Французский язык. Практический курс по развитию навыков устной речи

<div><p>Nitrite is recognized as a bioactive nitric oxide (NO) metabolite. We have shown that nitrite inhibits platelet activation and increases platelet cGMP levels in the presence of partially deoxygenated erythrocytes. In this study, we investigated the effect of nitrite on phosphorylation of vasodilator-stimulated phosphoprotein on residue serine 239 (P-VASP^Ser239), a marker of protein kinase G (PKG) activation, in human platelets. In platelet-rich plasma (PRP), nitrite itself had no effect on levels of P-VASP^Ser239 while DEANONOate increased P-VASP^Ser239. Deoxygenation of PRP + erythrocytes (20% hematocrit) raised baseline P-VASP^Ser239 in platelets. At 20% hematocrit, nitrite (10 μM) increased P-VASP^Ser239 in platelets about 31% at 10–20 minutes of incubation while the levels of P-VASP^Ser157, a marker of protein kinase A (PKA) activation, were not changed. Nitrite increased P-VASP^Ser239 in platelets in the presence of deoxygenated erythrocytes at 20–40% hematocrit, but the effects were slightly greater at 20% hematocrit. In conclusion, our data confirm that nitrite increases P-VASP^Ser239 in platelets in the presence of deoxygenated erythrocytes. They also further support the idea that partially deoxygenated erythrocytes may modulate platelet activity, at least in part, via the NO/sGC/PKG pathway from NO formed by reduction of circulating nitrite ions.</p></div

Time-course curves suggest that nitrate is first converted to nitrite and subsequently to ammonia.

<p>Samples from <i>E.coli</i> (red line with circles) and <i>L</i>. <i>plantarum</i> (blue line with triangles) cultures grown at 2% O₂ with 5 mM nitrate were collected at regular intervals and analyzed for nitrite (panel A) and ammonia (panel B). (C). Ratio between nitrite and ammonia concentrations measured at each time point. Black lines represent <i>E.coli</i> cultures containing no added nitrate.</p

Bacterial species and strains used in this study.

<p>Corresponding final pH of culture media and lactic acid concentration after 24 h growth at 2% O₂ in LMRS are indicated.</p><p>^a pH of LMRS media after 24 h of bacterial growth. All are ± 0.1 (initial pH = 6.5)</p><p>^b Values are ± 1 mM and each sample was assayed in triplicates.</p><p>^c ND = non detectable</p><p>Bacterial species and strains used in this study.</p

Schematic representation of the link between different pathways of nitrogen oxides reduction in the human gut and the fate of ammonia.

<p>Each colored box represents a distinct pathway: Bacterial respiratory denitrification to dinitrogen in red box: the dissimilatory nitrate reduction to ammonia (DNRA) in blue box and the non-enzymatic conversion of nitrite to NO in green box (this route become significant only at pH<5.5). The endogenous L-arginine/NO synthase pathway from epithelial cells of the intestinal mucosa lining is also noted.</p

Bacterial NO generation and correlation with acidity of the growth medium.

<p>(A) Chemiluminescence detection of NO emission after injection of 100 μM nitrite in the vessel containing <i>E.coli</i> grown at different nitrate and oxygen conditions in modified LMRS broth for 24h. (B) Comparison of NO emission at 2% O₂ as in panel A, but using LAB cultures. Diagonal patter and solid bars indicate respectively the values detected before and after bacteria were re-suspended in fresh media at pH = 6.5 (as described in text). (C) Quantification of the amount of NO detected after injection of 100 μM or 250 μM nitrite in fresh LMRS media at different pH obtained by acidification with concentrated L-lactic acid. All data represent mean ± SD in duplicates.</p

Nitrate and oxygen effect on <i>E.coli</i> bacterial cultures growth and formation of nitrite and ammonia.

<p>(A) Growth curves for <i>E.coli</i> MG1655 grown in the absence (black closed symbols) or in the presence of 5 mM nitrate (red open symbols) at 37°C in LMRS broth at 21%, 2%, and 0% O₂ concentrations (respectively square, circle and diamond symbols). (B) Concentration of nitrite and ammonia (blue and red solid lines) in <i>E.coli</i> pellets after 24 h growth at different oxygen levels with 5 mM nitrate. (C) and (D) Respectively dependence on nitrate (at 0% O₂) and oxygen (at 5 mM nitrate) of nitrite and ammonia concentrations in the cell-free culture media after 24h growth. The ammonia content of LMRS alone is indicated by the dashed lines. Values are means ± SD (n = 3). The average SD resulted smaller than the symbols dimensions (0.04 OD) and it is not shown for clarity.</p

The effect of nitrate and oxygen gradients on the generation of nitrite and ammonia in different LAB cultures.

<p>Nitrite (A) and ammonia (B) concentrations were measured in LMRS media after 24 h growth at 2% O₂ with supplementation of different nitrate concentrations (0 to 10 mM). Similarly in (C) and (D) nitrate was fixed at 5 mM and we measured nitrite and ammonia dependence on oxygen concentrations (0, 2, 4, 6, 10 and 21%). Each point represents the mean ± SD (n = 3).</p

Comparative effects of nitrite and NO donors in deoxygenated whole blood.

<p>Quantification of P-VASP^Ser239/VASP at baseline (A) and after treatment of deoxygenated whole blood with nitrite, DEANONOate and sodium nitroprusside (B) are shown. Whole blood was deoxygenated by helium for 10 minutes. Nitrite (10 μM) was incubated in deoxygenated whole blood for 15 minutes while DEANONOate (1 μM) and sodium nitroprusside (10 μM) were incubated for 5 minutes, respectively. Data are mean ± SEM (n = 5). *<i>P</i> < 0.05 compared with PRP and tested by one-way ANOVA with Tukey’s multiple comparison. ^#<i>P</i> < 0.05 compared with control and tested by one-way ANOVA with Tukey’s multiple comparison.</p

Increased P-VASP^Ser239 induced by DEANONOate but not nitrite in PRP.

<p>Representative Western blot bands of P-VASP^Ser239 and VASP expression in PRP treated with 10 μM nitrite (A) or 1 μM DEANONOate (B) and quantification of P-VASP^Ser239/VASP (C) at 37 °C for 5, 10, 15, 20, 40 and 60 minutes are shown. Data are mean ± SEM (n = 3). *<i>P</i> < 0.05 tested by Student’s t-test.</p

Influences of different perturbations in NO metabolism on nitrite and nitrate levels in whole blood.

<p>C57BL/6 mice were randomly divided into four groups and treated with antibiotics (bacitracin (4 mg/ml), neomycin (4 mg/ml), tetracycline (1 mg/ml)) or L-NAME (1 g/L) or low nitrite/nitrate (NOx) diet for a week. Age-matched eNOS knock-out mice were used. Nitrite (A) and nitrate (B) were measured using a chemiluminescence NO analyzer (Sievers, Model 280 NO analyzer). Relative values to wild-type control on standard diets were calculated in each treatment group and inserted in both (A) and (B). Data are means ± SEM (n≥7). *p<0.05.</p