Liver and plasma levels of descarboxyprothrombin (PIVKA II) in vitamin K deficiency in rats

Pretreatment with Warfarin Attenuates the Development of Ischemia/Reperfusion-Induced Acute Pancreatitis in Rats

In acute pancreatitis (AP), pancreatic damage leads to local vascular injury, manifesting as endothelial damage and activation, increased vascular permeability, leukocyte rolling, sticking and transmigration to pancreatic tissue as well as activation of coagulation. Previous studies have shown that pretreatment with heparin or acenocoumarol inhibits the development of AP. The aim of the present study was to check the impact of pretreatment with warfarin, an oral vitamin K antagonist, on the development of ischemia/reperfusion-induced AP in rats. AP was induced by pancreatic ischemia followed by reperfusion of the gland. Warfarin (90, 180 or 270 µg/kg/dose) or vehicle were administered intragastrically once a day for 7 days before induction of AP. The effect of warfarin on the severity of AP was assessed 6 h after pancreatic reperfusion. The assessment included histological, functional, and biochemical analyses. Pretreatment with warfarin given at a dose of 90 or 180 µg/kg/dose increased the international normalized ratio and reduced morphological signs of pancreatic damage such as pancreatic edema, vacuolization of acinar cells, necrosis and the number of hemorrhages. These effects were accompanied by an improvement of pancreatic blood flow and a decrease in serum level amylase, lipase, pro-inflammatory interleukin-1β and plasma level of D-dimer. In contrast, pretreatment with warfarin given at a dose of 270 µg/kg/dose led to an increase in severity of pancreatic damage and biochemical indicators of AP. In addition, this dose of warfarin resulted in deaths in some animals. Pretreatment with low doses of warfarin inhibits the development of AP induced by pancreatic ischemia followed by reperfusion.

Thrombin generation test: A reliable tool to evaluate the pharmacodynamics of vitamin K antagonist rodenticides in rats

Vitamin K antagonist rodenticide pharmacodynamics (PD) is studied in rodents with traditional laboratory tests. We wondered if thrombin generation test (TGT) could add value. Difethialone (10 mg/kg) was administered per os to 97 OFA-Sprague Dawley rats. PD was studied over a 72 h-period using the Calibrated Automated Thrombogram on platelet poor plasma before and after intoxication (3 female and 3 male rats for each 13 time points) and TGT parameters were compared with the prothrombin time (PT) and vitamin K dependent factor activities previously reported. Following intoxication, preliminary tests evidenced rapid and full inhibition of thrombin generation triggered with 5 or 20 pM human recombinant tissue factor. To study the evolution of TGT parameters following difethialone intake, we adapted the test by complementing intoxicated rat samples with pooled normal rat plasma (3/1, v/v). Adapted TGT confirmed the known higher procoagulant basal level in females compared to males through higher endogenous thrombin potential (ETP) and peak height (PH) (p < 0.0001 and p = 0.0003, respectively). An exponential model fitted well the PH and ETP decay after intoxication. In contrast to PT, the decreases were observed immediately following VKA intake and had comparable time to halving values: 10.5 h (95% CI [8.2; 13.6]) for ETP and 10.4 h (95% CI [7.8; 14.1]) for PH. The decrease of FVII and FX preceded that of PH, ETP and FII while FIX decreased later on, contributing to the severe hypo-coagulability. We demonstrated that TGT performed in samples of intoxicated rats complemented with normal plasma is a reliable tool for evaluation of VKA rodenticide PD in rats.

Monitoring of antivitamin K-dependent anticoagulation in rodents - Towards an evolution of the methodology to detect resistance in rodents

Vitamin K antagonists are used as rodenticides for pest control management. In rodents, prothrombin time is used to monitor their effect despite its limits and the emergence of many coagulation methods. The aim of this study is to explore different coagulation monitoring methods in order to propose the best method and the best parameter to monitor vitamin K antagonists effect in rodents. The coagulation function was thus monitored with global coagulation assays and specialty assays after difethialone administration in rats. Despite many parameters obtained by thromboelastometry, only clotting time and clot formation time obtained by ExTEM were modified. Their evolution was fast with doubling time respectively of 4.0h and 3.7h but their increases were delayed with a lag time higher than 8h. Conversely, prothrombin time evolution presented a lag time of only 2h, but a higher doubling time of 7.2h. The measurements of factor VII and X activities were the most sensitive assays to monitor vitamin K antagonists effect with almost no lag time and the fastest evolution. Nevertheless, factor X was shown to be the only key factor driving prothrombin time. Monitoring factor X activity enables to follow most effectively the anticoagulation status in rats after rodenticides administration.

Bothrops jararaca envenomation: Pathogenesis of hemostatic disturbances and intravascular hemolysis

To attain fully functional biological activity, vitamin-K dependent coagulation factors (VKDCF) are γ-carboxylated prior to secretion from liver. Warfarin impairs the γ-carboxylation, and consequently their physiological function. Bothrops jararaca snake venom (BjV) contains several activators of blood coagulation, especially procoagulant enzymes (prothrombin and factor X activators) and thrombin-like enzymes. In order to clarify the relative contribution of prothrombin and factor X activators to the hemostatic disturbances occurring during experimental B. jararaca envenomation, warfarin was used to deplete VKDCF, prior to BjV administration. Male Wistar rats were pretreated with saline (Sal) or warfarin (War) and inoculated subsequently with BjV or saline, thus forming four groups: Sal + Sal (negative control), Sal + BjV (positive control), War + Sal (warfarinization control), and War + BjV. Three hours after inoculation, prothrombin and factor X levels fell 40% and 50%, respectively; levels of both factors decreased more than 97% in the War + Sal and War + BjV groups. Platelet counts dropped 93% and 76% in Sal + BjV and War + BjV, respectively, and plasma fibrinogen levels decreased 86% exclusively in Sal + BjV. After 6 and 24 h, platelet counts and fibrinogen levels increased progressively. A dramatic augmentation in plasma hemoglobin levels and the presence of schizocytes and microcytes in the Sal + BjV group indicated the development of intravascular hemolysis, which was prevented by warfarin pretreatment. Our findings show that intravascular thrombin generation has the foremost role in the pathogenesis of coagulopathy and intravascular hemolysis, but not in the development of thrombocytopenia, in B. jararaca envenomation in rats; in addition, fibrinogenases (metalloproteinases) may contribute to coagulopathy more than thrombin-like enzymes.

Development of a cell culture/ELISA assay to detect anticoagulant rodenticides and its application to analysis of rodenticide treated grain

This study describes a generic biological screening assay designed to detect anticoagulant rodenticides based on their inhibitory action on the vitamin K epoxide reductase protein complex, resulting in an accumulation of under-carboxylated prothrombin or proteins induced by vitamin K antagonism (PIVKA-II). A combined cell culture/ELISA assay was optimized to measure PIVKA-II production by the human hepatoma HepG2 cell line cultured in the presence of anticoagulant rodenticides. The specificity and sensitivity of the assay was validated using 41 grain extracts containing representative concentrations of rodenticide or appropriate nonrodenticide control compounds. In all cases, PIVKA-II produced by HepG2 cells in response to grain extracts spiked with rodenticides was detected by ELISA, while PIVKA-II was not detected in supernatants collected from cells exposed to nonrodenticide controls. This represents a novel, class-specific biological assay for the detection of anticoagulant rodenticides present in contaminated grain.

Battery of tests for profiling abnormalities of vitamin K-dependent coagulation factors in drug-toxicity studies in rats

A battery of simple tests for profiling abnormalities of vitamin K-dependent coagulation factors encountered in drug-toxicity studies was verified in rats treated with warfarin (3 and 10 mg/kg, p.o). The thrombotest, or hepaplastin-test, is useful as a follow-up test after routine screening tests for coagulation abnormalities based on PT and APTT, to rule out other coagulation-factor abnormalities. Measurement of coagulation factor activities (factors II, VII, IX and X) using factor-deficient human plasmas provides direct evidence of decreased activities of vitamin K-dependent factors. Furthermore, Echis carinatus venom coagulation time, together with factor II activity, allows us to confirm the generation of PIVKA-II.

Viability and Plasma Vitamin K Levels in the Common Bile Duct-Ligated Rats

The common bile duct-ligated (CBDL) rat, which is widely used as a model of human cirrhosis, rapidly develops secondary biliary cirrhosis (SBC) within 4 weeks. The CBDL rat shows poor viability, however, a detailed examination of the causes of its death has not been made. In this study, we investigated the outcome of bile duct ligation in detail and attempted to extend the life span of this model by feeding the animals a diet supplemented with nutrients. Survival rate, blood chemistry, blood cell counts, plasma levels of K vitamins and liver histology were compared among CBDL rats fed a standard diet and an enriched diet. Sham-operated rats were used as a control. Six out of 18 CBDL rats fed the standard diet died within 32 days of operation. The cause of death was massive internal hemorrhage in various organs or body cavities. All CBDL rats fed the enriched diet survived more than 31 days, but the viability of CBDL rats was not significant between those fed the standard diet and the enriched diet. The degree of anemia correlated significantly with the prolongation of prothrombin time. Plasma vitamin K1 levels in CBDL rats were significantly lower than those in sham-operated rats, but vitamin K2 levels were similar. We suggest that massive hemorrhage, which was the direct cause of death, is caused by the impairment of hemostasis resulting from vitamin K deficiency. The enriched diet with vitamin K nutritional supplements seemed to contribute to the prolongation of the life span of CBDL rats.

BLOOD COAGULATION TESTS IN TOXICOLOGICAL STUDIES-REVIEW OF METHODS AND THEIR SIGNIFICANCE FOR DRUG SAFETY ASSESSMENT-

In general toxicological studies, prothrombin time and activated partial thromboplastin time are routinely measured to assess blood coagulation. Special (problem-driven) tests for blood coagulation are of significance to detect abnormalities and investigate the mechanism of toxicity in detail. In this review, we compiled widely scattered information on blood coagulation testing from different fields in the biological area, and reviewed the methods available and their significance in toxicological studies. The relevant literature cited here reports large species differences in platelet aggregation, coagulation factors or fibrinolysis, and technical limitations. However, the following tests are basically applicable to laboratory animals; (1) assays for individual coagulation factors and protein induced by vitamin K absence or antagonists (PIVKA) to investigate coagulation factor abnormalities; (2) platelet aggregation-, platelet adhesion-, platelet release-tests and von Willebrand factor assay to screen and/or investigate platelet dysfunction; (3) fibrin/fibrinogen degradation products (FDP), D-dimer and thromboelastogram to detect fibrinolitic abnormalities, and assays for plasminogen, plasmin and their activator/inhibitor to investigate fibrinolysis in detail; and (4) bleeding-time to grossly evaluate blood coagulation capability in vivo. An appropriate battery of these tests provides significant information for risk assessment of drugs.

Prothrombin and PIVKA-II levels in cord blood from newborn exposed to anticonvulsants during pregnancy

PURPOSE

To determine whether anticonvulsant exposure during human pregnancy caused an increase of the abnormal form of prothrombin, known as PIVKA-II (prothrombin induced by vitamin K absence for factor II), and a decrease in total prothrombin, in the blood of the newborn.

METHODS

Cord blood was collected from the placenta at the time of parturition from 12 women who had received anticonvulsant therapy during pregnancy and from 11 control women.

RESULTS

PIVKA-II was present in cord blood from control mothers at low or nondetectable levels. In the same samples, total prothrombin concentrations were approximately 50% of adult levels, but there was wide variation between individuals. Exposure to carbamazepine (CBZ) alone during pregnancy was associated with markedly increased PIVKA-II levels in four of six samples and decreased total prothrombin levels for the whole group. High PIVKA-II levels also were recorded in one cord blood sample from a mother who received phenytoin (PHT) and vigabatrin (VGB). Two cases of PHT alone and one of valproic acid (VPA) alone were not associated with increased PIVKA-II levels.

CONCLUSIONS

These results are consistent with the hypothesis that some anticonvulsants (particularly CBZ) interfere with vitamin K metabolism during pregnancy and may result in hematologic signs of vitamin K deficiency in the newborn.

Comparison of the half-lives and regeneration rates of blood clotting factors II, VII, and X in anticoagulant-resistant and susceptible Norway rats (Rattus norvegicus Berk.)

The half-lives and regeneration rates of clotting factors II, VII, and X in the plasma of anticoagulant-resistant and susceptible rats were determined. There is little or no difference in the half-lives of factors II and X in anticoagulant-resistant rats compared to susceptible rats, but the half-life of factor VII is longer in anticoagulant-resistant rats. In anticoagulant-resistant rats critical clotting factors appear to be carboxylated in preference to factor II, whereas the opposite occurs in susceptible rats; this may contribute to an animal's resistance status.

O/W lipid emulsions for parenteral drug delivery. IV. Changes in the pharmacokinetics and pharmacodynamics of a highly lipophilic drug, menatetrenone

The pharmacokinetics and pharmacodynamics of antihemorrhagic vitamin, menatetrenone after intravenous injection as the lipid emulsion, were compared to those as the micellar solutions. Menatetrenone was selectively delivered to the liver, lungs and spleen and retained in them. Hepatic and splenetic concentration at 6 h (C6h) increased 21.6- and 27.1-fold, respectively, and the area under the tissue concentration-time curve up to 6 h (AUC(0-6h)) were 2.3- and 11.4-fold, respectively, when compared with its micellar solution. Antihemorrhagic effect of menatetrenone was assessed using warfarin-induced hypoprothrombinemic rats. The lipid emulsion of menatetrenone decreased the prothrombin time at 6h after intravenous injection more effectively than micellar solution. The dose response curves indicated that the efficacy of the lipid emulsion was 2.4-2.9 times that of a micellar solution, and this was correlated with AUC(0-6h) rather than C6h. The plasma level of clotting factor VII and the hepatic level of descarboxyprothrombin were also recovered more effectively, while no significant differences were noted between the two formulations for the plasma level of factor II or descarboxyprothrombin at the dose levels examined. Although selective delivery of menatetrenone in the liver by the lipid emulsion was due to phagocytosis by non-parenchymal cells, menatetrenone in the whole liver appeared to contribute to recovery from hypoprothrombinemia.

Comparison of plasma prothrombin and factor VII and urine prothrombin F1 concentrations in patients on long-term warfarin therapy and those in the initial phase

Control of warfarin anticoagulation during the initial phase of therapy is difficult and empirically based. Plasma and urine samples were obtained from normal controls, patients under stable anticoagulation, and patients in the initial phase of anticoagulation. Total plasma prothrombin, des-carboxy (non-adsorbable with barium chloride) prothrombin, and native (total minus non-adsorbable) prothrombin were quantitated using Echis carinatus venom activation. Functional plasma factor VII (VII) was measured using a one-stage clotting assay. Total and des-carboxy urine prothrombin F1 (F1) were measured by ELISA. All urine F1 in normals and both anticoagulated groups was adsorbed by barium chloride. Plasma des-carboxy prothrombin concentration was similar for the two anticoagulated groups and did not correlate with 1/INR. Native prothrombin correlated with 1/INR in both the stable (r = 0.76) and initial phase (r = 0.74) groups. For any given INR, the subjects on stable anticoagulation had lower native prothrombin concentrations than the initial phase patients. Functional factor VII concentration also correlated significantly with 1/INR in both the stable (r = 0.64) and initial phase (r = 0.76) patients. Unlike native prothrombin, VII concentrations did not vary between the two cohorts for any given INR. Previous studies indicate that native prothrombin is a superior predictor of both hemorrhagic and thromboembolic complications during warfarin therapy. Our findings indicate that VII, and not prothrombin, may be the predominant factor monitored by the INR. This further supports the need to reevaluate the usefulness of the INR in the monitoring of warfarin therapy during the initial phase.

Sex differences in the anticoagulant effects of warfarin

Sex differences in the anticoagulant effects of warfarin were studied in rats. Warfarin was administered to rats from 7 days of gestation until 14 weeks of age. In male rats, the normal prothrombin level in the plasma was reduced, and the blood coagulation time was prolonged by treatment with warfarin at 4, 9 and 14 weeks of age. However, in female rats, the effects of warfarin on the prothrombin level and blood coagulation time were observed at 4 weeks to the same degree as in male rats, but these effects were reduced with aging, and at 14 weeks, no effect of warfarin was observed. Rats ovariectomized at 12 weeks of age and subsequently treated with warfarin for 2 weeks showed prolongation of blood coagulation time to the same level as in warfarin-treated male rats, which was inhibited by administration of 17 beta-estradiol (100 micrograms/kg/day for 4 days, i.m.). In male rats, treatment with 17 beta-estradiol also inhibited the anticoagulant effects of warfarin without changing the warfarin level in plasma. These results suggest that there is a sex difference in the anticoagulant effects of warfarin, and that this difference may be related to the estradiol level in plasma.

Effect of warfarin on plasma and liver vitamin K levels and vitamin K epoxide reductase activity in relation to plasma clotting factor levels in rats

Changes in plasma and liver vitamin K1 and vitamin K1 epoxide levels, liver microsomal vitamin K epoxide reductase activity, and plasma clotting factor II and VII levels were determined in rats after a single injection of warfarin (2.5 mg/kg, s.c.). The plasma and liver vitamin K1 levels gradually decreased after warfarin injection, attaining the lowest values at 2-3 hrs and remaining low for 48 hrs. They then returned to the control levels at 72 hrs. The changes in vitamin K1 epoxide levels were opposite, with an increase being seen soon after the warfarin injection, the highest values at 3 hrs and a gradual decrease to the initial levels occurring subsequently. The combined levels of vitamin K1 plus vitamin K1 epoxide, however, remained almost constant in both plasma and liver after the warfarin injection. The liver vitamin K epoxide reductase activity decreased to its lowest level soon after the injection and then gradually increased after 12 hrs, but the activity at 72 hrs was only about 30% of the initial activity. The plasma clotting factor levels gradually decreased after the injection, bottomed at 24 hrs and then began to increase, recovering almost to the initial levels at 72 hrs. A positive correlation was found between plasma and liver levels for both vitamin K1 and vitamin K1 epoxide, and the slope of the vitamin K1 epoxide curve was steeper than that for vitamin K1 in the warfarin-treated rats. A similar positive correlation was found for both vitamin K1 and vitamin K1 epoxide after vitamin K1 injection in normal untreated rats, but the slope of the vitamin K1 epoxide curve was much shallower. These results suggest that warfarin inhibits vitamin K epoxide reductase and decreases blood clotting factor synthesis, thus increasing plasma and liver vitamin K1 epoxide levels. A vitamin K epoxide reductase activity one third of that in normal rats is sufficient to maintain normal reduction of vitamin K1 epoxide and synthesis of blood clotting factors.

Depression of liver microsomal vitamin K epoxide reductase activity associated with antibiotic-induced coagulopathy

Hypoprothrombinemic changes in blood coagulation parameters, such as prolongation of prothrombin time, increase in the level of plasma protein induced by vitamin K absence, and decrease in plasma prothrombin level, were detected in rats fed a vitamin K-deficient diet. These changes were enhanced by the administration of beta-lactam antibiotics containing N-methyltetrazolethiol, thiadiazolethiol or methyl-thiadiazolethiol. Microsomal vitamin K epoxide reductase activity was suppressed with the maximum effect at 1-2 days after the treatment and with recovery, thereafter, gradually to the normal level after 5-7 days. Hypoprothrombinemic alterations in blood coagulation parameters following a single administration of antibiotic to vitamin K-deficient rats were somewhat delayed compared with the change in the epoxide reductase activity, but the effects of the antibiotic on both blood coagulation parameters and the enzyme activity disappeared completely 7 days after the antibiotic treatment. Antibiotic-induced depression of the epoxide reductase activity was observed even in the vitamin K sufficient rats, although the hypoprothrombinemic changes in the blood coagulation parameters did not develop. Vitamin K administration could normalize the blood coagulation parameters in the hypoprothrombinemic rats caused by treatment with the antibiotics but without recovery of the decreased epoxide reductase activity. These results suggest that some antibiotics inhibit liver microsomal vitamin K epoxide reductase, which causes hypoprothrombinemia to develop under vitamin K-deficient conditions.

Biosynthesis and clearance of prothrombin in warfarin-treated rats

The steady-state concentration of abnormal plasma prothrombin in warfarin-treated rats (10 mg/kg) was found to be approx. 6% of the plasma prothrombin level in normal rats. The clearance of abnormal plasma prothrombin in warfarin-treated rats was studied using either cycloheximide, to inhibit the synthesis, or vitamin K, to block the appearance of abnormal prothrombin in plasma. The clearance of abnormal plasma prothrombin corresponded to a half-life of approx. 6 h, which is similar to the half-life of normal plasma prothrombin. The de novo synthesis of prothrombin in warfarin-treated and normal rats was compared by measuring the incorporation of [3H]leucine into plasma prothrombin 90 min after an intravenous injection of the isotope. In warfarin-treated rats, accumulated prothrombin precursor was carboxylated and transported into circulation by injecting vitamin K 30 min after isotope administration. On comparing the incorporation of [3H]leucine into plasma prothrombin in warfarin-treated and normal rats, no significant difference in the de novo synthesis was detected. Our results suggest that the secretion of prothrombin in warfarin-treated rats is decreased to 6% of the normal rate. As the de novo synthesis is not affected by warfarin treatment, more than 90% of the newly synthesized prothrombin appears to be degraded intracellularly.

In vivo effects of beta-lactam antibiotics and heterocyclic thiol compounds on vitamin K-dependent carboxylation activity and blood coagulation factors in vitamin K-deficient rats

The in vivo effects of heterocyclic thiol compounds, corresponding to the 3'-position substituents of several beta-lactam antibiotics, on blood coagulation factors and on liver microsomal gamma-glutamylcarboxylation (gamma-carboxylation) activity were evaluated in rats maintained on a vitamin K-deficient diet. These rats, when compared to normal control animals, exhibited hypoprothrombinemic changes: prolongation of both prothrombin time and activated partial thromboplastin time, decreases in factor VII and plasma prothrombin, and increases in PIVKA II (descarboxyprothrombin) both in plasma and liver. They also displayed a marked increase in liver microsomal gamma-carboxylation activity. These blood coagulation variables could be altered markedly by administering various heterocyclic thiol compounds to the vitamin K-deficient rats, although these compounds did not inhibit gamma-carboxylation activity in an assay system using phylloquinone. A similar pattern of alteration was observed when some beta-lactam antibiotics were administered. Increased microsomal gamma-carboxylation activity in antibiotic-treated vitamin K-deficient rats was normalized by the administration of vitamin K, concomitant with the recovery of blood coagulation variables to the normal range. The results indicate that antibiotic-induced hypoprothrombinemia in vivo is not caused by inhibition of enzymes of the gamma-carboxylation system, such as vitamin K reductase and gamma-glutamylcarboxylase, but is related to the endogenous vitamin K level.

Phase I clinical studies of 7432-S: effect of 7432-S on platelet aggregation and blood coagulation

The effects of 7432-S, a new oral cephalosporin antibiotic, on platelet functions and vitamin K-dependent blood coagulation parameters were studied in human volunteers and animals. Although the ADP- and collagen-induced aggregations of human and animal platelets were inhibited in vitro by extremely high concentrations of 7432-S, the inhibitory effect of 7432-S was weaker than that of latamoxef or cefotaxime. When administered orally to human volunteers or animals, 7432-S caused no inhibition of platelet aggregation. Its administration also caused no change in prothrombin time and activated partial thromboplastin time both in human volunteers and in rats. The conclusion reached was that the new oral antibiotic 7432-S does not affect platelet functions and blood coagulation.

A study on the intracellular transport of prothrombin, albumin and transferrin in rat

The intracellular transport of prothrombin in rat has been studied and compared with the transport of albumin and transferrin. The proteins were immunoisolated from plasma samples after pulse labelling with [3H]leucine and the secretion kinetics were determined. The half-times for secretion (t1/2) were approx. 30, 53 and 75 min for albumin, prothrombin and transferrin, respectively, whereas the minimal transit time for prothrombin was approx. 30 min, and those for albumin and transferrin 15-20 min. After injection of vitamin K-1 into warfarin-treated rats, the accumulated prothrombin precursor was gamma-carboxylated and secreted with a t1/2 of 37 min. This indicates that the gamma-carboxylation of prothrombin in rough endoplasmic reticulum cannot account for the delay in the transport of prothrombin as compared to albumin. Comparison of the incorporation of [3H]leucine and [3H]glucosamine into plasma prothrombin and transferrin suggested that transferrin is secreted randomly from an intracellular pool, whereas prothrombin is transported in a more orderly sequence. Moreover, treatment of rough microsomes with 0.05% sodium deoxycholate indicated that prothrombin is more tightly associated with the membranes of rough endoplasmic reticulum than albumin and transferrin.