Adenosine kinase inhibitor GP515 attenuates hepatic leukocyte adhesion after hemorrhagic hypotension

Adhesion of leukocytes to the vascular endothelium hallmarks a key event in neutrophil-mediated organ injury after ischemia-reperfusion. The autacoid adenosine has been shown to inhibit activated neutrophil function and to interfere with leukocyte-endothelial adherence. Its therapeutic use in ischemia-reperfusion, however, has been limited by severe cardiovascular side effects. We therefore investigated the effects of the adenosine kinase inhibitor GP515 in vivo on hepatic leukocyte-endothelial interactions in a rat model of hemorrhagic hypotension and resuscitation, using intravital microscopy. Rats were pretreated with either GP515 (0.25 mg/kg) or saline in a randomized and blinded manner and subjected to pressure-controlled hemorrhagic hypotension at a mean arterial pressure of 40 mmHg for 60 min followed by 5 h of resuscitation. Five hours after resuscitation in saline-treated animals, firm leukocyte-sinusoidal adhesion was strongly enhanced in the periportal and midzonal sublobular regions, and sinusoidal diameters were also markedly reduced. Compared with saline treatment, GP515 significantly attenuated shock and resuscitation-induced leukocyte adhesion in both sublobular regions. Moreover, although GP515 did not significantly affect macrohemodynamical and hematological parameters, it enlarged narrowed sinusoidal diameters and tended to improve sinusoidal blood flow. We propose that the adenosine-regulating agent GP515 has a therapeutic potential to attenuate ischemia-reperfusion-induced inflammation by capitalizing on the beneficial anti-inflammatory effects of endogenous adenosine.

Posttranscriptional regulation of collagenase-1 gene expression in synoviocytes by adenosine receptor stimulation

OBJECTIVE

To characterize the transcriptional and posttranscriptional regulation of collagenase-1 by adenosine receptor stimulation in interleukin-1 (IL-1)-stimulated fibroblast-like synoviocytes (FLS).

METHODS

FLS were stimulated with IL-1 and either the nonselective adenosine agonist 5'-N-ethylcarboxamidoadenosine (NECA) or the adenylate cyclase activator forskolin. Electrophoretic mobility shift assays were performed to determine AP-1 and cAMP-responsive element binding protein (CREB) activation. Transcriptional activation was determined by transfecting HS68 dermal fibroblasts with a collagenase-chloramphenicol acetyltransferase construct. Finally, collagenase messenger RNA (mRNA) half-life was determined by activating cells in the presence of IL-1, IL-1 + NECA, or IL-1 + forskolin and culturing cells in the presence of actinomycin D.

RESULTS

NECA and forskolin had no effect on AP-1 activation, c-jun or c-fos gene expression, or CREB phosphorylation. IL-1 markedly increased collagenase promoter activity, and neither NECA nor forskolin blocked this action. Studies of mRNA half-life showed that both NECA and forskolin decreased the half-life of collagenase mRNA in IL-1-stimulated FLS and HS68 cells.

CONCLUSION

The findings of this study demonstrate that NECA and forskolin decrease collagenase gene expression in FLS and dermal fibroblasts due to enhanced mRNA degradation.

Alternatively spliced CS-1 fibronectin isoform and its receptor VLA-4 in rheumatoid arthritis synovium

OBJECTIVE

Extracellular matrix components and cell adhesion molecules play a role in the pathogenesis of rheumatoid arthritis (RA). Interaction between the integrin very late antigen-4 (VLA-4) and the connecting segment-1 (CS-1) fibronectin (FN) isoform may contribute to lymphocyte interaction in RA synovium. We examined both mRNA and protein expression of CS-1 FN in inflamed synovium, and VLA-4 expression in synovial tissue and on cultured fibroblast-like synoviocytes from patients with RA.

METHODS

Snap frozen synovial tissue specimens of 10 patients with RA and 4 patients with osteoarthritis were examined for expression of CS-1 FN mRNA and protein by in situ hybridization and immunohistochemistry. VLA-4 expression of synovial fibroblasts and in synovial tissue was evaluated by flow cytometry and immunohistochemistry.

RESULTS

CS-1 FN mRNA was detected in RA lining layer synoviocytes, around terminal vessels, and in endothelial cells. Double labeling revealed that most lining synoviocytes expressing CS-1 FN mRNA were CD68 negative. VLA-4 was found in RA synovial fibroblasts, sublining mononuclear cells, and lymphoid aggregates.

CONCLUSION

Our findings suggest that expression of CS-1 FN may partially correlate with cell proliferation in the RA lining layer. VLA-4 was found in RA synovial lining, as well as on cultured synovial fibroblasts. Thus, VLA-4/CS-1 FN interaction may facilitate lymphocyte interaction and synovial proliferation in RA.

Somatic mutations in the p53 tumor suppressor gene in rheumatoid arthritis synovium

The factors that regulate the perpetuation and invasiveness of rheumatoid synovitis have been the subject of considerable inquiry, and the possibility that nonimmunologic defects can contribute to the disease has not been rigorously addressed. Using a mismatch detection system, we report that synovial tissue from the joints of severe chronic rheumatoid arthritis patients contain mutant p53 transcripts, which were not found in skin samples from the same patients or in joints of patients with osteoarthritis. Mutant p53 transcripts also were identified in synoviocytes cultured from rheumatoid joints. The predicted amino acid substitutions in p53 were identical or similar to those commonly observed in a variety of tumors and might influence growth and survival of rheumatoid synoviocytes. Thus, mutations in p53 and subsequent selection of the mutant cells may occur in the joints of patients as a consequence of inflammation and contribute to the pathogenesis of the disease.

Pannocytes: distinctive cells found in rheumatoid arthritis articular cartilage erosions

A distinctive cell was identified from sites of rheumatoid arthritis cartilage injury. Similar cells are not found in lesions of osteoarthritis cartilage. We have designated them as pannocytes (PCs). Their rhomboid morphology differs from the bipolar shape of fibroblast-like synoviocytes or the spherical configuration of primary human articular chondrocytes. Chondrocytes are short-lived, whereas the original PC line grew for 25 passages before becoming senescent. Features in common with cultured primary chondrocytes include maximal proliferation in response to transforming growth factor-beta a catabolic response to interleukin-1 beta, collagenase production, and mRNA for the induced lymphocyte antigen and inducible nitric oxide synthase. Despite the presence of the inducible nitric oxide synthase message, PCs do not produce NO either constitutively or when cytokine stimulated. Each of the mesenchymal cells, fibroblast-like synoviocytes, primary chondrocytes, and PCs have the gene for type I collagen, but the type II collagen gene is detected only in primary chondrocytes. PCs can be distinguished from fibroblast-like synoviocytes and primary chondrocytes by their morphology, bright VCAM-1 staining, and growth response to cytokines and growth factors. Their prolonged life span in vitro suggests that PCs might represent an earlier stage of mesenchymal cell differentiation, and they could have a heretofore unrecognized role in rheumatoid arthritis joint destruction.

Dual activation of adenosine A1 and A3 receptors mediates preconditioning of isolated cardiac myocytes

Ischemic preconditioning reduces post-ischemic myocardial injury by activating myocellular adenosine A1 receptors. Adenosine A3 receptors have also been implicated but there is no evidence for A3 receptors in cardiac myocytes. The aim of this study was to develop a model of preconditioning in isolated cardiac myocytes to evaluate the role of the adenosine A1 and A3 receptors in preconditioning-induced protection from ischemic injury. Reverse transcription polymerase chain reaction (PCR) was also employed to establish the presence of adenosine A3 receptors in these cells. In the preconditioning studies, ischemic injury was simulated by exposing isolated rabbit myocytes (placed in the cell chamber and paced at l Hz) to buffer containing (in mM) 2'-deoxyglucose (20), NaCN (1), Na (+)-lactate (20), KCl (10) at pH 6.6 (37 degrees C). Changes of diastolic and systolic cell length were monitored with an optical-video edge imaging system, and hypercontracture was assessed as an index of irreversible cell injury. Preconditioning (2 min brief ischemia and 15 min reperfusion) significantly reduced cell injury resulting from a subsequent prolonged ischemia (10 min) and reperfusion (15 min), as indicated by a reduction in the incidence of cell hypercontracture from 67 +/- 6% to 29 +/- 5% (P < 0.001). Preconditioning-induced cardioprotection was only partially blocked by a maximally effective concentration (100 nM) of the adenosine A1 receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) (cell hypercontracture = 43 +/- 3%, P < 0.05 vs. control) but completely blocked by either the combination of DPCPX (100 nM) with the adenosine A1/A3 receptor antagonist DPCPX +8-(4-carboxyethylphenyl)-1,3-dipropylxanthine (BWA1433; 1 microM) or the non-selective adenosine receptor antagonist, 8-(p-sulfophenyl)theophylline (8-SPT; 100 microM) (cell hypercontracture = 64 +/- 4%, 59 +/- 5%, respectively; P = NS vs. control). In non-hypercontractured myocytes, preconditioning also substantially enhanced the recovery of the contractile amplitude and, similarly, this effect was only partially blocked by DPCPX but completely blocked by either the combination of DPCPX with BWA1433, or 8-SPT. These studies suggest that preconditioning protects isolated cardiac myocytes from ischemic injury independent of other cell types, and that maximal preconditioning-induced cardioprotection requires activation of both adenosine A1 and A3 receptors. Reverse transcription-PCR using primers for the rabbit receptor provide evidence for the presence of adenosine A3 receptors in these cells.

Spinal cord adenosine receptor stimulation in rats inhibits peripheral neutrophil accumulation. The role of N-methyl-D-aspartate receptors

The effect of spinal adenosine receptor ligation on peripheral leukocyte accumulation was studied in two rat models of inflammation. Neutrophil infiltration into dermal inflammatory sites was signficantly reduced by adenosine A1 receptor agonists injected through intrathecal catheters. These effects were reversed by N-methyl-D-aspartate (NMDA), and were mimicked by (+/-)-2-amino-5-phosphonopentanoic acid (AP-5), a glutamate NMDA receptor antagonist. Peripheral adenosine levels, as measured in air pouch exudates, decreased markedly in inflamed pouches but remained near normal after intrathecal treatment with AP-5. Moreover, the antiinflammatory effects of intrathecal A1 receptor agonists and AP-5 were reversed by an adenosine A2 receptor antagonist administered intraperitoneally. Hence, central NMDA receptor activity can regulate neutrophil accumulation in peripheral inflammatory sites by reducing local levels of adenosine, an antiinflammatory autacoid which inhibits neutrophil function through A2 receptor activation. This represents a previously unknown pathway by which the central nervous system influences inflammatory responses.

Apoptosis in rheumatoid arthritis: p53 overexpression in rheumatoid arthritis synovium

DNA damage induces p53 tumor suppressor gene expression and protein production, which in turn facilitates DNA repair or apoptosis. Wild-type p53 protein has a short half-life, so it is rarely detected in non-neoplastic tissue. Because DNA fragmentation is abundant in the intimal lining in rheumatoid arthritis (RA) synovial tissue (ST) using in situ end-labeling (Firestein GS, Yeo M, Zvaifler NJ: Apoptosis in rheumatoid arthritis synovium. J Clin Invest 1995, 96:1631-1638), we assessed ST p53 expression. Immunohistochemical analysis of fixed RA synovium using antibody PAb 1801 showed prominent p53 staining in the cytoplasm and nuclei of intimal lining cells. Noninflammatory and osteoarthritis (OA) ST had significantly less p53 in the lining. These data were confirmed by Western blot analysis of ST extracts, with abundant p53 found in RA compared with OA. p53 expression in cultured fibroblast-like synoviocytes (FLS) was then examined. Flow cytometry on permeabilized cells showed that RA FLS constitutively express p53 protein. Western blots showed that RA FLS expressed significantly more p53 than either OA FLS or dermal fibroblasts. Immunohistochemistry of FLS cultured in chamber slides localized the p53 to the cytoplasm of most resting FLS, with nuclear staining in only 10.7 +/- 2.4%. Exposure to hydrogen peroxide for increased nuclear staining to 70.7 +/- 12.8% after 8 hours (P = 0.003). These data indicate that p53 is overexpressed in RA ST in the intimal lining, which is the primary site of DNA damage, and is constitutively expressed by FLS.

Prostaglandins increase proMMP-1 and proMMP-3 secretion by human ciliary smooth muscle cells

PURPOSE

The mechanism by which prostaglandin(PG)F2 alpha increases uveoscleral outflow and lowers intraocular pressure in primates is not known. In cultured human ciliary muscle cells, PGF2 alpha induces the expression of the protooncogene c-fos which is known to induce the transcription of genes such as matrix metalloproteinase-1 (MMP-1) and MMP-3 in other cell systems. As these enzymes are initially secreted as proenzymes, the present study was undertaken to determine if PG treatment induces ciliary muscle cells to secrete either proMMP-1 or proMMP-3.

METHODS

Human ciliary smooth muscle cells were grown to confluence in monolayer cell cultures and then treated with PGF2 alpha, 17-phenyltrinor-PGF2 alpha, or 11-deoxy-PGE1. Medium harvested at various times after treatment was assayed for proMMP-1 and proMMP-3 content using sandwich ELISAs.

RESULTS

Three days after adding 10 nM PGF2 alpha, proMMP-1 and proMMP-3, concentrations in the culture medium were increased by 254 +/- 33% (mean +/- SE) and 128 +/- 13%, respectively. Compared with vehicle controls, 24 h treatment with 200 nM PGF2 alpha, 17-phenyltrinor-PGF2 alpha, or PGE1, increased proMMP-1 by 116 +/- 29%, 169 +/- 26%, and 273 +/- 16%, respectively. In parallel experiments, proMMP-3 was increased by 99 +/- 18%, 82 +/- 24%, and 214 +/- 16%, respectively.

CONCLUSIONS

These results suggest that induction of MMPs in situ following topical PG treatment may degrade ciliary muscle extracellular matrix and possibly contribute to increased uveoscleral outflow, as well.

Carbohydrate- and CD18-dependent neutrophil adhesion to cardiac myocytes: effects of adenosine

OBJECTIVE

Adenosine inhibits neutrophil adhesion and injury to isolated cardiac myocytes. In the present study, the contribution of selectin and CD18 interactions to neutrophil-myocyte adhesion and their sensitivity to adenosine were assessed.

METHODS

Activated human neutrophils and canine myocytes were incubated with inhibitors of CD18 or selectin binding, adenosine, or combinations of both for 30-50 min at 37 degrees C. Neutrophils were pretreated with 0.1 microM fMLP for 10 min to study L-selectin-independent adhesion. Adhesion was measured by phase contrast microscopy.

RESULTS

Anti-L-selectin mAb and the selectin-blocking carbohydrates sialyl Lewisx or mannose-6-phosphate, as well as anti-CD18 or anti-ICAM-1 mAbs, inhibited cell adhesion (by 84-99%, P < 0.05). CD11a, but not CD11b, was responsible for most of the CD18-mediated binding. An L-selectin-independent interaction between neutrophils and cardiac myocytes was observed that was delayed (peak adhesion at 40-50 min, rather than 30 min), but still inhibited by anti-CD18 mAb (by 65 +/- 11%, P < 0.05) and carbohydrates (by 87-97%, each P < 0.05). Adenosine (100 nM) inhibited this late CD18-dependent/L-selectin-independent phase of adhesion (by 61 +/- 14%, P < 0.05). The combination of adenosine and anti-CD18 mAb was additive such that adhesion was completely blocked (P < 0.05, compared to either agent alone). Inhibition of adhesion by adenosine was prevented by the A2 antagonist, DMPX (100 nM), and mimicked by the A2 agonist, CGS-21680 (10 nM) or the adenosine regulating agents, acadesine (100 microM) or GP531 (10 microM).

CONCLUSION

Neutrophil-myocyte adhesion involved both L-selectin-dependent and L-selectin-independent carbohydrate binding as well as CD11a/CD18. Inhibition of adhesion by adenosine interferes with L-selectin-independent carbohydrate binding and possibly CD18.

Inhibition of synoviocyte collagenase gene expression by adenosine receptor stimulation

OBJECTIVE

To characterize the regulation of matrix metalloproteinases (MMPs) by adenosine.

METHODS

Cultured fibroblast-like synoviocytes (FLS) were stimulated with interleukin-1 (IL-1) in the presence or absence of adenosine receptor agonists. Immunoreactive MMPs were measured using specific enzyme-linked immunosorbent assays, and gene expression was assessed by Northern blot analysis.

RESULTS

The nonselective adenosine receptor agonist 5'-N-ethylcarboxamidoadenosine (NECA) decreased collagenase production by IL-1-stimulated synoviocytes from 196 +/- 28 ng/ml (mean +/- SEM) to 66 +/- 9 ng/ml (P < 0.001). There was minimal effect on stromelysin production (decrease from 107 +/- 16 ng/ml to 97 +/- 15 ng/ml). Selective adenosine receptor agonists implicated the A2b adenosine receptor in this activity, and reverse transcriptase-polymerase chain reaction studies confirmed that FLS express this receptor. Northern blot analysis demonstrated that the mechanism of action was pre-translational since NECA decreased collagenase, but not stromelysin or tissue inhibitor of metalloproteinases 1 (TIMP-1), messenger RNA levels. Cyclic AMP levels were increased by NECA, and a direct adenylate cyclase activator (forskolin) also suppressed collagenase gene expression. These data suggest that cAMP mediates the inhibitory effect of NECA on collagenase production.

CONCLUSION

Stimulation of the A2b receptor on FLS decreases collagenase gene expression, with little or no effect on stromelysin and TIMP-1. The combination of antiinflammatory and MMP-regulating properties of adenosine or adenosine-regulating agents suggest that treatment based on this approach might be useful in rheumatoid arthritis.

Inhibition of TNF-alpha expression by adenosine: role of A3 adenosine receptors

Adenosine agonists inhibit TNF-alpha production in macrophage and monocytes, but the mechanism is unknown. Therefore, we studied the human macrophage cell line U937 to determine the adenosine receptor subtypes responsible and the intracellular signaling mechanisms involved. The A1/A3 agonist N6-(4-amino-3-iodobenzyl)adenosine (I-ABA) decreased LPS-stimulated TNF-alpha protein production by 79 +/- 5% (p = 0.003). The mechanism was pretranslational, as adenosine receptor stimulation caused a marked decrease in TNF-alpha mRNA. IL-1 beta, IL-6, and IL-8 mRNA were not changed by adenosine agonists. The rank order of agonists as TNF-alpha inhibitors suggested that the A3 receptor might be involved (N6-(3-iodobenzyl)-9-[5-(methylcarbamoyl)-beta-D-ribofuranosyl] adenosine > 2-chloroadenosine > or = I-ABA > N6 benzyl 5'-N-ethylcarboxamidoadenosine (NECA) > NECA > CGS21680 > N6-cyclohexyladenosine), and this was supported by the fact that a mixed A1/A3 antagonist (xanthine amine congener) reversed the effect, whereas A1-specific (1,3-dipropyl-8-cyclopentylxanthine) and A2-specific (3,7-dimethyl-1-propargylxanthine) antagonists did not. Receptor signaling did not involve cAMP or protein kinase A, nor did it alter the activation and binding characteristics of the transcription factor NF-kappa B. However, the composition of the AP-1 transcription complex was altered by I-ABA. These data suggest that stimulation of the A3 adenosine receptor can alter the cytokine milieu by decreasing TNF-alpha. Adenosine agonists or adenosine regulating agents have potential therapeutic uses in acute and chronic inflammatory diseases.

Inhibition of TNF-alpha expression by adenosine: role of A3 adenosine receptors

Adenosine agonists inhibit TNF-alpha production in macrophage and monocytes, but the mechanism is unknown. Therefore, we studied the human macrophage cell line U937 to determine the adenosine receptor subtypes responsible and the intracellular signaling mechanisms involved. The A1/A3 agonist N6-(4-amino-3-iodobenzyl)adenosine (I-ABA) decreased LPS-stimulated TNF-alpha protein production by 79 +/- 5% (p = 0.003). The mechanism was pretranslational, as adenosine receptor stimulation caused a marked decrease in TNF-alpha mRNA. IL-1 beta, IL-6, and IL-8 mRNA were not changed by adenosine agonists. The rank order of agonists as TNF-alpha inhibitors suggested that the A3 receptor might be involved (N6-(3-iodobenzyl)-9-[5-(methylcarbamoyl)-beta-D-ribofuranosyl] adenosine &gt; 2-chloroadenosine &gt; or = I-ABA &gt; N6 benzyl 5'-N-ethylcarboxamidoadenosine (NECA) &gt; NECA &gt; CGS21680 &gt; N6-cyclohexyladenosine), and this was supported by the fact that a mixed A1/A3 antagonist (xanthine amine congener) reversed the effect, whereas A1-specific (1,3-dipropyl-8-cyclopentylxanthine) and A2-specific (3,7-dimethyl-1-propargylxanthine) antagonists did not. Receptor signaling did not involve cAMP or protein kinase A, nor did it alter the activation and binding characteristics of the transcription factor NF-kappa B. However, the composition of the AP-1 transcription complex was altered by I-ABA. These data suggest that stimulation of the A3 adenosine receptor can alter the cytokine milieu by decreasing TNF-alpha. Adenosine agonists or adenosine regulating agents have potential therapeutic uses in acute and chronic inflammatory diseases.

cDNA cloning and characterization of A3i, an alternatively spliced rat A3 adenosine receptor variant

A cDNA encoding variant form of the A3 adenosine (Ado) receptor was isolated from rat by reverse transcription of brain mRNA followed by PCR. The full-length receptor (A3i) cDNA encodes 337 amino acids and shares complete sequence identity with the rat A3 Ado receptor, except for the presence of a seventeen amino acid insert located in the second intracellular domain. In contrast to the rat A3 receptor, stable expression of A3i in CHO cells resulted in poor coupling to Gi proteins. Analysis of receptor transcripts by RT-PCR suggests that the A3 Ado receptor mRNAs are products of alternative splicing. Sequence analysis of A3 genomic DNA identified a 1.7 kb intron that is likely alternatively spliced to produce the A3 and A3i receptors.

Adenosine activates A2 receptors to inhibit neutrophil adhesion and injury to isolated cardiac myocytes

Inhibition of neutrophil-myocyte adhesion and adhesion-dependent myocyte injury by adenosine was evaluated using isolated TNF-alpha-activated canine cells. Adenosine inhibited adhesion of activated neutrophils to cardiac myocytes with an IC50 of 11 +/- 4 nM. Inhibition of neutrophil adhesion (92 +/-3% by 100 nM adenosine) led to inhibition of myocyte injury (by 90 +/- 6%, as assessed by dye exclusion). Inhibition of cell adhesion by adenosine was blocked by the A2 antagonist, 1,3-dimethyl-1-propylxanthine, but not by the A1 antagonist, 8-cyclopentyl-1,3-dipropylxanthine. Moreover, the A2 agonist, CGS21680 (2-[4-(2-carboxymethyl)phenethylamino]-5'-N-ethylcarboxamido adenosine), but not the A1 agonist, N6-cyclopentyladenosine, mimicked adenosine in preventing cell adhesion. These observations implicate the A2 receptor in the mechanism of inhibition of cell adhesion. pretreatment and washing of neutrophils, but not cardiac myocytes, with adenosine or CGS21680 led to inhibition of adhesion, suggesting that the neutrophil A2 receptor is the target of adenosine's action. In contrast, inhibition of cell adhesion by adenosine was poteniated by 8-cyclopentyl-1,3-dipropylxanthine (IC50 = 4 +/- 1 nM) and attenuated by N6-cyclopentyladenosine, suggesting that occupancy of A1 receptors can conversely increase cell adhesion. Neutrophil-myocyte adhesion was inhibited by acadesine (IC50 = 12 +/- 2 microM) also via an adenosine-dependent mechanism because it was blocked by 1,3-dimethyl-1-propylxanthine or adenosine deaminase, an enzyme that degrades any adenosine that is formed. Acadesine-induced inhibition if cell adhesion (83 +/- 4% by 100 microM) resulted in inhibition of myocyte injury (by 76 +/- 6%). Other adenosine-regulating agents, including the acadesine analogue, GP531 (5-amino-1 beta-D-(5-benzylamino-5-deoxyribofuranosyl) imidazole-4-carboxamide), and inhibitors of adenosine transport and intracellular metabolism also inhibited cell adhesion. These results indicate that exogenous or endogenous adenosine can inhibit neutrophil-myocyte adhesion and injury in cells activated with TNF-alpha by an A2-mediated mechanism. Although the predominant activity of adenosine is to attenuate cell adhesion, stimulation of A1 receptors has the opposite effect, i.e., to augment adhesive interactions.

Apoptosis in rheumatoid arthritis synovium

RA synovial tissue (ST) was studied to determine if and where apoptosis occurs in situ. Genomic DNA was extracted from 5 RA and 1 osteoarthritis ST samples. Agarose gel electrophoresis demonstrated DNA ladders characteristic for apoptosis from each tissue. In situ and labeling (ISEL) was used to identify DNA strand breaks consistent with apoptosis in frozen sections. 12 RA and 4 osteoarthritis ST were studied by ISEL and all were positive, but only 2 of 4 normal tissues were positive. The primary location of apopotic cells was the synovial lining. Some sublining cells were also positive, but lymphoid aggregate staining was conspicuously absent. Immunohistochemistry and ISEL were combined and showed that the lining cells with DNA strand breaks were mainly macrophages, although some fibroblastlike cells were also labeled. Sublining cells with fragmented DNA included macrophages and fibroblasts, but T cells in lymphoid aggregates, which expressed large amounts of bcl-2, were spared. DNA strand breaks in cultured fibroblastlike synoviocytes was assessed using ISEL. Apoptosis could be induced by actinomycin D, anti-fas antibody, IL-1, and TNF-alpha but not by IFN-gamma. Fas expression was also detected on fibroblast-like synoviocytes using flow cytometry. Therefore, DNA strand breaks occur in synovium of patients with arthritis. Cytokines regulate this process, and the cytokine profile in RA (high IL-1/TNF; low IFN-gamma) along with local oxidant injury might favor induction of apoptosis.

Adenosine activates A2 receptors to inhibit neutrophil adhesion and injury to isolated cardiac myocytes

Inhibition of neutrophil-myocyte adhesion and adhesion-dependent myocyte injury by adenosine was evaluated using isolated TNF-alpha-activated canine cells. Adenosine inhibited adhesion of activated neutrophils to cardiac myocytes with an IC50 of 11 +/- 4 nM. Inhibition of neutrophil adhesion (92 +/-3% by 100 nM adenosine) led to inhibition of myocyte injury (by 90 +/- 6%, as assessed by dye exclusion). Inhibition of cell adhesion by adenosine was blocked by the A2 antagonist, 1,3-dimethyl-1-propylxanthine, but not by the A1 antagonist, 8-cyclopentyl-1,3-dipropylxanthine. Moreover, the A2 agonist, CGS21680 (2-[4-(2-carboxymethyl)phenethylamino]-5'-N-ethylcarboxamido adenosine), but not the A1 agonist, N6-cyclopentyladenosine, mimicked adenosine in preventing cell adhesion. These observations implicate the A2 receptor in the mechanism of inhibition of cell adhesion. pretreatment and washing of neutrophils, but not cardiac myocytes, with adenosine or CGS21680 led to inhibition of adhesion, suggesting that the neutrophil A2 receptor is the target of adenosine's action. In contrast, inhibition of cell adhesion by adenosine was poteniated by 8-cyclopentyl-1,3-dipropylxanthine (IC50 = 4 +/- 1 nM) and attenuated by N6-cyclopentyladenosine, suggesting that occupancy of A1 receptors can conversely increase cell adhesion. Neutrophil-myocyte adhesion was inhibited by acadesine (IC50 = 12 +/- 2 microM) also via an adenosine-dependent mechanism because it was blocked by 1,3-dimethyl-1-propylxanthine or adenosine deaminase, an enzyme that degrades any adenosine that is formed. Acadesine-induced inhibition if cell adhesion (83 +/- 4% by 100 microM) resulted in inhibition of myocyte injury (by 76 +/- 6%). Other adenosine-regulating agents, including the acadesine analogue, GP531 (5-amino-1 beta-D-(5-benzylamino-5-deoxyribofuranosyl) imidazole-4-carboxamide), and inhibitors of adenosine transport and intracellular metabolism also inhibited cell adhesion. These results indicate that exogenous or endogenous adenosine can inhibit neutrophil-myocyte adhesion and injury in cells activated with TNF-alpha by an A2-mediated mechanism. Although the predominant activity of adenosine is to attenuate cell adhesion, stimulation of A1 receptors has the opposite effect, i.e., to augment adhesive interactions.

Anti-inflammatory effects of an adenosine kinase inhibitor. Decreased neutrophil accumulation and vascular leakage

Adenosine inhibits neutrophil function, but also causes cardiovascular side effects when administered systemically. To regulate local adenosine concentrations and minimize toxicity, a novel adenosine kinase inhibitor, GP-1-515, was tested in several acute inflammation models in rats. GP-1-515 inhibited carrageenan-induced rat paw swelling in a dose-dependent manner (maximum inhibition, 47 +/- 3%). In a rat skin lesion model, GP-1-515 significantly reduced cutaneous neutrophil infiltration following an intradermal injection of carrageenan or zymosan-activated plasma, or induction of a reverse passive Arthus reaction. This action appeared to be mediated by endogenous adenosine, inasmuch as a specific A2 adenosine receptor antagonist reversed the effect. GP-1-515 also decreased vascular leakage induced by carrageenan (which is partly neutrophil dependent) and by the neutrophil-independent mediators histamine and bradykinin. Inhibition of leakage was reversed by co-administration of adenosine receptor antagonist. Treatment with anti-inflammatory doses of GP-1-515 had no effect on heart rate or blood pressure. In conclusion, GP-1-515 significantly reduced both neutrophil infiltration and vascular leakage through the release of endogenous adenosine without evidence of cardiovascular side effects.

Anti-inflammatory effects of an adenosine kinase inhibitor. Decreased neutrophil accumulation and vascular leakage

Adenosine inhibits neutrophil function, but also causes cardiovascular side effects when administered systemically. To regulate local adenosine concentrations and minimize toxicity, a novel adenosine kinase inhibitor, GP-1-515, was tested in several acute inflammation models in rats. GP-1-515 inhibited carrageenan-induced rat paw swelling in a dose-dependent manner (maximum inhibition, 47 +/- 3%). In a rat skin lesion model, GP-1-515 significantly reduced cutaneous neutrophil infiltration following an intradermal injection of carrageenan or zymosan-activated plasma, or induction of a reverse passive Arthus reaction. This action appeared to be mediated by endogenous adenosine, inasmuch as a specific A2 adenosine receptor antagonist reversed the effect. GP-1-515 also decreased vascular leakage induced by carrageenan (which is partly neutrophil dependent) and by the neutrophil-independent mediators histamine and bradykinin. Inhibition of leakage was reversed by co-administration of adenosine receptor antagonist. Treatment with anti-inflammatory doses of GP-1-515 had no effect on heart rate or blood pressure. In conclusion, GP-1-515 significantly reduced both neutrophil infiltration and vascular leakage through the release of endogenous adenosine without evidence of cardiovascular side effects.

Inhibition of neutrophil adhesion by adenosine and an adenosine kinase inhibitor. The role of selectins

Adenosine and adenosine analogues exhibit anti-inflammatory effects in vitro and in vivo, but their usefulness is limited by profound cardiovascular side effects. Therefore, we synthesized inhibitors of an enzyme involved in adenosine metabolism, adenosine kinase (AK) (EC 2.7.1.20), to enhance endogenous adenosine concentrations at sites of inflammation. GP-1-515 (4-amino-1-(5-amino-5-deoxy-1-beta-D- ribofuranosyl)-3-bromo-pyrazolo[3,4-d]pyrimidine), a novel AK inhibitor, decreased adhesion of activated human neutrophils to cultured endothelial cell monolayers by increasing local adenosine levels. The mechanism of inhibition in this assay seemed to involve selectin blockade and was independent of the beta 2 integrins. GP-1-515 and 2-chloroadenosine (a nonmetabolizable adenosine analogue) had no effect on the surface expression or shedding of adhesion molecules. An agent that disrupts the cytoskeleton, cytochalasin B, mimicked the effect of adenosine on cell adhesion. Interactions between L-selectin and the neutrophil cytoskeleton might be altered by adenosine and could contribute to adenosine-mediated adhesion inhibition.

Inhibition of neutrophil adhesion by adenosine and an adenosine kinase inhibitor. The role of selectins

Adenosine and adenosine analogues exhibit anti-inflammatory effects in vitro and in vivo, but their usefulness is limited by profound cardiovascular side effects. Therefore, we synthesized inhibitors of an enzyme involved in adenosine metabolism, adenosine kinase (AK) (EC 2.7.1.20), to enhance endogenous adenosine concentrations at sites of inflammation. GP-1-515 (4-amino-1-(5-amino-5-deoxy-1-beta-D- ribofuranosyl)-3-bromo-pyrazolo[3,4-d]pyrimidine), a novel AK inhibitor, decreased adhesion of activated human neutrophils to cultured endothelial cell monolayers by increasing local adenosine levels. The mechanism of inhibition in this assay seemed to involve selectin blockade and was independent of the beta 2 integrins. GP-1-515 and 2-chloroadenosine (a nonmetabolizable adenosine analogue) had no effect on the surface expression or shedding of adhesion molecules. An agent that disrupts the cytoskeleton, cytochalasin B, mimicked the effect of adenosine on cell adhesion. Interactions between L-selectin and the neutrophil cytoskeleton might be altered by adenosine and could contribute to adenosine-mediated adhesion inhibition.