The impact of vitamin K-dependent factor depletion by warfarin on platelet-rich thrombosis after deep arterial injury.

Although the central role of thrombin in arterial thrombosis is well established, the efficacy of vitamin K-dependent factor depletion by warfarin at preventing this process has not been established. To assess the efficacy of warfarin in the prevention of arterial thrombosis, two intensities of anticoagulation were compared in a well-characterized porcine model of carotid angioplasty. For 10 days prior to angioplasty, pigs received either high-dose warfarin (n = 9), low-dose warfarin plus aspirin (n = 9), or control tablets (n = 10). Injured arteries were assessed for (111)In-platelet ( x 10(6) cm(-2)) and (125)I-fibrin(ogen) (molecules x 10(12) cm(-2)) deposition and the incidence of macroscopic thrombus. Platelet (30 +/- 7 vs. 332 +/- 137; P = 0.001) and fibrinogen (156 +/- 17 vs. 365 +/- 90; P < 0.05) deposition were significantly reduced in animals receiving high-intensity warfarin whereas low-intensity warfarin/ASA (520 +/- 240 and 1193 +/- 638) was similar to control (P =NS). At the time of angioplasty, the PT-INR and vitamin K-dependent factors varied over a broad range. The greatest reduction of platelet and fibrinogen deposition occurred as the PT-INR increased from 1.0 to 2.2. Increasing the PT-INR beyond 3.0 resulted in little, if any, incremental reduction of either platelet or fibrinogen deposition. Macroscopic thrombus was abolished at PT-INR > 2.2. Despite a broad range of vitamin K factor activities, no single factor was predictive of either platelet or fibrinogen deposition. Warfarin at PT-INR > 2.2 effectively eliminates thrombosis following deep arterial injury. Arterial thrombosis correlates poorly with any single vitamin K-dependent factor but rather appears to be a function of the entire extrinsic coagulation pathway as measured by the PT-INR.

Sulfonylurea drugs increase early mortality in patients with diabetes mellitus after direct angioplasty for acute myocardial infarction.

OBJECTIVES: The purpose of this study was to examine the impact of sulfonylurea drug use on outcome in diabetic patients undergoing direct coronary angioplasty for acute myocardial infarction. BACKGROUND: Sulfonylurea drugs impair ischemic preconditioning. Whether sulfonylurea drugs affect outcome adversely in diabetic patients undergoing direct angioplasty for acute myocardial infarction is unknown. METHODS: Clinical outcomes after direct balloon angioplasty for acute myocardial infarction were evaluated in 67 diabetic patients taking oral sulfonylurea drugs and 118 diabetic patients not taking these drugs. RESULTS: Hospital mortality was significantly higher among diabetics treated with sulfonylurea drugs at the time of myocardial infarction (24% vs. 11%). Univariate analysis identified sulfonylurea drug, age, ventricular function, ejection fraction less than 40%, prior bypass surgery and congestive heart failure as correlates of increased in-hospital mortality. Logistic regression found sulfonylurea drug use (odds ratio 2.77, p=0.017) to be independently associated with early mortality. Congestive heart failure, but not sulfonylurea drug use, was associated with an increased incidence of in-hospital ventricular arrhythmias. Congestive heart failure, prior bypass surgery and female gender, but not sulfonylurea drug use, were associated with late adverse events. CONCLUSIONS: Sulfonylurea drug use is associated with an increased risk of in-hospital mortality among diabetic patients undergoing coronary angioplasty for acute myocardial infarction. This early risk is not explained by an increase in ventricular arrhythmias, but may reflect deleterious effects of sulfonylurea drugs on myocardial tolerance for ischemia and reperfusion. For surviving patients sulfonylurea drug use is not associated with an increased risk of serious late adverse events.

Tissue prothrombin. Universal distribution in smooth muscle.

Immunohistochemical analysis of surgically obtained porcine tissue samples reveals ubiquitous staining for prothrombin in organs rich in smooth muscle content and universal staining of smooth muscle in tissue vasculature. The native character of tissue prothrombin is verified first by chromogenic substrate hydrolysis and hirudin inhibition after incubation of tissue extracts with taipan snake venom and phospholipid. Western analysis of tissue extracts confirms the native zymogen molecular weight. In addition, prothrombin purified in good yield from porcine uterus is activated by Echis carinatus venom which, like taipan venom, is 4-carboxyglutamic acid-sensitive. After correction for blood (gross heme) and interstitial fluid (albumin), excess functional prothrombin is observed in extracts of tissues having abundant smooth muscle. In contrast with factor X, the yield of prothrombin purified from porcine uterus greatly exceeds that attributable to contamination by whole blood. Northern blot analysis from selected bovine tissues extracted for polyadenylated messenger RNA is equivocal for prothrombin mRNA with the exception of liver, which is positive. It is concluded that functionally intact prothrombin is widely distributed among tissues owing to smooth muscle content, although the mechanism of emplacement and physiologic significance of prothrombin in these tissues remains unclear.

Genetic analysis and functional characterization of prothrombins Corpus Christi (Arg382-Cys), Dhahran (Arg271-His), and hypoprothrombinemia.

The structural abnormalities and functional characteristics of dysfunctional prothrombin variants in two new kindreds have been determined. Prothrombin Corpus Christi (family 1) was purified and found to have markedly reduced fibrinogen clotting activity, yet normal amidolytic and near-normal platelet aggregating activity. A transition (C to T) at nucleotide position 8885, present in the heterozygous form in affected family members, resulted in the substitution of Cys for Arg 382. This substitution results in the loss of a positive charge within the fibrinogen-binding exosite of thrombin, thus accounting for the observed functional defect. A heterozygous C to T transition was also present at position 19994 in other family members with a hypoprothrombinemic phenotype. This mutation results in the replacement of Gln 541 (CAA) by a premature stop codon (TAA). Prothrombin Dhahran (family 2) was found to have markedly reduced fibrinogen clotting activity, but normal amidolytic activity. Affected family members were found to have a G to A transition at nucleotide position 7312 resulting in the substitution of His for Arg 271. This substitution results in the abolition of a factor Xa cleavage site, yielding meizothrombin rather than thrombin, on activation of prothrombin Dhahran by factor Xa. All but one of the above mutations occur at CpG dinucleotides, thus further supporting the observation of a high incidence of CpG transitions in hereditary dysprothrombinemia. The significant bleeding tendencies of individuals homozygous for prothrombin Dhahran (prothrombin clotting activity 5% to 7%) contrast sharply with the absence of significant chronic bleeding in the proband expressing prothrombin Corpus Christi (prothrombin clotting activity 2%). Our findings underscore the capacity of thrombin to contribute to clinical hemostasis by mechanisms other than its fibrinogen clotting activity.