Nitric Oxide Synthase Inhibitor Aminoguanidine Research Articles

Aminoguanidine ameliorates and L-arginine worsens brain damage from intraluminal middle cerebral artery occlusion.

We studied whether the inducible nitric oxide synthase (iNOS) inhibitor aminoguanidine reduces focal cerebral ischemic damage in a relatively noninvasive stroke model in which the rat middle cerebral artery (MCA) is occluded using an intravascular filament. In rats anesthetized with halothane, a nylon filament was advanced into the internal carotid artery until its tip occluded the origin of the MCA. The filament was left in place for 2 hours and then withdrawn. Twenty-four hours later, rats received intraperitoneal injections of aminoguanidine (100 mg/kg BID; n = 7), aminoguanidine+L-arginine (300 mg/kg QID; n = 7), L-arginine alone (n = 6), D-arginine alone (n = 6), or vehicle (n = 10). Drugs were administered for 3 consecutive days. Infarct volume was determined by image analysis in thionin-stained brain sections 4 days after ischemia. iNOS mRNA was detected with the use of reverse transcription polymerase chain reaction. Cerebral ischemia led to iNOS mRNA expression in the affected brain 48 hours after induction of ischemia. Administration of aminoguanidine reduced neocortical infarct volume by 26% (P < .05 versus vehicle, ANOVA and Tukey's test), a reduction that was antagonized by coadministration of L-arginine (P > .05 versus vehicle). Administration of L-arginine alone, but not D-arginine, enlarged the infarct by 29% (P < .05). Aminoguanidine or L-arginine did not influence the increase in water content in the postischemic brain, indicating that the effect on infarct volume is not related to modulation of ischemic edema. These results demonstrate that cerebral ischemia is also associated with iNOS expression in a minimally invasive model of transient MCA occlusion and that iNOS inhibition reduces focal ischemic damage. The findings support the hypothesis that nitric oxide produced by iNOS contributes to ischemic brain damage and that inhibition of iNOS may be a valuable tool in the management of cerebral ischemia.

Inhibition of nitric oxide synthesis does not improve interleukin-2-mediated antitumor effects in vivo.

Nitric oxide (NO) decreases cytotoxicity and proliferation of cytotoxic lymphocytes (CTLs) in vitro. Both can be prevented by inhibitors of the NO synthase (NOS). To elucidate whether inhibition of the IL-2-induced NOS could boost efficacy of IL-2-stimulated CTLs in vivo, we assessed lung metastases in mice injected with IL-2, the NOS inhibitor aminoguanidine (AG), their combination and the diluent. No improvement was observed for IL-2 + AG compared to IL-2 while NO production was normalized. Since NO causes one of the two major side effects of IL-2 treatment, hypotension, we further studied whether capillary leak could be attributed to NO, too. While IL-2-inducible NO was reduced to control levels by AG, pulmonary edema was unaffected. Thus a decrease in NO does not improve antitumor effects of IL-2-stimulated CTLs nor does it attenuate IL-2-associated capillary leak.

Relationship of tumor necrosis factor alpha, the nitric oxide synthase pathway, and lipopolysaccharide to the killing of gamma interferon-treated macrophage-like RAW264.7 cells by Rickettsia prowazekii.

Macrophage-like RAW264.7 cells are killed by the combination of gamma interferon (IFN-gamma) treatment and infection with Rickettsia prowazekii. The roles of tumor necrosis factor alpha (TNF-alpha), the nitric oxide synthase pathway, and lipopolysaccharide (LPS) in this killing were investigated. R. prowazekii, both the Breinl and Madrid E strains, induced RAW264.7 cells to produce TNF-alpha. However, dead rickettsiae (which cannot kill the IFN-gamma-treated RAW264.7 cells) induced the production of as much TNF-alpha as viable rickettsiae. Inhibition of the production of TNF-alpha (by the addition of actinomycin D or emetine during the rickettsial infection) or neutralization of TNF-alpha (by the addition of polyclonal rabbit anti-mouse TNF-alpha serum both during the IFN-gamma treatment and during the rickettsial infection) did not inhibit the killing of the RAW264.7 cells. Addition of polymyxin B (which inhibits many effects of LPS) during the IFN-gamma treatment did not inhibit the ability of IFN-gamma to prepare the RAW264.7 cells to be killed by R. prowazekii. Suppression of nitrite production by addition of the nitric oxide synthase inhibitor aminoguanidine both during the IFN-gamma treatment and during the rickettsial infection also did not inhibit the killing of the RAW264.7 cells. R. prowazekii-mediated killing of the RAW264.7 cells was dramatically suppressed in cultures treated with IFN-gamma plus LPS compared with that in cultures treated with IFN-gamma alone, and inhibition of nitric oxide synthase restored the rickettsia-induced killing of the RAW264.7 cells in cultures treated with IFN-gamma plus LPS. These data indicate that (i) TNF-alpha, LPS, and the nitric oxide synthase pathway are not required in order for IFN-gamma to prepare RAW264.7 cells to be killed by R. prowazekii; (ii) neither TNF-alpha nor the nitric oxide synthase pathway is responsible for the killing of the IFN-gamma-treated RAW264.7 cells by R. prowazekii; and (iii) in cultures treated with IFN-gamma plus LPS and then incubated with rickettsiae, a nitric oxide synthase pathway-dependent mechanism inhibits the killing of the RAW264.7 cells.

Nitric Oxide Mediates IL-1β-Induced Islet Dysfunction and Destruction: Prevention by Dexamethasone

Nitric oxide has recently been implicated as a cellular molecule that mediates interleukin-1 beta (IL-1 beta)-induced inhibition of glucose-stimulated insulin secretion by islets of Langerhans. In this study evidence is presented which demonstrates that islets contain both the cytokine inducible and the constitutive isoforms of nitric oxide synthase as determined by NADPH diaphorase staining and immunohistochemical localization. Untreated islets contain NADPH diaphorase activity, and the intensity of NADPH diaphorase staining is dramatically increased after culture for 18 hrs with IL-1 beta. Both control and IL-1 beta-induced NADPH diaphorase staining of islets is inhibited by the nitric oxide synthase inhibitor NG-monomethyl-L-arginine (NMMA). Importantly, approximately 60-70% of islet cells stained positive for NADPH diaphorase (under both IL-1 beta treated and control conditions), suggesting that a subset of islet cells contain nitric oxide synthase. The beta-cell appears to be the endocrine cell type which contains constitutive nitric oxide synthase as demonstrated by immunohistochemical co-localization of constitutive nitric oxide synthase and insulin. IL-1 beta is believed to stimulate the expression of cytokine inducible nitric oxide synthase because the synthetic glucocorticoid, dexamethasone, prevents IL-1 beta induced inhibition of glucose stimulated insulin secretion and cGMP accumulation by islets. Both dexamethasone, and the nitric oxide synthase inhibitors NMMA and aminoguanidine also prevent IL-1 beta induced islet degeneration. These results indicate that nitric oxide produced by the inducible isoform of nitric oxide synthase mediates cytokine induced islet dysfunction and destruction, and that the beta-cell is the islet endocrine cellular source of constitutive nitric oxide synthase.