Carbon Monoxide and Nitric Oxide as Examples of the Youngest Class of Transmitters

Prognostic value of plasma secretoneurin concentration in patients with heart failure with reduced ejection fraction in one-year follow-up

BACKGROUND

This is the first study to examine the clinical utility of measuring plasma secretoneurin (SN) levels in patients with heart failure with reduced ejection fraction (HFrEF), as a predictor of unplanned hospitalization, and all-cause mortality independently, and as a composite endpoint at one-year follow-up.

METHODS

The study group includes 124 caucasian patients in New York Heart Association (NYHA) classes II to IV. Plasma SN concentrations were statistically analyzed in relation to sex, age, BMI, etiology of HFrEF, pharmacotherapy, clinical, laboratory and echocardiographic parameters. Samples were collected within 24 h of admission to the hospital.

KEY RESULTS

In the 12-month follow-up, high SN levels were noted for all three endpoints.

CONCLUSIONS

SN positively correlates with HF severity measured by NYHA classes and proves to be a useful prognostic parameter in predicting unplanned hospitalizations and all-cause mortality among patients with HFrEF. Patients with high SN levels may benefit from systematic follow-up and may be candidates for more aggressive treatment.

Electrochemical Detection of Gasotransmitters: Status and Roadmap

Gasotransmitters, including nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S), are a class of gaseous, endogenous signaling molecules that interact with one another in the regulation of critical cardiovascular, immune, and neurological processes. The development of analytical sensing mechanisms for gasotransmitters, especially multianalyte mechanisms, holds vast importance and constitutes a growing area of study. This review provides an overview of electrochemical sensing mechanisms with an emphasis on opportunities in multianalyte sensing. Electrochemical methods demonstrate good sensitivity, adequate selectivity, and the most well-developed potential for the multianalyte detection of gasotransmitters. Future research will likely address challenges with sensor stability and biocompatibility (i.e., sensor lifetime and cytotoxicity), sensor miniaturization, and multianalyte detection in biological settings.

Recent advances on the development of NO-releasing molecules (NORMs) for biomedical applications

Nitric oxide (NO) is an important biological messenger as well as a signaling molecule that participates in a broad range of physiological events and therapeutic applications in biological systems. However, due to its very short half-life in physiological conditions, its therapeutic applications are restricted. Efforts have been made to develop an enormous number of NO-releasing molecules (NORMs) and motifs for NO delivery to the target tissues. These NORMs involve organic nitrate, nitrite, nitro compounds, transition metal nitrosyls, and several nanomaterials. The controlled release of NO from these NORMs to the specific site requires several external stimuli like light, sound, pH, heat, enzyme, etc. Herein, we have provided a comprehensive review of the biochemistry of nitric oxide, recent advancements in NO-releasing materials with the appropriate stimuli of NO release, and their biomedical applications in cancer and other disease control.

Should Emollients Be Recommended for the Prevention of Atopic Dermatitis?-New Evidence and Current State of Knowledge

INTRODUCTION

Atopic dermatitis (AD) is a chronic, pruritic skin disease with complex pathogenesis, which affects about 43 million children aged 1-4 years. One of the most known methods of alleviating symptoms of AD is emollient treatment, which varies depending on formulation and additional active ingredients. There is some evidence that emollients could be used in AD prevention in high-risk children.

MATERIALS AND METHODS

A search of the literature from Cochrane Library, PubMed and Medline was conducted between August and September 2023 with the following keywords: "atopic dermatitis", "emollients", and "prevention". Only randomised clinical trials published in the last 5 years were included into the meta-analysis.

RESULTS

Considering the inclusion criteria only 11 randomized clinical trials were taken into account, and six of them proved lack of effect of emollients in the prevention of atopic dermatitis among neonates from AD risk groups.

CONCLUSIONS

Emollient treatment has a good safety profile and most of the ingredients used in formulations are nonirritant for sensitive newborn and infant skin. There is some evidence of the positive effects of emollient treatment in prevention of AD in predisposed populations. The relatively high cost of emollient treatment (vs regular infant skin-care routine) would support the necessity for further evaluation of their effectiveness in nonpredisposed populations.

Serelaxin Protects H9c2 Cardiac Myoblasts against Hypoxia and Reoxygenation-Induced Damage through Activation of AMP Kinase/Sirtuin1: Further Insight into the Molecular Mechanisms of the Cardioprotection of This Hormone

Serelaxin (RLX), namely the human recombinant Relaxin-2 hormone, protects the heart from ischemia/reperfusion (I/R)-induced damage due to its anti-inflammatory, anti-apoptotic and antioxidant properties. RLX acts by binding to its specific RXFP1 receptor whereby it regulates multiple transduction pathways. In this in vitro study, we offer the first evidence for the involvement of the AMP kinase/Sirtuin1 (AMPK/SIRT1) pathway in the protection by RLX against hypoxia/reoxygenation (H/R)-induced damage in H9c2 cells. The treatment of the H/R-exposed cells with RLX (17 nmol L-1) enhanced SIRT1 expression and activity. The inhibition of SIRT1 signaling with EX527 (10 µmol L-1) reduced the beneficial effect of the hormone on mitochondrial efficiency and cell apoptosis. Moreover, RLX upregulated the AMPK pathway, as shown by the increase in the expression of phospho-AMPK-activated protein. Finally, AMPK pathway inhibition by Compound C (10 and 20 μmol L-1) abrogated the increase in SIRT1 expression induced by RLX, thus suggesting the involvement of the AMPK pathway in this effect of RLX. These results strengthen the concept that RLX exerts its cardioprotective effects against H/R-induced injury through multiple pathways which also include AMPK/SIRT1. These new findings support the use of RLX or RLX-derived molecules as a promising therapeutic for those diseases in which I/R and oxidative stress play a pathogenic role.

Gasotransmitter Research Advances in Respiratory Diseases

Significance: Gasotransmitters are small gas molecules that are endogenously generated and have well-defined physiological functions. The most well-defined gasotransmitters currently are nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S), while other potent gasotransmitters include ammonia, methane, cyanide, hydrogen gas, and sulfur dioxide. Gasotransmitters play a role in various respiratory diseases such as asthma, chronic obstructive pulmonary disease, obstructive sleep apnea, lung infection, bronchiectasis, cystic fibrosis, primary ciliary dyskinesia, and COVID-19. Recent Advances: Gasotransmitters can act as biomarkers that facilitate disease diagnosis, indicate disease severity, predict disease exacerbation, and evaluate disease outcomes. They also have cell-protective properties, and many studies have been conducted to explore their pharmacological applications. Innovative drug donors and drug delivery methods have been invented to amplify their therapeutic effects. Critical Issues: In this article, we briefly reviewed the physiological and pathophysiological functions of some gasotransmitters in the respiratory system, the progress in detecting exhaled gasotransmitters, as well as innovative drugs derived from these molecules. Future Directions: The current challenge for gasotransmitter research includes further exploring their physiological and pathological functions, clarifying their complicated interactions, exploring suitable drug donors and delivery devices, and characterizing new members of gasotransmitters. Antioxid. Redox Signal. 40, 168-185.

Decoding signaling mechanisms: unraveling the targets of guanylate cyclase agonists in cardiovascular and digestive diseases

Soluble guanylate cyclase agonists and guanylate cyclase C agonists are two popular drugs for diseases of the cardiovascular system and digestive systems. The common denominator in these conditions is the potential therapeutic target of guanylate cyclase. Thanks to in-depth explorations of their underlying signaling mechanisms, the targets of these drugs are becoming clearer. This review explains the recent research progress regarding potential drugs in this class by introducing representative drugs and current findings on them.

The Triple Crown: NO, CO, and H2S in cancer cell biology

Nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S) are three endogenously produced gases with important functions in the vasculature, immune defense, and inflammation. It is increasingly apparent that, far from working in isolation, these three exert many effects by modulating each other's activity. Each gas is produced by three enzymes, which have some tissue specificities and can also be non-enzymatically produced by redox reactions of various substrates. Both NO and CO share similar properties, such as activating soluble guanylate cyclase (sGC) to increase cyclic guanosine monophosphate (cGMP) levels. At the same time, H2S both inhibits phosphodiesterase 5A (PDE5A), an enzyme that metabolizes sGC and exerts redox regulation on sGC. The role of NO, CO, and H2S in the setting of cancer has been quite perplexing, as there is evidence for both tumor-promoting and pro-inflammatory effects and anti-tumor and anti-inflammatory activities. Each gasotransmitter has been found to have dual effects on different aspects of cancer biology, including cancer cell proliferation and apoptosis, invasion and metastasis, angiogenesis, and immunomodulation. These seemingly contradictory actions may relate to each gas having a dual effect dependent on its local flux. In this review, we discuss the major roles of NO, CO, and H2S in the context of cancer, with an effort to highlight the dual nature of each gas in different events occurring during cancer progression.

Understanding human aging and the fundamental cell signaling link in age-related diseases: the middle-aging hypovascularity hypoxia hypothesis

Aging-related hypoxia, oxidative stress, and inflammation pathophysiology are closely associated with human age-related carcinogenesis and chronic diseases. However, the connection between hypoxia and hormonal cell signaling pathways is unclear, but such human age-related comorbid diseases do coincide with the middle-aging period of declining sex hormonal signaling. This scoping review evaluates the relevant interdisciplinary evidence to assess the systems biology of function, regulation, and homeostasis in order to discern and decipher the etiology of the connection between hypoxia and hormonal signaling in human age-related comorbid diseases. The hypothesis charts the accumulating evidence to support the development of a hypoxic milieu and oxidative stress-inflammation pathophysiology in middle-aged individuals, as well as the induction of amyloidosis, autophagy, and epithelial-to-mesenchymal transition in aging-related degeneration. Taken together, this new approach and strategy can provide the clarity of concepts and patterns to determine the causes of declining vascularity hemodynamics (blood flow) and physiological oxygenation perfusion (oxygen bioavailability) in relation to oxygen homeostasis and vascularity that cause hypoxia (hypovascularity hypoxia). The middle-aging hypovascularity hypoxia hypothesis could provide the mechanistic interface connecting the endocrine, nitric oxide, and oxygen homeostasis signaling that is closely linked to the progressive conditions of degenerative hypertrophy, atrophy, fibrosis, and neoplasm. An in-depth understanding of these intrinsic biological processes of the developing middle-aged hypoxia could provide potential new strategies for time-dependent therapies in maintaining healthspan for healthy lifestyle aging, medical cost savings, and health system sustainability.

MicroRNA and lncRNA as the Future of Pulmonary Arterial Hypertension Treatment

Pulmonary hypertension (PH) is characterized by a progressive increase in pulmonary arterial pressure and pulmonary vascular resistance. In a short time, it leads to right ventricular failure and, consequently, to death. The most common causes of PH include left heart disease and lung disease. Despite the significant development of medicine and related sciences observed in recent years, we still suffer from a lack of effective treatment that would significantly influence the prognosis and prolong life expectancy of patients with PH. One type of PH is pulmonary arterial hypertension (PAH). The pathophysiology of PAH is based on increased cell proliferation and resistance to apoptosis in the small pulmonary arteries, leading to pulmonary vascular remodeling. However, studies conducted in recent years have shown that epigenetic changes may also lie behind the pathogenesis of PAH. Epigenetics is the study of changes in gene expression that are not related to changes in the sequence of nucleotides in DNA. In addition to DNA methylation or histone modification, epigenetic research focuses on non-coding RNAs, which include microRNAs (miRNAs) and long non-coding RNAs (lncRNAs). Preliminary research results give hope that targeting epigenetic regulators may lead to new, potential therapeutic possibilities in the treatment of PAH.

Inclisiran-Safety and Effectiveness of Small Interfering RNA in Inhibition of PCSK-9

Dyslipidemia is listed among important cardiovascular disease risk factors. Treating lipid disorders is difficult, and achieving desirable levels of LDL-cholesterol (LDL-C) is essential in both the secondary and primary prevention of cardiovascular disease. For many years, statins became the basis of lipid-lowering therapy. Nevertheless, these drugs are often insufficient due to their side effects and restrictive criteria for achieving the recommended LDL-C values. Even the addition of other drugs, i.e., ezetimibe, does not help one achieve the target LDL-C. The discovery of proprotein convertase subtilisin/kexin type 9 (PCSK9) discovery has triggered intensive research on a new class of protein-based drugs. The protein PCSK9 is located mainly in hepatocytes and is involved in the metabolism of LDL-C. In the beginning, antibodies against the PCSK9 protein, such as evolocumab, were invented. The next step was inclisiran. Inclisiran is a small interfering RNA (siRNA) that inhibits the expression of PCSK9 by binding specifically to the mRNA precursor of PCSK9 protein and causing its degradation. It has been noticed in recent years that siRNA is a powerful tool for biomedical research and drug discovery. The purpose of this work is to summarize the molecular mechanisms, pharmacokinetics, pharmacodynamics of inclisiran and to review the latest research.

Soluble Guanylyl Cyclase Activators-Promising Therapeutic Option in the Pharmacotherapy of Heart Failure and Pulmonary Hypertension

Endogenous nitric oxide (NO)-dependent vascular relaxation plays a leading role in the homeostasis of the cardiovascular, pulmonary, and vascular systems and organs, such as the kidneys, brain, and liver. The mechanism of the intracellular action of NO in blood vessels involves the stimulation of the activity of the soluble cytosolic form of guanylyl cyclase (soluble guanylyl cyclase, sGC), increasing the level of cyclic 3'-5'-guanosine monophosphate (cGMP) in smooth muscle and subsequent vasodilation. In recent years, a new group of drugs, soluble guanylyl cyclase stimulators, has found its way into clinical practice. Based on the CHEST-1 and PATENT-1 trials, riociguat was introduced into clinical practice for treating chronic thromboembolic pulmonary hypertension (CTEPH). In January 2021, the FDA approved the use of another drug, vericiguat, for the treatment of heart failure.

Beta-blockers in cardiac arrhythmias-Clinical pharmacologist's point of view

β-blockers is a vast group of antiarrhythmic drugs which differ in their pharmacokinetic and chemical properties. Some of them block β-adrenergic receptors selectively while the others work non-selectively. Consequently, they reduce the influence of the sympathetic nervous system on the heart, acting negatively inotropic, chronotropic, bathmotropic and dromotropic. Although they have been present in medicine since the beginning of the 1960s, they still play a crucial role in the treatment of cardiac arrhythmias. They are also first-line group of drugs used to control the ventricular rate in patients with the most common arrhythmia-atrial fibrillation. Previous reports indicate that infection with SARS-CoV-2 virus may constitute an additional risk factor for arrhythmia. Due to the aging of the population in developed countries and the increase in the number of patients with cardiac burden, the number of people suffering from cardiac arrhythmias will increase in the upcoming years. As a result the role of above-mentioned beta-blockers will remain significant. Particularly noteworthy is propranolol-the oldest beta adrenergic antagonist, which in recent years has found additional applications due to its unique properties. In this article, we reviewed the accessible literature and summarized the current guidelines on the use of beta-blockers in the treatment of cardiac arrhythmias.

Neuronal Nitric Oxide Synthase as a Shared Target for the Effects of Adiponectin and Resistin on the Mechanical Responses of the Mouse Gastric Fundus

It has been reported that adiponectin (ADPN) and resistin are co-secreted by white mouse adipocytes and exert similar inhibitory effects in the mouse gastric fundus, in which resistin was observed to increase neuronal nitric oxide synthase (nNOS) expression. On these grounds, the present work aimed to investigate whether the effects of the two adipokines on the neurally-induced relaxant responses potentiate each other and whether there is a possible correlation with changes in nNOS expression in preparations from the mouse gastric fundus. In carbachol (CCh)-precontracted strips, electrical field stimulation elicited nitrergic relaxant responses, whose amplitude was increased by ADPN or resistin, but no additional enhancements were observed in their concomitant presence. Western blot and immunofluorescence analyses revealed that ADPN, like resistin, was able to up-regulate nNOS expression and to increase the percentage of nNOS-positive neurons in the myenteric plexus: co-treatment with the two adipokines did not induce additional changes. The results indicate that the two adipokines modulate nitrergic neurotransmission, and both do so by up-regulating nNOS expression. Therefore, nNOS appears to be a shared target for the two adipokines' effects, which, rather than mutually reinforcing each other, may represent a dual physiological control mechanism to guarantee gastric fundus relaxation.

Acetylsalicylic Acid-Primus Inter Pares in Pharmacology

Acetylsalicylic acid (ASA) is one of the first drugs to be obtained by synthesis while being the most used. It has experienced the longest lasting commercial success and is considered the most popular drug of the modern era. ASA, originally used as an anti-inflammatory medication, nowadays is predominantly used as an antiplatelet agent for prophylaxis in cardiac patients. Many studies show that the benefits of using ASA far outweigh the potential risk of side effects. With particular emphasis on the possibility of ASA repositioning for new therapies, extending the indications for use beyond the diseases from the spectrum of atherosclerotic diseases, such as cancer, requires shifting the benefit-risk ratio, although very good, even more towards safety. Interesting activities consisting not only of changing the formulation but also modifying the drug molecule seem to be an important goal of the 21st century. ASA has become a milestone in two important fields: pharmacy and medicine. For a pharmacist, ASA is a long-used drug for which individual indications are practically maintained. For a doctor, acetylsalicylic acid is primarily an antiplatelet drug that saves millions of lives of patients with coronary heart disease or after a stroke. These facts do not exempt us from improving therapeutic methods based on ASA, the main goal of which is to reduce the risk of side effects, as well as to extend effectiveness. Modified acetylsalicylic acid molecules already seem to be a promising therapeutic option.

Nitric oxide/cGMP/CREB pathway and amyloid-beta crosstalk: From physiology to Alzheimer's disease

The nitric oxide (NO)/cGMP pathway has been extensively studied for its pivotal role in synaptic plasticity and memory processes, resulting in an increase of cAMP response element-binding (CREB) phosphorylation, and consequent synthesis of plasticity-related proteins. The NO/cGMP/CREB signaling is downregulated during aging and neurodegenerative disorders and is affected by Amyloid-β peptide (Aβ) and tau protein, whose increase and deposition is considered the key pathogenic event of Alzheimer's disease (AD). On the other hand, in physiological conditions, the crosstalk between the NO/cGMP/PKG/CREB pathway and Aβ ensures long-term potentiation and memory formation. This review summarizes the current knowledge on the interaction between the NO/cGMP/PKG/CREB pathway and Aβ in the healthy and diseased brain, offering a new perspective to shed light on AD pathophysiology. We will focus on the synaptic mechanisms underlying Aβ physiological interplay with cGMP pathway and how this balance is corrupted in AD, as high levels of Aβ interfere with NO production and cGMP molecular signaling leading to cognitive impairment. Finally, we will discuss results from preclinical and clinical studies proposing the increase of cGMP signaling as a therapeutic strategy in the treatment of AD.

Carbon monoxide and its role in human physiology: A brief historical perspective

Carbon monoxide is a molecule with notoriety in modern culture and extensive documentation regarding its toxic physiological effects, long predating its formal discovery in the 18th century. Upon its discovery as a molecule in 1772, subsequent investigations into its properties have provided mechanisms describing its toxicity and insights into its function as an endogenously produced molecule and as a therapeutic agent. This brief review aims to provide a historical perspective on this molecule and recognize research regarding its physiological functions and therapeutic applications, often overshadowed by its reputation as a lethal substance. Historicizing science is an acknowledgment of the pioneers and helps us better conceptualize the issues.

Neurotransmitters-Key Factors in Neurological and Neurodegenerative Disorders of the Central Nervous System

Neurotransmitters are molecules that amplify, transmit, and convert signals in cells, having an essential role in information transmission throughout the nervous system. Hundreds of such chemicals have been discovered in the last century, continuing to be identified and studied concerning their action on brain health. These substances have been observed to influence numerous functions, including emotions, thoughts, memories, learning, and movements. Thus, disturbances in neurotransmitters’ homeostasis started being correlated with a plethora of neurological and neurodegenerative disorders. In this respect, the present paper aims to describe the most important neurotransmitters, broadly classified into canonical (e.g., amino acids, monoamines, acetylcholine, purines, soluble gases, neuropeptides) and noncanonical neurotransmitters (e.g., exosomes, steroids, D-aspartic acid), and explain their link with some of the most relevant neurological conditions. Moreover, a brief overview of the recently developed neurotransmitters’ detection methods is offered, followed by several considerations on the modulation of these substances towards restoring homeostasis.

Gases in Sepsis: Novel Mediators and Therapeutic Targets

Sepsis, a potentially lethal condition resulting from failure to control the initial infection, is associated with a dysregulated host defense response to pathogens and their toxins. Sepsis remains a leading cause of morbidity, mortality and disability worldwide. The pathophysiology of sepsis is very complicated and is not yet fully understood. Worse still, the development of effective therapeutic agents is still an unmet need and a great challenge. Gases, including nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H₂S), are small-molecule biological mediators that are endogenously produced, mainly by enzyme-catalyzed reactions. Accumulating evidence suggests that these gaseous mediators are widely involved in the pathophysiology of sepsis. Many sepsis-associated alterations, such as the elimination of invasive pathogens, the resolution of disorganized inflammation and the preservation of the function of multiple organs and systems, are shaped by them. Increasing attention has been paid to developing therapeutic approaches targeting these molecules for sepsis/septic shock, taking advantage of the multiple actions played by NO, CO and H₂S. Several preliminary studies have identified promising therapeutic strategies for gaseous-mediator-based treatments for sepsis. In this review article, we summarize the state-of-the-art knowledge on the pathophysiology of sepsis; the metabolism and physiological function of NO, CO and H₂S; the crosstalk among these gaseous mediators; and their crucial effects on the development and progression of sepsis. In addition, we also briefly discuss the prospect of developing therapeutic interventions targeting these gaseous mediators for sepsis.

The Role of Serotonin Neurotransmission in Gastrointestinal Tract and Pharmacotherapy

5-Hydroxytryptamine (5-HT, serotonin) is a neurotransmitter in both the central nervous system and peripheral structures, acting also as a hormone in platelets. Although its concentration in the gut covers >90% of all organism resources, serotonin is mainly known as a neurotransmitter that takes part in the pathology of mental diseases. Serotonin modulates not only CNS neurons, but also pain transmission and platelet aggregation. In the periphery, 5-HT influences muscle motility in the gut, bronchi, uterus, and vessels directly and through neurons. Serotonin synthesis starts from hydroxylation of orally delivered tryptophan, followed by decarboxylation. Serotonin acts via numerous types of receptors and clinically plays a role in several neural, mental, and other chronic disorders, such as migraine, carcinoid syndrome, and some dysfunctions of the alimentary system. 5-HT acts as a paracrine hormone and growth factor. 5-HT receptors in both the brain and gut are targets for drugs modifying serotonin neurotransmission. The aim of the present article is to review the 5-HT receptors in the gastrointestinal (GI) tract to determine the role of serotonin in GI physiology and pathology, including known GI diseases and the role of serotonin in GI pharmacotherapy.

Complex Interplay of Heme-Copper Oxidases with Nitrite and Nitric Oxide

Nitrite and nitric oxide (NO), two active and critical nitrogen oxides linking nitrate to dinitrogen gas in the broad nitrogen biogeochemical cycle, are capable of interacting with redox-sensitive proteins. The interactions of both with heme-copper oxidases (HCOs) serve as the foundation not only for the enzymatic interconversion of nitrogen oxides but also for the inhibitory activity. From extensive studies, we now know that NO interacts with HCOs in a rapid and reversible manner, either competing with oxygen or not. During interconversion, a partially reduced heme/copper center reduces the nitrite ion, producing NO with the heme serving as the reductant and the cupric ion providing a Lewis acid interaction with nitrite. The interaction may lead to the formation of either a relatively stable nitrosyl-derivative of the enzyme reduced or a more labile nitrite-derivative of the enzyme oxidized through two different pathways, resulting in enzyme inhibition. Although nitrite and NO show similar biochemical properties, a growing body of evidence suggests that they are largely treated as distinct molecules by bacterial cells. NO seemingly interacts with all hemoproteins indiscriminately, whereas nitrite shows high specificity to HCOs. Moreover, as biologically active molecules and signal molecules, nitrite and NO directly affect the activity of different enzymes and are perceived by completely different sensing systems, respectively, through which they are linked to different biological processes. Further attempts to reconcile this apparent contradiction could open up possible avenues for the application of these nitrogen oxides in a variety of fields, the pharmaceutical industry in particular.

Impact of Hydrogen Sulfide on Mitochondrial and Bacterial Bioenergetics

This review focuses on the effects of hydrogen sulfide (H2S) on the unique bioenergetic molecular machines in mitochondria and bacteria-the protein complexes of electron transport chains and associated enzymes. H2S, along with nitric oxide and carbon monoxide, belongs to the class of endogenous gaseous signaling molecules. This compound plays critical roles in physiology and pathophysiology. Enzymes implicated in H2S metabolism and physiological actions are promising targets for novel pharmaceutical agents. The biological effects of H2S are biphasic, changing from cytoprotection to cytotoxicity through increasing the compound concentration. In mammals, H2S enhances the activity of FoF1-ATP (adenosine triphosphate) synthase and lactate dehydrogenase via their S-sulfhydration, thereby stimulating mitochondrial electron transport. H2S serves as an electron donor for the mitochondrial respiratory chain via sulfide quinone oxidoreductase and cytochrome c oxidase at low H2S levels. The latter enzyme is inhibited by high H2S concentrations, resulting in the reversible inhibition of electron transport and ATP production in mitochondria. In the branched respiratory chain of Escherichia coli, H2S inhibits the bo3 terminal oxidase but does not affect the alternative bd-type oxidases. Thus, in E. coli and presumably other bacteria, cytochrome bd permits respiration and cell growth in H2S-rich environments. A complete picture of the impact of H2S on bioenergetics is lacking, but this field is fast-moving, and active ongoing research on this topic will likely shed light on additional, yet unknown biological effects.

Nitric Oxide: From Gastric Motility to Gastric Dysmotility

It is known that nitric oxide (NO) plays a key physiological role in the control of gastrointestinal (GI) motor phenomena. In this respect, NO is considered as the main non-adrenergic, non-cholinergic (NANC) inhibitory neurotransmitter responsible for smooth muscle relaxation. Moreover, many substances (including hormones) have been reported to modulate NO production leading to changes in motor responses, further underlying the importance of this molecule in the control of GI motility. An impaired NO production/release has indeed been reported to be implicated in some GI dysmotility. In this article we wanted to focus on the influence of NO on gastric motility by summarizing knowledge regarding its role in both physiological and pathological conditions. The main role of NO on regulating gastric smooth muscle motor responses, with particular reference to NO synthases expression and signaling pathways, is discussed. A deeper knowledge of nitrergic mechanisms is important for a better understanding of their involvement in gastric pathophysiological conditions of hypo- or hyper-motility states and for future therapeutic approaches. A possible role of substances which, by interfering with NO production, could prove useful in managing such motor disorders has been advanced.