mutations in both sides of the photosystem I reaction center identify the phylloquinone observed by electron paramagnetic resonance spectroscopy

The core of photosystem I (PS1) is composed of the two related integral membrane polypeptides, PsaA and PsaB, which bind two symmetrical branches of cofactors, each consisting of two chlorophylls and a phylloquinone, that potentially link the primary electron donor and the tertiary acceptor. In an effort to identify amino acid residues near the phylloquinone binding sites, all tryptophans and histidines that are conserved between PsaA and PsaB in the region of the 10th and 11th transmembrane alpha-helices were mutated in Chlamydomonas reinhardtii. The mutant PS1 reaction centers appear to assemble normally and possess photochemical activity. An electron paramagnetic resonance (EPR) signal attributed to the phylloquinone anion radical (A(1)(-)) can be observed either transiently or after illumination of reaction centers with pre-reduced iron-sulfur clusters. Mutation of PsaA-Trp(693) to Phe resulted in an inability to photo-accumulate A(1)(-), whereas mutation of the analogous tryptophan in PsaB (PsaB-Trp(673)) did not produce this effect. The PsaA-W693F mutation also produced spectral changes in the time-resolved EPR spectrum of the P(700)(+) A(1)(-) radical pair, whereas the analogous mutation in PsaB had no observable effect. These observations indicate that the A(1)(-) phylloquinone radical observed by EPR occupies the phylloquinone-binding site containing PsaA-Trp(693). However, mutation of either tryptophan accelerated charge recombination from the terminal Fe-S clusters.

Separation and determination of minor photosynthetic pigments by reversed-phase HPLC with minimal alteration of chlorophylls

Reversed-phase HPLC conditions for separation of chlorophyll (Chl) a, Chl a' (the C132-epimer of Chl a), pheophytin (Pheo) a (the primary electron acceptor of photosystem (PS) II), and phylloquinone (PhQ) (the secondary electron acceptor of PS 1), have been developed. Pigment extraction conditions were optimized in terms of pigment alteration and extraction efficiency. Pigment composition analysis of light-harvesting complex II, which would not contain Chl a' nor Pheo a, showed the Chl a'/Chl a ratio of 3-4 x 10(-4) and the Pheo a/Chl a ratio of 4-5 x 10(-4), showing that the conditions developed here were sufficiently inert for Chl analysis. Preliminary analysis of thylakoid membranes with this analytical system gave the PhQ/Chl a' ratio of 0.58 +/- 0.03 (n = 4), in line with the stoichiometry of one molecule of Chl a' per PS I.

Determination of phylloquinone and menaquinones in animal products with fluorescence detection after postcolumn reduction with metallic zinc

A high-performance liquid chromatographic (HPLC) method for the determination of phylloquinone and menaquinones in foods of animal origin is described. The K vitamers were quantified with a fluorescence detector after postcolumn reduction with metallic zinc using K1(25) as an internal standard. Extraction was done either with 2-propanol-hexane (meat and fish products) or with acid hydrolysis method (dairy products). Prior to quantification, sample extracts were purified by semipreparative HPLC; in addition, the fats of cheese and rainbow trout samples were removed with lipase hydrolysis. By this method the phylloquinone and menaquinones (MK-4 to MK-10) present in a few representative samples of different animal food groups were determined. HPLC-MS was used to confirm the identification of K vitamers. Long-chain menaquinones were found from bovine and pig livers as well as from various cheeses. The total vitamin K contents calculated as the sum of quantified K vitamers were in general low (mean content 10-100 ng/g); the highest amount was analyzed in chicken meat (600 ng/g).

Solubilization of vitamin K1 by bile salts and phosphatidylcholine-bile salts mixed micelles

The solubilization of vitamin K1 by bile salts (sodium deoxycholate, sodium cholate and their corresponding glycine conjugates) and phosphatidylcholine (egg)-bile salt mixed micelles has been investigated. The solubilization curves were not always linear with increasing bile salts, but the vitamin was appreciably solubilized in the region below their CMCs. In the bile salt solutions (20 mM, phosphate buffered saline, pH 7.5, ions strength 0.2), the solubilized vitamin ranged from 0.3 to 0.9 mM. With increasing phosphatidylcholine, the amount of vitamin solubilized was dramatically increased; at the molar ratio of 1:1 (both 20 mM), the amount of vitamin solubilized was about 25-30 times more than by the corresponding bile salts alone. There is a possibility that exogenous phospholipid given orally as liposomal forms assists the solubilization of vitamin K1, in the intestine. This characteristic is suggested as being responsible, in part, for the enhanced recovery of blood coagulation after oral administration of liposomal vitamin K1 to warfarin-treated rabbits.

Application of high-performance liquid chromatography to assay phylloquinone (vitamin K1) in rat liver

A specific and sensitive method based on high-performance liquid chromatography to measure vitamin K1 in rat liver is described. The procedure consists of three chromatographic steps, a preliminary purification of lipid extracts on Sep-Pak silica columns, a preparative stage using adsorption HPLC, and a final reversed-phase HPLC stage in which vitamin K1 is resolved from remaining contaminants and quantified by reference to an internal standard (vitamin K1 2,3-epoxide). The "within-run" coefficient of variation of the assay for vitamin K1 in 12 livers was 11.1% (n = 24). The concentration of vitamin K1 in liver of male rats fed a control diet containing no alfalfa was 8.0 ng/g (wet weight of liver) while female rat liver gave a mean value of 7.3 ng/g (wet weight of liver). Liver from male rats fed chow containing alfalfa gave a mean value of 44 ng K1/g (wet weight of liver).

Metabolism and biological activity of cis- and trans-phylloquinone in the rat

The separation of sufficient cis and trans forms of vitamin K for feeding and metabolic studies was accomplished on silica gel columns eluted with solvent containing n-butyl ether. The lack of biological activity of the cis isomer of phylloquinone was observed. The cis isomer was retained longer in liver, particularly in mitochondria, but had low retention in that portion of the endoplasmic reticulum isolated as the rough membrane fraction. The cis isomer of phylloquinone was a poor substrate for 2,3-epoxidation in vivo and in vitro. These data are consistent with the hypothesis that epoxidation of vitamin K is coupled to the biological activity of the vitamin, and that microsomes are the site of metabolism and function of vitamin K.