Development and Validation of a Simoa Assay for Determination of Recombinant Batroxobin in Human Serum.

Recombinant batroxobin (S3101) is a thrombin-like serine protease that binds to fibrinogen or is taken up by the reticuloendothelial system. A literature survey showed no adequate method that could determine sufficient concentrations to evaluate pharmacokinetic parameters for phase I clinical studies. Therefore, a sensitive method is urgently needed to support the clinical pharmacokinetic evaluation of S3101. In this study, a sensitive bioanalytical method was developed and validated, using a Quanterix single molecular array (Simoa) assay. Moreover, to thoroughly assess the platform, enzyme-linked immunosorbent assay and electrochemiluminescence assay were also developed, and their performance was compared with that of this novel technology platform. The assay was validated in compliance with the current guidelines. Measurements with the Simoa assay were precise and accurate, presenting a valid assay range from 6.55 to 4000 pg/mL. The intra- and inter-run accuracy and precision were within -19.3% to 15.3% and 5.5% to 17.0%, respectively. S3101 was stable in human serum for 280 days at -20°C and -70°C, for 2 h prior to pre-treatment and 24 h post pre-treatment at room temperature (22°C-28°C), respectively, and after five and two freeze-thaw cycles at -70°C and -20°C, respectively. The Simoa assay also demonstrated sufficient dilution linearity, assay sensitivity, and parallelism for quantifying S3101 in human serum. The Simoa assay is a sensitive and adequate method for evaluating the pharmacokinetic parameters of S3101 in human serum.

Coagulant Effect and Tolerability of Yeast-Produced Recombinant Batroxobin in Healthy Adult Subjects.

BACKGROUND AND OBJECTIVE: Batroxobin, a snake venom thrombin-like enzyme, converts fibrinogen into fibrin by cleaving fibrinopeptide A. It is used for hemostasis; however, the supply of native batroxobin is limited. Therefore, we developed a recombinant batroxobin (r-batroxobin) from Pichia pastoris and evaluated its pharmacodynamics and safety in humans. METHODS: A randomized, double-blind, placebo-controlled, single ascending-dose study was performed. Eight healthy subjects were enrolled in each r-batroxobin dose group (2.5, 5.0, or 10.0 BU/2.0 mL administered intravenously), and randomized to receive r-batroxobin (n = 6) or matching placebo (n = 2). Safety was evaluated during the study, and pharmacodynamics was assessed using prothrombin time (PT), activated partial thromboplastin time (aPTT), thrombin time (TT), and fibrinogen level. RESULTS: All subjects in each cohort completed the study. No significant changes in PT or aPTT occurred after intravenous r-batroxobin administration. Compared with the placebo group, the fibrinogen level in all r-batroxobin dose groups decreased significantly to 8.68-33.57% from the baseline within 12 h (p ≤ 0.05). The TT in the 5.0 and 10.0 BU/2.0 mL groups significantly increased to 7.53-18.48% from baseline within 12 h compared with that of the placebo group (p ≤ 0.05), whereas that of the 2.5 BU/2.0 mL group exhibited non-significant changes compared with the placebo group. No serious adverse events occurred. CONCLUSIONS: A single intravenous injection of r-batroxobin within a dose range of 2.5-10.0 BU/2.0 mL was well tolerated and resulted in a significant decrease in fibrinogen and prolongation of TT. REGISTRATION: This study is registered at the Clinical Research Information Service (CRIS, http://cris.nih.go.kr ), number KCT0002518.

[Pharmacodynamics and pharmacokinetics of batroxobin in Beagle dog].

Healthy Beagle dogs were administrated with batroxobin by intravenous infusion at high, medium and low doses. The study of pharmacodynamics and pharmacokinetics was intended to clarify the relevance of them and provided strong evidence for clinical use of batroxobin. The blood samples were collected after injection based on the time schedule and samples were tested by ELISA method to get the concentration of batroxobin. At the same time, changes of prothrombin time (PT), thrombin time (TT), activated partial thromboplastin time (APTT), fibrinogen (Fib) and D-dimmer were tested. The results showed that the concentration of D-D increased significantly after administration compared with that of before administration. The main pharmacokinetic parameters were as follows: t1/2 were (2.27 +/- 0.42) h, (10.65 +/- 2.19) h and (11.01 +/- 3.51) h; C(max) were (11.9 +/- 1.72) ng x mL(-1), (154.53 +/- 12.38) ng x mL(-1) and (172.14 +/- 47.33) ng x mL(-1); AUC(last) were (29.38 +/- 3.69) ng xh x mL(-1), (148.43 +/- 72.85) ng x h x mL(-1) and (599.22 +/- 359.61) ng x h x mL(-1). The elimination of batroxobin was found to be in accord with linear kinetics characteristics. The results of pharmacodynamics showed that D-dimmer level increased significantly after the administration of batroxobin, which was similar with the changes of batroxobin plasma concentration. Simultaneously, Fib concentrations in Beagle dog blood decreased significantly after the iv administration of batroxobin, while recovered to base level after 48 hours. PT, TT and APTT significantly became longer after administration, which returned to normal level after 48 hours. Especially, the D-dimmer levels and the batroxobin concentration in plasma after intravenous infusion of the drug were synchronized in Beagle dogs. Changes between PD/PK results had obvious correlation, and the D-dimmer levels in plasma can be one of the important monitoring indicators of batroxobin in thrombolytic medication.

Fibrinogen Longmont: a dysfibrinogenemia that causes prolonged clot-based test results only when using an optical detection method.

A new fibrinogen variant was discovered as a result of discrepancies found in routine laboratory screening. The patient, a healthy 37-year-old woman, had a mild bleeding history. Initial coagulation studies on the patient revealed a prolonged prothrombin time (PT) and a normal activated partial thromboplastin time (APTT). Further investigation on the patient and her mother demonstrated both had a PT with no end point using an optical detection method (ACL3000+) and a normal PT using an electromechanical detection method (ST4 Clot Detection System). The APTT for both the patient and her mother were essentially normal with both optical and mechanical detection methods. The patient and her mother also had markedly prolonged thrombin time and reptilase time results on the ACL3000+, but they were normal on the ST4. Coagulation test results on the patient's father were all normal. We believe the fibrinogen defect in this family may affect fibrin polymerization only enough to effect light scatter interpretation, while there is enough polymerization to increase plasma viscosity and yield an end point using an electromechanical analyzer. This report should alert pathologists and clinicians to possible discrepancies between mechanical and spectrophotometric clot testing methods.

Activation of the clotting system during extracorporeal membrane oxygenation in term newborn infants.

OBJECTIVES: To determine the degree of clotting activation that occurs with the usual anticoagulation regimen with systemic heparinization. METHODS: To allow a standardized comparison of the patients, this study focused on the first 48 hours of extracorporeal membrane oxygenation (ECMO) in term newborn infants. The ECMO perfusion circuit consisted of a roller pump, silicone membrane lungs, and silicone rubber tubing. Coagulation was controlled routinely by measuring prothrombin time, fibrinogen, antithrombin III, and reptilase time. Platelet counts, activated clotting time, and heparin concentration were controlled regularly. The following specific activation markers of the clotting system were measured: prothrombin activation fragment 1 + 2(F1+2), thrombin-antithrombin III complexes, and D-dimer. Measurements were done before the start of ECMO, after 5 minutes, and at hours 1, 2, 3, 4, 6, 12, 24 and 48. RESULTS: All seven term infants had excessively high levels of clotting activation markers within the first 2 hours of ECMO: F1+2, 11.6(+/- O.9) nmol/L (mean +/- SEM); thrombin-antithrombin, 920(+/- 2.2) microg/L; D-dimer, 15.522(+/- 3.689) ng/L. During the next 46 hours of ECMO, F1+2 and thrombin-antithrombin III complexes decreased from those high values, whereas D-dimer did not. The increase of activation markers was accompanied by low fibrinogen, low platelet counts. and prolongation of reptilase time. CONCLUSIONS: These findings fit the pattern of consumptive coagulopathy during neonatal ECMO, especially in the first 24 hours.

Determination of batroxobin levels in the plasma of guinea pigs after epicutaneous and intravenous applications.

An enzyme immunoassay has been set up to measure batroxobin levels in plasma. This assay allowed the detection of amounts of batroxobin greater than 0.5 ng/ml plasma. After the epicutaneous application of 50 or 100 batroxobin units (BU)/kg body weight, no batroxobin could be detected in plasma samples taken 15, 30, 60, 120 or 240 min after the start of the experiment. In contrast, batroxobin could be detected in plasma samples after i.v. injection of 10 BU/kg body weight.

Circulating thrombin time anticoagulant in a procainamide-induced syndrome.

Circulating anticoagulants are unusual in drug-induced syndromes. We evaluated the prolonged thrombin time of plasma from a patient with a procainamide-induced syndrome. This defect was shown to be due to a circulating anticoagulant that was not of fibrin or fibrinogen origin and that prolonged thrombin and reptilase clotting times of plasma. Subclinical doses of heparin sodium induced hemorrhagic manifestations in this patient. Following cessation of heparin therapy, the circulating anticoagulant persisted but the bleeding tendency abated. All clinical and laboratory manifestations of this syndrome abated gradually following cessation of procainamide therapy.