High-performance liquid chromatographic assay of vitamin K in human serum

Role of Vitamin K in Bone and Muscle Metabolism

Vitamin K, a cofactor for the γ-glutamyl carboxylase enzyme, is required for the post-translational activation of osteocalcin and matrix Gla protein, which play a key role in bone and muscle homeostasis. In vivo and in vitro models for osteoporosis and sarcopenia suggest the vitamin K could exert a positive effect in both conditions. In bone, it increases osteoblastogenesis, whilst decreases osteoclast formation and function. In muscle, it is associated with increased satellite cell proliferation and migration and might play a role in energy metabolism. Observational trials suggest that high levels of vitamin K are associated with increased bone mineral density and reduced fracture risk. However, interventional studies for vitamin K supplementation yielded conflicting results. Clinical trials in sarcopenia suggest that vitamin K supplementation could improve muscle mass and function. One of the main limitations on the vitamin K studies are the technical challenges to measure its levels in serum. Thus, they are obtained from indirect sources like food questionnaires, or levels of undercarboxylated proteins, which can be affected by other environmental or biological processes. Although current research appoints to a beneficial effect of vitamin K in bone and muscle, further studies overcoming the current limitations are required in order to incorporate this supplementation in the clinical management of patients with osteosarcopenia.

Determination of vitamin K homologues by high-performance liquid chromatography with on-line photoreactor and peroxyoxalate chemiluminescence detection

A sensitive and highly selective high-performance liquid chromatography (HPLC) method was developed for the determination of vitamin K homologues including phylloquinone (PK), menaquinone-4 (MK-4) and menaquinone-7 (MK-7) in human plasma using post-column peroxyoxalate chemiluminescence (PO-CL) detection following on-line ultraviolet (UV) irradiation. The method was based on ultraviolet irradiation (254 nm, 15 W) of vitamin K to produce hydrogen peroxide and a fluorescent product at the same time, which can be determined with PO-CL detection. The separation of vitamin K by HPLC was accomplished isocratically on an ODS column within 35 min. The method involves the use of 2-methyl-3-pentadecyl-1,4-naphthoquinone as an internal standard. The detection limits (signal-to-noise ratio = 3) were 32, 38 and 85 fmol for PK, MK-4 and MK-7, respectively. The recoveries of PK, MK-4 and MK-7 were greater than 82% and the inter- and intra-assay R.S.D. values were 1.9-5.4%. The sensitivity and selectivity of this method were sufficient for clinical and nutritional applications.

Automatic determination of phylloquinone in vegetables and fruits using on-line photochemical reduction and fluorescence detection via solid phase extraction and flow injection

A very simple, rapid and highly sensitive flow injection fluorimetric method was developed for the determination of phylloquinone. The assay was based on the on-line reduction of phylloquinone in dodecylsulfate micelles after irradiation with UV light. The micellar medium enhanced the fluorescence and stability of the reduced phylloquinone. Under optimum experimental conditions, the range of application of the technique was between 0.09 and 45.0 microg mL(-1) and the detection limit was 0.05 microg mL(-1). The sample throughput was 90 injections per hour. The reliability of the method for the routine analysis of phylloquinone in vegetables and fruits is demonstrated. Extractions were made with hexane, and an automated solid phase extraction system was used to purify the sample extracts prior to injection into the flow injection manifold.

Method for the determination of vitamin K homologues in human plasma using high-performance liquid chromatography-tandem mass spectrometry

We report here the development of a precise and sensitive method for the determination of vitamin K homologues including phylloquinone (PK), menaquinone-4 (MK-4), and menaquinone-7 (MK-7) in human plasma using HPLC-tandem mass-mass spectrometry with atmospheric pressure chemical ionization (LC-APCI-MS/MS). The method involves the use of stable isotope (18)O-labeled internal standard compounds, which were synthesized in our laboratory, and the selection of a precursor and product ion with a MS/MS multiple reaction monitoring method. The average intraassay and interassay variation values for PK, MK-4, and MK-7 were <10%. Average spiked recoveries from authentic compounds added to normal human plasma samples for PK, MK-4, and MK-7 were 98-102%. Mean plasma concentrations of PK, MK-4, and MK-7 from healthy subjects (n = 20) were 1.22 +/-0.57, 0.39 +/- 0.46, and 6.37 +/- 7.45 ng/mL, respectively. We conclude that this novel LC-APCI-MS/MS method should be useful for the evaluation of vitamin K status in postmenopausal women and elderly subjects and provides useful information for the treatment and prevention of osteoporosis with vitamin K.

Determination of vitamin K1 in serum using catalytic-reduction liquid chromatography with fluorescence detection

A new method for the liquid chromatographic-fluorescence determination of serum vitamin K1 is described using reduction of the K-quinone to the fluorescent K-hydroquinone. The reduction reaction occurs "on-line" in the LC system using a catalytic reducer column and an alcohol mobile phase as reductant. A procedure for serum determination utilizes a liquid-liquid serum lipid extraction followed by normal-phase fractionation on a solid-phase extraction cartridge. The final measurement uses a reversed-phase (C18) separation with a ethanol-methanol mobile phase and provides a detection limit of approximately 20 pg/ml.

Chromatography of fat-soluble vitamins in clinical chemistry

A review is presented of current gas and liquid chromatographic methods for the determination of the fat-soluble vitamins A, D, E and K and the provitamin A beta-carotene in biological samples of human origin. For each vitamin, the discussion successively focuses on procedures for sample preparation, gas and liquid chromatographic systems and principles of detection. The emphasis is on liquid chromatography, which is gradually becoming a standard technique in fat-soluble vitamin assays. New trends in the liquid chromatography of these compounds include the use of smaller particles and shorter columns, to improve speed, and the advance of electrochemical detection as an alternative to absorbance and fluorescence detection. Bonded phases, both normal and reversed phase, tend to be preferred over underivatized silica as column supports. Gas chromatography remains of particular value in combination with mass spectrometry, a technique which may form the basis of reference methods. In general, despite the availability of well established analytical methods for fat-soluble vitamins, the wealth of recent literature in this area indicates that there continues to be a need for new assays with enhanced speed, specificity and sensitivity.

Serum vitamin K1 concentration and vitamin K-dependent clotting factor activity in maternal and fetal cord blood

The serum concentration of phylloquinone (vitamin K1) was measured in 34 healthy mothers and in the arterial cord blood of their newborn infants. In addition, the activities of factor II and of factors VII plus X were determined simultaneously in 16 paired maternal and fetal bloods. The serum vitamin K1 concentration was similar to that of control subjects in 27 mothers: 9.03 +/- 4.9 micrograms/L (mean and SD), with a simultaneous concentration of 10.4 +/- 5.3 micrograms/L in cord blood. Six mothers exhibited high serum vitamin K1 concentrations from 40 to 240 micrograms/L (median, 82) and the concentration in cord blood ranged from 25 to 115 micrograms/L (median, 71). One mother had a normal concentration of vitamin K1: 9 micrograms/L while no vitamin K1 was detectable in the serum of her infant. The activity of factor II and factors VII plus X was 7% and 7%, respectively, in this infant and 100% in the mother. All other mothers showed normal factor II and factors VII plus X activity, while the median activity was 47% (28%-56%) for factor II and 65% (35%-100%) for factors VII plus X in cord blood. These data suggest that vitamin K1 can cross the placental barrier but not in every case. Therefore the systematic administration of vitamin K1 to the newborn infant seems to be required to prevent the occurrence of the hemorrhagic disease.

Differential pulse polarographic determination of plasma menadione

A differential pulse polarographic assay for plasma vitamin K3 (menadione) has been developed. Details of the assay are (i) lipid-soluble material is extracted from plasma into ether by the method of Bjornsson et al. [(1978) Thromb. Haemostas. 2, 466-473]; (ii) ether is evaporated under nitrogen and the residue is dissolved in the supporting electrolyte, methanol: 0.2 M borate buffer (9:1), pH 6.8; (iii) current height is measured at -0.32 V vs SCE on the differential pulse polarogram. The lower sensitivity limit of this technique after addition of standard vitamin K3 to plasma is 0.3 microM; the calibration curve is linear from 0.6 through 10 microM. Two patients treated with a single dose of menadiol sodium diphosphate, 20 mg/M2 i.m., achieved measurable plasma vitamin K3 levels at 0.5 to 1.0 h ranging between 0.5 (0.08 micrograms/ml) and 2 microM (0.3 micrograms/ml).

Determination of (endogenous) vitamin K1 in human plasma by reversed-phase high-performance liquid chromatography using fluorometric detection after post-column electrochemical reduction. Comparison with ultraviolet, single and dual electrochemical detection

A new method for the fluorometric detection of K1 and K2 vitamins using post-column electrochemical reduction is described. Dual electrochemical detection in the reduction/reoxidation mode for coulometric/coulometric as well as coulometric/amperometric detection appears to be more sensitive and selective towards the plasma background than simple reductive electrochemical detection, but fluorometric detection after coulometric reduction offers the best results. Combination of normal-phase chromatography and the described method is only possible if supporting electrolyte is added post-column, but leads to higher detection limits. This highly sensitive method is applied to the determination of vitamin K1 in human plasma samples.

High-pressure liquid chromatographic-reductive electrochemical detection analysis of serum trans-phylloquinone

A sensitive method for the determination of human serum trans-phylloquinone levels has been developed. Serum samples were extracted with hexane and subjected to preliminary separation on a silica semipreparative HPLC column with an 80% recovery as determined by the addition of [3H]phylloquinone. The portion of the eluate containing trans-phylloquinone was dried and injected into a muBondapak C-18 analytical HPLC column, and the concentration of the vitamin was determined by reductive electrochemical detection utilizing a glassy carbon electrode and an Ag/AgCl reference electrode. The presumed vitamin peak was confirmed as trans-phylloquinone by rechromatography at different HPLC conditions, hydrodynamic voltamography, and photodegradation. As little as 300 pg/ml trans-phylloquinone could be detected, and normal human serum concentrations were found to be in the range of 1 ng/ml.

Post-translational carboxylation of preprothrombin

In summary, in this review on the function of vitamin K in post-translational modification of precursor proteins by carboxylation of certain glutamyl residues, I have tried to cover in particular the recent work on the reaction, the enzymes involved and the mechanisms being considered. In doing this I have also considered vitamin K, its discovery, its functional form and the possible relation of its metabolism to the carboxylation reaction. Equally the various vitamin K-dependent gla-containing proteins currently known have been described. The carboxylation of synthetic small molecule exogenous substrates and the synthesis and metabolism of the products of carboxylation are of great help in studying the reaction. Structural specificity of vitamin K analogs in vivo and in vitro has been compared and the use of various antagonists in vivo and in vitro considered in attempts to gain an understanding of the overall reaction. The reactions subsequent to carboxylation, e.g., the activation of prothrombin to thrombin via serine proteases and the related activation of the other vitamin K-dependent proteins have not been considered in this review. The review has not covered prothrombin or other vitamin K-dependent protein isolation, nor the determination of these proteins. As the vitamin K-dependent protein carboxylation story has developed over the past six years, a number of reviews have been written which help in keeping up with the various aspects of the field as it has expanded. These reviews refer to many of the papers I have had to eliminate due to space limitations. They are referenced as 469-489. The review is in no sense comprehensive and many papers have been missed or only mentioned. I have tried to concentrate on the more recent work and, thus, much of the very fine work of the 1940's on vitamin K chemistry is hardly mentioned. Some redundancy has been built into the organization of the review so that a reader can obtain a reasonable view of any one section without having to search the whole review for all possible relevant information on any particular part of the field.