Cathepsin G: the significance in rheumatoid arthritis as a monocyte chemoattractant

A cystatin C similar protein from Musa acuminata that inhibits cathepsin B involved in rheumatoid arthritis using in silico approach and in vitro cathepsin B inhibition by protein extract

Rheumatoid arthritis (RA) is an auto-immune disease that affects the synovial lining of the joints, causes synovitis and culminates to joint destruction. Cathepsin B is responsible for digesting unwanted proteins in extracellular matrix but its hyper expression could implicate in pathological diseases like RA. Available treatments for RA are classified into non-steroidal anti-inflammatory drugs (NSAIDs), disease-modifying anti-rheumatic drugs (DMARDs), and steroids, but the severe side effects associated with these drugs is one of concerns and cannot be ignored. Thus, any alternative therapy with minimum or no side effects would be a cornerstone. In our in silico studies a cystatin C similar protein (CCSP) has been identified from Musa acuminata that could effectively inhibit the cathepsin B activity. In silico and molecular dynamics studies showed that the identified CCSP and cathepsin B complex has binding energy -66.89 kcal/mol as compared to cystatin C - cathepsin B complex with binding energy of -23.38 kcal/mol. These results indicate that CCSP from Musa acuminata has better affinity towards cathepsin B as compared to its natural inhibitor cystatin C. Hence, CCSP may be suggested as an alternative therapeutic in combating RA by inhibiting its one of the key proteases cathepsin B. Further, in vitro experiments with fractionated protein extracts from Musa sp. peel inhibited cathepsin B to 98.30% at 300 µg protein concentration and its IC50 was found to be 45.92 µg indicating the presence of cathepsin B inhibitor(s) in protein extract of peel which was further confirmed by reverse zymography.Communicated by Ramaswamy H. Sarma.

Neutrophils in Inflammatory Diseases: Unraveling the Impact of Their Derived Molecules and Heterogeneity

Inflammatory diseases involve numerous disorders and medical conditions defined by an insufficient level of self-tolerance. These diseases evolve over the course of a multi-step process through which environmental variables play a crucial role in the emergence of aberrant innate and adaptive immunological responses. According to experimental data accumulated over the past decade, neutrophils play a significant role as effector cells in innate immunity. However, neutrophils are also involved in the progression of numerous diseases through participation in the onset and maintenance of immune-mediated dysregulation by releasing neutrophil-derived molecules and forming neutrophil extracellular traps, ultimately causing destruction of tissues. Additionally, neutrophils have a wide variety of functional heterogeneity with adverse effects on inflammatory diseases. However, the complicated role of neutrophil biology and its heterogeneity in inflammatory diseases remains unclear. Moreover, neutrophils are considered an intriguing target of interventional therapies due to their multifaceted role in a number of diseases. Several approaches have been developed to therapeutically target neutrophils, involving strategies to improve neutrophil function, with various compounds and inhibitors currently undergoing clinical trials, although challenges and contradictions in the field persist. This review outlines the current literature on roles of neutrophils, neutrophil-derived molecules, and neutrophil heterogeneity in the pathogenesis of autoimmune and inflammatory diseases with potential future therapeutic strategies.

Homogeneous, Synthetic, Non-Saccharide Glycosaminoglycan Mimetics as Potent Inhibitors of Human Cathepsin G

Cathepsin G (CatG) is a pro-inflammatory neutrophil serine protease that is important for host defense, and has been implicated in several inflammatory disorders. Hence, inhibition of CatG holds much therapeutic potential; however, only a few inhibitors have been identified to date, and none have reached clinical trials. Of these, heparin is a well-known inhibitor of CatG, but its heterogeneity and bleeding risk reduce its clinical potential. We reasoned that synthetic small mimetics of heparin, labeled as non-saccharide glycosaminoglycan mimetics (NSGMs), would exhibit potent CatG inhibition while being devoid of bleeding risks associated with heparin. Hence, we screened a focused library of 30 NSGMs for CatG inhibition using a chromogenic substrate hydrolysis assay and identified nano- to micro-molar inhibitors with varying levels of efficacy. Of these, a structurally-defined, octasulfated di-quercetin NSGM 25 inhibited CatG with a potency of ~50 nM. NSGM 25 binds to CatG in an allosteric site through an approximately equal contribution of ionic and nonionic forces. Octasulfated 25 exhibits no impact on human plasma clotting, suggesting minimal bleeding risk. Considering that octasulfated 25 also potently inhibits two other pro-inflammatory proteases, human neutrophil elastase and human plasmin, the current results imply the possibility of a multi-pronged anti-inflammatory approach in which these proteases are likely to simultaneously likely combat important conditions, e.g., rheumatoid arthritis, emphysema, or cystic fibrosis, with minimal bleeding risk.

Glycosaminoglycans and glycoproteins influence the elastic response of synovial fluid nanofilms on model oxide surfaces

Synovial fluid (SF) is the natural lubricant found in articulated joints, providing unique cartilage surface protecting films under confinement and relative motion. While it is known that the synergistic interactions of the macromolecular constituents provide its unique load-bearing and tribological performance, it is not fully understood how two of the main constituents, glycosaminoglycans (GAGs) and glycoproteins, regulate the formation and mechanics of robust load-bearing films. Here, we present evidence that the load-bearing capabilities, rather than the tribological performance, of the formed SF films depend strongly on its components' integrity. For this purpose, we used a combination of enzymatic treatments, quartz crystal microbalance with dissipation (QCM-D), and the surface forces apparatus (SFA) to characterize the formation and load-bearing capabilities of SF films on model oxide (i.e., silicates) surfaces. We find that, upon cleavage of proteins, the elasticity of the films is reduced and that cleaving GAGs results in irreversible (plastic) molecular re-arrangements of the film constituents when subjected to confinement. Understanding thin film mechanics of SF can provide insight into the progression of diseases, such as arthritis, but may also be applicable to the development of new implant surface treatments or new biomimetic lubricants.

Lysosomes in Stem Cell Quiescence: A Potential Therapeutic Target in Acute Myeloid Leukemia

Lysosomes are cellular organelles that regulate essential biological processes such as cellular homeostasis, development, and aging. They are primarily connected to the degradation/recycling of cellular macromolecules and participate in cellular trafficking, nutritional signaling, energy metabolism, and immune regulation. Therefore, lysosomes connect cellular metabolism and signaling pathways. Lysosome's involvement in the critical biological processes has rekindled clinical interest towards this organelle for treating various diseases, including cancer. Recent research advancements have demonstrated that lysosomes also regulate the maintenance and hemostasis of hematopoietic stem cells (HSCs), which play a critical role in the progression of acute myeloid leukemia (AML) and other types of cancer. Lysosomes regulate both HSCs' metabolic networks and identity transition. AML is a lethal type of blood cancer with a poor prognosis that is particularly associated with aging. Although the genetic landscape of AML has been extensively described, only a few targeted therapies have been produced, warranting the need for further research. This review summarizes the functions and importance of targeting lysosomes in AML, while highlighting the significance of lysosomes in HSCs maintenance.

Exploring the role of cathepsin in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disease which is marked by leukocytes infiltration inside synovial tissue, joints and also inside synovial fluid which causes progressive destruction of joint cartilage. There are numerous genetical and lifestyle factors, responsible for rheumatoid arthritis. One such factor can be cysteine cathepsins, which act as proteolytic enzymes. These proteolytic enzyme gets activated at acidic pH and are found in lysosomes and are also termed as cysteine proteases. These proteases belong to papain family and have their elucidated role in musculoskeletal disorders. Numerous cathepsins have their targeted role in rheumatoid arthritis. These proteases are secreted through various cell types which includes matrix metalloproteases and papain like cysteine proteases. These proteases can potentially lead to bone and cartilage destruction which causes an immune response in case of inflammatory arthritis.

Targeting lysosomes in human disease: from basic research to clinical applications

In recent years, accumulating evidence has elucidated the role of lysosomes in dynamically regulating cellular and organismal homeostasis. Lysosomal changes and dysfunction have been correlated with the development of numerous diseases. In this review, we interpreted the key biological functions of lysosomes in four areas: cellular metabolism, cell proliferation and differentiation, immunity, and cell death. More importantly, we actively sought to determine the characteristic changes and dysfunction of lysosomes in cells affected by these diseases, the causes of these changes and dysfunction, and their significance to the development and treatment of human disease. Furthermore, we outlined currently available targeting strategies: (1) targeting lysosomal acidification; (2) targeting lysosomal cathepsins; (3) targeting lysosomal membrane permeability and integrity; (4) targeting lysosomal calcium signaling; (5) targeting mTOR signaling; and (6) emerging potential targeting strategies. Moreover, we systematically summarized the corresponding drugs and their application in clinical trials. By integrating basic research with clinical findings, we discussed the current opportunities and challenges of targeting lysosomes in human disease.

Linagliptin, A Xanthine-Based Dipeptidyl Peptidase-4 Inhibitor, Ameliorates Experimental Autoimmune Myocarditis

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Treatment with linagliptin, a DPP-4 inhibitor, alleviates not only EAM but also ICIM.

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DPP-4 physically interacts with cathepsin G and enhances its activity.

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Linagliptin promotes SerpinA3N activity, thereby suppressing cathepsin G activity.

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Cathepsin G aggravates EAM through upregulating angiotensin II.

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Linagliptin suppresses oxidative stress in EAM hearts.

This study sought to show the mechanism of how to ameliorate experimental autoimmune myocarditis (EAM) by administering dipeptidyl peptidase (DPP)-4 inhibitor linagliptin. The number of RAR-related orphan nuclear receptor gamma–positive Th17 cells infiltrated to the EAM myocardium was significantly attenuated by linagliptin treatment. Tandem mass spectrometry–based analysis demonstrated that DPP-4 binds to cathepsin G in EAM hearts, thereby protecting cathepsin G activity through inhibiting SerpinA3N activity. Linagliptin suppresses oxidative stress in EAM hearts as well. Thus, we found that DPP-4 plays a detrimental role in the progression of EAM by interacting with cathepsin G, which, in turn, suppresses SerpinA3N activity.

Activity-Based Probes to Utilize the Proteolytic Activity of Cathepsin G in Biological Samples

Neutrophils, migrating to the site of infection, are able to release serine proteases after being activated. These serine proteases comprise cathepsin G (CatG), neutrophil elastase protease 3 (PR3), and neutrophil serine protease 4 (NSP4). A disadvantage of the uncontrolled proteolytic activity of proteases is the outcome of various human diseases, including cardiovascular diseases, thrombosis, and autoimmune diseases. Activity-based probes (ABPs) are used to determine the proteolytic activity of proteases, containing a set of three essential elements: Warhead, recognition sequence, and the reporter tag for detection of the covalent enzyme activity–based probe complex. Here, we summarize the latest findings of ABP-mediated detection of proteases in both locations intracellularly and on the cell surface of cells, thereby focusing on CatG. Particularly, application of ABPs in regular flow cytometry, imaging flow cytometry, and mass cytometry by time-of-flight (CyTOF) approaches is advantageous when distinguishing between immune cell subsets. ABPs can be included in a vast panel of markers to detect proteolytic activity and determine whether proteases are properly regulated during medication. The use of ABPs as a detection tool opens the possibility to interfere with uncontrolled proteolytic activity of proteases by employing protease inhibitors.

Cathepsin G and its Dichotomous Role in Modulating Levels of MHC Class I Molecules

Cathepsin G (CatG) is involved in controlling numerous processes of the innate and adaptive immune system. These features include the proteolytic activity of CatG and play a pivotal role in alteration of chemokines as well as cytokines, clearance of exogenous and internalized pathogens, platelet activation, apoptosis, and antigen processing. This is in contrast to the capability of CatG acting in a proteolytic-independent manner due to the net charge of arginine residues in the CatG sequence which interferes with bacteria. CatG is a double-edged sword; CatG is also responsible in pathophysiological conditions, such as autoimmunity, chronic pulmonary diseases, HIV infection, tumor progression and metastasis, photo-aged human skin, Papillon-Lefèvre syndrome, and chronic inflammatory pain. Here, we summarize the latest findings for functional responsibilities of CatG in immunity, including bivalent regulation of major histocompatibility complex class I molecules, which underscore an additional novel role of CatG within the immune system.

Cathepsin g Degrades Both Glycosylated and Unglycosylated Regions of Lubricin, a Synovial Mucin

Lubricin (PRG4) is a mucin type protein that plays an important role in maintaining normal joint function by providing lubrication and chondroprotection. Improper lubricin modification and degradation has been observed in idiopathic osteoarthritis (OA), while the detailed mechanism still remains unknown. We hypothesized that the protease cathepsin G (CG) may participate in degrading lubricin in synovial fluid (SF). The presence of endogenous CG in SF was confirmed in 16 patients with knee OA. Recombinant human lubricin (rhPRG4) and native lubricin purified from the SF of patients were incubated with exogenous CG and lubricin degradation was monitored using western blot, staining by Coomassie or Periodic Acid-Schiff base in gels, and with proteomics. Full length lubricin (∼300 kDa), was efficiently digested with CG generating a 25-kDa protein fragment, originating from the densely glycosylated mucin domain (∼250 kDa). The 25-kDa fragment was present in the SF from OA patients, and the amount was increased after incubation with CG. A CG digest of rhPRG4 revealed 135 peptides and 72 glycopeptides, and confirmed that the protease could cleave in all domains of lubricin, including the mucin domain. Our results suggest that synovial CG may take part in the degradation of lubricin, which could affect the pathological decrease of the lubrication in degenerative joint disease.

The association between synovial fluid serine proteinase activity and response to intra-articular corticosteroid injection in psoriatic arthritis

INTRODUCTION/OBJECTIVES

Intra-articular corticosteroid (IAS) injections are often used for the immediate relief of pain and inflammation in the joint of psoriatic arthritis (PsA) patients. However, studies identifying factors that predict response to the IAS injections are lacking. We aimed to assess the usefulness of serine proteinase activity measurements in PsA synovial fluid (SF) samples obtained at the time of injection in predicting clinical response.

METHODS

The PsA patients with available SF samples from the knee joint were identified from the University of Toronto PsA cohort. Clinical response was defined as an absence of tenderness or swelling in the injected joint at the first post-injection visit, at either 3 or 6 months. SF proteinase activity was determined by measuring cleavage of fluorogenic tri-peptide substrates for trypsin-like (VPR-AMC and VLK-AMC) and chymotrypsin-like (AAPF-AMC) serine proteinases. Generalized estimating equation (GEE) models were used to investigate factors associated with response.

RESULTS

A total of 32 patients with 60 injected joints and data available for follow-up at 3 or 6 months were included in the analysis, with 25 (41.7%) injected joints resulting in clinical response. Age, sex, active joint count, systemic medications and SF serine proteinase activity at the time of injection were included as covariates. Only treatment with biologics was significantly associated with response at 3 or 6 months in the multivariate reduced model (OR 3.02, p = 0.027).

CONCLUSIONS

We could not demonstrate an association between SF serine proteinase activity and response to IAS injection. Biologic agents significantly improve the likelihood of achieving clinical response.

Lysosomes as a therapeutic target

Lysosomes are membrane-bound organelles with roles in processes involved in degrading and recycling cellular waste, cellular signalling and energy metabolism. Defects in genes encoding lysosomal proteins cause lysosomal storage disorders, in which enzyme replacement therapy has proved successful. Growing evidence also implicates roles for lysosomal dysfunction in more common diseases including inflammatory and autoimmune disorders, neurodegenerative diseases, cancer and metabolic disorders. With a focus on lysosomal dysfunction in autoimmune disorders and neurodegenerative diseases - including lupus, rheumatoid arthritis, multiple sclerosis, Alzheimer disease and Parkinson disease - this Review critically analyses progress and opportunities for therapeutically targeting lysosomal proteins and processes, particularly with small molecules and peptide drugs.

Association of autoimmunity and cancer: An emphasis on proteolytic enzymes

Cancer and autoimmune diseases are the two devastating conditions that together constitute a leading health problem worldwide. The rising burden of these disorders in the developing world demands a multifaceted approach to address the challenges it poses. Understanding the root causes and specific molecular mechanisms by which the progression of the diseases takes place is need of the hour. A strong inflammatory background and common developmental pathways, such as activation of immune cells, proliferation, increased cell survival and migration which are controlled by growth factors and inflammatory cytokines have been considered as the critical culprits in the progression and complications of these disorders. Enzymes are the potential immune modulators which regulate various inflammatory events and can break the circulating immune complexes via macrophages production. In the current manuscript, we have uncovered the possible role of proteolytic enzymes in the pathogenesis and progression of cancer and autoimmune diseases. In the light of the available scientific literature, we advocate in-depth comprehensive studies which will shed light towards the role of proteolytic enzymes in the modulation of inflammatory responses in cancer and autoimmune diseases together.

Proteinases and their receptors in inflammatory arthritis: an overview

Proteinases are enzymes with established roles in physiological and pathological processes such as digestion and the homeostasis, destruction and repair of tissues. Over the past few years, the hormone-like properties of circulating proteinases have become increasingly appreciated. Some proteolytic enzymes trigger cell signalling via proteinase-activated receptors, a family of G protein-coupled receptors that have been implicated in inflammation and pain in inflammatory arthritis. Proteinases can also regulate ion flux owing to the cross-sensitization of transient receptor potential cation channel subfamily V members 1 and 4, which are associated with mechanosensing and pain. In this Review, the idea that proteinases have the potential to orchestrate inflammatory signals by interacting with receptors on cells within the synovial microenvironment of an inflamed joint is revisited in three arthritic diseases: osteoarthritis, spondyloarthritis and rheumatoid arthritis. Unanswered questions are highlighted and the therapeutic potential of modulating this proteinase-receptor axis for the management of disease in patients with these types of arthritis is also discussed.

Cathepsin G and Its Role in Inflammation and Autoimmune Diseases

Cathepsin G belongs to the neutrophil serine proteases family, known for its function in killing pathogens. Studies over the past several years indicate that cathepsin G has important effects on inflammation and immune reaction, and may be a key factor in the pathogenesis of some autoimmune diseases. In this article, we discuss the roles of cathepsin G in inflammation, immune reaction, and autoimmune diseases. To our knowledge, this is the first study providing important information about cathepsin G in the pathogenesis of autoimmune diseases and suggesting that cathepsin G may be a new biomarker or treatment target.

Protease Inhibitors in Tick Saliva: The Role of Serpins and Cystatins in Tick-host-Pathogen Interaction

The publication of the first tick sialome (salivary gland transcriptome) heralded a new era of research of tick protease inhibitors, which represent important constituents of the proteins secreted via tick saliva into the host. Three major groups of protease inhibitors are secreted into saliva: Kunitz inhibitors, serpins, and cystatins. Kunitz inhibitors are anti-hemostatic agents and tens of proteins with one or more Kunitz domains are known to block host coagulation and/or platelet aggregation. Serpins and cystatins are also anti-hemostatic effectors, but intriguingly, from the translational perspective, also act as pluripotent modulators of the host immune system. Here we focus especially on this latter aspect of protease inhibition by ticks and describe the current knowledge and data on secreted salivary serpins and cystatins and their role in tick-host-pathogen interaction triad. We also discuss the potential therapeutic use of tick protease inhibitors.

Protease Inhibitors Extracted from Caesalpinia echinata Lam. Affect Kinin Release during Lung Inflammation

Inflammation is an essential process in many pulmonary diseases in which kinins are generated by protease action on kininogen, a phenomenon that is blocked by protease inhibitors. We evaluated kinin release in an in vivo lung inflammation model in rats, in the presence or absence of CeKI (C. echinata kallikrein inhibitor), a plasma kallikrein, cathepsin G, and proteinase-3 inhibitor, and rCeEI (recombinant C. echinata elastase inhibitor), which inhibits these proteases and also neutrophil elastase. Wistar rats were intravenously treated with buffer (negative control) or inhibitors and, subsequently, lipopolysaccharide was injected into their lungs. Blood, bronchoalveolar lavage fluid (BALF), and lung tissue were collected. In plasma, kinin release was higher in the LPS-treated animals in comparison to CeKI or rCeEI groups. rCeEI-treated animals presented less kinin than CeKI-treated group. Our data suggest that kinins play a pivotal role in lung inflammation and may be generated by different enzymes; however, neutrophil elastase seems to be the most important in the lung tissue context. These results open perspectives for a better understanding of biological process where neutrophil enzymes participate and indicate these plant inhibitors and their recombinant correlates for therapeutic trials involving pulmonary diseases.

Cathepsin G Controls Arterial But Not Venular Myeloid Cell Recruitment

BACKGROUND

Therapeutic targeting of arterial leukocyte recruitment in the context of atherosclerosis has been disappointing in clinical studies. Reasons for such failures include the lack of knowledge of arterial-specific recruitment patterns. Here we establish the importance of the cathepsin G (CatG) in the context of arterial myeloid cell recruitment.

METHODS

Intravital microscopy of the carotid artery, the jugular vein, and cremasteric arterioles and venules in Apoe^-/-and CatG-deficient mice (Apoe^-/-Ctsg^-/-) was used to study site-specific myeloid cell behavior after high-fat diet feeding or tumor necrosis factor stimulation. Atherosclerosis development was assessed in aortic root sections after 4 weeks of high-fat diet, whereas lung inflammation was assessed after inhalation of lipopolysaccharide. Endothelial deposition of CatG and CCL5 was quantified in whole-mount preparations using 2-photon and confocal microscopy.

RESULTS

Our observations elucidated a crucial role for CatG during arterial leukocyte adhesion, an effect not found during venular adhesion. Consequently, CatG deficiency attenuates atherosclerosis but not acute lung inflammation. Mechanistically, CatG is immobilized on arterial endothelium where it activates leukocytes to firmly adhere engaging integrin clustering, a process of crucial importance to achieve effective adherence under high-shear flow. Therapeutic neutralization of CatG specifically abrogated arterial leukocyte adhesion without affecting myeloid cell adhesion in the microcirculation. Repetitive application of CatG-neutralizing antibodies permitted inhibition of atherogenesis in mice.

CONCLUSIONS

Taken together, these findings present evidence of an arterial-specific recruitment pattern centered on CatG-instructed adhesion strengthening. The inhibition of this process could provide a novel strategy for treatment of arterial inflammation with limited side effects.

Neutrophil anti-neutrophil cytoplasmic autoantibody proteins: bactericidal increasing protein, lactoferrin, cathepsin, and elastase as serological markers of inflammatory bowel and other diseases

Inflammatory bowel disease (IBD) is a chronic inflammatory disorder of the gastrointestinal tract comprising Crohn's disease and ulcerative colitis. Although the pathogenesis of the disease is not clearly defined yet, environmental, genetic and other factors contribute to the onset of the disease. Apart from the clinical and histopathological findings, several serological biomarkers are also employed to detect IBD. One of the most thoroughly studied biomarker is anti-neutrophil cytoplasmic autoantibody (ANCA). We herein provide an overview of the current knowledge on the use of ANCA and certain ANCA proteins, such as bactericidal increasing protein, lactoferrin, cathepsin G and elastase, as serological markers for IBD and other diseases.

Lactoferrin Is an Allosteric Enhancer of the Proteolytic Activity of Cathepsin G

Protease-mediated degradation of proteins is critical in a plethora of physiological processes. Neutrophils secrete serine proteases including cathepsin G (CatG), neutrophile elastase (NE), and proteinase 3 (PR3) together with lactoferrin (LF) as a first cellular immune response against pathogens. Here, we demonstrate that LF increases the catalytic activity of CatG at physiological concentration, with its highest enhancing capacity under acidic (pH 5.0) conditions, and broadens the substrate selectivity of CatG. On a functional level, the enzymatic activity of CatG was increased in the presence of LF in granulocyte-derived supernatant. Furthermore, LF enhanced CatG-induced activation of platelets as determined by cell surface expression of CD62P. Consequently, LF-mediated enhancement of CatG activity might promote innate immunity during acute inflammation.

Quantitative analysis of elastase and cathepsin G mRNA levels in peripheral blood CD14(+) cells from patients with rheumatoid arthritis

In rheumatoid arthritis (RA) activity of serine proteases is an important factor contributing to destructive changes in the joints. The aim of this study was to compare elastase (ELANE) and cathepsin G (CTSG) mRNA levels in peripheral blood CD14(+) cells obtained from RA patients, healthy subjects (HS) and patients with osteoarthritis (OA). CD14(+) cells were isolated from peripheral blood by positive magnetic selection. The expression levels of ELANE and CTSG were determined by quantitative real-time PCR. ELANE mRNA expression was significantly higher in RA patients when compared to HS (p<0.001) and OA patients (p<0.001). The results suggest that in RA, peripheral blood CD14(+) cells express serine protease mRNA as a result of systemic mechanisms probably related to inflammation/cytokines before entering inflamed joints.

Boswellia serrata: an overall assessment of in vitro, preclinical, pharmacokinetic and clinical data

Non-steroidal anti-inflammatory drug (NSAID) intake is associated with high prevalence of gastrointestinal or cardiovascular adverse effects. All efforts to develop NSAIDs that spare the gastrointestinal tract and the cardiovasculature are still far from achieving a breakthrough. In the last two decades, preparations of the gum resin of Boswellia serrata (a traditional ayurvedic medicine) and of other Boswellia species have experienced increasing popularity in Western countries. Animal studies and pilot clinical trials support the potential of B. serrata gum resin extract (BSE) for the treatment of a variety of inflammatory diseases like inflammatory bowel disease, rheumatoid arthritis, osteoarthritis and asthma. Moreover, in 2002 the European Medicines Agency classified BSE as an 'orphan drug' for the treatment of peritumoral brain oedema. Compared to NSAIDs, it is expected that the administration of BSE is associated with better tolerability, which needs to be confirmed in further clinical trials. Until recently, the pharmacological effects of BSE were mainly attributed to suppression of leukotriene formation via inhibition of 5-lipoxygenase (5-LO) by two boswellic acids, 11-keto-β-boswellic acid (KBA) and acetyl-11-keto-β-boswellic acid (AKBA). These two boswellic acids have also been chosen in the monograph of Indian frankincense in European Pharmacopoiea 6.0 as markers to ensure the quality of the air-dried gum resin exudate of B. serrata. Furthermore, several dietary supplements advertise the enriched content of KBA and AKBA. However, boswellic acids failed to inhibit leukotriene formation in human whole blood, and pharmacokinetic data revealed very low concentrations of AKBA and KBA in plasma, being far below the effective concentrations for bioactivity in vitro. Moreover, permeability studies suggest poor absorption of AKBA following oral administration. In view of these results, the previously assumed mode of action - that is, 5-LO inhibition - is questionable. On the other hand, 100-fold higher plasma concentrations have been determined for β-boswellic acid, which inhibits microsomal prostaglandin E synthase-1 and the serine protease cathepsin G. Thus, these two enzymes might be reasonable molecular targets related to the anti-inflammatory properties of BSE. In view of the results of clinical trials and the experimental data from in vitro studies of BSE, and the available pharmacokinetic and metabolic data on boswellic acids, this review presents different perspectives and gives a differentiated insight into the possible mechanisms of action of BSE in humans. It underlines BSE as a promising alternative to NSAIDs, which warrants investigation in further pharmacological studies and clinical trials.

Regulation of cathepsin G reduces the activation of proinsulin-reactive T cells from type 1 diabetes patients

Autoantigenic peptides resulting from self-proteins such as proinsulin are important players in the development of type 1 diabetes mellitus (T1D). Self-proteins can be processed by cathepsins (Cats) within endocytic compartments and loaded to major histocompatibility complex (MHC) class II molecules for CD4⁺ T cell inspection. However, the processing and presentation of proinsulin by antigen-presenting cells (APC) in humans is only partially understood. Here we demonstrate that the processing of proinsulin by B cell or myeloid dendritic cell (mDC1)-derived lysosomal cathepsins resulted in several proinsulin-derived intermediates. These intermediates were similar to those obtained using purified CatG and, to a lesser extent, CatD, S, and V in vitro. Some of these intermediates polarized T cell activation in peripheral blood mononuclear cells (PBMC) from T1D patients indicative for naturally processed T cell epitopes. Furthermore, CatG activity was found to be elevated in PBMC from T1D patients and abrogation of CatG activity resulted in functional inhibition of proinsulin-reactive T cells. Our data suggested the notion that CatG plays a critical role in proinsulin processing and is important in the activation process of diabetogenic T cells.

Alpha-1 antitrypsin protein and gene therapies decrease autoimmunity and delay arthritis development in mouse model

Background

Alpha-1 antitrypsin (AAT) is a multi-functional protein that has anti-inflammatory and tissue protective properties. We previously reported that human AAT (hAAT) gene therapy prevented autoimmune diabetes in non-obese diabetic (NOD) mice and suppressed arthritis development in combination with doxycycline in mice. In the present study we investigated the feasibility of hAAT monotherapy for the treatment of chronic arthritis in collagen-induced arthritis (CIA), a mouse model of rheumatoid arthritis (RA).

Methods

DBA/1 mice were immunized with bovine type II collagen (bCII) to induce arthritis. These mice were pretreated either with hAAT protein or with recombinant adeno-associated virus vector expressing hAAT (rAAV-hAAT). Control groups received saline injections. Arthritis development was evaluated by prevalence of arthritis and arthritic index. Serum levels of B-cell activating factor of the TNF-α family (BAFF), antibodies against both bovine (bCII) and mouse collagen II (mCII) were tested by ELISA.

Results

Human AAT protein therapy as well as recombinant adeno-associated virus (rAAV8)-mediated hAAT gene therapy significantly delayed onset and ameliorated disease development of arthritis in CIA mouse model. Importantly, hAAT therapies significantly reduced serum levels of BAFF and autoantibodies against bCII and mCII, suggesting that the effects are mediated via B-cells, at least partially.

Conclusion

These results present a new drug for arthritis therapy. Human AAT protein and gene therapies are able to ameliorate and delay arthritis development and reduce autoimmunity, indicating promising potential of these therapies as a new treatment strategy for RA.

Osteosarcoma is characterised by reduced expression of markers of osteoclastogenesis and antigen presentation compared with normal bone

Background:

Osteosarcoma (OS) is the most common primary bone tumour in children and adolescents. Patients who respond poorly to chemotherapy have a higher risk of metastatic disease and 5-year survival rates of only 10–20%. Therefore, identifying molecular targets that are specific for OS, or more specifically, metastatic OS, will be critical to the development of new treatment strategies to improve patient outcomes.

Methods:

We performed a transcriptomic analysis of chemo-naive OS biopsies and non-malignant bone biopsies to identify differentially expressed genes specific to OS, which could provide insight into OS biology and chemoresistance.

Results:

Statistical analysis of the OS transcriptomes found differential expression of several metallothionein family members, as well as deregulation of genes involved in antigen presentation. Tumours also exhibited significantly increased expression of ID1 and profound down-regulation of S100A8, highlighting their potential as therapeutic targets for OS. Finally, we found a significant correlation between OS and impaired osteoclastogenesis and antigen-presenting activity. The reduced osteoclastogenesis and antigen-presenting activity were more profound in the chemoresistant OS samples.

Conclusion:

Our results indicate that OS displays gene signatures consistent with decreased antigen-presenting activity, enhanced chemoresistance, and impaired osteoclastogenesis. Moreover, these alterations are more pronounced in chemoresistant OS tumour samples.

Release of the soluble urokinase-type plasminogen activator receptor (suPAR) by activated neutrophils in rheumatoid arthritis

Soluble form of the urokinase-type plasminogen activator receptor (suPAR) is markedly increased in biological fluids during different inflammatory conditions. It has previously been observed that the highest suPAR concentrations in inflammatory exudates tend to be associated with the presence of high number of neutrophils. Guided by this observation and our recent finding that activated neutrophils release suPAR we investigated whether neutrophils can be a source of suPAR during the inflammatory response in vivo. To address this question we conducted the comparative analysis of neutrophils isolated from the paired samples of synovial fluid (SF) and peripheral blood (PB) of rheumatoid arthritis patients. Freshly isolated SF neutrophils released significantly (p < 0.01) higher amounts of suPAR compared with PB neutrophils. We demonstrated that neutrophils from both sources release predominantly the truncated D2D3 form of suPAR. Migration of formyl peptide receptor-like 1 (FPRL1)-transfected human embryonic kidney (HEK) 293 cells toward the supernatants harvested from in vitro cultured SF neutrophils was significantly diminished when D2D3 form of suPAR was immunodepleted from the supernatants. Taken together, these data demonstrate that neutrophils, first, contribute to or are responsible for the generation of the increased suPAR levels during the inflammatory response and, second, release the chemotactically active form of suPAR that might be involved in the recruitment of formyl peptide receptors-expressing leukocytes into the inflamed tissues.

Cathepsin G: roles in antigen presentation and beyond

Contributions from multiple cathepsins within endosomal antigen processing compartments are necessary to process antigenic proteins into antigenic peptides. Cysteine and aspartyl cathepsins have been known to digest antigenic proteins. A role for the serine protease, cathepsin G (CatG), in this process has been described only recently, although CatG has long been known to be a granule-associated proteolytic enzyme of neutrophils. In line with a role for this enzyme in antigen presentation, CatG is found in endocytic compartments of a variety of antigen presenting cells. CatG is found in primary human monocytes, B cells, myeloid dendritic cells 1 (mDC1), mDC2, plasmacytoid DC (pDC), and murine microglia, but is not expressed in B cell lines or monocyte-derived DC. Purified CatG can be internalized into endocytic compartments in CatG non-expressing cells, widening the range of cells where this enzyme may play a role in antigen processing. Functional assays have implicated CatG as a critical enzyme in processing of several antigens and autoantigens. In this review, historical and recent data on CatG expression, distribution, function and involvement in disease will be summarized and discussed, with a focus on its role in antigen presentation and immune-related events.

Cellular and histopathological changes in the infrapatellar fat pad in the monoiodoacetate model of osteoarthritis pain

OBJECTIVE

The infrapatellar fat pad (IPFP) has been identified as a source of anterior knee pain. Fibrosis and marked inflammatory infiltrate in the IPFP of patients with arthritis of the knee and reduction in pain post knee replacement in patients following resection of the IPFP have been observed. We have investigated changes in the IPFP of rats undergoing the monoiodoacetate (MIA) model of degenerative joint disease, a model that exhibits some histopathological similarities to osteoarthritis (OA).

METHODS

Rats were injected intra-articularly with MIA and the development of weight bearing asymmetry was followed for 21 days as compared to vehicle-injected animals. In addition, IPFPs were removed from both ipsilateral and contralateral joints. Both inflammatory infiltrate and histopathological changes were analysed.

RESULTS

MIA injection caused marked weight bearing asymmetry. Ipsilateral IPFP wet weights were significantly increased on days 1 and 3 in MIA-treated animals. MIA treatment also resulted in significant increases in IPFP total white blood cells and monocytes on days 1, 3, and 7 and neutrophils on days 1 and 3. This was supported by histopathological findings at early time points which progressed to adipocyte necrosis, IPFP fibrosis, patellar cartilage and subchondral bone necrosis with synovial hyperplasia at later timepoints.

CONCLUSIONS

The current study clearly demonstrated that marked inflammatory changes in the IPFP occur during the early stage of the MIA model of OA which may contribute to the pain observed at this early stage. The role of the IPFP in later stages of the model needs to be further explored.

Developments in the synovial biology field 2006

Synovial pathophysiology is a complex and synergistic interplay of different cell populations with tissue components, mediated by a variety of signaling mechanisms. All of these mechanisms drive the affected joint into inflammation and drive the subsequent destruction of cartilage and bone. Each cell type contributes significantly to the initiation and perpetuation of this deleterious concert, especially in rheumatoid arthritis. Rheumatoid arthritis synovial fibroblasts and macrophages, both cell types with pivotal roles in inflammation and destruction, but also T cells and B cells are crucial for complex network in the inflamed synovium. An even more complex cellular crosstalk between these key players maintains a process of chronic inflammation. As outlined in the present review, in the past year substantial progress has been made to elucidate further details of the rich pathophysiology of rheumatoid arthritis, which may also facilitate the identification of novel targets for future therapeutic strategies.

Macrophages and their products in rheumatoid arthritis

PURPOSE OF REVIEW

Macrophages differentiate from peripheral-blood monocytes. Both monocytes and synovial macrophages are key players in rheumatoid arthritis. These cells are involved in the initiation and perpetuation of inflammation, leukocyte adhesion and migration, matrix degradation and angiogenesis. Macrophages express adhesion molecules, chemokine receptors and other surface antigens. They also secrete a number of chemokines, cytokines, growth factors, proteases and other mediators.

RECENT FINDINGS

Macrophage migration-inhibitory factor has drawn significant attention recently. This cytokine is involved in macrophage activation and cytokine production. Migration-inhibitory factor also regulates glucocorticoid sensitivity and may be a pathogenic link between rheumatoid arthritis and atherosclerosis. Novel macrophage-derived chemokines and chemokine receptors have been identified. Interleukin-10 may have several proinflammatory effects that may influence its action in rheumatoid arthritis. Several proteinases including cathepsin G are produced by macrophages during rheumatoid arthritis-associated inflammatory and angiogenic events. Antirheumatic drugs, imatinib, chemokine receptor inhibitors and other specific strategies may become included in the therapy of rheumatoid arthritis.

SUMMARY

Macrophages and their products are key players in the pathogenesis of rheumatoid arthritis and may be good therapeutic targets.