Pharmacological interference with dimerization of human neuronal nitric-oxide synthase expressed in adenovirus-infected DLD-1 cells

Discovery of a novel inhibitor of nitric oxide production with potential therapeutic effect on acute inflammation

Inflammation as a host's excessive immune response to stimulation, is involved in the development of numerous diseases. To discover novel anti-inflammatory agents and based on our previous synthetic work on marine natural product Chrysamide B, it and a series of derivatives were synthesized and evaluated for their anti-inflammatory activity on inhibition of LPS-induced NO production. Then the preliminary structure-activity relationships were conducted. Among them, Chrysamide B is the most potent anti-inflammatory agent with low cytotoxicity and strong inhibition on the production of NO (IC₅₀ = 0.010 μM) and the activity of iNOS (IC₅₀ = 0.082 μM) in LPS-stimulated RAW 264.7 cells. Primary studies suggested that the mechanism of action may be that it interfered the formation of active dimeric iNOS but not affected transcription and translation. Furthermore, its good performance of anti-inflammatory effect on LPS-induced multiple inflammatory cytokines production, carrageenan-induced paw edema, and endotoxin-induced septic mice, was observed. We believe that these findings would provide an idea for the further modification and research of these analogs in the future.

Dynamic roles for the N-terminus of the yeast G protein-coupled receptor Ste2p

The Saccharomyces cerevisiae α-factor receptor Ste2p has been used extensively as a model to understand the molecular mechanism of signal transduction by G protein-coupled receptors (GPCRs). Single and double cysteine mutants of Ste2p were created and served as surrogates to detect intramolecular interactions and dimerization of Ste2p using disulfide cross-linking methodology. When a mutation was introduced into the phylogenetically conserved tyrosine residue at position 26 (Y26C) in the N-terminus of Ste2p, dimerization was increased greatly. The amount of dimer formed by this Y26C mutant was greatly reduced by ligand binding even though the ligand binding site is far removed from the N-terminus; the lowering of the dimer formation was consistent with a conformational change in the N-terminus of the receptor upon activation. Dimerization was decreased by double mutations Y26C/V109C or Y26C/T114C indicating that Y26 is in close proximity to V109 and T114 of extracellular loop 1 in native Ste2p. Combined with earlier studies, these results indicate previously unrecognized roles for the N-terminus of Ste2p, and perhaps of GPCRs in general, and reveal a specific N-terminus residue or region, that is involved in GPCR signaling, intrareceptor interactions, and receptor dimerization.

Development of nitric oxide synthase inhibitors for neurodegeneration and neuropathic pain

Nitric oxide (NO) is an important signaling molecule in the human body, playing a crucial role in cell and neuronal communication, regulation of blood pressure, and in immune activation. However, overproduction of NO by the neuronal isoform of nitric oxide synthase (nNOS) is one of the fundamental causes underlying neurodegenerative disorders and neuropathic pain. Therefore, developing small molecules for selective inhibition of nNOS over related isoforms (eNOS and iNOS) is therapeutically desirable. The aims of this review focus on the regulation and dysregulation of NO signaling, the role of NO in neurodegeneration and pain, the structure and mechanism of nNOS, and the use of this information to design selective inhibitors of this enzyme. Structure-based drug design, the bioavailability and pharmacokinetics of these inhibitors, and extensive target validation through animal studies are addressed.

Gender and estradiol as major factors in the expression and dimerization of nNOSα in rats with experimental diabetic gastroparesis

BACKGROUND

The molecular mechanisms of cellular changes responsible for diabetic gastroparesis, primarily seen in middle-aged women, still remain incompletely defined. We hypothesized that a decrease in the expression, dimerization, and post-translational modification of neuronal nitric oxide synthase alpha (nNOSα) is estrogen mediated and responsible for the gender-specific prevalence of this malady.

METHODS

We induced diabetes by injecting male and female rats with streptozotocin. Male diabetic rats without gastroparesis were then injected with estrogen for 3 weeks and evaluated for gastroparesis development. Gastric tissues were analyzed for the elucidation of biochemical events associated with diabetes and gastroparetic dysfunction.

RESULTS

Although male diabetic, gastroparetic (either streptozotocin- or estrogen-induced) rats exhibited similarity in disease pathology to that of females, the molecular mechanisms of development were different. Our results indicate that slow gastric emptying in both male diabetic, gastroparetic rat groups was not associated with the level of expression of nNOSα in gastric tissues. However, nNOSα dimerization, which reflects nNOSα activation, did decline slightly in the antrum of diabetic males with estrogen-induced gastroparesis, suggesting a possible estrogen role. Females with diabetic gastroparesis, in contrast, demonstrated significantly impaired levels and dimerization of nNOSα in the antrum and pylorus. Although the precise mechanism remains unknown, nNOSα dimerization impairment in female antrum is apparently associated with reduced phosphorylation of Ser(1416) in the activation loop of nNOSα.

CONCLUSION

Taken together, these results demonstrate that gender and estrogens may be leading factors, through molecular changes involved in nitric oxide synthesis down-regulation, within the antrum and pylorus of female diabetic, gastroparetic rats.

Novel nitric oxide synthase inhibitors: a patent review

INTRODUCTION

Knowledge of NO and its function in cell signaling has rapidly developed since its biological effects were first described in 1977. It is formed from L-arginine by NOS isoforms (nNOS, iNOS and eNOS). These enzymes are products of separate genes, encoded on three different chromosomes and responsible for regulating a variety of functions within cells and tissues. NOS isoforms are currently under investigation as targets for novel therapeutics in especially neurodegenerative disorders, inflammation and pain. Many important questions regarding these messengers and signaling molecules remain to be answered.

AREAS COVERED

This review gives an overview of patents covering drug-like inhibitors for the NOS isoforms filed and published within the last 6 years, up to September 2010, as well as insight into recent highlights in this area.

EXPERT OPINION

The NOS isoforms are attractive targets in drug design for various pathological conditions and have received considerable interest over recent years. With the advances in molecular biology, modeling software, synthesis, bioassays, and our understanding of the NOS enzymes and the function of NO, novel bioavailable and highly selective drug therapies utilizing this mode of action may soon see the light.

The Novel Imidazopyridine 2-[2-(4-Methoxy-pyridin-2-yl)-ethyl]-3H-imidazo[4,5-b]pyridine (BYK191023) Is a Highly Selective Inhibitor of the Inducible Nitric-Oxide Synthase

We have identified imidazopyridine derivatives as a novel class of NO synthase inhibitors with high selectivity for the inducible isoform. 2-[2-(4-Methoxy-pyridin-2-yl)-ethyl]-3H-imidazo[4,5-b]pyridine (BYK191023) showed half-maximal inhibition of crudely purified human inducible (iNOS), neuronal (nNOS), and endothelial (eNOS) NO synthases at 86 nM, 17 microM, and 162 microM, respectively. Inhibition of inducible NO synthase was competitive with l-arginine, pointing to an interaction of BYK191023 with the catalytic center of the enzyme. In radioligand and surface plasmon resonance experiments, BYK191023 exhibited an affinity for iNOS, nNOS, and eNOS of 450 nM, 30 microM, and >500 microM, respectively. Inhibition of cellular nitrate/nitrite synthesis in RAW, rat mesangium, and human embryonic kidney 293 cells after iNOS induction showed 40- to 100-fold higher IC(50) values than at the isolated enzyme, in agreement with the much higher l-arginine concentrations in cell culture media and inside intact cells. BYK191023 did not show any toxicity in various rodent and human cell lines up to high micromolar concentrations. The inhibitory potency of BYK191023 was tested in isolated organ models of iNOS (lipopolysaccharide-treated and phenylephrine-precontracted rat aorta; IC(50) = 7 microM), eNOS (arecaidine propargyl ester-induced relaxation of phenylephrine-precontracted rat aorta; IC(50) > 100 microM), and nNOS (field-stimulated relaxation of phenylephrine-precontracted rabbit corpus cavernosum; IC(50) > 100 microM). These data confirm the high selectivity of BYK191023 for iNOS over eNOS and nNOS found at isolated enzymes. In summary, we have identified a new highly selective iNOS inhibitor structurally unrelated to known compounds and l-arginine. BYK191023 is a valuable tool for the investigation of iNOS-mediated effects in vitro and in vivo.

Biology and chemistry of the inhibition of nitric oxide synthases by pteridine-derivatives as therapeutic agents

Inhibitors of the family of nitric oxide synthases (NOS-I-III; EC 1.14.13.39) are of interest as pharmacological agents to modulate pathologically high nitric oxide (NO) levels in inflammation, sepsis, and stroke. In this article, we discuss the approach for targeting the unique (6R)-5,6,7,8-tetrahydro-L-biopterin (H4Bip) binding site of NOS by appropriate inhibitors. This binding site maximally increases enzyme activity and NO production from the substrate L-arginine upon cofactor binding. The first generation of H4Bip-based NOS inhibitors was based on 4-amino H4Bip derivatives in analogy to anti-folates such as methotrexate. In addition, we discuss the structure-activity relationship of a related series of 4-oxo-pteridine derivatives. Furthermore, molecular modeling studies provide an understanding of pterin antagonism on a structural level based on favorable and unfavorable interactions between protein binding site and ligands. These techniques include 3D-QSAR (CoMFA, CoMSIA) to understand ligand affinity and GRID/consensus principal component analysis (CPCA) to learn about selectivity requirements. Collectively these approaches, in combination with the presented SAR and structural data, provide useful information for the design of novel NOS inhibitors with increased isoform selectivity.

1-Methyl-4-phenylpyridinium-induced apoptosis in cerebellar granule neurons is mediated by transferrin receptor iron-dependent depletion of tetrahydrobiopterin and neuronal nitric-oxide synthase-derived superoxide

In this study, we investigated the molecular mechanisms of toxicity of 1-methyl-4-phenylpyridinium (MPP(+)), an ultimate toxic metabolite of a mitochondrial neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, that causes Parkinson-like symptoms in experimental animals and humans. We used rat cerebellar granule neurons as a model cell system for investigating MPP(+) toxicity. Results show that MPP(+) treatment resulted in the generation of reactive oxygen species from inhibition of complex I of the mitochondrial respiratory chain, and inactivation of aconitase. This, in turn, stimulated transferrin receptor (TfR)-dependent iron signaling via activation of the iron-regulatory protein/iron-responsive element interaction. MPP(+) caused a time-dependent depletion of tetrahydrobiopterin (BH(4)) that was mediated by H(2)O(2) and transferrin iron. Depletion of BH(4) decreased the active, dimeric form of neuronal nitric-oxide synthase (nNOS). MPP(+)-mediated "uncoupling" of nNOS decreased *NO and increased superoxide formation. Pretreatment of cells with sepiapterin to promote BH(4) biosynthesis or cell-permeable iron chelator and TfR antibody to prevent iron-catalyzed BH(4) decomposition inhibited MPP(+) cytotoxicity. Preincubation of cerebellar granule neurons with nNOS inhibitor exacerbated MPP(+)-induced iron uptake, BH(4) depletion, proteasomal inactivation, and apoptosis. We conclude that MPP(+)-dependent aconitase inactivation, Tf-iron uptake, and oxidant generation result in the depletion of intracellular BH(4), leading to the uncoupling of nNOS activity. This further exacerbates reactive oxygen species-mediated oxidative damage and apoptosis. Implications of these results in unraveling the molecular mechanisms of neurodegenerative diseases (Parkinson's and Alzheimer's disease) are discussed.

Inducible nitric oxide synthase dimerization inhibitor prevents cardiovascular and renal morbidity in sheep with combined burn and smoke inhalation injury

Inducible nitric oxide synthase (iNOS) is implicated in the pathogenesis of acute respiratory distress syndrome (ARDS). ARDS treatment is frequently complicated by significant extrapulmonary comorbidity. This study was designed to clarify the role of iNOS in mediating extrapulmonary comorbidity in sheep after combined burn and smoke inhalation injuries using a potent and highly selective iNOS dimerization inhibitor, BBS-2. Twenty-two female sheep were operatively prepared. After 5 days of recovery, tracheostomy was performed under ketamine-halothane anesthesia. Sheep were given a 40% total body surface third-degree burns and insufflated with cotton smoke (48 breaths, <40 degrees C). Sheep were divided into four groups: noninjured and nontreated (sham group; n = 6), noninjured but treated with BBS-2 (sham/BBS-2 group; n = 4), injured but nontreated (control group, n = 6), and injured but treated with 100 microg.kg-1.h-1 BBS-2 (BBS-2 group; n = 6). Evaluation was in a laboratory intensive care unit setting for 48 h. The sham group had stable cardiopulmonary and systemic hemodynamics. Control animals showed multiple signs of morbidity. Decreased left ventricular stroke work index and stroke volume index with elevated left atrial pressure indicated myocardial depression. Systemic vascular leak was evidenced by robust hemoconcentration, decreased plasma oncotic pressure, and increased transvascular fluid flux into the lymphatic system. Finally, severely impaired renal function (urinary output) was associated with adverse net fluid balance. Treatment with BBS-2 prevented all these morbidities without adversely effecting cardiovascular hemodynamics such as cardiac index and mean arterial pressure. The results identify a major role for iNOS in mediating extrapulmonary comorbidity in a clinically relevant and severe trauma model and support the use of highly selective iNOS inhibitors as novel treatments in critical care medicine.

A selective inducible NOS dimerization inhibitor prevents systemic, cardiac, and pulmonary hemodynamic dysfunction in endotoxemic mice

Increased nitric oxide (NO) production by inducible NO synthase (NOS2), an obligate homodimer, is implicated in the cardiovascular sequelae of sepsis. We tested the ability of a highly selective NOS2 dimerization inhibitor (BBS-2) to prevent endotoxin-induced systemic hypotension, myocardial dysfunction, and impaired hypoxic pulmonary vasoconstriction (HPV) in mice. Mice were challenged with Escherichia coli endotoxin before treatment with BBS-2 or vehicle. Systemic blood pressure was measured before and 4 and 7 h after endotoxin challenge, and echocardiographic parameters of myocardial function were measured before and 7 h after endotoxin challenge. The pulmonary vasoconstrictor response to left mainstem bronchus occlusion, which is a measure of HPV, was studied 22 h after endotoxin challenge. BBS-2 treatment alone did not alter baseline hemodynamics. BBS-2 treatment blocked NOS2 dimerization and completely inhibited the endotoxin-induced increase of plasma nitrate and nitrite levels. Treatment with BBS-2 after endotoxin administration prevented systemic hypotension and attenuated myocardial dysfunction. BBS-2 also prevented endotoxin-induced impairment of HPV. In contrast, treatment with NG-nitro-l-arginine methyl ester, which is an inhibitor of all three NOS isoforms, prevented the systemic hypotension but further aggravated the myocardial dysfunction associated with endotoxin challenge. Treatment with BBS-2 prevented endotoxin from causing key features of cardiovascular dysfunction in endotoxemic mice. Selective inhibition of NOS2 dimerization with BBS-2, while sparing the activities of other NOS isoforms, may prove to be a useful treatment strategy in sepsis.

Intracellular formation of "undisruptable" dimers of inducible nitric oxide synthase

Overproduction of nitric oxide (NO) by inducible NO synthase (iNOS) has been implicated in the pathogenesis of many diseases. iNOS is active only as a homodimer. Dimerization of iNOS represents a potentially critical target for therapeutic intervention. In this study, we show that intracellular iNOS forms dimers that are "undisruptable" by boiling, denaturants, or reducing agents. Undisruptable (UD) dimers are clearly distinguishable from the easily dissociated dimers formed by iNOS in vitro. UD dimers do not form in Escherichia coli-expressed iNOS and could not be assembled in vitro, which suggests that an in vivo cellular process is required for their formation. iNOS UD dimers are not affected by intracellular depletion of H4B. However, the mutation of Cys-115 (critical for zinc binding) greatly affects the formation of UD dimers. This study reveals insight into the mechanisms of in vivo iNOS dimer formation. UD dimers represent a class of iNOS dimers that had not been suspected. This unanticipated finding revises our understanding of the mechanisms of iNOS dimerization and lays the groundwork for future studies aimed at modulating iNOS activity in vivo.

Signaling molecules as therapeutic targets in allergic diseases

A molecular understanding of physiologic and pathologic processes requires complete knowledge about the signal transduction mechanism of involved cells. Signal transduction research is a rapidly growing field in basic science. Unlike intercellular inflammatory mediators, signaling molecules show less functional redundancy. This allows inhibition of multiple cytokines/mediators by blocking one common signaling molecule. Interference with signaling pathways has shown significant potential for inhibition of fundamental processes as well as clinical phenotype of allergic diseases. The purpose of this review was to provide a theoretical classification of signaling molecules based on their function and to analyze various strategies for developing effective signaling inhibitors for allergic diseases.