Characterization of the effects of two new arginine/citrulline analogues on constitutive and inducible nitric oxide synthases in rat aorta

Abstract

1 New potent inhibitors of nitric oxide synthase (NOS) may be useful in the treatment of septic shock, a disorder characterized by a vascular hyporeactivity to catecholamines caused by an overproduction of nitric oxide (NO-). We examined the effects of L-thiocitrulline (L-TC) and S-methyl-L-thiocitrulline (L-SMTC), novel NOS inhibitors, on the constitutive and inducible NOS in rat aorta and compared those effects with inhibition due to NG-methyl-L-arginine (L-NMA). 2 Phenylephrine evoked similar concentration-contraction curves in the control rings and in the rings treated with these different NOS inhibitors (10 gM), whereas 100 MM of L-NMA, L-TC or L-SMTC increased significantly, and to a similar extent, contractions evoked by phenylephrine in aortic rings with endothelium without significantly affecting the maximal responses. 3 Relaxations evoked by acetylcholine, adenosine triphosphate, or calcium ionophore were significantly inhibited in a dose-dependent manner by L-NMA, L-SMTC, or L-TC (10-100 gM). The potencies of these inhibitors in reducing the relaxations of these vasodilators were not significantly different. 4 In endotoxin-treated preparations with endothelium, the three L-arginine analogues (10 MM) significantly potentiated contractile responses to phenylephrine (pEC5o: 6.73 ± 0.12 and 7.3 + 0.12, 7.34 + 0.13, or 7.22 ± 0.14; in the absence and the presence of L-NMA, L-TC, or L-SMTC respectively) and increased maximal contractions from 1.53 +0.15 g to 1.95 +0.13 g, 2.08 ±0.12 g, and 2.03 ±0.13 g with L-NMA, L-TC, and L-SMTC respectively. A higher concentration of these NOS inhibitors (100 MM) further increased contractions evoked by this a,-agonist without further enhancing the maximal contractions; however, contractions evoked by 10 nM phenylephrine were significantly greater in the presence of L-SMTC or L-TC than in the presence of L-NMA (100 gM) (L-NMA: 0.4 + 0.11 g; L-TC: 0.78 +0.14 g and L-SMTC: 0.82+±0.17 g). The effects of these inhibitors on NO-synthesis induced by endotoxin were significantly reversed by addition of L-arginine (1 mM) but not by L-citrulline (1 mM). In LPS-treated rings with endothelium, all three NOS inhibitors (100 FM) shifted the concentrationcontraction curves evoked by phenylephrine significantly to the left (pEC5o: 7.19 + 0.03 and 7.79 + 0.08, 8.01 + 0.07, or 8.02 + 0.07, in the absence and the presence of L-NMA, L-TC, or L-SMTC, respectively) and increased significantly maximal contractions from 2.05 + 0.05 g to 2.38 + 0.14 g, 2

Brain Nitric Oxide and Its Dual Role in Neurodegeneration / Neuroprotection: Understanding Molecular Mechanisms to Devise Drug Approaches

“…Among arginine derivatives, N ω -allyl-L-arginine and N ω -propyl-L-arginine appear to affect catalytic activity with a mechanism more complex than simple competitive inhibition and display relative selectivity towards different isoforms by inhibiting some of them at concentrations much lower than others [466,467,468]. Other amino acid analogs are effective NOS inhibitors, sometimes showing some degree of selectivity, as it is the case for S-methyl and Sethyl derivatives of L-thiocitrulline whose action is exerted through block of the heme-dependent oxygen activation [469,470]. Derivatives of other amino acids, such as N 5 -(1-iminoethyl)-L-ornithine (L-NIO) and N 6 -(1-iminoethyl)-Llysine (L-NIL) are effective NOS inhibitors showing a limited degree of selectivity [460].…”

Local isoform‐specific NOS inhibition: A promising approach to promote motor function recovery after nerve injury

“…Unfortunately, Wang and colleagues (2009) did not use an inhibitor that specifically targets eNOS, thus limiting the specificity of their findings. Another nNOS inhibitor (SMTC) has been reported to be a very potent vasopressor in anesthetized rats (Narayanan et al, 1995) and an inhibitor of endothelium‐dependent relaxation responses of the isolated rat aorta, with a potency similar to that of a broad spectrum NOS inhibitor (Joly et al, 1995). These data strongly suggest that SMTC causes significant eNOS inhibition in vivo and, consequently, its use to study the function of nNOS‐derived NO in intact animals is not advised (Moore and Handy, 1997).…”

Functional effects of econazole on inducible nitric oxide synthase: production of a calmodulin‐dependent enzyme

“…One approach has been to develop novel substrate analogues of L-arginine. Compounds such as aminoguanidine (Griffiths et al, 1994), isothioureas (Southan et al, 1995) and L-thiocitrulline (Joly et al, 1995), have been reported to exhibit some isoform selectivity for iNOS. However, compounds based on inhibiting enzyme expression might also show some selectivity and we reported that anti-fungal imidazoles inhibit expression of the iNOS activity in murine macrophages (Bogle et al, 1994).…”