Pharmacokinetics and delayed experimental anti-thrombotic effect of two domain non-glycosylated tissue factor pathway inhibitor.

Tissue Factor Pathway Inhibitor (TFPI) is a naturally occurring inhibitor of the TF-FVIIa induced coagulation in the presence of FXa. Recombinant two domain TFPI, where Asn 117 on the FXa-inhibitory domain was exchanged to a Gln yielding non-glycosylated TFPI (117QTFPI1-161), was evaluated regarding pharmacokinetics and delayed antithrombotic potential in the rabbit. Pharmacokinetic study; 117QTFPI1-161 vs glycosylated TFPI1-161. Three rabbits/group were used and received 1,0 mg/kg a bolus iv injection. Plasma-TFPI was measured for three hours. The alpha-phase half-life was similar, the beta-phase half-life was close to four times longer for 117QTFPI1-161 (37 vs 10 min). Clearance of 117QTFPI1-161 was nearly two times lower (45 vs 21 ml/kg/min). Delayed anti-thrombotic study; 10 rabbits/group were used. 5 Groups; placebo + placebo, placebo + LMWH60 anti-Xa IU/kg, placebo + 117QTFPI1-161 0,25 mg/kg, 117QTFPI1-161 1,0 and 4,0 mg/kg + placebo. First injection 60 min prior to the second one, which coincided with the thrombus induction. The experimental thrombosis used combines a chemical destruction of the endothelium with a partial restriction of the bloodflow in the jugular veins. The thrombusweight was significantly reduced in LMWH and 117QTFPI1-161 1,0 and 4,0 mg/kg groups (0,6-2,6 vs 11,8 mg). Frequency of occlusive thrombosis was significantly reduced in the LMWH and 117QTFPI1-161 4,0 mg groups. All groups significantly effected the aXa-assay, the LMWH-group the most (0,85 IU/ml). LMWH was the only substance to prolong the dilute-PT-assay at the different timepoints. Absence of glycosylation increases the beta-phase half-life and decreases clearance of two domain TFPI. 117QTFPI1-161 (1,0 and 4,0 mg) has an antithrombotic effect indistinguishable from LMWH even though given 60 min before the thrombusinduction but with a considerable less effect on anti-Xa, APTT and no effect on dilute-PT. Glycosylation of TFPI influences the pharmacokinetics but not the antithrombotic capacity in this experimental setting.

The effect of recombinant aprotinin on t-PA-induced bleeding in rats.

High dose aprotinin administered during cardiopulmonary bypass (CPB) has been shown to reduce post-operative bleeding substantially. The exact mechanism of action is still debated. A reduction in fibrinolytic activity by inhibition of plasmin generated during CPB may be the primary mode of action. However, this hypothesis has been questioned as the apparent inhibitory constant of aprotinin for plasmin is orders of magnitude lower than the clinically effective plasma concentration of aprotinin. In the present study the effect of various plasma levels of aprotinin on a plasmin-induced bleeding in rats was investigated. The mean time of bleeding was 10 min in rats receiving only saline whereas a prolonged bleeding of up to > 45 min was seen in rats given t-PA and saline. The steady-state plasma concentration of recombinant aprotinin during infusion of 11 mg/kg/h was approximately 2 microM which roughly corresponds to the clinical use of aprotinin. This dose reduced the t-PA-induced bleeding to a mean value of 11 min, whereas no effects were observed with lower doses. The effect of aprotinin in clinical care of blood loss in CPB in man may therefore be caused by direct inhibition of plasmin.

Pharmacokinetics of full length and two-domain tissue factor pathway inhibitor in combination with heparin in rabbits.

Tissue factor pathway inhibitor (TFPI) is a feed back inhibitor of the initial activation of the extrinsic pathway of coagulation. In humans, injection of heparin results in a 2-6 fold increase in plasma TFPI and recent studies suggest that TFPI may be important for the anticoagulant activity of heparin. Full length (FL) TFPI, but not recombinant two-domain (2D) TFPI, has a poly cationic C-terminus showing very strong heparin binding. Therefore, we have investigated if heparin affects the pharmacokinetics of TFPI with and without this C-terminus. FL-TFPI (608 U/kg) and 2D-TFPI (337 U/kg) were injected intravenously in rabbits with and without simultaneous intravenous injections of low molecular weight heparin (450 anti-XaU/kg). Heparin decreased the volume of distribution and the clearance of FL-TFPI by a factor 10-15, whereas the pharmacokinetics of 2D-TFPI were unaffected by heparin. When heparin was administered 2 h following TFPI the recovery of FL-TFPI was similar to that found in the group receiving the two compounds simultaneously, suggesting that the releasable pool of FL-TFPI is removed very slowly in the absence of circulating heparin.

Recombinant human factor VIIa (rFVIIa) in a rabbit stasis model.

The thrombogenicity of recombinant human FVIIa (rFVIIa) and FEIBA was studied in a rabbit stasis model. Only minor thrombus formation in isolated vein segments during 10 min. of stasis was seen following the administration of rFVIIa 100-1000 micrograms/kg or FEIBA 50-100 U/kg whereas both compounds caused clear thrombus formation during 30 min. of stasis. RFVIIa caused no change in platelet counts or plasma fibrinogen 3 hours after administration, whereas a small decrease of APTT was seen due to the direct effect of rFVIIa in this assay. In contrast, FEIBA caused a significant and dose-dependent decrease of platelet counts as well as of fibrinogen, and an increase of APTT which demonstrate a general consumption of coagulation factors. In conclusion the study demonstrated a local pharmacological effect of rFVIIa in the absence of a general activation of the coagulation cascade.

Triiodothyronine stimulates growth of peripheral blood mononuclear cells in serum-free cultures in uremic patients.

The effect of triiodothyronine (T3) on the responses to mitogens and on the production of prostaglandin E2 and interleukin 2 were studied in serum-free cultures of peripheral blood mononuclear cells (PBMC) in 20 patients undergoing hemodialysis and in 30 control subjects. T3 increased the growth of PMBC induced by phytohemagglutinin and pokeweed mitogen in both groups. PBMC reached growth maximum at 0.5 nM T3 when stimulated by phytohemagglutinin in both groups. At higher concentrations of T3 the effect declined in the control group, but the response of uremic PBMC was constant. The response to T3 of pokeweed mitogen stimulated PBMC was lower in the uremic patients. The production of prostaglandin E2 by PBMC was higher in the uremic patients than in the controls. T3 had no effect on prostaglandin E2 production. Indomethacin alone and in combination with T3 had a stimulatory effect on cell growth in the patient group. T3 had no effect on the release of interleukin 2 by PBMC. An additive effect of interleukin 2 and T3 was observed in cultures stimulated by suboptimal concentrations of the mitogens. In conclusion, the impaired growth of PBMC in serum-free cultures from uremic patients was enhanced, however, not normalized, by external addition of T3, inhibition of prostaglandin E2 synthesis, and addition of interleukin 2.

Platelet aggregation and fatty acid composition of platelets in type 1 diabetes mellitus.

A raised content of arachidonic acid in platelets from diabetic patients with retinopathy was found without differences in platelet aggregation: platelet aggregability was not related to platelet fatty acid composition. In diabetes, platelet aggregation was inversely correlated to non-esterified fatty acids in plasma and may suggest an inhibiting effect. Mean platelet volume was raised in the diabetic patients, but without hyperaggregability. The findings do not exclude a relationship between platelet fatty acids and platelet aggregability, but suggest that variations in levels of non-esterified fatty acids in plasma might interfere with platelet aggregation.

Concentrations of thyroxine, 3,5,3'-triiodothyronine, 3,3',5'-triiodothyronine, 3,3'-diiodothyronine, and 3',5'-diiodothyronine in human red blood cells.

A simple and rapid method for the estimation of cellular concentration of thyroxine (T4), 3,5,3'-triiodothyronine (T3), 3,3',5'-triiodothyronine (rT3), 3,3'-diiodothyronine (3,3'-T2), and 3',5'-diiodothyronine (3',5'-T2) as well as their distribution between cytosol and membranes in human red blood cells (RBC) is presented. Concentrations of iodothyronines in RBC (RBC-T) were calculated by multiplying the total serum concentrations by the ratio of radioactivity in equal volumes of packed RBCs and serum, pre-incubated with 125I-labelled iodothyronines of high specific activity. Plasma and RBC were separated by centrifugation in capillary glass tubes. The separation of membranes and cystosol was performed by hypotone lysis and centrifugation. The median RBC-T of T4, T3, rT3, 3,3'-T2, and 3',5'-T2 from 17 euthyroid subjects were 360 pmol/l, 156 pmol/l, 2.77 pmol/l, 6.81 pmol/l, and 2.17 pmol/l, respectively. The cytosol/cytosol + membrane ration were 66%, 40%, 84%, 77%, and 97%, respectively. The differences in RBC-T were not similar to the differences in free serum concentrations. The ratio of RBC-T to free serum concentration differed considerably between T4 (16.6), T3 (24.4), and 3,3'-T2 (15.5) as compared to rT3 (5.8) and 3',5'-T2 (2.6). Data on three patients with thyroid diseases suggested that RBC-T values were increased in hyperthyroidism and decreased in hypothyroidism, whereas the cytosol/cytosol + membrane-ratio was unaltered.

Metabolic clearance and production of diiodotyrosine in healthy man.

Metabolic clearance rate (MCR) and daily production rate (PR) of diiodotyrosine (DIT) were estimated using a constant infusion technique of trace amounts of [125-I]-DIT followed by chromatographical isolation of tracer. Median DIT MCR was in eight healthy subjects estimated to 162 l/day x 70 kg (range 135-242), whereas PR was 52 nmol/day x 70 kg (range 25-126). The median serum DIT concentration was 0.27 nmol/l (range 0.16-0.62). In five L-thyroxine substituted subjects without endogenous thyroxine (T4) production, serum DIT concentrations were below 0.02 nmol/l, suggesting that more than 94% of daily produced DIT is secreted by the thyroid gland.