Simultaneous determination of vitamin K1, vitamin K1 2,3-epoxide and menaquinone-4 in human plasma by high-performance liquid chromatography with fluorimetric detection

A simple, sensitive, and high-throughput LC-APCI-MS/MS method for simultaneous determination of vitamin K1, vitamin K1 2,3-epoxide in human plasma and its application to a clinical pharmacodynamic study of warfarin

Warfarin exerts its anticoagulation activity by blocking the vitamin K-epoxide cycle. A quantitative understanding of how warfarin and related genes interact with the vitamin K-epoxide cycle and the associated change of coagulation activity in the human body may help study the pharmacodynamics of warfarin. The plasma concentration of vitamin K₁ (VK₁) and vitamin K₁ 2,3-epoxide (VK₁O) could reflect the status of vitamin K-epoxide cycle. However, their determination is a challenging task due to their extremely low concentrations in human plasma and the severe interferences caused by co-extracted lipids. In this study, we developed an LC-APCI-MS/MS method for the simultaneous determination of VK₁ and VK₁O in human plasma using stable deuterium-labeled vitamin K₁ (vitamin K₁-d7) as the internal standard (IS). Plasma samples were prepared through protein denaturation followed by one-step liquid extraction with cyclohexane. Chromatographic separation of analytes from isobaric interferences and endogenous ion suppressor was performed on a Synergi Hydro-RP column (150 mm × 4.6 mm, 4 μm) under the reversed-phase condition with isocratic elution. The selective reaction monitoring (SRM) transitions were chosen as m/z = 451.5→187.3 for VK₁, m/z = 467.5→161.2 for VK₁O, and m/z = 458.6→194.3 for IS in APCI positive mode. The assay was linear in the range of 100-10,000 pg/mL for the two analytes and achieved considerable extraction recoveries (87.8-93.3%, 91.0-96.9%, and 92.0% for VK₁, VK₁O, and IS, respectively), negligible matrix effects (93.6-96.0%, 96.3-100.1%, and 95.5%), and high selectivity with a small sample volume requirement (0.2 mL) and short run time (15 min). The validated method was successfully applied in a clinical pharmacodynamic study of warfarin, and the clotting activity was found to be negatively correlated with the plasma concentration ratio of VK₁O to VK₁.

Management of vitamin K deficiency after biliopancreatic diversion with or without duodenal switch

BACKGROUND

Reduced serum vitamin K levels are frequently observed after biliopancreatic diversion (BPD) and BPD with duodenal switch (BPD/DS). The criteria for treatment are not precisely defined.

OBJECTIVES

To assess the effects of standardized vitamin K supplementation in patients who develop vitamin K deficiency after BPD or BPD/DS.

SETTING

Teaching hospital specializing in bariatric surgery.

METHODS

Serum vitamin K levels, clotting times, and vitamin K-dependent coagulation factors were measured after an overnight fast at baseline and then at 4 days and 1, 4, and 52 weeks after the start of vitamin K supplementation in 10 consecutive patients who had developed severe vitamin K deficiency after BPD or BPD/DS. Vitamin K was administered in a dose of 5 mg/d for 1 week, followed by a maintenance dose of 5 mg once a week.

RESULTS

At baseline, all patients had serum vitamin K1 levels below the limit of detection, but none reported symptoms of easy bleeding. Minor prolongation of the prothrombin time and minimal decreases of some coagulation factors were observed in a minority of patients. During the first week of vitamin K loading, median serum vitamin K1 levels rose into the high normal range. During maintenance treatment, median vitamin K1 levels settled in the low normal range.

CONCLUSION

Vitamin K1 deficiency in patients with BPD or BPD/DS is not commonly associated with bleeding or clinically relevant decreases in coagulation factor activity. We hypothesize that vitamin K2 production in the large intestine is usually sufficient to compensate for vitamin K1 deficiency and to maintain total liver vitamin K stores within the range required for (near) normal coagulation factor production.

The external quality assurance of phylloquinone (vitamin K(1)) analysis in human serum

The vitamin K external quality assurance scheme (KEQAS) aims to assist in the harmonization of phylloquinone (vitamin K(1)) analysis in order to improve the comparability of clinical and nutritional studies. Serum samples were despatched to 17 groups from eight countries during 2000-2006. Using pilot data (1996-1999), an analytical performance target of 20% absolute difference from the all-laboratory trimmed mean (ALTM) was assigned and formed the basis for interlaboratory comparison. Assay specificity, analytical bias and assay performance were evaluated. From 21 batches of samples distributed, 414 results were reported of which 2.7% were outliers. The mean interlaboratory absolute difference from the ALTM was 21.7% with 47% of groups consistently meeting the performance target. The mean interlaboratory coefficient of variation was 29.6%. The false positive rate for phylloquinone depleted samples was high at 35%. Bias was found to be independent of HPLC-detector type (fluorescence vs electrochemical). Assay characteristics for the measurement of phylloquinone in human serum compare favourably with methods for analytes at equivalent concentrations. The high proportion of false positive results suggest that poor assay specificity at low phylloquinone concentrations is a common problem, which in the clinical setting could lead to underreporting of vitamin K deficiency.

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.

Vitamin K contents in liver tissue of hepatocellular carcinoma patients

Serum protein induced in vitamin K absence-II (PIVKA-II) is used as a tumor marker because it increases at a notably higher rate in patients with hepatocellular carcinoma. To clarify the mechanism causing the elevation of serum PIVKA-II, we measured the contents of vitamins K1 (phylloquinone, PK) and K2 (menaquinone, MK) (MK-4, MK-5, MK-6, MK-7, MK-8, MK-9, MK-10) in liver tissue resected from 21 hepatic cancer patients (12 patients with hepatocellular carcinoma and 9 patients with metastatic hepatic cancer), using HPLC combined with coulometric reduction and fluorometric detection. In the cancerous tissue of hepatocellular carcinoma patients, PK, MK-7, MK-8, and MK-10 were significantly lower than that found in the noncancerous tissue. Furthermore, MK-6, MK-7, MK-8, and MK-10 in the cancerous tissue of hepatocellular carcinoma patients were significantly lower than that in the cancerous tissue of metastatic hepatic cancer patients. These data suggested that one of the mechanisms of the elevation of serum PIVKA-II levels in hepatocellular carcinoma patients is a vitamin K deficiency in the local cancerous tissue.

Vitamin K1 and K2 status and faecal flora in breast fed and formula fed 1-month-old infants

Faecal vitamin K1 (VK1, phylloquinone) and vitamin K2 (menaquinone, MK) concentrations were measured in 12 breast fed and 9 formula fed 1-month-old infants. Faecal concentrations of VK1 and MK-5 to -9 were significantly higher in the formula fed than in the breast fed infants. There was also a tendency for higher total faecal MK (4-10) concentrations in the formula fed [geometric mean (95% confidence intervals); 8995.0 (3872.6, 20,893.0) pmol/g of dry faeces] than in the breast fed infants [2937.7 (1285.3, 6714.3), P = 0.051]. The numbers of streptococci and Escherichia coli were 100 and 10 times higher, respectively, in the faeces of the formula fed than in those of the breast fed infants. Faecal concentrations of MK-6, -7 and -8, and MK-8 were correlated with the numbers of streptococci and E. coli in the faeces, respectively. Serum VK1 and MK concentrations were measured in 9 out of 12 breast fed and eight out of nine formula fed infants. The serum VK1 concentration was much higher in the formula fed infants [average (95% CI); 2.20 (1.48, 2.92) pmol/ml] than in the breast fed ones [0.30 (-0.10, 0.70), P = 0.000], but MKs were not detected in the sera of most of the formula fed infants.

Fluorescence properties of plastoquinol, ubiquinol and alpha-tocopherol quinol in solution and liposome membranes

It was found that plastoquinol-9, ubiquinol-10 and alpha-tocopherol quinol show intrinsic fluorescence in organic solvents and in liposomes. Their fluorescence spectra in solution showed the presence of one emission band with maximum intensity in the range 319.0-327.0 nm for plastoquinol and 321.5-326.5 nm for alpha-tocopherol quinol, which is the longest wavelength shifted in polar solvents. The emission band at about 371 nm for ubiquinol was not sensitive to solvent polarity. For all three prenylquinones the fluorescence quantum efficiency changed significantly in solvents of different polarities, being the highest in ethanol and the lowest in hexane in the case of plastoquinol and alpha-tocopherol quinol, whereas ubiquinol fluorescence showed the opposite effect. These spectral parameters were applied to determination of prenylquinol localization in liposome membranes.

High clearance of (S)-warfarin in a warfarin-resistant subject

A 30 year old black male required a 60 mg daily dose of warfarin to elicit a therapeutic anticoagulant response (normal warfarin dose 2.5-10 mg day-1; maximum 15 mg day-1). Hereditary warfarin resistance was suspected after compliance, diet, concurrent medication and any gastrointestinal disorder were eliminated as contributory causes. The disposition of vitamin K and vitamin K epoxide was examined in the propositus, his two sisters and 13 control black male subjects. Each subject was given an i.v. bolus dose (5 mg) of vitamin K prior to and after 2 weeks of warfarin therapy (5 mg day-1). The oral clearances of (S)- and (R)-warfarin were also measured in each subject during the last day of warfarin therapy. The mean (+/- s.d.) systemic clearance of vitamin K was similar in all subjects before (114 +/- 35 ml min-1) and after (112 +/- 40 ml min-1) warfarin therapy. The mean (+/- s.d.) AUC value for vitamin K epoxide was increased by warfarin treatment (6.5 +/- 5.4 micrograms ml-1 min before and 139 +/- 78 micrograms ml-1 min after) in all subjects. In the propositus, the oral clearance of (S)-warfarin (14.5 ml min-1) and the clearance ratio for (S)/(R)warfarin (2.6) differed by more than 7 standard deviations from the control group (4.3 +/- 1.1 ml min-1 and 1.2 +/- 0.2, respectively). In one sister of the propositus, the stereoselective disposition of warfarin was comparable with that of her brother ((S)-warfarin clearance = 16.2 ml min-1; and (S)/(R)-warfarin clearance ratio = 2.7).

Pharmacokinetics and hemostasis following administration of a new, injectable oxacephem (6315-S, flomoxef) in volunteers and in patients with renal insufficiency

Flomoxef is a new oxacephem of broad antibacterial activity. The compound is mainly excreted through the kidneys. Two dose finding studies in patients with various degrees of renal insufficiency revealed that the dosage of flomoxef has to be reduced exactly according to the renal function. Although the N-methylthiotetrazole group has been replaced by a hydroxyethyl group, an inhibitory effect of flomoxef on vitamin K metabolism persisted. This effect was, however, less pronounced than with latamoxef. Only patients with low vitamin K stores are endangered. For those in whom low vitamin K stores are suspected repeated controls of prothrombin time are advised during the treatment. In contrast to latamoxef the platelet system was not affected by flomoxef. With the exception of loose stools in some patients no other clinical side effects during treatment were observed.

Vitamin K (menaquinone-4) metabolism in liver disease

We measured menaquinone-4 (MK-4) and MK-4 epoxide concentrations in plasma and liver tissue after intravenous injection of 200 micrograms/kg MK-4 in 42 patients who underwent hepatectomy. They were classified into normal (N; n = 10), chronic hepatitis (CH; n = 12), and liver cirrhosis (LC; n = 20) groups, on the basis of the diagnosis given by the pathologist after examining resected liver specimens. The plasma MK-4 epoxide concentration reached maximum level (Cmax) 60 min after MK-4 injection. The Cmax in groups LC and CH were 85.9 and 126.3 nmol/l, respectively, which is significantly reduced compared with that of group N (184.4 nmol/l) (p less than 0.01 and p less than 0.05, respectively). The MK-4 concentrations in liver tissues of 24 patients 60 min after MK-4 injection were 2.77 in group N, 3.79 in group CH, and 3.83 nmol/g in group LC, and the MK-4 epoxide concentrations were 4.01, 3.09, and 2.62 nmol/g in the respective groups. Consequently, the ratio of MK-4 epoxide to total MK-4 (MK-4 + MK-4 epoxide) in groups CH and LC was significantly lower than in group N (p less than 0.01). It is concluded that the Cmax of MK-4 epoxide after MK-4 injection may serve as an indicator of liver function and that the low ratio of MK-4 epoxide to total MK-4 in the liver shows impairment in vitamin K metabolism.

Temporal variation in the effects of warfarin on the vitamin K cycle

In this in vivo study, the time-dependent effect of oral sodium warfarin was studied in male rats synchronized under a 12-hr light-dark cycle (light 0600-1800). Groups of 5 animals received an oral dose of 500 micrograms/kg of warfarin or saline at 0600 or 1800 and 1 mg/kg of vitamin K 8 hr later and the rats were sacrificed 240 min after vitamin K administration. The activities of the vitamin K reductase and vitamin K epoxide reductase were measured indirectly by determining the content of vitamin K1 and vitamin K epoxide reductase in the plasma and liver. The data obtained in control rats indicated that vitamin K and vitamin K 2,3 epoxide concentrations in plasma and liver were higher (P less than 0.05) at 1800 than at 0600. Warfarin had a greater (P less than 0.05) inhibitory effect on the vitamin K and vitamin K-epoxide reductases at 0600 compared to 1800; plasma levels of S- and R-warfarin did not vary with time of administration. The findings suggest that the activity of both reductases under control conditions, and the warfarin-induced inhibition of these enzymes varied depending on the time of drug administration.

Measurement of K vitamins in animal tissues by high-performance liquid chromatography with fluorimetric detection

A highly sensitive method for measuring endogenous phylloquinone and menaquinones in animal tissues was developed, based on high-performance liquid chromatography with coulometric reduction and fluorimetric detection, following extraction from tissue homogenate and purification on a Sep-Pak silica cartridge followed by thin-layer chromatography. The detection limits of phylloquinone, menaquinone-4, -6, -10 and -13 were 40, 40, 50, 70 and 80 pg/g in rat liver, respectively.