Stimulation of macrophages with endotoxin and/or cytokines is responsible for the expression of the inducible isoform of nitric oxide synthase (iNOS). Because macrophages are exposed to low pH within the microenvironment of inflammatory lesions, the potential role of acidic pH as an additional regulator of iNOS was investigated. Substitution of the culture medium of rat peritoneal macrophages at pH 7.4 with medium at pH 7.0 up-regulated iNOS activity, as reflected by a 2.5-fold increase in nitrite accumulation. The increase in iNOS activity was associated with a similar increase in iNOS mRNA expression that reflected an increase in iNOS mRNA synthesis rather than stability. Low environmental pH-induced iNOS gene transcription involved the activation of nuclear factor-B (NF-B) transcription factor since exposure of macrophages to low environmental pH both increased NF-B binding activity in the nucleus and enhanced NF-B-driven reporter gene expression. In addition, treatment of macrophages with pyrrolidine dithiocarbamate or n-acetyl-leucinyl-leucinyl-norleucinal, two drugs preventing NF-B translocation to the nucleus, canceled low pH-induced nitrite accumulation. The overall mechanism required the synthesis of tumor necrosis factor ␣ (TNF␣). Indeed, 1) elevated TNF␣ bioactivity was observed in the medium of macrophages exposed to pH 7.0, and 2) incubation of macrophages with a neutralizing anti-TNF␣ antibody impaired both NF-B activation and nitrite accumulation in response to acid challenge. In summary, exposure of macrophages to acidic microenvironment in inflammatory lesions leads to the up-regulation of iNOS activity through the activation of NF-B.Acidosis is a hallmark of both ischemia and inflammation processes. The decrease of pH in tissue ischemia is secondary to the release of H ϩ during ATP hydrolysis and to the accumulation of CO 2 (1). The acidic environment in inflammatory lesions and abscesses (2) is due to increased metabolic acid generation during cell activation. This originates primarily from the hexose monophosphate shunt, by the dissociation of hydrated CO 2 (3).In most cases, acidosis occurs along with nitric oxide (NO) 1 generation. In ischemia, NO generation is due in one part to the acidification and reduction of the large pool of nitrite present within the tissue (4). In inflammatory processes, macrophage exposure to bacterial lipopolysaccharide (LPS) or cytokines such as tumor necrosis factor ␣ (TNF␣) and interferon-␥ (IFN-␥) causes the expression of the inducible isoform of NO synthase (NOS II or iNOS) that is responsible for high output production of NO (5). The expression of iNOS is regulated mainly at the transcriptional level. Analyses of the murine iNOS promoter have shown the presence of numerous consensus sequences for the binding of transcription factors (6, 7), of which nuclear factor-B (NF-B) (8), interferon regulatory factor-1 (IRF-1) (9), and signal transducer and activator of transcription (STAT) 1␣ (10) are functionally important for iNOS induction. NF-B is composed of a p...

Catecholamines have been shown to inhibit some aspects of macrophage activation through a beta receptor-dependent mechanism. This study was undertaken to analyze the effects of isoproterenol, a specific beta-adrenergic agonist, on the synthesis of interleukin-10 (IL-10), a major macrophage-deactivating factor. Isoproterenol increased IL-10 release from lipopolysaccharide-(LPS)-activated mouse peritoneal macrophages in a dose-dependent manner. A significant effect was already observed with 1 microM isoproterenol, while a 4.5-fold increase was achieved with 10 microM. This increase was observed only if macrophages were exposed to isoproterenol for at least 2 h before LPS challenge. It was apparent within 0.5 h and persisted through 24 h at all the LPS concentrations used. A similar increase was observed at the IL-10 mRNA level, as judged by enzyme-linked immunosorbent assay-polymerase chain reaction. The macrophage response to isoproterenol that led to cyclic AMP accumulation was markedly inhibited by H-89, a potent inhibitor of protein kinase A. These data suggest the involvement of cyclic AMP in the regulation of IL-10 synthesis by isoproterenol. IL-10 was in turn partly responsible for a reduction in tumor necrosis factor-alpha synthesis. In vivo, the administration of oxprenolol, a beta-receptor antagonist, significantly reduced serum IL-10 levels 90 min after LPS challenge. Thus, the present study provides the first evidence that endogenous catecholamines are of critical importance in determining the magnitude of the IL-10 response in experimental endotoxemia.

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Inflammatory processes within the glomerulus are switched off by the local generation of anti-inflammatory mediators. These mediators include eicosanoids (e.g., lipoxins), anti-inflammatory cytokines (interleukins 4 and 13), antagonists of proinflammatory cytokines (interleukin 1 receptor antagonist), neuropoietic cytokines (leukemia inhibitory factor and interleukin 6), as well as deactivators of inflammatory macrophages (transforming growth factor beta and interleukin 10). They limit the effects of proinflammatory mediators by inhibiting their production, stability, or function. Recent attempts to reduce inflammatory lesions in experimental glomerulonephritis have focused on upregulating the expression of these anti-inflammatory mediators by using protein or gene transfer. In particular administration of interleukin 4, interleukin 1 receptor antagonist, leukemia inhibitory factor, or interleukin 10 has been shown to be effective in the treatment of nephrotoxic nephritis. Of all the mediators already tested, interleukin 10 has the greatest potential because of its strong anti-inflammatory effects and weak adverse effects.