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S B Abramson

Publications and source records attributed to S B Abramson.

At least 55 records · Page 3Linked to original sources
PubMed1998

Regulation of nitric oxide production by salicylates and tenidap in human OA-affected cartilage, rat chondrosarcomas and bovine chondrocytes.

OBJECTIVE: To examine the effects of non-steroidal anti-inflammatory drugs (NSAIDS) on nitric oxide (NO) and prostaglandin E2 (PGE2) production in chondrocytes from three different species. METHODS: We have estimated NO production by Griess method, and PGE2 by RIA from the supernatants of articular cartilage obtained from osteoarthritis joints (OA-affected cartilage), rat chondrosarcomas (in ex vivo conditions) and bovine chondrocytes (stimulated with cytokines + endotoxin in vitro conditions) in the presence or absence of aspirin, indomethacin, sodium salicylate, tenidap and glucocorticoids. RESULTS: NO, which was spontaneously released in ex vivo conditions by OA-affected cartilage and rat chondrosarcomas (maintained in vivo), was susceptible to inhibition by pharmacologically relevant concentrations of aspirin, sodium salicylate and tenidap, but not to concentrations of indomethacin or glucocorticoids that significantly inhibited PGE2 production under the same conditions. Similarly, the production of NO by bovine chondrocytes grown in monolayer cultures that had been stimulated with cytokines + endotoxins (in vitro) to release both NO and PGE2 (at 48-72 h post stimulation), were inhibited by aspirin, sodium salicylate and tenidap, but not by indomethacin or glucocorticoids at concentrations sufficient to PGE2 production. Inhibition of NO in the cytokines + endotoxin stimulated bovine chondrocytes (like the human OA-affected cartilage) augmented PGE2 production. CONCLUSION: These experiments demonstrate that NO production by chondrocytes across species show a similar profile of susceptibility to inhibition by selected anti-inflammatory drugs. The insensitivity of NO production to glucocorticoids is an important characteristics of these cells that merits further investigation.

Aged↗
PubMed1998

The role of nitric oxide in articular cartilage breakdown in osteoarthritis.

It is increasingly appreciated that mediators typically associated with inflammatory arthritis, such as catabolic cytokines and nitric oxide, are produced by synovium and cartilage in osteoarthritis. The role that such mediators play in the progression of cartilage degradation in osteoarthritis is under intensive investigation. Nitric oxide is a highly reactive, cytotoxic free radical that has been implicated in tissue injury in a variety of diseases. Cartilage obtained from patients with osteoarthritis produces significant amounts of nitric oxide ex vivo, even in the absence of added stimuli such as interleukin-1 or lipopolysaccharide. In vitro, nitric oxide exerts detrimental effects on chondrocyte functions, including the inhibition of collagen and proteoglycan synthesis, enhanced apoptosis, and an inhibition of B1 integrin-dependent adhesion to the extra-cellular matrix. This paper reviews recent observations regarding the role of nitric oxide in osteoarthritis and presents evidence suggesting that the inhibition of nitric oxide production could be a desirable future therapeutic strategy.

Animals↗
PubMed1998

Cyclooxygenase in biology and disease.

Cyclooxygenase (COX), the key enzyme required for the conversion of arachidonic acid to prostaglandins was first identified over 20 years ago. Drugs, like aspirin, that inhibit cyclooxygenase activity have been available to the public for about 100 years. In the past decade, however, more progress has been made in understanding the role of cyclooxygenase enzymes in biology and disease than at any other time in history. Two cyclooxygenase isoforms have been identified and are referred to as COX-1 and COX-2. Under many circumstances the COX-1 enzyme is produced constitutively (i.e., gastric mucosa) whereas COX-2 is inducible (i.e., sites of inflammation). Here, we summarize the current understanding of the role of cyclooxygenase-1 and -2 in different physiological situations and disease processes ranging from inflammation to cancer. We have attempted to include all of the most relevant material in the field, but due to the rapid progress in this area of research we apologize that certain recent findings may have been left out.

Animals↗
PubMed1998

The classification of cyclooxygenase inhibitors.

In summary, precise classification of COX inhibitors has important clinical implications for efficacy and toxicity. However, classification of these agents clinically is difficult because there are insufficient data to predict correlations between biochemical and pharmacologic properties and the clinical effect of a given agent. In any case, specific COX-2 inhibitors are expected to show antiinflammatory and analgesic activities equivalent to those of NSAID, as well as significant reductions in the incidence of the life threatening side effects (i.e., GI bleeding) associated with COX-1 inhibition. The advantages of preferential COX-2 inhibitors may be more subtle and therefore more difficult to verify in clinical trials.

Animals↗
PubMed1997

Outside-in signaling in the chondrocyte. Nitric oxide disrupts fibronectin-induced assembly of a subplasmalemmal actin/rho A/focal adhesion kinase signaling complex.

Elevated levels of fibronectin (Fn) in articular cartilage have been linked to the progression of both rheumatoid and osteoarthritis. In this study, we examined intracellular events which follow ligation of Fn to its receptor, the integrin alpha5beta1. In addition, we examined the regulatory influence of nitric oxide on these events, since this free radical has been implicated in cartilage degradation. Exposure of chondrocytes to Fn-coated beads resulted in the circumferential clustering of the alpha5beta1 integrin receptor, which was accompanied by the subplasmalemmal assembly of a focal activation complex comprised of F-actin, the tyrosine kinase, focal adhesion kinase (FAK), the ras related G protein rho A, as well as tyrosine-phosphorylated proteins. Treatment with exogenous nitric oxide (NO) or catabolic cytokines which induce nitric oxide synthase blocked the assembly of F-actin, FAK, rho A and tyrosine-phosphorylated proteins while not affecting the total number of beads bound per cell nor the clustering of alpha5beta1 integrin. Use of a cGMP antagonist (Rp-8-Br cGMPS) or cGMP agonist (Sp-cGMPS) either abolished or mimicked the NO effect, respectively. Adherence of chondrocytes to fibronectin enhanced proteoglycan synthesis by twofold (vs. albumin). In addition, basic fibroblast growth factor (FGF) and insulin growth factor (IGF-1) induced proteoglycan synthesis in chondrocytes adherent to Fn but not albumin suggesting a costimulatory signal transduced by alpha5betal and the FGF receptor. Both constitutive and FGF stimulated proteoglycan synthesis were completely inhibited by nitric oxide. These data indicate that the ligation of alpha5beta1 in the chondrocyte induced the intracellular assembly of an activation complex comprised of the cytoplasmic tail of alpha5beta1 integrin, actin, and the signaling molecules rho A and FAK. We show that NO inhibits the assembly of the intracellular activation complex and the synthesis of proteoglycans, but has no effect on the extracellular aggregation of alpha5beta1 integrin. These observations provide a basis by which nitric oxide can interfere with chondrocyte functions by affecting chondrocyte-matrix interactions.

Actins↗
PubMed1997

Post-transcriptional regulation of inducible nitric oxide synthase mRNA in murine macrophages by doxycycline and chemically modified tetracyclines.

Chemically modified tetracyclines [CMT-3 (IC50 approximately 6-13 microM = approximately 2.5-5 microg/ml) and CMT-8 (IC50 approximately 26 microM = 10 microg/ml), but not CMT-1, -2 or -5], which lack anti-microbial activity, inhibited nitrite production in LPS-stimulated macrophages. Unlike competitive inhibitors of L-arginine which inhibited the specific activity of inducible nitric oxide synthase (iNOS) in cell-free extracts, CMTs exerted no such direct effect on the enzyme. CMTs could, however, be shown to inhibit both iNOS mRNA accumulation and protein expression in LPS-stimulated cells. Tetracyclines (doxycycline and CMT-3) unlike hydrocortisone had no significant effect on murine macrophages transfected with iNOS promoter (tagged to a luciferase reporter gene) in the presence of LPS. However, doxycycline and CMT-3 augmented iNOS mRNA degradation, in LPS-stimulated murine macrophages. These studies show a novel mechanism of action of tetracyclines which harbours properties to increase iNOS mRNA degradation and decrease iNOS protein expression and nitric oxide production in macrophages. This property of tetracyclines may have beneficial effects in the treatment of various diseases where excess nitric oxide has been implicated in the pathophysiology of these diseases.

Animals↗
PubMed1997

Superinduction of cyclooxygenase-2 activity in human osteoarthritis-affected cartilage. Influence of nitric oxide.

Cartilage specimens from osteoarthritis (OA)-affected patients spontaneously released PGE2 at 48 h in ex vivo culture at levels at least 50-fold higher than in normal cartilage and 18-fold higher than in normal cartilage + cytokines + endotoxin. The superinduction of PGE2 production coincides with the upregulation of cyclooxygenase-2 (COX-2) in OA-affected cartilage. Production of both nitric oxide (NO) and PGE2 by OA cartilage explants is regulated at the level of transcription and translation. Dexamethasone inhibited only the spontaneously released PGE2 production, and not NO, in OA-affected cartilage. The NO synthase inhibitor HN(G)-monomethyl-L-arginine monoacetate inhibited OA cartilage NO production by > 90%, but augmented significantly (twofold) the spontaneous production of PGE2 in the same explants. Similarly, addition of exogenous NO donors to OA cartilage significantly inhibited PGE2 production. Cytokine + endotoxin stimulation of OA explants increased PGE2 production above the spontaneous release. Addition of L-NMMA further augmented cytokine-induced PGE2 production by at least fourfold. Inhibition of PGE2 by COX-2 inhibitors (dexamethasone or indomethacin) or addition of exogenous PGE2 did not significantly affect the spontaneous NO production. These data indicate that human OA-affected cartilage in ex vivo conditions shows (a) superinduction of PGE2 due to upregulation of COX-2, and (b) spontaneous release of NO that acts as an autacoid to attenuate the production of the COX-2 products such as PGE2. These studies, together with others, also suggest that PGE2 may be differentially regulated in normal and OA-affected chondrocytes.

Adult↗
PubMed1997

Nitric oxide attenuates cellular hexose monophosphate shunt response to oxidants in articular chondrocytes and acts to promote oxidant injury.

Nitric oxide (NO) has been implicated in both cartilage degradation and cell survival. Importantly, NO has been shown, in a cell-type-dependent manner, to directly cause cell death or indirectly promote cell death by compromising the ability of cells to detoxify intra- or extracellular oxidants. In this study we examined the role of NO in the survival of bovine chondrocytes exposed to catabolic cytokines (interleukin-1 (IL-1); tumor necrosis factor [TNF]) with or without the addition of an exogenous oxidant stress (e.g., H2O2, HOOCl, etc.). The exposure of chondrocytes to a mixture of IL-1 and TNF (IL-1/TNF) results in the release of NO but did not alter cell viability. However, there was evidence of NO-dependent oxidative responses in the IL-1/TNF group, as we observed an increased level of intracellular oxidants as well as the appearance of a 55 kD nitrated protein which reflects the formation of peroxynitrite. We next analyzed viability with H2O2. The LD50 for IL-1/TNF-treated cells was 0.1 mM (vs. 1 mM for control). The enhanced sensitivity was completely reversed when cells were incubated with the NO synthase inhibitor 1-n5-1-iminoethylornithine (NIO). To test whether cell death was caused by compromising the ability of cells to detoxify extracellular oxidants, we examined the hexose monophosphate shunt (HMPS) response in cells given H2O2. Treatment of control cells with H2O2 resulted in a fourfold increase in HMPS activity. In contrast, IL-1/TNF cells exhibited no increase in HMPS activity. The attenuation of stimulated HMPS activity was reversed by the coaddition of NIO. Thus, these data indicate that 1) endogenous NO mediates cytokine-dependent susceptibility to oxidant injury and 2) this effect is in part due to impaired activation of the HMPS. In inflamed joints replete with cytokines and oxidants, NO may contribute to chondrocyte death and progressive joint destruction.

Animals↗
PubMed1997

Interleukin-17 up-regulation of nitric oxide production in human osteoarthritis cartilage.

OBJECTIVE: To examine the effect of human interleukin-17 (IL-17) on nitric oxide (NO) production in human osteoarthritis (OA) cartilage under ex vivo conditions. METHODS: OA cartilage from patients undergoing knee replacement surgery was used in explant assays to assess the effect of IL-17. NO production was measured by estimating the stable NO metabolite, nitrite, in conditioned medium. RESULTS: IL-17 augmented the spontaneous production of nitric oxide. This augmentation was sensitive to cycloheximide and pyrrolidine dithiocarbamate, but not to dexamethasone or soluble IL-1 receptor. CONCLUSION: IL-17 augments nitric oxide production in OA cartilage via nuclear factor kappaB activation, but independently of IL-1beta signaling.

Aged↗
PubMed1997

Increased nitric oxide production accompanied by the up-regulation of inducible nitric oxide synthase in vascular endothelium from patients with systemic lupus erythematosus.

OBJECTIVE: To investigate whether systemic lupus erythematosus (SLE) is accompanied by increased serum nitrite levels, whether active compared with inactive disease is associated with greater nitric oxide (NO) production, and whether endothelial cells or keratinocytes serve as cellular sources of NO by virtue of their increased expression of either constitutive nitric oxide synthase (cNOS) or inducible NOS (iNOS). METHODS: Fifty-one serum samples (46 from patients with SLE) were analyzed for NO production by measuring nitrite levels in a calorimetric assay. Skin biopsy samples from 21 SLE patients and 11 healthy volunteers were evaluated immunohistochemically, using monoclonal antibodies, for endothelial cell and keratinocyte cNOS and iNOS expression. RESULTS: Serum nitrite levels were significantly elevated in the 46 patients with SLE (mean +/- SEM 37 +/- 6 microM/liter) compared with controls (15 +/- 7 microM/liter; P < 0.01), and were elevated in patients with active SLE compared with those with inactive disease (46 +/- 7 microM/liter versus 30 +/- 7 microM/liter; P < 0.01). Serum nitrite levels correlated with disease activity (r = 0.47, P = 0.04) and with levels of antibodies to double-stranded DNA (r = 0.35, P = 0.02). Endothelial cell expression of iNOS in SLE patients (mean +/- SEM score 1.5 +/- 0.2) was significantly greater compared with controls (0.6 +/- 0.2; P < 0.01), and higher in patients with active disease compared with those with inactive SLE (1.7 +/- 0.2 versus 1.2 +/- 0.2; P < 0.01). Keratinocyte expression of iNOS was also significantly elevated in SLE patients (0.9 +/- 0.1) compared with controls (0.4 +/- 0.1; P < 0.001). With regard to expression of cNOS, there were no differences between patients with active SLE, those with inactive SLE, and normal controls in either the vascular endothelium or the keratinocytes. CONCLUSION: NO production is increased in patients with SLE, and 2 potential sources of excessive NO are activated endothelial cells and keratinocytes via up-regulated iNOS.

Adult↗
PubMed1997

Differential phosphorylation of the beta2 integrin CD11b/CD18 in the plasma and specific granule membranes of neutrophils.

Neutrophil aggregation is mediated by the beta2 integrin CD11b/CD18, which has limited expression on the surface membrane of resting cells but is recruited from intracellular organelles after cell activation. We have previously found that CD11b/CD18 newly translocated to the plasma membrane does not contribute to adhesion but must be modified to be functional. Because neutrophil aggregation induced by phorbol myristate acetate (PMA) is accompanied by de novo phosphorylation of the CD18 cytoplasmic tail, we sought to determine whether CD11b/CD18 phosphorylation is separately regulated in the different cellular compartments. Accordingly, [32P]-labeled CD11b/CD18 was immunoprecipitated from purified neutrophil-specific granule or plasma membrane lysates. In plasma membrane fractions, as in whole cell lysates, CD18 became phosphorylated in cells exposed to PMA but not in untreated cells or cells treated with N-formyl-methionyl-leucyl-phenylalanine (fMLP). The alpha chain, CD11b, was phosphorylated under all conditions. In contrast, only marginal phosphorylation of specific granule-associated CD18 or CD11b was observed. Calyculin A, an inhibitor of serine/threonine phosphatases (pp1 > pp2a), induced strong phosphorylation of CD18 in the plasma membrane but not in the specific granules. Addition of intact specific granule membranes to the plasma membranes from PMA-treated neutrophils markedly decreased phosphorylation in both CD11b and CD18 subunits. These data suggest that the phosphorylation of CD11b/CD18, which accompanies neutrophil activation, is limited to plasma membrane-associated molecules. Phosphorylation, either constitutive or induced, is absent in the specific granule membranes. The difference may be due to a specific granule-associated phosphatase, probably distinct from ppl. Therefore adhesion-competent plasma membrane CD11b/CD18 and adhesion-incompetent specific granule CD11b/CD18 differ in their state of phosphorylation.

CD18 Antigens↗
PubMed1997

Transplantation of adenovirally transduced allogeneic chondrocytes into articular cartilage defects in vivo.

Gene transfer to chondrocytes followed by intra-articular transplantation may allow for functional modulation of chondrocyte biology and enhanced repair of damaged articular cartilage. We chose to examine the loss of chondrocytes transduced with a recombinant adenovirus containing the gene for Escherichia coli beta-galactosidase (Ad.RSVntlacZ), followed by transplantation into deep and shallow articular cartilage defects using New Zealand White rabbits as an animal model. A type I collagen matrix was used as a carrier for the growth of the transduced chondrocytes and to retain the cells within the surgically created articular defects. Histochemical analysis of matrices recovered from the animals 1, 3 and 10 days after implantation showed the continued loss of lacZ positive chondrocytes. The number of cells recovered from the matrices was also compared with the initial innoculum of transduced cells present within the matrices at the time of implantation. The greatest loss of transduced cells was observed in the first 24 h after implantation. The numbers of transduced cells present within the matrices were relatively constant between 1 and 3 days postimplantation, but had progressively declined by 10 days postimplantation. These results suggest that transduction of chondrocytes followed by intra-articular transplantation in this rabbit model may enable us to examine the biological effects of focal transgenic overexpression of proteins involved in cartilage homeostasis and repair.

Adenoviridae↗
PubMed1996

A novel mechanism of action of tetracyclines: effects on nitric oxide synthases.

Tetracyclines have recently been shown to have "chondroprotective" effects in inflammatory arthritides in animal models. Since nitric oxide (NO) is spontaneously released from human cartilage affected by osteoarthritis (OA) or rheumatoid arthritis in quantities sufficient to cause cartilage damage, we evaluated the effect of tetracyclines on the expression and function of human OA-affected nitric oxide synthase (OA-NOS) and rodent inducible NOS (iNOS). Among the tetracycline group of compounds, doxycycline > minocycline blocked and reversed both spontaneous and interleukin 1 beta-induced OA-NOS activity in ex vivo conditions. Similarly, minocycline > or = doxycycline inhibited both lipopolysaccharide- and interferon-gamma-stimulated iNOS in RAW 264.7 cells in vitro, as assessed by nitrite accumulation. Although both these enzyme isoforms could be inhibited by doxycycline and minocycline, their susceptibility to each of these drugs was distinct. Unlike acetylating agents or competitive inhibitors of L-arginine that directly inhibit the specific activity of NOS, doxycycline or minocycline has no significant effect on the specific activity of iNOS in cell-free extracts. The mechanism of action of these drugs on murine iNOS expression was found to be, at least in part, at the level of RNA expression and translation of the enzyme, which would account for the decreased iNOS protein and activity of the enzyme. Tetracyclines had no significant effect on the levels of mRNA for beta-actin and glyceraldehyde-3-phosphate dehydrogenase nor on levels of protein of beta-actin and cyclooxygenase 2 expression. These studies indicate that a novel mechanism of action of tetracyclines is to inhibit the expression of NOS. Since the overproduction of NO has been implicated in the pathogenesis of arthritis, as well as other inflammatory diseases, these observations suggest that tetracyclines should be evaluated as potential therapeutic modulators of NO for various pathological conditions.

Animals↗
PubMed1996

Effects of nitric oxide on chondrocyte migration, adhesion, and cytoskeletal assembly.

OBJECTIVE: The migration of cells of chondrocyte lineage is believed to play a role in cartilage growth and repair. The present study examined 1) whether chondrocytes are capable of migration in vitro; and 2) the effects of nitric oxide (NO) on chondrocyte migration, adhesion, and cytoskeletal assembly. METHODS: Chondrocyte migration was evaluated by 2 assays: 1) "centrifugal" migration within a 3-dimensional collagen matrix (dot culture); and 2) directed migration under agarose in response to bone morphogenetic protein. To assess the effects of NO, chondrocytes were treated with either exogenous NO (S-nitrosoglutathione [SNO-GSH]) or a mixture of cytokines known to induce endogenous NO production. The effects of NO on chondrocyte adhesion to fibronectin-coated surfaces, as well as on actin polymerization (determined by indirect immunofluorescence), were also examined. RESULTS: The capacity of chondrocytes to migrate was demonstrated both by the dot culture and by agarose methods. Both SNO-GSH and endogenous NO induced by cytokines inhibited this migration. Exposure to NO also inhibited attachment of chondrocytes to fibronectin and disrupted assembly of actin filaments. These effects of SNO-GSH and cytokine-induced NO production were reversed in the presence of hemoglobin and the NO synthase inhibitor NG-monomethyl arginine, respectively. CONCLUSION: NO interferes with chondrocyte migration and attachment to fibronectin, an extracellular matrix protein, probably via effects on the actin cytoskeleton. These effects of NO may result in impairment of cartilage repair, by interfering with the extracellular matrix regulation of chondrocyte function.

Animals↗
PubMed1995

The expression and regulation of nitric oxide synthase in human osteoarthritis-affected chondrocytes: evidence for up-regulated neuronal nitric oxide synthase.

Classically, osteoarthritis (OA) has been considered a noninflammatory disease. However, the detection of selected inflammatory mediators in osteoarthritic fluid, in the absence of significant inflammatory cell infiltrate, is increasingly appreciated. We sought to identify the inflammatory component in human OA-affected cartilage that may be involved in cartilage damage/destruction. Using Western blot analysis and an antibody to the conserved region of nitric oxide synthase (NOS), we have observed up-regulation of NOS, one of the "key players" of inflammation, in chondrocytes of OA-affected patients. Remarkably, none of the cartilage samples examined from normal joints demonstrated detectable amounts of this NOS. Western blot analysis using the same alpha-NOS antibody indicated that this NOS from OA-affected cartilage (OA-NOS) was larger in size than (and distinct from) transfected human hepatocyte or murine inducible NOS (iNOS) (150 versus 133 kD) and similar in size to neuronal constitutive NOS (ncNOS). Antibodies specific for iNOS showed binding to murine and human iNOS but not to OA-NOS, endothelial constitutive NOS, or ncNOS. Antibodies specific for ncNOS bound to ncNOS and also to OA-NOS, but not to murine or human iNOS or endothelial constitutive NOS. Incubation of OA cartilage in serum-free medium resulted in spontaneous release, for up to 72 h, of substantial amounts of nitrite (up to approximately 80 microM/100 mg wet tissue), which could be inhibited by at least 80% with various inhibitors of iNOS, including inhibitors of protein synthesis and transcription factor NF-kappa B, but which (unlike murine macrophage iNOS) was not sensitive to hydrocortisone or TGF-beta. Exposure of OA-affected cartilage to interleukin 1 beta, tumor necrosis factor-alpha, and lipopolysaccharide resulted in approximately 20-50% augmentation of nitrite accumulation, which was also sensitive to cycloheximide and pyrrolidine dithiocarbamate. Hence, our data indicate that OA-NOS (based on immunoreactivity and molecular weight) is similar to ncNOS and that it releases nitric oxide, which may contribute to the inflammation and pathogenesis of cartilage destruction in OA.

Animals↗
PubMed1995

The mode of action of aspirin-like drugs: effect on inducible nitric oxide synthase.

Nitric oxide synthesized by inducible nitric oxide synthase (iNOS) has been implicated as a mediator of inflammation in rheumatic and autoimmune diseases. We report that exposure of lipopolysaccharide-stimulated murine macrophages to therapeutic concentrations of aspirin (IC50 = 3 mM) and hydrocortisone (IC50 = 5 microM) inhibited the expression of iNOS and production of nitrite. In contrast, sodium salicylate (1-3 mM), indomethacin (5-20 microM), and acetaminophen (60-120 microM) had no significant effect on the production of nitrite at pharmacological concentrations. At suprapharmacological concentrations, sodium salicylate (IC50 = 20 mM) significantly inhibited nitrite production. Immunoblot analysis of iNOS expression in the presence of aspirin showed inhibition of iNOS expression (IC50 = 3 mM). Sodium salicylate variably inhibited iNOS expression (0-35%), whereas indomethacin had no effect. Furthermore, there was no significant effect of these nonsteroidal anti-inflammatory drugs on iNOS mRNA expression at pharmacological concentrations. The effect of aspirin was not due to inhibition of cyclooxygenase 2 because both aspirin and indomethacin inhibited prostaglandin E2 synthesis by > 75%. Aspirin and N-acetylimidazole (an effective acetylating agent), but not sodium salicylate or indomethacin, also directly interfered with the catalytic activity of iNOS in cell-free extracts. These studies indicate that the inhibition of iNOS expression and function represents another mechanism of action for aspirin, if not for all aspirin-like drugs. The effects are exerted at the level of translational/posttranslational modification and directly on the catalytic activity of iNOS.

Acetaminophen↗
PubMed1995

Translocation of p21rac2 from cytosol to plasma membrane is neither necessary nor sufficient for neutrophil NADPH oxidase activity.

Activation of the membrane-associated NADPH oxidase of neutrophils requires several cytosolic factors including p47phox, p67phox and p21rac2. We compared NADPH oxidase activity with the membrane translocation of p47phox, p67phox, and p21rac2. In a cell-free system, GTP gamma S stimulated translocation of p47phox and p67phox to the plasma membrane only in the presence of arachidonate, and this translocation correlated with NADPH oxidase activity of the reisolated plasma membranes (R = 0.94 and 0.97, respectively). In contrast, GTP gamma S-stimulated p21rac2 translocation with or without arachidonate, and the extent of translocation did not correlate with oxidase activity (R = 0.17). Neutrophil cytoplasts were used to relate membrane translocation of p47phox, p67phox and p21rac2 to membrane oxidase activity in response to the inflammatory agonists. Whereas N-formyl-methionyl-leucyl-phenylalanine stimulated equimolar, transient membrane translocation of p47phox and p67phox which kinetically paralleled NADPH oxidase activity, relatively little p21rac2 translocated (moles of p47phox/p21rac2 = 16.6). Moreover, although phorbol 12-myristate 13-acetate stimulated both the stable translocation of p47phox and p67phox and sustained NADPH oxidase activity, it did not stimulate p21rac2 translocation. From these data we conclude that membrane translocation of p21rac2 does not regulate NADPH oxidase activity stoichiometrically.

Cell Fractionation↗