Method for determining the spatiotemporal distribution of activity of a proteolytic enzyme in a heterogeneous system (variations), a device for realizing same and a method for diagnosing the defects in the hemostatic system on the basis of a change in the spatiotemporal distribution of activity of a proteolytic enzyme in a heterogeneous system

Abstract

The invention relates to the field of biotechnology. The method for determining the spatial and temporal distribution of the activity of a proteolytic enzyme in an in vitro heterogeneous system, such as blood or blood plasma, involves the introduction of a luminescent, fluorogenic or chromogenic substrate into a sample with the subsequent release of a detectable tag as the proteolytic enzyme cleaves the substrate, and the recording of the optical characteristics of the sample, which makes it possible to assess the spatial and temporal distribution of the activity of the enzyme. The device for the implementation of the above method comprises an in vitro system, a means for illuminating the sample, a recording means and a control means. A method for diagnosing homeostatic imbalances according to a change in the spatial and temporal distribution of the activity of a proteolytic enzyme in a blood sample is also proposed.

Claims

1. A method for determining the spatial distribution of activity of a proteolytic coagulation factor in the determined points of time in vitro comprising the steps of: obtaining a sample of a test medium from the subject, wherein the test medium is one of blood plasma and whole blood; adding a fluorogenic substrate to the test medium to obtain a test medium with the fluorogenic substrate; combining the test medium with the fluorogenic substrate and an activating agent in a cuvette of an in vitro system, wherein the activating agent induces the formation of an activated proteolytic coagulation factor from its inactive zymogen and causes the formation of a fibrin clot, the fluorogenic substrate is cleaved by the activated proteolytic coagulation factor, and a fluorescent mark is released upon cleavage of the fluorogenic substrate and the activating agent is a tissue factor; providing and maintaining constant pressure within the in vitro system, wherein the constant pressure is a pressure elevated compared to the atmospheric pressure; illuminating the cuvette with the light of the fluorescent mark's excitation wavelength in determined points of time to excite a fluorescence signal of the fluorescent mark; recording the spatial distribution of the intensity of the fluorescence signal within a volume of the cuvette in the determined points of time, and obtaining a set of recorded spatial distributions of the intensity of the fluorescence signal; illuminating the cuvette with the light of visible wavelength in determined points of time to induce light scattering by the fibrin clot; recording the spatial distribution of the intensity of the light scattering signal within a volume of the cuvette in the determined points of time, and obtaining a set of recorded spatial distributions of the intensity of the light scattering signal; converting the set of the recorded spatial distributions of the intensity of the fluorescence signal into a set of spatial distributions of the activity of the proteolytic coagulation factor in the determined points of time by solving the inverse reaction-diffusion-convection equation, wherein the step of converting further includes correction of the distortion of the fluorescence signal caused by light scattering in the fibrin clot at each of the determined points of time wherein the set of spatial distributions of the activity of the proteolytic coagulation factor in the determined point of time reflects the state of coagulation system of the subject.

2. A method for determining the spatial distribution of activity of a proteolytic coagulation factor in the determined points of time in vitro comprising the steps of: obtaining a sample of a test medium from the subject, wherein the test medium is one of blood plasma and whole blood; adding a chromogenous substrate to the test medium to obtain a test medium with the chromogenous substrate; combining the test medium with the chromogenous substrate and an activating agent in a cuvette of an in-vitro system, wherein the activating agent induces the formation of an activated proteolytic coagulation factor from its inactive zymogen and causes the formation of a clot, the chromogenous substrate is cleaved by the activated proteolytic coagulation factor, and a chromogenic mark is released upon cleavage of the chromogenous substrate and the activating agent is a tissue factor; providing and maintaining constant pressure within the in vitro system, wherein the constant pressure is a pressure elevated compared to the atmospheric pressure; illuminating the cuvette by light having a wavelength corresponding to substantial absorption thereof by the chromogenic mark in determined points of time; recording the spatial distribution of light absorption of the chromogenic mark within a volume of the cuvette in determined points of time and obtaining a set of recorded spatial distributions of the light absorption points; illuminating the cuvette with the light of visible wavelength in determined points of time to induce light scattering by the fibrin clot; recording the spatial distribution of the intensity of the light scattering signal within a volume of the cuvette in the determined points of time, and obtaining a set of recorded spatial distributions of the intensity of the light scattering signal; converting the set of the recorded spatial distributions of the light absorption of the chromogenic mark into a set of spatial distributions of the activity of the proteolytic coagulation factor in the determined points of time by solving the inverse reaction-diffusion-convectionequation, wherein the step of converting further includes correction of the distortion of the light absorption caused by light scattering in the fibrin clot at each of the determined points of time, wherein the set of spatial distributions of the activity of the proteolytic coagulation factor in the determined points of time reflects the state of coagulation system of the subject.

3. A method for determining the spatial distribution of activity of a proteolytic coagulation factor in the determined points of time in vitro comprising the steps of: obtaining a sample of a test medium from the subject, wherein the test medium is one of blood plasma and whole blood; adding a luminescent substrate to the test medium to obtain a test medium with the luminescent substrate; combining the test medium with the luminescent substrate and an activating agent in a cuvette of an in-vitro system, wherein the activating agent induces the formation of an activated proteolytic coagulation factor from its inactive zymogen and causes the formation of a clot, the luminescent substrate is cleaved by the activated proteolytic coagulation factor, and a luminescent mark is released upon cleavage of the luminescent substrate and the activating agent is a tissue factor; providing and maintaining constant pressure within the in vitro system, wherein the constant pressure is a pressure elevated compared to the atmospheric pressure; recording the spatial distribution of the intensity of a luminescence signal of the luminescent mark within a volume of the cuvette in the determined points of time, and obtaining a set of recorded spatial distributions of the intensity of the luminescent signal; illuminating the cuvette with the light of visible wavelength in determined points of time to induce light scattering by the fibrin clot; recording the spatial distribution of the intensity of the light scattering signal within a volume of the cuvette in the determined points of time, and obtaining a set of recorded spatial distributions of the intensity of the light scattering signal; converting the set of the recorded spatial distributions of the intensity of the luminescent signal into a set of spatial distributions of the activity of the proteolytic coagulation factor in the determined points of time by solving the inverse reaction-diffusion-convectionequation, wherein the step of converting further includes correction of the distortion of the light absorption caused by light scattering in the fibrin clot at each of the determined points of time, wherein the set of spatial distributions of the activity of the proteolytic coagulation factor in the determined points of time reflects the state of coagulation system of the subject.

4. The method according to any one of claims 1 to 3, wherein the tissue factor is selected from the group consisting of tissue factor immobilized on a surface, and soluble tissue factor.

5. The method according to any one of claims 1 to 3, wherein the fluorogenic substrate, the chromogenous substrate, or the luminescent substrate is a solution.

6. The method according to any one of claims 1 to 3, wherein the fluorogenic substrate, the chromogenous substrate, or the luminescent substrate is applied in the freeze-dried form.

7. The method according to any one of claims claims 1 to 3, wherein the blood plasma is selected from the group consisting of platelet-rich plasma, platelet-free plasma, and platelet-poor plasma.

8. The method according to any one of claims 1 to 3, wherein the steps of illuminating or recording are performed with a frequency of 1 to 1800 times per minute.

9. The method according to any one of claims 1 to 3, wherein the in vitro system is maintained at a temperature of about 37 degrees C.

10. The method according to any one of the claims 1 to 3, wherein a pH of the test medium is stabilized within the range of 7.2-7.4.

11. The method according to any one of claims 1 to 3 further comprising visualizing the set of the recorded spatial distributions of the intensity of the fluorescence signal, light absorption of the chromogenic mark, or the intensity of the luminescent signal and the set of the recorded spatial distributions of the intensity of the light scattering signal.

12. The method according to any one of claims 1 to 3, wherein the correction includes subtracting a second value from a first value, wherein the first value is a value of the recorded intensity of the fluorescence signal in each point within the volume of the cuvette and the second value is the first value multiplied by a coefficient proportional to the recorded intensity of the light scattering signal in the corresponding point within the volume of the cuvette.

13. The method according to any one of claims 1 to 3 further comprising determining at least one parameter of a coagulation system by using the set of spatial distributions of the activity of the proteolytic coagulation factor and the set of the recorded spatial distributions of intensity of the light scattering signal, wherein the at least one parameter is selected from the group consisting of: the rate of spatial propagation of the proteolytic coagulation factor wave from the activating agent, the peak activity of the proteolytic coagulation factor, the peak activity of the proteolytic coagulation factor in the moving part of the wave, the rate of spatial propagation of the fibrin front from the activating agent, the rate of increase of the proteolytic coagulation factor activity, the integral of the proteolytic coagulation factor activity as function of space, the integral of the proteolytic coagulation factor activity as function of time and space, and the peak fibrin concentration in the test medium.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The invention will be further illustrated by description of preferred embodiments thereof with reference to the accompanying drawings, where:

(2) FIG. 1 depicts schematically the spatial concept of blood coagulation regulation;

(3) FIG. 2 is a schematic diagram of a known device for determining spatial dynamics of the coagulation factors;

(4) FIG. 3 shows typical dependences of AMC concentration on distance and time obtained in studies of spatiotemporal distribution of clotting factor XIa; coagulation activator is located at the origin of coordinates;

(5) FIG. 4 is a schematic diagram of an apparatus for determining the spatiotemporal distribution of activity of a proteolytic enzyme in a heterogeneous system, according to the invention;

(6) FIG. 5a-b shows visualization of spatial dynamics of formation of a fibrin clot (a) and a fluorophore (b), according to the invention;

(7) FIG. 6a-b depict an example of spatiotemporal dynamics of formation of a fibrin clot (a) and concentration of proteolytic enzyme (thrombin) (b) in an in-vitro system, obtained using the apparatus according to the invention; the clotting activator is at the origin of coordinates.

DESCRIPTION OF EMBODIMENTS

(8) First Embodiment of the Method

(9) According to the invention, a method provided for determining the spatiotemporal distribution of activity of a proteolytic enzyme in a heterogeneous system is implemented as follows.

(10) An in-vitro system that includes a sample of a test medium, wherein the test medium is selected from the group consisting of blood plasma, whole blood, water, lymph, colloidal solution, crystalloid solution and gel, and a proteolytic enzyme or its zymogen, wherein the proteolytic enzyme or its zymogen is distributed in the sample of the test medium.

(11) A fluorogenic substrate is combined (or immersed, or contacted) with the in-vitro system.

(12) In reaction between the proteolytic enzyme and the fluorogenic substrate, the fluorogenic substrate is cleaved by the proteolytic enzyme, and a fluorescent mark (fluorophore) is released upon cleavage of the fluorogenic substrate.

(13) The sample of the test medium is illuminated with exciting radiation (in determined times) to excite a fluorescence signal of the fluorescent mark; simultaneously (in determined times), the spatial distribution of the fluorescence signal of the fluorescent mark in the sample of the test medium is recorded.

(14) In addition to recording of the spatial distribution of the mark in the sample, it is possible to illuminate the test medium sample in determined times and to record optical characteristics of the sample selected from the group consisting of: the spatial distribution of light scattering, the spatial distribution of light transmission in the sample, or a combination thereof. Therewith, the spatial distribution of fibrin is recorded.

(15) The spatiotemporal distribution of the proteolytic enzyme activity is calculated by using the set of spatial distributions of the fluorescence signal and solving the inverse reaction-diffusion-convection problem. The step of calculating includes correcting the spatiotemporal distribution by taking into account the binding of the mark to components of the test medium.

(16) The excitation wavelength is selected in accordance with the excitation spectrum of the mark (fluorophore). The illumination wavelength is selected so as to ensure a maximum signal/noise ratio; in particular, within the coagulation system study, signal is the light scattering from the fibrin clot, and noise is the light scattering from plasma and other elements of the in-vitro system.

(17) In the experiments, an activating agent can be added in the in-vitro system to induce a change in the spatiotemporal distribution of the proteolytic enzyme activity. The activating agent can be an agent selected from the group consisting of: tissue factor immobilized on the surface, soluble tissue factor, tissue-type plasminogen activator, cells with ability of tissue factor expression, samples of body tissues, glass or plastic.

(18) In the embodiment, the proteolytic enzyme under analysis is formed directly in the test medium from its zymogen, as a result of biochemical processes. In another embodiment, the analyzed proteolytic enzyme is gradually destroyed in the test medium due to biochemical processes occurring in the medium.

(19) Spatial distributions of light scattering and fluorescence of the mark in the sample can be recorded by means of confocal microscopy, which provides refocusing of the optical system and the illuminating/radiation processing system in determined times, or by means of fluorescence microscopy.

(20) Spatial distribution of the mark and the resulting clot are further visualized in determined times.

(21) Light scattering from the test medium sample is recorded using the dark-field microscopy.

(22) Second Embodiment of the Method

(23) The second embodiment differs from the first embodiment in that the substrate is a chromogenic substrate.

(24) In reaction between the proteolytic enzyme and the chromogenic substrate, the substrate is cleaved and releases a chromophore. The system is illuminated with light having a wavelength at which the light is substantially absorbed by the chromophore. Spatial distribution of the change of color of the test medium is recorded in determined times. Spatial distribution of the chromophore in the sample is determined from the spatial distribution of the change of color of the sample. Spatiotemporal distribution of the proteolytic enzyme activity is calculated by using the set of spatial distributions of the chromophore and solving the inverse reaction-diffusion-convection problem. The step of calculating includes correcting the spatiotemporal distribution by taking into account the binding of the mark to components of the test medium.

(25) In determined times, the sample of the test medium is illuminated, and optical characteristics of the sample selected from the group consisting of: the spatial distribution of light scattering, the spatial distribution of optical transmission in the sample, or a combination thereof, are recorded by the photographic camera.

(26) Third Embodiment of the Method

(27) The third embodiment of the method is different from the first embodiment in that the substrate is a substrate which is cleaved in reaction with the proteolytic enzyme to release a chemiluminescent product. Spatial distribution of luminescence intensity in the sample is recorded in determined times. Spatiotemporal distribution of activity of the proteolytic enzyme is calculated by using the set of spatial distributions of the luminescence and solving the inverse reaction-diffusion-convection problem. The step of calculating includes correcting the spatiotemporal distribution by taking into account the binding of the mark to components of the test medium.

(28) In determined times, the test medium sample is illuminated, and optical characteristics of the test sample, selected from the group consisting of: the spatial distribution of light scattering, the spatial distribution of optical transmission in the sample, or a combination thereof are recorded by the photographic camera.

(29) In all embodiments of the method, the constant temperature is maintained in the whole volume of the in-vitro system, preferably of about 37 degrees C.; the system is thermally regulated for this purpose. To avoid formation of air bubbles in the test sample, the pressure in the in-vitro system is maintained preferably at an elevated level as to the atmospheric one. The pH of the sample is stabilized to the range of 7.2-7.4.

(30) The substrate can be added to the sample of the test medium in the form of a solution. It is also possible to apply the substrate in the freeze-dried form, for example on the walls of the in-vitro system before placing the sample of the test medium.

(31) Illuminating and recording of the mark signal are performed with a frequency of 1 to 1800 times per minute. Illumination is carried out after establishing a constant temperature in the sample.

(32) A mixture is prepared out of test plasma sample, contact phase inhibitor, calcium chloride, and substrate specific to the tested coagulation factor; this mixture is used for all variations of the study.

(33) The sample is, in particular, whole blood or plasma selected from the group consisting of: platelet-rich plasma, platelet-free plasma, and platelet-poor plasma.

(34) The analyzed coagulation factor is, in particular, thrombin.

(35) According to the invention, a method is also provided for diagnosing disorders in the hemostatic system based on the change of the spatiotemporal distribution of activity of a proteolytic enzyme (coagulation factor) in a heterogeneous in-vitro system: the method involves the use as a sample of blood components selected from the group consisting of: whole blood, platelet-free plasma, platelet-poor plasma, platelet-rich plasma, blood with addition of anticoagulant, blood plasma with addition of anticoagulant.

(36) Conditions are provided for formation of a proteolytic enzyme in the test sample and for observation thereof by performing at least one operation selected from the group consisting of: bringing the test sample into contact with the blood coagulation activator immobilized on a surface; adding a substrate to be cleaved by the studied proteolytic enzyme; adding a calcium salt; adding an inhibitor of the contact coagulation activation.

(37) In determined times, the spatial distribution of the signal of the mark within the sample cleaved from the substrate is recorded.

(38) The temperature of the sample is maintained constant with the accuracy of 1 degree in the range of 25-45 degrees C. pH of the sample is stabilized in the range of 7.2-7.4.

(39) Spatiotemporal distribution of the proteolytic enzyme activity (coagulation factor) is calculated by using the set of spatial distributions of the mark signal and solving the inverse reaction-diffusion-convection problem. At the basis thereof, the spatiotemporal distribution of the coagulation factor distribution in time is calculated. The step of calculating includes correcting the spatiotemporal distribution by taking into account the binding of the mark to components of the test medium.

(40) The state of hemostasis in the subject is assessed basing on the spatiotemporal distribution of the proteolytic enzyme activity by comparing spatiotemporal distribution to a proper control.

(41) Additionally, the test sample is illuminated in determined times, and spatial distribution of the light scattering from the formed fibrin clot in the test medium sample is recorded to visualize the formed fibrin clot.

(42) The investigated coagulation factor is the proteolytic enzyme selected from the group: thrombin, factor Xa, factor VIIa, factor IXa, factor XIIa, factor XIa, plasmin.

(43) At least one parameter of spatiotemporal thrombin or fibrin distribution is used in order to assess the state of the coagulation system in the sample and to make a diagnosis; the parameter is selected from the group consisting of: the rate of spatial propagation of the thrombin wave, the high concentration of thrombin in the sample, the high concentration of thrombin in the moving part of the wave, the rate of increase of thrombin concentration, integral of thrombin concentration according to space, the integral of thrombin concentration as function of time and space, the rate of spatial propagation of fibrin front, light scattering and the high fibrin concentration (volume of light scattering) in the test sample.

(44) The device (apparatus) for realization of the said method (the variations of execution thereof) determining the spatiotemporal distribution of activity of a proteolytic enzyme in a heterogeneous system comprises an in-vitro system that includes cuvette 20 (FIG. 4) to place sample 21 of a test medium selected from the group consisting of: blood plasma, whole blood, water, gel and lymph, colloidal solution, crystalloid solution and gel, and a proteolytic enzyme or its zymogen, wherein the proteolytic enzyme or its zymogen is distributed in the sample of the test medium. The cuvette 20 has specific geometric dimensions and form, rectangular cross-section, and is made of plastic.

(45) To reduce convective flows (the thinner the layer, the faster the liquid motion decays) and to ensure fast heating, the thickness of the sample layer should be minimal. To increase the signal strength, the sample layer thickness should be maximal. The optimum thickness is between 0.1-1.5 mm.

(46) The apparatus further includes activating means 22 designed to place and insert into the cuvette a process activator 23 that induces a change of the spatiotemporal distribution of proteolytic enzyme activity.

(47) The device (apparatus) further includes means 24 for ensuring a constant temperature in the in-vitro system. The device enables different types of temperature control, including water temperature control and air temperature control; gel can also be used for temperature control, but in this case it should be taken into account that the medium must be transparent to the radiation. In the described embodiment, water temperature control is used. For temperature control, the temperature is maintained within the range of 25-45 degrees C. with the accuracy of one degree C. The apparatus also includes means (not shown) for maintaining pressure in the in-vitro system; said means are designed to maintain a constant air pressure in the space surrounding the test sample medium (together with means 24 for maintaining a constant temperature they form temperature and pressure control unit 25). The means maintain an excess pressure from 0.2 to 0.5 atm, which prevents formation of gas bubbles in the sample under analysis. Formation of bubbles is due to the decrease of solubility of dissolved gases contained in the sample. Usually, this phenomenon is associated with heating of the sample. Bubbles give rise to local distortions, both in terms of making the medium less physiological, i.e. drift from the simulated conditions, and in terms of calculating the distribution of enzymes.

(48) The apparatus includes means 26 for illuminating sample 21 of the test medium in determined times with exciting radiation to excite fluorescence of the mark in case of addition to the sample of fluorogenic substrate, or with the light with a wavelength corresponding to substantial absorption thereof by the mark in case of addition of chromogenic substrate to the sample. Means 26 apply radiation perpendicularly to the wall of cuvette 20 through a window in thermostat 24. Illuminating means 26 comprises UV sources, for example, UV LEDs. Means 27 for illuminating the test medium sample with visible light provides light at an angle to the wall of cuvette 20. The apparatus contains mirror 28 for directing the radiation to the cuvette, as well as excitation filter 29 and emission filter 30 for extracting the fluorescence signal. The emission of the optical elements should not cause local heating of the sample. The combination of means 26-30 forms illuminating/lightening unit 31.

(49) The apparatus further includes unit 32 for recording the spatial distribution of the mark fluorescence intensity/light scattering (or absorption by the chromophore mark) in the sample of the test medium in determined times. The recording unit 32 includes means for taking images from different depths of the sample, including optical system 33 for focusing the optics, and apertures (not shown). The fluorescence intensity depends on the activity of the proteolytic enzyme under analysis. Fluorescence from the substrate propagates perpendicularly to the wall of cuvette 20, passes through mirror 28 being transparent to this emission spectrum, then through emission filter 30 and enters through optical system 33 into recording device 34 which can be represented by a digital photographic camera.

(50) The apparatus includes means to control illuminating/lightening means such as a processor (not shown) and the recording means (not shown) are capable of regulating time of switching on and off, an in an intensity and duration of illuminating/lightening and synchronization of operation of the illuminating/lightening means and the recording means.

(51) A computing device (not shown) calculates the spatial distribution of the proteolytic enzyme activity over time.

(52) Means for visualizing the forming/dissolving clot by the dark-field microscopy and means for visualizing the spatial image of formation/destruction of mark (fluorophore/chromophore) (not shown) are also connected to the control means.

(53) The functioning of the apparatus and the way of definition of the spatiotemporal distribution of the proteolytic enzyme activity in the heterogeneous system is considered hereinafter as an inexhaustive example of execution.

(54) Materials

(55) The following agents were used: phosphatidylserine and phosphatidylcholine; 7-amino-4-methyl-coumarin (AMC); Z-Gly-Gly-Arg-AMC; corn trypsin inhibitor; factor VIII; factor VIII test; factor VIII-deficient plasma; glycoprotein IIb-IIIa antagonist.

(56) Blood Collection and Plasma Preparation

(57) Samples of normal plasma were obtained from fresh human blood of healthy donors. Blood was collected in 3.8% sodium citrate (pH 5.5) at the ratio of 9:1 by volume. Blood was centrifuged for 15 min at 1600 g, and the supernatant was then further centrifuged for 5 min at 10 000 g to obtain platelet-free plasma; the supernatant was then frozen and stored at 70 degrees C. Before each experiment, samples were thawed in a water bath.

(58) To prepare platelet-rich plasma, blood was centrifuged at 100 g for 8 minutes. The concentration of platelets was brought to 250 000 cells/l by dissolving with a platelet-free plasma. To stabilize pH, 28 mM of Hepes were added into plasma (pH 7.4).

(59) Commercially available plasmas deficient in some clotting factors were thawed and treated with Hepes to stabilize pH, as was done with platelet-rich plasma.

(60) Preparation of the Activator

(61) As mentioned earlier, coagulation was activated using an activatora monolayer of tissue factor (TF) immobilized on a plastic surface. Activators were stored at +4 to +8 degrees C.

(62) Experiment

(63) Spatial clot growth in different test medium samples was considered.

(64) A) Spatial Clot Growth in Platelet-Free Plasma

(65) The plasma prepared as stated above was supplemented with an inhibitor, for example, corn tripsin inhibitor (0.2 mg/ml), 0.1 M lipid vesicles (phosphatidylserine/phosphatidylcholine in 20/80 molar ratio). A substrate Z-GGR-AMC (800 M) was added for monitoring the formation of thrombin. The sample was incubated for 10 min at 37 degrees C., then a calcium salt was added, in particular, CaCl.sub.2 (20 mM). The investigated sample was put into the experimental cuvette, and the formation of clot was initiated by the activator, the surface of which was covered with tissue factor: the activator was brought into contact with the prepared plasma sample.

(66) Experiments were performed using specially designed video microscopy system which allowed simultaneous observing of the spatial distribution or growth of fibrin clot and proteolytic enzyme, in particular, thrombin. The temperature in the chamber was maintained at 37 degrees C., and illumination was performed by red (625 nm) and ultraviolet (365 nm) LEDs. Growth of the clot was detected from light scattering of the sample when illuminated with red light (FIG. 5a), and AMC fluorescence was excited by ultraviolet LEDs (FIG. 5b). A multilane emissive filter was used to isolate the red light scattering, AMC emission, and exciting emission. Fluorescence and scattering of the red light passing through a macro lens were detected by a digital CCD camera. Images in red and blue light were obtained sequentially, usually one to four times per minute. To prevent AMC burnout, LEDs were synchronized with the camera and switched on only for the duration of exposure, i.e. for about 0.5 sec.

(67) B) Spatial Clot Growth in Platelet-Rich Plasma

(68) To prevent retraction of the clot, 25 g/ml of glycoprotein inhibitor IIb/IIIa was used. Also, experiments were performed on 0.5% low melting temperature agarose gel, because in some cases even a high concentration of antagonist didn't completely inhibit the retraction.

(69) Samples were prepared as described above, except for using platelet-rich plasma instead of platelet-free plasma. After recalcification, plasma was preheated to 42 degrees C. for 2 minutes. Agarose solution was added, and the mixture was incubated in an experimental chamber for 3 min to form a gel. Then the experiment was initiated as described above.

(70) Data Processing

(71) Image Processing

(72) Images in red and ultraviolet light were initially processed in the same way. To obtain profiles of light scattering (FIG. 6a) or AMC fluorescence, the light intensity was measured for each frame in the respective range along the line perpendicular to the surface of the activator. The values were averaged to 150-300 lines.

(73) The clot growth rate was calculated from the movement of a half-maximal intensity point on light scattering profiles. The initial growth rate was determined as the slope of the linearized portion of the clot size time dependence diagram in the first 10 min of its growth. The steady rate was calculated in the same way, after 40 min of growth of the clot; when the clot boundary is so far from the activator, the effect thereof on the growth of the clot becomes insignificant.

(74) Profiles of AMC fluorescence intensity were converted into profiles of its concentration by means of calibration. The intensity calibration profile was calculated within the uniform distribution with a known AMC concentration in the same plasma. AMC concentration at each point (C.sub.i) was calculated as follows:

(75) $C_i=\frac{\left(I_i-I_{\mathrm{bgr}}\right)*C_{\mathrm{cal}}}{\left(I_{\mathrm{cal}}-I_{\mathrm{bgr}}\right)}$

(76) where: I.sub.i is fluorescence intensity, I.sub.bgr is background intensity, I.sub.cal is fluorescence intensity with a known AMC concentration, all at the same point of the frame, and C.sub.cal is calibration concentration of AMC.

(77) Calculation of Thrombin Concentration

(78) Concentration of thrombin (FIG. 6b) was calculated from one-dimensional distribution of AMC by solving the inverse problem for the following reaction-diffusion equation:

(79) $\frac{\mathrm{AMC}}{t}{D}_{\mathrm{AMC}}\frac{{}^2\mathrm{AMC}}{x^2}+k_{\mathrm{cat}}\frac{\mathrm{IIa}S}{K_m+S}$$\mathrm{IIa}\left(x,t\right)=\frac{\mathrm{Km}+S}{S{k}_{\mathrm{cat}}}\left(\frac{\mathrm{AMC}\left(x,t\right)}{t}-D_{\mathrm{AMC}}\frac{{}^2\mathrm{AMC}\left(x,t\right)}{x^2}\right)$

(80) where: AMC, S and IIa are concentrations of AMC, fluorogenic substrate and thrombin, respectively; D.sub.AMC is AMC diffusion coefficient; Km, kcat are Michaelis constants, or constants of reaction of the substrate cleavage by thrombin.

(81) The AMC diffusion coefficient was measured experimentally by fitting the experimental diffusion profiles to the theoretical ones.

(82) The inverse problem for distribution of thrombin concentration is ill-conditioned, so the experimental noise and even small AMC profile distortions lead to the absence of solution thereof. To overcome this, numerical algorithms were used to reduce noise and distortion levels of the AMC signal.

(83) AMC signal distortions are due to excitation of light scattering on the fibrin clot. Intensity of fluorescence increases inside the clot. This increase is proportional to the AMC concentration and the clot density. To overcome this and to calculate the actual AMC concentration, the following formula was used:

(84) ${\mathrm{AMC}}_{\mathrm{visible}}={\mathrm{AMC}}_{\mathrm{real}}+\left(k_1+k_2.Math.{\mathrm{AMC}}_{\mathrm{real}}\right)\frac{\mathrm{Clot}}{k_2}$

(85) where: AMC.sub.visible is AMC concentration obtained by calibration; AMC.sub.real is real AMC concentration; Clot is scattering of light intensity by fibrin; coefficients k.sub.1, k.sub.2, k.sub.3 have been measured experimentally.

(86) To reduce noise, the following algorithms of calculation of derivatives were used:

(87) $\frac{\left[\mathrm{AMC}\right]}{t}=\frac{1}{J}\stackrel{J}{\underset{j}{.Math.}}\frac{\left[\mathrm{AMC}\right]\left(x,t+j*t\right)-\left[\mathrm{AMC}\right]\left(x,t\right)}{j*t}$$\frac{{}^2\left[\mathrm{AMC}\right]}{x^2}=\frac{1}{I}\stackrel{I}{\underset{i}{.Math.}}\frac{\left[\mathrm{AMC}\right]\left(x+i*x,t\right)-2.Math.\left[\mathrm{AMC}\right]\left(x,t\right)+\left[\mathrm{AMC}\right]\left(x-i*x,t\right)}{{\left(i*x\right)}^2}$

(88) where: t is time between frames, typically 1 min; x is pixel size (4.3 m); values of I and J are chosen optimal so as to minimize noise at minimal distortion of the signal. Typically, J=3 and I=40 were selected, in this case summing could start from I and J values greater than unity.