Synthesis and Structural Characterization of Macrocyclic Plasmin Inhibitors

Two series of macrocyclic plasmin inhibitors with a C-terminal benzylamine group were synthesized. The substitution of the N-terminal phenylsulfonyl group of a previously described inhibitor provided two analogues with sub-nanomolar inhibition constants. Both compounds possess a high selectivity against all other tested trypsin-like serine proteases. Furthermore, a new approach was used to selectively introduce asymmetric linker segments. Two of these compounds inhibit plasmin with K_i values close to 2 nM. For the first time, four crystal structures of these macrocyclic inhibitors could be determined in complex with a Ser195Ala microplasmin mutant. The macrocyclic core segment of the inhibitors binds to the open active site of plasmin without any steric hindrance. This binding mode is incompatible with other trypsin-like serine proteases containing a sterically demanding 99-hairpin loop. The crystal structures obtained experimentally explain the excellent selectivity of this inhibitor type as previously hypothesized.

The Importance of 6-Aminohexanoic Acid as a Hydrophobic, Flexible Structural Element

6-aminohexanoic acid is an ω-amino acid with a hydrophobic, flexible structure. Although the ω-amino acid in question is mainly used clinically as an antifibrinolytic drug, other applications are also interesting and important. This synthetic lysine derivative, without an α-amino group, plays a significant role in chemical synthesis of modified peptides and in the polyamide synthetic fibers (nylon) industry. It is also often used as a linker in various biologically active structures. This review concentrates on the role of 6-aminohexanoic acid in the structure of various molecules.

Binding characteristics of polyphenols as milk plasmin inhibitors

BACKGROUND

The potential use of polyphenols to improve the functional characteristics of dairy products has gained much attention. However, the effects of the polyphenols on naturally occurring enzymes in milk have not been studied extensively. Excess plasmin activity in dairy products might result in several quality defects. The objective of this study was to assess the ability of polyphenols to inhibit plasmin in milk using a molecular and kinetic approach.

RESULTS

Epicatechin gallate (ECG), epigallocatechin gallate (EGCG), quercetin (QUER), and myricetin (MYR) caused a significant decrease in plasmin activity by 60, 86, 65, and 90%, respectively. The inhibition rates were alleviated in the presence of milk proteins. EGCG, QUER, and MYR, exhibited noncompetitive inhibition against plasmin, whereas ECG caused a mixed-type inhibition. A decrease in the random structure of plasmin upon the complex formation with ECG, EGCG, QUER, and MYR was found. The other phenolics that were evaluated did not cause any significant changes in plasmin conformation. The observed inhibitory phenolic-plasmin interactions were dominated by H-bonds and electrostatic attractions. Green tea extract (GTE) rich in catechins also inhibited plasmin activity in the milk.

CONCLUSION

Significant changes in the secondary structure of plasmin upon binding of ECG, EGCG, QUER, and MYR led to diminished plasmin activity both in the absence and presence of milk proteins. These flavonoids with promising plasmin inhibitory potential could be used in new dairy formulations leading to controlled undesired consequences of plasmin activity. © 2019 Society of Chemical Industry.

Topical tranexamic acid inhibits fibrinolysis more effectively when formulated with self-propelling particles

BACKGROUND

Endogenous fibrinolytic activation contributes to coagulopathy and mortality after trauma. Administering tranexamic acid (TXA), an antifibrinolytic agent, is one strategy to reduce bleeding; however, it must be given soon after injury to be effective and minimize adverse effects. Administering TXA topically to a wound site would decrease the time to treatment and could enable both local and systemic delivery if a suitable formulation existed to deliver the drug deep into wounds adequately.

OBJECTIVES

To determine whether self-propelling particles could increase the efficacy of TXA.

METHODS

Using previously developed self-propelling particles, which consist of calcium carbonate and generate CO2 gas, TXA was formulated to disperse in blood and wounds. The antifibrinolytic properties were assessed in vitro and in a murine tail bleeding assay. Self-propelled TXA was also tested in a swine model of junctional hemorrhage consisting of femoral arteriotomy without compression.

RESULTS

Self-propelled TXA was more effective than non-propelled formulations in stabilizing clots from lysis in vitro and reducing blood loss in mice. It was well tolerated when administered subcutaneously in mice up to 300 to 1000 mg/kg. When it was incorporated in gauze, four of six pigs treated after a femoral arteriotomy and without compression survived, and systemic concentrations of TXA reached approximately 6 mg/L within the first hour.

CONCLUSIONS

A formulation of TXA that disperses the drug in blood and wounds was effective in several models. It may have several advantages, including supporting local clot stabilization, reducing blood loss from wounds, and providing systemic delivery of TXA. This approach could both improve and simplify prehospital trauma care for penetrating injury.

Characterization of the PEGylated Functional Upstream Domain Peptide (PEG-FUD): a Potent Fibronectin Assembly Inhibitor with Potential as an Anti-Fibrotic Therapeutic

PURPOSE

To develop PEGylated variants of pUR4/FUD (FUD), a fibronectin assembly inhibitor, using 10 kDa, 20 kDa, and 40 kDa PEGs to evaluate their binding affinity and inhibitory potency.

METHODS

The FUD peptide was recombinantly expressed, purified, and PEGylated at the N-terminus using 10 kDa, 20 kDa, and 40 kDa methoxy-PEG aldehyde. The PEGylates were purified and fractionated using ion-exchange chromatography. The molecular weight and degree of PEGylation of each conjugate was verified using MALDI-TOF. The binding affinity of each PEG-FUD conjugate was studied using isothermal titration colorimetry (ITC) and their inhibitory potency was characterized by a cell-based matrix assembly in vitro assay.

RESULTS

The 10 kDa, 20 kDa, and 40 kDa PEG-FUD conjugates were synthesized and isolated in good purity as determined by HPLC analysis. Their molecular weight was consistent with attachment of a single PEG molecule to one FUD peptide. The binding affinity (Kd) and the fibronectin fibrillogenesis inhibitory potency (IC50) of all PEG-FUD conjugates remained nanomolar and unaffected by the addition of PEG.

CONCLUSIONS

Retention of FUD fibronectin binding activity following PEGylation with three different PEG sizes suggest that PEG-FUD holds promise as an effective anti-fibrotic with therapeutic potential and a candidate for further pharmacokinetic and biodistribution studies.

Compaction of fibrin clots reveals the antifibrinolytic effect of factor XIII

Essentials Factor XIIIa inhibits fibrinolysis by forming fibrin-fibrin and fibrin-inhibitor cross-links. Conflicting studies about magnitude and mechanisms of inhibition have been reported. Factor XIIIa most strongly inhibits lysis of mechanically compacted or retracted plasma clots. Cross-links of α2-antiplasmin to fibrin prevent the inhibitor from being expelled from the clot.

SUMMARY

Background Although insights into the underlying mechanisms of the effect of factor XIII on fibrinolysis have improved considerably in the last few decades, in particular with the discovery that activated FXIII (FXIIIa) cross-links α2 -antiplasmin to fibrin, the topic remains a matter of debate. Objective To elucidate the mechanisms of the antifibrinolytic effect of FXIII. Methods and Results Platelet-poor plasma clot lysis, induced by the addition of tissue-type plasminogen activator, was measured in the presence or absence of a specific FXIIIa inhibitor. Both in a turbidity assay and in a fluorescence assay, the FXIIIa inhibitor had only a small inhibitory effect: 1.6-fold less tissue-type plasminogen activator was required for 50% clot lysis in the presence of the FXIIIa inhibitor. However, when the plasma clot was compacted by centrifugation, the FXIIIa inhibitor had a strong inhibitory effect, with 7.7-fold less tissue-type plasminogen activator being required for 50% clot lysis in the presence of the FXIIIa inhibitor. In both experiments, the effects of the FXIIIa inhibitor were entirely dependent on the cross-linking of α2 -antiplasmin to fibrin. The FXIIIa inhibitor reduced the amount of α2 -antiplasmin present in the compacted clots from approximately 30% to < 4%. The results were confirmed with experiments in which compaction was achieved by platelet-mediated clot retraction. Conclusions Compaction or retraction of fibrin clots reveals the strong antifibrinolytic effect of FXIII. This is explained by the cross-linking of α2 -antiplasmin to fibrin by FXIIIa, which prevents the plasmin inhibitor from being fully expelled from the clot during compaction/retraction.

Discovery and safety profiling of a potent preclinical candidate, (4-[4-[[(3R)-3-(hydroxycarbamoyl)-8-azaspiro[4.5]decan-3-yl]sulfonyl]phenoxy]-N-methylbenzamide) (CM-352), for the prevention and treatment of hemorrhage

Discovery of potent and safe therapeutics that improve upon currently available antifibrinolytics, e.g., tranexamic acid (TXA, 1) and aprotinin, has been challenging. Matrix metalloproteinases (MMPs) participate in thrombus dissolution. Then we designed a novel series of optimized MMP inhibitors that went through phenotypic screening consisting of thromboelastometry and mouse tail bleeding. Our optimized lead compound, CM-352 (2), inhibited fibrinolysis in human whole blood functional assays and was more effective than the current standard of care, 1, in the tail-bleeding model using a 30 000 times lower dose. Moreover, 2 reduced blood loss during liver hepatectomy, while 1 and aprotinin had no effect. Molecule 2 displayed optimal pharmacokinetic and safety profiles with no evidence of thrombosis or coagulation impairment. This novel mechanism of action, targeting MMP, defines a new class of antihemorrhagic agents without interfering with normal hemostatic function. Furthermore, 2 represents a preclinical candidate for the acute treatment of bleeding.

Recent advances on plasmin inhibitors for the treatment of fibrinolysis-related disorders

Growing evidence suggests that plasmin is involved in a number of physiological processes in addition to its key role in fibrin cleavage. Plasmin inhibition is critical in preventing adverse consequences arising from plasmin overactivity, e.g., blood loss that may follow cardiac surgery. Aprotinin was widely used as an antifibrinolytic drug before its discontinuation in 2008. Tranexamic acid and ε-aminocaproic acid, two small molecule plasmin inhibitors, are currently used in the clinic. Several molecules have been designed utilizing covalent, but reversible, chemistry relying on reactive cyclohexanones, nitrile warheads, and reactive aldehyde peptidomimetics. Other major classes of plasmin inhibitors include the cyclic peptidomimetics and polypeptides of the Kunitz and Kazal-type. Allosteric inhibitors of plasmin have also been designed including small molecule lysine analogs that bind to plasmin's kringle domain(s) and sulfated glycosaminoglycan mimetics that bind to plasmin's catalytic domain. Plasmin inhibitors have also been explored for resolving other disease states including cell metastasis, cell proliferation, angiogenesis, and embryo implantation. This review highlights functional and structural aspects of plasmin inhibitors with the goal of advancing their design.

Intravenous hemostats: challenges in translation to patients

Excessive bleeding and the resulting complications are a leading killer of young people globally. There are many successful methods to halt bleeding in the extremities, including compression, tourniquets, and dressings. However, current treatments for internal hemorrhage (including from head or truncal injuries), termed non-compressible bleeding, are inadequate. For these non-compressible injuries, blood transfusions are the current treatment standard. However, they must be refrigerated, may potentially transfer disease, and are of limited supply. In addition, time is of the essence for halting hemorrhage, since more than a third of civilian deaths due to hemorrhage from trauma occur before the patient even reaches the hospital. As a result, particles that can cross-link activated platelets through the glycoprotein IIb/IIIa receptor expressed on activated platelets are being investigated as an alternative treatment for non-compressible bleeding. Ideally, these particles would interact specifically with platelets to stabilize the platelet plug. Initial designs used biologically derived microparticles with red blood cell fragment or albumin cores decorated with RGD or fibrinogen, which bind to GPIIb/IIIa. More recently there has been research into the use of fully synthetic nanoparticles with liposomal or polymer cores that crosslink platelets through a targeting peptide bound to the surface. Some of the challenges for the development of these particles include appropriate sizing to prevent blocking the capillaries of the lungs, immune system evasion to prevent strong reactions and increase circulation time, and storage and resuspension so that first responders can easily use the particles. In addition, the effectiveness of the variety of animal bleeding models in predicting outcomes must be examined before test results can be fully understood. Progress has been made in the development of particles to combat hemorrhage, but issues of immune sensitivity and storage must be resolved before these types of particles can be translated for human use.

A spider-derived Kunitz-type serine protease inhibitor that acts as a plasmin inhibitor and an elastase inhibitor

Kunitz-type serine protease inhibitors are involved in various physiological processes, such as ion channel blocking, blood coagulation, fibrinolysis, and inflammation. While spider-derived Kunitz-type proteins show activity in trypsin or chymotrypsin inhibition and K⁺ channel blocking, no additional role for these proteins has been elucidated. In this study, we identified the first spider (Araneus ventricosus) Kunitz-type serine protease inhibitor (AvKTI) that acts as a plasmin inhibitor and an elastase inhibitor. AvKTI possesses a Kunitz domain consisting of a 57-amino-acid mature peptide that displays features consistent with Kunitz-type inhibitors, including six conserved cysteine residues and a P1 lysine residue. Recombinant AvKTI, expressed in baculovirus-infected insect cells, showed a dual inhibitory activity against trypsin (K_i 7.34 nM) and chymotrypsin (K_i 37.75 nM), defining a role for AvKTI as a spider-derived Kunitz-type serine protease inhibitor. Additionally, AvKTI showed no detectable inhibitory effects on factor Xa, thrombin, or tissue plasminogen activator; however, AvKTI inhibited plasmin (K_i 4.89 nM) and neutrophil elastase (K_i 169.07 nM), indicating that it acts as an antifibrinolytic factor and an antielastolytic factor. These findings constitute molecular evidence that AvKTI acts as a plasmin inhibitor and an elastase inhibitor and also provide a novel view of the functions of a spider-derived Kunitz-type serine protease inhibitor.

The plasmin-antiplasmin system: structural and functional aspects

The plasmin-antiplasmin system plays a key role in blood coagulation and fibrinolysis. Plasmin and α(2)-antiplasmin are primarily responsible for a controlled and regulated dissolution of the fibrin polymers into soluble fragments. However, besides plasmin(ogen) and α(2)-antiplasmin the system contains a series of specific activators and inhibitors. The main physiological activators of plasminogen are tissue-type plasminogen activator, which is mainly involved in the dissolution of the fibrin polymers by plasmin, and urokinase-type plasminogen activator, which is primarily responsible for the generation of plasmin activity in the intercellular space. Both activators are multidomain serine proteases. Besides the main physiological inhibitor α(2)-antiplasmin, the plasmin-antiplasmin system is also regulated by the general protease inhibitor α(2)-macroglobulin, a member of the protease inhibitor I39 family. The activity of the plasminogen activators is primarily regulated by the plasminogen activator inhibitors 1 and 2, members of the serine protease inhibitor superfamily.

Biomaterials, fibrosis, and the use of drug delivery systems in future antifibrotic strategies

All biomaterials, when implanted into the body, elicit an inflammatory response that evolves into fibrovascular tissue formation on and around the material. As a result, material scientists and tissue engineers should be concerned about host response to tissue-engineered constructs that have a biomaterial component, because the host response to this component will interfere with device function and reduce the lifespan of tissue engineering devices in vivo. The fibrotic response to biomaterials is not unlike pathological fibrosis of the liver, lung, kidney, and peritoneum in many ways: i) the presence of mononuclear leukocytes are common in the local environment of both pathological fibrosis and biomaterial-induced fibrosis even though cells of mesenchymal origin are responsible for laying the majority of the extracellular matrix; ii) paracrine-signaling molecules, such as transforming growth factor beta;1, are essential mediators of fibrosis, whether it is pathological or biomaterial induced; and iii) injury and/or the presence of foreign materials (including bacterial components, toxins, or man-made objects) are essential initiators for the development of the fibrotic response. This review discusses mechanisms and research methodology related to pathological fibrosis that is of interest to researchers focused on biomaterials. Potential research models for the study of fibrosis from the fields of biomaterials and drug delivery are also discussed, which may be of interest to scientists working on the pathology of fibrotic disease.

Influence of a 4-aminomethylbenzoic acid residue on competitive fragmentation pathways during collision-induced dissociation of metal-cationized peptides

Formation of [bn+17+cat]+ is a prominent collision-induced dissociation (CID) pathway for Li+- and Na+-cationized peptides. Dissociation of protonated and Ag+-cationized peptides instead favors formation of the rival bn+/[bn-1+cat]+ species. In this study the influence of a 4-aminomethylbenzoic acid (4AMBz) residue on the relative intensities of [b(3)-1+cat]+ and [b(3)+17+cat]+ fragment ions was investigated using several model tetrapeptides including those with the general formula A(4AMBz)AX and A(4AMBz)GX (where X=G, A, V). For Li+- and Na+-cationized versions of the peptides there was a significant increase in the intensity of [b(3)-1+cat]+ for the peptides that contain the 4AMBz residue, and in some cases the complete elimination of the [b(3)+17+cat]+ pathway. The influence of the 4AMBz residue may be attributed to the fact that [b(3)-1+cat]+ would be a highly conjugated species containing an aromatic ring substituent. Comparison of CID profiles generated from Na+-cationized AAGV and A(4AMBz)GV suggests an apparent decrease in the critical energy for generation of [b(3)-1+Na]+ relative to that of [b(3)+17+Na]+ when the aromatic amino acid occupies a position such that it leads to the formation of the highly conjugated oxazolinone, thus leading to an increase in formation rate for the former compared to the latter.

Effect of epsilon-aminocaproylamino acids on fibrin formation

Effect of three epsilon-aminocaproylamino acids with significant antifibrinolytic activity on polymerization of fibrin monomer, clot retraction, fibrin structure, prothrombin consumption and thrombin activity was examined. epsilon-Aminocaproyl-L-norleucine and epsilon-aminocaproyl-L-leucine were weak inhibitors of thrombin activity and epsilon-aminocaproyl-L-norleucine slightly inhibited polymerization of fibrin monomers.

Structures of importance for the stability of antiplasmin as studied by site-directed mutagenesis

Human antiplasmin, a fast-acting inhibitor of plasmin in plasma, belongs to the serpin super-family of proteins. Like other members of this family, antiplasmin has a scissile peptide bond exposed within a reactive centre loop, typically present at the surface of the molecule. Antiplasmin is stable at neutral pH, but at acidic pH or at elevated temperatures it rapidly becomes inactivated. Data regarding "native" antiplasmin have demonstrated that both polymerization processes and formation of latent molecules are important in this respect. In this work we used site-directed mutagenesis to produce 11 single-site mutants (mainly within Abeta-sheet, Bbeta-sheet and reactive centre loop), which were expressed in Drosophila S2 cells, purified and characterized. Five of the 11 mutants were found to have a deviating stability at decreased pH. Glu346Thr was the only mutant with a lesser stability as compared to wt-antiplasmin, but the other 4 were more stable. The most stable mutant, His341Thr, was 7-fold more stable at pH 4.9 as compared to wt-antiplasmin. The wt-antiplasmin had a much more pronounced tendency to polymerize at decreased pH, as compared to "native" antiplasmin. However, many of the mutants clearly rather formed latent molecules, as judged both from PAGE-analysis at non-denaturing condition and reactivation experiments.

Antimalarial efficacy of methylene blue and menadione and their effect on glutathione metabolism of Plasmodium yoelii-infected albino mice

Plasmodium yoelii infection caused significant decline in the hepatic and splenic glutathione content and the activities of the key enzymes, that is, glutamate cysteine ligase (EC 6.3.2.2) and glutathione reductase (EC 1.8.1.7) of their murine host, that is, Swiss albino mice. Methylene blue as well as menadione were found to restore these constituents when given to P. yoelii-infected mice at the dose levels of 2.5 and 100 mg/kg, respectively, compared to mefloquine which does the same at 5.0 mg/kg dose. Methylene blue, like mefloquine also caused a rapid decline in percent parasitaemia, whereas menadione caused a delay in maturation of the infection, but could not cure the mice.

A Comparison of Cyclohexanone and Tetrahydro-4H-thiopyran-4-one 1,1-Dioxide as Pharmacophores for the Design of Peptide-Based Inhibitors of the Serine Protease Plasmin

The plasminogen system is important in the proteolytic cascade that facilitates angiogenesis, a process that is essential for tumor growth and metastasis. The serine protease plasmin has a central role in the plasminogen system. This protease acts by degrading several components of the basement membrane and by activating other proteases. Therefore, inhibition of plasmin may be an effective method for blocking angiogenesis and, as a result, inhibiting the growth of primary tumors and secondary metastases. Three pairs of plasmin inhibitors were synthesized to compare the relative potency of inhibitors that are based upon a cyclohexanone or a tetrahydro-4H-thiopyran-4-one 1,1-dioxide nucleus. Compounds 1, 3, and 5 were cyclohexanone-based inhibitors, whereas compounds 2, 4, and 6 were tetrahydro-4H-thiopyran-4-one 1,1-dioxide-based inhibitors. Compounds 5 and 6 are reasonable inhibitors with IC50 values of 25 and 5.5 microM, respectively. Comparisons of the IC50 values of the three pairs show that the electron-withdrawing sulfone functional group is a beneficial element for the design of plasmin inhibitors. The presence of the sulfone increases inhibitor potency by a factor of 3-5 when compared to inhibitors that are based upon a simple cyclohexanone core.

Functional hierarchy of plasminogen kringles 1 and 4 in fibrinolysis and plasmin-induced cell detachment and apoptosis

Plasmin(ogen) kringles 1 and 4 are involved in anchorage of plasmin(ogen) to fibrin and cells, an essential step in fibrinolysis and pericellular proteolysis. Their contribution to these processes was investigated by selective neutralization of their lysine-binding function. Blocking the kringle 1 lysine-binding site with monoclonal antibody 34D3 fully abolished binding and activation of Glu-plasminogen and prevented both fibrinolysis and plasmin-induced cell detachment-induced apoptosis. In contrast, blocking the kringle 4 lysine-binding site with monoclonal antibody A10.2 did not impair its activation although it partially inhibited plasmin(ogen) binding, fibrinolysis and cell detachment. This remarkable, biologically relevant, distinctive response was not observed for plasmin or Lys-plasminogen; each antibody inhibited their binding and activation of Lys-plasminogen to a limited extent, and full inhibition of fibrinolysis required simultaneous neutralization of both kringles. Thus, in Lys-plasminogen and plasmin, kringles 1 and 4 act as independent and complementary domains, both able to support binding and activation. We conclude that Glu-/Lys-plasminogen and plasmin conformations are associated with transitions in the lysine-binding function of kringles 1 and 4 that modulate fibrinolysis and pericellular proteolysis and may be of biological relevance during athero-thrombosis and inflammatory states. These findings constitute the first biological link between plasmin(ogen) transitions and functions.

Anticoagulant and antifibrinogenolytic properties of the aqueous extract from Bauhinia forficata against snake venoms

The aqueous extract from aerial parts of Bauhinia forficata was able to neutralize the clotting activity induced by Bothrops and Crotalus crude venoms. The clotting time, upon human plasma, induced by B. moojeni venom was significantly prolonged. Clotting and fibrinogenolytic activities induced by isolated thrombin-like enzyme from Bothrops jararacussu were totally inhibited after incubation at different ratios. The extract was not able to neutralize the hemorrhagic activity induced by an Bothrops venoms, but it efficiently inhibited the edema induced by Crotalus durissus terrificus venom and isolated PLA2s. In addition, it did not inhibited the phospholipase A2 activity of Bothrops snake venoms. Interaction studies between Bauhinia forficata extract and snake venoms, when analyzed by SDS-PAGE, did not reveal any apparent degradation of the venom proteins. This extract is a promising source of natural inhibitors of serine-proteases involved in blood clotting disturbances induced by snake venoms.

Influence of Vitamin K on Anticoagulant Therapy Depends on Vitamin K Status and the Source and Chemical Forms of Vitamin K

Warfarin therapy requires close monitoring to avoid excessive bleeding and to maintain the effective therapeutic concentration assessed with the internationalized ratio (INR). High vitamin K intake can decrease the therapeutic effectiveness of warfarin, while poor vitamin K status appears to increase the sensitivity to small changes in vitamin K intake, especially from supplements. Very large amounts of vitamin K from a single meal with vegetables (400 g of vegetables with 700 to 1500 microg of vitamin K1) can measurably change INR, but occasional typical servings (<100 g) would probably have little lasting impact on INR. Warfarin requirements may change in those altering their intake of dark-green vegetables. The 2005 Dietary Guidelines for Americans recommends 3 cups/week of dark-green vegetables, which contain about 100 to 570 microg/serving of vitamin K1. Less well-known sources and chemical forms of vitamin K, such as MK-7 in natto (a fermented Japanese product), also measurably influence INR. Additional research is needed in warfarin-treated patients to fully quantify the interactions among various sources and chemical forms of vitamin K, age, genotype, and other factors.

Determination of phylloquinone (vitamin K1) in plasma and serum by HPLC with fluorescence detection

A modified high-performance liquid chromatography (HPLC) method, based on Davidson and Sadowski [Meth. Enzymol. 282 (1997) 408], with fluorescence detection after zinc postcolumn reduction was developed and validated for the analysis of phylloquinone (vitamin K1) in plasma or serum samples. Compensation for procedural losses of vitamin K1 was made by the method of internal standardization using a proprietary vitamin K derivative. Increased sensitivity of detection by the use of a high-sensitivity Waters 440 fluorescence detector and optimized chromatography conditions increased the sensitivity to 4 fmol vitamin K1. The response was linear and free from interfering peaks and from baseline drift. It is therefore adequately sensitive for 0.25 ml or less of plasma sample. Long-term reproducibility of quality assurance (QA) samples was verified over a period of 4 months. The intraassay precision estimates of the QA samples within-run with mean vitamin K1 concentrations of 0.4, 1.4 and 3.4 nmol/l were 5.2% (n=6), 8.2% (n=6) and 3.0% (n=12), respectively, while interassay precision estimates between runs were 16% (n=22), 12% (n=21) and 8.1% (n=15), respectively. The assay accuracy was validated by comparing the results we obtained for 14 samples from the Vitamin K External Quality Assessment Scheme (KEQAS) with the consensus of the results from the other participating laboratories. Good agreement was obtained, with y=1.06x-0.09, R2=0.99. Validation also included linearity of response, absence of interference and confirmation of vitamin K1 peak purity.

Immunoglobulins G could prevent adherence of Candida albicans to polystyrene and extracellular matrix components

Immunocompromised patients are at high risk of developing Candida infections. Although cell-mediated immunity is generally believed to play the main role in defence against fungi, antibodies could also be effective in immune defence by different mechanisms of action. The adherence capacity of four strains of Candida albicans to polystyrene and to some extracellular matrix components was investigated after incubation of the yeasts with non-specific and specific anti-C. albicans IgG. Experiments were carried out using a colorimetric method based upon the reduction of XTT tetrazolium (2,3-bis[2-methoxy-4-nitro-5-sulfophenyl]-2H-tetrazolium-5-carboxanilide) by mitochondrially active blastospores in the presence of menadione. Incubation of the yeasts with IgG, specific or not, caused a decrease in the capacity for adherence to the surfaces studied. There was no significant effect of the specificity of the tested antibodies on the reduction of adherence capacity. In conclusion, total IgG could play a role in blocking the binding of C. albicans to host and medical device surfaces. These results suggest that regular survey of levels of total IgG in patients suffering from severe hypogammaglobulinaemia could be of interest for the prevention of systemic candidiasis.

Identification of amino acids in antiplasmin involved in its noncovalent 'lysine-binding-site'-dependent interaction with plasmin

The lysine-binding-site-mediated interaction between plasmin and antiplasmin is of great importance for the fast rate of this reaction. It also plays an important part in regulating the fibrinolytic enzyme system. To identify structures important for its noncovalent interaction with plasmin, we constructed seven single-site mutants of antiplasmin by modifying charged amino acids in the C-terminal part of the molecule. All the variants were expressed in the Drosophila S2 cell system, purified, and shown to form stable complexes with plasmin. A kinetic evaluation revealed that two mutants of the C-terminal lysine (K452E or K452T) did not differ significantly from wild-type antiplasmin in their reactions with plasmin, in either the presence or absence of 6-aminohexanoic acid, suggesting that this C-terminal lysine is not important for this reaction. On the other hand, modification of Lys436 to Glu decreased the reaction rate about fivefold compared with wild-type. In addition, in the presence of 6-aminohexanoic acid, only a small decrease in the reaction rate was observed, suggesting that Lys436 is important for the lysine-binding-site-mediated interaction between plasmin and antiplasmin. Results from computerized molecular modelling of the C-terminal 40 amino acids support our experimental data.

Spectrophotometric methods for the rapid determination of menadione and menadione sodium bisulphite and their application in pharmaceutical preparations

Two simple, rapid and sensitive spectrophotometric determination of menadione and its sodium bisulphite derivative (MSB) have been carried out. The first method involves the reaction of menadione and its sodium bisulphite derivative with 3-methyl-2-benzothiazolinone hydrazone hydrochloride (MBTH) is sodium hydroxide medium to give blue coloured product having maximum absorption at 625 nm and the coloured species is stable for more than 1 h. The Beer's law is obeyed in the range 0.4-16 microg ml(-1). The second method proposes the reaction of menadione and its sodium bisulphite derivative with resorcinol in concentrated sulphuric acid medium to give red coloured product having maximum absorption at 520 nm and is stable for 3 h. The Beer's law was obeyed in the range of 1-24 microg ml(-1). Molar absorptivity for the above two methods were found to be 7.6 x 10(3) and 4.5 x 10(3) l mol(-1) cm(-1), respectively. All the measurements were carried out at room temperature. These two methods have been successfully applied for menadione and its sodium bisulphite derivatives in injections and tablets of pharmaceutical formulations. The results compare favourably with official method.

Development of novel topical tranexamic acid liposome formulations

The aims of this study were to develop novel liposome formulations for tranexamic acid (TA) from various lipid compositions [neutral (hydrogenated soya phosphatidylcholine and cholesterol), positive (stearylamine) or negative (dicetyl phosphate) charged lipid], and to investigate the effects of concentrations of TA (5 and 10% in DI water) and charges on the physicochemical properties of liposomes. Liposomes were prepared by chloroform film method with sonication. The physical (appearance, pH, size, morphology) and chemical (drug encapsulation efficiency, transition temperature, enthalpy of transition) properties of liposomes were characterized. The TA contents were determined spectrophotometrically at 415 nm, following derivatization with 2,4,6-trinitrobenzosulfonic acid. The charged liposomes demonstrated better physical stability than the neutral liposomes. The percentages of TA entrapped in all liposome formulations varied between 13.2 and 15.6%, and were independent of TA concentrations and charges of liposomes. Charges affected the physical stability, pH and size of liposomes. The particle sizes of negative blank and positive liposomes (with and without the entrapped drug) were approximately 10 times larger than the negative liposome with the entrapped TA. The multilamellar 7:2:1 molar ratio of hydrogenated soy phosphatidylcholine/cholesterol/dicetyl phosphate entrapped with 10% TA liposome (10%TA,-) was selected for further release study, due to its high physical stability, small particle size and relatively high drug encapsulation efficiency.

Quantitative effects of interacting variables on vitamin K1, phylloquinone, entrapment in liposomes

Vitamin K1 is poorly absorbed by the oral route in certain diseased conditions. Entrapment of this vitamin in liposomes is expected to improve oral absorption. In this study, vitamin K1 has been encapsulated into multilamellar vesicles (MLVs) composed of either egg phosphatidylcholine (egg PC, EPC) or dipalmitoyllecithin (DPPC) by the classical film method involving hydration of lipids by either hand shaking or vigorous vortex mixing. Amounts of vitamin K1 ranging from 4.4 to 22.1 microMol were employed to medicate liposome suspensions (26 microMm or 13.6 microM). A 2(3) factorial design was employed to quantitative the effects of the interaction of certain variables viz: nature of lipid (L), method of agitation (M) and initial drug concentration (C), on encapsulation capacity (EC) of liposomes. The results of this study suggest, in particular, that the concentration of the drug (C) and the nature of the lipid-drug interactions (L-C) are the most influential variables. This probably infers that any pre-formulation studies with this drug delivery system should start with a consideration of L-C interaction. A negative correlation was found between initial drug concentration and encapsulation capacity of liposomes.

Antifibrinolytic effect of single apo(a) kringle domains: relationship to fibrinogen binding

Elevated plasma concentrations of lipoprotein(a) [Lp(a)] are associated with an increased risk for the development of atherosclerotic disease which may be attributable to the ability of Lp(a) to attenuate fibrinolysis. A generally accepted mechanism for this effect involves direct competition of Lp(a) with plasminogen for fibrin(ogen) binding sites thus reducing the efficiency of plasminogen activation. Efforts to determine the domains of apolipoprotein(a) [apo(a)] which mediate fibrin(ogen) interactions have yielded conflicting results. Thus, the purpose of the present study was to determine the ability of single KIV domains of apo(a) to bind plasmin-treated fibrinogen surfaces as well to determine their effect on fibrinolysis using an in vitro clot lysis assay. A bacterial expression system was utilized to express and purify apo(a) KIV (2), KIV (7), KIV (9) DeltaCys (which lacks the seventh unpaired cysteine) and KIV (10) which contains a strong lysine binding site. We also expressed and examined three mutant derivatives of KIV (10) to determine the effect of changing critical residues in the lysine binding site of this kringle on both fibrin(ogen) binding and fibrin clot lysis. Our results demonstrate that the strong lysine binding site in apo(a) KIV (10) is capable of mediating interactions with plasmin-modified fibrinogen in a lysine-dependent manner, and that this kringle can increase in vitro fibrin clot lysis time by approximately 43% at a concentration of 10 microM KIV (10). The ability of the KIV (10) mutant derivatives to bind plasmin-modified fibrinogen correlated with their lysine binding capacity. Mutation of Trp (70) to Arg abolished binding to both lysine-Sepharose and plasmin-modified fibrinogen, while the Trp (70) -->Phe and Arg (35) -->Lys substitutions each resulted in decreased binding to these substrates. None of the KIV (10) mutant derivatives appeared to affect fibrinolysis. Apo(a) KIV (7) contains a lysine- and proline-sensitive site capable of mediating binding to plasmin-modified fibrinogen, albeit with a lower apparent affinity than apo(a) KIV (10). However, apo(a) KIV (7) had no effect on fibrinolysis in vitro. Apo(a) KIV (2) and KIV (9) DeltaCys did not bind measurably to plasmin-modified fibrinogen surfaces and did not affect fibrinolysis in vitro.

Reaction of canine plasminogen with 6-aminohexanoate: a thermodynamic study combining fluorescence, circular dichroism, and isothermal titration calorimetry

The thermodynamics of the binding of 6-aminohexanoate (6-AH) to dog glu-plasminogen has been studied. Fluorescence titrations revealed four binding sites. Three yielded positive fluorescence changes on ligand binding; one yielded a negative fluorescence change. The fluorescence data gave no indication of cooperative interactions. Binding was studied using circular dichroism (CD). Near 295 nm there were small changes associated with binding ligand. These were magnified at 235 nm, a wavelength that is mainly associated with tryptophan bands. The dissociation constants obtained from the fluorescence were applied to the CD data and fit quite well. Below 220 nm, there were no significant differences between samples with or without 6-AH and, therefore, no substantial change in the secondary structure of the protein. Isothermal titration calorimetry was used in combination with the binding constants from fluorescence to study the enthalpy and entropy contributions to 6-AH binding. The enthalpies of association for the four sites are all negative. Their absolute values are small for the tight sites and large for the weakest. -TDeltaS is negative for the tight sites and positive for the weakest. The binding of 6-AH to plasminogen is entropically driven for the two tightest sites and enthalpically driven for the weakest site. The binding of 6-AH to lys-plasminogen has been studied and differs slightly from binding to glu-plasminogen. Most importantly, the binding of 6-AH for the weak site goes from enthalpy- to entropy-driven as is found with the other sites.

Development of potent and selective plasmin and plasma kallikrein inhibitors and studies on the structure-activity relationship

Based on structure-activity relationship studies, we designed and synthesized plasmin (PL) and plasma kallikrein (PK) inhibitors. Trans-(4-aminomethylcyclohexanecarbonyl)-Tyr(O-Pic)-octylamide inhibited PL, PK, urokinase (UK) and thrombin (TH) with IC50 values of 0.53, 30, 5.3 and > 400 microm, respectively. Trans-(4-aminomethylcyclohexanecarbonyl)-Tyr(O-2-Pyrim)-4-carboxyanilide inhibited PL, PK, UK and TH with IC50 values of 36, 0.56, 440 and > 1,000 microM, respectively.

Novel, potent and selective chimeric FXa inhibitors featuring hydrophobic P1-ketoamide moieties

Judicious combination of P-region sequences of highly potent anticoagulant proteins including NAP5, NAP6, Ecotin, and Antistasin with SAR from small molecule FXa inhibitors led to a series of chimeric inhibitors of formula 1a-j. We report herein the design, synthesis, and biological activity of this novel family of FXa inhibitors that express both high in vitro potency and superb selectivity against related serine proteases.

Understanding the fluorescence changes of human plasminogen when it binds the ligand, 6-aminohexanoate: a synthesis

This work attempts to explain several aspects of the response of plasminogen to 6-aminohexanoate (6-AH). These responses include the overall fluorescent changes that occur when plasminogen binds the ligand, the changes shown by the individual domains when they bind the ligand, and the changes in structure shown by the holoprotein when it binds 6-AH. The results have implications for understanding the physicochemical behavior of all kringle based proteins.

Solid dosage form preparations from oily medicines and their drug release. Effect Of degree of surface-modification of silica gel on the drug release from phytonadione-loaded silica gels

A surface-modified silica gel was produced to improve the surface affinity to an oily medicine, phytonadione (VK1). The effect of the degree of surface modification of the silica gel on the drug release behavior from the silica porous matrix was investigated. The silica gels were surface-modified using the silan coupling agent, 3-methacryloxypropyltrimethoxysilane (C7), octadecyltriethoxysilane (C18), or 3,3,3-trifluoropropyltrimethoxysilane (F3). A mixture of VK1 solution and surface-modified silica gel was evaporated under reduced pressure at room temperature, then the resulting powder was dried in vacuo. The degree of surface modification was evaluated based upon elementary analysis. The dissolution profiles of the samples were investigated in Japanese Pharmacopoeia XII, 1st fluid buffer (pH 1.2, 37+/-0.5 degrees C) containing 1.5% sodium lauryl sulfate. The FT-IR spectra of VK1-loaded surface-modified silica gels suggested that the amount of hydrogen-bonded VK1 with the silanol group on the gel surface decreased with increasing hydrophobicity of the silica gel. Since the modified group was rotating on the silica gel surface, and inhibited the adsorption of VK1 to the surface, the attractive molecular interaction between VK1 and the silica gel surface might decrease with increasing length of the modified functional group. However, the characteristics of the affinity of VK1 to the functional groups significantly differed among the groups. The VK1 release from the modified silica gels was initially rapid, slowed markedly after 1 h, and continued for more than 24 h. The amount of VK1 released from the modified surface silica gels by C7, C18 or F3 increased with increasing density of the surface modification group. The mean drug release moment (MDT) decreased with an increase in surface-modified group density.

Development of fibrin derivatives for controlled release of heparin-binding growth factors

The goal of this work was to develop a growth factor delivery system for use in wound healing that would provide localized release of heparin-binding growth factors in a biomimetic manner, such that release occurs primarily in response to cell-associated enzymatic activity during healing. A key element of the drug delivery system was a bi-domain peptide with an N-terminal transglutaminase substrate and a C-terminal heparin-binding domain, based on antithrombin III. The bi-domain peptide was covalently cross-linked to fibrin matrices during coagulation by the transglutaminase activity of factor XIIIa and served to immobilize heparin electrostatically to the matrix, which in turn immobilized the heparin-binding growth factor and slowed its passive release from the matrix. Basic fibroblast growth factor (bFGF) was considered as an example of a heparin-binding growth factor, and cell culture experimentation was performed in the context of peripheral nerve regeneration. A mathematical model was developed to determine the conditions where passive release of bFGF would be slow, such that active release could dominate. These conditions were tested in an assay of neurite extension from dorsal root ganglia to determine the ability of the delivery system to release bioactive growth factor in response to cell-mediated processes. The results demonstrated that bFGF, immobilized within fibrin containing a 500-fold molar excess of immobilized heparin relative to bFGF, enhanced neurite extension by up to about 100% relative to unmodified fibrin. A variety of control experiments demonstrate that all components of the release system are necessary and that the bi-domain peptide must be covalently bound to the fibrin matrix. The results thus suggest that these matrices could serve as therapeutic materials to enhance peripheral nerve regeneration through nerve guide tubes and may have more general usefulness in tissue engineering.

Bovine protein C inhibitor has a unique reactive site and can transiently inhibit plasmin

Protein C inhibitor (PCI) regulates the anticoagulant protein C pathway by neutralizing activated protein C and thrombin-thrombomodulin complex in the human hemostatic system. In this study, we cloned a full-length bovine PCI cDNA encoding a putative 19-residue signal peptide and a 385-residue mature protein; this showed 70.6%, 70.6%, 57.5% and 59.6% amino acid sequence homology with the human, rhesus monkey, rat and mouse PCIs, respectively. Bovine PCI mRNA (2.1 kb in size) was expressed strongly in the liver, and moderately in the kidney and testis, but not in other tissues tested. Bovine PCI has a putative reactive site peptide bond, Lys-Ser, that is different from the reactive site sequence (Arg-Ser) of other species' PCI. We found that bovine PCI transiently inhibits bovine plasmin, but not human plasmin. Western blot analysis showed that the reactive site of bovine PCI is cleaved during the course of complex formation with bovine plasmin; degraded PCI is released from the complex gradually concomitant with the recovery of plasmin activity. These findings suggest that bovine PCI plays a role not only in the protein C pathway but also in the fibrinolytic activity of bovine hemostatic system.

Solution structure and dynamics of the plasminogen kringle 2-AMCHA complex: 3(1)-helix in homologous domains

The kringle 2 (K2) module of human plasminogen (Pgn) binds L-lysine and analogous zwitterionic compounds, such as the antifibronolytic agent trans-(aminomethyl)cyclohexanecarboxylic acid (AMCHA). Far-UV CD and NMR spectra reveal little conformational change in K2 upon ligand binding. However, retarded (1)H-(2)H isotope exchange kinetics induced by AMCHA indicate stabilization of the K2 conformation by the ligand. Assessment of secondary structure content from CD spectra yields approximately 26% beta-STRAND, approximately 13% beta-TURN, approximately 15% 3(1)-HELIX, and approximately 6% 3(10)-HELIX. The NMR solution conformation of the K2 domain complexed to AMCHA has been determined [heavy atom rmsd = 0.49 +/- 0.09A (BACKBONE) AND 1.02+/- 0.08 (ALL)]. The K2 molecule has overall dimensions of approximately 34.5A times approximately 33.4A times approximately 22.7A . Analogous with the polypeptide outline of homologous domains, K2 contains three short antiparallel beta-sheets (paired strands 15-16/20-21, 24-25/48-49, and 62-64/72-74) and four defined beta-turns (residues 6-9, 16-19, 53-56, AND 67-70). Consistent with the CD analysis, albeit novel in the context of kringle folding, the NMR structure reveals an unpaired beta-strand structured by residues 30-32, a turn of 3(10)-helix compromising residues 38-41, and a 3(1)-helix for residues 21-24 and 74-79. We also identify alignable 3(1)-helices in previously reported homologous kringle structures. Rather high order parameter S(2) values (<S(2)>= approximately 0.85 +/- 0.04) characterize the K2 backbone dynamics. The lowest flexibility is observed for the two inner loop segments of residues 51-63 AND 63-75 (<S(2)>= approximately 0.86-0.87 +/- 0.03). Overhauser connectivities reveal close hydrophobic contacts of the ligand ring with side chains of Tyr(36), Trp(62), Phe(64), Trp(72), AND Leu(74). In most K2 structures, the N atom of AMCHA places itself approximately 3.9 and 4.4A from the anionic groups of Glu(57) and Asp(55), respectively, while its carboxylate group, H-bonded to the Tyr(36) side chain OH(eta), ion-pairs the Arg(71) guanidinium group. Consistent with the preference of K2 for binding 5-aminopentanoic acid over 6-aminohexanoic acid, the positions of the ionic centers within the K2 binding site approach each other approximately 1A closer relative to what is observed in lysine binding sites of homologous Pgn modules.

Topical trans-4-aminomethylcyclohexanecarboxylic acid prevents ultraviolet radiation-induced pigmentation

We have studied the effect of a plasmin inhibitor, trans-4-aminomethylcyclohexanecarboxylic acid (trans-AMCHA), on skin pigmentation induced by ultraviolet (UV) exposure in Weiser-Maples guinea pigs. When guinea pigs are exposed to UV radiation (840 mJ cm-2), skin pigmentation is clearly observed from seven days after exposure and continued to increase to 29 days. Post-exposure applications of 2 and 3% solutions of trans-AMCHA to the exposed regions prevent or inhibit the pigmentation process. When the skin is removed and stained by the Fontana-Masson method, melanin content in the basal layer of UV-exposed epidermis is significantly reduced in the regions to which 2 and 3% trans-AMCHA solutions have been applied, compared with the vehicle control. As plasmin is known to contribute to the release of arachidonic acid (AA) and the production of prostaglandins (PGs), we have examined the effects of trans-AMCHA on AA-induced pigmentation in guinea pig skin. Topical application of trans-AMCHA causes a dose-dependent decrease in AA-induced pigmentation. These results suggest that trans-AMCHA reduces melanocyte tyrosinase activity by suppressing the production of PGs, UV-induced melanogens, through the suppression of the UV-induced increase in epidermal plasmin activity.

Effect of phenylglyoxal-modified alpha2-antiplasmin on urokinase-induced fibrinolysis

One of the functions of activated blood clotting factor XIII (FXIIIa) is the crosslinking of alpha2-antiplasmin (alpha2AP) to fibrin. This process results in localization and concentration of alpha2AP throughout fibrin, thereby making fibrin more resistant to digestion by plasmin. We reasoned that competition by chemically-modified inactive alpha2AP (mod alpha2AP) with native alpha2AP would diminish the resistance of fibrin to digestion by plasmin. Mod alpha2AP was prepared by treating native alpha2AP with an Arg-specific reagent, phenylglyoxal. An average of four of the total nineteen Arg residues in alpha2AP reacted with phenylglyoxal and resulted in complete loss of plasmin inhibitory activity; however, mod alpha2AP competed effectively with native alpha2AP for becoming crosslinked to fibrin by FXIIIa catalysis. In the presence of mod alpha2AP, urokinase (UK)-induced plasma clot lysis time shortened significantly. Mod alpha2AP enhanced UK-induced clot lysis in a whole blood system as shown by the similarities of rates of clot lysis for a mixture of 20 U/ml UK and 1.5 microM mod alpha2AP versus that induced by 100 U/ml UK without mod alpha2AP. Less fibrinogenolysis occurred in whole blood when mod alpha2AP was present since much lower UK concentrations were needed to achieve the same level of fibrinolysis than when only native alpha2AP was present. Our results indicate that mod alpha2AP enhances UK-induced fibrinolysis by competitive inhibition of factor XIIIa-mediated incorporation of native alpha2AP into fibrin.

Annexin II tetramer inhibits plasmin-dependent fibrinolysis

In this paper, we have characterized the regulation of plasmin activity by annexin II tetramer (AIIt). Plasmin activity was measured by a fibrin lysis assay in which a fibrin polymer was produced from purified components and the extent of polymer lysis was determined by following changes in turbidity. Extrinsic lysis of the fibrin polymer, initiated by addition of tissue plasminogen activator (t-PA), was totally blocked if AIIt was present during fibrin polymer formation. Furthermore, fibrin polymer formed in the presence of AIIt was resistant to extrinsic lysis initiated by addition of plasmin. AIIt bound to fibrin polymer under conditions in which polymer lysis was inhibited. Plasmin-dependent extrinsic lysis of the fibrin polymer was also blocked if AIIt was present in the incubation medium, and under these conditions the amidolytic activity of plasmin, measured with an artificial substrate, was inhibited about 5-fold. In contrast, in the absence of fibrin, and at an AIIt/plasmin molar ratio of 526, the amidolytic activity of plasmin was inhibited by only 22.3% +/- 7.4% (mean +/- SD, n = 5) by AIIt. Plasmin-dependent fibrinolysis was only slightly inhibited if fibrin polymer was formed in the presence of annexins I, II, V, or VI. These results identify AIIt as an in vitro regulator of plasmin activity.

Crystal structures of the recombinant kringle 1 domain of human plasminogen in complexes with the ligands epsilon-aminocaproic acid and trans-4-(aminomethyl)cyclohexane-1-carboxylic Acid

The X-ray crystal structures of the complexes of the recombinant kringle 1 domain of human plasminogen (Klpg) with the ligands epsilon-aminocaproic acid (EACA) and trans-4-(aminomethyl)cyclohexane-1-carboxylic acid (AMCHA), which are representative of a class of in vivo antifibrinolytic agents, have been determined at 2.1 angstroms resolution. Each Klpg/ligand unit cell contained a dimer of the complexes, and some small differences were noted in the kringle/ligand interatomic distances within the monomeric components of the dimers. The structures obtained allowed predictions to be made of the amino acid residues of Klpg that are likely important to ligand binding. In the crystal structure, the anionic center of Klpg responsible for coordinating the amino group of the ligands is composed of both Asp54 and Asp56, and the cationic center that stabilizes binding of the carboxylate moiety of the ligands is Arg70, with a possible contribution from Arg34. A hydrogen bond between the carboxylate of the ligand to the hydroxyl group of Tyr63 also appears to contribute to the kringle/ligand binding energies. The methylene groups of the ligand are stablized in the binding pocket by van der Waals contacts with side-chain atoms of Trp61 and Tyr71. These conclusions are in general agreement with site-directed mutagenesis results that implicate many of the same amino acid residues in the binding process, thus showing that the crystal and solution structures are in basic accord with each other. Further comparisons of the X-ray crystal structures of the Klpg/ligand complexes with each other and with apo-Klpg show that while small differences in Klpg side-chain geometries may exist in the three structures, the binding pocket can be considered to be preformed in the apokringle and not substantially altered by the nature of the omega-amino acid ligand that is inserted into the site. From the similar geometries of the binding of EACA and AMCHA, it appears that the kon is an important component to the tighter binding of AMCHA to Klpg, as compared to EACA. Ordered solvation effects of the bound AMCHA may contribute to its longer lifetime on Klpg, thereby retarding koff, both effects thus accounting for the higher binding energy of AMCHA as compared to EACA.

Influence of dipeptide derivatives of S-substituted cysteines on the time of fibrinolysis

Amino acids containing sulphur, dipeptide derivatives of methionine and S-substituted derivatives of cysteine are potent antifibrinolytic agents. The structural moiety of the substances responsible for the effect on the clot formation is not known. Present study was undertaken in order to evaluate the effect of some analogues of dipeptides containing S-substituted derivatives of cysteine with the formula A-Cys(S-X)-Y (where A-amino acid, X-benzyl, butyl, hexyl, nonyl and Y-OH or OMe) on clot dissolution under the antifibrinolytic test conditions. It has been found that dipeptide derivatives of S-substituted cysteine (except benzyl derivative) at low concentration evoke antifibrynolytic activity, while at high concentration they prevent clot formation. The results suggest that antifibrinolytic activity of tested compounds at low concentration may be due to the formation of antifibrinolitycally active conformation, while high concentration overcome the effect.

Outcome of disseminated intravascular coagulation in relation to the score when treatment was begun. Mie DIC Study Group

We examined 395 patients with disseminated intravascular coagulation (DIC) divided into two groups: non-leukemic and leukemic. In 58% of the patients as a whole, treatment of DIC resulted in complete or partial remission, while exacerbation and death occurred in 31%. The efficacy of DIC treatment in the non-leukemic group was less than that in the leukemic group, indicating that the outcome of DIC depended, in part, on the underlying disease. We examined hemostatic indicators in relation to DIC score: prothrombin time (PT) ratio, FDP, platelet count, and fibrinogen levels were found to be important indicators for the diagnosis of DIC, but not for Pre-DIC. Plasma levels of fibrin-D-dimer, thrombin-antithrombin complex (TAT), and plasmin-plasmin inhibitor complex (PPIC) were significantly increased in pre-DIC. The efficacy of treatment in relation to the DIC score when the treatment was begun showed that greater efficacy was achieved in pre-DIC than in DIC patients. The outcome was poorer with increasing DIC score, suggesting that early diagnosis and early treatment are important. On examining the relationship between outcome and hemostatic indicators, we found that the PT ratio and the levels of antithrombin, plasminogen, PPIC, the PPIC/TAT ratio, and thrombomodulin were related to outcome, suggesting that very high consumption of blood coagulation factors, liver dysfunction, hypofibrinolysis, or organ failure caused a poor outcome. Although the outcome in DIC patients may not depend substantially on plasma levels of TAT and fibrin-D-dimer, we can use these indicators to treat DIC patients at an early stage.

[Fibrin fragment beta 15-118. Inhibitory and complex-forming properties]

Peptide beta 15-118 isolated from desAABB-NDSK preserves fibrin polymerization active site "B", inhibits polymerization process at 12 degrees C, eliminates the inhibitory properties of plasmin D-D-fragment but does not influence inhibitory properties of a D-monomer fragment. Complex formation between peptide beta 15-118 and both D- and D-D fragments was electrophoretically demonstrated. Peptide beta 15-118 forms more stable complex with the D-D fragment which does not dissociate in the medium of polymerizing fibrin as the complex of the peptide with monomer D fragment does. Gel filtration data confirm dimerization of D-monomer fragments after their complexing with beta 15-118. This phenomenon suggests that mutual affinity of D-domains in fibrin increases after loci interactions of the "B"-"b" type.

Dissociation of alpha 2-plasmin-inhibitor-plasmin complex and regeneration of plasmin activity by SDS treatment

In order to understand the mechanism for the complex between alpha 2-plasmin-inhibitor (alpha 2-PI) and plasmin to express its specific activity on fibrin autography after SDS-PAGE, we analyzed the effects of SDS on alpha 2-PI molecule and alpha 2-PI-plasmin complex. Treatment of alpha 2-PI by SDS at the concentrations of 0.01% and 0.1% abolished the activity of alpha 2-PI to form a stoichiometric complex with plasmin, whereas it did not interfere with plasmin's activity. More interestingly, in the case of 0.01% SDS, alpha 2-PI was further cleaved to a smaller molecule. Treatment of previously formed alpha 2-PI-plasmin complex by SDS at the concentrations of both 0.01% and 0.1% dissociated the complex and expressed specific amidolytic activity against tripeptide substrate (S-2251), which activity was totally quenched by aprotinin. When alpha 2-PI-plasmin complex was treated by higher concentration of SDS for 12 hours, dissociated free plasmin's band could be observed on SDS-PAGE analysis. It is likely, therefore, that the exposure of alpha 2-PI-plasmin complex to SDS during the procedure of SDS-PAGE dissociates the complex and expresses its specific proteolytic activity in fibrin autography. These features of alpha 2-PI and its complex with plasmin are similar to those of plasminogen activator inhibitor type 1 (PAI-1) and its complex with plasminogen activators (PAs), thus they may represent some common features of the SERPINS.

The hemodynamic and fibrinolytic response to low dose epinephrine and phenylephrine infusions during total hip replacement under epidural anesthesia

Lower rates of deep vein thrombosis have been noted following total hip replacement under epidural anesthesia in patients receiving exogenous epinephrine throughout surgery. To determine whether this is due to enhanced fibrinolysis or to circulatory effects of epinephrine, 30 patients scheduled for primary total hip replacement under epidural anesthesia were randomly assigned to receive intravenous infusions of either low dose epinephrine or phenylephrine intraoperatively. All patients received lumbar epidural anesthesia with induced hypotension and were monitored with radial artery and pulmonary artery catheters. Patients receiving low dose epinephrine infusion had maintenance of heart rate and cardiac index whereas both heart rate and cardiac index declined significantly throughout surgery in patients receiving phenylephrine (p = 0.0001 and p = 0.0001, respectively). Tissue plasminogen activator (t-PA) activity increased significantly during surgery (p < 0.005) and declined below baseline postoperatively (p < 0.005) in both groups. Low dose epinephrine was not associated with any additional augmentation of fibrinolytic activity perioperatively. There were no significant differences in changes in D-Dimer, t-PA antigen, alpha 2-plasmin inhibitor-plasmin complexes or thrombin-antithrombin III complexes perioperatively between groups receiving low dose epinephrine or phenylephrine. The reduction in deep vein thrombosis rate with low dose epinephrine is more likely mediated by a circulatory mechanism than by augmentation of fibrinolysis.