Faculty Bibliography

It was recently reported that sera from patients with systemic lupus erythematosus contain antibodies reactive with the second extracellular loop of the serotoninergic 5-HT(4) receptor expressed in the human heart. This antibody response was associated with antibodies to 52kD SSA/Ro, a reactivity prevalent in mothers of children with congenital heart block (CHB). The current study was undertaken to determine whether the 5-HT(4) receptor is a target of the immune response in these mothers. Initial experiments demonstrated mRNA expression of the 5-HT(4) receptor in the human foetal atrium. Electrophysiologic studies established that human foetal atrial cells express functional 5-HT(4) receptors. Sera from 116 mothers enrolled in the Research Registry for Neonatal Lupus, whose children have CHB, were evaluated. Ninety-nine (85%) of these maternal sera contained antibodies to SSA/Ro, 84% of which were reactive with the 52kD SSA/Ro component by immunoblot. None of the 116 sera were reactive with the peptide spanning aa165-185 of the serotoninergic receptor. Rabbit antisera which recognized this peptide did not react with 52kD SSA/Ro or peptide aa365-382 in the C terminus. Although 5-HT(4) receptors are present and functional in the human foetal heart, maternal antibodies to the 5-HT(4) receptor are not associated with the development of CHB

Articular chondrocyte production of nitric oxide (NO) and other inflammatory mediators, such as eicosanoids and cytokines, are increased in human osteoarthritis. The excessive production of nitric oxide inhibits matrix synthesis and promotes its degradation. Furthermore, by reacting with oxidants such as superoxide anion, nitric oxide promotes cellular injury and renders the chondrocyte susceptible to cytokine-induced apoptosis. PGE(2) exerts anabolic and catabolic effects on chondrocytes, depending on the microenvironment and physiologic condition. The increased expression of inducible NOS (iNOS) and cyclo-oxygenase-2 (COX-2) in OA chondrocytes is largely due to the increased expression of pro-inflammatory cytokines, particularly IL-1, which act in an autocrine/paracrine fashion to perpetuate a catabolic state that leads to progressive destruction of articular cartilage. The initiating factors for the production of inflammatory mediators include altered biomechanical forces; their continued production may be augmented by an increase in extracellular matrix proteins acting through ligation of surface integrins

Nitric oxide (NO) is synthesized via the oxidation of arginine by a family of nitric oxide synthases (NOS), which are either constitutive (ie. endothelial (ec)NOS and neuronal (nc)NOS) or inducible (iNOS). The production of nitric oxide plays a vital role in the regulation of physiological processes, host defence, inflammation and immunity. Pro-inflammatory effects include vasodilation, oedema, cytotoxicity and the mediation of cytokine-dependent processes that can lead to tissue destruction. Nitric oxide-dependent tissue injury has been implicated in a variety of rheumatic diseases, including systemic lupus erythematosus (SLE), rheumatoid arthritis and osteoarthritis. Conversely, the production of NO by endothelial cell NOS may serve a protective, or anti-inflammatory, function by preventing the adhesion and release of oxidants by activated neutrophils in the microvasculature. In this chapter we describe the multifaceted role of nitric oxide in inflammation and address the potential therapeutic implications of NOS inhibition

In this report, a protocol for the preparation of the hydrochloride of S-nitroso-L-cysteine ethyl ester (SNCEE.HCl; 2) is presented. The synthesis of 2 has been targeted because S-nitroso-L-cysteine (SNC; 2b), which is extensively used for trans-S-nitrosation of thiol-containing proteins, has a limited ability of crossing cellular membranes. The nitrosothiol 2 was prepared via direct S-nitrosation of the hydrochloride of L-cysteine ethyl ester (CEE.HCl; 1a) with ethyl nitrite. 2 is relatively stable in crystal form and when neutralized to SNCEE (2a) in aqueous solutions treated with chelators of metal ions. Traces of metal ions, however, triggered the decomposition of 2a to nitric oxide and a S-centered radical, which were detected by ESR spectrometry. In contrast to 2b, 2a is a lipophilic compound that was taken up by human neutrophils. The latter process was paralleled by inhibition of the NADPH oxidase-dependent generation of superoxide anion radicals, presumably via reaction(s) of intracellular trans-S-nitrosation. Intracellular accumulation of S-nitrosothiols was observed with 2a but not with 2b. It is expected that the use of 2a will be advantageous when intracellular reactions of trans-S-nitrosation are to be studied

Objective We have demonstrated in bovine chondrocytes that nitric oxide (NO) mediates IL1 dependent apoptosis under conditions of oxidant stress. This process is accompanied by activation of c-Jun NH2-terminal kinase (JNK; also called stress-activated protein kinase). In these studies we examined activation of JNK in explant cultures of human osteoarthritic cartilage obtained at joint replacement surgery and we characterized the role of peroxynitrite to act as an upstream trigger.Design A novel technique to isolate chondrocyte proteins (<10% of total cartilage protein) from cartilage specimens was developed. It was used to analyse JNK activation by a western blot technique. To examine the hypothesis that chondrocyte JNK activation is a result of increased peroxynitrite, in vitro experiments were performed in which cultured chondrocytes were incubated with this oxidant.Results Activated JNK was detected in the cytoplasm of osteoarthritis (OA) affected chondrocytes but not in that of controls. In vitro, chondrocytes produce NO and superoxide anion. IL-1 (48 h), which induces nitric oxide synthase, resulted in an activation of JNK; this effect was reversed by N-monomethylarginine (NMA). TNFalpha treated chondrocytes at 48 h produce superoxide anion (EPR method). Exposure of cells to peroxynitrite led to an accumulation of intracellular oxidants, in association with JNK activation and cell death by apoptosis.Conclusion We suggest that JNK activation is among the IL-1 elicited responses that injure articular chondrocytes and this activation of JNK is dependent on intracellular oxidant formation (including NO peroxynitrite). In addition, the extraction technique here described is a novel method that permits the quantitation and study of proteins such as JNK involved in the signaling pathways of chondrocytes within osteoarthritic cartilage.

OBJECTIVE: In flares of systemic lupus erythematosus (SLE), endothelial cells (EC; activated by immune stimuli) are potential participants in the inflammatory processes that contribute to tissue damage. Accordingly, elevated levels of circulating endothelial cells (CEC) may be a marker for vascular injury. This study was undertaken to examine the possibility that stimulated EC are found in the circulation in patients with active SLE. METHODS: The study cohort included 38 patients with SLE and 16 healthy controls. Immunostaining was performed on mononuclear isolates, using mouse P1H12 (endothelial-specific antibody) and rabbit antinitrotyrosine (a 'footprint' of a reactive form of nitric oxide [peroxynitritel). RESULTS: Levels of CEC were significantly higher in patients with active SLE compared with those in healthy controls (mean +/- SEM 32+/-7/ml versus 5+/-2/ml; P = 0.0028) and were correlated positively with plasma C3a in these patients (r = 0.81, P = 0.0008). Furthermore, CEC from these patients expressed an activated phenotype, as indicated by staining for nitrotyrosine. CONCLUSION: Elevated levels of CEC observed in patients with active SLE may represent a marker of endothelial injury. The activated phenotype of these cells suggests that they may be capable of further potentiating vascular injury by the production of inflammatory and prothrombotic mediators and engaging in heterotypic aggregation with neutrophils or platelets

Despite the near universal association of congenital heart block and maternal Abs to SSA/Ro and SSB/La, the intracellular location of these Ags has made it difficult to substantiate their involvement in pathogenicity. To define whether components of the SSA/Ro-SSB/La complex, which translocate during apoptosis, are indeed accessible to extracellular Abs, two approaches were taken: immunoprecipitation of surface biotinylated proteins and scanning electron microscopy. Human fetal cardiocytes from 16-24-wk abortuses were cultured and incubated with staurosporine to induce apoptosis. Surface biotinylated 48-kDa SSB/La was reproducibly immunoprecipitated from apoptotic, but not nonapoptotic cardiocytes. Surface expression of SSA/Ro and SSB/La was further substantiated by scanning electron microscopy. Gold particles (following incubation with gold-labeled sera containing various specificities of anti-SSA/Ro-SSB/La Abs and murine mAb to SSB/La and 60-kDa SSA/Ro) were consistently observed on early and late apoptotic cardiocytes. No particles were seen after incubation with control antisera. To evaluate whether opsonized apoptotic cardiocytes promote inflammation, cells were cocultured with macrophages. Compared with nonapoptotic cardiocytes or apoptotic cardiocytes incubated with normal sera, apoptotic cardiocytes preincubated with affinity-purified Abs to SSB/La, 52-kDa SSA/Ro, or 60-kDa SSA/Ro increased the secretion of TNF-alpha from cocultured macrophages. In summary, apoptosis results in surface accessibility of all SSA/Ro-SSB/La Ags for recognition by circulating maternal Abs. It is speculated that in vivo such opsonized apoptotic cardiocytes promote an inflammatory response by resident macrophages with damage to surrounding conducting tissue

OBJECTIVE: Nitric oxide (NO) is induced by exposure of endothelial cells (EC) to acetylcholine, where it acts in a paracrine manner to relax smooth muscle and as a defensive molecule to inhibit the adhesion of leukocytes to EC. The mechanism(s) of the antiadhesive properties of constitutive NO are poorly understood. In these studies, we found that NO induced by acetylcholine exerts autocrine effects, which interfere with normal adhesion mechanisms. METHODS: The function of the adhesion molecule intercellular adhesion molecule 1 (CD54) of EC was measured using latex beads coated with antibody to CD54 as a model for CD54 ligation by the leukocyte beta2 integrin. Recruitment of filamentous actin (F-actin) and of the signaling molecule vasodilator-stimulated phosphoprotein (VASP) was measured by immunofluorescence microscopy. RESULTS: Exposure of EC to anti-CD54 beads induced the subplasmalemmal assembly of F-actin and VASP. Acetylcholine blocked the anti-CD54 bead-induced translocation of F-actin and VASP; this effect was reversed by inhibition of NO production. The NO action did not interfere with binding, but completely inhibited the assembly of the focal activation complex, which we believe is necessary for firm heterotypic adhesion between leukocyte and EC. Further studies indicated that the NO effect was due to its capacity to raise cGMP. Platelet endothelial cell adhesion molecule 1 (CD31, also implicated in leukocyte adhesion) did not mimic CD54 responses. CONCLUSION: These results indicate that the ligation of endothelial cell CD54 induces the assembly of subplasmalemmal F-actin and the recruitment of VASP. NO derived from constitutive nitric oxide synthase acts to disrupt these CD54-elicited endothelial cell responses. This action may protect vascular endothelium from leukocyte-mediated injury

It is recognized that there is molecular cross-talk between the inflammatory mediators NO and PGs that may regulate tissue homeostasis and contribute to pathophysiological processes. However, the literature is divided with respect to whether NO activates or inhibits PG production. In this study, we sought to determine whether conflicting observations could be accounted for by divergent effects of NO on the two cyclooxygenase (COX) isoforms. Exposure of resting macrophages to NO (30 microM) enhanced PGE2 release by 4. 5-fold. This enhancement was inhibited by indomethacin but not by the COX-2 selective inhibitor NS398. To separate the activation of phospholipase A2 and COX, we performed experiments using fibroblasts derived from COX-1-deficient or COX-2-deficient mice. These cells exhibit increased basal PG production, which is due to a constitutively stimulated cytosolic phospholipase A2 and enhanced basal expression of the remaining COX isozyme. The exposure of COX- 2-deficient cells to exogenous NO (10 microM) resulted in a 2.4-fold increase of PGE2 release above controls. Further studies indicated that NO stimulated PGE2 release in COX-2-deficient cells, without altering COX-1 mRNA or protein expression. In contrast, NO inhibited COX-2-derived PGE2 production in both LPS-stimulated macrophages and COX-1 knockout cells. This inhibition was associated with both decreased expression and nitration of COX-2. Thus, these studies demonstrate divergent effects of NO on the COX isoforms. The regulation of PGE production by NO is therefore complex and will depend on the local environment in which these pleiotropic mediators are produced