Con A-induced Increase Research Articles

Ferulic acid ameliorates concanavalin A-induced hepatic fibrosis in mice via suppressing TGF-β/smad signaling

Background and aimHepatic fibrosis, one of the main reasons for death globally, is a serious complication of chronic liver disorders. However, the available therapies for liver fibrosis are limited, ineffective, and often associated with adverse events. Hence, seeking for a novel, effective therapy is warranted. Our objective was to investigate the potential efficacy of ferulic acid (FA), a phenolic phytochemical, at different doses in hindering the progress of concanavalin A (Con A)-induced hepatic fibrosis and explore the involved mechanisms. MethodsThirty-six mice were assorted into 6 groups (n = 6): Group I (control); group II received FA (20 mg/kg/day orally for 4 weeks); group III received Con A (6 mg/kg/week/i.v.) for 4 weeks; groups IV, V, and VI received Con A and were offered FA at 5, 10, and 20 mg/kg/day, respectively. ResultsThe data showed the palliative effect of FA against Con A-induced fibrosis in a dose-dependent manner. This was obvious from the recovery of liver markers and hepatic architecture with the regression of fibrosis in FA-treated mice. FA abolished Con A-mediated oxidative insults and promoted the antioxidant enzyme activities, which run through the Nrf2/HO-1 signaling. Additionally, FA suppressed Con A-induced increase in NF-kB and IL-β levels, and TNF-α immune-expression. The anti-fibrotic effect of FA was evident from the drop in TGF-β, smad3 levels, α-SMA expression, and hydroxyproline content. ConclusionFA attenuated Con A-induced liver fibrosis through stimulating Nrf2 signaling, suppressing NF-kB, and inhibiting the TGF-β/smad3 signaling pathway. Thus FA can be considered as a promising therapy for combating liver fibrosis.

Interleukin-39 exacerbates concanavalin A-induced liver injury

Background Interleukin (IL)-39 is a novel member of IL-12 family and has been reported to play a pro-inflammatory role in lupus-like mice, but its function in concanavalin A (ConA)-induced liver injury is currently unclear. Materials and methods In this study, we investigated the effects of IL-39 expression in a mouse model of ConA induced-hepatitis. We first showed that delivery of plasmid DNA encoding mouse IL-39 using the hydrodynamic tail vein injection method increased IL-39 mRNA and protein levels in the liver. We then administrated mice with IL-39 plasmid before ConA injection and measured serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels, inflammatory infiltration, and hepatocyte necrosis in the liver. Additionally, we further explored the potential mechanism of IL-39 in ConA-induced liver injury by measuring several inflammatory mediators. Results We found that ectopic IL-39 expression promoted the ConA-induced increase in serum ALT and AST levels, inflammatory infiltration, and hepatocyte necrosis in the liver. We also observed that IL-39 plasmid administration significantly increased serum and liver interferon-γ, tumor necrosis factor-α, and IL-17A levels, but did not affect serum and liver IL-10 levels in ConA-induced hepatitis. Conclusion Our results suggest that IL-39 can exacerbate ConA-induced hepatitis and may be a therapeutic target in inflammatory liver disease.

Mycophenolate mofetil attenuates concanavalin A-induced acute liver injury through modulation of TLR4/NF-κB and Nrf2/HO-1 pathways.

Acute liver injury (ALI) is a serious health condition associated with rising morbidity and sudden progression. This study was designed to investigate the possible hepatocurative potential of two dose levels (30 and 60mg/kg) of Mycophenolate mofetil (MMF), an immune-suppressant agent, against Concanavalin A (Con A)-induced ALI in mice. A single dose of Con A (20mg/kg, IV) was used to induce ALI in mice. MMF (30mg/kg and 60mg/kg) was administered orally for 4days post Con A injection. MMF (30mg/kg) failed to cause significant amelioration in Con A-induced ALI while MMF (60mg/kg) significantly alleviated Con A-induced ALI. Administration of MMF (60mg/kg) significantly decreased Con A-induced increase in serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels. Additionally, MMF significantly restored the disrupted oxidant/antioxidants status induced by Con A. MMF caused marked increase in hepatic nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) levels. Moreover, MMF significantly reduced Con A-induced increase in the expression of hepatic toll-like receptor 4 (TLR4), nuclear factor kappa-B (NF-κB), tumor necrosis factor-α (TNF-α), interferon-γ (INF-γ) and interleukin-1β (Il-1β). Also, MMF administration significantly decreased Con A-induced increase in the immune-expression of pro-apoptotic Bcl-2-associated X protein (Bax) and markedly increased Con A-induced decrease in the anti-apoptotic B-cell lymphoma 2 protein (Bcl2). The observed ameliorative effect of MMF against Con A-induce ALI may be contributed to its anti-inflammatory, anti-oxidant and anti-apoptotic potentials taking into consideration that TLR4/NF-κB and Nrf2/HO-1 are the main implicated pathways. Schematic diagram summarizing the possible mechanisms underlying the ameliorative potential of Mycophenolate Mofetil against Con A-induced acute liver injury. Bax Bcl-2-associated X protein, Bcl2 B-cell lymphoma 2, MMF Mycophenolate mofetil, Con A Concanavalin A, GSH reduced glutathione, HO-1 Heme oxygenase-1, IL-1β Interleukin-1β, IFN-γ Interferon-γ, MDA Malondialdehyde, NF-κB Nuclear Factor Kappa B, Nrf2 Nuclear factor erythroid 2-related factor 2, NO Nitric Oxide, SOD Superoxide Dismutase, TLR4 Toll-like receptor 4, TNF-α tumor necrosis factor-α.

Taraxasterol from Taraxacum prevents concanavalin A-induced acute hepatic injury in mice via modulating TLRs/NF-κB and Bax/Bc1-2 signalling pathways

Immune hepatic injury is a liver disease closely related to an immune imbalance of T cells and macrophages. Our previous series of studies have demonstrated that taraxasterol isolated from Taraxacum possesses great anti-inflammatory and immunomodulatory effects in vivo and in vitro. In this study, we explored the preventive effects of taraxasterol and its underlying mechanisms on concanavalin A (Con A)-induced acute hepatic injury in mice. It was found that treatment with taraxasterol significantly decreased the Con A-induced increase of liver index, serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) and hepatic malondialdehyde (MDA) levels, and increased the Con A-induced decrease of hepatic glutathione (GSH) and superoxide dismutase (SOD) production. Taraxasterol also significantly inhibited the release of pro-inflammatory cytokines tumour necrosis factor-α (TNF-α), interleukin-6 (IL-6), IL-1β, interferon-γ (IFN-γ) and IL-4. In addition, treatment with taraxasterol alleviated the hepatic histopathological injury and apoptosis induced by Con A. Furthermore, taraxasterol dramatically down-regulated the expressions of T toll-like receptor (TLR2), TLR4 and nuclear factor-κappaB (NF-κB) p65, and decreased the expression ratio of Bax/Bc1-2 in hepatic tissues. These findings suggest that taraxasterol prevents Con A-induced acute hepatic injury in mice by inhibiting TLRs/NF-κB inflammatory signalling pathway and promoting Bax/Bc1-2 anti-apoptotic signalling pathway.

Pristimerin as a Novel Hepatoprotective Agent Against Experimental Autoimmune Hepatitis.

Pristimerin (Pris) is bioactive natural quinonoid triterpene that has anti-inflammatory and anti-cancer activities. Meanwhile, its effect against hepatitis needs to be elucidated. This investigation aimed to evaluate the ability of Pris to protect against autoimmune hepatitis (AIH). A mouse model of AIH was established using single concanavalin A (Con A) intravenous injection. Mice were treated with Pris at two different doses (0.4 and 0.8 mg/kg) for 5 days prior to Con A challenge. Markers of hepatic injury, oxidative, inflammatory, and apoptotic damage were estimated. Results have revealed that Pris pretreatment ameliorated Con A-induced hepatic damage. There was decrease in the elevated serum indices of hepatic damage (ALT, AST, ALP, and LDH) and improvement of the histopathological picture of the liver. Pris effectively decreased Con A-induced neutrophil infiltration into the hepatic tissue as presented by amelioration of the level and immuno-expression of myeloperoxidase (MPO). Additionally, Pris attenuated Con A-induced increase in CD4+ T-cells in hepatic tissue. Lipid peroxidation was significantly depressed simultaneously with enhancement of the antioxidant capacity in Pris pretreated animals. Pris also enhanced nuclear factor erythroid 2-related factor 2 (Nrf2) mRNA expression and its binding capacity. In addition, Pris increased mRNA expression of heme-oxygenase-1 (HO-1) and restored its normal level. Furthermore, Pris decreased the level and immuno-expression of nuclear factor kappa-B (NF-κB) as well as the downstream inflammatory cascade (TNF-α, IL-6, and IL-1β). Finally, Pris showed inhibitory effect on Con A-induced apoptotic alteration in liver as it decreased the mRNA expression and levels the apoptotic markers (Bax and caspase-3) and increased mRNA expression and level of the anti-apoptotic protein (Bcl2). In conclusion, this study demonstrates the potent hepatoprotective efficacy of Pris against Con A-induced hepatitis which may be related to anti-oxidative, anti-inflammatory, and anti-apoptotic pathways. Pris could serve as a new candidate for the management of hepatitis.

Mobiloization of intracellular calcium ions in chicken and rat lymphocytes induced by T cell mitogens

Cytosolic Ca(2+) is known to be an important factor in intracellular signaling pathways that regulate several cellular functions. The present study was designed to measure the intracellular concentrations of Ca(2+) ([Ca(2+)](i)) in T cell mitogen-stimulated chicken lymphocytes, and to compare the results with those in rat lymphocytes. [Ca(2+)](i) was increased in the thymocytes, splenocytes and bursacytes of chickens, and in the thymocytes and splenocytes of rats following exposure to the mitogens phytohaemagglutinin (PHA) and concanavalin A (ConA). Increases were greatest in the thymocytes followed by the splenocytes and bursacytes. The PHA-induced changes in the thymocytes and splenocytes were similar in chickens and rats, but the ConA-induced increases were significantly lower in the chickens than rats. Pretreatment with EGTA before the application of PHA and ConA completely suppressed the rise in [Ca(2+)](i) in all the chicken lymphocytes, indicating that the increases that occurred in PHA- and ConA-treated chicken lymphocytes could be entirely attributed to the influx of extracellular Ca(2+). On the other hand, the PHA- and ConA-induced increase in [Ca(2+)](i) in rat lymphocytes was not completely suppressed by EGTA, indicating the recruitment of Ca(2+) from the intracellular Ca(2+) pool. The results suggest species differences in the Ca(2+)-based responses to T cell mitogens between chicken lymphocytes and rat lymphocytes.

Allicin, the active component of garlic, prevents immune‐mediated, concanavalin A‐induced hepatic injury in mice

Allicin, the immunologically active component of garlic, has been found to affect oxidative stress and immune response in several experimental systems. In the present study, we examined the ability of allicin to prevent immune-mediated, concanavalin A (Con A)-induced liver damage in mice. Mice were pretreated with allicin for 7 days before their inoculation with Con A (15 mg/kg). The serum levels of liver enzymes and liver histology were examined 24 h after Con A administration. The effect of Con A and allicin on serum levels of tumor necrosis factor-alpha (TNF-alpha) and nuclear factor-kappaB (NF-kappaB) activation in the liver were examined 2 h after Con A administration, in a separate group of rats, and the effect of allicin on Con A-induced expression of inducible nitric oxide synthase (iNOS) was determined by western blot analysis 24 h after Con A injection. The histopathologic damage in the mouse livers, and the Con A-induced increase of aminotransferases and TNF-alpha were markedly inhibited in the mice pretreated with allicin before Con A injection (P < 0.01). NF-kappaB binding activity to the nucleus, which increased 2 h after Con A administration, was attenuated by allicin. The expression of iNOS protein which was induced following Con A administration was significantly attenuated by allicin. In vitro studies showed that allicin inhibited TNF-alpha-mediated T cell adhesion to extracellular matrix components and to endothelial cells. Allicin also inhibited TNF-alpha-mediated intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 expression on human vascular endothelial cells. This study demonstrates that immune-mediated liver damage in mice can be prevented by allicin, probably because of its immunomodulatory effects on T cells and adhesion molecules and inhibition of NF-kappaB activation.

Reduction of concanavalin A-induced expression of interferon-γ by bovine lactoferrin in feline peripheral blood mononuclear cells

Lactoferrin (LF), a glycoprotein present in milk, mucosal secretions and neutrophils, contributes to host defense and immunomodulation. In the present study, we investigated the effect of bovine LF (bLF) on cytokine messenger RNA (mRNA) expression in concanavalin A (ConA)-stimulated feline peripheral blood mononuclear cells (PBMC). Semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR) and real-time PCR showed a ConA-induced increase of interferon-gamma (IFN-gamma) mRNA expression but not of interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha) and IL-12 p40 mRNA in feline PBMC. This ConA-induced increase of IFN-gamma mRNA expression was inhibited by addition of bLF not only 30 min before ConA stimulation but also 10, 20 and 40 min after ConA stimulation. Western blotting showed that protein tyrosine kinase (PTK) and extracellular signal-regulated kinase (ERK) in feline PBMC were activated within 10 min after the ConA stimulation and that the activation of both kinases had almost disappeared by 40 min after stimulation. Moreover, the ConA-induced IFN-gamma mRNA expression was partly prevented by genistein, a global PTK inhibitor, and PD-98059, an ERK inhibitor, respectively. These results suggest that bLF is able to inhibit the ConA-induced IFN-gamma mRNA expression by abrogation of intracellular signaling activated after interaction between ConA and its receptor.

The role of B7 molecules in the cell contact-mediated suppression of T cell mitogenesis by immunosuppressive macrophages induced with mycobacterial infection.

We found previously that immunosuppressive macrophages (Mphis) induced by Mycobacterium intracellulare infection (MI-Mphis) transmitted their suppressor signals to target T cells through cell contact with target T cells. In this study, we examined what kinds of Mphi surface molecules are required for such cell-to-cell interaction. First, it was found that a B7-1-like molecule (B7-1LM) recognizable with one of three test clones of anti-B7-1 monoclonal antibodies (mAbs) was required for expression of the Mphi suppressor activity. Neither anti-B7-2, anti-ICAM-1, nor anti-VCAM-1 mAb blocked the Mphi suppressor activity. Second, MI-Mphis increased the expression of B7-1LM in parallel with the acquisition of the suppressor activity. Moreover, MI-Mphis bound with target T cells in a B7-1LM-dependent fashion. Third, mAb blocking of CTLA-4 on target T cells did not reduce the suppressor activity of MI-Mphis, suggesting the role of a putative molecule on target T cells other than CTLA-4 as the receptor for B7-1LM of MI-Mphis. Fourth, concanavalin A (Con A) stimulation of MI-Mphis was needed for effective cell contact with target T cells and subsequent expression of the suppressor activity of MI-Mphis. Fifth, the Con A-induced increase in the suppressor activity of MI-Mphis was inhibited by KN-62 but not by herbimycin A, H-7, nor H-88, indicating that Con A-induced up-regulation of MI-Mphi function is mediated by calmodulin-dependent protein kinase II or ATP/P2Z receptors, but independent of protein tyrosine kinase, protein kinase C, and protein kinase A. These findings indicate that a B7/CTLA-4-independent mechanism is needed for the transmission of the suppressor signals from MI-Mphis to target T cells.

Murine Concanavalin A–Induced Hepatitis Is Prevented by Interleukin 12 (IL-12) Antibody and Exacerbated by Exogenous IL-12 Through an Interferon-γ–Dependent Mechanism

Concanavalin A (ConA)-induced hepatitis is a cell-mediated immunoinflammatory condition similar to human autoimmune hepatitis. We investigated the role of interleukin 12 (IL-12) in hepatitis induced in NMRI and C57/BL6 mice by a single injection of ConA. Recombinant murine IL-12 administered 24 hours and 1 hour prior to ConA exacerbated both transaminase activities in plasma and histologic signs of hepatitis. These markers of liver injury were significantly reduced by prophylactic, but not therapeutic treatment with anti–IL-12 monoclonal antibody (mAb). The disease-modulatory effects of IL-12 and anti–IL-12 mAb were associated with profound and reverse modifications of a ConA-induced increase in the circulating levels of IL-4, IL-6, interferon gamma (IFN-γ) and tumor necrosis factor (TNF). Relative to control animals receiving ConA alone, the plasma levels of these cytokines were all augmented in IL-12/ConA-treated mice and diminished in anti–IL-12 mAb/ConA-treated mice. Anti–IFN-γ mAb also impeded the appearance of IL-12/ConA-induced hepatitis. Thus, IL-12–induced production of IFN-γ might play a role in mediating the hepatitis-inducing effect of ConA. However, IL-12p40–deficient C57/BL6 mice were as susceptible as wild-type controls to the hepatitis-inducing effect of ConA.(Hepatology 2000;32:728-733.)

PGE2 suppresses mitogen-induced Ca2+ mobilization in T cells.

PGE2-mediated suppression of T cell proliferation during sepsis could result from altered Ca2+ signaling. The present study evaluated the effects of PGE2 on Ca2+ release from intracellular stores and its influx through the plasma membrane in splenic T cells from Sprague-Dawley rats. Intracellular Ca2+ concentration ([Ca2+]i) responses in individual T cells were assessed using the Ca2+ imaging technique, and the release of Ca2+ from intracellular stores and Ca2+ influx were spectrofluorometrically quantified in T cell suspensions. Under unstimulated conditions, nearly 85% of T cells exhibited [Ca2+]i </=50 nM. After stimulation with concanavalin A (Con A), an increase in [Ca2+]i was recorded in approximately 60% of the cells. The pretreatment of T cells with PGE2 had no apparent effect on [Ca2+]i in resting cells; it significantly suppressed the Con A-induced increase in [Ca2+]i in all of the Con A-responsive cells. Ca2+ release from the intracellular stores contributed to the early spike in [Ca2+]i, and the late phase of elevation in [Ca2+]i was dependent on Ca2+ influx through the plasma membrane. Our data suggest that PGE(2) causes an overall suppression of the Con A-induced [Ca2+]i elevation in T cells via inhibiting both Ca2+ influx and its release from the intracellular stores.

Concanavalin A-induced Hepatitis in Mice is Prevented by Interleukin (IL)-10 and Exacerbated by Endogenous IL-10 Deficiency

One single intra-venous (i.v.) injection of Concanavalin A (Con A) into mice provokes a cell-mediated immunoinflammatory hepatitis. We have presently evaluated the immunopharma-cological effects of exogenous interleukin (IL)-10 and the role of endogenous IL-10 in this model by using exogenous IL-10, anti-IL-10 monoclonal antibody (mAb) and mice with disrupted IL-10 gene (IL-10 KO mice). Whilst exogenous IL-10 administered in a prophylactic (lh prior to Con A) and even “early” therapeutic fashion (30min after Con A) reduced the elevation of transaminase activities in plasma in a dose-dependent manner, observed in control mice, these biochemical markers of liver injury were significantly increased both in IL-10 KO mice as well as in those receiving anti-IL-10 mAb. Interestingly, doses of Con A lower than 20 mg/kg that were only capable of inducing slight serological signs of hepatitis in mice, exerted marked hepatitic effects when administered to either anti-IL-10 mAb-treated mice or to IL-10 KO mice. The disease modulating effects of exogenous IL-10 and either genetical or pharmacologically-induced IL-10 deficiency were associated with profound and opposite modifications of the Con A-induced increase in the circulating levels of IFN-y and TNF-a. Relative to control animals, the blood levels of these cytokines were diminished in IL-10-treated mice and augmented in both IL-10 KO mice and anti-IL-10 mAb-treated mice. These results prove the physiological antiinflammatory role of endogenous IL-10 in Con A induced hepatitis and the beneficial effects of IL-10 treatment to prevent this condition.

The hyperinsulinemia produced by concanavalin A in rats is opioid-dependent and hormonally regulated

The present study examines the effect of concanavalin A (Con A) on the blood insulin and glucose levels of rats. Male and female rats treated with Con A (62.5-500 micrograms/kg) for three days showed a dose- and time-dependent hyperinsulinemia that lasted more than 48 h. Male rats were more sensitive to Con A. Thus, 6 h after treatment with Con A the circulating insulin levels in male rats had increased by 85% (control: 10.2 +/- 0.9 mU/l and Con A-treated: 18.8 +/- 1 mU/l) compared to only 38% (control: 7.5 +/- 0.2 mU/l; Con A-treated: 10.3 +/- mU/l) in females. An identical response was seen after 12 h. Con A (250 micrograms/kg) produced time-dependent hypoglycemia in both sexes but more pronounced in males. There was no correlation between the hypoglycemia and hyperinsulinemia described above. The Con A-induced hyperinsulinemia in rats of both sexes was abolished in gonadectomized animals (intact males: +101 +/- 17% vs orchiectomized males: -5 +/- 3%; intact females: +86 +/- 23% vs ovariectomized females: -18 +/- 7.2%). Pretreating intact male and female rats with human chorionic gonadotropin also significantly inhibited the Con A-induced hyperinsulinemia. Estradiol (10 micrograms/kg,i.m.) significantly blocked the Con A-induced increase in circulating insulin in male rats (101 +/- 17% for controls vs 32 +/- 5.3% for estradiol-treated animals, P < 0.05) while testosterone (10 mg/kg, i.m.) had no similar effect on intact female rats. Pretreating Con A-injected rats with opioid antagonists such as naloxone (1 mg/kg, s.c.) and naltrexone (5 mg/kg, s.c.) blocked the hyperinsulinemia produced by the lectin in males (control: +101 +/- 17% vs naloxone-treated: +5 +/- 14%, or naltrexone-treated: -23 +/- 4.5%) and females (control: +86 +/- 23% vs naloxone-treated: +21 +/- 20%, or naltrexone-treated: -18 +/- 11%). These results demonstrate that Con A increases the levels of circulating insulin in rats and that this response is opioid-dependent and hormonally regulated.

Docosahexaenoic acid lowers phosphatidate level in human activated lymphocytes despite phospholipase D activation

N–3 polyunsaturated fatty acids from marine oil have been shown to decrease T cell-mediated immune function both in animals and humans, and to inhibit the mitogen-induced lymphoproliferative response when added to lymphocyte culture medium. As phosphatidic acid (PA) is a key mediator of the mitogenic process, the present study aims to investigate whether docosahexaenoic (DHA) and eicosapentaenoic (EPA) acids, the main n–3 fatty acids from fish oil, are able to alter the mitogen-induced synthesis of PA, when added to the culture medium of human peripheral blood mononuclear cells (PBMC). Incubation of PBMC in a medium containing 5 μM DHA bound to 5 μM human delipidated serum albumin induced a 2–fold increase in the basal PA mass whereas incubation with EPA, in the same conditions, had no effect. In contrast, both fatty acids markedly reduced the concanavalin A (ConA)-induced production of PA as compared with untreated cells. Paradoxically, phospholipase D (PLD) activity, evidenced by the synthesis of phosphatidylbutanol, was only detected in DHA-treated cells further stimulated by ConA, indicating that both DHA and ConA are required for PLD activation. Similarly, an increased diacylglycerol (DAG) mass was only observed in DHA-treated cells stimulated by ConA, whereas no modification occurred in control or EPA-treated cells stimulated or not by ConA. Furthermore, 1-butanol suppressed the ConA-induced increase of DAG mass observed in DHA-treated cells, indicating that phosphatidate was the source of the newly synthesized diacylglycerol. Altogether, these results show that, in concanavalin A-activated human peripheral blood mononuclear cells, docosahexaenoate stimulates both phospholipase D and phosphatidate phosphohydrolase activities, which ultimately results in an increased diacylglycerol production at the expense of phosphatidate.—Bechoua, S., M. Dubois, G. Némoz, M. Lagarde, and A-F. Prigent. Docasahexaenoic acid lowers phosphatidate level in human activated lymphocytes despite phospholipase D activation. J. Lipid Res. 1998. 39: 873–883.

Beta-endorphin enhances Concanavalin-A-stimulated calcium mobilization by murine splenic T cells.

Intracellular calcium mobilization is an important early event involved in T cell activation. The endogenous opioid peptide beta-endorphin is known to modulate immune functions that depend on T cell activation, therefore its effect on intracellular calcium mobilization was investigated. The intracellular calcium concentration ([Ca2+]i) of T cell-enriched splenocytes was measured by flow cytofluorometric analysis using the calcium-sensitive dye, Fluo-3. By gating on the T cell marker, Thy-1, a 95%-pure population of T cells was identified for study. Cells preincubated with beta-endorphin showed significantly enhanced [Ca2+]i responses to the mitogen, Concanavalin A (Con A). This was detectable with concentrations of beta-endorphin as low as 10(-13) M; maximal enhancement required 10(-10) to 10(-9) M doses. The efficacy of beta-endorphin was dependent on the duration of pretreatment. beta-Endorphin amplified the Con A-induced increase in [Ca2+]i by reducing the lag time for the response to Con A and by increasing the mean [Ca2+]i of the cells. N-Ac-beta-endorphin, which shows minimal potency at neuronal opiate receptors, was unable to substitute for beta-endorphin. Naltrindole, a highly selective delta opiate receptor antagonist, inhibited the action of beta-endorphin, whereas a selective mu opiate receptor antagonist was ineffective. Although less potent than beta-endorphin, the delta opiate receptor agonist D-Ala2-D-Leu5-enkephalin also significantly enhanced [Ca2+]i responses. In summary, concentrations of beta-endorphin, within the physiological range found in the systemic circulation, modulate the increase in T cell [Ca2+]i induced by Con A. Both the efficacy of D-Ala2-D-Leu5-enkephalin alone and the antagonism of beta-endorphin by naltrindole suggest that a delta-type opiate receptor may mediate these effects.

Cytosolic phospholipase C activity: II. Relationship to concanavalin A‐induced phosphatidylinositol‐turnover in splenocytes

We have described in the first paper the coupling between cytosolic Gi alpha and cytosolic PLC activity in a cell free preparation. In order to establish the functional significance of the cytosolic Gi alpha coupled soluble PLC, we examined the effects of DEX, NaF, and trifluoperizine (TFP) on concanavalin A (Con A)-induced PI-turnover in intact splenocytes and, in parallel, on soluble PLC activity in cytosol preparations. Cytosolic PLC activity was measured with [3H]PI and [3H]PIP2 as substrates. 1) The Con A-induced increase (2-4 fold) in PI-turnover in intact splenocytes was paralleled by an 1.2-5-fold increase in soluble PLC activity in vitro. Con A administration also increased cytosolic Gi alpha immunoreactivity 3-6-fold as expected if cytosolic Gi alpha was coupled to soluble PLC activation. 2) DEX (10(-7) M), administered 6 h prior to Con A administration, inhibited the Con A-induced increase in PI-turnover in intact splenocytes. This was paralleled by DEX inhibition of the Con A-induced increase in soluble PLC activity measured in vitro and cytosolic Gi alpha immunoreactivity. 3) We have demonstrated in the first paper that NaF and TFP inhibited soluble PLC activity. Here we show that NaF and TFP inhibited the Con A-induced increase in PI-turnover extending the similarities between soluble PLC activity and Con A-stimulated PLC activity in intact splenocytes. 4) In order to examine whether or not the Con A-induced PLC was similar to PLC gamma, we measured PI-turnover induced by Con A or NaVO3 in combination with DEX and PMA. Whereas the Con A-induced PI-turnover was significantly inhibited (40-60%) by DEX, the NaVO3-induced PI-turnover was not affected by DEX. The Con A-induced PI-turnover was not affected by PMA (50 nM), but the NaVO3-induced PI-turnover was increased over 2-fold by PMA (50 nM), suggesting that the Con A-induced PLC in intact splenocytes is different from NaVO3-induced PLC. Based on these results a model for the sequential activation of substrate-specific PLCs in splenocyte by mitogen is presented.

Modulation of intracellular formation of reactive oxygen intermediates in peritoneal macrophages and microglia/brain macrophages by propentofylline.

Ischemia-induced nerve cell death can partly be prevented by propentofylline, a pharmacon structurally related to xanthine derivates that interacts with the neuromodulatory function of endogenous adenosine. To evaluate a possible mechanism of neuroprotection by propentofylline, we studied its effect on the cellular production of reactive oxygen intermediates in microglial cells, which under pathological conditions can differentiate into brain macrophages, in comparison to peritoneal macrophages. Using a flow cytometric assay, we determined the intracellular formation of reactive oxygen intermediates by measuring the oxidation of the membrane-permeable and nonfluorescent dihydrorhodamine 123 to the cationic and intracellularly trapped, green fluorescent rhodamine 123 in single viable cells. Propentofylline at the therapeutic concentration of 50 microM completely inhibited the Ca(2+)-dependent Con A-induced increase in the production of reactive oxygen intermediates in peritoneal macrophages. In isolated and cultured microglial cells, which have a high spontaneous respiratory burst activity, the spontaneous production of reactive oxygen intermediates was reduced by approximately 30%. A phorbol 12-myristate 13-acetate-induced rise in the respiratory burst activity could not be inhibited by propentofylline in either cell type. An increased generation of reactive oxygen intermediates is thought to contribute to nerve cell death after brain ischemia, edema, and neurodegenerative diseases like Alzheimer's disease. These pathological conditions are all accompanied by an activation of microglial cells. We therefore suggest that the neuroprotective properties of propentofylline might in part be due to a modulation of the microglial production of potentially harmful reactive oxygen intermediates.

Inhibition of calcium signalling in murine splenocytes by polyamines: differential effects on CD4 and CD8 T-cells.

Transmembrane Ca2+ influx is recognized as a universal second messenger that transduces T-cell activation signals to cytoplasm and nucleus, thereby stimulating transcription and cell division. To examine the role of endogenous factors that regulate mitogenic Ca2+ signalling of T-cells, we measured the concanavalin (Con) A-induced increase in cytoplasmic free calcium ([Ca2+]i) in spleen cells of BALB/c mice, using flow cytometry with an indicator dye, Indo-1 acetoxymethyl ester (Indo-1/AM). Con A is a polyclonal activator of T-cells. Unstimulated splenocytes had a [Ca2+]i of 100 nM. [Ca2+]i increased with Con A in a dose-dependent manner up to a concentration of 50 micrograms/ml. In the presence of 50 micrograms/ml Con A, [Ca2+]i was 350 nM. Natural polyamines (putrescine, spermidine and spermine) inhibited Con-A-induced Ca2+ influx in a dose-dependent manner. Putrescine was the most effective polyamine in desensitizing the Ca2+ signal, and decreased [Ca2+]i from 350 nM in the absence of putrescine to 250 nM in the presence of 100 microM putrescine. This effect was not mimicked by structurally related homologues or inorganic cations, suggesting a specific structural effect of the polyamine. H.p.l.c. analysis showed that polyamines were internalized during incubation of cells in vitro. In experiments using monoclonal anti-CD4 and anti-CD8 antibodies, we found a differential effect of putrescine on Ca2+ influx in CD4 and CD8 subpopulations of T cells. For CD4+ cells, [Ca2+]i decreased from 625 nM to 420 nM in the presence of 500 microM putrescine, whereas [Ca2+]i was not affected by putrescine in CD8+ cells. These data suggest that natural polyamines have cell-specific effects on mitogen-stimulated Ca(2+)-influx in T-cell subsets.

The effect of endotoxemia on concanavalin A induced alterations in cytoplasmic free calcium in rat spleen cells as determined with Fluo-3

The effects of acute (3 h) and chronic (30 h) in vivo infusions of Escherichia coli endotoxin on the Ca 2+ homeostasis of rat spleen cells was investigated. Conditions were established for obtaining reliable estimates of [Ca 2+] i in these cells using the newly-developed Ca 2+ indicator Fluo-3. The resting [Ca 2+] i of splenocytes and T lymphocyte-enriched preparations were 119 ± 35 and 102 ± 31 nM, respectively. Treatment of the cells with concanavalin A (Con A) resulted in a rapid increase in [Ca 2+] i. The magnitude of the increase was positively correlated with the concentration of Con A, whereas the time required to reach the maximum [Ca 2+] i was inversely related to the amount of Con A. The peak [Ca 2+] i was attained more rapidly in splenocytes (i.e. ≤ 30 s) than in the T cell-enriched fraction (i.e. 1.5–2.0 min). Both the resting [Ca 2+] i and the Con A-induced increase in [Ca 2+] i were similar to values previously reported for other lymphocyte cell types using different Ca 2+ indicators, thereby supporting the values obtained with Fluo-3. Infusions of saline or endotoxin prior to the isolation of the cells did not result in significant alterations of either resting [Ca 2+] i or the cells' response to Con A. Since chronic infusions of endotoxin have previously been shown to cause a reduction in blastogenic responsiveness of splenocytes to Con A [1], these data suggest that the endotoxin-induced lesion occurs distal to the mobilization of intracellular Ca 2+.

Early increase in lymphocyte cyclic nucleotide phosphodiesterase activity upon mitogenic activation of human peripheral blood mononuclear cells.

Cyclic nucleotide phosphodiesterase activity of human peripheral blood mononuclear cells was significantly increased following a short (30 min) incubation with the mitogenic lectin Concanavalin A. Con A stimulated phosphodiesterase activity to the same extent whatever the subcellular compartment (homogenate, cytosol or pellet). Further separation of the Con A-activated mononuclear cells into lymphocyte-enriched and monocyte-enriched populations showed that the Con A-induced increase of phosphodiesterase activity exclusively affected the lymphocyte-enriched population. In lymphocytes, cyclic GMP phosphodiesterase activity was more importantly enhanced by Con A (+275%) than cyclic AMP phosphodiesterase activity (+75%). The increase of both activities occurred as early as from 10 min of Con A incubation and proved to be maximal with Con A doses of 2.5 and 5 micrograms per 10(6) cells, lower and higher doses being less effective. Inhibition experiments with reference inhibitors suggested that, among the high affinity phosphodiesterase isoforms, the cyclic GMP-inhibited enzyme might be more selectively enhanced by Con A than the cyclic AMP-specific, Rolipram-sensitive one. The non-mitogenic lectin Helix pomatia hemagglutinin, was not able to enhance cyclic nucleotide phosphodiesterase activity of human mononuclear cells whereas anti-CD3 monoclonal antibody, although being less effective than Con A, exhibited a significant stimulatory effect. Putting together these results suggest that the early increase in phosphodiesterase activity might be a normal step involved in the mitogenic activation of human lymphocyte.