Factor II antigen in liver disease and warfarin-induced vitamin K deficiency: correlation with coagulant activity using Echis venom

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.

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.

Avidin-biotin ELISA for measurement of prothrombin in human plasma

In this study, IgG was partially purified from rabbit antisera against human normal prothrombin. The presence of antibodies against prothrombin was shown by Ouchterlony's double immunodiffusion method. This IgG was adsorbed to microwells and an enzyme-linked immunosorbent assay (ELISA) method was developed by using biotinylated prothrombin. We used alkaline phosphatase as the labeling enzyme. Plasma prothrombin concentrations in 30 healthy individuals and 15 patients with liver cirrhosis were measured using this ELISA method. Prothrombin levels of the cirrhotic patients (61+/-36 microg/ml) were significantly lower than those of the control values (117+/-43 microg/ml) (P<.001). In addition to the ELISA method in the same samples, we assayed prothrombin levels by nephelometry and prothrombin activities using staphylocoagulase and chromogenic substrate. With nephelometry, in healthy individuals, a mean value of 104+/-17 microg/ml and, in cirrhotic patients, a mean value of 51+/-26 microg/ml of prothrombin levels were detected. The prothrombin activities were 10532+/-2429 and 2433+/-330 U/l, respectively. In both methods, the prothrombin values of cirrhotic patients were also significantly lower than those of the healthy individuals (P<.001). The correlation coefficient between ELISA and nephelometry was r=.90, P<.01, and between ELISA and the amidolytic assay was r=.69, P<.01. Prothrombin times (PT) of cirrhotic patients (18.5+/-2.3 s) were significantly longer and albumin (2.4+/-0.5 g/dl) levels were significantly lower than those of normal values (P<.001). PT were negatively correlated with prothrombin levels assayed by ELISA (r=-.59, P<.01). This enzyme immunoassay technique can be used to measure prothrombin levels in plasma.

Determination of the N-terminal amino acid sequence of the purified prothrombin from a patient with liver cirrhosis

The reasons for the decreased functional activity of prothrombin in liver diseases are still speculative. When a highly purified preparation of prothrombin from a patient with liver cirrhosis is available, the cause of prothrombin abnormalities may be researched on a molecular basis. In this study, prothrombin (6.7 mg) was purified from the ascites fluid (1130 mL) of a patient with liver cirrhosis by barium citrate adsorption, ammonium sulfate elution, DEAE Sephacel and Heparin Sepharose CL-6B column chromatography steps. The molecular weight of this prothrombin was the same as that of normal prothrombin purified from a normal plasma pool. The specific activities were found to be 3.36 U/mg in the one stage clotting assay and 28.9 U/mg in the staphylocoagulase/chromogenic substrate assay, while the normal prothrombin specific activities were 3.92 U/mg and 30.1 U/mg respectively. When N-terminal amino acid sequence analysis was carried out, it was seen that the first 20 residues were identical to the normal human prothrombin excepting the Gla at position #14.

Blood coagulation factors changes during liver regeneration in rats

Effects of partial hepatectomy on blood coagulation factors were investigated in rats. Analysis were performed 24, 48 and 72 hours after surgery. Howell's time was significantly higher after 24 and 48 h compared to the control value. Prothrombin time was significantly prolonged after 24 h. Partial thromboplastin time did not differ significantly in any time. FII values were significantly reduced after 24 and 48 h, but FV values only after 24 h. FVII showed significant decrease after 24 h, but significant increase at 48 h. FVIII and ATIII average values were significantly lower after 24, 48 and 72 h. Plasma fibrinogen increased. Significant differences were observed 48 and 72 h after surgery. Differences in normalization time of these coagulation factors are most probably the consequence of their synthesis in various cell types, regenerated at different periods after partial hepatectomy.

Induction of prothrombin biosynthesis and inhibition of gamma carboxylase activity in experimental models of liver regeneration and fibrosis

1. When acute liver damage is induced in rats treated with CCl4, both prothrombin biosynthesis and gamma carboxylase activity decreases, originating a prolongation of prothrombin time in plasma. 2. Then, during the regenerative process, prothrombin biosynthesis increases higher than normal, but gamma carboxylase activity remain decreased. In this case, prolongation of prothrombin time occurs in spite of high levels of descarboxylated prothrombin in plasma. 3. An increase of descarboxylated prothrombin in plasma is also detected in the CCl4-liver fibrosis model.

Effects of chronic beta-carotene supplementation on vitamin K status in adults

Plasma vitamin K concentrations and prothrombin coagulation activity were determined in 26 normal adults who had received daily beta-carotene supplementation (0, 15, 30, or 60 mg) for six months. Neither plasma vitamin K nor coagulation activity were significantly decreased at any supplementation level. Thus, chronic beta-carotene supplementation, even at high daily doses, is not expected to result in clinical vitamin K deficiency. The data suggest separate mechanisms for intestinal absorption of beta-carotene and vitamin K.

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.

Effect of liver damage on the level of coagulation factor II, X and VII in human and bovine plasma

The thrombin generation test using thromboplastin reagent and synthetic substrate for thrombin and determination of factors II, X and VII using chromogenic substrates were applied to bovine and human plasma from objects with liver disease. The liver damage was accompanied with a lowering of the concentration of at least one factor of the extrinsic pathway of prothrombin activation. Use of some of these methods for laboratory diagnosis of liver damage is proposed.

Abnormal prothrombin in the vitamin K-deficient rat

Vitamin K is required for the post-translational formation of gamma-carboxyglutamyl residues in the vitamin K-dependent plasma clotting factors. Interference with vitamin K action results in the appearance of undercarboxylated, "abnormal," forms of prothrombin in bovine and human plasma, but the extent of this response in the rat has been controversial. Development of amidolytic and immunochemical assays for rat prothrombin have now shown that plasma from vitamin K-deficient or Warfarin-treated rats contains a non-BaSO4 adsorbable (undercarboxylated) pool of prothrombin that is equivalent to between 5 and 10% of the normal plasma prothrombin concentration.

The multiple coagulopathies of biliary atresia

Detailed coagulation studies were done prospectively on 43 patients with biliary atresia who had undergone Kasai operation (hepatic portoenterostomy). Patients were divided into three groups based on levels of factor V, factor II, and Echis II and/or response to vitamin K: no coagulopathy (46.5% of patients); coagulopathy of liver disease (30.2% of patients); and coagulopathy of vitamin K deficiency (23.3% of patients). Patients with the coagulopathy of liver disease had significantly lower levels of factors XII, V, and antithrombin III as well as longer thrombin times than patients with no coagulopathy or vitamin K deficiency. Factor V levels were decreased only in patients with more advanced liver disease; normal levels of factor V were not usually helpful in differentiating liver disease and vitamin K deficiency. The prothrombin time, factor VII-X levels, and factor II levels were significantly different for all three groups; the most abnormal values occurred in the vitamin K-deficient group. Comparison of the Echis II level to factor II coagulant activity was helpful in deciding whether a coagulopathy was due to liver disease, vitamin K deficiency, or both. Factor VIII levels were elevated in all groups. Factor VIII coagulant activity was significantly higher by the two-stage (TGT) method than by the one-stage (PTT) method. Hypersplenism causing neutropenia and thrombocytopenia was commonly seen after the age of 5 years. Vitamin E deficiency was more common than vitamin K deficiency; however, all vitamin K-deficient patients were vitamin E deficient. Coagulation status correlated well with hepatobiliary scan data, but not serum bilirubin levels. Recommendations for treatment of patients with vitamin K deficiency and/or liver disease are discussed.

Prothrombin determination in plasma and in liver biopsies in chronic liver diseases

Following ribosomal synthesis of the protein moiety of prothrombin, postribosomal carboxylation in the liver is necessary to obtain prothrombin ready for physiologic activation. Both decarboxyprothrombin and carboxyprothrombin can be determined by means of specific activators. Using synthetic substrates for thrombin, a micro-prothrombin assay suitable for functional determinations of decarboxy- and carboxy-prothrombin in liver biopsies was evolved. Decarboxyprothrombin was not found in plasma, independent of the kind of liver disease. Prothrombin determination in 31 liver samples showed no relation between the absolute concentration of carboxyprothrombin and decarboxyprothrombin and the kind of disease. The carboxyprothrombin fraction of total prothrombin was correlated with the activity of histologically estimated fibrosis in the liver.

The effect of vitamin E on warfarin-induced vitamin K deficiency

Vitamin K-deficient animals and humans developed a more severe coagulopathy when treated with vitamin E, which was due to further reduction in the vitamin K-dependent coagulation factors (II, VII, IX, and X). This phenomenon was not seen in normal vitamin K-sufficient animals or human subjects. The mechanism by which vitamin E causes this effect is not known. These coagulation factors are produced by the liver in precursor forms and are converted to functional proteins by a vitamin K-dependent reaction. Analysis of one of these coagulation factors, prothrombin (factor II), in plasma of vitamin K-deficient animals and humans treated with vitamin E was done in this study. The precursor of factor II is antigenically similar to biologically active factor II and can be activated to form thrombin by Echis carinatus venom. The data showed that functional factor II coagulant activity was reduced below base in warfarin-treated humans and animals given vitamin E. Factor II antigen as determined by electroimmunoassay in humans and factor II coagulant activity as measured using Echis venom in animals were unchanged and no different from untreated controls. The data suggest that vitamin E acts at the vitamin K-carboxylase step of carboxylation of precursor prothrombin and not in the synthesis of the precursor protein.

Envenomation by the northern blacktail rattlesnake (Crotalus molossus molossus): report of two cases and the in vitro effects of the venom on fibrinolysis and platelet aggregation

In two cases of human envenomation by the northern blacktail rattlesnake (Crotalus molossus molossus) there was marked swelling and ecchymosis of the bitten extremity and thrombocytopenia and, in one case, hypofibrinogenemia. Treatment consisted of i.v. antivenin, crystalloid solution, fresh frozen plasma and cryoprecipitates, with recovery in each case. In vitro studies showed that the venom had fibrinolytic and platelet aggregating properties; a coagulant effect, although present, was much less marked.