Complement inhibitors: a resurgent concept in anti-inflammatory therapeutics

Development of a new pharmacophore model that discriminates active compstatin analogs

Compstatin and its active peptide analogs can potentially be used for therapeutic purposes because their binding to the third component of complement prohibits its conversion into the proteolytically activated form of the third component of complement, thus inhibiting complement cascades in all three complement pathways. Mallik and Morikis built three quasi-dynamic pharmacophore models for compstatin peptide analogs before, but only nine compstatin peptide analogs were incorporated in their study and the most active compstatin analog had only medium inhibitory activity. Since then, many more compstatin analogs have been synthesized and their inhibitory activities tested. Furthermore, the X-ray structure of AcCompNH2-V4W-H9A bound to the third component of complement has become available (PDB ID: 2QKI). In this paper, we utilized all the new information and built a new pharmacophore model using a distinct approach. Our model demonstrated good performance in a separate test set of 82 compstatin analogs: it accurately identified 70% of the analogs of medium or high inhibitory activities and misclassified only 8.5% of the analogs of low or no inhibitory activities. The results proved our pharmacophore model to be a filter of great sensitivity and specificity.

Absence of the complement regulatory molecule CD59a leads to exacerbated neuropathology after traumatic brain injury in mice

Background

Complement represents a crucial mediator of neuroinflammation and neurodegeneration after traumatic brain injury. The role of the terminal complement activation pathway, leading to generation of the membrane attack complex (MAC), has not been thoroughly investigated. CD59 is the major regulator of MAC formation and represents an essential protector from homologous cell injury after complement activation in the injured brain.

Methods

Mice deleted in the Cd59a gene (CD59a^-/-) and wild-type littermates (n = 60) were subjected to focal closed head injury. Sham-operated (n = 60) and normal untreated mice (n = 14) served as negative controls. The posttraumatic neurological impairment was assessed for up to one week after trauma, using a standardized Neurological Severity Score (NSS). The extent of neuronal cell death was determined by serum levels of neuron-specific enolase (NSE) and by staining of brain tissue sections in TUNEL technique. The expression profiles of pro-apoptotic (Fas, FasL, Bax) and anti-apoptotic (Bcl-2) mediators were determined at the gene and protein level by real-time RT-PCR and Western blot, respectively.

Results

Clinically, the brain-injured CD59a^-/- mice showed a significantly impaired neurological outcome within 7 days, as determined by a higher NSS, compared to wild-type controls. The NSE serum levels, an indirect marker of neuronal cell death, were significantly elevated in CD59a^-/- mice at 4 h and 24 h after trauma, compared to wild-type littermates. At the tissue level, increased neuronal cell death and brain tissue destruction was detected by TUNEL histochemistry in CD59a^-/- mice within 24 hours to 7 days after head trauma. The analysis of brain homogenates for potential mediators and regulators of cell death other than the complement MAC (Fas, FasL, Bax, Bcl-2) revealed no difference in gene expression and protein levels between CD59a^-/- and wild-type mice.

Conclusion

These data emphasize an important role of CD59 in mediating protection from secondary neuronal cell death and further underscore the key role of the terminal complement pathway in the pathophysiology of traumatic brain injury. The exact mechanisms of complement MAC-induced secondary neuronal cell death after head injury require further investigation.

Functional characterization of human C3/cobra venom factor hybrid proteins for therapeutic complement depletion

Cobra venom factor (CVF) is a structural and functional analog of complement C3 isolated from cobra venom. Both CVF and C3b can bind factor B and subsequently form the bimolecular C3/C5 convertases CVF,Bb or C3b,Bb, respectively. The two homologous enzymes exhibit several differences of which the difference in physico-chemical stability is most important, allowing continuous activation of C3 and C5 by CVF,Bb, leading to serum complement depletion. Here we describe the detailed functional properties of two hybrid proteins in which the 113 or 315 C-terminal residues of C3 were replaced with corresponding CVF sequences. Both hybrid proteins formed stable convertases that exhibited C3-cleaving activity, although at different rates. Neither convertase cleaved C5. Both convertases showed partial resistance to inactivation by factors H and I, allowing them to deplete complement in human serum. These data demonstrate that functionally important structural differences between CVF and C3 are located in the very C-terminal region of both homologous proteins, and that small substitutions in human C3 with homologous CVF sequence result in C3 derivatives with CVF-like functions. Such hybrid proteins are important tools to study the structure/function relationships in both C3 and CVF, and these "humanized CVF" proteins may become reagents for therapeutic complement depletion.

Isolation and characterization of an anti-complementary protein-bound polysaccharide from the stem barks of Eucommia ulmoides

EWDS-1, a homogeneous protein-bound polysaccharide, was isolated as an anti-complementary agent from the stem barks of Eucommia ulmoides. EWDS-1 was identified as a branched proteoglycan with average molecular weight about 2,000,000 Da, composed of Gal, Glc and Ara in the ratio of 2.1:1.0:0.9, along with trace of Rha, Xyl, Man, as well as 3.95% of protein. The linkages of the residues of EWDS-1 were deduced by methylation analysis and NMR technique. Bioassay showed that EWDS-1 inhibited complement activation on both the classic and alternative pathways with CH(50) and AP(50) values of 203+/-20 microg/ml and 45+/-8 microg/ml, respectively. Preliminary mechanism studies by using complement component depleted-sera indicated that EWDS-1 inhibits activation of complement system by interacting with C1q, C1r, C1s, C2, C3, C4, C5 and C9. The results suggested that EWDS-1 could be of promising benefits in treatment of the complement associated diseases.

Anticomplementary principles of a Chinese multiherb remedy for the treatment and prevention of SARS

AIM OF THE STUDY

To elucidate the anticomplementary principles of a Chinese multiherb remedy used for the treatment and prevention of SARS, which contains five ingredients of Herba Houttuyniae, Flos Chrysanthemi Indici, Herba Artemisiae Scopariae, Herba Eupatorii and Fructus Tsaoko.

MATERIALS AND METHODS

The anticomplementary activity was evaluated from hemolytic assays through the classical pathway (CP) and the alternative pathway (AP) of complement system in vitro. Compounds were isolated using bioactivity-guided fractionation and tested in vitro for their complement-inhibiting properties on the CP and AP. HPLC-DAD-ESI-MS was used to assign the isolated compounds in the five ingredient herbs.

RESULTS

15 compounds, including chlorogenic acid (1), rutin (2), hyperoside (3), p-hydroxyacephenone (4), scopoletin (5), quercitrin (6) (3R,4R,6S)-3,6-dihydroxy-1-menthene (7), acaciin (8), scoparone (9), luteolin (10), quercetin (11), apigenin (12), acacetin (13), aristolactam (14), and apigenin-7,4'-dimethyl ether (15) were isolated and identified. Nine flavonoids (2, 3, 6, 8, 10-13, 15) were found to show inhibitory effects towards the CP and AP of complement system, luteolin (10) was the most potent with the CH50 and AP50 values of 0.19 and 0.17 mM. The bioactive flavonoids were mainly derived from Herba Houttuyniae, Flos Chrysanthemi Indici and Herba Artemisiae Scopariae.

CONCLUSIONS

A Chinese multiherb remedy used for the treatment and prevention of SARS has robust inhibitory effect on complement system through the CP and AP, and its anticomplementary activity could be attributed to the flavonoids present in some ingredient herbs. Luteolin could be a potential anticomplementary agent.

The classical complement cascade mediates CNS synapse elimination

During development, the formation of mature neural circuits requires the selective elimination of inappropriate synaptic connections. Here we show that C1q, the initiating protein in the classical complement cascade, is expressed by postnatal neurons in response to immature astrocytes and is localized to synapses throughout the postnatal CNS and retina. Mice deficient in complement protein C1q or the downstream complement protein C3 exhibit large sustained defects in CNS synapse elimination, as shown by the failure of anatomical refinement of retinogeniculate connections and the retention of excess retinal innervation by lateral geniculate neurons. Neuronal C1q is normally downregulated in the adult CNS; however, in a mouse model of glaucoma, C1q becomes upregulated and synaptically relocalized in the adult retina early in the disease. These findings support a model in which unwanted synapses are tagged by complement for elimination and suggest that complement-mediated synapse elimination may become aberrantly reactivated in neurodegenerative disease.

Complement driven by conformational changes

Complement in mammalian plasma recognizes pathogenic, immunogenic and apoptotic cell surfaces, promotes inflammatory responses and marks particles for cell lysis, phagocytosis and B-cell stimulation. At the heart of the complement system are two large proteins, complement component C3 and protease factor B. These two proteins are pivotal for amplification of the complement response and for labelling of the target particles, steps that are required for effective clearance of the target. Here we review the molecular mechanisms of complement activation, in which proteolysis and complex formation result in large conformational changes that underlie the key offensive step of complement executed by C3 and factor B. Insights into the mechanisms of complement amplification are crucial for understanding host defence and pathogen immune evasion, and for the development of complement-immune therapies.

Complement-targeted therapeutics

The complement system is a central component of innate immunity and bridges the innate to the adaptive immune response. However, it can also turn its destructive capabilities against host cells and is involved in numerous diseases and pathological conditions. Modulation of the complement system has been recognized as a promising strategy in drug discovery, and a large number of therapeutic modalities have been developed. However, successful marketing of complement-targeted drugs has proved to be more difficult than initially expected, and many strategies have been discontinued. The US Food and Drug Administration's approval of the first complement-specific drug, an antibody against complement component C5 (eculizumab; Soliris), in March 2007, was a long-awaited breakthrough in the field. Approval of eculizumab validates the complement system as therapeutic target and might facilitate clinical development of other promising drug candidates.

Structure of compstatin in complex with complement component C3c reveals a new mechanism of complement inhibition

Undesired complement activation is a major cause of tissue injury in various pathological conditions and contributes to several immune complex diseases. Compstatin, a 13-residue peptide, is an effective inhibitor of the activation of complement component C3 and thus blocks a central and crucial step in the complement cascade. The precise binding site on C3, the structure in the bound form, and the exact mode of action of compstatin are unknown. Here we present the crystal structure of compstatin in complex with C3c, a major proteolytic fragment of C3. The structure reveals that the compstatin-binding site is formed by the macroglobulin (MG) domains 4 and 5. This binding site is part of the structurally stable MG-ring formed by domains MG 1-6 and is far away from any other known binding site on C3. Compstatin does not alter the conformation of C3c, whereas compstatin itself undergoes a large conformational change upon binding. We propose a model in which compstatin sterically hinders the access of the substrate C3 to the convertase complexes, thus blocking complement activation and amplification. These insights are instrumental for further development of compstatin as a potential therapeutic.

The structure of OMCI, a novel lipocalin inhibitor of the complement system

The complement (C) system is a potent innate immune defence system against parasites. We have recently characterised and expressed OmCI, a 16 kDa protein derived from the soft tick Ornithodoros moubata that specifically binds C5, thereby preventing C activation. The structure of recombinant OmCI determined at 1.9 A resolution confirms a lipocalin fold and reveals that the protein binds a fatty acid derivative that we have identified by mass spectrometry as ricinoleic acid. We propose that OmCI could sequester one of the fatty acid-derived inflammatory modulators from the host plasma, thereby interfering with the host inflammatory response to the tick bite. Mapping of sequence differences between OmCI and other tick lipocalins with different functions, combined with biochemical investigations of OmCI activity, supports the hypothesis that OmCI acts by preventing interaction with the C5 convertase, rather than by blocking the C5a cleavage site.

Selective inhibition of the interaction of C1q with immunoglobulins and the classical pathway of complement activation by steroids and triterpenoids sulfates

Since undesirable activation of the complement system through the classical pathway is associated with tissue damage and other pathologic proinflammatory consequences at ischemia/reperfusion injury, autoimmune diseases, and rejection of allo- and xenografts, creation of selective inhibitors of the classical pathway leaving the alternative pathway intact is of great importance. Classical pathway is triggered by binding of its recognizing unit, protein C1q, to a number of targets like antibodies, pentraxins, apoptotic cells, and others. In order to obtain inhibitors blocking the first step of the classical cascade, synthesis of sulfates of steroids (Delta(5)-3beta-hydroxycholenic, Delta(5)-3beta-hydroxyetiocholenic, deoxycholic, and cholic acids) and triterpenoids (betulin, 20,29-dihydro-20,29-dichloromethylenbetulin, betulinic, ursolic, and oleanolic acids) has been performed. Testing of the compounds in classical pathway inhibition assay has displayed derivatives of triterpenoid betulin (betulin disulfate and betulinic acid sulfate) to be the most potent inhibitors. Further studies of the two compounds established that their activity to inhibit the classical pathway had been due to their capability to block the interaction of C1q with antibodies. Betulin disulfate and betulinic acid sulfate have shown weak inhibition of the alternative route of activation, what makes them promising inhibitors for the selective suppression of the classical complement pathway at the earliest possible level as well as perspective agents for blocking the interaction of C1q with its other targets.

Dense deposit disease: new insights

PURPOSE OF REVIEW

Dense deposit disease is a rare but devastating disease primarily affecting children. This review focuses on new information regarding the pathophysiology of dense deposit disease, its appearance histopathologically, its relationship to other diseases including macular degeneration and acquired partial lipodystrophy and potential new therapies.

RECENT FINDINGS

The microscopic features of dense deposit disease have been separated into five patterns with only about 25% of patients showing membranoproliferative features. The subtle interplay between genetic changes in complement regulatory proteins and dysregulation of the alternative pathway of complement is now more evident. Haplotype mapping has shown at-risk phenotypes of complement factor H associated with the development of dense deposit disease. Treatment protocols are empiric and not very effective. New information on complement inhibitors and plasma exchange, however, has brought hope for new therapies in the near future.

SUMMARY

Understanding of the pathology and the pathophysiology of dense deposit disease has advanced rapidly in the last decade. New efforts in genetic mapping along with the development of novel inhibitors of the complement system will lead to improved care for patients afflicted with this uncommon condition.

Conformational analysis of compstatin analogues with molecular dynamics simulations in explicit water

The cyclic 13-residue peptide compstatin is a potential therapeutic agent against the unregulated activation of the complement system. A thorough knowledge of its structural and dynamical properties in solution may assist the design of improved complement inhibitors. NMR studies have suggested that the 5-8 segment of free compstatin folds into a critical for activity 5-8 beta turn and the rest of the peptide is mainly disordered. Earlier computational studies of compstatin analogues with a polar-hydrogen/generalized-Born approximation reproduced the 5-8 turn, but also indicated the formation of beta-hairpin or alpha-helical elements and the existence of interactions between certain charged or aromatic sidechains. However, these features are absent or partly present in the NMR spectra, due to extensive conformational averaging. In order to check the compstatin properties with a more rigorous model of the intra- and intermolecular interactions, we conduct here 98-ns all-atom/explicit-water simulations of three compstatin analogues with variable activity; a native analogue, the more active mutant V4W/H9A and the inactive mutant Q5G. The 5-8 beta-turn population is in good accord with NMR. For the systems studied here, the simulations suggest that the 5-8 turn population does not correlate strictly with activity, in agreement with earlier mutational studies. Furthermore, they show structural differences among the analogues outside the 5-8 region. The possible role of these differences in activity is discussed. The probability of beta-hairpin or alpha-helix elements is much smaller with respect to the polar-hydrogen/GB simulations, and the persistent Trp4-Trp7 or Asp6-Arg11 sidechain interactions of the earlier GB studies are not reproduced. The present simulations extend the NMR data and improve our understanding of the properties of compstatin and related analogues.

Complement inactivating proteins and intraspecies venom variation in Crotalus oreganus helleri

Complement inactivating properties were detected in venom from the southern California distribution of Crotalus oreganus helleri (Southern Pacific Rattlesnake). This activity showed strong geographic bias to the San Bernardino Mountain range, and venom from this area reacted strongly with Fraction 5 antiserum (AF5). However, venoms from the San Jacinto Mountain range, which have been previously shown to contain Mojave toxin, did not inhibit complement and did not react with AF5. AF5 has been previously shown to recognize a protease in C. scutulatus venom that inactivates complement, but the identity of this protein has remained unknown. Using a functional venomic approach, utilizing two-dimensional gel electrophoresis coupled with liquid chromatography and tandem mass spectrometry (LC/MS/MS), we have identified catrocollastatin and hemorrhagic toxin II (HT-2) as the primary proteins recognized by AF5. The information we present within this manuscript further illustrates the now well-known reality of intraspecies venom variation and the challenges faced in providing comprehensive polyvalent antivenoms.

Synthesis of 3H-spiro[benzofuran-2,1′-cyclohexane] derivatives from naturally occurring filifolinol and their classical complement pathway inhibitory activity

Six 3H-spiro[benzofuran-2,1'-cyclohexane] derivatives were synthesized from naturally occurring filifolinol, and their classical complement pathway inhibitory activity was determined. IC(50) values of the most potent compounds were comparable to the activity of the natural complement inhibitor K76-COOH and some synthetic tricyclic analogs of it.

The role of complement in biomaterial-induced inflammation

Biomaterials are regularly used in various types of artificial tissues and organs, such as oxygenators, plasmapheresis equipment, hemodialysers, catheters, prostheses, stents, vascular grafts, miniature pumps, sensors and heart aids. Although progress has been made regarding bioincompatibility, many materials and procedures are associated with side effects, in particular bioincompatibility-induced inflammation, infections and subsequent loss of function. After cardiopulmonary bypass, coagulopathies can occur and lead to cognitive disturbances, stroke and extended hospitalization. Hemodialysis is associated with anaphylatoid reactions that cause whole-body inflammation and may contribute to accelerated arteriosclerosis. Stents cause restenosis and, in severe cases, thrombotic reactions. This situation indicates that there is still a need to try to understand the mechanisms involved in these incompatibility reactions in order to be able to improve the biomaterials and to develop treatments that attenuate the reactions and thereby reduce patients' discomfort, treatment time and cost. This overview deals with the role of complement in the incompatibility reactions that occur when biomaterials come in contact with blood and other body fluids.

Defining the CD59-C9 binding interaction

CD59 is a membrane glycoprotein that regulates formation of the cytolytic membrane attack complex (MAC or C5b-9) on host cell membranes. It functions by binding to C8 (alpha chain) and C9 after their structural rearrangement during MAC assembly. Previous studies indicated that the CD59 binding site in C9 was located within a 25-residue disulfide-bonded loop, and in C8alpha was located within a 51-residue sequence that overlaps the CD59 binding region of C9. By peptide screens and the use of peptides in binding assays, functional assays, and computer modeling and docking studies, we have identified a 6-residue sequence of human C9, spanning residues 365-371, as the primary CD59 recognition domain involved in CD59-mediated regulation of MAC formation. The data also indicate that both C8alpha and C9 bind to a similar or overlapping site on CD59. Furthermore, data from CD59-peptide docking models are consistent with the C9 binding site on CD59 located at a hydrophobic pocket, putatively identified previously by CD59 mutational and modeling studies.

Complement activation by sulfonated poly(ethylene glycol)-acrylate copolymers through alternative pathway

Previously, novel poly(ethylene glycol) (PEG) and sulfonated PEG acrylate (PEG-SO(3)A/OA) copolymers were prepared as coating and/or blending materials for biomedical applications. Surfaces modified with copolymers exhibited increased anti-coagulation properties and decreased plasma adsorption level due to increased hydrophilic properties and reorientation characteristics of PEG/PEG-SO(3)A chains in water phase. As continuation study, anti-complement effects of PEG-SO(3)/OA copolymers were investigated in vitro, and compared with those of low-density polyethylene (LDPE) and PEG/OA. C3 activation by PEG-SO(3)/OA samples was lower than that by PEG/OA samples, which was attributed to decreased surface nucleophile level of samples. PEG-SO(3)/OA samples increased inhibition of Bb production, resulting in decreased C5 activation. Owing to reduced activations of C3 and C5, PEG-SO(3)/OA samples markedly decreased SC5b-9 levels in plasma.

Drug design using the example of the complement system inhibitors' development

Undesired activation of the complement system, a part of the immune system, is a major pathogenic factor contributing to various diseases, such as ischemia-reperfusion injury, sepsis, asthma, allergic reactions, rheumatoid arthritis, Alzheimer's disease, myasthenia, multiple sclerosis and others. The history of the development of complement system inhibitors, preventing its destructive action on the body, represents the evolution of the main methods of drug design. This review illustrates the main approaches of drug design, ranging from screening and modification of natural products to structure-based ligand design, on the basis of complement inhibitors' creation. The current status of the field of complement inhibitors is also discussed.

Insights into the Human CD59 Complement Binding Interface Toward Engineering New Therapeutics

CD59 is a 77-amino acid membrane glycoprotein that plays an important role in regulating the terminal pathway of complement by inhibiting formation of the cytolytic membrane attack complex (MAC or C5b-9). The MAC is formed by the self assembly of C5b, C6, C7, C8, and multiple C9 molecules, with CD59 functioning by binding C5b-8 and C5b-9 in the assembling complex. We performed a scanning alanine mutagenesis screen of residues 16-57, a region previously identified to contain the C8/C9 binding interface. We have also created an improved NMR model from previously published data for structural understanding of CD59. Based on the scanning mutagenesis data, refined models, and additional site-specific mutations, we identified a binding interface that is much broader than previously thought. In addition to identifying substitutions that decreased CD59 activity, a surprising number of substitutions significantly enhanced CD59 activity. Because CD59 has significant therapeutic potential for the treatment of various inflammatory conditions, we investigated further the ability to enhance CD59 activity by additional mutagenesis studies. Based on the enhanced activity of membrane-bound mutant CD59 molecules, clinically relevant soluble mutant CD59-based proteins were prepared and shown to have up to a 3-fold increase in complement inhibitory activity.

Mannose-binding lectin is a regulator of inflammation that accompanies myocardial ischemia and reperfusion injury

The mannose-binding lectin (MBL), a circulating pattern recognition molecule, recognizes a wide range of infectious agents with resultant initiation of the complement cascade in an Ab-independent manner. MBL recognizes infectious non-self and altered self in the guise of apoptotic and necrotic cells. In this study, we demonstrate that mice lacking MBL, and hence are devoid of MBL-dependent lectin pathway activation but have fully active alternative and classical complement pathways, are protected from cardiac reperfusion injury with resultant preservation of cardiac function. Significantly, mice that lack a major component of the classical complement pathway initiation complex (C1q) but have an intact MBL complement pathway, are not protected from injury. These results suggest that the MBL-dependent pathway of complement activation is a key regulator of myocardial reperfusion ischemic injury. MBL is an example of a pattern recognition molecule that plays a dual role in modifying inflammatory responses to sterile and infectious injury.

Immune evasion by a staphylococcal complement inhibitor that acts on C3 convertases

The complement system is pivotal in host defense but also contributes to tissue injury in several diseases. The assembly of C3 convertases (C4b2a and C3bBb) is a prerequisite for complement activation. The convertases catalyze C3b deposition on activator surfaces. Here we describe the identification of staphylococcal complement inhibitor, an excreted 9.8-kilodalton protein that blocks human complement by specific interaction with C4b2a and C3bBb. Staphylococcal complement inhibitor bound and stabilized C3 convertases, interfering with additional C3b deposition through the classical, lectin and alternative complement pathways. This led to a substantial decrease in phagocytosis and killing of Staphylococcus aureus by human neutrophils. As a highly active and small soluble protein that acts exclusively on surfaces, staphylococcal complement inhibitor may represent a promising anti-inflammatory molecule.

Design and synthesis of low molecular weight compounds with complement inhibition activity

An attempt was made to synthesize a series of non-cytotoxic low molecular weight compounds of varying substitutions and functionalities having pharmacophore activity like carbonyl compounds, carboxylic acid and bioisosteres like tetrazole and phenyl acrylic acid. The in vitro assay of these analogues for the inhibition of complement activity revealed significant inhibitory activity for varying substituents and, particularly, for bioisosteres, that is, tetrazole and phenyl acrylic acid derivatives.

Binding of C3 fragments on top of adsorbed plasma proteins during complement activation on a model biomaterial surface

In the present study we investigate whether complement activation in blood in contact with a model biomaterial surface (polystyrene) occurs directly on the material surface or on top of an adsorbed plasma protein layer. Quartz crystal microbalance-dissipation analysis (QCM-D) complemented with enzyme immunoassays and Western blotting were used. QCM-D showed that the surface was immediately covered with a plasma protein film of approximately 8 nm. Complement activation that started concomitantly with the adsorption of the protein film was triggered by a self-limiting classical pathway activation. After adsorption of the protein film, alternative pathway activation provided the bulk of the C3b deposition that added 25% more mass to the surface. The build up of alternative pathway convertase complexes using purified C3 and factors B and D on different protein films as monitored by QCM-D showed that only adsorbed albumin, IgG, but not fibrinogen, allowed C3b binding, convertase assembly and amplification. Western blotting of eluted proteins from the material surface demonstrated that the C3 fragments were covalently bound to other proteins. This is consistent with a model in which the activation is triggered by initiating convertases formed by means of the initially adsorbed proteins and the main C3b binding is mediated by the alternative pathway on top of the adsorbed protein film.

Activation of the complement system and leukocyte recruitment by Tityus serrulatus scorpion venom

The scorpion Tityus serrulatus is considered one of the most dangerous species in Brazil. Its venom evokes an inflammatory response, although the exact mechanism of this effect is still unknown. The aim of the present study was to investigate the effect of Tityus serrulatus venom (TsV) on the complement system (CS) and on leukocyte recruitment. Complement consumption by TsV was evaluated using in vitro hemolytic assays, immunoelectrophoresis and two-dimensional immunoelectrophoresis of complement components (factor B and C3). In order to evaluate neutrophil migration induced in normal human serum (NHS) in the presence of TsV, in vitro chemotaxis assays were performed using the Boyden chamber model. In vitro TsV induced a concentration- and time-dependent reduction in hemolytic activity of the classical/lectin and alternative complement pathways, with samples of 43.0 microg and 43.4 microg, respectively, inhibiting 50% of the lytic activity. Alterations in C3 and factor B electrophoretic mobility after incubation of NHS with TsV, were identical to those obtained with zymosan (positive control). Incubation of NHS with TsV induced neutrophil chemotaxis similar to that observed with zymosan-activated serum. Our results show that TsV activates the CS, leading to factor B and C3 cleavage, to reduction of serum lytic activity and generation of complement chemotactic factors. Therefore, CS may play an important role in the inflammatory response observed upon scorpion envenomation.

Role of anti-C1q autoantibodies in the pathogenesis of lupus nephritis

Anti-C1q autoantibodies can be found in the sera of patients with several autoimmune diseases, but also in healthy individuals. Although these anti-C1q autoantibodies were already identified several decades ago, they still puzzle both immunologists and nephrologists. The main reason for this puzzling effect are observations that seemed to indicate quite clearly that anti-C1q should be pathogenic to the kidney and the observation on the other hand that anti-C1q autoantibodies can be found in several disease conditions, as well as in healthy individuals, and are then unrelated to overt renal inflammation. This puzzle is the focus of the current review, which will provide an overview of the historical data, define the clinical interests and, importantly, will try to put several aspects in perspective based on recent observations in patients and in murine models. In addition, the paper will discuss therapeutic intervention possibilities regarding anti-C1q-mediated damage in systemic lupus erythematosus, as well as the therapeutic potential of anti-C1q antibodies in other conditions.

Complement inhibitor of C5 activation from the soft tick Ornithodoros moubata

Blood-feeding ticks must control C activation or be damaged by the host inflammatory response. We report the characterization and expression of a novel, relatively small, broad-acting C inhibitory protein (termed OmCI) from the soft tick Ornithodoros moubata. The native 17-kDa nonglycosylated protein inhibits both human and guinea pig classical and alternative C activation pathways. The IC50 values for each pathway were 12 and 27 nM, respectively, in hemolytic assays using human serum diluted 40-fold. The cDNA encodes a protein of 168 aa, including an 18-aa secretion signal sequence that is absent in the mature form. The inhibitor has 46% amino acid identity with moubatin, a platelet aggregation inhibitor also from O. moubata that is an outlying member of the lipocalin family. Native OmCI had no inhibitory effect on the addition of C8 and C9 to preformed C5b-C7 and C5b-C8 to form the membrane attack complex and no effect on the rate of C3a production by the C3 convertase enzymes C4bC2a, C3(H2O)Bb, or C3bBb. Both recombinant and native OmCI abolish production of C5a by human classical (C4bC3bC2a) and alternative (C3bC3bBb) C5 convertases. Addition of excess C5 but not C3 competes away the inhibitory activity of OmCI, indicating that OmCI targets C5 itself rather than inhibiting the C5 convertase C4bC3bC2a itself. Direct binding of OmCI to C5 was demonstrated by Western blotting and gel filtration chromatography using 125I-labeled proteins. OmCI is the first lipocalin family member shown to inhibit C and also the first natural inhibitor that specifically targets the C5 activation step.

Inhibition of classical pathway of complement activation with negative charged derivatives of bisphenol A and bisphenol disulphates

In order to obtain strong inhibitors of classical pathway of complement activation the low weight negative charged compounds have been investigated. On the basis of bisphenol A anionic derivatives with one or two carboxylic, sulphate and phosphate groups the critical role of negative charged groups for complement-inhibiting activity has been established. It was determined that two sulphate or phosphate groups in the molecule provide the most inhibiting effect. At the next stage a set of bisphenol disulphates of varying structures has been synthesized and investigated. Bulky hydrophobic groups (cyclohexyliden, fluorenyliden, anthronyliden) at the central part of the bisphenol molecule it was found to increase complement-inhibiting activity markedly. The replacement of the ortho-positions to the charged group by halogens or alkyl groups (allyl, propyl) increases the inhibiting effect. It was showed by ELISA that several compounds studied interact with C1q, C1r /C1s components of complement. For the set of bisphenol disulphates the QSAR equation with hydrophobic coefficient and electronic parameters has been formulated. Both hydrophobic and electrostatic interactions it was established to have a great significance for the inhibition of classical pathway of complement activation.

Using animal models to determine the significance of complement activation in Alzheimer's disease

Complement inflammation is a major inflammatory mechanism whose function is to promote the removal of microorganisms and the processing of immune complexes. Numerous studies have provided evidence for an increase in this process in areas of pathology in the Alzheimer's disease (AD) brain. Because complement activation proteins have been demonstrated in vitro to exert both neuroprotective and neurotoxic effects, the significance of this process in the development and progression of AD is unclear. Studies in animal models of AD, in which brain complement activation can be experimentally altered, should be of value for clarifying this issue. However, surprisingly little is known about complement activation in the transgenic animal models that are popular for studying this disorder. An optimal animal model for studying the significance of complement activation on Alzheimer's – related neuropathology should have complete complement activation associated with senile plaques, neurofibrillary tangles (if present), and dystrophic neurites. Other desirable features include both classical and alternative pathway activation, increased neuronal synthesis of native complement proteins, and evidence for an increase in complement activation prior to the development of extensive pathology. In order to determine the suitability of different animal models for studying the role of complement activation in AD, the extent of complement activation and its association with neuropathology in these models must be understood.

Complement: structure, functions, evolution, and viral molecular mimicry

The complement (C') system has long been recognized as an important mediator of innate immune defense and inflammation. In recent years there is increasing evidence suggesting that complement components may also participate in non-inflammatory and developmental processes. Here we review our current work on the structural-functional aspects of C3-ligand interactions and the rational design of small-sized complement inhibitors. We present a novel, proteomics-based, approach to studying protein-protein interactions within the C' system and discuss our progress in the study of viral immune evasion strategies. Furthermore we discuss the involvement of complement proteins in organ regeneration and hematopoietic development.

Clinical and laboratory evaluation of complement deficiency

The complement system provides innate defense against microbial pathogens and is a "complement" to humoral (antibody-mediated) immunity. Consisting of plasma and membrane proteins, this proinflammatory system works in part by a cascade involving limited proteolysis whereby one component activates the next, resulting in a dramatic amplification. The overall goal is deposition of complement fragments on pathologic targets for the purposes of opsonization, lysis, and liberation of peptides that promote the inflammatory response. Deficiencies of complement components predispose to infections and autoimmune syndromes. Even though total deficiency of a complement component is rare, patients presenting with certain bacterial infections and autoimmune syndromes, especially SLE, have a much greater incidence of deficiency. This review will summarize the clinical manifestations and pathophysiology of congenital and acquired complement deficiency diseases. We will also present an algorithm for laboratory diagnosis of complement deficiency and discuss current and future therapeutic options.

Conformational interconversion in compstatin probed with molecular dynamics simulations

Compstatin is a 13-residue cyclic peptide that has the potential to become a therapeutic agent against unregulated complement activation. In our effort to understand the structural and dynamic characteristics of compstatin that form the basis for rational and combinatorial optimization of structure and activity, we performed 1-ns molecular dynamics (MD) simulations. We used as input in the MD simulations the ensemble of 21 lowest energy NMR structures, the average minimized structure, and a global optimization structure. At the end of the MD simulations we identified five conformations, with populations ranging between 9% and 44%. These conformations are as follows: 1) coil with alphaR-alphaR beta-turn, as was the conformation of the initial ensemble of NMR structures; 2) beta-hairpin with epsilon-alphaR beta-turn; 3) beta-hairpin with alphaR-alphaR beta-turn; 4) beta-hairpin with alphaR-beta beta-turn; and 5) alpha-helical. Conformational switch was possible with small amplitude backbone motions of the order of 0.1-0.4 A and free energy barrier crossing of 2-11 kcal/mol. All of the 21 MD structures corresponding to the NMR ensemble possessed a beta-turn, with 14 structures retaining the alphaR-alphaR beta-turn type, but the average minimized structure and the global optimization structures were converted to alpha-helical conformations. Overall, the MD simulations have aided to gain insight into the conformational space sampled by compstatin and have provided a measure of conformational interconversion. The calculated conformers will be useful as structural and possibly dynamic templates for optimization in the design of compstatin using structure-activity relations (SAR) or dynamics-activity relations (DAR).

Complement Activation During Hemorrhagic Shock and Resuscitation in Swine

Activation of the complement (C) cascade is known to play a key role in the adverse immune consequences of hemorrhagic trauma with subsequent shock and resuscitation. However, it is not clear whether hypovolemia per se, without trauma and resuscitation, can also lead to C activation. To address this question, we studied the presence, kinetics, and cause of C activation in a porcine model of hemorrhagic shock and resuscitation in the absence of trauma. Pigs were bled to and kept at 35 mmHg for 90 min, followed by hypotensive resuscitation with different fluids and, finally, with shed blood. The animals developed severe lactic acidosis between 30 and 90 min, which was accompanied by a trend for initial rise and subsequent 40% drop of CH50/mL, indicating massive C activation even before resuscitation, i.e., before reperfusion damage could have occurred. Resuscitation with plasma expanders caused 20% additional C consumption, whereas whole blood raised CH50/mL. Plasma C5a decreased initially and then significantly increased at 60 and 180 min, whereas thromboxane B2 showed a 3-fold increase at 30 and 60 min. Plasma LPS was also increased above baseline at 90 and 180 min. In in vitro studies with pig blood, spontaneous C5a formation, as well as zymosan-induced C consumption, was significantly enhanced under the conditions of lactic acidosis. Our data suggest that lactic acidosis, endotoxemia, and possibly other ischemia-related tissue alterations act in a vicious cycle in inducing C activation and, hence, aggravation of shock. The biphasic course of CH50/mL and C5a changes may reflect yet unrecognized physiological responses to hemorrhage-related C activation.

Interaction of fucoidan with the proteins of the complement classical pathway

Fucoidan inhibits complement by mechanisms that so far remain to be unraveled, and the objective of this work was to delineate the mode of inhibition by this sulfated polysaccharide. For that purpose, low molecular weight fractions of algal (Ascophyllum nodosum) fucoidan containing the disaccharide unit [-->3)-alpha-L-Fuc(2SO3(-))-(1-->4)-alpha-L-Fuc(2,3diSO3(-))-(1-->](n) have been studied. Gel co-affinity electrophoresis and a new affinity capillary electrophoresis (ACE) method have been implemented to characterize fucoidan-complement protein complexes. Fucoidan binds C1q, likely to its collagen-like region through interactions involving lysine residues, and then prevents the association of the C1r(2)-C1s(2) subunit, required to form the fully active C1. In addition to C1q, fucoidan forms a complex with the protein C4 as observed by ACE. The fucoidan inhibits the first steps of the classical pathway activation that is of relevance in view of the proinflammatory effects of the subsequent products of the cascade. This study shows that a high level of inhibitory activity can be achieved with low molecular weight carbohydrate molecules and that the potential applicability of fucoidan oligosaccharides for therapeutic complement inhibition is worthy of consideration.

Inhibition of complement activation by recombinant Sh-CRIT-ed1 analogues

Sh-CRIT-ed1 is a potent anti-complement peptide that inhibits the classical complement-activation pathway by interfering with the formation of the C3-convertase complex, C4b2a. C2 is an essential serum glycoprotein that provides the catalytic subunit of the C3 and C5 convertases of the classical pathways of complement activation. Because only in its C4-bound state is C2a capable of cleaving its physiological protein substrates C3 and C5, the interaction of Sh-CRIT-ed1 with C2 plays a decisive role of inhibition in the classical complement-activation process. However, the role of individual Sh-CRIT-ed1 amino acid residues in C2 binding is not fully understood. We constructed nine recombinant Sh-CRIT-ed1 (rSh1) analogues, substituted at conserved residues, and evaluated their anti-complement and C2-binding activities. Results from glutathione S-transferase (GST) pull-down and haemolytic assays suggested that residues 10K, 17E, 19K and 26Y are critical for the interaction of rSh1 with C2. We then constructed an improved anti-complement peptide by duplicating Sh-CRIT-ed1 C-terminal motifs (17H-26Y). This linear homodimer (rH17d) was more potent than rSh1 with respect to binding to C2 and anti-complement activity (the 50% inhibitory concentration value was approximately equal 1.2 micro m versus approximately equal 6.02 micro m for rSh1). Furthermore, rH17d showed higher anti-complement activity in vivo, providing additional evidence that this duplication is a more effective inhibitor of complement activation than rSh1. Taken together, these results identify four key residues in rSh1 and strongly suggest that rH17d is a potent inhibitor of complement activation that may have therapeutic applications.

Studies of structure-activity relations of complement inhibitor compstatin

Compstatin, a 13-mer cyclic peptide, is a novel and promising inhibitor of the activation of the complement system. In our search for a more active analog and better understanding of structure-functions relations, we designed a phage-displayed random peptide library based on previous knowledge of structure activity relations, in which seven amino acids deemed necessary for structure and activity were kept fixed while the remaining six were optimized. Screening of this library against C3 identified four binding clones. Synthetic peptides corresponding to these clones revealed one analog, called acetylated Ile(1)Leu/His(9)Trp/Thr(13)Gly triple replacement analog of compstatin corresponding to clone 640 (Ac-I1L/H9W/T13G), which was more active than compstatin. This newly identified peptide had 4-fold higher activity when compared with the originally isolated form of compstatin and 1.6-fold higher activity when compared with acetylated compstatin (Ac-compstatin). The structures of Ac-I1L/H9W/T13G and Ac-compstatin were studied by nuclear magnetic resonance, compared with the structure of compstatin, and found to be very similar. The binding of Ac-I1L/H9W/T13G and the equally active acetylated analog with His(9)Ala replacement (Ac-H9A) to C3 was evaluated by surface plasmon resonance, which suggested similarity in their binding mechanism but difference when compared with Ac-compstatin. Compensatory effects of flexibility outside the beta-turn and tryptophan ring stacking may be responsible for the measured activity increase in Ac-I1L/H9W/T13G and acetylated analog with His(9)Ala replacement and the variability in binding mechanism compared with Ac-compstatin. These data demonstrate that tryptophan is a key amino acid for activity. Finally, the significance of the N-terminal acetylation was examined and it was found that the hydrophobic cluster at the linked termini of compstatin is essential for binding to C3 and for activity.

Administration of a soluble recombinant complement C3 inhibitor protects against renal disease in MRL/lpr mice

Complement receptor 1-related gene/protein y (Crry) in rodents is a potent membrane complement regulator that inhibits complement C3 activation by both classical and alternative pathways. To clarify the role of complement in lupus nephritis, MRL/lpr mice were given Crry as a recombinant protein (Crry-Ig) from 12 to 24 wk of age. Control groups were given saline or normal mouse IgG. Sera and urine were collected biweekly. Only 1 of 20 (5%) Crry-Ig-treated mice developed renal failure (BUN > 50 mg/dl) compared with 18 of 38 (47.4%) mice in control groups (P = 0.001). BUN levels at 24 wk were reduced from 68.8 +/- 9.7 mg/dl in control groups to 38.5 +/- 3.9 mg/dl in the Crry-Ig-treated group (P < 0.01). Urinary albumin excretion at 24 wk was also significantly reduced from 5.3 +/- 1.4 mg/mg creatinine in the control groups to 0.5 +/- 0.2 mg/mg creatinine in the Crry-Ig-treated group (P < 0.05). Of the histologic data at 24 wk, there was a significant reduction in scores for glomerulosclerosis and C3d, IgG, IgG3, and IgA staining intensity in glomeruli in complement-inhibited animals. Crry-Ig-treated animals were also protected from vasculitic lesions. Although there was no effect on relevant autoimmune manifestations such as anti-double stranded DNA titers or cryoglobulin IgG3 levels, circulating immune complex levels were markedly higher in complement-inhibited animals. Thus, inhibition of complement activation with Crry-Ig significantly reduces renal disease in MRL/lpr lupus mice. The data support the strategy of using recombinant complement C3 inhibitors to treat human lupus nephritis.

Expression and purification of the anticomplementary peptide Sh-CRIT-ed1 (formerly Sh-TOR-ed1) as a tetramultimer in Escherichia coli

Many complement inhibitors found in plants and other organisms have been recognized as an antiinflammatory drug. Sh-CRIT-ed1 is a complement inhibitory peptide, present on the Schistosoma parasite surface. In the present study, we expressed chemically synthesized oligonucleotides encoding Sh-CRIT-ed1 with an additional hexahistidine codon at the C-terminus and purified in Escherichia coli BL21. The cloned gene, which was multimerized four times in pBlue-script II KS (+) at the isoschizomer sites (BamHI, BglII), was named Sh4, and expressed in E. coli BL21 harboring pGEX-KG. The fusion protein (GST-Sh4) was purified with high yield successively by affinity chromatographies of glutathione-Sepharose 4B and Ni-NTA-agarose. Recombinant Sh-CRIT-ed1 was obtained readily by thrombin digestion and CNBr cleavage of GST-Sh4, and the yield was 9.03 mg from 1-liter culture of E. coli BL21 harboring pGEX-Sh4. The recombinant Sh-CRIT-ed1 showed strong anticomplementary activity (IC(50) = 6.02 microM) by complement haemolysis assay.

Viral mimicry of the complement system

The complement system is a potent innate immune mechanism consisting of cascades of proteins which are designed to fight against and annul intrusion of all the foreign pathogens. Although viruses are smaller in size and have relatively simple structure, they are not immune to complement attack. Thus, activation of the complement system can lead to neutralization of cell-free viruses, phagocytosis of C3b-coated viral particles, lysis of virus-infected cells, and generation of inflammatory and specific immune responses. However, to combat host responses and succeed as pathogens, viruses not only have developed/adopted mechanisms to control complement, but also have turned these interactions to their own advantage. Important examples include poxviruses, herpesviruses, retroviruses, paramyxoviruses and picornaviruses. In this review, we provide information on the various complement evasion strategies that viruses have developed to thwart the complement attack of the host. A special emphasis is given on the interactions between the viral proteins that are involved in molecular mimicry and the complement system.

Generation and characterization of transgenic mice expressing cobra venom factor

Cobra venom factor (CVF), the anticomplementary protein in cobra venom, activates the alternative complement pathway, eventually leading to complement consumption. Here, we describe the development of a transgenic mouse model for CVF. We generated a DNA construct containing the full-length cDNA for single-chain pre-pro-CVF. Expression of CVF was controlled by the alpha(1)-antitrypsin promoter to achieve liver-specific expression. Linearized DNA was microinjected into murine ovary cells (strain CD(2)F(1) (BALB/cxDBA/2J)) and the newborn mice were analyzed for stable integration of CVF DNA. After establishing the transgene, mice were propagated in a BALB/c background. The CVF mRNA was detected in the liver and, in some animals, in the kidney. CVF protein was detected in small amounts in the serum. Serum complement hemolytic activity in CVF-transgenic mice was virtually absent. The concentration of plasma C3 was significantly reduced. The CVF-transgenic animals show no unusual phenotype. They provide an animal model to study the effect of long-term complement depletion by continued activation, as well as the role of complement in host immune response and pathogenesis of disease.

Immunomodulating properties of Argentine plants with ethnomedicinal use

Five Argentine medicinal plants selected according to folk traditional or ethnomedical use, references and primary pharmacological screening; were chosen to elucidate their immunomodulating properties. Dichloromethane, methanolic and aqueous extracts of the aerial parts of Achyrocline flaccida (A. flaccida), Eupatorium arnottianum (E. arnottianum) and Eupatorioum buniifolium (E. buniifolium), leaves of Lithraea molleoides (L. molleoides) and leaves and stems of Phyllanthus sellowianus (P. sellowianus) were analyzed to disclose their effects on murine normal and tumor cell growth as well as on complement hemolytic activity. Modulation of cell growth was evaluated by tritiated thymidine incorporation while inhibition of complement activity was measured on both classical and alternative complement pathways (CP and AP respectively). The results obtained show that most of the extracts exerted inhibitory effect on tumor as well as on mitogen activated normal spleen cell growth. On tumor cells, IC50 ranged between 1-75 microg/ml for most of the extracts with the exception of dichloromethane of L. molleoides and P. sellowianus which required concentrations higher than 100 microg/ml to produce the effect. On mitogenic activated splenocytes, IC50 ranged between < 1 to 85 microg/ml with the exception of methanolic extract of E. buniifolium or P. sellowianus which were not effective on ConA or LPS stimulated splenocytes respectively. Only E. buniifolium was active on murine normal splenocytes proliferation (IC50 0.5-1.5 microg/ml). Finally, one (7%) of 15 extracts showed inhibition of complement activity on CP and 6 extracts (40%) presented moderate activity on CP. The dichloromethane extract of E. arnottianum was the most active (IC50 5 microg/ml), although remarkable effect was also obtained with dichloromethane and methanolic extracts of P. sellowianus (IC50 11.2 and 17.3 microg/ml respectively). Besides, 2 extracts (13%), dichloromethane extract of E. arnottianum and aqueous extract of P. sellowianus, showed moderate inhibition on AP.

Use of complement inhibitors in tissue injury

A great deal of information has accumulated implicating the complement system in several human disease processes. Although some of this information is circumstantial, protein inhibitors of the complement system have been developed and applied successfully to experimental disease models in animals. Two inhibitors, soluble complement receptor 1 (sCR1) and anti-C5 monoclonal antibody, are now being investigated in a variety of clinical conditions such as systemic lupus erythematosus and rheumatoid arthritis (RA), diseases for which current therapy has changed little and remains unsatisfactory. Preliminary successes in Phase II clinical trials of RA have provided optimism that complement inhibition might prove useful in these diseases and become part of standard medical therapy.

Structure-function analysis of decay-accelerating factor: identification of residues important for binding of the Escherichia coli Dr adhesin and complement regulation

Decay-accelerating factor (DAF), a complement regulatory protein, also serves as a receptor for Dr adhesin-bearing Escherichia coli. The repeat three of DAF was shown to be important in Dr adhesin binding and complement regulation. However, Dr adhesins do not bind to red blood cells with the rare polymorphism of DAF, designated Dr(a(-)); these cells contain a point mutation (Ser165-Leu) in DAF repeat three. In addition, monoclonal antibody IH4 specific against repeat three was shown to block both Dr adhesin binding and complement regulatory functions of DAF. Therefore, to identify residues important in binding of Dr adhesin and IH4 and in regulating complement, we mutated 11 amino acids-predominantly those in close proximity to Ser165 to alanine-and expressed these mutations in Chinese hamster ovary cells. To map the mutations, we built a homology model of repeat three based on the poxvirus complement inhibitory protein, using the EXDIS, DIAMOD, and FANTOM programs. We show that perhaps Ser155, and not Ser165, is the key amino acid that interacts with the Dr adhesin and amino acids Gly159, Tyr160, and Leu162 and also aids in binding Dr adhesin. The IH4 binding epitope contains residues Phe148, Ser155, and L171. Residues Phe123 and Phe148 at the interface of repeat 2-3, and also Phe154 in the repeat three cavity, were important for complement regulation. Our results show that residues affecting the tested functions are located on the same loop (148 to 171), at the same surface of repeat three, and that the Dr adhesin-binding and complement regulatory epitopes of DAF appear to be distinct and are approximately 20 A apart.

Heparin attenuates cytotoxic and inflammatory activity of Alzheimer amyloid-beta in vitro

Amyloid-beta protein (Abeta) is implicated in the pathogenesis of Alzheimer's disease because of its neurotoxicity and the ability to trigger local inflammation. Compounds that interact with the amino acids of the N-terminal region or interfere with aggregation can reduce the Abeta biologic activity. We evaluated the effect of heparin on Abeta (1-42) neurotoxicity and on its ability to activate complement and contact system. On differentiated PC12 cells, a reliable model of neuronal cells, heparin at the doses of 10 and 20 microg/ml significantly counteracted Abeta cytotoxicity as assessed by measuring MTT conversion. We then explored the effect of heparin on Abeta (1-42)-induced complement and contact system activation. Abeta (1-42) was incubated with heparin in presence of normal plasma as the source of complement and contact system factors. Heparin reduced, in a dose-dependent manner, complement and contact system activation, assessed by measuring the degree of C4 and high molecular weight kininogen cleavage. The present data show that heparin can attenuate neurotoxic and pro-inflammatory activity of Abeta and suggest that this drug could represent a new strategy to reduce the progressive neurodegeneration in AD.