A DNA nanorobot functions as a cancer therapeutic in response to a molecular trigger in vivo

Nanoscale robots have potential as intelligent drug delivery systems that respond to molecular triggers. Using DNA origami we constructed an autonomous DNA robot programmed to transport payloads and present them specifically in tumors. Our nanorobot is functionalized on the outside with a DNA aptamer that binds nucleolin, a protein specifically expressed on tumor-associated endothelial cells, and the blood coagulation protease thrombin within its inner cavity. The nucleolin-targeting aptamer serves both as a targeting domain and as a molecular trigger for the mechanical opening of the DNA nanorobot. The thrombin inside is thus exposed and activates coagulation at the tumor site. Using tumor-bearing mouse models, we demonstrate that intravenously injected DNA nanorobots deliver thrombin specifically to tumor-associated blood vessels and induce intravascular thrombosis, resulting in tumor necrosis and inhibition of tumor growth. The nanorobot proved safe and immunologically inert in mice and Bama miniature pigs. Our data show that DNA nanorobots represent a promising strategy for precise drug delivery in cancer therapy.

Thrombin-binding DNA aptamer forms a unimolecular quadruplex structure in solution

We have used two-dimensional 1H NMR spectroscopy to study the conformation of the thrombin-binding aptamer d(GGTTGGTGTGGTTGG) in solution. This is one of a series of thrombin-binding DNA aptamers with a consensus 15-base sequence that was recently isolated and shown to inhibit thrombin-catalyzed fibrin clot formation in vitro [Bock, L. C., Griffin, L. C., Latham, J. A., Vermaas, E. H. & Toole, J. J. (1992) Nature (London) 355, 564-566]. The oligonucleotide forms a unimolecular DNA quadruplex consisting of two G-quartets connected by two TT loops and one TGT loop. A potential T.T bp is formed between the two TT loops across the diagonal of the top G-quartet. Thus, all of the invariant bases in the consensus sequence are base-paired. This aptamer structure was determined by NMR and illustrates that this molecule forms a specific folded structure. Knowledge of this structure may be used in the further development of oligonucleotide-based thrombin inhibitors.

Oligonucleotide inhibitors of human thrombin that bind distinct epitopes

Thrombin, a multifunctional serine protease, recognizes multiple macromolecular substrates and plays a key role in both procoagulant and anticoagulant functions. The substrate specificity of thrombin involves two electropositive surfaces, the fibrinogen-recognition and heparin-binding exosites. The SELEX process is a powerful combinatorial methodology for identifying high-affinity oligonucleotide ligands to any desired target. The SELEX process has been used to isolate single-stranded DNA ligands to human thrombin. Here, a 29-nucleotide single-stranded DNA ligand to human thrombin, designated 60-18[29], with a Kd of approximately 0.5 nM is described. DNA 60-18[29] inhibits thrombin-catalyzed fibrin clot formation in vitro. Previously described DNA ligands bind the fibrinogen-recognition exosite, while competition and photocrosslinking experiments indicate that the DNA ligand 60-18[29] binds the heparin-binding exosite. DNA 60-18[29] is a quadruplex/duplex with a 15-nucleotide "core" sequence that has striking similarity to previously described DNA ligands to thrombin, but binds with 20 to 50-fold higher affinity. The 15-nucleotide core sequence has eight highly conserved guanine residues and forms a G-quadruplex structure. A single nucleotide within the G-quadruplex structure can direct the DNA to a distinct epitope. Additional sequence information in the duplex regions of ligand 60-18[29] contribute to greater stability and affinity of binding to thrombin. A low-resolution model for the interaction of DNA 60-18[29] to human thrombin has been proposed.

The refined 1.9-A X-ray crystal structure of D-Phe-Pro-Arg chloromethylketone-inhibited human alpha-thrombin: structure analysis, overall structure, electrostatic properties, detailed active-site geometry, and structure-function relationships

Thrombin is a multifunctional serine proteinase that plays a key role in coagulation while exhibiting several other key cellular bioregulatory functions. The X-ray crystal structure of human alpha-thrombin was determined in its complex with the specific thrombin inhibitor D-Phe-Pro-Arg chloromethylketone (PPACK) using Patterson search methods and a search model derived from trypsinlike proteinases of known spatial structure (Bode, W., Mayr, I., Baumann, U., Huber, R., Stone, S.R., & Hofsteenge, J., 1989, EMBO J. 8, 3467-3475). The crystallographic refinement of the PPACK-thrombin model has now been completed at an R value of 0.156 (8 to 1.92 A); in particular, the amino- and the carboxy-termini of the thrombin A-chain are now defined and all side-chain atoms localized; only proline 37 was found to be in a cis-peptidyl conformation. The thrombin B-chain exhibits the characteristic polypeptide fold of trypsinlike serine proteinases; 195 residues occupy topologically equivalent positions with residues in bovine trypsin and 190 with those in bovine chymotrypsin with a root-mean-square (r.m.s.) deviation of 0.8 A for their alpha-carbon atoms. Most of the inserted residues constitute novel surface loops. A chymotrypsinogen numbering is suggested for thrombin based on the topological equivalences. The thrombin A-chain is arranged in a boomeranglike shape against the B-chain globule opposite to the active site; it resembles somewhat the propeptide of chymotrypsin(ogen) and is similarly not involved in substrate and inhibitor binding. Thrombin possesses an exceptionally large proportion of charged residues. The negatively and positively charged residues are not distributed uniformly over the whole molecule, but are clustered to form a sandwichlike electrostatic potential; in particular, two extended patches of mainly positively charged residues occur close to the carboxy-terminal B-chain helix (forming the presumed heparin-binding site) and on the surface of loop segment 70-80 (the fibrin[ogen] secondary binding exosite), respectively; the negatively charged residues are more clustered in the ringlike region between both poles, particularly around the active site. Several of the charged residues are involved in salt bridges; most are on the surface, but 10 charged protein groups form completely buried salt bridges and clusters. These electrostatic interactions play a particularly important role in the intrachain stabilization of the A-chain, in the coherence between the A- and the B-chain, and in the surface structure of the fibrin(ogen) secondary binding exosite (loop segment 67-80).(ABSTRACT TRUNCATED AT 400 WORDS)

Platelet gel: an autologous alternative to fibrin glue with applications in oral and maxillofacial surgery

The preparation and use of platelet gel, an autologous formulation of fibrin glue, are described. The unique features of this biologic sealant are that it is derived from autologous blood collected in the immediate preoperative period by the anesthesiologist, it contains a high concentration of platelets, and it can be used in patients who are not candidates for blood bank donation. Platelet gel has been used successfully in the area of reconstructive oral and maxillofacial surgery in conjunction with ablative surgery of the maxillofacial region, mandibular reconstruction, surgical repair of alveolar clefts and associated oral-antral/ oral-nasal fistulas, and adjunctive procedures related to the placement of osseointegrated implants.

Reagentless, reusable, ultrasensitive electrochemical molecular beacon aptasensor

A bifunctional derivative of the thrombin-binding aptamer with a redox-active Fc moiety and a thiol group at the termini of the aptamer strand was synthesized. The ferrocene-labeled aptamer thiol was self-assembled through S-Au bonding on a polycrystalline gold electrode surface and the surface was blocked with 2-mercaptoethanol to form a mixed monolayer. By use of a fluorescent molecular beacon, the effect of counterions on quadruplex formation was established. The aptamer-modified electrode was characterized electrochemically by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). The modified electrode showed a voltammetric signal due to a one-step redox reaction of the surface-confined ferrocenyl moiety of the aptamer immobilized on the electrode surface in 10 mM N-(2-hydroxyethyl)piperazine-N'-2-ethanesulfonic acid (HEPES) buffer of pH 8.0. An increase in the DPV current signal was evident after blocking with 2-mercaptoethanol, effectively removing aptamer nonspecifically absorbed rather than bound to electrode surface or due to the formation of the aptamer-thrombin affinity interaction. The impedance measurement, in agreement with the differential pulse voltammetry (DPV), showed decreased Faradaic resistances in the same sequence. The "signal-on" upon thrombin association could be attributed to a change in conformation from random coil-like configuration on the probe-modified film to the quadruplex structure. The DPV of the modified electrode showed a linear response of the Fc oxidation signal to the increase in the thrombin concentration in the range between 5.0 and 35.0 nM with a linear correlation of r = 0.9988 and a detection limit of 0.5 nM. The molecular beacon aptasensor was amenable to full regeneration by simply unfolding the aptamer in 1.0 M HCl, and could be regenerated 25 times with no loss in electrochemical signal upon subsequent thrombin binding.

Aptamer beacons for the direct detection of proteins

We have designed a new class of molecules, which we term aptamer beacons, for detecting a wide range of ligands. Similar to molecular beacons, aptamer beacons can adopt two or more conformations, one of which allows ligand binding. A fluorescence-quenching pair is used to report changes in conformation induced by ligand binding. An anti-thrombin aptamer was engineered into an aptamer beacon by adding nucleotides to the 5'-end which are complementary to nucleotides at the 3'-end of the aptamer. In the absence of thrombin, the added nucleotides will form a duplex with the 3'-end, forcing the aptamer beacon into a stem-loop structure. In the presence of thrombin, the aptamer beacon forms the ligand-binding structure. This conformational change causes a change in the distance between a fluorophore attached to the 5'-end and a quencher attached to the 3'-end. Aptamer beacon can be a sensitive tool for detecting proteins and other chemical compounds.

Polyphosphate modulates blood coagulation and fibrinolysis

Inorganic polyphosphate is an abundant component of acidocalcisomes of bacteria and unicellular eukaryotes. Human platelet dense granules strongly resemble acidocalcisomes, and we recently showed that they contain substantial amounts of polyphosphate, which is secreted upon platelet activation. We now report that polyphosphate is a potent hemostatic regulator, accelerating blood clotting by activating the contact pathway and promoting the activation of factor V, which in turn results in abrogation of the function of the natural anticoagulant protein, tissue factor pathway inhibitor. Polyphosphate was also found to delay clot lysis by enhancing a natural antifibrinolytic agent, thrombin-activatable fibrinolysis inhibitor. Polyphosphate is unstable in blood or plasma, owing to the presence of phosphatases. We propose that polyphosphate released from platelets or microorganisms initially promotes clot formation and stability; subsequent degradation of polyphosphate by blood phosphatases fosters inhibition of clotting and activation of fibrinolysis during wound healing.

Structural origins of fibrin clot rheology

The origins of clot rheological behavior associated with network morphology and factor XIIIa-induced cross-linking were studied in fibrin clots. Network morphology was manipulated by varying the concentrations of fibrinogen, thrombin, and calcium ion, and cross-linking was controlled by a synthetic, active-center inhibitor of FXIIIa. Quantitative measurements of network features (fiber lengths, fiber diameters, and fiber and branching densities) were made by analyzing computerized three-dimensional models constructed from stereo pairs of scanning electron micrographs. Large fiber diameters and lengths were established only when branching was minimal, and increases in fiber length were generally associated with increases in fiber diameter. Junctions at which three fibers joined were the dominant branchpoint type. Viscoelastic properties of the clots were measured with a rheometer and were correlated with structural features of the networks. At constant fibrinogen but varying thrombin and calcium concentrations, maximal rigidities were established in samples (both cross-linked and noncross-linked) which displayed a balance between large fiber sizes and great branching. Clot rigidity was also enhanced by increasing fiber and branchpoint densities at greater fibrinogen concentrations. Network morphology is only minimally altered by the FXIIIa-catalyzed cross-linking reaction, which seems to augment clot rigidity most likely by the stiffening of existing fibers.

What is all that thrombin for?

The hemostatic process initiated by the exposure of tissue factor to blood is a threshold limited reaction which occurs in two distinct phases. During an initiation phase, small amounts of factor (F)Xa, FIXa and thrombin are generated. The latter activates the procofactors FV and FVIII to the activated cofactors which together with their companion serine proteases form the intrinsic FX activator (FVIIIa-FIXa) and prothrombinase (FVa-FXa) which generate the bulk of FXa and thrombin during a propagation phase. The clotting process (fibrin formation) occurs at the inception of the propagation phase when only 5-10 nM thrombin has been produced. Consequently, the vast majority (greater than 95%) of thrombin is produced after clotting during the propagation phase of thrombin generation. The blood of individuals with either hemophilia A or hemophilia B has no ability to generate the intrinsic FXase, and hence is unable to support the propagation phase of the reaction. Since clot based assays conclude before the propagation phase they are not sensitive to hemophilia A and B. The inception and magnitude of the propagation phase of thrombin generation is influenced by genetic polymorphisms associated with thrombotic and hemorrhagic disease, by the natural abundance of pro- and anticoagulants in healthy individuals and by pharmacologic interventions which influence thrombotic pathology. Therefore, it is our suspicion that the performance of the entire process of thrombin generation from initiation through propagation and termination phases of the reaction are relevant with respect to both hemorrhagic and thrombotic pathology.

A reagentless signal-on architecture for electronic, aptamer-based sensors via target-induced strand displacement

Thrombin binding stabilizes the alternative G-quadruplex conformation of the aptamer, liberating the methylene blue (MB)-tagged oligonucleotide to produce a flexible, single-stranded DNA element. This allows the MB tag to collide with the gold electrode surface, producing a readily detectable Faradaic current at thrombin concentrations as low as approximately 3 nM.

Optical Sensors Based on Hybrid Aptamer/Conjugated Polymer Complexes

Single-stranded DNA (aptamer) can specifically bind potassium ions or human alpha-thrombin. When binding takes place, the aptamer undergoes a conformational transition from an unfolded to a folded structure. This conformational change of the negatively charged oligonucleotide can be detected by adding a water-soluble, cationic polythiophene derivative, which transduces the new complex formation into an optical (colorimetric or fluorometric) signal without any labeling of the probe or of the target. This simple and rapid methodology has enabled the detection of human thrombin in the femtomole range. This new biophotonic tool can easily be applied to the detection of various other proteins as well as being useful in the high-throughput screening of new drugs.

A player of many parts: the spotlight falls on thrombin's structure

The wealth of structural information now available for thrombin, its precursors, its substrates, and its inhibitors allows a rationalization of its many roles. alpha-thrombin is a rather rigid molecule, binding to its target molecules with little conformational change. Comparison of alpha-thrombin with related trypsin-like serine proteinases reveals an unusually deep and narrow active site cleft, formed by loop insertions characteristic of thrombin. This canyon structure is one of the prime causes for the narrow specificity of thrombin. The observed modularity of thrombin allows a diversity in this specificity; its "mix-and-match" nature is exemplified by its interactions with macromolecules (Fig. 20). The apposition of the active site to a hydrophobic pocket (the apolar binding site) on one side and a basic patch (the fibrinogen recognition exosite) on the other allows for a fine tuning of enzymatic activity, as seen for fibrinogen. Thrombin receptor appears to use the same sites, but in a different way. Protein C seems only able to interact with thrombin if the recognition exosite is occupied by thrombomodulin. These two sites are also optimally used by hirudin, allowing the very tight binding observed; thrombin inhibition is effected by blocking access to the active site. On the other hand, antithrombin III makes little use of the recognition exosite; instead, its interactions are tightened with the help of heparin, which binds to a second basic site (the heparin binding site). Thrombin's modularity is a result of the conjunction of amino acid residues of like properties, such as charge or hydrophobicity. The charge distribution plays a role, not only in the binding of oppositely charged moieties of interacting molecules, but also in selection and preorientation of them. Nonproteolytic cellular properties are attributed to 1) the rigid insertion loop at Tyr60A, and 2) a partially inaccessible RGD sequence. The former can interact with cells in the native form; the latter would appear to be presented only in an (at least partially) unfolded state. The membrane binding properties of prothrombin can be understood from the ordered arrangement of calcium ions on binding to the Gla domain. Kringle F2 binds to thrombin at the heparin binding site through charge complementarity; a conformational change appears to occur on binding. The observed rigidity of the thrombin molecule in its complexes makes thrombin ideal for structure based drug design. Thrombin can be inhibited either at the active site or at the fibrinogen recognition exosite, or both.(ABSTRACT TRUNCATED AT 400 WORDS)

Single-walled carbon nanotube biosensors using aptamers as molecular recognition elements

We report the real-time detection of protein using SWNT-FET-based biosensors comprising DNA aptamers as molecular recognition elements. Anti-thrombin aptamers that are highly specific to serine protein thrombin were immobilized on the sidewall of a SWNT-FET using CDI-Tween linking molecules. The binding of thrombin aptamers to SWNT-FETs causes a rightward shift of the threshold gate voltages, presumably due to the negatively charged backbone of the DNA aptamers. While the addition of thrombin solution causes an abrupt decrease in the conductance of the thrombin aptamer immobilized SWNT-FET, no noticeable change was observed with elastase.

Structure of human des(1-45) factor Xa at 2.2 A resolution

The structure of a large molecular fragment of factor Xa that lacks only a Gla (gamma-carboxyglutamic acid) domain (N-terminal 45 residues) has been solved by X-ray crystallography and refined at 2.2 A resolution to a crystallographic R-value of 0.168. The fragment identity was clearly established by automated Edman degradation. X-ray structure analysis confirmed the biochemical characterization and also revealed that the N-terminal epidermal growth factor (EGF)-like domain is flexibly disordered in crystals. The second EGF module, however, is positionally ordered making contacts with the catalytic domain. The overall folding of the catalytic domain is similar to that of alpha-thrombin, excluding the insertion loops of the latter with respect to simpler serine proteinases. The C-terminal arginine of the A-chain interacts in a substrate-like manner with the S1 specificity site of the active site of a crystallographically neighboring molecule. Based on this interaction and the structure of D-PheProArg methylene-thrombin, a model of the commonly used dansylGluGlyArg methylene inhibitor-factor Xa interaction is proposed. The region of factor Xa corresponding to the fibrinogen recognition site of thrombin has a reversed electrical polarity to the anion binding fibrinogen recognition site of thrombin but possesses a site similar to the Ca2+ binding site of trypsin and other serine proteinases. The structure of the C-terminal EGF domain of factor Xa is the first to be determined crystallographically. Its folding has been comprehensively compared with similar domains determined by NMR. Although the A-chain makes 44 contacts at less than 3.5 A with the catalytic domain, only 16 involve the EGF module. In addition, the A-chain makes 30 intermolecular contacts with a neighboring catalytic domain.

Structure-based design of novel potent nonpeptide thrombin inhibitors

The clinical syndromes of thromboembolism are evoked by an excessive stimulation of the coagulation cascade. In this context, the serine protease thrombin plays a key role. Considerable efforts have therefore been devoted to the discovery of safe, orally active inhibitors of this enzyme. On the basis of the X-ray crystal structure of the peptide-like thrombin inhibitor NAPAP complexed with bovine thrombin, we have designed a new structural class of nonpeptidic inhibitors employing a 1,2,5-trisubstituted benzimidazole as the central scaffold. Supported by a series of X-ray structure analyses, we optimized the activity of these compounds. Thrombin inhibition in the lower nanomolar range could be achieved although the binding energy mainly results from nonpolar, hydrophobic interactions. To improve in vivo potency, we increased the overall hydrophilicity of the molecules by introducing carboxylate groups. The very polar compound 24 (BIBR 953) exhibited the most favorable activity profile in vivo. This zwitterionic molecule was converted into the double-prodrug 31 (BIBR 1048), which showed strong oral activity in different animal species. On the basis of these results, 31 was chosen for clinical development.

Serine peptidases: classification, structure and function

Serine peptidases play key roles in human health and disease and their biochemical properties shaped the molecular evolution of these processes. Of known proteolytic enzymes, the serine peptidase family is the major cornerstone of the vertebrate degradome. We describe the known diversity of serine peptidases with respect to structure and function. Particular emphasis is placed on the S1 peptidase family, the trypsins, which underwent the most predominant genetic expansion yielding the enzymes responsible for vital processes in man such as digestion, blood coagulation, fibrinolysis, development, fertilization, apoptosis and immunity.

Structure of the antithrombin-thrombin-heparin ternary complex reveals the antithrombotic mechanism of heparin

The maintenance of normal blood flow depends completely on the inhibition of thrombin by antithrombin, a member of the serpin family. Antithrombin circulates at a high concentration, but only becomes capable of efficient thrombin inhibition on interaction with heparin or related glycosaminoglycans. The anticoagulant properties of therapeutic heparin are mediated by its interaction with antithrombin, although the structural basis for this interaction is unclear. Here we present the crystal structure at a resolution of 2.5 A of the ternary complex between antithrombin, thrombin and a heparin mimetic (SR123781). The structure reveals a template mechanism with antithrombin and thrombin bound to the same heparin chain. A notably close contact interface, comprised of extensive active site and exosite interactions, explains, in molecular detail, the basis of the antithrombotic properties of therapeutic heparin.

Snake venom proteases affecting hemostasis and thrombosis

The structure and function of snake venom proteases are briefly reviewed by putting the focus on their effects on hemostasis and thrombosis and comparing with their mammalian counterparts. Up to date, more than 150 different proteases have been isolated and about one third of them structurally characterized. Those proteases are classified into serine proteases and metalloproteinases. A number of the serine proteases show fibrin(ogen)olytic (thrombin-like) activities, which are not susceptible to hirudin or heparin and perhaps to most endogenous serine protease inhibitors, and form abnormal fibrin clots. Some of them have kininogenase (kallikrein-like) activity releasing hypotensive bradykinin. A few venom serine proteases specifically activate coagulation factor V, protein C, plasminogen or platelets. The venom metalloproteinases, belonging to the metzincin family, generally show fibrin(ogen)olytic and extracellular matrix-degrading (hemorrhagic) activities. A few venom metalloproteinases show a unique substrate specificity toward coagulation factor X, platelet membrane receptors or von Willebrand factor. A number of the metalloproteinases have chimeric structures composed of several domains such as proteinase, disintegrin-like, Cys-rich and lectin-like domains. The disintegrin-like domain seems to facilitate the action of those metalloproteinases by interacting with platelet receptors. A more detailed analysis of snake venom proteases should find their usefulness for the medical and pharmacological applications in the field of thrombosis and hemostasis.

Fragment-Based Lead Discovery Using X-ray Crystallography

Fragment screening offers an alternative to traditional screening for discovering new leads in drug discovery programs. This paper describes a fragment screening methodology based on high throughput X-ray crystallography. The method is illustrated against five proteins (p38 MAP kinase, CDK2, thrombin, ribonuclease A, and PTP1B). The fragments identified have weak potency (>100 microM) but are efficient binders relative to their size and may therefore represent suitable starting points for evolution to good quality lead compounds. The examples illustrate that a range of molecular interactions (i.e., lipophilic, charge-charge, neutral hydrogen bonds) can drive fragment binding and also that fragments can induce protein movement. We believe that the method has great potential for the discovery of novel lead compounds against a range of targets, and the companion paper illustrates how lead compounds have been identified for p38 MAP kinase starting from fragments such as those described in this paper.

Refined structure of the hirudin-thrombin complex

The structure of a recombinant hirudin (variant 2, Lys47) human alpha-thrombin complex has been refined using restrained least-squares methods to a crystallographic R-factor of 0.173. The hirudin structure consists of an N-terminal domain folded into a globular unit and a long 17-peptide C-terminal in an extended chain conformation. The N-terminal domain binds at the active-site of thrombin where Ile1' to Tyr3' penetrates to the catalytic triad. The alpha-amino group of Ile1' of hirudin makes a hydrogen bond with OG of Ser195 of thrombin, the side-chains of Ile1' and Tyr3' occupy the apolar site, Thr2' is at the entrance to, but does not enter, the S1 specificity site and Ile1' to Tyr3' form a parallel beta-strand with Ser214 to Gly219. The latter interaction is antiparallel in all other serine proteinase-protein inhibitor complexes. The extended C-terminal segment of hirudin, which is abundant in acidic residues, makes many electrostatic interactions with the fibrinogen binding exosite while the last five residues are in a 3(10) helical turn residing in a hydrophobic patch on the thrombin surface. The precision of the complementarity displayed by these two molecules produces numerous interactions, which although independently generally weak, together are responsible for the high degree of affinity and specificity. Although hirudin-thrombin and D-Phe-Pro-Arg-chloromethyl ketone-thrombin differ in conformation in the autolysis loop (Lys145 to Gly150), this is most likely due to different crystal packing interactions and changes in circular dichroism between the two are probably due to the inherent flexibility of the loop. An RGD sequence, which is generally known to be involved in cell surface receptor interactions, occurs in thrombin and is associated with a long solvent channel filled with water molecules leading to the surface from the end of the S1 site. However, the RGD triplet does not appear to be able to interact in concert in a surface binding mode.

Quantification of growth factor levels using a simplified method of platelet-rich plasma gel preparation

PURPOSE

This study compared two methods of preparing platelet-rich plasma (PRP) gel and the levels of PDGF and TGFbeta in each preparation.

MATERIALS AND METHODS

Platelet-rich plasma gel was prepared by centrifugation and clotted using the ITA gelling agent (Natrex Technologies Inc, Greenville, NC) or by the addition of thrombin and calcium chloride. The levels of platelet-derived growth factor (PDGF) and transforming growth factor beta (TGFbeta) generated by clot formation were assayed by enzyme-linked immunoassay (ELISA).

RESULTS

Both methods of preparation yielded PRP gel in less than 30 minutes. However, the ITA preparation did not require thrombin to achieve adequate gel formation. The levels of PDGF and TGFbeta were similar regardless of which method was used for initiation of clot formation.

CONCLUSION

Use of ITA for gel preparation is equivalent to using calcium chloride and thrombin, without the need for special equipment and the risk of coagulopathy.

Inducible expression of Tau repeat domain in cell models of tauopathy: aggregation is toxic to cells but can be reversed by inhibitor drugs

We generated several cell models of tauopathy in order to study the mechanisms of neurodegeneration in diseases involving abnormal changes of tau protein. N2a neuroblastoma cell lines were created that inducibly express different variants of the repeat domain of tau (tau(RD)) when exposed to doxycycline (Tet-On system). The following three constructs were chosen: (i) the repeat domain of tau that coincides with the core of Alzheimer paired helical filaments; (ii) the repeat domain with the deletion mutation DeltaK280 known from frontotemporal dementia and highly prone to spontaneous aggregation; and (iii) the repeat domain with DeltaK280 and two proline point mutations that inhibit aggregation. The comparison of wild-type, pro-aggregation, and anti-aggregation mutants shows the following. (a) Aggregation of tau(RD) is toxic to cells. (b) The degree of aggregation and toxicity depends on the propensity for beta-structure. (c) Soluble mutants of tau(RD) that cannot aggregate are not toxic. (d) Aggregation is preceded by fragmentation. (e) Fragmentation of tau(RD) in cells is initially due to a thrombin-like protease activity. (f) Phosphorylation of tau(RD) (at KXGS motifs) precedes aggregation but is not correlated with the degree of aggregation. (g) Aggregates of tau(RD) disappear when the expression is silenced, showing that aggregation is reversible. (h) Aggregation can be prevented by drugs and even pre-formed aggregates can be dissolved again by drugs. Thus, the cell models open up new insights into the relationship between the structure, expression, phosphorylation, aggregation, and toxicity of tau(RD) that can be used to test current hypotheses on tauopathy and to develop drugs that prevent the aggregation and degeneration of cells.

Platelet gel for healing cutaneous chronic wounds

Wound healing is a specific host immune response for restoration of tissue integrity. Experimental studies demonstrated an alteration of growth factors activity due to their reduced synthesis, increased degradation and inactivation. In wound healing platelets play an essential role since they are rich of alpha-granules growth factors (platelet derived growth factor--PDGF; transforming growth factor-beta--TGF-beta; vascular endothelial growth factor--VEGF). Topical use of platelet gel (PG), hemocomponent obtained from mix of activated platelets and cryoprecipitate, gives the exogenous and in situ adding of growth factors (GF). The hemocomponents are of autologous or homologous origin. We performed a technique based on: multicomponent apheretic procedure to obtain plasma rich platelet and cryoprecipitate; manual processing in an open system, in sterile environment, for gel activation. Every step of the gel synthesis was checked by a quality control programme. The therapeutic protocol consists of the once-weekly application of PG. Progressive reduction of the wound size, granulation tissue forming, wound bed detersion, regression and absence of infective processes were considered for evaluating clinical response to hemotherapy. 24 patients were enrolled. They had single or multiple cutaneous ulcers with different ethiopathogenesis. Only 3 patients could perform autologous withdrawal; in the others homologous hemocomponent were used, always considering suitability and traceability criteria for transfusional use of blood. Complete response was observed in 9 patients, 2 were subjected to cutaneous graft, 4 stopped treatment, 9 had partial response and are still receiving the treatment. In each case granulation tissue forming increased following to the first PG applications, while complete re-epithelization was obtained later. Pain was reduced in every treated patient. Topical haemotherapy with PG may be considered as an adjuvant treatment of a multidisciplinary process, useful to enhance therapy of cutaneous ulcers.