Isolation and characterization of pharmaceutical grade human pentraxins, serum amyloid P component and C-reactive protein, for clinical use

Neutrophils enhance the clearance of systemic amyloid deposits in a murine amyloidoma model

Introduction

Amyloid-specific antibodies have been shown to opsonize and enhance amyloid clearance in systemic amyloidosis mouse models. However, the immunological mechanisms by which amyloid is removed have not been clearly defined. Previous reports from preclinical in vivo studies suggest polymorphonuclear cells (i.e., neutrophils) can affect amyloid removal. Therefore, we sought to analyze how neutrophils may contribute to the clearance of human AL amyloid extracts, using a murine amyloidoma model.

Methods

Immunocompromised nude mice injected subcutaneously with patient-derived AL amyloid extract (generating a localized "amyloidoma") were used to circumvent confounding factors contributed by the adaptive immune system and served as the model system. Two representative AL amyloid extracts were used, ALλ(CLA), which is refractory to clearance, and ALκ(TAL), which is readily cleared in mice. Neutrophil recruitment to the amyloid masses, cellular activation, and propensity to engulf amyloid were assessed.

Results

Immunophenotyping of amyloidomas from animals implanted with 2 mg of either ALλ or ALκ revealed that more neutrophils were recruited to ALκ amyloid masses as compared to the ALλ material, which was generally devoid of neutrophils. Ex vivo analyses indicated neutrophils do not efficiently phagocytose amyloid directly. However, histological evaluation of the ALκ amyloidoma revealed the abundant presence of neutrophil extracellular traps, which were absent in the ALλ amyloidomas. Using neutrophil depletion experiments in mice, we determined that mice devoid of neutrophils cleared the human amyloid lesions less efficiently. Moreover, mice devoid of neutrophils also had significantly reduced intra-amyloid expression of inflammatory cytokines.

Discussion

Neutrophils may not directly mediate amyloid clearance through phagocytosis; however, these cells can be stimulated by the amyloid and may function to facilitate phagocytosis and amyloid clearance by professional phagocytes (e.g., macrophages).

Efficient expression and purification of rat CRP in Pichia pastoris

C-reactive protein (CRP) plays a crucial role in the diagnosis and monitoring of the non-specific acute phase response in humans. In contrast, rat CRP (rCRP) is an atypical acute-phase protein that possesses unique features, such as a possible incapacity to trigger the complement system and markedly elevated baseline plasma concentrations. To facilitate in vitro studies on these unique characteristics, obtaining high-quality pure rCRP is essential. Here we explored various strategies for rCRP purification, including direct isolation from rat plasma and recombinant expression in both prokaryotic and eukaryotic systems. Our study optimized the recombinant expression system to enhance the secretion and purification efficiency of rCRP. Compared to traditional purification methods, we present a streamlined and effective approach for the expression and purification of rCRP in the Pichia pastoris system. This refined methodology offers significant improvements in the efficiency and effectiveness of rCRP purification, thereby facilitating further structural and functional studies on rCRP.

C-reactive protein: structure, function, regulation, and role in clinical diseases

C-reactive protein (CRP) is a plasma protein that is evolutionarily conserved, found in both vertebrates and many invertebrates. It is a member of the pentraxin superfamily, characterized by its pentameric structure and calcium-dependent binding to ligands like phosphocholine (PC). In humans and various other species, the plasma concentration of this protein is markedly elevated during inflammatory conditions, establishing it as a prototypical acute phase protein that plays a role in innate immune responses. This feature can also be used clinically to evaluate the severity of inflammation in the organism. Human CRP (huCRP) can exhibit contrasting biological functions due to conformational transitions, while CRP in various species retains conserved protective functions in vivo. The focus of this review will be on the structural traits of CRP, the regulation of its expression, activate complement, and its function in related diseases in vivo.

Biomimetic affinity membrane roll column for rapid purification of C-reactive protein

To in-depth explore the action mechanism of C-reactive protein (CRP) and precisely study its signaling pathways, it is essential to acquire high-purity CRP while preserving its intact structure and functionality. In this study, we propose and fabricate a high-density 2-methacryloyloxyethyl phosphorylcholine (MPC)-modified membrane roll column (MPC-MRC) using a surface-initiated atom transfer radical polymerization (SI-ATRP) approach, which can overcome these limitations (long incubation time and low adsorption capacity) of conventional enrichment materials. The MPC-MRC incorporates a high-density 2-hydroxyethyl methacrylate polymer brush to prevent non-specific protein adsorption and multiple MPC polymer brush layers for high-performance enrichment of CRP in the company of calcium ions. Furthermore, the MPC-MRC exhibits high permeability, hydrophilicity, and mechanical strength. Compared to previous technologies, this novel material demonstrates significantly higher CRP binding capacity (310.3 mg/g), shorter processing time (only 15 min), and lower cost (only 12 USD/column). Notably, the MPC-MRC enables fast and effective purification of CRP from both human and rat serum, exhibiting good selectivity, recovery (> 91.3 %), and purity (> 95.2 %). Thus, this proposed purification approach based on MPC-MRC holds great potential for target protein enrichment from complex samples, as well as facilitating in-depth studies of its biological functions.

Serum amyloid P component accumulates and persists in neurones following traumatic brain injury

The mechanisms underlying neurodegenerative sequelae of traumatic brain injury (TBI) are poorly understood. The normal plasma protein, serum amyloid P component (SAP), which is normally rigorously excluded from the brain, is directly neurocytotoxic for cerebral neurones and also binds to Aβ amyloid fibrils and neurofibrillary tangles, promoting formation and persistence of Aβ fibrils. Increased brain exposure to SAP is common to many risk factors for dementia, including TBI, and dementia at death in the elderly is significantly associated with neocortical SAP content. Here, in 18 of 30 severe TBI cases, we report immunohistochemical staining for SAP in contused brain tissue with blood-brain barrier disruption. The SAP was localized to neurofilaments in a subset of neurones and their processes, particularly damaged axons and cell bodies, and was present regardless of the time after injury. No SAP was detected on astrocytes, microglia, cerebral capillaries or serotoninergic neurones and was absent from undamaged brain. C-reactive protein, the control plasma protein most closely similar to SAP, was only detected within capillary lumina. The appearance of neurocytotoxic SAP in the brain after TBI, and its persistent, selective deposition in cerebral neurones, are consistent with a potential contribution to subsequent neurodegeneration.

Collagen inhibits phagocytosis of amyloid in vitro and in vivo and may act as a 'don't eat me' signal

BACKGROUND

Systemic amyloidosis refers to a group of protein misfolding disorders characterized by the extracellular deposition of amyloid fibrils in organs and tissues. For reasons heretofore unknown, amyloid deposits are not recognized by the immune system, and progressive deposition leads to organ dysfunction.

METHODS

In vitro and in vivo phagocytosis assays were performed to elucidate the impact of collagen and other amyloid associated proteins (eg serum amyloid p component and apolipoprotein E) had on amyloid phagocytosis. Immunohistochemical and histopathological staining regimens were employed to analyze collagen-amyloid interactions and immune responses.

RESULTS

Histological analysis of amyloid-laden tissue indicated that collagen is intimately associated with amyloid deposits. We report that collagen inhibits phagocytosis of amyloid fibrils by macrophages. Treatment of 15 patient-derived amyloid extracts with collagenase significantly enhanced amyloid phagocytosis. Preclinical mouse studies indicated that collagenase treatment of amyloid extracts significantly enhanced clearance as compared to controls, coincident with increased immune cell infiltration of the subcutaneous amyloid lesion.

CONCLUSIONS

These data suggest that amyloid-associated collagen serves as a 'don't eat me' signal, thereby hindering clearance of amyloid. Targeted degradation of amyloid-associated collagen could result in innate immune cell recognition and clearance of pathologic amyloid deposits.

Dementia in the older population is associated with neocortex content of serum amyloid P component

Despite many reported associations, the direct cause of neurodegeneration responsible for cognitive loss in Alzheimer’s disease and some other common dementias is not known. The normal human plasma protein, serum amyloid P component, a constituent of all human fibrillar amyloid deposits and present on most neurofibrillary tangles, is cytotoxic for cerebral neurones in vitro and in experimental animals in vivo. The neocortical content of serum amyloid P component was immunoassayed in 157 subjects aged 65 or more with known dementia status at death, in the large scale, population-representative, brain donor cohort of the Cognitive Function and Ageing Study, which avoids the biases inherent in studies of predefined clinico-pathological groups. The serum amyloid P component values were significantly higher in individuals with dementia, independent of serum albumin content measured as a control for plasma in the cortex samples. The odds ratio for dementia at death in the high serum amyloid P component tertile was 5.24 (95% confidence interval 1.79–15.29) and was independent of Braak tangle stages and Thal amyloid-β phases of neuropathological severity. The strong and specific association of higher brain content of serum amyloid P component with dementia, independent of neuropathology, is consistent with a pathogenetic role in dementia.

Biomimetic Polymer-Based Method for Selective Capture of C-Reactive Protein in Biological Fluids

Selective capturing and purification of C-reactive protein (CRP) from complex biological fluids plays a pivotal role in studying biological activities of CRP in various diseases. However, obvious nonspecific adsorption of proteins was observed on current affinity sorbents, and thus additional purification steps are often required, which could compromise the recovery of the target protein and/or introduce new impurities. In this study, inspired by the highly specific interaction between CRP and the cell membrane, an excellent anti-biofouling compound 2-(methacryloyloxy)ethyl phosphorylcholine and a highly hydrophilic crosslinker N, N'-methylenebisacrylamide were employed to fabricate a novel cell membrane biomimetic polymer for selective capture of CRP in the presence of calcium ions. Based on the polymer described above, a facile enrichment approach was established after systematic optimization of the washing and elution conditions. With its favorable properties, such as good porosity, weak electrostatic interaction, high hydrophilicity, and biocompatibility, the novel biomimetic polymer exhibits good specificity, selectivity, recovery (near 100%), purity (95%), and a lower nonspecific protein adsorption for CRP in comparison with commercial immobilized p-aminophenyl phosphoryl choline gel and other purification materials. Furthermore, the structural integrity and functionality of CRP in the elution fraction were well preserved and confirmed by circular dichroism spectroscopy, fluorescence spectroscopy, and immunoturbidimetric assay. Finally, the biomimetic polymer was successfully applied to the selective enrichment of CRP from sera of patients with inflammation and rats. The proposed novel enrichment approach based on the versatile biomimetic polymer can be used for effective CRP purification, which will benefit the in-depth study of its biological roles.

The Pentraxins 1975-2018: Serendipity, Diagnostics and Drugs

The phylogenetically ancient, pentraxin family of plasma proteins, comprises C-reactive protein (CRP) and serum amyloid P component (SAP) in humans and the homologous proteins in other species. They are composed of five, identical, non-covalently associated protomers arranged with cyclic pentameric symmetry in a disc-like configuration. Each protomer has a calcium dependent site that mediates the particular specific ligand binding responsible for all the rigorously established functional properties of these proteins. No genetic deficiency of either human CRP or SAP has been reported, nor even any sequence polymorphism in the proteins themselves. Although their actual functions in humans are therefore unknown, gene deletion studies in mice demonstrate that both proteins can contribute to innate immunity. CRP is the classical human acute phase protein, routinely measured in clinical practice worldwide to monitor disease activity. Human SAP, which is not an acute phase protein, is a universal constituent of all human amyloid deposits as a result of its avid specific binding to amyloid fibrils of all types. SAP thereby contributes to amyloid formation and persistence in vivo. Whole body radiolabelled SAP scintigraphy safely and non-invasively localizes and quantifies systemic amyloid deposits, and has transformed understanding of the natural history of amyloidosis and its response to treatment. Human SAP is also a therapeutic target, both in amyloidosis and Alzheimer's disease. Our drug, miridesap, depletes SAP from the blood and the brain and is currently being tested in the DESPIAD clinical trial in Alzheimer's disease. Meanwhile, the obligate therapeutic partnership of miridesap, to deplete circulating SAP, and dezamizumab, a humanized monoclonal anti-SAP antibody that targets residual SAP in amyloid deposits, produces unprecedented removal of amyloid from the tissues and improves organ function. Human CRP binds to dead and damaged cells in vivo and activates complement and this can exacerbate pre-existing tissue damage. The adverse effects of CRP are completely abrogated by compounds that block its binding to autologous ligands and we are developing CRP inhibitor drugs. The present personal and critical perspective on the pentraxins reports, for the first time, the key role of serendipity in our work since 1975. (345 words).

Antigen B from Echinococcus granulosus is a novel ligand for C-reactive protein

Antigen B (EgAgB) is a phosphatidylcholine (PC)-rich lipoprotein of Echinococcus granulosus s.l. larva, potentially capable of modulating the activation of various myeloid cells, including macrophages. As C-reactive protein (CRP) can act as an innate receptor with ability to bind the phosphocholine moiety of PC in lipoproteins, we investigated whether EgAgB and CRP could interact during cystic echinococcosis infection (CE), and how CRP binding could affect the modulation activities exerted by EgAgB on macrophages. To that end, we firstly investigated the occurrence of CRP induction during human CE. We found that 61% of CE patients, but none of healthy donors, exhibited serum CRP levels higher than 10 mg/mL, suggesting that CRP can be induced during the chronic phase of CE. Furthermore, human CRP was capable of binding specifically to EgAgB with high affinity (0.6 ± 0.1 nM); this binding was Ca²⁺ -dependent and involved the phosphocholine moiety of PC, but not EgAgB8/1, EgAgB8/2 or EgAgB8/3 apolipoproteins. Finally, CRP presence altered the modulation exerted by EgAgB on the cytokine response of LPS-activated macrophages. Overall, our results suggest that CRP presence during CE may contribute to a complex scenario of interactions between EgAgB and myeloid cells, influencing the cytokine response induced during macrophage activation.

A Conformational Change in C-Reactive Protein Enhances Leukocyte Recruitment and Reactive Oxygen Species Generation in Ischemia/Reperfusion Injury

Introduction

C-reactive protein circulates as a pentameric protein (pCRP). pCRP is a well-established diagnostic marker as plasma levels rise in response to tissue injury and inflammation. We recently described pro-inflammatory properties of CRP, which are mediated by conformational changes from pCRP to bioactive isoforms expressing pro-inflammatory neo-epitopes [pCRP* and monomeric C-reactive protein (mCRP)]. Here, we investigate the role of CRP isoforms in renal ischemia/reperfusion injury (IRI).

Methods

Rat kidneys in animals with and without intraperitoneally injected pCRP were subjected to IRI by the time of pCRP exposure and were subsequently analyzed for monocyte infiltration, caspase-3 expression, and tubular damage. Blood urea nitrogen (BUN) was analyzed pre-ischemia and post-reperfusion. CRP effects on leukocyte recruitment were investigated via intravital imaging of rat-striated muscle IRI. Localized conformational CRP changes were analyzed by immunohistochemistry using conformation specific antibodies. 1,6-bis(phosphocholine)-hexane (1,6-bisPC), which stabilizes CRP in its native pentameric form was used to validate CRP effects. Leukocyte activation was assessed by quantification of reactive oxygen species (ROS) induction by CRP isoforms ex vivo and in vitro through electron spin resonance spectroscopy. Signaling pathways were analyzed by disrupting lipid rafts with nystatin and subsequent ROS detection. In order to confirm the translational relevance of our findings, biopsies of microsurgical human free tissue transfers before and after IRI were examined by immunofluorescence for CRP deposition and co-localization of CD68⁺ leukocytes.

Results

The application of pCRP aggravates tissue damage in renal IRI. 1,6-bisPC reverses these effects via inhibition of the conformational change that leads to exposure of pro-inflammatory epitopes in CRP (pCRP* and mCRP). Structurally altered CRP induces leukocyte–endothelial interaction and induces ROS formation in leukocytes, the latter can be abrogated by blocking lipid raft-dependent signaling pathways with Nystatin. Stabilizing pCRP in its native pentameric state abrogates these pro-inflammatory effects. Importantly, these findings are confirmed in human IRI challenged muscle tissue.

Conclusion

These results suggest that CRP is a potent modulator of IRI. Stabilizing the native pCRP conformation represents a promising anti-inflammatory therapeutic strategy by attenuation of leukocyte recruitment and ROS formation, the primary pathomechanisms of IRI.

The role of complement activation in rhabdomyolysis-induced acute kidney injury

Rhabdomyolysis (RM) may cause kidney damage and results primarily in acute kidney injury (AKI). Complement is implicated in the pathogenesis of renal diseases and ischemia-reperfusion injury (IRI), but the role of complement, especially its activation pathway(s) and its effect in RM-induced AKI, is not clear. This study established a rat model of AKI induced by RM via intramuscular treatment with glycerol. Cobra venom factor (CVF) was administered via tail vein injection to deplete complement 12 h prior to intramuscular injection of glycerol. We found that the complement components, including complement 3 (C3), C1q, MBL-A, factor B(fB), C5a, C5b-9, and CD59, were significantly increased in rat kidneys after intramuscular glycerol administration. However, the levels of serum BUN and Cr, renal tubular injury scores, and the number of TUNEL-positive cells decreased significantly in the CVF+AKI group. These results suggest that complement plays an important role in RM-induced AKI and that complement depletion may improve renal function and decrease renal tissue damage by reducing the inflammatory response and apoptosis.

C-Reactive Protein Binds to Cholesterol Crystals and Co-Localizes with the Terminal Complement Complex in Human Atherosclerotic Plaques

Inflammation is a part of the initial process leading to atherosclerosis and cholesterol crystals (CC), found in atherosclerotic plaques, which are known to induce complement activation. The pentraxins C-reactive protein (CRP), long pentraxin 3 (PTX3), and serum amyloid P component (SAP) are serum proteins associated with increased risk of cardiovascular events and these proteins have been shown to interact with the complement system. Whether the pentraxins binds to CC and mediate downstream complement-dependent inflammatory processes remains unknown. Binding of CRP, PTX3, and SAP to CC was investigated in vitro by flow cytometry and fluorescence microscopy. CRP, PTX3, and SAP bound to CC in a concentration-dependent manner. CRP and PTX3 interacted with the complement pattern recognition molecule C1q on CC by increasing the binding of both purified C1q and C1q in plasma. However, CRP was the strongest mediator of C1q binding and also the pentraxin that most potently elevated C1q-mediated complement activation. In a phagocytic assay using whole blood, we confirmed that phagocytosis of CC is complement dependent and initiated by C1q-mediated activation. The pathophysiological relevance of the in vitro observations was examined in vivo in human atherosclerotic plaques. CRP, PTX3, and SAP were all found in atherosclerotic plaques and were located mainly in the cholesterol-rich necrotic core, but co-localization with the terminal C5b-9 complement complex was only found for CRP. In conclusion, this study identifies CRP as a strong C1q recruiter and complement facilitator on CC, which may be highly relevant for the development of atherosclerosis.

Purification of recombinant C-reactive protein mutants

C-reactive protein (CRP) is an evolutionarily conserved protein, a component of the innate immune system, and an acute phase protein in humans. In addition to its raised level in blood in inflammatory states, CRP is also localized at sites of inflammation including atherosclerotic lesions, arthritic joints and amyloid plaque deposits. Results of in vivo experiments in animal models of inflammatory diseases indicate that CRP is an anti-pneumococcal, anti-atherosclerotic, anti-arthritic and an anti-amyloidogenic molecule. The mechanisms through which CRP functions in inflammatory diseases are not fully defined; however, the ligand recognition function of CRP in its native and non-native pentameric structural conformations and the complement-activating ability of ligand-complexed CRP have been suggested to play a role. One tool to understand the structure-function relationships of CRP and determine the contributions of the recognition and effector functions of CRP in host defense is to employ site-directed mutagenesis to create mutants for experimentation. For example, CRP mutants incapable of binding to phosphocholine are generated to investigate the importance of the phosphocholine-binding property of CRP in mediating host defense. Recombinant CRP mutants can be expressed in mammalian cells and, if expressed, can be purified from the cell culture media. While the methods to purify wild-type CRP are well established, different purification strategies are needed to purify various mutant forms of CRP if the mutant does not bind to either calcium or phosphocholine. In this article, we report the methods used to purify pentameric recombinant wild-type and mutant CRP expressed in and secreted by mammalian cells.

Transitional changes in the CRP structure lead to the exposure of proinflammatory binding sites

C-reactive protein (CRP) concentrations rise in response to tissue injury or infection. Circulating pentameric CRP (pCRP) localizes to damaged tissue where it leads to complement activation and further tissue damage. In-depth knowledge of the pCRP activation mechanism is essential to develop therapeutic strategies to minimize tissue injury. Here we demonstrate that pCRP by binding to cell-derived microvesicles undergoes a structural change without disrupting the pentameric symmetry (pCRP*). pCRP* constitutes the major CRP species in human-inflamed tissue and allows binding of complement factor 1q (C1q) and activation of the classical complement pathway. pCRP*–microvesicle complexes lead to enhanced recruitment of leukocytes to inflamed tissue. A small-molecule inhibitor of pCRP (1,6-bis(phosphocholine)-hexane), which blocks the pCRP–microvesicle interactions, abrogates these proinflammatory effects. Reducing inflammation-mediated tissue injury by therapeutic inhibition might improve the outcome of myocardial infarction, stroke and other inflammatory conditions.

C-reactive protein is a pentameric protein secreted by the liver in response to injury and infection. Here Braig et al. show that conformational changes in CRP on the surface of monocyte-derived microvesicles enable binding of complement C1q and lead to activation of the complement cascade and aggravation of inflammation.

Comparative analysis of the serum proteome for biomarker discovery to reveal hepatotoxicity induced by iron ion radiation in mice

AIMS

Proteomic analysis of serum biomarkers to determine liver toxicity after exposure to cosmic radiation has not been performed previously. This study was to identify serum biomarkers associated with hepatotoxicity following exposure to iron ion radiation.

MAIN METHODS

Male mice were whole-body irradiated with a 2grayunit (Gy) iron ion beam, and after 3months, serum and liver samples were collected. Two-dimensional electrophoresis (2-DE) was used to separate the identified serum proteins, and matrix-assisted laser desorption/ionization tandem mass spectrometry (MALDI-TOF-TOF) was performed to identify differentially expressed proteins. Enzyme-linked immunosorbent assays and immunoblotting were applied to evaluate protein expression, and immunohistochemistry and immunofluorescence were used to investigate protein localization. Real-time polymerase chain reaction (PCR) was performed to confirm altered gene expression.

KEY FINDINGS

A total of 11 spots that showed differential expression were screened and identified as seven proteins. Of these, six proteins were in the same bioinformatics network and included complement component 3, serum amyloid P-component, apolipoprotein E, alpha-2-macroglobulin, fibrinogen alpha chain, and fibrinogen gamma chain. All of these proteins are synthesized by the liver, and may play an important role in liver toxicity. We also confirmed the mRNA transcription, and found that mRNA expression of the six identified proteins increased in the liver in irradiated mice.

SIGNIFICANCE

These results suggest that these proteins may be potential biomarkers of hepatotoxicity in astronauts enduring long space missions.

The pentraxins PTX3 and SAP in innate immunity, regulation of inflammation and tissue remodelling

Pentraxins are a superfamily of fluid phase pattern recognition molecules conserved in evolution and characterized by a cyclic multimeric structure. C-reactive protein (CRP) and serum amyloid P component (SAP) constitute the short pentraxin arm of the superfamily. CRP and SAP are produced in the liver in response to IL-6 and are acute phase reactants in humans and mice respectively. In addition SAP has been shown to affect tissue remodelling and fibrosis by stabilizing all types of amyloid fibrils and by regulating monocyte to fibrocyte differentiation. Pentraxin 3 (PTX3) is the prototype of the long pentraxin arm. Gene targeted mice and genetic and epigenetic studies in humans suggest that PTX3 plays essential non-redundant roles in innate immunity and inflammation as well as in tissue remodelling. Recent studies have revealed the role of PTX3 as extrinsic oncosuppressor, able to tune cancer-related inflammation. In addition, at acidic pH PTX3 can interact with provisional matrix components promoting inflammatory matrix remodelling. Thus acidification during tissue repair sets PTX3 in a tissue remodelling and repair mode, suggesting that matrix and microbial recognition are common, ancestral features of the humoral arm of innate immunity.

Targeting C-Reactive Protein in Inflammatory Disease by Preventing Conformational Changes

C-reactive protein (CRP) is a pentraxin that has long been employed as a marker of inflammation in clinical practice. Recent findings brought up the idea of CRP to be not only a systemic marker but also a mediator of inflammation. New studies focused on structural changes of the plasma protein, revealing the existence of two distinct protein conformations associated with opposed inflammatory properties. Native, pentameric CRP (pCRP) is considered to be the circulating precursor form of monomeric CRP (mCRP) that has been identified to be strongly proinflammatory. Recently, a dissociation mechanism of pCRP has been identified on activated platelets and activated/apoptotic cells associated with the amplification of the proinflammatory potential. Correspondingly, CRP deposits found in inflamed tissues have been identified to exhibit the monomeric conformation by using conformation-specific antibodies. Here we review the current literature on the causal role of the dissociation mechanism of pCRP and the genesis of mCRP for the amplification of the proinflammatory potential in inflammatory reactions such as atherosclerosis and ischemia/reperfusion injury. The chance to prevent the formation of proinflammatory mediators in ubiquitous inflammatory cascades has pushed therapeutic strategies by targeting pCRP dissociation in inflammation. In this respect, the development of clinically applicable derivatives of the palindromic compound 1,6-bis(phosphocholine)-hexane (1,6-bis PC) should be a major focus of future CRP research.

A conformational change of C-reactive protein in burn wounds unmasks its proinflammatory properties

Tissue damage in burn injury leads to a rapid increase of leukocytes and acute phase reactants. Plasma levels of C-reactive protein (CRP) rise within hours after the insult. No deficiency of this protein has been reported in humans, suggesting it plays a pivotal role in innate immunity. CRP in circulation is composed of five identical subunits [pentameric CRP (pCRP)]. Recently, deposits of structurally modified CRP (mCRP) have been found in inflammatory diseases. Little is known about this structural change and how it affects CRP functions. We analyzed CRP deposits in burn wounds and serum by immunohistochemistry, western blot and dot blot analysis. CRP was deposited in necrotic and inflamed tissue, but not in adjacent healthy tissue. Tissue deposited CRP was detected by mCRP-specific antibodies and structurally different from serum pCRP. mCRP but not pCRP induced reactive oxygen species production by monocytes and facilitated uptake of necrotic Jurkat cells by macrophages. In addition, it accelerated migration of keratinocytes in a scratch wound assay. The structural changes that occur in pCRP upon localization to damaged and inflamed tissue in burn wounds result in a functionally altered protein with distinct functions. mCRP exhibits opsonic, proinflammatory and promigratory properties which modulate wound healing.

Protection of human podocytes from shiga toxin 2-induced phosphorylation of mitogen-activated protein kinases and apoptosis by human serum amyloid P component

Hemolytic uremic syndrome (HUS) is mainly induced by Shiga toxin 2 (Stx2)-producing Escherichia coli. Proteinuria can occur in the early phase of the disease, and its persistence determines the renal prognosis. Stx2 may injure podocytes and induce proteinuria. Human serum amyloid P component (SAP), a member of the pentraxin family, has been shown to protect against Stx2-induced lethality in mice in vivo, presumably by specific binding to the toxin. We therefore tested the hypothesis that SAP can protect against Stx2-induced injury of human podocytes. To elucidate the mechanisms underlying podocyte injury in HUS-associated proteinuria, we assessed Stx2-induced activation of mitogen-activated protein kinases (MAPKs) and apoptosis in immortalized human podocytes and evaluated the impact of SAP on Stx2-induced damage. Human podocytes express Stx2-binding globotriaosylceramide 3. Stx2 applied to cultured podocytes was internalized and then activated p38α MAPK and c-Jun N-terminal kinase (JNK), important signaling steps in cell differentiation and apoptosis. Stx2 also activated caspase 3, resulting in an increased level of apoptosis. Coincubation of podocytes with SAP and Stx2 mitigated the effects of Stx2 and induced upregulation of antiapoptotic Bcl2. These data suggest that podocytes are a target of Stx2 and that SAP protects podocytes against Stx2-induced injury. SAP may therefore be a useful therapeutic option.

Infusion of pharmaceutical-grade natural human C-reactive protein is not proinflammatory in healthy adult human volunteers

RATIONALE

Baseline circulating concentrations of C-reactive protein (CRP) are significantly associated with cardiovascular disease risk in general populations. This modest association has been inappropriately conflated with causality, and it has been claimed that CRP is proatherogenic. Most of the known causative factors for atherosclerosis stimulate increased CRP production, but comprehensive genetic epidemiology studies provide no support for a pathogenic role of CRP. The reported proinflammatory effects of human CRP preparations on healthy cells in vitro and in healthy animals in vivo have all been produced by poorly characterized CRP preparations, demonstrably caused by impurities, or elicited by CRP made in recombinant Escherichia coli not by humans. None of the in vitro or animal findings have been reproduced with pure natural human CRP. Nevertheless, the strong proinflammatory effects of infusing recombinant bacterial CRP into humans have still been inappropriately ascribed to CRP.

OBJECTIVE

To investigate the effects of infusion into healthy adult human volunteers of pure natural human CRP.

METHODS AND RESULTS

Comprehensively characterized, pharmaceutical-grade, endotoxin-free, purified CRP, prepared to GMP standard from pooled normal human donor plasma was infused as an intravenous bolus in 7 healthy adult human volunteers at ≤2 mg/kg to provide circulating CRP concentrations ≤44 mg/L. No recipient showed any significant clinical, hematologic, coagulation, or biochemical changes, or any increase in proinflammatory cytokines or acute phase proteins.

CONCLUSIONS

The human CRP molecule itself is not proinflammatory in healthy human adults.

C-reactive protein and the biology of disease

The C-reactive protein (CRP) is a plasma protein of hepatic origin, belonging to pentraxin family and forms a major component of any inflammatory reaction. A key component of the innate immunity pathway, the concentration of CRP may rapidly increase to levels more than 1,000-folds above normal values as a consequence to tissue injury or infection. Although functioning as a classical mediator of innate immunity, it functions via interaction of components of both humoral and cellular effector systems of inflammation. Initially considered as an acute-phase marker in tissue injury, infection and inflammation, it now has a distinct status of a disease marker in cardiovascular diseases and is well known of its clinical and pathological significance. The present torrent of studies in a large number of diseases and associated conditions has highly elucidated the role of CRP as a therapeutic and research reagent. In this review, we focus our attention to role of CRP in health and disease. The future prospect of this review lies in the applicability of CRP as a molecule in understanding and monitoring of the biology of disease.

Efflux transport of serum amyloid P component at the blood-brain barrier

Serum amyloid P component (SAP), a member of the innate immune system, does not penetrate the brain in physiological conditions; however, SAP is a stabilizing component of the amyloid plaques in neurodegenerative diseases. We investigated the cerebrovascular transport of human SAP in animal experiments and in culture blood-brain barrier (BBB) models. After intravenous injection, no SAP could be detected by immunohistochemistry or ELISA in healthy rat brains. Salmonella typhimurium lipopolysaccharide injection increased BBB permeability for SAP and the number of cerebral vessels labeled with fluorescein isothiocyanate (FITC)-SAP in mice. Furthermore, when SAP was injected to the rat hippocampus, a time-dependent decrease in brain concentration was seen demonstrating a rapid SAP efflux transport in vivo. A temperature-dependent bidirectional transport of FITC-SAP was observed in rat brain endothelial monolayers. The permeability coefficient for FITC-SAP was significantly higher in abluminal to luminal (brain to blood) than in the opposite direction. The luminal release of FITC-SAP from loaded endothelial cells was also significantly higher than the abluminal one. Our data indicate the presence of BBB efflux transport mechanisms protecting the brain from SAP penetration. Damaged BBB integrity due to pathological insults may increase brain SAP concentration contributing to development of neurodegenerative diseases.

Monomerization of C-reactive protein requires glycoprotein IIb-IIIa activation: pentraxins and platelet deposition

BACKGROUND

Pentraxins are inflammatory mediators linked to cardiovascular disease; however, their role in thrombosis remains to be fully elucidated.

AIMS

We investigated the role of pentraxins in thrombus formation on different vascular substrates under flow conditions.

METHODS

Native C-reactive protein (nCRP) and serum amyloid P (SAP) effects on thrombosis were evaluated under flow conditions on substrates placed in flat perfusion chambers. nCRP and dissociated monomeric CRP (mCRP) distributions were visualized by use of confocal microscopy. The effects of nCRP on vascular substrates were tested in the Badimon chamber.

RESULTS

mCRP, but not nCRP, induced a significant activation in platelet deposition, whereas SAP induced an activation only on fibrinogen-coated substrates. The effects of CRP on platelet deposition were significantly reduced by statin treatment. mCRP resulting from recirculation of blood containing nCRP over a thrombogenic vessel wall induced increased platelet deposition. Blocking glycoprotein IIb-IIIa prevented the effects of CRP dissociation and significantly reduced platelet deposition. Annexin V treatment did not block monomerization of CRP on activated platelets.

CONCLUSIONS

Under flow conditions, platelet deposited on all tested biological substrates support nCRP dissociation into mCRP. The effect is dependent on the thrombogenic potency of the substrate to trigger initial platelet deposition. Exposure of glycoprotein IIb-IIIa in the platelet surface supports nCRP dissociation. CRP monomerization was not dependent on the aminophospholipid exposed on the surface of activated platelets. The dissociated mCRP is trapped in the growing platelet aggregate and stimulates further platelet deposition. SAP increases platelet deposition only on fibrin monolayers. Therefore, pentraxins induce a platelet activation effect linking inflammation and thrombosis.

Pentraxins: structure, function, and role in inflammation

The pentraxins are an ancient family of proteins with a unique architecture found as far back in evolution as the Horseshoe crab. In humans the two members of this family are C-reactive protein and serum amyloid P. Pentraxins are defined by their sequence homology, their pentameric structure and their calcium-dependent binding to their ligands. Pentraxins function as soluble pattern recognition molecules and one of the earliest and most important roles for these proteins is host defense primarily against pathogenic bacteria. They function as opsonins for pathogens through activation of the complement pathway and through binding to Fc gamma receptors. Pentraxins also recognize membrane phospholipids and nuclear components exposed on or released by damaged cells. CRP has a specific interaction with small nuclear ribonucleoproteins whereas SAP is a major recognition molecule for DNA, two nuclear autoantigens. Studies in autoimmune and inflammatory disease models suggest that pentraxins interact with macrophage Fc receptors to regulate the inflammatory response. Because CRP is a strong acute phase reactant it is widely used as a marker of inflammation and infection.

Serum amyloid P inhibits granulocyte adhesion

Background

The extravasation of granulocytes (such as neutrophils) at a site of inflammation is a key aspect of the innate immune system. Signals from the site of inflammation upregulate granulocyte adhesion to the endothelium to initiate extravasation, and also enhance granulocyte adhesion to extracellular matrix proteins to facilitate granulocyte movement through the inflamed tissue. During the resolution of inflammation, other signals inhibit granulocyte adhesion to slow and ultimately stop granulocyte influx into the tissue. In a variety of inflammatory diseases such as acute respiratory distress syndrome, an excess infiltration of granulocytes into a tissue causes undesired collateral damage, and being able to reduce granulocyte adhesion and influx could reduce this damage.

Results

We found that serum amyloid P (SAP), a constitutive protein component of the blood, inhibits granulocyte spreading and granulocyte adhesion to extracellular matrix components. This indicates that in addition to granulocyte adhesion inhibitors that are secreted during the resolution of inflammation, a granulocyte adhesion inhibitor is present at all times in the blood. Although SAP affects adhesion, it does not affect the granulocyte adhesion molecules CD11b, CD62L, CD18, or CD44. SAP also has no effect on the production of hydrogen peroxide by resting or stimulated granulocytes, or N-formyl-methionine-leucine-phenylalanine (fMLP)-induced granulocyte migration. In mice treated with intratracheal bleomycin to induce granulocyte accumulation in the lungs, SAP injections reduced the number of granulocytes in the lungs.

Conclusions

We found that SAP, a constitutive component of blood, is a granulocyte adhesion inhibitor. We hypothesize that SAP allows granulocytes to sense whether they are in the blood or in a tissue.

Probing the phosphocholine-binding site of human C-reactive protein by site-directed mutagenesis

Human C-reactive protein (CRP) can activate the classical pathway of complement and function as an opsonin only when it is complexed to an appropriate ligand. Most known CRP ligands bind to the phosphocholine (PCh)-binding site of the protein. In the present study, we used oligonucleotide-directed site-specific mutagenesis to investigate structural determinants of the PCh-binding site of CRP. Eight mutant recombinant (r) CRP, Y40F; E42Q; Y40F, E42Q; K57Q; R58G; K57Q, R58G; W67K; and K57Q, R58G, W67K were constructed and expressed in COS cells. Wild-type and all mutant rCRP except for the W67K mutants bound to solid-phase PCh-substituted bovine serum albumin (PCh-BSA) with similar apparent avidities. However, W67K rCRP had decreased avidity for PCh-BSA and the triple mutant, K57Q, R58G, W67K, failed to bind PCh-BSA. Inhibition experiments using PCh and dAMP as inhibitors indicated that both Lys-57 and Arg-58 contribute to PCh binding. They also indicated that Trp-67 provides interactions with the choline group. The Y40F and E42Q mutants were found to have increased avidity for fibronectin compared to wild-type rCRP. We conclude that the residues Lys-57, Arg-58, and Trp-67 contribute to the structure of the PCh-binding site of human CRP. Residues Tyr-40 and Glu-42 do not appear to participate in the formation of the PCh-binding site of CRP, however, they may be located in the vicinity of the fibronectin-binding site of CRP.