2-Iminopyrrolidines as potent and selective inhibitors of human inducible nitric oxide synthase.

A series of substituted 2-iminopyrrolidines has been prepared and shown to be potent and selective inhibitors of the human inducible nitric oxide synthase (hiNOS) isoform versus the human endothelial nitric oxide synthase (heNOS) and the human neuronal nitric oxide synthase (hnNOS). Simple substitutions at the 3-, 4-, or 5-position afforded more potent analogues than the parent 2-iminopyrrolidine 1. The effect of ring substitutions on both potency and selectivity for the different NOS isoforms is described. Substitution at the 4- and 5-positions of the 2-iminopyrrolidine yielded both potent and selective inhibitors of hiNOS. In particular, (+)-cis-4-methyl-5-pentylpyrrolidin-2-imine, monohydrochloride (20), displayed potent inhibition of hiNOS (IC50 = 0.25 microM) and selectivities of 897 (heNOS IC50/hiNOS IC50) and 13 (hnNOS IC50/hiNOS IC50). Example 20 was shown to be an efficacious inhibitor of NO production in the mouse endotoxin assay. Furthermore, 20 displayed in vivo selectivity, versus heNOS isoform, by not elevating blood pressure at multiples of the effective dose in the mouse.

2-Iminohomopiperidinium salts as selective inhibitors of inducible nitric oxide synthase (iNOS).

An attractive approach to the treatment of inflammatory conditions such as osteo- and rheumatoid arthritis, inflammatory bowel disease, and sepsis is through the selective inhibition of human inducible nitric oxide synthase (hiNOS) since localized excess nitric oxide (NO) release has been implicated in the pathology of these diseases. A series of monosubstituted iminohomopiperidinium salts possessing lipophilic functionality at ring positions 3, 5, 6, and 7 has been synthesized, and series members have demonstrated the ability to inhibit the hiNOS isoform with an IC50 as low as 160 nM (7). Compounds were found that selectively inhibit hiNOS over the human endothelial constitutive enzyme (heNOS) with a heNOS/hiNOS IC50 ratio in excess of 100 and as high as 314 (9). Potencies for inhibition of hiNOS and the human neuronal constitutive enzyme (hnNOS) are comparable. Substitution in the 3 and 7 positions provides compounds that exhibit the greatest degree of selectivity for hiNOS and hnNOS over heNOS. Submicromolar potencies for 6 and 7 in a mouse RAW cell assay demonstrated the ability of these compounds to inhibit iNOS in a cellular environment. These latter compounds were also found to be orally bioavailable and efficacious due to their ability to inhibit the increase in plasma nitrite/nitrate levels in a rat LPS model.

Inhibitors of human nitric oxide synthase isoforms with the carbamidine moiety as a common structural element.

Identification of potent and selective inhibitors of inducible nitric oxide synthase (NOS) is of great interest because of their therapeutic potential for treatment of diseases mediated by excess production of nitric oxide. We present here a comparison of potency and selectivity for amino acid and nonamino acid based compounds as inhibitors of human inducible, human endothelial constitutive and human neuronal constitutive NOS isoforms. In addition, a novel series of substituted amidines has been identified as NOS inhibitors. 2-Methylthioacetamidine and 2-thienylcarbamidine were the most potent of the series examined with IC50 values of 3.9 and 2.9 microM for human neuronal constitutive NOS. Cyclopropylcarbamidine and 2-thienylcarbamidine were the most potent inhibitors for human inducible NOS with IC50 values of 5.2 and 6.5 microM, respectively. These substituted amidines represent a new class of NOS inhibitors and provide a foundation for potential therapeutic agents.

Potential role of nitric oxide in a model of chronic colitis in rhesus macaques.

BACKGROUND/AIMS: Excess nitric oxide formation, via the inducible NO synthase isoform, has been implicated in the pathogenesis of experimental and clinical inflammatory bowel disease. The aim of this study was to assess the site, enzyme source, and magnitude of NO production in juvenile rhesus macaques with idiopathic colitis. METHODS: NO production was assessed systemically from plasma and urine levels of reactive nitrogen intermediates and locally by the formation of [3H]citrulline from [3H]arginine and reduced nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase histochemistry. Inducible NO synthase gene expression was assessed by reverse-transcription polymerase chain reaction. RESULTS: Plasma and urine levels of reactive nitrogen intermediates were greater in colitic animals than in control monkeys by 13- and 5-fold, respectively. NADPH diaphorase activity in normal animals was confined to the myenteric plexus. In colitis, staining was also apparent in crypt abscesses and superficial epithelial and mucosal bands. Gene expression for inducible NO synthase was only found in colitic specimens. Colonic [3H]citrulline formation was markedly elevated in colitic specimens, and the inducible isoform accounted for 58% of total activity. CONCLUSIONS: It is proposed that excess NO, formed via the inducible form of NO synthase, contributes to the mucosal inflammation and symptoms of this idiopathic colitis model.

The glycoprotein alpha-subunit is critical for secretion and stability of the human thyrotropin beta-subunit.

TSH is a member of a family of heterodimeric glycoprotein hormones which have a common alpha-subunit but differ in their hormone-specific beta-subunit. To study the posttranslational processing and assembly of human TSH, eukaryotic expression vectors were constructed that contained either the human TSH beta gene only or both the TSH beta and alpha-genes. These vectors were transfected into Chinese hamster ovary cells and stable cell lines synthesizing TSH beta or TSH dimer were isolated. The kinetics of secretion of TSH beta and the rate of assembly of TSH dimer were compared to the known secretion and assembly of human LH and human CG. In the absence of the alpha-subunit, CG beta is secreted efficiently, but TSH and LH beta-subunits are slowly degraded intracellularly (t1/2 approximately equal to 6 h) and less than 10% is secreted into the medium. In the presence of the alpha-subunit CG beta was also secreted efficiently as dimer but only 50% of the LH beta appeared in the medium as LH dimer. However, unlike LH beta, the alpha-subunit efficiently combines with TSH beta since greater than 95% was secreted as TSH dimer. Thus, the determinants for human TSH beta secretion and assembly are unique from the other human glycoprotein hormone beta-subunits.