Novel Thrombolytic Drug Based on Thrombin Cleavable Microplasminogen Coupled to a Single-Chain Antibody Specific for Activated GPIIb/IIIa.

BACKGROUND: Thrombolytic therapy for acute thrombosis is limited by life-threatening side effects such as major bleeding and neurotoxicity. New treatment options with enhanced fibrinolytic potential are therefore required. Here, we report the development of a new thrombolytic molecule that exploits key features of thrombosis. We designed a recombinant microplasminogen modified to be activated by the prothrombotic serine-protease thrombin (HtPlg), fused to an activation-specific anti-glycoprotein IIb/IIIa single-chain antibody (SCE5), thereby hijacking the coagulation system to initiate thrombolysis. METHODS AND RESULTS: The resulting fusion protein named SCE5-HtPlg shows in vitro targeting towards the highly abundant activated form of the fibrinogen receptor glycoprotein IIb/IIIa expressed on activated human platelets. Following thrombin formation, SCE5-HtPlg is activated to contain active microplasmin. We evaluate the effectiveness of our targeted thrombolytic construct in two models of thromboembolic disease. Administration of SCE5-HtPlg (4 µg/g body weight) resulted in effective thrombolysis 20 minutes after injection in a ferric chloride-induced model of mesenteric thrombosis (48±3% versus 92±5% for saline control, P<0.01) and also reduced emboli formation in a model of pulmonary embolism (P<0.01 versus saline). Furthermore, at these effective therapeutic doses, the SCE5-HtPlg did not prolong bleeding time compared with saline (P=0.99). CONCLUSIONS: Our novel fusion molecule is a potent and effective treatment for thrombosis that enables in vivo thrombolysis without bleeding time prolongation. The activation of this construct by thrombin generated within the clot itself rather than by a plasminogen activator, which needs to be delivered systemically, provides a novel targeted approach to improve thrombolysis.

Multiparity upregulates placental plasminogen and urokinase-type plasminogen activator.

PROBLEM: Multiparity increased the number of trophoblast cells in decidua of both low and high fetal loss mouse models. However, they differ in fetal survival rate and maternal thymocyte subpopulations, suggesting that trophoblast invasiveness is not equivalent. Our aim was to explore the involved mechanism. METHOD OF STUDY: We studied placentae from primiparous and multiparous females of low and high fetal loss models. We investigated invasiveness in vitro, expression of plasminogen, and its activators: tissue type (tPA)-urokinase type (uPA), and activity and expression of matrix metalloproteinases (MMP)-2 and MMP-9. RESULTS: Placental invasiveness is upregulated by multiparity, but lesser in the high fetal loss model. Multiparous animals showed elevated expression of plasminogen and uPA. However, the high fetal loss combination showed higher expression of a short and less active fragment of uPA (LMW-uPA). MMP-2, MMP-9, and tPA were unaffected. CONCLUSION: uPA would participate in the increased multiparity-associated placental invasiveness.

Procoagulant and fibrinolytic activity after polytrauma in rat.

The purpose of this study was to determine whether trauma-induced coagulopathy is due to changes in 1) thrombin activity, 2) plasmin activity, and/or 3) factors that stimulate or inhibit thrombin or plasmin. Sprague-Dawley rats were anesthetized with 1-2% isoflurane/100% oxygen, and their left femoral artery and vein were cannulated. Polytrauma included right femur fracture, and damage to the small intestines, the left and medial liver lobes, and right leg skeletal muscle. Rats were then bled 40% of blood volume. Plasma samples were taken before trauma, and at 30, 60, 120, and 240 min. Polytrauma and hemorrhage led to a significant fall in prothrombin levels. However, circulating thrombin activity did not change significantly over time. Antithrombin III and α2 macroglobulin fell significantly by 2 h, then rose by 4 h. Soluble thrombomodulin was significantly elevated over the 4 h. Circulating plasmin activity, plasminogen, and D-dimers were elevated for the entire 4 h. Tissue plasminogen activator (tPA) was elevated at 30 min, then decreased below baseline levels after 1 h. Plasminogen activator inhibitor-1 was significantly elevated at 2-4 h. Neither tissue factor pathway inhibitor nor thrombin activatable fibrinolysis inhibitor changed significantly over time. The levels of prothrombin and plasminogen were 30-100 times higher than their respective active enzymes. Polytrauma and hemorrhage in rats lead to a fibrinolytic coagulopathy, as demonstrated by an elevation in plasmin activity, D-dimers, and tPA. These results are consistent with the observed clinical benefit of tranexamic acid in trauma patients.

High-level expression, purification, and enzymatic characterization of truncated human plasminogen (Lys531-Asn791) in the methylotrophic yeast Pichia pastoris.

BACKGROUND: Plasmin is a serine protease that plays a critical role in fibrinolysis, which is a process that prevents blood clots from growing and becoming problematic. Recombinant human microplasminogen (rhµPlg) is a derivative of plasmin that solely consists of the catalytic domain of human plasmin and lacks the five kringle domains found in the native protein. Developing an industrial production method that provides high yields of this protein with high purity, quality, and potency is critical for preclinical research. RESULTS: The human microplasminogen gene was cloned into the pPIC9K vector, and the recombinant plasmid was transformed into Pichia pastoris strain GS115. The concentration of plasmin reached 510.1 mg/L of culture medium. Under fermentation conditions, the yield of rhµPlg was 1.0 g/L. We purified rhµPlg to 96% purity by gel-filtration and cation-exchange chromatography. The specific activity of rhµPlg reached 23.6 U/mg. The K m of substrate hydrolysis by recombinant human microplasmin was comparable to that of human plasmin, while rhµPlm had higher k cat /Km values than plasmin. The high purity and activity of the rhµPlg obtained here will likely prove to be a valuable tool for studies of its application in thrombotic diseases and vitreoretinopathies. CONCLUSIONS: Reliable rhµPlg production (for use in therapeutic applications) is feasible using genetically modified P. pastoris as a host strain. The successful expression of rhµPlg in P. pastoris lays a solid foundation for its downstream application.

Estriol-induced fibrinolysis due to the activation of plasminogen to plasmin by nitric oxide synthesis in platelets.

Estriol, an oestrogen, at 0.6 nmol/l was reported to inhibit ADP-induced platelet aggregation through nitric oxide synthesis. As nitric oxide has been reported to cause fibrinolysis due to the activation of plasminogen to plasmin, the role of estriol as a fibrinolytic agent was investigated. Also, the mechanism of estriol-induced nitric oxide synthesis in anucleated platelets was investigated. The estriol-induced lysis of platelet-rich plasma (PRP) clot was determined by photography of the clot lysis and by the assay of fibrin degradation products in the lysate and was obtained by SDS-PAGE. Nitric oxide was determined by methemoglobin method. The platelet membrane protein was isolated from the platelets by using Triton X-100 (0.05% v/v). The binding of estriol to the protein was determined by Scatchard plot by using an ELISA for estriol. Estriol at 0.6 nmol/l was found to lyse the clotted PRP due to fibrinolysis that produced fibrin degradation products in the lysate. The amino acid analysis of the platelet membrane protein, which resembles with nitric oxide synthase (NOS) activity, was activated nearly 10-fold over the control in the presence of estriol and was identified to be a human serum albumin precursor (Mr. 69 kDa) that binds to estriol with Kd1 of 6.0 × 10 mol/l and 39 ±â€Š2 molecules of estriol bound the NOS molecule. The estriol-induced nitric oxide is capable of inducing fibrinolysis of the clotted PRP. The binding of estriol to platelet membrane NOS activated the enzyme in the absence of DNA in the platelet.

Shark cartilage extract induces cytokines expression and release in endothelial cells and induces E-selectin, plasminogen and t-PA genes expression through an antioxidant-sensitive mechanism.

Neovastat® is a standardized extract of marine cartilage, an avascular tissue, which contains many biologically active molecules and has multiple antiangiogenic properties. In addition to VEGFR2 and MMPs inhibition, shark cartilage extract (SCE) has recently been shown to induce tissue plasminogen activator gene (PLAT) expression in bovine endothelial cells in a TNF like manner, by inducing the typical mediators NF-κB and JNK. There is now compelling evidences that the NF-κB and JNK pathways are activated by cytokines induced generation of reactive oxygen species (ROS). We used macroarray genes expression analysis on human umbilical vein endothelial cells, to investigate if that mechanism could mediate the effect of SCE. Transcriptomic results showed that SCE induced expression of several cytokines. Their impact must be important, given that treatment of endothelial cells with the cytokine TNF-α was able to reproduce most of the effects of cartilage extract on genes expression. In addition, most of the genes, known to be inducible by NF-κB or JNK following cytokines stimulation, were less induced by SCE when endothelial cells were pretreated with the antioxidant N-Acetylcysteine (NAC), suggesting a role of ROS in endothelial cell activation by SCE. Finally, the possible effects of PLAT, PLG, SELE, IL8 and PRDX2 (those validated by q-PCR) on angiogenesis, will also be discussed.

[Isolation and purification of recombinant soluble and non-fusion angiogenesis inhibitor Kringle 5 using chromatography].

The Kringle 5 domain of plasminogen is one of the most potent angiogenesis inhibitors known to date, which can inhibit cell proliferation and migration efficiently. In the study, on the foundation of successful clone and expression of recombinant soluble and non-fusion angiogenesis inhibitor Kringle 5, a two-step chromatographic method, including the use of SP Sepharose Fast Flow cation exchanger and Sephacryl S-100 HR size exclusion chromatography in sequence, was established to separate and purify angiogenesis inhibitor Kringle 5. On the SP Sepharose Fast Flow column, the buffer A consisted of 50.0 mmol/L acetic acid-sodium acetate (pH 5.2), and the buffer B consisted of buffer A with the addition of 0.5 mol/L sodium chloride (pH 5.2); on Sephacryl S-100 HR column, the elution buffer was 5.0 mmol/L phosphate solution (pH 7.0). Through the two-step chromatographic purification process, the purity of the obtained Kringle 5 was more than 98%. In addition, it was found that the obtained Kringle 5 could inhibit the blood vessel growth of chick embryo chorioallantoic membrane effectively. Finally it is concluded that this method can effectively separate active recombinant soluble and non-fusion angiogenesis inhibitor Kringle 5.

iTRAQ-based proteomic profiling of human serum reveals down-regulation of platelet basic protein and apolipoprotein B100 in patients with hematotoxicity induced by chronic occupational benzene exposure.

Benzene is an important industrial chemical and an environmental contaminant, but the pathogenesis of hematotoxicity induced by chronic occupational benzene exposure (HCOBE) remains to be elucidated. To gain an insight into the molecular mechanisms and developmental biomarkers for HCOBE, isobaric tags for relative and absolute quantitation (iTRAQ) combined with two-dimensional liquid chromatography-tandem mass spectrometry (2D-LC-MS/MS) were utilized. Identification and quantitation of differentially expressed proteins between HCOBE cases and healthy control were thus made. Expressions of selected proteins were confirmed by western blot and further validated by ELISA. A total of 159 unique proteins were identified (≥95% confidence), and relative expression data were obtained for 141 of these in 3 iTRAQ experiments, with fifty proteins found to be in common among 3 iTRAQ experiments. Plasminogen (PLG) was found to be significantly up-regulated, whereas platelet basic protein (PBP) and apolipoprotein B100 (APOB100) were significantly down-regulated in the serum of HCOBE cases. Additionally, the altered proteins were associated with the molecular functions of binding, catalytic activity, enzyme regulator activity and transporter activity, and involved in biological processes of apoptosis, developmental and immune system process, as well as response to stimulus. Furthermore, differential expressions of PLG, PBP and APOB100 were confirmed by western blot, and the clinical relevance of PBP and APOB100 with HCOBE was validated by ELISA. Overall, our results showed that lowered expression of PBP and APOB100 proteins served as potential biomarkers of HCOBE, and may play roles in the benzene-induced immunosuppressive effects and disorders in lipid metabolism.

[Assessment of protein synthesizing function of the liver in experimental hepatitis].

Liver protein synthesis was estimated comparing the levels of prothrombin and its inactive form PIVKA-prothrombin. The latter indicates liver dysfunction. These diagnostic tests allow monitoring the effectiveness of the commonly applied preparation "Essentiale Forte" and that of the liposomal form of the biologically active additive (BAA) FLP-MD based on phospholipids of various origin.

[Purification and characterization of a kringle-deficit mutant of human plasminogen with Arg-Gly-Asp tripeptide expressed in Pichia pastorsis].

To obtain a recombinant human plasminogen (hPLG) with potential anti-platelet aggregation activity, we cloned the cDNA coding Pro544 to Asn791 of hPLG, a kringle-deficit derivative (hPLG-deltaK). The Pro559 in activation loop was then mutated into Asp559 to provide Arg-Gly-Asp (RGD) motif. The constructed pPICZalphaA-RGD-HPLG-deltaK plasmid was expressed in yeast Pichia pastoris GS115, which produced RGD-hPLG-deltaK about 0.160 g/L broth. After affinity chromatography, the purity of the recombinant protein reached above 90%. Western blotting test confirmed that it retained the immunological reaction capability as human PLG. Its urokinase activation rate in 24 hours and its fibrinolytic activity made no deference against native hPLG-deltaK (P=0.630, n=5). Importantly, after activation by urokinase, RGD-hPLG-deltaK showed a significantly higher platelet aggregation inhibition rate (Ri) (21.8% +/- 1.57%) than hPLG-deltaK (3.8% +/- 0.33%) (P=0.000, n=5). These results proved that we constructed an hPLG mutant with anti-platelet aggregation activity, which made a foundation for developing innovative thrombolytic drugs with multifunction.

Differential expression of oxidized/native lipoprotein(a) and plasminogen in human carotid and cerebral artery plaques.

OBJECTIVE: Lipoprotein(a) [Lp(a)] is a risk factor for stroke, as has recently been further confirmed by meta analysis, and consists of low-density lipoprotein and apolipoprotein(a), which shares a significant amino acid homology with plasminogen. Oxidized Lp(a) [Ox-Lp(a)] is a more pathogenic species of Lp(a). A monoclonal antibody, specific to Ox-Lp(a), distinguishes immunolocalization of Ox-Lp(a) from that of Lp(a) and that of plasminogen which carries highly homologous domains. It is worth examining their possibly differential immunolocalizations around atherosclerotic lesions in human carotid and cerebral arteries. METHODS AND RESULTS: Stage-related differences in immunolocalization of Ox-Lp(a), native Lp(a), and plasminogen were investigated in various atherosclerotic lesions of the human carotid (obtained from 13 patients undergoing carotid endarterectomy) and cerebral arteries (from 11 cadavers). Native Lp(a) was seen in the fibrous cap, extracellular matrix, endothelial cells, and subendothelial layer. Unorganized mural thrombi were positive for plasminogen, but not Lp(a). In contrast, fibrin deposits in thickened intima were positive for Lp(a), but not plasminogen. Ox-Lp(a)-like immunoreactivity was seen in endothelial cells in the early stage of atherosclerosis. Ox-Lp(a) deposition was more abundant in synthetic phase vascular smooth muscle cells (VSMC) than in contractile phase VSMC. CONCLUSION: We demonstrated differential immunoexpression patterns between native Lp(a) and plasminogen, and suggested that Lp(a)-plasminogen interaction may play a part in differential mechanisms in all atherosclerotic lesions of human carotid and cerebral arteries. The preferential presence of Ox-Lp(a) seen in endothelial cells suggests initial dysfunction of endothelial cells in atherosclerosis. The relative abundance of Ox-Lp(a) in synthetic phase VSMC is associated with their phenotypic changes during the progression of atherosclerosis.

Identification of three novel plasminogen (PLG) gene mutations in a series of 23 patients with low PLG activity.

Inherited severe hypoplasminogenaemia is a multisystemic disorder leading to deficient extravascular fibrinolysis. As a clinical consequence wound healing capacity of mucous membranes is markedly impaired leading to ligneous conjunctivitis and several other manifestations. Here we report the molecular genetic and clinical findings on 23 new cases with severe hypoplasminogenaemia. Homozygous or compound-heterozygous mutations in the plasminogen (PLG) gene were found in 16 of 23 patients (70%), three of which were novel mutations reported here for the first time (C166Y, Y264S, IVS10-7T/G). Compared to 79 previously published cases, clinical manifestations of the current group of patients showed higher percentages of ligneous periodontitis, congenital hydrocephalus, and involvement of the female genital tract. In contrast, involvement of the gastrointestinal or urogenital tract was not observed in any of the cases. Patients originated to a large extent (61%) from Turkey and the Middle East, and showed a comparably frequent occurrence of consanguinity of affected families and a greater female to male ratio than was derived from previous reports in the literature. Individual treatment of ligneous conjunctivitis included topical plasminogen or heparin eye drops, topical or systemic fresh frozen plasma, and surgical removal of ligneous pseudomembranes, mostly with modest or transient efficacy. In conclusion, the present study underscores the broad range of clinical manifestations in PLG-deficient patients with a trend to regional differences. Transmission of genetic and clinical data to the recently established Plasminogen Deficiency Registry should help to determine the prevalence of the disease and to develop more efficient treatment strategies.

Preparation and characterization of RGD tumour-homing-peptide-modified plasminogen K5.

Plasminogen K5 (kringle 5) has strong inhibitory effects on endothelial-cell proliferation and migration. It was reported that K5 can reduce tumour neovascularization, resulting in clinically relevant antitumour effects. To determine whether addition of a tumour-targeting peptide could improve the tumour homing and antitumour activities of K5, we genetically modified K5 with an RGD (Arg-Gly-Asp) motif, which is a ligand with high affinity for αvß3 and αvß5 integrins. The fusion protein RGD-K5 was expressed in the Pichia pastoris system and the biological activity of RGD-K5 was assessed in vitro and in vivo. The results showed that the RGD-K5 exhibited a more potent effect of inhibiting endothelial cell proliferation and migration compared with that of traditional K5. RGD-K5 also displayed stronger anti-angiogenic activity in a CAM (chick chorioallantoic membrane) assay. Furthermore, RGD-K5 also showed stronger anti-angiogenic and antitumour effects in B16F10 melanoma-bearing mice compared with traditional K5. In conclusion, the biological activity of K5 can be further improved by the addition of a tumour-homing peptide, and the RGD-K5 may prove to be a promising novel candidate for cancer therapy.

Role of fibrinolytic markers in acute stroke.

INTRODUCTION: The fibrinolytic system plays an important role in normal haemostasis and endothelial function. This study was conducted to compare three fibrinolytic markers, i.e. plasminogen, tissue-plasminogen activator (t-PA) and plasminogen activator inhibitor type-1 (PAI-1) between acute stroke and stable non-stroke patients and to investigate the clinical significance of these markers. METHODS: A prospective study was done for a one-year period upon obtaining ethical approval from the local institution. 106 non-stroke individuals from general outpatient clinics (control group) and 51 acute stroke patients were selected. All subjects were tested for t-PA and PAI-1 levels using the enzyme immunoassay technique (Biopool TintElize) and for plasminogen level by colorimetric assay (HemosIL). They were followed up over a period of three months for survival and neurological recovery. RESULTS: Only the mean t-PA level was significantly higher in acute stroke patients compared to the control group, including after adjusting for confounders (using ANCOVA). There was no statistical association between the three fibrinolytic markers and the age, gender, stroke subtypes, number of risk factors, functional impairment, survival and neurological recovery. We observed that all the eight patients who died within one month of stroke onset had high levels of t-PA. An association between high t-PA antigen and acute stroke was found during a cerebrovascular event with a 4.6-fold odds ratio compared to non-stroke controls. CONCLUSION: High t-PA antigen in acute stroke patients probably indicates a poor prognosis. Its value as a marker for monitoring and prognostication needs to be evaluated as a routine clinical practice.

Transcript-specific expression profiles derived from sequence-based analysis of standard microarrays.

BACKGROUND: Alternative mRNA processing mechanisms lead to multiple transcripts (i.e. splice isoforms) of a given gene which may have distinct biological functions. Microarrays like Affymetrix GeneChips measure mRNA expression of genes using sets of nucleotide probes. Until recently probe sets were not designed for transcript specificity. Nevertheless, the re-analysis of established microarray data using newly defined transcript-specific probe sets may provide information about expression levels of specific transcripts. METHODOLOGY/PRINCIPAL FINDINGS: In the present study alignment of probe sequences of the Affymetrix microarray HG-U133A with Ensembl transcript sequences was performed to define transcript-specific probe sets. Out of a total of 247,965 perfect match probes, 95,008 were designated "transcript-specific", i.e. showing complete sequence alignment, no cross-hybridization, and transcript-, not only gene-specificity. These probes were grouped into 7,941 transcript-specific probe sets and 15,619 gene-specific probe sets, respectively. The former were used to differentiate 445 alternative transcripts of 215 genes. For selected transcripts, predicted by this analysis to be differentially expressed in the human kidney, confirmatory real-time RT-PCR experiments were performed. First, the expression of two specific transcripts of the genes PPM1A (PP2CA_HUMAN and P35813) and PLG (PLMN_HUMAN and Q5TEH5) in human kidneys was determined by the transcript-specific array analysis and confirmed by real-time RT-PCR. Secondly, disease-specific differential expression of single transcripts of PLG and ABCA1 (ABCA1_HUMAN and Q5VYS0_HUMAN) was computed from the available array data sets and confirmed by transcript-specific real-time RT-PCR. CONCLUSIONS: Transcript-specific analysis of microarray experiments can be employed to study gene-regulation on the transcript level using conventional microarray data. In this study, predictions based on sufficient probe set size and fold-change are confirmed by independent means.

Monoclonal antibody to cytokeratin VKIALEVEIATY sequence motif reduces plasminogen activation in breast tumour cells.

Cytokeratins (CKs) are the main structural proteins of epithelial cells. Although they mainly form cytoplasmic structures, they are also localized at the plasma membrane or secreted from the cells. Some CKs are over-expressed in tumour cells and are used as diagnostic and prognostic biomarkers. A stable hybridoma cell line producing anti-cytokeratin monoclonal antibody (anti-CK MAb) was prepared after immunizing mice with breast cancer MCF-7 cell lysate. As shown by 2D electrophoresis, immunoblotting and mass spectroscopy, the monoclonal antibody recognizes an epitope on CK1, CK2, CK8, CK10 and CK18 in MCF-7 cells. To identify the binding site of the antibody three peptides of 12 amino acids were synthesized, each overlapping a 27 amino acid consensus sequence of the recognized CKs. Anti-CK MAb expressed high affinity for a dodecapeptide with the sequence VKIALEVEIATY, localized in the CK alpha-helical B2 domain, as shown by ELISA and surface plasmon resonance. Treatment of MCF-7 cells by anti-CK MAb impaired plasminogen activation and consequently invasiveness of the cells. Our results show that, besides their use in diagnosis, anti-cytokeratin antibodies could be used in therapy of invasive breast cancer.

Direct effects of alcohol on hepatic fibrinolytic balance: implications for alcoholic liver disease.

BACKGROUND/AIMS: The pathogenesis of alcoholic liver disease (ALD) remains uncertain. Fibrin production and degradation are altered in experimental liver injury. We have recently identified increased expression of a number of genes (annexin A2 (ANXA2), p11, tPA and PAI-1) that implicate fibrinolysis in ALD progression. Aim of our study was to study the direct effect of alcohol on fibrinolysis and plasmin activity in hepatic cell lines and in vivo. METHODS: Expression of pro- and anti-fibrinolytic genes was determined in liver biopsies from patients with progressive ALD and in HepG2, Huh7 and LX-2 cells exposed to alcohol. The functional effects on fibrinolysis and plasmin activities were determined. C57BL6 female mice were given a single dose of alcohol and serum and liver triglyceride content and serum plasmin activity determined. RESULTS: Alcohol induced a significant up-regulation of ANXA2, PLG, PAI-1 and p11 in human ALD, cell lines and in mice exposed to alcohol. Up-regulation of ANXA2 and p11 was inhibited by the alcohol dehydrogenase inhibitor 4-methylpyrazole. Fibrinolysis and plasmin were increased in HepG2 and LX-2 cells by 10mM alcohol and was inhibited by ANXA2 blocking antibody. Plasmin also increased in mice given a moderate dose of alcohol. By contrast, there was striking up-regulation of PAI-1 in mice given a high dose of alcohol with associated decrease in plasmin. CONCLUSIONS: Alcohol directly alters hepatic expression of pro- and anti-fibrinolytic genes in a dose dependent manner with low dose promoting fibrinolysis and high dose inhibiting fibrinolysis. After a large dose of alcohol in vivo, the dominant effect was up-regulation of hepatic PAI-1 with suppression of plasmin. The effect of alcohol on fibrinolysis and plasmin is mediated in part by ANXA2. Alcohol directly influences hepatic pathways of fibrinolysis that may contribute to ALD.

Decorin promotes plasminogen/plasmin expression within acute spinal cord injuries and by adult microglia in vitro.

Spinal cord scar tissue presents a combined physical and molecular barrier to axon regeneration. Theoretically, spinal cord injuries (SCIs) can be rendered more permissive to axon growth by either suppressing synthesis of misaligned, fibrotic scar tissue and associated axon growth inhibitors, or enzymatically degrading them. We have previously shown that acute infusion of human recombinant decorin core protein into discreet stab injuries of the rat dorsal column pathways effected a major suppression of inflammation, astrogliosis, and multiple axon growth inhibitory chondroitin sulfate proteoglycans, which combined to promote rapid axon growth across the injury site. The high efficiency of chondroitin sulfate proteoglycan (CSPG) core protein suppression (approximately 90%) suggested that decorin may promote CSPG degradation in addition to suppressing CSPG synthesis. As the serine protease plasmin can degrade axon growth inhibitory CSPGs (neurocan and phosphacan) and its zymogen, plasmininogen is synthesized by microglia, we have investigated whether decorin treatment of acute SCIs and cultured adult spinal cord microglia can increase plasminogen/ plasmin synthesis. Infusion of hr-decorin over the first 8 days post-SCI induced 10- and 17-fold increases in plasminogen and plasmin protein levels, respectively, within sites of injury and a threefold increase in microglial plasminogen mRNA in vitro. In addition to potentially degrading multiple axon growth inhibitory components of the glial scar, plasmin is known to play major roles in activating neurotrophins and promoting central nervous system (CNS) plasticity. The wider implications of decorin induction of plasmin in the injured spinal cord for axon regeneration, and recovery of function at acute and chronic time points post-SCI are reviewed.

Incorporation of fragment X into fibrin clots renders them more susceptible to lysis by plasmin.

Bleeding, the most serious complication of thrombolytic therapy with tissue-type plasminogen activator (t-PA), is thought to result from lysis of fibrin in hemostatic plugs and from the systemic lytic state caused by unopposed plasmin. One mechanism by which systemic plasmin can impair hemostasis is by partially degrading fibrinogen to fragment X, a product that retains clottability but forms clots with reduced tensile strength that stimulate plasminogen activation by t-PA more than fibrin clots. The purpose of this study was to elucidate potential mechanisms by which fragment X accelerates t-PA-mediated fibrinolysis. In the presence of t-PA, clots containing fragment X were degraded faster than fibrin clots and exhibited higher rates of plasminogen activation. Although treatment with carboxypeptidase B, an enzyme that reduces plasminogen binding to fibrin, prolonged the lysis times of fragment X and fibrin clots, clots containing fragment X still were degraded more rapidly. Furthermore, plasmin or trypsin also degraded clots containing fragment X more rapidly than fibrin clots, suggesting that this effect is largely independent of plasminogen activation. Fragment X-derived degradation products were not preferentially released by plasmin from clots composed of equal concentrations of fibrinogen and fragment X, indicating that fragment X does not constitute a preferential site for proteolysis. These data suggest that structural changes resulting from incorporation of fragment X into clots promote their lysis. Thus, attenuation of thrombolytic therapy-induced fragment X formation may reduce the risk of bleeding.

Expression of recombinant kringle 1-5 domains of human plasminogen by a prokaryote expression system.

Kringle1-5 (K1-5), a proteolytic fragment containing five kringle domains of human plasminogen generated by plasmin-mediated proteolysis, has been already identified by Cao et al. with relation to anti-angiogenesis and proliferation of endothelial cells. To investigate anti-angiogenesis activity of recombinant human K1-5 (rhK1-5) expressed in Escherichia coli BL21, the cDNA of human K1-5 obtained from cloning vector pUC57-K1-5 by PCR, was inserted into an expression vector pET30(+) to construct a prokaryotic expression vector pET-K1-5. Recombinant K1-5 efficiently expressed in E. coli BL21 after IPTG induction was monitored by SDS-PAGE and Western blotting with an anti-angiostatin monoclonal antibody and an anti-hexahistidine tag antibody. The expressed K1-5 accounted for approximately 32% of the total bacterial proteins as estimated by densitometry, and existed mainly as inclusion bodies. The inclusion bodies were washed, lysed, purified, and refolded to a purity of 96% as estimated by capillary electrophoresis and the final purification yield of K1-5 in E. coli system was approximately 5.8 mg/L. Purified K1-5 protein was tested on chicken embryo chorioallantoic membranes (CAMs), and a large number of newly formed blood vessels were significantly regressed. In the present study, we demonstrated that bacterial-expressed K1-5 effectively inhibited angiogenesis of the chicken embryo in a dose-dependent manner through CAM assay. In addition, the rhK1-5 potently inhibited endothelial cell proliferation but not non-endothelial cells. For the first time, these findings demonstrate that the rhK1-5 produced by a prokaryote expression system effectively inhibited angiogenesis of the chicken embryo in a dose-dependent manner and specially suppressed in vitro the proliferation of human umbilical vein endothelial cells. This fact derived from the present study further suggests the rhK1-5 can be used for anti-angiogenesis therapy of cancer.