Potentiation Of Nitric Oxide Production Research Articles

Seasonal dynamics and profiles of soil NO concentrations in a temperate forest

Soils are known to be significant sources of atmospheric nitric oxide (NO), a key compound in atmospheric chemistry. NO is a key regulating substance for inter- and intra-species signalling and competition and affects plant growth and soil microbial metabolisms. However, little is known about NO concentration in soils and production of NO in the soil profile. Here we report on soil NO concentrations down to 65 cm soil depth and soil surface flux measurements over a 15 months period in subdaily resolution. This is supplemented by information on aerobic and anaerobic NO production in various soil layers of a spruce stand in SW Germany. NO concentrations showed a clear seasonality with highest concentrations of up to 800 nmol mol−1 (or part per billion in volume mixing ratio; ppbv) at the interface between the organic Of-Oh sub-layers in the summer. NO concentrations in the mineral subsoil (−65 cm) were approx. One order of magnitude lower than in the organic layer. Dynamic changes of soil NO concentrations were closely correlated with soil surface NO fluxes. Differences in soil NO concentrations across the soil profile reflected differences in aerobic and anaerobic NO production potential. The importance of such high NO concentrations for soil microbial and plant physiological processes remains unclear, but should be addressed in future research in order to improve our understanding of microbe-microbe and plant-microbe interactions.

TGFβ1 and TNFα potentiate nitric oxide production in astrocyte cultures by recruiting distinct subpopulations of cells to express NOS-2

Nitric oxide (NO) synthase-2 (NOS-2), a key source of NO at sites of neuroinflammation, is induced in astrocyte cultures treated with lipopolysaccharide (LPS) plus interferon-γ (IFNγ). A recent study examining the regulation of astrocytic NOS-2 expression demonstrated that transforming growth factor-β1 (TGFβ1) potentiated LPS plus IFNγ-induced NOS-2 expression via expansion of the pool of astrocytes that express NOS-2. Results in the current report indicate that this population-based mechanism of increasing NOS-2 expression is not restricted to TGFβ1, since it also accounts for the potentiation of NO production in astrocyte cultures by tumor necrosis factor-α (TNFα). In contrast to TGFβ1, which required 24 h preincubation for optimal potentiation of NO production, TNFα was maximally effective when added concurrently with LPS plus IFNγ. Nevertheless, under conditions that optimally potentiated NO production, both cytokines recruited similar numbers of astrocytes to express NOS-2 (% NOS-2-positive cells after LPS plus IFNγ alone or with TNFα or TGFβ1 was 9.5 ± 1.2, 25.3 ± 2.9, and 32.4 ± 3.0, respectively). Interestingly, stimulation of astrocytes in the presence of both TGFβ1 and TNFα additively increased the number of astrocytes that expressed NOS-2 protein (% NOS-2-positive cells was 61.0 ± 4.2) relative to each cytokine alone. Potentiation of NO production by either TNFα or TGFβ1 was not ablated by neutralizing antibodies to TGFβ1 or TNFα, respectively. Thus, the two cytokines act independently to recruit separate pools of astrocytes to express NOS-2. These results are consistent with the notion that astrocytes possess an innate heterogeneity with respect to responsiveness to these cytokines.

Highly purified lipoteichoic acid induced pro‐inflammatory signalling in primary culture of rat microglia through Toll‐like receptor 2: selective potentiation of nitric oxide production by muramyl dipeptide

In contrast to the role of lipopolysaccharide from Gram-negative bacteria, the role of Gram-positive bacterial components in inducing inflammation in the CNS remains controversial. We studied the potency of highly purified lipoteichoic acid and muramyl dipeptide isolated from Staphylococcus aureus to activate primary cultures of rat microglia. Exposure of pure microglial cultures to lipoteichoic acid triggered a significant time- and dose-dependent production of pro-inflammatory cytokines (tumour-necrosis factor-alpha, interleukin-1beta, interleukin-6) and nitric oxide. Muramyl dipeptide strongly and selectively potentiated lipoteichoic acid-induced inducible nitric oxide synthase expression and nitric oxide production. However, it did not have any significant influence on the production of pro-inflammatory cytokines. As bacterial components are recognised by the innate immunity through Toll-like receptors (TLRs) we showed that lipoteichoic acid was recognised in microglia by the TLR2 and lipopolysaccharide by the TLR4, as cells isolated from mice lacking TLR2 or TLR4 did not produce pro-inflammatory cytokines and nitric oxide upon lipoteichoic acid or lipopolysaccharide stimulation, respectively. Lipoteichoic acid-induced glia activation was mediated by p38 and ERK1/2 MAP kinases, as pretreatment with inhibitor of p38 or ERK1/2 decreased lipoteichoic acid-induced cytokine release, iNOS mRNA expression and nitric oxide production. The observed pro-inflammatory response induced by lipoteichoic acid-activated microglia could play a major role in the inflammatory response of CNS induced by Gram-positive bacteria.

Potentiation by high potassium of lipopolysaccharide-induced nitric oxide production from cultured astrocytes

Uptake of K + is an important role of astrocytes to maintain physiological lower extracellular K + concentration in the CNS. In this study, the effect of high K + concentration was examined on the cellular function of astrocytes from embryonic rat brain in primary culture. Nitric oxide (NO) production induced by lipopolysaccharide (LPS) was measured as an index of cellular function of astrocytes. Increasing KCl concentration to about 40 mM did not directly evoke NO production, but doubled the level of LPS (1 ng/ml)-induced NO production. K-gluconate showed a similar enhancing effect although the degree of enhancement was about half of that of KCl. Neither NaCl nor Na-gluconate showed any effect. The K +-channel blocker, 4-aminopyridine, but not tetraethylammonium or apamin, inhibited the enhancing effect of KCl. The LPS-induced iNOS protein expression determined by immunoblotting analysis was enhanced by high K + treatment. The level of iNOS mRNA determined by real-time RT-PCR technique was also augmented by the presence of 40 mM KCl. These results indicate that the elevation of extracellular K + concentration regulates astrocytic cell functions through a mechanism involving K A-type K +-channels and that potentiation of NO production by high K + is due to the augmentation of iNOS mRNA and iNOS protein levels.

Capacity of AE to Modulate Nitric Oxide Production Depended on Intercellular Contact

Aloe emodin (AE) is a naturally occurring compound with wide spectrum of biological properties, including antimicrobial, vasorelaxant, immunosuppressive and anticancer actions. This anthraquinone induces apoptosis in several tumour cell lines with special affinity to tumours of neuroectodermal origin. High amounts of nitric oxide (NO) released by activated macrophages induce tumour cell death. Therefore, we explored the capacity of AE to modulate NO‐mediated antitumour response in vitro. Interestingly, while AE markedly suppressed NO release from macrophages alone, it significantly potentiated NO production in cocultures of macrophages and C6 cells, after 48 h of cultivation. Accordingly, the viability of C6 cells cocultivated with macrophages was reduced in the presence of AE. Moreover, the observed AE‐imposed potentiation of NO production in macrophages was closely related to macrophage culture cell density. According to these data, we proposed that NO modulator capacity of AE strongly depended on intercellular contact, indicating that macrophage antitumour response was not compromised but even potentiated by AE.

Stimulation of endothelin B receptor modulates the inflammatory activation of rat astrocytes.

Inside the brain tissue, endothelins play numerous important biological roles. One of the targets, astrocytes, predominantly display endothelin receptor subtype B (ET(B)). On cultured primary rat astroglial cells, we analyzed the effect of IRL1620, a selective ET(B) receptor agonist, on the production of nitric oxide (NO) and the synthesis of interleukin (IL)-6 and tumor necrosis factor (TNF)-alpha. We performed these experiments in the presence or absence of interferon-gamma (IFN-gamma) and/or lipopolysaccharide (LPS). IRL1620 decreases NO production under basal conditions and after IFN-gamma stimulation. However, during LPS-induced NO production, IRL1620 enhances this release. The basal IL-6 secretion and especially the LPS-induced synthesis are enhanced by the IRL1620 stimulation. The LPS-dependent TNF-alpha production is increased by the ET(B) stimulation. The IRL1620-induced decrease of basal NO production is not dependent on Ca2+ entry or on phospholipase C (PLC) activation, as shown by the use of LaCl3 and U73122, respectively. In the presence of LPS, the IRL1620 potentiation of NO production is inhibited by LaCl3 and U73122. The IRL1620-induced increase of IL-6 is dependent on PLC activation. These results suggest that endothelins can have dual effects depending on the costimulatory factors present. Endothelins thus have important immunomodulatory functions in the brain.

Iron potentiates nitric oxide scavenging by dithiocarbamates in tissue of septic shock mice

Vanin and co-workers (Kubrina et al., Biochim. Biophys. Acta 1176 (1993) 240–244; Mikoyan et al., Biochim. Biophys. Acta 1269 (1995) 19–24) reported that short term (30 min) iron (Fe) exposure potentiates nitric oxide (NO) production in tissues of septic shock mice, based on increased formation of NO complex by diethyldithiocarbamate (DETC). We have reexamined the effect of Fe administration in mice treated with Escherichia coli lipopolysaccharide (LPS) and have not found any changes in nitrosylhemoglobin (HbNO) or (NO 2 −+NO 3 −) levels in blood 30 min after Fe-citrate complex injection. However, Fe-citrate promotes NO complex formation by iron-dependent NO traps: DETC, pyrrolidinedithiocarbamate (PDTC) and N-methyl- d-glucamine dithiocarbamate (MGD), when given simultaneously at 6 h after LPS. Rather than potentiation of NO production, our data support that short-term iron treatment (30 min) enhances in vivo spin trapping ability of dithiocarbamate.