Dicoumarol-induced prothrombins

Distribution of the heterogeneity of des-gamma-carboxyprothrombin in patients with hepatocellular carcinoma

BACKGROUND AND AIM

Our aim was to evaluate the heterogeneity of des-gamma-carboxyprothrombin (DCP) in the plasma of patients with hepatocellular carcinoma (HCC), benign liver diseases, and normal controls and compare the DCP values by enzyme-linked immunosorbent assay (ELISA) for two types monoclonal antibodies (MU-3 and 19B7).

METHODS

We purified DCP from the plasma of 17 patients with HCC, three patients with metastatic liver tumors (MTLT), 12 with acute hepatitis (AH), five with chronic hepatitis (CH), nine with liver cirrhosis (LC), and 10 normal controls (NC). The DCP was analyzed by using immunoaffinity chromatography, reversed-phase high-performance liquid chromatography and measured by using an ELISA.

RESULTS

In HCC, the synthesis of the 1-, 3-, and 4-Gla (gamma-carboxyglutamic acid) DCP variants markedly increased, and those levels accounted for more than 50% of the DCP. The synthesis of the 3-, and 4-Gla DCP gradually increased in order of AH, CH, and LC patients. The MU-3 antibody reacted with the 1-, 3- and 4-Gla DCP variants, whereas the 19B7 antibody reacted with the 6-, 7- and 8-Gla variants. The DCP was measured by ELISA, markedly increased in order of NC, AH, CH, LC, and HCC cases. The correlation of the ratios (1 + 3 + 4)-Gla/(6 + 7 + 8)-Gla DCP and MU-3/19B7 was positive and statistically significant (r = 0.786, n = 56).

CONCLUSIONS

According to the severity of liver damages, the synthesis of the 1-, 3- and 4-Gla DCP variants that lost the Ca binding from the outside of the Gla-domain of the prothrombin molecule increases and the MU-3/19B7 ratio is believed to reflect this.

A variant of des-gamma-carboxy prothrombin was increased in alcoholic liver disease without hepatocellular carcinoma

Serum variants of des-gamma-carboxy prothrombin (DCP) recognized by two different monoclonal antibodies, 19B7 and MU-3, were measured in patients with alcoholic liver disease (ALD), and the values were compared with those of viral liver disease (VLD) and hepatocellular carcinoma (HCC). In the assay that used 19B7 antibody, DCP levels in ALD and HCC were significantly higher than that of VLD, although there was no significant difference in the values between ALD and HCC. In the assay that used MU-3 antibody, DCP level of HCC was significantly higher than those of ALD and VLD, although there was no significant difference in values between ALD and VLD. The ratio of 19B7/MU-3 assay values was significantly higher for ALD than the ratios for VLD and HCC. It is suggested that ALD has a different DCP variant pattern compared with VLD and HCC, which suggests that ALD has a different mechanism of DCP production.

Process of carboxylation of glutamic acid residues in the gla domain of human des-gamma-carboxyprothrombin

In the absence of vitamin K (VK) or in the presence of VK antagonists, hepatic VK-dependent carboxylase activity is inhibited and des-gamma-carboxyprothrombin (DCP) is released into the blood. We analyzed the number of glutamic acid (Glu) residues and their positions in the Gla domain (GD) of DCP to investigate the gamma-carboxylation mechanism of VK-dependent carboxylase. Several DCPs were found in each subject studied. The 10 Gla residues of human prothrombin were carboxylated in order from the N-terminal (residues 26, 25, 16, 29, 20, 19, 14, 32, 7 and 6). The process of Glu carboxylation seemed to proceed three-dimensionally from inside to outside the molecule.

Cooperativity in the calcium ion-induced quenching of the intrinsic fluorescence of a series of normal and GLA-deficient bovine prothrombin fragment 1 molecules

Ca2+ titrations of the intrinsic fluorescence of a series of gamma-carboxyglutamic acid (GLA)-deficient bovine prothrombin fragments 1 yield response Hill plot parameters useful for characterization of the metal ion-binding process. 11-, 10-, and 9-GLA fragments 1 exhibit Tm (the (Ca2+)total concentration at which ln (B/F) = 0 in the response Hill plot) values between 0.2 and 0.3 mM. A 22-fold increase in Tm to 5.4 mM is observed for 8-GLA fragment 1. Tm decreases to 3.8 mM for the 7- and 6-GLA proteins. The value of h, about 2.8 +/- 0.2 for 11-, 10-, and 9-GLA fragments 1, abruptly decreases to 1.2-1.3 for 8-, 7-, and 6-GLA fragments 1. The observed degree of quenching induced by saturating levels of calcium ions is affected by both changes in the intrinsic fluorescence of the metal ion-free proteins and in the maximum possible degree of quenching in the presence of calcium. The kinetic characteristics of the calcium ion-induced quenching of the intrinsic fluorescence of 6-GLA fragment 1 are identical to those observed in 10-GLA fragment 1, suggesting that the fluorescence quenching observed in the 6- and 10-GLA fragments 1, while different in magnitude, involves similar processes. Observation of an abrupt change in the relative electrophoretic mobilities of 11- to 9-GLA fragments 1 compared to 8- to 6-GLA fragments 1, in the absence or presence of Ca2+, suggests the existence of a major protein conformation change which occurs concomitantly with the noted changes in Tm and h response Hill plot parameters. Molecular mechanics calculations suggest a structural hypothesis unifying these observations. Central to this model is the presumption of the existence of hydrogen bond-mediated interactions between metal ion-binding sites.

Purification and characterization of dicoumarol-induced prothrombins. Evidence of 5-Gla variant with two (or more) polypeptide chains

A 5-Gla prothrombin, adsorbable onto barium oxalate and containing an admixture of one- and two-chain molecules, has been purified from the plasma of steers on a dicoumarol regimen for three years. Double-chain molecules were not detected in any of our six other variants containing zero to nine Gla residues. In this double-chain variant, the peptide bond between Arg52-Asn appears to be missing, as the preparation showed amino-terminal alanine and aspartic acid, and released both double- and single-chain F1 upon digestion with thrombin. The molecular masses of the F1 and its heavy chain were 24,000 and 19,000 daltons, respectively. The double-chain variant was similar to its single-chain counterpart [Malhotra, O.P. (1979) Thromb. Res. 14, 439-448] in that it (a) yielded thrombin equivalent to 30% of normal in three hr, (b) moved in the alpha 1 region in the absence of calcium ions and between the alpha 1 and alpha 2 macroglobulins in the presence of calcium ions, (c) contained five gamma-carboxyglutamyl residues (Gla), and (d) showed comparable antigenic activity with normal prothrombin.

Electroimmunoassay of prothrombin

Electroimmunoassay of normal (10-Gla) and Gla-deficient prothrombins containing 0 to 9 Gla (gamma-carboxyglutamyl) residues performed in EDTA against anti- (normal) prothrombin showed that each of the Gla-deficient proteins contained as much antigenic activity as does the normal molecule. In the presence of Ca2+, however, normal prothrombin appeared to show the least while 0- to 2-Gla variants, the most activity. This anomaly arises from the presence of antibodies (Ca-IIAb) which form antigen-antibody (Ag-Ab) complexes when the conformation of the antigen is stabilized in Ca2+. For example, upon fractionation of the antisera and mixing Ca-IIAb (bound to 10-Gla prothrombin, Affi-gel column and eluted by replacing Ca2+ with EDTA) with those reacting with prethrombin1 (non-Gla portion of the molecule), rocket heights in Ca2+ decreased the most with 10- and 9-Gla (32%), followed by 13% with 8-Gla, 2% with 7-Gla and none with 2-Gla prothrombins--indicating that Ca-IIAb do cross react with 7-, 8- and particularly 9-Gla prothrombins. This was also confirmed by the fact that anti 7-Gla but not anti 0-Gla sera contained some antibodies which reacted only in the presence of Ca2+.

Warfarin and the biochemistry of the vitamin K dependent proteins

We have reviewed the biochemistry of the normal and warfarinized vitamin K-dependent coagulation proteins, both individually and as members of their respective macromolecular enzyme complexes. Much has been learned in the past 10-15 years about the molecular mechanisms of coagulation. However, we have only scratched the surface and are beset by a number of interesting challenges. Clearly, we must begin to dissect the other vitamin K-dependent macromolecular enzyme complexes as has been done for prothrombinase. Prothrombin differs in fundamental ways from the other vitamin K-dependent proteins and we can anticipate significant differences as well as similarities in the other complexes. The presence of potentially functional domains in the non-catalytic portions of the vitamin K-dependent proteins and their similarities within this family of proteins should prove a fruitful area of future research. Finally, the evaluation of warfarinized vitamin K-dependent proteins, both in fundamental studies with purified systems and using uniquely engineered immunoassays, should shed light on basic molecular mechanisms and modes of monitoring warfarin therapy.

The biochemical basis of warfarin therapy

Vitamin K is required for a liver microsomal enzyme that catalyzes the posttranslational conversion of specific glutamyl residues in precursors of the vitamin K-dependent clotting factors to gamma-carboxyglutamyl residues in the plasma form of these proteins. A second product of this carboxylation reaction is the 2,3-epoxide of the vitamin. The anticoagulant warfarin blocks the enzyme which reduces this epoxide to vitamin K quinone, and also blocks one of the microsomal pathways which converts the quinone to the active coenzyme form of the vitamin, the hydroquinone. Warfarin anticoagulation therefore reduces the activity of the vitamin K-dependent carboxylase and results in the secretion of vitamin K-dependent clotting factors that are under carboxylated. The presence of gamma-carboxyglutamyl residues is essential for the normal Ca++/phospholipid-mediated activation of prothrombin, and the des-gamma-carboxy forms of prothrombin secreted by patients receiving warfarin therapy lack biological activity and have a reduced thrombotic potential.

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.

Partially carboxylated prothrombins. II. Effect of gamma-carboxyglutamyl residues on the properties of prothrombin fragment 1

Purified prothrombin fragments 1 derived from normal (10-carboxyglutamyl) and dicoumarol-induced 7-, 5-, 2-, 1-, and 0-carboxyglutamyl prothrombins contained the same number of gamma-carboxyglutamyl residues as their respective parent molecules. The effect of gamma-carboxyglutamyl residues was more pronounced on the fragments 1 than on the prothrombins. Consequently, the pI values of the fragments 1 were very well differentiated, with normal fragment 1 focusing at pH 3.58, 7-carboxyglutamyl fragment 1 at 3.79, 5- at 3.97, and 2- at pH 4.29. Similarly, by agar gel electrophoresis, normal fragment 1 was the most mobile, followed by 7-, 5-, 2-, 1- and lastly 0-carboxyglutamyl fragment 1. Because of Ca2+ being bound to the carboxyglutamyl residues, the electrophoretic mobility of normal fragment 1, in the presence of Ca2+, was reduced the most, followed by 7-, 5- and then 2-carboxyglutamyl fragment 1, while the mobilities of the 1- and 0-carboxyglutamyl fragments 1 were not affected. In contrast to their parent molecules, all of the fragments 1 in the presence of EDTA gave negative immunoprecipitation reactions against antibodies produced against normal prothrombin. In the presence of Ca2+, conversely, the fragments 1 containing comparable amounts of antigenic activity all gave positive reactions. However, the intensity of the immunoprecipitates varied, as normal fragment 1 gave the most prominent immunoprecipitation reaction, consecutively followed by 7-, 5-, 2-, 1- and lastly 0-carboxyglutamyl fragment 1 where the precipitation was so faint that it was hardly visible.