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Biomedical subjects

L Baud

Publications and source records attributed to L Baud.

At least 55 records · Page 3Linked to original sources
PubMed1992

Heat shock prevents lipopolysaccharide-induced tumor necrosis factor-alpha synthesis by rat mononuclear phagocytes.

Tumor necrosis factor-alpha (TNF-alpha), a mononuclear phagocyte-derived peptide is known to participate in the pathogenesis of fever. To determine whether a feedback mechanism exists by which elevated temperatures influence TNF-alpha generation, we have examined the effects of heat shock on the in vitro synthesis of TNF-alpha by rat glomeruli, inflammatory peritoneal macrophages and blood monocytes. Preexposure of peritoneal macrophages to elevated temperatures for 20 min decreased the subsequent lipopolysaccharide-induced release of TNF-alpha bioactivity. The mean reductions were 11.9 +/- 5.0%, 86.3 +/- 12.0%, and 95.2 +/- 3.5% after pretreatment at 39, 41 and 43 degrees C, respectively. Reductions, that were transient, were maximum when lipopolysaccharide was added 0-2 h after heat shock. They correlated with the decreased release of immunoreactive TNF-alpha and the decreased expression of both cell-associated TNF-alpha molecule and TNF-alpha mRNA. Heat shock-induced inhibition of TNF-alpha release was independent of variations of prostaglandin synthesis, but was possibly related to the induction of heat-shock proteins since (a) macrophages exposed to heat shock synthesized the major 70- and 90-kDa heat-shock proteins, and (b) chemical inducers of the heat-shock response were also effective inhibitors of TNF-alpha release. The mean reduction of TNF-alpha release after pretreatment at 41 degrees C was found to be identical in glomerular tissue (82.0 +/- 7.5%), but significantly less in blood monocytes (43.9 +/- 10.9%). This supports the hypothesis that a negative-feedback mechanism exists between elevated temperature and lipopolysaccharide-induced TNF-alpha synthesis, and suggests that this regulation is less active in blood monocytes than in tissue macrophages.

Animals↗
PubMed1992

Up-regulation of tumour necrosis factor-alpha receptors on monocytes by desferrioxamine.

The effect of endogenously generated reactive oxygen metabolites on the interaction of human blood monocytes with tumour necrosis factor-alpha (TNF-alpha) was investigated. Pre-exposure of unactivated human blood monocytes to dimethylthiourea, a scavenger of hydroxyl radical (OH.), or to desferrioxamine (DFX), an iron chelator preventing the synthesis of OH., enhanced the specific binding of 125I-TNF-alpha to its receptors. Scavengers of superoxide anion or hydrogen peroxide were without effect. DFX-induced up-regulation of 125I-TNF-alpha binding depended on the concentration of the drug (1-5 mM) and on the duration of the treatment (1-18 h). It was not due to a reduction of receptor occupancy by endogenously generated TNF-alpha. Scatchard analysis of binding data revealed that DFX caused an approximately two-fold increase in the number of type II TNF-alpha receptors, with no change in their affinity. This up-regulation, that did not require synthesis of new proteins, was associated with a decrease in the internalization rate of TNF-alpha receptors, the half-life of which was doubled. Conversely, these findings suggest that OH. generation by monocytes may have a physiological role in reducing the activity of membrane-associated TNF-alpha receptors.

Binding, Competitive↗
PubMed1992

Reactive oxygen species as glomerular autacoids.

There is considerable evidence suggesting that reactive oxygen species (ROS; superoxide anion, hydrogen peroxide, hydroxyl radical, hypochlorous acid) are implicated in the pathogenesis of toxic, ischemic, and immunologically mediated glomerular injury. The capacity of glomerular cells, especially mesangial cells, to generate ROS in response to several stimuli suggests that these autacoids may play a role in models of glomerular injury that are independent of infiltrating polymorphonuclear leukocytes and monocytes. The mechanisms whereby ROS formation results in morphologic lesions and in modifications of glomerular permeability, blood flow, and filtration rate have been inferred from in vitro studies. They involve direct and indirect injury to resident cells (mesangiolysis) and glomerular basement membrane (in concert with metalloproteases) and alteration of both the release and binding of vasoactive substances, such as bioactive lipids (e.g., prostaglandin E2, prostacyclin, thromboxane), cytokines (e.g., tumor necrosis factor alpha), and possibly endothelium-derived relaxing factor. The importance of such processes appears to be modulated by the intrinsic antioxidant defenses of the glomeruli. Further studies are needed to address the role of ROS in human glomerular diseases.

Animals↗
PubMed1991

Desferrioxamine regulates tumor necrosis factor release in mesangial cells.

Cultured rat mesangial cells have been demonstrated to express tumor necrosis factor alpha (TNF alpha) mRNA and to release TNF activity into the medium upon stimulation by bacterial lipopolysaccharide (LPS). The present study was undertaken to determine whether TNF was only secreted by mesangial cells or was also present as a cell-associated molecule. LPS-activated mesangial cells which had been fixed in paraformaldehyde lysed the TNF-sensitive L-929 fibroblasts, as assessed by 51Cr release. This cytotoxic activity was inhibited by anti-TNF alpha antiserum. Cell-associated TNF expression was demonstrable after less than one hour of exposure to LPS, peaked at two hours and decreased progressively thereafter, while TNF activity increased in the medium. Mesangial cell-associated TNF was localized at the cell surface, as shown by immunohistochemical demonstration and by the ability of plasma membranes purified from LPS-activated mesangial cells to lyse L-929 fibroblasts. Flow cytometry experiments revealed that two-thirds of LPS-activated mesangial cells were stained by anti-TNF alpha antiserum. The major part of these cell-associated TNF molecules persisted after low pH treatment, indicating that they were integral membrane proteins. As assessed by immunoprecipitation analysis, these proteins were 26 kDa molecules, whereas the released forms of TNF were 17 kDa molecules. Pretreatment of mesangial cells with desferrioxamine (DFX), an iron chelator preventing the synthesis of hydroxyl radicals (OH.), delayed the release of TNF from the membranes into the medium, and enhanced its cell surface expression. It also subsequently accelerated its decay in the medium.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Reduction in tumor necrosis factor binding and cytotoxicity by hydrogen peroxide.

The regulatory effect of H2O2 on both the cytotoxic activity and the specific binding of TNF-alpha was studied by using TNF-alpha-sensitized murine L929 cells. When these cells were exposed simultaneously to TNF-alpha and H2O2 (100 to 500 microM), the cytotoxic activity of TNF-alpha was inhibited by up to 66.6%. This inhibition was also effective when the cells were pretreated by H2O2, but not when TNF-alpha alone was preexposed to H2O2. These data suggest that H2O2 altered the cell sensitivity to TNF-alpha, without modifying the activity of the TNF-alpha molecule. Maximum loss of cell sensitivity to TNF-alpha occurred after 30-min preexposure to 500 microM H2O2. Complete restoration of TNF-alpha sensitivity was obtained within 12 h after H2O2 removal. It required protein synthesis as demonstrated by the suppressive effect of actinomycin D. The inhibitory effect of H2O2 was suppressed by catalase, but was unaffected by the scavengers of hydroxyl radical and hypochlorous acid, suggesting that H2O2 but not one of its metabolites was responsible for this inhibition. H2O2 inhibitory effect did not implicate any change in prostaglandin production or in PKC activity. In contrast, H2O2 effect was associated with an about 50% loss of the density of cell membrane 125I-TNF-alpha receptors (2949 vs 5620 binding sites per cell), without change in their affinity (3.9 vs 3.4 nM). Moreover H2O2 did not affect the rate of degradation of TNF-alpha, and only slightly increased the degree of internalization of 125I-TNF-alpha receptors. These findings indicate that H2O2 can down-regulate the cellular response to TNF-alpha, possibly by reducing the TNF-alpha-binding capacity.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1990

In vitro production of tumour necrosis factor and prostaglandin E2 by peripheral blood mononuclear cells from tuberculosis patients.

We investigated the production of tumour necrosis factor-alpha (TNF-alpha) and prostaglandin E2 (PGE2) by peripheral blood mononuclear cells (PBMC) from tuberculosis patients and healthy controls. PBMC from tuberculosis patients generated constitutively more TNF-alpha than did control PBMC. This production was significantly higher for patients with high-grade fever and cachexia. The increase of TNF-alpha production by PBMC from tuberculosis patients was associated with a comparatively weaker elevation of PGE2 synthesis which did not parallel fever or weight loss. In vitro treatment of control PBMC with the tuberculin purified protein derivative (PPD) promoted an increased TNF-alpha production which was similar to that of untreated PBMC from tuberculosis patients. Thus, the increased TNF-alpha production in tuberculosis could be explained by the in vivo exposure of PBMC to mycobacterial antigens. In contrast, the concentration of PGE2 was weaker in the medium of untreated PBMC from tuberculosis patients than in the medium of PPD-treated control PBMC, suggesting that PGE2 synthesis by PBMC was limited in tuberculosis by unidentified factors.

Adult↗
PubMed1990

Increased lung epithelial permeability in HIV-infected patients with isolated cytotoxic T-lymphocytic alveolitis.

HIV-related lymphocytic alveolitis is common in HIV-seropositive patients without lung infection or tumor. In some of them a fraction of alveolar lymphocytes are HIV-specific cytotoxic T-lymphocytes (CTL) bearing the CD8 and D44 cell surface markers and capable of killing HIV-infected alveolar macrophages. In order to evaluate the in vivo effect of these CTL on lung function, we measured the pulmonary clearance of aerosolized 99mTc-diethylene triamine penta-acetate (DTPA-CI) on 24 occasions in 22 patients with lymphocytic alveolitis. DTPA-CI has been selected as a highly sensitive test to detect injury of the lung epithelium. In 13 of the patients, we found a high DTPA-CI of 4.56 +/- 2.54%.min-1 (mean +/- SD), suggesting an increase of the epithelial permeability. The lymphocytic alveolitis was then characterized by a high cellularity, a high proportion of lymphocytes (59 +/- 18%), mainly composed of CD8+D44+ T-lymphocytes (149 +/- 109 cells/mm3), which spontaneously exhibited a cytolytic activity against the autologous alveolar macrophages in a standard 51Cr release assay. In the remaining 11 patients, DTPA-CI was normal (less than 1.78%.min-1), lymphocytic alveolitis being characterized by a low number or an absence of CD8+D44+ alveolar lymphocytes (9 +/- 13 cells/mm3) with no significant cytolytic activity. In the whole group, a significant correlation (r = 0.74, p = 0.0004) was found between the DTPA-CI and the number of CD8+D44+ lymphocytes and their cytotoxic activity against alveolar macrophages. Altogether, these results suggest that an injury of the lung epithelium could result from a HIV-specific CTL-induced immunologic conflict.

Adult↗
PubMed1990

[Specificity and serum concentrations of tumor necrosis factor in septic shock].

Several lines of evidence implicate tumor necrosis factor (TNF), a cytokine produced by monocytes-macrophages, in the systemic manifestations of shock induced by Gram-negative bacteria. Whether the increase of circulating TNF levels is specific to septic shock as compared to sepsis without shock or to non-septic shock is still unclear. Since TNF values recorded at the time of admission to the hospital vary widely, statistical analysis has not been possible. Therefore, we postulated that the evolution of a patient's TNF serum level as compared to his initial value may better distinguish the survivor from the non-survivor than a single initial determination. Using a radioimmunoassay, we measured the TNF concentrations in the sera of 7 patients with severe infections without shock, 16 patients with septic shock and 8 patients with non-septic shock. Blood samples were drawn within the first 12 hours after the onset of shock. Patients with cancer, HIV infection, or under steroid therapy were excluded. Repeated measurements were made during the first 3 days of septic shock in 10 patients. The circulating TNF level, determined upon admission, appears to be neither specific nor predictive of the outcome of septic shock. In contrast, persistently high levels of circulating TNF seem to be well correlated with a poor prognosis, since 5 out of 6 patients with elevated TNF values died of septic shock.

Adult↗
PubMed1989

Effects of bradykinin on prostaglandin synthesis and cytosolic calcium in rabbit subcultured renal cortical smooth muscle cells.

Smooth muscle cells were cultured from an arteriole-rich fraction of the rabbit renal cortex and characterized by their ultrastructural and immunohistochemical features, their high content in creatine kinase (60-times that of the initial preparation) and their ability to synthesize renin. Cells, studied between passages 2 and 5, produced mainly PGE2 and, to a lesser extent, PGF2 alpha. Bradykinin (BK) (0.1 nM-1 microM) induced a concentration-dependent increase in PGE2 (28-40-times basal value at 1 microM after a 5 min incubation period) and stimulated also the free cytosolic calcium concentration [( Ca2+]i) with a 2-fold maximal rise to its basal value. Both effects, inhibited by the anti-B2 receptor [Thi5.8D-Phe7] BK, were not reproduced by DesArg9 BK. A decrease in the extracellular calcium concentration and incubation in the presence of a calcium-channel blocker (lanthanum chloride) inhibited the BK-dependent rise of [Ca2+]i but not that of PGE2. Preincubation with phorbol myristate acetate increased basal and BK-induced PGE2 synthesis but prevented the effect of BK on [Ca2+]i. These results demonstrate the ability of BK to increase [Ca2+]i and PGE2 production in cultured vascular cells from the rabbit renal cortex and suggest that kinins might act on the cortical microcirculation via their direct effects on arteriolar smooth muscle cells.

Animals↗
PubMed1989

Production of tumor necrosis factor by rat mesangial cells in response to bacterial lipopolysaccharide.

Tumor necrosis factor (TNF) is a cytokine which is produced by mononuclear phagocytes upon activation by bacterial lipopolysaccharide (LPS) and various other stimuli. In immune-mediated glomerulonephritis, infiltration of glomeruli by monocytes-macrophages is associated with production of TNF. The purpose of the present experiments was to determine whether mesangial cells could also contribute to glomerular TNF synthesis. TNF activity has been determined in the culture medium of rat mesangial cells using a L-929 fibroblast lytic assay. This activity was detectable only when the cells were exposed to LPS (0.1 to 10 micrograms/ml) and for periods longer than one hour. The cytotoxic factor was identified as TNF since: (1) the lytic activity was completely inhibited by an anti-mouse TNF polyclonal antibody and was associated with suppression of lipoprotein lipase activity in adipocytes; (2) its molecular weight (110,000 daltons) corresponded to that observed for murine TNF under non-denaturing conditions; and (3) mRNA encoding TNF was expressed by mesangial cells two hours after addition of LPS. To assess the mechanisms whereby TNF production was regulated, the role of prostaglandin E2 (PGE2) was determined. LPS caused a dose-dependent increase of PGE2 synthesis by mesangial cells. Treatment by indomethacin promoted a suppression of PGE2 production together with an increase of TNF synthesis, indicating that PGE2 acted in a negative feedback manner to regulate the production of TNF. Addition of PGE2 (0.1 to 300 nM) or 8-bromo cyclic AMP (0.1 to 100 microM) induced similar dose-dependent reductions of TNF synthesis. Thus the inhibitory effect of PGE2 probably required in part cyclic AMP accumulation.(ABSTRACT TRUNCATED AT 250 WORDS)

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1989

Leukotriene D4-induced proliferation of glomerular epithelial cells: PKC- and Na+-H+ exchanger-mediated response.

The growth-promoting effect of leukotriene D4 (LTD4) has been observed in a variety of cells, including human glomerular epithelial cells. The purpose of this study was to determine the mechanisms underlying this process. LTD4 induction of [3H]thymidine uptake in human glomerular epithelial cells was blocked by the LTD4 receptor antagonist L648,051 when added in a 50-fold excess and by pertussis toxin. Neither drug affected basal DNA synthesis. These results suggest that the LTD4-mediated signal transduction implies activation of a GTP-binding protein that is coupled to a specific receptor. The possible role of protein kinase C (PKC) activation was also studied. In the presence of the PKC inhibitor H-7 or after downregulation of PKC levels by chronic treatment with phorbol ester, stimulation of [3H]thymidine uptake by LTD4 was greatly inhibited. Moreover, treatment of the cells by LTD4 resulted in a time-dependent increase of cytosolic PKC activity, whereas addition of phorbol 12-myristate 13-acetate reduced this activity. Therefore PKC-dependent mechanisms are likely to mediate the growth-promoting effect of LTD4. Finally, three approaches were used to determine the potential role of the Na+-H+ exchanger. First, progressive removal of extracellular Na+ using N-methyl-D-glucamine+ as a substitute inhibited LTD4-induced [3H]thymidine uptake with a 50% inhibitory concentration (IC50) of 85 mM. Second, addition of amiloride reduced the LTD4 growth effect with an IC50 of 6.5 microM, whereas three amiloride analogues exhibited lower IC50 values in accordance with their greater affinity for the Na+-H+ exchanger.(ABSTRACT TRUNCATED AT 250 WORDS)

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗