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

Modulation of endotoxin-induced cardiopulmonary dysfunction by S-nitroso-albumin

Nitric oxide (NO) is an endogenous vasodilator and modulator of inflammation. During endotoxemia, the beneficial effects of NO are overwhelmed by the inflammatory cascade, resulting in a functional depletion of NO. S-nitroso-albumin ( S-NO-alb) exists as a novel and highly stable NO thiol complex that slowly releases NO into the vascular micro-environment. Using a porcine model, we examined the ability of intravenous S-NO-alb to modulate cardiopulmonary dysfunction characteristic of endotoxemia. Pigs were anesthetized, instrumented for standard cardiopulmonary function measurements, and randomly assigned to receive: (i) albumin + saline; (ii) albumin + LPS; or (iii) S-NO-alb + LPS. Cardiopulmonary parameters were evaluated every 30 min and ex vivo phorbol myristate acetate (PMA)-stimulated superoxide release was serially determined as a marker of in vivo neutrophil priming. Lung myeloperoxidase (MPO) activity was measured as a marker of neutrophil migration into the lung. LPS-induced cardiopulmonary dysfunction was characterized by a sustained elevation in mean pulmonary arterial pressure, pulmonary vascular resistance, and peak intratracheal pressure, as well as a reduction in cardiac index, stroke volume index and PaO2 over 6 h. Pretreatment with S-NO-alb attenuated LPS-induced cardiopulmonary dysfunction without adversely affecting systemic hemodynamics. Moreover, S-NO-alb blunted the LPS-induced hypoxemic response and reduced neutrophil activation. S-NO-alb did not, however, attenuate LPS-induced increases in lung MPO. Our results suggest that S-NO-alb can selectively modulate endotoxin-induced pulmonary dysfunction, attenuate neutrophil priming and block the early mortality (40%) in this model.

Different contributions of clathrin- and caveolae-mediated endocytosis of vascular endothelial cadherin to lipopolysaccharide-induced vascular hyperpermeability

Vascular hyperpermeability induced by lipopolysaccharide (LPS) is a common pathogenic process in cases of severe trauma and sepsis. Vascular endothelial cadherin (VE-cad) is a key regulatory molecule involved in this process, although the detailed mechanism through which this molecule acts remains unclear. We assessed the role of clathrin-mediated and caveolae-mediated endocytosis of VE-cad in LPS-induced vascular hyperpermeability in the human vascular endothelial cell line CRL-2922 and determined that vascular permeability and VE-cad localization at the plasma membrane were negatively correlated after LPS treatment. Additionally, the loss of VE-cad at the plasma membrane was caused by both clathrin-mediated and caveolae-mediated endocytosis. Clathrin-mediated endocytosis was dominant early after LPS treatment, and caveolae-mediated endocytosis was dominant hours after LPS treatment. The caveolae-mediated endocytosis of VE-cad was activated through the LPS-Toll-like receptor 4 (TLR4)-Src signaling pathway. Structural changes in the actin cytoskeleton, specifically from polymerization to depolymerization, were important reasons for the switching of the VE-cad endocytosis pathway from clathrin-mediated to caveolae-mediated. Our findings suggest that clathrin-mediated and caveolae-mediated endocytosis of VE-cad contribute to LPS-induced vascular hyperpermeability, although they contribute via different mechanism. The predominant means of endocytosis depends on the time since LPS treatment.

Stöber Synthesis of Nitric Oxide-Releasing S-Nitrosothiol-Modified Silica Particles

We report the synthesis of S-nitrosothiol-modified silica particles capable of nitric oxide (NO) release. The thiol precursor modification to form S-nitrosothiol NO donors was introduced into the silica network via co-condensation of mercaptosilane and alkoxysilane precursors. Both the concentrations of reactants (i.e., water, ammonia, and silane) and the silane feed rate into the reaction proved important in the yield of monodisperse, spherical particles with tunable diameters ranging from 241-718 nm. Subsequent nitrosation resulted in NO storage approaching ~4.40 μmol NO mg(-1), as determined by total NO release. Behaving similar to low molecular weight S-nitrosothiol NO donors, the NO release from the macromolecular silica vehicles was influenced by light, temperature, and metal ions.

Enteric glia regulate intestinal barrier function and inflammation via release of S-nitrosoglutathione

BACKGROUND & AIMS

Barrier functions across epithelia and endothelia are essential for homeostatic tissue regulation. Astroglia interact with cerebral endothelia to maintain the blood-brain barrier. Whether similar interactions between astrocyte-like enteric glia and epithelia regulate intestinal barrier function is not known.

METHODS

Fluorescent permeability markers were used to measure intestinal barrier function in vivo after conditional ablation of enteric glia in transgenic mice. Enteric glial cell regulation of epithelial barrier integrity then was modeled in vitro using coculture. Glial-derived barrier-inducing factors were characterized using size-exclusion chromatography and mass spectrometry. Epithelial barrier integrity was assessed by transepithelial resistance readings and by quantitative measurement of tight-junction-associated protein expression by quantitative polymerase chain reaction and Western blot.

RESULTS

We show that ablation of enteric glial cells in transgenic mice causes intestinal mucosal barrier dysfunction, resulting in inflammation. Glial-derived s-nitrosoglutathione (GSNO) was identified as a potent inducer of mucosal barrier function in vitro and in vivo and of attenuated tissue inflammation after ablation of enteric glia in transgenic mice. GSNO regulation of mucosal barrier function was associated directly with an increased expression of perijunctional F-actin and tight-junction-associated proteins zonula occludens-1 and occludin. GSNO also significantly restored mucosal barrier function in colonic biopsy specimens from patients with Crohn's disease, a well-described inflammatory permeability disorder associated with enteric glial-cell disruption.

CONCLUSIONS

Enteric glia therefore share the ability of astrocytes to regulate tight-junction integrity, and cellular interactions comparable with those maintaining blood-brain barrier function also regulate epithelial permeability at mucosal surfaces.

Nitric oxide and the gut injury induced by non-steroidal anti-inflammatory drugs

Nitric oxide (NO) can protect the gastrointestinal tract from injury, including that provoked by non-steroidal anti-inflammatory drugs (NSAIDs). This protective profile of NO, which predominantly reflects actions on the microcirculation, is mimicked by NO donors. Moreover, the NO-donating agents know as the NO-NSAIDs or CINODs (cyclo-oxygenase-inhibiting nitric oxide-donating drugs) exhibit reduced gut injury in experimental models, which is considered to reflect these local beneficial actions of NO. NSAIDs cause chronic inflammatory lesions in the small intestine in experimental models. This injury results from initial COX inhibition and other local events, with translocation of indigenous luminal bacteria, leading to induction of NO synthase isoform, iNOS, and subsequent production of the cytotoxic moiety, peroxynitrite from NO and superoxide. Agents that inhibit iNOS or superoxide production can attenuate such intestinal injury. In the absence of reactive oxygen moieties, NO may play a beneficial role in the resolution of inflammatory damage to the gut, thus reconciling the potential opposing properties of NO in tissue inflammation and injury.

Understanding gastrointestinal perfusion in critical care: so near, and yet so far

An association between abnormal gastrointestinal perfusion and critical illness has been suggested for a number of years. Much of the data to support this idea comes from studies using gastric tonometry. Although an attractive technology, the interpretation of tonometry data is complex. Furthermore, current understanding of the physiology of gastrointestinal perfusion in health and disease is incomplete. This review considers critically the striking clinical data and basic physiological investigations that support a key role for gastrointestinal hypoperfusion in initiating and/or perpetuating critical disease.

Enhancement of vascular permeability by specific activation of protease-activated receptor-1 in rat hindpaw: a protective role of endogenous and exogenous nitric oxide

1. To clarify the role of the first thrombin receptor/protease-activated receptor (PAR)-1 in an inflammatory process, we tested and characterized the effect of intraplantar (i.pl.) administration of the highly specific PAR-1 agonist TFLLR-NH2 in rat hindpaw. 2. TFLLR-NH2 administered i.pl. at 0.01-0.03 micromol per paw enhanced vascular permeability in the hindpaw and produced paw oedema in a dose-dependent manner. This effect was almost completely abolished by repeated pretreatment with compound 48/80 to deplete inflammatory mediators in mast cells. 3. The NO synthase inhibitor N(G)-nitro-L-arginine methyl ester or N-iminoethyl-L-ornithine, preadministered i.pl., stereospecifically potentiated the i.pl. TFLLR-NH2-induced permeability increase, while the NO donor sodium nitroprusside or NOC-18, given i.pl., suppressed the effect of TFLLR-NH2. 4. These findings demonstrate that specific activation of PAR-1 produces increased vascular permeability accompanied by oedema formation in the rat hindpaw, predominantly via mast cell degranulation, and that endogenous and exogenous NO plays a protective role in the PAR-1-mediated inflammatory event.

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.

Nitroglycerin does not alter pulmonary vascular permeability in isolated rabbit lungs

Nitroglycerin (NTG) produces vasodilation by releasing nitric oxide (NO) at the cellular level. Other studies have suggested that NO may directly alter vascular permeability and may alter the development of tissue injury. We therefore examined the effects of NTG on vascular permeability in the buffer-perfused rabbit lung under normal conditions and during lung injury. Vascular permeability was assessed by measurement of the capillary filtration coefficient (Kf,c). In normal lungs, NTG did not alter Kf,c or the rate of weight gain. Oxidant lung injury was produced by the addition of purine and xanthine oxidase and resulted in increased Kf,c and increased weight gain. However, NTG did not alter these effects of oxidant lung injury. We conclude that NTG does not alter pulmonary vascular permeability in either normal or oxidant-injured lungs.

Bradykinin and changes in microvascular permeability in the hamster cheek pouch: role of nitric oxide

1. The objective of this study in the hamster cheek pouch was to investigate the role of nitric oxide in bradykinin-induced microvascular leakage. The cheek pouch microcirculatory bed of the anaesthetized hamster was directly observed under microscope and vascular leakage was evidenced by dextranfluorescein isothiocyanate (FITC-dextran) extravasation. 2. Bradykinin superfusion (but not [des-Arg9]-bradykinin up to 3 x 10(-6) M) induced an increase in microvascular permeability (log EC50: -6.5 +/- 0.4) which was exclusively located on the post-capillary venule. Plasma extravasation was blocked by intravenous pretreatment with Hoe 140, a bradykinin B2 receptor antagonist (estimated log ID50: -9.5 +/- 0.2). 3. The effects of bradykinin (3 x 10(-7) M) superfusion were partially but significantly inhibited by indomethacin (10(-5) M, P < 0.05) and abolished by pretreatment with L-nitro-arginine (L-NOARG; 10(-5) M). 4. Acetylcholine (10(-6) M, which releases endothelial nitric oxide (NO), and sodium nitroprusside (10(-6) M, a nitrovasodilator) superfusion did not induce any changes in permeability, per se. Cromakalim (10(-5) M, a potassium channel opener) superfusion induced a moderate but significant plasma extravasation. 5. The effects of bradykinin, blocked by L-NOARG pretreatment, were restored by the co-perfusion of either sodium nitroprusside or cromakalim. Conversely vasoconstriction, produced by a stable analogue of thromboxane A2 (U46619, 3 x 10(-7) M), inhibited the increase in permeability produced by bradykinin. 6. The measurement of arteriolar diameter showed that bradykinin induced a vasodilatation which was blocked by L-NOARG. L-NOARG in itself was a powerful vasoconstrictor. Sodium nitroprusside and cromakalim, in the presence of L-NOARG, were able to restore the inhibited vasodilator response to bradykinin. 7. These results suggest: (1) bradykinin-induced microvascular leakage is mediated by bradykinin B2 receptor activation; (2) the increase in permeability is due to two different independent phenomena, i.e. post-capillary venular endothelial gap formation and arteriolar vasodilatation which increases the post-capillary venular transmural pressure: (3) NO is only involved in the arteriolar dilatation component of the bradykinin-induced increase in microvascular permeability.

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.