Structure-function relationship and role of tumor necrosis factor-alpha-converting enzyme in the down-regulation of L-selectin by non-steroidal anti-inflammatory drugs

Evaluation of cell adhesion molecules (LFA-1 and L-selectin) in ankylosing spondylitis patients after treatment with β-D-mannuronic acid (M2000)

Background & objectives

To examine β-D-mannuronic acid (M2000) effects on L-selectin shedding and leucocyte function-associated antigen-1 (LFA-1) expression as mechanisms of action of this drug in patients with ankylosing spondylitis (AS).

Methods

To investigate the molecular consequences of β-D-mannuronic acid on L-selectin shedding, flow cytometry method was used. Furthermore, the effect of it on LFA-1 gene expression was analyzed by using quantitative real time (qRT)-PCR technique.

Results

The LFA-1 expression in patients with AS was higher than controls (P=0.046). The LFA-1 expression after 12 wk therapy with β-D-mannuronic acid was meaningfully decreased (P=0.01). After 12 wk treatment with β-D-mannuronic acid, the frequency of CD62L-expressing CD4+ T cells in patients with AS, was not considerably altered, compared to the patients before therapy (P=0.5). Furthermore, after 12 wk therapy with β-D-mannuronic acid, L-selectin expression levels on CD4+ T-cells in patients with AS, were not remarkably changed, compared to the expression levels of these in patients before treatment (P=0.2).

Interpretation & conclusions

The results of this study for the first time showed that β-D-mannuronic acid can affect events of adhesion cascade in patients with AS. Moreover, β-D-mannuronic acid presented as an acceptable benefit to AS patients and could aid in the process of disease management.

The Role of ADAM17 in Inflammation-Related Atherosclerosis

Atherosclerosis is a chronic inflammatory disease that poses a huge economic burden due to its extremely poor prognosis. Therefore, it is necessary to explore potential mechanisms to improve the prevention and treatment of atherosclerosis. A disintegrin and metalloprotease 17 (ADAM17) is a cell membrane-bound protein that performs a range of functions through membrane protein shedding and intracellular signaling. ADAM17-mediated inflammation has been identified to be an important contributor to atherosclerosis; however, the specific relationship between its multiple regulatory roles and the pathogenesis of atherosclerosis remains unclear. Here, we reviewed the activation, function, and regulation of ADAM17, described in detail the role of ADAM17-mediated inflammatory damage in atherosclerosis, and discussed several controversial points. We hope that these insights into ADAM17 biology will lead to rational management of atherosclerosis. ADAM17 promotes vascular inflammation in endothelial cells, smooth muscle cells, and macrophages, and regulates the occurrence and development of atherosclerosis.

Reducing Pain in Experimental Models of Intestinal Inflammation Affects the Immune Response

The incidence of inflammatory bowel disease with its two main manifestations, colitis ulcerosa and Crohn's disease, is rising globally year after year. There is still a tremendous need to study the underlying pathomechanisms and a well-established tool in order to better understand the disease are colitis models in rodents. Since the concept of the 3Rs was proposed by Russell and Burch, this would include pain medication in animal models of intestinal inflammation as a reduction of suffering. This review argues against pain medication because the administration of pain medication in its current form has an impact on the inflammatory process and the immune response, thus falsifying the results and the reproducibility and therefore leading to misconceptions.

Contribution of ADAM17 and related ADAMs in cardiovascular diseases

A disintegrin and metalloproteases (ADAMs) are key mediators of cell signaling by ectodomain shedding of various growth factors, cytokines, receptors and adhesion molecules at the cellular membrane. ADAMs regulate cell proliferation, cell growth, inflammation, and other regular cellular processes. ADAM17, the most extensively studied ADAM family member, is also known as tumor necrosis factor (TNF)-α converting enzyme (TACE). ADAMs-mediated shedding of cytokines such as TNF-α orchestrates immune system or inflammatory cascades and ADAMs-mediated shedding of growth factors causes cell growth or proliferation by transactivation of the growth factor receptors including epidermal growth factor receptor. Therefore, increased ADAMs-mediated shedding can induce inflammation, tissue remodeling and dysfunction associated with various cardiovascular diseases such as hypertension and atherosclerosis, and ADAMs can be a potential therapeutic target in these diseases. In this review, we focus on the role of ADAMs in cardiovascular pathophysiology and cardiovascular diseases. The main aim of this review is to stimulate new interest in this area by highlighting remarkable evidence.

A comprehensive guide to the pharmacologic regulation of angiotensin converting enzyme 2 (ACE2), the SARS-CoV-2 entry receptor

The recent emergence of coronavirus disease-2019 (COVID-19) as a global pandemic has prompted scientists to address an urgent need for defining mechanisms of disease pathology and treatment. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent for COVID-19, employs angiotensin converting enzyme 2 (ACE2) as its primary target for cell surface attachment and likely entry into the host cell. Thus, understanding factors that may regulate the expression and function of ACE2 in the healthy and diseased body is critical for clinical intervention. Over 66% of all adults in the United States are currently using a prescription drug and while earlier findings have focused on possible upregulation of ACE2 expression through the use of renin angiotensin system (RAS) inhibitors, mounting evidence suggests that various other widely administered drugs used in the treatment of hypertension, heart failure, diabetes mellitus, hyperlipidemias, coagulation disorders, and pulmonary disease may also present a varied risk for COVID-19. Specifically, we summarize mechanisms on how heparin, statins, steroids and phytochemicals, besides their established therapeutic effects, may also interfere with SARS-CoV-2 viral entry into cells. We also describe evidence on the effect of several vitamins, phytochemicals, and naturally occurring compounds on ACE2 expression and activity in various tissues and disease models. This comprehensive review aims to provide a timely compendium on the potential impact of commonly prescribed drugs and pharmacologically active compounds on COVID-19 pathology and risk through regulation of ACE2 and RAS signaling.

Neutrophils: Novel key players in Rheumatoid Arthritis. Current and future therapeutic targets

Rheumatoid Arthritis (RA) is a complex systemic autoimmune disease in which various cell types are involved. Among them, neutrophils have been recognized as important players in the onset and the progression of RA. The pathogenic role of neutrophils in RA lies in the alteration of several processes, including increased cell survival and migratory capacity, abnormal inflammatory activity, elevated oxidative stress and an exacerbated release of neutrophil extracellular traps. Through these mechanisms, neutrophils can activate other immune cells, thus perpetuating inflammation and leading to the destruction of the cartilage and bone of the affected joint. Given the considerable contribution of neutrophils to the pathophysiology of RA, several studies have attempted to clarify the effects of various therapeutic agents on this subtype of leukocyte. To date, recent studies have envisaged the role of new molecules on the pathogenic profile of neutrophils in RA, which could represent novel targets in future therapies. In this review, we aim to review the pathogenic role of neutrophils in RA, the effect of conventional treatments and biologic therapies, and the new, potential targets of neutrophil-derived molecules for the treatment of RA.

Early Targeting of L-Selectin on Leukocytes Promotes Recovery after Spinal Cord Injury, Implicating Novel Mechanisms of Pathogenesis

L-selectin, a lectin-like receptor on all leukocyte classes, functions in adhesive and signaling roles in the recruitment of myeloid cells from the blood to sites of inflammation. Here, we consider L-selectin as a determinant of neurological recovery in a murine model of spinal cord injury (SCI). Spinal cord-injured, L-selectin knock-out (KO) mice (male) showed improved long-term recovery with greater white matter sparing relative to wild-type (WT) mice and reduced oxidative stress in the injured cord at 72 h post-SCI. There was a partial and transient reduction in accumulation of neutrophils in the injured spinal cords of KOs at 24 h post-injury. To complement these findings with KO mice, we sought a pharmacologic means for lowering L-selectin levels. We found that diclofenac, a nonsteroidal anti-inflammatory drug (NSAID), induced the shedding of L-selectin from the cell surface of myeloid subsets, specifically neutrophils and non-classical monocytes, in the blood and the injured spinal cord. Diclofenac administration to injured WT mice enhanced neurological recovery to a level comparable to that of KOs but did not improve recovery in KOs. While diclofenac treatment had no effect on myeloid cell accumulation, there was a reduction in oxidative stress at 72 h post-SCI. These findings implicate L-selectin in secondary pathogenesis beyond a role in leukocyte recruitment and raise the possibility of repurposing diclofenac for the treatment of SCI.

NSAIDs: learning new tricks from old drugs

Nonsteroidal anti-inflammatory drugs (NSAIDs) comprise a heterogeneous group of pharmacological agents used for the symptomatic treatment of fever, pain, and inflammation. Although the main mechanism of action of NSAIDs consists of inhibiting prostaglandin synthesis by blocking the enzyme cyclooxygenase (COX), clinical, and experimental data strongly indicate the existence of additional mechanisms. Some of the COX-independent effects are related to the ability of NSAIDs to penetrate biological membranes and disrupt important molecular interactions necessary for a wide array of cellular functions, including cell adhesion. These effects, in particular those that interfere with L-selectin function in neutrophils during the inflammatory response, may contribute to the anti-inflammatory properties that NSAIDs exert in vivo. Recent contributions in this field have shown that the anti-L-selectin effect of NSAIDs is related to the NADPH-oxidase-dependent generation of superoxide anion at the plasma membrane. These findings might represent a novel approach for developing new and effective anti-inflammatory compounds with a better safety profile than the currently available NSAIDs.

Synthesis and characterization of quantum dots for application in laser soft desorption/ionization mass spectrometry to detect labile metal–drug interactions and their antibacterial activity

Synthesis and characterization of quantum dot modified mercaptopropionic acid (CdS@MPA) and its application in laser soft desorption/ionization for labile metal–drug interactions is reported.

Chemerin15 inhibits neutrophil-mediated vascular inflammation and myocardial ischemia-reperfusion injury through ChemR23

Neutrophils are shown to express ChemR23 and respond to C15, which inhibits integrin activation and clustering, reducing neutrophil adhesion and chemotaxis in vitro, and neutrophil recruitment and heart damage in a murine myocardial infarction model.

Neutrophil activation and adhesion must be tightly controlled to prevent complications associated with excessive inflammatory responses. The role of the anti-inflammatory peptide chemerin15 (C15) and the receptor ChemR23 in neutrophil physiology is unknown. Here, we report that ChemR23 is expressed in neutrophil granules and rapidly upregulated upon neutrophil activation. C15 inhibits integrin activation and clustering, reducing neutrophil adhesion and chemotaxis in vitro. In the inflamed microvasculature, C15 rapidly modulates neutrophil physiology inducing adherent cell detachment from the inflamed endothelium, while reducing neutrophil recruitment and heart damage in a murine myocardial infarction model. These effects are mediated through ChemR23. We identify the C15/ChemR23 pathway as a new regulator and thus therapeutic target in neutrophil-driven pathologies.

Perioperative diclofenac application during video-assisted thoracic surgery pleurodesis modulates early inflammatory and fibrinolytic processes in an experimental model

BACKGROUND/PURPOSE

It has been substantiated that the quality of pleurodesis is reduced when non-steroidal anti-inflammatory drugs (NSAIDs) are used perioperatively. The effects of NSAID administration on the early inflammatory and fibrinolytic processes after mechanical pleurodesis were investigated in an established pig model.

METHODS

Left-sided mechanical pleural abrasion was performed on 24 pigs assigned to either an NSAID or a control group. Pleural fluid and blood samples were analysed over a 24-hour period. Histological evaluation of neutrophil influx at the site of pleural abrasion was performed.

RESULTS

The volume of pleural effusion was significantly decreased in the diclofenac group at 10 and 24 h, and the protein content was significantly lower. The diclofenac group at 24 h had a diminished total number of white blood cells and a reduced content of transforming growth factor-β. Moreover, the diclofenac group had a reduced percentage of neutrophils at 6 h. Significantly increased levels of D-dimers and tissue plasminogen activator were measured at 6 h and of interleukin-10 at 24 h. Neutrophils at the site of pleural abrasion were significantly reduced.

CONCLUSIONS

Systemic application of diclofenac led to a local enhancement of fibrinolysis and attenuation of pro-inflammatory and fibrotic processes necessary for adhesion formation in our model.

Superoxide anion mediates the L-selectin down-regulation induced by non-steroidal anti-inflammatory drugs in human neutrophils

Non-steroidal anti-inflammatory drugs (NSAIDs) induce the shedding of L-selectin in human neutrophils through a mechanism still not well understood. In this work we studied both the functional effect of NSAIDs on the neutrophils/endothelial cells dynamic interaction, and the potential involvement of reactive oxygen species (ROS) in the NSAIDs-mediated down-regulation of L-selectin. When human neutrophils were incubated with diclofenac, a significant reduction in the number of cells that rolled on activated endothelial cells was observed. Different NSAIDs (flufenamic acid, meclofenamic acid, diclofenac, indomethacin, nimesulide, flurbiprofen, meloxicam, phenylbutazone, piroxicam, ketoprofen and aspirin) caused variable increase in neutrophil intracellular ROS concentration, which was inversely proportional to the change produced in L-selectin surface expression. Pre-incubation of neutrophils with superoxide dismutase, but not with catalase, showed both a significant protective effect on the L-selectin down-regulation induced by several NSAIDs and a diminished effect of diclofenac on neutrophil rolling. Interestingly, diclofenac and flufenamic acid but not piroxicam significantly increased the extracellular superoxide anion production by neutrophils, and inhibition of nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase activity with diphenyleneiodonium prevented the down-regulation of L-selectin by diclofenac. In accordance with these results, neutrophils from patients with chronic granulomatous disease, a hereditary disease in which neutrophils show a reduced capacity to form superoxide radicals, exhibited a lower down-regulation of L-selectin (IC50: 15.3 μg/ml) compared to normal controls (IC50: 5.6 μg/ml) in response to diclofenac.

CONCLUSION

A group of NSAIDs is capable of interfering with the ability of neutrophils to interact with endothelial cells by triggering L-selectin-shedding through the NADPH-oxidase-dependent generation of superoxide anion at the plasma membrane.

In vivo modulation of the inflammatory response by nonsteroidal antiinflammatory drug-related compounds that trigger L-selectin shedding

Diphenylamine-based nonsteroidal antiinflammatory drugs (NSAIDs) are able to cause in vitro the shedding of L-selectin. The aim of this work was to determine the physio-logic relevance of L-selectin shedding in the antiinflammatory effect exerted by NSAIDs in vivo. Chemical compounds structurally related to NSAIDs - including diphenyl-amine, N-phenylanthranilic acid (N-Ph), diphenylacetic acid - as well as the traditional NSAID indomethacin were studied using the zymosan air-pouch mouse model. Animals intramuscularly pretreated with indomethacin or N-Ph, but not with diphenyl-amine or diphenylacetic acid, showed a significant dose-dependent reduction in the number of neutrophils compared with untreated animals (N-Ph, IC50 = 6.7 mg/kg). Except for indomethacin, none of these compounds caused any significant reduction in cyclooxygenase-1 activity in vivo. In flow chamber experiments, N-Ph reduced the capability of human neutrophils to pass across the endothelial barrier by interfering with leukocyte rolling step on HUVEC. N-Ph, but not diphenylacetic acid, induced activation-independent L-selectin shedding in mouse neutrophils. Interestingly, N-Ph exerted an antiinflammatory effect similar to that of the anti-L-selectin blocking antibody Mel-14, although no additive action was observed when both compounds were combined. These data suggest that the L-selectin shedding induced by NSAIDs may be involved in the antiinflammatory action exerted by these compounds in clinical settings.

The role of ADAM-mediated shedding in vascular biology

Within the vasculature the disintegrins and metalloproteinases (ADAMs) 8, 9, 10, 12, 15, 17, 19, 28 and 33 are expressed on endothelial cells, smooth muscle cells and on leukocytes. As surface-expressed proteases they mediate cleavage of vascular surface molecules at an extracellular site close to the membrane. This process is termed shedding and leads to the release of a soluble substrate ectodomain thereby critically modulating the biological function of the substrate. In the vasculature several surface molecules undergo ADAM-mediated shedding including tumour necrosis factor (TNF) α, interleukin (IL) 6 receptor α, L-selectin, vascular endothelial (VE)-cadherin, the transmembrane CX3C-chemokine ligand (CX3CL) 1, Notch, transforming growth factor (TGF) and heparin-binding epidermal growth factor (HB-EGF). These substrates play distinct roles in vascular biology by promoting inflammation, permeability changes, leukocyte recruitment, resolution of inflammation, regeneration and/or neovascularisation. Especially ADAM17 and ADAM10 are capable of cleaving many substrates with diverse function within the vasculature, whereas other ADAMs have a more restricted substrate range. Therefore, targeting ADAM17 or ADAM10 by pharmacologic inhibition or gene knockout not only attenuates the inflammatory response in animal models but also affects tissue regeneration and neovascularisation. Recent discoveries indicate that other ADAMs (e.g. ADAM8 and 9) also play important roles in vascular biology but appear to have more selective effects on vascular responses (e.g. on neovascularisation only). Although, targeting of ADAM17 and ADAM10 in inflammatory diseases is still a promising approach, temporal and spatial as well as substrate-specific inhibition approaches are required to minimise undesired side effects on vascular cells.

Studies on the role of acid sphingomyelinase and ceramide in the regulation of tumor necrosis factor alpha (TNFalpha)-converting enzyme activity and TNFalpha secretion in macrophages

Acid sphingomyelinase (ASMase) has been proposed to mediate lipopolysaccharide (LPS) signaling in various cell types. This study shows that ASMase is a negative regulator of LPS-induced tumor necrosis factor alpha (TNFalpha) secretion in macrophages. ASMase-deficient (asm(-/-)) mice and isolated peritoneal macrophages produce severalfold more TNFalpha than their wild-type (asm(+/+)) counterparts when stimulated with LPS, whereas the addition of exogenous ceramides or sphingomyelinase reduces the differences. The underlying mechanism for these effects is not transcriptional but post-translational. The TNFalpha-converting enzyme (TACE) catalyzes the maturation of the 26-kDa precursor (pro-TNFalpha) to an active 17-kDa form (soluble (s)TNFalpha). In mouse peritoneal macrophages, the activity of TACE was the rate-limiting factor regulating TNFalpha production. A substantial portion of the translated pro-TNFalpha was not processed to sTNFalpha; instead, it was rapidly internalized and degraded in the lysosomes. TACE activity was 2-3-fold higher in asm(-/-) macrophages as compared with asm(+/+) macrophages and was suppressed when cells were treated with exogenous ceramide and sphingomyelinase. Indirect immunofluorescence analyses revealed distinct TNFalpha-positive structures in the close vicinity of the plasma membrane in asm(-/-) but not in asm(+/+) macrophages. asm(-/-) cells also had a higher number of early endosomal antigen 1-positive early endosomes. Experiments that involved inhibitors of TACE, endocytosis, and lysosomal proteolysis suggest that in the asm(-/-) cells a significant portion of pro-TNFalpha was sequestered within the early endosomes, and instead of undergoing lysosomal proteolysis, it was recycled to the plasma membrane and processed to sTNFalpha.

Sulindac metabolism and synergy with tumor necrosis factor-alpha in a drug-inflammation interaction model of idiosyncratic liver injury

Sulindac (SLD) is a nonsteroidal anti-inflammatory drug (NSAID) that has been associated with a greater incidence of idiosyncratic hepatotoxicity in human patients than other NSAIDs. In previous studies, cotreatment of rats with SLD and a modestly inflammatory dose of lipopolysaccharide (LPS) led to liver injury, whereas neither SLD nor LPS alone caused liver damage. In studies presented here, further investigation of this animal model revealed that the concentration of tumor necrosis factor-alpha (TNF-alpha) in plasma was significantly increased by LPS at 1 h, and SLD enhanced this response. Etanercept, a soluble TNF-alpha receptor, reduced SLD/LPS-induced liver injury, suggesting a role for TNF-alpha. SLD metabolites in plasma and liver were determined by LC/MS/MS. Cotreatment with LPS did not increase the concentrations of SLD or its metabolites, excluding the possibility that LPS contributed to liver injury through enhanced exposure to SLD or its metabolites. The cytotoxicities of SLD and its sulfide and sulfone metabolites were compared in primary rat hepatocytes and HepG2 cells; SLD sulfide was more toxic in both types of cells than SLD or SLD sulfone. TNF-alpha augmented the cytotoxicity of SLD sulfide in primary hepatocytes and HepG2 cells. These results suggest that TNF-alpha can enhance SLD sulfide-induced hepatotoxicity, thereby contributing to liver injury in SLD/LPS-cotreated rats.

The "a disintegrin and metalloprotease" (ADAM) family of sheddases: physiological and cellular functions

There is an exciting increase of evidence that members of the disintegrin and metalloprotease (ADAM) family critically regulate cell adhesion, migration, development and signalling. ADAMs are involved in "ectodomain shedding" of various cell surface proteins such as growth factors, receptors and their ligands, cytokines, and cell adhesion molecules. The regulation of these proteases is complex and still poorly understood. Studies in ADAM knockout mice revealed their partially redundant roles in angiogenesis, neurogenesis, tissue development and cancer. ADAMs usually trigger the first step in regulated intramembrane proteolysis leading to activation of intracellular signalling pathways and the release of functional soluble ectodomains.

Therapeutic potential of selectin antagonists in psoriasis

Psoriasis is a systemic chronic inflammatory disorder. One of the major characteristics is an excess of infiltration of inflammatory cells, mainly lymphocytes, into the skin. Because the adhesion family of selectins is suggested to play a relevant role in this process, selectins have emerged as an interesting target for drug discovery and development in psoriasis. Different strategies targeting selectins have been described. This review discusses these approaches and summarises the current development of selectin antagonists for the treatment of psoriasis. An expert opinion will give the authors' personal opinion about selectin antagonism in psoriasis and which approach might be preferable.

Characterisation of endothelin converting enzyme-1 shedding from endothelial cells

The aim of this study was to determine if endothelin converting enzyme-1 (ECE-1) like other members of this metalloprotease family undergoes ectodomain shedding. The release/shedding of catalytically active ECE-1 was measured by monitoring the fluorescence resulting from the cleavage of a specific quenched fluorescent substrate. Catalytically active ECE-1 was detected in the media of human umbilical vein endothelial cells, and was confirmed by mass spectrometry based assays. Specificity of cleavage was confirmed by using both narrow and broad specificity inhibitors. In conclusion we demonstrate and characterize for the first time, ECE-1 shedding from the surface of endothelial cells.

Expression and regulation of the metalloproteinase ADAM-8 during human neutrophil pathophysiological activation and its catalytic activity on L-selectin shedding

A disintegrin and metalloproteinase domain (ADAM) proteins are a family of transmembrane glycoproteins with heterogeneous expression profiles and proteolytic, cell-adhesion, -fusion, and -signaling properties. One of its members, ADAM-8, is expressed by several cell types including neurons, osteoclasts, and leukocytes and, although it has been implicated in osteoclastogenesis and neurodegenerative processes, little is known about its role in immune cells. In this study, we show that ADAM-8 is constitutively present both on the cell surface and in intracellular granules of human neutrophils. Upon in vitro neutrophil activation, ADAM-8 was mobilized from the granules to the plasma membrane, where it was released through a metalloproteinase-dependent shedding mechanism. Adhesion of resting neutrophils to human endothelial cells also led to up-regulation of ADAM-8 surface expression. Neutrophils isolated from the synovial fluid of patients with active rheumatoid arthritis expressed higher amounts of ADAM-8 than neutrophils isolated from peripheral blood and the concentration of soluble ADAM-8 in synovial fluid directly correlated with the degree of joint inflammation. Remarkably, the presence of ADAM-8 both on the cell surface and in suspension increased the ectodomain shedding of membrane-bound L-selectin in mammalian cells. All these data support a potential relevant role for ADAM-8 in the function of neutrophils during inflammatory response.

Regulated proteolytic processing of LRP6 results in release of its intracellular domain

Low-density lipoprotein receptor-related protein 6 (LRP6) is a member of low-density lipoprotein receptor (LDLR) family which cooperates with Frizzled receptors to transduce the canonical Wnt signal. As a critical component of the canonical Wnt pathway, LRP6 is essential for appropriate brain development, however, the mechanism by which LRP6 facilitates Wnt canonical signaling has not been fully elucidated. Interestingly, LRP6 which lacks its extracellular domain can constitutively activate TCF/LEF and potentiate the Wnt signal. Further, the free cytosolic tail of LRP6 interacts directly with glycogen synthase kinase (GSK3) and inhibits GSK3's activity in the Wnt canonical pathway which results in increased TCF/LEF activation. However, whether these truncated forms of LRP6 are physiologically relevant is unclear. Recent studies have shown that other members of the LDLR family undergo gamma-secretase dependent regulated intramembrane proteolysis (RIP). Using independent experimental approaches, we show that LRP6 also undergoes RIP. The extracellular domain of LRP6 is shed and released into the surrounding milieu and the cytoplasmic tail is cleaved by gamma-secretase-like activity to release the intracellular domain. Furthermore, protein kinase C, Wnt 3a and Dickkopf-1 modulate this process. These findings suggest a novel mechanism for LRP6 in Wnt signaling: induction of ectodomain shedding of LRP6, followed by the gamma-secretase involved proteolytic releasing its intracellular domain (ICD) which then binds to GSK3 inhibiting its activity and thus activates the canonical Wnt signaling pathway.

Breaking up the tie: Disintegrin-like metalloproteinases as regulators of cell migration in inflammation and invasion

Cell adhesion and cell migration are essential for a variety of important events in both embryonic development and in the adult organism. Cell adhesion molecules (CAM) like selectins, immunoglobulin superfamily members, integrins, and cadherins undergo diverse mechanisms of regulation. Dysregulation of adhesion can lead to pathological processes, including inflammatory diseases or tumor metastasis either by disrupting the normal anchorage, thereby altering cell movement and regulatory signalling, or by promoting inappropriate temporal and spatial adhesion. An increasing body of evidence has emerged showing that members of the a disintegrin and metalloproteinase (ADAM) family critically contribute to the regulation of CAM functions. While the disintegrin domain can interact with integrins and mediate adhesion, the metalloproteinase domain can mediate anti-adhesive functions by cleaving the membrane bound adhesion molecules. This "shedding" process leads to the release of often still functional soluble ectodomains and can additionally influence intracellular cell signalling pathways. Several soluble CAMs have been detected in vitro and in vivo. Some of them are strongly increased in inflammatory diseases or in the serum of cancer patients. Therefore the level of soluble CAMs but also the expression of the metalloproteinases responsible for their release might provide prognostic information. It could also be useful for monitoring malignant disease stages and for evaluating the effectiveness of various therapeutic approaches. Moreover, metalloproteases of the ADAM family are emerging as promising targets for new therapeutic options.

Monocyte matrix and ADAM metalloproteinase expression in type 2 diabetes after aspirin therapy

The matrix metalloproteinase system (MMP and the TIMP inhibitors), and the ADAM metalloproteinases, have roles in maintaining vascular plaque stability and the shedding of cell surface molecules, such as TNF-alpha and adhesion molecules; aspirin suppresses MMP expression and ADAM activity from some cell lines in vitro. In a randomised prospective controlled study, we examined peripheral venous monocyte MMP-9, TIMP-1 and ADAM mRNA levels, and protein expression, in subjects with type 2 diabetes (n=10) and controls (n=14) before and after oral aspirin therapy (150mg daily for 14 days) or no active intervention. Baseline monocyte TIMP-1 mRNA levels were significantly lower in the diabetes group (p=0.0014), although monocyte MMP-9 mRNA, and MMP-9 and TIMP-1 protein expression after culture did not differ significantly between groups. Plasma MMP-9 (p=0.027) and TIMP-1 (p=0.016) concentrations were significantly greater, and the ratio of plasma TIMP-1:MMP-9 concentrations significantly lower, in the diabetes group (p=0.023). ADAM mRNA levels did not differ significantly between groups and oral aspirin therapy had no significant effect on any variable. Type 2 diabetes is characterised by reduced monocyte TIMP-1 mRNA levels, and a lower plasma MMP-9 to TIMP-1 protein ratio compared to controls, a pattern that would promote coronary plaque instability if reproduced within vascular plaque. Monocyte ADAM mRNA levels do not differ between group and oral aspirin has no significant effect on these variables.

Aspirin Induces Platelet Receptor Shedding via ADAM17 (TACE)

Aspirin is effective in the therapy of cardiovascular diseases, because it causes acetylation of cyclooxygenase 1 (COX-1) leading to irreversible inhibition of platelets. Additional mechanisms can be suspected, because patients treated with other platelet COX inhibitors such as indomethacin do not display an increased bleeding tendency as observed for aspirin-treated patients. Recently, aspirin and other anti-inflammatory drugs were shown to induce shedding of L-selectin in neutrophils in a metalloproteinase-dependent manner. Therefore, we investigated the effects of aspirin on the von Willebrand Factor receptor complex glycoprotein (GP) Ib-V-IX, whose lack or dysfunction causes bleeding in patients. As quantified by fluorescence-activated cell sorting analysis in whole blood, aspirin, but not its metabolite salicylic acid, induced dose-dependent shedding of human and murine GPIbalpha and GPV from the platelet surface, whereas other glycoproteins remained unaffected by this treatment. Biotinylated fragments of GPV were detected by immunoprecipitation in the supernatant of washed mouse platelets, and the expression level of GPIbalpha was decreased in these platelets as measured by Western blot analysis. Although shedding occurred normally in COX-1-deficient murine platelets, shedding was completely blocked by a broad-range metalloproteinase inhibitor and, more importantly, in mouse platelets expressing an inactive form of ADAM17. Shed fragments of GPIbalpha and GPV were elevated in the plasma of aspirin-injected mice compared with animals injected with control buffer. These data demonstrate that aspirin at high concentrations induces shedding of GPIbalpha and GPV by an ADAM17-dependent mechanism and that this process can occur in vivo.

Losartan attenuates the antimigratory effect of diclofenac in spontaneously hypertensive rats

Many patients with hypertension, particularly elderly patients, take nonsteroidal antiinflammatory drugs (NSAIDs) and antihypertensive agents. However, few studies describe the effect of the association of antihypertensive agents with NSAIDs on inflammatory response in hypertension. To investigate this, spontaneously hypertensive rats (SHRs) were treated with either diclofenac alone or diclofenac combined with losartan (an AT1 angiotensin II antagonist). The leukocyte-endothelial interaction was then observed using intravital microscopy. Blood pressure of SHR (169.6+/-3.6) was increased by diclofenac (186.4+/-2.9), reduced by losartan (152.6+/-3.5), and reduced by the combination of the 2 (158.9+/-3.7). All the treatments tested reduced the number of rollers, adherent and migrated leukocytes, and the expression of endothelial intercellular adhesion molecule-1 and P-selectin. The association of losartan reduced the effect of diclofenac on leukocyte migration. Neither treatment tested increased the venular shear rate or modified the venular diameters, number of circulating leukocytes, and L-selectin expression on granulocytes. The reduction of CD11/CD18 expression induced by diclofenac alone was hindered by losartan. A pharmacokinetic interference between losartan and diclofenac was ruled out since no significant differences were observed in the plasma concentrations of each drug when they were associated. In conclusion, although diclofenac does not interfere with the losartan antihypertensive effect, losartan attenuates the effect of diclofenac has on leukocyte behavior and expression of adhesion molecules. Losartan has an antimigratory effect, reducing leukocyte migration by reducing ICAM-1 and P-selectin expression. Losartan may hinder the full expression of the antimigratory effect of diclofenac.

L-selectin: mechanisms and physiological significance of ectodomain cleavage

L-selectin is a cell adhesion molecule consisting of a large, highly glycosylated, extracellular domain, a single spanning transmembrane domain and a small cytoplasmic tail. It is expressed on most leukocytes and is involved in their rolling on inflamed vascular endothelium prior to firm adhesion and transmigration. It is also required for the constitutive trafficking of lymphocytes through secondary lymphoid organs. Like most adhesion molecules, L-selectin function is regulated by a variety of mechanisms including gene transcription, post-translational modifications, association with the actin cytoskeleton, and topographic distribution. In addition, it is rapidly downregulated by proteolytic cleavage near the cell surface by ADAM-17 (TACE) and at least one other "sheddase". This process of "ectodomain shedding" results in the release of most of the extracellular portion of L-selectin from the cell surface while retaining the cytoplasmic, transmembrane, and eleven amino acids of the extracellular domain on the cell. This review will examine the mechanism(s) of L-selectin ectodomain shedding and discuss the physiological implications.

Calmodulin binds to the cytoplasmic domain of angiotensin-converting enzyme and regulates its phosphorylation and cleavage secretion

The rate of cleavage secretion of the enzymatically active ectodomain of angiotensin-converting enzyme (ACE) is regulated by tyrosine phosphorylation of the protein and by the phorbol ester, phorbol 12-myristate 13-acetate (PMA), an activator of protein kinase C. Here, we report that both calmodulin inhibitor (CaMI) and calmodulin kinase inhibitor could also enhance cleavage secretion of ACE. This effect was accompanied by the dissociation of calmodulin from a specific region within the cytoplasmic domain of ACE to which it had been bound. The same domain of ACE was phosphorylated, and both CaMI and PMA caused dephosphorylation of ACE as well. Mass spectrometric and mutational analyses identified Ser730 as the only phosphorylated residue in the cytoplasmic domain of ACE. The Ser730 --> Ala mutant of ACE was not phosphorylated, but it still bound calmodulin, and its cleavage secretion was enhanced by both CaMI and PMA. Similarly, when Ser730 was replaced by the phosphoserine mimetic, Asp, cleavage secretion of the resultant mutant remained susceptible to the enhancing effect of CaMI and PMA. These results demonstrate that, although CaMI and PMA can enhance both cleavage secretion of ACE and its dephosphorylation, the two effects are not mutually interdependent.

Licofelone, a novel 5-LOX/COX-inhibitor, attenuates leukocyte rolling and adhesion on endothelium under flow

The main mechanism of action of non-steroidal anti-inflammatory drugs (NSAIDs) is the inhibition of cycloxygenases COX-1 and COX-2. During recent years, combined 5-LOX/COX-inhibition, interfering with the biosynthesis of both prostaglandins and leukotrienes (LTs), has emerged as a possibility to avoid side effects related to COX-inhibition. The aim of the present study was to investigate if there is a contribution of mechanisms other than the reduction of inflammatory prostaglandins and leukotrienes to the anti-inflammatory effect of the LOX/COX inhibitor licofelone. In a flow chamber assay, licofelone (10-30 microM) dose-dependently decreased both the rolling and adhesion of leukocytes on endothelial cells (EC). In contrast, no effects were found after treatment of EC with the unselective COX-1/COX-2 inhibitor indomethacin (30 microM), the potent and selective 5-LOX inhibitor, ZD-2138 (30 microM), the mainly COX-2 inhibitor aceclofenac (30 microM), the selective COX-2 inhibitor celecoxib (30 microM) and the combination of ZD-2138 with the selective COX-2 inhibitor celecoxib (30 microM). In the presence of licofelone (30 microM) the expression of E-selectin mRNA in cytokine-stimulated EC was attenuated, whereas no NSAID (30 microM) tested showed any effect on E-selectin expression. Moreover, licofelone treatment (30 microM) attenuated expression of VCAM-1 and ICAM-1 on inflammatory EC. The effect of licofelone on leukocyte recruitment was also evaluated in vivo. Using a mouse peritonitis model it was found that leukocyte accumulation was markedly reduced in licofelone treated animals (100mg/kg) compared to untreated mice. Thus, the novel 5-LOX/COX inhibitor licofelone possesses anti-inflammatory activity that, in addition to COX/LOX inhibition, involves effects on leukocyte-endothelial interactions.

Shedding light on ADAM metalloproteinases

ADAM metalloproteinase disintegrins have emerged as the major proteinase family that mediates ectodomain shedding, the proteolytic release of extracellular domains from their membrane-bound precursors. Recent gene-manipulation studies have established the role of ADAM-mediated shedding in mammalian physiology and, in addition, raised the issue of functional redundancy among ADAM sheddases. ADAM sheddases activate, for example, growth factors and cytokines, thus regulating signalling pathways that are important in development and pathological processes such as cancer. The recent studies have also begun to elucidate the substrate specificity and the mechanisms that control ADAM-mediated shedding events that regulate, for example, growth-factor and Notch signalling, and the processing of the amyloid precursor protein.

Extracellular proteases in atherosclerosis and restenosis

Extracellular proteolysis plays a key role in many pathophysiologic processes including cancer, inflammatory diseases, and cardiovascular conditions such as atherosclerosis and restenosis. Whereas matrix metalloproteinases are their best known member, many others are becoming better known. The extracellular proteases are a complex and heterogeneous superfamily of enzymes. They include metalloproteinases (matrix metalloproteinases, adamalysins, or pappalysins), serine proteases (elastase, coagulation factors, plasmin, tissue plasminogen activator, urokinase plasminogen activator), and the cysteine proteases (such cathepsins). In addition to their matrix degradation capabilities, they have other less well known biologic functions that include angiogenesis, growth factor bioavailability, cytokine modulation, receptor shedding, enhancing cell migration, proliferation, invasion, and apoptosis. This review discusses extracellular proteases relevant to the vasculature, their classification and function, and how protease disorders contribute to arterial plaque growth, including chronic atherosclerosis, acute coronary syndromes, restenosis, and vascular remodeling. These broad extracellular protease functions make them potentially interesting therapeutic targets.

Pain and osteoarthritis: new drugs and mechanisms

PURPOSE OF REVIEW

This review discusses the recent literature on drugs used for symptomatic pain relief in patients with osteoarthritis (OA) as well as potential mechanisms underlying their pharmacologic action.

RECENT FINDINGS

Recent research has shed light on the molecular mechanisms underlying the contribution of prostaglandins to pain sensation. Moreover, the role of the enzymes cyclooxygenase-2 (COX-2) and 5-lipoxygenase (5-LOX) in inflammation and subsequent structural changes of joints has been clarified. Based on the COX-1/COX-2 hypothesis, various selective COX-2 inhibitors with improved gastrointestinal tolerability as compared with conventional nonsteroidal anti-inflammatory drugs (NSAIDs) have been established for the symptomatic treatment of OA in recent years. Rational therapy with these compounds should be based on their diverse pharmacokinetic characteristics. Among the traditional NSAIDs, the mode of action of aceclofenac has been recently clarified in that the compound was shown to elicit preferential inhibition of COX-2 as a result of limited but sustained biotransformation to diclofenac. Novel mechanisms have also been proposed to account for the action of acetaminophen. Finally, there is evidence from animal models to suggest that the dual LOX/COX inhibitor licofelone may stop disease progression in OA. Clinical studies are under way to establish this compound for treatment of OA.

SUMMARY

It is anticipated that new insights into the pathophysiology of OA as well as novel therapeutics will improve the pharmacologic options in OA.

Mutagenesis of the Ezrin-Radixin-Moesin Binding Domain of L-selectin Tail Affects Shedding, Microvillar Positioning, and Leukocyte Tethering

L-selectin is a cell adhesion molecule that mediates the initial capture (tethering) and subsequent rolling of leukocytes along ligands expressed on endothelial cells. We have previously identified ezrin and moesin as novel binding partners of the 17-amino acid L-selectin tail, but the biological role of this interaction is not known. Here we identify two basic amino acid residues within the L-selectin tail that are required for binding to ezrin-radixinmoesin (ERM) proteins: arginine 357 and lysine 362. L-selectin mutants defective for ERM binding show reduced localization to microvilli and decreased phorbol 12-myristate 13-acetate-induced shedding of the L-selectin ectodomain. Cells expressing these L-selectin mutants have reduced tethering to the L-selectin ligand P-selectin glycoprotein ligand-1, but rolling velocity on P-selectin glycoprotein ligand-1 is not affected. These results suggest that ERM proteins are required for microvillar positioning of L-selectin and that this is important both for leukocyte tethering and L-selectin shedding.

Loss of ectodomain shedding due to mutations in the metalloprotease and cysteine-rich/disintegrin domains of the tumor necrosis factor-alpha converting enzyme (TACE)

Tumor necrosis factor-alpha converting enzyme (TACE), a multidomain protease essential for development and disease, releases the ectodomains from many transmembrane proteins in a regulated fashion. To understand the mechanism underlying the regulation of TACE activity, we sought to identify the cause of ectodomain shedding deficiencies in two mutated CHO sublines designated M1 and M2. Transfection of expression vectors for human and mouse TACE restored ectodomain shedding of TNF-alpha and TGF-alpha, suggesting that defects in the TACE gene contribute to the phenotype of M1 and M2 cells. The overall levels of endogenous TACE forms in M1 cells were significantly lower than those found in their parental cells, whereas only TACE zymogen, but not its mature form, was detectable in M2 cells. Molecular analyses suggested that M1 cells contained only one expressible TACE allele encoding an M435I point mutation in the catalytic center of the protease, and M2 cells produced two TACE variants with distinct point mutations in the catalytic domain (C225Y) and the cysteinerich/disintegrin domain (C600Y). Overexpression of the C225Y and C600Y TACE by transient transfection largely compensated for maturation defects in the variants but failed to restore TNF-alpha and TGF-alpha release in the shedding-defective CHO cell lines and fibroblasts derived from TACE-null mouse embryo. Further mutagenesis and functional analyses demonstrated that Cys(600) was absolutely essential for ectodomain shedding, suggesting that Cys(600), similar to Cys(225), participates in disulfide bonding, which is critical for both the processing and catalysis of TACE.

ADAMs family members as amyloid precursor protein alpha-secretases

In the non-amyloidogenic pathway, the Alzheimer's amyloid precursor protein (APP) is cleaved within the amyloid-beta domain by alpha-secretase precluding deposition of intact amyloid-beta peptide. The large ectodomain released from the cell surface by the action of alpha-secretase has several neuroprotective properties. Studies with protease inhibitors have shown that alpha-secretase is a zinc metalloproteinase, and several members of the adamalysin family of proteins, tumour necrosis factor-alpha convertase (TACE, ADAM17), ADAM10, and ADAM9, all fulfil some of the criteria required of alpha-secretase. We review the evidence for each of these ADAMs acting as the alpha-secretase. What seems to be emerging from numerous studies, including those with mice in which each of the ADAMs has been knocked out, is that there is a team of zinc metalloproteinases able to cleave APP at the alpha-secretase site. We also discuss how upregulation of alpha-secretase activity by muscarinic agonists, cholesterol-lowering drugs, steroid hormones, non-steroidal anti-inflammatory drugs, and metal ions may explain some of the therapeutic actions of these agents in Alzheimer's disease.