Plasminogen activation: biochemistry, physiology, and therapeutics

Effects of earthworm extract on the lipid profile and fatty liver induced by a high-fat diet in guinea pigs

Background

Non-alcoholic fatty liver disease (NAFLD), characterized by the accumulation of excess fat in the liver in people who consume little or no alcohol, is becoming increasingly common around the world, especially in developed countries. Extracts from earthworms have been used as alternative therapies for a variety of diseases but not in NAFLD. Therefore, the aim of this study was to investigate the effect of earthworm extract (EE) on diet-induced fatty liver disease in guinea pigs.

Methods

EE was extracted, and the effect of EE on the lipid levels and liver damage in guinea pigs fed a high-fat diet (HFD) was assessed. Thirty male guinea pigs at 3 weeks of age were allocated equally to five groups, namely, chow diet, HFD, and HFD with different dosages (0.3, 1.4 and 6.8 µg per kg bodyweight per day) of EE for 4 weeks, and their body weight was monitored throughout the experiment. Liver tissues were examined for gross morphology and histology. Serum levels of total cholesterol (TC), triglycerides (TG), low-density lipoprotein cholesterol (LDL-C), alanine transaminase (ALT) and aspartate aminotransferase (AST) were determined using an autoanalyser.

Results

HFD induced NAFLD in guinea pigs. HFD-fed guinea pigs that received EE treatment showed milder increases in the serum levels of TC, TG and LDL-C, as well as in the body weight growth rate, compared to the HFD group without EE supplementation. EE intervention reduced the number of lipid-containing hepatocytes, hepatocellular ballooning and sinusoidal distortion in the liver in HFD-fed animals. ALT in serum was significantly elevated by HFD. No statistically significant difference in ALT levels was found between the chow diet group and the HFD group with EE treatment.

Conclusions

This study demonstrates that the administration of EE suppressed the induction of serum TC, TG and LDL-C in response to HFD. EE also reduced liver damage in HFD-fed guinea pigs. These findings suggest that EE has alleviating effects on dyslipidaemia and liver damage associated with NAFLD.

Peptidylarginine Deiminase of Porphyromonas gingivalis Modulates the Interactions between Candida albicans Biofilm and Human Plasminogen and High-Molecular-Mass Kininogen

Microorganisms that create mixed-species biofilms in the human oral cavity include, among others, the opportunistic fungus Candida albicans and the key bacterial pathogen in periodontitis, Porphyromonas gingivalis. Both species use arsenals of virulence factors to invade the host organism and evade its immune system including peptidylarginine deiminase that citrullinates microbial and host proteins, altering their function. We assessed the effects of this modification on the interactions between the C. albicans cell surface and human plasminogen and kininogen, key components of plasma proteolytic cascades related to the maintenance of hemostasis and innate immunity. Mass spectrometry was used to identify protein citrullination, and microplate tests to quantify the binding of modified plasminogen and kininogen to C. albicans cells. Competitive radioreceptor assays tested the affinity of citrullinated kinins to their specific cellular receptors. The citrullination of surface-exposed fungal proteins reduced the level of unmodified plasminogen binding but did not affect unmodified kininogen binding. However, the modification of human proteins did not disrupt their adsorption to the unmodified fungal cells. In contrast, the citrullination of kinins exerted a significant impact on their interactions with cellular receptors reducing their affinity and thus affecting the role of kinin peptides in the development of inflammation.

Reduction of steroid-induced intraocular pressure elevation in sheep by tissue plasminogen activator

PURPOSE

To investigate whether tissue plasminogen activator (tPA) can prevent and/or reverse steroid-induced IOP elevation in an ovine model.

METHODS

Three animal groups were subjected to bilateral steroid-induced IOP elevation using thrice daily topical ocular prednisolone administration. In the first group (N = 8), one eye each of two sheep was injected intravitreally with 100 μg, 200 μg, 500 μg, or 1 mg human recombinant tPA, while contralateral eyes received vehicle. In the second group (N = 2), one eye was injected intravitreally with tPA (100 μg), while contralateral eyes received vehicle containing L-arginine. In the third group (N = 4), each animal received intravitreal tPA in one eye concurrently with initiation of bilateral steroid administration. IOP was monitored for the duration of the experiment. Tissues from eyes of the third group were used to determine relative gene expression.

RESULTS

In the first and second groups, IOP decreased by 9.7 (±2.8) and 9.7 (±1.6) mm Hg, respectively, 24 hours after tPA administration. In the third group, tPA-treated eyes did not develop IOP elevation with ΔIOP of 11.8 (±1.3) mm Hg 8 days later. In all tPA-treated eyes, IOP remained low until the end of the study. mRNA levels in the trabecular meshwork were decreased for plasminogen activator tissue (PLAT), increased for matrix-metalloproteinase 1 (MMP-1), and stable for plasminogen activator inhibitor 1 (PAI-1), MMP-2, MMP-9, and MMP-13 in tPA-treated eyes compared with contralateral controls. PAI-1 mRNA levels in ciliary processes also remained similar.

CONCLUSIONS

Recombinant human tPA is effective in both preventing and reversing steroid-induced IOP elevation in sheep. Tissue plasminogen activator may be useful as a therapeutic agent in steroid-induced glaucoma.

Molecular biology of bladder cancer: prognostic and clinical implications

The role of various molecular determinants involved in the genesis, progression, and outcome of bladder cancer has been the focus of investigations for the past 2 decades. Increasingly, the analysis of the interplay between these molecular factors is taking center stage. We review herein the studies examining the effects of deregulation of the various molecules implicated in the cell cycle, apoptosis, and angiogenesis pathways and analyze the central role of p53 in regulating these pathways. Technological advancements enable detection and quantification of gene transcripts and protein products, helping us move toward achieving the goal of establishing diagnostic, prognostic, and therapeutic marker panels. Recent studies have therefore focused on multiple-marker analyses to generate informative panels that can have greater clinical value for bladder cancer management. The use of molecular marker panels can provide a more objective alternative to clinical parameters for diagnosis and treatment decisions. Clinical trials aimed at treating urothelial carcinoma based on a patient's molecular profile can be predicted to empower clinicians to personalize patient management through increased therapeutic efficacy.

Tumor-stroma interactions: their role in the control of tumor cell invasion

The development and progression of tumors result from the concerted activity not only of tumor cells with neighboring cells e.g., fibroblasts and inflammatory cells. Host-tumor interactions are considered critical in tumor invasion and metastasis. In vitro studies as well as established in vivo models have analysed the reciprocal effects of tumor-host interactions for the tumor invasion process. These studies have shown that modifications in the extracellular matrix composition surrounding the tumors as well as alterations in the expression of tumor cell receptors or in the expression of growth factors/cytokines and proteases, are critical regulators of a developing tumor. We shortly review the most important and well characterized mechanisms involved in the progression of tumor cells through tissues, especially those participating in cellular communication, cell adhesion, and proteolysis.

Cleavage of Chromogranin A N-terminal Domain by Plasmin Provides a New Mechanism for Regulating Cell Adhesion

It has been proposed that chromogranin A (CgA), a protein secreted by many normal and neoplastic neuroendocrine cells, can play a role as a positive or a negative modulator of cell adhesion. The mechanisms that regulate these extracellular functions of CgA are unknown. We show here that plasmin can regulate the anti/pro-adhesive activity of CgA by proteolytic cleavage of the N-terminal domain. Limited proteolytic processing decreased its anti-adhesive activity and induced pro-adhesive effects in fibronectin or serum-dependent fibroblast adhesion assays. Cleavage of Lys(77)-Lys(78) dibasic site in CgA(1-115) was relatively rapid and associated with an increase of pro-adhesive effect. In contrast, antibodies against the region 53-90 enhanced the anti-adhesive activity of CgA and CgA(1-115). Structure-activity relationship studies showed that the conserved region 47-64 (RILSILRHQNLLKELQDL) is critical for both pro- and anti-adhesive activity. These findings suggest that CgA might work on one hand as a negative modulator of cell adhesion and on the other hand as a precursor of positive modulators, the latter requiring proteolytic processing for activation. Given the importance of plasminogen activation in tissue invasion and remodeling, the interplay between CgA and plasmin could provide a novel mechanism for regulating fibroblast adhesion and function in neuroendocrine tumors.

Zymogen activation in the streptokinase-plasminogen complex. Ile1 is required for the formation of a functional active site

Plasminogen (Plgn) is usually activated by proteolysis of the Arg561-Val562 bond. The amino group of Val562 forms a salt-bridge with Asp740, which triggers a conformational change producing the active protease plasmin (Pm). In contrast, streptokinase (SK) binds to Plgn to produce an initial inactive complex (SK.Plgn) which subsequently rearranges to an active complex (SK.Plgn*) although the Arg561-Val562 bond remains intact. Therefore another residue must substitute for the amino group of Val562 and provide a counterion for Asp740 in this active complex. Two candidates for this counterion have been suggested: Ile1 of streptokinase and Lys698 of Plgn. We have investigated the reaction of SK mutants and variants of the protease domain of microplasminogen (muPlgn) in order to determine if either of these residues is the counterion. The mutation of Ile1 of SK decreases the activity of SK.Plgn* by 100-fold (Ile1Val) to >/= 104-fold (Ile1-->Ala, Gly, Trp or Lys). None of these mutations perturb the binding affinity of SK, which suggests that Ile1 is not required for formation of SK.Plgn but is necessary for SK.Plgn*. The substitution of Lys698 of muPlgn decreases the activity of SK.Plgn* by only 10-60-fold. In contrast with the Ile1 substitutions, the Lys698 mutations also decreased the dissociation constant of the SK complex by 15-50-fold. These observations suggest that Lys698 is involved in formation of the initial SK.Plgn complex. These results support the hypothesis that Ile1 provides the counterion for Asp740.

Invasiveness of hepatocellular carcinoma cell lines: contribution of membrane-type 1 matrix metalloproteinase

Intrahepatic metastasis is one of the malignant features of hepatocellular carcinoma (HCC). Matrix metalloproteinases (MMPs) and urokinase-type plasminogen activator (u-PA)/plasmin, are known to be associated with the invasive properties of various types of tumor cells. In this study, we examined which proteinases play a role in the metastatic invasion of human HCC cell lines. JHH-5 and JHH-6 cells constitutively expressed mRNAs for both membrane-type 1 matrix metalloproteinase (MT1-MMP) and u-PA and invaded through reconstituted MATRIGEL in vitro, whereas JHH-7 cells expressed u-PA mRNA but not MT1-MMP and did not invade. However, hepatocyte growth factor (HGF) induced MT1-MMP expression on the surface of JHH-7 cells and markedly increased invasiveness of JHH-7 in a concentration-dependent manner. Moreover, cleavage activity for pro-MMP-2 was induced in HGF-treated JHH-7 cells. MMP inhibitor, rather than serine proteinase inhibitor, potently inhibited HCC cell invasion. Intrahepatic injection of HCC cell lines into athymic nude mice caused visible intrahepatic metastases in vivo. Moreover, JHH-7 tumors showed expression of MT1-MMP mRNA, while in vitro cultured JHH-7 cells did not. These findings suggest that MT1-MMP plays an important role in the invasive properties of HCC cells, and that HGF modifies the invasive properties of noninvasive HCC cells.

Processing of laminin-5 and its functional consequences: role of plasmin and tissue-type plasminogen activator

The laminin-5 component of the extracellular matrices of certain cultured cells such as the rat epithelial cell line 804G and the human breast epithelial cell MCF-10A is capable of nucleating assembly of cell- matrix adhesive devices called hemidesmosomes when other cells are plated upon them. These matrices also impede cell motility. In contrast, cells plated onto the laminin-5-rich matrices of pp126 epithelial cells fail to assemble hemidesmosomes and are motile. To understand these contradictory phenomena, we have compared the forms of heterotrimeric laminin-5 secreted by 804G and MCF-10A cells with those secreted by pp126 cells, using a panel of laminin-5 subunit-specific antibodies. The alpha3 subunit of laminin-5 secreted by pp126 cells migrates at 190 kD, whereas that secreted by 804G and MCF-10A cells migrates at 160 kD. The pp126 cell 190-kD alpha3 chain of laminin-5 can be specifically proteolyzed by plasmin to a 160-kD species at enzyme concentrations that do not apparently effect the laminin-5 beta and gamma chains. After plasmin treatment, pp126 cell laminin-5 not only impedes cell motility but also becomes competent to nucleate assembly of hemidesmosomes. The possibility that plasmin may play an important role in processing laminin-5 subunits is supported by immunofluorescence analyses that demonstrate colocalization of laminin-5 and plasminogen in the extracellular matrix of MCF-10A and pp126 cells. Whereas tissue-type plasminogen activator (tPA), which converts plasminogen to plasmin, codistributes with laminin-5 in MCF-10A matrix, tPA is not present in pp126 extracellular matrix. Treatment of pp126 laminin-5-rich extracellular matrix with exogenous tPA results in proteolysis of the laminin-5 alpha3 chain from 190 to 160 kD. In addition, plasminogen and tPA bind laminin-5 in vitro. In summary, we provide evidence that laminin-5 is a multifunctional protein that can act under certain circumstances as a motility and at other times as an adhesive factor. In cells in culture, this functional conversion appears dependent upon and is regulated by tPA and plasminogen.

Plasminogen in proliferative vitreoretinal disorders

OBJECTIVE

Intravitreal fibrin formation is a frequent observation after vitrectomy performed for a variety of vitreoretinal disorders including proliferative vitreoretinopathy (PVR), proliferative diabetic retinopathy (PDR), and endophthalmitis. Plasminogen activators (PA) have been used for the management of this postoperative complication. This approach requires the presence of plasminogen, the substrate for PA mediated fibrinolysis, in the vitreal cavity.

METHODS

Quantification of plasminogen in the vitreous of 60 patients with PVR, PDR, and macular pucker was performed by streptokinase mediated activation using a chromogenic substrate. The presence of immunoreactive plasminogen was confirmed by immunoblot analysis of vitreal proteins and immunocytochemistry of surgically removed epiretinal membranes.

RESULTS

Plasminogen levels were dramatically increased in the vitreous of PVR and PDR patients compared with macular pucker patients and normal controls. Staining for plasminogen in epiretinal membranes was confined to the extracellular matrix. Predominant staining of perivascular areas in PDR specimens indicated that breakdown of the blood-retinal barrier is an important source of intravitreal plasminogen in that condition.

CONCLUSION

Plasminogen may play a role in traction membrane formation in PVR and PDR. Our biochemical analysis of presurgical vitreous indicates that there may be abundant substrate for PA mediated fibrinolysis in the vitreous cavity after vitrectomy.

Microparticle-enhanced nephelometric immunoassay of human plasminogen

A microparticle-enhanced nephelometric immunoassay was developed for plasminogen quantitation in human plasma. It is based on the nephelometric measurement of the light scattered by microparticle clusters formed during a sandwich reaction between plasminogen, microparticle--anti-plasminogen conjugate, and the free antibodies of anti-plasminogen rabbit antiserum. This immunoassay was sensitive (detection limit in reaction mixture, 34 micrograms/L) and could be performed in 500-fold diluted human plasma, excluding any interference or sample pretreatment. It allowed the quantitation of plasminogen on a large range of concentrations (17-550 mg/L), with a security in antigen excess reaching 1,100 mg/L, with accuracy (linear recovery in dilution-overloading assay and correlation with conventional immunonephelometry), and precision (within- and between-run coefficients of variation lower than 8%). A normal reference range from 54 to 148 mg/L (mean +/- 2 SD) was calculated from plasminogen concentration in plasma from 130 adults. Easy to perform (no washing or phase separation) and rapid (two steps of 30 minutes then 1 hour of incubation at room temperature), this microparticle-enhanced nephelometric immunoassay could be an interesting alternative method for human plasminogen quantitation.

The major N-linked carbohydrate chains from human urokinase. The occurrence of 4-O-sulfated, (alpha 2-6)-sialylated or (alpha 1-3)-fucosylated N-acetylgalactosamine(beta 1-4)-N-acetylglucosamine elements

The primary structure of the major N-linked carbohydrate chains attached to Asn302 of urinary-type plasminogen activator (urokinase) have been determined. Urokinase was completely deglycosylated with peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase F from Flavobacterium meningosepticum. Released oligosaccharides were separated from the remaining protein using gel-permeation chromatography on Bio-Gel P-100, and then on Bio-Gel P-6. Fractionation of the oligosaccharides was achieved by a combination of FPLC anion-exchange chromatography on Mono Q HR 5/5 and amine-adsorption HPLC on LiChrospher 100-NH2. Analysis by 1H-NMR spectroscopy demonstrated that the collection of N-glycans comprises di-, tri-, and tri'-antennary structures. The glycans contain predominantly GalNAc beta 1-4GlcNAc beta instead of Gal beta 1-4GlcNAc beta elements. The GalNAc residue is mainly sulfated at O4, or to a lesser extent it bears N-acetylneuraminic acid at O6; alternatively the GlcNAc residue can be fucosylated at O3. The major component, which accounts for more than 30 mol/100 mol of the total oligosaccharide pool, consists of an (alpha 1-6)-fucosylated diantennary N-linked carbohydrate chain with (SO4-)-4GalNAc beta 1-4GlcNAc beta 1-2 antennae.