Statins, vascular calcification, and vitamin K-dependent proteins: Is there a relation?

The present cross-sectional clinical study aimed to examine the connection between statin exposure, coronary artery calcification (CAC), and vitamin K-dependent proteins (VKDPs) in patients with cardiovascular (CV) conditions. Two groups of patients were studied: patients with established CV disease (CVD) and healthy patients at moderate risk for CVD (a control group). The groups were also split into statin users and non-users. The following VKDPs were measured in plasma: uncarboxylated Matrix Gla-protein (ucMGP), undercarboxylated (ucOC), and carboxylated osteocalcin (cOC), Gla-rich protein (GRP). CAC score (CACS) was determined by multislice computed tomography. Among all the participants in the study, CACS was more pronounced in statin users compared to non-users; the same was found also among the CVD patients and among the controls. While the levels of ucMGP and GRP did not differ between statin users and non-users, ucOC and ucOC/cOC were significantly elevated in statin users, indicating vitamin K deficiency. There was a positive correlation between the levels of ucOC and CACS in the entire population and in the group of statin users, but not in statin non-users. No association was found between ucMGP or GRP and CACS. Statins had also an impact on the international normalized ratio and interacted with vitamin K antagonists (VKAs). Our results are in agreement with the existing evidence about positive association between statins and vascular calcification. They enlighten to a certain extent the possible mechanisms through which statins may enhance calcium accumulation in arterial wall, namely, by inhibition of vitamin K dependent proteins and functions involved in vascular protection.

[Diseases Due to the Deficiency in Vitamin K Conversion System and Its Prevention]

Vitamin K is a fat-soluble vitamin that plays an important role in blood coagulation and bone formation. Vitamin K has homologues due to differences in the side chain structure, phylloquinone (abbreviated as vitamin K1, PK) having a phytyl side chain and menaquinones (MK-n, n=1 to 14) having an isoprenoid side chain structure. The main vitamin K that we take from our daily diet is PK, and a fermented food, natto, contains MK-7 produced by Bacillus subtilis natto. However, the majority of vitamin K present in the tissues of mammals, including humans, is menaquinone-4 (abbreviated as vitamin K2, MK-4) having a geranylgeranyl side chain. This reason is that PK or MK-n obtained in the diet is converted into MK-4 in the body. We identified that the UbiA prenyltransferase domain containing protein 1 (UBIAD1) is the conversion enzyme of PK and MK-n to MK-4. The physiological roles of MK-4 in all tissues of the whole body and the physiological significance of MK-4 converted from PK and MK-n by UBIAD1 have not been sufficiently elucidated yet. To investigate the function of UBIAD1 in vivo, we generated UBIAD1 systemic knockout mice and tissue-specific UBIAD1 knockout mice. In this paper, we introduce the usefulness of vitamin K for diseases that may involve vitamin K and UBIAD1.

Daylight-Induced Antibacterial and Antiviral Nanofibrous Membranes Containing Vitamin K Derivatives for Personal Protective Equipment

During the development of antibacterial and antiviral materials for personal protective equipment (PPE), daylight active functional polymeric materials containing vitamin K compounds (VKs) and impacts of polymer structures to the functions were investigated. As examples, hydrophobic polyacrylonitrile (PAN) and hydrophilic poly(vinyl alcohol-co-ethylene) (PVA-co-PE) polymers were directly blended with three VK compounds and electrospun into VK-containing nanofibrous membranes (VNFMs). The prepared VNFMs exhibited robust photoactivity in generating reactive oxygen species (ROS) under both daylight (D65, 300-800 nm) and ultraviolet A (UVA, 365 nm) irradiation, resulting in high antimicrobial and antiviral efficiency (>99.9%) within a short exposure time (<90 min). Interestingly, the PVA-co-PE/VK₃ VNFM showed higher ROS production rates and better biocidal functions than those of the PAN/VK₃ VNFM under the same photoirradiation conditions, indicating that PVA-co-PE is a better matrix polymer material for these functions. Moreover, the prepared PVA-co-PE/VK₃ VNFM maintains its powerful microbicidal function even after five times of repeated exposures to bacteria and viruses, showing the stability and reusability of the antimicrobial materials. The fabrication of photoinduced antimicrobial VNFMs may provide new insights into the development of non-toxic and reusable photoinduced antimicrobial materials that could be applied in personal protective equipment with improved biological protections.

Synthesis of Naphthoquinone Derivatives: Menaquinones, Lipoquinones and Other Vitamin K Derivatives

Menaquinones are a class of isoprenoid molecules that have important roles in human biology and bacterial electron transport, and multiple methods have been developed for their synthesis. These compounds consist of a methylnaphthoquinone (MK) unit and an isoprene side chain, such as found in vitamin K₁ (phylloquinone), K₂, and other lipoquinones. The most common naturally occurring menaquinones contain multiple isoprene units and are very hydrophobic, rendering it difficult to evaluate the biological activity of these compounds in aqueous assays. One way to overcome this challenge has been the application of truncated MK-derivatives for their moderate solubility in water. The synthesis of such derivatives has been dominated by Friedel-Crafts alkylation with BF₃∙OEt₂. This attractive method occurs over two steps from commercially available starting materials, but it generally produces low yields and a mixture of isomers. In this review, we summarize reported syntheses of both truncated and naturally occurring MK-derivatives that encompass five different synthetic strategies: Nucleophilic ring methods, metal-mediated reactions, electrophilic ring methods, pericyclic reactions, and homologation and side chain extensions. The advantages and disadvantages of each method are discussed, identifying methods with a focus on high yields, regioselectivity, and stereochemistry leading to a detailed overview of the reported chemistry available for preparation of these compounds.

Microwave Assisted Cloud Point Extraction for the Determination of Vitamin K Homologues in Vegetables by Liquid Chromatography with Tandem Mass Spectrometry

Liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) with a triple quadrupole (QqQ) is proposed for determining the vitamin K homologues, phylloquinone (PK), menaquinone-4 (MK) and menadione (MD), in vegetables. The analytes were isolated from the samples (1-1.5 g) by ultrasound assisted extraction using acetonitrile (2 mL), and the liquids were submitted to microwave assisted cloud point extraction with Triton X-45. The enrichment factors were between 20 and 50, depending on the vitamin homologue in question. The analytes were determined by LC-ESI-QqQ-MS/MS in the multiple reaction monitoring (MRM) mode, providing unequivocal identification and quantification, with limits of detection of 0.8, 1.0, and 16 ng/g for MK, PK, and MD, respectively. Recovery assays for samples spiked at two concentration levels, between 40 and 600 ng/g depending on the compound, provided recoveries in the 90-114% range. Only PK was detected in the samples analyzed, at concentrations in the 90-2350 ng/g range.

Mixed micellar system stabilized with saponins for oral delivery of vitamin K

Poorly soluble vitamin K cannot be absorbed by patients suffering from cholestasis due to extremely low level of bile salts in the intestine. A formulation of vitamin K including glycocholic acid (i.e. Konakion® MM), does not increase bioavailability because it is unstable due to protonation of glycocholic acid at gastric pH. To develop a stable formulation, saponins were introduced as neutral surfactants to (partly) replace glycocholic acid. Experimental design was made to investigate the effect of the composition on particle size at neutral pH and upon acidification at pH 1.5. Two formulations that were within the optimized composition window were loaded with vitamin K and those showed superior stability at low pH as compared to Konakion® MM: sizes were between 43 and 46 nm at pH 7.3 and between 46 and 58 nm after 1 h incubation at pH 1.5, respectively, but large aggregates were formed at pH 1.5 in presence of Konakion® MM. Micelles were cytocompatible with Caco-2 cells at concentration of surfactants (saponins and glycocholic acid) up to 0.15 mg/ml. Uptake of vitamin K by Caco-2 cells was 4.2-4.9 nmol/mg protein for saponins-containing formulations and 7.1 nmol/mg protein for Konakion® MM. This, together with the superior stability at low pH, makes saponins-containing mixed micelles promising oral formulations for vitamin K.

During warfarin induction, the Fiix-prothrombin time reflects the anticoagulation level better than the standard prothrombin time

Essentials Fiix-prothrombin time (PT) monitoring of warfarin measuring factor (F) II and X, is effective. Plasma obtained during warfarin induction and stable phase in Fiix-trial was assayed. Fiix-PT stabilized anticoagulation earlier than monitoring with traditional PT-INR. FVII had little effect on thrombin generation that was mainly determined by FII and FX.

SUMMARY

Background The prothrombin time (PT) is equally prolonged by reduction of each of the vitamin K-dependent (VKD) factors (F) II, VII and X. The Fiix-PT is only affected by FII and FX, the main contributors to thrombin generation (TG). Objective To test the hypothesis that variability in warfarin anticoagulation is reduced early during monitoring with the normalized PT-ratio calculated from Fiix-PT (Fiix-International Normalized Ratio [INR]) compared with traditional PT-INR monitoring. Also, that because of its insensitivity to FVII, Fiix-PT more accurately reflects TG when Fiix-INR and PT-INR are discrepant. Methods Samples from Fiix-trial participants monitored with either Fiix-PT or PT were used. VKD coagulation factors and TG were measured in samples from 40 patients during stable anticoagulation and in serial samples obtained from 26 patients during warfarin induction. TG was assessed in relation to selective reduction in single VKD factors. Results During Fiix-warfarin induction full anticoagulation measured as FII or FX activity was achieved at a similar rate to that with PT-warfarin but subsequently stabilized better. Fiix-INR but not PT-INR mirrored total TG during initiation. During induction, FII (R2 = 0.66) and FX (R2 = 0.52) correlated better with TG and with a steeper slope than did FIX (R2 = 0.37) and in particular FVII (R2 = 0.21). In vitro, FII and FX were the main determinants of TG at concentrations observed during VKA anticoagulation, whereas FVII and FIX had little influence. Conclusions Fiix-PT monitoring reduces anticoagulation variability, suggesting that monitoring FVII has a limited role during VKA management. TG is better reflected by Fiix-PT.

A Mixed Micelle Formulation for Oral Delivery of Vitamin K

PURPOSE

To develop a stable micellar formulation of vitamin K for oral delivery, because the commercial and clinically used formulation of vitamin K (Konakion® MM) destabilizes at gastric pH resulting in low bioavailability of this vitamin in neonates with cholestasis.

METHODS

Mixed micelles composed of EPC, DSPE-PEG 2000 and glycocholic acid, with and without vitamin K, were prepared by a film hydration method. The influence of pH on the stability of the micelles was analyzed by dynamic light scattering (DLS). The critical micelle concentration (CMC) was determined by fluorescence spectroscopy using pyrene and the morphology was evaluated by transmission electron microscopy . Caco-2 cells were used to study the cytocompatibilty.

RESULTS

Mixed micelles with mean diameters from 7.1 to 11.0 nm and a narrow size distribution (PDI < 0.2) were obtained after 3 membrane extrusion cycles. Konakion® MM formed aggregated particles at gastric pH, which was avoided through steric stabilization by introducing PEG. TEM showed that mixed micelles had a spherical size (diameter of around 10 nm) with a narrow size distribution in agreement with the DLS results. The loading capacities for vitamin K of mixed micelles with varying molar fractions of DSPE-PEG and EPC (from 0/100 to 50/50 (mol/mol)) were 10.8-5.0 w%, respectively. The mixed micelles showed good cytocompatibility at concentrations of glycocholic acid between 0.12 and 1.20 mM.

CONCLUSIONS

Mixed micelles with superior stability to Konakion® MM at low pH were obtained by introducing DSPE-PEG 2000. These are therefore attractive oral formulations for vitamin K.

The safety and persistence of non-vitamin-K-antagonist oral anticoagulants in atrial fibrillation patients treated in a well structured atrial fibrillation clinic

AIMS

To examine the long-term persistence and safety of the non-vitamin-K-antagonist oral anticoagulants (NOACs) dabigatran (D), rivaroxaban (R) and apixaban (A) in patients with non-valvular atrial fibrillation (AF) treated in the framework of a well structured, nurse-based AF unit for initiation and follow-up of NOAC.

METHODS

Retrospective clinical data were collected for 766 consequent patients from a single cardiology outpatient clinic incorporating the AF unit.

RESULTS

The follow-up time, median (q1-q3), was 367 days (183-493) for D patients (n = 233), 432 days (255-546) for R patients (n = 282) and 348 days (267-419) for A patients (n = 251). No significant differences were found between the three groups with regard to age, sex, renal function, or CHA2DS2-VASc score. For all bleeding events the incidence rates per 100 patient-years of follow-up (95% confidence interval [CI], p-value) were reported more often for treatment with R (17.2, 12.7-22.8) than for D (7.0, 4.0-11.3, p = 0.001) and A (8.7, 5.2-13.6, p = 0.013). The differences remained significant after adjustment for clinically relevant variables. Discontinuation rates (n = 167) were lower for A (11.5, 7.5-16.8) than for D (30, 23.4-37.9, p < 0.001) and R (23.9, 18.6-30.1, p = 0.001), and were mainly attributed to drug-specific side effects and bleedings. The majority of discontinued patients (n = 142, 85%) proceeded with other types of oral anticoagulants.

LIMITATION

The main limitation of the study is the small patient population with a short follow-up time.

CONCLUSION

In a retrospective study at a single AF clinic, NOACs showed significantly different bleeding rates and varied discontinuation rates when compared to each other, related mainly to agent-specific side effects and bleedings. The majority of patients that discontinued proceeded with other types of oral anticoagulant.

Bleeding risk in warfarinized patients with a therapeutic international normalized ratio: the effect of low factor IX levels

OBJECTIVE

Bleeding is the main complication of warfarin therapy, even patients with an international normalized ratio (INR) in the target range can suffer bleeding, suggesting that INR does not perfectly reflect the therapeutic effect of warfarin. We hypothesized the INR might underestimate the level of anticoagulation in a subject with a lower factor (F) IX level than average.

METHODS AND RESULTS

We modeled warfarin anticoagulation in our in vitro thrombin generation (TG) model by adjusting the levels of vitamin K-dependent factors to those of patients with an INR of 2-3. Variation in FIX had a marked effect on TG but had no effect on the prothrombin time (PT)-INR. A prospective observational, cross-sectional clinical study including 341 consecutive patients admitted to the emergency department with an INR between 2 and 3, showed a statistically lower FIX activity in bleeders (P = 0.004) compared with others. No correlation was found between TG capacity and PT-INR results (P = 0.36). However, in patients, presenting with a warfarin-related hemorrhage, TG was significantly lower (P < 0.001) than others. A correlation on the boundary of significance was observed between TG capacity and FIX levels (P = 0.09).

CONCLUSION

These data demonstrates that patients who bleed when their PT-INR is in the target range 2-3 might have defective TG related to a lower level of FIX than expected.

Vitamins K interact with N-terminus α-synuclein and modulate the protein fibrillization in vitro. Exploring the interaction between quinones and α-synuclein

In the last decades, a series of compounds, including quinones and polyphenols, has been described as having anti-fibrillogenic action on α-synuclein (α-syn) whose aggregation is associated to the pathogenesis of Parkinson's disease (PD). Most of these molecules act as promiscuous anti-amyloidogenic agents, interacting with the diverse amyloidogenic proteins (mostly unfolded) through non-specific hydrophobic interactions. Herein we investigated the effect of the vitamins K (phylloquinone, menaquinone and menadione), which are 1,4-naphthoquinone (1,4-NQ) derivatives, on α-syn aggregation, comparing them with other anti-fibrillogenic molecules such as quinones, polyphenols and lipophilic vitamins. Vitamins K delayed α-syn fibrillization in substoichiometric concentrations, leading to the formation of short, sheared fibrils and amorphous aggregates, which are less prone to produce leakage of synthetic vesicles. In seeding conditions, menadione and 1,4-NQ significantly inhibited fibrils elongation, which could be explained by their ability to destabilize preformed fibrils of α-syn. Bidimensional NMR experiments indicate that a specific site at the N-terminal α-syn (Gly31/Lys32) is involved in the interaction with vitamins K, which is corroborated by previous studies suggesting that Lys is a key residue in the interaction with quinones. Together, our data suggest that 1,4-NQ, recently showed up by our group as a potential scaffold for designing new monoamine oxidase inhibitors, is also capable to modulate α-syn fibrillization in vitro.

ABCC6 as a target in pseudoxanthoma elasticum

The ABCC6 gene encodes an organic anion transporter protein, ABCC6/MRP6. Mutations in the gene cause a rare, recessive genetic disease, pseudoxanthoma elasticum, while the loss of one ABCC6 allele is a genetic risk factor in coronary artery disease. We review here the information available on gene structure, evolution as well as the present knowledge on its transcriptional regulation. We give a detailed description of the characteristics of the protein, and analyze the relationship between the distributions of missense disease-causing mutations in the predicted three-dimensional structure of the transporter, which suggests functional importance of the domain-domain interactions. Though neither the physiological function of the protein nor its role in the pathobiology of the diseases are known, a current hypothesis that ABCC6 may be involved in the efflux of one form of Vitamin K from the liver is discussed. Finally, we analyze potential strategies how the gene can be targeted on the transcriptional level to increase protein expression in order to compensate for reduced activity. In addition, pharmacologic correction of trafficking-defect mutants or suppression of stop codon mutations as potential future therapeutic interventions are also reviewed.

Recovery of solanesol from tobacco as a value-added byproduct for alternative applications

Solanesol in the waste streams of a bioprocess designed for alternative applications of low-alkaloid tobacco was recovered using three different extraction methods. Compared to the conventional heat-reflux extraction (HRE) and ultrasound-assisted extraction (UAE), microwave-assisted extraction (MAE) using 1:3 hexane:ethanol (v/v) as the solvent after saponification treatment of tobacco biomass was found the most effective in terms of solanesol yield, processing time, and volume of solvent consumed. Quantification of solanesol was achieved by optimizing the mobile phase at 60/40 acetonitrile-isopropanol and lowering the oven temperature to 22 degrees C using a standard reverse-phase high performance liquid chromatography (RP-HPLC). The total solanesol recovered from tobacco biomass and chloroplast accounted for 30% (w/w) of the total solanesol in the fresh leaves. Since solanesol is the precursor of metabolically active quinones such as coenzyme Q10 and vitamin K analogues, extraction of solanesol from tobacco bioprocess waste is a feasible operation and could leverage the overall profitability of biorefining tobacco for alternative, value-added uses.

Effects of various vitamins and coenzymes Q on reactions involving α-hydroxyl-containing radicals

Effects of vitamins B, C, E, K and P, as well as coenzymes Q, on formation of final products of radiation-induced free-radical transformations of ethanol, ethylene glycol, alpha-methylglycoside and glucose in aqueous solutions were studied. Based on the obtained results, it can be concluded that there are substances among vitamins and coenzymes that effectively interact with alpha-hydroxyl-containing radicals. In the presence of these substances, recombination reactions of alpha-hydroxyalkyl radicals and fragmentation of alpha-hydroxy-beta-substituted organic radicals are suppressed. It has been established that the observed effects are due to the ability of the vitamins and coenzymes under study to either oxidize alpha-hydroxyl-containing radicals yielding the respective carbonyl compounds or reduce them into the initial molecules.

VKORC1 deficiency in mice causes early postnatal lethality due to severe bleeding

Vitamin K hydroquinone is oxidised to the epoxide form (K>O) during vitamin K-dependent posttranslational gamma-glutamyl carboxylation resulting in biological active so called vitamin K-dependent proteins. In turn, K>O is reduced by the enzyme VKORC1 (vitamin K epoxide reductase complex component 1) to complete the vitamin K cycle. To investigate the biological role of VKORC1 in vivo, we generated VKORC1 knockout mice. Homozygous VKORC1-deficient mice developed normally until birth. Within 2-20 days after birth, the knockout mice died due to extensive, predominantly intracerebral haemorrhage. Bleeding resulted from a severe deficiency of gamma-carboxylated clotting factors. This lethal phenotype could be rescued by oral administration of vitamin K. Additionally, morphometric analysis of the limbs in VKORC1-deficient animals revealed reduced length of bone calcification relative to wild-type control mice. The observed phenotype of VKORC1 knockout mice excludes the existence of other enzymes with VKOR activity that can substitute to supply vitamin K hydroquinone required for maturation of blood clotting factors. Thus, our study underscores the essential role of VKORC1 in vitamin K-dependent gamma-glutamyl carboxylation.

Participation of low molecular weight electron carriers in oxidative protein folding

Oxidative protein folding is mediated by a proteinaceous electron relay system, in which the concerted action of protein disulfide isomerase and Ero1 delivers the electrons from thiol groups to the final acceptor. Oxygen appears to be the final oxidant in aerobic living organisms, although the existence of alternative electron acceptors, e.g. fumarate or nitrate, cannot be excluded. Whilst the protein components of the system are well-known, less attention has been turned to the role of low molecular weight electron carriers in the process. The function of ascorbate, tocopherol and vitamin K has been raised recently. In vitro and in vivo evidence suggests that these redox-active compounds can contribute to the functioning of oxidative folding. This review focuses on the participation of small molecular weight redox compounds in oxidative protein folding.

Metabolism and cell biology of vitamin K

Naturally occurring vitamin K compounds comprise a plant form, phylloquinone (vitamin K(1)) and a series of bacterial menaquinones (MKs) (vitamin K(2)). Structural differences in the isoprenoid side chain govern many facets of metabolism of K vitamins including the way they are transported, taken up by target tissues, and subsequently excreted. In the post-prandial state, phylloquinone is transported mainly by triglyceride-rich lipoproteins (TRL) and long-chain MKs mainly by low-density lipoproteins (LDL). TRL-borne phylloquinone uptake by osteoblasts is an apoE-mediated process with the LRP1 receptor playing a predominant role. One K(2) form, MK-4, has a highly specific tissue distribution suggestive of local synthesis from phylloquinone in which menadione is an intermediate. Both phylloquinone and MKs activate the steroid and xenobiotic receptor (SXR) that initiates their catabolism, but MK-4 specifically upregulates two genes suggesting a novel MK-4 signalling pathway. Many studies have shown specific clinical benefits of MK-4 at pharmacological doses for osteoporosis and cancer although the mechanism(s) are poorly understood. Other putative non-cofactor functions of vitamin K include the suppression of inflammation, prevention of brain oxidative damage and a role in sphingolipid synthesis. Anticoagulant drugs block vitamin K recycling and thereby the availability of reduced vitamin K. Under extreme blockade, vitamin K can bypass the inhibition of Gla synthesis in the liver but not in the bone and the vessel wall. In humans, MK-7 has a greater efficacy than phylloquinone in carboxylating both liver and bone Gla proteins. A daily supplement of phylloquinone has shown potential for improving anticoagulation control.

Enhancement of skin penetration of vitamin K using monoolein-based liquid crystalline systems

Application of vitamin K (vitK) to the skin has been used for suppression of pigmentation and resolution of bruising. However, there is no report concerning the extent of its penetration in the skin. In this study, we investigated the in vitro skin penetration and transdermal delivery of vitK, and whether these parameters may be enhanced by lipid-based drug delivery systems. The lipid formulation used in this study contains monoolein (MO), which is structured as a liquid crystalline phase, named hexagonal phase. The skin penetration of vitK was assessed in vitro using porcine ear skin mounted in a Franz diffusion cell. VitK (2.5%, w/w) was incorporated in either of three formulations: liquid vaseline, MO-based hexagonal phase gel (MO-vitK-water at 77.5/2.5/20, w/w/w) and MO-based nanodispersion of hexagonal phase (MO-vitK-poloxamer-water at 15/2.5/0.9/81.6, w/w/w/w). When vaseline was used, vitK was delivered mainly to the stratum corneum (SC): 9.50+/-0.97 microg/cm(2) of vitK was delivered to the SC at 12 h post-application, whereas 4.90 +/- 1.28 microg/cm(2) of vitK was delivered to the epidermis (E)+dermis (D) at the same time point. The hexagonal phase gel and the nanodispersion delivered approximately 2 times more vitK to the SC and 2.0-3.7 times more vitK to the [E+D] than the vaseline solution. The nanodispersion (but not the gel) also increased the transdermal delivery of vitK at 9 h ( approximately 3-fold increase). These results demonstrate that the topical delivery of vitK incorporated in a lipophilic vehicle is small, but it may be enhanced by MO-based systems, which might be useful to increase the effectiveness of topical vitK therapy.

A quantum chemical study of the mechanism of action of Vitamin K epoxide reductase (VKOR)

A reaction path including transition states is generated for the Silverman mechanism [R.B. Silverman, Chemical model studies for the mechanism of Vitamin K epoxide reductase, J. Am. Chem. Soc. 103 (1981) 5939-5941] of action for Vitamin K epoxide reductase (VKOR) using quantum mechanical methods (B3LYP/6-311G**). VKOR, an essential enzyme in mammalian systems, acts to convert Vitamin K epoxide, formed by Vitamin K carboxylase, to its (initial) quinone form for cellular reuse. This study elaborates on a prior work that focused on the thermodynamics of VKOR [D.W. Deerfield II, C.H. Davis, T. Wymore, D.W. Stafford, L.G. Pedersen, Int. J. Quant. Chem. 106 (2006) 2944-2952]. The geometries of proposed model intermediates and transition states in the mechanism are energy optimized. We find that once a key disulfide bond is broken, the reaction proceeds largely downhill. An important step in the conversion of the epoxide back to the quinone form involves initial protonation of the epoxide oxygen. We find that the source of this proton is likely a free mercapto group rather than a water molecule. The results are consistent with the current view that the widely used drug Warfarin likely acts by blocking binding of Vitamin K at the VKOR active site and thereby effectively blocking the initiating step. These results will be useful for designing more complete QM/MM studies of the enzymatic pathway once three-dimensional structural data is determined and available for VKOR.

A quantum chemical study of the mechanism of action of Vitamin K carboxylase (VKC)

A reaction path including transition states is generated for the Dowd mechanism [P. Dowd, R. Hershlne, S.W. Ham, S. Naganathan. Vitamin K and energy transduction: a base strength amplification mechanism. Science 269 (2005) 1684-1691] of action for Vitamin K carboxylase (VKC) using quantum chemical methods (B3LYP/6-311G**). VKC, an essential enzyme in mammalian systems, catalyzes the conversion of hydroquinone form of Vitamin K to the epoxide form in the presence of oxygen. An intermediate species of the oxidation of Vitamin K, an alkoxide, acts apparently to abstract the gamma hydrogen from specifically located glutamate residues. We are able to follow the Dowd proposed path to generate this alkoxide species. The geometries of the proposed model intermediates and transition states in the mechanism are energy optimized. We find that the most energetic step in the mechanism is the uni-deprotonation of the hydroquinone - once this occurs, there is only a small barrier of 3.5kcal/mol for the interaction of oxygen with the carbon to be attacked - and then the reaction proceeds downhill in free energy to form the critical alkoxide species. The results are consistent with the idea that the enzyme probably acts to facilitate the formation of the epoxide by reducing the energy required to deprotonate the hydroquinone form.

Excretion of the urinary 5C- and 7C-aglycone metabolites of vitamin K by young adults responds to changes in dietary phylloquinone and dihydrophylloquinone intakes

The physiological function and putative health roles of vitamin K-dependent proteins now extend beyond their classical role in hemostasis and include bone mineralization, arterial calcification, apoptosis, phagocytosis, growth control, chemotaxis, and signal transduction. Current assessments of vitamin K status do not reflect the variety of molecular forms of vitamin K. We assessed whether urinary excretion of 2-methyl-3-(5'-carboxy-3'-methyl-2'-pentenyl)-1,4-naphthoquinone (7C-aglycone) and 2-methyl-3-(3'-3'-carboxymethylpropyl)-1,4-naphthoquinone (5C-aglycone), vitamin K metabolites common to both phylloquinone and the menaquinone series, reflect dietary vitamin K intake. In a randomized crossover study, 9 adults resided in a metabolic unit for two 30-d periods separated by a free-living period of > or = 4 wk. During each residency, subjects consumed 3 sequential diets: a control diet (93 microg phylloquinone/d) for 5 d, a phylloquinone-restricted diet (11 microg/d) for 15 d, followed by a randomly assigned repletion diet for 10 d with either phylloquinone (206 microg/d) or dihydrophylloquinone (240 microg/d). During the second residency, the alternative repletion diet was assigned. Urinary excretion of the 5C- and 7C-aglycones was measured in sequential 24-h collections. The 5C-aglycone accounted for approximately 75% of total excretion and declined in response to phylloquinone restriction (P = 0.001) to approximately 30% of that during the control diet period. Repletion with phylloquinone and dihydrophylloquinone doubled the excretion rate of the major 5C-aglycone by 24 h (P < 0.001), and tripled excretion by 4 d. There was a linear relationship between the logarithm of total urinary excretion and dietary vitamin K intake (r = 0.699, P < 0.001). We conclude that the urinary excretion of vitamin K metabolites reflects dietary phylloquinone intake and offers the first candidate marker of global vitamin K status.

Quantum chemical study of the mechanism of action of vitamin K carboxylase (VKC). IV. Intermediates and transition states

We studied proposed steps for the enzymatic formation of gamma-carboxyglutamic acid by density functional theory (DFT) quantum chemistry. Our results for one potentially feasible mechanism show that a vitamin K alkoxide intermediate can abstract a proton from glutamic acid at the gamma-carbon to form a carbanion and vitamin K epoxide. The hydrated carbanion can then react with CO2 to form gamma-carboxyglutamic acid. Computations at the B3LYP/6-311G** level were used to determine the intermediates and transition states for the overall process. The activation free energy for the gas-phase path is 22 kcal/mol, with the rate-limiting step for the reaction being the attack of the carbanion on CO2. Additional solvation studies, however, indicate that the formation of the carbanion step can be competitive with the CO2 attack step in high-dielectric systems. We relate these computations to the entire vitamin K cycle in the blood coagulation cascade, which is essential for viability of vertebrates.

Huge intrathyroidal hematoma causing airway obstruction: a multidisciplinary challenge

Thyroid hemorrhage is a relatively frequent event that in most cases causes pain and discomfort only, while rarely can cause significant neck swelling. Even more rarely, however, extensive thyroid hemorrhage can result in a rapidly expanding hematoma with airway compromise. We report a case of a rapidly expanding thyroid hemorrhage that occurred secondary to oral anticoagulation therapy in an 80-year-old patient with a previously existing goiter. The patient presented with acute onset of neck pain, dysphagia, and respiratory distress caused by tracheal compression from the thyroid mass. Computed tomography demonstrated a 6 x 9 x 10 cm mass consistent with an intrathyroidal hematoma projecting into the anterior mediastinum and displacing the trachea to the left. Rapid reversal of the coagulopathy was achieved with fresh frozen plasma and vitamin K. Consequently, the patient was managed conservatively with close observation, antibiotics, and steroids because no progression of airway compromise was manifested. Although the diagnosis can be easily established in these patients, no management guidelines of this condition exist. The potential of rapid airway compromise and the risk for exacerbation of bleeding in the light of significant elevation in the international normalized ratio (INR), make any airway management decisions very difficult. The importance of managing the airway and the haemostatic problem with the help of a multidisciplinary team is discussed.

Comparative uptake, metabolism, and utilization of menaquinone-4 and phylloquinone in human cultured cell lines

It is generally accepted that the availability of vitamin K in vivo depends on its homologues, the biological activities of which would differ among organs. To test this hypothesis, we examined the uptake, metabolism, and utilization of menaquinone-4 (MK-4) and phylloquinone (PK) using 18O-labeled compounds in two cultured human cell lines (HepG2 and MG-63). Lipid extracts were prepared from the cells and media after 1, 3, and 6h of incubation. The detection of the vitamin K analogues (18O-, 16O-quinone, and epoxide forms) was carried out with LC-APCI-MS/MS as previously reported. The 18O of vitamin K was replaced with atmospheric 16O2 during the formation of vitamin K epoxide with a carboxylative catalytic reaction. As a result, a significant difference was observed between MK-4 and PK in the amounts taken up into the cells. The 18O-labeled MK-4 was rapidly and remarkably well absorbed into the cells and metabolized to the epoxide form via a hydroquinone form as compared to the 18O-labeled PK. The difference in uptake of MK-4 and PK was not affected by treatment with warfarin although the metabolism of both compounds was markedly inhibited. This methodology should be utilized to clarify some of the actions of vitamin K in target cells and facilitate the development of new vitamin K drugs.

Vitamin K epoxide reductase complex subunit 1 (VKORC1): the key protein of the vitamin K cycle

Vitamin K epoxide, a by-product of the carboxylation of blood coagulation factors, is reduced to vitamin K by an enzymatic system possessing vitamin K epoxide reductase (VKOR) activity. This system is the target of coumarin-derived drugs widely used in thrombosis therapy and prophylaxis. Recently, the key protein of the VKOR system has been identified. The human VKORC1 gene maps to chromosome 16 and consists of 3 exons encoding a 163-amino acid integral ER membrane protein with three or four predicted transmembrane alpha- helices. Expression of human VKORC1 in Spodoptera frugiperda (Sf9) cells and in Pichia pastoris results in enhanced VKOR activity over low endogenous constitutive levels. Sequence based search methods reveal that human VKORC1 belongs to a large family of homologous genes found in vertebrates, insects, plants, protists, archea, and bacteria. All orthologs share five completely conserved amino acids, including two cysteines found in a tetrapeptide motif presumably required for redox function. The recent discovery of the VKORC1 gene has initiated renewed interest in understanding VKOR activity. Analysis of VKORC1 protein structure and function will be crucial in understanding the VKOR catalytic mechanism, how anticoagulant drugs modulate VKOR activity, and the role of VKORC1 in downstream physiological and pathological pathways.

Solid lipid nanoparticles (SLN) for topical drug delivery: incorporation of the lipophilic drugs N,N-diethyl-m-toluamide and vitamin K

Solid lipid nanoparticles (SLN) for topical delivery were prepared by high pressure homogenization using solid lipids. The lipophilic agents DEET (N,N-diethyl-m-toluamide) and vitamin K were used as model drugs. These topical agents were incorporated into SLN which were characterized. Differential scanning calorimetry studies were performed in order to detect probable interactions in the SLN dispersions. Physical stability of SLN in aqueous dispersions and the effect of drug incorporation into SLN were investigated by photon correlation spectroscopy and zeta potential measurements. Characterization and short-term stability studies showedthat DEET and vitamin K are good candidates for topical SLN formulations.

The functional significance of the autolysis loop in protein C and activated protein C

The autolysis loop of activated protein C (APC) is five residues longer than the autolysis loop of other vitamin K-dependent coagulation proteases. To investigate the role of this loop in the zymogenic and anticoagulant properties of the molecule, a protein C mutant was constructed in which the autolysis loop of the protein was replaced with the corresponding loop of factor X. The protein C mutant was activated by thrombin with approximately 5-fold higher rate in the presence of Ca2+. Both kinetics and direct binding studies revealed that the Ca2+ affinity of the mutant has been impaired approximately 3-fold. The result of a factor Va degradation assay revealed that the anticoagulant function of the mutant has been improved 4-5-fold in the absence but not in the presence of protein S. The improvement was due to a better recognition of both the P1-Arg506 and P1-Arg306 cleavage sites by the mutant protease. However, the plasma half-life of the mutant was markedly shortened due to faster inactivation by plasma serpins. These results suggest that the autolysis loop of protein C is critical for the Ca(2+)-dependence of activation by thrombin. Moreover, a longer autolysis loop in APC is not optimal for interaction with factor Va in the absence of protein S, but it contributes to the lack of serpin reactivity and longer half-life of the protease in plasma.

The vitamin K-dependent carboxylase has been acquired by Leptospira pathogens and shows altered activity that suggests a role other than protein carboxylation

Leptospirosis is an emerging infectious disease whose pathology includes a hemorrhagic response, and sequencing of the Leptospira interrogans genome revealed an ortholog of the vitamin K-dependent (VKD) carboxylase as one of several hemostatic proteins present in the bacterium. Until now, the VKD carboxylase was known to be present only in the animal kingdom (i.e. metazoans that include mammals, fish, snails, and insects), and this restricted distribution and high sequence similarity between metazoan and Leptospira orthologs strongly suggests that Leptospira acquired the VKD carboxylase by horizontal gene transfer. In metazoans, the VKD carboxylase is bifunctional, acting as an epoxidase that oxygenates vitamin K to a strong base and a carboxylase that uses the base to carboxylate Glu residues in VKD proteins, rendering them active in hemostasis and other physiologies. In contrast, the Leptospira ortholog showed epoxidase but not detectable carboxylase activity and divergence in a region of identity in all known metazoan VKD carboxylases that is important to Glu interaction. Furthermore, although the mammalian carboxylase is regulated so that vitamin K epoxidation does not occur unless Glu substrate is present, the Leptospira VKD epoxidase showed unfettered epoxidation in the absence of Glu substrate. Finally, human VKD protein orthologs were not detected in the L. interrogans genome. The combined data, then, suggest that Leptospira exapted the metazoan VKD carboxylase for some use other than VKD protein carboxylation, such as using the strong vitamin K base to drive a new reaction or to promote oxidative damage or depleting vitamin K to indirectly inhibit host VKD protein carboxylation.

The functional significance of the autolysis loop in protein C and activated protein C

The autolysis loop of activated protein C (APC) is five residues longer than the autolysis loop of other vitamin K-dependent coagulation proteases. To investigate the role of this loop in the zymogenic and anticoagulant properties of the molecule, a protein C mutant was constructed in which the autolysis loop of the protein was replaced with the corresponding loop of factor X. The protein C mutant was activated by thrombin with approximately 5-fold higher rate in the presence of Ca2+. Both kinetics and direct binding studies revealed that the Ca2+ affinity of the mutant has been impaired approximately 3-fold. The result of a factor Va degradation assay revealed that the anticoagulant function of the mutant has been improved 4-5-fold in the absence but not in the presence of protein S. The improvement was due to a better recognition of both the P1-Arg506 and P1-Arg306 cleavage sites by the mutant protease. However, the plasma half-life of the mutant was markedly shortened due to faster inactivation by plasma serpins. These results suggest that the autolysis loop of protein C is critical for the Ca(2+)-dependence of activation by thrombin. Moreover, a longer autolysis loop in APC is not optimal for interaction with factor Va in the absence of protein S, but it contributes to the lack of serpin reactivity and longer half-life of the protease in plasma.

Influence of Vitamin K on Anticoagulant Therapy Depends on Vitamin K Status and the Source and Chemical Forms of Vitamin K

Warfarin therapy requires close monitoring to avoid excessive bleeding and to maintain the effective therapeutic concentration assessed with the internationalized ratio (INR). High vitamin K intake can decrease the therapeutic effectiveness of warfarin, while poor vitamin K status appears to increase the sensitivity to small changes in vitamin K intake, especially from supplements. Very large amounts of vitamin K from a single meal with vegetables (400 g of vegetables with 700 to 1500 microg of vitamin K1) can measurably change INR, but occasional typical servings (<100 g) would probably have little lasting impact on INR. Warfarin requirements may change in those altering their intake of dark-green vegetables. The 2005 Dietary Guidelines for Americans recommends 3 cups/week of dark-green vegetables, which contain about 100 to 570 microg/serving of vitamin K1. Less well-known sources and chemical forms of vitamin K, such as MK-7 in natto (a fermented Japanese product), also measurably influence INR. Additional research is needed in warfarin-treated patients to fully quantify the interactions among various sources and chemical forms of vitamin K, age, genotype, and other factors.

Engineering of a Recombinant Vitamin K-dependent γ-Carboxylation System with Enhanced γ-Carboxyglutamic Acid Forming Capacity

The vitamin K-dependent gamma-carboxylation system in the endoplasmic reticulum membrane responsible for gamma-carboxyglutamic acid modification of vitamin K-dependent proteins includes gamma-carboxylase and vitamin K 2,3-epoxide reductase (VKOR). An understanding of the mechanism by which this system works at the molecular level has been hampered by the difficulty of identifying VKOR involved in warfarin sensitive reduction of vitamin K 2,3-epoxide to reduced vitamin K(1)H(2), the gamma-carboxylase cofactor. Identification and cloning of VKORC1, a proposed subunit of a larger VKOR enzyme complex, have provided opportunities for new experimental approaches aimed at understanding the vitamin K-dependent gamma-carboxylation system. In this work we have engineered stably transfected baby hamster kidney cells containing gamma-carboxylase and VKORC1 cDNA constructs, respectively, and stably double transfected cells with the gamma-carboxylase and the VKORC1 cDNA constructs in a bicistronic vector. All engineered cells showed increased activities of the enzymes encoded by the cDNAs. However increased activity of the gamma-carboxylation system, where VKOR provides the reduced vitamin K(1)H(2) cofactor, was measured only in cells transfected with VKORC1 and the double transfected cells. The results show that VKOR is the rate-limiting step in the gamma-carboxylation system and demonstrate successful engineering of cells containing a recombinant vitamin K-dependent gamma-carboxylation system with enhanced capacity for gamma-carboxyglutamic acid modification. The proposed thioredoxin-like (132)CXXC(135) redox center in VKORC1 was tested by expressing the VKORC1 mutants Cys(132)/Ser and Cys(135)/Ser in BHK cells. Both of the expressed mutant proteins were inactive supporting the existence of a CXXC redox center in VKOR.

Media to simulate the postprandial stomach I. Matching the physicochemical characteristics of standard breakfasts

To better predict food effects on the bioavailability/bioequivalence of drugs and drug products from in-vitro data, a dissolution medium that simulates the initial composition of the postprandial stomach was developed. First, the physical parameters of two homogenized standard breakfasts often administered to assess food effects in pharmacokinetic studies were measured. These included pH, buffer capacity, osmolality, surface tension and viscosity. Subsequently, the match of the physical parameters of several commercially available liquid meals, including long-life milk, Ensure and Ensure Plus to those of the breakfasts was evaluated. Of the three liquid meals studied, Ensure Plus had the closest physicochemical behaviour to that of homogenized standard breakfasts. By increasing the viscosity of Ensure Plus with 0.45% pectin, it was possible to obtain a medium that closely resembles the FDA standard breakfast.

Influence of coexisting phases on the surface dilatational viscosity of Langmuir monolayers

Monolayer hydrodynamics are usually described in terms of a Newtonian constitutive relationship. However, this macroscopic view fails to account for small-scale coexisting phase domains, which are generally present in the monolayer and appear to have profound macroscopic effects. Here, we provide direct evidence of these effects, consisting of Brewster angle microscopy images of the monolayer, space- and time-resolved interfacial velocity measurements, and comparisons with predictions based on the Navier-Stokes equations together with the classic model for a Newtonian interface.

Binding of the Factor IX γ-Carboxyglutamic Acid Domain to the Vitamin K-dependent γ-Glutamyl Carboxylase Active Site Induces an Allosteric Effect That May Ensure Processive Carboxylation and Regulate the Release of Carboxylated Product

Propeptides of the vitamin K-dependent proteins bind to an exosite on gamma-glutamyl carboxylase; while they are bound, multiple glutamic acids in the gamma-carboxyglutamic acid (Gla) domain are carboxylated. The role of the propeptides has been studied extensively; however, the role of the Gla domain in substrate binding is less well understood. We used kinetic and fluorescence techniques to investigate the interactions of the carboxylase with a substrate containing the propeptide and Gla domain of factor IX (FIXproGla41). In addition, we characterized the effect of the Gla domain and carboxylation on propeptide and substrate binding. For the propeptide of factor IX (proFIX18), FIXproGla41, and carboxylated FIXproGla41, the Kd values were 50, 2.5, and 19.7 nM and the koff values were 273 x 10(-5), 9 x 10(-5), and 37 x 10(-5) s(-1), respectively. The koff of proFIX18 is reduced 3-fold by FLEEL and 9-fold by the Gla domain (residues 1-46) of FIX. The pre-steady state rate constants for carboxylation of FIXproGla41 was 0.02 s(-1) in enzyme excess and 0.016 s(-1) in substrate excess. The steady state rate in substrate excess is 4.5 x 10(-4) s(-1). These results demonstrate the following. 1) The pre-steady state carboxylation rate constant of FIXproGla41 is significantly slower than that of FLEEL. 2) The Gla domain plays an allosteric role in substrate-enzyme interactions. 3) Carboxylation reduces the allosteric effect. 4) The similarity between the steady state carboxylation rate constant and product dissociation rate constant suggests that product release is rate-limiting. 5) The increased dissociation rate after carboxylation contributes to the release of product.

Homologous metabolic and gene activating routes for vitamins E and K

Vitamins E and K share structurally related side chains and are degraded to similar final products. For vitamin E the mechanism has been elucidated as initial omega-hydroxylation and subsequent beta-oxidation. For vitamin K the same mechanism can be suggested analogously. omega-Hydroxylation of vitamin E is catalyzed by cytochrome p450 enzymes, which often are induced by their substrates themselves via the activation of the nuclear receptor PXR. Vitamin E is able to induce CYP3A-forms and to activate a PXR-driven reporter gene. It is shown here that K-type vitamins are also able to activate PXR. A ranking showed that compounds with an unsaturated side chain were most effective, as are tocotrienols and menaquinone-4 (vitamin K(2)), which activated the reporter gene 8-10-fold. Vitamers with a saturated side chain, like tocopherols and phylloquinone were less active (2-5-fold activation). From the fact that CYPs commonly responsible for the elimination of xenobiotics are involved in the metabolism of fat-soluble vitamins and the ability of the vitamins to activate PXR it can be concluded that supranutritional amounts of these vitamins might be considered as foreign.

Effects of Site-Directed Mutations on Heme Reduction in Escherichia coli Nitrate Reductase A by Menaquinol: A Stopped-Flow Study

We have studied the effects of site-directed mutations in Escherichia coli nitrate reductase A (NarGHI) on heme reduction by a menaquinol analogue (menadiol) using the stopped-flow method. For NarGHI(H66Y) and NarGHI(H187Y), both lacking heme b(L) but having heme b(H), the heme reduction by menadiol is abolished. For NarGHI(H56R) and NarGHI(H205Y), both without heme b(H) but with heme b(L), a smaller and slower heme reduction compared to that of the wild-type enzyme is observed. These results indicate that electrons from menadiol oxidation are transferred initially to heme b(L). A transient species, likely to be associated with a semiquinone radical anion, was generated not only on reduction of the wild-type enzyme as observed previously (1) but also on reduction of NarGHI(H56R) and NarGHI(H205Y). The inhibitors 2-n-heptyl-4-hydroxyquinoline-N-oxide and stigmatellin both have significant effects on the reduction kinetics of NarGHI(H56R) and NarGHI(H205Y). We have also investigated the reoxidation of menadiol-reduced heme by nitrate in the mutants. Compared to the wild type, no significant heme reoxidation is observed for NarGHI(H56R) and NarGHI(H205Y). This result indicates that a single mutation removing heme b(H) blocks the electron-transfer pathway from the subunit NarI to the catalytic dimer NarGH.

Photoprocesses of p-naphthoquinones and vitamin K(1): effects of alcohols and amines on the reactivity in solution

The photochemistry of 1,4-naphthoquinone (NQ), the 2-methyl, 2,3-dichloro and 2-bromo derivatives, and vitamin K(1) was studied in non-aqueous solvents by time-resolved UV-vis spectroscopy after ns laser pulses at 248 and 308 nm. The triplet state of the NQs reacts with alcohols and amines, e.g. triethylamine (TEA) and DABCO, yielding semiquinone radicals (HQ(*)/Q (*)(-)). They are the major intermediates and their second-order decay kinetics depend on the properties of the additives and the medium. Transient conductivity measurements suggest the occurrence of photoinduced electron transfer from amines to the triplet state of NQs in acetonitrile. The photoconversion lambda (irr)= 254 nm) of NQs to the 1,4-dihydroxynaphthalenes (H(2)Q) was measured in the absence and presence of varying concentrations of electron and H-atom donors, and the quantum yield was found to increase with increasing electron- or proton-donor concentration. The mechanisms of photoreduction of NQs by propan-2-ol and TEA in acetonitrile exhibit a number of similarities. Oxygen quenches the triplet state, thereby forming singlet molecular oxygen. Oxygen also reacts with the semiquinone radical, thereby forming HO(2)(*)/O(2) (*) (-) radicals, and reacts with H(2)Q, thereby re-forming the quinone. A different pattern, involving intramolecular H-atom transfer, holds for vitamin K(1), where 1,3-quinone methide (1,3-QM) diradicals were observed in acetonitrile prior to formation of two 1,2-QM tautomers, but a triplet was not. The decay of the 1,3-QM intermediates becomes faster in the presence of alcohols and amines due to proton-transfer reactions.

Structural basis of membrane binding by Gla domains of vitamin K-dependent proteins

In a calcium-dependent interaction critical for blood coagulation, vitamin K-dependent blood coagulation proteins bind cell membranes containing phosphatidylserine via gamma-carboxyglutamic acid-rich (Gla) domains. Gla domain-mediated protein-membrane interaction is required for generation of thrombin, the terminal enzyme in the coagulation cascade, on a physiologic time scale. We determined by X-ray crystallography and NMR spectroscopy the lysophosphatidylserine-binding site in the bovine prothrombin Gla domain. The serine head group binds Gla domain-bound calcium ions and Gla residues 17 and 21, fixed elements of the Gla domain fold, predicting the structural basis for phosphatidylserine specificity among Gla domains. Gla domains provide a unique mechanism for protein-phospholipid membrane interaction. Increasingly Gla domains are being identified in proteins unrelated to blood coagulation. Thus, this membrane-binding mechanism may be important in other physiologic processes.

K vitamins, PTP antagonism, and cell growth arrest

The main function of K vitamins is to act as co-factors for gamma-glutamyl carboxylase. However, they have also recently been shown to inhibit cell growth. We have chemically synthesized a series of K vitamin analogs with various side chains at the 2 or 3 position of the core naphthoquinone structure. The analogs with short thio-ethanol side chains are found to be more potent growth inhibitors in vitro of various tumor cell lines. Cpd 5 or [2-(2-mercaptoethanol)-3-methyl-1,4-naphthoquinone] is one of the most potent. The anti-proliferation activity of these compounds is antagonized by exogenous thiols but not by non-thiol antioxidants. This suggests that the growth inhibition is mediated by sulfhydryl arylation of cellular glutathione and cysteine-containing proteins and not by oxidative stress. The protein tyrosine phosphatases (PTP) are an important group of proteins that contain cysteine at their catalytic site. PTPs regulate mitogenic signal transduction and cell cycle progression. PTP inhibition by Cpd 5 results in prolonged tyrosine phosphorylation and activation of several kinases and transcription factors including EGFR, ERK1/2, and Elk1. Cpd 5 could activate ERK1/2 either by signaling from an activated EGFR, which is upstream in the signaling cascade, or by direct inhibition of ERK1/2 phosphatase(s). Prolonged ERK1/2 phosphorylation strongly correlates with Cpd 5-mediated growth inhibition. Cpd 5 can also bind to and inhibit the Cdc25 family of dual specific phosphatases. As a result, several Cdc25 substrates (Cdk1, Cdk2, Cdk4) involved in cell cycle progression are tyrosine phosphorylated and thereby inhibited by its action. Cpd 5 could also inhibit both normal liver regeneration and hepatoma growth in vivo. DNA synthesis during rat liver regeneration following partial hepatectomy, transplantable rat hepatoma cell growth, and glutathione-S-transferase-pi expressing hepatocytes after administration of the chemical carcinogen diethylnitrosamine, are all inhibited by Cpd 5 administration. The growth inhibitory effect during liver regeneration and transplantable tumor growth is also correlated with ERK1/2 phosphorylation induced by Cpd 5. Thus, Cpd 5-mediated inhibition of PTPs, such as Cdc25 leads to cell growth arrest due to altered activity of key cellular kinases involved in signal transduction and cell cycle progression. This prototype K vitamin analog represents a novel class of growth inhibitor based upon its action as a selective PTP antagonist. It is clearly associated with prolonged ERK1/2 phosphorylation, which is in contrast with the transient ERK1/2 phosphorylation induced by growth stimulatory mitogens.

Autoschizis: a novel cell death

Vitamin C (VC) and vitamin K(3) (VK(3)) administered in a VC:VK(3) ratio of 100:1 exhibit synergistic antitumor activity and preferentially kill tumor cells by autoschizis, a novel type of necrosis characterized by exaggerated membrane damage and progressive loss of organelle-free cytoplasm through a series of self-excisions. During this process, the nucleus becomes smaller, cell size decreases one-half to one-third of its original size, and most organelles surround an intact nucleus in a narrow rim of cytoplasm. While the mitochondria are condensed, tumor cell death does not result from ATP depletion. However, vitamin treatment induces a G(1)/S block, diminishes DNA synthesis, increases H(2)O(2) production, and decreases cellular thiol levels. These effects can be prevented by the addition of catalase to scavenge the H(2)O(2). There is a concurrent 8- to 10-fold increase in intracellular Ca(2+) levels. Electrophoretic analysis of DNA reveals degradation due to the caspase-3-independent reactivation of deoxyribonuclease I and II (DNase I, DNase II). Redox cycling of the vitamins is believed to increase oxidative stress until it surpasses the reducing ability of cellular thiols and induces Ca(2+) release, which triggers activation of Ca(2+)-dependent DNase and leads to degradation of DNA. Recent experiments indicate that oral VC:VK(3) increases the life-span of tumor-bearing nude mice and significantly reduces the growth rate of solid tumors without any significant toxicity by reactivating DNase I and II and inducing autoschizis. This report discusses the mechanisms of action employed by these vitamins to induce tumor-specific death by autoschizis.

Type IV hypersensitivity to vitamin K

The day after intramuscular injection of vitamin K1 (phytomenadione) into her thigh, a 27-year-old-woman with normal liver function developed a relapsing and remitting eczematous reaction localized to the injection site, and later a further eczematous reaction under an adhesive dressing (Duoderm). On patch testing, she was positive to vitamin K1 and cross-reacted to vitamin K4; she was also positive to colophonium and to ester gum rosin, the dressing adhesive. Recurrent angioedema persisted for several months and, 2 years later, symptoms were still occurring over the injection sites. Structure-activity relationships among vitamin K allergens are discussed.

Tumor cell growth inhibition and extracellular signal-regulated kinase (ERK) phosphorylation by novel K vitamins

2-(2-hydroxy-ethylsulfanyl)-3-methyl-1,4-naphthoquinone or CPD-5, a K vitamin analog, was previously indicated to be a potent growth inhibitor for Hep 3B hepatoma cells in vitro. Here, we show that CPD-5 and two newly synthesized analogs, 2-(2-hydroxy-ethylsulfanyl)-3-methyl-5- nitro-1,4-naphthoquinone (PD-37) and 2-(2-hydroxy-ethylsulfanyl)-3- methyl-5-acetylamino-1,4-naphthoquinone (PD-42), are potent growth inhibitors of 13 different human cancer cell lines, with IC50 values in the range of 3-54 microM. Phospho-ERK was induced by each of three K vitamin analogs in every cell line in a dose-dependent manner, at growth inhibitory doses. ERK phosphorylation and growth inhibitory effects were strongly correlated, with p=0.0080 for CPD-5, p=0.0076 for PD-37 and p=0.0251 for PD-42. The induction of phospho-ERK and growth inhibition were antagonized by thiol-containing anti-oxidants, but not by catalase, consistent with a possible arylating mechanism. The data show a novel class of growth inhibitors with a wide spectrum of action that induces ERK hyper-phosphorylation, as a possible new growth inhibitory feature.

[Vitamin K in the Norwegian diet and osteoporosis]

BACKGROUND

In search of vitamin K literature, interesting results were discovered. A summary is presented.

MATERIAL AND METHODS

The literature was found by using Medline. The level of vitamin K1 in the Norwegian diet was estimated from tables of food consumption and vitamin K1 per 100 g.

RESULTS

Vitamin K is required for the carboxylation of the amino acid glutamic acid to gamma-carboxyglutamic acids on proteins, which is essential for the calcium binding capacity of Gla proteins (such as osteocalcin). These proteins are found in tissues such as bone, brain, pancreas and lungs, showing that Gla proteins have further important functions. Low intakes of the vitamin may be an important factor for osteoporosis and possibly also for atherosclerosis. The level of vitamin K1 in the Norwegian diet (purchase level) is estimated to be 60 micrograms K1/day before correction of waste. This level is lower than the recommended dietary allowance (1 microgram/kg body weight/day).

INTERPRETATION

There is a discussion in the literature of whether the allowances should be considerably higher (375 micrograms K1/day). Deep green vegetables and soybean oil are the best sources of vitamin K1, while cheese gives some K2. On the basis of this knowledge about the importance of vitamin K and osteoporosis, an intervention test should be done with respect to the high incidence of osteoporosis in Norway. Analysis of Norwegian foods for vitamin K1 and K2 is needed.

Folate activation and catalysis in methylenetetrahydrofolate reductase from Escherichia coli: roles for aspartate 120 and glutamate 28

The flavoprotein Escherichia coli methylenetetrahydrofolate reductase (MTHFR) catalyzes the reduction of 5,10-methylenetetrahydrofolate (CH(2)-H(4)folate) to 5-methyltetrahydrofolate (CH(3)-H(4)folate). The X-ray crystal structure of the enzyme has revealed the amino acids at the flavin active site that are likely to be relevant to catalysis. Here, we have focused on two conserved residues, Asp 120 and Glu 28. The presence of an acidic residue (Asp 120) near the N1-C2=O position of the flavin distinguishes MTHFR from all other known flavin oxidoreductases and suggests an important function for this residue in modulating the flavin reactivity. Modeling of the CH(3)-H(4)folate product into the enzyme active site also suggests roles for Asp 120 in binding of folate and in electrostatic stabilization of the putative 5-iminium cation intermediate during catalysis. In the NADH-menadione oxidoreductase assay and in the isolated reductive half-reaction, the Asp120Asn mutant enzyme is reduced by NADH 30% more rapidly than the wild-type enzyme, which is consistent with a measured increase in the flavin midpoint potential. Compared to the wild-type enzyme, the mutant showed 150-fold decreased activity in the physiological NADH-CH(2)-H(4)folate oxidoreductase reaction and in the oxidative half-reaction involving CH(2)-H(4)folate, but the apparent K(d) for CH(2)-H(4)folate was relatively unchanged. Our results support a role for Asp 120 in catalysis of folate reduction and perhaps in stabilization of the 5-iminium cation. By analogy to thymidylate synthase, which also uses CH(2)-H(4)folate as a substrate, Glu 28 may serve directly or via water as a general acid catalyst to aid in 5-iminium cation formation. Consistent with this role, the Glu28Gln mutant was unable to catalyze the reduction of CH(2)-H(4)folate and was inactive in the physiological oxidoreductase reaction. The mutant enzyme was able to bind CH(3)-H(4)folate, but reduction of the FAD cofactor was not observed. In the NADH-menadione oxidoreductase assay, the mutant demonstrated a 240-fold decrease in activity.

Methylenetetrahydrofolate reductase from Escherichia coli: elucidation of the kinetic mechanism by steady-state and rapid-reaction studies

The flavoprotein methylenetetrahydrofolate reductase (MTHFR) from Escherichia coli catalyzes the reduction of 5,10-methylenetetrahydrofolate (CH(2)-H(4)folate) to 5-methyltetrahydrofolate (CH(3)-H(4)folate) using NADH as the source of reducing equivalents. The enzyme also catalyzes the transfer of reducing equivalents from NADH or CH(3)-H(4)folate to menadione, an artificial electron acceptor. Here, we have determined the midpoint potential of the enzyme-bound flavin to be -237 mV. We have examined the individual reductive and oxidative half-reactions constituting the enzyme's activities. In an anaerobic stopped-flow spectrophotometer, we have measured the rate constants of flavin reduction and oxidation occurring in each half-reaction and have compared these with the observed catalytic turnover numbers measured under steady-state conditions. We have shown that, in all cases, the half-reactions proceed at rates sufficiently fast to account for overall turnover, establishing that the enzyme is kinetically competent to catalyze these oxidoreductions by a ping-pong Bi-Bi mechanism. Reoxidation of the reduced flavin by CH(2)-H(4)folate is substantially rate limiting in the physiological NADH-CH(2)-H(4)folate oxidoreductase reaction. In the NADH-menadione oxidoreductase reaction, the reduction of the flavin by NADH is rate limiting as is the reduction of flavin by CH(3)-H(4)folate in the CH(3)-H(4)folate-menadione oxidoreductase reaction. We conclude that studies of individual half-reactions catalyzed by E. coli MTHFR may be used to probe mechanistic questions relevant to the overall oxidoreductase reactions.

Oxygen free radical generating mechanisms in the colon: do the semiquinones of vitamin K play a role in the aetiology of colon cancer?

It is proposed that bile acids (deoxycholic acid), the K vitamins, iron(II) complexes and oxygen interact to induce an oncogenic effect in the colon by the generation of free radicals. In the relatively low oxidising/reducing conditions of the colonic lumen the K vitamins exist in the reduced form; however, if absorbed into the mucosa they have the capacity to be chemically oxidised and to enter into a redox cycle yielding oxygen radicals. The semiquinone radical of K(1) (phylloquinone) has been stabilised in bile acid mixed micelles and investigated by electron paramagnetic resonance spectroscopy and quantum chemical calculations. The estimated half-life of the radical was about 30 min which confirms a remarkably high stability in aqueous micellar solution. A model is presented in which the reduced K vitamins may initiate superoxide radical, O2(-*) generation leading to Fe(II) mediated Fenton reactions in the stem colon cells.

Generation of a proton potential by succinate dehydrogenase of Bacillus subtilis functioning as a fumarate reductase

The membrane fraction of Bacillus subtilis catalyzes the reduction of fumarate to succinate by NADH. The activity is inhibited by low concentrations of 2-(heptyl)-4-hydroxyquinoline-N-oxide (HOQNO), an inhibitor of succinate: quinone reductase. In sdh or aro mutant strains, which lack succinate dehydrogenase or menaquinone, respectively, the activity of fumarate reduction by NADH was missing. In resting cells fumarate reduction required glycerol or glucose as the electron donor, which presumably supply NADH for fumarate reduction. Thus in the bacteria, fumarate reduction by NADH is catalyzed by an electron transport chain consisting of NADH dehydrogenase (NADH:menaquinone reductase), menaquinone, and succinate dehydrogenase operating in the reverse direction (menaquinol:fumarate reductase). Poor anaerobic growth of B. subtilis was observed when fumarate was present. The fumarate reduction catalyzed by the bacteria in the presence of glycerol or glucose was not inhibited by the protonophore carbonyl cyanide m-chlorophenyl hydrazone (CCCP) or by membrane disruption, in contrast to succinate oxidation by O2. Fumarate reduction caused the uptake by the bacteria of the tetraphenyphosphonium cation (TPP+) which was released after fumarate had been consumed. TPP+ uptake was prevented by the presence of CCCP or HOQNO, but not by N,N'-dicyclohexylcarbodiimide, an inhibitor of ATP synthase. From the TPP+ uptake the electrochemical potential generated by fumarate reduction was calculated (Deltapsi = -132 mV) which was comparable to that generated by glucose oxidation with O2 (Deltapsi = -120 mV). The Deltapsi generated by fumarate reduction is suggested to stem from menaquinol:fumarate reductase functioning in a redox half-loop.

Concerted action of DT-diaphorase and superoxide dismutase in preventing redox cycling of naphthoquinones: an evaluation

It has been suggested that the enzymes DT-diaphorase and superoxide dismutase act in concert to prevent redox cycling of naphthoquinones and thus protect against the toxic effects of such substances. Little is known, however, about the scope of this process or the conditions necessary for its operation. In the presence of low levels of DT-diaphorase, 2-methyl-1,4-naphthoquinone was found to undergo redox cycling. This was very effectively inhibited by SOD, and in the presence of both enzymes the hydroquinone was maintained in the reduced form. The inhibitory effect of the enzyme combination was overcome, however, at high concentrations of the quinone, or by small increases in pH. Furthermore, redox cycling was re-established by addition of haemoproteins such as cytochrome c and methaemoglobin. DT-diaphorase and SOD strongly inhibited redox cycling by 2,3-dimethyl- and 2,3-dimethoxy-1,4-naphthoquinone, but not that of 2-hydroxy-, 5-hydroxy- or 2-amino-1,4-naphthoquinone. Inhibition of redox cycling by a combination of DT-diaphorase and SOD is therefore not applicable to all naphthoquinone derivatives, and when it does occur, it may be overwhelmed at high quinone concentrations, and it may not operate under slightly alkaline conditions or in the presence of tissue components capable of initiating hydroquinone autoxidation.