Up-regulation of inducible nitric oxide synthase expression in cancer-prone p53 knockout mice

High concentrations of nitric oxide (NO) cause DNA damage and apoptosis in many cell types. Thus, regulation of NO synthase (NOS) activity is essential for minimizing effects of cytotoxic and genotoxic nitrogen oxide species. We have shown previously that NO-induced p53 protein accumulation down-regulates basal and cytokine-modulated inducible NOS (NOS2) expression in human cells in vitro. To further characterize the feedback loop between NOS2 and p53, we have investigated NO production, i.e., urinary nitrate plus nitrite excretion, and NOS2 expression in homozygous p53 knockout (KO) mice. We report here that untreated p53 KO mice excreted 70% more nitrite plus nitrate than mice with wild-type (wt) p53. NOS2 protein expression was constitutively detected in the spleen of untreated p53 KO mice, whereas it was undetectable in the spleen of wt p53 controls. Upon treatment with heat-inactivated Corynebacterium parvum, urinary nitrite plus nitrate excretion of p53 KO mice exceeded that of wt controls by approximately 200%. C. parvum treatment also induced p53 accumulation in the liver. Splenectomy reduced the NO output of C. parvum-treated p53 KO mice but not of wt p53 controls. Although NO production and NOS2 protein expression were increased similarly in KO and wt p53 mice 10 days after injection of C. parvum, NOS2 expression returned to baseline levels only in wt p53 controls while remaining up-regulated in p53 KO mice. These genetic and functional data indicate that p53 is an important transrepressor of NOS2 expression in vivo and attenuates excessive NO production in a regulatory negative feedback loop.     

Endothelial nitric oxide synthase and caveolin‐1 are co‐localized in sinusoidal endothelial fenestrae

Abstract: Background/Aims: Nitric oxide is synthesized in diverse mammalian tissues by a family of calmodulin‐dependent nitric oxide synthases (NOS). Caveolin, the principal structural protein in caveolae, interacts with endothelial NOS leading to enzyme inhibition in a reversible process modulated by Ca⁺⁺‐calmodulin. The aim of the present study was to clarify the ultrastructural localization of eNOS and caveolin‐1 in hepatic sinusoidal endothelium by an electron immunogold method. Methods: Male Wistar rats were used. Liver tissues and hepatic sinusoidal endothelial cells isolated from rat livers by collagenase infusion were studied. For immunohistochemistry, liver specimens were reacted with anti‐eNOS or anti‐caveolin‐1 antibody. The ultrastructural localization of eNOS or caveolin‐1 was identified by electron microscopy using an immunogold post‐embedding method. Results: Immunohistochemical studies using liver tissues localized endothelial NOS in hepatic sinusoidal lining cells, portal veins and hepatic arteries; and caveolin‐1 in sinusoidal lining cells, bile canaliculi, portal vein and hepatic arteries. Immunogold particles indicating the presence of eNOS and caveolin‐1 were demonstrated on the plasma membrane of sinusoidal endothelial fenestrae in liver tissue and also in isolated sinusoidal endothelial cells. Conclusion: Endothelial NOS and caveolin are co‐localized on sinusoidal endothelial fenestrae, suggesting that interaction of the two may modulate cellular regulation of NO synthesis.     

Nitric oxide production in rheumatoid arthritis

Abstract

Nitric oxide (NO), originally found as endothelium-derived relaxing factor (EDRF), is a free radical synthesized by NO synthases (NOS). Two isoforms exist in NOS, i.e. constitutive NOS (cNOS) and inducible NOS (iNOS). Inflammatory cytokines such as interleukin-1, interferon-γ, tumor necrosis factor-α induce iNOS expression in various cells including macrophages. Enhanced NO production is observed in arthritic conditions both in rodent models and human. The onset of arthritis in rodent models is significantly inhibited by the NOS inhibitor, N ^G-monomethyl-l-arginine. These data suggest a possible involvement of NO in the induction and/or maintenance of rheumatoid arthritis.     

Cardioprotection mediated by rosiglitazone, a peroxisome proliferatoractivated receptor gamma ligand, in relation to nitric oxide

Activation of peroxisome proliferator-activated receptor (PPAR) gamma protects from myocardial ischemia/reperfusion injury. The aim of the study was to investigate whether the cardioprotective effect of PPARgamma is related to nitric oxide (NO). Methods Wild type (WT) and endothelial NO synthase (eNOS) knockout (KO) mice received 3 mg/kg of the PPARgamma agonist rosiglitazone or vehicle (n = 6–9 in each group) i. p. 45 min before anesthesia. The hearts were isolated, perfused in a Langendorff mode and subjected to global ischemia and 30 min reperfusion. The hearts of another two groups ofWT mice received the NOS inhibitor L-NNA (100 ìmol/l) or vehicle in addition to pre-treatment with vehicle or rosiglitazone. Results In the WT heart, rosiglitazone increased the recovery of left ventricular function and coronary flow following ischemia in comparison with the vehicle group.L-NNA did not affect recovery per se but significantly blunted the improvement in the recovery of left ventricular function induced by rosiglitazone. In the KO group rosiglitazone suppressed the recovery of myocardial function following ischemia. Expression of eNOS was not affected, but phosphorylated eNOS was significantly increased by rosiglitazone in the WT hearts (P < 0.05). Conclusion These results suggest that the cardioprotective effect of the PPARgamma agonist rosiglitazone is mediated via NO by phosphorylation of eNOS.     

Protective effect of Ferula gummosa hydroalcoholic extract against nitric oxide deficiency-induced oxidative stress and inflammation in rats renal tissues

Abstract

Nitric oxide (NO) synthase inhibition increases hypertension and causes renal injury. Ferula gummosa is used in Iranian traditional medicine for treatment of several diseases and has been reported to exert a potent anti-inflammatory and antioxidant action. The aim of this investigation was to evaluate the renoprotective effects of hydroalcoholic extract of Ferula gummosa (HEG) on Nω-nitro-l-arginine methyl ester (l-NAME)-induced oxidative stress and inflammation and explore the mechanisms that link NO deficiency with altered renal heat shock protein (HSP70). Rats were injected intraperitoneally with l-NAME (10?mg/kg) to induce renal injury. Simultaneously, HEG (90?mg/kg) was administered by gastric gavage to l-NAME-treated rats for 6 days/week during an 8-week period. Renal thiobarbituric acid reactive substances (TBARS), superoxide dismutase (SOD), interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-α), HSP70, plasma NO and total antioxidant capacity (TAC) were evaluated. The administration of l-NAME significantly increased renal TBARS, TNF-α, IL-6, HSP70 levels and decreased renal SOD activity, that these changes were accompanied by the reduced plasma NO and TAC levels. HEG administration decreased TBARS, HSP70, TNF-α and IL-6 levels and increased SOD activity in the kidney tissues of l-NAME treated rats (p?<?0.05). Also, plasma TAC level and NO bioavailability have been elevated after administration of HEG (p?<?0.05). These findings support that NO deficiency induces renal stress oxidative and inflammation, which markedly increased renal HSP70 and HEG could protect kidney against these damaging effects via its anti-oxidative, anti-inflammatory action and modulate renal HSP70.     

Apoptotic mechanisms are involved in the death of Strongyloides venezuelensis after triggering of nitric oxide

Despite progress in understanding the role of nitric oxide (NO) in the pathogenesis of helminth infections, the role in strongyloidosis is unknown. Firstly, we studied the production of NO in mice infected with Strongyloides venezuelensis as well as in macrophage cultures stimulated with parasite antigens. Somatic larvae 3 (L3) and excretory–secretory female antigens stimulate specific NO production measured by Griess reaction and expression of inducible NO synthase by RT‐PCR and quantitative PCR. Moreover, mice infected with S. venezuelensis produce NO in migration stages. Secondly, we analysed the effect of NO production on L3 and females of S. venezuelensis using NO donors such as diethylenetriamine and 3,3‐bis(aminoethyl)‐1‐hydroxy‐2‐oxo‐1‐triazene. Parasites died after NO donor treatment in a dose‐dependent manner. Finally, apoptotic mechanisms are involved in the death of S. venezuelensis larvae.     

去甲肾上腺素预处理对大鼠供心热休克蛋白70、一氧化氮及一氧化氮合酶表达的影响

目的:探讨去甲肾上腺素预处理是否可诱导心肌热休克蛋白70(HSP70)的合成,并研究其对供心一氧化氮(NO)、一氧化氮合酶(NOS)的影响,探讨去甲肾上腺素预处理心肌保护作用机制。方法:Wistar大鼠18只,分为2组:对照组(C,n=9),腹腔注射0.9%氧化钠注射液0.5 mL,24 h后取离体心脏灌注(Histidine-tryptophan-ketoglutarte,HTK)心脏保护液,4℃保存3 h后建立Langendorff离体心脏灌注模型,灌注(Krebs-Henseleit,K-H)液2 h;实验组(E,n=9)腹腔注射重酒石酸去甲肾上腺素(溶于0.9%氯化钠液中)3.1μmol/kg(0.53 mg/kg),腹腔注射24 h后取离体心脏,处理方法同C组。测定心肌HSP70、NO、NOS的含量以及相关生化指标并做统计学处理比较。结果:HSP70含量E组较C组明显增高(P<0.01),NO、NOS的含量E组较C组明显增多(P<0.01),生化指标E组明显优于C组。结论:去甲肾上腺素预处理能诱导供心心肌组织HSP70、NO、NOS高表达,其对供心具有明显的保护效应,并且其促进心肌NO、NOS的表达,这可能是去甲肾上腺素预处理发挥供心保护作用的机制之一。     

Endothelial,but not the inducible,nitric oxide synthase is detectable in normal and portal hypertensive rats

Abstract: Background: Chronic portal hypertension is accompanied by a nitric oxide (NO) dependent vasodilation. Three isoforms of NO producing synthases (NOS) are characterized: neuronal NOS (nNOS), endothelial NOS (eNOS) and inducible NOS (iNOS). Sources of increased NO levels in chronic hypertension is disputed. Methods: To determine eNOS and iNOS expression in different organs of portal hypertensive and control rats, we divided Sprague-Dawley rats in 6 groups: (1) Partial portal vein ligated rats, (2) Bile duct ligated rats, (3) Carbon tetrachloride treated rats, (4) Sham operated rats, (5) Untreated control rats, and (6) LPS treated rats. Immunohistochemistry (IHC) and immunoblotting (IB) using antibodies against eNOS or iNOS were carried out on samples from thymus, aorta, heart, lung, oesophagus, liver, spleen, kidney, pancreas, small and large intestine. Results: IHC revealed an even eNOS expression in all groups. Expression of iNOS was restricted to macrophages in organs of LPS treated and the thymus of rats. IB mirrored these results. Conclusion: In chronic portal hypertension, the main source for NO production depends on eNOS activity.     

Inducible nitric oxide synthase controls experimental Strongyloides infection

Infection with Strongyloides sp. induces a host immune response, predominantly the Th2 type, that is able to eliminate the parasite. However, little is known about the role of the nitric oxide (NO) mediator, induced by the enzyme nitric oxide synthase (NOS), in strongyloidiasis. Therefore, in this study, we investigated the immune response of mice genetically deficient in the enzyme inducible nitric oxide synthase (iNOS^?/?), infected with Strongyloides venezuelensis. C57BL/6 wild‐type (WT) and iNOS^?/? mice were individually inoculated by subcutaneous injection of 3000 S. venezuelensis L3 larvae. In the absence of iNOS, mice were more susceptible to the infection than WT animals, in which the parasite was completely eliminated. The overall production of cytokines and specific IgG, IgG1 or IgE antibodies against the parasite was significantly lowered in infected iNOS^?/? mice. The expression of iNOS was observed in the intestine of WT hosts but mainly in the wall of the parasite, despite the presence of iNOS in mice. Altogether, we concluded that iNOS expression may play an important role in the control of S. venezuelensis infection.     

Myocardial contractile effects of nitric oxide

Recent experimental and clinical research solved some of the controversies surrounding the myocardial contractile effects of NO. These controversies were: (1) does NO exert a contractile effect at baseline? (2) is NO a positive or a negative inotrope? (3) Are the contractile effects of NO similar when NO is derived from NO-donors or from the different isoforms of NO synthases (NOS)? (4) Does NO exert the same effects in hypertrophied, failing or ischemic myocardium? Transgenic mice with cardioselective overexpression of NOS revealed NO to produce a small reduction in basal developed LV pressure and a LV relaxation-hastening effect mainly through myofilamentary desensitization. Similar findings had previously been reported during intracoronary infusions of NO-donors in isolated rodent hearts and in humans. The LV relaxation hastening effect was accompanied by increased diastolic LV distensibility, which augmented LV preload reserve especially in heart failure patients. This beneficial effect on diastolic LV function always overrode the small NO-induced attenuation in LV developed pressure in terms of overall LV performance. In most experimental and clinical conditions, contractile effects of NO were similar when NO was derived from NO-donors or produced by the different isoforms of NOS. Because expression of inducible NOS (NOS2) is frequently accompanied by elevated oxidative stress, NO produced by NOS2 can lead to peroxynitrite-induced contractile impairment as observed in ischemic or septic myocardium. Finally, shifts in isoforms or in concentrations of myofilaments can affect NO-mediated myofilamentary desensitization and alter the myocardial contractile effects of NO in hypertrophied or failing myocardium.     

Conservation of whole body nitric oxide metabolism in human alcoholic liver disease: Implications for nitric oxide production

Objective. Patients with advanced liver diseases tend to develop a hyperdynamic circulation which complicates cirrhosis. Impairment of nitric oxide (NO) metabolism has been implicated in the pathogenesis of portal hypertension. The aim of this study was to determine nitric oxide synthase (NOS)-dependent whole body NO production in patients with decompensated liver cirrhosis and portal hypertension. Material and methods. Ten patients with decompensated alcoholic liver disease and portal hypertension (Child-Pugh Classifications B and C with no signs of infection) and 10 age- and gender-matched control subjects received an intravenous infusion of L-[¹⁵N]₂-arginine (50 µmol/min for 30 min). Urine and serum nitrite and nitrate concentrations were determined using ion chromatography-mass spectrometry. Results. NOS-dependent whole body NO synthesis was estimated by the conversion of [¹⁵N]guanidino nitrogen of arginine to urine ¹⁵N-nitrite and ¹⁵N-nitrate. The amount of ¹⁵N-nitrite and ¹⁵N-nitrate in the urine of patients and control subjects was significantly correlated with the amount of urine nitrite and nitrate over 36 h (r=0.91 and 0.77, respectively, p<0.0001). However, neither a median of 12 h ¹⁵N-nitrite and ¹⁵N-nitrate nor nitrite and nitrate excretion in the urine was different between patients and control subjects, 46.4 (9.4–152.2) versus 98.7 (29.9–146.5) nmol/mmol creatinine and 20.6 (2.1–69.0) versus 40.0 (27.0–70.1) µmol/mmol creatinine, respectively. No differences were found in serum nitrite and nitrate concentrations and glomerular filtration rates between patients and control subjects, 111.4 (73.2–158.8) versus 109.3 (83.5–176.4) µmol/l. Conclusion. Our results contraindicate a greater basal NOS-dependent whole body NO production in patients with decompensated liver disease and portal hypertension.     

Intestinal nitric oxide synthase activity changes during experimental colon obstruction

Objective. The experiments in this study were designed to follow the time course of nitric oxide (NO) synthesis in the large bowel during acute mechanical ileus. Material and methods. Occlusion of the mid-transverse colon was maintained for 420 min in anesthetized dogs. Strain-gauge transducers were used to analyze motility changes on the hepatic and lienal flexures, respectively. Constitutive NO synthase (cNOS) and inducible NOS (iNOS) activities were determined in tissue biopsies, and plasma nitrite/nitrate (NO_x) level was measured in the portal blood. Following completion of the baseline studies, the animals were treated with either 7-nitroindazole (7-NI, selective neuronal NOS inhibitor), or N-nitro-L-arginine (NNA, non-selective NOS inhibitor). Results. In the sham-operated group the cNOS activities differed significantly in the oral and aboral tissue samples (oral: 102.9; versus aboral: 62.1 fmol/mg protein/min). The obstruction elicited a significant increase in portal NO_x and elevated tissue inducible NO synthase (iNOS) activity. NNA treatment decreased the motility index in both intestinal segments for 60 min, but 120 min later the motility index was significantly elevated (2.5-fold increase in the oral part, and 1.8-fold enhancement in the aboral segment, respectively). Treatment with 7-NI decreased the cNOS activity in the oral and aboral parts by approximately 40% and 70%, respectively, and suppressed the motility increase in the aboral colon segment. Conclusions. The motility of the colon was either significantly increased or decreased, depending on the type and selectivity of the NOS inhibitor compounds applied. NO of neuronal origin is a transmitter that stimulates peristaltic activity; but an increased iNOS/nNOS ratio significantly moderates the obstruction-induced motility increase.     

Antisteroidogenic action of nitric oxide on human corpus luteum in vitro: mechanism of action

To analyze the mechanism by which nitric oxide (NO) exerts its antisteroidogenic action, human luteal cells were cultured during 24 and 48 h with l-arginine (l-Arg, 1 mmol/L); 1,2(2-trifluoromethylphenyl)imidazole (TRIM) (50 μmol/L and 1 mmol/L) and cyclic guanosine monophosphate (cGMP) analog (8-Br-cGMP, 1 mmol/L). Estradiol, nitrite, and P_{450 AROM} activity were determined in culture media. Total cGMP concentration was evaluated in the cells and culture media by radioimmunoassay, and NADPH diaphorase was used as a histochemical marker for NO synthase (NOS) activity. During the corpus luteum (CL) life-span, NO affected estradiol secretion in an age-dependent manner, with an inhibition in mid-CL (37%; p<0.05) in agreement with our previous results, and no significant modification in early and late CL. Basal nitrite concentration in 24 and 48 h of midluteal cell cultures (42 and 93 pmol/10⁶ cells, respectively) was increased by l-Arg (53% and 88%) and inhibited by the two TRIM concentrations; also, an intense diaphorase reactivity was observed in endothelial cells and luteal parenchyma. Total cGMP was not detected in cell cultures and 8-Br-cGMP did not modify estradiol secretion, whereas aromatase activity was strongly inhibited by l-Arg (70%, p<.05). These results suggest that both NOS isoforms are active in midluteal cells, and the mechanism of action for NO on in vitro estradiol secretion may be an inhibition of P_{450 AROM} activity.     

一氧化氮及一氧化氮合酶抑制剂对小鼠血吸虫病肝纤维化程度的影响

目的研究一氧化氮(NO)对小鼠日本血吸虫病肝纤维化程度的影响。方法昆明小鼠经腹部皮肤感染日本血吸虫,于感染后第4周末治疗组和抑制剂组分别给予NO前体-L-精氨酸(L-Arg)及一氧化氮合酶(NOS)抑制剂-NG-左旋-硝基精氨酸甲基乙酯(L-NAME),于第10周末处死小鼠,取血,分离血清,剖取肝脏。应用病理组织学方法及生物化学方法,观察各组小鼠血吸虫病肝纤维化程度,同时测定血清NO、层粘连蛋白(LN)、透明质酸(HA)、谷-草转氨酶(AST)及谷-丙转氨酶(ALT)活性和肝组织羟脯氨酸(Hyp)含量。结果小鼠感染血吸虫后,感染组肝脏有明显的纤维化,血清中HA、LN、AST、ALT等指标显著升高,肝组织内Hyp含量也明显增加。与感染组相比:L-Arg高、中剂量组肝纤维化程度评分降低显著,低剂量组虽有减轻但无统计学意义,同时,L-Arg高、中剂量组血清LN、HA、AST、ALT的水平和肝组织Hyp的含量有所降低;低剂量组HA、LN、AST、ALT的水平虽然降低,但无统计学意义,Hyp水平降低明显;抑制剂组血清LN、HA、AST、ALT含量和肝组织Hyp的水平均明显升高。血清NO的水平随着精氨酸剂量的增加而显著增加,而精氨酸抑制剂组NO的水平降低明显。结论NO能明显降低血吸虫病肝纤维化的程度和减轻肝纤维化所造成的损伤作用。     

High red blood cell nitric oxide synthase activation is not associated with improved vascular function and red blood cell deformability in sickle cell anaemia

Human red blood cells (RBC) express an active and functional endothelial‐like nitric oxide (NO) synthase (RBC‐NOS). We report studies on RBC‐NOS activity in sickle cell anaemia (SCA), a genetic disease characterized by decreased RBC deformability and vascular dysfunction. Total RBC‐NOS content was not significantly different in SCA patients compared to healthy controls; however, using phosphorylated RBC‐NOS‐Ser¹¹⁷⁷ as a marker, RBC‐NOS activation was higher in SCA patients as a consequence of the greater activation of Akt (phosphorylated Akt‐Ser⁴⁷³). The higher RBC‐NOS activation in SCA led to higher levels of S‐nitrosylated α‐ and β‐spectrins, and greater RBC nitrite and nitrotyrosine levels compared to healthy controls. Plasma nitrite content was not different between the two groups. Laser Doppler flowmetric experiments demonstrated blunted microcirculatory NO‐dependent response under hyperthermia in SCA patients. RBC deformability, measured by ektacytometry, was reduced in SCA in contrast to healthy individuals, and pre‐shearing RBC in vitro did not improve deformability despite an increase of RBC‐NOS activation. RBC‐NOS activation is high in freshly drawn blood from SCA patients, resulting in high amounts of NO produced by RBC. However, this does not result in improved RBC deformability and vascular function: higher RBC‐NO is not sufficient to counterbalance the enhanced oxidative stress in SCA.     

Environmental exposures,nitric oxide synthase genes,and exhaled nitric oxide in asthmatic children

Exhaled nitric oxide (FeNO), a measure of airway inflammation, is being explored as a tool to guide asthma management in children. Investigators have identified associations of genetic polymorphisms in nitric oxide synthase genes (NOS1 and NOS3) with FeNO levels; however, none have explored whether these polymorphisms modify the relationship of environmental exposures with FeNO. The objective of this project was to evaluate the association of NOS polymorphisms and environmental exposures with FeNO levels among children with asthma. We conducted a 12‐month prospective cohort study of 225 tobacco‐smoke exposed children (6–12 years) with doctor‐diagnosed asthma. We assessed environmental exposures (tobacco, indoor allergens, & airborne particulates), polymorphisms in NOS1 (an intronic AAT tandem repeat) and NOS3 (G894T), and FeNO levels. There was no association of NOS1 or NOS3 polymorphisms with FeNO levels. There were no significant interactions of environmental exposures and the NOS1 polymorphism with FeNO levels. In contrast, there was an interaction of the NOS3 polymorphism and airborne nicotine concentration with FeNO levels (P = 0.01). Among GG genotype individuals, nicotine exposure did not affect FeNO levels; however, among individuals with at least one T allele, higher nicotine exposure was associated with lower FeNO levels (approximately 5 ppb decrease from the lowest to the highest quartile). We conclude that genetic differences may explain some of the conflicting results in studies of the effects of tobacco smoke exposure on FeNO levels and may make FeNO interpretation difficult for a subset of children with asthma. Pediatr Pulmonol. 2009; 44:812–819. © 2009 Wiley‐Liss, Inc.     

Activation of the inducible nitric oxide synthase pathway contributes to inflammation‐induced osteoporosis by suppressing bone formation and causing osteoblast apoptosis

Objective

Osteoporosis is a major clinical problem in chronic inflammatory diseases such as rheumatoid arthritis. The mechanism of bone loss in this condition remains unclear, but previous studies have indicated that depressed bone formation plays a causal role. Since cytokine‐induced nitric oxide (NO) production has been shown to inhibit osteoblast growth and differentiation in vitro, this study was undertaken to investigate the role of the inducible NO synthase (iNOS) pathway in the pathogenesis of inflammation‐mediated osteoporosis (IMO) by studying mice with targeted inactivation of the iNOS gene (iNOS knockout [iNOS KO] mice).

Methods

IMO was induced in wild‐type (WT) and iNOS KO mice by subcutaneous injections of magnesium silicate. The skeletal response was assessed at the tibial metaphysis by measurements of bone mineral density (BMD), using peripheral quantitative computed tomography, by bone histomorphometry, and by measurements of bone cell apoptosis.

Results

NO production increased 2.5‐fold (P < 0.005) in WT mice with IMO, but did not change significantly in iNOS KO mice. Total BMD values decreased by a mean ± SEM of 14.4 ± 2.0% in WT mice with IMO, compared with a decrease of 8.6 ± 1.2% in iNOS KO mice with IMO (P < 0.01). Histomorphometric analysis confirmed that trabecular bone volume was lower in WT mice with IMO compared with iNOS KO mice with IMO (16.2 ± 1.5% versus 23.4 ± 2.6%; P < 0.05) and showed that IMO was associated with reduced bone formation and a 320% increase in osteoblast apoptosis (P < 0.005) in WT mice. In contrast, iNOS KO mice with IMO showed less inhibition of bone formation than WT mice and showed no significant increase in osteoblast apoptosis.

Conclusion

Inducible NOS–mediated osteoblast apoptosis and depressed bone formation play important roles in the pathogenesis of IMO.

     

Human blood platelets lack nitric oxide synthase activity

Reports on expression and functionality of nitric oxide synthase (NOS) activity in human blood platelets and erythrocytes are contradictory. We used a specific gas chromatography–mass spectrometry (GC–MS) method to detect NOS activity in human platelets. The method measures simultaneously [¹⁵N]nitrite and [¹⁵N]nitrate formed from oxidized ¹⁵N-labeled nitric oxide (¹⁵NO) upon its NOS-catalyzed formation from the substrate l-[guanidino-¹⁵N₂]-arginine. Using this GC–MS assay, we did not detect functional NOS in non-stimulated platelets and in intact platelets activated by various agonists (adenosine diphosphate, collagen, thrombin, or von Willebrand factor) or lysed platelets. l-[guanidino-nitro]-Arginine-inhibitable NOS activity was measured after addition of recombinant human endothelial NOS to lysed platelets. Previous and recent studies from our group challenge expression and functionality of NOS in human platelets and erythrocytes.