A New Concept of Action of Hemostatic Proteases on Inflammation, Neurotoxicity, and Tissue Regeneration.

Key hemostatic serine proteases such as thrombin and activated protein C (APC) are signaling molecules controlling blood coagulation and inflammation, tissue regeneration, neurodegeneration, and some other processes. By interacting with protease-activated receptors (PARs), these enzymes cleave a receptor exodomain and liberate new amino acid sequence known as a tethered ligand, which then activates the initial receptor and induces multiple signaling pathways and cell responses. Among four PAR family members, APC and thrombin mainly act via PAR1, and they trigger divergent effects. APC is an anticoagulant with antiinflammatory and cytoprotective activity, whereas thrombin is a protease with procoagulant and proinflammatory effects. Hallmark features of APC-induced effects result from acting via different pathways: limited proteolysis of PAR1 localized in membrane caveolae with coreceptor (endothelial protein C receptor) as well as its targeted proteolytic action at a receptor exodomain site differing from the canonical thrombin cleavage site. Hence, a new noncanonical tethered PAR1 agonist peptide (PAR1-AP) is formed, whose effects are poorly investigated in inflammation, tissue regeneration, and neurotoxicity. In this review, a concept about a role of biased agonism in effects exerted by APC and PAR1-AP via PAR1 on cells involved in inflammation and related processes is developed. New evidence showing a role for a biased agonism in activating PAR1 both by APC and PAR1-AP as well as induction of antiinflammatory and cytoprotective cellular responses in experimental inflammation, wound healing, and excitotoxicity is presented. It seems that synthetic PAR1 peptide-agonists may compete with APC in controlling some inflammatory and neurodegenerative diseases.

Effects of activated protein C on the size of modeled ischemic focus and morphometric parameters of neurons and neuroglia in its perifocal zone.

The effects of activated protein C (APC) on the quantitative parameters of neurons and neuroglia in the perifocal zone of infarction induced in the left hemispheric cortex were studied in two groups of rats. Group 1 animals served as control (control infarction). Group 2 rats were injected with APC (50 µg/kg) in the right lateral cerebral ventricle 3 h after infarction was induced, and after 72 h the infarction size was evaluated and the neurons and neuroglia in the perifocal zone were counted. APC reduced the infarction size 2.5 times in comparison with the control and reduced by 16% the neuronal death in the perifocal zone layer V, causing no appreciable changes in layer III, and did not change the size of neuronal bodies but increased (by 11%) the size of neuronal nuclei in layer III. The protein maintained the sharply increased count of gliocytes in the perifocal zone of infarction and promoted their growth. Hence, APC protected the neurons from death in the ischemic focus by increasing the gliocyte count and stimulating the compensatory reparative processes.

[Peptide-agonist of protease-activated receptor (PAR 1), similar to activated protein C, promotes proliferation in keratinocytes and wound healing of epithelial layer].

Activated protein C (APC) is serine protease hemostasis, independent of its anticoagulant activity, exhibits anti-inflammatory and anti-apoptotic properties that determine the possibility of the protective effects of APC in different diseases, including sepsis and chronic wound healing. APC, binding of endothelial protein C receptor (EPCR) and specifically cleaving PAR1 receptor and releasing peptide agonist PAR1 stabilizes not only endothelial cells, but also many others, including epidermal keratinocytes of the skin. We develop the hypothesis that the cytoprotective effect of APC on the cells, involved in wound healing, seem to imitate peptide - analogous of PAR1 "tethered ligand" that activate PAR1. In our work, we synthesized a peptide (AP9) - analogue of PAR1 tethered ligand, released by APC, and firstly showed that peptide AP9 (0.1-10 мM), like to APC (0.01-100 nM), stimulates the proliferative activity of human primary keratinocytes. Using a model of the formation of epithelial wounds in vitro we found that peptide AP9, as well as protease APC, accelerates wound healing. Using specific antibodies to the receptor PAR1 and EPCR was studied the receptor mechanism of AP9 action in wound healing compared with the action of APС. The necessity of both receptors - PAR1 and EPСR, for proliferative activity of agonists was revealed. Identified in our work imitation by peptide AP9 - PAR1 ligand, APC acts on keratinocytes suggests the possibility of using a peptide AP9 to stimulate tissue repair.

Effect of enteropeptidase on survival of cultured hippocampal neurons under conditions of glutamate toxicity.

The effects of full-size bovine enteropeptidase (BEK) and of human recombinant light chain enteropeptidase (L-HEP) on survival of cultured hippocampal neurons were studied under conditions of glutamate excitotoxicity. Low concentrations of L-HEP or BEK (0.1-1 and 0.1-0.5 nM, respectively) protected hippocampal neurons against the death caused by 100 µM glutamate. Using the PAR1 (proteinase-activated receptor) antagonist SCH 79797, we revealed a PAR1-dependent mechanism of neuroprotective action of low concentrations of enteropeptidase. The protective effect of full-size enteropeptidase was not observed at the concentrations of 1 and 10 nM; moreover, 10 nM of BEK caused death of 88.9% of the neurons, which significantly exceeded the cell death caused by glutamate (31.9%). Under conditions of glutamate cytotoxicity the survival of neurons was 26.8% higher even in the presence of 10 nM of L-HEP than in the presence of 10 nM BEK. Pretreatment of cells with 10 nM of either form of enteropeptidase abolished the protective effect of 10 nM thrombin under glutamate cytotoxicity. High concentrations of BEK and L-HEP caused the death of neurons mainly through necrosis.

[Biodegradable polymer microparticles with entraped herbal extracts: preparation with supercritical carbon dioxide and use for tissue repair].

Biodegradable microparticles based on poly-D,L-lactide with entrapped mixture of herbal water-soluble extracts of Plantago major and Calendula officinalis were prepared. For preparation of these microparticles the previously developed method based on the usage of supercritical carbon dioxide (SC-CO2) was proposed. Microparticles were obtained by two techniques: 1) by preparing porous polymer monolith containing entrapped mixture of herbal extracts, which was then reduced to fine microparticles (ca. 0.1 mm) by dry ice grinding (called here as "monolithisation technique") and 2) by spraying of this polymer/extracts mixture through a jet (spray technique). In vitro release kinetic profile of herbal extract mixture was found to depend on the microparticle preparation technique, on the microparticle structure as well as on the initial ratio polymer/extracts (w/w). The microparticles were used for gastric ulcer treatment in a rat model. The extracts released from microparticles were found to accelerate tissue repair.

Activated protein C via PAR1 receptor regulates survival of neurons under conditions of glutamate excitotoxicity.

The effect of an anticoagulant and cytoprotector blood serine proteinase--activated protein C (APC)--on survival of cultured hippocampal and cortical neurons under conditions of glutamate-induced excitotoxicity has been studied. Low concentrations of APC (0.01-10 nM) did not cause neuron death, but in the narrow range of low concentrations APC twofold and stronger decreased cell death caused by glutamate toxicity. High concentrations of APC (>50 nM) induced the death of hippocampal neurons similarly to the toxic action of glutamate. The neuroprotective effect of APC on the neurons was mediated by type 1 proteinase-activated receptor (PAR1), because the inactivation of the enzyme with phenylmethylsulfonyl fluoride or PAR1 blockade by a PAR1 peptide antagonist ((Tyr1)-TRAP-7) prevented the protective effect of APC. Moreover, APC inhibited the proapoptotic effect of 10 nM thrombin on the neurons. Geldanamycin, a specific inhibitor of heat shock protein Hsp90, completely abolished the antiapoptotic effect of 0.1 nM APC on glutamate-induced cytotoxicity in the hippocampal neurons. Thus, APC at low concentrations, activating PAR1, prevents the death of hippocampal and cortical neurons under conditions of glutamate excitotoxicity.

[Various effects of serine proteinases, activated protein C and duodenase, on mast cells].

Some serine proteinases of haemostasis can regulate blood clotting and inflammation acting at proteinase-activated receptors (PARs). It is known that the anticoagulant proteinase, activated protein C (APC), exhibits anti-inflammatory effects on endothelial cells and macrophages and this involves endothelial protein C receptor--EPCR and proteinase-activated receptor--PAR1. We have studied the effect of wide range of APC concentrations on functional activity of rat peritoneal mast cells (PMC), which secrete the proinflammatory mediators, under normal conditions and during acute inflammation in rats. APC was able to reduce beta-hexosaminidase release from PMC. APC at very low concentrations (0.2-2 nM) modulated the mediator secretion from PMC under normal conditions and also during acute inflammation in rats. APC abolished the proinflammatory activity of duodenase (80 nM), the proteinase from gastrointestinal tract and mast cells. Mast cells pretreated with cathepsin G (PAR1 antagonist) or duodenase abolished protective antiinflammatory effect of low concentrations of APC on PMC degranulation. Our data indicated that blockade of the mast cells proinflammatory mediator secretion by APC involved PAR1 activation.

[Duodenase activates rat peritoneal mast cells via protease-activated receptors of type 1].

It was found that duodenase, a serine protease from the bovine duodenum, activates rat peritoneal mast cells (PMC) in vitro presumably via protease-activated receptors (PARs). Like thrombin (a serine protease from the blood coagulation system) and the PAR1 agonist peptide (PAR1-AP), duodenase was shown to accelerate the secretion of beta-hexosaminidase (a marker of cell degranulation) by PMC in a dose-dependent manner. The blockage of the proteolytic activity of duodenase toward the substrate Tos-Gly-Pro-Lys-pNA by the soybean Bauman-Birk protease inhibitor substantially reduced (by 40%) the ability of duodenase to stimulate the secretory activity of PMC. Pretreatment of PMC with duodenase decreased the beta-hexosaminidase secretion induced by thrombin and PAR1-AP by 35 and 41.7%, respectively, and abolished the antiinflammatory effect of activated protein C. At the same time, pretreatment of PMC with duodenase did not affect the secretion of beta-hexosaminidase induced by compound 48/80, a nonspecific degranulator of mast cells. Duodenase, unlike PAR1-AP (30-100 microM), in a broad concentration range (10-100 nM) did not induce aggregation of human platelets, but suppressed the platelet aggregation elicited by PAR1-AP.

[The role of PAR1 in the protective action of activated protein C in the non-immune mast cell activation].

Activated protein C (APC) regulates the functional activity of mast cells by reducing release of beta-hexosaminidase, the marker of mast cell degranulation. APC could modulate the cell secretion of both: the rest mast cells and the activated cells with degranulators, such as proteinase-activated receptor agonist peptide (PAR1-AP) and compound 48/80. PAR1 desensitization with thrombin abolishes the effect of low APC concentration (< or =1,5 nM) on beta-hexosaminidase release by mast cells. APC, inactivated with phenilmethylsulfonilftoride (PMSF), did non mimic the enzyme action on mast cells. The duodenal proteinase, duodenase, activates the peritoneal mast cell via PAR1. APC abolishes the proinflammatory action of duodenase and PAR1-AP by means of reducing release of mast cell mediators. Pretreatment of mast cell with L-NAME abolished these APC effects. Thus, APC-induced decrease of mediator release could be attributed to NO generation by mast cells. Our data indicate that PAR1 takes part in the mechanism of regulatory anti-inflammatory APC action.

[Entrapment of herbal extracts in biodegradable microcapsules].

The microcapsules with entrapped herbal water-soluble extracts Plantago major and Calendula officinalis L. (HE) were prepared by LbL-adsorption of carrageenan and modificated chitosan onto CaCO3 microparticles with their subsequent dissolving after the treatment of EDTA. Entrapment of HE was performed by adsorption and co-precipitation techniques. The co-precipitation provided better entrapment of HE compared to adsorption. In vitro release kinetics in an artificial gastric juice (AGJ) was studied. The HE release was shown to accelerate gastric ulcer treatment in a rat model.

Effect of PAR1 agonist on acetylcholine secretion in a newly formed neuromuscular synapse in mice.

Peptide agonist of PARI in a concentration of 10 microM significantly facilitated neuromuscular transmission in newly formed synapses in mice. The absence of changes in the amplitude of miniature end-plate potentials attests to presynaptic mechanism of the effect of PAR1 agonist. The effect of the peptide was blocked by protein kinase A inhibitor H89 (1 microM). Blockade of inositol-1,4,5-trisphosphate receptors with 2-amino-ethoxydiphenylborate (30 microM) did not prevent the effects of PARI agonist. Inhibition of protein kinase C with bisindolylmaleimide (1 microM) facilitated neuromuscular transmission in newly formed synapses. Protein kinase C inhibition was associated with reversal of the object of PARI agonist: transmission inhibition instead of facilitation.

Proteinase-activated receptor agonists stimulate the increase in intracellular Ca2+ in cardiomyocytes and proliferation of cardiac fibroblasts from chick embryos.

We studied activation of cultured cardiomyocytes and cardiac fibroblasts from chick embryos induced by agonists of PAR1 (thrombin and PAR1 peptide agonist) and PAR2 (trypsin, factor Xa, and peptide SLIGRL) by analyzing changes in intracellular Ca2+ concentration ([Ca2+]i) and cardiac fibroblast proliferation. Exposure of cardiomyocytes with thrombin induced immediate permanent dose-dependent increase in [Ca2+]i. Ca2+ response decreased in a calcium-free medium. Peptide agonists of PAR1 and PAR2 also stimulated the increase in [Ca2+]i in cardiomyocytes. Thrombin induced a short-term increase in [Ca2+]i in cardiac fibroblasts and potentiated cell proliferation. PAR2 agonists trypsin and peptide SLIGRL stimulated proliferation of cardiac fibroblasts. Our results indicate that cardiomyocytes and cardiac fibroblasts from chick embryos have at least two types of PAR (types 1 and 2).

Modulation of hippocampal neuron survival by thrombin and factor Xa.

Effects of thrombin, factor Xa (FXa), and protease-activated receptor 1 and 2 agonist peptides (PAR1-AP and PAR2-AP) on survival and intracellular Ca2+ homeostasis in hippocampal neuron cultures treated with cytotoxic doses of glutamate were investigated. It is shown that at low concentrations (

[Biodegradable microparticles with immobilized peptide for wound healing].

Thrombin receptor agonist peptide (TRAP-6) may effectively replace thrombin for stimulation of damaged tissue regeneration. (Thrombin employment is limited by its high cost, instability and proinflammatory effect at high concentrations.) Immobilization of TRAP-6 into a poly(D,L)-lactide-co-glycolide (PLGA)-based matrix can protect peptides from a destruction by peptidases located in a wound area, and can also provide controlled release of the peptide. PLGA microparticles with immobilized peptide were produced by double emulsion/evaporation technique. An observation of microparticle morphology by scanning electron microscopy highlighted that peptide immobilization resulted in the increase of the microparticle porosity. TRAP-6 release kinetics was characterized by burst increase of TRAP-6 concentration in HEPES buffer solution (pH 7.5) for first 2 hours from the beginning of the experiment, and TRAP-6 complete release occurred for 20 hours. An investigation of TRAP-6 destruction by scanning electron microscopy revealed that the increase of microparticle size and surface porosity were observed already after 1 day of incubation in the buffer solution, and an aggregation of destructing microparticles was obvious by the 7th day of the incubation. Thus, peptide immobilization into PLGA microparticles can allow to develop a novel controlled release drug delivery system.

Thrombin receptor agonist Peptide immobilized in microspheres stimulates reparative processes in rats with gastric ulcer.

The effect of synthetic thrombin receptor (PAR1) agonist peptide encapsulated in microspheres made of lactic and glycolic acid copolymer on tissue reparation was studied in rats with acetate-induced ulcer. PAR1 agonist peptide was immobilized in biodegraded lactic and glycolic acid microspheres by double emulgation, the kinetics of peptide release was analyzed, and the dynamics of ulcer healing was studied in experimental (administration of microspheres with the peptide into the stomach) and two control groups (administration of saline or spheres without peptide). Thrombin receptor agonist peptide gradually released from lactic and glycolic acid microspheres into the stomach shortened the inflammation phase and shifted the proliferation phase to the earlier period, thus accelerating healing of experimental ulcers in rats.

Effect of activated protein C on secretory activity of rat peritoneal mast cells.

Generation of thrombin and activated protein C in the inflammatory focus was demonstrated in rats with experimental acute peritonitis. The contents of thrombin and activated protein C peaked by the 30th and 120th minute of inflammation, respectively. In vitro study showed a decrease in spontaneous and compound 48/80-induced secretion of beta-hexosaminidase by peritoneal mast cells under the influence of activated protein C in low concentrations. The antiinflammatory effect of protein C in the focus of acute peritonitis is probably realized through NO release from peritoneal mast cells. This conclusion is derived from the data that L-NAME abolishes the protective effect of activated protein C.

Proteinase-activated type 1 receptors are involved in the mechanism of protection of rat hippocampal neurons from glutamate toxicity.

Survival of cultured rat hippocampal neurons was estimated 4, 24, and 48 h after 15-min exposure to the toxic effect of glutamate under conditions of pre- or coincubation with 10 nM thrombin. Thrombin inhibited glutamate-induced apoptosis in neurons 24 and 48 h after treatment, but had no effect on necrosis. Selective peptide agonist of proteinase-activated type 1 receptors simulated, but receptor antagonist suppressed the neuroprotective effect of thrombin. Our results suggest that peptide antagonist of type 1 receptors play a role in the mechanisms of neuronal protection from glutamate toxicity.

Study of neurotrophic activity of thrombin on the model of regenerating mouse nerve.

Experiments demonstrated a dose-dependent facilitating effect of thrombin and peptide thrombin receptor agonist PAR1 (TRAP6) on regeneration of mouse peripheral nerve after its crushing. The maximum neurotrophic effect was observed at low concentrations of thrombin (10 nM) and TRAP6 (10 microM).

[Effect of thrombin on survival of hippocampal neurons].

The effect of thrombin on the rat hippocampal neurons death in model of neurotoxicity induced by hemoglobin or glutamate, was studied. Thrombin (10 nM) was shown to inhibit 100-mkM glutamate--or 10-mkM hemoglobin-induced apoptosis of the rat hippocampal neurons. With the aid of PAR1 (protease-activated receptor1) agonist peptide and PAR1 antagonist, the PAR1 was found to be necessary for protective action of thrombin in hippocampal neurons in models of neurotoxicity induced by hemoglobin or glutamate. Because the prolonged elevation [Ca2+] ib neurons is a critical part of neurodestructive processes in CNS, the effect of thrombin on Ca2+-homeostatis of neurons after its injury by the inducer of neuronal apoptosis: a synthetic agonist of the NMDA receptors N-methyl-D-aspartate (NMDA), was studied. We hypothesized that thrombin via receptors PAR may prove to be neuroprotective for the hippocampus. Thrombin was shown to stimulate via PAR1 a transient increase in [Ca2+] in neurons in a concentration-dependent manner. Thrombin (1 nM) decreased the [Ca2+] signal induced by activation of the NMDA-subtype of glutamate receptors. This thrombin effect may be one of the reasons of the protective action of thrombin in hippocampal neurons.

Role of platelets and serine proteinases in coupling of blood coagulation and inflammation.

In addition to having a key role in thrombogenesis, platelets are actively involved in acute and chronic inflammation: they induce the release of proinflammatory mediators, expose adhesion molecules, and recruit leukocytes. The inflammation-induced expression of tissue factor by endothelium and monocytes leads to production of hemostatic serine proteinases, which can regulate both blood coagulation and the inflammatory response of the body. Serine proteinases activate blood and connective tissue cells and regulate blood coagulation, inflammation, tissue repair, atherogenesis, etc. This review considers new functions of platelets in thrombogenesis and inflammation, stabilization of platelet-platelet and platelet-leukocyte aggregations, receptor functions of tissue factor, proinflammatory properties of hemostatic serine proteinases mediated by proteinase-activated receptors (PAR), activation of transcriptional factors (NFkappaB and other), and antiinflammatory and cytoprotective properties of the anticoagulant proteinase (activated protein C) mediated through binding of the endothelial protein C receptor (EPCR) and cleavage of PAR1.