title: Potent inhibition of the inducible isoform of nitric oxide synthase by aminoethylisoselenourea and related compounds.
abstract: The generation of nitric oxide (NO) by nitric oxide synthase (NOS) can be inhibited by certain guanidines and S-alkylisothioureas. In particular, aminoethylisothiourea (AE-TU) shows selectivity towards the inducible isoform (iNOS) over the endothelial isoform (ecNOS). Here we report on the effects of the selenium analog of AE-TU, aminoethylisoselenourea (AE-SeU), and its homologue, aminopropylisoselenourea (AP-SeU), on the activities of iNOS and ecNOS. AE-SeU and AP-SeU inhibited the conversion of L-arginine to L-citrulline in homogenates of lung taken from endotoxin-treated rats (a model of iNOS acitivity) with potencies (EC50=1.1, and 0.1 microM, respectively) greater than that of N(G)-methyl-L-arginine (L-NMA) (22 microM). In contrast, AE-SeU and AP-SeU were weaker than or similar to L-NMA at inhibiting ecNOS activity in homogenized bovine endothelial cells (EC50 values = 104, 15, and 16 microM, respectively). AE-SeU and AP-SeU potently inhibited nitrite formation by immunostimulated J774 macrophages (a model of iNOS activity) with EC50 values of 10 and 4 microM respectively. The corresponding EC50 value for L-NMA was 160 microM. The inhibition was dose-dependently reduced by increasing concentrations of L-arginine in the medium. In vivo, AE-SeU had only modest effects on blood pressure when given as a bolus to anesthetized rats, suggesting only a small effect on ecNOS in vivo, whereas AP-SeU had potent pressor effects similar to those of L-NMA. We found that both AE-SeU and AP-SeU were unstable in aqueous solution at pH values above 6. Their disappearance from solution was accompanied by the appearance of a reductive species, probably free selenol. These findings suggest that AE-SeU and AP-SeU exert their inhibitory effects through intramolecular rearrangement to yield selenoethylguanidine and seleno-propylguanidine. Thus, selenoalkylguanidines are novel inhibitors of iNOS.
authors.affiliation: Children's Hospital Medical Center, Division of Critical Care, Cincinnati, Ohio 45229, USA.
authors.forename: G J
authors.initials: GJ
authors.lastname: Southan
authors.forename: A L
authors.initials: AL
authors.lastname: Salzman
authors.forename: C
authors.initials: C
authors.lastname: Szabo
mesh_terms: D000276:Adjuvants, Immunologic / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D004790:Enzyme Induction; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D007527:Isoenzymes / Q000037:antagonists & inhibitors* / Q000096:biosynthesis; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism; D008297:Male; D051379:Mice; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors* / Q000096:biosynthesis; D009573:Nitrites / Q000378:metabolism; D016566:Organoselenium Compounds / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D000276:Adjuvants, Immunologic; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D009573:Nitrites; D016566:Organoselenium Compounds; C011642:aminoethylisoselenouronium; D019001:Nitric Oxide Synthase