Arginine inhibits hemostasis activation

The role of amino acid metabolism alterations in acute ischemic stroke: From mechanism to application

Acute ischemic stroke (AIS) is the most prevalent type of stroke, and due to its high incidence, disability rate, and mortality rate, it imposes a significant burden on the health care system. Amino acids constitute one of the most crucial metabolic products within the human body, and alterations in their metabolic pathways have been identified in the microenvironment of AIS, thereby influencing the pathogenesis, severity, and prognosis of AIS. The amino acid metabolism characteristics in AIS are complex. On one hand, the dynamic progression of AIS continuously reshapes the amino acid metabolism pattern. Conversely, changes in the amino acid metabolism pattern also exert a double-edged effect on AIS. This interaction is bidirectional, dynamic, heterogeneous, and dose-specific. Therefore, the distinctive metabolic reprogramming features surrounding amino acids during the AIS process are systematically summarized in this paper, aiming to provide potential investigative strategies for the early diagnosis, treatment approaches, and prognostic enhancement of AIS.

Arginine-grafted porcine pericardium by copolymerization to improve cytocompatibility, hemocompatibility and anti-calcification properties of bioprosthetic heart valve materials

Bioprosthetic heart valves (BHVs) have been used widely due to the development of transcatheter heart valve replacement technology. However, glutaraldehyde crosslinked pericardium (GA), which is widely used as a leaflet...

Heparin and Arginine Based Plasmin Nanoformulation for Ischemic Stroke Therapy

Ischemic stroke is the most common type of stroke and thrombolytic therapy is the only approved treatment. However, current thrombolytic therapy with tissue plasminogen activator (tPA) is often hampered by the increased risk of hemorrhage. Plasmin, a direct fibrinolytic, has a significantly superior hemostatic safety profile; however, if injected intravenously it becomes rapidly inactivated by anti-plasmin. Nanoformulations have been shown to increase drug stability and half-life and hence could be applied to increase the plasmin therapeutic efficacy. Here in this paper, we report a novel heparin and arginine-based plasmin nanoformulation that exhibits increased plasmin stability and efficacy. In vitro studies revealed significant plasmin stability in the presence of anti-plasmin and efficient fibrinolytic activity. In addition, these particles showed no significant toxicity or oxidative stress effects in human brain microvascular endothelial cells, and no significant blood brain barrier permeability. Further, in a mouse photothrombotic stroke model, plasmin nanoparticles exhibited significant efficacy in reducing stroke volume without overt intracerebral hemorrhage (ICH) compared to free plasmin treatment. The study shows the potential of a plasmin nanoformulation in ischemic stroke therapy.

Management considerations for stroke-like episodes in MELAS with concurrent COVID-19 infection

There have been considerations since the beginning of the Coronavirus pandemic that COVID-19 infection, like any other viral illness, can trigger neurological and metabolic decompensation in patients with mitochondrial diseases. At the time of writing, there were no published reports reviewing experiences and guidelines about management of COVID-19 infection in this patient population. We present a challenging case of an adult patient with a known diagnosis of Mitochondrial Encephalomyopathy, Lactic Acidosis and Stroke-like Episodes (MELAS) complicated by COVID-19 infection. She initially presented with altered mental status and vomiting and went on to develop a stroke-like episode, pancreatitis, and pneumatosis intestinalis. We review salient features of her hospitalization, including initiation of thromboprophylaxis in relation to intravenous arginine therapy, caution regarding medications such as remdesivir, and the incidence of gastrointestinal complications.

Contact activation-induced complex formation between complement factor H and coagulation factor XIIa

BACKGROUND

The complement and coagulation systems share an evolutionary origin with many components showing structural homology. Certain components, including complement factor H (FH) and coagulation factor XII (FXII), have separately been shown to have auxiliary activities across the two systems.

OBJECTIVES

The interaction between FXII and FH was investigated.

METHODS

Using enzyme-linked immunosorbent assay (ELISA) and surface plasmon resonance (SPR) complex formation between different FXII forms and FH was investigated. The presence of α-FXIIa:FH complexes upon contact activation in plasma was evaluated by ELISA and immunoprecipitation.

RESULTS

We identified and characterized a direct interaction between the components and demonstrated that among different forms of FXII, only the activated α-FXIIa formed complexes with FH, with an apparent binding strength Kd of 34 ± 9 nmol/L. The complex formation involved the kringle domain of the heavy chain of FXII. C1-inhibitor induced inhibition of α-FXIIa did not alter the binding of α-FXIIa toward FH. We further demonstrated the presence of α-FXIIa:FH complexes in normal human plasma upon contact activation, indicating formation of α-FXIIa:FH complexes as a consequence of α-FXIIa generation. Complex formation between α-FXIIa and FH was also assessed in hereditary angioedema (HAE) patients with C1-inhibitor deficiency as well as rheumatoid arthritis (RA) patients with high levels of anti-cyclic citrullinated peptide (anti-CCP) upon contact activation. We observed elevated levels of α-FXIIa:FH complexes in HAE patients, and equal levels of complexes in RA patients and healthy individuals upon contact activation.

CONCLUSION

A direct interaction between α-FXIIa and FH is demonstrated. Our findings represent a new crosstalk between these systems, potentially important in the onset and pathology of inflammatory vascular diseases.

l-Arginine and allopurinol supplementation attenuates inflammatory mediators in human osteoblasts-osteoarthritis cells

This study investigated the synergistic effects of l-arginine and allopurinol on antioxidant and inflammatory mediators in human osteoblasts-osteoarthritis (HOb-OA) cells. The cells were treated with allopurinol (50-150 mg/kg bwt) and l-arginine (50-150 mg/kg bwt) for 72 h. Cell viability, catalase, superoxide dismutase (SOD), glutathione peroxidase (Gpx), reduced glutathione (GSH), lipid peroxidation, and the inflammatory markers interleukin 6 (IL-6), interleukin 1β (IL-1β), nuclear factor κB (NF-κB) and tumor necrosis factor alpha (TNF-α) were measured. The combined supplementation with allopurinol and l-arginine increased catalase, SOD, GSH, and Gpx, while it decreased lipid peroxidation, IL-6, IL-1β, and TNF-α. While TNF-α, IL-6, IL-1β, and NF-κB mRNA and protein expression were higher in control HOb-OA cells, the combined supplementation with allopurinol and l-arginine substantially reduced their expression in HOb-OA cells by >40%. In summary, combined supplementation with allopurinol and l-arginine might be very effective in osteoarthritis. A search for therapeutic agents that inhibit inflammation could help to prevent and manage osteoarthritis. However, further studies need to determine the biochemical and molecular mechanisms of these agents in osteoarthritis.

Functional Determination of Plasminin Arginine-stabilized Plasma

Reliable data on plasmin activities in blood of patients during fibrinolytic treatment are lacking. This is due to continuing plasminogen activation by plasminogen activators after blood withdrawal. The purpose of this study was to establish a new method for stabilization of blood and to detect plasmin activity in stabilized plasma. For optimization of plasma stabilization by arginine, 50 μL pooled normal citrated plasma was incubated with 50 μL of 0 to 1500 m M arginine, pH 8.7, and 25 μL 100 IU/mL u-PA, 1250 IU/mL t-PA, 10000 U/mL reteplase, 400 U/mL plasminogen-streptokinase-activator complex, 10 μg/mL tenecteplase in 6% BSA-PBS or 25 μL 25 μg/mL plasmin in 20% glycerol. Twenty-five microliters 3 m M HDVal-Leu-Lys-pNA were added immediately (1 step) or after 90 minutes (room temperature [RT]). The same experiment was performed with pooled normal citrated plasma supplemented with 3.2 mg/mL EDTA, preoxidized with 0 m M or 20 m M chloramine-T for 10 minutes (37°C). For optimization of plasmin activity, the oxidation time of the arginine-stabilized plasma sample containing 0.5 U/mL active plasmin and the chloramine-T amount was varied. Citrated plasma is stabilized against the in vitro action of all six plasminogen activators tested if the final arginine concentration is greater than 500 mM. Neither the addition of EDTA nor the addition of chloramine-T changes this plasma-stabilizing power of arginine. The optimized functional plasmin assay consists of incubation of 10 μL arginine-stabilized plasma with 10 μL 1.5 M arginine, pH 8.7, and 10 μL 100 m MCT in PBS. After 30 minutes (37°C), 75 μL 1.2 M KCl, 1.6 M Arg, 0.75 m M Val-Leu-Lys-pNA (Stop-CS Reagent), and 175 μL 6% BSAPBS are added and the absorbance increase (ΔA) at 405 nm is determined. With the present arginine stabilization procedure of plasma and the determination of plasmin activity in arginine-stabilized plasma as described, it is feasible to determine the activity of plasmin in blood of patients receiving fibrinolytic treatment without artefactual in vitro changes in the samples.

Point of Care: Diagnostics in Hemostasisthe Wrong Direction?

Point-of-care-testing (POCT) is performance of a laboratory assay outside the laboratory by nontrained personnel. The advantages of POCT are: more rapid medical decisions, avoidance of long sample transports, and small samples. The disadvantages of POCT are: no laboratory personnel, insufficient calibration, quality control and maintenance, poor documentation, high costs, difficult comparability POCT/central laboratory. Therefore, disposing of a 24-hour central laboratory, the POCT spectrum should be limited to the vital parameters: K+, Ca++, Na+, glucose, creatinine, blood gases, hemoglobin or hematocrit, NH3, lactate. POCT offers no advantages, if the hospital has a rapid transport system such as a pneumatic delivery to the central laboratory. The rapid diagnosis of the acute hemostasis state of a patient should be performed in the 24-hour central laboratory that is connected to all hospital wards via a good pneumatic delivery.

Singlet Oxygen Enhances Intrinsic Thrombolysis: The Intrinsic Oxidative Clot Lysis Assay (INOXCLA)

Granulocytes are important cells of inflammation and cellular thrombolysis. They produce urokinase (u-PA) and chloramines. In this study, u-PA/chloramine—mediated fibrinolysis is imitated in a microtiter-plate. Seventy-five microliters plasma are incubated with 50 μL 50% Pathromtin SL, 6% BSA, and 38 mM CaCl2 for 30 minutes (37°C). Then, 50 μL 10 mM chloramine-T in PBS are added. After 30 minutes (37°C), 50 μL 0, 100, or 10 IU/mL u-PA in 6% BSA-PBS are added and the turbidity is determined at 405 nm after 0, 3, or 16 hours. Clot lysis was increased more than tenfold by 0.5 to 1 μmoles chloramine (ED50 after 3h = about 0.25 μmoles = 2mM final concentration). The normal range for the present intrinsic oxidative clot lysis assay (INOXCLA) is 100% ± 25% (MV ± SD; 100 relative % of norm; the normal lysis being 60 absolute %; CVs < 10%). Fifty percent lysis of adherent microclots occurred after 0.75 hours, 2 hours, 14 hours, 13 days, or 17 days when using 1000, 100, 10, 1, or 0 IU/mL u-PA reagent. If the u-PA activity is quenched by PAI-2, no clot lysis appears. Chloramines are important physiologic generators of nonradical excited singlet oxygen and enhance u-PA—mediated lysis of plasma clots. Based on the u-PA/chloramines coaction, a new global fibrinolysis assay has been derived.

In vitro Simulation of Therapeutic Plasmatic Fibrinolysis

One type of therapy for thromboembolism is plasmatic thrombolysis. Several plasminogen activators (PA) are clinically available, including urokinase (u-PA), tissue plasminogen activator (t-PA), streptokinase (SK), plasminogen-streptokinase-activator-complex (PSAC), or mutants of t-PA such as reteplase (RP) or tenecteplase (TP). Therapeutic plasmatic fibrinolysis was simulated, using the PA at relevant plasma concentrations, and plasmin (Pli) and PA activities were determined. Normal citrated plasma was supplemented with 31 to 1,000 IU/mL u-PA, 0.31 to 20 μg/mL t-PA, 125 to 4,000 IU/mL SK, 12.5 to 400 U/mL PSAC, 125 to 4,000 U/mL RP, or 0.31 to 10,μg/mL TP. Ten IU/mL urokinase was also incubated with pooled plasma of stroke patients, that was previously oxidized with the singlet oxygen (1O2) donor chloramine T® (CT), to destroy plasmatic PAI-1 and a2-antiplasmin. After 0 to 80 minutes (37°C), 50-μL samples were withdrawn and added to 100 μL 1.5 M arginine, pH 8.7, and oxidized with 50 μL of 20 mM CT. For determination of plasmin activity, 10 μL thereof was incubated with 150 μL 1.5 M arginine, pH 8.7, and 100 μL 20 mM CT preoxidized (15 minutes 37°C) pooled normal citrate buffered EDTA-plasma for 30 minutes (37°C). For determination of [PA+Pli]-activity, arginine was added after this incubation. 25-μL 6 mM Val-Leu-Lys-pNA were added and AA/h at room temperature (RT) was monitored, using a microtiterplate reader. [PA+Pli]-Pli = PA. The PA concentration required to induce 25% [ED25] of the maximally inducible Pli-activity in plasma (= 1 U/mL = 45 mg/L = 0.53 Amol/L active Pli; AA = 363 + 8 mA/h RT) after 10 minutes (37°C) were 320 IU/mL u-PA, 8 μg/mL t-PA, 140 U/mL PSAC, 6,000 IU/mL SK, 720 U/mL RP, and approximately 150 μg/mL TP. The approximate activity half-lives of the PA in plasma were 30 minutes for u-PA, 30 minutes for t-PA, greater than 80 minutes for SK, greater than 80 minutes for PSAC, 50 minutes for RP, and 80 minutes for TP. The present study shows-for the first time-a combined kinetic in vitro simulation of the plasmatic activity of six different PAs. At clinically used concentrations, RP induces the highest plasmatic Pli activity. Due to unselective generation of plasmin in plasma, all PA are of some danger in inducing severe hemorrhagias. Clinical thrombolysis might be improved by usage of more physiologic activators of thrombolysis, such as activators of polymorphonuclear neutrophils.

Specific Determination of Plasmatic Thrombin Activity

Thrombin is the key enzyme of coagulation. Its activity can be determined via fibrinogen øfibrin conversion or via cleavage of a chromogenic substrate. The latter method is easier than the first one, but in plasma it is hampered due to unspecific cleavage of the chromogenic substrate by thrombin-like enzymes of hemostasis, especially those of the contact phase. The concentration of the thrombin substrate (HD-CHG-Ala-Arg-pNA) was optimized, using final substrate concentrations of 0 to 5 mM, a final arginine concentration of 1.13 M, and samples of 10 mIU/mL purified thrombin in 7% human albumin or pooled normal citrated plasma without and with EDTA. Twenty microliters pooled normal citrated plasma (frozen/thawed) or factor II–deficient plasma (lyophilized) were incubated with 10 µL 0% to 0.5% Thromborel S® (100% = 162 ng/mL tissue factor [TF]) in 6% BSA or with 10 µL 0% (physiol. NaCl) to 50% Pathromtin SL®and with 20 µL 25 mM CaCl2. After 0 to 22 minutes (37°C), 20 µL 1.7 M arginine, pH 8.7 were added. Fifteen microliters 0.9 mM HD-CHGAla-Arg-pNA in 2.3 M arginine, pH 8.6, were added and the increase in absorbance (δA) at 405 nm was determined. Thrombin activity was standardized against the 3A measured for 1 IU/mL thrombin in 7% human albumin (8.8 mA/min RT). The optimal final chromogenic substrate concentration to detect thrombin in this assay system is less than 0.6 mM. Higher substrate concentrations in a plasma milieu result in unspecific cleavage of the substrate. Using final concentrations of chromogenic substrate less than 0.4 mM (the approximate Km- value for thrombin) and final concentrations of arginine greater than 800 mM, in factor II–depleted plasma, when activated either by TF or by the contact phase, there is no significant thrombin generation. The circulating thrombin activity measured in EDTA plasma of 39 healthy donors is 100 ± 20% of norm (mean value ± 1 SD; 100% = 5.5 mIU/mL thrombin). This chromogenic assay detects thrombin activity independent of clotting seconds or fibrin mediated turbidity increases. This technique allows to standardize the thrombin activity generated in any biologic system in international thrombin units.

Thrombin Generation by Exposure of Blood to Endotoxin: A Simple Model to Study Disseminated Intravascular Coagulation

Pathologic disseminated intravascular coagulation (PDIC) is a serious complication in sepsis. In an in-vitro system consisting of incubation of fresh citrated blood with lipopolysaccharides (LPS) or glucans and subsequent plasma recalcification plasmatic thrombin was quantified. Five hundred microliters of freshly drawn citrated blood of healthy donors were incubated with up to 800 ng/mL LPS ( Escherichia coli) or up to 80 μg/mL Zymosan A (ZyA; Candida albicans) for 30 minutes at room temperature (RT). The samples were centrifuged, and 30 μL plasma were recalcified with 1 volume or less of CaCl2 (25 μmoles Ca2+/mL plasma). After 0 to 12 minutes (37°C), 20 μL 2.5 M arginine, pH 8.6, were added. Thirty microliters 0.9 m M HD-CHG-Ala-Arg-pNA in 2.3 M arginine were added, and the absorbance increase at 405 nm was determined. Fifty microliters plasma were also incubated with 5 μL 250 m M CaCl2 for 5, 10, or 15 minutes (37°C). Fifty microliters 2.5 M arginine stops coagulation, and 50 μL 0.77 m M HD-CHG-Ala-Arg-pNA in 2.3 M arginine starts the thrombin detection. The standard was 1 IU/mL thrombin in 7% human albumin instead of plasma. Arginine was also added in the endotoxin exposure time (EET) or in the plasma coagulation reaction time (CRT). Tissue factor (TF)-antigen and soluble CD14 were determined. LPS at blood concentrations greater than 10 ng/mL or ZyA at greater than 1 μg/mL severalfold enhance thrombin generation, when the respective plasmas are recalcified. After 30 minutes EET at RT, the thrombin activity at 12 minutes CRT generated by the addition of 200 ng/mL LPS or 20 μg/mL ZyA is approximately 200 mIU/mL compared to approximately 20 mIU/mL without addition of endotoxin, or compared to about 7 mIU/mL thrombin at 0 minutes CRT. Arginine added to blood or to plasma inhibits thrombin generation; the inhibitory concentration 50% (IC 50) is approximately 15 m M plasma concentration. Endotoxin incubation of blood increases neither TF nor sCD14. This assay allows the study of the hemostasis alteration in PDIC, particularly in PDIC by sepsis. The thrombin generated by blood plus endotoxin incubation and plasma recalcification suggests that the contact phase of coagulation; e.g., triggered by cell components of (phospholipase-) lysed cells such as monocyte or endothelium DNA or phospholipid-vesicles (microparticles), is of primary pathologic importance in sepsis-PDIC. Arginine at plasma concentrations of 10 to 50 m M might be a new therapeutic for sepsis-PDIC.

Effects of exercise and L-arginine intake on inflammation in aorta of high-fat diet induced obese rats

PURPOSE

In the present study, we investigated the effect of exercise and arginine on the inflammatory makers and Cu-Mn superoxide dismutase (SOD) expression in the aortas of high-fat-induced obese rats.

METHODS

Fifty 6-month-old male Sprague-Dawley rats were randomly assigned as follows: HF-Con: high-fat diet, HF-Ex: high-fat diet and exercise, HF-Ex+A: high-fat diet and combined exercise and arginine, HF-A: high-fat diet and arginine. The high-fat diet was fed for 12 weeks following 1 week of environmental adaptation with mixed solid chow. The rats performed treadmill exercise 6 times per week for 12 weeks at20 m/min for 60 min. L-argininewas mixed with saline and orally administered at 150 mg/kg once a day. Expressions of inflammatory markers (including NF- κB, TNF-α, COX-2) and SOD were evaluated using western blotting.

RESULTS

NF-κB expression decreased significantly (p<0.05) in the HF-Ex group compared with HF-Con group, and we found additional effects(p<0.01) on NF-κB expression in HF-EX+A compared withHF-Ex. TNF-α expression decreased significantly (p<0.01) in HF-Ex, FH-Ex+A, and FH-A compared with HF-Con. In a similar trend with NF-κB expression, COX-2 expression decreased significantly in HF-Ex compared withHF-Con. In Cu-Mn SOD expression, there was no difference between HF and HF-Ex, but significant increases (p<0.01) inCu-Mn SOD werefound in HF-Ex+A and HF-A.

CONCLUSION

Based on our results, treatment that combines exercise and arginine might be effective for modulatingvascular inflammation and oxidative stress in obesity.

Mature coconut water exhibits antidiabetic and antithrombotic potential via L-arginine-nitric oxide pathway in alloxan induced diabetic rats

BACKGROUND

The aims of the present study were to assess whether the antidiabetic activity of mature coconut water (MCW) is mediated through L-arginine-nitric oxide pathway in diabetic rats, and to study the effects of MCW on blood coagulation.

METHODS

Diabetes was induced in male Sprague-Dawley rats by injecting them with alloxan (150 mg/kg body weight). MCW (4 mL/100 g body weight) and L-arginine (7.5 mg/100 g body weight) was given orally for 45 days. L-NAME was given at a dose of 0.5 mg/kg body weight. Concentrations of blood glucose, plasma insulin, glycosylated hemoglobin (HbA1c), L-arginine, urine volume and urinary creatinine levels, activity of nitric oxide synthase (NOS), and arginase as well as the abnormalities in hemostasis and thrombosis were measured in all the experimental groups.

RESULTS

Treatment with MCW and L-arginine reduced the concentration of blood glucose and HbA1c in diabetic rats. MCW and L-arginine treatment exhibited significant antithrombotic activity in diabetic rats, which was evident from the reduced levels of WBC, platelets, fibrin, and fibrinogen. MCW and L-arginine treatment prolonged the prothrombin time in diabetic rats and reduced the activity of Factor V. In addition to this, the activity of nitric oxide synthase, liver and plasma arginine content, and urinary nitrite were higher in MCW-treated diabetic rats whereas L-NAME treatment inhibited the beneficial effects induced by MCW and arginine.

CONCLUSIONS

The results clearly indicate that L-arginine is a major factor responsible for the antidiabetic and antithrombotic potential of coconut water, and is mediated through the L-arginine-nitric oxide pathway.

Transgenic mice overexpressing arginase 1 in monocytic cell lineage are affected by lympho-myeloproliferative disorders and disseminated intravascular coagulation

Arginase (ARG) is a metabolic enzyme present in two isoforms that hydrolyze l-arginine to urea and ornithine. In humans, ARG isoform 1 is also expressed in cells of the myeloid lineage. ARG activity promotes tumour growth and inhibits T lymphocyte activation. However, the two ARG transgenic mouse lines produced so far failed to show such effects. We have generated, in two different genetic backgrounds, transgenic mice constitutively expressing ARG1 under the control of the CD68 promoter in macrophages and monocytes. Both heterozygous and homozygous transgenic mice showed a relevant increase in mortality at early age, compared with wild-type siblings (67/267 and 48/181 versus 8/149, respectively, both P < 0.005). This increase was due to high incidence of haematologic malignancies, in particular myeloid leukaemia, myeloid dysplasia, lymphomas and disseminated intravascular coagulation (DIC), diseases that were absent in wild-type mice. Atrophy of lymphoid organs due to reduction in T-cell compartment was also detected. Our results indicate that ARG activity may participate in the pathogenesis of lymphoproliferative and myeloproliferative disorders, suggest the involvement of alterations of L-arginine metabolism in the onset of DIC and confirm a role for the enzyme in regulating T-cell homeostasis.

Improved blood compatibility of poly(ethylene terephthalate) films modified with L-arginine

In order to improve the blood compatibility of the commonly used blood-contacting biomaterial poly(ethylene terephthalate) (PET), in this study PET films were chemically modified with L-arginine (L-Arg) by a three-step-procedure using glutaraldehyde (GA) as a cross-linker. The composition and chemical structure of PET and its change with surface modification were examined by X-ray photoelectron spectroscopy (XPS) and attenuated total reflection Fourier transform infrared (ATR-FT-IR) spectroscopy, while the change in hydrophilicity was judged by water contact angles measurement. The result of water contact measurement indicated that the modified films became more hydrophilic than PET with the contact angle decreasing from 78.5 degrees for PET to 43.7 degrees for PET-Arg. The protein adsorption on the film surface was evaluated by bicinchoninic acid assay (BCA) method, and the result showed that the L-Arg-modified films decreased the amount of protein adsorption by about 25%. The in vitro blood compatibility such as platelet adhesion (observed by scanning electron microscopy) and thrombus formation was also investigated, and the results demonstrated that the L-Arg-modified films significantly suppressed platelet adhesion and aggregation and reduced the thrombus formation by about 67% compared with PET.

The Fibrinogen Functional Turbidimetric Assay

Hitherto, clinical fibrinogen methods were based on coagulation seconds, with assay conditions not similar to a plasma milieu. The fibrinogen functional turbidimetric assay included 50 µL citrated plasma + 100 µL 300 mIU/mL thrombin, 400 µg/mL polybrene, and 6% albumin—phosphate-buffered saline; an increase in absorbance at 405 nm/5 min at room temperature (or 2 minutes at 37°C) was observed. In all, 6% albumin in the fibrinogen functional turbidimetric assay reagent abolishes falsely elevated fibrinogen to fibrin turbidity in hypoproteinemic plasma samples. This assay can detect fibrinogen activity of 250% to 300% of normal, the lower detection limit being 7% of normal (0.2 g/L). The normal range of this assay is 100% ± 20% (mean value ± 1 SD; coefficient of variations <4%). This assay imitates fibrinogen to fibrin conversion in clotting blood plasma; it is independent of plasmatic albumin or heparin and can be performed everywhere. This assay has a diagnostic value in pathology-disseminated intravascular coagulation and in assessing risk for atherothrombosis.

Analysis of hemostasis alterations in sepsis

This laboratory study tested new methods to analyze hemostasis alterations in septic patients. Samples of ethylenediamine tetraacetic acid (EDTA) plasma and citrated plasma were collected from 62 patients with clinical diagnosis of sepsis. Additionally, a subset of EDTA-plasma samples from each patient was stabilized 1 + 1 with 2.5 mol/l arginine, pH 8.6, to conserve the real hemostasis activation state. EDTA-arginine plasma, EDTA plasma and citrated plasma samples were tested in duplicate. The patients at admission to the intensive care unit had 36 +/- 26 (normal, 0.8 +/- 0.2) ng/ml global endotoxin reactivity, 188 +/- 66% (normal, 100 +/- 20%) fibrinogen function, 179 +/- 66% (normal, 100 +/- 20%) fibrinogen antigen, 4.0 +/- 3.6 (normal, 0.049 +/- 0.025) microg/ml D-dimer, 313 +/- 307% (normal, 100 +/- 30%) plasmin-antiplasmin complex, 8.7 +/- 11.4 (normal, 1.1 +/- 0.7) U/ml plasminogen activator inhibitor-1, 12.1 +/- 10.5 (normal, 1.3 +/- 0.4) ng/ml thrombin-antithrombin III complex, 173 +/- 62% (normal, 100 +/- 20%) thrombin, 568 +/- 225 (normal, 140 +/- 42) pg/ml tissue factor, and 2.56 +/- 2.48 (normal, 0.19 +/- 0.04) microg/ml soluble intercellular adhesion molecule-1. Endotoxin (lipopolysaccharide and/or beta-glucan) reactivity (EDTA plasma), fibrinogen function + antigen + ratio and plasminogen activator inhibitor-1 (citrated plasma), and D-dimer, soluble intercellular adhesion molecule-1, thrombin activity (EDTA-arginine-stabilized plasma) presented large aberrations in septic patients when compared with normal values and may therefore be particularly interesting as markers of hemostasis alteration. Whether the observed alterations are of clinical significance has to be determined in well defined patient groups.

Inhibition of thrombin in plasma by heparin or arginine

The inhibition of plasmatic thrombin is of clinical importance in a broad range of diseases. To obtain reliable data the assay system should be as similar to physiology as possible. Using a newly developed physiologic assay system for fibrinogen/thrombin interaction (the FIFTA), the inhibition of plasmatic thrombin by heparin or by arginine was studied. The standard fibrinogen functional turbidimetric assay (FIFTA) was performed, varying heparin or arginine concentrations and varying the time point the inhibitor was added to the FIFTA. Plasmatic heparin concentrations equal to or greater than 0.63 IU/mL completely inhibit thrombin in the assay system described. The IC(50) is 0.1 IU/mL heparin. Heparin can only inhibit fibrin generation within the first 2 minutes at room temperature (RT=23 degrees C). The 50% inhibitory time point, that is, the time point that a 10 IU/mL final concentration of heparin results in 50% inhibition of FIFTA, is 30 seconds at RT. A final arginine concentration of at least 125 mM in the first 100 seconds of the FIFTA reaction at RT completely inhibits turbidity increase. Half-maximal turbidity increase occurs at 63 mM arginine. Final arginine concentrations of at least 250 mM completely inhibit turbidity increase, when arginine acts in the first 4 minutes (RT) of the thrombin/ fibrinogen interaction. A final arginine concentration of 477 mM added at the 12-minute or 30-minute thrombin/ fibrinogen reaction time point decreases the resulting turbidity by 50% after an additional 30 minutes at RT. Pathologic disseminated intravascular coagulation occurs in a multitude of diseases; in common is always the generation of thrombin either by the contact phase or by the tissue factor phase of coagulation. Such pathologically elevated thrombin activity in blood or blood products must be prevented or inhibited. This study demonstrates the efficiency of two physiologic thrombin inhibitors: heparin and arginine.

Arginine Inhibits Serpins

Serine protease inactivators (serpins) are important regulators in biochemistry. Often it is necessary to block the serpin action, that is, to stabilize the sample. The guanidine group of arginine is the ligand for the active center pocket of many serine proteases. Arginine or guanidine inhibits serine proteases, and arginine belongs to the reactive P1-P1' center of many serpins. The plasmatic antithrombin, antiplasmin, or anti-C1-esterase activity was determined: A total of 20 µL of pooled normal plasma or 7% human albumin was added to 100 µL of 0—2.67 M arginine, pH 8.6, 10 µL of 26 mIU/mL thrombin in 7% human albumin, and 30 µL of 1.7 mM CHG-Ala-Arg-pNA (37°C). ΔA at 405 nm was determined, by using a microtiter plate reader. Thrombin was substituted by plasmin or C1-esterase, and the chromogenic peptide substrates <Glu-Phe-Lys-pNA or MeOC-Lys(eCBO)-Gly-Arg-pNA, respectively, were used. The IC50 of arginine against plasmatic antithrombin activity is 580 mM; the IC 25 is 440 mM. The IC25 of arginine against plasmatic α 2-antiplasmin or C1-inactivator is 1650 mM. The amidolytic activity of thrombin, plasmin, and C1-esterase is inhibited similarly by arginine: the IC50 for arginine against the amidolytic activity of these proteases is about 400 mM. Arginine at very high concentrations inhibits serpins. This is important, if stabilization of a biological fluid is a prerequisite for valid activities of serine proteases. In addition, these high concentrations of arginine might be a new gentle principle to inhibit pathogens that need serpins for their pathophysiology.

Monitoring of plasmin and plasminogen activator activity in blood of patients under fibrinolytic treatment by reteplase

There are no reliable data on plasmin or plasminogen activator (PA) activities in blood of patients receiving fibrinolytic treatment. This is due to continuing in vitro action of PA after blood withdrawal. These artefactual changes of PA or plasmin activities have been prevented by arginine stabilization of blood samples of myocardial infarction patients treated with plasminogen activators. Twelve patients with myocardial infarction were treated with reteplase 2 x 10,000,000 units in bolus application; one patient was treated with 100 mg t-PA in continuous infusion. Blood was immediately stabilized with EDTA and arginine. The plasma was analyzed with newly developed assays for plasmin and PA. Maximal plasmin activities in blood were obtained at 40 to 60 minutes reteplase treatment time (0.1-0.6 U/mL = approximately 0.05-0.3 micromol/L plasmin). The 50% clearance rate for plasmatic Pli was greater than 30 minutes. The plasmatic reteplase concentration peaked at approximately 2,000 U/mL after the first bolus infusion and at approximately 1,500-3,500 U/mL after the second bolus infusion. Reteplase was cleared to 50% within less than 30 minutes, also with great inter-individual variation. Arginine stabilization of blood allows reliable determinations of activities of plasmin and PA in blood of patients under fibrinolytic treatment: substantial plasmin activities occur in patients treated by reteplase. Therapeutic thrombolysis might be improved, imitating the physiologic cellular thrombolysis; i.e., polymorphonuclear phagocytes (PMN) that can be activated by singlet oxygen ((1)O(2)). PMN might be superior to PA in selective lysis of pathologic thrombi.

Oral L-arginine administration does not inhibit thrombosis on an experimental model of arterial thrombosis: the effect on the apyrasic activity of the arterial wall

Despite the extensive research on the pharmacology of L-arginine, there are only few data on its antithrombotic properties. We studied the effect of oral L-arginine administration in a model of arterial thrombosis in rabbits divided into three groups: group 1, group without intervention; group 2, control group, treated with normal diet and submitted to the thrombosis-triggering protocol; group 3, treated for 2 weeks with L-arginine (2.25%) prior the protocol. L-Arginine did not alter platelet aggregation nor coagulation parameters but reduced vascular activities of both ADPase (49.1 +/- 8.5 versus 28.9 +/- 8.3 versus 18.8 +/- 10.3 nmoles inorganic phosphate/min per mg protein; mean +/- SD; group 1 versus group 2 versus group 3, respectively; ANOVA F = 19.21; P < 0.0001) and ATPase (97.8 +/- 15.8 versus 52.1 +/- 11.6 versus 31.9 +/- 16.3 nmoles inorganic phosphate/min per mg protein; mean +/- SD; group 1 versus group 2 versus group 3, respectively; ANOVA, F = 34.65; P < 0.0001). L-Arginine did not reduce the thrombi area (17.1 mm, 9.02 and 48.07, versus 27.04 mm, 25.4 and 70.39, median, percentile 25 and 75 respectively, P = 0.079; group 2 versus group 3, respectively). In conclusion, oral L-arginine administration did not inhibit thrombosis, and, conversely, it significantly reduced the arterial wall ADPase and ATPase activities. This effect may limit its antithrombotic properties.

The intrinsic coagulation activity assay

A new assay for the contact-phase-mediated generation of thrombin activity has been developed - the intrinsic coagulation activity assay (INCA). Citrated plasma (50 microl) is incubated with 5 microl SiO2, 250 mmol/l CaCl2 in polystyrole flat-bottom wells. After exactly 4 and 5 min (37 degrees C) coagulation reaction times (INCA-4 and INCA-5), 100 microl of 2.5 mol/l arginine, pH 8.6, is added to inhibit hemostasis activation in the important ascending part of the thrombin generation curve and to depolymerize fibrin. After 20 min, 50 microl of 1 mmol/l (final concentration 0.24 mmol/l) chromogenic thrombin substrate CHG-Ala-Arg-pNA in 1.25 mol/l arginine, pH 8.7, is added. The increase in absorbance is determined at 405 nm using a microtiterplate photometer. The assay is calibrated against 1 IU/ml thrombin. The normal thrombin activity range of INCA-4 (main value) or INCA-5 (control value) is 100 +/- 30% of normal (mean value +/- 1 SD; 100% = 0.5 IU/ml for INCA-4 and 1.9 IU/ml for INCA-5). With the INCA the normal range of intrinsic hemostasis is reflected, low-molecular-weight heparins can be monitored, the plasma matrix is not changed significantly, and the assay results are a percentage of normal generated thrombin activity and not coagulation seconds.

The cardiovascular risk marker asymmetrical dimethylarginine is not affected by venous thromboembolism

Asymmetrical dimethylarginine (ADMA) is an endogenous inhibitor of endothelial nitric oxide synthase, causes vasoconstriction, impairs cardiac function, and may predict cardiovascular risk. The prognostic value of plasma ADMA concentrations in acute vascular situations may be confounded by concomitant factors such as clot formation. In an effort to address the effect of hemostatic system activation, the authors have measured plasma concentrations of ADMA, its stereoisomer symmetrical dimethylarginine (SDMA), and L-arginine in 74 patients with suspected deep vein thrombosis (DVT). DVT was confirmed by sonography or venography in 39 subjects. There was no difference of L-arginine, ADMA, or SDMA (all P > 0.05) between subjects with or without DVT. ADMA correlated with SDMA, L-arginine, and plasma creatinine (all P < 0.05) but not with age, body mass index, D-dimer, thrombus extension, or history of symptoms. Venous thrombembolism does not influence circulating ADMA concentrations. The lack of association between ADMA and DVT argues against a contribution of endogenous NO synthase inhibition in hemostatic systemic activation.

In vitro simulation of therapeutic thrombolysis with microtiter plate clot-lysis assay

Only limited comparable data are available on the clot lysis power of the clinically used plasminogen activators (PA). Here the PA were used at different clinically relevant concentrations, and the lysis of the microclots was determined. A microclot lysis assay was used to study thrombolysis by urokinase, tissue-PA (t-PA), streptokinase, plasminogen-streptokinase activator complex (PSAC), reteplase, or tenecteplase. The clot turbidity served as a tool to determine clot mass: 100 microL fresh microclots were incubated with 25 microL PA in 6% bovine serum albumin (BSA)-phosphate-buffered saline (PBS) and 100 microL BSA-PBS or pooled normal human plasma; that is, the PA were in the liquid supernatant of a plasma clot and were not entrapped in the clot, an assay system comparable to normal physiology. The turbidity was determined after 0 to 5 hours (37 degrees C) by a microtiter plate reader. The lysable clot turbidity (clot mass) was expressed in percent of 100% lysable clot control. The clot lysis activity is 100% minus the clot mass in percent. The effective doses at 50% (ED(50)) of lysis of fresh clots after 4 hours (37 degrees C) with 6% BSA or pooled normal human plasma in the clot-supernatant were urokinase 128 or 180 IU/mL; t-PA 0.3 or 0.2 microg/mL; streptokinase 215 or 1371 IU/mL; PSAC 60 or 91 U/mL; reteplase 664 or 996 U/mL; tenecteplase 0.2 or 0.2 microg/mL. The presence of a plasma thrombus with plasma supernatant increases the activity of t-PA approximately 20-fold and that of tenecteplase approximately 400-fold after 4 hours (37 degrees C), when compared to urokinase; in contrast, the lytic activity induced by reteplase decreases; i.e., the plasmin generated by reteplase is hampered on its lytic action against a thrombus. When comparing the clot lysability of microclots of 29 different donors, the only correlation (r > 0.6) was that between u-PA and t-PA. The lysability of individual clots by PA can be measured with the present routine-suited technique. It is suggested that different thrombolytic agents or concentrations thereof would have a different clinical outcome in different individuals.

Dynamic change of coagulation and anticoagulation markers of patients with acute cerebral infarction during intravenous urokinase thrombolysis

BACKGROUND AND OBJECTIVE

The variations of blood coagulation and anticoagulation are of clinical importance in patients with acute cerebral infarction during intravenous urokinase (UK) thrombolysis. Although intravenous heparin is commonly used after thrombolytic therapy, few reports have addressed the relationship between the degree of anticoagulation and clinical outcomes, specifically the effect of thrombolytic agents on hemostasis. In this study, we dynamically monitored the activated partial thromboplastin time (APTT), the prothrombin time (PT), the thrombin time (TT) and the activated partial thromboplasmin time (APTT) in 56 patients with acute cerebral infarction during intravenous urokinase thrombolysis and analysed the relationship among the blood coagulation biomarkers (APTT, PT, TT, AT-III), as well as baseline patient characteristics and clinical outcomes. This allowed us to explore the valuable biomarkers for securing the thrombolysis regimen in clinical practice.

METHODS

The levels of PT, APTT, TT and AT-III in peripheral blood of 56 patients with acute cerebral infarction and 50 normal controls were assayed by ELISA. Dynamic transformation of these markers at the baseline and the time points of the first, second, fourth, eighth, 12th, 24th, 48th, 72nd and 96th hour after intravenous UK thrombolysis was monitored serially. The relationship between the levels of these biomarkers and the clinical effectiveness and safety of urokinase thrombolysis was evaluated.

RESULTS

The levels of PT, APTT, TT and AT-III in patients before intravenous UK thrombolysis were significantly lower than those in age- and sex-matched normal controls (all p<0.05). After treatment with UK, the levels of PT and APTT rose quickly during the first 4 hours (all p< 0.05), and then gradually recovered, reaching baseline at about the 48th hour. The activity of AT-III was slightly increased and showed fluctuations after UK infusion (p< 0.05), however the fluctuated range was not remarkable and lacked specificity.

CONCLUSIONS

Dynamic monitoring of PT, APTT and TT can indicate coagulative and anticoagulative functions of patients with acute cerebral infarction during intravenous urokinase thrombolysis. Monitoring of these markers can be helpful both in regulating the infusion speed and the dosage of UK, as well as increasing the efficacy and safety of UK therapy. However, assay for AT-III might be unnecessary.

Functional determination of plasminogen activator in arginine-stabilized plasma

Reliable data on plasminogen activator (PA) activities in blood of patients receiving fibrinolytic treatment are lacking. This is due to the continuing in vitro action of PA after blood withdrawal. We have elaborated a new simple stabilization technique for plasma involving the addition of arginine in final concentrations greater than 500 mM. In this study, new assays for PA in stabilized plasma are developed. The assay was performed with substrate plasma, that is, pooled normal plasma, preoxidized with chloramine-T; oxidant amount and oxidation time were optimized. The chloramine consumption by plasma was assayed with a KJ-assay (absorbance increase at 405 nm by addition of 200 microL 4 M KJ to 25 microL oxidized plasma). The substrate plasma concentration in the PA assay and the PA acting time was optimized. The inhibition of PA by the cations Na(+), K(+), Mg(2+), and Ca(2+) was evaluated. The optimized PA assay consists of incubation of 10 microL arginine-stabilized plasma with 10 microL 1.5 M arginine, pH 8.7 and 10 microL 100 mM CT in PBS. After 30 minutes (37 degrees C), 175 microL 15 mM CT oxidized EDTA plasma are added. After 40 minutes (37 degrees C), 75 microL Stop-CS Reagent is added and DeltaA at 405 nm was determined, giving PA + plasmin activity in plasma. A control value (basal plasmin activity) consists of the addition of Stop-CS Reagent before 175 microL oxidized EDTA plasma. To obtain plasmatic PA activity, the control value has to be subtracted from the PA main value. The assay is matrix-independent and linear up to 1250 IU/mL t-PA, 790 U/mL reteplase, or 199 IU/mL u-PA (37 nM). With arginine stabilization of plasma and the described determination of plasminogen activator activity in arginine-stabilized plasma, it is feasible to determine the activity of plasminogen activators in blood of patients receiving fibrinolytic treatment without artefactual in vitro changes of the samples.

Effects of a novel platelet nitric oxide donor (LA816), aspirin, clopidogrel, and combined therapy in inhibiting flow- and lesion-dependent thrombosis in the porcine ex vivo model

BACKGROUND

Acetylsalicylic acid (ASA), or aspirin, plus clopidogrel is becoming the standard antithrombotic treatment in people with coronary disease. Novel approaches such as the use of platelet-selective nitric oxide (NO) donors may provide additional protection against thrombosis. We evaluated the antithrombotic properties of a novel platelet-selective NO donor (LA816) administered alone and in combination with ASA, clopidogrel, or ASA+clopidogrel.

METHODS AND RESULTS

Thrombogenicity was measured in the porcine experimental model and assessed as platelet-thrombus formation in the ex vivo Badimon perfusion chamber. Pigs were randomly divided into 4 groups: (1) placebo control, (2) clopidogrel, (3) ASA, and (4) ASA+clopidogrel (ASA and clopidogrel were given orally, 10 mg x kg(-1) x d(-1) for 3 d). The animals were anesthetized, heparinized, and catheterized, and the Badimon perfusion chamber was placed in an extracorporeal shunt. After baseline perfusions, all animal groups received the intravenous infusion of LA816 for 2 hours. Platelet aggregation, blood pressure, and heart rate also were evaluated during the experiments. LA816, clopidogrel, and ASA+clopidogrel produced a reduction of approximately 45% on thrombus mass versus placebo control perfusions (P<0.05). Combined treatment of oral ASA+clopidogrel and intravenous LA816 produced a significant further reduction of 25% in platelet deposition (70% from placebo controls; P<0.0001). LA816 intravenous treatment did not modify blood pressure or heart rate.

CONCLUSIONS

Acute NO donation with LA816, without modifying hemodynamic parameters, provides the same inhibitory effect as that obtained with chronic treatment with clopidogrel+ASA. Moreover, LA816 provides platelet inhibitory effects in addition to those of the combined blockade of cyclooxygenase and P2y(12) receptor.

A chitosan-arginine conjugate as a novel anticoagulation biomaterial

Chitosan (CS) was modified with arginine using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS) as coupling agents. FTIR and 13C NMR spectra showed that arginine was chemically coupled to CS to form a chitosan-arginine conjugate (CS-ArgC). The substitution degree of arginine in CS estimated from elemental analysis was 20.1%. The circular dichroism spectra indicated that the incorporation of arginine significantly altered the conformation of thrombin; while no obvious variation in the conformation of thrombin was observed with the addition of CS. The anticoagulation activity of glucose aldehyde crosslinked CS-ArgC and CS membranes was evaluated by assaying prothrombin time (PT), thrombin time (TT) and activated partial thromboplastin time (APTT). The APTT of CS-ArgC membrane was prolonged two times as that of CS counterpart, suggesting that the CS-ArgC is a promising candidate as an anticoagulation biomaterial.

Effects of blood product storage protectants on blood coagulation1 1The opinions expressed herein are the private views of the authors and are not to be construed as official or reflecting the views of the Department of the Army or the Department of Defense

The ever-increasing demand for blood products challenges scientists to develop new and more effective techniques for their preservation. The progress of these novel preservation technologies uses a wide variety of cryoprotectant, lyoprotectant, and other preservatives, which will need to be explored and assessed for their biological effects during blood product formulation. The leading factor in protectant selection is for their ability to provide superior preservation for a particular blood product. We believe that such protectants used in blood product development should also be evaluated for their ability to preserve normal hemostasic mechanisms. In this review, high-molecular-weight cryoprotectants, lyoprotectants, polyols, amino acids, antioxidants, and surfactants, used because of their protective properties, were evaluated for their possible role in relation to their effect on normal hemostatic mechanisms.