Loss of pentameric symmetry in C-reactive protein induces interleukin-8 secretion through peroxynitrite signaling in human neutrophils

A tale of two functions: C-reactive protein complement-ary structures and their role in rheumatoid arthritis

C-reactive protein (CRP) is an inflammatory biomarker with associated clinical utility in a wide number of inflammatory disorders, including rheumatoid arthritis (RA). The interaction of CRP with pro-inflammatory cytokines has been explored before, however its role in complement regulation is more subtle, where CRP is capable of both up and downregulating the complement cascade. CRP is produced in a pentameric form and can dissociate to a monomeric form in circulation which has significant implications for its ability to interact with receptors and binding partners. This dichotomy of CRP structure could have relevance in patients with RA who have significant dysfunction in their complement cascade and also widely varying CRP levels including at the time of flare. This review aims to bring together current knowledge of CRP in its various forms, its effects on complement function and how this could influence pathology in the context of RA.

Interorgan communication with the liver: novel mechanisms and therapeutic targets

The liver is a multifunctional organ that plays crucial roles in numerous physiological processes, such as production of bile and proteins for blood plasma, regulation of blood levels of amino acids, processing of hemoglobin, clearance of metabolic waste, maintenance of glucose, etc. Therefore, the liver is essential for the homeostasis of organisms. With the development of research on the liver, there is growing concern about its effect on immune cells of innate and adaptive immunity. For example, the liver regulates the proliferation, differentiation, and effector functions of immune cells through various secreted proteins (also known as "hepatokines"). As a result, the liver is identified as an important regulator of the immune system. Furthermore, many diseases resulting from immune disorders are thought to be related to the dysfunction of the liver, including systemic lupus erythematosus, multiple sclerosis, and heart failure. Thus, the liver plays a role in remote immune regulation and is intricately linked with systemic immunity. This review provides a comprehensive overview of the liver remote regulation of the body's innate and adaptive immunity regarding to main areas: immune-related molecules secreted by the liver and the liver-resident cells. Additionally, we assessed the influence of the liver on various facets of systemic immune-related diseases, offering insights into the clinical application of target therapies for liver immune regulation, as well as future developmental trends.

C-Reactive Protein: Pathophysiology, Diagnosis, False Test Results and a Novel Diagnostic Algorithm for Clinicians

The current literature provides a body of evidence on C-Reactive Protein (CRP) and its potential role in inflammation. However, most pieces of evidence are sparse and controversial. This critical state-of-the-art monography provides all the crucial data on the potential biochemical properties of the protein, along with further evidence on its potential pathobiology, both for its pentameric and monomeric forms, including information for its ligands as well as the possible function of autoantibodies against the protein. Furthermore, the current evidence on its potential utility as a biomarker of various diseases is presented, of all cardiovascular, respiratory, hepatobiliary, gastrointestinal, pancreatic, renal, gynecological, andrological, dental, oral, otorhinolaryngological, ophthalmological, dermatological, musculoskeletal, neurological, mental, splenic, thyroid conditions, as well as infections, autoimmune-supposed conditions and neoplasms, including other possible factors that have been linked with elevated concentrations of that protein. Moreover, data on molecular diagnostics on CRP are discussed, and possible etiologies of false test results are highlighted. Additionally, this review evaluates all current pieces of evidence on CRP and systemic inflammation, and highlights future goals. Finally, a novel diagnostic algorithm to carefully assess the CRP level for a precise diagnosis of a medical condition is illustrated.

A biofunctional review of C-reactive protein (CRP) as a mediator of inflammatory and immune responses: differentiating pentameric and modified CRP isoform effects

C-reactive protein (CRP) is an acute phase, predominantly hepatically synthesized protein, secreted in response to cytokine signaling at sites of tissue injury or infection with the physiological function of acute pro-inflammatory response. Historically, CRP has been classified as a mediator of the innate immune system, acting as a pattern recognition receptor for phosphocholine-containing ligands. For decades, CRP was envisioned as a single, non-glycosylated, multi-subunit protein arranged non-covalently in cyclic symmetry around a central void. Over the past few years, however, CRP has been shown to exist in at least three distinct isoforms: 1.) a pentamer of five identical globular subunits (pCRP), 2.) a modified monomer (mCRP) resulting from a conformational change when subunits are dissociated from the pentamer, and 3.) a transitional isoform where the pentamer remains intact but is partially changed to express mCRP structural characteristics (referred to as pCRP* or mCRPm). The conversion of pCRP into mCRP can occur spontaneously and is observed under commonly used experimental conditions. In careful consideration of experimental design used in published reports of in vitro pro- and anti-inflammatory CRP bioactivities, we herein provide an interpretation of how distinctive CRP isoforms may have affected reported results. We argue that pro-inflammatory amplification mechanisms are consistent with the biofunction of mCRP, while weak anti-inflammatory mechanisms are consistent with pCRP. The interplay of each CRP isoform with specific immune cells (platelets, neutrophils, monocytes, endothelial cells, natural killer cells) and mechanisms of the innate immune system (complement), as well as differences in mCRP and pCRP ligand recognition and effector functions are discussed. This review will serve as a revised understanding of the structure-function relationship between CRP isoforms as related to inflammation and innate immunity mechanisms.

Pentameric C-reactive protein is a better prognostic biomarker and remains elevated for longer than monomeric CRP in hospitalized patients with COVID-19

The differing roles of the pentameric (p) and monomeric (m) C-reactive protein (CRP) isoforms in viral diseases are not fully understood, which was apparent during the COVID-19 pandemic regarding the clinical course of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Herein, we investigated the predictive value of the pCRP and mCRP isoforms for COVID-19 severity in hospitalized patients and evaluated how the levels of the protein isoforms changed over time during and after acute illness. This study utilized samples from a well-characterized cohort of Swedish patients with SARS-CoV-2 infection, the majority of whom had known risk factors for severe COVID-19 and required hospitalization. The levels of pCRP were significantly raised in patients with severe COVID-19 and in contrast to mCRP the levels were significantly associated with disease severity. Additionally, the pCRP levels remained elevated for at least six weeks post inclusion, which was longer compared to the two weeks for mCRP. Our data indicates a low level of inflammation lasting for at least six weeks following COVID-19, which might indicate that the disease has an adverse effect on the immune system even after the viral infection is resolved. It is also clear that the current standard method of testing pCRP levels upon hospitalization is a useful marker for predicting disease severity and mCRP testing would not add any clinical relevance for patients with COVID-19.

C-reactive protein: a target for therapy to reduce inflammation

C-reactive protein (CRP) is well-recognized as a sensitive biomarker of inflammation. Association of elevations in plasma/serum CRP level with disease state has received considerable attention, even though CRP is not a specific indicator of a single disease state. Circulating CRP levels have been monitored with a varying degree of success to gauge disease severity or to predict disease progression and outcome. Elevations in CRP level have been implicated as a useful marker to identify patients at risk for cardiovascular disease and certain cancers, and to guide therapy in a context-dependent manner. Since even strong associations do not establish causality, the pathogenic role of CRP has often been over-interpreted. CRP functions as an important modulator of host defense against bacterial infection, tissue injury and autoimmunity. CRP exists in conformationally distinct forms, which exhibit distinct functional properties and help explaining the diverse, often contradictory effects attributed to CRP. In particular, dissociation of native pentameric CRP into its subunits, monomeric CRP, unmasks "hidden" pro-inflammatory activities in pentameric CRP. Here, we review recent advances in CRP targeting strategies, therapeutic lowering of circulating CRP level and development of CRP antagonists, and a conformation change inhibitor in particular. We will also discuss their therapeutic potential in mitigating the deleterious actions attributed to CRP under various pathologies, including cardiovascular, pulmonary and autoimmune diseases and cancer.

Fueling the flames of colon cancer – does CRP play a direct pro-inflammatory role?

Background

Systemic inflammation, diagnostically ascribed by measuring serum levels of the acute phase reactant C-reactive protein (CRP), has consistently been correlated with poor outcomes across cancer types. CRP exists in two structurally and functionally distinct isoforms, circulating pentameric CRP (pCRP) and the highly pro-inflammatory monomeric isoform (mCRP). The aim of this pilot study was to map the pattern of mCRP distribution in a previously immunologically well-defined colon cancer (CC) cohort and explore possible functional roles of mCRP within the tumor microenvironment (TME).

Methods

Formalin-fixed, paraffin-embedded (FFPE) tissue samples from 43 stage II and III CC patients, including 20 patients with serum CRP 0-1 mg/L and 23 patients with serum CRP >30 mg/L were immunohistochemically (IHC) stained with a conformation-specific mCRP antibody and selected immune and stromal markers. A digital analysis algorithm was developed for evaluating mCRP distribution within the primary tumors and adjacent normal colon mucosa.

Results

mCRP was abundantly present within tumors from patients with high serum CRP (>30 mg/L) diagnostically interpreted as being systemically inflamed, whereas patients with CRP 0-1 mg/L exhibited only modest mCRP positivity (median mCRP per area 5.07‰ (95%CI:1.32-6.85) vs. 0.02‰ (95%CI:0.01-0.04), p<0.001). Similarly, tissue-expressed mCRP correlated strongly with circulating pCRP (Spearman correlation 0.81, p<0.001). Importantly, mCRP was detected exclusively within tumors, whereas adjacent normal colon mucosa showed no mCRP expression. Double IHC staining revealed colocalization of mCRP with endothelial cells and neutrophils. Intriguingly, some tumor cells also colocalized with mCRP, suggesting a direct interaction or mCRP expression by the tumor itself.

Conclusion

Our data show that the pro-inflammatory mCRP isoform is expressed in the TME of CC, primarily in patients with high systemic pCRP values. This strengthens the hypothesis that CRP might not only be an inflammatory marker but also an active mediator within tumors.

Monomeric CRP regulates inflammatory responses in human intervertebral disc cells

Aims

CRP is an acute-phase protein that is used as a biomarker to follow severity and progression in infectious and inflammatory diseases. Its pathophysiological mechanisms of action are still poorly defined. CRP in its pentameric form exhibits weak anti-inflammatory activity. The monomeric isoform (mCRP) exerts potent proinflammatory properties in chondrocytes, endothelial cells, and leucocytes. No data exist regarding mCRP effects in human intervertebral disc (IVD) cells. This work aimed to verify the pathophysiological relevance of mCRP in the aetiology and/or progression of IVD degeneration.

Methods

We investigated the effects of mCRP and the signalling pathways that are involved in cultured human primary annulus fibrosus (AF) cells and in the human nucleus pulposus (NP) immortalized cell line HNPSV-1. We determined messenger RNA (mRNA) and protein levels of relevant factors involved in inflammatory responses, by quantitative real-time polymerase chain reaction (RT-qPCR) and western blot. We also studied the presence of mCRP in human AF and NP tissues by immunohistochemistry.

Results

We demonstrated that mCRP increases nitric oxide synthase 2 (NOS2), cyclooxygenase 2 (COX2), matrix metalloproteinase 13 (MMP13), vascular cell adhesion molecule 1 (VCAM1), interleukin (IL)-6, IL-8, and Lipocalin 2 (LCN2) expression in human AF and NP cells. We also showed that nuclear factor-κβ (NF-κβ), extracellular signal-regulated kinase 1/2 (ERK1/2), and phosphoinositide 3-kinase (PI3K) are at play in the intracellular signalling of mCRP. Finally, we demonstrated the presence of mCRP in human AF and NP tissues.

Conclusion

Our results indicate, for the first time, that mCRP can be localized in IVD tissues, where it triggers a proinflammatory and catabolic state in degenerative and healthy IVD cells, and that NF-κβ signalling may be implicated in the mediation of this mCRP-induced state.

Cite this article: Bone Joint Res 2023;12(3):189–198.

Monomeric C-Reactive Protein in Atherosclerotic Cardiovascular Disease: Advances and Perspectives

This review aimed to trace the inflammatory pathway from the NLRP3 inflammasome to monomeric C-reactive protein (mCRP) in atherosclerotic cardiovascular disease. CRP is the final product of the interleukin (IL)-1β/IL-6/CRP axis. Its monomeric form can be produced at sites of local inflammation through the dissociation of pentameric CRP and, to some extent, local synthesis. mCRP has a distinct proinflammatory profile. In vitro and animal-model studies have suggested a role for mCRP in: platelet activation, adhesion, and aggregation; endothelial activation; leukocyte recruitment and polarization; foam-cell formation; and neovascularization. mCRP has been shown to deposit in atherosclerotic plaques and damaged tissues. In recent years, the first published papers have reported the development and application of mCRP assays. Principally, these studies demonstrated the feasibility of measuring mCRP levels. With recent advances in detection techniques and the introduction of first assays, mCRP-level measurement should become more accessible and widely used. To date, anti-inflammatory therapy in atherosclerosis has targeted the NLRP3 inflammasome and upstream links of the IL-1β/IL-6/CRP axis. Large clinical trials have provided sufficient evidence to support this strategy. However, few compounds target CRP. Studies on these agents are limited to animal models or small clinical trials.

A novel phosphocholine-mimetic inhibits a pro-inflammatory conformational change in C-reactive protein

C-reactive protein (CRP) is an early-stage acute phase protein and highly upregulated in response to inflammatory reactions. We recently identified a novel mechanism that leads to a conformational change from the native, functionally relatively inert, pentameric CRP (pCRP) structure to a pentameric CRP intermediate (pCRP*) and ultimately to the monomeric CRP (mCRP) form, both exhibiting highly pro-inflammatory effects. This transition in the inflammatory profile of CRP is mediated by binding of pCRP to activated/damaged cell membranes via exposed phosphocholine lipid head groups. We designed a tool compound as a low molecular weight CRP inhibitor using the structure of phosphocholine as a template. X-ray crystallography revealed specific binding to the phosphocholine binding pockets of pCRP. We provide in vitro and in vivo proof-of-concept data demonstrating that the low molecular weight tool compound inhibits CRP-driven exacerbation of local inflammatory responses, while potentially preserving pathogen-defense functions of CRP. The inhibition of the conformational change generating pro-inflammatory CRP isoforms via phosphocholine-mimicking compounds represents a promising, potentially broadly applicable anti-inflammatory therapy.

Transitional changes in the structure of C-reactive protein create highly pro-inflammatory molecules: Therapeutic implications for cardiovascular diseases

C-reactive protein (CRP) is the prototypic acute-phase reactant that has long been recognized almost exclusively as a marker of inflammation and predictor of cardiovascular risk. However, accumulating evidence indicates that CRP is also a direct pathogenic pro-inflammatory mediator in atherosclerosis and cardiovascular diseases. The 'CRP system' consists of at least two protein conformations with distinct pathophysiological functions. The binding of the native, pentameric CRP (pCRP) to activated cell membranes leads to a conformational change resulting in two highly pro-inflammatory isoforms, pCRP* and monomeric CRP (mCRP). The deposition of these pro-inflammatory isoforms has been shown to aggravate the localized tissue injury in a broad range of pathological conditions including atherosclerosis and thrombosis, myocardial infarction, and stroke. Here, we review recent findings on how these structural changes contribute to the inflammatory response and discuss the transitional changes in the structure of CRP as a novel therapeutic target in cardiovascular diseases and overshooting inflammation.

The Role of Zinc and Copper in Platelet Activation and Pathophysiological Thrombus Formation in Patients with Pulmonary Embolism in the Course of SARS-CoV-2 Infection

To date, many studies have proved that COVID-19 increases the incidence of thrombus formation and coagulopathies but the exact mechanism behind such a disease outcome is not well known. In this review we collect the information and discuss the pathophysiology of thrombus formation in patients with pulmonary embolism in the course of COVID-19 disease and the role of zinc and copper in the process. Supplementation of zinc and copper may be beneficial for COVID-19 patients due to its anti-inflammatory and anti-oxidative properties. On the other hand, excess of those microelements in the organism may be harmful, that is why marking the level of those micronutrients should be done at first. We also propose further investigation of diagnostic and therapeutic options of zinc and copper in course of COVID-19 thrombus formation to their potential in patient care, with particular emphasis on the dosage and the duration of their misbalance.

Monomeric C‑reactive protein level is associated with osteoarthritis

Osteoarthritis (OA) is a chronic joint disease characterized by articular cartilage degeneration and secondary bone hyperplasia. C-reactive protein (CRP) is an acute-phase protein that is widely used as a marker of inflammation. Elevated plasma levels of CRP are commonly observed in patients with OA during the acute phase. Current evidence indicates that CRP dissociating into a monomeric form (mCRP) is the main functional conformation at inflammatory loci. However, it remains unclear whether mCRP is associated with OA and whether mCRP can be used as a biomarker for its pathogenesis. In the present study, the concentration of CRP, mCRP and anti-mCRP autoantibody were detected by performing ELISA. The levels of plasma CRP, mCRP and anti-mCRP autoantibody between healthy subjects and patients with OA were compared. The results revealed that plasma mCRP was strongly associated with OA, while mCRP autoantibodies exhibited little correlation with this condition. Additionally, it was identified that the plasma mCRP levels in Kellgren-Lawrence (KL) grade 4 patients were significantly higher than in those with KL grade 3. Thus, it was revealed in the present study that plasma level of mCRP is associated with OA, which may directly reflect the disease degree of patients. Therefore, mCRP may be a potential indicator that can be used to monitor the disease activity and evaluate the efficiency of OA therapy.

Renal allograft-related inflammation complicated by acute coronary syndromes: A case report

INTRODUCTION

Persistent systemic inflammation is considered to be predictive for future cardiovascular events. Here, in a patient with pyelonephritis of his failed renal allograft, consecutive coronary angiograms proved that coronary artery disease progressed within 3 weeks, when infection was uncontrolled.

PATIENT CONCERNS

A 52-year-old male type 2 diabetic with a failed renal allograft suffering from hematuria, leukocyturia, and chest pain at rest was hospitalized.

DIAGNOSES

An acute coronary syndrome in presence of pyelonephritis was diagnosed. Besides pyelonephritis, the histological examination of the kidney transplant revealed signs of chronic rejection and the presence of a renal cell carcinoma in situ.

INTERVENTIONS

A percutaneous coronary intervention was performed, and an elective surgery for allograft removal was scheduled. However, within 5 weeks after discharge, two more surges of infection coincided with episodes of unstable angina.

OUTCOMES

Once the renal allograft has been removed, systemic inflammation was contained. The patient was not re-hospitalized for acute-coronary syndrome within the next 12 months.

CONCLUSION

Surges of systemic inflammation due to infection were paralleled by instability of coronary plaques as documented by repeat coronary angiograms.

The Complex Role of C-Reactive Protein in Systemic Lupus Erythematosus

C-reactive protein (CRP) is well-known as a sensitive albeit unspecific biomarker of inflammation. In most rheumatic conditions, the level of this evolutionarily highly conserved pattern recognition molecule conveys reliable information regarding the degree of ongoing inflammation, driven mainly by interleukin-6. However, the underlying causes of increased CRP levels are numerous, including both infections and malignancies. In addition, low to moderate increases in CRP predict subsequent cardiovascular events, often occurring years later, in patients with angina and in healthy individuals. However, autoimmune diseases characterized by the Type I interferon gene signature (e.g., systemic lupus erythematosus, primary Sjögren’s syndrome and inflammatory myopathies) represent exceptions to the general rule that the concentrations of CRP correlate with the extent and severity of inflammation. In fact, adequate levels of CRP can be beneficial in autoimmune conditions, in that they contribute to efficient clearance of cell remnants and immune complexes through complement activation/modulation, opsonization and phagocytosis. Furthermore, emerging data indicate that CRP constitutes an autoantigen in systemic lupus erythematosus. At the same time, the increased risks of cardiovascular and cerebrovascular diseases in patients diagnosed with systemic lupus erythematosus and rheumatoid arthritis are well-established, with significant impacts on quality of life, accrual of organ damage, and premature mortality. This review describes CRP-mediated biological effects and the regulation of CRP release in relation to aspects of cardiovascular disease and mechanisms of autoimmunity, with particular focus on systemic lupus erythematosus.

Monomeric C reactive protein (mCRP) regulates inflammatory responses in human and mouse chondrocytes

C-reactive protein (CRP) is an acute-phase protein that is used as an established biomarker to follow disease severity and progression in a plethora of inflammatory diseases. However, its pathophysiologic mechanisms of action are still poorly defined and remain elusive. CRP, in its pentameric form, exhibits weak anti-inflammatory activity. On the contrary, the monomeric isoform (mCRP) exhibits potent pro-inflammatory properties in endothelial cells, leukocytes, and platelets. So far, no data exists regarding mCRP effects in human or mouse chondrocytes. This work aimed to verify the pathophysiological relevance of mCRP in the etiology and/or progression of osteoarthritis (OA). We investigated the effects of mCRP in cultured human primary chondrocytes and in the chondrogenic ATDC5 mouse cell line. We determined mRNA and protein levels of relevant factors involved in inflammatory responses and the modulation of nitric oxide synthase type II (NOS2), an early inflammatory molecular target. We demonstrate, for the first time, that monomeric C reactive protein increases NOS2, COX2, MMP13, VCAM1, IL-6, IL-8, and LCN2 expression in human and murine chondrocytes. We also demonstrated that NF-kB is a key factor in the intracellular signaling of mCRP-driven induction of pro-inflammatory and catabolic mediators in chondrocytes. We concluded that mCRP exerts a sustained catabolic effect on human and murine chondrocytes, increasing the expression of inflammatory mediators and proteolytic enzymes, which can promote extracellular matrix (ECM) breakdown in healthy and OA cartilage. In addition, our results implicate the NF-kB signaling pathway in catabolic effects mediated by mCRP.

CATALYST trial protocol: a multicentre, open-label, phase II, multiarm trial for an early and accelerated evaluation of the potential treatments for COVID-19 in hospitalised adults

INTRODUCTION

Severe SARS-CoV-2 infection is associated with a dysregulated immune response. Inflammatory monocytes and macrophages are crucial, promoting injurious, proinflammatory sequelae. Immunomodulation is, therefore, an attractive therapeutic strategy and we sought to test licensed and novel candidate drugs.

METHODS AND ANALYSIS

The CATALYST trial is a multiarm, open-label, multicentre, phase II platform trial designed to identify candidate novel treatments to improve outcomes of patients hospitalised with COVID-19 compared with usual care. Treatments with evidence of biomarker improvements will be put forward for larger-scale testing by current national phase III platform trials. Hospitalised patients >16 years with a clinical picture strongly suggestive of SARS-CoV-2 pneumonia (confirmed by chest X-ray or CT scan, with or without a positive reverse transcription PCR assay) and a C reactive protein (CRP) ≥40 mg/L are eligible. The primary outcome measure is CRP, measured serially from admission to day 14, hospital discharge or death. Secondary outcomes include the WHO Clinical Progression Improvement Scale as a principal efficacy assessment.

ETHICS AND DISSEMINATION

The protocol was approved by the East Midlands-Nottingham 2 Research Ethics Committee (20/EM/0115) and given urgent public health status; initial approval was received on 5 May 2020, current protocol version (V.6.0) approval on 12 October 2020. The MHRA also approved all protocol versions. The results of this trial will be disseminated through national and international presentations and peer-reviewed publications.

TRIAL REGISTRATION NUMBERS

EudraCT2020-001684-89, ISRCTN40580903.

C-Reactive Protein and Cancer: Interpreting the Differential Bioactivities of Its Pentameric and Monomeric, Modified Isoforms

C-reactive protein (CRP) was first recognized in the 1940s as a protein that appeared in blood during acute episodes of infectious disease. Its presence and pharmacodynamics were found in essentially all diseases that involved tissue damage and inflammation. Identified as a major component of the innate, unlearned immunity, it became a useful diagnostic marker for the extent of inflammation during disease exacerbation or remission. Efforts to define its true biological role has eluded clear definition for over a half-century. Herein, a unifying concept is presented that explains both pro-inflammatory and anti-inflammatory activities of CRP. This concept involves the recognition and understanding that CRP can be induced to undergo a pronounced, non-proteolytic reorganization of its higher-level protein structures into conformationally distinct isomers with distinctive functional activities. This process occurs when the non-covalently associated globular subunits of the pentameric isoform ("pCRP") are induced to dissociate into a monomeric isoform ("mCRP"). mCRP consistently and potently provides pro-inflammatory activation and amplification activities. pCRP provides weak anti-inflammatory activities consistent with low-level chronic inflammation. mCRP can spontaneously form in purified pCRP reagents in ways that are not immediately recognized during purification and certification analyses. By now understanding the factors that influence pCRP dissociate into mCRP, many published reports investigating CRP as a biological response modifier of host defense can be reevaluated to include a discussion of how each CRP isoform may have affected the generated results. Specific attention is given to in vitro and in vivo studies of CRP as an anti-cancer agent.

Pattern Recognition Proteins: First Line of Defense Against Coronaviruses

The rapid outbreak of COVID-19 caused by the novel coronavirus SARS-CoV-2 in Wuhan, China, has become a worldwide pandemic affecting almost 204 million people and causing more than 4.3 million deaths as of August 11 2021. This pandemic has placed a substantial burden on the global healthcare system and the global economy. Availability of novel prophylactic and therapeutic approaches are crucially needed to prevent development of severe disease leading to major complications both acutely and chronically. The success in fighting this virus results from three main achievements: (a) Direct killing of the SARS-CoV-2 virus; (b) Development of a specific vaccine, and (c) Enhancement of the host's immune system. A fundamental necessity to win the battle against the virus involves a better understanding of the host's innate and adaptive immune response to the virus. Although the role of the adaptive immune response is directly involved in the generation of a vaccine, the role of innate immunity on RNA viruses in general, and coronaviruses in particular, is mostly unknown. In this review, we will consider the structure of RNA viruses, mainly coronaviruses, and their capacity to affect the lungs and the cardiovascular system. We will also consider the effects of the pattern recognition protein (PRP) trident composed by (a) Surfactant proteins A and D, mannose-binding lectin (MBL) and complement component 1q (C1q), (b) C-reactive protein, and (c) Innate and adaptive IgM antibodies, upon clearance of viral particles and apoptotic cells in lungs and atherosclerotic lesions. We emphasize on the role of pattern recognition protein immune therapies as a combination treatment to prevent development of severe respiratory syndrome and to reduce pulmonary and cardiovascular complications in patients with SARS-CoV-2 and summarize the need of a combined therapeutic approach that takes into account all aspects of immunity against SARS-CoV-2 virus and COVID-19 disease to allow mankind to beat this pandemic killer.

CRP immunodeposition and proteomic analysis in abdominal aortic aneurysm

OBJECTIVE

The molecular mechanisms of the degeneration of the aortic wall in abdominal aortic aneurysm (AAA) are poorly understood. The monomeric form of C-reactive protein (mCRP) is deposited in damaged cardiovascular organs and aggravates the prognosis; however, it is unknown whether mCRP is deposited in the degenerated aorta of abdominal aortic aneurysm (AAA). We investigated whether mCRP is deposited in AAA and examined the associated pathogenic signaling pathways.

METHODS

Twenty-four cases of AAA were analyzed and their histological features were compared according to the level of serum CRP and the degree of mCRP deposition. Proteomic analysis was performed in AAA cases with strong and diffuse CRP immunopositivity (n = 7) and those with weak, focal, and junctional CRP immunopositivity (n = 3).

RESULTS

mCRP was deposited in the aortic specimens of AAA in a characteristic pattern that coincided with the lesion of the diminished elastic layer of the aortic wall. High serum CRP level was associated with stronger mCRP immunopositivity and a larger maximal diameter of aortic aneurysm. Proteomic analysis in AAA showed that multiple proteins were differentially expressed according to mCRP immunopositivity. Also, ingenuity pathway analysis showed that pathways associated with atherosclerosis, acute phase response, complement system, immune system, and coagulation were enriched in AAA cases with high mCRP immunopositivity.

CONCLUSIONS

AAA showed a characteristic deposition of mCRP, and multiple potentially pathologic signaling pathways were upregulated in AAA cases with strong CRP immunopositivity. mCRP and the aforementioned pathological pathways may serve as targets for managing the progression of AAA.

The effect of hypochlorous acid on the tribocorrosion of CoCrMo/Ti-6Al-4V bearing couples

Mechanically assisted corrosion (MAC) of metallic orthopedic alloys is a consequence of the use of modular devices where opposing metal surfaces are tightly mated and loaded at the taper junction. MAC processes are affected by material surface characteristics and local solution chemistry. During inflammation, active immune cells may generate reactive oxygen species (such as hypochlorous acid [HOCl]) adjacent to surfaces undergoing micromotion, which may affect the tribocorrosion behavior of an implanted device. This study investigated the fretting current response of CoCrMo/Ti-6Al-4 V couples in a pin-on-disk apparatus utilizing HOCl solutions as a proxy for a severe inflammatory environment. Testing in 1 and 5 mM HOCl solutions were shown to generate a threefold and fivefold increase (p < 0.01), respectively, in fretting currents over pH 7.4 phosphate-buffered saline control conditions. Fretting currents were shown to be dependent on the energy dissipated during fretting and the concentration of HOCl where the currents within a single HOCl concentration were linearly dependent of energy dissipated, but different HOCl levels shifted (increased and then decreased) fretting currents with concentration. Fretting currents, governed by regrowth of an abraded oxide film, were affected by the oxidative power of the solution, which caused positive shifts in open circuit potential and likely resulted in a thicker oxide for 1 mM and 5 mM and fell with 30 mM. Small amounts of HOCl release within a joint may result in increased release of tribocorrosion products such as oxide particles.

Role of Ischemic Preconditioning in the Cardioprotective Mechanisms of Monomeric C-Reactive Protein-Deposited Myocardium in a Rat Model

Background

The deposition of monomeric C-reactive protein (mCRP) in the myocardium aggravates ischemia-reperfusion injury (IRI) and myocardial infarction. Ischemic preconditioning (IPC) is known to protect the myocardium against IRI.

Methods

We evaluated the effects of IPC on myocardium upon which mCRP had been deposited due to IRI in a rat model. Myocardial IRI was induced via ligation of the coronary artery. Direct IPC was applied prior to IRI using multiple short direct occlusions of the coronary artery. CRP was infused intravenously after IRI. The study included sham (n=3), IRI-only (n=5), IRI+CRP (n=9), and IPC+IRI+CRP (n=6) groups. The infarcted area and the area at risk were assessed using Evans blue and 2,3,5-triphenyltetrazolium staining. Additionally, mCRP immunostaining and interleukin-6 (IL-6) mRNA reverse transcription-polymerase chain reaction were performed.

Results

In the IRI+CRP group, the infarcted area and the area of mCRP deposition were greater, and the level of IL-6 mRNA expression was higher, than in the IRI-only group. However, in the IPC+IRI+CRP group relative to the IRI+CRP group, the relative areas of infarction (20% vs. 34%, respectively; p=0.079) and mCRP myocardial deposition (21% vs. 44%, respectively; p=0.026) were lower and IL-6 mRNA expression was higher (fold change 407 vs. 326, respectively; p=0.376), although the difference in IL-6 mRNA expression was not statistically significant.

Conclusion

IPC was associated with significantly decreased deposition of mCRP and with increased expression of IL-6 in myocardium damaged by IRI. The net cardioprotective effect of decreased mCRP deposition and increased IL-6 levels should be clarified in a further study.

Current Position on the Role of Monomeric C-reactive Protein in Vascular Pathology and Atherothrombosis

C-reactive Protein (CRP) is an acute phase reactant, belonging to the pentraxin family of proteins. Its level rises up to 1000-fold in response to acute inflammation. High sensitivity CRP level is utilized as an independent biomarker of inflammation and cardiovascular disease. The accumulating data suggests that CRP has two distinct forms. It is predominantly produced in the liver in a native pentameric form (nCRP). At sites of local inflammation and tissue injury it may bind to phosphocholine-rich membranes of activated and apoptotic cells and their microparticles, undergoing irreversible dissociation to five monomeric subunits, termed monomeric CRP (mCRP). Through dissociation, CRP deposits into tissues and acquires distinct proinflammatory properties. It activates both classic and alternative complement pathways, binding complement component C1q and factor H. mCRP actively participates in the development of endothelial dysfunction. It activates leukocytes, inducing cytokine release and monocyte recruitment. It may also play a role in the polarization of monocytes and T cells into proinflammatory phenotypes. It may be involved in low-density lipoproteins (LDL) opsonization and uptake by macrophages. mCRP deposits were detected in samples of atherosclerotic lesions from human aorta, carotid, coronary and femoral arteries. mCRP may also induce platelet aggregation and thrombus formation, thus contributing in multiple ways in the development of atherosclerosis and atherothrombosis. In this mini-review, we will provide an insight into the process of conformational rearrangement of nCRP, leading to dissociation, and describe known effects of mCRP. We will provide a rationalization for mCRP involvement in the development of atherosclerosis and atherothrombosis.

CRP Is Transported by Monocytes and Monocyte-Derived Exosomes in the Blood of Patients with Coronary Artery Disease

The objective of this work was to study the ability of blood cells and their microparticles to transport monomeric and pentameric forms of C-reactive protein (mCRP and pCRP) in the blood of patients with coronary artery disease (CAD). Blood was obtained from 14 patients with CAD 46 ± 13 years old and 8 healthy volunteers 49 ± 13.6 years old. Blood cells and microparticles with mCRP and pCRP on their surface were detected by flow cytometry. Messenger RNA (mRNA) of CRP was extracted from peripheral blood monocytes stimulated with lipopolysaccharide (LPS) and granulocyte-macrophage colony-stimulating factor (GM-CSF). mRNA of CRP in monocytes was detected with PCR. Monocytes were predominantly pCRP-positive (92.9 ± 6.8%). mCRP was present on 22.0 ± 9.6% of monocyte-derived exosomes. mCRP-positive leukocyte-derived microparticle counts were significantly higher (8764 ± 2876/µL) in the blood of patients with CAD than in healthy volunteers (1472 ± 307/µL). LPS and GM-CSF stimulated monocytes expressed CRP mRNA transcripts levels (0.79 ± 0.73-fold), slightly lower relative to unstimulated hepatocytes of the HepG2 cell line (1.0 ± 0.6-fold), but still detectable. The ability of monocytes to transport pCRP in blood flow, and monocyte-derived exosomes to transmit mCRP, may contribute to the maintenance of chronic inflammation in CAD.

The plasma level of mCRP is linked to cardiovascular disease in antineutrophil cytoplasmic antibody-associated vasculitis

Background

C-reactive protein (CRP) has two natural isomers: C-reactive protein pentamer (pCRP) and C-reactive protein monomer (mCRP). The levels of CRP are significantly elevated in patients with anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). mCRP not only activates the endothelial cells, platelets, leukocytes, and complements, but also has a proinflammatory structural subtype that can localize and deposit in inflammatory tissues. Thus, it regulates a variety of clinical diseases, such as ischemia/reperfusion (I/R) injury, Alzheimer’s disease, age-related macular degeneration, and cardiovascular disease. We hypothesized that plasma mCRP levels are related to cardiovascular disease in AAV.

Methods

In this cross-sectional study, 37 patients with AAV were assessed. Brain natriuretic peptide (BNP) and mCRP in plasma were assessed by enzyme-linked immunosorbent assay (ELISA). The acute ST-segment elevation myocardial infarction (STEMI) was diagnosed by coronary angiography, and the Gensini score calculated. Echocardiography evaluated the ejection fraction (EF%), left ventricular end-diastolic volume (LVEDV), left ventricular end-systolic volume (LVESV), and left ventricular mass index (LVMI). Estimated glomerular filtration rate (eGFR) was calculated based on serum creatinine, age, and gender.

Results

The plasma level of mCRP in AAV was significantly higher than that in healthy volunteers (P < 0.001). Then, mCRP and CRP levels were compared with and without STEMI complications in AAV. The plasma level of mCRP was higher, but that of CRP was lower in STEMI. The plasma level of mCRP was correlated with Birmingham vasculitis activity score (BVAS), eGFR, BNP, EF%, LVEDV, LVESV, LVMI, and STEMI complications’ Gensini score in AAV; however, CRP did not correlate with BNP, EF%, LVEDV, LVESV, LVMI, and Gensini score.

Conclusions

The plasma level of mCRP was related to cardiovascular diseases in AAV patients.

effects of azide-containing human CRP isoforms and oxLDL on U937-derived macrophage production of atherosclerosis-related cytokines

Atherosclerosis is an inflammatory chronic disease of the arterial wall. Monomeric (m) and pentameric (p) C-reactive protein (CRP) and oxidized low density lipoproteins (oxLDL) seem to affect the pattern of cytokine production by macrophages, thus playing an important role in atherogenesis. Azide, the commercial preservative of CRP, may influence its action in vitro. The present study aimed to determine the effects of both isoforms of azide-containing CRP (mCRP and pCRP) with and without oxLDL on cytokine production by U937-derived macrophages. U937 monocytes were cultured and differentiated into macrophages and treated with mCRP, pCRP, oxLDL and azide individually and in combination. ELISA were performed to measure the levels of interferon-γ (IFN-γ), interleukin (IL)-4, IL-6, IL-10 and tumor necrosis factor (TNF)-α in culture supernatants collected from U937-derived macrophages following their respective treatments. Most single and combined treatments, especially in triple combination, were able to downregulate the levels of IFN-γ and IL-6 compared with control untreated cells, whilst the combination of mCRP and pCRP increased IL-4 levels. Regarding IL-10, except for an increase induced by mCRP, no significant effect was caused by any treatment compared with the control. On the other hand, the levels of TNF-α were not significantly affected by any treatment except for a decreasing trend that was observed with mCRP/oxLDL treatment compared with control. By contrast, double azide caused a significant decrease in the levels of IFN-γ and IL-6. The results of the present study indicated that mCRP, pCRP, oxLD and possibly azide, individually or in different combinations, had the tendency to upregulate the expression of IL-4 and to downregulate that of the pro-atherogenic cytokines, IFN-γ and IL-6, suggesting that the intima microenvironment serves a crucial role in atherogenesis.

How C-Reactive Protein Structural Isoforms With Distinctive Bioactivities Affect Disease Progression

C-reactive protein (CRP) is a widely known, hepatically synthesized protein whose blood levels change rapidly and pronouncedly in response to any tissue damaging event associated with an inflammatory response. The synthesis and secretion of CRP is stimulated by interleukin-6, an early pleiotropic cytokine released by macrophages, endothelial, and other cells that are activated when localized normal tissue structures are compromised by trauma or disease. Serum CRP levels can change rapidly and robustly from 10-100-fold within 6–72 h of any tissue damaging event. Elevated blood levels correlate with the onset and extent of both activated inflammation and the acute phase biochemical response to the tissue insult. Because its functional bioactivity as the prototypic acute phase reactant has eluded clear definition for decades, diagnosticians of various conditions and diseases use CRP blood levels as a simple index for ongoing inflammation. In many pathologies, which involves many different tissues, stages of disease, treatments, and responses to treatments, its interpretive diagnostic value requires a deeper understanding of the localized tissue processes and events that contribute signals which regulate protective or pathological host defense bioactivities. This report presents concepts that describe how local tissue activation events can lead to a non-proteolytic, conformational rearrangement of CRP into a unique isoform with distinctive solubility, antigenicity, binding reactivities and bioactivities from that protein widely known and measured in serum. By describing factors that control the expression, tissue localization, half-life and pro-inflammatory amplification activity of this CRP isoform, a unifying explanation for the diagnostic significance of CRP measurement in disease is advanced.

C-Reactive Protein and Its Structural Isoforms: An Evolutionary Conserved Marker and Central Player in Inflammatory Diseases and Beyond

C-reactive protein (CRP) is an evolutionary highly conserved member of the pentraxin superfamily of proteins. CRP is widely used as a marker of inflammation, infection and for risk stratification of cardiovascular events. However, there is now a large body of evidence, that continues to evolve, detailing that CRP directly mediates inflammatory reactions and the innate immune response in the context of localised tissue injury. These data support the concept that the pentameric conformation of CRP dissociates into pro-inflammatory CRP isoforms termed pCRP* and monomeric CRP. These pro-inflammatory CRP isoforms undergo conformational changes that facilitate complement binding and immune cell activation and therefore demonstrate the ability to trigger complement activation, activate platelets, monocytes and endothelial cells. The dissociation of pCRP occurs on the surface of necrotic, apoptotic, and ischaemic cells, regular β-sheet structures such as β-amyloid, the membranes of activated cells (e.g., platelets, monocytes, and endothelial cells), and/or the surface of microparticles, the latter by binding to phosphocholine. Therefore, the deposition and localisation of these pro-inflammatory isoforms of CRP have been demonstrated to amplify inflammation and tissue damage in a broad range of clinical conditions including ischaemia/reperfusion injury, Alzheimer's disease, age-related macular degeneration and immune thrombocytopaenia. Given the potentially broad relevance of CRP to disease pathology, the development of inhibitors of CRP remains an area of active investigation, which may pave the way for novel therapeutics for a diverse range of inflammatory diseases.

Intra-subunit Disulfide Determines the Conversion and Structural Stability of CRP Isoforms

C-reactive protein (CRP) is a major human acute-phase reactant that is composed of five identical subunits. CRP dissociates into subunits at inflammatory loci forming monomeric CRP (mCRP) with substantially enhanced activities, which can be further activated by reducing the intra-subunit disulfide bond. However, conformational changes underlying the activation process of CRP are less well understood. Conformational changes accompanying the conversion of CRP to mCRP with or without reduction were examined with circular dichroism spectroscopy, fluorescence spectroscopy, electron microscopy, size-exclusion chromatography, and neoepitope expression. The conversion of CRP to mCRP follows a two-stage process. In the first stage, CRP dissociates into molten globular subunits characterized by intact secondary structure elements with greatly impaired tertiary packing. In the second stage, these intermediates completely lose their native subunit conformation and assemble into high-order aggregates. The inclusion of reductant accelerates the formation of molten globular subunits in the first step and promotes the formation of more compact aggregates in the second stage. We further show a significant contribution of electrostatic interactions to the stabilization of native CRP. The conformational features of dissociated subunits and the aggregation of mCRP may have a key impact on their activities.

Monomeric C-reactive protein regulates fibronectin mediated monocyte adhesion

The acute phase reactant C-reactive protein (CRP) binds with high affinity to fibronectin (FN), but this binding occurs only at pH 6.5 or lower, and the binding is inhibited by calcium ions at physiological pH. Since CRP in the circulating blood exists in a calcium-binding form, the interaction between CRP and FN in vivo has been uncertain. CRP can undergo a conformational rearrangement in the absence of calcium or in the local microenvironment (e.g., acidic pH) of inflamed tissue to dissociate into monomeric CRP (mCRP). Therefore, we tested whether these discrepancies can be explained by the different isoforms and locations of CRP. Surface plasmon resonance and ELISA assays showed that mCRP binds with high affinity to FN, and the binding of mCRP to FN was unaffected by calcium or pH. Peptide competition assay, deletion mutant binding assay and protein docking analyse verified that the binding site of mCRP to FN is residues a.a.35-47. Furthermore, mCRP can significantly enhance the adhesion of monocytes to FN as well as upregulate the adhesion molecules expression on endothelial cell. Colocalization of mCRP with FN was observed in mice with DSS-induced colitis, whereas there was very little signal orcolocalization of CRP. These results provide in vitro and in vivo evidence that mCRP formed by local dissociation from circulating CRP is the major isoform that interacts with FN and regulates FN-mediated monocyte adhesion, which is involved in the pro-inflammatory process.

The Multiple Faces of C-Reactive Protein-Physiological and Pathophysiological Implications in Cardiovascular Disease

C-reactive protein (CRP) is an intriguing protein which plays a variety of roles in either physiological or pathophysiological states. For years it has been regarded merely as a useful biomarker of infection, tissue injury and inflammation, and it was only in the early 80s that the modified isoforms (mCRP) of native CRP (nCRP) appeared. It soon became clear that the roles of native CRP should be clearly discriminated from those of the modified form and so the impacts of both isoforms were divided to a certain degree between physiological and pathophysiological states. For decades, CRP has been regarded only as a hallmark of inflammation; however, it has since been recognised as a significant predictor of future episodes of cardiovascular disease, independent of other risk factors. The existence of modified CRP isoforms and their possible relevance to various pathophysiological conditions, suggested over thirty years ago, has prompted the search for structural and functional dissimilarities between the pentameric nCRP and monomeric mCRP isoforms. New attempts to identify the possible relevance between the diversity of structures and their opposing functions have initiated a new era of research on C-reactive protein. This review discusses the biochemical aspects of CRP physiology, emphasizing the supposed relevance between the structural biology of CRP isoforms and their differentiated physiological and pathophysiological roles.

Sarcopenia: Aging-Related Loss of Muscle Mass and Function

Sarcopenia is a loss of muscle mass and function in the elderly that reduces mobility, diminishes quality of life, and can lead to fall-related injuries, which require costly hospitalization and extended rehabilitation. This review focuses on the aging-related structural changes and mechanisms at cellular and subcellular levels underlying changes in the individual motor unit: specifically, the perikaryon of the α-motoneuron, its neuromuscular junction(s), and the muscle fibers that it innervates. Loss of muscle mass with aging, which is largely due to the progressive loss of motoneurons, is associated with reduced muscle fiber number and size. Muscle function progressively declines because motoneuron loss is not adequately compensated by reinnervation of muscle fibers by the remaining motoneurons. At the intracellular level, key factors are qualitative changes in posttranslational modifications of muscle proteins and the loss of coordinated control between contractile, mitochondrial, and sarcoplasmic reticulum protein expression. Quantitative and qualitative changes in skeletal muscle during the process of aging also have been implicated in the pathogenesis of acquired and hereditary neuromuscular disorders. In experimental models, specific intervention strategies have shown encouraging results on limiting deterioration of motor unit structure and function under conditions of impaired innervation. Translated to the clinic, if these or similar interventions, by saving muscle and improving mobility, could help alleviate sarcopenia in the elderly, there would be both great humanitarian benefits and large cost savings for health care systems.

Acetylcholine Inhibits Monomeric C-Reactive Protein Induced Inflammation, Endothelial Cell Adhesion, and Platelet Aggregation; A Potential Therapeutic?

Objectives: In this study, we examined the possibility of using targeted antibodies and the potential of small molecular therapeutics (acetylcholine, nicotine and tacrine) to block the pro-inflammatory and adhesion-related properties of monomeric C-reactive protein (mCRP). Methods: We used three established models (platelet aggregation assay, endothelial leucocyte binding assay and monocyte inflammation via ELISA and Western blotting) to assess the potential of these therapeutics. Results: The results of this study showed that monocyte induced inflammation (raised tumor necrosis factor-alpha-TNF-α) induced by mCRP was significantly blocked in the presence of acetylcholine and nicotine, whilst tacrine and targeted antibodies (clones 8C10 and 3H12) had less of or no significant effects. Western blotting confirmed the ability of acetylcholine to inhibit mCRP-induced cell signaling phosphorylation of extracellular signal regulated kinase 1/2 (ERK1/2), p38 and nuclear factor-kappa B (NF-κB). There was no evidence of direct binding between small molecules and mCRP. mCRP also induced endothelial cell-monocyte adhesion in a dose dependent fashion, however, both acetylcholine and nicotine as well as targeting antibodies notably inhibited adhesion. Finally, we investigated their effects on mCRP-induced platelet aggregation. All three small molecules significantly attenuated platelet aggregation as did the antibody 8C10, although 3H12 had a weaker effect. Discussion: Acetylcholine and to a lesser extent nicotine show potential for therapeutic inhibition of mCRP-induced inflammation and cell and platelet adhesion. These results highlight the potential of targeted antibodies and small molecule therapeutics to inhibit the binding of mCRP by prevention of membrane interaction and subsequent activation of cellular cascade systems, which produce the pro-inflammatory effects associated with mCRP.

The contribution of chronic intermittent hypoxia to OSAHS: From the perspective of serum extracellular microvesicle proteins

OBJECTIVE

Obstructive sleep apnea hypopnea syndrome (OSAHS) is an independent risk factor for many clinical complications. However, how OSAHS cause multiple organ injury and initiate inter-organ communication remains unclear. Moreover, despite it is well-recognized that chronic intermittent hypoxia (CIH) is a main feature of OSAHS, specific contribution of CIH to overall OSAHS-initiated pathological complications remains unclear. This study aimed to use an unbiased proteomic approach to determine whether OSAHS alters protein profiles of serum extracellular microvesicles (SEMVs) and how CIH contributes to such alterations.

METHODS

Tandem mass tag (TMT)-labeled quantitative proteomics assay was used to compare the differentially expressed proteins (DEPs) in SEMVs of OSAHS patients and non-OSAHS subjects. To evaluate the contribution of CIH to OSAHS, CIH rodent model was constructed and the same comparative proteomics study was performed in SEMVs from CIH and normoxia rats. The similarity and disparity of DEPs and DEPs-related functions predicted by bioinformatics tools were compared in above-mentioned two models, and several DEPs were selected and further verified by ELISA or Western blotting.

RESULTS

TMT-labeled quantitative proteomics assay unravels 32 DEPs in OSAHS patient SEMVs from a total of 560 human SEMV proteins identified. Four DEPs, namely C-reactive protein (CRP), Haptoglobin (HP),Fibronectin (FN1) and Platelet factor 4 (PF4), were further verified by ELISA and three of them (CRP, FN1 and Hp) showed significant difference in expression level between OSAHS and non-OSAHS groups. In SEMVs of rat CIH model, 121 DEPs out of 723 proteins were identified. By comparing the DEPs identified from the two models, 3 proteins (CRP and FN1 and F13a1) were found identical with the same alteration pattern (CRP was upregulated, FN1 and F13a1 were downregulated) in SEMVs from OSAHS patients and CIH rats, which were further verified by Western blotting. Computational functional analysis further revealed the common and distinct DEP-involved pathways under OSAHS or CIH status.

CONCLUSIONS

This study provides the first evidence that OSAHS causes significant alteration in SEMV protein composition, which may contribute to OSAHS-triggered multiple organ injury and organ-to-organ communication. Moreover, we have demonstrated that CIH is the primary contributor for increased inflammatory protein expression in SEMV. As CRP is being increasingly recognized not only as a marker but also a mediator of inflammatory response to tissue injury, increased SEMV CRP in CIH/OSAHS may play an important role in OSAHS-induced tissue injury, suggesting SEMV CRP might be a therapeutic target against OSAHS-related complications.

The Effect of C-Reactive Protein Isoforms on Nitric Oxide Production by U937 Monocytes/Macrophages

Inflammation is regulated by many endogenous factors including estrogen, a steroid hormone that declines with increasing age, leading to excessive inflammation in the elderly. C-reactive protein (CRP) is an acute phase inflammatory protein that exists in two forms, native CRP (nCRP) and monomeric CRP (mCRP), which mediate distinct biological activities. It is unclear how each CRP isoform mediates nitric oxide (NO), a signaling molecule generated by NO synthase (NOS). This study investigated whether CRP isoforms have distinct effects on NO production by unstimulated and lipopolysaccharide (LPS)-activated monocytes/macrophages and whether estrogen mediates CRP-induced NO production in an in vitro model of aging. NO and inducible NOS (iNOS) were measured (n = 12) by the Griess assay and an enzyme-linked immunosorbent assay, respectively following incubation (24 h) of human-derived U937 monocytes/macrophages with CRP isoforms [(nCRP) = 500 and 1,000 µg/ml; (mCRP) = 100 and 250 µg/ml] in the absence or presence of 17 beta-estradiol (1 × 10-7, 1 × 10-8, and 1 × 10-9 M). The response to each CRP isoform and estrogen was dependent on the differentiation and activation status of cells. Monocytes with or without prior LPS-activation significantly increased (P < 0.01) NO/iNOS production when treated with mCRP. The mCRP isoform had no effect (P > 0.05) on NO/iNOS production by unactivated or LPS-activated macrophages, whereas nCRP significantly (P < 0.05) reduced NO/iNOS production by macrophages, with or without prior LPS-activation. The nCRP isoform had opposing actions on monocytes, significantly (P < 0.01) increasing and reducing NO/iNOS by unactivated and LPS-activated monocytes, respectively. Estrogen significantly (P < 0.01) reversed nCRP-mediated NO inhibition by unactivated macrophages but decreased CRP-induced NO by unactivated monocytes treated with nCRP or mCRP and LPS-activated monocytes treated with mCRP. NO was differentially mediated by CRP isoforms in a cell-type/state-specific manner, with production corresponding to concomitant changes in iNOS levels. Collectively, the findings indicate nCRP and estrogen predominantly reduce NO production, whereas mCRP increases NO production. This supports growing evidence that mCRP exacerbates inflammation while nCRP and estrogen dampen the overall inflammatory response. Therapeutic strategies that restore estrogen levels to those found in youth and promote the stability of nCRP or/and prevent the formation of mCRP may reduce NO production in age-related inflammatory conditions.

Dissociation of C-Reactive Protein Localizes and Amplifies Inflammation: Evidence for a Direct Biological Role of C-Reactive Protein and Its Conformational Changes

C-reactive protein (CRP) is a member of the pentraxin superfamily that is widely recognized as a marker of inflammatory reactions and cardiovascular risk in humans. Recently, a growing body of data is emerging, which demonstrates that CRP is not only a marker of inflammation but also acts as a direct mediator of inflammatory reactions and the innate immune response. Here, we critically review the various lines of evidence supporting the concept of a pro-inflammatory “CRP system.” The CRP system consists of a functionally inert circulating pentameric form (pCRP), which is transformed to its highly pro-inflammatory structural isoforms, pCRP* and ultimately to monomeric CRP (mCRP). While retaining an overall pentameric structure, pCRP* is structurally more relaxed than pCRP, thus exposing neoepitopes important for immune activation and complement fixation. Thereby, pCRP* shares its pro-inflammatory properties with the fully dissociated structural isoform mCRP. The dissociation of pCRP into its pro-inflammatory structural isoforms and thus activation of the CRP system occur on necrotic, apoptotic, and ischemic cells, regular β-sheet structures such as β-amyloid, the membranes of activated cells (e.g., platelets, monocytes, and endothelial cells), and/or the surface of microparticles, the latter by binding to phosphocholine. Both pCRP* and mCRP can cause activation of platelets, leukocytes, endothelial cells, and complement. The localization and deposition of these pro-inflammatory structural isoforms of CRP in inflamed tissue appear to be important mediators for a range of clinical conditions, including ischemia/reperfusion (I/R) injury of various organs, cardiovascular disease, transplant rejection, Alzheimer’s disease, and age-related macular degeneration. These findings provide the impetus to tackle the vexing problem of innate immunity response by targeting CRP. Understanding the “activation process” of CRP will also likely allow the development of novel anti-inflammatory drugs, thereby providing potential new immunomodulatory therapeutics in a broad range of inflammatory diseases.

C-Reactive Protein as a Therapeutic Target in Age-Related Macular Degeneration

Age-related macular degeneration (AMD), a retinal degenerative disease, is the leading cause of central vision loss among the elderly population in developed countries and an increasing global burden. The major risk is aging, compounded by other environmental factors and association with genetic variants for risk of progression. Although the etiology of AMD is not yet clearly understood, several pathogenic pathways have been proposed, including dysfunction of the retinal pigment epithelium, inflammation, and oxidative stress. The identification of AMD susceptibility genes encoding complement factors and the presence of complement and other inflammatory mediators in drusen, the hallmark deposits of AMD, support the concept that local inflammation and immune-mediated processes play a key role in AMD pathogenesis that may be accelerated through systemic immune activation. In this regard, increased levels of circulating C-reactive protein (CRP) have been associated with higher risk of AMD. Besides being a risk marker for AMD, CRP may also play a role in the progression of the disease as it has been identified in drusen, and we have recently found that its monomeric form (mCRP) induces blood retinal barrier disruption in vitro. In this review, we will address recent evidence that links CRP and AMD pathogenesis, which may open new therapeutic opportunities to prevent the progression of AMD.

Role of C-Reactive Protein at Sites of Inflammation and Infection

C-reactive protein (CRP) is an acute inflammatory protein that increases up to 1,000-fold at sites of infection or inflammation. CRP is produced as a homopentameric protein, termed native CRP (nCRP), which can irreversibly dissociate at sites of inflammation and infection into five separate monomers, termed monomeric CRP (mCRP). CRP is synthesized primarily in liver hepatocytes but also by smooth muscle cells, macrophages, endothelial cells, lymphocytes, and adipocytes. Evidence suggests that estrogen in the form of hormone replacement therapy influences CRP levels in the elderly. Having been traditionally utilized as a marker of infection and cardiovascular events, there is now growing evidence that CRP plays important roles in inflammatory processes and host responses to infection including the complement pathway, apoptosis, phagocytosis, nitric oxide (NO) release, and the production of cytokines, particularly interleukin-6 and tumor necrosis factor-α. Unlike more recent publications, the findings of early work on CRP can seem somewhat unclear and at times conflicting since it was often not specified which particular CRP isoform was measured or utilized in experiments and whether responses attributed to nCRP were in fact possibly due to dissociation into mCRP or lipopolysaccharide contamination. In addition, since antibodies for mCRP are not commercially available, few laboratories are able to conduct studies investigating the mCRP isoform. Despite these issues and the fact that most CRP research to date has focused on vascular disorders, there is mounting evidence that CRP isoforms have distinct biological properties, with nCRP often exhibiting more anti-inflammatory activities compared to mCRP. The nCRP isoform activates the classical complement pathway, induces phagocytosis, and promotes apoptosis. On the other hand, mCRP promotes the chemotaxis and recruitment of circulating leukocytes to areas of inflammation and can delay apoptosis. The nCRP and mCRP isoforms work in opposing directions to inhibit and induce NO production, respectively. In terms of pro-inflammatory cytokine production, mCRP increases interleukin-8 and monocyte chemoattractant protein-1 production, whereas nCRP has no detectable effect on their levels. Further studies are needed to expand on these emerging findings and to fully characterize the differential roles that each CRP isoform plays at sites of local inflammation and infection.

C-Reactive Protein in Atherothrombosis and Angiogenesis

C-reactive protein (CRP) is a short pentraxin mainly found as a pentamer in the circulation, or as non-soluble monomers CRP (mCRP) in tissues, exerting different functions. This review is focused on discussing the role of CRP in cardiovascular disease, including recent advances on the implication of CRP and its forms specifically on the pathogenesis of atherothrombosis and angiogenesis. Besides its role in the humoral innate immune response, CRP contributes to cardiovascular disease progression by recognizing and binding multiple intrinsic ligands. mCRP is not present in the healthy vessel wall but it becomes detectable in the early stages of atherogenesis and accumulates during the progression of atherosclerosis. CRP inhibits endothelial nitric oxide production and contributes to plaque instability by increasing endothelial cell adhesion molecules expression, by promoting monocyte recruitment into the atheromatous plaque and by enzymatically binding to modified low-density lipoprotein. CRP also contributes to thrombosis, but depending on its form it elicits different actions. Pentameric CRP has no involvement in thrombogenesis, whereas mCRP induces platelet activation and thrombus growth. In addition, mCRP has apparently contradictory pro-angiogenic and anti-angiogenic effects determining tissue remodeling in the atherosclerotic plaque and in infarcted tissues. Overall, CRP contributes to cardiovascular disease by several mechanisms that deserve an in-depth analysis.

Cardiovascular Risk Factors and Markers

Cardiovascular risk is assessed for the prediction and appropriate management of patients using collections of identified risk markers obtained from clinical questionnaire information, concentrations of certain blood molecules (e.g., N-terminal proB-type natriuretic peptide fragment and soluble receptors of tumor-necrosis factor-α and interleukin-2), imaging data using various modalities, and electrocardiographic variables, in addition to traditional risk factors.

Platelets, inflammation and anti-inflammatory effects of antiplatelet drugs in ACS and CAD

Platelets play a pivotal role in chronic inflammation leading to progression of atherosclerosis and acute coronary events. Recent discoveries on novel mechanisms and platelet-dependent inflammatory targets underpin the role of platelets to maintain a chronic inflammatory condition in cardiovascular disease. There is strong and clinically relevant crosslink between chronic inflammation and platelet activation. Antiplatelet therapy is a cornerstone in the prevention and treatment of acute cardiovascular events. The benefit of antiplatelet agents has mainly been attributed to their direct anti-aggregatory impact. Some anti-inflammatory off-target effects have also been described. However, it is unclear whether these effects are secondary due to inhibition of platelet activation or are caused by direct distinct mechanisms interfering with inflammatory pathways. This article will highlight novel platelet associated targets that contribute to inflammation in cardiovascular disease and elucidate mechanisms by which currently available antiplatelet agents evolve anti-inflammatory capacities, in particular by carving out the differential mechanisms directly or indirectly affecting platelet mediated inflammation. It will further illustrate the prognostic impact of antiplatelet therapies by reducing inflammatory marker release in recent cardiovascular trials.

The combination of CRP isoforms with oxLDL decreases TNF-α and IL-6 release by U937-derived macrophages

C-reactive protein (CRP) and oxidized low density lipoprotein (oxLDL) serve major roles at both early and advanced stages of atherosclerosis. CRP exists in two isoforms, monomeric (m) and pentameric (p), that bring about pro- or anti-inflammatory effects in macrophages. In addition, CRP may form a complex with oxidized low-density lipoprotein (oxLDL) via phosphatidylcholine, thus decreasing its pro-inflammatory effects within macrophages. The aim of the present study was to investigate the single and the combined effects of mCRP, pCRP and oxLDL on U937-derived macrophages. In the current study, U937-derived macrophages were treated in vitro with different combinations of CRP isoforms with or without oxLDL. The levels of major inflammatory cytokines [interleukin (IL)-1β, IL-6, IL-8 and tumor necrosis factor (TNF)-α] along with the production of reactive oxygen species (ROS) were determined. TNF-α and IL-6 levels were significantly decreased (P<0.05) by the effect of mCRP and pCRP combined with oxLDL. No significant changes were observed in IL-1β, IL-8 or ROS levels.

Structure and functionalities of the human c-reactive protein compared to the zebrafish multigene family of c-reactive-like proteins

Because of the recent discovery of multiple c-reactive protein (crp)-like genes in zebrafish (Danio rerio) with predicted heterogeneous phospholipid-binding amino acid sequences and heterogeneous transcript expression levels in viral survivors and adaptive-deficient mutants, zebrafish constitute an attractive new model for exploring the evolution of these protein's functions, including their possible participation in fish trained immunity. Circulating human CRP belongs to the short pentraxin family of oligomeric proteins that are characteristic of early acute-phase innate responses and is widely used as a clinical inflammation marker. In contrast to pentameric human CRP (pCRP), zebrafish CRPs are trimeric (tCRP); however monomeric CRP (mCRP) conformations may also be generated when associated with cellular membranes as occurs in humans. Compared to human CRP, zebrafish CRP-like proteins show homologous amino acid sequence stretches that are consistent with, although not yet demonstrated, cysteine-dependent redox switches, calcium-binding spots, phosphocholine-binding pockets, C1q-binding domains, regions interacting with immunoglobulin Fc receptors (FcR), unique mCRP epitopes, mCRP binding peptides to cholesterol-enriched rafts, protease target sites, and/or binding sites to monocyte, macrophage, neutrophils, platelets and/or endothelial cells. Amino acid variations among the zebrafish CRP-like multiprotein family and derived isoforms in these stretches suggest that functional heterogeneity best fits the wide variety of aquatic pathogens. As occurs in humans, phospholipid-tagged tCRP-like multiproteins might also influence local inflammation and induce innate immune responses; however, in addition, different zebrafish tCRP-like proteins and/or isoforms might fine tune new still unknown functions. The information reviewed here could be of value for future studies not only to comparative but also medical immunologists and/or fisheries sectors. This review also introduces some novel speculations for future studies.

Presence of multimeric isoforms of human C-reactive protein in tissues and blood

The baseline concentration of C-reactive protein (CRP) has been associated with a wide array of human diseases. In epidemiological studies and in the clinic, CRP is typically measured as a pentamer, composed of 5 identical CRP subunits. The present study aimed to determine whether other isoforms were present in the blood by examining CRP conformations. Transgenic rats expressing human CRP under the mouse albumin promoter were generated and genotyped. Non-reducing western blotting was performed using the blood and tissues of transgenic rats and human patients. CRP concentrations in human blood were examined by enzyme-linked immunosorbent assay. In addition to the pentameric isoform, CRP was detected as a trimer and tetramer in the blood of human CRP transgenic rats. Furthermore, trimeric and tetrameric CRP was observed in various tissues, including aorta, liver, kidney, pancreas, heart and skeletal muscle. Notably, these two isoforms appeared to be age-associated, as they were detected only in the blood and tissues of older transgenic rats. The existence of additional CRP isoforms was confirmed in the blood of human patients by non-reducing western blotting. Clinical and epidemiological studies typically focus on CRP concentration. However, the results of the present study suggest that, in addition to concentration, CRP conformation may require analysis.

Accumulation of C-reactive protein in basal keratinocytes of normal skins

BACKGROUND

C-reactive protein (CRP) is a prototypic acute phase protein which increases dramatically in the blood during the first 48h of tissue inflammation and has been recognized as a risk factor for atherosclerosis. CRP interacts with a variety of proteins.

OBJECTIVE

To know the role of accumulated CRP in the skin.

METHODS

Interaction of CRP with basal keratinocytes was studied using immunohistochemical method and keratinocyte culture system.

RESULTS

We found an immunohistochemical deposition of CRP on the basal keratinocyte membrane in some normal human skins (23 out of 46 skins). When added to cultured keratinocytes, heat-denatured but not native CRP was found to adhere to keratinocyte cell membrane after 1h, then internalized into cytoplasm after 24h. The heat-denatured CRP recognized at least four keratinocyte polypeptides with the molecular weights of 56, 42, 32 and 24kDa. Ligand binding assays suggested that multiple populations of receptor-ligand interactions were involved in the binding between CRP and keratinocyte. Cultured dermal microvascular endothelial cells were found to express CRP of which expression was greatly induced by interleukin-1β (IL-1β) treatment, suggesting that the deposited CRP in the basal keratinocytes can be derived from local dermal microvasculatures as well as from systemic circulation (serum). Treatment of cultured keratinocytes with heat-denatured CRP induced interleukin-8 (IL-8) expression, a potent leukocyte chemotactic cytokine. CRP in the medium (liquid phase) and CRP-coated dishes (solid phase) both inhibited the adhesion of keratinocytes in culture.

CONCLUSION

Accumulation of CRP may regulate the skin inflammation and keratinocyte proliferation by modulating keratinocyte cytokine expression and adhesion to substrate.

Disordered haematopoiesis and athero-thrombosis

Atherosclerosis, the major underlying cause of cardiovascular disease, is characterized by a lipid-driven infiltration of inflammatory cells in large and medium arteries. Increased production and activation of monocytes, neutrophils, and platelets, driven by hypercholesterolaemia and defective high-density lipoproteins-mediated cholesterol efflux, tissue necrosis and cytokine production after myocardial infarction, or metabolic abnormalities associated with diabetes, contribute to atherogenesis and athero-thrombosis. This suggests that in addition to traditional approaches of low-density lipoproteins lowering and anti-platelet drugs, therapies directed at abnormal haematopoiesis, including anti-inflammatory agents, drugs that suppress myelopoiesis, and excessive platelet production, rHDL infusions and anti-obesity and anti-diabetic agents, may help to prevent athero-thrombosis.

Complement factor H binding of monomeric C-reactive protein downregulates proinflammatory activity and is impaired with at risk polymorphic CFH variants

Inflammation and immune-mediated processes are pivotal to the pathogenic progression of age-related macular degeneration (AMD). Although plasma levels of C-reactive protein (CRP) have been shown to be associated with an increased risk for AMD, the pathophysiological importance of the prototypical acute-phase reactant in the etiology of the disease is unknown, and data regarding the exact role of CRP in ocular inflammation are limited. In this study, we provide mechanistic insight into how CRP contributes to the development of AMD. In particular, we show that monomeric CRP (mCRP) but not the pentameric form (pCRP) upregulates IL-8 and CCL2 levels in retinal pigment epithelial cells. Further, we show that complement factor H (FH) binds mCRP to dampen its proinflammatory activity. FH from AMD patients carrying the “risk” His402 polymorphism displays impaired binding to mCRP, and therefore proinflammatory effects of mCRP remain unrestrained.

Plasma Levels of Endothelial Microparticles Bearing Monomeric C-reactive Protein are Increased in Peripheral Artery Disease

C-reactive protein (CRP) as an indicator of cardiovascular disease (CVD) has shown limited sensitivity. We demonstrate that two isoforms of CRP (pentameric, pCRP and monomeric, mCRP) present in soluble form or on microparticles (MPs) have different biological effects and are not all measured by clinical CRP assays. The high-sensitivity CRP assay (hsCRP) did not measure pCRP or mCRP on MPs, whereas flow cytometry did. MPs derived from endothelial cells, particularly those bearing mCRP, were elevated in peripheral artery disease (PAD) patients compared to controls. The numbers of mCRP(+) endothelial MPs did not correlate with hsCRP measurements of soluble pCRP, indicating their independent modulation. In controls, statins lowered mCRP(+) endothelial MPs. In a model of vascular inflammation, mCRP induced endothelial shedding of MPs and was proinflammatory, while pCRP was anti-inflammatory. mCRP on endothelial MPs may be both an unmeasured indicator of, and an amplifier of, vascular disease, and its detection might improve risk sensitivity.