Biology of nitric oxide signaling

Potential Effects of NO-Induced Hypoxia-Inducible Factor-1α on Yak Meat Tenderness during Post-Mortem Aging

The objective of this study was to investigate the mechanism underlying nitric oxide (NO)-induced hypoxia-inducible factor-1α (HIF-1α) and its impact on yak muscle tenderness during post-mortem aging. The Longissimus thoracis et lumborum (LTL) muscle of yak were incubated at 4 °C for 0, 3, 6, 9, 12, 24, and 72 h after treatment with 0.9% saline, NO activator, or a combination of the NO activator and an HIF-1α inhibitor. Results indicated that elevated NO levels could increase HIF-1α transcription to achieve stable expression of HIF-1α protein (P < 0.05). Additionally, elevated NO triggered HIF-1α S-nitrosylation, which further upregulated the activity of key glycolytic enzymes, increased glycogen consumption, accelerated lactic acid accumulation, and decreased pH (P < 0.05). These processes eventually improved the tenderness of yak muscle during post-mortem aging (P < 0.05). The results demonstrated that NO-induced activation of HIF-1α S-nitrosylation enhanced glycolysis during post-mortem aging and provided a possible pathway for improving meat tenderness.

Nitric Oxide: Physiological Functions, Delivery, and Biomedical Applications

Nitric oxide (NO) is a gaseous molecule that has a central role in signaling pathways involved in numerous physiological processes (e.g., vasodilation, neurotransmission, inflammation, apoptosis, and tumor growth). Due to its gaseous form, NO has a short half-life, and its physiology role is concentration dependent, often restricting its function to a target site. Providing NO from an external source is beneficial in promoting cellular functions and treatment of different pathological conditions. Hence, the multifaceted role of NO in physiology and pathology has garnered massive interest in developing strategies to deliver exogenous NO for the treatment of various regenerative and biomedical complexities. NO-releasing platforms or donors capable of delivering NO in a controlled and sustained manner to target tissues or organs have advanced in the past few decades. This review article discusses in detail the generation of NO via the enzymatic functions of NO synthase as well as from NO donors and the multiple biological and pathological processes that NO modulates. The methods for incorporating of NO donors into diverse biomaterials including physical, chemical, or supramolecular techniques are summarized. Then, these NO-releasing platforms are highlighted in terms of advancing treatment strategies for various medical problems.

Direct hydrogen selenide (H2Se) release from activatable selenocarbamates

Hydrogen selenide (H₂Se) is a possible bioregulator, potential gasotransmitter, and important precursor in biological organoselenium compound synthesis. Early tools for H₂Se research have benefitted from available mechanistic understanding of analogous small molecules developed for detecting or delivering H₂S. A now common approach for H₂S delivery is the use of small molecule thiocarbamates that can be engineered to release COS, which is quickly converted to H₂S by carbonic anhydrase. To expand our understanding of the chemical underpinnings that enable H₂Se delivery, we investigated whether selenocarbamates undergo similar chemistry to release carbonyl selenide (COSe). Using both light- and hydrolysis-activated systems, we demonstrate that unlike their lighter thiocarbamate congeners, selenocarbamates release H₂Se directly with concomitant isocyanate formation rather than by the intermediate release of COSe. This reaction mechanism for direct H₂Se release is further supported by computational investigations that identify a ΔΔG^‡ ∼ 25 kcal mol^-1 between the H₂Se and COSe release pathways in the absence of protic solvent. This work highlights fundamentally new approaches for H₂Se release from small molecules and advances the understanding of reactivity differences between reactive sulfur and selenium species.

Inhaled Nitric Oxide in Acute Respiratory Distress Syndrome Subsets: Rationale and Clinical Applications

Acute respiratory distress syndrome (ARDS) is a life-threatening condition, characterized by diffuse inflammatory lung injury. Since the coronavirus disease 2019 (COVID-19) pandemic spread worldwide, the most common cause of ARDS has been the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Both the COVID-19-associated ARDS and the ARDS related to other causes-also defined as classical ARDS-are burdened by high mortality and morbidity. For these reasons, effective therapeutic interventions are urgently needed. Among them, inhaled nitric oxide (iNO) has been studied in patients with ARDS since 1993 and it is currently under investigation. In this review, we aim at describing the biological and pharmacological rationale of iNO treatment in ARDS by elucidating similarities and differences between classical and COVID-19 ARDS. Thereafter, we present the available evidence on the use of iNO in clinical practice in both types of respiratory failure. Overall, iNO seems a promising agent as it could improve the ventilation/perfusion mismatch, gas exchange impairment, and right ventricular failure, which are reported in ARDS. In addition, iNO may act as a viricidal agent and prevent lung hyperinflammation and thrombosis of the pulmonary vasculature in the specific setting of COVID-19 ARDS. However, the current evidence on the effects of iNO on outcomes is limited and clinical studies are yet to demonstrate any survival benefit by administering iNO in ARDS.

Dual role of nitric oxide in Alzheimer's Disease

Nitric oxide (NO), an enzymatic product of nitric oxide synthase (NOS), has been associated with a variety of neurological diseases such as Alzheimer's disease (AD). NO has long been thought to contribute to neurotoxic insults caused by neuroinflammation in AD. This perception shifts as more attention is paid to the early stages before cognitive problems manifest. However, it has revealed a compensatory neuroprotective role for NO that protects synapses by increasing neuronal excitability. NO can positively affect neurons by inducing neuroplasticity, neuroprotection, and myelination, as well as having cytolytic activity to reduce inflammation. NO can also induce long-term potentiation (LTP), a process by which synaptic connections among neurons become more potent. Not to mention that such functions give rise to AD protection. Notably, it is unquestionably necessary to conduct more research to clarify NO pathways in neurodegenerative dementias because doing so could help us better understand their pathophysiology and develop more effective treatment options. All these findings bring us to the prevailing notion that NO can be used either as a therapeutic agent in patients afflicted with AD and other memory impairment disorders or as a contributor to the neurotoxic and aggressive factor in AD. In this review, after presenting a general background on AD and NO, various factors that have a pivotal role in both protecting and exacerbating AD and their correlation with NO will be elucidated. Following this, both the neuroprotective and neurotoxic effects of NO on neurons and glial cells among AD cases will be discussed in detail.

High glucose-induced increasing reactive nitrogen species accumulation triggered mitochondrial dysfunction, inflammation, and apoptosis in keratinocytes

Growing evidence indicates that skin injuries are a common complication of diabetes. However, the cellular and molecular mechanisms of high glucose (HG) environment trigger nitrosative stress-mediated inflammation and apoptosis in keratinocytes remains unknown. Here we investigated whether reactive nitrogen species (RNS) induced by HG environment restrain antioxidant activity, and mitochondrial dysfunction leading to inflammation, and apoptosis via stress signaling pathways in keratinocytes. Our results established that the HG environment enhanced the production of nitric oxide (NO) and peroxynitrite anion (ONOO-) by inducible NO synthase (iNOS) in keratinocytes. Overproduction of RNS in HG environment suppress the antioxidants activity leading to mitochondrial dysfunction, characterized by loss of mitochondrial membrane potential (ΔΨm), increase in mitochondrial mass, decrease in mitochondrial transcription factor A(TFAM), increase in mitochondrial DNA (mtDNA) displacement loop (D-loop) and decrease in glycolytic flux concentration, which was attenuated by pharmacological inhibitors of NO/ONOO-, Nω-Nitro-l-argininemethyl ester hydrochloride (NAME)/hydralazine hydrochloride (Hyd.HCl). Excess production of RNS in HG environment restrained 8-oxoguanine DNA glycosylase-1 (OGG1) expression and increased 8-hydroxydeoxyguanosine (8-OHdG) accumulations in DNA were regulated by NO or ONOO-. Further, HG-induced RNA production caused an increase in the production of inflammatory mediators accompanied by activation of ERK1/2MAPK/Akt/tuberin-mTOR/IRF3 signaling cascade, lipid peroxidation (LPO), and protein carbonylation (PC) reactions followed by breakdown the cell-cell communication and apoptosis. Pre-treatment of cell with NAME/Hyd.HCl, diminished the expression of ERK1/2MAPK/Akt/tuberin-mTOR/IRF3, inflammatory mediators, and attenuated apoptosis in keratinocytes. Together, our results indicated that excess production of RNS in HG environment triggered inflammation and apoptosis, mediated by activation of ERK1/2MAPK/Akt/tuberin-mTOR/IRF3 signaling cascades in keratinocytes.

Probing nitric oxide signaling using molecular MRI

Wide field measurements of nitric oxide (NO) signaling could help understand and diagnose the many physiological processes in which NO plays a key role. Magnetic resonance imaging (MRI) can support particularly powerful approaches for this purpose if equipped with molecular probes sensitized to NO and NO-associated targets. In this review, we discuss the development of MRI-detectable probes that could enable studies of nitrergic signaling in animals and potentially human subjects. Major families of probes include contrast agents designed to capture and report integrated NO levels directly, as well as molecules that respond to or emulate the activity of nitric oxide synthase enzymes. For each group, we outline the relevant molecular mechanisms and discuss results that have been obtained in vitro and in animals. The most promising in vivo data described to date have been acquired using NO capture-based relaxation agents and using engineered nitric oxide synthases that provide hemodynamic readouts of NO signaling pathway activation. These advances establish a beachhead for ongoing efforts to improve the sensitivity, specificity, and clinical applicability of NO-related molecular MRI technology.

Inhaled nitric oxide: role in the pathophysiology of cardio-cerebrovascular and respiratory diseases

Nitric oxide (NO) is a key molecule in the biology of human life. NO is involved in the physiology of organ viability and in the pathophysiology of organ dysfunction, respectively. In this narrative review, we aimed at elucidating the mechanisms behind the role of NO in the respiratory and cardio-cerebrovascular systems, in the presence of a healthy or dysfunctional endothelium. NO is a key player in maintaining multiorgan viability with adequate organ blood perfusion. We report on its physiological endogenous production and effects in the circulation and within the lungs, as well as the pathophysiological implication of its disturbances related to NO depletion and excess. The review covers from preclinical information about endogenous NO produced by nitric oxide synthase (NOS) to the potential therapeutic role of exogenous NO (inhaled nitric oxide, iNO). Moreover, the importance of NO in several clinical conditions in critically ill patients such as hypoxemia, pulmonary hypertension, hemolysis, cerebrovascular events and ischemia-reperfusion syndrome is evaluated in preclinical and clinical settings. Accordingly, the mechanism behind the beneficial iNO treatment in hypoxemia and pulmonary hypertension is investigated. Furthermore, investigating the pathophysiology of brain injury, cardiopulmonary bypass, and red blood cell and artificial hemoglobin transfusion provides a focus on the potential role of NO as a protective molecule in multiorgan dysfunction. Finally, the preclinical toxicology of iNO and the antimicrobial role of NO-including its recent investigation on its role against the Sars-CoV2 infection during the COVID-19 pandemic-are described.

Nitric oxide: Clinical applications in critically ill patients

Inhaled nitric oxide (iNO) acts as a selective pulmonary vasodilator and it is currently approved by the FDA for the treatment of persistent pulmonary hypertension of the newborn. iNO has been demonstrated to effectively decrease pulmonary artery pressure and improve oxygenation, while decreasing extracorporeal life support use in hypoxic newborns affected by persistent pulmonary hypertension. Also, iNO seems a safe treatment with limited side effects. Despite the promising beneficial effects of NO in the preclinical literature, there is still a lack of high quality evidence for the use of iNO in clinical settings. A variety of clinical applications have been suggested in and out of the critical care environment, aiming to use iNO in respiratory failure and pulmonary hypertension of adults or as a preventative measure of hemolysis-induced vasoconstriction, ischemia/reperfusion injury and as a potential treatment of renal failure associated with cardiopulmonary bypass. In this narrative review we aim to present a comprehensive summary of the potential use of iNO in several clinical conditions with its suggested benefits, including its recent application in the scenario of the COVID-19 pandemic. Randomized controlled trials, meta-analyses, guidelines, observational studies and case-series were reported and the main findings summarized. Furthermore, we will describe the toxicity profile of NO and discuss an innovative proposed strategy to produce iNO. Overall, iNO exhibits a wide range of potential clinical benefits, that certainly warrants further efforts with randomized clinical trials to determine specific therapeutic roles of iNO.

Albumin is an interface between blood plasma and cell membrane, and not just a sponge

Albumin is the most abundant protein in blood plasma and acts as a carrier for many circulating molecules. Hypoalbuminaemia, mostly caused by either renal or liver disease or malnutrition, can perturb vascular homeostasis and is involved in the development of multiple diseases. Here we review four functions of albumin and the consequences of hypoalbuminaemia on vascular homeostasis. (i) Albumin is the main determinant of plasma colloid osmotic pressure. Hypoalbuminaemia was therefore thought to be the main mechanism for oedema in nephrotic syndrome (NS), however, experimental studies showed that intrarenal mechanisms rather than hypoalbuminaemia determine formation and, in particular, maintenance of oedema. (ii) Albumin functions as an interface between lysophosphatidylcholine (LPC) and circulating factors (lipoproteins and erythrocytes) and the endothelium. Consequently, hypoalbuminaemia results in higher LPC levels in lipoproteins and erythrocyte membrane, thereby increasing atherosclerotic properties of low-density lipoprotein and blood viscosity, respectively. Furthermore, albumin dose-dependently restores LPC-induced inhibition of vasodilation. (iii) Hypoalbuminaemia impacts on vascular nitric oxide (NO) signalling by directly increasing NO production in endothelial cells, leading to reduced NO sensitivity of vascular smooth muscle cells. (iv) Lastly, albumin binds free fatty acids (FFAs). FFAs can induce vascular smooth muscle cell apoptosis, uncouple endothelial NO synthase and decrease endothelium-dependent vasodilation. Unbound FFAs can increase the formation of reactive oxygen species by mitochondrial uncoupling in multiple cell types and induce hypertriglyceridemia in NS. In conclusion, albumin acts as an interface in the circulation and hypoalbuminaemia impairs multiple aspects of vascular function that may underlie the association of hypoalbuminaemia with adverse outcomes. However, hypoalbuminaemia is not a key to oedema in NS. These insights have therapeutic implications.

Participation of nitrogen oxide and its metabolites in the genesis of hyperimmune inflammation in COVID-19

Despite the success in the tactics of treating COVID-19, there are many unexplored issues related to the development and progression of the process in the lungs, brain, and other organs, as well as the role of individual elements, in particular, nitric oxide (NO), and in the pathogenesis of organ damage. Based on the analyzed literature data, we considered a possible pathophysiological mechanism of action of NO and its derivatives in COVID-19. It can be noted that hyperimmune systemic inflammation and "cytokine storm" are enhanced by the production of NO, products of its oxidation ("nitrosative stress"). It is noted in the work that as a result of the oxidation of NO, a large amount of the toxic compound peroxynitrite is formed, which is a powerful proinflammatory agent. Its presence significantly damages the endothelium of the vascular walls and also oxidizes lipids, hemoglobin, myoglobin, and cytochrome, binds SH-groups of proteins, and damages DNA in the target cells. This is confirmed by the picture of the vessels of the lungs on computed tomography and the data of biochemical studies. In case of peroxynitrite overproduction, inhibition of the synthesis of NO and its metabolic products seems to be justified. Another aspect considered in this work is the mechanism of damage by the virus to the central and peripheral nervous system, which remains poorly understood but may be important in understanding the consequences, as well as predicting brain functions in persons who have undergone COVID-19. According to the analyzed literature, it can be concluded that brain damage is possible due to the direct effect of the virus on the peripheral nerves and central structures, and indirectly through the effect on the endothelium of cerebral vessels. Disturbances in the central nervous regulation of immune responses may be associated with the insufficient function of the acetylcholine anti-inflammatory system. It is proposed to further study several approaches to influence various links of NO exchange, which are of interest for theoretical and practical medicine.

Hypercapnia in the critically ill: insights from the bench to the bedside

Carbon dioxide (CO2) has long been considered, at best, a waste by-product of metabolism, and at worst, a toxic molecule with serious health consequences if physiological concentration is dysregulated. However, clinical observations have revealed that 'permissive' hypercapnia, the deliberate allowance of respiratory produced CO2 to remain in the patient, can have anti-inflammatory effects that may be beneficial in certain circumstances. In parallel, studies at the cell level have demonstrated the profound effect of CO2 on multiple diverse signalling pathways, be it the effect from CO2 itself specifically or from the associated acidosis it generates. At the whole organism level, it now appears likely that there are many biological sensing systems designed to respond to CO2 concentration and tailor respiratory and other responses to atmospheric or local levels. Animal models have been widely employed to study the changes in CO2 levels in various disease states and also to what extent permissive or even directly delivered CO2 can affect patient outcome. These findings have been advanced to the bedside at the same time that further clinical observations have been elucidated at the cell and animal level. Here we present a synopsis of the current understanding of how CO2 affects mammalian biological systems, with a particular emphasis on inflammatory pathways and diseases such as lung specific or systemic sepsis. We also explore some future directions and possibilities, such as direct control of blood CO2 levels, that could lead to improved clinical care in the future.

Immunomodulatory Approaches in Diabetes-Induced Cardiorenal Syndromes

Immunomodulatory approaches are defined as all interventions that modulate and curb the immune response of the host rather than targeting the disease itself with the aim of disease prevention or treatment. A better understanding of the immune system continues to offer innovative drug targets and methods for immunomodulatory interventions. Cardiorenal syndrome is a clinical condition that defines disorders of the heart and kidneys, both of which communicate with one another through multiple pathways in an interdependent relationship. Cardiorenal syndrome denotes the confluence of heart-kidney relationships across numerous interfaces. As such, a dysfunctional heart or kidney has the capacity to initiate disease in the other organ via common hemodynamic, neurohormonal, immunological, and/or biochemical feedback pathways. Understanding how immunomodulatory approaches are implemented in diabetes-induced cardiovascular and renal diseases is important for a promising regenerative medicine, which is the process of replacing cells, tissues or organs to establish normal function. In this article, after a brief introduction on the immunomodulatory approaches in diseases, we will be reviewing the epidemiology and classifications of cardiorenal syndrome. We will be emphasizing on the hemodynamic factors and non-hemodynamic factors linking the heart and the kidneys. In addition, we will be elaborating on the immunomodulatory pathways involved in diabetes-induced cardiorenal syndrome namely, RAS, JAK/STAT, and oxidative stress. Moreover, we will be addressing possible therapeutic approaches that target the former pathways in an attempt to modulate the immune system.

Antimicrobial carbon nanodots: photodynamic inactivation and dark antimicrobial effects on bacteria by brominated carbon nanodots

The evolving threat of antibiotic resistance development in pathogenic bacteria necessitates the continued cultivation of new technologies and agents to mitigate associated negative health impacts globally. It is no surprise that infection prevention and control are cited by the Centers for Disease Control and Prevention (CDC) as two routes for combating this dangerous trend. One technology that has gained great research interest is antimicrobial photodynamic inactivation of bacteria, or APDI. This technique permits controllable activation of antimicrobial effects by combining specific light excitation with the photodynamic properties of a photosensitizer; when activated, the photosensitizer generates reactive oxygen species (ROS) from molecular oxygen via either a type I (electron transfer) or type II (energy transfer) pathway. These species subsequently inflict oxidative damage on nearby bacteria, resulting in suppressed growth and cell death. To date, small molecule photosensitizers have been developed, yet the scalability of these as widespread sterilization agents is limited due to complex and costly synthetic procedures. Herein we report the use of brominated carbon nanodots (BrCND) as new photosensitizers for APDI. These combustion byproducts are easily and inexpensively collected; incorporation of bromine into the nanodot permits photosensitization effects that are not inherent to the carbon nanodot structure alone-a consequence of triplet character gained by the heavy atom effect. BrCND demonstrate both type I and type II photosensitization under UV-A irradiation, and furthermore are shown to have significant antimicrobial effects against both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus and Listeria monocytogenes as well. A mechanism of "dark" toxicity is additionally reported; the pH-triggered release of reactive nitrogen species is detected from a carbon nanodot structure for the first time. The results described present the BrCND structure as a competitive new antimicrobial agent for controllable sterilization of bacteria.

The restorative effect of apocynin and catalase in l-arginine induced hypotension on normotensive subjects – the role of oxidative stress

L-arginine is a substrate for nitric oxide synthase (NOS) responsible for the production of NO. This investigation studied the effect of apocynin, an NADPH oxidase inhibitor and catalase, an H2O2 scavenger on L-arginine induced oxidative stress and hypotension. Forty Wistar-Kyoto rats were treated for 14 days with vehicle, L-arginine (12.5mg/ml p.o.), L-arginine+apocynin (2.5mmol/L p.o.), L-arginine+catalase (10000U/kg/day i.p.) and L-arginine plus apocynin+catalase respectively. Weekly renal functional and hemodynamic parameters were measured and kidneys harvested at the end of the study for histopathological and renal NADPH oxidase 4 (Nox4) assessments. L-arginine administration in normotensive rats decreased systolic blood pressure (120±2 vs 91±2mmHg) and heart rate (298±21 vs 254±15b/min), enhanced urinary output (21.5±4.2 vs 32±1.9ml/24h , increased creatinine clearance (1.72±0.56 vs 2.62±0.40ml/min/kg), and fractional sodium excretion (0.88±0.16 vs 1.18±0.16 %), caused proteinuria (28.10±1.93 vs 35.26±1.69mg/kg/day) and a significant decrease in renal cortical blood perfusion (292±3 vs 258±5bpu) and pulse wave velocity (3.72±0.20 vs 2.84±0.13m/s) (all P<0.05). L-arginine increased plasma malondialdehyde (by ~206 % P<0.05) and NO (by ~51 %, P<0.05) but decreased superoxide dismutase (by ~31 %, P<0.05) and total antioxidant capacity (by ~35 %, P<0.05) compared to control. Renal Nox4 mRNA activity was approximately 2.1 fold higher (P<0.05) in the L-arginine treated rats but was normalized by apocynin and apocynin plus catalase treatment. Administration of apocynin and catalase, but not catalase alone to rats fed L-arginine, restored the deranged renal function and structure, prevented hypotension and enhanced the antioxidant capacity and suppressed Nox4 expression. These findings suggest that apocynin and catalase might be used prophylactically in states of oxidative stress.

S-nitrosocysteine and glutathione depletion synergize to induce cell death in human tumor cells: Insights into the redox and cytotoxic mechanisms

Nitric oxide (NO)-dependent signaling and cytotoxic effects are mediated in part via protein S-nitrosylation. The magnitude and duration of S-nitrosylation are governed by the two main thiol reducing systems, the glutathione (GSH) and thioredoxin (Trx) antioxidant systems. In recent years, approaches have been developed to harness the cytotoxic potential of NO/nitrosylation to inhibit tumor cell growth. However, progress in this area has been hindered by insufficient understanding of the balance and interplay between cellular nitrosylation, other oxidative processes and the GSH/Trx systems. In addition, the mechanistic relationship between thiol redox imbalance and cancer cell death is not fully understood. Herein, we explored the redox and cellular effects induced by the S-nitrosylating agent, S-nitrosocysteine (CysNO), in GSH-sufficient and -deficient human tumor cells. We used l-buthionine-sulfoximine (BSO) to induce GSH deficiency, and employed redox, biochemical and cellular assays to interrogate molecular mechanisms. We found that, under GSH-sufficient conditions, a CysNO challenge (100-500 μM) results in a marked yet reversible increase in protein S-nitrosylation in the absence of appreciable S-oxidation. In contrast, under GSH-deficient conditions, CysNO induces elevated and sustained levels of both S-nitrosylation and S-oxidation. Experiments in various cancer cell lines showed that administration of CysNO or BSO alone commonly induce minimal cytotoxicity whereas BSO/CysNO combination therapy leads to extensive cell death. Studies in HeLa cancer cells revealed that treatment with BSO/CysNO results in dual inhibition of the GSH and Trx systems, thereby amplifying redox stress and causing cellular dysfunction. In particular, BSO/CysNO induced rapid oxidation and collapse of the actin cytoskeletal network, followed by loss of mitochondrial function, leading to profound and irreversible decrease in ATP levels. Further observations indicated that BSO/CysNO-induced cell death occurs via a caspase-independent mechanism that involves multiple stress-induced pathways. The present findings provide new insights into the relationship between cellular nitrosylation/oxidation, thiol antioxidant defenses and cell death. These results may aid future efforts to develop NO/redox-based anticancer approaches.

Nitric Oxide (NO) and NO Synthases (NOS)-Based Targeted Therapy for Colon Cancer

Colorectal cancer (CRC) is one of the most lethal malignancies worldwide and CRC therapy remains unsatisfactory. In recent decades, nitric oxide (NO)-a free-radical gas-plus its endogenous producer NO synthases (NOS), have attracted considerable attention. NO exerts dual effects (pro- and anti-tumor) in cancers. Endogenous levels of NO promote colon neoplasms, whereas exogenously sustained doses lead to cytotoxic functions. Importantly, NO has been implicated as an essential mediator in many signaling pathways in CRC, such as the Wnt/β-catenin and extracellular-signal-regulated kinase (ERK) pathways, which are closely associated with cancer initiation, metastasis, inflammation, and chemo-/radio-resistance. Therefore, NO/NOS have been proposed as promising targets in the regulation of CRC carcinogenesis. Clinically relevant NO-donating agents have been developed for CRC therapy to deliver a high level of NO to tumor sites. Notably, inducible NOS (iNOS) is ubiquitously over-expressed in inflammatory-associated colon cancer. The development of iNOS inhibitors contributes to targeted therapies for CRC with clinical benefits. In this review, we summarize the multifaceted mechanisms of NO-mediated networks in several hallmarks of CRC. We review the clinical manifestation and limitations of NO donors and NOS inhibitors in clinical trials. We also discuss the possible directions of NO/NOS therapies in the immediate future.

Effects of nitric oxide donor on the lung functions in a saline lavage-induced model of ARDS

Acute respiratory distress syndrome (ARDS) is characterized by acute hypoxemia, neutrophil-mediated inflammation, and lung edema formation. Whereas lung damage might be alleviated by nitric oxide (NO), goal of this study was to evaluate if intratracheal NO donor S-nitroso-N-acetylpenicillamine (SNAP) can positively influence the lung functions in experimental model of ARDS. New Zealand rabbits with respiratory failure induced by saline lavage (30 ml/kg, 9+/-3 times) were divided into: ARDS group without therapy, ARDS group treated with SNAP (7 mg/kg i.t.), and healthy Control group. During 5 h of ventilation, respiratory parameters (blood gases, ventilatory pressures) were estimated. After anesthetics overdosing, left lung was saline-lavaged and cell count, cell viability and protein content in bronchoalveolar lavage fluid (BALF) were measured. Right lung tissue was used for estimation of wet/dry weight ratio, concentration of NO metabolites, and histomorphological investigation. Repetitive lung lavage induced lung injury, worsened gas exchange, and damaged alveolar-capillary membrane. Administration of SNAP reduced cell count in BALF, lung edema formation, NO metabolites, and histopathological signs of injury, and improved respiratory parameters. Treatment with intratracheal SNAP alleviated lung injury and edema and improved lung functions in a saline-lavaged model of ARDS suggesting a potential of NO donors also for patients with ARDS.

Molecular Magnetic Resonance Imaging of Nitric Oxide in Biological Systems

Detection of nitric oxide (NO) in biological systems is challenging due to both physicochemical properties of NO and limitations of current imaging modalities and probes. Magnetic resonance imaging (MRI) could be applied for studying NO in living tissue with high spatiotemporal resolution, but there is still a need for chemical agents that effectively sensitize MRI to biological NO production. To develop a suitable probe, we studied the interactions between NO and a library of manganese complexes with various oxidation states and molecular structures. Among this set, the manganese(III) complex with N,N'-(1,2-phenylene)bis(5-fluoro-2-hydroxybenzamide) showed favorable changes in longitudinal relaxivity upon addition of NO-releasing chemicals in vitro while also maintaining selectivity against other biologically relevant reactive nitrogen and oxygen species, making it a suitable NO-responsive contrast agent for T₁-weighted MRI. When loaded with this compound, cells ectopically expressing nitric oxide synthase (NOS) isoforms showed MRI signal decreases of over 20% compared to control cells and were also responsive to NOS inhibition or calcium-dependent activation. The sensor could also detect endogenous NOS activity in antigen-stimulated macrophages and in a rat model of neuroinflammation in vivo. Given the key role of NO and associated reactive nitrogen species in numerous physiological and pathological processes, MRI approaches based on the new probe could be broadly beneficial for studies of NO-related signaling in living subjects.

The Role of C-8 OH on the Antioxidant Activity of Norwogonin and Isowogonin

In the present study, the antioxidant property of 4 flavones (moslosooflavone, wogonin, isowogonin, and norwogonin) was evaluated using 6 different assays: 1,1-diphenyl-2-picrylhydrazyl (DPPH·), superoxide (O2 •−), and nitric oxide (NO) radical scavenging assays, ferrous iron chelation, reducing power, and total antioxidant capacity. The 4 flavones exhibited antioxidant activities with decreasing order as norwogonin > isowogonin >> wogonin> moslosooflavone. The present results demonstrated that norwogonin and isowogonin exhibited excellent antioxidant activity, which was mainly based on the presence of C-8 hydroxyl group.

Fractional Exhaled Nitric Oxide (FENO) in the management of asthma: a position paper of the Italian Respiratory Society (SIP/IRS) and Italian Society of Allergy, Asthma and Clinical Immunology (SIAAIC)

Asthma prevalence in Italy is on the rise and is estimated to be over 6% of the general population. The diagnosis of asthma can be challenging and elusive, especially in children and the last two decades has brought evidences that asthma is not a single disease but consists of various phenotypes. Symptoms can be underestimated by the patient or underreported to the clinician and physical signs can be scanty. Usual objective measures, like spirometry, are necessary but sometimes not significant. Despite proper treatment, asthma can be a very severe condition (even leading to death), however new drugs have recently become available which can be very effective in its control. Since asthma is currently thought to be caused by inflammation, a direct measure of the latter can be of paramount importance. For this purpose, the measurement of Fractional Exhaled Nitric Oxide (FE_NO) has been used since the early years of the current century as a non-invasive, easy-to-assess tool useful for diagnosing and managing asthma. This SIP-IRS/SIAAIC Position Paper is a narrative review which summarizes the evidence behind the usefulness of FE_NO in the diagnosis, management and phenotypization of asthma.

Norvaline Reduces Blood Pressure and Induces Diuresis in Rats with Inherited Stress-Induced Arterial Hypertension

Growing evidence suggests that increased arginase activity affects vital bioprocesses in various systems and universally mediates the pathogenesis of numerous metabolic diseases. The adverse effects of arginase are associated with a severe decline in L-arginine bioavailability, which leads to nitric oxide synthase substrate insufficiency, uncoupling, and, eventually, superoxide anion generation and substantial reduction of nitric oxide (NO) synthesis. In cooperation, it contributes to chronic oxidative stress and endothelial dysfunction, which might lead to hypertension and atherosclerosis. Recent preclinical investigations point arginase as a promising therapeutic target in ameliorating metabolic and vascular dysfunctions. In the present study, adult rats with inherited stress-induced arterial hypertension (ISIAH) were used as a model of hypertension. Wistar rats served as normotensive controls. Experimental animals were intraperitoneally administered for seven days with nonproteinogenic amino acid L-norvaline (30 mg/kg/day), which is a potent arginase inhibitor, or with the vehicle. Blood pressure (BP), body weight, and diuresis were monitored. The changes in blood and urine levels of creatinine, urea, and NO metabolites were analyzed. We observed a significant decline in BP and induced diuresis in ISIAH rats following the treatment. The same procedure did not affect the BP of control animals. Remarkably, the treatment had no influence upon glomerular filtration rate in two experimental groups, just like the daily excretion of creatinine and urea. Conversely, NO metabolite levels were amplified in normotonic but not in hypertensive rats following the treatment. The data indicate that L-norvaline is a potential antihypertensive agent and deserves to be clinically investigated. Moreover, we suggest that changes in blood and urine are causally related to the effect of L-norvaline upon BP regulation.

Remifentanil Protects against Lipopolysaccharide-Induced Inflammation through PARP-1/NF-κB Signaling Pathway

Sepsis is a leading cause of death in patients with severe infection worldwide. Remifentanil is an ultra-short-acting, potent opioid analgesic. In the study, we aimed to investigate the role and underlying mechanism of remifentanil in lipopolysaccharide- (LPS-) induced inflammation in human aortic endothelial cells (HAECs). HAECs were pretreated with phosphate-buffered saline (PBS) or remifentanil (2.5 μM) for 30 min, then stimulated by LPS (10 μg/ml) for another 24 h. Poly(ADP-ribose) polymerase 1 (PARP-1) was inhibited by small interfering RNA (siRNA). Superoxide anion production and DNA damage were analyzed by dihydroethidium (DHE) staining and comet assay. The inducible nitric oxide synthase (iNOS), intercellular adhesion molecule 1 (ICAM-1), PARP-1, poly(ADP-ribose) (PAR), and nuclear factor-kappa B p65 (NF-κB p65) expressions were analyzed by RT-PCR or western blotting analysis. NF-κB p65 nuclear translocation was assessed by immunofluorescence. Compared with the control group, pretreatment with remifentanil significantly reduced superoxide anion production and DNA damage, with downregulation of iNOS, ICAM-1, and PARP-1 expressions as well as PAR expression. Moreover, pretreatment with PARP-1 siRNA or remifentanil inhibited LPS-induced NF-κB p65 expression and nuclear translocation. Remifentanil reduced LPS-induced inflammatory response through PARP-1/NF-κB signaling pathway. Remifentanil might be an optimal choice of analgesia in septic patients.

Dietary intake as a predictor for all-cause mortality in hemodialysis subjects (NUGE-HD study)

This study aimed to identify the factors capable of mortality prediction in patients on hemodialysis, using a prospective cohort with three years of follow-up. We hypothesized that lack of clinical-metabolic control, impairment of nutritional status, and inadequate food consumption are risk factors for mortality in this population. This is a longitudinal study on a non-probabilistic sample of 85 adults and elderly patients undergoing hemodialysis, aged ≥ 18 years (66.0% male, 61.6±13.7 years). Data on anthropometric, biomarkers, body composition and food intake were obtained. Predictors of mortality were evaluated using Cox regression analysis. During the three years follow-up, 16 patients (18.8%) died. We observed that age (HR = 1.319, CI 95% = 1.131–1.538), calcium-phosphorus product (HR = 1.114, CI 95% = 1.031–1.205), ferritin (HR = 1.001, CI 95% = 1.001–1.002), nitric oxide (HR = 1.082, CI 95% = 1.006–1.164), and vitamin C intake (HR = 1.005, CI 95% = 1.001–1.009) were positively associated with mortality. Serum iron (HR = 0.717, CI 95% = 0.567–0.907), triceps skinfold thickness (HR = 0.704, CI 95% = 0.519–0.954), lean mass (HR = 0.863, CI 95% = 0.787–0.945), and the ratio of dietary monounsaturated/polyunsaturated fat (HR = 0.022, CI 95% = 0.001–0.549) were independent negative predictors of mortality. Our results suggest that dietary intake is also a predictor of mortality in patients on hemodialysis, besides nutritional status, body composition, oxidative stress, inflammation, and bone metabolism, indicating the importance of evaluation of these factors altogether for better prognosis.

Effects of infection of MRSA on the expression and activity of renal cytochrome P450s in mice

Methicillin-resistant Staphylococcus aureus (MRSA) leads to serious infections, but it is not known whether it changes the expression of kidney drug metabolizing enzymes during infection. The mice were infected with different doses of MRSA and the oxidative stress and inflammation levels in the kidney were examined. The mRNA expression and activity of cytochrome P450 enzyme was analysed. Mice infected with high levels of MRSA showed a decrease in renal antioxidant capability and an elevated level of oxidative metabolites, which was accompanied by the release of inflammatory cytokines. The levels of interleukin 1β, tumour necrosis factor alpha, and macrophage inflammatory protein-1α were significantly increased along with the levels of nitric oxide and malondialdehyde. On day 7, mRNA expression of Cyp1a2, 2d22, and 3a11 were decreased by the high level of MRSA, but the low level of MRSA increased their expressions. Cyp2e1 mRNA expression was increased by MRSA in the kidney of mice. High dose of MRSA infection increased the oxidative stress and inflammatory response in mouse kidney, leading to the decrease in the expression of renal drug-metabolizing enzymes and no recovery within 7 days.

The Emerging Role of Electrophiles as a Key Regulator for Endoplasmic Reticulum (ER) Stress

The unfolded protein response (UPR) is activated by the accumulation of misfolded proteins in the endoplasmic reticulum (ER), which is called ER stress. ER stress sensors PERK, IRE1, and ATF6 play a central role in the initiation and regulation of the UPR; they inhibit novel protein synthesis and upregulate ER chaperones, such as protein disulfide isomerase, to remove unfolded proteins. However, when recovery from ER stress is difficult, the UPR pathway is activated to eliminate unhealthy cells. This signaling transition is the key event of many human diseases. However, the precise mechanisms are largely unknown. Intriguingly, reactive electrophilic species (RES), which exist in the environment or are produced through cellular metabolism, have been identified as a key player of this transition. In this review, we focused on the function of representative RES: nitric oxide (NO) as a gaseous RES, 4-hydroxynonenal (HNE) as a lipid RES, and methylmercury (MeHg) as an environmental organic compound RES, to outline the relationship between ER stress and RES. Modulation by RES might be a target for the development of next-generation therapy for ER stress-associated diseases.

l-NIL prevents the ischemia and reperfusion injury involving TLR-4, GST, clusterin, and NFAT-5 in mice

On renal ischemia-reperfusion (I/R) injury, recruitment of neutrophils during the inflammatory process promotes local generation of oxygen and nitrogen reactive species, which, in turn, are likely to exacerbate tissue damage. The mechanism by which inducible nitric oxide synthase (iNOS) is involved in I/R has not been elucidated. In this work, the selective iNOS inhibitor l- N6-(1-iminoethyl)lysine (l-NIL) and the NOS substrate l-arginine were employed to understand the role of NOS activity on the expression of particular target genes and the oxidative stress elicited after a 30-min of bilateral renal ischemia, followed by 48-h reperfusion in Balb/c mice. The main findings of the present study were that pharmacological inhibition of iNOS with l-NIL during an I/R challenge of mice kidney decreased renal injury, prevented tissue loss of integrity, and improved renal function. Several novel findings regarding the molecular mechanism by which iNOS inhibition led to these protective effects are as follows: 1) a prevention of the I/R-related increase in expression of Toll-like receptor 4 (TLR-4), and its downstream target, IL-1β; 2) reduced oxidative stress following the I/R challenge; noteworthy, this study shows the first evidence of glutathione S-transferase (GST) inactivation following kidney I/R, a phenomenon fully prevented by iNOS inhibition; 3) increased expression of clusterin, a survival autophagy component; and 4) increased expression of nuclear factor of activated T cells 5 (NFAT-5) and its target gene aquaporin-1. In conclusion, prevention of renal damage following I/R by the pharmacological inhibition of iNOS with l-NIL was associated with the inactivation of proinflammatory pathway triggered by TLR-4, oxidative stress, renoprotection (autophagy inactivation), and NFAT-5 signaling pathway.

Crosstalk Between Nitric Oxide and Endocannabinoid Signaling Pathways in Normal and Pathological Placentation

Endocannabinoids are a group of endogenous lipid mediators that act as ligands of cannabinoid and vanilloid receptors, activating multiple signal transduction pathways. Together with enzymes responsible for their synthesis and degradation, these compounds constitute the endocannabinoid system (ECS), which is involved in different physiological processes in reproduction. The placenta, which is essential for the success of gestation and optimal fetal growth, undergoes constant tissue remodeling. ECS members are expressed in trophoblast cells, and current evidence suggests that this system is involved in placental development, apoptosis, and syncytialization. Impairment of endocannabinoid signaling has been associated with several pathological conditions such as intrauterine growth restriction and preeclampsia. Both clinical entities are characterized by dysregulation on vascular perfusion where nitrergic system performs a pivotal role. Nitric oxide (NO) is a potent local vasodepressor that exerts a critical role in the regulation of hemodynamic flow, contributing to the maintenance of low vascular resistance in the feto-placental circulation. NO production could be affected by different factors and growing evidence suggests that the endocannabinoid mediators may regulate nitrergic signaling. Herein, we review emerging knowledge supporting ECS-mediated regulation of NO production in normal placentation. Finally, we discuss how alterations in these systems could affect homoeostasis and contribute to the occurrence of placental-mediated pregnancy complications. Given the impact on women and perinatal heath, we will focus on current knowledge regarding the effects of ECS on nitrergic system in normal and pathological placentation.

Physiology of nitric oxide in the respiratory system

Nitric oxide (NO) is an important endogenous neurotransmitter and mediator. It participates in regulation of physiological processes in different organ systems including airways. Therefore, it is important to clarify its role in the regulation of both airway and vascular smooth muscle, neurotransmission and neurotoxicity, mucus transport, lung development and in the. surfactant production. The bioactivity of NO is highly variable and depends on many factors: the presence and activity of NO-producing enzymes, activity of competitive enzymes (e.g. arginase), the amount of substrate for the NO production, the presence of reactive oxygen species and others. All of these can change NO primary physiological role into potentially harmful. The borderline between them is very fragile and in many cases not entirely clear. For this reason, the research focuses on a comprehensive understanding of NO synthesis and its metabolic pathways, genetic polymorphisms of NO synthesizing enzymes and related effects. Research is also motivated by frequent use of exhaled NO monitoring in the clinical manifestations of respiratory diseases. The review focuses on the latest knowledge about the production and function of this mediator and understanding the basic physiological processes in the airways.

Endothelial dysfunction: comparative evaluation of ultrasound dopplerography, laser dopplerflowmetry and direct monitoring of arterial pressure for conducting pharmacological tests in rats

Introduction: The importance of the problem of endothelial dysfunction makes it essential to improve approaches to its evaluation. Due to the high diagnostic potential of ultrasound dopplerography, this method is promising in the study of endothelial function.

Objective:To study endothelial function when conducting vascular pharmacological tests in the norm and with the blockade of the nitric oxide synthesis by means of the ultrasound method for examining the central blood flow velocity in the femoral artery of the rat in comparison with changes of systemic haemodynamics and microcirculation velocity in the medial vastus muscle using laser Doppler flowmetry.

Materials and methods: In the norm and in conditions of deficiency of endogenous nitric oxide, three methods for assessing haemodynamics were used simultaneously: 1) dopplerography using the ultrasoundDoppler system (Minimax-Doppler-K, St Petersburg); 2) laser doppler flowmetry using the TDS144 sensor (Biopac MP-150, USA); 3) recording the arterial pressure in the carotid artery by means of a catheter connected to a TDS-160-A sensor (Biopac MP-150, USA). To study the vasoregulatory function of the endothelium under conditions of multicomponent monitoring of haemodynamics, functional vascular tests were performed using acetylcholine and sodium nitroprusside.

Results: Quantification of endothelial dysfunction when conducting pharmacological tests with endothelium-dependent (acetylcholine) and endothelium-independent (sodium nitroprusside) vasodilation is most significant when calculating the coefficient reflecting the ratio of areas of vascular response. Theblood flow velocity parameters recorded by using Doppler ultrasound showed a high correlation level with both arterial pressure and with a linear microcirculation rate. The most comprehensive dopplerographic indices for evaluating the function of the endothelium by conducting pharmacological tests in the norm and in the case of pathology, are the estimated systolic-diastolic difference in blood flow velocities (ΔVs-Vd) in the femoral artery. The study of the endothelial function when conducting vascular pharmacological tests in the norm and with nitric oxide synthesis blockaded, by means of the ultrasound examination of the central blood flow velocity in the femoral artery, is comparable to changing the haemodynamics parameters as well as velocity in microcirculation of the medial vastus muscle using laser Doppler flowmetry.

Conclusions: Ultrasonic dopplerography using the Minimax-Doppler-K device reflects the systemic and local vascular response to the administration of vasodilators both in the norm and with the blockade of the nitric oxide synthesis and makes it possible to conduct an informative assessment of the endothelial function.

Methylene Blue for Acute Septic Cardiomyopathy in a Burned Patient

The objective of this case summary was to describe the use of methylene blue (MB) in a burned patient with acute septic cardiomyopathy. A 60-year-old Caucasian man was admitted to the Burn Intensive Care Unit with 45% TBSA burns after a house explosion. During the course of his care, he experienced hypotension that was refractory to fluid therapy and vasoactive medications. Echocardiography and right heart catheterization showed new acute systolic dysfunction with concurrent elevated systemic vascular resistance (SVR). High-dose inotropic agents did not improve cardiac function, and septic shock rendered him a poor candidate for mechanical intra-aortic balloon pump support. MB was administered to sensitize the myocardium to catecholamines and improve contractility with the goal of weaning the other vasoactive medications and diuresing for afterload reduction when hemodynamic stability was achieved. MB has been described in critical care medicine predominately for vasoplegia after cardiopulmonary bypass and vasodilatory septic shock., Our patient had acute septic cardiomyopathy that was refractory to standard pharmacologic approaches to inotropy with concurrent elevated SVR. Hypothesizing the differential temporal effect of inducible nitric oxide synthase on the vasculature and myocardium, we administered MB to improve contractility and support the impending vasodilatory effects of distributive shock. Although MB is not a new drug, the application for septic cardiomyopathy with a supranormal SVR is a unique application. Because of the risk profile associated with MB, we recommend drug monitoring utilizing serial echocardiography and/or right heart catheterization.

Role of Oxidative Stress and Mitochondrial Dysfunction in Sepsis and Potential Therapies

Sepsis is one of the most important causes of death in intensive care units. Despite the fact that sepsis pathogenesis remains obscure, there is increasing evidence that oxidants and antioxidants play a key role. The imbalance of the abovementioned substances in favor of oxidants is called oxidative stress, and it contributes to sepsis process. The most important consequences are vascular permeability impairment, decreased cardiac performance, and mitochondrial malfunction leading to impaired respiration. Nitric oxide is perhaps the most important and well-studied oxidant. Selenium, vitamin C, and 3N-acetylcysteine among others are potential therapies for the restoration of redox balance in sepsis. Results from recent studies are promising, but there is a need for more human studies in a clinical setting for safety and efficiency evaluation.

Aripiprazole prevents renal ischemia/reperfusion injury in rats, probably through nitric oxide involvement

Renal ischemia/reperfusion (I/R) injury is strongly related to morbidity and mortality. Oxidative stress, inflammation, and apoptosis play key roles in renal dysfunction following renal I/R. Aripiprazole is an atypical antipsychotic which used for the treatment of schizophrenia and bipolar disorder. Recent studies have reported aripiprazole as displaying certain anti-inflammatory effects. Regarding the underlying mechanisms of renal ischemia-reperfusion, therefore, nephroprotective effects might be predicted to be seen with aripiprazole. I/R injury was induced by bilateral clamping of the renal pedicles (45min) followed by reperfusion (24h). The mechanism of aripiprazole-mediated nephroprotection was explored by a combined use of aripiprazole and L-NAME (non-selective nitric oxide synthase inhibitor). Animals were given aripiprazole (2.5, 5, 10 and 20mg/kg) intraperitoneally, 30min before ischemia. L-NAME was administered before the aripiprazole injection. Serum creatinine and blood urea nitrogen were assessed after 24h of reperfusion. Serum levels of malondialdehyde (MDA), TNF-α and IL-1β were measured for rats treated with aripiprazole. The extent of necrosis was measured by the stereology method. Ischemia/reperfusion caused significant renal dysfunction and marked renal injury. Aripiprazole reduced creatinine and blood urea nitrogen. Serum levels of MDA, IL-1β and TNF-α were significantly lower in the aripiprazole group. Aripiprazole treatment also decreased the volume of kidney necrosis. The administration of L-NAME reversed the renoprotective effect of aripiprazole on BUN and creatinine, but enhanced the anti-necrotic effect of aripiprazole. The results show that a single dose of aripiprazole significantly improved renal function following ischemia/reperfusion injury - probably through the involvement of nitric oxide.

Role of nitric oxide in liver transplantation: Should it be routinely used?

Ischemia-reperfusion injury (IRI) continues to be a major contributor to graft dysfunction, thus supporting the need for therapeutic strategies focused on minimizing organ damage especially with growing numbers of extended criteria grafts being utilized which are more vulnerable to cold and warm ischemia. Nitric oxide (NO·) is highly reactive gaseous molecule found in air and regarded as a pollutant. Not surprising, it is extremely bioactive, and has been demonstrated to play major roles in vascular homeostasis, neurotransmission, and host defense inflammatory reactions. Under conditions of ischemia, NO· has consistently been demonstrated to enhance microcirculatory vasorelaxation and mitigate pro-inflammatory responses, making it an excellent strategy for patients undergoing organ transplantation. Clinical studies designed to test this hypothesis have yielded very promising results that includes reduced hepatocellular injury and enhanced graft recovery without any identifiable complications. By what means NO· facilitates extra-pulmonary actions is up for debate and speculation. The general premise is that they are NO· containing intermediates in the circulation, that ultimately mediate either direct or indirect effects. A plethora of data exists explaining how NO·-containing intermediate molecules form in the plasma as S-nitrosothiols (e.g., S-nitrosoalbumin), whereas other compelling data suggest nitrite to be a protective mediator. In this article, we discuss the use of inhaled NO· as a way to protect the donor liver graft against IRI in patients undergoing liver transplantation.

Hydrogen sulfide, an enhancer of vascular nitric oxide signaling: mechanisms and implications

Nitric oxide (NO) vascular signaling has long been considered an independent, self-sufficient pathway. However, recent data indicate that the novel gaseous mediator, hydrogen sulfide (H₂S), serves as an essential enhancer of vascular NO signaling. The current article overviews the multiple levels at which this enhancement takes place. The first level of interaction relates to the formation of biologically active hybrid S/N species and the H₂S-induced stimulation of NO release from its various stable "pools" (e.g., nitrite). The next interactions occur on the level of endothelial calcium mobilization and PI3K/Akt signaling, increasing the specific activity of endothelial NO synthase (eNOS). The next level of interaction occurs on eNOS itself; H₂S directly interacts with the enzyme: sulfhydration of critical cysteines stabilizes it in its physiological, dimeric state, thereby optimizing eNOS-derived NO production and minimizing superoxide formation. Yet another level of interaction, further downstream, occurs at the level of soluble guanylate cyclase (sGC): H₂S stabilizes sGC in its NO-responsive, physiological, reduced form. Further downstream, H₂S inhibits the vascular cGMP phosphodiesterase (PDE5), thereby prolonging the biological half-life of cGMP. Finally, H₂S-derived polysulfides directly activate cGMP-dependent protein kinase (PKG). Taken together, H₂S emerges an essential endogenous enhancer of vascular NO signaling, contributing to vasorelaxation and angiogenesis. The functional importance of the H₂S/NO cooperative interactions is highlighted by the fact that H₂S loses many of its beneficial cardiovascular effects when eNOS is inactive.

Evaluation of the presence of reduced nicotinamide adenine dinucleotide phosphate in bacterial metabolites used as immunostimulators and its role in nitric oxide induction

Bacterial metabolites that act as immunostimulators have aroused interest because of their therapeutic potential in several immune disorders. These metabolites are complex, heterogeneous, and comprise numerous immune-boosting biomolecules. To better understand their immune stimulatory properties, characterization of their components is essential. An ether extract of metabolites from nine bacterial species was analyzed for the presence of reduced nicotinamide adenine dinucleotide phosphate (NADPH) or other fluorophores. This metabolite in combination with bile lipids is a licensed immune stimulatory drug. Excitation of the extract at 340 nm resulted in fluorescence with an emission maximum of around 410 nm, which is fairly specific for NADH and NADPH. Reverse-phase-HPLC and electro-spray ionization-mass analysis confirmed the presence of NADPH in the bacterial metabolites. Quantification by glutathione reductase assay indicated 11.90 ± 0.01 µM of NADPH in the metabolites. Further characterization of the individual bacterial extracts of the metabolite confirmed the presence of NADPH. Subsequently, studies were performed to evaluate the role/s of NADPH in immune-stimulatory drugs. NADPH is known to be involved in production of nitric oxide (NO), which has versatile roles in the immune system. The biological function of NADPH in NO induction by RAW 264.7 (mouse macrophage) cells was evaluated and it was found that bacterial NADPH has a significant role in inducing NO and that NADPH from individual bacterial extracts is capable of inducing NO. Investigation on the stability and biological potency of NADPH in bacterial metabolites is important because of NADPH's wide therapeutic applications, most of which are associated with its role in NO induction.

Gasotransmitters in cancer: from pathophysiology to experimental therapy

The three endogenous gaseous transmitters - nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H2S) - regulate a number of key biological functions. Emerging data have revealed several new mechanisms for each of these three gasotransmitters in tumour biology. It is now appreciated that they show bimodal pharmacological character in cancer, in that not only the inhibition of their biosynthesis but also elevation of their concentration beyond a certain threshold can exert anticancer effects. This Review discusses the role of each gasotransmitter in cancer and the effects of pharmacological agents - some of which are in early-stage clinical studies - that modulate the levels of each gasotransmitter. A clearer understanding of the pharmacological character of these three gases and the mechanisms underlying their biological effects is expected to guide further clinical translation.

Effects of Artemetin on Nitric Oxide Release and Protection against Peroxidative Injuries in Porcine Coronary Artery Endothelial Cells

Artemetin is one of the main components of Achillea millefolium L. and Artemisia absinthium, which have long been used for the treatment of various diseases. To date, however, available information about protective effects of their extracts on the cardiovascular system is scarce. Therefore, we planned to analyze the effects of artemetin on nitric oxide (NO) release and the protection exerted against oxidation in porcine aortic endothelial (PAE) cells. In PAE, we examined the modulation of NO release caused by artemetin and the involvement of muscarinic receptors, β2-adrenoreceptors, estrogenic receptors (ER), protein-kinase A, phospholipase-C, endothelial-NO-synthase (eNOS), Akt, extracellular-signal-regulated kinases 1/2 (ERK1/2) and p38 mitogen activated protein kinase (p38 MAPK). Moreover, in cells treated with hydrogen peroxide, the effects of artemetin were examined on cell survival, glutathione (GSH) levels, apoptosis, mitochondrial membrane potential and transition pore opening. Artemetin increased eNOS-dependent NO production by the involvement of muscarinic receptors, β2-adrenoreceptors, ER and all the aforementioned kinases. Furthermore, artemetin improved cell viability in PAE that were subjected to peroxidation by counteracting GSH depletion and apoptosis and through the modulation of mitochondrial function. In conclusion, artemetin protected endothelial function by acting as antioxidant and antiapoptotic agent and through the activation of ERK1/2 and Akt. Copyright © 2015 John Wiley & Sons, Ltd.

Levosimendan inhibits peroxidation in hepatocytes by modulating apoptosis/autophagy interplay

Background

Levosimendan protects rat liver against peroxidative injuries through mechanisms related to nitric oxide (NO) production and mitochondrial ATP-dependent K (mitoK_ATP) channels opening. However, whether levosimendan could modulate the cross-talk between apoptosis and autophagy in the liver is still a matter of debate. Thus, the aim of this study was to examine the role of levosimendan as a modulator of the apoptosis/autophagy interplay in liver cells subjected to peroxidation and the related involvement of NO and mitoK_ATP.

Methods and Findings

In primary rat hepatocytes that have been subjected to oxidative stress, Western blot was performed to examine endothelial and inducible NO synthase isoforms (eNOS, iNOS) activation, apoptosis/autophagy and survival signalling detection in response to levosimendan. In addition, NO release, cell viability, mitochondrial membrane potential and mitochondrial permeability transition pore opening (MPTP) were examined through specific dyes. Some of those evaluations were also performed in human hepatic stellate cells (HSC). Pre-treatment of hepatocytes with levosimendan dose-dependently counteracted the injuries caused by oxidative stress and reduced NO release by modulating eNOS/iNOS activation. In hepatocytes, while the autophagic inhibition reduced the effects of levosimendan, after the pan-caspases inhibition, cell survival and autophagy in response to levosimendan were increased. Finally, all protective effects were prevented by both mitoK_ATP channels inhibition and NOS blocking. In HSC, levosimendan was able to modulate the oxidative balance and inhibit autophagy without improving cell viability and apoptosis.

Conclusions

Levosimendan protects hepatocytes against oxidative injuries by autophagic-dependent inhibition of apoptosis and the activation of survival signalling. Such effects would involve mitoK_ATP channels opening and the modulation of NO release by the different NOS isoforms. In HSC, levosimendan would also play a role in cell activation and possible evolution toward fibrosis. These findings highlight the potential of levosimendan as a therapeutic agent for the treatment or prevention of liver ischemia/reperfusion injuries.

Potential pharmacokinetic interactions of therapeutic cytokines or cytokine modulators on small-molecule drugs: mechanistic understanding via studies using in vitro systems

The potential pharmacokinetic interactions between macromolecules and small-molecule drugs have received more and more attention with the increasing development of macromolecule therapeutics. Studies have shown that cytokines can differentially modulate drug-metabolizing enzymes and transporters, which raises concerns on the potential interactions of therapeutic cytokines and cytokine modulators on the disposition of small-molecule drugs. Although many in vitro studies have been conducted to characterize the effects of cytokines on drug-metabolizing enzymes and transporters, these studies were limited to only a handful of cytokines, such as interleukin-1 (IL-1), IL-6, tumor necrosis factor-α, and interferon. It is also challenging to translate these in vitro results to in vivo. In addition, information on the impact of cytokine modulators on drug-metabolizing enzymes and transporters is rather limited. More research is needed in this area. The present review is to provide a summary of the in vitro findings on the pharmacokinetic interactions of therapeutic cytokines and cytokine modulators on small-molecule drugs. Discussion on current challenges in assessing these interactions is also included.

The role of oxidative stress during inflammatory processes

Abstract The production of various reactive oxidant species in excess of endogenous antioxidant defense mechanisms promotes the development of a state of oxidative stress, with significant biological consequences. In recent years, evidence has emerged that oxidative stress plays a crucial role in the development and perpetuation of inflammation, and thus contributes to the pathophysiology of a number of debilitating illnesses, such as cardiovascular diseases, diabetes, cancer, or neurodegenerative processes. Oxidants affect all stages of the inflammatory response, including the release by damaged tissues of molecules acting as endogenous danger signals, their sensing by innate immune receptors from the Toll-like (TLRs) and the NOD-like (NLRs) families, and the activation of signaling pathways initiating the adaptive cellular response to such signals. In this article, after summarizing the basic aspects of redox biology and inflammation, we review in detail the current knowledge on the fundamental connections between oxidative stress and inflammatory processes, with a special emphasis on the danger molecule high-mobility group box-1, the TLRs, the NLRP-3 receptor, and the inflammasome, as well as the transcription factor nuclear factor-κB.

Inducible nitric oxide synthase inhibition reverses pulmonary arterial dysfunction in lung transplantation

BACKGROUND

Ischemia-reperfusion injury (IRI) after lung transplantation remains a significant cause of morbidity and mortality. Lung IRI induces nitric oxide synthesis (iNOS) and reactive nitrogen species, decreasing nitric oxide bioavailability. We hypothesized that ischemia-induced iNOS intensifies with reperfusion and contributes to IRI-induced pulmonary arterial regulatory dysfunction, which may lead to early graft failure and cause pulmonary edema. The aim of this study was to determine whether ischemia-reperfusion alters inducible and endothelial nitric oxide synthase expression, potentially affecting pulmonary perfusion. We further evaluated the role of iNOS in post-transplantation pulmonary arterial disorder.

METHODS

We randomized 32 Sprague-Dawley rats into two groups. The control group was given a sham operation whilst the experimental group received orthotropic lung transplants with a modified three-cuff technique. Changes in lung iNOS, and endothelial nitric oxide synthase expression were measured after lung transplantation by enzyme-linked immunosorbent assay (ELISA). Vasoconstriction in response to exogenous phenylephrine and vasodilation in response to exogenous acetylcholine of pulmonary arterial rings were measured in vitro as a measure of vascular dysfunction. To elucidate the roles of iNOS in regulating vascular function, an iNOS activity inhibitor (N6-(1-iminoethyl)-L-lysine, L-NIL) was used to treat isolated arterial rings. In order to test whether iNOS inhibition has a therapeutic effect, we further used L-NIL to pre-treat transplanted lungs and then measured post-transplantation arterial responses.

RESULTS

Lung transplantation caused upregulation of iNOS expression. This was also accompanied by suppression of both vasoconstriction and vasodilation of arterial rings from transplanted lungs. Removal of endothelium did not interfere with the contraction of pulmonary arterial rings from transplanted lungs. In contrast, iNOS inhibition rescued the vasoconstriction response to exogenous phenylephrine of pulmonary arterial rings from transplanted lungs. In addition, lung transplantation led to suppression of PaO2/FiO2 ratio, increased intrapulmonary shunt (Q s/Q t), and increase of lung wet to dry ratio (W/D), malondialdehyde and myeloperoxidase levels, all of which were reversed upon iNOS inhibition. Furthermore, inhibition of iNOS significantly rescued vascular function and alleviated edema and inflammatory cell infiltration in the transplanted lung.

CONCLUSIONS

Our data suggest that lung transplantation causes upregulation of iNOS expression, and pulmonary vascular dysfunction. iNOS inhibition reverses the post-transplantational pulmonary vascular dysfunction.