Inhibition by fenamates of calcium influx and proliferation of human lymphocytes

Autumnalamide targeted proteins of the immunophilin family

Previous works with autumnalamide reported that Store Operated Calcium (SOC) channels were blocked through mitochondrial modulation. In the present paper we studied the effect of autumnalamide on ionomycin Ca²⁺ fluxes. Thus, autumnalamide did not modify ionomycin-sensitive intracellular pools while the ionomycin-induced Ca²⁺ influx was blocked with similar potency whether the incubation was done before or after ionomycin-sensitive pools depletion. Nevertheless, autumnalamide was not able to inhibit ionomycin-induced Ca²⁺ influx once the membrane channels were activated. Moreover, the compound efficiently inhibited flufenamic acid (FFA) Ca²⁺ release induced in this organelle but no the next influx. Since in previous work the effect of autumnalamide was inhibited by cyclosporine A (CsA), structures that target this drug were studied. Therefore, the affinity of autumnalamide for cyclophilin D (Cyp D) was examined. The K_D obtained for Cyp D- autumnalamide was 1.51±1.399. Moreover, the K_D for Cyp A- autumnalamide was calculated. The peptide had a similar order of Cyp A binding affinity than CsA (8.08±1.23 and 6.85±1.1μM respectively). After testing autumnalamide-binding capacity for Cyp A, the activity of this compound on Cyp A pathway was tested. Thus, the effect on interleukin (IL)-2 release on activated T-lymphocytes was checked. Autumnalamide was able to reduce IL-2 levels near to T cells in resting conditions. Next, the effect over calcineurin and NFATc1 was also evaluated. While CsA inhibits both calcineurin and NFATc1, autumnalamide did not produce any effect. From these results we can conclude that, autumnalamide targeted mitochondrion and prevent T-cells from IL-2 production through the modulation of SOC Ca²⁺ channels.

Calcium mobilization is both required and sufficient for initiating chromatin decondensation during activation of peripheral T-cells

Antigen engagement of the T-cell receptor (TCR) induces a rapid and dramatic decondensation of chromatin that is necessary for T-cell activation. This decondensation makes T-cells competent to respond to interleukin-2 providing a mechanism to ensure clonotypic proliferation during an immune response. Using murine T-cells, we investigated the mechanism by which TCR signaling can initiate chromatin decondensation, focusing on the role of calcium mobilization. During T-cell activation, calcium is first released from intracellular stores, followed by influx of extracellular calcium via store operated calcium entry. We show that mobilization of intracellular calcium is required for TCR-induced chromatin decondensation. However, the decondensation is not dependent on the activity of the downstream transcription factor NFAT. Furthermore, we show that the influx of extracellular calcium is dispensable for initiating chromatin decondensation. Finally, we show that mobilization of calcium from intracellular stores is sufficient to induce decondensation, independent of TCR engagement. Collectively, our data suggest that chromatin decondensation in peripheral T-cells is controlled by modulating intracellular calcium levels.

Store-operated calcium entry mediates intracellular alkalinization, ERK1/2, and Akt/PKB phosphorylation in bovine neutrophils

Neutrophil's responses to G protein-coupled chemoattractants are highly dependent on store-operated calcium (Ca(2+)) entry (SOCE). Platelet-activating factor (PAF), a primary chemoattractant, simultaneously increases cytosolic-free Ca(2+), intracellular pH (pH(i)), ERK1/2, and Akt/protein kinase B (PKB) phosphorylation. In this study, we looked at the efficacy of several putative SOCE inhibitors and whether SOCE mediates intracellular alkalinization, ERK1/2, and Akt/PKB phosphorylation in bovine neutrophils. We demonstrated that the absence of external Ca(2+) and the presence of EGTA reduced the intracellular alkalinization and ERK1/2 phosphorylation induced by PAF, apparently via SOCE influx inhibition. Next, we tested the efficacy of several putative SOCE inhibitors such as 2-aminoethoxydiphenyl borate (2-APB), capsaicin, flufenamic acid, 1-{beta-[3-(4-methoxy-phenyl)propoxy]-4-methoxyphenethyl}-1H-imidazole hydrochloride (SK&F 96365), and N-(4-[3,5-bis(trifluoromethyl)-1H-pyrazol-1-yl]phenyl)-4-methyl-1,2,3-thiadiazole-5-carboxamide (BTP2) on Ca(2+) entry induced by PAF or thapsigargin. 2-APB was the most potent SOCE inhibitor, followed by capsaicin and flufenamic acid. Conversely, SK&F 96365 reduced an intracellular calcium ([Ca(2+)](i)) peak but SOCE partially. BTP2 did not show an inhibitory effect on [Ca(2+)](i) following PAF stimuli. 2-APB strongly reduced the pH(i) recovery, whereas the effect of flufenamic acid and SK&F 96365 was partial. Capsaicin and BTP2 did not affect the pH(i) changes induced by PAF. Finally, we observed that 2-APB reduced the ERK1/2 and Akt phosphorylation completely, whereas the inhibition with flufenamic acid was partial. The results suggest that 2-APB is the most potent SOCE inhibitor and support a key role of SOCE in pH alkalinization and PI-3K-ERK1/2 pathway control. Finally, 2-APB could be an important tool to characterize Ca(2+) signaling in neutrophils.

Topological models for prediction of anti-inflammatory activity of N-arylanthranilic acids

Relationship of anti-inflammatory activity of N-arylanthranilic acids with distance based Wiener's index, adjacency based Zagreb indices M1 and M2, and distance-cum-adjacency based eccentric connectivity index (ECI) was investigated. A dataset comprising of 112 N-arylanthranilic acids was selected. The values of all the four indices for each of the 112 compounds were calculated using an in-house computer program. The dataset was divided randomly into training and test sets. The data was analyzed and suitable models were developed after identification the active ranges in the training set. Subsequently, a biological activity was assigned to each of the compound involved in the test set using these models, which was then compared with the reported anti-inflammatory activity. High accuracy of prediction ranging from 83% to 90% was observed using models based upon topological indices.

Fenamates stimulate BKCa channel osteoblast-like MG-63 cells activity in the human

BACKGROUND

The fenamates, a family of nonsteroidal anti-inflammatory drugs that are derivatives of N-phenylanthranilic acid, are the inhibitors of cyclo-oxygenase. The ionic mechanism of actions of these compounds in osteoblasts is not well understood.

METHODS

The effects of the fenamates on ionic currents were investigated in a human osteoblast-like cell line (MG-63) with the aid of the whole-cell and inside-out configurations of the patch-clamp technique.

RESULTS

In MG-63 cells, niflumic acid and meclofenamic acid increased K+ outward currents (IK). The niflumic acid-stimulated IK was reversed by subsequent application of iberiotoxin or paxilline, yet not by that of glibenclamide or apamin. In the inside-out configuration, niflumic acid (30 micromol/L) added to the bath did not modify single-channel conductance but increased the activity of large-conductance Ca2+-activated K+ (BKCa) channels. The EC50 values for niflumic acid- and meclofenamic acid-induced channel activity were 22 and 24 micromol/L, respectively. Niflumic acid (30 micromol/L) and meclofenamic acid (30 micromol/L) shifted the activation curve of BKCa channels to less positive membrane potentials. Membrane stretch potentiated niflumic acid-stimulated channel activity. The rank order of potency for the activation of BKCa channels in these cells was niflumic acid = meclofenamic acid > tolfenamic acid > flufenamic acid > nimesulide. Evans blue and nordihydroguaiaretic acid increased channel activity; however, indomethacin, piroxicam, and NS-398 had no effect on it.

CONCLUSIONS

The fenamates can stimulate BKCa channel activity in a manner that seems to be independent of the action of these drugs on the prostaglandin pathway. The activation of the BKCa channel may hyperpolarize the osteoblast, thereby modulating osteoblastic function.

Suppression of EGF-induced cell proliferation by the blockade of Ca2+ mobilization and capacitative Ca2+ entry in mouse mammary epithelial cells

The role of intracellular Ca2+ stores and capacitative Ca2+ entry on EGF-induced cell proliferation was investigated in mouse mammary epithelial cells. We have previously demonstrated that EGF enhances Ca2+ mobilization (release of Ca2+ from intracellular Ca2+ stores) and capacitative Ca2+ entry correlated with cell proliferation in mouse mammary epithelial cells. To confirm their role on EGF-induced cell cycle progression, we studied the effects of 2,5-di-tert-butylhydroquinone (DBHQ), a reversible inhibitor of the Ca2+ pump of intracellular Ca2+ stores, and SK&F 96365, a blocker of capacitative Ca2+ entry, on mitotic activity induced by EGF. Mitotic activity was examined using an antibody to PCNA for immunocytochemistry. SK&F 96365 inhibited capacitative Ca2+ entry in a dose-dependent manner (I50: 1-5 microM). SK&F 96365 also inhibited EGF-induced cell proliferation in the same range of concentration (I50: 1-5 microM). DBHQ suppressed [Ca2+]i response to UTP and thus depleted completely Ca2+ stores at 5 microM. DBHQ also inhibited EGF-induced cell proliferation at an I50 value of approximately 10 microM. The removal of these inhibitors from the culture medium increased the reduced mitotic activity reversibly. Using a fluorescent assay of DNA binding of ethidium bromide, no dead cells were detected in any of the cultures. These results indicate that the inhibitory effects of SK&F 96365 and DBHQ on cell proliferation were due to the inhibition of capacitative Ca2+ entry and Ca2+ mobilization suggesting the importance of capacitative Ca2+ entry and Ca2+ mobilization in the control of EGF-induced cell cycle progression in mouse mammary epithelial cells.

Effects of K(+) channel inhibitors on relaxation induced by flufenamic and tolfenamic acids in guinea-pig trachea

The effects of different K(+) channel inhibitors on flufenamic- and tolfenamic-acids-induced relaxation were studied in prostaglandin F(2alpha) (1 microM) precontracted guinea-pig trachea. Flufenamic and tolfenamic acids (each 0.1-33 microM) and lemakalim (0.01-33 microM), but not indomethacin (0.1-33 microM), caused relaxation. Iberiotoxin (33 and 100 nM) inhibited flufenamic- and tolfenamic-acids-, but not lemakalim-, induced relaxation. Iberiotoxin (100 nM) inhibited nifedipine (10 nM-10 microM)-induced relaxation. Nifedipine (0.1 microM) inhibited the blockade of fenamate-induced relaxation by iberiotoxin. Apamin (0.1 and 1 microM) did not affect flufenamic- and tolfenamic-acids- and lemakalim-induced relaxation. Glibenclamide (10 and 33 microM) inhibited lemakalim-, but not flufenamic- and tolfenamic-acids-, induced relaxation. 4-Aminopyridine (0.5 and 2 mM) inhibited flufenamic- and tolfenamic- acids- and lemakalim-induced relaxation. Flufenamic- and tolfenamic-acids-induced relaxation is likely to be activation of Ca(2+)-activated K(+) channels and differs from that of lemakalim.

Antagonism between the metabolic responses induced by epinephrine and piroxicam on isolated rat hepatocytes

Nonsteroidal anti-inflammatory drugs (NSAIDs) are one of the most employed therapeutic agents. They have a wide spectrum of biological effects, some of which are independent of cyclooxygenase inhibition, such as the alterations on the components of signal transduction systems. In particular, previous data from our laboratory suggested an antagonism between epinephrine and piroxicam, one of the most prescribed NSAIDs. Thus, this study deals with the epinephrine-piroxicam antagonism recorded for metabolic responses in isolated rat hepatocytes. The obtained results show that epinephrine stimulates lactate and ethanol consumption, stimulates glucose release from lactate only, and has no effect on cellular triacylglycerides content. Otherwise, in a dose-dependent basis, piroxicam stimulates lactate and ethanol consumption accompanied by an increase in triacylglycerides content, without changes in glucose release by hepatocytes. Piroxicam blocks the epinephrine-induced stimulation of glucose release from lactate, and epinephrine blocks the piroxicam-mediated increase in triacylglycerides content from lactate or ethanol. In contrast, the effects of epinephrine and piroxicam, promoting the consumption of lactate and ethanol, are not antagonized or added after the simultaneous administration of both compounds. This last result is probably related to the ability of both compounds to stimulate oxygen consumption. On isolated rat liver mitochondria, micromolar doses of piroxicam partially uncouple oxidative phosphorylation, and paradoxically stimulates an ATP-dependent mitochondrial function as citrullinogenesis. These results show for first time, on isolated rat hepatocytes, an antagonism between the metabolic responses of epinephrine and piroxicam, at the concentration found in plasma after its therapeutical administration.

Ca2+ mobilization and capacitative Ca2+ entry regulate DNA synthesis in cultured chick retinal neuroepithelial cells

Release of Ca2+ from intracellular Ca2+ stores (Ca2+ mobilization) and capacitative Ca2+ entry have been shown to be inducible in neuroepithelial cells of the early embryonic chick retina. Both types of Ca2+ responses decline parallel with retinal progenitor cell proliferation. To investigate their potential role in the regulation of neuroepithelial cell proliferation, we studied the effects of 2,5-di-tert-butylhydroquinone (DBHQ), an inhibitor of the Ca2+ pump of intracellular Ca2+ stores, and of SK&F 96365, an inhibitor of capacitative Ca2+ entry, on DNA synthesis in retinal organ cultures from embryonic day 3 (E3) chicks and in dissociated cultures from E7 and E9 chick retinae. We demonstrate that both antagonists inhibit [3H]-thymidine incorporation in a dose-dependent manner without affecting cell viability or morphology. The inhibition of [3H]-thymidine incorporation by SK&F 96365 occurred in the same concentration range (IC50: approximately 4 microM) as the blockade of capacitative Ca2+ entry in the E3 retinal organ culture. At a concentration of 5 microM SK&F 96365. DNA synthesis was reduced by 71, 40 and 32% in the E3, E7 and E9 cultures, respectively. Application of DBHQ at concentrations which led to depletion of intracellular Ca2+ stores also inhibited [3H]-thymidine incorporation with IC50 values of 20-30 microM in the different cultures. Our results suggest the involvement of Ca2+ mobilization and capacitative Ca2+ entry in the regulation of DNA synthesis in the developing neural retina.