Antiangiogenic antithrombin blocks the heparan sulfate-dependent binding of proangiogenic growth factors to their endothelial cell receptors: evidence for differential binding of antiangiogenic and anticoagulant forms of antithrombin to proangiogenic heparan sulfate domains

Mutual Inhibition of Antithrombin III and SARS-CoV-2 Cellular Attachment to Syndecans: Implications for COVID-19 Treatment and Vaccination

Antithrombin III (ATIII) is a potent endogenous anticoagulant that binds to heparan sulfate proteoglycans (HSPGs) on endothelial cells' surfaces. Among these HSPGs, syndecans (SDCs) are crucial as transmembrane receptors bridging extracellular ligands with intracellular signaling pathways. Specifically, syndecan-4 (SDC4) has been identified as a key receptor on endothelial cells for transmitting the signaling effects of ATIII. Meanwhile, SDCs have been implicated in facilitating the cellular internalization of SARS-CoV-2. Given the complex interactions between ATIII and SDC4, our study analyzed the impact of ATIII on the virus entry into host cells. While ATIII binds to all SDC isoforms, it shows the strongest affinity for SDC4. SDCs' heparan sulfate chains primarily influence ATIII's SDC attachment, although other parts might also play a role in ATIII's dominant affinity toward SDC4. ATIII significantly reduces SARS-CoV-2's cellular entry into cell lines expressing SDCs, suggesting a competitive inhibition mechanism at the SDC binding sites, particularly SDC4. Conversely, the virus or its spike protein decreases the availability of SDCs on the cell surface, reducing ATIII's cellular attachment and hence contributing to a procoagulant environment characteristic of COVID-19.

Crosstalk between Circulating Tumor Cells and Plasma Proteins-Impact on Coagulation and Anticoagulation

Cancer metastasis is a complex process. After their intravasation into the circulation, the cancer cells are exposed to a harsh environment of physical and biochemical hazards. Whether circulating tumor cells (CTCs) survive and escape from blood flow defines their ability to metastasize. CTCs sense their environment with surface-exposed receptors. The recognition of corresponding ligands, e.g., fibrinogen, by integrins can induce intracellular signaling processes driving CTCs' survival. Other receptors, such as tissue factor (TF), enable CTCs to induce coagulation. Cancer-associated thrombosis (CAT) is adversely connected to patients' outcome. However, cancer cells have also the ability to inhibit coagulation, e.g., through expressing thrombomodulin (TM) or heparan sulfate (HS), an activator of antithrombin (AT). To that extent, individual CTCs can interact with plasma proteins, and whether these interactions are connected to metastasis or clinical symptoms such as CAT is largely unknown. In the present review, we discuss the biological and clinical relevance of cancer-cell-expressed surface molecules and their interaction with plasma proteins. We aim to encourage future research to expand our knowledge of the CTC interactome, as this may not only yield new molecular markers improving liquid-biopsy-based diagnostics but also additional targets for better cancer therapies.

Coatings in Decellularized Vascular Scaffolds for the Establishment of a Functional Endothelium: A Scoping Review of Vascular Graft Refinement

Developments in tissue engineering techniques have allowed for the creation of biocompatible, non-immunogenic alternative vascular grafts through the decellularization of existing tissues. With an ever-growing number of patients requiring life-saving vascular bypass grafting surgeries, the production of functional small diameter decellularized vascular scaffolds has never been more important. However, current implementations of small diameter decellularized vascular grafts face numerous clinical challenges attributed to premature graft failure as a consequence of common failure mechanisms such as acute thrombogenesis and intimal hyperplasia resulting from insufficient endothelial coverage on the graft lumen. This review summarizes some of the surface modifying coating agents currently used to improve the re-endothelialization efficiency and endothelial cell persistence in decellularized vascular scaffolds that could be applied in producing a better patency small diameter vascular graft. A comprehensive search yielding 192 publications was conducted in the PubMed, Scopus, Web of Science, and Ovid electronic databases. Careful screening and removal of unrelated publications and duplicate entries resulted in a total of 16 publications, which were discussed in this review. Selected publications demonstrate that the utilization of surface coating agents can induce endothelial cell adhesion, migration, and proliferation therefore leads to increased re-endothelialization efficiency. Unfortunately, the large variance in methodologies complicates comparison of coating effects between studies. Thus far, coating decellularized tissue gave encouraging results. These developments in re-endothelialization could be incorporated in the fabrication of functional, off-the-shelf alternative small diameter vascular scaffolds.

Mass Spectrometry Reveals a Multifaceted Role of Glycosaminoglycan Chains in Factor Xa Inactivation by Antithrombin

Factor Xa (fXa) inhibition by antithrombin (AT) enabled by heparin or heparan sulfate is critical for controlling blood coagulation. AT activation by heparin has been investigated extensively, while interaction of heparin with trapped AT/fXa intermediates has received relatively little attention. We use native electrospray ionization mass spectrometry to study the role of heparin chains of varying length [hexa-, octa-, deca-, and eicosasaccharides (dp6, dp8, dp10, and dp20, respectively)] in AT/fXa complex assembly. Despite being critical promoters of AT/Xa binding, shorter heparin chains are excluded from the final products (trapped intermediates). However, replacement of short heparin segments with dp20 gives rise to a prominent ionic signal of ternary complexes. These species are also observed when the trapped intermediate is initially prepared in the presence of a short oligoheparin (dp6), followed by addition of a longer heparin chain (dp20), indicating that binding of heparin to AT/fXa complexes takes place after the inhibition event. The importance of the heparin chain length for its ability to associate with the trapped intermediate suggests that the binding likely occurs in a bidentate fashion (where two distinct segments of oligoheparin make contacts with the protein components, while the part of the chain separating these two segments is extended into solution to minimize electrostatic repulsion). This model is corroborated by both molecular dynamics simulations with an explicit solvent and ion mobility measurements in the gas phase. The observed post-inhibition binding of heparin to the trapped AT/fXa intermediates hints at the likely role played by heparan sulfate in their catabolism.

The GAG-specific branched peptide NT4 reduces angiogenesis and invasiveness of tumor cells

Heparan sulfate proteoglycans, HSPGs, modulate major transformations of cancer cells, leading to tumor growth, invasion and metastasis. HSPGs also regulate neo-angiogenesis which prompts cancer progression and metastatic spread. A different aspect of heparin and analogs is their prominent role in the coagulation of blood. The interplay between coagulation and metastasis is being actively studied: anticoagulants such as heparin-derivatives have anticancer activity and procoagulants, such as thrombin, positively modulate proliferation, migration and invasion. The branched peptide NT4 binds to HSPGs and targets selectively cancer cells and tissues. For this, it had been extensively investigated in the last years and it proved to be efficient as chemotherapeutic and tumor tracer in in vivo models of cancer. We investigated the effects of the branched peptide in terms of modulation of angiogenesis and invasiveness of cancer cells. NT4 proved to have a major impact on endothelial cell proliferation, migration and tube formation, particularly when induced by FGF2 and thrombin. In addition, NT4 had important effects on aggressive tumor cells migration and invasion and it also had an anticoagulant profile.The peptide showed very interesting evidence of interference with tumor invasion pathways, offering a cue for its development as a tumor-targeting drug, and also for its use in the study of links between coagulation and tumor progression involving HSPGs.

Phase I Study of Dalteparin in Combination With Sunitinib in Patients With Metastatic Clear Cell Renal Carcinoma

BACKGROUND

Based on the tumor-driven concomitant activation of angiogenesis and coagulation we conducted a phase I combination study of sunitinib with the low molecular weight heparin dalteparin in patients with metastatic clear cell renal cell carcinoma (ccRCC).

MATERIALS AND METHODS

Patients received standard treatment with sunitinib (50 mg daily, 4 weeks on, 2 weeks off). During the second week of no sunitinib in the first cycle (week 6) patients received dalteparin monotherapy (in escalating doses). Combination therapy of the 2 agents was administered from the second cycle onward. Seventeen patients were enrolled at 3 dose levels of dalteparin.

RESULTS

Diarrhea and fatigue were the most frequent reported drug-related toxicities (41%). One dose-limiting toxicity (grade 3 anemia) was observed at the highest dose level of dalteparin. There were 4 partial responses (24%) and the median progression-free survival in this study was 14 months (95% confidence interval, 8.0-23.4). Anti-factor Xa levels were increased during combination therapy compared with dalteparin monotherapy.

CONCLUSIONS

Combination therapy of sunitinib with therapeutic doses of dalteparin is safe and well tolerated. The increased anti-factor Xa levels during combination treatment suggest that sunitinib might increase the anticoagulation activity of dalteparin. The positive safety profile warrants prospective evaluation of the clinical benefit of this combination strategy in patients with ccRCC.

Heparin-gelatin mixture improves vascular reconstruction efficiency and hepatic function in bioengineered livers

Whole organ decellularization is a cell removal process that creates a natural extracellular matrix for use in transplantation. A lack of an intact endothelial layer in the vascular network of decellularized organs results in blood clotting even with anti-coagulation treatment. Furthermore, shear stress caused by blood flow may affect reseeded parenchymal cells. We hypothesized that a heparin-gelatin mixture (HG) can act as an antithrombotic coating reagent and induce attachment and migration of endothelial cells (ECs) on vascular wall surfaces within decellularized livers, with subsequent parenchymal cell function enhancement. Portal vein (PV) perfusion was performed for right lateral lobe decellularization of porcine livers. We tested if HG-precoating of isolated decellularized PV could increase EC attachment and migration. Additionally, we coated PV and hepatic artery walls in decellularized liver with HG, and then repopulated it with ECs and maintained it under vascular flow in a bioreactor for 10days. Re-endothelialized scaffolds were perfused with porcine blood for thrombogenicity evaluation. We then co-cultured hepatocellular carcinoma (HepG2) cells and ECs to evaluate the effect of endothelialization on parenchymal cells. Finally, we transplanted these scaffolds heterotopically in pigs. HG improved ECs' ability to migrate and adhere to vessel discs. ECs efficiently covered the vascular compartments within decellularized scaffolds and maintained function and proliferation after HG-precoating. No thrombosis was observed after 24h blood perfusion in HG-precoated scaffolds, indicating an efficiently endothelialized vascular tree. HepG2 cells displayed a higher function in scaffolds endothelialized after HG-precoating compared to uncoated scaffolds in vitro and after in vivo transplantation. Our results lay the groundwork for engineering human-sized whole-liver scaffolds for clinical applications.

STATEMENT OF SIGNIFICANCE

A major obstacle to successful organ bioengineering is vasculature reconstruction to avoid thrombosis and deliver nutrients through blood to the whole scaffold after in vivo transplantation. Although many attempts have been made to construct endothelial cell layers on the vascular network within decellularized organs, complete coverage has not be achieved. Here, we describe an effective approach for endothelial cell seeding to reconstruct a patent vascular tree within decellularized livers by coating the vasculature using heparin-gelatin mixture. Our results have demonstrate that enhancement of endothelial cell attachment by heparin-gelatin treatment could improve vascular patency and parenchymal cell function in vitro and in vivo. These results represent a significant advancement toward bioengineering functional liver tissue that maintains vascular patency for transplantation.

Heparin/Heparan sulfate proteoglycans glycomic interactome in angiogenesis: biological implications and therapeutical use

Angiogenesis, the process of formation of new blood vessel from pre-existing ones, is involved in various intertwined pathological processes including virus infection, inflammation and oncogenesis, making it a promising target for the development of novel strategies for various interventions. To induce angiogenesis, angiogenic growth factors (AGFs) must interact with pro-angiogenic receptors to induce proliferation, protease production and migration of endothelial cells (ECs). The action of AGFs is counteracted by antiangiogenic modulators whose main mechanism of action is to bind (thus sequestering or masking) AGFs or their receptors. Many sugars, either free or associated to proteins, are involved in these interactions, thus exerting a tight regulation of the neovascularization process. Heparin and heparan sulfate proteoglycans undoubtedly play a pivotal role in this context since they bind to almost all the known AGFs, to several pro-angiogenic receptors and even to angiogenic inhibitors, originating an intricate network of interaction, the so called "angiogenesis glycomic interactome". The decoding of the angiogenesis glycomic interactome, achievable by a systematic study of the interactions occurring among angiogenic modulators and sugars, may help to design novel antiangiogenic therapies with implications in the cure of angiogenesis-dependent diseases.

Hydrogel surfaces to promote attachment and spreading of endothelial progenitor cells

Endothelialization of artificial vascular grafts is a challenging process in cardiovascular tissue engineering. Functionalized biomaterials could be promising candidates to promote endothelialization in repair of cardiovascular injuries. The purpose of this study was to synthesize hyaluronic acid (HA) and heparin-based hydrogels that could promote adhesion and spreading of endothelial progenitor cells (EPCs). We report that the addition of heparin into HA-based hydrogels provides an attractive surface for EPCs promoting spreading and the formation of an endothelial monolayer on the hydrogel surface. To increase EPC adhesion and spreading, we covalently immobilized CD34 antibody (Ab) on HA-heparin hydrogels, using standard EDC/NHS amine-coupling strategies. We found that EPC adhesion and spreading on CD34 Ab-immobilized HA-heparin hydrogels was significantly higher than their non-modified analogues. Once adhered, EPCs spread and formed an endothelial layer on both non-modified and CD34 Ab-modified HA-heparin hydrogels after 3 days of culture. We did not observe significant adhesion and spreading when heparin was not included in the control hydrogels. In addition to EPCs, we also used human umbilical cord vein endothelial cells (HUVECs), which adhered and spread on HA-heparin hydrogels. Macrophages exhibited significantly less adhesion compared to EPCs on the same hydrogels. This composite material could possibly be used to develop surface coatings for artificial cardiovascular implants, due to its specificity for EPC and endothelial cells on an otherwise non-thrombogenic surface.

Three case reports of inherited antithrombin deficiency in China: double novel missense mutations, a nonsense mutation and a frameshift mutation

Antithrombin is a plasma protein critical to the regulation of coagulation. It plays a pivotal anticoagulant role by preventing the activation of procoagulant proteinases. Inherited and (or) acquired deficiency of AT is an established risk factor for venous thromboembolism. Sequencing analysis of SERPINC1 gene of three families revealed that Family I had double novel missense mutations (c.134G > A&c.342T > G), Family II had a nonsense mutation (c.770G > A) while Family III had a frameshift mutation (c.800-803del). In addition, all of them had a large number of carriers in their families what was very rare in China.

Heparosan-derived heparan sulfate/heparin-like compounds: one kind of potential therapeutic agents

Heparan sulfate (HS) is a highly sulfated glycosaminoglycan and exists in all animal tissues. HS and heparin are very similar, except that heparin has higher level of sulfation and higher content of iduronic acid. Despite the fact that it is a century-old drug, heparin remains as a top choice for treating thrombotic disorders. Pharmaceutical heparin is derived from porcine intestine or bovine lung via a long supply chain. This supply chain is vulnerable to the contamination of animal pathogens. Therefore, new methods for manufacturing heparin or heparin-like substances devoid of animal tissues have been explored by many researchers, among which, modifications of heparosan, the capsular polysaccharide of Escherichia coli K5 strain, is one of the promising approaches. Heparosan has a structure similar to unmodified backbone of natural HS and heparin. It is feasible to obtain HS or heparin derivatives by modifying heparosan with chemical or enzymatic methods. These derivatives display different biological activities, such as anticoagulant, anti-inflammatory, anticancer, and antiviral activities. This review focuses on the recent studies of synthesis, activity, and structure-activity relationship of HS/heparin-like derivatives prepared from heparosan.

In vitro and in vivo antiangiogenic properties of the serpin protease nexin-1

The serpin protease nexin-1 (PN-1) is expressed by vascular cells and secreted by platelets upon activation, and it is known to interact with several modulators of angiogenesis, such as proteases, matrix proteins, and glycosaminoglycans. We therefore investigated the impact of PN-1 on endothelial cell angiogenic responses in vitro and ex vivo and in vivo in PN-1-deficient mice. We found that PN-1 is antiangiogenic in vitro: it inhibited vascular endothelial growth factor (VEGF)-induced endothelial cell responses, including proliferation, migration, and capillary tube formation, and decreased cell spreading on vitronectin. These effects do not require the antiprotease activity of PN-1 but involve PN-1 binding to glycosaminoglycans. In addition, our results indicated that PN-1 does not act by blocking VEGF binding to its heparan sulfate proteoglycan coreceptors. The results obtained in vitro were supported ex vivo in PN-1-deficient mice, where the microvascular network sprouting from aortic rings was significantly enhanced. Moreover, in vivo, neovessel formation was promoted in the Matrigel plug assay in PN-1-deficient mice compared to wild-type mice, and these effects were reversed by the addition of recombinant PN-1. Taken together, our results demonstrate that PN-1 has direct antiangiogenic properties and is a yet-unrecognized player in the angiogenic balance.

Anti-angiogenic poly-L-lysine dendrimer binds heparin and neutralizes its activity

The interaction between heparin, a polyanion, and a polycationic dendrimer with a glycine core and lysine branches Gly-Lys63(NH2)64 has been investigated. Complexation was assessed by transmission electron microscopy, size and zeta potential measurements, methylene blue spectroscopy, and measuring the anti-coagulant activity of heparin in vitro and in vivo. Complete association between the heparin and the dendrimer occurred a 1:1 mass ratio (2:1 molar ratio or +/-charge ratio) with formation of quasi-spherical complexes in the size range of 99-147 nm with a negative zeta potential (-47 mV). Heparin-dendrimer (dendriplex) formation led to a concentration-dependent neutralization of the anticoagulant activity of heparin in human plasma in vitro, with complete loss of activity at a 1:1 mass ratio. The anticoagulant activity of the dendriplexes in Sprague-Dawley rats was also evaluated after subcutaneous administration with uncomplexed heparin as a comparator. The in vivo anticoagulant activity of heparin in plasma, evaluated using an antifactor Xa assay, was abolished after complexation. Measurement of [(3)H]-heparin showed that both free heparin and dendriplexes were present in plasma and in organs. Such data confirmed stably the formation of dendriplexes, which could be essential in developing novel dendrimer-based anti-angiogenic therapeutics suitable in combinatory therapeutics and theranostics.

Heparin impairs angiogenesis through inhibition of microRNA-10b

Heparin, which has been used as an anticoagulant drug for decades, inhibits angiogenesis, whereas thrombin promotes tumor-associated angiogenesis. However, the mechanisms underlying the regulation of angiogenesis by heparin and thrombin are not well understood. Here, we show that microRNA-10b (miR-10b) is down-regulated by heparin and up-regulated by thrombin in human microvascular endothelial cells (HMEC-1). Overexpression of miR-10b induces HMEC-1 cell migration, tube formation, and angiogenesis, and down-regulates homeobox D10 (HoxD10) expression via direct binding of miR-10b to the putative 3' UTR of HoxD10. In addition, HMEC-1 cell migration and tube formation are induced by HoxD10 knockdown, whereas angiogenesis is arrested when HoxD10 expression is increased after anti-miR-10b or heparin treatments. Furthermore, expression of miR-10b and its transcription factor Twist are up-regulated by thrombin, whereas HoxD10 expression is impaired by thrombin. Using quartz crystal microbalance analysis, we show that heparin binds to thrombin, thereby inhibiting thrombin-induced expression of Twist and miR-10b. However, the expression of miR-10b is not attenuated by heparin any more after thrombin expression is silenced by its siRNA. Interestingly, we find that heparin attenuates miR-10b expression and induces HoxD10 expression in vivo to inhibit angiogenesis and impair the growth of MDA-MB-231 tumor xenografts. These results provide insight into the molecular mechanism by which heparin and thrombin regulate angiogenesis.

Novel insights in FGFR1 regulation: lessons from Kallmann syndrome

Disrupted fibroblast growth factor receptor (FGFR)1 signalling has been shown to cause Kallmann syndrome (KS), a human genetic disorder characterised by olfactory bulb dysgenesis and hypogonadotrophic hypogonadism. Loss-of-function mutations in the KS gene KAL-2/FGFR1 account for roughly 10% of KS cases, leading to the autosomal dominant form of the disease. Anosmin-1, the KAL-1 gene product underlying X-linked KS, modulates FGFR1 signalling via regulation of FGF2/FGFR1/heparin signalling complex assembly and activity. This review covers recent advances in the potential interactions of KS-associated molecules within the FGFR1 signalling complex, and demonstrates a novel mechanism of pre-signalling modulation that mechanistically links an autosomal dominant and sex-linked mode of inheritance of this disease, highlighting the central role of FGFR1 signalling in KS.

Mutation in the heparan sulfate biosynthesis enzyme EXT1 influences growth factor signaling and fibroblast interactions with the extracellular matrix

Heparan sulfate (HS) chains bind and modulate the signaling efficiency of many ligands, including members of the fibroblast growth factor (FGF) and platelet-derived growth factor families. We previously reported the structure of HS synthesized by embryonic fibroblasts from mice with a gene trap mutation of Ext1 that encodes a glycosyltransferase involved in HS chain elongation. The gene trap mutation results in low expression of Ext1, and, as a consequence, HS chain length is substantially reduced. In the present study, Ext1 mutant and wild-type mouse embryonic fibroblasts were analyzed for the functional consequences of the Ext1 mutation for growth factor signaling and interaction with the extracellular matrix. Here, we show that the phosphorylation of ERK1/2 in response to FGF2 stimulation was markedly decreased in the Ext1 mutant fibroblasts, whereas neither PDGF-BB nor FGF10 signaling was significantly affected. Furthermore, Ext1 mutants displayed reduced ability to attach to collagen I and to contract collagen lattices, even though no differences in the expression of collagen-binding integrins were observed. Reintroduction of Ext1in the Ext1 mutant fibroblasts rescued HS chain length, FGF2 signaling, and the ability of the fibroblasts to contract collagen. These data suggest that the length of the HS chains is a critical determinant of HS-protein interactions and emphasize the essential role of EXT1 in providing specific binding sites for growth factors and extracellular matrix proteins.

Novel mechanisms of fibroblast growth factor receptor 1 regulation by extracellular matrix protein anosmin-1

Activation of fibroblast growth factor (FGF) signaling is initiated by a multiprotein complex formation between FGF, FGF receptor (FGFR), and heparan sulfate proteoglycan on the cell membrane. Cross-talk with other factors could affect this complex assembly and modulate the biological response of cells to FGF. We have previously demonstrated that anosmin-1, a glycosylated extracellular matrix protein, interacts with the FGFR1 signaling complex and enhances its activity in an IIIc isoform-specific and HS-dependent manner. The molecular mechanism of anosmin-1 action on FGFR1 signaling, however, remains unknown. Here, we show that anosmin-1 directly binds to FGFR1 with high affinity. This interaction involves domains in the N terminus of anosmin-1 (cysteine-rich region, whey acidic protein-like domain and the first fibronectin type III domain) and the D2-D3 extracellular domains of FGFR1. In contrast, anosmin-1 binds to FGFR2IIIc with much lower affinity and displays negligible binding to FGFR3IIIc. We also show that FGFR1-bound anosmin-1, although capable of binding to FGF2 alone, cannot bind to a FGF2.heparin complex, thus preventing FGFR1.FGF2.heparin complex formation. By contrast, heparin-bound anosmin-1 binds to pre-formed FGF2.FGFR1 complex, generating an anosmin-1.FGFR1.FGF2.heparin complex. Furthermore, a functional interaction between anosmin-1 and the FGFR1 signaling complex is demonstrated by immunofluorescence co-localization and Transwell migration assays where anosmin-1 was shown to induce opposing effects during chemotaxis of human neuronal cells. Our study provides molecular and cellular evidence for a modulatory action of anosmin-1 on FGFR1 signaling, whereby binding of anosmin-1 to FGFR1 and heparin can play a dual role in assembly and activity of the ternary FGFR1.FGF2.heparin complex.

Mutagenesis studies toward understanding the intracellular signaling mechanism of antithrombin

SUMMARY BACKGROUND

Recent studies have indicated that antithrombin (AT) possesses both anti-inflammatory and antiangiogenic properties.

OBJECTIVES

The purpose of this study was to investigate the mechanism of the intracellular signaling activities of AT using wild-type and mutant serpins that have reduced anticoagulant activities due to mutations in either the reactive center loop (RCL) or the heparin-binding site.

METHODS

Direct cellular effects of the AT derivatives were compared in the LPS-stimulated endothelial cells by employing permeability and neutrophil adhesion assays in the absence and presence of pertussis toxin (PTX) and siRNAs for either syndecan-4 or sphingosine 1-phosphate receptor 1 (S1P(1)). Furthermore, the roles of prostacyclin and nuclear factor (NF)-kappaB in modulating these effects were investigated.

RESULTS

Both wild-type and the RCL mutant, AT/Proth-2, exhibited similar potent barrier protective activities and inhibited the adhesion of neutrophils to endothelial cells via inhibition of the NF-kappaB pathway. Indomethacin abrogated both activities. The heparin-binding site mutants, AT-K114E and AT-K125E, did not exhibit any protective activity in either one of these assays, but a potent pro-apoptotic activity was observed for the AT-K114E in endothelial cells. Both PTX and siRNA for syndecan-4 inhibited the protective effect of AT, but the siRNA for S1P(1) was inconsequential.

CONCLUSIONS

The interaction of AT with syndecan-4 is required for its prostacyclin-dependent protective effect through a PTX-sensitive and non-S1P(1)-related G(i)-protein coupled receptor. The RCL mutant, AT/Proth-2, with a markedly reduced anticoagulant but normal protective signaling properties, may potentially be developed as a safer anti-inflammatory drug without increasing the risk of bleeding.

Effect of covalent antithrombin-heparin complex on developmental mechanisms in the lung

We have developed a potent antithrombin (AT)-heparin conjugate (ATH) that is retained in the lung to prevent pulmonary thrombosis associated with respiratory distress in premature newborns. During continuing maturation, pulmonary angiogenesis in premature infants would be a crucial process in lung development. A naturally occurring latent form of antithrombin (L-AT) has antiangiogenic effects on lung vascularization. However, impact of latent ATH (L-ATH) on developing lung vascularization is unknown. Thus, effects of L-AT and L-ATH on fetal murine lung development were compared. Lung buds from embryonic day 11.5 (E11.5) Tie2-LacZ mouse embryos were incubated in DMEM plus FBS supplemented with PBS, AT, L-AT, heparin, ATH, or L-ATH. Vasculature of cultured explants was quantified by X-galactosidase staining. RNA was analyzed with murine gene probes for angiopoietin (Ang)-1, Ang-2, fibroblast growth factor 2 (FGF2), platelet endothelial cell adhesion molecule (PECAM), and vascular endothelial growth factor (VEGF). FGF2-supplemented medium was used to test contribution to effects of L-AT and L-ATH on angiogenesis. Epithelial branching morphogenesis was inhibited by L-AT (P = 0.003) and heparin (P < 0.001). L-AT and heparin decreased relative vascular area compared with PBS, ATH, and L-ATH. Expressions of all genes studied were downregulated by L-AT. However, L-AT and L-ATH inhibited branching morphogenesis and vasculature with added FGF2. These findings indicate that covalent linkage of AT to heparin negates disruptive effects of these moieties on lung morphology, vascularization, and growth factor gene expression. ATH may have enhanced safety as an anticoagulant during vascular development.

Protein biomarker identification in the CSF of patients with CNS lymphoma

PURPOSE

Elucidation of the CSF proteome may yield insights into the pathogenesis of CNS disease. We tested the hypothesis that individual CSF proteins distinguish CNS lymphoma from benign focal brain lesions.

METHODS

We used a liquid chromatography/mass spectrometry-based method to differentially quantify and identify several hundred CSF proteins in CNS lymphoma and control patients. We used enzyme-linked immunosorbent assay (ELISA) to confirm one of these markers in an additional validation set of 101 cases.

RESULTS

Approximately 80 CSF proteins were identified and found to be present at significantly different concentrations, both higher and lower, in training and test studies, which were highly concordant. To further validate these observations, we defined in detail the expression of one of these candidate biomarkers, antithrombin III (ATIII). ATIII RNA transcripts were identified within CNS lymphomas, and ATIII protein was localized selectively to tumor neovasculature. Determination of ATIII concentration by ELISA was significantly more accurate (> 75% sensitivity; > 98% specificity) than cytology in the identification of cancer. Measurement of CSF ATIII levels was found to potentially enhance the ability to diagnose and predict outcome.

CONCLUSION

Our findings demonstrate for the first time that proteomic analysis of CSF yields individual biomarkers with greater sensitivity in the identification of cancer than does CSF cytology. We propose that the discovery of CSF protein biomarkers will facilitate early and noninvasive diagnosis in patients with lesions not amenable to brain biopsy, as well as provide improved surrogates of prognosis and treatment response in CNS lymphoma and brain metastasis.

Serpins in thrombosis, hemostasis and fibrinolysis

Hemostasis and fibrinolysis, the biological processes that maintain proper blood flow, are the consequence of a complex series of cascading enzymatic reactions. Serine proteases involved in these processes are regulated by feedback loops, local cofactor molecules, and serine protease inhibitors (serpins). The delicate balance between proteolytic and inhibitory reactions in hemostasis and fibrinolysis, described by the coagulation, protein C and fibrinolytic pathways, can be disrupted, resulting in the pathological conditions of thrombosis or abnormal bleeding. Medicine capitalizes on the importance of serpins, using therapeutics to manipulate the serpin-protease reactions for the treatment and prevention of thrombosis and hemorrhage. Therefore, investigation of serpins, their cofactors, and their structure-function relationships is imperative for the development of state-of-the-art pharmaceuticals for the selective fine-tuning of hemostasis and fibrinolysis. This review describes key serpins important in the regulation of these pathways: antithrombin, heparin cofactor II, protein Z-dependent protease inhibitor, alpha(1)-protease inhibitor, protein C inhibitor, alpha(2)-antiplasmin and plasminogen activator inhibitor-1. We focus on the biological function, the important structural elements, their known non-hemostatic roles, the pathologies related to deficiencies or dysfunction, and the therapeutic roles of specific serpins.