The systems involved in vitaminK-dependent carboxylation and vitaminK metabolism have been extensively studied in rat liver. To determine how clinically applicable this information is, similar in vitro studies were completed using human liver. One major difference exists in the pathways that provide reduced vitamin K1 cofactor for the carboxylation reaction. The coumarin-sensitive DT-diaphorase (EC.18.104.22.168) in human liver appears to play a relatively minor role in the dehydrogenase pathway. However, similar to rat liver, the human liver contains a warfarin-insensitive enzyme in this dehydrogenase pathway. The data suggest that this enzyme is responsible for the antidotic effect of vitamin K1 in cases of coumarin intoxication. Human vitaminK epoxide reductase, which constitutes the other pathway for vitamin K1 reduction, has kinetic and enzymological characteristics that are very similar to the rat enzyme. This enzyme exhibited similar activity in rat and human microsomes. Initial velocities for vitamin K1 epoxide reduction in rat and human microsomes were 20 and 32 pmol/mg X min, respectively. The human enzyme is highly sensitive to warfarin inhibition. The mechanism for this inhibition appears to be similar to what has been proposed for the rat enzyme. Also, a vitaminK-dependent carboxylation system is described that allows both pathways to support the carboxylation reaction with reduced vitamin K1 cofactor. The effect of warfarin on this in vitro […]
The pathogenesis of valvar calcification, which complicates the course of cardiac valve disease and also affects tissue valve prostheses, is incompletely understood. The present work explores the possible role of the vitaminK-dependent, calcium-binding amino acid, g- carboxyglutamic acid (Gla) in valve mineralization. Gla is normally found in the vitaminK- dependent clotting factor proteins, and is also present in unique calcium binding proteins in bone, kidney, and lung. Unique Gla-containing proteins have also been isolated from pathologic calcifications including calcium containing renal stones and calcified
Mapping of the vitaminK-dependent carboxylase to identify functional regions has revealed several general insights, some consistent with the identification of a functionally important motif within the central region of the enzyme. Roth (25) dem- onstrated that truncation of 46 amino acids at the C terminus of bovine carboxylase did not interfere with enzymatic function in vitro, whereas truncation of 82 residues from the C terminus interfered with epoxidation but not propeptide binding or glu- tamate binding. A naturally occurring carboxylase mutation in a patient with deficiency of the vitaminK-dependent carboxyl- ase occurs at leucine 394 (26), within the most conserved region of the motif that we have identified. This residue is highly conserved, but it is not known how this mutation interferes with enzymatic activity. Modified scanning mutagenesis of bo- vine carboxylase included mutation of arginine 406 to alanine and histidine 408 to alanine (27). Expression of this double mutant in CHO cells was characterized by a carboxylase activ- ity with a requirement for high propeptide concentrations for stimulation of carboxylation of FLEEL, suggesting defects in the propeptide binding site.
Other side effects of warfarin use include; warfarin necrosis in patients deficient in protein C (Chan et al., 2000), purple toe syndrome (Talmadge and Spyropoulos, 2003), osteoporosis has also been seen to likely be a result of the warfarin side effect. as seen in three studies in 1999 (Caraballo et al., 1999), 2002 (Pilon et al., 2004) and 2006 (Gage et al., 2006). Several studies have implicated warfarin use in vascular and valvularcalcification (Palaniswamy et al., 2011). A rarely talked about side effect is calcification of cartilages, blood vessels and even heart valves. Any suggestion that warfarin might be associated with vascularcalcification raises the question as to why so many people, when placed on warfarin, do not develop vascularcalcification. Perhaps the complexity of the vitaminK-dependent carboxylation process might explain why some patients may be at higher risk for the development of associated vascularcalcification. Ultimately, these observations raise questions about whether the risk of vascularcalcification should be added to the risk of bleeding when considering whether to initiate certainpatients on warfarin. Interestingly, patients anticoagulated for peripheralvascular disease had an almost 10 times higher risk of bleeding than those anticoagulated for other reasons (Anand et al., 2007). It is intriguing to wonder whether certainpatients have global underactivity of their carboxylation processes, such as those with undetected vitaminK deficiency, and if suchpatients develop premature vascular disease and/or higher rates of bleeding complications when placed on warfarin. Although this is purely speculative at this point, it raises interesting questions about whether there might be certainidentifiablepopulations that are particularly at risk
90 preterm infants with a gestational age of less than 32 weeks born in the perinatal center of the University Hospital of Bonn between May 2008 and February 2010 were included in this prospective cohort study. IVH oc- curred in 17 infants (18.9%). Clinical characteristics and routine laboratory parameters of the study population are summarized in Table 1. Infants who developed an IVH were born at a significantly lower gestational age, were more frequently intubated and mechanically venti- lated, and received less frequently respiratory support by CPAP compared to those without IVH. More also re- quired surgical closure of patent ductus arteriosus. Com- parison of laboratory parameters revealed significantly lower levels of the vitaminK-dependent coagulation factors II and X in the IVH group (Table 1). Clinical data stratified for F7-323Ins10 and VKORC1 -1639G>A poly- morphisms are presented in Tables 2 and 3.
VitaminK–dependent (VKD) proteins undergo γ-glutamyl carboxylation characterized by the conversion of specific glutamic acid (Glu) residues to γ-carboxylated Glu (Gla) (reviewed in ref. 1). Carboxylation is essential for the functions of VKD proteins, which include coagulation factors like prothrombin (PT) and factors VII, IX, and X that are produced in the liver. VKD proteins are modified in the ER by the γ-glutamyl carboxylase (GGCX), which requires the vitaminK hydroquinone (KH 2 ) cofactor that is oxygenated to vitaminK 2,3-epoxide (KO) during carboxylation. KO is then recycled by VKORC1, a vitaminK oxidore- ductase (VKOR) (2, 3) that is evolutionarily conserved (4). VKORC1 recycles KO to KH 2 in 2 steps, wherein KO is first converted to vitaminK quinone (K) and then to KH 2 (5). Together, the enzymatic activities of GGCX and VKORC1 form the vitaminK cycle (1). Warfarin, an anticoagulant used by millions of people, suppresses VKD protein carboxylation by inhibiting VKORC1 (3, 6).
prothrombin. Crossed immunoelectrophoresis of patients' plasmas and studies of partially purified patient prothrombin suggested the presence of a relatively homogeneous species of dysfunctional prothrombin, distinct from the heterologous species found in the plasma of warfarin-treated persons. These studies are most consistent with a posttranslational defect in hepatic carboxylation of vitaminK-dependent factors. This kindred uniquely possesses an autosomal recessive disorder of vitaminK-dependent factor formation that causes production of an apparently homogeneous species of dysfunctional prothrombin; the functional deficiencies in clotting factors are totally corrected by oral or parenteral administration of vitamin K1.
Hereditary combined vitaminK-dependent clotting factors deficiency (VKCFD) is a rare congenital bleeding disorder resulting from variably decreased levels of coagulation factors II, VII, IX and X as well as natural anticoagulants protein C, protein S and protein Z. The spectrum of bleeding symptoms ranges from mild to severe with onset in the neonatal period in severe cases. The bleeding symptoms are often life-threatening, occur both spontaneously and in a surgical setting, and usually involve the skin and mucosae. A range of non-haemostatic symptoms are often present, including developmental and skeletal anomalies. VKCFD is an autosomal recessive disorder caused by mutations in the genes of either gamma-glutamyl carboxylase or vitamin K2,3-epoxide reductase complex. These two proteins are necessary for gamma-carboxylation, a post-synthetic modification that allows coagulation proteins to display their proper function. The developmental and skeletal anomalies seen in VKCFD are the result of defective gamma-carboxylation of a number of non-haemostatic proteins. Diagnostic differentiation from other conditions, both congenital and acquired, is mandatory and genotype analysis is needed to confirm the defect. VitaminK administration is the mainstay of therapy in VKCFD, with plasma supplementation during surgery or severe bleeding episodes. In addition, prothrombin complex concentrates and combination therapy with recombinant activated FVII and vitaminK supplementation may constitute alternative treatment options. The overall prognosis is good and with the availability of several effective therapeutic options, VKCFD has only a small impact on the quality of life of affected patients.
Abstract: Objectives: To evaluate plasma protein Z (PZ) levels in healthy and high-risk newborn infants. Background: Protein Z (PZ) is a vitaminK-dependent plasma protein , As is the case with other coagulation proteins and inhibitors, protein Z is consumed during disseminated intravascular coagulation (DIC), Functionally protein Z has been shown to be a direct requirement for the binding of thrombin to endothelial phospholipids , Protein Z also serves as a cofactor for the inhibition of coagulation factor Xa by a plasma serein called protein Z-dependent protease inhibitor (ZPI), The inhibitory function is exerted by the Protein Z- dependent protease inhibitor (ZPI), which circulates in the human plasma in a complex with PZ , The physiological function of protein Z is still rather ill-defined and may play role in high risk newborn. Methods: This study was conducted on 85 newborns divided in 4 groups ,(group I newborns affected by respiratory distress syndrome (RDS) , group II newborns from mothers with pre-eclampsia, group III newborns small for gestational age (SGA) and group IV healthy term and preterm newborns normal for gestational age. Newborns with sepsis, congenital malformation or hemorrhagic disorders were excluded, Plasma PZ levels was measured. Results: In the neonates of the study groups, protein z level was significant lower in patient group than control group, in group I ( 0.79 ±0.32), group II (0.70± 0.30), group III (0.78 ±0.32) and group IV (1.44 ±0.43) (p value<0.001). Conclusion: PZ deficiency occurs in newborns affected by severe RDS, in newborns from preeclampsic mothers and in SGA newborns, probably owing to activated coagulation in the first two conditions and to reduced PZ synthesis in the last one.
Low vitaminK status (indicated by undercarboxylated MGP) is associated with increased vascular calci ﬁ cations, and these levels can be improved by effective vitaminK supplementation 28–32 It was long believed that vitaminK was only involved in forming coagulation factors (ie, maintaining haemostasis). However, other vitamin-Kdependent proteins (containing γ -carboxyglutamate or Gla) are dependent on vitamin-K carboxylation for func- tionality. 33 VitaminK acts as a cofactor in the conversion of glutamate into Gla. Gla-containing proteins (MGP and osteocalcin) regulate many anticalci ﬁ cation and bone-forming processes in the body, which are depend- ent on vitaminK in order to be produced. Low levels of vitaminK impair activation of osteocalcin and decrease the activity of osteoblasts (cells important for building bone). 33 34 Thus, vitaminK is vital to the functionality of proteins such as osteocalcin (important for building bone), (MGP, the most potent arterial calci ﬁ cation inhibitor known) and the growth-arrest sequence-6 protein (Gas6, involved in cell growth regulation 35
As PCCs were originally designed for the treatment of haemophilia B, their labelling, and thus dosage, is based on the concentration of factor IX. When PCCs are used for VKA reversal, it is important to recognise that warfarin reduces the levels of the vitaminK-dependent coagulation factors to varying degrees, with factor IX remaining at 40 to 50% of normal levels, factor VII at around 30% of normal, prothrombin at 20% of normal and factor X is usually lowest at around 10% of normal . As a result, it is diﬃ cult to deﬁ ne the optimal ratio of factors in a PCC. Care should be taken, however, to avoid excessive substitution with prothrombin, particu- larly during repetitive administration of PCCs when prothrombin levels can accumulate because of its long half-life. Co-administration of vitaminK is recommended when PCCs are used for anticoagulation reversal . VitaminK has a slow onset of action, and the reason for its use is to facilitate hepatic production of coagulation factors after the constituents of the PCC infusion have been metabolised. By reducing the need for repeat administration of PCC, co-adminis tration of vitaminK is one way of reducing thrombotic risk.
the duration of action of a single dose of racemic warfarin is 2 to 5 days. Under normal pharmacological therapy the drugs are administered to decrease the action of the clotting factors they affect by 30 to 50% 3 . Warfarin exerts its anticoagulant and antithrombotic activity by inhibiting the vitaminK-dependent carboxylation of clotting factors II, VII, IX, and X to a greater extent than the vitaminK-dependent natural anticoagulants, proteins C and S 8, 9 . Specifically, it inhibits an enzyme called the vitaminK 1 2, 3-epoxide
Bone that was virtually depleted of the vitaminK-dependent protein, osteocalcin, and 93% reduced in the concentration of its characteristic amino acid, gamma-carboxyglutamic acid, was obtained from rats treated with warfarin for 6 wk. Osteocalcin-deficient bone particles were resistant to resorption when implanted subcutaneously in normal rats. The relative resorption was 60% of control bone, as measured by histomorphometry as percent of bone particles in the field. Additionally, the number of multinucleated cells around the bone particles was reduced by 54%. These data suggest that osteocalcin is an essential
normalize coagulation within one hour (62.2 versus 9.6%; P <0.05) . The role of vitaminK in association with PCC, in maintaining the normalized coagulation over six hours has been emphasized . The importance of rapid hemorrhage control has led international guidelines to recommend the use of PCC rather than FFP [10-12]. For complete VKA reversal, all guidelines recommend an infusion of PCC (at least 20 IU/kg factor IX equivalent) related to admission INR value in combination with at least 5 mg of vitaminK to rapidly achieve a post-reversal INR ≤1.5 and maintain a normal coagulation profile over six hours. So as to save time, French guidelines suggest, on the basis of a previous study, the possibility of adminis- tering a probabilistic single-regimen dose of 25 IU/kg of PCC and 10 mg of vitaminK as soon as a severe hemorrhage is diagnosed [9,10]. In all situations, post- reversal INR must be measured 30 minutes after the infusion to evaluate the efficacy of the treatment and make any necessary adjustments thereafter, and measured six hours later to control the efficacy of vitaminK [10-12]. French guidelines were published in 2008 and have become a standard of care for the management of these patients in France . Treatment time frames were not specified in the international guidelines and the effect of early reversal on mortality has not been studied. At a time when new oral anticoagulant agents without specific antidotes are emerging as promising alternatives to VKAs, it appears important to better define the prognosis benefit of anti- coagulant reversal in the management of patients on oral anticoagulants with severe hemorrhage .
We chose to develop the FFQ and the dietary recall instead of using existing questionnaires. This has both advantages and disadvantages. Advantages are that the questionnaires were developed specifically to measure vitaminK intake and that they were directed to the studied population by including food items contributing most to vitaminK intake in the Dutch population. This is important because typical Dutch food includes many vitaminK-rich foods such as curly kale and sauerkraut. A disadvantage is that the questionnaires have not been validated. However, there was a correlation between the FFQ and the dietary recall questionnaire, providing a relative validation. A more general problem with measuring dietary vitaminK intake is the substantial difference in the reported vitaminK content of foods analyzed in different laboratories. 31
Vitamin K3 inhibits the conversion of benzo(a)pyrene to its more polar metabolites in an in vitro rat liver microsomal system. Vitamin K3 also inhibits benzo(a)pyrene metabolism in rat liver fragments and reduces its mutagenicity in the Ames test. Higher concentrations of vitamin K3 are required to comparably reduce benzo(a)pyrene metabolism when the microsomal system has been induced with 3-methylcholanthrene. High pressure liquid chromatography analysis of the products of benzo(a)pyrene metabolism shows a uniform reduction of all the metabolic products. When tumors were induced in ICR/Ha female mice by the intraperitoneal injection of benzo(a)pyrene, those mice given vitamin K3 before or both before and after benzo(a)pyrene had a slower rate of tumor appearance and tumor death rate as compared with those receiving benzo(a)pyrene alone. However, vitamin K1 increased the rate of tumor death while vitaminK deprivation and warfarin decreased the rate of tumor appearance and death in benzo(a)pyrene-injected mice. These studies indicate that vitamin K3 is an inhibitor of aryl hydrocarbon hydroxylase and reduces the carcinogenic and mutagenic metabolites in vitro, and inhibits benzo(a)pyrene tumorigenesis in vivo. That vitamin K1 enhances the benzo(a)pyrene effect while warfarin and vitaminK deficiency inhibit benzo(a)pyrene tumorigenesis indicates that vitamin K1, vitaminK deprivation, or possibly blockade of its metabolic cycle also modulates benzo(a)pyrene metabolism in vivo but by a mechanism or at a […]