The Soluble Guanylyl Cyclase Inhibitor 1H-[1,2,4]Oxadiazolo[4,3,-a]quinoxalin-1-one Is a Nonselective Heme Protein Inhibitor of Nitric Oxide Synthase and Other Cytochrome P-450 Enzymes Involved in Nitric Oxide Donor Bioactivation1

  1. Martin Feelisch1,
  2. Peter Kotsonis2,
  3. Jan Siebe3,
  4. Bernd Clement3 and
  5. Harald H. H. W. Schmidt2
  1. 1The Wolfson Institute for Biomedical Research, University College London, London, United Kingdom (M.F.); 2Department of Pharmacology and Toxicology, Julius-Maximilians-University, Würzburg, Germany (P.K., H.H.H.W.S.); and 3Institute of Pharmacy, Christian-Albrecht-University, Kiel, Germany (J.S., B.C.)

    Abstract

    Soluble guanylyl cyclase (sGC) is an important effector for nitric oxide (NO). It acts by increasing intracellular cyclic GMP (cGMP) levels to mediate numerous biological functions. Recently, 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ) was identified as a novel and selective inhibitor of this enzyme. Therefore, ODQ may represent an important pharmacological tool for differentiating cGMP-mediated from cGMP-independent effects of NO. In the present study, we examined the inhibitory action of ODQ both functionally and biochemically. In phenylephrine-preconstricted, endothelium-intact, isolated aortic rings from the rat, ODQ, in a concentration-dependent manner, increased contractile tone and inhibited relaxations to authentic NO with maximal effects at 3 μM. Pretreatment of vascular rings with ODQ induced a parallel, 2-log-order shift to the right of the concentration-response curves (CRCs) to histamine, ATP, NO, the NO-donorsS-nitrosoglutathione,S-nitroso-N-acetyl-d,l-penicillamine, and spermine NONOate [N-[4-[1-(3-amino propyl)-2-hydroxy-2-nitroso hydrazino]butyl]-1,3-propane diamine], and the direct sGC-stimulant [3-(5′-hydroxymethyl-2′furyl)-1-benzyl indazole] YC-1 but did not affect relaxations induced by papaverine and atriopeptin II. Moreover, the rightward shift of the CRCs to Angeli’s salt, peroxynitrite, and linsidomine was similar to that of NO. These results suggested that ODQ is specific for sGC. Furthermore, they indicate that NO can cause vasorelaxation independent of cGMP. Three interesting exceptions were observed to the otherwise rather uniform inhibitory effect of ODQ: the responses to acetylcholine, glycerol trinitrate, and sodium nitroprusside. The latter two agents are known to require metabolic activation, possibly by cytochrome P-450-type proteins. The 3- to 5-log-order rightward shift of their CRCs suggests that, in addition to sGC, ODQ may interfere with heme proteins involved in the bioactivation of these NO donors and the mechanism of vasorelaxation mediated by acetylcholine. In support of this notion, ODQ inhibited hepatic microsomal NO production from both glycerol trinitrate and sodium nitroprusside as well as NO synthase activity in aortic homogenates. The latter effect seemed to require biotransformation of ODQ. Collectively, these data reveal that ODQ interferes with various heme protein-dependent processes in vascular and hepatic tissue and lacks specificity for sGC.

    Footnotes

    • Send reprint requests to: Dr. Martin Feelisch, The Wolfson Institute for Biomedical Research, University College London, St. Martin’s House, 140 Tottenham Court Road, London, W1P 9LN, U.K. E-mail: feelisch{at}aol.com

    • ↵1 Part of this work was presented at the 1997 Winter Meeting of the British Pharmacological Society [abstract appeared inBr J Pharmacol (1998) 123 (Suppl):6P].

    • This work was supported in part by a grant from Lacer (M.F.), the Deutsche Forschungsgemeinschaft (SFB 355/C7), and a C.J. Martin fellowship from the National Health and Medical Research Council of Australia (P.K.).

    • Abbreviations:
      NO
      nitric oxide
      sGC
      soluble guanylyl cyclase
      NOS
      nitric oxide synthase
      ODQ
      1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one
      cGMP
      cyclic GMP
      SNP
      sodium nitroprusside
      YC-1
      3-(5′-hydroxymethyl-2′furyl)-1-benzyl indazole
      l-NAME
      Nω-nitro-l-arginine methyl ester
      AP II
      atriopeptin II
      Sper-NO
      spermine NONOate (N-[4-[1-(3-amino propyl)-2-hydroxy-2-nitroso hydrazino]butyl]-1,3-propane diamine)
      GSNO
      S-nitrosoglutathione
      SNAP
      S-nitroso-N-acetyl-d,l-penicillamine
      ONOO−
      peroxynitrite
      GTN
      glycerol trinitrate
      SIN-1
      linsidomine
      DMSO
      dimethyl sulfoxide
      ACh
      acetylcholine
      CHAPSO
      3-[(3-cholamidopropyl)dimethyl-ammonio]-2-hydroxy-1-propanesulfonate
      CRC
      concentration response curve
      NO2−
      nitrite
      • Received December 10, 1998.
      • Accepted April 16, 1999.
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    1. Molecular Pharmacology August 1, 1999 vol. 56 no. 2 243-253
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