Current Medicinal Chemistry (v.23, #24)

The cellular reaction to external challenges is a tightly regulated process consisting of integrated processes mediated by a variety of signaling molecules, generated as a result of modulation of corresponding biosynthetic systems. Both, nitric oxide synthase (NOS) and cyclooxygenase (COX) systems, consist of constitutive forms (NOS1, NOS3 and COX-1), which are mostly involved in housekeeping tasks, and inducible forms (NOS2 and COX-2), which shape the cellular response to stress and variety of bioactive agents. The complex interplay between NOS and COX pathways can be observed at least at three levels. Firstly, products of NOS and Cox systems can mediate the regulation and the expression of inducible forms (NOS2 and COX-2) in response of similar and dissimilar stimulus. Secondly, the reciprocal modulation of cyclooxygenase activity by nitric oxide and NOS activity by prostaglandins at the posttranslational level has been shown to occur. Mechanisms by which nitric oxide can modulate prostaglandin synthesis include direct S-nitrosylation of COX and inactivation of prostaglandin I synthase by peroxynitrite, product of superoxide reaction with nitric oxide. Prostaglandins, conversely, can promote an increased association of dynein light chain (DLC) (also known as protein inhibitor of neuronal nitric oxide synthase) with NOS1, thereby reducing its activity. The third level of interplay is provided by intracellular crosstalk of signaling pathways stimulated by products of NOS and COX which contributes significantly to the complexity of cellular signaling. Since modulation of COX and NOS pathways was shown to be principally involved in a variety of pathological conditions, the dissection of their complex relationship is needed for better understanding of possible therapeutic strategies. This review focuses on implications of interplay between NOS and COX for cellular function and signal integration.

Nitric Oxide-Releasing Biomaterials for Biomedical Applications by Xin Zhou, Jimin Zhang, Guowei Feng, Jie Shen, Deling Kong, Qiang Zhao (2579-2601).
Nitric oxide (NO), as an essential signaling molecule, participates in various physiological processes such as cardiovascular homeostasis, neuronal transmission, immunomodulation, and tumor growth. The multiple role of NO in physiology and pathophysiology has triggered a massive interest in the strategies of delivering exogenous NO for biomedical applications. Hence, different kinds of NO prodrugs have been developed up to date, including diazeniumdiolates, S-nitrosothiol, metal-nitrosyl, nitrobenzene, and so on. However, the clinical application of these low molecular weight NO donors has been restricted due to the problems of burst release, low payloads, and untargeted delivery. The delivery of NO by biomaterialbased carrier offers a beneficial strategy to realize the controlled and sustained delivery of NO to the targeted tissues or organs. In detail, NO-donor prodrugs have been attached and loaded to diverse biomaterials to fabricate nanoparticles, hydrogels, and coating platforms by means of physical, chemical, or supramolecular techniques. These NO-releasing biomaterials hold promise for a number of biomedical applications ranging from therapy of the ischemic disease and several types of cancer to cardiovascular devices and wound dressing. First, surface coating with NO-releasing biomaterials could mimic the physiological function of vascular endothelium, therefore promoting vascularization and improving the patency of cardiovascular implants. Next, because NO also mediates many important processes that take place after cutaneous injury, NO-releasing biomaterials could serve as ideal wound dressing to accelerate tissue regeneration. Finally, biomaterials enable localized delivery of high dose of NO to tumors in a sustained manner, thus generating potent tumoricidal effect. In this review, we will summarize the progress of different NO-releasing biomaterials, and highlight their biomedical applications with a hope to inspire new perspectives in the area of biomaterial-based NO-delivery systems.

Despite long and intensive investigation, the mechanisms by which nitric oxide (NO) regulates immune function and carcinogenesis remain incompletely understood. Protein S-nitrosylation, the covalent attachment of a nitroso group to a cysteine thiol, has emerged as a central mechanism of NO-dependent cellular regulation. In particular, recent research has revealed important roles for S-nitrosylation/denitrosylation in modulating the activity of macrophage and tumor cell proteins, implicating Snitrosylation in the regulation of macrophage function as well as in tumor development and response to therapy. This review summarizes recent progress in the identification and characterization of S-nitrosylated proteins in macrophages and cancer cells. The review highlights key findings and insights obtained from functional and proteomic studies about the roles of S-nitrosylation in signaling, transcription, apoptosis and other cellular processes relevant to macrophage function and cancer progression. Some of the implications of recent discoveries for the development of novel anticancer approaches are also discussed.

Immunoregulatory and Effector Activities of Nitric Oxide and Reactive Nitrogen Species in Cancer by Cinzia Fionda, Maria Pia Abruzzese, Angela Santoni, Marco Cippitelli (2618-2636).
Nitric Oxide (NO) is a signaling radical, highly diffusible pleiotropic regulator of a large set of different molecular and biological pathways, including, neurotransmission, vasodilatation and macrophagemediated responses against infections. It is produced from the amino acid L-Arginine and oxygen by the enzymatic action of three isoforms of the Nitric Oxide Synthase (NOS), differently expressed and regulated in tissues.
Increasing evidence highlights the wide spectrum of action of NO in different pathologic conditions, including cancer. In this regard, a dual role for this molecule as a pro- and anti-tumorigenic mediator has been described, in a context and concentration-dependent manner. Moreover, NO exerts numerous immunologic effects, by operating as an effector molecule in innate immune responses as well as a regulator of adaptive immune components.
Here, we will review recent advances in the field of biology of this pleiotropic signaling molecule in cancer, also providing a concise description of the immunoregulatory and effector activities of NO and Reactive Nitrogen Species (RNS). In particular, we will summarize recent knowledge of the molecular mechanisms underlying the complex functions of NO in cancer pathogenesis. We will also address emerging immune-mediated mechanisms regulated by NO to provide a comprehensive view of the complex cellular interactions which control cancer progression and that can be influenced by NO at multiple levels. In the light of different immunologic effects of this molecule, the potential therapeutic implications of novel drugs targeting NO to treat cancer and to improve anti-tumor immune responses will be discussed.

Professor Ferid Murad has been a remarkable colleague and a mentor. During our very first meeting, he not only shared unresolved puzzles in Nitric Oxide (NO) research but also listened to my questions pointing to protein nitration and nitrosylation. This was start of a new avenue in my laboratory involving protein nitration, inducible nitric oxide synthase and nitrite production in the context of signaling and gene expression in cancer cells. Dynamic changes in the cytoskeleton remodeling in response to the cell membrane generated signals are regulated by p21-activated kinase 1 (PAK1) which also feed into microtubules (MT) dynamic via phosphorylating Tubulin Cofactor B (CoB) on serine 65 and serine 128. While While searching for the mechanism through which MT biogenesis might be counteracted for the purpose of maintaining the balance in MT dynamic, we explored the possibility of nitration of tyrosine residues in TCoB. We found that TCoB is nitrated on tyrosine 64 and tyrosine 98 and that nitrated TCoB inhibits TCoB phosphorylation and that intact PAK1 phosphorylation sites are also essential for the ability of TCoB to undergo nitration. We suggested a model wherein TCoB nitration acts as a feedback mechanism to counteract PAK1- signaling dependent microtubule dynamics, and thus, revealed an inherent regulatory coordination of growth factor and nitric oxide signaling in microtubule dynamics. In addition, cytoskeleton remodeling and NO production and resulting post-translational modifications in signaling modules serve as important modifiers of cellular processes. Here, I will discuss the cascade of events leading to my first meeting with Professor Murad, the development of scientific interactions, the recognition of our overlapping scientific interests in NO Signaling in cancer cells, and how these interactions have allowed us to connect NO - Cytoskeleton Signaling in cancer cells.

Nitric Oxide: A Universal Modulator of Brain Function by Athineos Philippu (2643-2652).
Background: The pioneering work of Robert F. Furchgott, Luis J. Ignaro and Ferid Murad has led us to investigate whether nitric oxide (NO) is present in the brain, its origin and whether it possesses a functional role in brain structures. This review is mainly an outline of own findings obtained by using the push-pull superfusion technique. Method: We have used the push-pull superfusion technique that makes it possible to determine quantitatively endogenous transmitters released from their neurons in the synaptic cleft. In some experiments, a NO sensor was inserted into the pushpull cannula for online determination of NO released in the synaptic cleft together with neurotransmitters. Results: The release rates of endogenous NO are not constant but oscillate according to an ultradian rhythm with an apparent frequency of about 24 min per cycle. Similar rhythmic changes have been found in the release of neurotransmitters in several brain regions, as well as in the EEG delta band. Endogenous NO modulates the release of acetylcholine, glutamate, aspartate, GABA, serotonin, histamine in distinct brain areas. The release of adenosine is also increased by NO suggesting the synchronous release of ATP. Endogenous NO influences various brain functions such as blood pressure regulation and responses to stress. Recordings of evoked potentials revealed that NO plays a crucial role in the integration of afferent signals. Furthermore, NO in involved in amphetamine-induced neurotoxicity. Conclusion: The multifarious influences of endogenous NO on central neuronal activity, brain functions and integration of afferent signals underpin its universal modulatory role in the brain.

Physiological Functions of NO-Sensitive Guanylyl Cyclase Isoforms by Doris Koesling, Evanthia Mergia, Michael Russwurm (2653-2665).
NO-sensitive guanylyl cyclase (NO-GC) acts as the receptor for nitric oxide and by the increase in cGMP executes most of the NO effects in the cardiovascular and neuronal system. Two isoforms of NO-GC exist whose existence has not been paid much attention to probably because they reveal comparable regulatory and catalytic properties and therefore cannot be differentiated in vivo. Analysis of mice in which either one of the isoforms has been genetically deleted unequivocally establishes the coexpression of NO-GC1 and NOGC2 in any tissue tested to date with the exception of platelets. In tissues other than brain and platelets, no particular function could be ascribed to a specific NO-GC isoform so far. In contrast, NO-GC1 and NO-GC2 serve different functions in the central nervous system. With NO-GC1's presynaptic role and NO-GC2's postsynaptic action, two NO/cGMP pathways have been shown to exist that enhance the strength of synaptic transmission on either side of the synaptic cleft.

An Update on the Role of Nitric Oxide in the Neurodegenerative Processes of Parkinson's Disease by Félix Javier Jiménez-Jiménez, Hortensia Alonso-Navarro, María Trinidad Herrero, Elena García-Martín, José A.G. Agúndez (2666-2679).
Background: The pathogenesis of Parkinson's disease (PD) is not fully understood. Together with some important physiological functions in the Central Nervous System (CNS), nitric oxide (NO) can have both, neuroprotective or neurotoxic actions, depending on its redox state. An important body of evidence suggests the involvement of NO in many of the processes leading to neurodegeneration in several neurological disorders including PD. Objective: The main aim of this review is to update the data regarding the possible involvement of NO in the pathogenesis of PD. Methods: We performed a literature review on neuropathological, biochemical and genetic studies in PD patients and in several experimental models of parkinsonism and role of NO in these models. Results: Both studies in humans and in experimental models of parkinsonism give support to the contribution of NO in excitotoxicity, inflammation, oxidative stress, mitochondrial function impairment, DNA damage, and Snitrosylation of diverse proteins. The interaction of these mechanisms leads finally to neuronal death. The fact that selective of specific inhibitors of NO synthase (NOS, the enzyme responsible of NO synthesis) should prevent neuronal death through their actions of these pathogenic mechanisms supports the role of NO on PD as well. Conclusion: NO participates in the pathogenesis of PD by multiple mechanisms described in this review.

Nitric Oxide's Involvement in the Spectrum of Psychotic Disorders by João Paulo Maia-de-Oliveira, Ludmyla Kandratavicius, Emerson Arcoverde Nunes, João Paulo Machado-de-Sousa, Jaime E. Hallak, Serdar Murat Dursun (2680-2691).
Background: Recent findings suggest that dopaminergic abnormalities found in psychotic disorders may be secondary to nitric oxide dysfunctions. Nitric oxide seems to influence glutamatergic and dopaminergic neurotransmission, both of which have been associated with psychosis. Objective: To search and review published works which examined the influence of nitric oxide in psychotic disorders subjects. Method: The research was executed in the on-line collections of Pubmed and ISI Web of Science. The key aspects utilized were “Psychotic Disorders AND Nitric Oxide”, “Psychosis AND Nitric Oxide”,“Schizotypal Personality Disorder AND Nitric Oxide”, “Delusional Disorder AND Nitric Oxide”, “Brief Psychotic Disorder AND Nitric Oxide”, “Schizophreniform Disorder AND Nitric Oxide”, “Schizoaffective Disorder AND Nitric Oxide”, and “Schizophrenia AND Nitric Oxide”. Empirical works utilizing human subjects, published in the last 10 years, in English language were included. Results: Initially, the search yielded a total of 95 studies. Then, 39 were elected according to the inclusion requirements. The selected articles were divided into five groups: biochemical studies (n=15; 38.5%), genetic studies (n=11; 28.2%), postmortem studies (n=6; 15.4%), clinical trials (n=6; 15.4%), and case reports (n=1; 2.5%). The studies evaluated only schizophrenic or schizoaffective disorder subjects. The great majority of them found evidence of nitric oxide dysfunctions in psychosis. Conclusion: The results of the review strengthen the idea that nitric oxide has a key participation in psychotic disorders and deserves deeper investigation as a target for future pharmacological intervention.

Close to 1% of the world population suffer from schizophrenia. Current medications for this chronic mental disorder have greatly improved treatment over the last half century or more, but, the newer atypical antipsychotics have proven to be disappointing, and enormous challenges remain. The negative symptoms and cognitive dysfunction in schizophrenia which greatly affect overall morbidity call for better treatments. Nitric oxide (NO), an intra- and inter-cellular messenger in the brain, is involved in the pathogenesis of schizophrenia, so excessive NO production might contribute to the pathology. This implies that it might be useful to reduce nitrergic activity, so molecules aiming to decrease NO production such as NO synthase (NOS) inhibitors might be candidates. Here, I critically review advances in research on these emerging molecules which hold promise although a note of caution is required on account of their potential neurotoxicity and narrow therapeutic window.

Cross-Talk Between NO Synthase Isoforms in Neuro-Inflammation: Possible Implications in HIV-Associated Neurocognitive Disorders by Tiziana Persichini, Sofia Mariotto, Hisanori Suzuki, Elena Butturini, Roberta Mastrantonio, Orazio Cantoni, Marco Colasanti (2706-2714).
Inducible nitric oxide synthase (iNOS) is expressed in several cell types, particularly in inflammatory cells, in response to diverse proinflammatory stimuli, including viral proteins as HIV Tat and gp120. This response is preceded by an early decline in basal nitric oxide (NO) levels, dependent on a signaling leading to inhibition of the constitutive isoform of NO synthase (cNOS). This process requires critical levels of arachidonic acid (AA), generated by Ca2+-dependent activation of cytosolic phospholipase A2, and is mediated by the downstream tyrosine kinase-dependent phosphorylation of cNOS. Lowering basal NO levels are necessary for the activation of nuclear factor-?B, and thus for the expression of a variety of genes regulated by this transcription factor, which include iNOS. Notably, NO and AA, two small lipid soluble molecules, can trigger the above responses also in distal cells. Thus, AA produced at the very early stages of the inflammatory response is a likely critical signal switching the regulation of the “NO tone” from physiological (i.e., mediated by cNOS) to pathological (i.e., mediated by iNOS). This later phase of the inflammatory response is often accompanied by the onset of deleterious effects in the tissue, in which a critical role is played by iNOS-derived NO (directly or indirectly, i.e., via formation of peroxynitrite) as well as by products of the AA cascade. In this review, the authors discuss the implications of the crosstalk between the NOS isoforms in HIV-associated neuro-pathogenesis highlighting the role of NO and AA as mediators of cytotoxicity.

Integrative Control of Gastrointestinal Motility by Nitric Oxide by Dieter Groneberg, Barbara Voussen, Andreas Friebe (2715-2735).
In the gastrointestinal (GI) tract, nitric oxide (NO) has been shown over the last 25 years to exert a prominent function as inhibitory neurotransmitter. Apart from the regulation of secretion and resorption, NO from nitrergic neurons has been demonstrated to be crucial for GI smooth muscle relaxation and motility. In fact, several human diseases such as achalasia, gastroparesis, slow transit constipation or Hirschsprung's disease may involve dysfunctional nitrergic signaling. Most of NO's effects as neurotransmitter are mediated by NO-sensitive guanylyl cyclase (NO-GC) and further transduced by cGMP-dependent mechanisms. In contrast to the vascular system where NO from the endothelium induces relaxation by acting on NO-GC solely in smooth muscle cells, GI tissues contain several different NO-GCexpressing cell types that include smooth muscle cells, interstitial cells of Cajal and fibroblast-like cells. Based on this diverse localization of the NO receptor, the exact pathway(s) leading to NO-induced relaxation are still unknown. Global and cell-specific knockout mouse strains have been generated that lack enzymes participating in nitrergic signaling. These animals have been helpful in examining the role of NO in smooth muscle of the GI tract. Here, we discuss the current knowledge on NO-mediated mechanisms in the relaxation of GI smooth muscle in stomach, small and large intestine including sphincters. Special focus is placed on the integration of nitrergic signals by specialized cell types within the gut smooth muscle layers.

Recent Advances on Nitric Oxide in the Upper Airways by Mauro Maniscalco, Andrea Bianco, Gennaro Mazzarella, Andrea Motta (2736-2745).
Exhaled nitric oxide (NO) originates from the upper airways, and takes action, to varying extents, in regulation, protection and defense, as well as in noxious processes. Nitric oxide retains important functions in a wide range of physiological and pathophysiological processes of the human body, including vaso-regulation, antimicrobial activity, neurotransmission and respiration. This review article reports the ongoing investigations regarding the source, biology and relevance of NO within upper respiratory tract. In addition, we discuss the role of NO, originating from nasal and paranasal sinuses, in inflammatory disorders such as allergic rhinitis, sinusitis, primary ciliary dyskinesia, and cystic fibrosis.

Targeting NO Signaling for the Treatment of Osteoporosis by Hema Kalyanaraman, Ghania Ramdani, Renate B. Pilz (2746-2753).
Osteoporosis is a major health problem, affecting over 10 million people in the U.S. and leading to fractures associated with significant morbidity and mortality. Normal bone mass is maintained by a balance between the anabolic effects of osteoblasts and catabolic effects of osteoclasts. Most osteoporosis therapies inhibit osteoclast activity; parathyroid hormone is the only FDA-approved agent that increases osteoblast activity, but its efficacy wanes over time, and there is a need for novel bone-anabolic agents. Nitrates, which generate nitric oxide (NO) in vivo, prevent bone loss from estrogen-deficiency in rodents, and some clinical data suggest beneficial effects of nitrates in post-menopausal osteoporosis. Here, we examine the sources of NO and regulation of NO synthesis in bone cells, review the effects of NO in cells of osteoblastic and osteoclastic lineage, and summarize existing preclinical and clinical data to document the skeletal effects of NO in vivo. Based on the anabolic and anti-resorptive effects of NO in bone, novel NO donors and other strategies to enhance NO production and bioavailability in vivo may represent a new treatment strategy for osteoporosis.

Multiple Means by Which Nitric Oxide can Antagonize Photodynamic Therapy by Albert W. Girotti, Jonathan M. Fahey, Witold Korytowski (2754-2769).
Photodynamic therapy (PDT) is a unique site-specific treatment for eradicating a variety of solid tumors, including prostate, lung, bladder, and brain tumors. PDT is a three-component modality involving (i) administration of a photosensitizing agent (PS), (ii) PS photoexcitation by visible or near-infrared light, and (iii) molecular oxygen. Upon photoexcitation, PS gives rise to tumor-damaging reactive oxygen species, most prominently singlet oxygen (1O2). Previous studies revealed that endogenous nitric oxide (NO) in various mouse tumor models significantly reduced PDT effectiveness. Recent studies in the authors' laboratory indicated that NO produced by photostressed tumor cells per se can elicit anti-PDT effects. For example, breast cancer COH-BR1 and prostate cancer PC3 cells exhibited a rapid and prolonged upregulation of inducible nitric oxide synthase (iNOS) after sensitization with 5- aminolevulinic acid (ALA)-induced protoporphyrin-IX, followed by broad-band visible irradiation. Use of iNOS inhibitors and NO scavengers demonstrated that iNOS/NO played a key role in cell resistance to apoptotic photokilling. Moreover, cells surviving an ALA/light challenge proliferated, migrated, and invaded more rapidly than controls, again in iNOS/NOdependent fashion. Thus, NO was found to play a crucial role in various manifestations of enhanced aggressiveness exhibited by remaining live cells. Recent work has revealed that induced NO in PDT-targeted PC3 cells can also translocate and increase aggressiveness of non-targeted bystander cells. These negative and potentially tumor-promoting side effects of NO in PDT may be averted through use of iNOS inhibitors as adjuvants. Each of the above aspects of PDT antagonism by NO will be discussed in this review.

Targeting NO/cGMP Signaling in the CNS for Neurodegeneration and Alzheimer's Disease by Manel Ben Aissa, Sue H. Lee, Brian M. Bennett, Gregory R.J. Thatcher (2770-2788).
cAMP-response element-binding protein (CREB) plays a central role in various aspects of central nervous system (CNS) function, ranging from the developmental stages to neuronal plasticity and survival in adult brain. Activation of CREB plays a crucial role in learning and memory and is at the convergence of multiple intracellular signaling cascades including CAMKII and MAPK. This review focuses on the important functions of nitric oxide (NO) in activating CREB via the NO receptor, soluble guanylyl cyclase (sGC), and production of the second messenger, cGMP. The involvement of the NO/cGMP signaling pathway in synaptic plasticity suggests several avenues for therapeutic intervention, and targeting early synaptic degeneration could be an attractive approach for the development of novel disease-modifying approaches to treat cognition and memory dysfunction in neurodegenerative diseases.