Interaction of short chain and long chain fatty acid phosphoglycerides and bile salts with prothrombin

Bile acids and coagulation factors: paradoxical association in children with chronic liver disease

OBJECTIVE

To examine whether there is an association between bile acids and coagulation factors in children with chronic liver disease.

METHODS

Forty-five patients (age 2.8 months-18.8 years) were included in this cross-sectional observational study carried out at a single tertiary referral center. Coagulation factors, prothrombin time, albumin, and total fasting serum bile acids were analyzed. The international normalized ratio (INR) and the pediatric end-stage liver disease score were calculated.

RESULTS

The 12 patients with bile acids more than 200 μmol/l showed a significant positive correlation between bile acids and factor V (FV), FVII, and prothrombin time (r(s) = 0.80, 0.72, 0.60, P<0.05) and a significant negative correlation between bile acids and INR (r(s) = -0.58, P<0.05). Conversely, in the group with bile acids less than 200 μmol/l, there was a significant negative correlation between bile acids and FVII and FIX (r(s) = -0.41 and -0.41, P<0.05) and a positive, albeit nonsignificant, correlation between bile acids and INR. No in-vitro analytical interference between bile acids and coagulation factors was found. Patients with bile acids more than 200 μmol/l had a significantly worse outcome than patients with lower levels of bile acids.

CONCLUSION

A positive correlation was found between bile acids and coagulation factors in patients with bile acids more than 200 μmol/l. Coagulation factors may be questionable as prognostic markers in patients with markedly elevated bile acids.

The inhibition of clotting complexes of the extrinsic coagulation cascade by the phospholipase A2 isoenzymes from Naja nigricollis venom

Phospholipase A2 (PLA2) isoenzymes from Naja nigricollis venom exhibit anticoagulant activity with varying potencies. To determine which complexes in the extrinsic coagulation cascade are inhibited by these PLA2 enzymes, we examined their effects on the coagulation of bovine plasma initiated by the addition of thromboplastin, Russell's viper venom (RVV) or thrombin. The weakly anticoagulant PLA2 enzymes, CM-I and CM-II, prolonged clotting initiated by thromboplastin, but not that initiated by RVV or thrombin. The strongly anticoagulant enzyme, CM-IV, prolonged clotting initiated by both thromboplastin and RVV, but not clotting initiated by thrombin. To confirm the differences in their inhibitory properties, we examined the effect of these PLA2 enzymes on reconstituted extrinsic tenase and prothrombinase complexes. The weakly anticoagulant enzymes inhibited the tenase complex, but did not inhibit the prothrombinase complex, whereas the strongly anticoagulant enzyme inhibited both complexes. Thus the enzymes showed distinct differences in their inhibition patterns in the extrinsic coagulation cascade. Their dissimilarity in inhibition of the two phospholipid dependent activation steps probably reflects the difference in phospholipid requirements and/or mechanism of inhibition between the two complexes. Inhibition of successive amplification steps in the extrinsic coagulation cascade by CM-IV is consistent with its potency as a strongly anticoagulant PLA2.

Assembly of the prothrombin activator complex on rabbit alveolar macrophage high-affinity factor Xa receptors. A kinetic study

Efficient prothrombin activation occurs after assembly of factors Va, Xa, and phospholipid surface cofactor as a multimolecular complex. These components are provided by platelets and plasma within the vascular space, but molecules and membranes for prothrombin activator assembly in extravascular spaces have not been identified. In the present study, purified alveolar macrophages were found to produce high-affinity factor Xa receptors that mediate formation of enzymatic prothrombinase complexes and rapid prothrombin to thrombin conversion in the absence of exogenous factor V/Va or platelets. Thus, in reaction mixtures with alveolar macrophages cultured for 20 h in serum-free medium, the thrombin formation rate was 152 nM/min/0.66 X 10(6) cells, after adding prothrombin (1.5 microM), Ca2+ (5 mM), and factor Xa (3.7 nM). The observed Kd of factor Xa interaction with macrophage receptors is 2.1 +/- 0.94 X 10(-10) M. Kinetic analysis and inhibition studies using isolated factor V and anti-factor V antibody show that macrophage Xa receptors are functionally and antigenically similar to plasma factor V. By contrast, freshly isolated cells lacked receptors promoting prothrombin conversion at high rates. Inhibitors of protein synthesis and glycosylation, puromycin and monensin, respectively, abrogated production of Xa receptors in culture. Additionally, subcellular fractionation and enzyme-marker studies (alkaline phosphodiesterase I) indicate that internal and external membranes of alveolar macrophages have phospholipid surface cofactor activity required for prothrombinase complexes. Pulmonary surfactant is also shown to express this cofactor activity. Alveolar macrophages and surfactant comprise an efficient prothrombin activator system that is independent of plasma factor V. This system may facilitate rapid extravascular alveolar thrombin formation even at very low concentrations of factor Xa during lung defense reactions to inflammation or edema.

Interactions of the components of the prothrombinase complex

The interaction of components of the prothrombinase complex, i.e. bovine Factor X or Factor Xa, bovine Factor V or Factor Va, phospholipid, and Ca2+, in various combinations was studied primarily by a gel filtration technique. In experiments, in which phospholipids ranging from those isolated from naturally occurring sources to those long chain (18 : 1) as well as short chain 6 : 0 and 7 : 0 fatty acids prepared by chemical and enzymatic synthesis were used, it was evident that a net negative surface charge on the lipid dispersions was one of the important requirements for interaction. Though the short chain fatty acid phospholipids interacted with the proteins of the prothrombinase complex, there was invariably a diminution in the activity of the enzyme complex. It was established that Factor V or Va did not bind Ca2+ and that the binding of either of these factors with phospholipids (with a net negative charge) was not dependent on Ca2+. However, the interaction of Factor X or Factor Xa with phospholipids with a negative charge required Ca2+. It was shown that Factor X could bind to the same type of lipid of lipid surface as that noted for Factor Xa. Of interest was the apparent difference in the phospholipid binding characteristics of the two variant forms of bovine plasma Factor X, i.e. X1 and X2, which might in part explain the differences in their specific activities. Of importance was the lack of demonstrable complex formation between Factors II, X and V in the absence of phospholipids and/or in the presence or absence of Ca2+. The significance of these results as they might apply to the configuration of the prothrombinase complex and its interaction with prothrombin plus the usefulness of the short chain fatty acid phospholipid in exploring these lipid-protein interactions are discussed.