Intrarenal urothelium proliferation: an unexpected early event following ischemic injury

Identification of renal cell progenitors and recognition of the events contributing to cell regeneration following ischemia-reperfusion injury (IRI) are a major challenge. In a mouse model of unilateral renal IRI, we demonstrated that the first cells to proliferate within injured kidneys were urothelial cells expressing the progenitor cell marker cytokeratin 14. A systematic cutting of the injured kidney revealed that these urothelial cells were located in the deep cortex at the corticomedullary junction in the vicinity of lobar vessels. Contrary to multilayered bladder urothelium, these intrarenal urothelial cells located in the upper part of the medulla constitute a monolayered barrier and express among uroplakins only uroplakin III. However, like bladder progenitors, intrarenal urothelial cells proliferated through a FGF receptor-2 (FGFR2)-mediated process. They strongly expressed FGFR2 and proliferated in vivo after recombinant FGF7 administration to control mice. In addition, IRI led to FGFR phosphorylation together with the selective upregulation of FGF7 and FGF2. Conversely, by day 2 following IRI, renal urothelial cell proliferation was significantly inhibited by FGFR2 antisense oligonucleotide administration into an intrarenal urinary space. Of notice, no significant migration of these early dividing urothelial cells was detected in the cortex within 7 days following IRI. Thus our data show that following IRI, proliferation of urothelial cells is mediated by the FGFR2 pathway and precedes tubular cell proliferation, indicating a particular sensitivity of this structure to changes caused by the ischemic process.

Transforming growth factor-beta inhibits interleukin-10 synthesis by human monocytic cells

Transforming growth factor-beta (TGF-beta1) enhances interleukin-10 (IL-10) synthesis by mouse monocytes/macrophages, suggesting a potential role of IL-10 in mediating some of the anti-inflammatory properties of TGF-beta1. Since differences exist between the transcriptional regulation of human and mouse IL-10, the studies reported here examined whether TGF-beta1 up-regulated IL-10 production by human monocytes/macrophages as well. Exposure of PMA-differentiated U-937 promonocytic cells to TGF-beta1 resulted in an unexpected, dose-dependent decrease in IL-10 production as assessed by specific ELISA. TGF-beta1 was effective when added at the time of the PMA stimulus or 6 hours after. In addition, TGF-beta1 suppressed induction of IL-10 by three different stimuli other than PMA. TGF-beta1 inhibition of IL-10 protein release was associated with proportional changes in IL-10 mRNA accumulation as assessed by quantitative kinetic ELISA PCR. This would result from a decrease in IL-10 gene transcription as TGF-beta1 did not affect IL-10 mRNA stability, and TGF-beta1 limited the luciferase activity in cells transfected with reporter gene constructs containing 1,308 bp of the 5' non-coding sequence of human IL-10 gene. Blocking tumour necrosis factor-alpha (TNF-alpha) with neutralizing anti-TNF-alpha antibody did not modify the response to TGF-beta1, indicating the involvement of TNF-alpha-independent mechanisms in the overall process. Thus, the present study provides the first evidence that TGF-beta1 prevents IL-10 production by human monocytic cells at a transcriptional level.

Cytokines and hormones with anti-inflammatory effects: new tools for therapeutic intervention

The inflammation that is involved in the development of glomerulonephritis is tightly regulated by the expression of anti-inflammatory factors. These include circulating hormones, such as glucocorticoids, and mediators that are produced by intrinsic cells and infiltrating leucocytes. The present review focuses on these anti-inflammatory factors, summarizing in particular their activities in existing models of glomerulonephritis. In addition, experimental evidence is presented that anti-inflammatory mediators are able to increase glucocorticoid binding or signalling in target cells. These data help to explain the in-vivo efficacy of anti-inflammatory mediators, and offer a promising new avenue for therapeutic intervention.

Glomerulosclerosis in mice transgenic for human insulin-like growth factor-binding protein-1

BACKGROUND

The growth hormone (GH)/insulin-like growth factor (IGF) system is thought to participate in the glomerulosclerosis process. Because IGF-binding proteins (IGFBPs) modulate IGF actions and hence GH secretion, this study assessed whether mice transgenic for human IGFBP-1 have altered susceptibility to glomerulosclerosis.

METHODS

A line of transgenic mice that express human IGFBP-1 mRNA in the liver under the control of the alpha1-antitrypsin promoter has been obtained, and morphological changes in the kidney tissue were assessed. Glomerulosclerosis was identified using light microscopy, light microscopic morphometry, and electron microscopy. Extracellular matrix components were analyzed by immunohistochemistry.

RESULTS

There was a marked increase in mesangial extracellular matrix area in homozygous transgenic mice at three months of age as compared with heterozygous transgenic mice and nontransgenic littermates. These changes were not associated with alterations in glomerular volume or cellularity. The expansion of extracellular matrix area was related to a marked increase in laminin and type IV collagen and to the appearance of type I collagen.

CONCLUSIONS

These observations indicate that the enhanced expression of IGFBP-1 may result in the development of glomerulosclerosis without glomerular hypertrophy. The changes are potentially related to a decrease in IGF-I availability and/or to an IGF-I-independent role of IGFBP-1.

[Interactions between glucocorticoids and anti-inflammatory peptides]

Both pro- and anti-inflammatory mediators regulate the anti-inflammatory actions of glucocorticoids, in part by modifying the binding of glucocorticoids to specific receptors. For instance, somatostatin has been shown to increase glucocorticoid binding and signaling in macrophages. The mechanism of this regulation does not require an increased expression of glucocorticoid receptors but, rather, a stabilization of glucocorticoid receptor-associated heat shock protein 90. This is related to a decrease in calpain activity. Thus calpain inhibition may offer a new and exciting possibility for enhancing the anti-inflammatory efficiency of glucocorticoids.

Somatostatin increases glucocorticoid binding and signaling in macrophages by blocking the calpain-specific cleavage of Hsp 90

Somatostatin has direct anti-inflammatory actions and participates in the anti-inflammatory actions of glucocorticoids, but the mechanisms underlying this regulation remain poorly understood. The objective of this study was to evaluate whether somatostatin increases glucocorticoid responsiveness by up-regulating glucocorticoid receptor (GR) expression and signaling. Somatostatin promoted a time- and dose-dependent increase in [(3)H]dexamethasone binding to RAW 264.7 macrophages. Cell exposure to 10 nM somatostatin for 18 h promoted a 2-fold increase in the number of GR sites per cell without significant modification of the affinity. Analysis of GR heterocomplex components demonstrated that somatostatin increased the level of heat shock protein (Hsp) 90, whereas the level of GR remained almost unchanged. The increase in Hsp 90 was associated with a decrease in the cleavage of its carboxyl-terminal domain. Evidence for the involvement of calpain inhibition in this process was obtained by the demonstration that 1) somatostatin induced a dose-dependent decrease in calpain activity and 2) calpain inhibitors, calpain inhibitor I and calpeptin, both abolished the cleavage of Hsp 90 and induced a dose-dependent increase in [(3)H]dexamethasone binding. Increases in glucocorticoid binding after somatostatin treatment were associated with similar increases in the ability of GR to transactivate a minimal promoter containing two glucocorticoid response elements (GRE) and to interfere with the activation of nuclear factor-kappaB (NF-kappaB). Thus, the present findings indicate that somatostatin increases glucocorticoid binding and signaling by limiting the calpain-specific cleavage of GR-associated Hsp 90. This mechanism may represent a novel target for intervention to increase glucocorticoid responsiveness.

Reactive oxygen and nitrogen intermediates increase transforming growth factor-beta1 release from human epithelial alveolar cells through two different mechanisms

Transforming growth factor (TGF)-beta1 is a growth factor involved in the mechanisms of lung repair and fibrosis that follow inflammatory processes. We sought to examine the link between the generation of reactive oxygen intermediates (ROI) or reactive nitrogen intermediates (RNI) by inflammatory cells and the expression of TGF-beta1 by alveolar epithelial cells. Exposure of the A549 lung epithelial cell line to either an ROI generating system (xanthine and xanthine oxidase) or an RNI donor (S-nitroso-N-acetyl-penicillamine [SNAP]) promoted a time- and dose-dependent increase in TGF-beta1 release, as measured by a specific enzyme-linked immunosorbent assay. At the peak, the levels of TGF-beta1 were twice the control values. The induction of TGF-beta1 release by ROI was blunted by catalase and unaffected by superoxide dismutase, indicating the involvement of hydrogen peroxide. The response was also blunted by 5, 6-dichloro-1-beta-D-ribofuranosyl benzimidazole (DRB), a specific RNA polymerase II inhibitor, and accompanied by a corresponding increase in TGF-beta1 messenger RNA, as measured by quantitative/competitive reverse transcription polymerase chain reaction, suggesting the involvement of transcriptional mechanisms and possibly other downstream mechanisms. In contrast, RNI-induced TGF-beta1 release was unaffected by DRB and blunted by the protein synthesis inhibitor cycloheximide, suggesting the involvement of translational and post-translational mechanisms. This response required cyclic guanosine monophosphate (cGMP)- mediated processes because (1) immunoreactive cGMP accumulated in the culture medium of SNAP-treated cells; (2) SNAP-induced TGF-beta1 release was blunted by KT 5823, an inhibitor of cGMP-dependent protein kinase; and (3) similar increase in TGF-beta1 release was obtained by cell exposure to membrane-permeable dibutyryl-cGMP or to atrial natriuretic factor, a known agonist of particulate guanylate cyclase. These data suggest that in vitro exposure of human alveolar epithelial cells to ROI and RNI enhances TGF-beta1 release through different mechanisms. In vivo, this control may constitute a molecular link between inflammatory and fibrotic processes.

[Inflammatory mechanisms of renal fibrosis: glomerulonephritis]

Studies of glomerulonephritis models have shown that inflammatory reaction is responsible for the development of glomerulosclerosis and tubulo-interstitial sclerosis and, hence, for the progression to end stage renal failure. That macrophage accumulation and fibrosis extension are frequently not closely related events suggests that macrophages are not involved in progression process. Glomerular sclerosis is rather associated with the release of mediators from resident cells-mainly growth factors such as platelet-derived growth factor and transforming growth factor-beta--the synthesis and bioactivity of which are enhanced by inflammatory mediators. Tubulo-interstitial sclerosis is induced by inflammatory lesions of the glomerulus that lead to proteinuria. Indeed, reabsorption of proteins in proximal tubule triggers epithelial cells to release proinflammatory and prosclerotic mediators into the interstitium. New therapeutic approaches including gene transfer strategies are directed at suppressing the efficiency of such mediators.

Reduction of tumour necrosis factor alpha expression and signalling in peripheral blood mononuclear cells from patients with thalassaemia or sickle cell anaemia upon treatment with desferrioxamine

Recent evidence indicates that the rate of progression of the HIV-1 disease is significantly reduced in thalassaemia major patients upon treatment with high doses of desferrioxamine (DFX). The authors have previously demonstrated that in vitro exposure of mononuclear cells to DFX decreases the bioavailability of tumour necrosis factor alpha (TNF-alpha) which has a stimulatory effect on HIV-1 replication. In this study, therefore, TNF-alpha bioavailability from mononuclear cells isolated from 10 patients with thalassaemia or sickle cell anaemia given DFX as compared to 10 untreated subjects has been evaluated. Evidence is presented showing that DFX treatment reduces TNF-alpha bioavailability (P<0.05) by inhibiting its steady state (P<0.05) and by enhancing its inactivation through binding to soluble TNF-alpha receptor type II (P<0.05). We also show that DFX treatment limits the in vivo activation of NF-kappaB, a transcription factor involved in both TNF-alpha gene transcription and TNF-alpha signalling (P<0.005). We conclude that TNF-alpha bioavailability and signalling are impaired in patients upon DFX treatment. This mechanism may contribute to delayed progression of the HIV-1 infection in vivo.

Growth hormone and somatostatin in glomerular injury

Among other neuropeptides and neurohormones, growth hormone (GH) and somatostatin (SRIF) have been shown to modulate the development of glomerular injury in various renal diseases. In particular, GH is implicated in the induction of glomerular hypertrophy and sclerosis in partial nephrectomy and diabetic nephropathy. While GH effects on glomerular hypertrophy are likely mediated by insulin-like growth factor I (IGF-I), GH effects on glomerular sclerosis are independent of IGF-I. Those effects rather require multiple signaling pathways functioning in series, e.g. angiotensin II binding preceding transforming growth factor beta (TGF-beta) release, or pro-inflammatory factor release preceding repair/scarring processes. In contrast with GH, SRIF administration prevents the development of glomerular lesions in experimental diabetes, partial nephrectomy and immune glomerulonephritis. Inhibitory effects of SRIF on glomerular hypotrophy may be through a decrease in GH secretion and/or IGF-I expression or through a direct blockade of glomerular cell proliferation. The mechanisms underlying the anti-inflammatory effects of SRIF are most likely a deactivation of inflammatory cells related in part to an upregulated response of these cells to glucocorticoids. Additional studies will be required to further define the role of GH and SRIF in the development of glomerular injury and, hence, to identify new targets for a therapeutic approach in glomerular diseases.

[Polyuropolydipsic syndromes]

PROGNOSIS

Intracellular dehydration is the major risk in case of a polyuropolydipsic syndrome. Excepting osmotic polyuria, prognosis depends on a possibly progressive functional anomaly of the hypothalamopituitary axis.

PATHOPHYSIOLOGY

Polyuropolydipsia occurs when antidiuretic hormone (ADH) secretion is absent (central diabetes insipidis), the kidney does not respond to ADH (nephrogenic diabetes insipidus) or in case of physiological inhibition of ADH secretion (primary polydipsia).

EXPLORATION

Dynamic explorations are associated with radioimmunoassay of ADH. They are particularly useful in case of atypical diabetes insipidus and include the water restriction test and a study of the sensitivity to exogenous ADH (dDAVP). The results orient the etiologic diagnosis and allow an evaluation of the fluid intake required as a function of the maximal concentrating capacity of the kidneys.

TREATMENT OF CENTRAL DIABETES INSIPIDUS

Treatment is based on ADH analogs (dDAVP). The aim is to obtain a constant antidiuretic effect without hyponatremia or escape. In case of partial central diabetes insipidus, a non-hormone treatment using compounds which increase vasopressin release or its effect on the kidney can be proposed.

Low environmental pH is responsible for the induction of nitric-oxide synthase in macrophages. Evidence for involvement of nuclear factor-kappaB activation

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-kappaB (NF-kappaB) transcription factor since exposure of macrophages to low environmental pH both increased NF-kappaB binding activity in the nucleus and enhanced NF-kappaB-driven reporter gene expression. In addition, treatment of macrophages with pyrrolidine dithiocarbamate or n-acetyl-leucinyl-leucinyl-norleucinal, two drugs preventing NF-kappaB translocation to the nucleus, canceled low pH-induced nitrite accumulation. The overall mechanism required the synthesis of tumor necrosis factor alpha (TNFalpha). Indeed, 1) elevated TNFalpha bioactivity was observed in the medium of macrophages exposed to pH 7.0, and 2) incubation of macrophages with a neutralizing anti-TNFalpha antibody impaired both NF-kappaB 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-kappaB.

Neutrophil alveolitis in bronchioloalveolar carcinoma: induction by tumor-derived interleukin-8 and relation to clinical outcome

Tumor infiltrate, predominantly constituted by lymphocytes, may represent an important prognostic factor in bronchioloalveolar carcinoma (BAC), in addition to tumor extension and histological type. In the present study, we determined the presence, the origin, and the prognostic importance of neutrophils that also participate in leukocyte infiltrates of BAC. Neutrophil alveolitis was determined immunohistochemically in both lung biopsies and bronchoalveolar lavage (BAL) fluid samples from 29 patients with histologically proved BAC. The local expression of interleukin (IL)-8 was determined by immunohistochemical and immunoenzymatic techniques. Neutrophil counts were analyzed in relation to the clinical outcome of patients by the Kaplan-Meier method and Cox's univariate and stepwise multivariate models. Lymphocytes and neutrophils dominated the inflammatory cell population in the lower respiratory tract of patients with BAC. Neutrophils were located mainly in the alveolar lumen and seldom in alveolar wall whereas lymphocytes were exclusively present in alveolar wall. A relationship was observed between the number of neutrophils and the level of IL-8 in BAL fluid suggesting the involvement of that chemokine in neutrophil recruitment. The tumor cells were the predominant cells that appeared to express IL-8 by immunolocalization. The presence of increased numbers of neutrophils was significantly associated with a poorer outcome in patients with BAC (P = 0.02). In a multivariate analysis, the neutrophil percentage in BAL fluid was an independent predictor of clinical outcome. The risk of death was increased substantially (rate ratio, 5.2; 95% confidence interval, 1.1 to 24.7) among patients with BAL neutrophil percentage of > or = 39% (median of the distribution) as compared with the others. In BAC, neutrophils accumulate in the alveolar lumen. Elaboration of IL-8 by tumor cells may be responsible for this event, which is associated with a significantly higher risk of death.

Interleukin 10: a logical candidate for suppressing glomerular inflammation?

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.

Insulin-like growth factors and their binding proteins in pleural fluid

We investigated the expression and potential regulatory role of insulin-like growth factors (IGFs) and their specific binding proteins (BPs) in tuberculous and nontuberculous pleuritis. By using a radioimmunoassay after acid gel filtration chromatography, we found that mean concentrations of IGF-I were 211.9 +/- 20.2 microg/l and 203.2 +/- 31.1 microg/l in pleural fluid of 14 patients with tuberculous pleuritis and 9 patients with malignant pleuritis respectively. These values were near those in serum of the same patients (221.3 +/- 19.5 microg/l and 204.6 +/- 21.0 microg/l respectively). By using a specific protein-binding assay, we found that mean concentrations of IGF-II were 345.3 +/- 61.0 microg/l and 167.6 +/- 22.7 microg/l in tuberculous and malignant pleural effusions respectively. These values were significantly lower than those in serum of the same patients (628.3 +/- 79.0 microg/l, P<0.025 and 532.0 +/- 85.9 microg/l, P<0.025 respectively). Because bioavailability and bioactivity of IGFs may be regulated by their binding to IGFBPs, we studied IGFBP patterns in the pleural fluid of 6 patients with tuberculous pleuritis. As assessed by Western ligand blotting the levels of IGFBP-1 and IGFBP-2 were increased whereas those of IGFBP-3 were decreased in pleural fluid in comparison with serum. The decrease in IGFPB-3 levels reflected increased proteolysis, as assessed by Western immunoblotting. In spite of this presence of IGFBPs, IGFs could be responsible for the local biosynthesis of 1.25-dihydroxyvitamin D (1,25-(OH)2D) since pleural fluid levels of both IGF-I and IGF-II significantly correlated with those of 1,25-(OH)2D. These results indicate that IGFs are detectable in pleural fluid and may contribute to control the activity of 25-hydroxyvitamin D-1alpha hydroxylase in tuberculous pleuritis.

[Low extracellular pH has a role in the induction of NO synthase type 2 in macrophages]

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 low 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 upregulated 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. Low environmental pH-induced iNOS gene expression involved the activation of nuclear factor-kappa B (NF-kappa B) transcription factor since [1] exposure of macrophages to low environmental pH increased NF-kappa B binding activity in the nucleus, and [2] treatment of macrophages with pyrrolidine dithiocarbamate or n-acetyl-leucinyl-norleucinal, two drugs preventing NF-kappa B translocation to the nucleus, canceled low pH-induced nitrite accumulation. The overall mechanism required the synthesis of tumor necrosis factor-alpha (TNF-alpha). Indeed, [1] elevated TNF-alpha bioactivity was observed in the medium of macrophages exposed to pH 7.0, and [2] incubation of macrophages with a neutralizing anti-TNF-alpha antibody impaired both NF-kappa B activation and nitrite accumulation in response to acid challenge. In summary, exposure of macrophages to acidic microenvironment in inflammatory lesions leads to the upregulation of iNOS activity through the activation of NF-kappa B.

Regulation of interleukin-10 production by beta-adrenergic agonists

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.

Phenotypic and DNA relatedness between nematode symbionts and clinical strains of the genus Photorhabdus (Enterobacteriaceae)

Bacterial strains isolated from wide ranges of nematode hosts and geographic sources and strains isolated from human clinical specimens were used to assess the taxonomic structure of the genus Photorhabdus. The following two methods were used: DNA relatedness and phenotypic characterization. Analysis of the DNA relatedness data revealed that all of the strains studied were congeneric and that the genus Photorhabdus is, on the basis of DNA relatedness data, more homogeneous than the other genus of nematode-symbiotic bacteria, the genus Xenorhabdus. In contrast to previous reports, only two DNA relatedness groups were identified in the genus Photorhabdus. These groups corresponded to the symbiotic strains and the clinical strains. There appeared to be some subgroups within the symbiotic strain group on the basis of the interactions of the strains with nematodes, which corresponded to some extent with the DNA relatedness data. However, there were significant ambiguities in the DNA relatedness data, and this group could not be subdivided on the basis of DNA relatedness data or phenotypic data. The distinct functional differences within and between the DNA relatedness groups of symbiotic Photorhabdus strains indicated that there are biologically significant sub-groups within the genus Photorhabdus that cannot be defined at this time. Further investigation of the taxonomy of Photorhabdus by using different approaches and a suitably wide range of strains is recommended. However, it is clear that the clinical strains form a recognizable subgroup within the genus even though no formal subtaxon can be defined at this time.

Insulin activates nuclear factor kappa B in mammalian cells through a Raf-1-mediated pathway

We examined the effect of insulin on nuclear factor kappa B (NF-kappa B) activity in Chinese ovary (CHO) cells overexpressing wild-type (CHO-R cells) or -defective insulin receptors mutated at Tyr1162 and Tyr1163 autophosphorylation sites (CHO-Y2 cells). In CHO-R cells, insulin caused a specific, time-, and concentration-dependent activation of NF-kappa B. The insulin-induced DNA-binding complex was identified as the p50/p65 heterodimer. Insulin activation of NF-kappa B: 1) was related to insulin receptor number and tyrosine kinase activity since it was markedly reduced in parental CHO cells which proved to respond to insulin growth factor-1 and phorbol 12-myristate 13-acetate (PMA) activation, and was dramatically decreased in CHO-Y2 cells; 2) persisted in the presence of cycloheximide and was blocked by pyrrolidine dithiocarbamate, aspirin and sodium salicylate, three compounds interfering with I kappa B degradation and/or NF-kappa B.I kappa B complex dissociation; 3) was independent of both PMA-sensitive and atypical (zeta) protein kinases C; and 4) was dependent on Raf-1 kinase activity since insulin-stimulated NF-kappa B DNA binding activity was inhibited by 8-bromo-cAMP, a Raf-1 kinase inhibitor. Moreover, insulin activation of NF-kappa B-driven luciferase reporter gene expression was blocked in CHO-R cells expressing a Raf-1 dominant negative mutant. This is the first evidence that insulin activates NF-kappa B in mammalian cells through a post-translational mechanism requiring both insulin receptor tyrosine kinase and Raf-1 kinase activities.

Transforming growth factor-beta stimulates arginase activity in macrophages. Implications for the regulation of macrophage cytotoxicity

Macrophage arginine metabolism via nitric oxide (NO) synthase and arginase pathways reduces and enhances tumor cell proliferation, respectively. Transforming growth factor-beta (TGF-beta) has been shown to down-regulate the NO synthase pathway. The present study describes the effect of TGF-beta on the arginase pathway. TGF-beta up-regulated arginase activity in rat peritoneal macrophages as assessed by measuring the generation of [14C]urea from [14C]-L-arginine in the presence of NG-monomethyl-L-arginine (L-NMMA). The stimulation, which reached fivefold after a 48-h exposure of macrophages to 10 ng/ml TGF-beta, was due to reduction in Km value of arginase. TGF-beta-induced up-regulation of arginase activity led to the release of more polyamines, mainly putrescine. The role of this up-regulation on macrophage cytotoxicity toward L-929 tumor cells was analyzed in coculture experiments. Macrophages blunted DNA synthesis by L-929 cells as assessed by measuring the incorporation of [3H]TdR into the cells and the proportion of cells in the G2 phase. Addition of TGF-beta in the presence of L-NMMA permitted L-929 cells cocultured with macrophages to resume DNA synthesis. The mechanism responsible for this restoration was the up-regulation of arginase activity rather than the down-regulation of NO synthase activity since TGF-beta in the presence of L-NMMA failed to further reduce NO synthase activity whereas it still enhanced arginase activity; synthetic putrescine (1-10 microM) also blunted macrophage cytotoxicity toward L-929 cells. This is the first evidence that TGF-beta up-regulates arginase activity in macrophages and, hence, limits macrophage-dependent cytostasis.

Transforming growth factor-beta stimulates arginase activity in macrophages. Implications for the regulation of macrophage cytotoxicity

Macrophage arginine metabolism via nitric oxide (NO) synthase and arginase pathways reduces and enhances tumor cell proliferation, respectively. Transforming growth factor-beta (TGF-beta) has been shown to down-regulate the NO synthase pathway. The present study describes the effect of TGF-beta on the arginase pathway. TGF-beta up-regulated arginase activity in rat peritoneal macrophages as assessed by measuring the generation of [14C]urea from [14C]-L-arginine in the presence of NG-monomethyl-L-arginine (L-NMMA). The stimulation, which reached fivefold after a 48-h exposure of macrophages to 10 ng/ml TGF-beta, was due to reduction in Km value of arginase. TGF-beta-induced up-regulation of arginase activity led to the release of more polyamines, mainly putrescine. The role of this up-regulation on macrophage cytotoxicity toward L-929 tumor cells was analyzed in coculture experiments. Macrophages blunted DNA synthesis by L-929 cells as assessed by measuring the incorporation of [3H]TdR into the cells and the proportion of cells in the G2 phase. Addition of TGF-beta in the presence of L-NMMA permitted L-929 cells cocultured with macrophages to resume DNA synthesis. The mechanism responsible for this restoration was the up-regulation of arginase activity rather than the down-regulation of NO synthase activity since TGF-beta in the presence of L-NMMA failed to further reduce NO synthase activity whereas it still enhanced arginase activity; synthetic putrescine (1-10 microM) also blunted macrophage cytotoxicity toward L-929 cells. This is the first evidence that TGF-beta up-regulates arginase activity in macrophages and, hence, limits macrophage-dependent cytostasis.

Mesangial cell-derived interleukin-10 modulates mesangial cell response to lipopolysaccharide

Interleukin (IL)-10 is a novel cytokine produced by a variety of cells, including monocytes/macrophages, upon exposure to lipopolysaccharide (LPS). Recent observations indicate that, in turn, IL-10 exerts suppressive effects on macrophage response to LPS. Because mesangial cells are also a target for LPS, we have examined the potential role of IL-10 in the regulation of mesangial cell response to LPS. To this aim, we have studied the synthesis and the autocrine/paracrine function of IL-10 in cultured mouse mesangial cells. IL-10 mRNA expression and IL-10 protein secretion were determined by a reverse transcription polymerase chain reaction technique and a specific enzyme-linked immunosorbent assay, respectively. No IL-10 mRNA expression was detectable in unactivated cells. LPS induced IL-10 mRNA expression in a dose-dependent fashion (1 to 100 micrograms/ml). In addition, LPS induced IL-10 protein release that was both dose dependent (1 to 100 micrograms/ml) and time dependent (24 to 72 hours). We have also studied the effect of IL-10 on the production of inflammatory mediators by LPS-activated mouse mesangial cells. Whereas recombinant IL-10 inhibited the generation of tumor necrosis factor-alpha (TNF-alpha) and IL-1 beta by 90 and 60%, respectively, it did not affect the formation of nitric oxide-derived nitrite (NO2-) and nitrate (NO3-). As shown by the use of anti-IL-10 monoclonal antibody, endogenously produced IL-10 affected the generation of TNF-alpha but neither that of IL-1 beta nor that of NO2- and NO3-. Finally, we have examined whether conditions known to also reduce the generation of TNF-alpha modified the expression of IL-10. Of all the conditions tested, only the addition of desferrioxamine and transforming growth factor-beta were found to increase IL-10 release. Together, these data demonstrate that mesangial cell-derived IL-10 has important regulatory effects on the inflammatory response of these cells to LPS because of its capacity to blunt TNF-alpha generation.

[Production and proinflammatory activity of tumor necrosis factor alpha in the glomerulus]

The production and the effects of tumor necrosis factor alpha (TNF alpha) have been studied in isolated glomeruli and cultured glomerular cells from animal or human origin. Glomeruli from rats injected with E. coli lipopolysaccharide (LPS) and glomeruli exposed to LPS in vitro release TNF alpha into the medium. The glomerular cells responsible for TNF alpha synthesis are mesangial cells. Production of TNF alpha is controlled by other locally produced mediators. Prostaglandin E2 and interleukin-10 are inhibitory. Hydroxyl radicals stimulate the transformation of the transmembrane form of TNF alpha into its soluble form which is secreted into the medium. TNF alpha acts on its producing cells and on the neighbouring cells. It induces contraction of mesangial cells, increases the synthesis of a variety of local mediators including prostaglandins, platelet-activating factor and chemotactic agents, particularly interleukin-8. Synthesis of this cytokine implies activation of tyrosine kinase and of transcription factors, essentially NFkB. Taken together, these results suggest that TNF alpha plays a marked role in the development of glomerular injury and incite us to search for treatments inhibiting its synthesis and its effects.

Fish oil supplementation and essential fatty acid deficiency reduce nitric oxide synthesis by rat macrophages

Both fish oil-derived omega-3 polyunsaturated fatty acid (omega 3 PUFA) supplementation and essential fatty acid (EFA) deficiency have been shown to exert anti-inflammatory effects and, hence, to ameliorate immune-mediated glomerulonephritis. The mechanisms underlying these effects include alterations in the production of eicosanoids, cytokines (that is, tumor necrosis factor, TNF-alpha) and reactive oxygen species by blood borne cells. Because, in addition to these mediators nitric oxide (NO) is also implicated in glomerular injury, we have examined if both diets affected macrophage NO production as well. Rats were fed a standard chow, an omega 3 PUFA-supplemented diet, or an EFA-deficient diet for six weeks before resident peritoneal macrophages were isolated. These cells were exposed to lipopolysaccharide (LPS) and the NO metabolite, nitrite (NO2-), was measured in the medium using the Griess reagent. Release of NO2- was enhanced by LPS in a dose-dependent manner. With 10 ng/ml LPS challenge, NO2- release was reduced by 37% and 57% by omega 3 PUFA supplementation and EFA deficiency, respectively. NO2- returned to control levels two weeks after the end of diet. Macrophage production of TNF-alpha responded in a similar manner. Diet-induced reduction of NO2- release was neither attributable to a reduction of inducible NO synthase mRNA levels as shown by Northern blot analysis, nor to an increased competition of NO synthase and arginase for the substrate (L-arginine). Indeed, arginase activity of macrophages was even slightly reduced by both omega 3 PUFA-supplemented diet and EFA-deficient diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Protection from tumor necrosis factor-mediated cytolysis by platelets

Infiltrating macrophages elicit tumor-destructive reactions by releasing cytolytic factors including tumor necrosis factor alpha (TNF-alpha). Because platelets represent another major component of the cell infiltrate in tumors, we examined whether they could affect TNF alpha-induced cell death. Exposure of L-929 fibrosarcoma cells to human platelets reduced TNF alpha-induced cytotoxicity and cytolysis, as determined by 51Cr release assay and DNA fragmentation assay. This inhibitory effect, which depended on the concentration of platelets (0.1 to 10 x 10(6)/0.1 ml), was as high as 50%. The decrease in responsiveness to TNF-alpha reflected neither a degradation of TNF-alpha nor an inability of L-929 cells to bind TNF-alpha. Indeed, even though Scatchard analysis indicated the presence of 100 to 150 125I-TNF-alpha binding sites/platelet with a kd of 3.8 to 6.4 nM, addition of platelets up to 5 x 10(6)/0.1 ml did not compete with 125I-TNF-alpha binding to L-929 cells. Furthermore, addition of platelets 1 or 2 hours after that of TNF-alpha was still protective suggesting that platelets rather promoted hyporesponsiveness of L-929 cells to a postbinding effect of TNF-alpha Platelet-induced reduction of TNF-alpha response could be reproduced with supernatant fluids from platelets incubated at 37 degrees C for 24 hours. The platelet-derived factor responsible for this effect was found to be a lipid of low molecular weight with high affinity for albumin and charcoal. A role for 12(S) hydroxyeicosatetraenoic acid is proposed because this metabolite reduced TNF-alpha-induced cytolysis in a dose-dependent manner, whereas other platelet-derived lipids including thromboxane A2 and platelet activating factor were inactive. These observations indicate that the role of associated platelets has to be considered when analyzing the cytotoxic and cytolytic activity of macrophage-derived TNF-alpha on tumor cells.

Increased expression and occupancy of receptors for tumour necrosis factor on blood monocytes from tuberculosis patients

Blood monocytes from tuberculosis patients release high amounts of tumour necrosis factor-alpha (TNF-alpha). Because the biological efficiency of TNF-alpha would depend on the expression of TNF-alpha receptors on target cells, we thought to analyse the capacity of blood monocytes from a group of patients with pulmonary tuberculosis to bind 125I-TNF-alpha. We report a slight but not significant enhancement in specific binding of 125I-TNF-alpha on monocytes of 15 consecutively studied patients compared with 10 controls. Per cent cell surface bound and internalized 125I-TNF-alpha was identical in the two groups. To evaluate the receptor occupancy by endogenously generated TNF-alpha, similar experiments were performed after cell exposure to low-pH glycine buffer. Under these conditions, specific binding of 125I-TNF-alpha was significantly higher on tuberculosis monocytes compared with control monocytes. Moreover, the occupancy of TNF-alpha receptors by endogenously generated TNF-alpha that was found to be significantly higher on tuberculosis monocytes than on control monocytes, was directly related to the enhanced capacity of mononuclear cells to generate TNF-alpha in vitro. It normalized after 3 months of antituberculous therapy. Scatchard analysis of the binding data revealed that tuberculosis infection caused a significant increase in high affinity 125I-TNF-alpha binding to monocytes without any significant change in the dissociation constant. Collectively, these results indicate an up-regulation of TNF-alpha generation and binding to blood monocytes in patients with pulmonary tuberculosis. They provide support to the hypothesis that TNF-alpha is of critical importance in the pathogenesis of this infection.

Membrane expression and shedding of tumour necrosis factor receptors during activation of human blood monocytes: regulation by desferrioxamine

Previous studies have shown that desferrioxamine (DFX), an iron chelator preventing the synthesis of hydroxyl radical (OH.), up-regulates the cell-surface expression of tumour necrosis factor-alpha (TNF-alpha) receptors on unactivated human blood monocytes. In the present study, we investigated the regulatory action of DFX on 125I-TNF-alpha binding to monocytes upon exposure to bacterial lipopolysaccharide (LPS). Exposure to LPS (1 microgram/ml) resulted in almost complete loss of 125I-TNF-alpha binding to the surface of monocytes. This down-regulation was reversible and the recovery observed after 18 hr was enhanced by addition of DFX (5 mM). However, binding studies on monocytes pre-exposed to low pH suggested that the DFX-induced increase of 125I-TNF-alpha binding was not due to differences in the number of receptors available but was probably due to a reduction of receptor occupancy by endogenously generated TNF-alpha. Time-course studies of TNF-alpha release from monocytes confirmed the ability of DFX to reduce the extracellular concentration of bioactive TNF-alpha through a decrease of its synthesis and an increase of its inactivation. The latter process was associated with an increased expression of the soluble form of TNF-alpha receptor type II. These results indicate that, in the presence of LPS, DFX increases the release of soluble TNF-alpha receptors from monocytes. Thus, conversely, OH. generated in situ could reduce the shedding of soluble TNF-alpha receptors and, hence, increase the widespread release of bioactive TNF-alpha.

Tumor necrosis factor-induced contraction of cultured rat mesangial cells: interaction with angiotensin II

The role of tumor necrosis factor alpha in the regulation of renal function, particularly glomerular filtration rate, has not been completely defined. This study was designed to assess the intrinsic role of this cytokine on glomerular filtration rate by analyzing its short-term effect on the degree of contraction in cultured rat mesangial cells, not only directly but also in the presence of angiotensin II. Contraction was evaluated both morphologically--by measuring planar cell surface area of cultured rat mesangial cells and glomerular cross-sectional area of isolated rat glomeruli--and biochemically--by analyzing myosin light-chain phosphorylation in cells. Tumor necrosis factor alpha significantly decreased planar cell surface area in a dose-dependent and time-dependent manner, an effect completely abolished by preincubation of the cells with platelet-activating factor receptor antagonists BN 52021 and alprazolam. This effect was also observed in the presence of angiotensin II, whether tumor necrosis factor alpha was added before or after angiotensin II, increasing the reduction in planar cell surface area induced by angiotensin II in both cases. Changes in planar cell surface area were evident not only when the absolute values of this parameter were considered but also when the percentage of contracted cells (cells with a planar cell surface area reduction > 10%) was analyzed. Tumor necrosis factor alpha also induced a significant reduction of glomerular cross-sectional area in isolated rat glomeruli. The results of the morphologic studies were supported by myosin light-chain phosphorylation experiments.(ABSTRACT TRUNCATED AT 250 WORDS)

Involvement of reactive oxygen species in kidney damage

There is considerable evidence suggesting that reactive oxygen species (ROS) are implicated in the pathogenesis of ischemic, toxic, and immunologically-mediated renal injury. In experimental renal ischemia, ROS sources include the electron transport chain, oxidant enzymes (xanthine oxidase), phagocytes, and auto-oxidation of epinephrine. ROS cause lipid peroxidation of cell and organelle membranes and, hence, disruption of the structural integrity and capacity for cell transport and energy production, especially in the proximal tubule segment. In experimental immune glomerulonephritis, ROS are generated by both infiltrating blood-borne cells (polymorphonuclear leukocytes and monocytes) and resident glomerular cells, mainly mesangial cells. Their formation results in morphologic lesions and in modifications of glomerular permeability to proteins through activation of proteases and reduction of proteoglycan synthesis. Additionally, they promote a reduction in glomerular blood flow and glomerular filtration rate through liberation of vasoconstrictory bioactive lipids (prostaglandins, thromboxane, and platelet activating factor) and, possibly, inactivation of relaxing nitric oxide. Further studies are needed to address the role of ROS in human glomerular diseases.

[Therapeutic perspectives in primary glomerulonephritis from recent physiopathological data]

In this review the authors describe the physiopathological mechanisms responsible for inflammatory lesions in primary glomerulonephritis. Primary glomerular nephropathies can be reproduced experimentally: models have been set up for non-proliferative kidney diseases such as minimal change disease or membranous glomerulopathies, and for proliferative kidney diseases such as Berger's disease. Studies performed with these models have resulted in the identification of inflammatory mechanisms creating glomerular lesions which may be acute (proteinuria) or progressive (glomerular sclerosis). These mechanisms include activation of resident cells, notably mesangial cells, and recruitment of circulating cells such as neutrophils, monocytes/macrophages and platelets. These cells participate in the local inflammatory reaction by releasing soluble mediators including biologically active lipids, such as eicosanoids, reactive oxygen and nitrogen derivatives, proteases, cytokines and vasoactive polypeptides. The importance of these mediators has been deduced from the fact that they are produced locally in excess, their introduction produces lesions and, above all, their suppression by inhibitory or antagonistic pharmacological agents reduces the severity of the lesions. Several observations have shown that the development of all the lesions can be prevented simply by blocking the activity of only one of these mediators. It is therefore possible to consider replacing the conventional glucocorticoid treatment, which has multiple pharmacological actions, by a more specific treatment directed against a single mediator.