[Protective effect of gangliosides against the toxic action of bacterial lipopolysaccharide of various serotypes on PC12 cells].

The effect of bacterial lipopolysaccharide (LPS) from E. coli on the viability of PC12 neuronal cell line was studied. LPS of 0111:B4 serotype and LPS of 055:B5 serotype were shown to have toxic effect on PC12 cells. But the toxic effect of LPS of 0127:B8 serotype was not revealed. Preincubation of PC12 cells with GM1 or GD1a gangliosides was found to diminish significantly the death of the cells and the formation of reactive oxygen species induced by LPS of 0111:B4 and 055:B5 serotypes in them. The protective effect of GM1 and GD1a was found not to depend on the presence of the inhibitor of Trk receptor tyrosine kinase in the medium, though activation of this protein kinase was previously shown to mediate the protective effect of gangliosides against the action of excitatory amino acids, pro-oxidants and other toxins on neurons and cells of neuronal cell lines. The protective effect of gangliosides against the LPS action on PC12 cells was similar to the effect of methyl-beta-cyclodextrin, which was shown to disturb cell membrane raft structure. The suggestion is put forward that the pronounced diminution of toxic effect of LPS on PC12 cells by gangliosides may be explained by the alteration of structural organization of lipid rafts caused by the incorporation of exogenous gangliosides in cell plasma membranes, which diminishes the translocation of TLR4 receptor into the rafts and their activation by LPS.

[Gangliosides GM1 and GD1a modulate inflammatory effect of bacterial lipopolysaccharide in epithelial cells].

It is known that exogenous gangliosides (GL) inhibit acute inflammatory signals in different cells induced by Escherichia coli lipopolysaccharide (LPS). Until now the mechanisms underlying their effect are unknown. We hypothesize that the anti-inflammatory effect of GL is caused by their ability to modify TLR4 translocation into the lipid rafts. To test this hypothesis, we studied the effect of exogenous GL on LPS-induced inflammatory reactions associated with increased nitric oxide and prostaglandin E2 (PGE2) production in epithelial cells isolated from the frog Rana temporia urinary bladder. It was shown that preincubation of cells with GM1 and GD1a in the concentration range from 100 nm to 50 µM reduced the effect of 25 µg/ml LPS E. coli on the increase of NO and PGE2 production. The effect of LPS was also eliminated in the presence of polymyxin B, capable to interact with lipid A in LPS molecule, which makes it inaccessible for binding to TLR4. The subcellular fractionation of epithelial cells in the sucrose density gradient in combination with immunoblotting revealed that LPS stimulates translocation of TLR4 into the lipid rafts in the cytoplasmic membrane. Preincubation of cells with GM1 or GD1a at concentration 20 µM completely eliminated the effect of LPS. A similar effect was revealed with 1 mM methyl-ß-cyclodextrin, a classical destructor of the lipid rafts. The results indicate the existence of a previously unknown mechanism of the anti-inflammatory effect of exogenous GL associated with their ability to interfere with LPS-induced translocation of TLR4 into the lipid rafts preventing LPS signal transduction. It is assumed that the observed effect of GL is based on their incorporation into cytoplasmic membrane and modification of the lipid rafts organization.

[Regulatory interconnections of cyclooxigenase and inducible no-synthase in urinary bladder epithelial cells of the frog Rana temporaria under action of bacterial stimuli].

Earlier we have shown that in epithelial cells of the frog urinary bladder under action of bacterial lipopolysaccharides (LPS) there is activated expression of inducible NO-synthase (iNOS) and there is increased the NO production, which can play an important role in providing protective cell reactions from pathogens. The goal of the present work consisted in study of cyclooxigenase (cOG) products and mechanisms of their regulatory effect on expression of iNOS under action of LPS. In experiments on urinary bladder epithelial cells on the frog Rana temporaria it has been shown that incubation of the cells for 21 h with LPS leads to a rise in production of PGE2 and nitrites, stable NO metabolites. Inhibitor of iNOS 1400W decreased sharply production of nitrites, but did not affect the PGE2 level. Both the basal and the LPS-stimulated level of PGE2 and nitrites were inhibited in the presence of selective cOG inhibitors--SC-560 (cOG-1) and NS-398 (cOG-2). The IC50 value amounted to 90, 220, and 470 microM for NS-398, SC-560, and diclofenac (unspecific inhibitor of both isoforms), respectively. PGE2 and butaprost, the EP2-receptor agonist, but not agonists of EP1/EP3 or EP1 receptors, partially eliminated the inhibitory action of diclofenac on production of nitrites. Action of PGE2 was accompanied by an increase in the intracellular cAMP. Analysis of expression of iNOS mRNA in the epithelial cells incubated with LPS or LPS + inhibitor of cOG has shown the LPS-stimulated rise in expression of iNOS mRNA to decrease sharply in the presence of SC-560 or NS-398. Thus, the epithelial cells of the frog urinary bladder have the effectively functioning system of the congenital immune protection against bacterial pathogens, the most important component of this system being PGE2 and NO. Analysis of mechanisms of regulatory interactions of cOG and iNOS indicates that in this cell type the main regulators of iNOS expression and of the nitrogen oxide level are products of the cOG catalytic activity.

[Lipopolysaccharide E. coli inhibits the arginine-vasotocin-induced increase of osmotic water permeability in the frog urinary bladder].

Since Gram-negative bacteria are known to be present in the cavity of urinary bladders in amphibian species, it was interesting to study the effect of bacterial endotoxins on epithelial signaling network which provides the arginine-vasotocin-induced increase of osmotic water permeability (OWP). The effect of LPS E. coli on AVT-induced OWP was studied in isolated frog Rana temporaria L. urinary bladder incubated during 20-21 hours in modified L-15 culture medium in sterile conditions. The LPS (25 microg/ml) was added into the mucosal solution. It was shown that exposure to LPS caused a strong suppression of the increase of OWP under AVT (0.5 nM), forskolin (35 microM) or IBMX (200 microM). Moreover, LPS induced more than 2-folds decrease both ofbasal and AVT-stimulated content of cAMP in the bladder tissue. The inhibitory effect of LPS on AVT-induced increase of OWP was eliminated in the presence of ODQ, 20 microM, a cytosolic guanylate cyclase inhibitor. With the use of RT-PCR it was shown that the expression of mRNA iNOS was 10-fold increased in 6 hours after LPS administration. These findings demonstrate the ability of frog bladder mucosal epithelial cells to recognize bacterial LPS and initiate antipathogen immune response related to increased production of nitric oxide. The activation of signal transduction cascade mediated by the LPS-induced immune response leads to a decrease of intracellular cAMP and down-regulates AVT-stimulated OWP acting at least in part through NO/cGMP-dependent signaling pathway.

[No-synthase activity in primary cultured frog urinary bladder epithielial cells and no-dependent antimicrobial effect].

We have shown previously that endogenous NO modulates the effect of arginine-vasotocin on the increase in the osmotic water permeability of the frog urinary bladder epithelium. The aim of the present work was to develop a procedure of cultivation of epithelial cells from the frog urinary bladder as a primary culture in order to study in vitro the cellular production of NO and its regulation. Isolated cells were cultivated in modified L-15 medium with 10% FBS and gentamycin (40 microg/ml) at room temperature. Under these conditions, at least 50% cells kept their viability until 8 days of incubation. NO-synthase (NOS) activity was estimated as nitrite (NO2-) accumulation in culture medium; NO2- concentration in the presence of L-NAME, inhibitor of all NOS types, was considered as NOS-independent and was subtracted from each value. The nitrite accumulation was linear in time during 3 days of cultivation and was inhibited by 1400W, inducible NOS (iNOS) inhibitor, and 7-nitroindazole, constitutive NOS's inhibitor, at doses 5-50 and 10-200 microM, respectively. One-day incubation of he cells in the medium with low concentration of gentamycin (1 or 2 microg/ml) led to the significant increase in amount of bacterial in cultured fluid identified as E. coli and Acinetobacter sp. Addition of L-NAME (5 - 103 M) to the medium potentiated the bacteria growth 1.5- and 2.5-times in the presence of 2 and 1 microg gentamycin/ml, respectively. Thus, epithelial cells form the frog urinary bladder possess NO-dependent antibacterial effect which is probably provided by induction of iNOS expression. Taken together, these data demonstrate that the primary culture of the frog urinary bladder epithelial cells is a perspective experimental model for the study of regulation of NOS activity and NO production being of particular interest in relation to the defense effect of NO in epithelia.

[Arginase activity in the frog urinary bladder epithelial cells and its involvement in regulation of nitric oxide production].

The activity of arginase converting arginine into ornithine and urea is of particular interest among many factors regulating NO production in the cells. It is known that by competing with NO-synthase for common substrate, arginase can affect the NO synthesis. In the present work, the properties of arginase from the frog Rana temporaria L. urinary bladder epithelial cells possessing the NO-synthase activity were characterized, and possible contribution of arginase to regulation of NO production by epithelial cells was studied. It has been shown that the enzyme had the temperature optimum in the range of 55-60 degrees C, K(m) for arginine 23 mM, and V(max) about 10 nmol urea/mg protein/min, and its activity was effictively inhibited by (S)-(2-boronoethyl)-L-cysteine (BEC), an inhibitor of arginase, at concentrations from 10(-6) to 10(-4) M. The comparison of arginase activity in various frog tissues revealed the following pattern: liver > kidney >> brain > urinary bladder (epithelium) > heart > testis. The arginase activity in the isolated urinary bladder epithelial cells was 3 times higher than that in the intact urinary bladder. To evaluate the role of arginase in the regulation of NO production, epithelial cells were cultivated in the media L-15 or 199 containing different amounts of arginine; the concentration of NO2-, the stable NO metabolite, was determined in the culture fluid after 18-20 h of cells incubation. The vast majority of the produced nitrites are associated with the NOS activity, as L-NAME, the NOS-inhibitor, decreased their accumulation by 77.1% in the L-15 medium and by 80% in 199 medium. BEC (10(-4) M) increased the nitrite production by 18.0 % +/- 2.7 in the L-15 medium and by 24.2 +/- 3.5 in the 199 medium (p < 0.05). The obtained data indicate a relatively high arginase activity in the frog urinary bladder epithelium and its involvement in regulation of NO production by epithelial cells.

[The presence of nitric oxide synthase in mucosal epithelial cells of the frog urinary bladder].

In experiments on frog Rana temporaria L. urinary bladder, we investigated localization of NO-synthase (NOS) in urinary bladder slices and measured NOS activity in the suspension of mucosal epithelial cells. Intensive NADPH-diaphorase staining which is widely used as an indicator of NOS activity was found in mucosal epithelium. Almost all mucosal epithelial cells isolated in Ca2+ -free conditions demonstrated positive NADPH-diaphorase reactivity. Direct measurement of NOS activity in suspension of mucosal cells determined by the rate of conversion of L-arginine to L-citrullin showed that the enzyme activity was reduced in absence of external Ca2+ and was inhibited by L-NAME: non-specific NOS inhibitor, and 1400 W: a highly selective iNOS inhibitor (control: 754 +/- 184; L-NAME, 1 mM 329 +/- 87; 1400 W, 20 mM: 547 +/- 25; Ca2+ -free/EDTA: 490 +/- 184 cpm [3H]-citrullin/10(6) cells per 45 min, p < 0.05, n = 7-8). The data obtained demonstrate that frog urinary bladder mucosa epithelial cells provided antidiuretic hormone-induced increase of osmotic water permeability contain nitric oxide synthase. The presence of inducible (iNOS) as well as constitutive isoform(s) revealed in these cells allows to suggest involvement of NOS in intracellular signaling pathways regulated water transport across the epithelium.