Interactions of constitutive nitric oxide with PAF and thromboxane on rat intestinal vascular integrity in acute endotoxaemia

Loss of PAFR prevents neuroinflammation and brain dysfunction after traumatic brain injury

Traumatic brain injury (TBI) is a principal cause of death and disability worldwide, which is a major public health problem. Death caused by TBI accounts for a third of all damage related illnesses, which 75% TBI occurred in low and middle income countries. With the increasing use of motor vehicles, the incidence of TBI has been at a high level. The abnormal brain functions of TBI patients often show the acute and long-term neurological dysfunction, which mainly associated with the pathological process of malignant brain edema and neuroinflammation in the brain. Owing to the neuroinflammation lasts for months or even years after TBI, which is a pivotal causative factor that give rise to neurodegenerative disease at late stage of TBI. Studies have shown that platelet activating factor (PAF) inducing inflammatory reaction after TBI could not be ignored. The morphological and behavioral abnormalities after TBI in wild type mice are rescued by general knockout of PAFR gene that neuroinflammation responses and cognitive ability are improved. Our results thus define a key inflammatory molecule PAF that participates in the neuroinflammation and helps bring about cerebral dysfunction during the TBI acute phase.

Vasodilator factors in the systemic and local adaptations to pregnancy

We postulate that an orchestrated network composed of various vasodilatory systems participates in the systemic and local hemodynamic adaptations in pregnancy. The temporal patterns of increase in the circulating and urinary levels of five vasodilator factors/systems, prostacyclin, nitric oxide, kallikrein, angiotensin-(1-7) and VEGF, in normal pregnant women and animals, as well as the changes observed in preeclamptic pregnancies support their functional role in maintaining normotension by opposing the vasoconstrictor systems. In addition, the expression of these vasodilators in the different trophoblastic subtypes in various species supports their role in the transformation of the uterine arteries. Moreover, their expression in the fetal endothelium and in the syncytiotrophoblast in humans, rats and guinea-pigs, favour their participation in maintaining the uteroplacental circulation. The findings that sustain the functional associations of the various vasodilators, and their participation by endocrine, paracrine and autocrine regulation of the systemic and local vasoactive changes of pregnancy are abundant and compelling. However, further elucidation of the role of the various players is hampered by methodological problems. Among these difficulties is the complexity of the interactions between the different factors, the likelihood that experimental alterations induced in one system may be compensated by the other players of the network, and the possibility that data obtained by manipulating single factors in vitro or in animal studies may be difficult to translate to the human. In addition, the impossibility of sampling the uteroplacental interface along normal pregnancy precludes obtaining longitudinal profiles of the various players. Nevertheless, the possibility of improving maternal blood pressure regulation, trophoblast invasion and uteroplacental flow by enhancing vasodilation (e.g. L-arginine, NO donors, VEGF transfection) deserves unravelling the intricate association of vasoactive factors and the systemic and local adaptations to pregnancy.

Enantiomers of higenamine inhibit LPS-induced iNOS in a macrophage cell line and improve the survival of mice with experimental endotoxemia

The importance of development of single enantiomers (optically pure isomers) of chiral molecules has been recognized and manifested in countless pharmaceutical and biological advancement. (RS)-(+/-)-Higenamine (racemic mixture), an active ingredient of Aconite tuber, has been shown to have antioxidant activity along with inhibitory action of iNOS expression in various cells. In the present study, the effects of each enantiomer of higenamine [(S)-(-)-higenamine and (R)-(+)-higenamine] were investigated in comparison with the effects of racemic mixture [(RS)-(+/-)-higenamine] on iNOS expression and NO production in RAW 264.7 cells activated with LPS. In addition, the effects of higenamine enantiomers on the survival rates were also investigated using mice, in which each test compound was injected (i.p.) 90 min prior to LPS. All three forms of higenamine inhibited iNOS expression and reduced NO production with IC50 of 26.2, 86.3, and 53.4 microM, for (S)-, (R)-, and (RS)-higenamine, respectively. (S)-higenamine also significantly reduced serum NOx level and increased survival rates in LPS-treated mice. In contrast, (R)-isomer only showed tendency to increase the survival rates which was not statistically significant when compared to LPS-treated controls. Taken together, it was concluded that (S)-higenamine may be more beneficial than (R)-enantiomer in diseases associated with iNOS over-expression, such as septic shock.

Synergistic interaction of endogenous platelet-activating factor and vasopressin in generating angina in rats

We examined the involvement of endogenous vasopressin and platelet-activating factor (PAF) in the pathogenesis of two types of experimental angina in urethane-anaesthetised male Wistar rats. In the first model, epinephrine (10 microg kg(-1)) was injected into the tail vein, followed at the development of the maximum blood pressure response, i.e., 30 s later, by phentolamine (15 mg kg(-1)). In the second model, the vasopressin V1 receptor agonist ornithine-vasopressin (ornipressin; 0.5 IU kg(-1), i.v.) was administered. The heart rate, mean arterial blood pressure and surface electrocardiogram (ECG, standard lead II) were registered simultaneously. As a measure of myocardial ischaemia, at 1 min after phentolamine or ornipressin administration, we found significant ST-segment depression, lasting for more than 10 or 5 min, respectively. Pretreatment (15 min, s.c.) with the vasopressin V1 receptor antagonist Mca1,Tyr(Me)2AVP (the Manning peptide; 0.02-0.2 microg kg(-1)) or the platelet-activating factor receptor antagonist ginkgolide B (BN 52021; 0.25-2.5 mg kg(-1)) alone caused a dose-dependent reduction of the ST-segment depression. Concurrent administration of the two antagonists in their threshold doses (0.02 microg kg(-1) and 0.25 mg kg(-1)) also attenuated the ST-segment depression in both models. Neither antagonist affected the blood pressure or heart rate changes throughout the studies. Our results suggest that endogenous vasopressin and platelet-activating factor interact synergistically in provoking myocardial ischaemia in vivo in experimental angina in the rat.

PAR1-dependent and independent increases in COX-2 and PGE2 in human colonic myofibroblasts stimulated by thrombin

Subepithelial myofibroblast-derived prostaglandin E(2) (PGE(2)) regulates epithelial chloride secretion in the intestine. Thrombin is elevated in inflammatory conditions of the bowel. Therefore, we sought to determine a role for thrombin in regulating PGE(2) synthesis by colonic myofibroblasts. Incubation of cultured CCD-18Co colonic myofibroblasts with thrombin, the proteinase-activated receptor 1 (PAR(1))-activating peptide (Cit-NH(2)), and peptides corresponding to 2 noncatalytic regions of thrombin (TP367 and TP508) for 18 h increased both cyclooxygenase (COX)-2 expression (immunocytochemistry) and PGE(2) synthesis (enzyme immunoassay). Inhibition of thrombin by D-Phe-Pro-Arg-chloromethylketone (PPACK) did not significantly reduce PGE(2) synthesis, which remained elevated compared with control. We also investigated the basic fibroblast growth factor (bFGF) dependence of thrombin-induced PGE(2) elevations. Recombinant human bFGF concentration dependently increased PGE(2) synthesis, and a bFGF neutralizing antibody inhibited PGE(2) synthesis induced by TP367 and TP508 (approximately 40%) and by thrombin (approximately 20%) (but not Cit-NH(2)). Thrombin, therefore, upregulates COX-2-derived PGE(2) synthesis by both catalytic cleavage of PAR(1) and bFGF-dependent noncatalytic activity. This presents a novel mechanism by which intestinal myofibroblasts might regulate epithelial chloride secretion.

Is nitric oxide overproduction the target of choice for the management of septic shock?

Sepsis is a heterogeneous class of syndromes caused by a systemic inflammatory response to infection. Septic shock, a severe form of sepsis, is associated with the development of progressive damage in multiple organs, and is a leading cause of patient mortality in intensive care units. Despite important advances in understanding its pathophysiology, therapy remains largely symptomatic and supportive. A decade ago, the overproduction of nitric oxide (NO) had been discovered as a potentially important event in this condition. As a result, great hopes arose that the pharmacological inhibition of NO synthesis could be developed into an efficient, mechanism-based therapeutic approach. Since then, an extraordinary effort by the scientific community has brought a deeper insight regarding the feasibility of this goal. Here we present in summary form the present state of knowledge of the biological chemistry and physiology of NO. We then proceed to a systematic review of experimental and clinical data, indicating an up-regulation of NO production in septic shock; information on the role of NO in septic shock, as provided by experiments in transgenic mice that lack the ability to up-regulate NO production; effects of pharmacological inhibitors of NO production in various experimental models of septic shock; and relevant clinical experience. The accrued evidence suggests that the contribution of NO to the pathophysiology of septic shock is highly heterogeneous and, therefore, difficult to target therapeutically without appropriate monitoring tools, which do not exist at present.

Thromboxane mediates pulmonary hypertension and lung inflammation during hyperacute lung rejection

The role of thromboxane (Tx) in hyperacute rejection of pig lung by human blood was studied in an ex vivo model, wherein lungs from juvenile piglets were perfused with fresh heparinized human blood. In this model, hyperacute lung rejection was characterized by an abrupt rise in pulmonary vascular resistance (PVR; >1 cmH2O · ml−1· min) and prolific Tx elaboration (>15 ng/ml) within 5 min and loss of function within 10 min. Although papaverine significantly blunted the rise in PVR (<0.2 cmH2O · ml−1· min), Tx production was not inhibited (>20 ng/ml), and florid tracheal edema was usually evident within 20 min. In contrast, both inhibition of Tx synthesis (Tx < 3 ng/ml) with OKY-046 and blockade of the Tx receptor with SQ-30741 (Tx > 20 ng/ml) were not only associated with significantly lower peak PVRs (<0.2 cmH2O · ml−1· min) but also with attenuated increase in lung wet-to-dry ratio and airway edema. In concert, elaboration of histamine and tumor necrosis factor was blunted, and median survival increased >10-fold to 2 h (SQ-30741) and >4 h (OKY-046). Depletion of the pig lung macrophages with dichloromethyl bisphosphonate in liposomes, but not Pall filtration of the human blood or liposomes alone, significantly inhibited Tx elaboration (<0.2 vs. >8 ng/ml for Pall filtration or liposomes) and blunted PVR elevation (<0.3 cmH2O · ml−1· min) during initial perfusion. C3a and histamine elaboration were inhibited, and median survival was significantly prolonged (>4 h). These findings implicate Tx in the inflammation associated with hyperacute lung rejection and demonstrate that pulmonary intravascular macrophages are critical to its elaboration.

Helicobacter pylori lipopolysaccharide-provoked injury to rat gastroduodenal microvasculature involves inducible nitric oxide synthase

The actions of a purified Helicobacter pylori lipopolysaccharide (3 mg x kg(-1), i.v.) on rat gastric antral and duodenal microvascular integrity (determined as radiolabelled albumin leakage) and the expression of the inducible nitric oxide (NO) synthase (iNOS; assessed by the citrulline assay) were investigated 4 h after challenge. Significant increases of albumin leakage and expression of iNOS in both antral and duodenal tissues were observed following challenge. Concurrent administration of the selective iNOS inhibitor, 1400W (N-(8-(aminomethyl)benzyl)-acetamidine; 0.2-1 mg x kg(-1), s.c.), with lipopolysaccharide, caused a dose-dependent attenuation of the gastric and duodenal albumin leakage. Thus, H. pylori lipopolysaccharide can initiate the expression of iNOS in the stomach and duodenum following systemic challenge, which can provoke gastroduodenal microvascular dysfunction.

Interactions of pro-inflammatory and vasoactive mediators with nitric oxide in the regulation of rat vascular permeability during laparotomy

Inhibition of constitutive nitric oxide (NO) synthases by administration of N(G)-nitro-L-arginine methyl ester (L-NAME) during abdominal laparotomy provokes extensive vascular leakage in the rat gastrointestinal tract, assessed by the extravasation of [125I]human serum albumin. In the present study, the role of vasoactive or neutrophil-derived pro-inflammatory mediators in this process has been investigated. Administration of the thromboxane synthase inhibitor, 1-benzyl-imidazole (BZI, 25-50 mg kg(-1), s.c.), the platelet-activating factor (PAF) receptor antagonist, 3-[4-(2-chlorophenyl)-9-methyl-6H-thienol-[3,2-f][1,2,4]-triazolo- [4, 3-a][1,4]-diazepine-2-yl]-1-(4-morpholynil)-1-propionate (WEB 2086; 0.5-1 mg kg(-1), s.c.), the 5-lipoxygenase synthase inhibitor, N-(4-benzyloxybenzyl)-acetohydroxamic acid (BW A137C; 4-20 mg kg(-1), s.c.) or the vasopressin pressor receptor antagonist ([Mca(1), Tyr(Me)(2),Arg(8)]vasopressin/Manning peptide; 0.01-0.2 microg kg(-1), s.c.) dose-dependently reduced the intestinal plasma leakage provoked by L-NAME (5 mg kg(-1), s.c.), following a 5-cm abdominal laparotomy in anaesthetised rats. These findings suggest that constitutive NO synthase effectively counteracts the damaging actions on microvascular integrity of mediators, including thromboxanes, PAF, leukotrienes and vasopressin, released during surgical intervention.

Platelet activation and modulation of the induction of nitric oxide synthase in the conscious rat

Injection of lipopolysaccharide (LPS) (Salmonella W. Typhosa i.v. bolus) into conscious rats, induced a rapid drop of circulating platelets analogous to that induced by ADP. The animals showed a small fall in mean arterial blood pressure (MABP), an increase in heart rate and a significant increase in plasma nitrite and nitrate level. This result is consistent with the stimulation of an inducible NO synthase (i-NOS). The administration of the stable prostacyclin analogue, iloprost plus ADP or LPS, significantly protected against the decrease in free platelet number induced by ADP or LPS. The plasma nitrite and nitrate level stimulated by LPS was significantly reduced by iloprost and also by prostacyclin. These results are consistent with an inhibition of i-NOS by agents that increase the intracellular level of cAMP. The administration of the NO donor S-Nitroso-N-acyl-D-penicillamine (SNAP) plus ADP or LPS, significantly prevented thrombocytopenia induced by ADP and by LPS. SNAP did not decrease the plasma nitrite and nitrate level stimulated by LPS; furthermore it induced a significant increase of heart rate, without affecting MABP, suggesting a direct accelerating effect of NO on the sino-atrial node. The administration of S-nitroso-glutathione (GSNO), a stable nitrosothiol, plus ADP or LPS, significantly prevented thrombocytopenia induced by ADP but not by LPS. GSNO significantly reduced the plasma nitrite and nitrate level stimulated by LPS. These data demonstrate that the L-Arginine: NO pathway in vivo may be modulated by prostanoids and that compounds which increase cAMP, such as iloprost, are able to protect against LPS-induced early thrombocytopenia.

Nitric oxide modulates the gastrointestinal plasma extravasation following intraabdominal surgical manipulation in rats

The actions of nitric oxide (NO) on gastrointestinal plasma loss, assessed by the leakage of [125I]human serum albumin, provoked by intraabdominal surgery and organ manipulation has been investigated in pentobarbitone-anaesthesized rats. Gentle manipulation (3 min) of the stomach or the small intestine following laparotomy leads to an increase in albumin extravasation in the stomach, duodenum, jejunum and colon over 1 h. Administration of the NO synthase inhibitors, N(G)-nitro-L-arginine methyl ester (1-5 mg kg(-1), s.c.) and N(G)-monomethyl-L-arginine (12.5-50 mg kg(-1), s.c.), provoked a further substantial elevation of gastrointestinal albumin extravasation in the surgically manipulated rat, but not in control rats. This effect could be prevented by the pretreatment (15 min) with L-arginine (300 mg kg(-1), s.c.) or by the concurrent infusion of the NO donor, S-nitroso-glutathione (5 microg kg(-1) min(-1), i.v.). Endogenous NO, most likely formed by endothelial NO synthase, thus appears to maintain microvascular integrity during surgery and organ manipulation of the gastrointestinal tract.

Hyperbaric oxygen increases plasma exudation in rat trachea: involvement of nitric oxide

This study investigates the microvascular permeability changes in tracheal tissue of rats exposed to hyperbaric oxygen (HBO). Rats, following exposure to HBO or ambient air (control animals) for 1.5, 3 and 6 h, were prepared for recording of nitric oxide exhaled (FENO) in air using a chemiluminescence analyser. The level of FENO was not statistically different in the two groups. Plasma exudation, evaluated by measuring the leakage of Evans blue (EB) dye into the tracheal tissue, was significantly elevated (48, 86 and 105% at 1.5, 3 and 6 h, respectively) in HBO-treated rats. Plasma exudation in the trachea of control rats was significantly increased (42%, P<0.05) by NG-nitro-L-arginine methyl ester (L-NAME), whereas it was significantly reduced (31%, P<0.05) in rats exposed to HBO for 3 h. N-acetylcysteine (NAC) and flunisolide significantly prevented the increase in plasma leakage in HBO-treated rats. In contrast, indomethacin was devoid of anti-exudative activity in these experiments. Western immunoblot showed a significant increase in the level of inducible nitric oxide synthase (iNOS) protein in the tracheal homogenates of HBO-treated rats, as compared to basal levels. These results indicate that nitric oxide (NO) is involved in the maintenance of microvascular permeability in tracheal tissue of rats. The protective effect observed with the steroid seems to support this hypothesis. Furthermore, the beneficial action of NAC underlines that reactive oxygen species participate in the microvascular permeability changes observed in tracheal tissue of rats exposed to HBO.

Endogenous nitric oxide in the maintenance of rat microvascular integrity against widespread plasma leakage following abdominal laparotomy

1. The role of nitric oxide (NO) in the maintenance of microvascular integrity during minor surgical manipulation has been evaluated in the rat. 2. The NO synthase inhibitors, NG-nitro-L-arginine methyl ester (L-NAME, 5 mg kg(-1), s.c.) and N(G)-monomethyl-L-arginine (L-NMMA, 50 mg kg(-1), s.c.) had no effect on microvascular leakage of radiolabelled albumin over 1 h in the stomach, duodenum, jejunum, colon, lung and kidney in the un-operated conscious or pentobarbitone-anaesthetized rat. 3. In contrast, in anaesthetized rats with a midline abdominal laparotomy (5 cm), L-NAME (1-5 mg kg(-1), s.c.) or L-NMMA (12.5-50 mg kg(-1), s.c.) dose-dependently increased gastrointestinal, renal and pulmonary vascular leakage, effects reversed by L-arginine pretreatment (300 mg kg(-1), s.c., 15 min). These actions were not observed in anaesthetized rats that had only received a midline abdominal skin incision (5 cm). 4. Pretreatment with a rabbit anti-rat neutrophil serum (0.4 ml kg(-1), i.p.), 4 h before laparotomy, abolished the plasma leakage induced by L-NAME in all the organs investigated. 5. These results indicate that the following abdominal laparotomy, inhibition of constitutive NO synthase provokes vascular leakage in the general microcirculation, by a process that may involve neutrophils. Such effects could thus confound studies on the microvascular actions of NO synthase inhibitors using acute surgically prepared in vivo models. The findings thus suggest that constitutively-formed NO has a crucial role in the maintenance of acute microvascular integrity following abdominal surgical intervention.

The role of nitric oxide and metalloproteinases in the pathogenesis of hyperoxia-induced lung injury in newborn rats

The effects of nitric oxide (NO) and metalloproteinases (MMP-2 and MMP-9) in the pathogenesis of hyperoxia-induced lung damage in newborn rats were examined. Three-day-old rat pups were subjected to hyperoxia (> or = 95% O2) or room air for 7 and 14 days. Some animals were treated with NG-L-nitro-L-arginine methyl ester (L-NAME, 10 mg kg(-1), s.c., daily). Histology, morphometry, oedema, Ca2+-dependent and -independent NO synthase (NOS) activities, expression of NOS isoforms and the activities of MMP-2 and MMP-9 were measured in lungs of hyperoxic and control animals. Exposure of rats to hyperoxia for 7 days resulted in alveolar sac injury characterized by the presence of cellular debris, red cell extravasation and inflammatory infiltration with mononuclear cells. Lung water content, epithelial, smooth muscle layers and total airway thickness was similar to controls. In contrast, exposure of rats to hyperoxia for 14 days resulted in lung oedema, inflammation and epithelial proliferation. Hyperoxia caused a decrease in Ca2+-dependent NOS activity, an effect that was associated with increased expression of eNOS protein. In control rats, Ca2+-dependent NOS activity and expression of eNOS were reduced at 14 days. Hyperoxia caused 10 fold increase in the activity of Ca2+-independent NOS that remained significantly elevated after 14 days of exposure to hyperoxia. The activity of this enzyme was unchanged in control rats. In lungs of hyperoxic rats, the immunoblot showed time-dependent, biphasic expression (peak at 7 days) of iNOS. The profile of expression of iNOS in control rats was similar. The activities of MMPs were increased in lungs of hyperoxic animals. The L-NAME treatment of hyperoxic animals reduced lung oedema and epithelial proliferation, but enhanced the activities of MMPs. L-NAME exerted no significant effects in control rats. It is concluded that increased generation of NO contributes to the pathogenesis of hyperoxia-induced lung damage in newborn rats.

Early phase microvascular interactions in rat jejunum between nitric oxide and vasopressin following indomethacin administration

The involvement of endogenous vasopressin in the actions of indomethacin following the concurrent administration of the nitric oxide (NO) synthase inhibitor, N^G -nitro-l-arginine methyl ester (l-NAME), on acute intestinal microvascular permeability has been investigated in the rat. Administration of indomethacin (10mg/kg, s.c.) or L-NAME (10mg/kg, s.c.) alone did not affect jejunal and ileal vascular permeability after 1 h, as determined by the leakage of radiolabelled serum albumin. In contrast, when indomethacin (10mg/kg, s.c.) was injected concurrently with L-NAME (2-10mg/kg, s.c), significant dose-dependent plasma leakage occurred in the jejunum. Pretreatment with l-arginine (300 mg/kg s.c.) 15 min prior to l-NAME prevented these changes in microvascular permeability. Moreover, pretreatment with the vasopressin pressor-receptor antagonist, d(CH₂ )₅ Tyr(Me)AVP (0.01-0.2m̈g/kg, s.c.) dose-dependently attenuated such damage. These findings suggest that following indomethacin administration, the early inhibition of NO synthase leads to acute microvascular injury involving vasopressin in the rat jejunum. This suggests a protective role of NO, formed by constitutive NO synthase, counteracting effectively the deleterious actions of endogenous vasopressin.

Modulation of leukocyte-endothelial interactions by reactive metabolites of oxygen and nitrogen: relevance to ischemic heart disease

Ischemia and reperfusion (I/R) are thought to play an important role in the pathophysiology of ischemic diseases of the heart. It is now well appreciated that leukocyte-endothelial cell interactions are important determinants for I/R-induced microvascular injury and dysfunction. There is a growing body of experimental data to suggest that reactive metabolites of oxygen and nitrogen are important physiological modulators of leukocyte-endothelial cell interactions. A number of investigators have demonstrated that I/R enhances oxidant production within the microcirculation resulting in increases in leukocyte adhesion and transendothelial cell migration. Several other studies have shown that exogenous nitric oxide (NO) donors may attenuate leukocyte and platelet adhesion and/or aggregation in a number of different inflammatory conditions including I/R. The objective of this review is to discuss the physiological chemistry of reactive metabolites of oxygen and nitrogen with special attention given to those interactions that may modulate leukocyte-endothelial cell interactions, provide an overview of the evidence implicating reactive metabolites of oxygen and nitrogen as modulators of leukocyte-endothelial cell interactions in vivo, and discuss how these mechanisms may be involved in the pathophysiology of ischemic heart disease.

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.

Differential expression of inducible nitric oxide synthase messenger RNA along the longitudinal and crypt-villus axes of the intestine in endotoxemic rats

OBJECTIVES

To characterize the mechanisms leading to excessive production of nitric oxide within the gut as a consequence of endotoxemia. We sought to: a) determine the time course of inducible nitric oxide synthase (iNOS) messenger RNA (mRNA) expression in the intestine after challenging rats with lipopolysaccharide (LPS); and b) investigate whether there is differential expression of iNOS in enterocytes along the longitudinal or crypt-villus axes of the intestine in rats after LPS administration.

DESIGN

Prospective, randomized, unblinded study.

SETTING

Research laboratories at a large university-affiliated medical center.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

At T = 0 hr, rats were injected with O111:B4 Escherichia coli LPS (5 mg/kg) or a similar volume of the saline vehicle. At various time points thereafter, samples of duodenum, jejunum, ileum, colon, and liver were harvested for subsequent extraction of RNA. In some cases, populations of enterocytes enriched in either crypt or villus cells were harvested from the ileum. In some studies, rats were injected with cycloheximide (25 mg i.p.) 15 mins before being challenged with LPS or dexamethasone (2 mg i.p.) 30 mins before being injected with LPS.

MEASUREMENTS AND MAIN RESULTS

iNOS mRNA was undetectable in ileal tissue from rats under basal conditions, but was evident by T = 1 hr and was maximal at T = 2 hrs after injection of LPS. Thereafter, ileal iNOS mRNA concentrations decreased and were undetectable again at T = 24 hrs. At T = 2 hrs after LPS injection, there was marked expression of iNOS mRNA in the ileum, whereas much lower concentrations of iNOS mRNA were detected in the jejunum and colon, and no iNOS mRNA was detected in the duodenum. At T = 3 hrs after LPS injection, expression of iNOS mRNA was up-regulated in both villus and crypt cells, although LPS-induced iNOS mRNA was more prominent in the former than the latter cell type. Pretreatment of rats with dexamethasone virtually abrogated the expression of iNOS mRNA in ileal samples obtained 3 hrs after the injection of LPS. Prior treatment of rats with the protein synthesis inhibitor, cycloheximide, also blunted LPS-induced iNOS mRNA expression.

CONCLUSIONS

LPS-induced iNOS expression is differentially regulated along both the longitudinal and crypt villus axes of the intestinal mucosa, being most prominent in the villus cells of the ileum. LPS-induced iNOS expression is blunted by pretreating rats with dexamethasone or cycloheximide. The latter finding suggests that LPS-induced expression of iNOS mRNA in the gut requires new protein synthesis. Differential regulation of nitric oxide production along the longitudinal and crypt-villus axes of the gut may be a determinant of the pattern of sepsis-induced intestinal damage.

Role of nitric oxide and platelet-activating factor in the initiation of indomethacin-provoked intestinal inflammation in rats

The effect of indomethacin following the concurrent administration of the nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) on acute intestinal microvascular permeability has been investigated in the rat. Administration of indomethacin (10 mg/kg, s.c.) or L-NAME (10 mg/kg, s.c.) alone did not affect jejunal and ileal vascular permeability over a 12 h period, as determined by the leakage of radiolabelled serum albumin. By contrast, when indomethacin (10 mg/kg, s.c.) was injected concurrently with L-NAME (2-10 mg/kg, s.c.) significant time-dependent plasma leakage occurred in intestinal tissues over 12 h, being apparent within 1 h. Pretreatment with L-arginine (300 mg/kg, s.c.) 15 min prior L-NAME prevented these changes in microvascular permeability. Likewise, pretreatment with the platelet-activating factor receptor antagonist, WEB 2086 ((3-[4-(2-chlorophenyl)-9-methyl-6H-thienol[3,2-f][1,2,4]triazolo- [4,3-a][1,4]diazepine-2-yl]-1-(4-morpholynil)-1-propanone), 0.1-1 mg/kg, s.c.) dose-dependently attenuated such damage. These findings suggest that following indomethacin administration, the early inhibition of NO synthase leads to acute microvascular injury involving platelet-activating factor in the rat jejunum and ileum, indicating a protective role of NO, formed by constitutive NO synthase.

Time-dependent actions of nitric oxide synthase inhibition on colonic inflammation induced by trinitrobenzene sulphonic acid in rats

The time-dependent actions following pretreatment or delayed administration of the nitric oxide (NO) synthase inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME) on colonic inflammation and inducible NO synthase activity following the intrarectal administration of trinitrobenzene sulphonic acid (TNBS) were evaluated in the rat. Intracolonic instillation of TNBS (30 mg in 0.25 ml of 50% ethanol) led to macroscopic injury, an increase of mucosal myeloperoxidase activity and the expression of the Ca2+-independent inducible NO synthase over 8 days. The inflammatory response following TNBS reached maximum levels between 12 and 72 h and then it declined until 14 days. Oral administration of L-NAME (25 mg/kg per 24 h in the drinking water) 2 days before TNBS augmented macroscopic damage and increased colonic inducible NO synthase activity 6, 12, 24 and 72 h after TNBS administration. In contrast, when L-NAME was administered 6 h after TNBS instillation, at time of expression of inducible NO synthase, the macroscopic lesions were reduced, as well as the enhanced inducible NO synthase activity, determined, over 72 h. Delayed (6 h after TNBS) administration of L-NAME also attenuated the colonic myeloperoxidase activity provoked by TNBS, after 24 h. This activity was not affected by pretreatment (2 days before TNBS) with L-NAME. These findings indicate that the timing of administration of non-selective NO synthase inhibitors such as L-NAME, in models of colitis is critical to the eventual outcome. Thus, pretreatment with L-NAME, which will inhibit constitutive NO synthase, exacerbates the subsequent damage following challenge. In contrast, delayed administration of L-NAME at the time of inducible NO synthase expression, has a beneficial action on the colonic injury and inflammation.

Effect of endotoxin and platelet-activating factor on rat vascular permeability: role of vasoactive mediators

The contribution of several vasoactive mediators such as histamine, serotonin, bradykinin, arachidonic acid metabolites and PAF to vascular permeability changes was determined in a rat model of acute endotoxemia. Lipopolysaccharide (10-40 mg/kg, i.v.) from E. coli 0127:B8 (LPS) elicited an increase in Evans blue extravasation in trachea, thymus, seminal vesicle and stomach, whereas other organs remained unaffected. LPS (25 mg/kg)-induced extravasation was not inhibited by intravenous pretreatment with histamine (H1) antagonist mepyramine (5 mg/kg) or bradykinin (B2) antagonist HOE-140 (0.1 mg/kg), whereas other standard drugs selectively inhibited leakage in particular tissues, e.g. the cyclooxygenase inhibitor indomethacin (5 mg/kg) in trachea (78%) and seminal vesicle (64%), the serotonin and H1 antagonists cyproheptadine (2 mg/kg) in trachea (88%) and stomach (56%) and the dual cyclooxygenase/lipoxygenase inhibitor phenidone (10 mg/kg) in seminal vesicle (87%). PAF antagonists lexipafant and UR-12460 (10 mg/kg), but not apafant, potently inhibited extravasation in trachea (59, 84%) and seminal vesicle (81, 78%) and in stomach only UR-12460 (52%), whereas all of them were ineffective in thymus. When extravasation was induced by PAF (4 micrograms/kg) a low dose (0.1 mg/kg) of the three PAF antagonists strongly reduced extravasation in thymus and seminal vesicle, whereas lexipafant and UR-12460 did so in trachea (82, 100%) and only lexipafant in stomach (100%). Mepyramine, cyproheptadine, HOE-140 and indomethacin did not inhibit the effect of PAF, whereas phenidone inhibited it by 58% in trachea. These results suggest that most of the LPS-induced increase in vascular permeability is mediated by secondary vasoactive mediators among which PAF plays a pivotal role, although their relative contribution may vary from tissue to tissue.

Relationship between nitric oxide and platelet-activating factor in castor-oil induced mucosal injury in the rat duodenum

The modulation of platelet activating factor (PAF) formation in duodenal tissue by nitric oxide (NO) released in response to castor oil was studied in rats pretreated with NG-nitro-L-arginine methyl ester (L-NAME, 6.25-25 mg/kg, i.p.), an inhibitor of NO synthase, NG-nitro-D-arginine methyl ester (D-NAME, 25 mg/kg, i.p.), the inactive enantiomer of L-NAME or isosorbide-5-mononitrate (IMN, 30-90 mg/kg, p.o.), a NO donating compound. Castor oil (2 ml/rat orally) increased PAF production in the rat duodenum 3 h after challenge. L-NAME, but not D-NAME, enhanced the amount of PAF formed by duodenal tissue, while IMN (30-90 mg/kg) counteracted the effects of L-NAME (12.5 mg/kg) and also reduced PAF release in the tissue of rats treated with castor oil. L-NAME 12.5 mg/kg, but not D-NAME, enhanced both macroscopic damage and acid phosphatase release induced by castor oil. These effects were reduced by a PAF antagonist BN 52021 (3-t-Butyl-hexahydro-4, 7b, 11-trihydroxy-8-methyl-9H-1, 7a-epoxymethano-1H, 6aH-cyclopenta [c] furo [2, 3b] furo [3'2':3,4] cyclopenta [1.2-d]furan-5,9,12(4H)trione) 10 and 20 mg/kg i.p. Such findings suggest that endogenous nitric oxide could reduce PAF biosynthesis in castor oil-treated rats.

Aminoguanidine-provoked leukocyte adherence to rat mesenteric venules: role of constitutive nitric oxide synthase inhibition

1. The effects of aminoguanidine on neutrophil adherence to venules and on the diameter of arterioles in the mesenteric vascular bed of the pentobarbitone-anaesthetized rat have been compared with those of the nitric oxide synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME). 2. Administration of L-NAME (1-10 mg kg-1, i.v.) caused a dose-dependent increase in leukocyte adherence and a reduction in leukocyte rolling velocity in postcapillary venules of the rat mesentery over 1 h. 3. Likewise, aminoguanidine (10-100 mg kg-1, i.v.) dose-dependently increased leukocyte adherence and decreased leukocyte rolling velocity over 1 h. 4. Both L-NAME and aminoguanidine caused a dose-dependent reduction in mesenteric arteriolar diameter and an increase in systemic arterial blood pressure. 5. The effects of aminoguanidine (50 mg kg-1, i.v.) on leukocyte adherence, arteriolar diameter and on blood pressure were significantly reversed by pretreatment with L-arginine (300 mg kg-1, i.v.). 6. These findings indicate that, like L-NAME, aminoguanidine can acutely promote leukocyte adherence to the mesenteric venular wall and reduce arteriolar diameter. Moreover, these acute effects were reversed by L-arginine, suggesting they are mediated through inhibition of constitutive NO synthase.

Association of microvascular leakage with induction of nitric oxide synthase: effects of nitric oxide synthase inhibitors in various organs

Endotoxin (Escherichia coli lipopolysaccharide 0111:B4, 3 mg/kg i.v.) induced the expression of a calcium-independent nitric oxide (NO) synthase, determined after 5 h in cardiac, hepatic, pulmonary and renal tissues, as assessed by the conversion of radiolabelled L-arginine to L-citrulline. This widespread induction of NO synthase in these conscious rats was associated with microvascular injury, as assessed by the vascular leakage of radiolabelled human serum albumin. Concurrent administration of the NO synthase inhibitor. NG-nitro-L-arginine methyl ester (L-NAME, 1-5 mg/kg s.c.) with endotoxin, provoked acute vascular leakage within 2 h in the various organs. By contrast, the delayed injection of L-NAME (1-5 mg/kg s.c.) or NG-monomethyl-L-arginine (12.5-50 mg/kg s.c.) until 3 h after endotoxin challenge inhibited the subsequent microvascular leakage in these organs. These effects of NO synthase inhibitors were reversed by L-arginine (300 mg/kg s.c.) pretreatment. These results support a protective role of constitutive NO synthase in the early phase of endotoxin shock. Such actions contrast with the aggressive actions of the products of inducible NO synthase in the development of widespread microvascular injury in endotoxemic states.

Involvement of superoxide and xanthine oxidase in neutrophil-independent rat gastric damage induced by NO donors

1. Nitric oxide (NO) and the superoxide anion can interact to form the cytotoxic moiety, peroxynitrite. The involvement and potential source of superoxide in the gastric mucosal damage induced by local infusion of NO donors, has now been investigated in the pentobarbitone-anaesthetized rat. 2. Local intra-arterial infusion of the NO donor, sodium nitroprusside (40 micrograms kg-1 min-1) for 10 min induced macroscopically apparent gastric mucosal injury. 3. This mucosal damage was dose-dependently reduced by prior administration of a systemically acting form of superoxide dismutase conjugated with polyethylene glycol (500-2000 iu kg-1, i.v.). 4. Likewise, the mucosal damage induced by nitroprusside was dose-dependently reduced by prior administration of the xanthine oxidase inhibitor, allopurinol (20-100 mg kg-1, i.p. or 100 mg kg-1, p.o.). 5. Pretreatment with allopurinol (100 mg kg-1, i.p.) also reduced the mucosal injury induced by local intra-arterial infusion of the nitrosothiol, S-nitroso-N-acetyl-penicillamine (40 micrograms kg-1 min-1), but not that induced by local infusion of endothelin-1 (5 pmol kg-1 min-1), indicating specificity of action. 6. Prior administration (4h) of rabbit anti-rat neutrophil serum (0.4 ml kg-1, i.p.), which reduced circulating neutrophils by 90%, did not significantly protect against mucosal injury induced by nitroprusside. 7. Intravenous administration of the platelet-activating factor receptor antagonists, WEB 2086 (1 mg kg-1) or BN 52021 (10 mg kg-1), or the thromboxane synthase inhibitor, OKY 15181 (25 mg kg-1), did not modify mucosal damage induced by nitroprusside, showing lack of involvement of these neutrophil-derived mediators. 8. These findings indicate the involvement of superoxide in the injurious actions of the NO donors, implicating a cytotoxic role of peroxynitrite. Xanthine oxidase, but not neutrophils, appears to be a source of the superoxide.

Attenuation by nitrosothiol NO donors of acute intestinal microvascular dysfunction in the rat

1. The effects of the nitric oxide (NO) donors, S-nitroso-glutathione (SNOG) and S-nitroso-N-acetyl-penicillamine (SNAP), on the acute intestinal microvascular dysfunction induced by NG-nitro-L-arginine methyl ester (L-NAME) in combination with low doses of endotoxin were investigated in the anaesthetized rat. 2. Administration of L-NAME (5 mg kg-1, s.c.) concurrently with E. coli lipopolysaccharide (LPS, 3 mg kg-1, i.v.) provoked the leakage of radiolabelled albumin in the ileum and colon, as a measure of microvascular damage, determined 1 h after challenge. 3. Intravenous infusion of SNOG or SNAP (1-10 micrograms kg-1 min-1) dose-dependently attenuated the microvascular leakage induced by L-NAME and LPS. 4. Infusion of the lowest doses of SNOG or SNAP (1 microgram kg-1 min-1, i.v.) that significantly reduced the albumin leakage, did not affect the increase in blood pressure in response to L-NAME in LPS-treated rats. Higher doses of SNOG or SNAP (5-10 micrograms kg-1 min-1, i.v.) dose-dependently reduced this increase in blood pressure. 5. In control studies, intravenous infusion of glutathione (10 micrograms kg-1 min-1) or N-acetyl-penicillamine (10 micrograms kg-1 min-1) had no effect on microvascular leakage in the ileum and colon induced by LPS and L-NAME. 6. Pretreatment with rabbit anti-rat neutrophil serum (0.4 ml kg-1, i.p., 4 h before challenge), which reduced the neutrophil count in peripheral arterial blood, also inhibited the microvascular leakage in the ileum and colon. 7. The protective effects of the nitrosothiol NO donors in this model may reflect, in part, modulation of neutrophil interactions within the microcirculation or actions on endothelial cell integrity, in addition to any local vasodilator action.

Endothelin-1 induces neutrophil-independent vascular injury in the rat gastric microcirculation

Local intra-arterial infusion of picomole quantities of endothelin-1 induced gastric vascular leakage of radiolabelled albumin. This leakage was partially inhibited by the platelet activating factor (PAF) receptor antagonist WEB 2086 (0.5-2 mg kg-1), but was unaffected by the thromboxane synthase inhibitor OKY 1581 (5 mg kg-1) or by pretreatment with anti-neutrophil serum. These results indicate a partial role of PAF, but demonstrate that neutrophils are not involved in the gastric vascular dysfunction induced by locally administered endothelin-1.

Colonic microvascular integrity in acute endotoxaemia: interactions between constitutive nitric oxide and 5-lipoxygenase products

Administration of the nitric oxide synthase inhibitor, NG-nitro-L-arginine methyl ester (5 mg/kg s.c.) provoked acute microvascular injury (assessed by the leakage of radiolabelled human serum albumin) in the rat colon within 1 h, when administered concurrently with endotoxin (Escherichia coli lipopolysaccharide, 3 mg/kg i.v.). Pretreatment with the selective inhibitor of 5-lipoxygenase, BW A137C (N-[4-benzyloxybenzyl] acetohydroxamic acid; 1-20 mg/kg s.c., 15 min before endotoxin) attenuated such damage in a dose-dependent manner. These findings suggest a balance between protective constitutive nitric oxide and the detrimental actions of 5-lipoxygenase products in the maintenance of vascular integrity in the early stage of sepsis.

Rate of perfusion modulates colloidal carbon leakage from rat intestinal microvessels in vitro

In order to investigate the effects of varying the rate of flow on endothelial integrity the rat isolated small intestinal vasculature was perfused at 1, 5, 10 or 20 ml/min with a gelatin-containing physiological salt solution (GPSS), followed by an injection of colloidal carbon suspension (CC). Significantly greater microvascular CC leakage occurred at 1 or 5 ml/min than at 10 or 20 ml/ mitt. CC leakage at the two slower rates of flow was reduced by adding red blood cells to the GPSS, suggesting that the microvascular endothelium became hypoxic when perfused with GPSS at 1 or 5 ml/min. After perfusion at 20 ml/min with GPSS containing resiniferatoxin (1 μM) or 5-hydroxytryptamine (100 μM), CC leakage was significantly lower than after similar perfusion at 10 ml/min. Two nitric oxide (NO) synthesis blockers, N-nitro-L-arginine methyl ester (L-NAME, 100 μM) and methylene blue (20 μM), and an NO scavenger CPTIO (100 μM) each increased CC leakage. This suggests that NO was being produced at perfusion rates of 10 or 20 ml/min. Sodium nitroprusside (10 μM), 8-bromo-cGMP (100 μM) and BN52021 (10 μM) each significantly reduced CC leakage in the presence of L-NAME.