Endogenous nitric oxide production in canine osteoarthritis: Detection in urine, serum, and synovial fluid specimens

OBJECTIVE To measure nitric oxide (NO) concentrations in serum, urine, and synovial fluid (SF) of dogs with naturally occurring cranial cruciate ligament (CCL) rupture and normal dogs, and to compare these with clinical and histologic changes of osteoarthritis (OA). STUDY DESIGN Prospective clinical study including 2 groups of animals selected from the hospital population. ANIMALS Forty-three dogs (CCL group) with OA secondary to CCL rupture; 30 healthy dogs (control group) without CCL rupture. METHODS Serum, urine, and SF were collected before and during surgery in the CCL group or immediately after euthanasia in the control group. Articular cartilage and synovial membrane tissue specimens were prepared for routine histologic examination. The stable end products of NO, total nitrite and nitrate (NOt) activity, were measured in body fluids and compared with macroscopic and histologic degrees of OA. Urinary NOt concentration was compared with urinary creatinine concentration and stated as urinary NOt:creatinine ratio (UNCR). RESULTS-SF NOt concentrations were not significantly different between the 2 groups. Serum NOt concentrations (45.6 vs 28.9 micromol/L; P =.042) and the UNCR (0.007 vs 0.004; P =.035) were significantly higher in dogs of the CCL group compared with the control population. An association between UNCR and histologic and macroscopical OA grades could be demonstrated. CONCLUSION UNCR might be a useful indicator of nitrite and nitrate production and, therefore, osteoarthritic changes in joints. CLINICAL RELEVANCE UNCR could be used as a tool to evaluate the NOt production by joint tissues over time and might therefore provide a method of evaluating the effects of drugs in the control of osteoarthritis.

Correlation of urinary nitric oxide concentrations with the development of hip dysplasia in Labrador retrievers

Urinary nitric oxide was determined in terms of the ratio of the concentrations of total urinary nitrite and nitrate:creatinine in 40 juvenile labrador retrievers, and radiographic signs of hip dysplasia and distraction indices were investigated in the same dogs in later life. The ratio was correlated significantly with the Norberg angle and with subchondral sclerosis in both hips, and with the grade of dysplasia in each hip and the dogs' overall grade of hip dysplasia. No correlations were observed between the ratio and the distraction indices or other radiographic criteria for hip dysplasia.

Nitric oxide sustains IL-1β expression in human dendritic cells enhancing their capacity to induce IL-17-producing T-cells

The role played by lung dendritic cells (DCs) which are influenced by external antigens and by their redox state in controlling inflammation is unclear. We studied the role played by nitric oxide (NO) in DC maturation and function. Human DCs were stimulated with a long-acting NO donor, DPTA NONOate, prior to exposure to lipopolysaccharide (LPS). Dose-and time-dependent experiments were performed with DCs with the aim of measuring the release and gene expression of inflammatory cytokines capable of modifying T-cell differentiation, towardsTh1, Th2 and Th17 cells. NO changed the pattern of cytokine release by LPS-matured DCs, dependent on the concentration of NO, as well as on the timing of its addition to the cells during maturation. Addition of NO before LPS-induced maturation strongly inhibited the release of IL-12, while increasing the expression and release of IL-23, IL-1β and IL-6, which are all involved in Th17 polarization. Indeed, DCs treated with NO efficiently induced the release of IL-17 by T-cells through IL-1β. Our work highlights the important role that NO may play in sustaining inflammation during an infection through the preferential differentiation of the Th17 lineage.

Nitric oxide inhalation reduces brain damage, prevents mortality, and improves neurological outcome after subarachnoid hemorrhage by resolving early pial microvasospasms.

Subarachnoid hemorrhage is a stroke subtype with particularly bad outcome. Recent findings suggest that constrictions of pial arterioles occurring early after hemorrhage may be responsible for cerebral ischemia and - subsequently - unfavorable outcome after subarachnoid hemorrhage. Since we recently hypothesized that the lack of nitric oxide may cause post-hemorrhagic microvasospasms, our aim was to investigate whether inhaled nitric oxide, a treatment paradigm selectively delivering nitric oxide to ischemic microvessels, is able to dilate post-hemorrhagic microvasospasms; thereby improving outcome after experimental subarachnoid hemorrhage. C57BL/6 mice were subjected to experimental SAH. Three hours after subarachnoid hemorrhage pial artery spasms were quantified by intravital microscopy, then mice received inhaled nitric oxide or vehicle. For induction of large artery spasms mice received an intracisternal injection of autologous blood. Inhaled nitric oxide significantly reduced number and severity of subarachnoid hemorrhage-induced post-hemorrhage microvasospasms while only having limited effect on large artery spasms. This resulted in less brain-edema-formation, less hippocampal neuronal loss, lack of mortality, and significantly improved neurological outcome after subarachnoid hemorrhage. This suggests that spasms of pial arterioles play a major role for the outcome after subarachnoid hemorrhage and that lack of nitric oxide is an important mechanism of post-hemorrhagic microvascular dysfunction. Reversing microvascular dysfunction by inhaled nitric oxide might be a promising treatment strategy for subarachnoid hemorrhage.

Acquisition of a multifunctional IgA+ plasma cell phenotype in the gut

The largest mucosal surface in the body is in the gastrointestinal tract, a location that is heavily colonized by microbes that are normally harmless. A key mechanism required for maintaining a homeostatic balance between this microbial burden and the lymphocytes that densely populate the gastrointestinal tract is the production and transepithelial transport of poly-reactive IgA (ref. 1). Within the mucosal tissues, B cells respond to cytokines, sometimes in the absence of T-cell help, undergo class switch recombination of their immunoglobulin receptor to IgA, and differentiate to become plasma cells. However, IgA-secreting plasma cells probably have additional attributes that are needed for coping with the tremendous bacterial load in the gastrointestinal tract. Here we report that mouse IgA(+) plasma cells also produce the antimicrobial mediators tumour-necrosis factor-α (TNF-α) and inducible nitric oxide synthase (iNOS), and express many molecules that are commonly associated with monocyte/granulocytic cell types. The development of iNOS-producing IgA(+) plasma cells can be recapitulated in vitro in the presence of gut stroma, and the acquisition of this multifunctional phenotype in vivo and in vitro relies on microbial co-stimulation. Deletion of TNF-α and iNOS in B-lineage cells resulted in a reduction in IgA production, altered diversification of the gut microbiota and poor clearance of a gut-tropic pathogen. These findings reveal a novel adaptation to maintaining homeostasis in the gut, and extend the repertoire of protective responses exhibited by some B-lineage cells.

Evidence that N-acetylcysteine inhibits TNF-alpha-induced cerebrovascular endothelin-1 upregulation via inhibition of mitogen- and stress-activated protein kinase

N-acetylcysteine (NAC) is neuroprotective in animal models of acute brain injury such as caused by bacterial meningitis. However, the mechanism(s) by which NAC exerts neuroprotection is unclear. Gene expression of endothelin-1 (ET-1), which contributes to cerebral blood flow decline in acute brain injury, is partially regulated by reactive oxygen species, and thus a potential target of NAC. We therefore examined the effect of NAC on tumor necrosis factor (TNF)-alpha-induced ET-1 production in cerebrovascular endothelial cells. NAC dose dependently inhibited TNF-alpha-induced preproET-1 mRNA upregulation and ET-1 protein secretion, while upregulation of inducible nitric oxide synthase (iNOS) was unaffected. Intriguingly, NAC had no effect on the initial activation (i.e., IkappaB degradation, nuclear p65 translocation, and Ser536 phosphorylation) of NF-kappaB by TNF-alpha. However, transient inhibition of NF-kappaB DNA binding suggested that NAC may inhibit ET-1 upregulation by inhibiting (a) parallel pathway(s) necessary for full transcriptional activation of NF-kappaB-mediated ET-1 gene expression. Similar to NAC, the MEK1/2 inhibitor U0126, the p38 inhibitor SB203580, and the protein kinase inhibitor H-89 selectively inhibited ET-1 upregulation without affecting nuclear p65 translocation, suggesting that NAC inhibits ET-1 upregulation via inhibition of mitogen- and stress-activated protein kinase (MSK). Supporting this notion, cotreatment with NAC inhibited the TNF-alpha-induced rise in MSK1 and MSK2 kinase activity, while siRNA knock-down experiments showed that MSK2 is the predominant isoform involved in TNF-alpha-induced ET-1 upregulation.

Genetic and pharmacologic manipulation of oxidative stress after neonatal hypoxia-ischemia

Oxidative stress is a critical component of the injury response to hypoxia-ischemia (HI) in the neonatal brain, and this response is unique and at times paradoxical to that seen in the mature brain. Previously, we showed that copper-zinc superoxide-dismutase (SOD1) over-expression is not beneficial to the neonatal mouse brain with HI injury, unlike the adult brain with ischemic injury. However, glutathione peroxidase 1 (GPx1) over-expression is protective to the neonatal mouse brain with HI injury. To further test the hypothesis that an adequate supply of GPx is critical to protection from HI injury, we crossed SOD1 over-expressing mice (hSOD-tg) with GPx1 over-expressing mice (hGPx-tg). Resulting litters contained wild-type (wt), hGPx-tg, hSOD-tg and hybrid hGPx-tg/hSOD-tg pups, which were subjected to HI at P7. Confirming previous results, the hGPx-tg mice had reduced injury compared to both Wt and hSOD-tg littermates. Neonatal mice over-expressing both GPx1 and SOD1 also had less injury compared to wt or hSOD-tg alone. A result of oxidative stress after neonatal HI is a decrease in the concentration of reduced (i.e. antioxidant-active) glutathione (GSH). In this study, we tested the effect of systemic administration of alpha-lipoic acid on levels of GSH in the cortex after HI. Although GSH levels were restored by 24h after HI, injury was not reduced compared to vehicle-treated mice. We also tested two other pharmacological approaches to reducing oxidative stress in hSOD-tg and wild-type littermates. Both the specific inhibitor of neuronal nitric oxide synthase, 7-nitroindazole (7NI), and the spin-trapping agent alpha-phenyl-tert-butyl-nitrone (PBN) did not reduce HI injury, however. Taken together, these results imply that H2O2 is a critical component of neonatal HI injury, and GPx1 plays an important role in the defense against this H2O2 and is thereby neuroprotective.

Differential vulnerability of immature murine neurons to oxygen-glucose deprivation

In vivo studies support selective neuronal vulnerability to hypoxia-ischemia (HI) in the developing brain. Since differences in intrinsic properties of neurons might be responsible, pure cultures containing immature neurons (6-8 days in vitro) isolated from mouse cortex and hippocampus, regions chosen for their marked vulnerability to oxidative stress, were studied under in vitro ischemic conditions-oxygen-glucose deprivation (OGD). Twenty-four hours of reoxygenation after 2.5 h of OGD induced significantly greater cell death in hippocampal than in cortical neurons (67.8% vs. 33.4%, P = 0.0068). The expression of neuronal nitric oxide synthase (nNOS) protein, production of nitric oxide (NO), and reactive oxygen species (ROS), as well as glutathione peroxidase (GPx) activity and intracellular levels of reduced glutathione (GSH), were measured as indicators of oxidative stress. Hippocampal neurons had markedly higher nNOS expression than cortical neurons by 24 h of reoxygenation, which coincided with an increase in NO production, and significantly greater ROS accumulation. GPx activity declined significantly in hippocampal but not in cortical neurons at 4 and 24 h after OGD. The decrease in GSH level in hippocampal neurons correlated with the decline of GPx activity. Our data suggest that developing hippocampal neurons are more sensitive to OGD than cortical neurons. This finding supports our in vivo studies showing that mouse hippocampus is more vulnerable than cortex after neonatal HI. An imbalance between excess prooxidant production (increased nNOS expression, and NO and ROS production) and insufficient antioxidant defenses created by reduced GPx activity and GSH levels may, in part, explain the higher susceptibility to OGD of immature hippocampal neurons.

Inflammation and NO(X)-induced nitration: assay for 3-nitrotyrosine by HPLC with electrochemical detection

The identification of 15N-labeled 3-nitrotyrosine (NTyr) by gas chromatography/mass spectroscopy in protein hydrolyzates from activated RAW 264.7 macrophages incubated with 15N-L-arginine confirms that nitric oxide synthase (NOS) is involved in the nitration of protein-bound tyrosine (Tyr). An assay is presented for NTyr that employs HPLC with tandem electrochemical and UV detection. The assay involves enzymatic hydrolysis of protein, acetylation, solvent extraction, O-deacetylation, and dithionite reduction to produce an analyte containing N-acetyl-3-aminotyrosine, an electrochemically active derivative of NTyr. We estimate the level of protein-bound NTyr in normal rat plasma to be approximately 0-1 residues per 10(6) Tyr with a detection limit of 0.5 per 10(7) Tyr when > 100 nmol of Tyr is analyzed and when precautions are taken to limit nitration artifacts. Zymosan-treated RAW 264.7 cells were shown to have an approximately 6-fold higher level of protein-bound NTyr compared with control cells and cells treated with N(G)-monomethyl-L-arginine, an inhibitor of NOS. Intraperitoneal injection of F344 rats with zymosan led to a marked elevation in protein-bound NTyr to approximately 13 residues per 10(6) Tyr, an approximately 40-fold elevation compared with plasma protein of untreated rats; cotreatment with N(G)-monomethyl-L-arginine inhibited the formation of NTyr in plasma protein from blood and peritoneal exudate by 69% and 53%, respectively. This assay offers a highly sensitive and quantitative approach for investigating the role of reactive byproducts of nitric oxide in the many pathological conditions and disease states associated with NO(X) exposure such as inflammation and smoking.

Inhibition by interferon-gamma of human mononuclear cell-mediated low density lipoprotein oxidation. Participation of tryptophan metabolism along the kynurenine pathway

In this study we examined the potential inhibition by interferon-gamma (IFN gamma) of the early stages of low density lipoprotein (LDL) oxidation mediated by human peripheral blood mononuclear cells (PBMC) and monocyte-derived macrophages (MDM) in Ham's F-10 medium supplemented with physiological amounts of L-tryptophan (Trp). We assessed LDL oxidation by measuring the consumption of LDL's major antioxidant (i.e., alpha-tocopherol) and targets for oxidation (cholesteryllinoleate and cholesterylarachidonate), together with the accumulation of cholesterylester hydroperoxides and the increase in relative electrophoretic mobility of the lipoprotein particle. Exposure of PBMC or MDM to IFN gamma induced the degradation of extracellular Trp with concomitant accumulation of kynurenine, anthranilic and 3-hydroxyanthranilic acid (3HAA) in the culture medium. Formation of 3HAA, but neither Trp degradation nor formation of kynurenine and anthranilic acid, was inhibited by low amounts of diphenylene iodonium (DPI) in a concentration-dependent manner. In contrast to oxidative Trp metabolism, exposure of human PBMC or MDM to IFN gamma failed to induce degradation of arginine, and nitrite was not detected in the cell supernatant, indicating that nitric oxide synthase was not induced under these conditions. Incubation of LDL in Trp-supplemented F-10 medium resulted in a time-dependent oxidation of the lipoprotein that was accelerated in the presence of PBMC or MDM but inhibited strongly in the presence of both cells and IFN gamma, i.e., when Trp degradation and formation of 3HAA were induced. In contrast, when IFN gamma was added to PBMC or MDM in F-10 medium that was virtually devoid of Trp, inhibition of cell-accelerated LDL oxidation was not observed. Exogenous 3HAA added to PBMC or purified monocytes in the absence of IFN gamma also strongly and in a concentration-dependent manner inhibited LDL oxidation. Selective inhibition of IFN gamma-induced formation of 3HAA by DPI caused reversion of the inhibitory action of this cytokine on both PBMC- and MDM-mediated LDL oxidation. These results show that IFN gamma treatment of human PBMC or MDM in vitro attenuates the extent of LDL oxidation caused by these cells, and indicate that Trp degradation with formation of 3HAA is a major contributing factor to this inhibitory activity.

Endothelin A-receptor blockade in experimental diabetes improves glucose balance and gastrointestinal function

Secondary complications of diabetes mellitus often involve gastrointestinal dysfunction. In the experimental Goto Kakizaki rat, a model of Type II diabetes, hyperglycaemia and reduced glucose clearance is associated with elevated plasma endothelin (ET)-1 levels and selective decreases in nitric oxide synthase in circular muscle, longitudinal muscle and neuronal elements of the gastrointestinal tract. Functionally, this is accompanied by decreased nitrergic relaxatory responses of jejunal longitudinal muscle to tetrodotoxin-sensitive electrical field stimulation. Long-term treatment with a selective ET A-type receptor antagonist, markedly reduced hyperglycaemia and restored plasma glucose clearance rates towards normal. This was associated with a restoration of N(G)-nitro-L-arginine methyl ester-sensitive relaxatory responses of jejunal longitudinal muscle to electrical field stimulation. The results indicate that beneficial effects of ETA receptor blockade on gastrointestinal function may result from an improvement in insulin sensitivity with concomitant reduction of the severity of hyperglycaemia. ETA receptor blockade may represent a new therapeutic principle for improving glucose tolerance in Type II diabetes and could be beneficial in alleviating or preventing hyperglycaemia-related secondary complications in this condition.

Proliferation signal inhibitor-induced decrease of vascular endothelial cadherin expression and increase of endothelial permeability in vitro are prevented by an anti-oxidant

BACKGROUND: Rapamycines, sirolimus (SRL) and everolimus (ERL), are proliferation signal inhibitors (PSIs). PSI therapy often leads to edema. We hypothesized that increased oxidative stress in response to PSIs may modulate the expression of vascular endothelial (VE)-cadherin on endothelial cells (ECs) and, subsequently, vascular permeability, which in turn may be involved in the development of edema. METHODS: Experiments were performed on human umbilical vein ECs (HUVECs). Oxidative stress was measured by dichlorofluorescein-diacetate. Expression of VE-cadherin was evaluated by immunofluorescent staining and western blot analysis. Endothelial "permeability" was assessed using a transwell model. RESULTS: SRL and ERL, at concentrations of 1, 10 and 100 nmol/liter, enhanced oxidative stress (SRL: 24 +/- 12%, 29 +/- 9%, 41 +/- 13% [p < 0.05, in all three cases]; ERL: 13 +/- 10%, 27 +/- 2%, 40 +/- 12% [p < 0.05, in the latter two cases], respectively) on HUVECs, which was inhibited by the anti-oxidant, N-acetyl-cysteine (NAC) and, to a lesser extent, by the specific inhibitor of nitric oxide synthase, N-Omega-nitro-L-arginine methylester. By the use of NAC, VE-cadherin expression remained comparable with control, according to both immunocytochemistry and western blot analysis. Permeability was significantly increased by SRL and ERL at 100 nmol/liter (29.5 +/- 6.4% and 33.8 +/- 4.2%, respectively); however, co-treatment with NAC abrogated the increased permeability. CONCLUSIONS: EC homeostasis, as indicated by VE-cadherin expression, may be damaged by SRL and ERL, but resolved by the anti-oxidant NAC.

Olfactory bulb interneurons releasing NO exhibit the Reelin receptor ApoEr2 and part of those targeted by NO express Reelin

Nitric oxide (NO) and Reelin both modulate neuronal plasticity in developing and mature synaptic networks. We recently showed a loss of neuronal nitric oxide synthase (nNOS) protein in the olfactory bulb of reeler mutants and advanced the hypothesis that the Reelin and NO signalling pathways may influence each other. We now studied the distribution of NO sensitive guanylyl cyclase (NOsGC), Reelin and its receptor Apolipoprotein E2 (ApoEr2) in the olfactory bulb by multiple fluorescence labelling and tested whether nNOS and ApoEr2 colocalize in this area. We also essayed the protein content of NOsGC in the reeler olfactory bulb and tested whether there are any changes in nNOS and NOsGC protein in other reeler brain areas. Olfactory bulb interneurons expressing ApoEr2 and nNOS are only few in the glomerular layer but represent the large majority of granule cell layer interneurons. Conversely, NOsGC interneurons are rare in the granule cell layer and abundant as periglomerular cells. Reelin containing periglomerular cells almost entirely belong to the NOsGC subset. These data further support the hypothesis of a reciprocal signalling between Reelin/NOsGC and ApoEr2/nNOS expressing neurons to affect olfactory bulb activity. We also show that a significant rise in NOsGC content accompanies the decrease of nNOS protein in the reeler olfactory bulb. The same reciprocal changes present in the cortex/striatum and the hippocampus of reeler mice. Thus, the influence that the deficit of extracellular Reelin seems to exert on nNOS and its receptor is not limited to the olfactory bulb but is a general feature of the reeler brain.