Facing up the ROS labyrinth--Where to go?

Evidence indicates that oxidative stress refers to a condition where cells are subjected to excessive levels of reactive oxygen species (ROS). Overall vascular function is dependent upon a fine balance between oxidant and antioxidant mechanisms which is required, at least in part, for proper functioning of the endothelium. Considerable experimental and clinical data indicate that the intracellular oxidant milieu is also involved in several redox-sensitive cellular signaling pathways, such as ion transport systems, protein phosphorylation, and gene expression and thus also plays important roles as modulator of vascular cell function, such as cell growth, apoptosis, migration, angiogenesis and cell adhesion. Overproduction of ROS under pathophysiologic conditions is integral in the development of vascular disease. This fact stimulated an intensive search of new pharmacological approaches to improve vascular hemeostasis and, particularly those intended to decrease oxidative stress or augment the antioxidant defense mechanisms.     

Targeting Cellular Antioxidant Enzymes for Treating Atherosclerotic Vascular Disease

Atherosclerotic vascular dysfunction is a chronic inflammatory process that spreads from the fatty streak and foam cells through lesion progression. Therefore, its early diagnosis and prevention is unfeasible. Reactive oxygen species (ROS) play important roles in the pathogenesis of atherosclerotic vascular disease. Intracellular redox status is tightly regulated by oxidant and antioxidant systems. Imbalance in these systems causes oxidative or reductive stress which triggers cellular damage or aberrant signaling, and leads to dysregulation. Paradoxically, large clinical trials have shown that non-specific ROS scavenging by antioxidant vitamins is ineffective or sometimes harmful. ROS production can be locally regulated by cellular antioxidant enzymes, such as superoxide dismutases, catalase, glutathione peroxidases and peroxiredoxins. Therapeutic approach targeting these antioxidant enzymes might prove beneficial for prevention of ROS-related atherosclerotic vascular disease. Conversely, the development of specific antioxidant enzyme-mimetics could contribute to the clinical effectiveness.     

Role of sirtuins and calorie restriction in neuroprotection: implications in Alzheimer's and Parkinson's diseases

Aging is the major known risk factor for the onset of neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD). Mitochondria play a central role in aging as mitochondrial dysfunction increases with age and produces harmful levels of reactive oxygen species which leads to cellular oxidative stress (free-radical theory of aging). Oxidative stress is highly damaging to cellular macromolecules and is also a major cause of the loss and impairment of neurons in neurodegenerative disorders. A growing body of evidence suggests that modulation of sirtuin activity and restricting calorie intake has a strong neuroprotective effect. SIRT1 induction by the use of pharmacological activators or by calorie restriction (CR) diet regimen has been shown to protect against neuronal loss and impairment in the cellular and animal models of AD and PD. Here, we review the current knowledge and recent data related to the role of sirtuins and CR in neurodegeneration and discuss the potential underlying signaling pathways of neuroprotection that might serve as attractive targets for the future therapeutic intervention of these age-related neurodegenerative diseases.     

Characterization of indorenate effects on brain monoamine metabolism

The effect of indorenate, a central antihypertensive agent, on the catecholamine and indolamine metabolism was studied in the rat brain. Acute administration of 10 mg/kg of indorenate causes an increase in 5-HT concentrations and a decrease on its metabolite 5-hydroxyindolacetic acid (5-HIAA) in the brain stem, cerebral cortex, hypothalamus, and striatum. Maximal effects were observed between 1.5 and 3 hr after indorenate administration. Additionally, a significant decrease in homovanilic acid (HVA) and 3,4-dihydroxyphenylacetic (DOPAC) concentrations was noted after 1.5 hr of a 10 mg/kg indorenate injection. Modification of both catecholamine and indolamine metabolites was dose related. Control values were recovered 24 hr after indorenate administration. Activity of monoamine oxidase present in crude homogenates obtained from the cerebral cortex, brain stem, hypothalamus, and striatum was not affected by indorenate. The present results suggest that indorenate acts as an agonist at serotonin receptors in the central nervous system (CNS).     

NO signaling in the CNS: from the physiological to the pathological

Nitric oxide (NO) is a free radical gas that has a Janus nature. As indicated by the literature and by our studies, in the cell, NO can either function as a beneficial physiological agent utilized for essential functions such as differentiation or neurotransmission, or as a pathological agent that causes or exacerbates central nervous system (CNS) disease and injury. Whether NO is helpful or harmful depends on a variety of factors, such as the cellular environment in which NO is released, the rate of NO flux, as determined by which NOS isozyme is activated, and what array of second messenger cascades are available for utilization by NO for beneficial or toxic cell signalling. Understanding the mechanisms by which NO is salutary in one set of circumstances and toxic in another is critical and will offer therapeutic targets for the mitigation of NO-mediated damage seen during CNS disease and injury. In fact, we have utilized the duality the NO to, in motor neurons, induce adaptive resistance (IAR) to toxic doses of NO. Understanding how the actions of NO are transduced in the cell will lead us to more targeted application of therapies such as IAR.     

Portacaval shunt in the rat: selective alterations in behavior and brain serotonin

Portacaval shunted (PCS) rats and sham-operated controls were investigated for spontaneous activity, exploration, somatosensory reactivity, swim latencies in a water maze, motor coordination, and passive avoidance 2 to 3 weeks after operation. The rats were subsequently decapitated and indole metabolism was investigated in different brain regions. The results showed that shunted rats were impaired in both open field tests (spontaneous activity and exploration) and in somatosensory reactivity (latency to respond, maximal response and integrated response). Results from motor coordination tasks and learning and memory tests (water maze and passive avoidance) did not demonstrate differences between the groups. There was an increased brain indolamine metabolism in PCS compared to sham-operated rats. No correlation between the behavioral impairment and the altered indolamine metabolism could be demonstrated with multiple correlation analysis.     

Cardiac excitability and antiarrhythmic drugs: a different perspective

A matrix of active and passive cellular properties determines net cardiac excitability. The hypothesis of altered excitability suggests that for cardiac arrhythmias to arise, the normal matrix must be perturbed by arrhythmogenic influences to produce a proarrhythmic matrical configuration to permit rhythm disturbances caused by abnormalities of propagation, abnormal automaticity, or altered excitability. Antiarrhythmic drugs may act with one or more components of the normal or proarrhythmic matrix to normalize or to create new antiarrhythmic or, perhaps, proarrhythmic matrices. Traditionally, antiarrhythmic drug classifications have been based on predominant drug actions. These classifications have clinical and some experimental utility but fail to consider the complicated effects that pathophysiologic influences and pharmacologic actions may have on active and passive cellular properties. Cluster analysis may allow the development of new classifications of arrhythmogenesis and antiarrhythmic drugs. The matrical concept has important clinical implications and suggest strategies for treating patients with cardiac rhythm disturbances.     

Scavenger effect of experimental and clinically used cardiovascular drugs

Oxygen free radicals play an important role in several physiologic and pathophysiologic processes. In pathophysiologic circumstances they can modify and damage biologic systems. Their functional properties (exposed to high oxygen tension) place red blood cells among the most susceptible cells to the harmful effect of free radicals. Because oxygen free radicals are involved in a wide range of diseases, scavenging these radicals should be an important therapeutic approach. In this study the antioxidant capacities of experimental and clinically used cardiovascular drugs were investigated. Phenazine methosulfate was used to generate free radicals and thus harden red blood cells. Filtration technique and potassium leaking were used to detect the scavenging effect of the examined drugs. The experimental drug H-2545 provided 43% protection against phenazine methosulfate-induced changes in red blood cell filterability (p < 0.001). Although some of the examined, clinically used cardiovascular drugs (carvedilol, metoprolol, verapamil, trimetazidine) also showed significant (p < 0.05) antioxidant effect, they were less efficient than H-2545. The scavenger effect of this novel drug exceeded the antioxidant properties of vitamin E. Modification of mexiletine with a pyrroline ring significantly improved its antioxidant capacity, suggesting that this molecular segment is responsible for the antioxidant effect.     

Variability in toxicity of the dinoflagellate Alexandrium tamarense in response to different nitrogen sources and concentrations.

Nitrogen (N) supply in pulses was simulated by exposing Alexandrium tamarense which was acclimatized at low N concentration (6 microM-N) to sudden increase in concentrations of nitrate, ammonium and urea, and the variability in toxicity due to nutrient status of A. tamarense was examined. The toxin composition did not vary dramatically among the three N sources, however, ammonium induced the highest concentration of intracellular toxin, followed by urea and then nitrate. Therefore, populations utilizing high ammonium concentration could be more toxic than those growing on nitrate or urea. The toxin content was dependent on the cellular N status of nitrate grown cells only, suggesting that the competition for N in toxin production with other metabolic pathways such as growth may be different among N sources. The relationship between toxin and nutrient status is a complex interaction and it involves the redistribution of cellular N within the cells. Understanding the toxin dynamics of natural populations in relation to nutrient is essential for the mitigation of harmful dinoflagellates in a given coastal ecosystem.     

Carcinogenic chemicals in food: evaluating the health risk.

The presence of a low level of potentially harmful chemicals in food continues to be a concern to many individuals. A major concern is that these chemicals, which can be synthetic or naturally occurring, may be a causative factor in human cancer. Synthetic chemicals in food may be present either as specific additives or as contaminants derived from environmental or agricultural chemicals. Food also contains a variety of naturally occurring chemicals derived from vegetables or other plants. These may in some cases be considered as contaminants, and are occasionally used as specific additives. New chemicals can also be formed during the cooking or preserving processes. The capacity of any of these chemicals to induce cellular damage and mutation is minimized by natural defence systems such as an efficient cellular detoxification system and DNA repair. The factors influencing tumour formation in humans are numerous and interrelated and exposure to minor dietary chemicals needs to be considered in this context. Thus, the results of animal carcinogenicity assays on individual chemicals need to be interpreted with care, taking into account the mechanisms by which mutagenic and other chemicals initiate cancer, as well as the level of human exposure to these chemicals. Further research is necessary to determine the role, if any, of minor dietary components in tumour formation. Meanwhile, there needs to be a more holistic approach to the multitude of factors, including total diet, that may influence human cancer incidence. In this way, the relative risk of dietary chemicals may be given a more meaningful perspective for health professionals and consumers alike.     

Platelet-leukocyte interactions in hemodialysis patients: culprit or bystander?

The formation of circulating platelet-leukocyte complexes has been observed in a variety of conditions and may be pathophysiologically significant. Platelet-leukocyte interactions in fact facilitate metabolic cooperation and mutual activation, which may be of relevance in many biological processes including inflammation, atherogenesis and hemostasis. During hemodialysis procedure, the series of reactions that can occur upon blood contact with the foreign membrane surface may involve a variety of changes affecting almost every cellular and plasmatic component of the blood. This article reviews the evidence for abnormal interactions between circulating platelets and leukocytes in uremic patients undergoing maintenance hemodialysis and the pathophysiologic implications which may stem from such interactions.     

Cyclic amidine inhibitors of indolamine N-methyltransferase.

Syntheses of a large number of mono- and bicyclic, as well as a few tricyclic, amidine derivatives related to 2,3,4,6,7,8,-hexahydropyrrolo[1,2-a]pyrimidine (DBN) are reported. In vitro potencies for inhibition of the enzyme indolamine N-methyltransferase (INMT) from rabbit and human lung are presented. Four bicyclic amidine derivatives and 11 monocyclic derivatives were found to be equal or superior to DBN in in vitro potencies. With the bicyclic amidines, increasing ring size or introduction of substituents reduced activity. Among the monocyclic analogues, the most potent representatives were five- or six-membered systems with an exocyclic imino group, combined with methyl of ethyl substituents on the endocyclic nitrogen. Introduction of additonal substituents decreased inhibitory potency. 2,3,5,6-Tetrahydro-8H-imidazo[2,1-c][1,4]thiazine and 3-methyl-2-iminothiazolidine have been shown to cause inhibition of lung INMT when administered orally to rabbits.     

Antioxidant therapy in acute central nervous system injury: current state

Free radicals are highly reactive molecules generated predominantly during cellular respiration and normal metabolism. Imbalance between cellular production of free radicals and the ability of cells to defend against them is referred to as oxidative stress (OS). OS has been implicated as a potential contributor to the pathogenesis of acute central nervous system (CNS) injury. After brain injury by ischemic or hemorrhagic stroke or trauma, the production of reactive oxygen species (ROS) may increase, sometimes drastically, leading to tissue damage via several different cellular molecular pathways. Radicals can cause damage to cardinal cellular components such as lipids, proteins, and nucleic acids (e.g., DNA), leading to subsequent cell death by modes of necrosis or apoptosis. The damage can become more widespread due to weakened cellular antioxidant defense systems. Moreover, acute brain injury increases the levels of excitotoxic amino acids (such as glutamate), which also produce ROS, thereby promoting parenchymatous destruction. Therefore, treatment with antioxidants may theoretically act to prevent propagation of tissue damage and improve both the survival and neurological outcome. Several such agents of widely varying chemical structures have been investigated as therapeutic agents for acute CNS injury. Although a few of the antioxidants showed some efficacy in animal models or in small clinical studies, these findings have not been supported in comprehensive, controlled trials in patients. Reasons for these equivocal results may include, in part, inappropriate timing of administration or suboptimal drug levels at the target site in CNS. Better understanding of the pathological mechanisms of acute CNS injury would characterize the exact primary targets for drug intervention. Improved antioxidant design should take into consideration the relevant and specific harmful free radical, blood brain barrier (BBB) permeability, dose, and time administration. Novel combinations of drugs providing protection against various types injuries will probably exploit the potential synergistic effects of antioxidants in stroke.     

Wounding the immune system with its own blade: HIV-induced tryptophan catabolism and pathogenesis

Indoleamine 2,3-dioxygenase (IDO) is an immunoregulatory enzyme which plays a key role in maintaining the physiologic immune balance between the efficient responses to insulting pathogens and the control of harmful autoimmune reactions. During HIV infection, multiple mechanisms involving both viral and cellular components, contribute to enhance IDO expression and activity in an uncontrolled manner. The downstream effects of IDO overactivation collectively contribute to the immune alterations which characterize HIV disease. This review explores the cellular and molecular pathways which result in IDO upregulation during HIV infection and considers the consequences of IDO hyperactivity on the immune system, their relevance in the context of HIV immunopathogenesis and the potential for specific therapeutic intervention.     

Molecular remodeling of complement regulatory proteins for xenotransplantation.

In pig-to-human discordant xenotransplantation, human complement is a major barrier against long survival of xenografts. Human complement regulatory proteins expressed on xenografts have been adapted as safeguards against host-induced hyperacute rejection of xenografts. For successful xenotransplantation, there have been many attempts to generate molecules with potent human complement regulatory activity but without activities related to harmful functions such as infection, immunosuppression and signal transduction devastating cellular homeostasis. Here, we summarize the strategy by which molecules for xenotransplantation should be designed and propose a GPI-anchored form of monomeric human C4bp as a candidate for efficient protection of swine xenografts from human complement attack.     

Pharmacologic modulators of soluble guanylate cyclase/cyclic guanosine monophosphate in the vascular system - from bench top to bedside

Guanosine-dependent cyclic nucleotide second messenger signaling has been implicated as a pivotal mediator of vascular function under both homeostatic eutrophic conditions as well as in the inimical environs of injury and/or disease. This biological system is highly regulated through reciprocal, complimentary, and often redundant upstream and downstream molecular and cellular elements and feedback controls. Key endogenous factors of the guanosine-dependent cyclic nucleotide cascade include upstream gaseous activating ligands (nitric oxide, carbon monoxide), downstream substrates (cGMP-gated ion channels, cGMP-dependent protein kinases), and cGMP hydrolyzing phosphodiesterases. This intricate system also has capacity to "cross-talk" with parallel adenosine-dependent cyclic nucleotide machinery. Numerous complexes of ligands, enzymes, cofactors, and substrates present significant targets for pharmacologic modulation at the cellular, genetic, and/or molecular level eventuating therapeutically as constructive functional responses observed in vascular physiology and/or pathophysiology. Interestingly, emerging evidence based largely on transgenic mouse models challenges the historically accepted concept that this signaling system functions principally as a therapeutic modality in cardiac and vascular tissues. The general purpose of this update is to provide current information on recently described neoteric agents that impact multifaceted and critical cGMP-dependent signaling in the vascular system. Emphasis will be placed on novel agents that exert significant and often multiple actions on upstream and downstream sites and are capable of eliciting robust effects on guanosine-dependent cellular actions. Individual sections will be devoted to agents that rely on an intact and functional cyclase heme and those that operate independently of the sGC heme. Attention will be placed on the physiologic and pathophysiologic clinical manifestations of these pharmacologic regimens. This review will conclude with some thoughts for future directions for study and continued discovery of novel sGC/cGMP controllers in the vascular system at the basic science and clinical levels.     

Respiratory muscle dysfunction in COPD: from muscles to cell

Respiratory muscle dysfunction is a cardinal feature of acute and chronic respiratory failure in COPD. Diaphragm and accessory inspiratory muscles face increased load due to increased lung resistance and elastance, as well as increased ventilatory demands. Concomitantly, the capacity of the inspiratory muscles to generate pressure is decreased due to mechanical disadvantage imposed by hyperinflation. Additionally, inflammation and oxidative stress impair muscle fiber specific force generation and increase diaphragm susceptibility to sarcomer disruption during acute inspiratory loading. In response to this increased load diaphragm presents unique adaptations in its cellular structure and passive and contractile mechanical properties, and displays a more efficient metabolic armamentarium. A shift of muscle fiber type towards slow-twitch, oxidative type I fibers, which are more fatigue-resistant, increases diaphragmatic endurance but protein degradation and a significant reduction in myosin content decrease its force generating capacity. Furthermore, diaphragm adapts to chronic hyperinflation by sarcomere deletion so that its overall length is shortened, in an attempt to preserve optimum force-length relationship. Adaptation however may not be complete, or may be overwhelmed by pathophysiologic derangements during exercise or acute exacerbations, leading to obvious "dysfunction" of the respiratory muscles, and if sustained, ultimately to muscle fatigue and respiratory pump failure.