Progress in the development of selective nitric oxide synthase (NOS) inhibitors

Cerebrovascular risk factors in Alzheimer's disease: Brain hemodynamics and pharmacogenomic implications

Recent evidence indicates that different vascular risk factors are present in Alzheimer's disease (AD) and other prevalent dementia types probably contributing to deterioration of cerebrovascular function, thus enhancing neurodegeneration and premature neuronal death due to a reduction in brain perfusion. Brain blood flow shows a reduced velocity and increased pulsatility (PI) and resistance indices (RI) in different types of dementia and in diabetes and hypertension, as well. High levels of diastolic blood pressure correlate with diminished brain blood flow and elevated PI and RI, accompanied by cognitive deterioration. Nitric oxide (NO) levels are found increased in the sera and brain tissue of AD patients. Vascular risk factors (hyperglycemia, LDL-cholesterol, triglycerides, hypertension) and altered brain hemodynamic parameters correlate with APOE genotypes of which APOE-4/4 carriers represent the AD population with the highest cerebrovascular risk. In addition, the genomic profiles of patients with dementia integrating AD-related genes (APOE, PS1, PS2, cFOS) in a mini-tetragenic haplotype significantly differ from controls with an absolute genetic variation of about 50%-60%. Cerebrovascular dysfunction is a factor common to most types of dementia; however, genetic variation among different dementia types might be determinant for the activation of early vascular events inducing or accelerating neurodegeneration. In this regard, cerebrovascular dysfunction should be considered a potential therapeutic target in dementia.

Ulinastatin suppresses lipopolysaccharide-induced prostaglandin E2 synthesis and nitric oxide production through the downregulation of nuclear factor‑κB in BV2 mouse microglial cells

Ulinastatin is an intrinsic serine-protease urinary trypsin inhibitor that can be extracted and purified from human urine. Urinary trypsin inhibitors are widely used to treat patients with acute inflammatory disorders, such as shock and pancreatitis. However, although the anti-inflammatory activities of urinary trypsin inhibitors have been investigated, the mechanisms underlying their actions are not yet fully understood. In the present study, we evaluated the effect of ulinastatin on lipopolysaccharide (LPS)-induced inflammation in relation with nuclear factor-κB (NF-κB) activation using BV2 mouse microglial cells. To accomplish this, we performed a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, reverse transcription-polymerase chain reaction (RT-PCR), western blot analysis, electrophoretic mobility gel shift assay (EMSA), prostaglandin E(2) (PGE(2)) immunoassay and nitric oxide (NO) detection. The results demonstrated that ulinastatin suppressed PGE2 synthesis and NO production by inhibiting the LPS-induced mRNA and protein expression of cyclooxygenase-2 (COX-2) and inducible NO synthase (iNOS) in BV2 mouse microglial cells. Ulinastatin suppressed the activation of NF-κB in the nucleus. These findings demonstrate that ulinastatin exerts analgesic and anti-inflammatory effects that possibly occur via the suppression of COX-2 and iNOS expression through the downregulation of NF-κB activity.

The inhibitory effect of pterostilbene on inflammatory responses during the interaction of 3T3-L1 adipocytes and RAW 264.7 macrophages

Chronic inflammation is characterized by the upregulation of proinflammatory cytokines in obese adipose tissue. Accumulations of adipose tissue macrophages enhance a chronic inflammatory state in adipose tissues. Many studies have indicated that the adipocyte-related inflammatory response in obesity is characterized by an enhanced infiltration of macrophages. The aim of this work was to study the inhibitory effects of garcinol and pterostilbene on the change in inflammatory response due to the interaction between 3T3-L1 adipocytes and RAW 264.7 macrophages. In the TNF-α-induced 3T3-L1 adipocyte model, garcinol and pterostilbene significantly decreased the mRNA expression of COX-2, iNOS, IL-6, and IL-1β and IL-6 secretion by suppressing phosphorylation of p-IκBα and p-p65. In a coculture model of 3T3-L1 adipocytes and RAW 264.7 macrophages, pterostilbene suppressed IL-6 and TNF-α secretion and proinflammatory mRNA expression and also reduced the migration of macrophages toward adipocytes. In the RAW 264.7 macrophage-derived conditioned medium (RAW-CM)-induced 3T3-L1 adipocyte and 3T3-CM-induced RAW 264.7 macrophage models, pterostilbene significantly decreased IL-6 and TNF-α secretion and proinflammatory mRNA expression (COX-2, iNOS, IL-6, TNF-α, PAI-1, CRP, MCP-1, resistin, and leptin). Our findings suggest that garcinol and pterostilbene may provide novel and useful applications to reduce the chronic inflammatory properties of adipocytes. We also found that pterostilbene inhibits proinflammatory responses during the interaction between 3T3-L1 adipocytes and RAW 264.7 macrophages.

Sphingosine 1-phosphate protects primary human keratinocytes from apoptosis via nitric oxide formation through the receptor subtype S1P₃

Although the lipid mediator sphingosine 1-phosphate (S1P) has been identified to induce cell growth arrest of human keratinocytes, the sphingolipid effectively protects these epidermal cells from apoptosis. The molecular mechanism of the anti-apoptotic action induced by S1P is less characterized. Apart from S1P, endogenously produced nitric oxide (NO•) has been recognized as a potent modulator of apoptosis in keratinocytes. Therefore, it was of great interest to elucidate whether S1P protects human keratinocytes via a NO•-dependent signalling pathway. Indeed, S1P induced an activation of endothelial nitric oxide synthase (eNOS) in human keratinocytes leading to an enhanced formation of NO•. Most interestingly, the cell protective effect of S1P was almost completely abolished in the presence of the eNOS inhibitor L-NAME as well as in eNOS-deficient keratinocytes indicating that the sphingolipid metabolite S1P protects human keratinocytes from apoptosis via eNOS activation and subsequent production of protective amounts of NO•. It is well established that most of the known actions of S1P are mediated by a family of five specific G protein-coupled receptors. Therefore, the involvement of S1P-receptor subtypes in S1P-mediated eNOS activation has been examined. Indeed, this study clearly shows that the S1P(3) is the exclusive receptor subtype in human keratinocytes which mediates eNOS activation and NO• formation in response to S1P. In congruence, when the S1P(3) receptor subtype is abrogated, S1P almost completely lost its ability to protect human keratinocytes from apoptosis.

Nitric oxide: considerations for the treatment of ischemic stroke

Some 40 years ago it was recognized by Furchgott and colleagues that the endothelium releases a vasodilator, endothelium-derived relaxing factor (EDRF). Later on, several groups identified EDRF to be a gas, nitric oxide (NO). Since then, NO was identified as one of the most versatile and unique molecules in animal and human biology. Nitric oxide mediates a plethora of physiological functions, for example, maintenance of vascular tone and inflammation. Apart from these physiological functions, NO is also involved in the pathophysiology of various disorders, specifically those in which regulation of blood flow and inflammation has a key role. The aim of the current review is to summarize the role of NO in cerebral ischemia, the most common cause of stroke.

Suppression of Nitric Oxide Synthase by Thienodolin in Lipopolysaccharide-stimulated RAW 264.7 Murine Macrophage Cells

The measurement of nitric oxide in lipopolysaccharide (LPS)-stimulated RAW 264.7 cells is used as a model for evaluating the anti-inflammatory or chemopreventive potential of substances. Thienodolin, isolated from a Streptomyces sp. derived from Chilean marine sediment, inhibited nitric oxide production in LPS-stimulated RAW 264.7 cells (IC50 = 17.2 ± 1.2 μM). At both the mRNA and protein levels, inducible nitric oxide synthase (iNOS) was suppressed in a dose-dependent manner. Mitogen-activated protein kinases (MAPKs), one major upstream signaling pathway involved in the transcription of iNOS, were not affected by treatment of thienodolin. However, the compound blocked the degradation of IκBα resulting in inhibition of NF-κB p65 nuclear translocation, and inhibited the phosphorylation of signal transducers and activators of transcription 1 (STAT1) at Tyr701. This study supports further exploration of thienodolin as a potential therapeutic agent with a unique mechanistic activity.

Masseter inflammation differentially regulates three nitric oxide synthases in the rat trigeminal subnucleus caudalis

OBJECTIVE

The aim of the present study was to evaluate changes in expression levels of three nitric oxide synthases (NOSs), namely inducible NOS (iNOS), neuronal NOS (nNOS) and endothelial NOS (eNOS), in the subnucleus caudalis of the trigeminal sensory nuclear complex (Vc) under experimental myositis conditions.

DESIGN

Male Sprague Dawley rats were injected with an inflammatory agent, complete Freund's adjuvant (CFA), or capsaicin in the masseter muscle. The brainstem region containing the Vc was extracted at both immediate (30 and 60 min) and longer (1, 3, 7 days) time points to examine the changes in the three NOS protein levels via the Western blot technique. Subsequently, the RT-PCR experiments were carried out to verify the changes in iNOS mRNA.

RESULTS

Following the injections of CFA, there were no significant changes in the level of the three NOS proteins at the immediate time points. However, there was a significant upregulation of iNOS mRNA and protein 3 days after CFA-induced inflammation. Neither nNOS nor eNOS showed significant changes in the protein level at any of the longer time points. Capsaicin injection in the masseter, which we recently reported to upregulate all three NOS at the immediate time points, did not result in significant changes at longer time points.

CONCLUSION

Acute and chronic muscle inflammation differentially modulates the expression of the three NOS in the Vc. These data suggest that the contribution of each NOS in craniofacial muscle pain processing under inflammatory conditions may be anticipated with distinct temporal profiles.

Involvement of the L-arginine-nitric oxide pathway in the antinociception caused by fruits of Prosopis strombulifera (Lam.) Benth

ETHNOPHARMACOLOGICAL RELEVANCE

Prosopis strombulifera (Lam.) Benth. is a rhizomatous shrub that grows in the north and central zone of Argentina. In folk medicine, the fruits of this plant have been used as an astringent, anti-inflammatory and odontalgic agent and anti-diarrheic.

AIM OF THE STUDY

To investigate the antinociceptive effect of ethanol (EE), chloroform (CE) and ethyl acetate (EtOAcE) extracts of Prosopis strombulifera fruits and the involvement of the l-arginine-nitric oxide pathway in this effect.

MATERIALS AND METHODS

The antinociceptive effects of the EE, CE and EtOAcE of Prosopis strombulifera fruits were evaluated in vivo using the formalin-induced pain test in mice with aspirin and morphine as reference antinociceptive compounds. The participation of the l-arginine-nitric oxide pathway in the antinociceptive effect was investigated in the same animal model using l-arginine as a nitric oxide (NO) precursor. The in vitro inhibitory effect of the extracts on LPS-induced nitric oxide production and iNOS expression was investigated in a J774A.1 macrophage-derived cell line.

RESULTS

CE (300mg/kg), in contrast to EE and EtOAcE, caused significant inhibition (p<0.05) of the in vivo nociceptive response. Moreover, CE (100-1000mg/kg, p.o.) produced a dose-dependent inhibition of the neurogenic and the inflammatory phases of the formalin test with inhibition values (at 600mg/kg) of 42±7% and 62±7%, respectively. CE inhibition was more potent in the inflammatory phase, with an ID(50) of 400.1 (252.2-634.8)mg/kg. The antinociception caused by CE (600mg/kg, p.o.) was significantly attenuated (p<0.05) by i.p. treatment of mice with l-arginine (600mg/kg). In addition, CE (100μg/mL) produced significant in vitro inhibition (p<0.001) of LPS-induced NO production, which was not observed with EE and EtOAcE at the same concentration. The inhibition of NO production by CE (10-100μg/mL) was dose-dependent, with an IC(50) of 39.8 (34.4-46.1)μg/mL, and CE significantly inhibited LPS-induced iNOS expression in J774A.1 cells.

CONCLUSIONS

This study supports, in part, the ethnomedical use of Prosopis strombulifera fruits by showing that its CE produces moderate antinociception in vivo. The findings also provide scientific information for understanding the molecular mechanism involved in the analgesic effect of this plant.

Anti-inflammatory effects of resveratrol occur via inhibition of lipopolysaccharide-induced NF-κB activation in Caco-2 and SW480 human colon cancer cells

Resveratrol, a polyphenol abundantly found in grapes and red wine, exhibits beneficial health effects due to its anti-inflammatory properties. In the present study, we evaluated the effect of resveratrol on inflammatory responses induced by lipopolysaccharide (LPS) treatment of human intestinal Caco-2 and SW480 cell lines. In the LPS-treated intestinal cells, resveratrol dose-dependently inhibited the expression of inducible NO synthase (iNOS) mRNA as well as protein expression, resulting in a decreased production of NO. In addition, Toll-like receptor-4 expression was significantly diminished in LPS-stimulated cells after resveratrol pre-treatment. To investigate the mechanisms by which resveratrol reduces NO production and iNOS expression, we examined the activation of inhibitor of κB (IκB) in LPS-stimulated intestinal cells. Results demonstrated that resveratrol inhibited the phosphorylation, as well as the degradation, of the IκB complex. Overall, these results show that resveratrol is able to reduce LPS-induced inflammatory responses by intestinal cells, interfering with the activation of NF-κB-dependent molecular mechanisms.

Novel inhibitors of nitric oxide synthase with antioxidant properties

We previously described a series of imidazole-based inhibitors substituted at N-1 with an arylethanone chain as interesting inhibitors of neuronal nitric oxide synthase (nNOS), endowed with good selectivity vs endothelial nitric oxide synthase (eNOS). As a follow up of these studies, several analogs characterized by the presence of substituted imidazoles or other mono or bicyclic nitrogen-containing heterocycles instead of simple imidazole were synthesized, and their biological evaluation as in vitro inhibitors of both nNOS and eNOS is described herein. Most of these compounds showed improved nNOS and eNOS inhibitory activity with respect to reference inhibitors. Selected compounds were also tested to analyze their antioxidant properties. Some of them displayed good capacity to scavenge free radicals and ability to reduce lipid peroxidation.

The effect of nNOS inhibitors on toxin-induced cell death in dopaminergic cell lines depends on the extent of enzyme expression

Nitric oxide is linked with neurodegeneration in Parkinson's disease (PD) through the involvement of both inducible (iNOS) and neuronal nitric oxide synthase (nNOS). While non-selective NOS inhibitors are neuroprotective, the role of nNOS has not been determined using selective NOS inhibitors. The present study investigated the neuroprotective effect of selective iNOS and nNOS inhibitors on MPP(+)- and MG-132-induced cell death in cell lines with differing levels of nNOS expression. Inhibition of endogenously expressed nNOS by 7-NI and ARR17477 enhanced the toxicity of MPP(+) and MG-132 in N1E-115 cells, whereas in transfected SH-SY5Y cells overexpressing nNOS, ARR17477 and 7-NI protected against MPP(+)- and MG-132-induced cell death. In contrast, inhibition of iNOS by 1400W was ineffective in preventing MPP(+) and MG-132 toxicity in these cell lines. These results suggest a dual role for NOS in dopaminergic cell viability. nNOS is protective against toxic insult when produced endogenously. When nNOS is overexpressed, it becomes neurotoxic to cells suggesting that inhibition of nNOS may be a promising strategy to prevent cell death in PD.

The nitric oxide-cGMP signaling pathway plays a significant role in tolerance to the analgesic effect of morphine

Although the phenomenon of opioid tolerance has been widely investigated, neither opioid nor nonopioid mechanisms are completely understood. The aim of the present study was to investigate the role of the nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) pathway in the development of morphine-induced analgesia tolerance. The study was carried out on male Wistar albino rats (weighing 180-210 g; n = 126). To develop morphine tolerance, animals were given morphine (50 mg/kg; s.c.) once daily for 3 days. After the last dose of morphine was injected on day 4, morphine tolerance was evaluated. The analgesic effects of 3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole (YC-1), BAY 41-2272, S-nitroso-N-acetylpenicillamine (SNAP), N(G)-nitro-L-arginine methyl ester (L-NAME), and morphine were considered at 15 or 30 min intervals (0, 15, 30, 60, 90, and 120 min) by tail-flick and hot-plate analgesia tests (n = 6 in each study group). The results showed that YC-1 and BAY 41-2272, a NO-independent activator of soluble guanylate cyclase (sGC), significantly increased the development and expression of morphine tolerance, and L-NAME, a NO synthase (NOS) inhibitor, significantly decreased the development of morphine tolerance. In conclusion, these data demonstrate that the nitric oxide-cGMP signal pathway plays a pivotal role in developing tolerance to the analgesic effect of morphine.

Novel nanomolar imidazo[4,5-b]pyridines as selective nitric oxide synthase (iNOS) inhibitors: SAR and structural insights

Inducible arginine oxidation and subsequent NO production by correspondent synthase (iNOS) are important cellular answers to proinflammatory signals. Prolonged NO production has been proved in higher organisms to cause stroke or septic shock. Several classes of potent NOS inhibitors have been reported, most of them targeting the arginine binding site of the oxygenase domain. Here we disclose the SAR and the rational design of potent and selective iNOS inhibitors which may be useful as anti-inflammatory drugs.

Symmetric double-headed aminopyridines, a novel strategy for potent and membrane-permeable inhibitors of neuronal nitric oxide synthase

We report novel neuronal nitric oxide synthase (nNOS) inhibitors based on a symmetric double-headed aminopyridine scaffold. The inhibitors were designed from crystal structures of leads 1 and 2 (Delker, S. L.; Ji, H.; Li, H.; Jamal, J.; Fang, J.; Xue, F.; Silverman, R. B.; Poulos, T. L. Unexpected binding modes of nitric oxide synthase inhibitors effective in the prevention of cerebral palsy . J. Am. Chem. Soc. 2010, 132, 5437-5442) and synthesized using a highly efficient route. The best inhibitor, 3j, showed low nanomolar inhibitory potency and modest isoform selectivity. It also exhibited enhanced membrane permeability. Inhibitor 3j binds to both the substrate site and the pterin site in nNOS but only to the substrate site in eNOS. These compounds provide a basis for further development of novel, potent, isoform selective, and bioavailable inhibitors for nNOS.

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.

Effects of a selective iNOS inhibitor versus norepinephrine in the treatment of septic shock

Inhibition of NOS is not beneficial in septic shock; selective inhibition of the inducible form (iNOS) may represent a better option. We compared the effects of the selective iNOS inhibitor BYK191023 with those of norepinephrine (NE) in a sheep model of septic shock. Twenty-four anesthetized, mechanically ventilated ewes received 1.5 g/kg body weight of feces into the abdominal cavity to induce sepsis. Animals were randomized into three groups (each n = 8): NE-only, BYK-only, and NE + BYK. The sublingual microcirculation was evaluated with sidestream dark-field videomicroscopy. MAP was higher in the NE + BYK group than in the other groups, but there were no significant differences in cardiac index or systemic vascular resistance. Mean pulmonary arterial pressure was lower in BYK-treated animals than in the NE-only group. PaO2/FiO2 was higher and lactate concentration lower in the BYK groups than in the NE-only group. Mesenteric blood flow was higher in BYK groups than in the NE-only group. Renal blood flow was higher in the NE + BYK group than in the other groups. Functional capillary density and proportion of perfused vessels were higher in the BYK groups than in the NE-only group 18 h after induction of peritonitis. Survival times were similar in the three groups. In this model of peritonitis, selective iNOS inhibition had more beneficial effects than NE on pulmonary artery pressures, gas exchange, mesenteric blood flow, microcirculation, and lactate concentration. Combination of this selective iNOS inhibitor with NE allowed a higher arterial pressure and renal blood flow to be maintained.

Exploration of the active site of neuronal nitric oxide synthase by the design and synthesis of pyrrolidinomethyl 2-aminopyridine derivatives

Neuronal nitric oxide synthase (nNOS) represents an important therapeutic target for the prevention of brain injury and the treatment of various neurodegenerative disorders. A series of trans-substituted amino pyrrolidinomethyl 2-aminopyridine derivatives (8-34) was designed and synthesized. A structure-activity relationship analysis led to the discovery of low nanomolar nNOS inhibitors ((±)-32 and (±)-34) with more than 1000-fold selectivity for nNOS over eNOS. Four enantiomerically pure isomers of 3'-[2''-(3'''-fluorophenethylamino)ethoxy]pyrrolidin-4'-yl}methyl}-4-methylpyridin-2-amine (4) also were synthesized. It was found that (3'R,4'R)-4 can induce enzyme elasticity to generate a new "hot spot" for ligand binding. The inhibitor adopts a unique binding mode, the same as that observed for (3'R,4'R)-3'-[2''-(3'''-fluorophenethylamino)ethylamino]pyrrolidin-4'-yl}methyl}-4-methylpyridin-2-amine ((3'R,4'R)-3) (J. Am. Chem. Soc. 2010, 132 (15), 5437 - 5442). On the basis of structure-activity relationships of 8-34 and different binding conformations of the cis and trans isomers of 3 and 4, critical structural requirements of the NOS active site for ligand binding are revealed.

Anti-inflammatory effects and chemical study of a flavonoid-enriched fraction from adlay bran

Anti-inflammation-guided fractionation and purification were used to evaluate the bioactivity and components of adlay (Coix lachryma-jobi L. var. ma-yuen Stapf) bran. Results showed that the fraction with high phenolic and flavonoid contents from the ethanol extracts of adlay bran suppressed LPS-stimulated IL-6 and TNF-α secretions in a concentration-dependent manner in RAW 264.7 cells and murine peritoneal macrophages. Fifteen compounds, including a novel aurone derivative, two chromones, one dihydrochalcone, one chalcone, four flavanones, five flavones and one isoflavone, were isolated from the active fraction. The structure of the new compound was elucidated by spectroscopic methods, including 1D and 2D NMR and MS. All of the isolates are reported for the first time from adlay except naringenin. LC/MS was also provided as an analytical platform. Our results suggest that flavonoids in adlay bran, partially at least, contribute to its anti-inflammatory effect. Thus, adlay bran may be beneficial to the health of consumers.

Genetic analysis of nitric oxide synthase 1 variants in schizophrenia and bipolar disorder

Nitric oxide (NO) is a neurotransmitter that acts as a second messenger of the N-methyl-D-aspartate receptor and interacts with the dopaminergic and the serotonergic systems. NO involvement in pathological processes relevant to neuropsychiatric disorders stems from its ability to modulate certain forms of synaptic plasticity, and from its capacity to be transformed to a highly active free radical. Additionally, multiple links have been reported between the NO-producing enzyme, nitric oxide synthase (NOS) 1, and both schizophrenia and bipolar disorder (BPD). RNA and DNA isolated from dorsolateral-prefrontal cortices of schizophrenia patients, bipolar patients and controls (n = 26, 30 and 29, respectively) were donated by the Stanley Foundation Brain Collection. Gene expression was measured by Real-Time-PCR. Genetic polymorphisms were genotyped by restriction-fragment length-polymorphism analysis, and by product-size determination of PCR products amplified with a fluorescent primer.Expression analysis of pan-NOS1, as well as of 2 of its isoforms, "NOS1_1d" and "NOS1_1f", which differ in their first exons and translational strength, revealed a trend for pan-NOS1 over-expression (P = 0.075) in schizophrenia patients (1.33-fold), and significant over-expression (P < 0.05) of NOS1_1d and NOS1_1f in this group (1.54-fold and 1.61-fold, respectively). No expressional alteration was observed in BPD. Polymorphisms at the promoters of NOS1_1d and NOS1_1f, previously shown to be functional in vitro, revealed no significant allelic or genotypic differences among clinical groups and showed no effect on these transcripts' expression. In conclusion, understanding the molecular mechanisms underlying the over-expression of specific NOS1 isoforms, which is unique to schizophrenia, may assist in identifying targets for new drugs.

Unexpected binding modes of nitric oxide synthase inhibitors effective in the prevention of a cerebral palsy phenotype in an animal model

Selective inhibition of the neuronal isoform of nitric oxide synthase NOS (nNOS) has been shown to prevent brain injury and is important for the treatment of various neurodegenerative disorders. However, given the high active site conservation among all three NOS isoforms, the design of selective inhibitors is an extremely challenging problem. Here we present the structural basis for why novel and potent nNOS inhibitors exhibit the highest level of selectivity over eNOS reported so far (approximately 3,800-fold). By using a combination of crystallography, computational methods, and site-directed mutagenesis, we found that inhibitor chirality and an unanticipated structural change of the target enzyme control both the orientation and selectivity of these novel nNOS inhibitors. A new hot spot generated as a result of enzyme elasticity provides important information for the future fragment-based design of selective NOS inhibitors.

Effect of oleocanthal and its derivatives on inflammatory response induced by lipopolysaccharide in a murine chondrocyte cell line

OBJECTIVE

In joint diseases, cartilage homeostasis is disrupted by mechanisms that are driven by combinations of biologic factors that vary according to the disease process. In osteoarthritis (OA), biomechanical stimuli predominate, with up-regulation of both catabolic and anabolic factors. Likewise, OA progression is characterized by increased nitric oxide (NO) production, which has been associated with cartilage degradation. Given the relevance of cartilage degenerative diseases in our society, the development of a novel pharmacologic intervention is a critically important public health goal. Recently, oleocanthal isolated from extra virgin olive oil was found to display nonsteroidal antiinflammatory drug activity similar to that of ibuprofen, a drug widely used in the therapeutic management of joint inflammatory diseases. We undertook this study to evaluate the effect of oleocanthal and its derivatives on the modulation of NO production in chondrocytes.

METHODS

Cultured ATDC-5 chondrocytes were tested with different doses of oleocanthal and its derivatives. Cell viability was evaluated using the MTT assay. Nitrite accumulation was determined in culture supernatant using the Griess reaction. Inducible NO synthase (NOS2) protein expression was examined using Western blotting analysis.

RESULTS

Oleocanthal and its derivatives decreased lipopolysaccharide-induced NOS2 synthesis in chondrocytes without significantly affecting cell viability at lower concentrations. Among the derivatives we examined, derivative 231 was the most interesting, since its inhibitory effect on NOS2 was devoid of cytotoxicity even at higher concentrations.

CONCLUSION

This class of molecules shows potential as a therapeutic weapon for the treatment of inflammatory degenerative joint diseases.

Inhibitory effect of Agrimoniae Herba on lipopolysaccharide-induced nitric oxide and proinflammatory cytokine production in BV2 microglial cells

OBJECTIVES

Agrimoniae Herba has been used as an anti-inflammatory agent in traditional medicine. Nitric oxide and proinflammatory cytokines produced by activated microglia may be a possible etiological factor of neurodegenerative disorders. We evaluated whether Agrimoniae Herba could have an anti-inflammatory effect on lipopolysaccharide-induced BV2 microglial cells.

METHODS

The effects of Agrimoniae Herba on lipopolysaccharide-induced nitric oxide and proinflammatory cytokine production in BV2 microglial cells were evaluated by nitric oxide assay, enzyme-linked immunosorbent assay and western blotting.

RESULTS

Agrimoniae Herba had no cytotoxicity and suppressed lipopolysaccharide-induced nitric oxide production in BV2 microglial cells. Agrimoniae Herba also suppressed lipopolysaccharide-induced production of proinflammatory cytokines such as tumor necrosis factor, interleukin 1 beta and interleukin 6 in a dose-dependent manner. Agrimoniae Herba inhibited the expression of inducible nitric oxide synthase.

DISCUSSION

Taken together, these findings indicate that Agrimoniae Herba may be used as a form of pharmaceutical acupuncture therapy in the treatment of brain inflammation.

Antioxidant and anti-inflammatory effects of Orthosiphon aristatus and its bioactive compounds

Orthosiphon aristatus (Blume) Miq., which can be used as a food ingredient, is grown throughout Southeast Asia and Australia. O. aristatus is frequently used for the treatment of renal inflammation, kidney stones and dysuria. The focus of the current work was to study the antioxidant and anti-inflammatory effects of methanol, ethanol and water extracts from O. aristatus (abbreviated as MEOA, EEOA and WEOA, respectively). The evaluation of antioxidant activity was determined by total phenolics, Trolox equivalent antioxidant capacity (TEAC), oxygen-radical absorbance capacity (ORAC) and cellular antioxidant activity (CAA) assays. These assays demonstrated a relatively high antioxidant activity for MEOA and EEOA. These results revealed that EEOA had the most prominent inhibitory effect on lipopolysaccharide (LPS)-stimulated nitric oxide (NO), prostaglandin E(2) (PGE(2)) and intracellular reactive oxygen species (ROS) production in RAW 264.7 cells. A high performance liquid chromatography profile indicated that MEOA and EEOA contained both ursolic acid and oleanolic acid. Moreover, ursolic acid significantly reduced NO production in LPS-stimulated RAW 264.7 cells. Both EEOA and ursolic acid inhibited LPS-stimulated protein and mRNA expression of both inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in these cells. These results demonstrate that EEOA and its bioactive compound, ursolic acid, suppress LPS-induced NO and PGE(2) production by inhibiting ROS generation, along with reducing expression of iNOS and COX-2 in RAW 264.7 cells.

Neurobiological mechanisms of pain in sickle cell disease

Pain is a frequent complaint of people living with sickle cell disease (SCD); however, the neurobiology of pain in SCD remains poorly understood. Whereas this pain has been thought to be primarily related to visceral and somatic tissue injury subsequent to vaso-occlusion events, emerging evidence from human and animal studies has suggested that a component of SCD pain may be related to neuropathic processes. Significant knowledge has been obtained from studies of molecular and neurobiological mechanisms leading to and maintaining neuropathic pain. Some of the most promising evidence has implicated major roles of protein kinase C and Ca2+/calmodulin-dependent protein kinase II, and their interaction with the N-methyl-D-aspartate receptors and the transient receptor potential vanilloid 1 receptor in the development of neuropathic pain. The latest evidence from our studies suggests that these pathways are important for SCD pain as well. Coupled with emerging animal models of SCD pain, we can now start to elucidate neurobiological mechanisms underlying pain in SCD, which may lead to better understanding and effective therapies.

Concise route to the chiral pyrrolidine core of selective inhibitors of neuronal nitric oxide

2-(((3R,4R)-4-(Allyloxy)-1-benzylpyrrolidin-3-yl)methyl)-6-(2,5-dimethyl-1H-pyrrol-1-yl)-4-methylpyridine (2), a key intermediate for the preparation of novel neuronal nitric oxide synthase (nNOS) inhibitors, is synthesized using diisopropyl (R)-(+)-malate as the starting material. The key steps involve a Frater-Seebach diastereoselective alkylation and a fast intramolecular cyclization.

Design and Synthesis of Imidazopyrimidine Derivatives as Potent iNOS Dimerization Inhibitors

A series of imidazopyrimidine derivatives with the general formula I was synthesized and identified as potent inhibitors of iNOS dimer formation, a prerequisite for proper functioning of the enzyme. Stille and Negishi coupling reactions were used as key steps to form the carbon-carbon bond connecting the imidazopyrimidine core to the central cycloalkenyl, cycloalkyl and phenyl ring templates.

Anti-inflammatory, anti-nociceptive, and anti-psychiatric effects by the rhizomes of Alpinia officinarum on complete Freund's adjuvant-induced arthritis in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Alpinia officinarum Hance (Zingiberaceae) is an annual plant. Its rhizome has long been used as an anti-inflammatory, an analgesic, a stomachic and a carminative in traditional medicine.

OBJECTIVE

The aim of this study was to test the anti-inflammatory effects of Alpinia officinarum rhizomes on acute and chronic arthritis in SD rats.

METHODS

Alpinia officinarum rhizomes were extracted by refluxing using 80% ethanol. The fractions were prepared by the fractionation of ethyl acetate (EtOAc), n-butanol, and water. This extract was administrated to rats by peroral injection. Acute arthritis was induced by a subcutaneous injection of carrageenan into the hind paw of SD rats. Chronic arthritis was stimulated by a subcutaneous injection of complete Freund's adjuvant (CFA) into the hind paw of SD rats. The paw volume was measured using a plethysmometer, thermal hyperalgesia was tested using a thermal plantar tester, hyperalgesia was evaluated by ankle flexion evoked vocalizations, and the expression of c-Fos in the brain hippocampus was measured with the avidin-biotin-peroxidase technique. Nitric oxide (NO) production was evaluated on nitrite by a Griess assay in lipopolysaccharide (LPS)-induced murine macrophage RAW 264.7 cells.

RESULTS

An 80% ethanolic extract showed acute anti-inflammatory activity that it reduced the edema volume in carrageenan-stimulated arthritis and inhibited NO generation in LPS-induced RAW 264.7 cells. In addition, this extract showed chronic anti-rheumatic and analgesic activities by suppressing the swelling volume, by recovering the paw withdrawal latency, and by inhibiting the flexion scores in CFA-induced arthritis. Particularly, this medicine had potent meaningful effects on the second signal of the left hind paw in the form of an immunological reaction compared to its effects on the first signal in the right hind paw after the CFA treatment. This also shows an anti-psychiatric effect through control of the expression of the c-Fos protein of the brain hippocampus in CFA-stimulated arthritis. On the other hand, each fraction showed acute anti-inflammatory effects; the action of the EtOAc fraction may have resulted from the suppression of NO production.

CONCLUSIONS

Alpinia officinarum rhizomes may be viable therapeutic or preventive candidates for the treatment of acute and chronic arthritis.

Nitric oxide and pain: 'Something old, something new'

Challenges have emerged following the revival of nitric oxide (NO) from 'something old', a simple gas derived from nitrogen and oxygen with a role in the early stages of evolution, into 'something new', an endogenously formed biological mediator regulating a wide variety of physiological functions. Although pain is a common sensation, it encompasses multiple neurobiologic components, of which NO is only one. In pain research, the study of NO is complicated by convoluted problems related mostly to the effects of NO, which are pro- or anti-nociceptive depending on the circumstances. This dual function reflects the multi-faceted roles of the NO molecule described in physiology. This review covers current information about NO and its implications in pain mechanisms. In addition, it follows the pain pathways, demonstrating the role of NO in peripheral nociceptive transmission as well in central sensitization. This knowledge may provide the scientific basis for developing new drugs that are indicated for different types of pain, drugs that may be related to the chemical links of NO. A comprehensive approach to understanding the effects of NO will help clinicians identify novel agents that combine the pharmacological profile of native drugs with a controllable manner of NO release. Inhibitors of NO synthesis may have analgesic effects and would be of interest for treating inflammatory and neuropathic pain. Unfortunately, only a few of these compounds have reached the stage of clinical pain trials.

The role of nitric oxide in osteoarthritis

Elevated levels of markers of nitric oxide (NO) production are found in osteoarthritic joints suggesting that NO is involved in the pathogenesis of osteoarthritis (OA). In OA, NO mediates many of the destructive effects of interleukin-1 (IL-1) and tumour necrosis factor-alpha (TNF-alpha) in the cartilage, and inhibitors of NO synthesis have demonstrated retardation of clinical and histological signs and symptoms in experimentally induced OA and other forms of arthritis. As an important factor in cartilage, the regulation of inducible nitric oxide synthase (iNOS) expression and activity, and the effects of NO are reviewed, especially in relation to the pathogenesis of OA.

A cellular model for screening neuronal nitric oxide synthase inhibitors

Nitric oxide synthase (NOS) inhibitors are potential drug candidates because it has been well demonstrated that excessive production of nitric oxide critically contributes to a range of diseases. Most inhibitors have been screened in vitro using recombinant enzymes, leading to the discovery of a variety of potent compounds. To make inhibition studies more physiologically relevant and bridge the gap between the in vitro assay and in vivo studies, we report here a cellular model for screening NOS inhibitors. Stable transformants were generated by overexpressing rat neuronal NOS in HEK 293T cells. The enzyme was activated by introducing calcium ions into cells, and its activity was assayed by determining the amount of nitrite that was formed in culture medium using the Griess reagent. We tested a few NOS inhibitors with this assay and found that the method is sensitive, versatile, and easy to use. The cell-based assay provides more information than in vitro assays regarding the bioavailability of NOS inhibitors, and it is suitable for high-throughput screening.

Bioactive constituents from Chinese natural medicines. XXXIII. Inhibitors from the seeds of Psoralea corylifolia on production of nitric oxide in lipopolysaccharide-activated macrophages

The methanolic extract from the seeds of Psoralea corylifolia was found to inhibit production of nitric oxide (NO) in lipopolysaccharide-activated mouse peritoneal macrophages. Among the isolated compounds, bavachinin (IC(50)=26 microM), isobavachalcone (17 microM), neobavaisoflavone (ca. 29 microM), corylifol A (ca. 21 microM), and psoralidin (ca. 23 microM) significantly inhibited the accumulation of nitrite (NO(2)(-)) as a marker of production of NO. Bakuchiol, which is mainly contained in the extract, also showed weak activity at 10 microM, but cytotoxic effects were observed more than 30 microM.

Discovery of highly potent and selective inhibitors of neuronal nitric oxide synthase by fragment hopping

Selective inhibition of neuronal nitric oxide synthase (nNOS) has been shown to prevent brain injury and is important for the treatment of various neurodegenerative disorders. This study shows that not only greater inhibitory potency and isozyme selectivity but more druglike properties can be achieved by fragment hopping. On the basis of the structure of lead molecule 6, fragment hopping effectively extracted the minimal pharmacophoric elements in the active site of nNOS for ligand hydrophobic and steric interactions and generated appropriate lipophilic fragments for lead optimization. More potent and selective inhibitors with better druglike properties were obtained within the design of 20 derivatives (compounds 7-26). Our structure-based inhibitor design for nNOS and SAR analysis reveal the robustness and efficiency of fragment hopping in lead discovery and structural optimization, which implicates a broad application of this approach to many other therapeutic targets for which known druglike small-molecule modulators are still limited.

Dimethoxycurcumin, a synthetic curcumin analogue with higher metabolic stability, inhibits NO production, inducible NO synthase expression and NF-kappaB activation in RAW264.7 macrophages activated with LPS

Excess production of nitric oxide (NO) by inducible NO synthase (iNOS) in activated macrophages is linked to acute and chronic inflammation. Thus, it would be valuable to develop inhibitors of NO and/or iNOS for potential therapeutic use. We investigated whether dimethoxycurcumin (DiMC), a synthetic curcumin analogue with higher metabolic stability over curcumin, could inhibit NO production and iNOS expression in activated macrophages. RAW264.7 macrophages were activated with lipopolysaccharide (LPS) in the absence or presence of DiMC, which contains four methoxy groups at two aromatic rings, curcumin containing two, bis-demethoxycurcumin (BDMC) containing none, or tetrahydrocurcumin (THC) containing two but lacking conjugated double bonds in the central seven-carbon chain. NO production, iNOS expression and NF-kappaB activity were examined. DiMC, curcumin and BDMC inhibited NO production, iNOS expression and NF-kappaB activation, with DiMC being the most effective, followed by curcumin and BDMC. THC failed to inhibit NO production, iNOS expression and NF-kappaB activation. Our results suggest that DiMC inhibits NO production, iNOS expression and NF-kappaB activation in LPS-activated macrophages, which may be due not only to the conjugated double bonds but also the increased number of methoxy groups.

2,2,6,6-tetramethylpiperidin-1-oxyl probes for evaluating oxidative stress on the cell membrane and mitochondria

Oxidative stress is recognized to be involved in many pathological conditions, such as inflammation, arteriosclerosis, and neurodegenerative diseases. Reactive oxygen species (ROS), which induce oxidative stress responses, appear to induce different biochemical and cellular changes in each pathological condition. To elucidate the roles of ROS in these diverse pathological conditions, the measurement and evaluation of oxidative stress at subcellular levels would be very effective. We have developed EPR probes for oxidative stress in organelles, which are tagged with a fluorescent function, and assessed oxidative stress of the membrane and mitochondria using chemical probes for the corresponding organelles. These probes are localized to the expected cellular regions confirmed by confocal fluorescent microscopy, and for demonstration, the probes are employed to detect oxidative stress in RAW264.7 cells stimulated with LPS/IFN-gamma. From the radical clearance rate of the probes localized in both the membrane and mitochondria, oxidative stress has been found to be consistently more severe in the membrane region, where NADPH oxidase is known to be upregulated by LPS/IFN-gamma treatment. These specific probes have depicted each organelle under different oxidative stress conditions by a specific exogenous oxidative stimulus.

Involvement of neuronal, inducible and endothelial nitric oxide synthases in capsaicin-induced muscle hypersensitivity

Nitric oxide, which has been implicated in the development of hyperalgesia in the spinal system, has not been systematically studied in the trigeminal system, especially in the context of inflammatory muscle pain condition. In this study, we investigated the functional role of centrally released nitric oxide in the pathogenesis of orofacial muscle pain. Specifically, we examined the contribution of neuronal, inducible and endothelial nitric oxide synthases, nNOS, iNOS and eNOS, respectively, in mediating masseter hypersensitivity under acute inflammatory condition. Time-dependent changes in nNOS, iNOS and eNOS protein expression in the subnucleus caudalis (Vc) were assessed following capsaicin injection in the masseter muscle of male Sprague Dawley rats. The expression of all three nitric oxide synthases was significantly up-regulated 30-60 min following capsaicin stimulation, which paralleled the time course of the development of capsaicin-induced masseter hypersensitivity. Pretreatment with each NOS inhibitor significantly attenuated the masseter hypersensitivity. These data showed that all three NOS in the Vc are functionally important for the development of craniofacial muscle hyperalgesia and suggest that the three NOS are closely orchestrated to regulate the level of nitric oxide under normal and pathologic conditions.

Anti-inflammatory effects of phenolic compounds isolated from the fruits of Artocarpus heterophyllus

Artocarpus heterophyllus Lam is a large evergreen tree cultivated throughout Southeast Asia for its fruits. Its leaves and roots have been used for medicinal purposes. The aim of this work was to study the in vitro anti-inflammatory effects of phenolic compounds isolated from the ethyl acetate extracts of the fruits of Artocarpus heterophyllus. Three phenolic compounds were characterized as artocarpesin [5,7,2',4'-tetrahydroxy-6-(3-methylbut-3-enyl) flavone] ( 1), norartocarpetin (5,7,2',4'-tetrahydroxyflavone) ( 2), and oxyresveratrol [ trans-2,4,3',5'-tetrahydroxystilbene] ( 3) by spectroscopic methods and through comparison with data reported in the literatures. The anti-inflammatory effects of the isolated compounds ( 1- 3) were evaluated by determining their inhibitory effects on the production of proinflammatory mediators in lipopolysaccharide (LPS)-activated RAW 264.7 murine macrophage cells. These three compounds exhibited potent anti-inflammatory activity. The results indicated that artocarpesin ( 1) suppressed the LPS-induced production of nitric oxide (NO) and prostaglandin E 2 (PGE 2) through the down-regulation of inducible nitric oxide synthase (iNOS) and cyclooxygenase 2 (COX-2) protein expressions. Thus, artocarpesin ( 1) may provide a potential therapeutic approach for inflammation-associated disorders.