Interferon-gamma and tumor necrosis factor synergize to induce nitric oxide production and inhibit mitochondrial respiration in vascular smooth muscle cells

Chemical biology of nitric oxide: Insights into regulatory, cytotoxic, and cytoprotective mechanisms of nitric oxide

There has been confusion as to what role(s) nitric oxide (NO) has in different physiological and pathophysiological mechanisms. Some studies imply that NO has cytotoxic properties and is the genesis of numerous diseases and degenerative states, whereas other reports suggest that NO prevents injurious conditions from developing and promotes events which return tissue to homeostasis. The primary determinant(s) of how NO affects biological systems centers on its chemistry. The chemistry of NO in biological systems is extensive and complex. To simplify this discussion, we have formulated the "chemical biology of NO" to describe the pertinent chemical reactions under specific biological conditions. The chemical biology of NO is divided into two major categories, direct and indirect. Direct effects are defined as those reactions fast enough to occur between NO and specific biological molecules. Indirect effects do not involve NO, but rather are mediated by reactive nitrogen oxide species (RNOS) formed from the reaction of NO either with oxygen or superoxide. RNOS formed from NO can mediate either nitrosative or oxidative stress. This report discusses various aspects of the chemical biology of NO relating to biological molecules such as guanylate cyclase, cytochrome P450, nitric oxide synthase, catalase, and DNA and explores the potential roles of NO in different biological events. Also, the implications of different chemical reactions of NO with cellular processes such as mitochondrial respiration, metal homeostasis, and lipid metabolism are discussed. Finally, a discussion of the chemical biology of NO in different cytotoxic mechanisms is presented.

Proinflammatory cytokines depress cardiac efficiency by a nitric oxide-dependent mechanism

Proinflammatory cytokines (interleukin-1beta, tumor necrosis factor-alpha, and interferon-gamma; Cytomix) depress myocardial contractile work partially by stimulating expression of inducible nitric oxide (NO) synthase (iNOS). Because NO and peroxynitrite inhibit myocardial O2 consumption (MVO2), we examined whether this mechanism contributes to reduced cardiac work. In control isolated working rat hearts, cardiac work was stable for 60 min, followed by a decline from 60 to 120 min, without change in MVO2. Cardiac efficiency (work/MVO2) was therefore reduced from 60 to 120 min. Cytomix shortened the onset (within 20-40 min) and enhanced the depression in cardiac work and efficiency and inhibited MVO2 after 80 min. Mercaptoethylguanidine (MEG), an iNOS inhibitor and peroxynitrite scavenger, or the glucocorticoid dexamethasone (Dex) abolished the effects of Cytomix. iNOS expression was increased 10-fold by Cytomix and abolished by Dex but not MEG. That cytokine-induced depression in cardiac work precedes the reduction in MVO2 suggests, at least in the early response, that NO and/or peroxynitrite may not impair heart function by inhibiting mitochondrial respiration but reduce the heart's ability to utilize ATP for contractile work.

Nitric oxide modulates cardiac contractility and oxygen consumption without changing contractile efficiency

Nitric oxide (NO) affects myocardial contractility and myocardial oxygen consumption (MVO2) in vitro. In alpha-chloralose-anesthetized dogs instrumented for the measurements of left ventricular (LV) pressure, LV volume using a conductance catheter, coronary blood flow, and coronary venous oxygen saturation (ScvO2) using a fiber-optic catheter, LV end-systolic pressure-volume relationships (ESPVR) and the relationship between MVO2 and LV pressure-volume area (PVA) were analyzed before and after intravenous infusions of the NO synthase inhibitor NG-monomethyl-L-arginine acetate (L-NMMA; 5 mg/kg, 8 dogs) and the NO substrate L-arginine (600 mg/kg, 7 dogs). L-NMMA increased the slope of the ESPVR (Emax) (P < 0.05) without changing contractile efficiency indicated by the inverse of the slope of the MVO2-PVA line. L-NMMA also increased unloaded MVO2, indicated by the y-axis intercept of the MVO2-PVA line (P < 0.05). In contrast, L-arginine decreased Emax (P < 0.05) while decreasing MVO2 (P < 0.05), and without changing contractile efficiency. The basal oxygen metabolism was not affected by L-NMMA and L-arginine. These data imply that endogenous NO spares MVO2 by reducing oxygen use in excitation-contraction coupling and attenuates cardiac contractility without changing contractile efficiency.

Erratic behavior of nitric oxide within the immune system: illustrative review of conflicting data and their immunopharmacological aspects

The literature data assembled in this article document the variation of immunobiological effects of nitric oxide (NO). A number of factors are obviously responsible for the diversity, ranging from inactivity, alleviation, but not rarely to exacerbation of certain pathogenetic processes. A better understanding of NO interactions with the immune system can only be reached if more complex experimental designs to study the effects of reactive nitrogen species are adopted in the future. They should integrate major participating variables and take into account pharmacodynamic/kinetic aspects of NO production in triggering the ultimate effects. If manipulation of NO in the organism by means of recently developed NO inhibitors and NO donors is to become a rational tool of immunopharmacological strategies, detailed knowledge of their pharmacologies and toxicologies is urgently needed in order to differentiate between the effects of NO and other side effects. Hopefully, this approach could improve the predictability of the clinical outcomes of NO manipulation.

Role of nitric oxide and TPEN, a potent metal chelator, in ischaemic and reperfused rat isolated hearts

1. The role of nitric oxide (NO) was studied in the control of ischaemic/reperfused cardiac function and the effect of N,N,N',N'-tetrakis-[2-pyridylmethyl]-ethylenediamine (TPEN), a potent metal chelator, on the regulation of cardiac NO formation. 2. Rat isolated working hearts were subjected to 30 min ischaemia and reperfusion. The incidence of reperfusion-induced ventricular fibrillation (VF), ventricular tachycardia (VT) and the recovery of cardiac function were measured. Nitric oxide was detected by electron spin resonance (ESR) spectroscopy. 3. With 5.0, 7.5 and 10.0 mumol/L of TPEN administered prior to ischaemia, the drug produced a reduction in the incidence of VF from its control value of 100% to 25% (P < 0.05), 17% (P < 0.05) and 8% (P < 0.05), respectively. The incidence of VT followed the same pattern. 4. When TPEN was given at the moment of reperfusion, a reduction in the incidence of VF and VT was still observed. Reduction in the incidence of VF and VT was reflected in the improvement of cardiac function both in the pre- and post-ischaemic TPEN-treated groups. 5. TPEN reduced basal cardiac NO content and prevented the accumulation of NO during ischaemia/reperfusion. 6. The results show that TPEN exerts beneficial effects on postischaemic cardiac function and dysrhythmias in relation to inhibition of the accumulation of NO in ischaemic/reperfused myocardium.

Persistent inhibition of cell respiration by nitric oxide: crucial role of S-nitrosylation of mitochondrial complex I and protective action of glutathione

Both reversible and irreversible inhibition of mitochondrial respiration have been reported following the generation of nitric oxide (NO) by cells. Using J774 cells, we have studied the effect of long-term exposure to NO on different enzymes of the respiratory chain. Our results show that, although NO inhibits complex IV in a way that is always reversible, prolonged exposure to NO results in a gradual and persistent inhibition of complex I that is concomitant with a reduction in the intracellular concentration of reduced glutathione. This inhibition appears to result from S-nitrosylation of critical thiols in the enzyme complex because it can be immediately reversed by exposing the cells to high intensity light or by replenishment of intracellular reduced glutathione. Furthermore, decreasing the concentration of reduced glutathione accelerates the process of persistent inhibition. Our results suggest that, although NO may regulate cell respiration physiologically by its action on complex IV, long-term exposure to NO leads to persistent inhibition of complex I and potentially to cell pathology.

Protective effects of interleukin-10 on diaphragm muscle in a septic animal model

The effects of Interleukin (IL)-10 intravenous injection after endotoxin administration on diaphragm muscle were studied using Wistar rats. The animals were divided into two treatment groups: A saline + endotoxin group as control and an IL-10 + endotoxin group. E. coli endotoxin (10 mg/kg) was injected intraperitoneally 5 minutes after saline or IL-10 (1250 U, 0.25 mg) injection. The force-frequency curves, twitch kinetics and fatigability were measured at 0 and 4 hours after endotoxin injection. In the saline + endotoxin group, the force-frequency curves and half relaxation time were significantly decreased at 4 hours (p < 0.001 and p < 0.05, respectively) compared to those at 0 hour. In the IL-10 + endotoxin group, the decrement in the force-frequency curves by endotoxin was prevented at 4 hours compared to that at 0 hour. Nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase histochemistry showed positive staining in the saline + endotoxin at 4 hours, but there was no significant staining at 0 or 4 hours in the IL-10 + endotoxin group. These data suggest that IL-10 prevents the deterioration of contraction induced by endotoxin by inhibiting nitric oxide production in the diaphragm muscle.

Effects of L-NAME and L-arginine on diaphragm contraction in a septic animal model

The effects of nitric oxide on diaphragm contraction after endotoxin administration were studied in Wistar rats. The animals were divided into seven treatments: a saline-injected group as control, three groups injected with L-NAME (0.01, 0.1, 1 mg/kg) and three groups injected with L-arginine (1, 10, 100 mg/kg). Escherichia coli endotoxin was injected into the peritoneal cavity 15 min later. Twitch kinetics and force-frequency curves were measured 0, 2, and 4 hr after endotoxin injection. In the control group, the force-frequency curves significantly decreased from 0 hr to 4 hr. In the L-NAME group, the force-frequency curves at 4 hr showed significant increases in a dose-dependent manner. In the L-arginine group, the force-frequency curve with 100 mg/kg at 4 hr showed a significant increase. There was no consistent change in the contraction time, half relaxation time, or fatiguability. NADPH diaphorase histochemistry performed on diaphragm muscle samples 4 hr after endotoxin injection showed positive in the control and L-arginine group, but was only weakly observed in L-NAME group. These data suggest that nitric oxide contributes to the endotoxin induced diaphragm contractile deterioration.

Expression of nitric oxide synthase isoforms in normal ventilatory and limb muscles

Nitric oxide (NO), an important messenger molecule with widespread actions, is synthesized by NO synthases (NOS). In this study, we investigated the correlation between fiber type and NOS activity among ventilatory and limb muscles of various species. We also assessed the presence of the three NOS isoforms in normal skeletal muscles and how various NOS inhibitors influence muscle NOS activity. NOS activity was detected in various muscles; however, NOS activity in rabbits and rats varied significantly among different muscles. Immunoblotting of muscle samples indicated the presence of both the neuronal NOS and the endothelial NOS isoforms but not the cytokine-inducible NOS isoform. However, these isoforms were expressed to different degrees in various muscles. Although the neuronal NOS isoform was detectable in the canine diaphragm, very weak expression was detected in rabbit, rat, and mouse diaphragms. The endothelial NOS isoform was detected in the rat and mouse diaphragms but not in the canine and rabbit diaphragms. We also found that NG-nitro-L-arginine methyl ester, 7-nitroindazole, and S-methylisothiourea were stronger inhibitors of muscle NOS activity than was aminoguanidine. These results indicate the presence of different degrees of constitutive NOS expression in normal ventilatory and limb muscles of various species. Our data also indicate that muscle NOS activity is not determined by fiber type distribution but by other not yet identified factors. The functional significance of this expression remains to be assessed.

Interrelationships between astrocyte function, oxidative stress and antioxidant status within the central nervous system

Astrocytes have, until recently, been thought of as the passive supporting elements of the central nervous system. However, recent developments suggest that these cells actually play a crucial and vital role in the overall physiology of the brain. Astrocytes selectively express a host of cell membrane and nuclear receptors that are responsive to various neuroactive compounds. In addition, the cell membrane has a number of important transporters for these compounds. Direct evidence for the selective co-expression of neurotransmitters, transporters on both neurons and astrocytes, provides additional evidence for metabolic compartmentation within the central nervous system. Oxidative stress as defined by the excessive production of free radicals can alter dramatically the function of the cell. The free radical nitric oxide has attracted a considerable amount of attention recently, due to its role as a physiological second messenger but also because of its neurotoxic potential when produced in excess. We provide, therefore, an in-depth discussion on how this free radical and its metabolites affect the intra and intercellular physiology of the astrocyte(s) and surrounding neurons. Finally, we look at the ways in which astrocytes can counteract the production of free radicals in general by using their antioxidant pathways. The glutathione antioxidant system will be the focus of attention, since astrocytes have an enormous capacity for, and efficiency built into this particular system.

Induction of nitric oxide production by polyosides from the cell walls of Streptococcus mutans OMZ 175, a gram-positive bacterium, in the rat aorta

The cardiovascular dysfunctions associated with septic shock induced by gram-negative or gram-positive bacteria (gram-positive or gram-negative septic shock) are comparable. In gram-negative septic shock, lipopolysaccharide (LPS) induces nitric oxide (NO) synthase, which contributes to the vascular hypotension and hyporeactivity to vasoconstrictors. The role of NO in gram-positive septic shock and the nature of the bacterial wall components responsible for the vascular effects of gram-positive bacteria are not well known. This study investigated the vascular effects of cell wall serotype polyosides, rhamnose glucose polymers (RGPs), from Streptococcus mutans, in comparison with lipoteichoic acid (LTA) from Staphylococcus aureus, on the induction of NO synthase activity in the rat aorta. We show that 10 microg of both RGPs and LTA per ml induced hyporeactivity to noradrenaline, L-arginine-induced relaxation, increases of 2.2- and 7.8-fold, respectively, of cyclic GMP production, and increases of 7- and 12-fold in nitrite release. All of these effects appeared after several hours of incubation and were inhibited by N(omega)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of NO synthase. Electron paramagnetic resonance spin trapping experiments demonstrated directly that RGPs and LTA induced NO overproduction (four- to eightfold, respectively) in rat aortic rings; this production was inhibited by L-NAME and prevented by dexamethasone. These results demonstrate directly the induction of NO production in vascular tissue by LTA and show that another, chemically different component of gram-positive bacteria can also have these properties. This result suggests that different components of the gram-positive bacterial wall could be implicated in the genesis of cardiovascular dysfunctions observed in gram-positive septic shock.

Effects of carboxy-PTIO on systemic hemodynamics, liver energetics, and concentration of liver metabolites during endotoxic shock in rabbits: a 31P and 1H magnetic resonance spectroscopic study

OBJECTIVE

To investigate the effects of 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (carboxy-PTIO), a nitric oxide scavenger, on the lipopolysaccharide-induced hypotension, hepatocellular dysfunction, and liver damage in endotoxic rabbits.

DESIGN

Experimental, comparative study.

SETTING

Laboratory of a university hospital.

SUBJECTS

Eighteen Japanese white rabbits (3.0 to 3.2 kg body weight) anesthetized with ketamine-xylazine were studied.

INTERVENTIONS

We randomly divided the rabbits into three groups: saline controls (group 1, n = 5); animals receiving lipopolysaccharide (400 micrograms/kg) alone (group 2, n = 8); and animals receiving lipopolysaccharide plus carboxy-PTIO at a rate of 0.17 mg/kg/min for 3 hrs (group 3, n = 5). Blood gases and mean arterial pressure (MAP) were monitored. In vivo phosphorus-31 magnetic resonance spectra were continuously obtained every 30 mins. In addition, the livers were sampled and underwent fractionation at 7 hrs after lipopolysaccharide administration. The hydrophilic and hydrophobic extracts from the livers were analyzed by in vitro hydrogen-1 and phosphorus-31 magnetic resonance spectroscopy.

MEASUREMENTS AND MAIN RESULTS

After the administration of lipopolysaccharide, the first phase of decrease in MAP within 30 mins was followed by partial recovery within the next 30 mins. In group 2, MAP started to decrease progressively within 180 mins after lipopolysaccharide administration (second phase) and decreased by 33% from the baseline value to 49 +/- 9 mm Hg at 420 mins. In contrast, the infusion of carboxy-PTIO significantly attenuated the second decrease in MAP (68 +/- 10 mm Hg, at 420 mins). In group 2, a slow and progressive decrease in adenosine triphosphate (ATP) and increase in inorganic phosphate concentrations occurred from 120 mins after lipopolysaccharide administration, and continued throughout the observation period. These changes were accompanied by a progressive decrease in intracellular pH. On the other hand, in group 3, there were no significant changes in ATP and inorganic phosphate concentrations compared with the controls from 120 to 360 mins after lipopolysaccharide administration. Moreover, restorations of both arterial and hepatocellular acidosis were observed in group 3. The differences of the degree of liver damage--as determined by the total amount of phospholipid, free fatty acids concentration, and membrane fluidity--were not significant among the three groups. Three of eight rabbits in group 2 died within 7 hrs, but no animal in the other two groups died during the study.

CONCLUSIONS

The results of this study indicate that the infusion of carboxy-PTIO: a) prevented the delayed hypotension associated with endotoxic shock in rabbits; b) returned the hepatocellular ATP concentrations nearly to the level of the controls and alleviated hepatocellular acidosis; c) normalized various hydrophilic metabolites, such as lactate and alanine in the liver; and d) did not exacerbate liver injury after the administration of lipopolysaccharide. These findings indicate that carboxy-PTIO, a nitric oxide scavenger, may have a positive vasopressor effect during hypodynamic septic shock without exacerbating liver injury.

Characterization of the vasodilator properties of peroxynitrite on rat pulmonary artery: role of poly (adenosine 5'-diphosphoribose) synthase

1. The pulmonary vasculature is constantly exposed to oxygen and reactive oxygen species such as nitric oxide (NO) and superoxide anions which can combine at a near diffusion limited rate, to form the powerful, oxidant, peroxynitrite (ONOO-). When formed in large amounts, ONOO- is thought to contribute to tissue injury and vascular dysfunction seen in diseases such as the acute respiratory distress syndrome (ARDS) and septic shock. Recent studies have shown that ONOO- can cause vasodilatation and at higher concentrations can activate poly (adenosine 5'-diphosphoribose) synthase (PARS) leading to consumption of nicotinamide adenine dinucleotide (NAD+) and adenosine 5'-triphosphate (ATP). As the lung represents a prime site for ONOO- formation, we characterized its effects on pulmonary vascular tone and on endothelial function. In addition, we have assessed the role of PARS in producing the vasoactive properties of ONOO- on pulmonary artery rings. 2. Isolated pulmonary artery rings from rats were mounted in organ baths containing warmed and gassed (95% O2: 5% CO2) Krebs buffer. Force was measured with isometric force transducers. After equilibration, ONOO- (10 nM-100 microM) was added in a cumulative manner. In separate experiments designed to assess any vasodilator properties of ONOO-, tissues were pre-contracted with the thromboxane mimetic U46619 (1 microM). Once a stable base-line was achieved, ONOO- was added in a cumulative fashion. ONOO- had no significant effect on resting pulmonary artery tone but caused concentration-dependent relaxations of pre-contracted vessels in the range 1 microM to 100 microM. In some experiments the effects of freshly prepared ONOO- solutions were compared with those allowed to decay at 4 degrees C for 2 days. 3. In some experiments either vehicle or ONOO- (1, 10 or 100 microM) was added for 15 min before U46619 (1 microM). Concentration-response curves to the endothelium-dependent vasodilator, acetylcholine (10 nM-100 microM) were then constructed. In these experiments, ONOO- (1 microM or 10 microM) had no effect on the actions of acetylcholine. However, at the highest concentration tested (100 microM), ONOO- increased acetylcholine-induced relaxations. 4. The vasodilator actions of ONOO- were unaffected by the NO synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME; 100 microM) or by removal of superoxide anions with superoxide dismutase (SOD) (30 units ml-1). However, the relaxations induced by ONOO- were significantly inhibited by the PARS inhibitor, 3-aminobenzamide (10 microM). In contrast to its effects on ONOO-, 3-aminobenzamide had no effect on the relaxation caused by acetylcholine or sodium nitrite, but actually increased that induced by sodium nitroprusside. 5. These data show that ONOO- causes vasodilatation of rat pulmonary arteries, probably via activation of PARS. Moreover, at concentrations where relaxation was achieved, ONOO- did not affect the ability of pulmonary artery rings to relax to acetylcholine. We propose that ONOO-, but not endothelially derived NO, activates PARS resulting in the rapid depletion of ATP and a consequent reduction in contraction as well as other active processes of vascular smooth muscle. The finding that 3-aminobenzamide inhibited the actions of ONOO- but not acetylcholine, suggests that NO and ONOO- cause relaxation by independent mechanisms. It has been suggested that ONOO- is responsible for the vascular hyporesponsiveness to constrictor agents seen in experimental sepsis. This observation together with our current finding, that 3-aminobenzamide inhibits the relaxation induced by ONOO- but not by acetylcholine, suggests that inhibitors of PARS may reduce the persistent hypotension seen in sepsis without affecting the actions of endothelium-derived NO. Thus, the use of PARS inhibitors may represent a novel therapeutic approach to the treatment of septic shock.

Interferons suppress mitochondrial gene transcription by depleting mitochondrial transcription factor A (mtTFA)

Mitochondrial gene transcription activity in organello was suppressed after culturing HeLa cells with 1000 U/ml of interferon-alpha (IFN-alpha) or IFN-gamma for 18 h. The suppression was associated with reduced levels of mitochondrial gene transcripts. Northern blot analysis of HeLa cell RNA showed marked reduction of the mRNA encoding for mitochondrial transcription factor A (mtTFA). Immunoblotting with antiserum directed against recombinant mtTFA showed a reduced level of the protein as well. Consistently, gel-retardation assay of mitochondrial extract showed reduced level of functional mtTFA, which is known to bind to both heavy and light strand promoters of bidirectionally transcribed mitochondrial DNA. We suggest that depletion of mtTFA is a pathway through which IFNs depress the mitochondrial respiration.

Nitric oxide and shock

Shock can be defined as the failure of the circulatory system to provide necessary cellular nutrients, including oxygen, and to remove metabolic wastes. Although it is now recognized that more than 100 different forms of shock exist, this recognition is more a reflection of the widespread use of the term to describe a variety of disease states. For the purpose of this monograph, we concentrate on various forms of cardiovascular shock, in particular, shock that may be linked to inappropriate vasodilation from overproduction of the endogenous vasodilator, nitric oxide. Some forms of shock have been extensively studied, and convincing evidence exists for the role of nitric oxide. Other disease states have been less well characterized in terms of their association with excess nitric oxide production. Available evidence of a role for nitric oxide is discussed in the hope of stimulating the interest of investigators to explore these areas more thoroughly.

The role of nitric oxide in modulating ischaemia-induced arrhythmias in rats

The effect of a nitric oxide (NO) donor and the influence of endogenous NO in modulating ischaemia-induced arrhythmias was assessed in anaesthetised rats. The nitric oxide donor C87-3754 (1 mg/kg) caused a significant reduction in arterial blood pressure before coronary artery ligation but did not influence the incidence or severity of ventricular arrhythmias during a 30-min period of myocardial ischaemia [60 and 58% incidence of ventricular fibrillation (VF) in control and treated rats, respectively]. When the hearts were preconditioned by a short (3 min) coronary artery occlusion before the 30-min period of ischaemia, there was a marked reduction in both the number of ventricular ectopic beats (260 +/- 65 vs. 812 +/- 256 beats/min in controls; p < 0.05) and the incidence of ventricular fibrillation (9 vs. 67% in controls; p < 0.05). Neither NG-nitro-L-arginine methyl ester (L-NAME; 10-100 mg/kg) nor methylene blue (1-50 mg/kg) attenuated this marked antiarrhythmic effect of preconditioning. L-NAME caused a significant increase in blood pressure with all doses used, whereas methylene blue did not increase blood pressure. Both L-NAME and methylene blue attenuated ventricular arrhythmias in non-preconditioned hearts. L-NAME reduced the number of ventricular ectopic beats (from 812 +/- 256 to 318 +/- 81 beats/min at 10 mg/kg; p < 0.05), whereas methylene blue decreased the incidence of VF from 67 to 20% at a dose of 50 mg/kg (p < 0.05). These findings suggest that neither endogenous nor exogenously administered NO reduces ischaemic arrhythmias in anaesthetised rats. Furthermore, the antiarrhythmic effect of preconditioning in this species appears to be independent of NO. The antiarrhythmic effects seen with both methylene blue and L-NAME may be the result of actions other than inhibition of the production or actions of NO.

Inducible nitric oxide synthase and tumor necrosis factor-alpha in myocardium in human dilated cardiomyopathy

OBJECTIVES

We examined the mRNA expression and protein localization of inducible nitric oxide synthase (iNOS) and tumor necrosis factor-alpha (TNF-alpha) in myocardial tissue obtained from patients with dilated cardiomyopathy (DCM).

BACKGROUND

The etiology of DCM is unknown, but viral infection or autoimmune abnormalities that induce cytokine expression have been proposed as pathogenetic factors. Nitric oxide (NO), synthesized by nitric oxide synthase (NOS), has negative inotropic and cytotoxic effects on cardiomyocytes. Cytokines such as TNF-alpha are potent stimulators of iNOS expression. Expression of iNOS leads to excessive production of NO in the myocardium and may modulate cardiac contractility and ventricular morphology.

METHODS

We examined the mRNA expression and protein localization of iNOS and TNF-alpha in myocardial tissue obtained from 24 patients with DCM, 20 patients with hypertrophic cardiomyopathy (HCM) and 15 control subjects, using the reverse transcriptase-polymerase chain reaction method and immunohistochemical studies. We then compared the differences in clinical characteristics between DCM patient subgroups with and without myocardial iNOS expression.

RESULTS

Messenger RNA expression of iNOS and TNF-alpha was observed, respectively, in 13 (54%) and 18 (75%) patients with DCM. Gene expression of TNF-alpha was consistently detected in endomyocardial tissue from patients with DCM and INOS expression. Inducible NOS protein was evident only in cardiomyocytes, whereas TNF-alpha was apparent in both cardiomyocytes and endomyocardial endothelium. Neither mRNA expression nor protein localization of iNOS or TNF-alpha was observed in cardiac tissue obtained from patients with HCM or control subjects. Patients with DCM and iNOS mRNA showed a lower left ventricular ejection fraction (p < 0.01) and a higher left ventricular volume (p < 0.05) than the negative DCM group.

CONCLUSIONS

Inducible NOS was consistently coexpressed with TNF-alpha in myocardial tissue obtained from a subgroup of patients with DCM and advanced left ventricular dysfunction.

Near-infrared spectroscopy in experimental pneumococcal meningitis in the rabbit: cerebral hemodynamics and metabolism

Near-infrared spectroscopy is a noninvasive technique which measures oxidized cytochrome aa3, oxygenated Hb, and deoxygenated Hb and calculates total Hb in tissue. This technique, in conjunction with measurement of cerebral blood flow, was used in rabbits with experimental bacterial meningitis to determine whether there was evidence for cerebral energy depletion and alterations in the cerebral vascular bed with infection. Rabbits with meningitis had a significant reduction in cerebral blood flow, cerebral oxidized cytochrome aa3 and a relative increase in the deoxygenated Hb fraction and a decrease in the oxygenated Hb fraction compared with uninfected controls. Total Hb was not significantly different between the two groups. These findings may help clarify the mechanism for some of the intracranial pathophysiologic abnormalities in meningitis.

Altered regulation of inducible nitric oxide synthase expression in macrophages from senescent mice

We investigated the capacity of mouse macrophages obtained from senescent animals to respond in vitro to microbial stimuli. Significant hypersecretion of nitric oxide (NO) was observed in thioglycolate-elicited macrophages from senescent mice compared with those obtained from young mice in response to lipopolysaccharide (LPS). In contrast, both cell populations manifested equivalent responses to LPS with respect to tumor necrosis factor alpha secretion. Further, macrophages from senescent animals also showed potentiated responses to both zymosan and heat-killed Staphylococcus aureus, as assessed by NO production. Both cell populations were equivalently inhibited by a competitive inhibitor of NO synthase NG-monomethyl-L-arginine. Since endogenous beta interferon (IFN-beta) is recognized as an essential cofactor for LPS-induced NO production by macrophages, we investigated the role of IFN-beta in enhancing the capacity of both macrophage populations for LPS-induced NO production. Macrophages from young mice were minimally activated by LPS alone to express inducible NO synthase (iNOS), and the response was significantly potentiated by the addition of IFN-beta. These findings were confirmed by immunocytochemical staining of iNOS in which the frequency of iNOS-positive cells in response to LPS was enhanced in the presence of IFN-beta. Reverse transcription-PCR analyses revealed that macrophages from senescent animals produced larger amounts of iNOS mRNA in response to LPS. Further, exogenous IFN-beta potentiated iNOS mRNA expression in macrophages from young mice. In contrast, the frequency of LPS-activated macrophages for iNOS expression was markedly increased during senescence and addition of IFN-beta did not significantly change this frequency. These results correlated with reverse transcription PCR data showing high levels of iNOS mRNA in LPS-stimulated macrophages from senescent mice. LPS-induced NO production in macrophages from both young and senescent mice was inhibited by neutralizing antibody to either IFN-beta or IFN-gamma. Mixed cultures of macrophages from young and senescent mice stimulated with LPS manifested significantly enhanced NO production relative to that which would be predicted from an additive response of the two macrophage populations stimulated separately. The differential responsiveness of NO production observed with thioglycolate-elicited macrophages from young and senescent mice was also observed in resident macrophages but, interestingly, not in bone marrow culture-derived macrophages. These results suggest that environmental factors may be responsible for the potentiated NO responses of macrophages from senescent mice. Collectively, these data suggest that macrophages from senescent animals manifest an altered mechanism for regulation of macrophage function in NO production and iNOS expression by constitutive and/or induced expression of autoregulatory cytokines.

Atheroarteritis: a combined immunological and lipid imbalance

This report traces the development of our knowledge about immune-complex arteritis from the early 20th Century to the present time. The emphasis is on the work which began with the seminal observations of serum sickness by Longcope, MacKenzie, and Rich, to the pathogenetic studies of serum sickness arteritis in rabbits by several groups including the outstanding contributions by Dixon and coworkers concerning the role of circulating immune complexes. This work was followed by investigations of the relationship to atherosclerosis revealed by the sustained studies by Minick et al. on serum sickness arteritis in hypercholesterolemic rabbits. This pioneering research work has more recently been of pivotal value in understanding the arteritis observed in certain primate species such as the cynomolgus and the nemestrina, in human lupus erythematosus, and in organ transplantation arteritis. More recently it has become apparent that one of the microscopic hallmarks of this type of immune complex injury is the concentic micro-architecture of the inflammatory arterial lesions, for which, when they are also lipid containing, we have coined the term artheroarteritis. The contributions of the neoantigens from glycosylated LDL and oxidized LDL to the development of this type of atheroarteritis are considered. New frontiers in this area of research are being opened by the PDAY study which offers new opportunities to link circulating immune complexes and new antigens to arheroarteritis with its accelerated stenotic arterial lesion development.

Increased expression of interferon-gamma in a rat model of chronic intestinal allograft rejection

Chronic rejection remains a major cause of late graft dysfunction. Although much research has focused on acute rejection, little is known about the mechanisms of chronic rejection. Our group has recently reported evidence of significant intestinal smooth muscle hypertrophy and hyperplasia associated with abnormal contractile and electrical activities in a rat model of chronic intestinal rejection. The changes in the smooth muscle layer are associated with a significant inflammatory infiltrate. In order to further delineate the immune mechanisms of chronic rejection, we sought to clarify the nature of this infiltrate. Orthotopic small bowel transplantation was performed using an allogeneic (ACI-Lewis) rat combination. The rats only received immunosuppression for the first 28 days posttransplantation (cyclosporine 15 mg/kg daily from postoperative day 0 to 6 and every other day from postoperative day 7 to 28). This led to chronic rejection of the graft by day 90, at which time the rats were sacrificed. Analysis by immunohistochemistry revealed NK and CD5+ leukocytes infiltrating the muscular layer. Examination of cytokine production by radiolabeled polymerase chain reaction showed high levels of steady state interferon-gamma mRNA in full thickness intestinal segments and within the isolated muscularis of chronically rejecting intestinal allografts as compared to syngeneic and control grafts. Interferon-gamma mRNA was localized to both the muscularis and mucosa. Interestingly, positively hybridized cells within the muscularis tended to preferentially localize to the myenteric and submucosal plexuses suggesting potential role for this cytokine in chronic intestinal ejection.

Modulation by nitric oxide of metalloprotein regulatory activities

In many cells, a nitric oxide (NO) synthase inducible by immunological stimuli produces a sustained flow of NO that lasts a long time. NO is a short-lived molecule but it is a diffusible ligand believed to be capable of reaching distal target sites. Further, several lines of evidence indicate that cysteine-rich motifs of metal-binding proteins, as well as redox-sensitive metal clusters of metalloproteins, are natural sensors of bioradicals like NO. In metalloregulatory proteins, metals are often conveniently located at binding sites and bound to cysteine residues. Accordingly, disruption of the metal-thiolate polymetallic clusters should trigger significant remodelling of the protein structure involved in regulation. We can therefore postulate that the nitrosation reaction occurring at metal centres or cysteine-rich motifs will preclude correct binding to regulatory sites. Several examples are given of metalloregulatory proteins whose metal is bound to thiols and may then become sensitive to NO. Recent observations indicate that in response to NO synthesis, iron regulatory protein, a eukaryotic bifunctional [Fe-S] protein, switches from acting as aconitase to being an RNA-binding regulator, and we suggest that the interplay between NO or a NO-derived molecule and metal clusters at critical allosteric sites may be a crucial component of the cellular response to environmental stress.

Nitric oxide in sepsis

The synthesis of nitric oxide (NO) and its targets are reviewed physiologically during sepsis and wound healing, a self-limiting process in which mechanisms are still identified incompletely. NO also plays an active and direct role during infection, aimed at protecting the host and destroying the microbe. During septic shock, an overproduction of NO has been described experimentally and clinically that might be responsible for the systemic vasodilatation with hyporesponsiveness to exogenous vasoconstrictive agents. The different manipulations of NO pathway during sepsis are described (transcription and post-transcription of iNOS, enzymatic function, substrate availability, NO concentration, and NO effector molecules), although their clinical benefit remains controversial.

Nitric oxide and lung surfactant

Inhalation of nitric oxide (NO) is an experimental treatment for severe pulmonary hypertension. Being rapidly metabolized by hemoglobin, inhaled NO causes selective vasodilation in the pulmonary vascular bed. In addition to the vascular smooth muscle, other pulmonary structures are exposed to inhaled NO, resulting in suppression of NO synthesis in a variety of pulmonary cells and in potential toxicity. NO is a free radical that interacts with a number of proteins, particularly metalloproteins. Together with superoxide radical, it rapidly forms highly toxic peroxynitrite. Peroxynitrite is involved in the killing of microbes by activated phagocytosing macrophages. In severe inflammation, peroxynitrite may be responsible for damaging proteins, lipids, and DNA. Peroxynitrite added to surfactant in vitro is capable of decreasing the surface activity, inducing lipid peroxidation, decreasing the function of surfactant proteins, SP-A and SP-B, and inducing protein-associated nitro-tyrosine. Exposure of animals for prolonged periods (48 to 72 hours) to inhaled NO (80 to 120 ppm) has been associated with a decrease in surface activity. This is caused by binding of surfactant to iron-proteins that are modified by NO (particularly methemoglobin), or by peroxynitrite induced damage of surfactant. In contrast, exposure of isolated surfactant complex to NO during surface cycling strikingly decreases the inactivation of surfactant, preventing the conversion of surfactant to small vesicles that are no longer surface-active, and preventing lipid peroxidation. This finding is consistent with the function of NO as a lipid-soluble chain-braking antioxidant. It is possible that this lipophilic gas has as yet undefined roles in regulation of surfactant metabolism and maintenance of surface activity. Deficiency in pulmonary NO may be present during the early neonatal period in respiratory distress syndrome and in persistent fetal circulation. The premature lung is likely to be sensitive to NO toxicity that may include lung damage, abnormal alveolarization, and mutagenicity. Defining of the indications, the dosage, and the toxicity of inhaled NO therapy remains the challenge for experimental and clinical research.

Increased expression of inducible nitric oxide synthase in psoriatic skin and cytokine-stimulated cultured keratinocytes

Since nitric oxide (NO) has been implicated in the pathogenesis of various hyperproliferative and inflammatory diseases, the mRNA expression of constitutive nitric oxide synthase (cNOS) and inducible nitric oxide synthase (iNOS) were investigated in psoriatic skin by reverse transcriptase coupled to the polymerase chain reaction (PCR). The study showed that the mRNA expression of brain nitric oxide synthase (bNOS), one of two isoforms of cNOS, was weak in both psoriatic plaques lesions and uninvolved skin, while mRNA transcripts for the second isoform, endothelial nitric oxide synthase (eNOS), were not detectable using the present method. In contrast, the mRNA expression of iNOS was markedly increased in lesional skin as compared to uninvolved skin. Cultured human keratinocytes exposed to a combination of interleukin-1 beta (IL-1 beta) and tumour necrosis factor-alpha (TNF-alpha) for 4 h, showed strong gene expression of iNOS, while in 24 h, the expression had returned to baseline expression. In summary, the study demonstrates that mRNA for the inducible form of NOS is over-expressed in psoriatic lesions. The cause of this may be the local presence of inflammatory cytokines. These findings imply that iNOS may play an important part in local regulation of NO synthesis in psoriasis and other inflammatory dermatoses.

Subchronic exposure of cardiomyocytes to low concentrations of tumor necrosis factor alpha attenuates the positive inotropic response not only to catecholamines but also to cardiac glycosides and high calcium concentrations

The main purpose of this study was to determine the subchronic effects of low concentrations of tumor necrosis factor alpha (TNF alpha) on the inotropic response and on the cellular level of high energy phosphates of cardiomyocytes. Therefore, the inotropic response of cultured neonatal rat heart cells to 10(-5) M isoproterenol-, 10(-6) M ouabain-, 10(-5) M forskolin- and 2,4 mM calcium-perfusion was studied 24 h after exposure to TNF alpha (0.01/0.1/1/10/100 U/ml). In parallel experiments high energy phosphates (CP, ATP, ADP, AMP) were determined by high performance liquid chromatography. Furthermore, the reversibility of TNF alpha-induced changes was studied after washout of TNF alpha or after administration of anti-TNF alpha-antibody. Whereas control cells showed an increase of cell wall motion to 150 +/- 5% of baseline value during 10(-5) M isoproterenol-perfusion respectively 180 +/- 7% during 2,4 mM calcium-perfusion, 24 h exposure of the cells to 1 U/ml up to 100 U/ml TNF alpha resulted in an inhibition of the inotropic response. Almost complete inhibition was observed 12 h after exposure to TNF alpha and was reversible 12 h after administration of the anti-TNF alpha-antibody. If the cells were perfused with 10(-6) M ouabain or 10(-5) M forskolin, a similar inhibition of the inotropic response was observed 24 h after TNF alpha-exposure. Determination of high energy phosphates showed that 24 h TNF alpha-exposure resulted in a reversible decrease of ATP, ADP, AMP and CP by 30-40% (p < 0.05). However, a similar reduction of cellular high energy phosphate levels using a TNF alpha independent mechanism (2,5 mM 2-deoxy-D-glucose) did not inhibit the inotropic response of the cardiomyocytes. From our results we conclude that subchronic exposure to low concentrations of TNF alpha resulted in an almost complete but reversible inhibition of the response of cardiomyocytes to different inotropic agents suggesting that a common final step of the inotropic cascade might be altered by TNF alpha. Though energy metabolism of TNF alpha exposed cells was affected also, reduction of high energy phosphate levels alone did not explain the observed inhibition of the inotropic response of the cardiomyocytes.

Autocrine growth inhibition of IL-1 beta-treated cultured human aortic smooth muscle cells: possible role of nitric oxide

This study was designed to investigate whether interleukin (IL)-1 beta would stimulate nitric oxide (NO) production in cultured aortic vascular smooth muscle cells (VSMCs), and to determine the basic effect of the liberated NO on VSMC proliferation. NO production was estimated from nitrite concentration of culture medium in multi-well plates, determined by the Griess method. VSMCs were IL-1 beta-pretreated in insert cups, and co-cultured with untreated VSMC in the wells. 3H-thymidine (3H-Tdr) incorporation into the VSMC in wells was evaluated for VSMC proliferative activity. IL-1 beta stimulated NO production in VSMCs in a concentration-dependent manner. This effect was further enhanced by the addition of a membrane-permeable cyclic adenosine monophosphate derivative, dibutyryl cyclic AMP (db-cAMP), and was significantly reduced by concomitant use of an NO synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME). IL-1 beta-pretreated VSMCs significantly inhibited 3H-Tdr incorporation of the co-cultured VSMC. This inhibitory effect was significantly enhanced by the addition of db-cAMP, while this inhibition was significantly decreased by preincubation with L-NAME, and was abolished in the L-arginine-free medium. These results suggest that, in human VSMC, IL-1 beta stimulates NO production that is enhanced by intracellular cAMP accumulation, and that the liberated NO inhibits further VSMC proliferation in an autocrine fashion.

Differentiated properties and proliferation of arterial smooth muscle cells in culture

The smooth muscle cell is the sole cell type normally found in the media of mammalian arteries. In the adult, it is a terminally differentiated cell that expresses cytoskeletal marker proteins like smooth muscle alpha-actin and smooth muscle myosin heavy chains, and contracts in response to chemical and mechanical stimuli. However, it is able to revert to a proliferative and secretory active state equivalent to that seen during vasculogenesis in the fetus, and this is a prerequisite for the involvement of the smooth muscle cell in the formation of atherosclerotic and restenotic lesions. A similar transition from a contractile to a synthetic phenotype occurs when smooth muscle cells are established in culture. Accordingly, an in vitro system has been used extensively to study the regulation of differentiated properties and proliferation of these cells. During the first few days after seeding, the cells are reorganized structurally with a loss of myofilaments and formation of a widespread endoplasmic reticulum and a prominent Golgi complex. In parallel, they lose their contractility and instead become competent to divide in response to a large variety of mitogens, including platelet-derived growth factor (PDGF) and basic fibroblast growth factor (bFGF). After entering the cell cycle, they start to produce these and other mitogens on their own, and continue to replicate in the absence of exogenous stimuli for a restricted number of generations. Furthermore, they start to secrete extracellular matrix components such as collagen, elastin, and proteoglycans. The mechanisms that control this change in morphology and function of the smooth muscle cells are still poorly understood. Adhesive proteins such as fibronectin and laminin apparently have an important role in determining the basic phenotypic state of the cells and exert their effects via integrin receptors. The proliferative and secretory activities of the cells are influenced by a multitude of growth factors, cytokines, and other molecules. Although much work remains before an integrated view of this regulatory machinery can be achieved, there is no doubt that the cell culture technique has contributed substantially to our knowledge of smooth muscle differentiation and growth. At the same time, it has been crucial in exploring the role of these cells in vascular disease and developing new therapeutic strategies to cope with major causes of human death and disability.

Role of nitric oxide and superoxide anion in leukotoxin-, 9,10-epoxy-12-octadecenoate-induced mitochondrial dysfunction

The present study was carried out to explore the involvement of nitric oxide (NO) and superoxide anion (O2.-) in Leukotoxin (Lx)-induced suppression of mitochondrial respiration. Glutamate- and succinate-dependent oxygen consumption and cytochrome c oxidase activity were assayed. Lx-induced mitochondrial damage was significantly attenuated by the pretreatment of lung with 4 x 10(-4) M NG-monomethyl-L-arginine (L-NMMA) or 500 units/ml superoxide dismutase (SOD) in ex vivo. However, L-NMMA plus SOD pretreatment showed no additive effect on the recovery of mitochondrial functions. The same assay was performed after the exposure of intact mitochondria to NO containing solution (1.25 x 10(-5) M) or 0.1 mM KO2/18-Crown-6 solution, which generated O2.-(6.4 x 10(-5) M). NO, but not O2.-, significantly inhibited the respiration of isolated mitochondria in vitro. Thus, there were great discrepancies in the involvement of NO and O2.- between ex vivo and in vitro system. Together with the previous reports, these facts suggested that the mechanisms by which NO and O2.- probably from vascular constituent cells inhibit mitochondrial respiration function of isolated perfused rat lung may not be simply due to their direct reactions with mitochondrial electron transport chain components, but may rely on the formation of peroxynitrite, and/or peroxynitrite-derived oxidants.

Immunological mechanisms in atherosclerosis

Immunological mechanisms seem to be potent modulators of the atherosclerotic process. The presence of substantial numbers of T-lymphocytes in the lesion and local and circulating autoantibodies to plaque components suggests that a specific immune response is operating. Focal expression of adhesion molecules and local secretion of chemoattractants could mediate the recruitment of inflammatory cells to the lesion. Local cytokine and growth factor networks may operate later, controlling cell migration and proliferation. Although it is still important to realize the complexity of these mechanisms, the ongoing characterization of the molecular mechanisms in atherogenesis may lead to new strategies for intervention with the disease process.

Induction of L-arginine transport and nitric oxide synthase in vascular smooth muscle cells: synergistic actions of pro-inflammatory cytokines and bacterial lipopolysaccharide

1. The interactions between pro-inflammatory cytokines and bacterial lipopolysaccharide (LPS) on L-arginine transporter and inducible nitric oxide synthase (iNOS) activities were examined in rat cultured aortic smooth muscle cells. 2. LPS induced a concentration (0.01-100 micrograms ml-1) and time (8-24 h)-dependent stimulation of nitrite production which was accompanied by a parallel increase in L-arginine transport. 3. Unlike LPS, activation of smooth muscle cells with either interferon-gamma (IFN-gamma, 100 u ml-1), tumour necrosis factor-alpha (TNF-alpha, 300 u ml-1) or interleukin-1 alpha (IL-1 alpha, 100 u ml-1) failed to stimulate L-arginine transport or increase nitrite accumulation. 4. When applied in combination with LPS (100 micrograms ml-1) both IFN-gamma and TNF-alpha, but not IL-1 alpha, enhanced the effects observed with LPS alone. Furthermore, activation of cells with LPS and IFN-gamma had no effect on uptake of the neutral amino acid L-citrulline but selectively increased the Vmax for L-arginine transport 2.8 fold and nitrite levels from 24 +/- 7 to 188 +/- 14 pmol micrograms-1 protein 24 h-1. 5. The substrate specificity, Na- and pH-independence of saturable L-arginine transport in both unactivated (K(m) = 44 microM, Vmax = 3 pmol micrograms-1 protein min-1) and activated (K(m) = 75 microM, Vmax = 8.3 pmol micrograms-1 protein min-1) smooth muscle cells were characteristic of the cationic amino acid transport system y+. 6. Cycloheximide (1 microM) abolished induction of L-arginine transport and nitrite accumulation in response to LPS and IFN-gamma. In contrast, the glucocorticoid dexamethasone (10 microM, 24 h) selectively inhibited nitrite production. 7. Our results demonstrate that pro-inflammatory mediators selectively enhance transport of L-arginine under conditions of sustained NO synthesis by vascular smooth muscle cells. In addition, the differential inhibition of iNOS and L-arginine transporter activity by dexamethasone suggests that distinct signalling pathways mediate induction of the cationic transport protein and iNOS. The close coupling between substrate supply and NO production may have important implications in the pathogenesis of several disease states including endotoxin shock.

Myocardial calcium-independent nitric oxide synthase activity is present in dilated cardiomyopathy, myocarditis, and postpartum cardiomyopathy but not in ischaemic or valvar heart disease

OBJECTIVE

To determine the activity of the calcium-dependent constitutive (cNOS) and calcium-independent inducible nitric oxide (iNOS) synthases in heart tissue from patients with different cardiac diseases.

PATIENTS AND DESIGN

Endomyocardial biopsy specimens were obtained from patients with dilated hearts (by echocardiography and ventriculography) and normal coronary arteries (by selective angiography). Recognised clinical, radiological, and histopathological criteria were used to diagnose non-inflammatory dilated cardiomyopathy (DCM) (n = 6), inflammatory cardiomyopathy (ICM) (n = 5), and peripartum cardiomyopathy (PPCM) (n = 3). Comparative groups were chosen with similarly dilated hearts caused by ischaemic (n = 5) or valvar disease (n = 4), and, in addition, non-dilated hearts with ischaemic (n = 5) and valvar (n = 3) disease. Venous blood was taken at the time of myocardial biopsy for assay of plasma tumour necrosis factor alpha (TNF alpha).

RESULTS

Myocardial tissue from patients with DCM, ICM, and PPCM showed considerable iNOS activity (16.8 (2.7) pmol citrulline/mg protein/min) with little or no cNOS activity (1.3 (0.9) pmol citrulline/mg protein/min). In contrast, myocardial tissue from patients with both dilated and non-dilated hearts of ischaemic or valvar aetiology showed cNOS and little, if any, iNOS activity (dilated--cNOS 11.7 (2.4) and iNOS 0.8 (0.6) pmol citrulline/mg protein/min; non-dilated--cNOS 12.1 (1.8) and iNOS 1.4 (0.8) pmol citrulline/mg protein/min). Plasma TNF alpha was detectable only in patients with inflammatory DCM.

CONCLUSIONS

These results support the hypothesis the generation of nitric oxide by iNOS accounts for some of the dilatation and impaired contractility associated with inflammatory and non-inflammatory dilated cardiomyopathy and peripartum cardiomyopathy.

Oxidative metabolism in sepsis and sepsis syndrome

The high mortality associated with sepsis syndrome and multiple organ dysfunction syndrome has persisted despite extraordinary research efforts in the laboratory and the intensive care unit. These syndromes produce systemic tissue damage that is likely to result from widespread inflammation and subsequent endothelial injury. This article reviews the oxidative metabolic effects and responses to sepsis syndrome at several levels: the oxygen transport system, the cell, and the mitochondrion. Specifically, aerobic metabolism of carbon substrates and oxygen is altered in sepsis. As a result of systemic inflammation and nonmetabolic oxygen use, oxidative stress may occur both outside and inside the cell. The consequences of these oxidative processes during sepsis may be ongoing cell damage mediated by reactive oxygen and nitrogen oxide species that culminates in multisystem organ failure.

Involvement of nitric oxide in IFN-gamma-mediated reduction of microvessel smooth muscle cell proliferation

Previous studies in our laboratory demonstrated that murine cerebral microvessel smooth muscle cells (SMC) activate syngeneic CD4+ T-cells in vitro. These T-cells, or their culture supernatants, in turn, strongly inhibit proliferation of the SMC. The present study focuses on IFN-gamma as a mediator of inhibition of SMC proliferation, and addresses the molecular mechanism of this inhibition. IFN-gamma profoundly reduced the proliferation of murine brain microvessel smooth muscle cells in vitro. Three lines of evidence indicate that nitric oxide contributed to this effect: (1) IFN-gamma-mediated inhibition of proliferation correlated with the quantity of nitrite, a stable breakdown product of nitric oxide, in culture supernatants; (2) the addition of N(g)- monomethyl-l-arginine, and inhibitor of nitric oxide synthesis, restored proliferation to control or near control levels; and (3) the addition of hemoglobin, which has a high affinity for, and thus sequesters nitric oxide, also resulted in significant restoration of the proliferative response. However, the nitric oxide donating chemical sodium nitro-prusside, at concentrations up to 100 microM, had no direct cytostatic effect. These results suggest that nitric oxide is a necessary but insufficient component in IFN-gamma-mediated inhibition of microvessel smooth muscle cell proliferation. TNF-alpha also stimulated nitric oxide production by the smooth muscle cells, but was not as potent as IFN-gamma at inhibiting proliferation. Knowledge of the physiological effects of lymphokines on cells of the brain microvasculature will contribute towards a better understanding of inflammatory processes in diseases such as multiple sclerosis and infectious encephalitis.

Nitric oxide regulates mitochondrial respiration and cell functions by inhibiting cytochrome oxidase

Nitric oxide (NO) reversibly inhibits mitochondrial respiration by competing with oxygen at cytochrome oxidase. Concentrations of NO measured in a range of biological systems are similar to those shown to inhibit cytochrome oxidase and mitochondrial respiration. Inhibition of NO synthesis results in a stimulation of respiration in a number of systems. It is proposed that NO exerts some of its main physiological and pathological effects on cell functions by inhibiting cytochrome oxidase. Further NO may be a physiological regulator of the affinity of mitochondrial respiration for oxygen, enabling mitochondria to act as sensors of oxygen over the physiological range.

Methylene blue increases myocardial function in septic shock

OBJECTIVE

To study whether the circulatory changes of human septic shock are mediated in part by nitric oxide.

DESIGN

Open-label, nonrandomized clinical trial on the effects of methylene blue, an inhibitor of nitric oxide action.

SETTING

Intensive care unit of a teaching hospital.

PATIENTS

Nine consecutive patients with documented septic shock and a pulmonary artery catheter in place, after initial resuscitation with fluids, sympathomimetics, and mechanical ventilation.

INTERVENTIONS

Hemodynamic and metabolic variables were measured before and then 15, 30, 60, and 120 mins after the start of a 20-min infusion of 2 mg/kg of methylene blue.

MEASUREMENTS AND MAIN RESULTS

Patients had a hyperdynamic circulation, and methylene blue increased (p < .01) mean arterial pressure from 84 +/- 18 to 109 +/- 31 mm Hg and cardiac index from 4.7 +/- 0.9 to 5.6 +/- 1.2 L/min/m2, before and 30 mins after starting the methylene blue infusion, respectively. Cardiac filling pressures did not change. In the same time interval, the subnormal systemic vascular resistance index increased (p = .09) and arterial compliance decreased (p < .05). Oxygen delivery and oxygen uptake increased (p < .05) from 714 +/- 188 to 865 +/- 250 mL/min/m2 and from 160 +/- 39 to 186 +/- 44 mL/min/m2, respectively. Except for heart rate, which increased by 11 +/- 8 beats/min (p < .01), variables returned to baseline values at time = 120 mins.

CONCLUSIONS

After initial resuscitation from human septic shock, a single dose of methylene blue transiently increases mean arterial pressure and oxygen uptake, associated with a decrease in arterial compliance and increases in myocardial function and oxygen delivery. Hence, nitric oxide may be a mediator of the circulatory changes of human septic shock.

Cyclic guanosine 3',5'-monophosphate mediates 3-morpholinosydnonimine-induced inhibition of human natural killer cells

Nitric oxide (NO) donors were used to investigate the effect of NO on and the role of cyclic GMP in the regulation of human natural killer (NK) cell function. NO-producing drugs, molsidomine and its metabolite 3-morpholinesydnonimine (SIN-1), inhibited NK cell-mediated cytotoxicity significantly at 0.04-5 mM. At 1 mM, SIN-1 completely inhibited NK cell activity while molsidomine decreased NK cell-mediated cytolysis by 35% of the control value. These data suggest that NO from exogenous NO-donors may down-regulate NK cell cytotoxic function. The stimulatory effect of interferon-gamma (IFN-gamma) on human NK cell-mediated killing could not overtake the NK cell inhibition induced by the NO releasing drugs, indicating different modes of action for IFN-gamma and SIN-1. The results in the present study also showed that SIN-1 (1 mM) stimulated cyclic GMP production 37-fold in NK cells. In the presence of 0.5 mM IBMX, a phosphodiesterase inhibitor, the increase in cyclic GMP was even more pronounced, demonstrating a relation between cyclic GMP stimulation and NK cell inhibition by SIN-1. Further evidence for mediation via cyclic GMP was provided by the finding that methylene blue (20 microM), an inhibitor of soluble guanylate cyclase, decreased both the inhibition of SIN-1-induced NK cell cytotoxicity as well as cyclic GMP formation. Moreover, membrane-penetrating cyclic GMP and its analogues inhibited NK cell-mediated cytolysis significantly. Molsidomine was without effect on cyclic GMP levels. Our data indicate that cyclic GMP may play a role in human NK cell regulation and suggest that the inhibitory effect of cGMP may be elicited by NO.

Involvement of inducible nitric oxide synthase in the inflammatory process of myocardial infarction

Inducible nitric oxide synthase (iNOS), which catalyzes the reaction of L-arginine to L-citrulline and nitric oxide (NO), plays an important role in immune-mediated cardiac disorders. The present report summarizes and discusses findings on the induction of NOS in myocardial infarction of rabbits. iNOS was significantly increased in infarcted myocardium 48 h after coronary artery ligation. The effect persisted for 14 days and declined thereafter. Immunohistochemical localization revealed macrophages as a major source of iNOS expression; iNOS expression was also present in infarcted human myocardium. Increased iNOS activity appeared to be related to the induction of apoptosis in infiltrating macrophages and cardiomyocytes. Moreover, preferential inhibition of iNOS by S-methylisothiourea sulfate (SMT) resulted in significant improvement of left ventricular performance and increased regional myocardial blood flow. These findings suggest that selective inhibition of iNOS activity may provide a therapeutic strategy in cardiac disorders such as myocardial infarction.

Cardiomyopathy: a role for nitric oxide?

The negative inotropism, myocardial dilatation and cytotoxicity in inflammatory heart disorders may be due to increased generation of nitric oxide (NO) by immunological induction of a high output NO pathway. This short review discusses the initial experiments which lead to this hypothesis, and evaluates data that this pathway exists in animal and human cardiomyopathic disorders. It is proposed that manipulation of this pathway may prove to be beneficial in patients with these disorders.

T lymphocytes from human atherosclerotic plaques recognize oxidized low density lipoprotein

Atherosclerosis, an underlying cause of myocardial infarction, stroke, and other cardiovascular diseases, consists of focal plaques characterized by cholesterol deposition, fibrosis, and inflammation. The presence of activated T lymphocytes and macrophages and high expression of HLA class II molecules are indicative of a local immunologic activation in the atherosclerotic plaque, but the antigen(s) involved has not yet been identified. We established T-cell clones from human atherosclerotic plaques using polyclonal mitogens as stimuli and exposed the clones to potential antigens in the presence of autologous monocytes as antigen-presenting cells. Four of the 27 CD4+ clones responded to oxidized low density lipoprotein (oxLDL) by proliferation and cytokine secretion; this response was dependent on autologous antigen-presenting cells and restricted by HLA-DR. All clones that responded to oxLDL secreted interferon gamma upon activation, but only one produced interleukin 4, suggesting that the response to oxLDL results in immune activation and inflammation but may not be a strong stimulus to antibody production. No significant response to oxLDL could be detected in CD4+ T-cell clones derived from the peripheral blood of the same individuals. Together, the present data suggest that the inflammatory infiltrate in the atherosclerotic plaque is involved in a T-cell-dependent, autoimmune response to oxLDL.

Direct measurement of the accumulation and mitochondrial conversion of nitric oxide within Chinese hamster ovary cells using an intracellular electron paramagnetic resonance technique

We have developed an electron paramagnetic resonance (EPR) method for the nondestructive detection and quantification of intracellular NO in real time. Based upon this technique, we have obtained evidence for the metabolism of this bioregulatory molecule by mitochondria. Line-broadening of the EPR signal of a coal derivative, fusinite, was calibrated as a function of NO concentration in aqueous solution. The methodology was validated using two compounds which release NO in a controlled and predictable manner with first-order rate constants k1 = 5.0 x 0.10(-3) s-1 and k'1 = 3.4 x 10(-4) s-1 (35 degrees C). Fusinite was internalized in Chinese hamster ovary cells (CHO) by phagocytosis, after which the cells were allowed to consume the available O2, producing an hypoxic environment. The NO released from one of the NO donors, added to the culture fluid at an initial concentration of 50 microM, was directly measured in the intracellular environment as line-broadening of the fusinite EPR signal. The linewidth diminished with time, indicating that NO was being converted to a non-paramagnetic species by the cells with an apparent zero-order rate constant of 5 x 10(8) NO molecules cell-1 min-1 (20 degrees C). Addition of cyanide to the culture medium (5 mM final concentration) inhibited this disappearance of NO. NO also was converted in the presence of isolated mitochondria in the absence of oxygen. These observations suggest that under hypoxic conditions, there exists in CHO cells a metabolic pathway for the conversion of NO to diamagnetic species, which involves interactions with mitochondria.