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Reptilase@'-R-A New Reagent in Blmd Coagulation

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Reptilase@'-R-A New Reagent in Blmd Coagulation British Journal of Haematology, 1971, 21, 43. Reptilase@'-R-A New Reagent in Blmd Coagulation C. FUNK,J. GMUR,R. HEROLDAND P. W. STRAUB Department of Medicine, Kantonsspital, University of Zurich, Switzerland (Received 8 September 1970; accepted for piiblication 29 September 1970) SUMMARY.Reptilase@-R, a purified thrombin-like snake-venom enzyme from Bothrops atrox, has been tested for its usefulness as a substitute for thrombin in two coagulation assay systems. Reptilase was found to be more stable than thrombin and not to be inhibited by heparin and hirudin. Performance of the Reptilase time allows the rapid exclusion of heparin con- tamination in plasma samples with prolonged thrombin times. In the presence of fibrinogenlfibrin split products, the Reptilase time is less prolonged than the thrombin time, whereas in patients with prolonged thrombin times because of congenital dysfibrinogenaemia the inverse is found. Thus, performance of both Reptilase time and thrombin time allows the rapid identification of three major causes for a prolongation of the thrombin time. In patients on heparin therapy because of a defibrination syndrome, the Reptilase time may replace the thrombin time as a guide for the degree of coagulation inhibition by FDP, although our re- sults show that it is somewhat less sensitive. Reptilase can also be substituted for thrombin in the rapid chronometric fibrino- gen assay. Unfortunately the advantages of reagent stability and insensitivity to heparin are balanced by a lesser reproducibility, especially in the presence of FDP. While thrombin liberates the fibrinopeptides of both the a- and p-chains of fibrinogen, the thrombin-like snake-venom enzyme Reptilase exclusively acts on the a-chain, thus leading to coagulation by liberating only fibrinopeptide A (Blombick et al, 1957; Stocker & Straub, 1970). Since Reptilase, in contrast to thrombin, is stable, and because we expected that normal human plasma would be devoid of any inhibitor directed against this exogenous substance, we have tested the usefulness of Reptilase as a substitute for thrombin in various assay systems. METHODS For the preparation of plasma nine parts of blood were collected directly into one part of 0.1 M sodium-oxalate in siliconized glass tubes or into one volume of a three: two mixture of 0.166 M sodium oxalate with Trasylol 5000 u/inl. For some experiments nine parts of blood were collected into one part of 3.8% (w/v) sodium citrate. Dilutions were done in veronal-acetate buffer, pH 7.39 (Michaelis). Routine methods were used for the assay of clotting factors (Duckert, 1958). Fibrinogen (factor I) was determined with a biuret method on a washed clot, with the h.eat D 43 44 C. Funk et a1 precipitation method of Schulz (1955) and with the thrombin-clotting time method of Clauss (1957). In the latter method the clotting time of 0.1 ml of I in 10 diluted plasma is recorded after addition of 0.1 ml of a thrombin dilution. When Reptilase (34 mg/ml) was substituted for thrombin in this assay, one volume of the test plasma was diluted with four volumes of ammonium acetate buffer, pH 7.1 (Shainoff & Page, 1962). Calibration curves were estab- lished using normal plasmas with a known (biuret method) fibrinogen content and dilutions thereof. Thrombin time and Reptilase time were recorded after addition of 0.1 ml of a thrombin dilution or Reptilase to 0.2 ml of undiluted plasma. The dilution of thrombin was chosen so as to give the same normal range of 13-18 s as undiluted Reptilase. Fibrinolysis was assayed using a euglobulin lysis time method (von Kaulla & Schultz, 1958) and the fibrin plate technique (Astrup & Miillertz, 1952). Plasminogen was determined according to Alkjaersig et a1 (1959). Fibrinogenlfibrin degradation products (FDP) were detected qualitatively using immunoelectrophoresis (Straub et aE, 1966) and quantitatively using the tanned red cell haemagglutination inhibition immunoassay (TRCHII) of Merskey et a1 (1966). Fibrinogen degradation products (FDP) were produced by incubation of purified fibrinogen with Urokinase or plasmin for various periods. The fibrinolytic activity was blocked by addition of Trasylol400 u/ml. Materials Purified fibrinogen ‘Kabi’, 95% clottable, was obtained from Globopharm AG, Zurich. Bovine thrombin ‘Roche’ was acquired from Hoffmann-La Roche, Basel, one vial containing 5000 NIH-U = IOO mg of the dry powder. Hirudin, Grade 111, was obtained from Sigma Co., St Louis, U.S.A. Reptilase (reagent-grade) was obtained from Pentapharm Ltd, Basel, one vial containing 34 mg of the dry powder, which is reconstituted to I ml with distilled water. The solution is already buffered with glycine and stabilized with partially hydrolysed gelatin. It is stable for 5 days at 4°C and for 24 hr at room temperature. Trasylol ‘Bayer’ ampoules of 5 ml (5000 u/ml) was used. Urokinase was obtained through the courtesy of Dr F. Duckert, Burgerspital, Basel. RESULTS I. REPTILASE TIME VERSUS THROMBIN TIME For the comparison of Reptilase times with thrombin times Reptilase was used undiluted (34 mg/ml) and thrombin was diluted so as to produce identical clotting times in normal plasma as Reptilase. Injuence of Heparin and Hirudin As shown in Table I, the Reptilase time is not influenced by increasing amounts of heparin in vitro. Similarly the Reptilase time is found normal in heparinized patients (Table 11). Injluence of FibrinogenlFibrin Split Products and of Congenital Fibrinogen Variants Fig I shows Reptilase and thrombin times obtained in mixtures of normal plasma with Reptilase and Blood Coagulation 45 ncreasing amounts of FDP, as obtained by digestion of fibrinogen ‘Kabi’ to a thrombin time of 60 s. The Reptilase time is obviously less sensitive to interference by FDP than the thrombin time. This was also observed during progressive digestion of normal plasma with Urokinase, as shown in the lower part of Fig 2. Thus, early FDP had the same effect as later products. Fig I also demonstrates that admixture of dysfibrinogenaemia plasma produces the opposit TABLEI. Influence of heparin and hirudin addition to normal plasmas in vitro on thrombin- and Reptilase- times Clottirig time (3) of normal plasma containing increasing amounts of heparin and hirudin or buffer Heparin (NIH-U/ml) Hirudin I rng/nil I 2 Thrombin 4 NIH-U/ml Plasma I co Plasma 2 co Plasma 3 co Reptilase 34 mg/ml Plasma I I4 Plasma 2 16 Plasma 3 I3 Fibrinogen values Thrombiti time Reptilase time Heat precipit. Clam method (mg%) 4 NIH-U/ml 16 NIH-U/ml 34 wlml (v%) (4 (4 (3) Thrombin Reptilase 33 ulml 34 mginil Group I (u = 10) ISO-330 120-380 115-360 > 60 9-> 60 13-19 Group I1 (n = 6) 100-350 75-210 125-390 > 60 > 60 12-16 Normal values 150-soo 150-500 150-500 13-IS* 5-9 12-IS* relation between Reptilase and thrombin times. Identical results were obtained when citrate instead of oxalate was used as an anticoagulant. As shown in Fig 3 and Table 111, the Reptilase time was consistently shorter than the throm- bin time in 18 patients with elevated serum FDP and a prolonged thrombin time not nor- malized by BaSO, adsorption and thus not due to heparin, while it was longer than the 46 C. Funk et a1 thrombin time in all I I tested patients with congenital dysfibrinogenaemia. Details of the latter cases have been reported earlier (von Felten et af, 1966; Funk & Straub, 1970). loo/ (0) I I I I *O I 1 I 40 20 p--" L - I I I Normal plasma in mixture (%) FIG I. Comparison of thrombin times (0)and Reptilase times (0)in mixtures of normal plasma with increasing amounts of plasma of a patient (a) with Fibrinogen Zurich, (b) with a fibrinogen digest obtained with urokinase and (c) with buffer. 11. RAPID CHRONOMETRIC FIBRINOGEN DETERMINATIONS USING REPTILASE INSTEAD OF THROMBIN Normal lndivicltials Fig 4 shows typical calibration curves for the Clauss method using Reptilase and thrombin, and Fig 5 shows the correlation between fibrinogen values as determined with Reptilase and with thrombin in 27 normal subjects. Reptilase values are obviously less reliable than values obtained with thrombin, especially in the low and high range. Reptilase and Blood Coagulation 47 Iv$uence of Heparin and Himdin The fibrinogen values as obtained with Reptilase were compared with the values obtained with two different dilutions of thrombin in plasmas before and after in vitro addition of various amounts of heparin or hirudin. The Reptilase assay is insensitive to these inhibitors. Table I1 shows the fibrinogen values in two groups of heparinized patients: The first group Urokinase :' 0.. \ '.\ \ 50 - -., \ ...)A-- - - -6- 0.. - --- ', -. a-- -- -- -- *. +/ Reptilase Is, ...G '0 20- II I I I 0 10 35 60 90 '-0 Incubation time (min) FIG 2. Effect of urokinaseinduced fibrinolysis on normal plasma. Upper graph: fibrinogen as deter- mined by heat precipitation, .;biuret determination of clottable protein, 0;chronometric method of Clauss using thrombin, A ; and chronometric method using Reptilase, 0. had conventional heparin therapy, the second group consists of six patients who had under- gone cardiac surgery using the extracorporeal circulation immediately before the assay was done. The fibrinogen assay using Reptilase gives accurate values even in highly heparinized patients. Itlflztence of Fibrinogen Split Products Fig z shows the influence of fibrinogen split products, as produced by incubation of normal plasma with Urokinase, on the results of the different fibrinogen assays. The Reptilase assay is even more affected by split products than the assay with thrombin. It is noteworthy that 48 C. Funk et a1 because of difficulties in endpoint detection the Reptilase values were not well reproducible and therefore the variation was considerable. The values obtained with the heat precipitation method remained virtually unchanged because this method measures fibrinogen plus some FDP.
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