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Proteins are subject to oxidative modification and the formation of adducts with a broad spectrum of reactive species via enzymatic and non-enzymatic mechanisms. Here we report that in vitro non-enzymatic methylglyoxal (MGO) binding causes the inhibition and formation of MGO advanced glycation end-products (MAGEs) in Na+/K+-ATPase (NKA). Concretely, MGO adducts with NKA amino acid residues (mainly Arg) and Ne-(carboxymethyl)lysine (CML) formation were found. MGO is not only an inhibitor for solubilized NKA (IC50=91±16μM), but also for reconstituted NKA in the lipid bilayer environment, which was clearly demonstrated using a DPPC/DPPE liposome model in the presence or absence of the NKA-selective inhibitor ouabain. High-resolution mass spectrometric analysis of a tryptic digest of NKA isolated from pig (Sus scrofa) kidney indicates that the intracellular α-subunit is naturally (post-translationally) modified by MGO in vivo. In contrast to this, the β-subunit could only be modified by MGO artificially, and the transmembrane part of the protein did not undergo MGO binding under the experimental setup used. As with bovine serum albumin, serving as the water-soluble model, we also demonstrated a high binding capacity of MGO to water-poorly soluble NKA using a multi-spectral methodology based on electroanalytical, immunochemical and fluorimetric tools. In addition, a partial suppression of the MGO-mediated inhibitory effect could be observed in the presence of aminoguanidine (pimagedine), a glycation suppressor and MGO-scavenger. All the results here were obtained with the X-ray structure of NKA in the E1 conformation (3WGV) and could be used in the further interpretation of the functionality of this key enzyme in the presence of highly-reactive metabolic side-products, glycation agents and generally under oxidative stress conditions.

Background Sevoflurane induces preconditioning (SevoPC). The effect of aprotinin and the involvement of endothelial nitric-oxide synthase (NOS) on SevoPC are unknown. We investigated (1) whether SevoPC is strengthened by multiple preconditioning cycles, (2) whether SevoPC is blocked by aprotinin, and (3) whether endothelial NOS plays a crucial role in SevoPC. Methods Anesthetized male Wistar rats were randomized to 15 groups (each n = 6) and underwent 25-min regional myocardial ischemia and 2-h reperfusion. Controls were not treated further. Preconditioning groups inhaled 1 minimum alveolar concentration of sevoflurane for 5 min (SEVO-I), twice for 5 min each (SEVO-II), three times for 5 min each (SEVO-III), or six times for 5 min each (SEVO-VI). Aprotinin was administered with and without sevoflurane. Involvement of endothelial NOS was determined with the nonspecific NOS blocker N-nitro-l-arginine-methyl-ester, the specific neuronal NOS blocker 7-nitroindazole, and the specific inducible NOS blocker aminoguanidine. Results SevoPC reduced infarct size in all protocols (SEVO-I, 42 ± 6%; SEVO-II, 33 ± 4%; SEVO-III, 11 ± 5%; SEVO-VI, 16 ± 4%; all P < 0.001 vs. control, 67 ± 3%) and was least after three and six cycles of sevoflurane (P < 0.001 vs. SEVO-II and -I, respectively). Aprotinin alone had no effect on infarct size but blocked SevoPC. N-nitro-l-arginine-methyl-ester abolished SevoPC (67 ± 4%; P < 0.05 vs. SEVO-III). Aminoguanidine and 7-nitroindazole blocked SevoPC only partially (25 ± 6 and 31 ± 6%, respectively; P < 0.05 vs. SEVO-III and control). SevoPC induced endothelial NOS phosphorylation, which was abrogated by aprotinin. Conclusion SevoPC is strengthened by multiple preconditioning cycles, and phosphorylation of endothelial NOS is a crucial step in mediating SevoPC. These effects are abolished by aprotinin.

Nitric oxide (NO) signaling in tumors and endothelial cells regulates vascular permeability and blood flow and therefore influences tumor uptake and response to therapeutic compounds. As delivery and efficacy of chemotherapy is impaired in CNS neoplasms due to a partially intact blood–brain barrier (BBB), we studied the effects of NO released by the short-acting NO donor disodium 1-[2-(carboxylato)pyrrolidin-1-yl]diazen-1-ium-1,2-diolate methanolate (PROLI/NO) on BBB integrity and blood flow in C6 gliomas using [14C]-aminoisobutyric acid (AIB) and [14C]-iodoantipyrine quantitative autoradiography. PROLI/NO selectively increased intratumoral uptake of [14C]AIB and [14C]sucrose when given as a 3-minute intracarotid infusion or a 15-minute i.v. infusion (AIB: tumor, K1 = 68.7 ± 3.2 vs 24.9 ± 0.9 µL g−1 min−1, P < .0001; sucrose, K1 = 16.9 ± 0.9 vs 11.5 ± 0.9 µL g−1 min−1, P = .0007). This effect was achieved without significant changes in cerebral and tumor blood flow or arterial blood pressure, which indicates that the effect on vascular permeability is independent of changes in vascular tone induced by NO. This effect was mediated by activation of the NO/3',5'-cyclic guanosine monophosphate (cGMP) pathway, as it was blocked by guanylate cyclase inhibition by LY83583 and reproduced by the delivery of 8-bromoguanosine 5'-monophosphate or inhibition of cGMP degradation by the phosphodiesterase inhibitor zaprinast. Inhibition of inducible NO synthase by aminoguanidine or cyclooxygenase inhibition by indometacin or dexamethasone did not reduce the blood–tumor barrier (BTB) response to PROLI/NO. PROLI/NO, and perhaps other NO-donating compounds, can be used to selectively increase BTB permeability in gliomas through the NO/cGMP pathway at doses that do not cause unwanted vasodilatory changes in blood flow and that do not affect the systemic circulation.

Background Nitric oxide (NO) is produced by resident and inflammatory cells in the respiratory tract by the enzyme NO synthase (NOS), which exists in three isoforms: neuronal NOS (nNOS), inducible NOS (iNOS), and endothelial NOS. NO production is increased in patients with COPD, and the production of NO under oxidative stress conditions generates reactive nitrogen species that may amplify the inflammatory response in COPD. Methods To examine the role of increased NO in COPD, we administered a relatively selective iNOS inhibitor, aminoguanidine, by nebulization in a double-blind, placebo-controlled study in COPD patients, healthy smokers, and healthy nonsmoking subjects. We investigated whether aminoguanidine had any effect on exhaled NO produced in the central lung (flux of NO from the airways [J no ] and peripheral lungs (concentration of NO in peripheral lung [C alv ], on NO metabolites (nitrite [NO 2 − ]/nitrate [NO 3 − ], peroxinitrite [ONOO − ], nitrotyrosine), and on a marker of oxidative stress (8-isoprostane) in exhaled breath condensate (EBC) and in sputum. Results Aminoguanidine administration resulted in a significant reduction in J no compared with administration of the saline solution control in healthy subjects, smokers, and COPD patients. C alv in smokers and in COPD patients was not completely inhibited 1 h after aminoguanidine inhalation, in marked contrast to previous results in asthma. Moreover, ONOO − and NO 2 − /NO 3 − levels were also increased in EBC and in sputum of smokers and COPD and were not completely inhibited following aminoguanidine inhalation. 8-Isoprostane levels were also increased in smokers and in COPD patients but were not reduced after aminoguanidine inhalation. Conclusions These results suggest that the constitutive NOS isoform as well as iNOS might be involved in NO release and contribute to the high C alv and ONOO − production in patients with COPD. Trial registration: Clinicaltrials.gov Identifier: NCT00180635.

Background. Uropathogenic Escherichia coli (UPEC) is a common cause of urinary-tract infection. The mechanisms by which bacteria cause the symptoms of cystitis remain unclear. Methods. The contractions of isolated rat detrusor strips evoked by electrical field stimulations (EFS) or by exogenous agonists and immunoblotting for the detection of protein expression in the bladder were measured in the short (1 h) and long (24 h) term after the intravesical instillation of J96 (04:K6) strain or UPEC isolated from patients with acute E. coli pyelonephritis or E. coli lipopolysaccharide (LPS). Results. One hour after the instillation of UPEC, the level of endothelial nitric oxide synthase (eNOS) and the contractile response, but not protein kinase C (PKC) and extracellular signal-regulated kinase (ERK)-1/2 activation, were higher. Twenty-four hours after UPEC treatment, detrusor contractions were decreased, and inducible (i) NOS protein expression and ERK1/2 phosphorylation, but not PKC activation, were observed. Both aminoguanidine and PD98059 treatment markedly reversed the decrease of EFS- and acetylcholine-evoked detrusor contractions induced by UPEC. The instillation of LPS triggered PKC activation but not ERK1/2 phosphorylation. Conclusions. Short-term intravesical instillation of UPEC enhances detrusor contractions through an eNOS-related pathway, but iNOS-regulated ERK1/2 signaling may be involved in long-term UPEC treatment-induced responses. There are different mechanisms involved in the responses induced by UPEC and LPS.

Background The aim of this study was to observe the time-course changes of heme oxygenase-1 (HO-1) and inducible nitric oxide synthase (iNOS) induction in aorta during the development of hypertension, as well as the relationship of HO-1/carbon monoxide (CO) system and iNOS/nitric oxide (NO) system in spontaneously hypertensive rats (SHR). Methods The systolic blood pressure (SBP) was determined in conscious rats by the tail-cuff method. The tissue HO-1 and iNOS mRNA and protein levels were estimated with reverse transcription polymerase chain reaction and Western blot method. Results The expression of HO-1 and iNOS in aorta increased with the SBP elevation during the development of SHR and was attenuated when the hypertension was lowered with the vasodilator hydralazine. At 8 weeks, only HO-1 was induced, whereas at 12 and 16 weeks, both HO-1 and iNOS were observed. The level of plasma nitrite/nitrate was associated with the change in iNOS expression in SHR. In addition, the SBP of 8-week-old SHR was significantly increased after pretreatment with zinc protoporphyrin IX for 7 consecutive days. Chronic blockade of iNOS activity by aminoguanidine resulted in significant up-regulation of HO-1, but the pressor effect was blunt. Conclusions These results suggest that the up-regulation of HO-1 and iNOS in aorta is a compensatory mechanism for the elevation of SBP during the development of hypertension in SHR. The expression of HO-1 is earlier than that of iNOS. Our data suggest that the HO-1/CO system takes over and acts as a major modulator for the regulation of SBP when the iNOS/NO system is suppressed.

Aminoguanidine (AG), a nitric oxide synthase (NOS) inhibitor, has been widely used to study the role of inducible NOS (iNOS) in host defense against infections caused by various pathogens including Salmonella typhimurium. iNOS has been reported to play an important role in host defense against S. typhimurium infection both in vitro and in vivo. In this report we show those AG treatment lead to weight loss in both wild-type and iNOS knockout mice, and rendered them more susceptible to Salmonella infection. These results suggest that AG may have side effects other than the inhibition of iNOS, and that data obtained from studies using AG should be interpreted with caution.

Objective: We tested the hypothesis that occlusion of the superior mesenteric artery induces late preconditioning against myocardial infarction and examined the effects of pharmacological modifiers of inducible nitric oxide synthase activity on the late preconditioning in anesthetized rats. Methods: Rats underwent an intestinal ischemia preconditioning protocol (30 min occlusion of the superior mesenteric artery) or were sham-operated. They were subjected to a sustained 30 min of coronary occlusion and 180 min of reperfusion 24 h later. Results: In rats receiving no pharmacological intervention, the percentage of myocardial infarct within the area at risk and left ventricle was 72±4% and 31±2%, respectively, in sham-operated rats, and these were significantly reduced to 44±4% and 23±2% ( P

Background: Ischemia/reperfusion (I/R) leads to the induction of inducible nitric oxide synthase. The present study investigated the effects of selective and continuous inhibition of iNOS on myocardial performance, infarct size and histomorphological changes after I/R in rabbits. Methods and Results: Ischemia/reperfusion (I/R) was induced by occlusion of the circumflex coronary artery for 30 min followed by 48 h of reperfusion. Sham animals (group A) served as control. Three groups were subjected to I/R: (B) placebo; (C) aminoguanidine (AMG; 10 mg/kg bolus) given prior to and 48 h after I/R to test its acute effects; (D) AMG (300 mg/kg/day sc) to test effects of continuous treatment. Hemodynamics, myocardial blood flow, infarct size, iNOS activity, cGMP levels, immunohistochemical analysis of iNOS expression and AMG tissue levels were determined.Continuous AMG treatment improved myocardial performance (hemodynamics and blood flow) compared to placebo group. iNOS was highest in placebo-treated animals. AMG tissue levels were highest in tissues affected by I/R. Infarct size (% of the circumflex region) was significantly smaller in group D when compared to group B. Conclusions: This is the first study showing that activation of myocardial iNOS isozyme during 48 h of reperfusion contributes to a late phase of I/R-induced injury in rabbits. Selective and continuous modulation of iNOS by AMG over this time period exerts protective effects with respect to myocardial performance, coronary blood flow, cellular infiltration and reduction of infarct size; this may be a novel therapeutic approach in the clinical situation to limit irreversible myocardial injury associated with ischemia and reperfusion.

In the immunosuppression accompanying the lethal systemic graft-versus-host reaction (GVHR) directed against minor histocompatibility antigens in irradiated adult mice, we previously determined that non-T, non-B, L-leucine methyl ester (LME)-sensitive cells were implicated via two different mechanisms: one, which is interferon-gamma (IFN-gamma)-dependent and affects both T-cell proliferative responses and thymus-independent antibody production by CD5(+) B cells; and a second, which is IFN-gamma-independent and affects B-cell proliferative responses. Because IFN-gamma induces the production of nitric oxide (NO), a potent immunosuppressive molecule, we investigated the involvement of NO in the suppression mediated by the LME-sensitive cells. Inducible NO synthase (iNOS) mRNA, iNOS protein, and the stable end products of iNOS pathway, L-citrulline and nitrite, were detected early in GVHR in LME-sensitive spleen cells taken ex vivo and could be amplified in vitro by T and B mitogens. Inhibition of NO production with arginine analogs (aminoguanidine, N(G)-monomethyl-L-arginine [LMMA]), like anti-IFN-gamma antibodies, reversed suppression of both T-cell responses to concanavalin A and CD5(+) B-cell responses, but not of B-cell response to lipopolysaccharides (LPS). The GVHR-associated, IFN-gamma-dependent immunosuppression of T-cell proliferation and of antibody synthesis by CD5(+) B cells is the consequence of NO production by LME-sensitive cells. Immunohistochemical analyses indicate that these cells belong to the macrophage lineage.

Nitric oxide (NO) has been shown to play a role in cyclosporin (CsA) nephrotoxicity, but its mechanism of action is still unclear. As inducible NO synthase (iNOS) mRNA has been found to be expressed in rat medullary thick ascending limb (mTAL) cells, we investigated the effects of CsA on NO production in a model of mouse cultured mTAL cells.The experiments were carried out on sub-cultured cells derived from isolated mTAL microdissected from the kidney of C57BL/6 mice. The identification of the iNOS mRNA in mTAL microdissected segment and cultured cell was confirmed by RT PCR and RsaI digestion. Nitrite (NO2) released by mTAL cells was determined using the modified Griess reagent method and taken as an index of nitric oxide production. The cultured cells were treated with various concentrations of CsA and different signal transduction regulators to assess the effect and possible pathway(s) of action of CsA on NO production in mTAL cells.The basal production of NO by mTAL cells increased by 1.8-fold following incubation with bacterial lipopolysaccaride (LPS). Both aminoguanidine and L-NAME inhibited NO production. CsA (10-300 ng/ml) also inhibited NO production in a dose-dependent manner and prevented its increase induced by LPS. Phorbol 12-myristate 13-acetate (PMA), a PKC stimulator, enhanced slightly the production of NO under basal conditions and prevented the inhibitory action of CsA on NO production. These results suggest that the NO secreted by mouse cultured mTAL cells is dependent on the PKC pathway.These results show that CsA may down-regulate the production of NO by cultured mTAL cells expressing iNOS mRNA and that the PKC pathway is involved in this process.

The glyoxalase system is a metabolic pathway to hat catalyses the detoxification of α-oxoaldehydes RCOCHO to corresponding aldonic acids RCH(OH)CO2H. It thereby protects cells from α-oxoaldehyde-mediated formation of advanced glycation endproducts (AGEs). It is comprised of two enzymes, glyoxalase I and glyoxalase II, and a catalytic amount of reduced glutathione (GSH) as cofactor. It is present in the cytosol of cells of mammals and most micro-organisms. Physiological substrates of the glyoxalase system are: glyoxal—formed from lipid peroxidation and glycation reactions, methylglyoxal—formed from triosephosphates, ketone body metabolism and threonine catabolism, and 4,5-dioxovalerate—formed from 5-aminolevulinate and α-ketoglutarate. α-Oxoaldehydes react with guanyl residues in DNA and RNA, and with cysteine, lysine and arginine residues in proteins. The modification of DNA induces mutagenesis and apoptosis. The modification of proteins leads to protein degradation and activation of a cytokine-mediated immune response in monocytes and macrophages. An acute decrease in cellular GSH, as occurs in oxidative stress, leads to decreased in situ activity of glyoxalase I, accumulation of α-oxoaldehydes and cytotoxicity. Chronic exposure to increased methylglyoxal concentration occurs in diabetes mellitus and is associated with chronic clinical complications (retinopathy, neuropathy, nephropathy). The α-oxoaldehyde scavenger Pimagedine is under clinical evaluation for prevention of diabetic complications. Pharmacological inhibition of glyoxalase I induces an acute increase in methylglyoxal concentration, growth arrest and apoptosis. Glyoxalase I inhibitors are under development as antitumour and antimalarial agents.

This study explored the role of inducible nitric oxide (NO) synthase (iNOS) in an infant rat model of group B streptococcal meningitis. Brain iNOS activity increased during meningitis (P < .001), and iNOS was detected by immunocytochemistry in the walls of meningeal vessels and cells of the cerebrospinal fluid (CSF) inflammation. Animals treated with iNOS inhibitor aminoguanidine (AG; 130 mg/kg every 8 h) had reduced NO production (P < .05), higher CSF bacterial titers (P < .05), and increased incidence of seizures (P < .01) compared with untreated infected animals. AG also increased areas of severe hypoperfusion in the cortex (31% +/- 14% in controls vs. 56% +/- 16% in AG; P < .01) and the extent of cortical neuronal injury, both when administered at the time of infection (P < .05) and in established meningitis (P < .02). Thus, NO produced by iNOS may be beneficial in this model of experimental meningitis by reducing cerebral ischemia.

The role of nitric oxide in the immune response to allogeneic tissue was explored in an in vivo cardiac transplant model in the rat. Nitric oxide production during organ rejection was demonstrated by elevations in systemic serum nitrite/nitrate levels and by electron paramagnetic resonance spectroscopy. Messenger RNA for the inducible nitric oxide synthase enzyme was detected in the rejecting allografted heart, but not in the nonrejecting isografted heart. The enzyme was demonstrated to be biologically active by the in vitro conversion of L-arginine to L-citrulline and was immunohistochemically localized to the infiltrating inflammatory cells. Treatment with aminoguanidine, a preferential inhibitor of the inducible nitric oxide synthase isoform, prevented the increased nitric oxide production in the transplanted organ and significantly attenuated the pathogenesis of acute rejection. Aminoguanidine treatment prolonged graft survival, improved graft contractile function, and significantly reduced the histologic grade of rejection. These results suggest an important role for nitric oxide in mediating the immune response to allogeneic tissue. Inhibition of inducible nitric oxide synthase may provide a novel therapeutic modality in the management of acute transplant rejection and of other immune-mediated processes.

Subclinical lymphocytic choriomeningitis virus infection primes mice expressing a V beta 8.1D beta 2J beta 2.3C beta 2 T cell receptor as a transgene for induction of fatal hematogenous shock after administration of a dose of staphylococcal enterotoxin B (SEB) that is tolerated by uninfected controls. The lethal effect is greatly diminished by prior depletion of the virus-primed CD4+ T cells. Evidence of transient tumor necrosis factor (TNF) secretion is detected in serum within 1 h of SEB administration, and massive amounts of interferon-gamma (IFN-gamma) and interleukin-6 (IL-6) are present within 4-6 h. Mice are partly protected by treatment with dimeric soluble TNF receptor-Fc fusion protein or the nitric oxide synthase inhibitor, aminoguanidine, neither of which blocks SEB-induced IFN-gamma or IL-6 production. Administration of a monoclonal antibody to IFN-gamma concomitant with SEB effectively neutralizes this cytokine but has no effect on survival.

Nitric Oxide (NO) is now recognized as a mediator of several biological functions. In the present study we examined the effects of NO synthase (NOS) inhibitors on the ovulatory process in vivo, and whether this effect can be reversed by a NO generator. Immature eCG-hCG treated rats were injected intraperitonealy (ip) or unilaterally into the periovarian sac (intrabursal injection; ib) with inhibitors of the inducible form of NOS. Aminoguanidine (AG) suppressed ovulation in a dose-dependent manner, reaching a 54% inhibition at a dose of 20 mg/kg when injected ip (p < 0.001 vs. saline control). Likewise, local ib administration inhibited ovulation from the treated ovary; thus a dose of 2 mg/kg resulted in 48% inhibition, as compared to the contralateral ovary (p < 0.01). Similar results were obtained whether AG was administered 2 h prior to the stimulation of ovulation by hCG or deferred up to 4 h afterwards. An additional NOS inhibitor, NG-methyl-L-arginine (L-NMA) suppressed ovulation, albeit to a lower extent. Intrabursal administration of L-NMA (0.1 and 1 mg/kg) resulted in 34% and 32% inhibition, respectively (p < 0.05 vs. the saline treated control). The same doses of NG-methyl-D-arginine (D-NMA) did not inhibit ovulation significantly compared to the saline treated control. When sodium nitroprusside (0.5 mg/kg), a NO generator, was injected concomitantly with AG, it completely reversed its inhibitory action on ovulation. Thus, we have demonstrated the ability of NOS inhibitors to suppress hCG-induced ovulation in the rat in vivo. The specificity of this effect is confirmed by the ability of a NO generator to reverse the inhibitory action of AG. In conclusion, the ovarian NO/NOS system seems to be necessary for follicle rupture during ovulation.

BACKGROUND: We hypothesized that upregulation of angiotensin type 1 receptor (AT(1)R) and inducible nitric oxide (NO) synthase (iNOS) within the rostral ventrolateral medulla (RVLM) could contribute to two-kidney, one-clip (2K-1C) hypertension. METHODS: The experiments were performed in male Wistar rats, 6 weeks after the renal surgery. The animals were divided into control (SHAM, n = 18) and hypertensive groups (2K-1C, n = 18). Bilateral tissue punches were taken from sections containing the RVLM to perform iNOS gene expression analyses by the real-time PCR technique, and AT(1)R and iNOS protein expression analyses by western blotting. In addition, we injected losartan (1 nmol), an AT(1)R antagonist, and aminoguanidine (250 pmol), an iNOS inhibitor, bilaterally into the RVLM to analyze the mean arterial pressure (MAP) and renal sympathetic nerve activity (rSNA). RESULTS: iNOS mRNA expression levels were greater (P < 0.05) in the 2K-1C group compared to the SHAM group. Furthermore, the AT(1)R and iNOS protein expression were significantly increased in the RVLM of 2K-1C rats compared to SHAM rats. Injection of losartan into the RVLM reduced the MAP (11%) and rSNA (18%) only in the 2K-1C rats, whereas injection of aminoguanidine in the same region decreased the MAP (31%) and rSNA (34%) in hypertensive rats. CONCLUSIONS: The present study suggests that upregulation of AT(1)R and iNOS in the RVLM is important in the maintenance of high blood pressure and renal sympathetic activation in 2K-1C hypertension.

Increased blood flow and vascular leakage of proteins preferentially affect tissues that are sites of diabetic complications in humans and animals. These vascular changes in diabetic rats are largely prevented by aminoguanidine. Glucose-induced vascular changes in nondiabetic rats are also prevented by aminoguanidine and by NG-monomethyl-L-arginine (NMMA), an established inhibitor of nitric oxide (NO.) formation from L-arginine. Aminoguanidine and NMMA are equipotent inhibitors of interleukin-1 beta-induced 1) nitrite formation (an oxidation product of NO.) and cGMP accumulation by the rat beta-cell insulinoma cell line RINm5F, and 2) inhibition of glucose-stimulated insulin secretion and formation of iron-nitrosyl complexes by islets of Langerhans. In contrast, NMMA is approximately 40 times more potent than aminoquanidine in elevating blood pressure in nondiabetic rats. These results demonstrate that aminoguanidine inhibits NO. production and suggest a role for NO. in the pathogenesis of diabetic vascular complications.

Nitric oxide (NO) is produced by a variety of cells within the respiratory tract, particularly airway epithelial cells, and its increased concentration in asthma is likely to derive from inducible NO synthase (iNOS) expressed in inflamed airways. To evaluate whether an increased bronchial flux of NO (ie, airway wall NO flux [Jno] in picoliters per second) produced in the large airways is due to an enzyme overexpression, we administered a relatively selective iNOS inhibitor, aminoguanidine, by nebulization in a double-blind, placebo-controlled manner in asthmatic and healthy subjects and also investigated whether the same concentration of inhibitor has any effect on NO produced in the peripheral lungs (ie, alveolar NO concentration [Calv] in parts per billion [ppb]) or on the diffusing capacity of NO (Dno) [in picoliters per second(-1) per ppb(-1)) in the airways. Aminoguanidine administration resulted in a significant reduction in Jno compared with administration of the saline solution control in eight healthy subjects and in eight patients with asthma but caused no significant changes in Calv or in Dno in either group. No rise in BP, fall in FEV(1), or adverse effects were observed in either group. These results indicate that iNOS from larger airways is the predominant source of elevated large airway-derived NO in patients with asthma, and that exhaled NO from peripheral lungs is not affected by a nebulized iNOS inhibitor and, therefore, is more likely to be derived form constitutive forms of NO synthase.

Background Methylglyoxal (MG), a metabolite of glucose, and MG-induced advanced glycation endproducts (AGEs) are causatively associated with vascular complications of diabetes mellitus. We have previously reported elevated levels of MG and MG-induced AGEs in spontaneously hypertensive rats (SHR). The purpose of this study was to investigate the causative role of MG and MG-induced AGEs in the pathogenesis of hypertension in SHR. Methods Young SHR were treated with an AGE inhibitor, aminoguanidine, for 9 weeks. HPLC was used to determine plasma and aortic MG and reduced glutathione levels. The MG-induced AGEs, Ne-carboxyethyl-lysine (CEL) and argpyramidine, in the aorta were determined by immunohistochemistry. Vascular relaxation of small mesenteric arteries was measured using myograph. Results Chronic treatment with aminoguanidine attenuated age-dependent blood pressure (BP) increase in SHR. Plasma and aortic MG levels, and aortic levels of MG-induced AGEs, were significantly reduced after aminoguanidine treatment, which were comparable to those from age-matched Wistar Kyoto rats. Free radical level was significantly lowered, whereas reduced glutathione level was significantly increased by aminoguanidine treatment in the aortic tissues from SHR. Moreover, aminoguanidine therapy prevented the morphologic damage of vascular tissues in SHR and restored the endothelium-dependent relaxation to acetylcholine. Chronic aminoguanidine treatment also increased aortic endothelial nitric oxide synthase expression and reduced inducible nitric oxide synthase expression. Conclusions The MG and MG-induced AGEs contribute to the pathogenesis of hypertension by altering the redox balance, causing vascular eutrophic inward remodeling, and inducing endothelial dysfunction in SHR.

Inducible nitric oxide synthase (iNOS) is a key mediator of inflammation during pathological conditions. We examined, through the use of selective iNOS inhibitors, the role of iNOS in specific pathophysiological processes after spinal cord injury (SCI), including astrogliosis, blood-spinal cord barrier (BSCB) permeability, polymorphonuclear leukocyte infiltration, and neuronal cell death. Administration of iNOS antisense oligonucleotides (ASOs) (intraspinally at 3 h) or the pharmacological inhibitors, N-[3(Aminomethyl) benzyl] acetamidine (1400 W) (i.v./i.p. 3 and 9 h) or aminoguanidine (i.p. at 3 and 9 h) after moderate contusive injury decreased the number of iNOS immunoreactive cells at the injury site by 65.6% (iNOS ASOs), 62.1% (1400 W), or 59% (aminoguanidine) 24 h postinjury. iNOS activity was reduced 81.8% (iNOS ASOs), 56.7% (1400 W), or 67.9% (aminoguanidine) at this time. All iNOS inhibitors reduced the degree of BSCB disruption (plasma leakage of rat immunoglobulins), with iNOS ASO inhibition being more effective (reduced by 58%). Neutrophil accumulation within the injury site was significantly reduced by iNOS ASOs and 1400 W by 78.8% and 20.9%, respectively. Increased astrogliosis was diminished with iNOS ASOs but enhanced following aminoguanidine. Detection of necrotic and apoptotic neuronal cell death by propidium iodide and an FITC-conjugated Annexin V antibody showed that iNOS inhibition could significantly retard neuronal cell death rostral and caudal to the injury site. These novel findings indicate that acute inhibition of iNOS is beneficial in reducing several pathophysiological processes after SCI. Furthermore, we demonstrate that the antisense inhibition of iNOS is more efficacious than currently available pharmacological agents.

Aminoguanidine (AG) is a prototype therapeutic agent for the prevention of formation of advanced glycation endproducts. It reacts rapidly with alpha,beta-dicarbonyl compounds such as methylglyoxal, glyoxal, and 3-deoxyglucosone to prevent the formation of advanced glycation endproducts (AGEs). The adducts formed are substituted 3-amino-1,2,4-triazine derivatives. Inhibition of disease mechanisms, particularly vascular complications in experimental diabetes, by AG has provided evidence that accumulation of AGEs is a risk factor for disease progression. AG has other pharmacological activities, inhibition of nitric oxide synthase and semicarbazide-sensitive amine oxidase (SSAO), at pharmacological concentrations achieved in vivo for which controls are required in anti-glycation studies. AG is a highly reactive nucleophilic reagent that reacts with many biological molecules (pyridoxal phosphate, pyruvate, glucose, malondialdehyde, and others). Use of high concentrations of AG in vitro brings these reactions and related effects into play. It is unadvisable to use concentrations of AG in excess of 500 microM if selective prevention of AGE formation is desired. The peak plasma concentration of AG in clinical therapy was ca. 50 microM. Clinical trial of AG to prevent progression of diabetic nephropathy was terminated early due to safety concerns and apparent lack of efficacy. Pharmacological scavenging of alpha-oxoaldehydes or stimulation of host alpha-oxoaldehyde detoxification remains a worthy therapeutic strategy to prevent diabetic complications and other AGE-related disorders.

Long-lived structural proteins, collagen and elastin, undergo continual non-enzymatic crosslinking during aging and in diabetic individuals. This abnormal protein crosslinking is mediated by advanced glycation end products (AGEs) generated by non-enzymatic glycosylation of proteins by glucose. The AGE-derived protein crosslinking of structural proteins contributes to the complications of long-term diabetes such as nephropathy, retinopathy, and neuropathy. AGE-crosslinks have also been implicated in age-related cardiovascular diseases. Potential treatment strategies for these AGE-derived complications include prevention of AGE-formation and breaking of the existing AGE-crosslinks. The therapeutic potential of the AGE-inhibitor, pimagedine (aminoguanidine), has been extensively investigated in animal models and in Phase 3 clinical trials. This review presents the pre-clinical and clinical studies using ALT-711, a highly potent AGE-crosslink breaker that has the ability to reverse already-formed AGE-crosslinks. Oral administration of ALT-711 has resulted in a rapid improvement in the elasticity of stiffened myocardium in experimental animals. Topical administration of ALT-711 was effective in improving the skin hydration of aged rats. The therapeutic potential of crosslink breakers for cardiovascular complications and dermatological alterations associated with aging and diabetes is discussed.

Trypanosoma cruzi infection in mice is associated with severe hematological changes, including anemia, which may contribute to mortality. TNF-alpha and nitric oxide (NO) play a critical role in establishing host resistance to this pathogen. We hypothesized that phagocyte-derived NO damages erythrocytes and contributes to the anemia observed during T. cruzi infection. To test this hypothesis, two strains of mice that differed in susceptibility and NO response to T. cruzi infection were used in these studies. We also blocked endogenous NO production by aminoguanidine (AG) treatment or blocked TNF-alpha with a neutralizing antibody and used mice that cannot produce phagocyte-derived NO (C57BL/6 iNOS(-/-)). Following infection with T. cruzi, resistant (C57BL/6) and susceptible (Swiss) mice displayed a parasitemia that peaked at the same time (i.e., day 9), yet parasitemia was 3-fold higher in Swiss mice (P0.05). All Swiss mice were dead by day 23 post-infection, while no C57BL/6 mice died during the study. At 14 days post-infection anemia in C57BL/6 mice was more severe than in Swiss mice. Treatment of both strains with the NO inhibitor, AG (50 mg/kg), and the use of iNOS(-/-) mice, revealed that the anemia in T. cruzi-infected mice is not caused by NO. However, the reticulocytosis that occurs during infection was significantly reduced after treatment with AG in both Swiss and C57BL/6 mice (P0.05). In addition, we showed that neutralization of TNF-alpha in vivo induced a significant increase in circulating reticulocytes in T. cruzi-infected C57BL/6 mice (P0.05), but did not modify other hematologic parameters in these mice. The evaluation of the oxidative stress after induction by t-butyl hydroperoxide (t-BHT) revealed that the treatment with AG completely protected against NO-mediated haemoglobin oxidation. Further, treatment with AG, but not with anti-TNF-alpha, protected against the infection-induced reduction of antioxidant capacity of erythrocytes as assessed by oxygen uptake and induction time. In summary, this is the first report showing the participation of NO and TNF-alpha in the oxidative stress to erythrocytes in acute T. cruzi infection. Further, our data suggest that NO does not play a direct role in development of the anemia. However, NO may contribute to other hematological changes noted during T. cruzi infection, such as the elevation of circulating reticulocytes and the reduction in circulating leukocytes and neutrophils.

The aim of this study was to determine whether aminoguanidine (AG), an inhibitor of advanced glycation, prevents expression of the profibrotic cytokine, connective tissue growth factor (CTGF), as well as accumulation of the previously reported CTGF-dependent matrix protein, fibronectin, in a model of experimental diabetic nephropathy. Diabetic animals were randomly allocated into groups receiving 32 wk of AG or vehicle. Diabetic rats showed increases in CTGF mRNA and protein expression as well as in advanced glycation end-product (AGE) and fibronectin immunostaining, compared with nondiabetic rats. In the diabetic kidney, the increase in CTGF gene and protein expression as well as expression of the extracellular matrix protein fibronectin were prevented by AG. To further explore the relationship between AGEs and mesangial CTGF and fibronectin production, cultured human mesangial cells were exposed in vitro to soluble AGE-BSA and carboxymethyl lysine-BSA, and this led to induction of both CTGF and fibronectin. On the basis of our in vitro findings in mesangial cells linking AGEs to CTGF expression, the known prosclerotic effects of CTGF, and the ability of AG to attenuate mesangial expansion, it is postulated that the antifibrotic effects of AG in this animal model may be partially mediated by CTGF.

The cecal ligation and puncture (CLP) model was used to investigate whether failure of neutrophil migration occurs in sepsis and whether it correlates with disease outcome. It was observed that the severity of sepsis correlates with the number of punctures in the cecum: mice with 2 punctures (sublethal [SL]-CLP) developed mild peritonitis (100% survived), whereas mice with 12 punctures (lethal [L]-CLP) developed severe peritonitis and bacteremia that evolved to sepsis (none survived). The production of tumor necrosis factor-alpha, interleukin-1beta, and interleukin-10 was higher in L-CLP than in SL-CLP mice. The impairment of neutrophil migration to the peritoneum and to the cecum wall was observed only in L-CLP mice. This phenomenon was shown to be mediated by nitric oxide, because aminoguanidine prevented the failure of neutrophil migration and improved the survival of L-CLP animals. In conclusion, impairment of neutrophil migration is a crucial event in the worsening of sepsis, and nitric oxide seems to be responsible for the phenomenon.

Successful pregnancy is strictly dependent on the trophoblast-decidual interaction and on an adequate blood supply to the implantation sites. Nitric oxide (NO) has been shown to play an important role during advanced gestation, although its role during early pregnancy is unclear. The aim of the present study in rats was to evaluate whether NO plays a role during the preimplantation [days 1-4 post coitum (p.c.)] and peri-implantation (days 6-8 p.c.) phases of pregnancy. The rats were treated with the non-specific nitric oxide synthase (NOS) inhibitor N G -nitro-L-arginine methyl ester (L-NAME), and the iNOS inhibitor aminoguanidine in the presence and absence of low-dose antiprogestin, onapristone, and evaluated on days 9 p.c. and 19 p.c., respectively. Before implantation, the treatments alone (L-NAME, aminoguanidine, onapristone) had little effect on pregnancy outcome. Conversely, aminoguanidine plus onapristone treatment completely prevented pregnancy, whereas L-NAME plus onapristone reduced the pregnancy rate to approximately 50%. In addition, both treatments drastically reduced decidualization. Oviductal flushing experiments revealed arrest of embryo development at around the 8-cell stage after aminoguanidine plus onapristone treatment on days 1-4 p.c. Similarly, treatment during the peri-implantation period with L-NAME, aminoguanidine, and onapristone each had only marginal effects on pregnancy. However, a combination of L-NAME and onapristone, and aminoguanidine plus onapristone prevented pregnancy in 71% and 42% of dams, respectively, as determined on day 19 p.c. These treatments also markedly inhibited the decidualization process. This study demonstrates synergistic effects of NOS inhibitors and an antiprogestin in preventing pregnancy. NOS, particularly the cytokine- and progesterone-inducible iNOS, may represent a new target for novel therapeutic agents capable of promoting or inhibiting pregnancy.

Background The role of inducible nitric oxide synthase (iNOS) in endotoxin-induced bacterial translocation was investigated by using its specific blocker aminoguanidine in 46 albino mice (25–35 g) allocated into four groups. Methods The first group received intraperitoneal saline (control; 0·9 per cent w v−1 sodium chloride 1 ml kg−1; n = 6), the second group intraperitoneal endotoxin (Escherichia coli lipopolysaccharide 055:B5 20 mg kg−1; n = 19), the third group intraperitoneal aminoguanidine (20 mg kg−1, 20 min before and 12 h after saline; n = 6) and the fourth group both endotoxin and aminoguanidine intraperitoneally (n = 15). Some 24 h later, the animals were anaesthetized with ether and blood samples were collected by cardiac puncture together with mesenteric lymph node (MLN), spleen and liver specimens under aseptic conditions. Specimens were then cultured to determine the presence of colony-forming units as an index of bacterial translocation. Results No bacterial growth was detected in samples from the first and third groups. Colony-forming bacteria were found in ten of 14 MLN samples, eight of 14 spleens, four of 14 livers and three of 14 peripheral blood samples in the second group, with E. coli being the predominant pathogen. In contrast, in the fourth group, colony-forming bacteria were found in only three of 14 MLN samples (P = 0·02 versus the second group), three of 14 spleens and one of 14 liver specimens. None of the values in the fourth group was significantly different from those in the saline control group. Conclusion The inhibition of iNOS during endotoxaemia by its specific blocker aminoguanidine attenuates the incidence of bacterial translocation in mice. These results may be exploited clinically for the prophylaxis and treatment of septic states.

The NO synthases (NOS) generate NO from L-arginine. High concentrations of NO have been shown to be responsible for tissue injury and cell death, while low concentrations of NO induce vasodilatation and other signaling effects. We have investigated the involvement of NO in contact hypersensitivity (CHS) reactions. CHS induced by treatment of BALB/c mice with the contact allergen 2,4-dinitrofluorobenzene (DNFB) was significantly reduced by the NOS inhibitor N-methyl-L-arginine (L-NMA), but not by the stereoisomer D-NMA, as shown by reduced ear swelling responses and evaluation of ear tissue sections. The CHS response was also reduced by aminoguanidine, which is known to preferentially inhibit the inducible isoform of the enzyme (iNOS), suggesting that iNOS contributed to the inflammatory response. We therefore investigated whether iNOS was expressed by epidermal cells. Epidermal Langerhans cells produced low but significant amounts of iNOS mRNA at the single-cell level as indicated by RT-PCR. Likewise, keratinocytes expressed basic iNOS mRNA levels. Elicitation of a CHS response by DNFB in vivo resulted in enhanced iNOS mRNA expression in Langerhans cells and keratinocytes, with higher levels of expression in Langerhans cells. The enhanced mRNA expression in Langerhans cells correlated with iNOS protein production as shown by immunofluorescence staining of epidermal sheets performing double staining with anti-iNOS and anti-MHC class II antibodies. Our data suggest that epidermal cell-derived NO contributes to the ear swelling reaction in CHS.

The purpose of this study was to identify the duration of exposure of islets to interleukin 1beta (IL-1beta) that results in irreversible damage. Treatment of rat islets for 18 h with IL-1beta results in an inhibition of glucose-stimulated insulin secretion, mitochondrial aconitase activity, and total protein synthesis. The addition of N(G)-monomethyl-L-arginine (NMMA) or aminoguanidine to islets preincubated for 18 h with IL-1beta, followed by continued culture for 8 h (with both NMMA and IL-1beta), results in the recovery of islet secretory function, aconitase activity, and protein synthesis. However, islet metabolic function is irreversibly inhibited after a 36-h incubation with IL-1beta, as an additional 8-h incubation with NMMA or aminoguanidine does not stimulate the recovery of insulin secretion, aconitase activity, or protein synthesis. The irreversible inhibition of metabolic function correlates with the commitment of islets to destruction. Treatment of islets for 96 h with IL-1beta results in islet degeneration. NMMA, added to islets 24 h after the addition of IL-1beta, followed by continued culture for 72 h (with NMMA and IL-1beta), prevents islet degeneration. However, NMMA added to islets 36 h or 48 h after the addition of IL-1beta, followed by continued culture for a total of 96 h, does not prevent islet degeneration. New messenger RNA expression appears to be required for islet recovery from IL-1beta-induced damage as actinomycin D prevents the recovery of islet aconitase activity. Lastly, treatment of human islets with a combination of IL-1beta and interferon-gamma (IFNgamma) results in a potent inhibition of mitochondrial aconitase activity. NMMA, when cocultured with IL-1beta + IFNgamma, completely prevents cytokine-induced inhibition of human islet aconitase activity. NMMA, when added to human islets pretreated for 18 h with IL-1beta + IFNgamma, stimulates the recovery of mitochondrial aconitase activity after an additional 8 h incubation. These findings indicate that nitric oxide-induced islet damage is reversible; however, prolonged production of nitric oxide (after a 36-h exposure to IL-1beta) results in the irreversible inhibition of islet metabolic and secretory function.

Nitric oxide (NO) is synthesized from L-arginine by three isoforms of NO synthase (NOS). It is essential to suppress the function of the inducible isoform (macNOS) for amelioration of some inflammatory diseases in which the cytotoxic effect of NO is involved. S-Ethylsiothiourea (S-EIU) was reported to be a potent and specific inhibitor of macNOS. We also confirmed that it rather specifically inhibited the activity of the purified macNOS and the formation of nitrite by RAW264.7 cells compared to NG-monomethyl-L-arginine (L-NMA) and NG-nitro-L-arginine (L-NNA), the other isoforms being less effective. S-EIU suppressed the release of nitrite and lactate dehydrogenase from rat vascular smooth muscle cells treated with interleukin-1 beta and forskolin more potently than L-NMA or L-NNA. S-EIU also slightly suppressed internucleosomal DNA cleavage in pancreatic beta-cells induced by NO produced by macNOS. Intravenous administration of either S-EIU at 0.1 mg/kg/min or L-NMA at 1 mg/kg/min increased the blood pressure but decreased the heart rate in normal rabbits, while aminoguanidine at 1 mg/kg/min affected neither cardiovascular function. These inhibitors at these doses caused recovery of the blood pressure in lipopolysaccharide-treated rabbits that exhibited lowered blood pressure similar to that in the case of septic shock. Although S-EIU seemed not to be an adequate inhibitor for therapeutic use in vivo due to its side effects on cardiovascular functions, it is one of the most potent inhibitors of macNOS among reported inhibitors in vitro.

Overproduction of the free radical nitric oxide (NO) has been implicated in the pathogenesis of a variety of inflammatory and immunologically mediated diseases as well as complications of diabetes. In the present study we have demonstrated that aminoguanidine selectively inhibits the cytokine-inducible isoform of NO synthase which appears to be responsible for the excess production of NO linked to these disease states. By using organ, cell, and enzyme-based measurements we have shown that aminoguanidine is equipotent to NG-monomethyl-L-arginine (L-NMA) as an inhibitor of the cytokine-induced isoform of NO synthase but is 10 to 100-fold less potent as an inhibitor of the constitutive isoform. Thus, aminoguanidine may be useful as a selective inhibitor of the inducible NO synthase in the treatment of disease states characterized by the pathological overproduction of NO.

Platelets generate nitric oxide (NO) in response to agonist stimulation. Previous reports have shown that the endothelial nitric oxide synthase (eNOS) plays a role in agonist-stimulated platelet NO production and in platelet activation. Here we show that platelets from eNOS knockout mice (eNOS−/−) showed only partial reduction in thrombin-induced NO production compared to wild type platelets (50% reduction), indicating the presence of another NOS isoform in platelets. More importantly, we show that resting platelets express functional inducible nitric oxide synthase (iNOS), which participates in platelet activation. Compared to wild type platelets, thrombin-induced NO production was reduced by 54% in platelets isolated from iNOS knockout mice (iNOS−/−), indicating an iNOS-dependent NO production in platelets induced by thrombin. Since thrombin-induced NO production occurs during the first 3 min of thrombin stimulation, our findings provide the first evidence for a short-term regulation of iNOS activity independent of transcription regulation. In contrast, previous description of iNOS activation was primarily at the transcriptional level and required much longer time of induction. To determine the role of iNOS in platelet activation, platelets from wild type and iNOS−/− mice were stimulated with low concentrations of agonists. iNOS−/− platelets exhibited lower aggregation and secretion response compared to wild type control, indicating that iNOS plays a stimulatory role in platelet activation. We also examined the effect of iNOS inhibitors on platelet activation. Human and mouse platelets preincubated with iNOS specific inhibitors, 1400W and aminoguanidine, exhibited a dose-dependent inhibition of platelet secretion and aggregation induced by either low-dose thrombin or collagen. Furthermore, the inhibitory effect of iNOS-specific inhibitors was only shown in wild type mouse platelets, but was lacking in iNOS−/− platelets. Thus, activation of both iNOS and eNOS is important in agonist-induced NO production which stimulates platelet secretion and aggregation.